Symposium EC3 : Catalytic Materials for Energy and Sustainability

Oxides are used in many catalysis and energy applications. It is known that the reactivity of the oxide varies with it crystal structure. For example, anatase TiO2 is is a better photocatalyst than rutile TiO2. This is likely true for other structures, and other oxides as well, but in many cases some of the polymorphs are not directly accessible, or are not even stable as bulk phases. Epitaxy may be a way to stabilize some polymorphs as thin films, which could lead to novel reactive materials. It is difficult to know in advance though which polymorphs might be stabilized, and whether they would have desirable properties if they were. We have used density functional theory (DFT) to explore connections between oxide electronic structure and their reactivity, e.g. oxygen adsorption and vacancy formation. Not surprisingly, this connection is more complex than in metals, with the oxidation state and number of d-electrons, as well as strain playing important roles in modulating oxide reactivity. We use these results to assess whether novel polymorphs would have interesting properties. In parallel we examine the stability of the polymorphs to assess which are likely to be stabilized by epitaxy. We will show how these work together to identify promising candidates for synthesis, and discuss future challenges of modeling these materials.

Most model surface science studies on titania are performed on the rutile TiO₂(110) surface. Here we investigate second most common surface orientation of rutile, namely the (011) surface. This surface reconstructs in vacuum into a complex 2×1 reconstruction. This reconstruction removes dangling bonds and reduces the adsorption of test molecules like carboxylic acids. In order for these molecules to adsorb the surface restructures, allowing formation of carboxylates. In this adsorption process the reconstruction ‘steers’ the restructuring resulting in formation of quasi one-dimensional adsorbate clusters [1]. The surface instability of TiO₂(011) may also facilitate the formation of mixed oxide surfaces [2]. We investigate the formation of iron- and vanadium-oxide intermixed with the TiO₂(011) surface and identify mixed ordered surface line-phases, such that the surface segregates in the intermixed oxide and pure TiO₂(011)-2x1 surface [3]. These surfaces may form by controlled doping or due to segregation of bulk impurities to the surface and thus may be important in understanding the (photo)catalytic properties of titania. Finally, we compare the photocatalytic activity of rutile TiO₂(011) with that of anatase TiO₂(001). For the decomposition of dyes rutile is about half as active as anatase. Our studies on epitaxial TiO₂ films suggest that this difference can be attributed to bulk charge carrier diffusion rather than surface properties [4].

[1] Q. Cuan, J. Tao, X.Q. Gong, M.B. “Adsorbate Induced Restructuring of TiO₂ (011)-(2× 1) Leads to One-Dimensional Nanocluster Formation” Phys. Rev. Lett. 108, 106105 (2012).
[2] S. Halpegamage, P. Ding, X.Q. Gong, M.B. “Ordered Fe (II) Ti (IV) O3 Mixed Monolayer Oxide on Rutile TiO2 (011)” ACS Nano 9, 8627 (2015).
[3] S. Halpegamage, Z.H. Wen, X.Q. Gong, M.B. “Monolayer Intermixed Oxide Surfaces: Fe, Ni, Cr, V- Oxides on rutile TiO₂(011)” J. Phys. Chem. C (submitted 2016).
[4] T. Luttrell, S. Halpegamage, J. Tao, A. Kramer, E. Sutter, M.B. “Why is anatase a better photocatalyst than rutile?-Model studies on epitaxial TiO₂ films” Sci. Rep. 4, (2014).

Invited Speaker abstract body not yet provided

The use of heterogeneous catalysts for important chemical conversions often relies on the design of active sites consisting of metal nanoparticles supported on high surface area oxide materials. Key to design of these systems is the identification of active site geometries and compositions that are optimized for desired catalytic reactions. However, the exposure of oxide-supported metals to reactive environments can induce significant transformations in the structure of the metal, support, and interactions between the metal and support. The dynamic transformations in catalytic structures induced by exposure to reactions can cause significant changes in the reactivity of the structures, requiring detailed in-situ analysis to identify active site motifs.
I will highlight a few examples where we exploit quantitative and in-situ spectroscopy and microscopy to characterize heterogeneous catalysts at atomic scale and identify how reactive conditions modify active site structures and relate this to catalytic performance. The first example will focus on the identification of the most active configuration of Pt atoms on Al₂O₃ supported Pt nanoparticles in CO oxidation reaction conditions mimicking the catalytic convertor. We utilize quantitative in-situ IR spectroscopy to identify that reaction conditions reconstruct Pt surfaces, inducing surface faceting and minimizing the concentration of the active Pt sites, which are well-coordinated Pt atoms. In the second example, it will be shown that the selectivity of oxide-supported Rh catalysts in the reaction of CO₂ reduction by H₂ can be manipulated through a process where strongly bound HCO_x adsorbates on reducible supports dynamically induce the formation of discontinuous support overlayers on top of Rh nanoparticles. Mechanistic analysis using in-situ FTIR spectroscopy, transmission electron microscopy, electron energy loss spectroscopy and X-ray absorption spectroscopy provide insights into the formation and composition of the oxide overlayer on Rh and it’s resulting influence on Rh reactivity.

Selective oxidation is one of the most important goals in heterogeneous catalysis and is crucial to efficiently create intermediates for the chemical industry. Oxidation reactions include the formation of formaldehyde from methanol or the coupling of alcohols to esters. For selective oxidation, the “over-oxidation” is detrimental, yielding mainly CO₂. Therefore, a natural choice are the noble, coinage metals, such as Au [1]. In order to prepare selective and active catalysts, a good strategy is to design bifunctional catalysts, which have different active sites for O₂ activation and selective oxidation.

The bifunctional catalyst used in this work is nanoporous Au (np-Au). This is a sponge-like, support-free catalyst obtained by selective etching of AgAu alloys. After etching, a small amount of Ag remains behind, forming a bimetallic, diluted AgAu alloy. The Ag atoms act as an active site for O₂ dissociation, while the O atoms spillover to the Au surface, where they selectively oxidize, e.g, methanol [2].

To obtain stable and active np-Au catalysts, activation by ozone is needed. This treatment oxidize Ag at the np-Au surface, thereby enriching the surface with Ag. Both Ag and Au oxides are present on the freshly activated catalysts, based on in situ XPS measurements. These oxides are highly non-selective, forming mainly CO₂. However, environmental TEM observations show that these oxides are not stable in methanol oxidation conditions. This leads to the formation of Ag metallic nanoparticles on the np-Au surface and the formation of a new O species, which is highly selective towards coupling methanol. However, the Ag nanoparticles re-alloy with the np-Au, which could lead to deactivation. These studies show the importance to characterize the surface of bimetallic catalysts, during activation and reaction, both chemically and structurally.

Currently, we are extending our approach of employing nanoporous, diluted alloys as bifunctional catalyst to selective hydrogenation. As a model system, we are studying the selective hydrogenation of unsaturated aldehydes to unsaturated alcohols. In this case, the hydrogenation of the C=C double bond is thermodynamically preferred, forming the saturated aldehyde. On the other hand, the unsaturated alcohol is the industrially interesting product. Silver is an interesting candidate [3] for this selective hydrogenation reaction. In this study, we probe the influence of alloying Ag with small quantities of Pd, the surface orientation, and the roughness on the selectivity of acrolein hydrogenation towards allyl alcohol. The studies combines surface science work with traditional techniques on single crystals and in situ/operando measurements on np-Ag.



[1] A. Abad et al., Angew. Chem. Int. Ed., 44 (2005) 4066–4069
[2] B. Zugic et al., ACS Catal., 6 (2016) 1833–1839
[2] M. Bron et al, Phys. Chem. Chem. Phys., 9 (2007) 3559–3569

The stability of supported metal catalysts is a challenge for many industrially catalytic processes. Especially under harsh reaction conditions, such as biomass conversion and emission abatement (hydrothermal or high temperature), the loss of catalytic activity is either due to metal particle growth (“sintering”) or reaction of metal with the support materials to form solid solution. We have developed a novel synthesis approach to prepare a pure MgAl₂O₄ spinel material via controlled hydrolysis of alkoxide precursors in a non-aqueous solution (ethanol). We reported high thermal stability of Pt supported on this well-defined MgAl₂O₄ during highly severe thermal aging in oxidizing atmospheres. The strong interactions between spinel surface oxygens and Pt facets helped stabilize the Pt nanoparticles over the support surface. Conventional aqueous phase synthesized MgAl₂O₄ in house and commercial MgAl₂O₄ spinels were also investigated to compare. The bulk properties were similar according to XRD and TEM while the surface properties such as zeta potentials, acidity/basicity and degree of aluminum disorder (NMR) were very different between samples. The surface properties of spinel, dramatically affected by synthesis methods, would sequentially affect the initial dispersion and stability of the metal nanoparticles. Pt supported on MgAl₂O₄ from novel non-aqueous phase synthesis had the highest Pt dispersion and thermal stability. Accordingly, its catalytic activity of methanol oxidation and low temperature CO oxidation were the highest among the three. Meanwhile, the DFT calculation confirmed the oxygen terminated (100) surface (100_O) of spinel MgAl₂O₄ is the most stable surface under low oxygen pressure conditions. In sum, the metal can be highly dispersed over the novel synthesized spinel support and the metal nanoparticles could be stabilized via lattice matching between the spinel surface oxygens and epitaxial metals\metal oxides. In addition, a new kind of highly stable ceria supported Pt for CO oxidation by trapping atomically dispersed Pt over CeO₂ would be reported. Catalytic reaction kinetics combining with mechanistic studies using in-situ FTIR would be discussed to provide insight on the nature of active sites and reaction mechanism.
In sum, via state-of-art synthesis and characterization techniques, both redox and non-redox are able to stabilize the supported precious metal, which leads to higher activity and longer life time of the catalysts.

Au is capable of selectively and efficiently catalyzing oxidation reactions, such as methanol coupling to methyl formate, under mild conditions. However, many of these reactions require atomic oxygen to be adsorbed on the surface in order to proceed, which is a challenge since Au cannot normally dissociate O₂. Here, we use density functional theory and thermodynamic modeling to examine two routes for dissociating O₂ while maintaining high catalytic selectivity.

First, we examine AgAu alloys, motivated by the excellent catalytic performance of nanoporous Au, which is a nanostructured material with a small amount (~2%) of Ag. Using atomistic thermodynamics, we find that, under oxidation reaction conditions, the surfaces of dilute AgAu alloys have Au terraces and AgAu bimetallic steps. These bimetallic steps are likely responsible for O₂ dissociation, and the calculated barrier on the AgAu(211) structure that we find in the thermodynamic calculations has a low activation barrier for O₂ dissociation that is in agreement with experiment.

We also show that the reconstruction of bulk Au surfaces that occurs spontaneously plays an important role in preventing O₂ dissociation. For example, the barrier for O₂ dissociation on an unreconstructed Au(100) surface is lower than on Ag(110), which dissociates O₂ easily. Therefore, by preventing surface reconstruction, Au surfaces that can dissociate O₂ can be created. This shows that it is the geometric structure of Au, and not solely its position in the periodic table, that determines its nobility. The ability of unreconstructed surfaces to dissociate O₂ may play a role in the activity of small Au nanoparticles.

Thermal annealing is a common and often much-needed process to treat bimetallic nanoparticles in order to have the desired surface structure and composition showing high catalytic activity that matches with predictions. Traditionally, such thermal treatment is carried out either in air or under an inert atmosphere by a trial-and-error approach. Here, we present a new chemical vapor-assisted low-temperature thermal treatment for the preparation of highly active Ag-Pt octahedral nanoparticle catalysts. As carbon monoxide (CO) possessed dramatic difference in its affinity towards Ag and Pt surfaces, it was applied as the surface composition directing agent to reversibly control the arrangements of Ag and Pt atoms on the surface and near surface regions of the octahedral nanoparticle. The environmental responsive elemental distribution of octahedral nanoparticles was clearly revealed by Z-contrast high angle annular dark field STEM, showing a homogeneous distribution under CO and with Pt atoms being selectively segregated at the edges when switched from CO to argon (Ar) atmosphere. In situ environmental TEM study reveals the dynamic rearrangement process of Ag and Pt atoms under gaseous environment showing the rate of homogenization being much faster compared to the rate of segregation. In situ and ex situ experimental data suggest that the rate of atomic rearrangements were governed by the adsorption and desorption behaviors of CO, where adsorption favors over desorption at such low temperature. The altered surface composition directly impacted the electrocatalytic activity of Ag-Pt nanocrystal catalysts with the homogeneously distributed surface exhibiting higher activity towards the electrochemical oxidation of formic acid. The method developed in this work represents a novel approach to the post-synthesis processing of high performance catalysts.

Catalytic oxygen activation is a key step in organic oxidation reactions and oxygen reduction reaction (ORR) in fuel cells. Recently, UV pre-treatment has been reported to enhance the catalytic oxygen activation capacity of Pt/TiO₂ for formic acid oxidation, improving the oxidation rate by seven times¹. However, in fuel cell applications for instance, Pt catalyst faces the challenge of CO poisoning. The potential for Pt poisoning may be overcome by either: (i) using Au instead of Pt as the catalyst; or (ii) coupling Au with Pt (i.e. a bimetallic catalyst). In the present work we investigate whether Au (either by itself or coupled with Pt) exhibits similar benefits to those displayed by Pt when subject to UV pre-treatment.
Similar to Pt/TiO₂, Au/TiO₂ is enhanced upon UV pre-treatment, with it increasing the formic acid oxidation rate by up to four times. Photoluminescence spectra show that UV pre-treatment reduces electron-hole pair recombination, highlighting its role in enhancing catalytic oxygen activation. Electrochemical ORR analysis after UV pre-treatment shows a reduction in onset potential, suggesting a drop in ORR activation energy. Scanning Tunnelling Microscope and Density Functional Theory (DFT) calculations show evidence of new valence states at the Au/TiO₂ perimeter sites, suggesting these as the sites for oxygen activation.
Coupling Au and Pt to give a bimetallic catalyst introduces a synergy to the catalytic performance with UV pre-treatment amplifying the synergy, as illustrated by an increase in the formic acid oxidation rate by up to six times. Both the UV pre-treatment enhancement and the bimetallic synergy depend on the Au:Pt ratio, with a decrease in the benefit with decreasing Au:Pt ratio. X-ray photoelectron spectroscopy analyses on the AuPt/TiO₂ are supported by DFT calculations, suggesting two possible work-function-driven electron pathways: (i) a direct pathway from the TiO₂ support to Pt sites; (ii) an indirect pathway from the TiO₂ support to Au and then from Au to Pt.
At a high Au loading, the lattice mismatch between Au and Pt causes a lattice expansion in the Pt, weakening the Pt-Pt bonds and creating non-bonding electrons in the process. These non-bonding electrons are free to interact with surrounding entities, increasing the amount of surface adsorbed species (O₂ molecules in the present study) for catalytic activation, and hence responsible for the bimetallic synergism. DFT calculations also reveal that the bimetallic interface is the preferred adsorption region for O₂. UV pre-treatment facilitates the O₂ activation step by saturating the active sites with photoelectrons, hence the observed enhancement.
In summary, the present work provides valuable insights in catalyst design for oxygen activation and evidence of a good correlation between theoretical calculations, model system studies, and macroscopic experiments.
Reference:
(1) Scott, J.; Irawaty, W.; Low, G.; Amal, R. Appl. Catal. B Environ. 2015, 164, 10–17.

Precious-group-metal (PGM: Pt, Pd, Rh and/or Ru) catalysts are used in various areas of industrial applications especially for the remediation of automobile exhaust. It is an urgent issue to develop exhaust catalysts consisting of earth-abundant metals to meet the future depletion of the mineral resource of PGM. Herein, we report that nanophase-separated alloys which consist of cheap and abundant copper (Cu) and oxygen-deficient zirconium oxide (ZrO_x; x < 2) can be prepared by oxidative treatments on ordered alloy (i.e. Cu₅₁Zr₁₄). The prepared catalyst exhibits much higher activity than Pt- or Rh catalysts at low temperatures toward the remediation of simulated exhaust comprising nitrogen monoxide (NO) and carbon monoxide (CO).
Transmission electron microscopy (TEM) and hard X-ray photoemission spectroscopy with synchrotron radiation (HAXPS) have demonstrated that the prepared nanophase-separated catalyst, i.e. Cu@ZrO_x, consists of a filamentous network of Cu⁰ phase (average thickness = 10 nm) that is embedded in a matrix of amorphous ZrO_x. In-situ Fourier-transform infrared-spectroscopy (in-situ FTIR) and in-situ XPS have elucidated that the superior catalytic performance of the Cu@ZrO_x is due to an interfacial synergy effect between Cu⁰ and ZrO_x and the agglomeration tolerance of the Cu⁰ network, which results in the precious-metal-free, long-term-stable exhaust remediation over 200 hours.

Small clusters composed of tens of atoms exhibit electronic and chemical properties that can differ significantly from that of the bulk and offer a unique opportunity for preparing novel catalysts whose reactivity can be modified at the atomic level. Here, we use mass-selected cluster deposition to prepare model “inverse” catalysts comprised of small metal oxide (M_xO_y: M = Ti, Nb, Mo, W) and sulfide (M_xS_y: M = Ti, Mo) clusters deposited on Cu and Au surfaces, respectively, for studies the water-gas-shift reaction (WGSR) and for CO/CO₂ activation/hydrogenation. A key advantage of mass-selected cluster deposition for such studies is that it allows control over metal/non-metal stoichiometry, e.g., metal-to-oxygen ratio, which provides a means of introducing oxygen/sulfur “vacancies” and varying the average cation oxidation state. Recent work has focused on the correlation of electron transfer at the M_xO_y/Cu(111) interface and activity for water dissociation, the latter being a key step in the WGSR mechanism. Electron transfer is probed by a combination of XPS core level spectra and two-photon photoemission (2PPE) measurements of coverage-dependent work function shifts to extract surface dipoles.¹ All the oxide clusters on Cu(111) exhibit negative surface dipoles, indicative of Cu ® cluster charge transfer, with the dipoles for sub-stoichiometric and reducible oxides (i.e., Ti_xO_y and Nb_xO_y) being smaller. Temperature programmed reaction (TPR) experiments show that the Ti_xO_y and Nb_xO_y clusters promote water dissociation, with the ‘reduced’ Ti_xO_y clusters (x/y = 3/5, 4/7) more active than their stoichiometric counterparts (x/y = 3/6, 4/8). The Nb_xO_y clusters behave differently, with both stoichiometric (x/y = 3/7, 4/10) and reduced clusters (x/y = 3/5, 4/8) able to dissociate water on Cu(111).² Overall, these results suggest that both the reducibility and Lewis acid character of the cation sites play a role in promoting water dissociation. More recent studies are investigating CO₂ activation on alkali modified surfaces of Mo₆S₈ clusters on Au(111), which had been previously predicted to be active for CO₂ hydrogenation to methanol.³ Theoretical calculations suggest that addition of alkali modifier enhances reactivity of the Mo₆S₈ cluster and switches the mechanism from reverse-WGSR, i.e., CO hydrogenation, to a pathway involving CO₂ hydrogenation to formate.³
1. Y. X. Yang, J. Zhou, M. Nakayama, L. Z. Nie, P. Liu and M. G. White, J. Phys. Chem. C 118, 13697-13706 (2014).
2. M. Nakayama, M. Xue, W. An, P. Liu and M. G. White, J. Phys. Chem. C 119 14756–14768 (2015).
3. P. Liu, Y. Choi, Y. Yang and M. G. White, J. Phys. Chem. A 114, 3888-3895 (2010); C. Liu and P. Liu, ACS Catal. 5, 1004-1012 (2015).
This work was performed at Brookhaven National Laboratory under Contract No. DE-SC0012704 with the U.S Department of Energy, Office of Science, and supported by its Division of Chemical Sciences, Geosciences, and Biosciences.

In the last decade, complexity of catalytic nanoparticles attracted much attention as a major factor in catalytic processes. Atomic and electronic structure and dynamics of particles, as well as their interactions with support and adsorbates, are important descriptors of their catalytic activity. The main challenge is how to investigate these factors in a working catalyst, at high temperature and pressure, and how to do so without breaking the correlations between components of this complex system. I will give a brief overview of new methods developed recently to enable such combined studies under realistic reaction conditions. Our approach is to single out electronic charge of metal atoms in a cluster as an “observable” quantity and develop methods to “observe” it experimentally under realistic reaction conditions, and model theoretically. In this framework, complex interactions between metal and adsorbates, metal and support, and support and adsorbates can be all accounted for in terms of their effects on the cluster charge. I will review recent results utilizing this approach for a prototypical catalyst, 1nm Pt nanoparticles supported on silica. Using high energy resolution methods of X-ray absorption and emission spectroscopies (HERFD and RIXS), as well as in situ IR spectroscopy (DRIFTS) and electron microscopy, aided with first-principles (DFT) modeling, we deduced that the structure of atoms and charges in the catalyst is strongly heterogeneous and that it changes dynamically with the change in temperature and pressure of adsorbates (H₂ or CO).

Heterogeneous catalysis is a strategic science and technology for every sustainable energy system. Strategies will be needed to convert free electrons into chemical energy carriers and materials, as complete de-carbonization of the system is impossible. In addition, the reduction of CO₂ with renewable reducing agents presents an economical way to generate sinks for CO₂ emissions. Arguments will be presented that amongst all the many scientific challenges in energy catalysis the generation of reducing equivalents from free electrons may be the most critical bottleneck.
The catalytic electro-reduction of CO₂ is a hot topic in energy catalysis. Despite this focus the evolution of oxygen (OER) as source for the electrons needed in CO₂ reduction (and hydrogen evolution) is since long a critical bottleneck in (photo)electro-catalytic devices that convert volatile renewable energy into chemical energy. The non-stationary operation in grid structures mixed with fossil electrical energy is a particular challenge when overall CO₂ reduction is the target.
The contribution exemplifies with IrO₂ the current understanding of the mode of operation of OER catalysts. Electrophilic oxygen as ingredient into the activated form is a critical element when rationalizing stability and operation of this supposedly metallic oxide system.
If we follow the conjecture that Ir is too rare for a large-scale application we need replacement systems working in acid or basic electrolytes with better performance than Ni. Manganese compounds and composites with carbon are frequently studied. Standardization of results and the state of affairs in performance are discussed. The potential of carbon systems in OER is discussed with respect to stability and passivation against thermodynamically strongly favored oxidation. If carbon is synthesized from renewable precursors in low-temperature processes, its application as sacrificial catalyst in OER may be an option for non-noble metal electro-catalysts.
The integration is shown of such studies into a systemic approach to de-carbonize steel production by carbon capture and use.

ABO₃-type perovskite oxides are widely studied for cost-efficient oxygen evolution reaction (OER) catalysts. It was recently reported that the quadruple perovskite CaCu₃Fe₄O₁₂ has a higher OER activity than the CaFeO₃ perovskite. However, its origin is still unclear. We focus on the quadruple manganese perovskite oxides AMn₇O₁₂ (A = Ca, La). These oxides have the ABO₃-type counterparts AMnO₃ (A = Ca, La) whose constituent elements are identical to those of quadruple perovskites. In these compounds, we can investigate pure structural features concerning catalysis, in comparison with their corresponding simple perovskites AMnO₃. Our experiments displayed that the intrinsic OER acvitities of AMn₇O₁₂ are much higher than those of AMnO₃.
In this study, the structure-activity relationships are investigated in terms of electronic structures. Until now, many attempts have been made to clarify the relationships between electronic structures and catalytic activities in perovskites. Density functional calculations were systematically made for manganese perovskites AMn₇O₁₂ and AMnO₃ (A = Ca, La) using the plane-wave based projector augmented-wave (PAW) method as implemented in the VASP code. The exchange-correlation interaction was treated as generalized gradient approximation (GGA) using the Perdew-Burke-Ernzerhof (PBE) functional. The on-site Coulomb interactions on the localized Mn 3d electrons were treated with the GGA+U approach with U_eff = 3 eV.
Grimaud et al. proposed that the OER activities of cobalt perovskites are higher when the O 2p band centers are closer to Fermi energies. Our calculations indicated that the O 2p band centers of quadruple perovskites (–3.16 and –3.20 eV for CaMn₇O₁₂ and LaMn₇O₁₂, respectively) are not closer than those of the simple perovskites (–1.64 and –3.08 eV for CaMnO₃ and LaMnO₃, respectively), demonstrating that the energy level of O 2p band center is not a good descriptor for manganese quadruple perovskites. We also investigated the dependence of local electronic structures of Mn ions on the local coordination around each Mn site in AMn₇O₁₂ and AMnO₃. The calculated partial projected density-of-states (pDOS) show that both the valence and conduction bands consist of the hybridization between Mn 3d and O 2p orbitals. No significant differences in band gaps and Mn 3d band widths were found. By careful observations, however, the Mn 3d pDOS of quadruple perovskites AMn₇O₁₂ showed stronger peak near the Fermi level compared to those of AMnO₃. Assuming a reaction like that Mn^m+ exposed to aqueous solution is oxidized to Mn^(m+1)+ when an adsorbate OOH^- is reduced to OO^2-, this difference of Mn 3d pDOS could contribute to high activity of AMn₇O₁₂ because electrons near Fermi level are considered likely to move to adsorbates.

Designing efficient and durable catalysts towards oxygen evolution reaction (OER) has gained tremendous interest for the wide applications in clean energy technologies, such as solar or electrolytic water splitting and rechargeable metal-air batteries. Conventional OER catalysts, such as Ir, Ru, IrO₂ and RuO₂, suffer from high cost and limited natural reserves. Recent work on Ni,Fe/Co,Fe-oxyhydroxide reports superior OER catalytic activity, however, Ni and Co are unfavorable which cause poisoning and environmental pollution. Herein, we develop a novel, economical, ecofriendly and efficient Ta₂O₅-based OER catalytic system via DFT simulation and pulsed laser deposition (PLD)-controlled surface engineering [1]. Stable surface structures of Ta₂O₅ and the corresponding onset overpotentials towards OER are calculated via systematic first-principles calculations. Oxygen site on the stable (200) surface of Ta₂O₅ is explicitly identified as the most active OER site, possessing a small calculated onset overpotential of 0.25 V. Using the simulated oxygen condition, we successfully grow a (200)-surface-exposed Ta₂O₅ nanolayer on a carbon cloth by oxygen-controlled pulsed laser deposition. The designated (200) surface exhibits high OER activity with an onset overpotential of 0.29 V and overpotential of 0.385 V at 10 mA/cm² in good agreement with the simulation. Moreover, first-principles calculation suggests that Fe-dopant on surface can significantly increase the OER activity by creating additional active OER sites. After further depositing Fe on the Ta₂O₅ nanolayer by PLD, the OER activity is significantly enhanced with an onset overpotential of 0.27 V and overpotential of 0.34 V at 10 mA/cm². The proposed surface engineering to activate catalytic activity provides a novel strategy for effective development of new metal-oxide catalysts. [1] W. Xiao, X. Huang, W. Song, Y. Yang, T.S. Herng, J.M. Xue, Y.P. Feng, J. Ding, Nano Energy, 25 (2016) 60-67.

Extensive investigations in understanding the functional mechanisms of metal oxides behind oxygen evolution have been carried out since electrolyzer has demonstrated promising possibilities as a device to produce hydrogen for electrochemical energy conversion systems. In particular, perovskite oxides are reputable for outstanding activity towards the oxygen evolution reaction (OER). Here, we revisited the list of active perovskite oxides constructed based on theoretical oxygen binding energies of reaction intermediates to the catalyst surface. From this list, Ru-based perovskites, i.e. SrRuO3 and LaRuO3 have been predicted as active perovskites to exhibit a particularly high OER activity. We report on the stability of nano-scaled SrRuO3 perovskite prepared by a simple and scalable flame synthesis method. Attempts to attain LaRuO3 were made; however, its DFT calculated phase diagram suggests that its perovskite phase is not thermodynamically stable, which supports our experimental results such that only a mixture of different La-Ru-O phases has been obtained. Nano-scaled SrRuO3 is evaluated for its electrochemical activity with a particular emphasis pointed towards stability in both alkaline and acidic media. Through conjoining electrochemical methods, operando X-ray absorption spectroscopy (XAS), and theoretical calculations, we show that SrRuO3 exhibit trivial activity towards OER that decreases promptly. The loss in activity is rationalized through DFT based computations, which corroboratively suggest the poor chemical stability of both selected perovskites. Regardless of the predicted theoretical OER activity, the intrinsic instability strongly suggests that Sr- and La-based ruthenium oxides are not viable catalysts for OER in aqueous media. This further suggests that their activities are independent of their binding energies between intermediates and catalyst surface but rather closely associated with material dissolution. We highlight that understanding the origin of stability under real operating environment is absolutely essential for the design of a sustainable electrocatalyst with optimal balance between activity and stability.

Xi Cheng,*,† Emiliana Fabbri,*,† Maarten Nachtegaal,‡ Ivano E. Castelli,# Mario El Kazzi,†
Raphael Haumont,∥ Nicola Marzari,# and Thomas J. Schmidt†,§
†Electrochemistry Laboratory, Paul Scherrer Institut, 5232 Villigen, Switzerland
‡Paul Scherrer Institut, 5232 Villigen, Switzerland
#Theory and Simulation of Materials (THEOS) and National Centre for Computational Design and Discovery of Novel Materials (MARVEL), Ecole Polytechnique Federale de Lausanne, 1015 Lausanne, Switzerland
∥SP2M, ICMMO, Universite Paris Sud XI, 91405 Orsay, France
§Laboratory of Physical Chemistry, ETH Zurich, 8093 Zurich, Switzerland
[email protected]

Perovskite Oxides (ABO₃) with alkaline or rare-earth cations in the A-site and first row transition metal cations in the B-site have shown the potentials of being viable oxygen electrode catalysts in alkaline solution ¹. Furthermore, it was demonstrated that their physical-chemical properties as well as their catalytic activity can be significantly influenced by substitution or partial substitution of the A and/or B-site by other elements giving (A_xA’_1-x)(B_yB’_1-y)O₃ compositions. However, it is a difficult task to find the most active oxides among the many different families of perovskites. A descriptor-based analysis can provide a promising approach to predict and identify the most active materials, since it correlates the prospective electrocatalytic activity to other, simpler properties.
In the present work, the crystallographic structure, bulk electronic structure, conductivity and electrochemical activity toward the oxygen evolution reaction for two perovskite series (La_1-xSr_xCoO₃² with x=0, 0.2, 0.4, 0.6, 0.8, 1 and LaBO₃ with B=Cr, Mn, Fe, Co, Ni) are investigated experimentally and theoretically. Experimental characterizations (XRD, XAS, neutron diffraction, ex-situ electronic conductivity and OER measurements) demonstrate that the varying of the A site and B site delivers several changes in the physicochemical properties of the considered oxides. But by combining experiments with density-functional theory calculations, we show that it is possible to reliably relate some simple physico-chemical materials properties including the electronic structure to the observed activity towards the oxygen evolution reaction. This correlation will facilitate the search and design of highly active oxygen evolution catalysts, in the quest for efficient anodes in water electrolyzers.

1. E. Fabbri, A. Habereder, K. Waltar, R. Kotz, T.J. Schmidt, Developments and perspectives of oxide-based catalysts for the oxygen evolution reaction. Catal Sci Technol 2014, 4 (11), 3800-3821.
2. X. Cheng, E. Fabbri, M. Nachtegaal, I. E. Castelli, M. E. Kazzi, R. Haumont, N. Marzari, and T. J. Schmidt, Oxygen Evolution Reaction on La1−xSrxCoO3 Perovskites: A Combined Experimental and Theoretical Study of Their Structural, Electronic, and Electrochemical Properties. Chem. Mater. 2015, 27, 7662-7672.

Ni based compounds are attracting intense attentions as low cost and efficient catalysts for hydrogen production by water splitting [1]. In particular, NiFe alloys are demonstrated to have one of the lowest overpotential oxygen evolution reaction (OER) in an alkaline electrolyte [2].
Here, we present an efficient and low-cost NiFe inverse opal for enhanced OER in alkaline solutions. Inverse opal structures are used to increase the surface area for the OER and to facilitate the transport of the electrolyte and oxygen gases on the electrode surface. In order to form NiFe inverse opals, we first electrophoretically deposited polystyrene (PS) nanoparticles with 600 nm in diameter on a Au (200 nm)/Ti (5 nm)/Si substrate and NiFe was electroplated in the PS template. The layer thickness and composition of NiFe inverse opals were controlled by changing electroplating time and the composition of electroplating solutions. The OER performance of inverse opal structures increased with the layer thickness of inverse opal. For instance, Ni Fe inverse opal of 8 layers shows the OER overpotential of about 310 and 460 mV at the current density of 10 and 100 mA/cm² in 1M NaOH, respectively. This corresponds about 60 and 130 mV reduction of overpotential at 10 and 100 mA/cm², respectively, compared to its planar counterpart. In addition, we investigated the electrochemical OER performance of NiFe inverse opals as a function of inverse opal layer thickness and concentrations of NaOH. Detailed analysis of the role of the true surface area of a NiFe inverse opal on the OER will be given to envision charge and mass transfer on a gas evolving nanostructured electrode.

Reference
[1] Du, Pingwu, and Richard Eisenberg. "Catalysts made of earth-abundant elements (Co, Ni, Fe) for water splitting: recent progress and future challenges." Energy & Environmental Science 5.3 (2012): 6012-6021.
[2] McCrory, Charles CL, et al. "Benchmarking hydrogen evolving reaction and oxygen evolving reaction electrocatalysts for solar water splitting devices."Journal of the American Chemical Society 137.13 (2015): 4347-4357.

Efficient execution of the oxygen evolution reaction (OER) is critical for a number of energy conversion technologies, including water splitting cells, metal air batteries and regenerative fuel cells. However, OER involves four electron transfer reactions and multiple intermediates, whichs lead to sluggish kinetics. Various transition metal oxides and oxyhydroxides, such as cobalt oxides and nickel iron oxyhydroxides, have been investigated as OER catalysts and have shown promising activities in alkaline conditions.^{[1], [2]} Doping has been widely employed as a strategy to improve the OER activity and stability of these catalysts. Dopants consisting of 3d transition metals, including Ni, Fe, and Co^[2] are commonly investigated; however, much less focus is placed on 4f metals dopants such as Ce, which has been shown to enhance OER activity.^[3]

In this work, we investigate the OER activity of Ce-modified transition metal oxide thin films prepared by electrodeposition. Cerium is known to have a high electrochemical reduction potential and facilitates access to Ce³⁺ and Ce⁴⁺ oxidation states, both of which can influence the electrochemical behavior of ions such as Co and Ni. Our work aims to control Ce content in electrodeposited cobalt oxide and copper oxide films and correlate OER activity with Ce ion composition. Electrochemical characterization reveals that the OER activity of cobalt and copper oxides are enhanced with Ce incorporation. In addition, Ce incorporation also improves the stability of copper oxide OER catalysts.

[1] B. S. Yeo and A. T. Bell, J. Am. Chem. Soc. 2011, 133, 5587–5593
[2] D. Friebel et al., J. Am. Chem. Soc. 2015, 137, 1305−1313.
[3] J. W. D. Ng et al., Nat. Energy. 2016, 16053.

Using a ccombination of first-principles calculations, microkinetic modeling, and reactivity experiments, we establish a rigorous framework for developing a fundamental mechanistic understanding of chemical reactions catalyzed by heterogeneous catalysts. Based on that understanding, and insights derived for the importance of atomic-scale structure sensitivity, we then provide guidance to inorganic synthesis for prepraring shape- and composition-selected alloys which are predicted to hold promise for improved activity and selectivity for the reactions of interest. Examples may cover vapor phase catalysis and/or electrocatalysis.

Catalytic hydrogenations are critical steps in many industries including agricultural chemicals, foods and pharmaceuticals. In the petroleum refining, for instance, catalytic hydrogenations are performed to produce light and hydrogen rich products like gasoline. Typical heterogeneous hydrogenation catalysts involve nanoparticles composed of expensive noble metals or alloys based on platinum, palladium, rhodium, and ruthenium. We demonstrated for the first time how single palladium atoms can convert the otherwise catalytically inert surface of an inexpensive metal into an ultraselective catalyst.(1) High-resolution imaging allowed us to characterize the active sites in single atom alloy surfaces, and temperature programmed reaction spectroscopy to probe the chemistry. The mechanism involves facile dissociation of hydrogen at individual palladium atoms followed by spillover onto the copper surface, where ultraselective catalysis occurs by virtue of weak binding. The reaction selectivity is in fact much higher than that measured on palladium alone, illustrating the system’s unique synergy.

Our single atom alloy approach may in fact prove to be a general strategy for designing novel bi-functional heterogeneous catalysts in which a catalytically active element is atomically dispersed in a more inert matrix. Very recently we demonstrated that this strategy works in the design of real catalysts.(2) Palladium/copper nanoparticles containing <2% palladium exhibited highly selective hydrogenation of phenylacetylene under realistic reaction conditions and platinum/copper nanoparticles perform the industrially important butadiene hydrogenation at lower temperature using just 1% platinum (3). Moreover, some of the best industrial alloy catalysts to date may already be operating via this mechanism, but there is currently no method to directly probe the atomic geometry of a working catalyst. Our scientific approach allows one to parse out the minimal reactive ensembles in an alloy catalyst and provide design rules for selective catalytic nanoparticle. From another practical application standpoint, the small amounts of precious metal required to produce single atom alloys generates a very attractive alternative to traditional bimetallic catalysts.


References:
1) G. Kyriakou, M. B. Boucher, A. D. Jewell, E. A. Lewis, T. J. Lawton, A. E. Baber, H. L. Tierney, M. Flytzani-Stephanopoulos and E. C. H. Sykes – Science 2012, 335, 1209-1212
2) M. B. Boucher, B. Zugic, G. Cladaras, J. Kammert, M. D. Marcinkowski, T. J. Lawton, E. C. H. Sykes, and M. Flytzani-Stephanopolous - Physical Chemistry Chemical Physics 2013, 15, 12187-12196
3) F. R. Lucci, J. Liu, M. D. Marcinkowski, M. Yang, L. F. Allard, M. Flytzani-Stephanopoulos, and E. C. H. Sykes - Nature Communications 2015, 6, 8550

Atmospheric pressure CO₂ hydrogenation over supported metal catalysts leads to the formation of CH₄ and CO. Despite extensive work in the past decades aimed at understanding the site requirements and elementary steps of CO₂ hydrogenation over oxide-supported metal catalysts, the detailed reaction mechanisms and key intermediates are still under debate. The most widely proposed reaction mechanisms are the direct hydrogenation of CO₂ to CH₄ and the stepwise reduction of CO₂ with CO as the critical intermediate. Our recent work on supported Pd and Ru catalysts has indicated that the reaction required bifunctional catalysts: an oxide for the activation of CO₂ and a metal for the dissociation of H₂. In addition, large metal particles were found to favor the formation of CH₄ while smaller particles and single metal atoms tended to produce more CO. The underlying principles governing these changes in product selectivity with metal particle size, however, are not understood without ambiguity. This contribution will present results on a combined kinetic and spectroscopy study aimed at understanding the overall reaction mechanisms of CO₂ reduction over Pd/γ-Al₂O₃ catalysts with widely different metal dispersions. This is achieved by determining kinetic parameters and by identifying surface intermediates.
Transient DRIFTS and ME-FTIR measurements were conducted to gain insights into the surface species present under CO₂ reduction, and ultimately to help understand the reaction mechanism. The formation of adsorbed CO (on Pd/Ru) and bicarbonates (on Al₂O₃) are seen in the DRIFT spectra very shortly after the introduction of CO₂ onto the H₂-reduced catalysts. During a He purge no change in the adsorbed CO coverage, while large drop in the bicarbonate coverage were seen. The coverage of adsorbed CO declined fast after the introduction of H₂ into the He purge. The results of DRIFTS and MS experiments clearly show that the surface intermediate responsible for adsorbed CO formation is a surface formate, while CH₄ is produced through adsorbed CO. ME-FTIR experiments clearly substantiated that among the different surface formates produced, the mono-dentate ones (most probably residing at the metal/oxide interface) are responsible for the production of CO. The main difference between catalysts with high (atomic) and low metal dispersion is the ability of the metal to supply hydrogen to adsorbed CO. The large pool of active hydrogen on large metal particles promotes the formation of CH₄, while small particles (single atoms) selectively produce CO.

CO₂ conversion by hydrogen under atmospheric pressures mediated by Al₂O₃ supported copper nanoclusters has been investigated. The model catalyst systems were prepared by depositing size-selected Cu_n clusters (n = 3, 4, 12, and 20) on amorphous alumina support. A temperature-programmed reaction (TPRx) combined with in situ grazing incidence X-ray absorption near edge structure (GIXANES), and grazing incidence small angle X-ray scattering (GISAXS) measurements have been performed to study the evolution of the chemical state and size of the particles¹.
A significant rise in catalytic activity for methanol formation is observed under concentrated reactant gases for Al₂O₃ supported Cu₄ clusters above 225 C as found from turnover rate (TOR) calculation. The activity peaks at around 375 C and is an order of magnitude higher relative to that under dilute reactant gases². Methane production triggers at a higher temperature, but rapidly rises above 325 C.
GIXANES measurements indicate a reduced copper state for the active catalyst. Furthermore, we found that by controlling the traces of oxygen in the reactor, the selectivity towards methane and methanol formation can be tuned. From GISAXS analysis we find that the most active catalysts are Cu₄ nano- assemblies which form at higher temperature and redisperse on cooling. Strong size dependence has been observed, as under identical reaction conditions Cu₃ assemblies are weakly active whereas, Cu₁₂, and Cu₂₀ assemblies does not have noticeable activity.
Other nanocatalyst systems studied were prepared by depositing Cu_n on various amorphous metal oxide (ZnO, and ZrO₂), and carbon-based (UNCD = ultrananocrystaline diamond) supports. Clusters supported on ZnO and UNCD are found to be sintering resistant, while smaller assemblies form on ZrO₂ supports. Al₂O₃ supported cluster nanoassemblies were much more active compared to these later systems.

References:

[1] Halder, A., Yang, B., Kolipaka, K. L., Pellin, M., Seifert, S., and Vajda, S. Support dependent activity enhancement of subnanometer copper clusters for carbon dioxide conversion to methanol at low pressure (in preparation).
[2] Liu, C., Yang, B., Tyo, E., Seifert, S., DeBartolo, J., von Issendorff, B., Zapol, P., Vajda, S., and Curtiss, L.A., Journal of the American Chemical Society (2015) 27, 8676.

In this presentation, we will discuss fuel production from H₂O/CO₂ thermolysis in an oxygen permeable membrane reactor at elevated temperature. In such a membrane reactor, the thermolysis reaction rate is facilitated and thermodynamic equilibrium is shifted. Moreover, no electricity is consumed in this process. Therefore, clean heat sources from solar or nuclear power can be utilized in the thermolysis process.

Mixed ionic-electronic conductive perovskite La_0.9Ca_0.1FeO_3-δ (LCF-91) membrane is used [1] [2]. Surface reactions are identified as the rate-limiting steps in the oxygen transport process when a reducing gas is added on the sweep side. Therefore, surface modifications such as adding a porous perovskite layer and catalysts are introduced. As a result, the performances are improved by two orders of magnitude compared with the original flat membrane, and the maximum hydrogen production rate from water reaches 0.5 μmol/cm²-s when 5 vol% CH₄ is used as the sweep gas at 990^oC. Long term study shows that the catalytic layer maintains high performances for 54 hours. Similarly, the surface modified membrane also enhances CO₂ thermolysis. Preliminary results show that the oxygen flux can reach 0.14 μmol/cm²-s when CO₂ is the oxygen source and CO is the reducing gas.

Experimental results also show that when methane is introduced on the sweep side, optimum syngas composition for gas-to-liquid pathway i.e., H₂/CO = 2 is achieved on the surface modified membrane, depending on the availability of surface oxygen. Coking is suppressed by increasing the oxygen flux through the membrane and using nickel catalysts.

Reference:
[1] Wu, X. Y., Chang, L., Uddi, M., Kirchen, P., and Ghoniem, A. F., 2015, "Toward enhanced hydrogen generation from water using oxygen permeating LCF membranes," PCCP, 17(15), pp. 10093-10107.
[2] Wu, X. Y., Uddi, M., and Ghoniem, A. F., 2016, "Enhancing co-production of H2 and syngas via water splitting and POM on surface-modified oxygen permeable membranes," invited to submit AIChE Journal, under review.

We show an unexpected high yield electrochemical process that (i) reduces the cost of CNTs by 100-fold and (ii) directly converts carbon dioxide to these CNTs.^1-7 The cost and practicality of greenhouse gas removal processes, which are critical for environmental sustainability, pivots on high-value secondary applications derived from carbon capture and conversion techniques. Ambient CO₂ dissolved in molten carbonates is directly transformed by electrolysis to carbon nanofibers (CNFs) and CNTs at high yield through electrolysis using inexpensive steel electrodes. Whereas credits for CO₂ removal are currently valued at ~$30 per ton, industrial grade CNTs (a hollow form of CNFs) are valued at up to $400,000 per ton incentivizing removal of the greenhouse gas. Displaying superior strength, conductivity, flexibility and durability, CNF applications had been limited due to the cost intensive complexities of their synthesis. We present an inexpensive, high-yield and scale-able synthesis of CNFs. The process can be driven by conventional energy, as well as an efficient solar thermal electrochemical process. The CNT structure is tuned by controlling the electrolysis conditions, such as addition of trace common metals to act as nucleation sites, of added oxide, addition of initiators and the control of current density. An inexpensive source of CNTs from CO₂ will facilitate its adoption as an important societal resource for the building, aerospace, transportation, renewable energy, sporting and consumer electronics industries, while concurrently incentivizing the consumption and removal of carbon dioxide.

Licht group:
1. One-Pot Synthesis of Carbon Nanofibers from CO₂. Nano Lett 2015;15:6142.
open access at: http://pubs.acs.org/doi/10.1021/acs.nanolett.5b02427

2) Tracking airborne CO₂ mitigation and low cost transformation into valuable carbon nanotubes,
Scientific Reports, 6, 27760; open access at: http://www.nature.com/srep/2016/160609/srep27760/full/srep27760.html

3) Thermodynamic assessment of CO₂ to carbon nanofiber transformation for carbon sequestration
in a combined cycle gas or a coal power plant, Energy Conversion & Management 2016;
open access at: http://authors.elsevier.com/sd/article/S0196890416304861

4) One-pot synthesis of nanostructured carbon materials from carbon dioxide via electrolysis in molten carbonate salts.
Carbon 2016; open access article available at: http://dx.doi.org/10.1016/j.carbon.2016.05.031

5) How does amalgamated Ni cathode affect Carbon Nanotube growth? A density functional theory study.
RCS Adv 2016;6:2791.

6) The Minimum Electrolytic Energy Needed To Convert CO₂ to Carbon by Electrolysis in Carbonate Melts. J Phys Chem C 2015;119:23342; open access at: http://pubs.acs.org/doi/pdf/10.1021/acs.jpcc.5b07026

7) Carbon Nanotubes Produced from Ambient CO₂ for Environmentally Sustainable Li-Ion & Na-Ion Battery Anodes.
ACS Central Science 2016; 2:162; open access at: http://pubs.acs.org/doi/pdf/10.1021/acscentsci.5b00400

We have prepared a mixed-metal Fe–Cu oxide catalyst for photo-electrochemical CO₂ reduction. Electrochemical studies show that this catalyst displays selective photocurrent meaning that it is photoactive in CO₂-saturated aqueous electrolyte but produces no photocurrent in Ar-purged electrolyte, indicating that charge transfer from the catalyst surface to CO₂ is strongly preferred over proton reduction. This is unique compared to either of the pure oxides, which show no photocurrent in the case of Fe₂O₃ or high proton reduction current in the case of CuO. Reaction studies of the mixed Fe–Cu oxide show that this photo-electrocatalyst is also highly efficient for C–C bond coupling, producing acetate from CO₂ with greater than 70% Faradaic efficiency. To better understand the photo-physics of this catalyst leading to highly selective charge transfer to CO₂ and subsequent C–C bond coupling, we are investigating this system using ultrafast soft x-ray transient absorption spectroscopy at the Fe and Cu M edges of this mixed metal system. This experiment, which utilizes a tabletop high harmonic generation soft x-ray light source with femtosecond time resolution, enables us to elucidate the element-specific electron dynamics leading to efficient charge separation and injection during the photo-electrocatalytic reduction of CO₂ to acetate.

Electrochemical reduction of CO2, an artificial way of carbon recycling, represents one promising solution for energy and environmental sustainability. Despite the many advantages, electrochemical reduction of CO₂ is challenged by the absence of efficient catalysts for this reaction. Copper (Cu) is the most studied material capable of catalyzing CO2 reduction at significant rates, but it still requires large overpotentials; e.g., to reach a current density of 1 mA/cm2 on polycrystalline Cu electrode, it typically requires an overpotential of >0.5 V for producing CO and HCOOH (two-electron processes) and >0.8 V for further reduced products such as CH₄ and C₂H₄. Moreover, hydrogen evolution competes with CO2 reduction, reducing the Faradaic efficiency (FE) towards carbon-containing compounds.

Here we report the synthesis of highly dense Cu nanowires and tailoring of their surface structures to achieve superior performance for electrocatalytic CO₂ and CO reduction, with particular attention to low-overpotential conditions. CuO nanowires were first grown by oxidizing Cu mesh in air which were then subjected to electrochemical reduction or annealing in a reducing atmosphere to form Cu nanowires. By tailoring the conditions for the reduction, high activity and selectivity were achieved for the production of CO from CO₂, and ethanol/acetate from CO, at E < 0.4 V. It was found that the catalytic performances of the Cu nanowires are strongly correlated to the crystalline and surface structures in the nanoscale, based on which the active sites capable of selective reduction of CO₂ and CO were identified. Our work indicates the great potential of electrochemical conversion of CO₂ for synthesis of fuel molecules and production of chemical feedstocks.

The catalytic semi-hydrogenation of acetylene to produce ethylene is a common method for the removal of trace acetylene (~1%) in ethylene feed streams destined for ethylene polymerization. An effective catalyst for this reaction converts all of the acetylene to ethylene without further conversion of ethylene to ethane such that there is a net increase in the amount of ethylene. Pd-Ag alloys, and more recently, intermetallic Pd-Ga compounds, demonstrate high selectivity towards ethylene and long-term stability. Improved selectivity is a result of isolation of active Pd hydrogenation sites which reduces over-hydrogenation to form ethane, oligomerization products, and coke formation on the catalyst surface. Replacing Pd-based catalysts with base metal Ni-based catalysts would be highly beneficial in terms of cost and environmental impact. Bulk intermetallic catalysts contain little structural and compositional variance, a property that is not easily attainable with supported catalysts. We report on the catalytic selectivity of unsupported bulk intermetallic Ni-Zn and Pd-Zn catalysts for acetylene semi-hydrogenation. We demonstrate the addition of Ni to Zn improves selectivity to ethylene due to a reduction in acetylene oligomerization products rather than ethane over-hydrogenation. The most selective catalysts had the lowest Ni content with a g-brass bulk structure. Structural investigation by neutron diffraction demonstrated the presence of well-defined Ni (or Pd) trimers in the g-brass structure with the number of these trimers increasing with Ni (or Pd) content. The Ni alloys are active for H₂-D₂ exchange, but all surfaces (i.e, different Ni content) are indistinguishable with respect to their catalytic behavior. In the case of Pd-Zn alloys with the g-brass structure, there are apparent differences in the H₂-D₂ rates and ethylene hydrogenation as the Pd content (and therefore number of Pd trimers) increases. While the Ni and Pd trimers are stable in the bulk structure, the differences in the surface stability of these trimers in the Zn matrix and the corresponding percentage of the trimer-containing surface present in a Wulff reconstruction explain the disparate catalytic results in the seemingly related systems. From the observed catalytic behavior, we believe that trimer sites in proportion to the ideal speciation are present on the Pd-Zn intermetallic samples with a Pd count greater than or equal to nine. We demonstrate bulk intermetallics are useful systems to screen compositional and structural (from site-isolated to well-defined 2D clusters) variance on catalytic behavior.

The development of energy efficient carbon dioxide (CO₂) electroreduction processes would simultaneously curb anthropogenic CO₂ emissions and provide sustainable pathways for generation of fuels and chemicals. While significant efforts have focused on heterogeneous CO2 electroreduction to various products, to date, no process has demonstrated both high energetic efficiencies and high current densities. The electroreduction of CO₂ to formic acid (FA) is attractive due to the low charge requirement, liquid state product, and high selectivity on a number of low cost catalytic materials. Prior reports have demonstrated electroreduction of CO₂ to FA on Sn catalysts at high faradaic efficiencies (10-95%) on gas diffusion electrodes (GDEs) which operate at a range of currents (10-200 mA/cm²).[1] These studies have used Sn particles (150 nm to 150 µm) applied with an ionomer to a microporous carbon layer (MPL), supported by a gas diffusion layer (GDL). This approach limits the electroreduction process due to 1) low tin catalyst specific surface area due to the relatively large Sn particle size (>150 nm), and 2) unutilized Sn catalyst particles within the ionomer but not in electrical contact with the carbon in the MPL.

Previous work directed towards platinum catalyst utilization in PEM fuel cell GDEs demonstrated a novel “electrocatalyzation” approach to obtain highly dispersed (~5 nm) Pt catalyst particles using pulse and pulse reverse electrodeposition.[2] Additionally, since the Pt was electrodeposited through an ionomer applied to a carbon MPL, the catalyst was inherently in electronic and ion contact within the GDE and consequently catalyst utilization was enhanced.

Herein we investigate the electrocatalytic performance of novel Sn nanostructures electrodeposited directly onto the MPL using pulse and reverse pulse waveforms. We demonstrate that the electrochemical reduction of CO₂ is improved by 1) increasing the Sn catalyst specific surface area by decreasing the Sn catalyst particle size (<<150 nm), and 2) improve the Sn catalyst utilization by ensuring electronic & ionic contact with the carbon in the MPL. This approach enables the deposition of robust and uniform catalytic Sn layers on the surface of highly structured GDL/MPL substrates. State of the art Sn catalysts (150 nm) mixed within the ionomer and applied to the MPL are used as a benchmark for comparison. Electrolysis experiments are conducted in a continuous mode lab-scale reactor with flowing gaseous CO₂ delivered across a GDE using advanced flow fields. FA production is measured as at cell outlets and used to determine the activity, efficiency, and stability of these novel catalytic structures for CO₂ to FA conversions.

References

[1] D. Kopljar, A. Inan, P. Vindayer, N. Wagner and E. Klemm, J. Appl. Electrochem., 44, 1107 (2014)
[2] E. J. Taylor, E. B. Anderson and N. R. K. Vilambi, J. Electrochem. Soc.,139(5), L45 (1992)

Au has demonstrated the highest catalytic selectivity, activity, and stability for the reduction of CO₂ to CO of any metal, but the mechanism for this performance remains unclear. Studies of nanoparticle films have shown that higher index facets have improved performance, but the preeminent nanoparticle films, from oxide-derived Au, lack well-defined facets and morphological stability to illuminate their enabling mechanism. Here we demonstrate a facile and novel dendrite fabrication process that produces faceted crystals with tunable morphology and electrochemical activity. The dendrites show high catalytic selectivity, activity, and stability for CO₂ reduction to CO; along with morphological stability after 18 hours of operation, allowing for important correlation between morphology and performance. The influence of exposed facets will be discussed.

As a successful energy storage technology, Li-ion battery fails to meet societal needs in terms of energy and power densities. Post-Li-ion technologies look at conversion chemistry, which promises significantly greater capacities. Examples include Li-S and Li-O2 batteries. In this talk, we will examine issues connected to electrode and electrolyte stabilities of Li-O2 batteries. Because oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are of paramount importance to the chemistries, great attention is given to the catalysis at both the cathode and anode during both discharge and recharge. It is shown that reactive oxygen species play important roles in degrading the cell components. Based on these discussions, we will present our views on how to stabilize Li-O2 operations. New ideas on how to go beyond Li-O2 chemistries will be presented as well.

Rechargeable metal-air battery systems, such as lithium-air and zinc-air batteries, have recently gained tremendous attention due to their extremely high energy density and flat discharge profile. In particular, rechargeable zinc-air batteries are considered highly promising due to many advantages, including cost-effectiveness, safe operations, and environment benignity. For emerging electric drive vehicle applications, however, batteries capable of generating both high power and high energy are required to sufficiently provide vehicle acceleration and extended driving range, respectively. Previously, hybrid energy systems have been fabricated through simple electrical connections of different devices, or utilization of multiple active materials inside a single battery. However, this made them physically bulky or too expensive to harness energy in a cost-effect manner. In this present work, a novel hybrid rechargeable battery concept is demonstrated using a single type of active material to generate both high power and high energy without increasing system size or complexity. The active material consisting of nickel oxide/nickel hydroxide (NiO/Ni(OH)₂) nanoflakes self-assembled into mesoporous spheres is affordable, simple to fabricate, and environmental friendly. This cost-effective non-precious transition metal based active material is capable of exhibiting both Faradaic redox and reversible oxygen electrocatalytic reactions, which drive nickel-zinc and zinc-air battery reactions, respectively. Specifically, the hybrid battery is capable of demonstrating extremely high power density of 2700 W kg^-1 (volumetrically 14000 W L^-1), as well as very high energy density of 980 W h kg^-1, far exceeding those of commercial primary zinc-air batteries (~470 W h kg^-1), and lithium-ion batteries (~300 W h kg^-1). The hybrid battery performance is attributed to the dual functionality of the active nickel species demonstrating both nickel-zinc and zinc-air battery reactions.

Li-O₂ batteries, which is a high energy density and rate capacity system, requires an effective catalyst to facilitate the ORR and OER reactions. Herein, we report a transition metal alloy, Fe₇Ni₃ naonspheres, synthesized via a facile and cost-effective solvent thermal method，act as an effective catalyst in Li-O₂ batteries reactions. Characterization of this catalyst by X-ray diffraction, inductively Couple Plasma, transition electron microscopy, X-ray photoelectron spectroscopy confirms the formation of a single phase body-centered cubic Fe₇Ni₃ alloy nanospheres. The catalyst used in Li-O₂ batteries exhibits a superior catalytic activity with a high reversible capacity 7206 mAh/g_KB under current density of 150 mA/g_KB. Additionally, catalytic activity results in a lower over-potential both in OER and ORR reducing the voltage gap ca. 200 mV and cycling stability, which indicates it maybe a promising catalyst for Li-O₂ batteries.
ACKNOWLEDGMENTS
This work was supported by the National Science Foundations of China 21271028, 51242030 21471020and 21271001.

In this talk I will focus on computational studies used to help understand the electrocatalytic properties of supported subnanometer clusters[1] including CO₂ reduction, Li-O₂ electrochemistry, and water oxidation. Computational studies[2] of electrochemical reduction of CO₂ to CO, HCOOH and CH₄ were carried out using tetra-atomic transition metal clusters (Fe₄, Co₄, Ni₄, Cu₄ and Pt₄) at the B3LYP level of theory. Novel catalytic properties were discovered for these subnanometer clusters, suggesting that they may be good candidate materials for CO₂ reduction. Recent experimental studies [3] have shown that Cu subnanometer clusters have novel properties for CO₂ reduction. Studies of precisely controlled subnanometer silver clusters added to Li-O₂ battery cathodes has revealed a dramatic dependence of the performance of the battery on the silver cluster size. Density functional calculations indicate that oxygen reduction and nucleation occur at separate sites on the cathode through a solution phase process during discharge, which accounts for the different morphologies. [4] Recently, it has been discovered that Ir nanoparticles can be used to stabilize lithium superoxide.[5] DFT calculations on subnanometer Ir clusters are being used to identify the mechanism for formation of lithium superoxide in these Li-O₂ cells. Finally we have used DFT calculations to investigate the water oxidation reaction of size-selected clusters for understanding of experimental measurements.[6] Theoretical calculations suggest that this striking difference may be a demonstration that bridging Pd–Pd sites (which are only present in three-dimensional clusters) are active for the oxygen evolution reaction in Pd₆O₆.
…………………

References

[1] Y. Lei, F. Mehmood, S. Lee, J. P. Greeley, B. Lee, S. Seifert, R. E. Winans, J. W. Elam, R. J. Meyer, P. C. Redfern, D. Teschner, R. Schlögl, M. J. Pellin, L. A. Curtiss, and S. Vajda, Science 328, 224 (2010).
[2] C. ; Liu, H. He, P. Zapol, L. A. Curtiss, Phys. Chem. Chem. Phys., 16, 26584 (2014).
[3] Vajda et al, submitted.
[4] J. Lu, L. Cheng, K. C. Lau, E. Tyo, X. Luo, J. Wen, Dean Miller, R. S. Assary, H.-H. Wang, P. Redfern, H. Wu, J.-B. Park, Y.-K. Sun, S. Vajda, K. Amine, L. A. Curtiss, Nature Communications 5, 4895 (2014)
[5] J. Lu, Y. J. Lee, X. Luo, K. C. Lau, M. Asadi, H.-H. Wang, S. Brombosz, J. G. Wen, D. Zhai, Z. Chen, D. J. Miller, Y. S. Jeong, J.-B. Park, Z. Z. Fang, B. Kumar, A. Salehi-Khojin, Y.-K. Sun, L. A. Curtiss, K. Amine, Nature 529, 377 (2016)
[6] G. Kwon, G. A. Ferguson, C. J. Heard, E. C. Tyo, C. R. Yin, J. DeBartolo, S. Seifert, R. E. Winans, A. J. Kropf, J. Greeley, R. L. Johnston, L. A. Curtiss, M. J. Pellin, S. Vajda, ACS Nano 7, 5808-5817 (2013).

Surface structure of heterogeneous catalysts plays an important role in determining the activity and selectivity of many industrially relevant chemical processes. Controlling the surface structure of complex metal-oxide based catalysts (such as perovskite and nickelate oxides) has been appreciably challenging, and has mainly relied on utilization of thin film synthesis approaches, which lead to low surface area catalysts. In this presentation, we demonstrate through a combination of quantum chemical density functional theory (DFT) calculations, controlled synthesis of well-defined nanostructures, state-of-the-art characterization techniques (atomic level imaging and electron energy loss spectroscopy), and isotopic labeling kinetic studies that engineering the surface of layered nickelate oxides can significantly enhance their catalytic activity toward surface oxygen exchange.[1-3] Nickelate oxides are among complex, layered oxides with great potential toward efficiently catalyzing chemical and electrochemical reactions involving oxygen. DFT calculations show that (001)-NiO terminated La₂NiO₄ surfaces exhibit the highest rates for oxygen exchange by providing the best compromise between the energetics associated with oxygen adsorption/desorption and surface oxygen vacancy formation. These predictions are supported by experimental studies on oxygen exchange/reduction on La₂NiO₄ nanostructure with two different geometries: (i) nanorod geometry, predominantly terminated by (001)-NiO surface facets, and (ii) traditional spherical geometry. Our isotope-labeled thermochemical kinetic and electrochemical studies show that the thermochemical oxygen exchange and the electrochemical oxygen reduction kinetics are significantly more favorable on LNO nanorods as compared to the traditional polyhedron-type LNO catalyst. We have further developed composition/performance relationships that can guide the identification of optimal nanostructured nickelate oxide compositions for electrochemical oxygen exchange/reduction. These findings lay the groundwork for enhancing the catalytic activity of complex metal-oxide catalysts via engineering of their surface structure and composition.


References
[1] Ma X., Wang B., Xhafa E., Nikolla E., Chem Comm., 51, 137, 2015.
[2] Ma, X., Carneiro, J., Gu X-K., Qin H., Xin H., Sun K., Nikolla E., ACS Catal, 2015, 5 (7), 4013–4019.
[3] Carneiro, J., Brocca, R. A., Lucerna M. L. R. S., Nikolla E., Applied Catal B: Environmental, 2016.

The commercialization of hydrogen fuel cells is limited in part by the high cost of Pt catalysts used for the oxygen reduction reaction (ORR). Pt-Ni alloys have been shown to be highly active ORR catalysts with reduced platinum content, but their durability is limited by Ni dissolution. To facilitate the rational design of new ORR catalysts with high activity and stability, we have used a Bayesian cluster expansion to model the structure and catalytic properties of Pt-Ni-based catalysts. Our approach enables us to rapidly search for optimal structures, calculate thermodynamic averages at finite temperature, and model nanoparticles at experimentally relevant sizes with a level of accuracy close to that of density functional theory. We will demonstrate that there is significant atomic disorder in the sub-surface layers of Pt-Ni catalysts under operating conditions, and variations in local sub-surface atomic order can affect the catalytic activity of different surface sites by three orders of magnitude. In addition we will provide evidence explaining how doping Pt-Ni nanoparticles with small amounts of Mo results in nanoparticles with increased activity and greatly enhanced stability. Finally, we will discuss the atomic-scale mechanism for Ni dissolution from Pt-Ni nanoparticles and how the dissolution process can result in the creation of nanoframes and nanoparticles with concave facets.

Transition metal oxides, in particular perovskites (ABO₃), have generated huge interest as Pt-free oxygen electrocatalysts in alkaline solutions.^1,2 Although these materials have been extensively investigated in the field of solid oxide fuel cells, their properties as oxygen electrocatalysts at room temperature remain to be fully elucidated. The key challenge in this field involves establishing structure-activity relationships based on the electronic structure of the B-site, which is widely recognised as the main active site. Such information is extremely important towards designing catalysts with optimal B-site orbital occupancy, coordination number and metal-oxygen bond length.

In this contribution, we shall examine a family of Mn based perovskite nanoparticles obtained by an ionic liquid method.^3,4 This highly versatile synthetic approach allows the preparation of phase pure oxides particles with sizes ranging from 20 to 50 nm. We will first show that LaMnO₃ exhibits a reactivity orders of magnitude higher than other lanthanide perovskites (e.g. Co, Fe, Cr and Ni), which is linked to changes in the redox state at the Mn sites.⁵ Indeed, the electron population at Mn sites increases at potentials close to the formal ORR potential. We will then discuss the activity of a family of La_xCa_1-xMnO₃ nanoparticles, assessing their activity as a function of the Mn-valency. We will provide a detailed analysis of the bulk and surface structure employing X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). Studies employing rotating ring-disc electrodes of the nanoparticles supported on mesoporous carbon films show that their activity towards the ORR are among the highest reported for transition metal oxides.⁶ We finally establish that the mean ORR activity of surface Mn sites increases as the Mn valency decreases. These studies highlight the need for independent assessment of key aspects such as the extent of A-site surface segregation and average Mn valency in order to establish consistent structure-activity relationships.

References:
1- A. Grimaud et al. Nat. Mater. 2016, 15, 121
2- J. Suntivich et al. Nat. Chem. 2011, 3, 647
3- D.C. Green et al. Adv. Mater. 2012, 24, 5767
4- V. Celorrio et al. ChemElectroChem 2014, 1, 1667
5- V. Celorrio et al. ChemElectroChem 2016, 3, 283
6- K.A. Soerzinger, ACS Catalysis 2015, 5, 6021

Electrochemical reduction of carbon dioxide into value-added fuels will reduce today’s dependence on conventional fossil fuels, mitigating net CO2 emissions. Unfortunately, the electrical-to-chemical power conversion efficiency of the overall reaction is limited by the sluggish anodic oxygen evolution reaction (OER) in CO2-saturated solution (pH-neutral). In the best catalysts reported to date, the overpotential of OER in pH-neutral electrolytes exceeds 460 mV at 10 mA/cm2, degrading the efficiency of renewable energy storage systems. We took the view that generating transition metal sites with high valence at low applied bias should in principle improve the activity of neutral OER catalysts. Here we report a new approach, one that seeks to minimize the formation energy of high-valency active sites, and find that the new design strategy leads to dramatic reductions in neutral OER overpotential. Using density functional theory, we find that the formation energy of desired Ni4+ sites is systematically modulated using the combination of Co, Fe and non-metal phosphorus. We synthesized NiCoFeP oxyhydroxides and probed their oxidation kinetics employing in situ soft X-ray absorption. These first-ever in operando sXAS studies of neutral pH OER catalysts indicate ready promotion of Ni4+ under record-low overpotential conditions. The new catalyst exhibits exceptional OER performance, with a 330 mV overpotential at 10 mA/cm2 in CO2-saturated 0.5 M KHCO3 electrolyte. The new catalyst outperforms the commercial precious metal oxide IrO2 and retains its performance following 100 hours of operation. Finally, we achieved a 2.03-V cell voltage at 10 mA/cm2, splitting CO2 and H2O into CO and O2 by coupling NiCoFeP oxyhydroxides as OER catalysts and Au nanoneedles as CO2 reduction catalysts.

Oxygen evolution reaction (OER) catalysts play a central role in numerous renewable energy technologies including rechargeable metal-air batteries and hydrogen generation. However, enabling these technologies require efficient, cost effective and stable catalysts. In this contribution we show that redox active metal ion (e.g. Ni²⁺, Co²⁺) intercalation into the interlayer region of layered manganese oxide leads to excellent catalytic performance in both neutral and alkaline medium. Metal ion intercalation was carried out using an ion exchange reaction using the respective metal-hydrazine complex. State-of-the-art analytical characterization has revealed that interaction of interlayer water of layered manganese oxide with the intercalated metal ion led to hydroxide like metal clusters in the interlayer region. Electrocatalytic studies have revealed this hydroxide like metal cluster confined in the interlayer region as the active site for water oxidation. Moreover, molecular dynamics simulations were carried out to explain this system. Results from the simulation suggests that confinement of metal ions in the interlayer region can promote complex dipolar interactions between the metal cations, water, and layered manganese oxide and this can lead to improved OER catalysis.

In an increasingly carbon-constrained world, lignocellulosic biomass, natural gas, and carbon dioxide have emerged as attractive options to supply energy, fuels, and chemicals at scale in a cleaner and more sustainable manner. To enable the global deployment of renewable energy technologies, a grand challenge exists to increase the activity, improve the stability and reduce the loading of noble metal (NM) catalysts. In the last decade, intense research efforts have centered on engineering core-shell nanoparticles using mainly 3d transition metals (e.g., Co, Fe, Ni, and Cu) as earth-abundant core elements. However, despite achieving reduced NM loadings and, in some cases, improved catalytic properties, these structures are intrinsically metastable. Consequently, the cores typically alloy with the NM shell during thermal treatments or undergo excessive leaching and structural deformation during electrocatalytic cycling. Lastly, independent control over the particle size, core composition, shell composition, and shell thickness has remained elusive, impeding the synthetic optimization of inexpensive, active, and stable core-shell catalyst architectures for thermo- and electrocatalytic applications.
In this lecture, I will present a new class of core-shell materials comprised of transition metal carbide (TMC) nanoparticles coated with atomically-thin precious metal shells. Owing to their remarkable physicochemical properties, TMCs are ideal candidates for supporting NM monolayers, but the synthesis of NM/TMC (shell/core) nanoparticles has been unsuccessful to date. First, using DFT simulations, we explain why prior attempts to synthesize NM/TMC materials have been unsuccessful. Second, we demonstrate the first general method to synthesize NM/TMC catalysts and provide extensive characterization data confirming their structure. Finally, we show that our method allows for the design of highly active and stable electrocatalysts with reduced precious metal loadings. Specifically, Pt and PtRu monolayers supported on bimetallic titanium tungsten carbide (TiWC) cores are shown to be exceptionally CO-tolerant electrocatalysts for hydrogen oxidation, and achieve an order of magnitude higher activity for methanol electrooxidation over commercial catalysts even after 10,000 cycles. Structure-activity descriptors can then be elucidated and used to guide the design of new catalytic materials.

The endothermic cracking of n-dodecane is investigated over well-defined nanometer size Pt and Pt-Sn alloy catalysts to study the particle size effects, promotional effect of Sn and the role of the supports. The reaction was followed with simultaneous in situ monitoring of the particle size and oxidation state of the working catalysts by in situ SAXS (Small Angle X-ray Scattering) and XAS (X-ray Absorption Spectroscopy). The selectivity toward olefins products was found dominant in the 1 nm size platinum catalysts whereas paraffins are dominant in the 2 nm Pt catalysts. This reveals a strong correlation between catalytic performance and the size of catalysts as well as the stability of the nanoparticles in supercritical condition of n-dodecane. Addition of Sn leads to increased Pt dispersion and higher aromatic selectivity than the unpromoted Pt catalyst. Carbonaceous deposits over spent catalysts were characterized by Raman spectroscopy, indicating that the Sn loading is strongly correlated with the coke formation. In summary, the combination of in situ XAS and SAXS methods offer a great potential for the real-time monitoring of catalysts behavior in the supercritical condition. The presented results suggest that monitoring the catalysts in realistic reaction conditions could lead to a fundamentally new level of understanding of nanoscale materials.

Single atom catalysis is a rapidly emerging but controversial area of catalysis research that aims to maximize the efficient usage of precious metals through the use of single atom active sites [1]. Although catalytic activity has been demonstrated for several single atom catalyst systems, the inability to accurately characterize a catalyst based on single atom active sites ensures that that the field remains controversial, and little is really known about how a single atom adsorbed on a metal oxide support can catalyze a chemical reaction. In this lecture, I will describe how we are addressing the crucial issues of stability and reaction mechanism using a surface science approach. The work is based on the magnetite (001) surface, which exhibits an unusual reconstruction based on subsurface cation vacancies [2]. A remarkable property of this reconstruction is that it stabilizes ordered arrays of metal adatoms (of almost any variety) with a nearest neighbor distance of 0.84 nm to temperatures as high as 700 K [3]. Crucially, because the geometry of the adatoms is uniform and precisely known, reactivity experiments are performed on a well-defined model system, and theoretical calculations can be performed to shed light on the mechanisms underlying catalytic activity and deactivation. Several examples of our recent work will be used to illustrate the trends we have discovered to date, including how strong CO adsorption destabilizes Pd and Pt adatoms leading to mobility and rapid sintering [4], and how extraction of lattice oxygen from the metal-oxide is central to catalytic activity in the CO oxidation reaction [5].


[1] X.-F. Yang, A. Wang, B. Qiao, J. Li, J. Liu, T. Zhang, Single-Atom Catalysts: A New Frontier in Heterogeneous Catalysis, Accounts of Chemical Research 46 (2013) 1740-1748.
[2] R. Bliem, E. McDermott, P. Ferstl, M. Setvin, O. Gamba, J. Pavelec, M.A. Schneider, M. Schmid, U. Diebold, P. Blaha, L. Hammer, G.S. Parkinson, Subsurface Cation Vacancy Stabilization of the Magnetite (001) Surface, Science 346 (2014) 1215-1218.
[3] G.S. Parkinson, Iron Oxide Surfaces, Surface Science Reports http://dx.doi.org/10.1016/j.surfrep.2016.02.001 (2016).
[4] G.S. Parkinson, Z. Novotny, G. Argentero, M. Schmid, J. Pavelec, R. Kosak, P. Blaha, U. Diebold, Carbon Monoxide-Induced Adatom Sintering in a Pd–Fe₃O₄ Model Catalyst, Nature Materials 12 (2013) 724-728.
[5] R. Bliem, J. van der Hoeven, A. Zavodny, O. Gamba, J. Pavelec, P.E. de Jongh, M. Schmid, U. Diebold, G.S. Parkinson, An Atomic-Scale View of CO and H₂ Oxidation on a Pt/Fe₃O₄ Model Catalyst, Angewandte Chemie International Edition 54 (2015) 13999–14002.

We have improved the CO₂ reduction selectivity of inorganic semiconductor (SC) material by combining SC with metal complex catalyst (MC) (SC/[MC] hybrid photocatalyst)[1,2]. In addition, by conjugating the SC/[MC] hybrid photocatalyst for CO₂ reduction with a SC capable of H₂O oxidation, we have successfully achieved an artificial photosynthesis system, which reduces CO₂ to HCOOH with no external electrical bias using H₂O as electron and proton source[3,4]. The system can be applied to many other SCs and MCs. Thus, development of MC is an important factor for improvement in reaction rates and product selectivity of the artificial photosynthesis.
We have successfully developed mononuclear Ir complex photocatalysts for efficient and selective CO₂ reduction to CO, which are driven by visible light in a homogeneous solution even in the H₂O mixed solution. There has been no study that tried to carry out a photocatalytic CO₂ reduction using Ir complexes until our report. The most efficient Ir complex photocatalyst showed TN_CO value of 50 and the quantum yield value of 0.21, which is the best reported value in mononuclear homogeneous photocatalytic systems using visible light at wavelengths such as 480 nm[5].
Furthermore, we have also successfully developed a new Mn complex electrocatalyst for CO₂ reduction[6]. Mn complex catalysts for CO₂ reduction have been researched by a lot of researchers, because Mn is one of earth abundant elements. However, because of the high overpotential for CO₂ reduction, the limited operation conditions in organic solvents with H₂O additives only, and the instability under irradiation, new catalysts need to be developed. On the other hand, the developed Mn complex catalyzed selective CO₂ reduction even in aqueous solution, at very low overpotential under room light conditions. We will discuss research progress of the new Mn complex electrocatalysts and development of new SC/[MC] hybrid photocatalyst.

Reference
[1] S. Sato, et al. Angew. Chem. Int. Ed. 2010, 49, 5101.
[2] T. Arai, et al. Chem. Commun. 2010, 46, 6944.
[3] S. Sato, et al. J. Am. Chem. Soc. 2011, 133, 15240.
[4] T. Arai, et al. Energy. Environ. Sci. 2015, 8, 1998.
[5] S. Sato, et al. Angew. Chem. Int. Ed. 2013, 52, 988.
[6] S. Sato, et al. submitted.

Recycling carbon dioxide into carbon monoxide as a feedstock for industry and transportation has become of great interest as a means to reduce the impact of humanity on the environment. Due to the high thermodynamic efficiency inherent in electrochemical reduction of CO₂ at high temperatures (~800 ^oC), solid oxide electrolysis (SOE) is an attractive method for CO production. Furthermore, in steam and CO₂ co-electrolysis, the hydrogen and CO products constitute syngas, of significant importance to industry. Additionally, SOE of CO₂ is actively being explored by the National Aeronautics and Space Administration (NASA) to generate O₂ for future missions to Mars. Mitigating degradation of SOE cell performance over time remains a key challenge of the technology. For example, carbon accumulation (coking) on the cathode during reduction of CO₂, particularly problematic in dry conditions, leads to mechanical and electrochemical degradation of the cell. Other degradation modes, well known in the solid oxide fuel cell community, such as large electrode volume changes during redox with subsequent mechanical failure are also of concern. As a result, electrodes have been developed to counter these degradation modes in electrolysis and fuel cell operation. The majority of studies have largely been guided by empirical evidence indicating coke tolerant electrodes. In this presentation, we describe an investigation into the relationship between gas/solid interface compositional and operational factors that lead to the onset of coking.
In situ near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS ) was used to evaluate conditions leading to coking using CO/CO₂ mixtures at approx. 200 mTorr total pressure at 450 ^oC. Electrical bias was applied to ceria based films, deposited using pulsed laser deposition on “buried” Pt electrodes, supported on ionic conducting substrates of yttria stabilized zirconia to in situ drive the CO₂ reduction reaction. Two different Gd doped ceria based films were studied, one with Zr doping (suggested to exhibit greater coke tolerance) and one without. The surface spectroscopy analysis yielded information about the relationship between onset of coking, surface defect concentration (e.g., oxygen vacancies), surface composition (e.g., relative cation and impurity), and area specific resistance. In this presentation, we will discuss the relationship between these factors, as well as the role of gas composition (CO/CO₂). Coking was found to correlate with cathodic current density and CO concentration, whereby larger currents (i.e., higher CO production) and higher initial CO/CO₂ ratio both led to C deposition as identified by NAP-XPS, consistent with the CO disproportionation, or Boudouard, reaction. Ce³⁺ concentration was only loosely correlated with coking and indicated a threshold amount of Ce³⁺ for coking conditions, in contrast to prior studies. The mechanism behind these correlations will be discussed.

Carbon dioxide (CO₂) is generated in substantial quantities due to energy generating activities, accounting for 82% of the worldwide energy supply in 2014. Existing methods of reducing CO₂ emissions include: increasing the percentage of energy generated from renewable or nuclear sources, utilizing CO₂ capture and storage (CCS) at point sources such as power plants, and CO₂ capture and conversion (CCC) into fuels or value added products. Current methods of CO₂ conversion include reduction in solid oxide fuel cells, reduction by metal complexes, or electrochemical reduction on metal electrodes in aqueous solutions. Depending on the catalyst used, applied voltage and operating conditions, the main products of CO₂ reduction can be small chained carbon molecules (C₁-C₃) such as carbon monoxide (CO), formic acid (HCOOH), methane (CH₄), ethylene (C₂H₄), and alcohols (C_nH_2n+1OH). Among metal catalysts, Cu is unique in its ability to reduce CO₂ to small chained hydrocarbons and alcohols at low temperatures and atmospheric pressures with surprisingly high connversion[1].
The study herein presents a novel approach to synthesize unsupported, porous Cu nanoparticles with consistent and controllable morphology using a scalable sacrificial support method (SSM) [2-4]. With this process, highly selective generation of C₂H₄ over CH₄ can be achieved. While many of the barriers discussed remain (e.g. the CER over-potential), this study is a first step towards synthesis of very durable and scalable electrocatalysts for CO₂ electroreduction to small hydrocarbon molecules.
Materials synthesized by SSM were characterized by XRD, SEM, TEM BET and XPS. It was found that during CO₂ electroreduction surface of catalysts is reduced forming Cu@Cu₂O core-shell structure. The activity, selectivity and durability of catalysts were studied electrochemically. The mechanistic pathways were confirmed by using DFT calculations.
References:
[1] O. Baturina, Q. Lu, M. Padilla, L Xin, W. Li, A. Serov, P. Atanassov, F. Xu, A. Epshteyn, T. H. Brintlinger, M. Schuette, G. E. Collins, K. Artyushkova “CO₂ electroreduction to hydrocarbons on carbon-supported Cu nanoparticles”, ACS Catal. 4 (10) (2014) 3682–3695.
[2] U. Martinez, A. Serov, M. Padilla, P. Atanassov "Mechanistic Insight into Oxide-Promoted Palladium Catalysts for the Electro-Oxidation of Ethanol", ChemSusChem 7(8) (2014) 2351–2357.
[3] A. Serov, K. Artyushkova, P. Atanassov "Fe-N-C Oxygen Reduction Fuel Cell Catalyst Derived from Carbendazim: Synthesis, Structure and Reactivity", Adv. Energy Mater. 4: 1301735 (2014) doi: 10.1002/aenm.201301735.
[4] A. Serov, M. Padilla, A. J. Roy, P. Atanassov, T. Sakamoto, K. Asazawa, H. Tanaka "Anode Catalysts for Direct Hydrazine Fuel Cells: From Laboratory Test to an Electric Vehicle", Angewandte Chemie Int. Ed. 126 (39) (2014) 10419–10715.

The rational design of novel catalysts for CO₂ reduction has attracted considerable attention, owing to the increasing global fuel demand and greenhouse gas emission. Cu2O has been suggested to be thermodynamically capable of photocatalytically reducing CO₂ to methanol, but practically the stepwise CO₂ reduction reactions are significantly hindered by kinetic reasons. Earlier studies have shown that the CO₂ conversion rate is quite limited on stoichiometric, defect-free oxide surfaces due to the low catalytic activity; on the other hand, defected surfaces generally have higher activity and may provide better catalytic performance.

In this work, we performed density functional theory (DFT) studies to investigate the catalytic activity of Cu₂O(110) surface and to address the energetics of the initial two-electron reduction of CO₂, which is believed to be the rate-limiting step in CO₂ photo-/electroreduction due to the inertness of CO₂ molecules. The preferred CO₂ adsorption sites and configurations on both pristine and defected Cu₂O(110) surfaces are determined, and the surface stoichiometry that favors CO₂ adsorption is thus identified. Scanning tunneling microscopy (STM) images of various adsorption configurations were simulated and compared with experiments. Subsequently the reaction barriers of two possible CO₂ reduction pathways, namely CO₂+2H⁺+2e^-→CO+H₂O and CO₂+2H⁺+2e^-→HCOOH are investigated, and it is found that the favored pathway is determined by the initial CO₂ adsorption configuration. The results from this study demonstrate the importance of rational surface engineering of catalysts for effective CO₂ conversion.

The photoelectrochemical and electrochemical reduction of CO₂ can provide an alternative solution to the global warming, as well as popularize the storage of solar or electrical energy into chemical bonds.¹ In this sense, numerous catalysts and electrodes have been tested throughout the years, including Sn, a metal that has two allotropic forms, alfa and beta. Employed as an electrode, Sn can catalyze the reaction of bicarbonate into formate in near-neutral medium.² However, the mechanism of conversion is not well understood yet. ^1,2 In this work, we investigate these reactions on the surface of Sn-beta, which is the most stable allotropic form in the room temperature, within the framework of density functional theory (DFT).^. Among the different surface planes we have tested, it is found the (100) plane is the most stable, which is agreement with the literature report.³ The final slab optimization was then used to create the surfaces in a 3X3 arrangement. In this way, we could access the free energies of reaction intermediates adsorbed on the surface and shed light on the reaction mechanism. Solid-water interface effects have been assessed through implicit solvent models in connection with molecular dynamics simulations. Results on the Sn-SnO systems will also be presented and discussed.
References
1-G. A.Olah et al. Journal of Power Sources 223, 68 (2013).
2-T. J. Meyer, et al. J. Am. Chem. Soc. 136, 1734 (2014).
3- N. Y. Dzade et al. PCCP 16, 25444 (2014).

CO₂ is a major and highly stable component of greenhouse emissions and its reduction to renewable green fuels is an intensely researched subject at this time. Development of highly efficient and product-selective catalysts made of earth abundant transition metal oxides is thus a highly desired goal in this field. In this work we demonstrate that controlled synthetic stabilization of favorable catalytically active defects in hematite and the corresponding interesting surface chemistry can render a highly energy efficient catalytic hydrogenation of CO₂ to CH₄ even under ambient conditions. Thus, in our catalyst system synthesized by metallo-aerogel pyrolysis, surface decoration of catalytically active Fe-O^– occurs naturally on the interbraided highly uniform nanoscopic hematite support structure via cation deficiency resulting in Lewis base defect stabilized hematite (LbDH) and controls the surface chemistry. Such Lewis base sites embedded in the mesoporous LbDH matrix are highly promising in the field of heterogeneous catalytic hydrogenation of CO₂ to CH₄. The potential of LbDH as a heterogeneous frustrated Lewis base catalyst for the hydrogenation of CO₂ was evaluated and established under room temperature, importantly, we realize 100% selectivity of the catalyst towards CH₄ with an output of 928 μmolg^-1.

I will present results of our work in two different directions in computational materials science, whose underlying theme lies in creating materials with nanoscale structural features and searching for associated novel and possibly exploitable phenomena and properties.

First, I deal with heterogeneous catalysis by subnanometer (or ultranano) metal clusters, a rapidly developing field with very promising perspectives of delivering novel and more effective catalysts in the energy and environment fields. I focus on the conversion of CO₂ into more reduced chemicals, that is viewed as an attractive route for decreasing the atmospheric concentration of this greenhouse gas and recycling it, but whose industrial application is limited by the low selectivity and activity of the current catalysts. I report a DFT study of the mechanisms of catalytic hydrogenation of CO₂ by two model systems: (1) Ni₃/MgO(100) and (2) Ni₂Cu/MgO(100). The issues and the opportunities provided by judicious alloying the Ni₃ sub-nanometer cluster catalyst and the effect of the support are dealt with via an original approach consisting of systematic phase-space searches combined with filtering based on reaction energy barriers [1]. Ni₂Cu oxide-supported clusters are shown to be robust and efficient catalysts for the hydrogenation of CO₂ to formic acid.

The second direction deals with nanoporous metals and alloys, i.e., metallic structures whose framework exhibits continuously connected cavities (pores) of nanoscale size, obtained by electrochemical leaching an alloy of the target metal with a more electropositive element. These systems have recently attracted an explosive interest due to their unique properties leading to applications in catalysis, sensors, and opto-electronic devices. We focus on the prototypical case of nanoporous platinum obtained by dealloying Ni-Pt nanoparticles and its record catalytic activity in the oxygen reduction reaction (ORR) which is the rate determining step in low-temperature hydrogen fuel cells for sustainable and energy-efficient electrical power. A computational protocol is presented which allows one to prepare de-alloyed Pt nanoporous particles of realistic size (around 10 nm), analyze the resulting structures in terms of number of surface coordination environment, stress fields, and percolation characteristics of the overall nanostructure, and finally investigate their catalytic properties via DFT simulations. The relationship between structure and catalytic function and the origin of enhanced catalytic performance in Ni-dealloyed nanoporous platinum particles are unveiled. It turns out that this system exhibits a specific local coordination environment at both the internal and external surfaces which selectively reduces the energy barriers of the ORR. Possible developments to achieve ORR optimal catalytic activity are discussed.
[1] F. R. Negreiros et al. Nanoscale 4, 1208-1219 (2012)
[2] A. Fortunelli et al. Chem. Sci., 6, 3915-3925 (2015)

Is waiting on clearance from his company for abstract submission

In addition to finding alternative energy sources, the ever increasing global demand for energy calls for more efficient use of existing fuel sources. Natural gas, which is a widely available and accessible fuel source, is often under-utilized because it is not economically viable to store or transport methane as a compressed gas or liquid. One solution is to convert methane to more useful liquid fuels or chemicals, but traditional methods such as the Fischer–Tropsch process are complex and expensive. Therefore, an economical means of direct partial oxidation of methane to liquid fuel is of great importance.

In this study a process for direct catalytic Gas-To-Liquid (GTL) conversion of methane by electrochemical means is discussed. The process uses an Intermediate Temperature Solid Oxide Fuel Cell (ITSOFC) with an alkali carbonate/ceria based composite electrolyte and a GTL catalyst impregnated anode that converts methane rich fuel to methanol. The work described here focuses on the development of the ITSOFC, with an operating temperature of 500°C, with emphasis on the development of a fully dense ceria based electrolyte on a porous anode substrate using a versatile and cost-effective flame spray pyrolysis technique known as Reactive Spray Deposition Technology (RSDT). This synthesis technique has been used to create a fully dense electrolyte layer on a porous catalyst infiltrated anode support while keeping the substrate temperature at less than 700°C. The characterization of the deposited ITSOFC layers have been done using a combination of XRD, SEM and TEM, while a Ga ion FIB has been used to analyze the cross-section.

One of the most promising technologies for carbon dioxide (CO₂) Capture and Sequestration is oxyfuel combustion, i.e. the use of pure oxygen in the combustion of fossil fuels. When a hydrocarbon like methane reacts with oxygen, the main products of the combustion process are steam and carbon dioxide. By reducing the exit stream’s temperature, steam condenses and CO₂ can be fully captured and stored or used in other applications. However, the major energy penalty in oxyfuel combustion comes from the way oxygen separates from air. The current technology uses cryogenic methods and this process is extremely energy intensive; it can lead to approximately 25% reduction in the net efficiency of a power plant.
Ion transport membranes can serve as a better substitute. These materials have the potential of decreasing the energy consumption for oxygen separation significantly given that they operate under an oxygen chemical potential difference between the two sides. In addition, due to both oxygen separation and reaction, chemical processes become simpler and this leads to a lower operating cost. At the same time, the surfaces can be modified by applying porous supports or catalysts that enhance the membrane performance by promoting desired reactions. For these reasons, ion transport membranes are becoming very popular in the energy sector.
A potential candidate known to exhibit high stability under reducing conditions is La_0.9Ca_0.1FeO_3-δ (LCF). Our study investigates the performance of LCF in applications combining oxyfuel combustion, CO₂ reuse and syngas production under a reactive environment using methane-carbon dioxide mixtures in the oxygen lean side. In the presence of fuel, experimental measurements show that the oxygen flux through the membrane increases by one order of magnitude compared to the non-reactive case due to heterogeneous reactions of hydrogen and carbon monoxide with lattice oxygen ions. These surface reactions produce additional steam and carbon dioxide which further increase the syngas yield by reforming methane in the gas-phase. The aforementioned performance enhancement is accompanied by significant reuse of CO₂. Moreover, we investigate the catalytic activity of an unmodified LCF driven by the presence of iron in the B-site of the perovskite structure. Finally, we show how the addition of nickel on the fuel side of the LCF results in higher oxygen flux and methane conversion compared to the unmodified material.

With the growing abundance of natural gas resources, there is an increasing need for selective alkane functionalization catalysts to convert small alkanes into value-added products and transportable chemicals. Achieving high selectivity of partial oxidation or specific functionalization require novel approaches to heterogeneous catalyst design. Programming the specific chemistry of single-site transition metal centers at surfaces by organic ligand design is a promising route to improve selectivity in surface catalysts. We work as a multi-disciplinary research team to design redox-active components for on-surface metal-organic complexation to achieve a high degree of uniformity in single-site transition metal centers on metal and oxide surfaces. We combine ultra-high vacuum surface chemistry studies on model systems with flow reactor and IR spectroscopy experiments in operando conditions on high surface area oxide powder supports to gain two perspectives on the structure and catalytic function of these systems. Our group has recently demonstrated the formation of structurally ordered and chemically uniform platinum, chromium, iron, and vanadium single-site centers with organic ligands on surfaces (J. Am. Chem. Soc. 2014, 136, 9862-9865; J. Chem. Phys. 2015, 142, 101913; J. Am. Chem. Soc. 2015, 137, 7898). The on-surface redox process on model surfaces in UHV relies on straightforward vapor deposition protocols and takes advantage of the catalytic role of the surface to show promise as an approach for the growth of inorganic complexes at surfaces. For the high powder supports, we use a wet-impregnation style synthesis. The ability to tune the reactivity and catalysis of these systems is a central question in this field. We report new results here that probe the extent of oxidation state control in these systems using tailored tetrazine-based ligands and vanadium metal; vanadium is an excellent candidate for probing access to a variety of oxidation states. The oxidizing power of the tetrazine species is tuned by peripheral functional groups to access two and three electron oxidation processes, as determined by X-ray photoelectron spectroscopy (XPS). Platinum(II) centers have also been formed with these ligands. This strategy is also applied to earth-abundant metals such as iron and chromium using commonly available phenanthroline ligands. In each of these cases, the metal-ligand complexes take the form of nearly identical one-dimensional polymeric chains, resolved by molecular-resolution scanning tunneling microscopy (STM). These structures provide highly uniform quasi-square-planar coordination sites for the metal, which contributes to the well-defined chemical state of the metal. The chemical activity of the metal centers is characterized by adsorption studies on the model systems and by operando flow reactor and IR spectroscopy measurements.

Nanostructured materials, such as nanoporous catalysts with specific architectures, are currently being developed for energy applications. To improve the understanding of catalytic processes and optimize the catalytic reactions, information about the surface structure, composition and morphology of the active materials needs to be determined. Within the past few years, the dealloying method has been established as an efficient synthesis route towards high-quality monolithic nanoporous metals, which provides both compositional flexibility and a high level of morphological control. The mechanism of morphology evolution has been investigated in detail for single-phase solid solution precursor alloys. But the dealloying mechanism is less understood for more complex intermetallic starting alloys where both crystal structure and lattice constant change dramatically during dealloying.

Our current research focuses on the use of nanoporous copper (npCu) catalysts for ethanol hydrogenation. More specifically, we studied the grain morphology of different CuZn alloys via Electron BackScatter Diffraction (EBSD), before and after dealloying. Our results show that crystal grain structure and orientation of a bcc Cu₅₀Zn₅₀ starting alloy is surprisingly preserved during dealloying in 5M HCl, despite the bcc Cu₅₀Zn₅₀ to fcc npCu phase transformation. This is the first EBSD study for nanoporous metals from an intermetallic phase to clearly show this behavior.

In addition to this, we studied nanoporous gold (npAu) catalysts for selective methanol oxidation. The catalytic performance has been attributed to the presence of traces of silver, originating from the sample preparation by dealloying. In order to improve both the efficiency and selectivity, it is crucial to understand the behavior of Ag during the reaction and to control the micro- and nanostructure of the catalyst. Transmission-EBSD was used to study the nano-crystallography of npAu samples prepared as lamellae, which proves the monolithic nature of the sample down to the nanoscale. We also studied the evolution of the t-EBSD pattern at different stages of the catalytic reaction [1].

[1] This work was supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis - IMASC, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012573. C.B. acknowledges postdoctoral fellowships through the Belgian American Educational Foundation (BAEF) as well as Wallonie-Bruxelles International (Excellence grant WBI.WORLD) foundations.

There is a critical demand for the reduction of greenhouse emissions and energy consumption by increasing the fuel economy of cars and light trucks.^{[1, 2]} One of the main obstacles is the mediocre activity of the current diesel oxidation catalysts (DOCs) and aftertreatment technologies at low temperature (<200 ^oC).^[3] Here we report a scalable solvothermal approach for the integration of rutile TiO₂ nano-arrays onto various ceramic monolithic substrates with exceptional mechanical, thermal, and hydrothermal stability as well as tunable morphology and mesoporosity to serve as the catalyst support for DOC applications. We demonstrated that sub-nanometer Pt supported TiO₂ nano-array outperforms commercial DOC catalysts and can efficiently remove more than 90 % of hydrogen carbons and CO in the simulated exhaust at a temperature below 200 ^oC. This catalyst shows great potentials as low-temperature DOC catalysts as well as other practical industrial catalysis.

[1] Federal Register 2012,, Vol. 77, 62623-63200.
[2] Federal Register 2014,, Vol. 79, 23414-23886
[3] A. J. Binder, T. J. Toops, R. R. Unocic, J. E. Parks, S. Dai, Angewandte Chemie 2015, 127, 13461.

Metallic nanoparticles (NPs) are a promising material for various technological applications, in particular, in the field of catalysis. The advantage of NPs is that their properties can be tuned by changing NPs shape, size and composition. Such changes can occur also in situ, in reaction conditions. Understanding of NPs atomic structure and dynamics is therefore extremely important for studies of their catalytic mechanisms.

Extended X-ray absorption fine structure (EXAFS) spectroscopy is one of a very few experimental techniques that are able to give insights into the atomic structure of small (1 – 2 nm) NPs, and also to probe the dynamics of bond vibrations. EXAFS data thus contain unique information on the distribution of atoms within the mono- and hetero-metallic nanocatalysts, and their static and dynamic disorder that tracks structural perturbations caused by environment [1]. The conventional approach to EXAFS data analysis, however, does not work well for small NPs, due to (i) large number of structural parameters, required for the complete description of NPs 3D structure, and (ii) heterogeneous environments of surface and core atoms that cause the distribution of interatomic distances to be markedly asymmetric [2].

At the same time, it was demonstrated that theoretical modelling can complement significantly the information, provided by experimental techniques. For instance, the structure relaxation processes in NPs and their relation to chemical and catalytic properties can be simulated using density functional theory (DFT). Molecular dynamics (MD) simulations [2], in turn, allow one to model thermal disorder effects and anharmonic motion of atoms. The theoretical modelling, thus, can be a powerful tool to advance our understanding of NPs local structure and dynamics. The structure models obtained in such simulations, however, need to be validated using experimental data. While number of different techniques can be used for this purpose, (e.g., total scattering experiments coupled to atomic pair distribution functions analysis), in this study we demonstrate that the use of EXAFS may be advantageous due to its chemical sensitivity and high sensitivity to the arrangement of nearest neighbors and many-atomic distribution functions. Moreover, experimental EXAFS data can be used more directly to guide the construction of 3D structure model for investigated nanocatalyst, using approaches such as reverse Monte Carlo (RMC) and a recently proposed evolutionary algorithm (EA) modelling [3].

In this study the possibilities provided by combination of advanced EXAFS analysis with MD and RMC/EA simulations are exploited to advance our understanding of the structure of small, unsupported gold nanoparticles, synthesized for this purpose using dendrimer-encapsulation technique.

[1] A. I. Frenkel, Chem. Soc. Rev. 418, 163 (2012)
[2] A. Yevick, and A. I. Frenkel. Phys. Rev. B 81, 115451 (2010)
[3] J. Timoshenko et al J. Phys: Condens. Matter 26, 055401 (2014)

Recently, amorphous and polymorphs of nano-sized titania (TiO₂) particles were shown experimentally to enhance the burn rate of a composite propellant composition by an average of 30% [1]. It was speculated that this action occurs through catalyzing the decomposition of ammonium perchlorate (AP). The anatase polymorph exhibited a greater degree of enhancement than the others, suggesting that the catalytic mechanism involves more than just a surface area effect. Therefore, in order to gain a better understanding of TiO₂-based catalysts, it is important to obtain atomistic-scale information on well-characterized catalytic surfaces. Anatase and rutile show inherent particle size differences and this might cause some of the observed differences in chemical properties. Thus, it is necessary to find the most stable nano-cluster configurations and evaluate their activity toward AP decomposition.
In this work, we have studied the ammonium perchlorate adsorption on both TiO₂ surfaces and clusters using the density functional theory (DFT) approach [2]. From the surface calculations, it was conclude that the anatase (001) TiO₂ surface shows higher catalytic activity toward AP adsorption. However, this surface is less energetically stable than (101) surface. For cluster calculations, the calculated binding energy indicates that the most energetically stable cluster with diameter of 1 nm has brookite polymorph and for the larger diameters, the most stable clusters have anatase polymorph. The values of adsorption energy of AP on the TiO₂ clusters are larger as compared with AP adsorption on TiO₂ surface that can be associated both with the structural reconstruction due to interaction with AP and the large ratio of (001) face in anatase TiO₂ clusters.
The effects of transition metals doping and oxygen vacancy defects on the catalytic activity of TiO₂ clusters were also studied. It has been found that the Fe and Co doping stabilize the small cluster of TiO₂ anatase with size of 1 nm. The changes in adsorption energy are due to involving the transition metal atoms in adsorption process by charge transfer. For the large cluster sizes, it has been found that the formation of metal cluster on cluster surface is not energetically preferable since the configuration of transition metal doped cluster with uniform distribution of metal atoms is more stable. The lower vacancy formation energy was found in the case of anatase TiO₂ clusters and the formation energy decreases with increasing of cluster size. The oxygen vacancy defects significantly increases the adsorption energy of AP molecule on small TiO₂ clusters and it can be concluded that the anatase TiO₂ clusters with oxygen vacancy show higher catalytic activity toward AP adsorption.

[1] D. L. Reid et al. J. Phys. Chem. C 115 (2011) 10412.
[2] G. Kresse and D. Joubert, Phys. Rev. B 59 (1999) 1758.

The increasing demands for energy and environmental concerns motivate scientists to develop low cost and high performance materials for energy generation and storage. Hydrogen production by water splitting is one of the greenest ways to generate energy. Hydrogen evolution reaction (HER) is one of the key steps in water splitting process. Ideally, the thermodynamic potential for hydrogen evolution reaction should be at 0 V (vs. SHE). However, without an efficient catalyst, this reaction occurs at high overpotential. Presently, platinum is the most effective and durable catalyst for hydrogen evolution reaction, but its wide spread use is precluded due to its high cost and limited availability. On the other hand, energy storage using supercapacitors are getting popular due to their excellent power density and long cycle life. In this work, we have synthesized cobalt oxide (Co₃O₄) using a facile hydrothermal method and subsequently converted to cobalt sulfide (Co₉S₈). Structural characterization using X-ray diffraction method confirms phase purity of the synthesized materials. The performance of the cobalt sulfide as an electrocatalyst for HER and supercapacitor was examined. Our studies show excellent electrochemical properties of cobalt sulfide as an electrocatalyst for HER with a Tafel slope of 93 mV/decade. The electrochemical properties of the cobalt oxide and cobalt sulfide were studied using cyclic voltammetry and galvanostatic charge-discharge methods. It was observed that the electrochemical properties of cobalt oxide improved significantly after converting to cobalt sulfide. Cobalt oxide and cobalt sulfide showed specific capacitance of 983 and 7358 mF/cm² at 2 mA/cm², respectively. The effect of temperature on the electrochemical properties of supercapacitor device fabricated using cobalt sulfide was studied. It was observed that charge storage capacity of the device increases with increase in the temperature which could be due to decrease in series resistance of the device. Our results suggest that cobalt sulfide could be used as bifunctional material for energy generation and storage applications.

A one-pot synthesis of Ni-doped W₁₈O₄₉ nanorods (NRs) with controlled composition is presented. This synthetic protocol not only allows a precise control of the NRs composition and structure, but also can be extended to dope other 3d transition metals such as Co and Fe. These Ni-doped W₁₈O₄₉ NRs are active and stable electrocatalysts for the oxygen evolution reaction (OER) in 0.1M KOH. The best performance, obtained with a ratio of Ni:W=44:56 can generate a current density of 10 mA/cm² at 1.60 V (vs. RHE, without iR correction), showing no activity change after 1000 potential cycles between 1.4-1.8 V (vs. RHE). Their OER catalysis outperforms not only Co and Fe-doped tungsten oxide structures, but also the common iridium (Ir)-based catalyst. These Ni-doped W₁₈O₄₉ NRs represent a new class of oxide-based catalyst for efficient oxygen evolution reaction (OER) in water splitting and metal-air batteries.

Herein, we design a wearable power generator from a flexible, photocatalytic fuel cell (fPFC) using various biowaste sources (lactic acid, ethanol, methanol, urea, glycerol, and glucose) as fuel. The fPFC uses light irradiation and the decomposition of biowaste to generate electrical power under both flat and bending (r = 3 cm) conditions. When employed as a sweat band, the fPFC generates a maximum power 4.0 mW cm^-2 g^-1 from human sweat. The wearable fPFC is able to overcome many of the disadvantages of wearable microbial and enzymatic cells while providing comparable if not superior power density.

WO₃ is expected to be a semiconductor photocatalyst driven visible light because its band gap ranges from 2.5 to 2.8 eV. We have already reported on photoinduced superhydrophilicity and oxidative decomposition of organic compounds under visible light irradiation on polycrystalline WO₃ films deposited by conventional reactive magnetron sputtering [1-5], where deposition rate was very low of around 10 nm/min. In this study, reactive gas flow sputtering (GFS) is adopted to deposit visible-light active photocatalytic WO₃ films. GFS encompasses two techniques, namely, hollow-cathode discharge and gas-flow-driven material transport. During the WO₃ deposition, a hollow-cathode discharge occurs between a pair of facing rectangular W targets at gas pressures of 90 Pa. A stream of Ar gas was introduced, and directed between the facing targets. The forced Ar stream transported sputtered W atoms to the substrate. O₂ reactive gas was supplied in the vicinity of the substrate. The reactive GFS method offers great advantages over conventional reactive magnetron sputtering by providing stable high-rate deposition [6,7]. The WO₃ films loaded with Pt (Pt/WO₃) were also fabricated. The deposition rate for this process was over 10 times higher than that achieved by the conventional sputtering process. Furthermore, Pt nanoparticle- loaded WO₃ films deposited by the GFS process exhibited much higher photocatalytic activity than those deposited by conventional sputtering, where the photocatalytic activity was evaluated by the extent of decomposition of CH₃CHO under visible light irradiation [9]. [1] Proceedings of the 3rd ICCG , (2000) 137. [2] Proceedings of the 6th ICCG , (2006) 365. [3] J. Nanosci. Nanotechnol. 12 (2012) 5082. [4] Jpn. J. Appl. Phys. 51 (2012) 055501. [5] J. Vac. Sci. Technol. A 30 (2012) 031503. [6] J. Vac. Sci. Technol. A 26 (4) (2008) 893. [7] Thin Solid Films 532 (2013) 1. [8] APL MATERIALS 3 (2015) 104407.

We have been reported on photoinduced superhydrophilicity and oxidative decomposition of organic compounds under visible light irradiation on polycrystalline WO₃ films deposited by reactive magnetron sputtering at the substrate temperature at 800 ^oC [1,2,3]. On the other hand, Abe, et al. reported that WO₃ powder loaded with Pt nanoparticles exhibits high efficiency for the decomposition of organic compounds under visible light irradiation [4].
In this study, we deposited the photocatalytic WO₃ films with visible-light-activity on fused silica glass substrates by dc reactive magnetron sputtering using a W metal target. The substrate temperatures and total gas pressure during the deposition were 800 ^oC and 5.0 Pa, respectively. In addition, Pt was deposited on WO₃ film surfaces at RT by sputtering with various sputtering power and deposition time. The surface coverage of Pt on the WO₃ films were estimated by X-ray photoelectron spectroscopy (XPS), which implied that the Pt film followed Volmer-Weber type process, i.e., after an initial nucleation, an island structure grew and coalesced with each other with increasing film thickness. High resolution electron microscopy (HREM) revealed that Pt nano-particles with diameter of about 2 nm were generated at the early stages of the Pt film growth, which dispersed uniformly on the rough polycrystalline WO₃ films.
For the photocatalytic decomposition of acetaldehyde under the irradiation of visible light (Xe lamp with a 410-500 nm band pass filter, 1.0 mW/cm²), the decomposition rates for the Pt/WO₃ films were higher than that on the pristine WO₃ film with the increase in the Pt deposition time upto 10 sec. Especially, for the WO₃ films deposited with the Pt by 7 sec, acetaldehyde was completely decomposed within 150 min.
[1] M.Ebihara, Y.Shigesato,et al., Proceedings of the 3rd ICCG (2000) 137.
[2] M. Kikuchi, Y. Shigesato, et al., Abstract of the 21st IUPAC SYMPOSIUM (2006) 496.
[3] M. Kikuchi, Y. Shigesato, et al., Proceedings of the 6th ICCG (2006) .
[4] R. Abe, B. Ohtani, et al., J. Am. Chem. Soc. 130, (2008) 7780.

Despite their more complex construction, hybrid aqueous Li-air batteries have emerged as the most implementable Li-air battery technology due to a more facile oxygen electrochemistry than non-aqueous Li-air batteries. Alkaline electrolytes have been the most common aqueous phase in the hybrid design. The alkaline electrolytes are however vulnerable to electrolyte carbonation by atmospheric CO₂ resulting in performance degradation over time. The acid aqueous solution is immune to carbonation but is limited by the scarcity of non-noble metal catalysts effective for the oxygen electrochemical reactions, the oxygen evolution reaction (OER) in particular. We present here our design of non-noble metal N-Co-O doped carbon catalysts with substantial and ORR or OER activities in acid solution which may be easily tuned by the precursor mix composition in a salt-activated synthesis.

Water splitting by (photo)electrolysis is strongly needed and as a promising route to a storable fuel for overcoming the intermittent supply of primary energy sources as solar or wind. One of the major obstacles for efficient systems is the overvoltage loss for the oxygen evolution reaction (OER). First-row transition metal oxides and hydroxides have been identified as promising alternatives to the noble metal electro catalysts IrO₂ or RuO₂. However, for all electro-catalysts there is still a lack of understanding, as the mechanistic primary steps of oxygen evolution have not yet been identified.
We have started to use plasma enhanced CVD as deposition techniques for the preparation ofpreparing differently composed transition metal oxide/hydroxide catalysts. Combining surface science techniques like XPS before and after electrochemical characterization using sample emersion the initial state and the electrochemical induced changes in the oxidation states have been analyzed and are related to the observed electrochemical activity. These results contribute to the development of a better mechanistic understanding of the catalytically active sites. We observe that hydroxides of higher oxidation states are evidently the precursors of the active surface sites.
More detailed insights in the involved mechanism are to be expected for in-situ, in operando studies also of the valence band region in combination with DFT calculations, which will be available in future experiments.

Controlling the electrochemistry of nanoparticles is extremely critical for obtaining the next generation energy storage systems. As more and more synthesis strategies become established, which prevent particle agglomeration;large-scale integration of nanoparticle in devices is becoming a reality. One method routinely used is the stabilization of particles using some organic components, surfactants or capping agents. This does give the advantages of restricting the growth and homogeneous dispersions but can lead to serious problem of suppression of properties like conductivity, adsorption, catalysis, etc. Therefore, it is pertinent that more work continues towards making relevant nanoparticles without using surfactants, capping agents or reaction limiters.
This paper shows that nanoparticles of oxides such asNiO, Co₃O₄, MnO₂ etc., with high capacitive and catalytic activity can be stabilized, using a modified precipitation method. In the case of NiO nanoparticles, nucleation and growth mechanism was found to dominate the particle growth mechanism. The distribution of the obtained spherical shaped particles was quite homogenous.Such stable nanoparticles, with increased surface sites,become very relevant for energy applications such as catalysis and supercapacitors. The synthesizedNiO nanoparticles actually showedhigh capacity to perform catalytic activityfor reducing p-nitrophenolin~3 min, at catalyst concentration of 2 mg/mL. These value are comparable or, at times, higher than values obtained using hollow structures, which are considered as model particles for undertaking high speed catalysis. The reusability of the NiO nanoparticles was tested and confirmedfor four successive cycles.With the capacity to undergo faradic type process, these materials also become useful as electrode material insupercapacitor – a fast emerging technology for energy storage. NiO nanoparticles were used to fabricate a supercapacitor, which returned a specific capacitance of ~120 F/g, at a current density of 1A/g. The supercapacitor has acceptable cycling stability, which makes them useful for large number of industrial applications. For our NiO nanoparticles, the results are even better than previously reported in supercapacitors fabricated using smaller sized particles of the same system. The work describes the reasons for the observation of high capacitive performance. Interestingly, the material becomes a true multifunctional system because it also shows appreciable luminescence activity, which makes it useful for optical devices.

Cost-efficient catalysts for the oxygen evolution reaction (OER) have been extensively investigated^[1]. Noble metal oxides such as RuO₂ and IrO₂ have been utilized for the OER. Recently, ABO₃ (A = Ca, Sr, La etc., B = Ti, V, Mn, Fe etc.) perovskite oxides have been attracted much attention because of their higher catalytic OER activities and less use of precious elements^[2]. It was recently reported that the novel catalyst CaCu₃Fe₄O₁₂ with quadruple perovskite structure has a high activity and stability for OER^[3]. However, the reaction processes in perovskite oxides are still under debate.
The aim of this study is to elucidate the relationships between the OER activity and electronic structures of perovskite oxides for the establishment of rational design principle for OER catalysts. In this direction, Grimaud et al. systematically investigated the double perovskites LnBaCo₂O_6–δ and proposed that the distance from O 2p band center to the Fermi level was proportional to the catalytic activity^[4]. However, they did not consider possible factors concerning the electronic states calculations: oxygen defects, dependences of B-site cations, and magnetic structures.
In the present study, electronic structures of perovskite oxides SrBO₃ (B = Ti-Co) and LaBO₃ (B = Ti-Cu) with adequate magnetic structures were calculated. Then, we investigated relationships between calculations and catalytic activities. Electronic structure was calculated by DFT + U method. Based on the results of systematic experiments and calculations, we performed regression analysis by means of support vector machine in order to discover the good ‘descriptors’ for OER catalytic activities. We found that the O 2p band center relative to Fermi energy cannot be a universal descriptor for the OER activities of SrBO₃ and LaBO₃. The better prediction model was obtained when the B 3d band centroid relative to Fermi level was taken into account as an explanatory variable of the regression. The close relation between the B 3d band centroid and OER activities is probably ascribed to the covalency between B-site transition metal ions and neighboring oxygen ions. In other words, the deeper the B 3d band centroid, the B-O covalent bonding becomes stronger, which leads to the effective charge transfer during the OER.

References
1. Z.-L. Wang et al., Chem. Soc. Rev. 43, 7746–7786 (2014).
2. Y. Wang et al., J. Phys. Chem. C 117, 2106–2112 (2013).
3. S. Yagi et al., Nat. Commun. 6, (2015).
4. A. Grimaud et al., Nat. Commun. 4, 2439 (2013).

Transition metal oxides such as cobalt- and/or manganese-based compounds have been proved to be promising catalytic materials comparable to the novel metals for facilitating desirable electrochemical reactions. Most of those "conversion reaction" involved metal oxides, however, suffer from limited catalytic reaction and fast cyclic fade due to their poor electronic conductivity and large volume changes. Thus, fabrication of nanostructured materials with intrinsically enhanced electrically conductive materials has been demonstrated to be effective ways to alleviate these problems [1-3].
Nanostructured transition metal oxides with both porous structure and oxidation state of metal ions have attracted considerable attention with respect to improved electrochemical energy storage and enhanced catalytic activity [4-6]. While synthetic strategies for the preparation of binary metal oxide are well-established, the rational design and fabrication of complex phase with unique particle morphology is still a challenge.
Herein, both phase and morphology controllable CoO_x-based spinel oxides have been investigated for electrochemical active materials especially for the Li-air cathode catalysts. Spinel structured CoMn₂O₄ and binary phase CoO/Co₃O₄ were synthesized by using the facile solvothermal reaction. With the proper amine-based organic compound addition, we can modify both the polymorphic composition and nanoparticle morphology so as to further improve the catalytic performance. When evaluated as an anode material for Li⁺-ion battery anodes, the as-synthesized spherical/porous spinels exhibited superior initial charge/discharge capacity including good rate capability. In case of CoO/Co₃O₄ mixed phases, we can simply control both the phase ratio and sphere-like morphology via metal-organic framework precursor conditions conserving the synergistic effect of the multicomponent electrochemical catalysts. Additionally, we demonstrate directly measured the involved oxygen concentration during the Li⁺↔O₂(g) oxidation/reduction reaction by using the in-situ differential electrochemical mass spectroscopy (DEMS) evaluating the catalytic activity of the given CoO_x-based nanoparticles.

Ammonia (NH₃) is a compound that finds use in different applications: as soil fertilizer in agriculture, as cooling agent in refrigeration, and as reactant in chemical industries. However, ammonia is also known as a pollutant for the environment. The National Institute for Occupational Safety and Health has fixed at 300 ppm the amount of ammonia that is considered dangerous for health. Ammonia can be readily detected by a sensor. On the market, there are several different sorts of ammonia detectors, each one operating on a different mechanism.
Electrochemical sensors have the advantage to be very cheap and portable. Moreover, they are characterized by very low detection limit and large dynamic range (from 0,1ppb to 1000 ppm) and they can operate from -40 to 600°C. However, the lifetime of these sensors is short and does not exceed 18 months.
During the electroxidation reaction, ammonia is converted into nitrogen (N₂). In the literature, Platinum is one of the most studied materials for the electro-oxidation of ammonia [1]. Pt has a face centered cubic (fcc) structure and it was shown that (100) surface orientation is the most active Pt facet for ammonia detection. However, Pt (100) is sensitive to the presence of an intermediate reaction species, N_ads, which acts as a strong poison [2].
It is known that the resistance of polycrystalline Pt to poisoning by N_ads can be increased by adding noble metal elements like Ir and Rh. In this work, pulsed electrodeposition of Iridium on pre-formed (100) preferentially oriented Pt nanostructures will be investigated to increase both the activity and the poisoning resistance of the electrode. A wide range of Ir surface coverage was achieved by varying the number of pulses. A detailed structural characterization of the surface morphology was conducted. We will show there is an optimum value of Ir pulses that lead to an overall increase of the current for the oxidation of NH₃, and an increased reaction stability. The underlying mechanisms responsible of these enhanced properties will be discussed.

[1] E. Bertin, C. Roy, S. Garbarino, D. Guay, J. Solla-Gullòn, FJ. Vidal-Iglesias, Juan
M. Feliu, Electrochemistry Communications, 22 (2012) 197-199.
[2] F.J Vidal Iglesias, J. Solla-Gullòn, V. Montiel, J.M Feliu, A. Aldaz, Journal of Power
Sources 171 (2007) 448-456.

Finding a highly active and durable nanocatalyst under fuel cell operation condition is urgent and challenging for the commercialization of fuel cells. Many nanocatalysts have been reported to have much improved oxygen reduction reaction (ORR) activity compared to the commercially used Pt/C catalyst. But few of them can meet the durability requirement. In this report, monodisperse face-centered-tetragonal (fct) (L1₀) FePt nanoparticles with size of ~ 9 nm were synthesized from dumbbell-like face-center-cubic (fcc)-FePt-Fe₃O₄ nanoparticles. The durability of C-fct-FePt NPs as ORR catalysts under 60 ^oC were studied and they served as a highly active and durable ORR catalyst (its mass activity is about 5.4 times of commercial Pt/C and no obvious loss in ORR activity after 10000 cycles). The perchloric acid-treatment and the followed annealing treatment were found to improve the durability of fct-FePt nanoparticles under 60 ^oC. The highly ordered L1₀ structure with alternating layers of Fe and Pt atoms, as well as the Pt skin formed after the acid-treatment were thought to be the main reason for the durability enhancement. Our work demonstrates a reliable approach to a structurally ordered FePt nanoparticles as a promising candidate for practical use in fuel cell.

Nanostructured metal particles have emerged as a new type of efficient heterogeneous catalysts so-called nanocatalysts by controlling their size, surface structure, and composition. Also, it is well known that the direct functionalization of C-H bonds to construct C-C or C-X bonds takes place under oxidized metal states such as Pd (III or IV) and Rh (II or III), from the viewpoint that most organometallic reactions are coupled with the change of metal oxidation states, the reaction scope of metal nanocatalysts is not as wide as that of the homogeneous counterparts thus far. However, surface of metal nanoparticles have neutral metal state (0). Thus, for many organic reactions, including direct C-H activation, metal nanoparticles should be containing oxidized high-velant metal states. Recently, in our laboratory Kim et al. recently reported surface oxidized Pd@SiO₂ yolk-shell nanocatalyst which had high reactivity and stability superior to the other Pd-based catalysts for organic catalytic reactions. In this presentation we report surface activation of noble metal nanoparticles (rhodium and palladium) via various oxidants such as N-bromosuccinimide (NBS), N-chlorosuccinimide (NCS), PhICl₂ and PhI(OAc)_2. X-ray absorption spectroscopy analyses showed that most of surface existed with oxidized Rh³⁺ and Pd⁴⁺ state. In particular, activated Pd NPs shows efficiently promotes directed C-H halogenation reactions, which have been reported in homogeneous Pd catalysts. This system exhibits additional features superior to the homogeneous catalysis, including easy access to sterically demanded substrates, excellent recyclability, and more significantly, stable multiple valencies which enable the tandem process combining two distinct catalytic reactions.

A series of binary PtRu catalysts with different Pt:Ru atomic ratios from 7:3 to 3:7 are synthesized on carbon support using the colloidal method, and they are used for the electrooxidation of glycerol in acidic media. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption near-edge spectroscopy (XANES) analyses are used to investigate the particle size, size distribution, and structural and electronic properties of the prepared catalysts. The addition of Ru content to the Pt-based catalysts caused structural and electronic modifications over the PtRu alloy catalyst formation, which could directly affect the electrocatalytic activity of glycerol oxidation. The electrocatalytic activities of PtRu/C series catalysts are investigated by using cyclic voltammetry (CV) technique. Among the prepared catalysts, Pt₅Ru₅/C catalyst shows enhanced catalytic activity of at least 40% higher than Pt/C catalyst with improved stability for glycerol electrooxidation, which can be ascribed to structural and electronic modifications of the Pt catalysts. To study the mechanism of glycerol oxidation on the PtRu alloy surfaces, the ab-initio density functional theory (DFT) calculations, which are based on the d-band center theory, have been applied to correlate with the experimental results.

Ammonia is one of the most traded chemicals in the world with over 131 million tons (2010) being synthesized each year.¹ Currently, the Haber-Bosch process is employed to produce ammonia requiring high temperature and pressure¹. In addition H₂ from steam reformation is used making it a major sources of CO₂ pollution¹. A promising alternative for small scale applications is electrochemical ammonia production utilizing molten salts as electrolytes.² Such systems work at ambient pressure, moderate temperature and use renewable hydrogen sources like water enabling small local production of ammonia for energy storage and as building block chemical for fertilizer synthesis.²

'To date, only few metals and oxides have been tested as electrocatalysts for ammonia synthesis in molten salts. Metal nitrides, especially Co₃Mo₃N, are highly active in classical ammonia synthesis and have also been considered as electrocatalysts by computational studies.^2-4 Material tests for Li-batteries have shown that Li⁺ions from the melt can irreversibly replace transition metals in certain binary metal nitrides due to their high affinity for nitride ions.⁵ Here, we synthesize a selection of ternary metal nitrides for use as electrocatalysts in electrochemical ammonia synthesis and test their stability and structural integrity in molten alkali chloride salts.

Fe₃Mo₃N, Mo₂N, Co₃Mo₃N and Ni₂Mo₃N, were synthesized using temperature-programmed nitridation of oxide precursors and were characterized by powder XRD, BET, XPS, UV-Vis, SEM, TEM and SQUID. Furthermore, these materials were supported on different carbon materials in various kinds of micro- and nanostructures. The obtained porous, high surface area materials display promising properties for use in molten chloride electrolytes. A range of electrochemical tests (CV, amperometry, etc.) were carried out and XPS, as well as SEM were used to monitor compositional and structural changes on the surface.

The electrolysis of water to form hydrogen and oxygen is an effective method to store energy produced by intermittent sources of renewable energy like sun and wind^1,2. The oxygen evolution reaction (OER) occurring at the anode accounts for a large fraction of the voltage loss³. RuO₂ is one of the most active catalysts for this reaction^4,5. This research involves studying the pH-dependent OER activity of RuO₂ nanoparticles and oriented thin films in acidic and basic electrolytes to gain insight into the reaction mechanism. We propose that pH-dependent reference scales such as the reversible hydrogen electrode (RHE) are more suited to studies of pH dependence since they ensure a fixed overpotential with respect to the oxygen redox⁶. The redox peaks in the capacitive region of the cyclic voltammograms provide an initial understanding of the intermediate oxidation states of Ru prior to OER. The significant deviation from 60 mV/pH (SHE scale, 0 mV/pH RHE scale) in the position of redox peaks with pH of electrolyte indicates that RuO₂ exhibits super-Nernstian behavior. Reaction orders close to 0 obtained on an RHE scale in acidic and basic electrolytes implies that an electron-decoupled proton transfer is not the limiting step for the reaction. Epitaxial thin films were also used to study the effects of orientation on the activity of RuO₂. The unique OER activity and different redox features in the pseudocapacitance region can be discerned for the different facets, enabling us to understand the relation between structure and activity. In addition, we also use polycrystalline films to de-convolute the effect of grain boundaries and defect sites on OER activity. The understanding of the reaction mechanism of OER on precious metals, such as RuO₂ can provide a benchmark for the development of superior catalysts for electrolyzers, metal-air batteries and photoelectrochemical water splitting applications.


References

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2. J.O.M. Bockris, A.K.N. Reddy, Modern Electrochemistry Part 1: Ionics, 2^nd ed., Plenum Press, New York, 1998.
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Ammonia borane (NH₃BH₃) has been known as a potential hydrogen source because of its high hydrogen content. In this study, a mesoporous silica aerogel (SAG) is used as the support for preparation of a series of the SAG-supported platinum-cobalt co-catalysts, Pt_xCo_1-x/SAG (x = 0.03 ~ 0.92), by a facile chemical reduction and a simple microwave-assisted method, sequentially. The structure, morphology and chemical composition of the Pt_0.27Co_0.73/SAG catalyst were characterized by a combination of X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma emission spectroscopy (ICP) and pore and surface area measurements. The as-prepared Pt_xCo_1-x/SAGs (x = 0.03 ~ 0.92) are used as catalysts for hydrogen generation from the aqueous NH₃BH₃ solution. The results indicate that Pt_0.27Co_0.73/SAG exhibited the highest hydrogen generation rate for the NH₃BH₃ hydrolysis. It is attributed to that the Pt and Co nanoparticles of Pt_0.27Co_0.73/SAG are smaller (less than 3nm in diameter) and better-deposited in SAG than the other Pt_xCo_1-x/SAGs. It is found that the turnover frequency and activation energy of Pt_0.27Co_0.73/SAG catalyst in the hydrogenation of the aqueous NH₃BH₃ solution are superior to most of the bimetallic catalysts reported. Besides, after 5 recycles, the H₂/NH₃BH₃ mole ratio of the dehydrogenation of NH₃BH₃ by the used Pt_0.27Co_0.73/SAG still retains to 3.0 in less than 3 minutes. The results show that the Pt_0.27Co_0.73/SAG prepared in this study is a high potential catalyst for hydrogen generation from aqueous NH₃BH_3.

Platinum included nanoparticles with catalytic or magnetic properties are very important materials in chemical, energy, and pharmaceutical applications. Among the various synthesis systems, the development of core-shell nanoparticles that can be composed by two different materials has attracted lots of interest since their magnetic, biomedical, and catalytic properties. But these core-shell nanoparticles are usually synthesized by two step method, so the process is complicated and has lower yields.
In this study, we suggest the one step method synthesis of Pt@CoO_x core-shell nanoparticles using autoclave oven. The growth solution was prepared by dissolving Pt(acac)₂ and Co(acac)₃ in benzyl ether in the presence of oleylamine, oleic acid, and borane t-butylamine (BBA). By controlling the ratio of Pt and Co in precursor solution, we got the nanoparticles with different shape and morphology. These nanoparticles are analyzed by transmission electron microscopy (TEM).

Nanoframe structures of noble metals have received a great attention due to their high surface area per volume. Although nanoframes exhibit high catalytic activity, their inherent structural infirmity needs much improvement for practical applications. In order to increase the structural robustness of nanoframe, herein, we suggest double nanoframe concept to enhance the frame stability. We describe the rational synthesis of a novel double nanoframe nanostructure of Ir and its excellent electrocatalytic activity and stability toward oxygen evolution reaction.

Nanostructures with hollow interiors have found various applications in catalysis, sensor, and energy storages, and therefore various synthetic strategies to build hollow nanostructures are of a great interest. Ideally, hollow nanostructure can be prepared by removing the core component from a core-shell nanostructure. However, this concept is not operable with the impervious shell material in the core-shell nanocrystal. Herein, we introduce a very simple synthetic strategy for the preparation of robust ternary hollow nanostructures with enhanced durability as well as their catalytic activity. By introducing third metal dopant, which is easily leachable under etching condition thus provides channels for the core-component removal, to the binary core-shell nanostructures, the desired hollow nanostructures could be facilely prepared.

In this work, electrodeposited filmes of Co, Cu and MnO₂ from recycling of spent Li-ion and alkaline batteries were syntetized, characterized and applied in galvanic protection of AISI 1045 carbon steel corrosion. These batteries were physically dismantled, separated into its various constituents, leached in solution of acetic acid 3: 1 v / v and adjusted to pH 2.65. The electrodeposits were formed in potentiostatic condition with E = -0.90 V and fixed charge density of 10 C.cm^-2 on carbon steel AISI 1045 substrate. Analysis by x-ray diffraction showed the presence of metallic Cu (111) in body-centered cubicstructure, metallic Co (101) in compact hexagonal and MnO₂ (110). By measures of scanning electron microscopy, a covering of the steel surface was observed, showing no cracks. The corrosion tests were carried out in NaCl 3.5% w / v solution in standardized condition of ASTM G-106. The Tafel slope analysis showed corrosion potential equal to -0.35 V on the preferential dissolution of MnO₂ and Co, but less cathodic than the potential presented by the steel without deposition (-0.56 V), indicating a surface protection. The presented corrosion rate was equal to 0.023 mm / year. Electrochemical Impedande Spectroscopy (EIS) analysis showed an equivalent circuit R₁(R₂Q), where R₁ is the resistance of the solution, polarization resistance R₂ and Q, the element of constant phase, relative to the heterogeneity of the surface.

In this work, electrochemical de-alloying of an amorphous alloy, Au₄₀Cu₂₈Ag₇Pd₅Si₂₀, cast in ribbon form by melt spinning, has been performed, obtaining self standing nanoporous materials suitable for use as electrodes for electrocatalytic applications. The de-alloying encompasses removal of less noble elements and the crystallization of Au, resulting in interconnected ligaments whose size and morphology are described as a function of time. Depending on de-alloying time, the crystals may contain residual amounts of Cu, Ag and Pd, as shown by Auger Electron Spectroscopy (AES), Energy Dispersive Spectroscopy (EDS) and Cyclic Voltammetry (CV) in a basic solution.
Current density peaks in the 0.16-0.28 V range (vs Ag/AgCl) indicate that the porous ribbons are active for the electro-oxidation of methanol. The partially de-alloyed samples, which still partially contain the amorphous phase because of the shorter etching times, have finer ligaments and display peaks at lower potential. However, the current density decreases rapidly during repeated potential scans. This is attributed to the obstruction of Au sites, mainly by the Cu oxides formed during the scans. The fully de-alloyed ribbons display current peaks at about 0.20 V and remain active for hundreds of scans at more than 60% of the initial current density. They can be fully re-activated to achieve the same performance levels after a brief immersion in nitric acid. The good activity is due to trapped Ag and Pd atoms in combination with ligament morphology.

Electrochemical reduction has been recognized as one of the most promising ways to convert atmospheric CO₂, the major greenhouse gas, into value-added liquid fuels. [1] However, most of the electrode materials under study have shown that CO₂ conversion is taking place at high overpotentials, with poor selectivity and/or low faradic efficiency, which translates into a high-energy process. [2,3] Recently, it was found that porous electrodes with high electrochemical active surface area (EASA) increase the conversion efficiency of CO₂ to value-added products. [4]
In this study, porous Pb electrodes were prepared by galvanostatic electrodeposition from a lead perchlorate solution. The electrodeposition process was conducted at high current density, which leads to both Pb electrocrystallization and hydrogen gas evolution. Electrodeposition under these conditions is known as dynamic hydrogen bubble templating. The pore size, microstructure and the electrochemically active surface area of the deposits are dependent of the deposition conditions. They have been assessed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and cyclic voltammetry. The activity of these electrodes for the electrochemical reduction of CO₂ was studied in 1M KHCO₃ and compared to that of Pb plate electrodes. The electrocatalytic performances of these deposits for the electroreduction of CO₂ to HCOOH will be dicussed.

1. Qiao, J., Liu, Y., Hong, F. and Zhang, J., A Review of Catalysts for the Electroreduction of Carbon Dioxide to Produce Low-Carbon Fuels. Chemical Society reviews 2014, 43, 631-675.
2. Lu, Q., Rosen, J., Zhou, Y., Hutchings, G. S., Kimmel, Y. C., Chen, J. G. and Jiao, F., A Selective and Efficient Electrocatalyst for Carbon Dioxide Reduction. Nature communications 2014, 5, 3242.
3. Chen, Y. and Kanan, M. W., Tin Oxide Dependence of the CO₂ Reduction Efficiency on Tin Electrodes and Enhanced Activity for Tin/Tin Oxide Thin-Film Catalysts. Journal of the American Chemical Society 2012, 134, 1986-1989.
4. Sen, S., Liu, D. and Palmore, G. T. R., Electrochemical Reduction of CO₂ at Copper Nanofoams. ACS Catalysis 2014, 4, 3091-3095.

The functionalization of surfaces via the diazonium chemistry is well established and has been widely investigated to modify carbon and a wide range of metal electrodes [1]. The attachment of various aryl groups with specific chemical functionalities onto electrode surfaces leads to changes of their surface properties [2,3]. However, rarely this chemistry has been used to modify lead and tin electrodes, which could for instance, enhance their corrosion properties.

In the present study, the grafting of phenyl amines groups on lead electrode was achieved by spontaneous reduction of in situ generated diazonium cations in aqueous media. The grafting reaction was performed by cyclic voltammetry (CV) and at fixed current density in two different aqueous media. The corresponding diazonium cations of three different amine groups with different acidity, 4-aminobenzylamine, 3-aminobenzylamine and 4-(2-aminoethyl) aniline, were generated in situ with sodium nitrite in both HCl and H₂SO₄ solution. The formation of the aryl-metal bond was confirmed by cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). The influence of the reaction time of amino phenyl diazonium salt on the extent of grafting was also investigated.


[1] S.Baranton and D.Bélanger.J. Phys. Chem.109, 24401–24410, (2005).
[2] P. Allongue, M. Delamar, B. Desbat, O. Fagebaume, R. Hitmi, J. Pinson, and J. Save. J. Am. Chem. Soc.7863, 201–207, (1997).
[3] D. Bélanger and J. Pinson, Chem. Soc. Rev. 40, no. 7, p. 3995, 2011.

Fast depletion of fossil fuels and severe deterioration of ecology have stimulated extensive research on the utilization and storage of clean and sustainable energy. Rechargeable metal-air batteries possess high energy density, making them excellent candidate for next generation electrical vehicles (EVs). The major challenge associated with the commercialization of metal-air batteries resides in the sluggish kinetics of the electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reduction (OER) resulting in large overpotentials. Developing efficient electrocatalyst with high catalytic activities is of great importance for high performance metal-air batteries.
Precious catalysts such as platinum, palladium, iridium and alloys have been intensively studied showing superb catalytic properties. Unfortunately, the electrochemical instability of these catalysts have prevented their use due to extremely high costs and poor durability. Nonprecious transition metal-based catalysts have also been explored, however, they suffer from inefficient catalytic activity due to self-accumulation and poor electrical conductivity. Rational design strategy and efficient development of desired electrocatalysts is yet limited. An efficient electrocatalyst is expected to (i) exhibit high catalytic activity with a large amount of active sites for ORR and OER processes; (ii) possess sufficient mass transfer pathways for fast electrode kinetics; and (iii) be chemically stable with robust material and/or electrode architecture for high durability.
Herein, we demonstrate pomegranate-like electrocatalysts based on transition metal oxide nanocrystals embedded nitrogen-doped partially graphitized carbon framework with excellent catalytic activity for ORR and OER and outstanding durability. To demonstrate the design concept, cobalt oxide (Co₃O₄) is chosen as a model material. The Co₃O₄ nanocrystals embedded nitrogen-doped partially graphitized carbon framework (Co₃O₄/NPGC) with unique pomegranate-like composite architecture provides several major advantages: (i) low dimension of highly active Co₃O₄ nanocrystals seeds possess active sites for electrochemical reactions; (ii) the pomegranate-like structure efficiently prevents the metal oxide from self-accumulation and provide the mass transfer pathways, which further maintains the catalytic activity; (iii) graphitized carbon shell and framework is not only highly conductive which significantly increases electrical conductivity, but also chemically stable and highly robust which enhances the catalyst durability. Benefiting from the unique pomegranate-like architecture, the Co₃O₄-based composite electrocatalyst exhibits a high half-wave potential of 0.842 V for ORR, and a low overpotential of only 450 mV at the current density of 10 mA cm^-2 for OER. Single-cell zinc-air battery is also fabricated with superior durability, holding great promise in the practical implementation of rechargeable metal-air batteries.

Direct ethanol fuel cells (DEFCs) an emerging technology have attracted much attention recently in the search for alternative power resources. Indeed, ethanol is interesting as a green, nontoxic fuel with high theoretical energy density and can be produced from biomass (corn crops, sugar cane, domestic cellulosic biomass, algae, etc.), which could make DEFCs beneficial low Green House Gas emission power sources. The future of DEFC technologies is strictly reliant on the discovery of novel anode catalysts; catalyst supports that is corrosion resistant upon long-term operation.
Owing to its unique properties of two-dimensional structure, high active surface area, outstanding electronic properties, chemical stability and excellent mechanical and thermal stability, graphene is promising as the catalyst support for catalyst nanoparticles for fuel cells.
This work centers on optimizing binder-containing and binder-free graphene (Gr) and graphene oxide (GrO) composites of various compositions as catalyst support for ethanol fuel cells reactions. Gr and GrO were ink deposited onto an electrically conductive carbon paper similar to that used as gas diffusion electrodes in fuel cells, i.e., it is composed of a highly porous 3D networks of microfibers (~7 mm diameter). Briefly, the typical synthesis process was as follows: (i) produce GrO by a modified Hummers method, (ii) synthesize expanded graphite using a so-called explosion–expansion method and (iii) obtain graphene sheets through chemical vapour reduction. Such Gr and GrO are characterized by micro Raman spectroscopy and scanning electron microscopy. Whereas their electron transfer properties and the quality of electrical contact between the graphene composites and the CP substrate were assessed in a benchmark solution of 1.0 mM K₄Fe(CN)₆ and 1.0 M KCl by cyclic voltammetry (CV).
Afterwards, to discover the optimum structure and composition of the graphene composites, electrocatalytic activities towards ethanol electrooxidation are comparatively investigated by loading the same amount of Pt nanoparticles deposited by pulsed laser deposition technique.

Catalyst support materials exhibit great influence on the cost, performance, and durability of polymer electrolyte membrane (PEM) fuel cells. In this work, we report on the preparation and characterization of PdNi bimetallic nanoparticles supported on the onion-like carbon (OLC). The obtained PdNi/OLCs electrocatalysts are characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results show that PdNi bimetallic nanoparticles with an average particle size of 5.0 nm are dispersed quite uniformly on the surface of OLCs. The electrocatalytic activity of the Pd/OLCs electrocatalysts toward ethanol oxidation reaction (EOR) is investigated by cyclic voltammetry (CV) in basic solution. An increase in EOR activity has been observed when the atomic ratio of Pd to Ni was approximately Pd₃Ni. The existence of PdO is considered as the possible reason for the remarkably enhanced peak currents of EOR in the presence of Pd₃Ni/OLCs electrocatalysts. The accelerated durability test results show good stability for the Pd₃Ni/OLCs electrocatalysts at high potentials in terms of minimum loss in the Pd electrochemical surface area. The enhanced performance of Pd₃Ni/OLCs electrocatalyst arising from good stability and high dispersion should be contributed to the strong resistance to corrosion of OLCs and the specific interaction between Pd₃Ni nanoparticles and OLCs. The high stability of the Pd₃Ni/OLCs electrocatalysts offers a new approach to improve the reliability and durability of polymer electrolyte membrane-based fuel cell catalysts.

ACKNOWLEDGEMENT:
This work was supported by the National Research Foundation of Korea (NRF) grants funded by the Korea Government (MSIP) (No. 2013R1A1A2060918)

Ag is a promising candidate as an indispensable catalysts in alkaline medium due to its unique capability to resist against the corrosive environment and to enhance the ORR activity. Here, we have demonstrated shape-controlled synthesis of Ag catalysts by tailoring the reduction kinetics with adjusted electron densities in plasma. With low electron density of 7.1x10²² m^-3, the Ag nanowires with the corrugated structure induced by twinning and stacking faults formation were observed along the entire longitudinal <111> direction of nanowires. Whereas, with high electron density of 13.7x10²² m^-3, the Ag dendrites constructed via the coalescence between Ag nanoparticles could be obtained. These different kinetically-controlled growth behaviors were essential for achieving the shape transition between the nanowires and dendrites. From the linear sweep voltammetry, the Ag nanowires exhibited the highest kinetic current density with a value of 17.2 mA cm^-2, and the electron transfer number was calculated to be 3.54, which is the indicative of a four-electron ORR pathway. This improvement in ORR activity could be mainly attributed to the lattice strain, derived from defective structures.
Acknowledgment
This study was supported by the National Research Foundation of Korea (NRF) funded by the Korean Government (No. 2013R1A1A2060918).

Iron oxyhydroxides (FeOOH) including goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), and feroxyhyte (δ-FeOOH), are well-known materials as one component of the rust, and we can be easily obtained in the natural environment. They have the band gap energy of 1.8-2.6 eV, because of this, FeOOH had been receiving attention as a photo-functional material due to its strong absorption ability to the visible light.
In this study, we synthesized FeOOH (α, β, γ, and δ-FeOOH) by solution process, and investigated their photo-functional properties such as hydrogen production from methanol solution and photo-reduction of carbon dioxide (CO₂), under light irradiation.
XRD patterns of the synthesized samples revealed that they were composed of α-FeOOH (JCPDS 29-0713), β-FeOOH (JCPDS 34-1266), γ-FeOOH (JCPDS 44-1415), and δ-FeOOH (JCPDS 13-0087). From SEM observation, all samples had thin needle structure.
Investigation of hydrogen production and photo-reduction of CO₂ accomplished with using 10 vol% methanol aqueous solution and quartz vessel which composed of CO₂ atmosphere under UV light (200 W Hg-Xe lamp), respectively. As a result, hydrogen and increase of carbon monoxide (CO) gases were generated, and the amount of the generated gases increased linearly with the increase of irradiation time.

Solar hydrogen production using photocatalysis has been expected as one of the new clean energy sources. Particularly, visible light response photocatalytic materials have attracted much attention from the viewpoint of the effective use of solar energy. To date, a large number of evaluations for photocatalysis based on liquid-phase reactions have been carried out, where gas analysis during photocatalysis mainly detects only final products. On the other hand, evaluation of photocatalytic reactions in high vacuum has an advantage that intermediate products can be observed at a real-time scale. In the present work, we focused on iron oxide (Fe₂O₃) nanostructures as photocatalytic material showing a visible light response. Real-time observation of gas-phase photocatalytic reaction processes with nanostructured iron oxides in high vacuum was conducted under various light illuminations, in order to investigate the relationship between materials properties and photocatalytic functions in iron oxide nanostructures in detail.
Iron oxide nanostructures were prepared by anodizing pure iron foils with ethylene glycol based electrolyte containing ammonium fluoride and pure water, followed by post-annealing in air for crystallization. After that, platinum nanoparticles as co-catalyst were deposited on the prepared samples by photodeposition. Photocatalytic activity of the iron oxide nanostructures was evaluated by utilizing a home-made apparatus for investigating gas-phase photocatalysis in high vacuum. After an iron oxide sample was installed into the measurement chamber and the chamber was evacuated to the 10^-8 Torr range, gaseous methanol with a partial pressure of 2-3×10^-7 Torr was introduced onto the sample surface by employing a variable leak valve. Then, the change in the partial pressures of several gas species was observed using a quadrupole mass spectrometer (QMS), with the ON/OFF switching of illumination from various light sources such as ultraviolet A region (300-400 nm), visible region (400-700 nm), and a solar simulator (AM1.5).
Iron oxide nanotube arrays (FNAs) were successfully fabricated under a certain anodizing condition. X-ray diffraction measurement suggested that post-annealing FNAs in air resulted in the formation of a mixture of Fe₂O₃ and Fe₃O₄. Photocatalytic decomposition of gaseous methanol over the Pt-loaded FNA under visible light illumination was examined. As a result, switching phenomena in the partial pressures of H₂, carbon monoxide (CO), and water (H₂O) were observed simultaneously according to the ON/OFF sequence of the light illumination, while no change in these gas species appeared for FNAs without Pt, bare iron foils, and even for Pt-loaded TiO₂ nanotube arrays. From these results, we may conclude that visible light responsive photocatalysis clearly appeared due to the combination of FNAs and Pt, which causes decomposition of gaseous methanol and concurrent proton reduction toward hydrogen gas production.

Carbon/silicon composite materials are a promising anode substrate for use in lithium ion batteries. In this study, we suggest a novel architecture for a composite electrode made of an interconnected 3D porous carbon pattern decorated with silicon nanoparticles (SiNPs/3DCP). The 3D porous carbon pattern (3DPC) structure was fabricated using direct carbonization of the multi-beam interference lithography polymer patterns. Subsequent solution coating was applied to decorate the 3DCP with silicon nanoparticles. The SiNPs/3DPC electrode exhibited a specific capacity of 936 mAh/g, which is 3-fold greater than the specific capacity of the bare electrode. Specifically, the SiNPs/3DPC electrode exhibited an outstanding retention capacity of 81% after 50 cycles and a Coulombic efficiency of more than 98%. This rate capability performance was attributed to the 3DPC structure and the uniform decoration of the SiNPs.

More than 1% of world’s power production is being consumed for the ammonia synthesis using the Haber-Bosch process. The search of novel catalysts for efficient ammonia synthesis under low pressure and temperature conditions is urgently required for a sustainable society. In 2012, Kitano and co-workers reported Ru-loaded electride [Ca₂₄Al₂₈O₆₄]⁴⁺(e⁻)₄ (C12A7:e⁻) shows a high catalytic activity in ammonia synthesis (Nat.Chem. 4.11 (2012): 934-940.); e⁻ indicates an anionic electron loosely confined in subnanometer-sized cages of the material. C12A7:e⁻ has the strong electron-donation ability to Ru particles due to the low work function (WF), 2.4 eV, which facilitates the cleavage of strong N≡N bond. In addition to the advantage, the encapsulation of hydrogen as H⁻ into the cages of C12A7:e⁻ is also confirmed, which prevents hydrogen poisoning of Ru catalysts.
Recently, our group also found that Ru-loaded two-dimensional electride Ca₂N:e⁻ (Ru/Ca₂N:e⁻) works as an efficient and stable catalyst for ammonia synthesis down to 200°C. Ca₂N:e⁻ can encapsulate hydrogen as H⁻ in the anionic electron layer and [Ca₂N]⁺e_1-x⁻H_x⁻ is formed during ammonia synthesis.
This study investigates the catalytic role of an anionic electron and H⁻ of [Ca₂N]⁺e_1−x⁻H_x⁻ for ammonia synthesis by using density functional theory (DFT) calculations. We calculate the electronic structures of Ca₂NH, Ca₂NH_1−x, and Ru-loaded Ca₂NH surface, respectively. When a hydrogen vacancy (V_H) is formed in Ca₂NH, an anionic electron is localized at V_H position. The calculated WF of Ca₂N:e⁻, Ca₂NH and Ca₂NH with anionic electrons at V_H position (i.e., Ca₂NH_1−xe_x⁻) are 2.5, 2.8 and 2.3 eV, respectively, which indicates the WF of Ca₂NH_1−xe_x⁻ is much lower than that of Ca₂NH and Ca₂N:e⁻. This result suggests the strong electron-donation ability of Ca₂NH_1−xe_x⁻.
Ca₂NH_1−xe_x⁻ can be easily formed by the electronic interaction between Ca₂NH and Ru. The V_H formation energies calculated with DFT were 0.88-1.02 eV, which indicates a relative difficulty of V_H formation. However, once a Ru particle is loaded on Ca₂NH, the V_H formation energies are dramatically decreased to 0.43 eV at most. The decrease of formation energy was analyzed in term of chemical bonding, and we found the key is the anti-bonding state between Ru and surface H⁻. The easy formation of V_H on Ru-loaded Ca₂NH was experimentally observed in temperature-programmed desorption of H₂; hydrogen can easily desorb from the surface of Ca₂NH above 200 °C by Ru-loading, whereas hydrogen desorption from Ca₂NH without Ru occurs above 300 °C. That is, Ru particles on Ca₂NH decrease the temperature of H₂ desorption. This experimental result show excellent correspondence with the results obtained with DFT calculations.

Development of newer nanoparticles with enhanced surface area is one of the logical way forward in achieving materials for applications such as catalysis, energy storage, gas sensing, magnetism, adsorption, spintronics, etc. The large increase in the surface-to-volume ratio lead to significant quantum confinement and subsequent changes in the surface energy, density of states, band structure and reactivity. Most of the applications, where the surface kinetics is dominant also depend on the nanoparticle shape, which is determined by factors such as corners, edges, crystal faces, defects, volume, and density.
Monoclinic CuO continues to be amongst the model metal oxides, both in bulk and nanoscale, with wide ranging applications, including all the ones mentioned above. It is one of the most studied amongst the transition metal oxides for catalytic reduction of the industrial pollutant p-nitrophenol in presence of NaBH₄. The excellent electrocatalytic activity is attributed to the low electron transfer overpotential. In a very interesting reent paper, it was shown that the high surface area, which become available in hollow nanostructures of CuO bring tremendous increase the catalytic rate constants. The reported values were amongst the best reported till date in the case of CuO. But the paper had few limitations viz., low yield of particles per synthesis cycle and possibility of particle agglomeration, which may leave the system less useful when large quantity of polluted liquid needs to be treated. The work therefore clearly showed the importance of investigating newer morphologies of CuO nanoparticles, which can have higher reduction catalysis and not only photocatalysis, which is mostly the trend till now. In this paper, we show that the nanoflakes can have higher response characteristics than hollow, and commonly employed solid nanoparticles. The catalytic activity of the synthesized CuO nanoflakes increases as a function of cycling. The reasons for this observation are explained by based on the laws, which decide the formation of electrical double layer around the colloidal or metallic nanoparticles.

In this study, we report the ultrasound-assisted polyol synthesis (UPS) of well-dispersed Pt-Mn nanoparticles (NPs) on titanium carbide (TiC) and their electrochemical performance for methanol oxidation reaction (MOR). In order to prepare Pt-Mn/TiC samples, Pt(acac)₂, Mn(acac)₂ and TiC were dispersed in ethylene glycol and irradiated by ultrasound for 3 h. Ultrasound irradiation could generate a reducing condition of the volatile precursors which resulted in the formation of well-dispersed Pt-Mn NPs on the TiC. In this method, Pt-Mn/TiC samples with various metal loadings from by 16.0 wt.% to 33.2 wt.% were synthesized. The structural analyses were investigated by XRD, XPS, ICP, HRTEM and STEM-HAADF. We found that samples have uniform particle size (4~5 nm) and narrow size distribution. Also, there is no specific macroscopic phase segregation in samples. Electrocatalytic performance of samples was conducted by rotating disk electrode (RDE) measurement. Compared with commercial Pt/C (Premetek, 20 wt%), Pt-Mn/TiC samples showed the enhanced MOR activity and stability in acid media. In conclusion, we demonstrated that the strong metal-support interaction (SMSI) effect between Pt-Mn and TiC leads the improved electrocatalytic performance and durability.

Proton exchange membrane fuel cells (PEMFCs) are the most promising for transportation and portable applications among the different types of fuel cells (FCs). Hydrogen is considered, theoretically, as the best fuel for PEMFCs, however the complexity of its storage, production and transportation has driven the use of other hydrogen rich fuels, such as small organic liquid molecules. Among these liquids, ethanol, methanol, and formic acid are considered the most promising due to their high energy densities and high reversible cell potentials. Pt-base catalysts are known to be the most active materials for the oxidation of these fuels. However, due to the high susceptibility of Pt to poisoning by strongly adsorbed intermediate, such as CO (and aldehyde in case of ethanol), the addition of a second metal to Pt is necessary to enhance its catalytic activity and stability.

In this work we studied the effect of rhodium on Pt activity towards ethanol, methanol and formic acid along with the CO oxidation. Rh_core\Pt_shell nanoparticles were synthesized using the sequential reduction of Rh and Pt using polyol method, in which ethylene glycol works as a solvent and reducing agent and polyvinylpyrrolidone as a capping agent. Different Pt to Rh ratios were used to obtain different Pt coverages. With increasing the Pt coverage, the CO stripping potential was found to shift form 0.48 V vs. SCE (Rh₇₂\Pt₂₈ NPs) to 0.61 V vs. SCE (Rh₄₀\Pt₆₀ and Pt), showing that Rh enhances the Pt activity towards CO oxidation through both bi-functional and electronic effects. In the case of formic acid oxidation, Rh₇₂\Pt₂₈ shows the best activity and stability, improving both the direct and indirect pathways through the facile removal of adsorbed CO. While in the case of ethanol and methanol, the electronic effect shows a higher contribution to the improvement of the catalytic activity. Over all, Rh\Pt NPs show 3-4 higher activity than Pt NPs when the activity is normalized to Pt mass.

Solid oxide fuel cells (SOFC) are gaining increasing attention in the last decades as a low-emission alternative to traditional power sources. However, in order to increase sustainability, cell lifetime, and efficiency, and to decrease cost, efforts are put forward to develop SOFC that operate at lower temperatures (500-700°C). SOFC consists of three mayor parts; anode, electrolyte, and cathode. The SOFC cathode, often perovskites, has to obey the following: high catalytic activity and efficiency for the oxygen reduction reaction (ORR), high surface area for the ORR, a thermal expansion coefficient (TEC) compatible with electrolyte, and high ionic and electronic conductivity. Traditional SOFC cathode materials, such as La_1-xSr_xMnO_3-d, lose cathode performance at lowered temperatures, which introduces the urgent need to develop new cathode materials. Such new cathode materials are often referred to as mixed ionic and electronic conductors (MIECs), from which SmCoO₃ (SCO) is a promising example. SCO is a perovskite, which when doped on the Sm-site with +2-charged metals gain enhanced ionic conduction due to the formation of oxygen vacancies. Doping Co-site with +3-charged transition metals, on the other hand, can be used to tune the TEC to make the material more compatible with electrolytes.
Even though SCO has had experimental interest, available data is rather scarce. Thus, we here present an atomic level characterisation and study of the properties of SCO, starting from the undoped material and then introducing Co-site dopants to assess their effect on structural properties, magnetism, electronic strucutre, mechanical properties, and TEC. We have studied the diamagnetic ground state of SCO, in both its crystal structures, and then modelled the experimentally reported high temperature insulator-to-metal spin transition. We then evaluate the effect of doping on the atomic properties of SCO.

Conversion of CO₂ into hydrocarbon fuels using solar irradiation has been intensively studied, yet its efficiency and selectivity remains to be improved. In photocatalysis, CO adsorbed on the catalyst surface plays an important role in determining the activity and selectivity because only stabilized CO can allow coupling with the adsorbed proton or hydroxyl groups without detachment as CO gas. In this study, we carried out gas-phase conversion of CO₂ using Cu/TiO₂ nanoparticles as photocatalysts, showing significant enhancement when Bi₂O₃ is introduced as a promoter. The reaction conditions are 0.4 mg of catalyst in film, 300 W Xe lamp, and 1 atm of CO₂ gas with H₂O at room temperature. Interestingly, CH₄ production rate increased from 1.12 µmolg^-1h^-1 (Cu/TiO₂) to 11.90 µmolg^-1h^-1 (Cu-Bi₂O₃/TiO₂), while the selectivity of photogenerated electron toward CH₄ versus CO is increased from ca 30% to ca 90%. The Cu-Bi₂O₃/TiO₂ photocatalysts exhibit enhanced CH₄ generation rate because of facilitated supply of CO* (intermediate species) from Cu to Bi₂O₃ surface, on which CO* turns into CH₄. The hypothesis is corroborated by experimental results where mixture of Cu/TiO₂ and Bi₂O₃/SiO₂ results in decreased photocatalytic generation of CO compared to Cu/TiO₂ since CO*, migrated from Cu over to Bi₂O₃ surface, hardly protonates into CH₄ on Bi₂O₃/SiO₂. In short, the enhanced Cu-Bi₂O₃/TiO₂ catalyst reaction is attributed to the synergistic effect between Bi₂O₃ and Cu is manifested; the Cu particles lead to the generation of CO* species from CO₂ on the surface and the Bi₂O₃ particles provide adsorption sites for strong binding of CO*, which leads to the generation of CH₄. These findings provide a platform for the design of heterogeneous photocatalysts, with a primary focus being the architectured metal cocatalysts.

Despite the widespread usage of TiO₂ in photoelectrochemical (PEC) splitting of water (here, oxygen evolution Reactions, OER), the profound understanding on the charge transfer mechanisms at the interfaces is challenging. We employ the atomic layer deposition (ALD) technique for investigating the impact on the local doping with N and S in the planar TiO₂ as a model system. First, we studied the thickness effects on the exciton separation at given PEC conditions and found that there is a critical thickness of pristine TiO₂. Then, the PEC OER performances were monitored with different samples possessing the sub-nanometer thick doping layers of N or S at its interfaces via ALD. In, we correlate the charge transfer kinetics with the results of PEC OERs by the barrier layer tuning of TiO₂ with N- or S-doping in terms of the barrier height and width.

The catalytic behavior similarity between molybdenum carbides and the noble metals has brought great interest to the academic and industry fields. Most molybdenum carbides are produced via high temperature reaction between molybdenum oxide and a carburizing gas, leading to low surface area, which brings a negative impact on the ultimate catalytic performance of formed molybdenum carbides. To date, techniques for synthesizing MoS₂ with a high surface area are well developed, providing possibility to synthesize molybdenum carbides with high surface area through the carburization of MoS₂. Hence, it is necessary to study the carburization mechanism of MoS₂ in order to control the type of molybdenum carbide formation.
In the current in-situ investigation, a MoS₂ specimen was heated up to 900^oC in vacuum (10^-5 Pa). The accelerating high voltage of 100kV was applied to avoid apparent electron beam damage to the specimen. During the heating process, a separate region was monitored for thermal drifting check and microscope condition adjustment to avoid electron beam damage brought to the region for the in-situ investigation. After the thermal stabilization was achieved at 900^oC, a mixture of acetylene and hydrogen gases was delivered to the specimen chamber. Meanwhile, we quickly moved the specimen to the in-situ investigation region.
We found a molybdenum carbide single crystal formed before we moved to the investigation region. This single crystal starts to change from the top, proceeds to the bottom and eventually the whole crystal decomposes into smaller crystals. On the surface of one indicated crystal, we find that a graphitic cap emerges. Selected area electron diffraction (SAED) including this region reveals a ring pattern overlapping the [0001] zone axis diffraction pattern of MoS₂. The indexation for the ring pattern suggests that the molybdenum carbide formed from the decomposition of the elongated single crystal is hexagonal close-packing (hcp) β-Mo₂C. The phase transformation mechanism of carbide and its effect on the graphitic layer formation are discussed.

Developing earth-abundant and inexpensive catalytic materials is a crucial step towards using hydrogen fuels in clean energy technologies. Transition metal dichalcogenides (TMD), such as MoS₂ and WS₂, are a class of materials that have emerged as some of the most promising catalysts for the hydrogen evolution reaction (HER). The excellent catalytic activity of metallic MoS₂ edges for the HER has led to substantial efforts towards increasing the edge concentration. It has also been shown that the 1T metallic phase of MoS₂ has higher performance for the HER due to increased conductivity. The 2H basal plane is less active for the HER because it is less conducting and therefore possesses less efficient charge transfer kinetics. Using electron beam lithography we have fabricated electrochemical microcells to test the HER activity of CVD grown MoS₂ monolayers. We show that the activity of the 2H basal planes of monolayer MoS₂ nanosheets can be made comparable to state-of-the-art catalytic properties of metallic edges and the 1T phase by improving the electrical coupling between the substrate and the catalyst so that electron injection from the electrode and transport to the catalyst active site is facilitated. With electron beam lithography we can engineer the phase of the contacts to decrease resistance and more efficiently inject charges into the nanosheets so that its intrinsic activity towards the HER can be measured. We demonstrate that onset potentials and Tafel slopes of ∼−0.1 V and ∼50 mV per decade can be achieved from 2H-phase catalysts where only the basal plane is exposed. We show that efficient charge injection and the presence of naturally occurring sulfur vacancies are responsible for the observed increase in catalytic activity of the 2H basal plane. Our results provide new insights into the role of contact resistance and charge transport on the performance of two dimensional MoS₂ nanosheet catalysts for the HER.

We introduce surface interrogation scanning electrochemical microscopy (SI-SECM),[1] performed on an extended semiconducting electrode for obtaining information about individual surface features such as defects and terraces during photoanodic operation. This advance in SI-SECM enables its application on any semiconducting electrode of arbitrary size, thus departing from the substrate size limitations typically imposed in SI-SECM. Using convenient numerical analysis methods developed in our laboratory, we obtained the surface coverage and reaction dynamics of adsorbed reactive oxygen species (aROS) and photogenerated holes on lightly n-doped single crystal strontium titanate (SrTiO₃) electrodes.[2] We further introduce nano-electrodes to SI-SECM. New in situ methods capable of elucidating the surface dynamics of operating photocatalysts are required to provide a new leap in their design, rational modification and efficient utilization towards environmental, energy and synthetic and solar applications.

Our SrTiO₃ electrodes displayed a high quantum efficiency and contained native, defective, and metal covered sites on their surface. SECM feedback imaging using the ferricyanide redox mediator and carbon SECM tips of a few microns to few-hundred nm allowed us to detect reactive heterogeneities on the operating substrate during the photoanodic water oxidation reaction. Titration of these individual sites at the micro- and nano-scale was used to quantify photogenerated intermediates.[3] Agreement between simulated and experimental transients was excellent, and fitting allowed us to determine the potential-dependent surface coverage of aROS which displayed a limiting coverage of 50 μC/cm² on a native surface. Our simulated results suggest that, while diffusional broadening decreases the spatial resolution of the SI-SECM process at the nano-scale, it enhances significantly the measured signal. We will discuss the complex simulation space involved in the SI-SECM mode and advances towards simplifying the interpretation of experimental results. SI-SECM redox micro- and nano-titrations were thus established as a novel analytical tool for the mechanism-focused study of photocatalytic adsorbed intermediates. This new application to substrates of arbitrary size will provide an unprecedented view to the heterogeneous surface aspects of photocatalysis.


[1] Rodríguez-López, J. In Electroanalytical Chemistry. Vol. 24. Bard, A.J. and Zoski, C.G., Eds. 2012, CRC Press, pp. 287-352.
[2] B.H. Simpson, J. Rodriguez-Lopez. Electrochimica Acta, 179 (2015) 74.
[3] B.H. Simpson, J. Rodriguez-Lopez. J. Am. Chem. Soc. 137 (2015) 14845.

Gortex membranes have been studied as electrode substrates in alkaline fuel cells (AFCs). Gortex, also known as expanded PTFE (or ePTFE), comprises a highly hydrophobic, porous, fibrous network of microscopically-small Teflon filaments. It combines high porosity with high hydrophobicity to allow the passage of gases but not liquid water. Gortex membranes are commercially available in large volumes and at low cost. They may contain sub-micron hydrophobic pores with a pore-size distribution that is substantially narrower than that found in conventional AFC electrodes. We report the fabrication, characterization, and operation of Gortex electrodes sputter-coated with Pt, Au, and Ag nanolayers of different loadings, and their application in desktop AFCs. Polarisation, electrochemical impedance, microscopy, porometry and contact angle measurements were used to characterise the electrodes and their utility in AFCs. While the Gortex-based AFCs display current densities that are relatively small compared to conventional AFCs, they eliminate the need for a diaphragm between the electrodes and are robustly tolerant of CO₂. Gortex-based electrodes are also shown to offer other important advantages over conventional AFC electrodes that may, in future, be exploited with more active catalyst layers.

Solid oxide fuel cells (SOFCs) are a strong candidate for zero-emission electricity generation. However, the high temperatures necessary for operation lead to long start up times and short lifetimes. Decreasing this temperature leads to a decreased rate in the oxygen reduction reaction at the cathode site, leading to a need for new cathode materials active at reduced temperatures; 600 to 800°C. Doped perovskites materials, such as La_1-xSr_xFe_1-yCo_yO_3-δ (LSCF), show great promise as intermediate tempertature (IT) SOFC cathodes. However, optimisation of these materials can be difficult due to the large variation in stoichiometry that is possible, while their defect chemistry, key to understanding their conductivity and catalytic properties, is poorly understood. Here we present a detailed study of the intrinsic point defects, substitutional defects, including Sr and Co, and oxide ion migration in LaFeO₃, the parent compound of LSCF, employed both molecular mechanical and density functional theory calculations. We find that, under oxygen rich conditions, holes are compensated by the formation of cation vacancies through partial La₂O₃ and full Schottky disorder. Under oxygen rich conditions, oxygen vacancies dominate. These results explain the experimentally observed conductivity as a function of oxygen partial pressure.
Furthermore, a range of divalent dopants have been investigated for both the A and B cation sites in the perovskite structure and the most appropriate identified. For the A-site, we find that including both managnese and strontium, rather than strontium alone, provide the best combination, with strontium encouraging oxygen vacancy formation and managnese promoting hole compensation. On the B-site, cobalt was found to be the most appropriate dopant and, as with manganese on the A-site, favoured hole compensation over oxygen vacancy compensaton.
Fianlly, we have calcualted the activation energies for all possible oxide ion migration pathways. Our results are in good agreement with experiment; with two pathways giving activation energies of 0.66 and 0.58 eV compared to the reported experimental value of 0.77 eV.

Despite many years of research on solid oxide fuel cell (SOFC) electrolyte and electrode materials, the conventional anode formulation of nickel and yttria-stabilized zirconia cermet has not changed much, validating their good performance. However, most studies report results only under fuel rich conditions in the anode, which is not representative of how fuel cell stacks are operated. High fuel utilization conditions result in an increase of anodic polarization, reducing the electrochemical performance of the cell.

Increasing the TPB length via the deposition of sub-micron sized nickel particles in the cermet anode can improve fuel oxidation reaction kinetics. This research analyzes the effects of various nickel infiltration (liquid and vapor phase) processes on the performance of anode-supported SOFC over a wide range of hydrogen and water vapor partial pressures at intermediate temperatures (600-800 Celsius). The impact of the efficacy of various infiltration techniques and Ni particle coarsening were examined through long-term and/or accelerated testing. Cell performance was measured using I-V and EIS techniques, and the anodic polarization losses were calculated using a validated full cell model. Cell microstructure was characterized using SEM and micro-CT. The results identify the roles of the sub-micron size nickel particles and the infiltration processes in enhancing the anode performance at high fuel utilization.

Nanoparticles (NPs) are important for a range of catalytic processes due to their excellent surface area to volume ratio that enables a reduced loading of precious metals while maintaining a high activity. In proton exchange membrane fuel cells (PEMFCs), Pt NPs have been widely used in the preparation of both cathode and anode materials. During the catalyst preparation, other performance enhancing materials are added that are nonconductive, such as perfluorosulfonate containing polymers and iridium oxides used in the cathode and anode catalysts, respectively. The inclusion of these materials may, however, lead to the formation of regions within the catalytic ink of a PEMFC that isolate and render some of the Pt NPs ineffective for electrocatalytic processes. An alternative process is demonstrated here for preparing inks with Pt NPs that retain their activity within these porous inks. For example, Pt NPs were incorporated within a matrix of Vulcan carbon and a proton conducting polymer with specific nano-structures and densities of features. The influence of the process conditions will be discussed in detail for their influence on the final morphology and stability of these nanocatalysts. The new process for preparing these structured Pt nanocatalysts reduces the overall Pt loading (up to 5 times less) within PEMFC cathodes while maintaining similar performance for the oxygen reduction reaction. Composition, morphology, and structure of the as prepared materials and their changes following electrochemical cycling were determined using a variety of analytical techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and X-ray fluorescence spectroscopy (XRF). Total Pt loadings were determined using inductive coupled plasma mass spectroscopy. Materials prepared by this new process can achieve identical performance in the oxygen reduction reaction as a conventional NP catalyst ink, but these newly prepared materials are able to achieve this performance with up to five times less total platinum by weight. These materials processing techniques can be extended to other, more novel catalytic supports to seek further improvements in long-term catalyst stability.

There is a strong need for green energy which is available independently of daytime or seasonal conditions. Hydrogen (H₂) is a convenient carrier for intermediately stored energy. Fuel cells (FC) can generate electrical power as well as heat from H₂ by using a simple redox reaction, the oxidation of H₂ and reduction of O₂ followed by the formation of water (H₂O). In our work we focus on a new material system that allows for a fast H₂ oxidation reaction while also being stable in the electrochemical environment of the FC. Tungsten suboxide (WO_3-x) is used as support material with platinum (Pt) being deposited as the catalyst. In this work we want to understand the distribution and growth behavior of Pt on WO_3-x and investigate the performance of this material system when used as an electrode in high-temperature polymer-electrolyte-membrane FCs (HT-PEMFCs).
The synthesis of our Pt loaded WO_3-x electrodes is performed in a 2-step procedure. First the Pt precursor solution is deposited on the WO_3-x support by a wet chemical approach.¹ In a second step H₂ is used to reduce the Pt precursor salt. This 2-step procedure results in octahedral and truncated octahedral shaped 3D Pt catalyst morphologies on the WO_3-x support with lateral dimensions in the range of 2 – 4 µm. Transmission electron microscopy (TEM) investigations reveal that these Pt morphologies are formed by a highly porous network of interconnected, polycrystalline Pt nanorods with a width of a few nanometers. The connectivity of this network is visualized with the help of TEM tomography. The different growth stages of the Pt 3D network on the WO_3-x support were investigated by varying the reduction times of the Pt precursor in the second step of the synthesis (4 min, 20 min, 60 min). TEM investigations reveal that compact crystals of the precursor salt are formed on the WO_3-x support at first which are then reduced to metallic Pt in the second step when H₂ is present. The corresponding redox reaction starts at the outer shell of the bulk crystal and penetrates to its center while reducing the precursor step by step.
The long-term stability and performance continuity of the Pt/WO_3-x system as an anode for HT-PEMFCs was demonstrated in accelerated and continuous FC tests with operation times of up to 2000 h. The cell voltages of the Pt/WO_3-x system and a standard Pt/carbon (Pt/C) system were compared. At the beginning of the FC operation a slightly lower performance of the Pt/WO_3-x system was observed. However, the degradation rate is lower and as such the HT PEMFC using Pt/WO_3-x electrode system is supposed to outperform the one using the Pt/C system with ongoing operation time.²

(1) Perchthaler, M.; Ossiander, T.; Juhart, V.; Mitzel, J.; Heinzl, C.; Scheu, C.; Hacker, V. Journal of Power Sources 2013, 243, 472.
(2) Heinzl, C.; Hengge, K. A.; Perchthaler, M.; Hacker, V.; Scheu, C. Journal of The Electrochemical Society 2015, 162, F280.

Electrocatalysts are essential components in electrochemical energy conversion systems. For example, hydrogen fuel can be generated by electrochemically splitting water through the hydrogen evolution reaction (HER). Electricity can be regenerated in fuel cells where the oxygen reduction reaction (ORR) occurs in the air cathode. Developing noble-metal free electrocatalysts is of great importance for the low-cost and large-scale application of these technologies.
Metal-organic frameworks (MOFs) are a family of ordered porous materials constructed by metal clusters and organic ligands. In virtue of these compositional and structural features, they are very unique platforms to synthesize functional materials with desirable nanostructures and composition. We demonstrate a MOFs-assisted strategy to synthesize various high-performance electrocatalysts, including mesoporous molybdenum carbide for HER (Nature Communications 2015, 6, 6512) and hierarchically porous metal-nitrogen-carbon electrocatalyst for ORR.
The synthesis of mesoporous molybdenum carbide (MoC_x) relies on the confined and in-situ carburization reaction occurring in a unique MOFs-based compound (NENU-5) consisting of a Cu-based MOF (HKUST-1) host and guest Mo-based polyoxometalates (POMs) resided in pores. This approach enables the uniform formation of metal carbide nanocrystallites without coalescence and excess growth. The as-prepared MoC_x nano-octahedrons consist of ultrafine nanocrytallites with an unusual η-MoC phase embedded in an amorphous carbon matrix, and possess a uniform and highly mesoporous structure. Benefiting from the desirable nanostructure, these porous MoC_x nano-octahedrons exhibit remarkable electrocatalytic activity for HER with a small overpotential of 142 and 151 mV to drive a current density of 10 mA cm^-2 in acidic and basic solutions, respectively, with good stability.
We recently synthesize a high active metal-nitrogen-carbon electrocatalyst for ORR using a well-studied Zn-based MOF (ZIF-8). ZIF-8 nanocrystals serve as precursors for nitrogen-rich carbon and host to immobilize low-cost transition metal precursors to construct the active sites. The representative Fe-NC electrocatalyst exhibits hierarchical porosity that can both host active sites by micropores and facilitate mass transport by meso-/macropores. The optimized Fe-NC catalyst exhibits excellent electrocatalytic activity for ORR in 0.1 M NaOH with a half-wave potential of ca. 0.90 V at 1600 rpm, which matches that of high loading Pt/C catalyst and is among the best reported noble-metal free ORR catalysts.

Oxygen reduction and evolution reactions are essential for broad range of renewable energy technologies such as fuel cells, metal-air batteries and hydrogen production through water splitting, therefore, tremendous effort has been taken to develop excellent catalysts for these reactions. However, the development of cost-effective and efficient bi-functional catalysts for both reactions still remained a grand challenge¹. Surface engineering of the electrocatalysts is one of the most popular strategies to improve their catalytic activity^2,3. Herein, we, for the first time designed an advanced bi-functional electrocatalyst for the Oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) by in-situ synthesis of alternate structure of tungsten carbide (WC) and WS₂ sheets on carbon nanotube (CNT) with microwave irradiation technique. The as synthesized composites are found to be efficient bi-functional electrocatalyst for ORR and OER. The electrocatalytic activity strongly depends on the amount of WS₂ as well as formation of bond between tungsten and carbon atoms. The heterostructure could efficiently tune the electronic properties of CNT as well as WS₂, and the W-C bond could give stability for electrocatalysis, which can contribute significantly to the enhanced electrocatalytic performance for ORR and OER. The electrochemical results are revealed that as synthesized heterostructure composites show an excellent ORR activity that is close to commercial Pt/C catalyst and great OER activity. The novel strategy developed here provides a novel and efficient approach to prepare hybrid bi-functional electrocatalysts for ORR and OER.
References:
S. Dou et.al. Energy Environ. Sci. 9, 1320-1326 (2016).

Anand et.al. Nanoscale 7, 11928-11933 (2015).

Anand et.al. Nanoscale 7, 3404-3409 (2015).

Fuel cells offer one of the most sustainable solutions to the question of environmentally sustainable growth with diverse applications ranging from automotive propulsion to portable electronic systems. Unfortunately, though, the high cost of commercial platinum-based cathodic catalyst for the oxygen reduction reaction (ORR) is a serious limiting factor in the widespread deployment of this technology.¹ Metal-Nitrogen-Carbon (M-N-C) systems have provided some of the best platinum group metal free catalyst alternatives in recent days.

In this work, we demonstrate a direct, facile, one-step synthesis of a Iron-Nitrogen-Carbon (Fe-N-C) catalytic system comprising of unique 3D porous graphene ‘nano-stacks’, using a novel template generated by formation of sodium salt of carboxylic acid groups of the small organic molecule- benzimidazole carboxylic acid, in combination with the University of New Mexico patented silica sacrificial support method (SSM).² The morphology of these benzimidazole derived catalysts (BIDCs) evolves in the form of graphitic crystallites with a short-range order which we study by X-ray diffraction and Raman spectroscopy. A thorough compositional and morphological analysis has been performed with the help of X-ray photoelectron spectroscopy, BET surface area analysis and electron microscopy imaging.

The oxygen reduction reaction electrocatalytic performance of these BIDCs is studied in the alkaline exchange membrane fuel cell using rotating ring disk electrode and membrane electrode assembly (MEA) experiments. The linear sweep voltammetry (LSV) data of the best performing BIDC exhibits an E_1/2 potential of ~0.85 V and an onset potential of ~0.98 V (O₂ saturated 0.1 M KOH electrolyte), which is a significant improvement over the commercial Pt/C catalyst (40% Pt JM-Alfa Aesar). Furthermore, an excellent stability was demonstrated by the catalyst over 7500 cycles at a scan rate of 50 mV s^-1 and a rotation rate of 900 rpm (Department of Energy- Durability Working Group protocol), confirmed by the negligible shift in E_1/2 potential after cycling. The MEA fabricated using the BIDC shows an open circuit potential of ~0.97 V and a maximum power density of 71.6 mW cm^-2, values which are comparable to recent high impact literature in alkaline fuel cells.
This work offers intriguing future avenues to the direct synthesis of high performance carbon-based catalysts by tuning small molecule organic precursors for high temperature pyrolysis.

References:
1. M. Shao, Q. Chang, J.-P. Dodelet, R. Chenitz, Recent Advances in Electrocatalysts for Oxygen Reduction Reaction, Chemical Reviews, 2016, 116, 3594-3657.
2. A. Serov, K. Artyushkova, N. I. Andersen, S. Stariha, P. Atanassov "Original Mechanochemical Synthesis of Non-Platinum Group Metals Oxygen Reduction Reaction Catalysts Assisted by Sacrificial Support Method", Electrochim. Acta 179 (2015) 154-160.

We examine how elastic strain influences the catalytic reaction rate on metal films in the context of hydrogen evolution reaction. Thin metal films supported on elastic substrates are uniaxially loaded in compression and tension while they participate in the HER. We show that elastic strain tunes the catalytic activity in a controlled and predictable way. Three metals that span the volcano plot were chosen: Ni (left of the volcano peak), Pt (near the volcano peak) and Cu (right of the volcano peak). The experimental results show that Pt and Ni films have increased HER activity under compressive strain; while Cu's HER activity is retarded by compressive strain. The opposite was observed under tensile strain. Experimental observations are understood and interpreted by density functional theory calculations on strained Pt, Ni, and Cu(111) surfaces.

The requirements of the eco-friendly water splitting are presenting because of the fossil-fuel crisis and the increasing environment issues. Electrochemical water splitting is a suitable method for producing H₂ and O₂ with the minimum of pollution. Also, because it can be combined with photoelectrochemical and solar cell, the researchers have been made an effort to find active and stable electrocatalysts. Usually, to maximize the performance of electrocatalysts, the acidic or basic electrolyte was selected because of the sufficient proton or hydroxyl ions. The platinum (Pt) and ruthenium oxide (RuO₂) were well-known active electrocatalysts for HER at strongly acidic solution and OER at strongly basic solution, respectively. On the contrary, Pt and RuO₂ are non-active materials for OER and HER. Recently, transition-metal phosphides, such as Co₂P, CoP, and Ni₂P, have attracted for HER in acidic electrolytes. Also, in basic OER conditions, the active OER catalysts based on the oxide/hydroxide of transition metals (Ni, Co, Mn and Fe) have been reported. When transition metals have been mixed, the catalytic activity was greatly improved such as NiFe or CoFe oxide and hydroxide, which are not suitable for HER. To achieve the efficient full water splitting, the available electrocatalysts at both HER and OER in the same electrolyte is demanded.

In this study, mixed cobalt and iron with phosphorous (Co_xFe_1-x-P) films were prepared on copper plates by a facile electrodeposition galvanostatically. In case of Co/Fe ratio of 1.07, the Co_xFe_1-x-P films could be operated in strong alkaline solution for both HER and OER, which achieved overpotentials of -169 mV for HER and 307 mV at 10mA/cm² without any stirring. Also, our active Co_xFe_1-x-P films had the small Tafel slopes of 56.9 and 39.2 mV/dec for HER and OER, respectively. When Co_xFe_1-x-P films were deposited on dendritic copper with large surface area, the overpotential for OER could decrease to 290 mV but the overpotential for HER increased to 201 mV. With coupling of Co_xFe_1-x-P films on the copper plate without and with dendritic copper for full water splitting, superior activity of 1.64 V at 10 mA/cm² and stability over 72 hr could be obtained, which even comparable to Pt and RuO₂ couple.

Late transition metal phosphides have been reported to have high activity for catalyzing hydrogen evolution reaction (HER), yet their active site and stability are not well-understood. Here we report systematic activity and stability study of CoP for HER by combining electrochemical measurements for CoP nanoparticles (NPs) with ex situ and in situ synchrotron X-ray absorption (XAS) spectroscopy at phosphorus and cobalt K edges, as well as density functional theory (DFT) calculations. Colloidally synthesized CoP NPs showed high HER activity in both acid and base electrolytes, comparable to previous work, where no significant pH dependence was observed. Transmission electron microscopy-energy dispersive spectroscopy study of CoP NPs before and after exposure to potentials in the range from 0 to 1.4 V vs. the reversible hydrogen electrode (RHE) revealed that the P/Co ratio reduced with increasing potential in the potentiostatic measurements prior to HER measurements. The reduced P/Co ratio was accompanied with the emergence of (oxy)phosphate(s) as revealed by XAS, and reduced specific HER activity, suggesting the important role of P in catalyzing HER. This hypothesis was further supported by DFT calculations of HER on the most stable (011) surface of CoP and voltage dependent intensities of both phosphide and phosphate components from P-K edge X-ray spectroscopy. This work highlights the need of stabilizing metal phosphides and optimizing their surface P sites in order to realize the practical use of metal phosphides to catalyze HER in electrochemical and photoelectrochemical devices.

The development of efficient non-platinum group metal (non-PGM) catalysts for oxygen reduction reaction (ORR) is of paramount significance for the commercialization of fuel cells and metal-air batteries. So far, M–N–C catalysts (M=Fe and/or Co) synthesized through high temperature heat treatments (700-1100 ^oC) of transition metals, nitrogen, and carbon precursors is one of the most promising non-PGM candidates for ORR in terms of activity and stability. In view of the present trial-and-error approach optimizing performances via tuning the synthetic routes and precursor materials, further improvements relies heavily on proper understanding of the nature of active sites and their catalytic roles toward ORR.
Herein, we report a scalable metal organic framework-derived Fe-N-C catalyst with high ORR activity in acidic media. The porous and disordered carbon matrix of the catalyst plays pivotal roles for its measured high ORR activity by hosting high population of reactant-accessible active sites. Based on in situ x-ray absorption spectroscopy (XAS) together with complementary characterization techniques such as Mössbauer spectroscopy etc., an out-of-plane ferrous Fe-N₄ moiety embedded in disordered carbon matrix with a high Fe^2+/3+ redox potential is proposed as active site under working conditions (low potential), and such structure is drastically different from that characterized under ex situ conditions. The active site switches to an in-plane ferric Fe-N₄ moiety reversibly associated with the adsorption of oxygen species at high potentials/ex-situ conditions. The number of available active sites is controlled by the Fe^2+/3+ redox potential through the site-blocking effect.¹ The favorable biomimetic dynamic nature of the Fe-N₄ active sites with a near-optimal Fe^2+/3+ redox potential formed upon pyrolysis accounts for its high intrinsic ORR activity by balancing the site-blocking effect and O₂ dissociation.
Acknowledgements:
The authors deeply appreciate financial assistance from the U.S. Department of Energy, EERE (DE-EE-0000459). Use of the National Synchrotron Light Source (beamline X3B), Brookhaven National Laboratory (BNL), was supported by the U.S. Department of Energy, Office of Basic Energy Sciences. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.
References
[1] Jia, Q.; Ramaswamy, N.; Hafiz, H.; Tylus, U.; Strickland, K.; Wu, G.; Barbiellini, B.; Bansil, A.; Holby, E. F.; Zelenay, P.; Mukerjee, S.. ACS Nano 2015，9，12496.

SnO₂-based Transparent Conductive Oxides (TCOs) currently represent the TCOs-benchmark in different applications, such as in photovoltaics and photo-electrochemical applications (e.g. DSC, photo-electrodes for H₂O splitting or photo-catalysts supports). With respect to other TCOs, they benefit from high carrier density and mobility, low costs, high thermal stability, non-toxicity and high transparency in the visible spectrum. Moreover, the high chemical stability of F:SnO₂ (FTO) makes this the material of choice for PEC applications, both in acidic and basic environments. Ideal PEC electrodes design would require nanostructured host-guest architectures, to maximize their active area, together with ionic transport and precious photo-catalysts utilization efficiency. Moreover nanostructured architectures can enhance performances also in combination with materials that provide high photo-generation efficiency, but poor electrical conductivity, e.g. α-FeO_2. This poses the need to manage simultaneously charge injection, collection and selectivity, and band engineering together with the orthogonalization of light absorption, to enhance the optical density of the photoactive electrode. These features naturally require nanostructured (ns) TCOs. The state of the art provides many works on ns TCOs, obtained with Physical Vapor Deposition as well as with wet techniques, but, so far, FTO nanostructuration remains unreported. In order to improve the electrodes electrical transport properties 1D nanostructures would be beneficial, while light-path can be engineered with highly scattering 3D nanostructures. This naturally trades off for quasi-1D hierarchical nanostructures and the advantages of this morphology have been already studied by our group with excellent results.
In this work we present the first quasi-1D hierarchically nanostructured FTO thin film, obtained via Pulsed Laser Deposition from a SnO₂ target. As deposited SnO_x nanostructures have been doped by gas phase reaction with dry HF. The resulting ns FTO electrodes have been analyzed from electrical, optical and structural point of view. Dopant concentration in the films is correlated with characteristic electrodes I-V curves slope in cross-contact configuration (i.e. transport along the nanostructures) and with electrodes absorption features arising from the excitation of Surface Plasmon Resonances. XRD spectra reveal a good grade of crystallinity and a preferential growth in the direction perpendicular to the substrate. As a proof-of-concept system, the ns FTO scaffold have been functionalized with Pt nanoparticles and tested in an electrochemical cell as a catalytic system for Oxygen Reduction Reaction (ORR). The results show high activity towards the reaction, demonstrating its efficacy as a catalyst scaffold.
The implications of this work may disclose potential for effective use of out-of-plane NS FTO TCOs in devices architectures beyond the common stacked layers approach.

In heterogeneous catalysis, a single catalytic event is typically performed on a catalytic site consisting of a couple of or a few atoms of metal, oxide, carbide, or their support. Electronic state of atoms of a catalytic site is the key factor determining its catalytic performance since it dominates the fundamental surface process in a catalytic cycle including adsorption and dissociation of reactant molecules, surface diffusion of reactant molecules or dissociated species, coupling between different reactant molecules or dissociated species, adsorption of intermediates, and desorption of product molecules. Tailoring electronic state of a catalyst at atomic or nano scale for tuning a catalytic performance has been applied to the development of a catalyst with higher catalytic activity and selectivity.
One important category of heterogeneous catalysts is bimetallic catalyst M-A (M and A denotes metal elements) which consists of continuous bimetallic sites at a metallic state. The second metal A could tune catalytic performance of the first metal M through electronic, geometric, bi-functional, or lattice strain effects compared to a monometallic catalyst. Single dispersion of such bimetallic sites through separately anchoring them on a non-metallic support can offer a distinctly different catalytic performance in contrast to continuous sites on an alloy nanoparticle (M-A). These isolated bimetallic catalytic sites M₁A_n offer quite high catalytic activity in removal of nitric oxide or production of hydrogen since metal atoms of these isolated bimetallic sites exist at a cationic state instead of a metallic state. In addition, the minimized choice of potential binding configurations of reactant molecules on a single site increases selectivity for production of some product. These studies suggest that formation of singly dispersed bimetallic sites on a non-metallic support is a promising approach to developing catalysts since these isolated sites have an electronic state different from those continuous bimetallic sites on the surface of an alloy nanoparticle.

Heterogeneous catalysts often undergo dramatic changes in their structure as the mediate a chemical reaction. Multiple experimental approaches have been developed to understand these changes, but each has its particular limitations. Electron microscopy can provide analytical characterization with high spatial resolution, but generally requires that the sample be imaged both ex situ and ex post facto. Photon probes have superior depth penetration and thus can be used to characterize samples in operando conditions (i.e. when they are actively working). But they generally lack appropriate spatial resolution and thus give only ensemble average information. We have taken advantage of the recent developments in closed-cell microscopy methods to develop an approach that allows us to successfully combine electron, x-ray and optical probes to characterize supported nanoparticle catalysts in operando conditions. By measuring the reaction products at each stage of the reaction, we can directly correlate the information that can be obtained from each approach, and thus gain a deep insight into the
structural dynamics of the system. In this presentation, we will show how we can use this approach to understand the dynamic segregation that occurs in NiPt bimetallic nanoparticles supported on SBA-15, during oxidation, reduction and the reverse water-gas shift reaction. We
will describe how we can use this approach to correlate x-ray absorption spectroscopy (both near- edge and extended fine structure), scanning transmission electron microscopy, energy dispersive energy dispersive x-ray spectroscopy and electron energy loss spectroscopy, in order to deconvolute both atomistic and mesoscopic processes during reaction. Finally, we will show how this method provides a robust experimental approach to characterizing compositional changes in bimetallic nanoparticle systems.

Subnanometer metal clusters can exist in three states: bare; supported; ligand protected. We explore their structures, properties, and catalytic applications from a computational perspective. For the bare metal clusters, we are interested in structure evolution with the number of atoms; here we use first principles global minimization to show their interesting geometric and electronic structure evolution. For the ligand-protected metal clusters, we explore the metal-ligand interface and the role of the ligands in dictating cluster stability. Most important, we will show how ligand-protected Au clusters catalyze different types of reactions.

The development of new routes to base chemicals and fuels from renewable resources has drawn much attention worldwide. Synthesis gas (CO + H₂) derived from renewable sources (e.g., biomass) and its conversion to dimethyl ether (DME) provides an attractive option with respect to a wide range of applications (e.g, as liquefied petroleum gas, intermediate product for base chemicals or as clean diesel substitute). In the conventional two-step DME process, synthesis gas is converted to methanol over Cu-based catalysts in the first stage, which is subsequently dehydrated to DME over an acidic catalyst in the second stage. Alternatively, the single-step, syngas-to-dimethylether (STD) process, where methanol synthesis is coupled in situ with its dehydration to DME, allows for higher CO conversions [1]. The design of efficient bifunctional STD catalysts with balanced methanol and dehydration functionalities, however, remains a crucial issue. In this context, model systems derived from well-defined nanoparticles provide further fundamental understanding of structure-performance relationships, enabling a future rational design of highly efficient catalysts.
We address the preparation of bifunctional model catalysts via the precursor concept for the single-step synthesis of DME from syngas [2]. Well-defined colloidal nanoparticles (e.g., Cu/Zn- and Pd/Zn-based particles) with small particle size and narrow size distribution were synthesized via an organometallic procedure and used as precursors for the methanol active component. The nanoparticles were subsequently integrated in bifunctional STD model catalysts using different types of acidic materials. The catalytic properties of the nanoparticle-derived, bifunctional catalysts in the STD process were evaluated in a continuously operated, fixed-bed reactor using simulated biomass-derived, CO rich synthesis gas and different reaction parameters. The bifunctional catalysts revealed high CO conversions and DME selectivities. The effect of the materials characteristics of the two catalytically active components on the overall catalytic performance is elucidated. Long-term studies of selected bifunctional catalysts displayed outstanding stability under the reaction conditions.

Literature
[1] R. Ahmad, D. Schrempp, S. Behrens, J. Sauer, M. Döring, U. Arnold, Fuel Processing Technology 121 (2014) 38.
[2] M. Gentzen, W. Habicht, D. E. Doronkin, J.-D. Grunwaldt, J. Sauer, S. Behrens, Catal. Sci. Technol.6 (2016) 1054.

In spite of the accumulated knowledge about the synthesis of near-monodisperse metallic nanoparticles, the kinetic mechanism responsible for the formation of crystalline particles is still not very well understood ^[1]. Such kinetic data can reveal important information about the course of action of the nucleation and growth processes ^[2]. The difficulty in monitoring nanoparticles growth in liquids arises from the scarcity of techniques for such an in situ analysis of the solution, given the nature of the fast reactions involved in such processes.
Here we show that a simple ionic conductivity measurement can precisely monitor the reduction reaction that ultimately results into the formation of metallic nanoparticles. We make use here of the change in ionic conductivity associated to the reduction process.

By monitoring the reduction reaction (in a polyol process) of various noble metal salts (K₂PtCl₄, K₂PtCl₆, H₂PtCl₆ and RuCl₃), it was found that the temperature-conductivity profile exhibits four stages. In the first stage where the conductivity is constant, no reduction takes place. At the second stage where the conductivity gradually increases, metal nucleation is supposed to take place followed by a faster change in the conductivity that is attributed to particle growth. TEM analysis confirmed the above hypothesis where no nanoparticles were observed up to the end of stage II as only metal nuclei are formed. The rapid increase in conductivity at stage III is attributed to the nanoparticle growth and is also supported by TEM analysis. This is expected as the consumption of metal ions, and thus release of chloride ions, is faster for the metal growth than that for nucleation. Once a maximum conductivity is achieved, particle growth stops as no more precursor is available for reduction.

The Temperature-Conductivity profiles were not only used to differentiate between nucleation and growth, but they were also successfully utilized in distinguishing between homogeneous nucleation and heterogeneous nucleation. It has been always reported that heterogeneous nucleation starts at earlier temperature than that needed for homogeneous nucleation, but it has never been observed experimentally. Here we show homogeneous vs. heterogeneous nucleation profiles and explain the significant differences between the two systems.

Due to the precise monitoring of the polyol reduction process, we studied the reaction kinetics of H₂PtCl₆ polyol reduction and determined the reaction order to be Pseudo-Zero-Order reaction. The activation energies of both nucleation and growth processes were also determined to be 1.1 and 0.5 eV, respectively. We also discuss in the presentation how the pH affects the reaction rate and whether it affects both nucleation and growth processes.

[1] E. E. Finney, R. G. Finke, Journal of colloid and interface science 2008, 317, 351–374.
[2] J. Boita, L. Nicolao, Alves, Maria C. M., J. Morais, Phys. Chem. Chem. Phys. 2014, 16, 17640.

Electride is an exotic compound in which electrons serve as anions. We reported the first RT-stable electride [Ca₂₄Al₂₈O₆₄](4e), which is called C12A7:e[1]. This compound has unique properties of having a low work function of 2.4 eV comparable to that of metal potassium but chemical& thermal stability [2]. We applied C12A7:e as a catalytic support of Ru nanoparticles to synthesize NH₃ at mild conditions such as ambient pressure and 250-350C, and obtained the following results [3,4]; (1) The activation energy for this catalyst is ~50kJ/mol, which is half of the conventional Ru-loaded catalysts. (2) The TOF value is higher by an order of magnitude than that of the latter. (3) No serious hydrogen poisoning occurs which is commonly observed for Ru-catalysts. (4) Kinetic analysis of ¹⁴N-¹⁵N exchange reaction revealed that dissociation of N-N bond is not the rate determination step for this catalyst. (5) The reaction mechanism switches from conventional to a new type at metal-insulator transition of C12A7.
By extending the material concept of electride, we found several new electride materials such as Y₅Si₃ [5] and its effectiveness as the catalysts. In this talk, we report the effectiveness of Ru-loaded electride materials as the catalyst for ammonia synthesis and a common mechanism.

[1] S.Matsuishi et al. Science,301, 626 (2003), [2] Y.Toda et al. Adv. Mater. 19, 3564 (2007).[3] M.Kitano et al. Nat.Chem. 4, 934(2012) ; Nat.Comm. 6, 6731(2015), [4] S.Kanbara et al. JACS 137, 14517(2015), [5] Y.Lu et al.JACS 138, 3970(2016)

Single-atom catalysts with Au, Ag and Cu atoms at the surface of ceria are gaining more interest due to their low cost and high performance. However, it is difficult to achieve a high concentration of atomically dispersed metal atoms at ceria surfaces due to the strong tendency of agglomeration for the metal atoms. Having understood how dislocations in ceria can serve as traps for charged point defects, we propose that dislocations can anchor single metal atoms and enhance the ceria-based catalyst performance.

A wide range of charge states and configurations of the Cu defects in the dislocation free ceria are calculated with density functional theory, first to elucidate the defect chemistry for Cu ions in ceria. The formation energies of these defects as a function of chemical potential of oxygen and the Fermi energy indicates that the most preferred Cu defect is Cu¹⁺ interstitials. This finding differs from previous calculations in literature where only a defect complex of copper and oxygen vacancy is calculated, but is consistent with the reported experimental observations. An ½ <110>{100} edge dislocation model in ceria was also constructed. We found that the Cu defect formation energy at the edge dislocation core is 1.2 eV lower than that in the bulk, indicating a tendency for Cu to enrich at the dislocation compared to the bulk ceria, which has a very low solubility of Cu. More interestingly, and importantly, Cu has a lower oxidation state in the dislocation core than in the bulk. This lower oxidation state is more active for catalytic activity. In summary, both the enrichment of Cu at the dislocation core and the more active oxidation state indicate that dislocations in ceria are beneficial to the increasing surface electro-catalytic reaction kinetics with single atom catalysts.

Lignin is a renewable polymer derived from the lignocellulosic biomass, which represents more than 20% of the total mass of the Earth's biosphere. The transformation of lignin into value-added chemicals currently presents a major challenge in terms of both sustainability and energy efficiency, requiring innovative chemistries and catalytic approaches. In this context, solubilization and valorization of lignin using heterogeneous catalysis has received increased attention in recent years. Here we report a suite of new catalysts based on Metal-Organic Frameworks (MOFs) designed to perform the following functions: (1) reductive hydrogenolysis of C-O bonds in lignin oligomers; (2) oxidative cleavage of C-O and C-C bonds in lignin oligomers, such as guaiacylglycerol-β-guaiacyl ether (GGE); (3) a new MOF-catalyzed lignin solubilization route that can be tuned to yield either aromatic products or commercially valuable ring-opened polyacids usable as dispersants. MOFs are exceptionally tunable, thermally and chemically robust nanoporous materials that provide a completely new avenue for lignin valorization. The versatile IRMOF-74(n) series is used as a platform for creating efficient hydrogenolysis catalysts, as it has a tunable pore size and the required thermal and chemical robustness. The catalytic bond cleavage of β-O-4, α-O-4, and 4-O-5 linkages occurs under mild conditions (10 bar hydrogen pressure and temperatures as low as 120 °C). The oxidative chemistry is performed using water stable UiO-type MOFs that catalyze selective cleavage of lignin ether linkages. For instance, the β-O-4 linkage in lignin dimer GGE is cleaved in 24 hours at room temperature using less than 1.0 % (w/v) hydrogen peroxide. Conversions as high as 99% with selectivity up to 97% highlight the potential of MOF-based catalysts for lignin solubilization and valorization. Coupled with known MOFs that now number in the thousands, our results suggest that MOFs can be developed as a new class of industrially robust, tailorable catalysts.

Nanoparticles and nanomaterials represent viable solutions to solve environment related problems, such as water contamination. This is why we report the reduction of nitrates (NO₃^-) by photocatalytic reaction of tin dioxide (SnO₂) incorporated on graphene/graphene oxide (G/GO) sheets. G/GO, with its good surface-to-volume ratio, serves as a support for SnO₂ nanoparticles that enhances the photocatalytic performance of the composite in comparison with bare SnO₂. Such integration has shown to provide a photoreduction of up to 4 times more efficient than the photoactive material alone, as well as abatement of around 60% without microbial assistance. Consequently, the SnO₂/G/GO composite can be employed in the reclamation of water for the reduction of (NO_x^-) species.

Photocatalysis using solar light and with a semiconductor catalyst has been studied for many years and recently attracted great interest as a clean-up technology. Among various metal oxide semiconductor, ZnO, which is widely known as a kind of wide-band gap semiconductor, has been proved to be an excellent catalytic material. A number of chemical and/or physical methods have been employed in the production of ZnO nanostructure, however, usually these methods require relatively high energy consumption, pressure and/or vacuum. In this work, we report a green synthesis of ZnO flowers-like nanoparticles using microwave-assisted hydrothermal method. ZnO hexagonal flowers-like structures were grown in aqueous solutions using, zinc nitrate [Zn(NO₃)₃6H₂O] and potassium hydroxide solution [KOH] in a molar concentration of 0.3 mol.L^-1 and 2.0 mol.L^-1, respectively. The samples growth process in domestic microwave furnace at 140^oC for 4, 8, 16 and 32 minutes. The ZnO samples were investigated by XRD, Micro-Raman Spectroscopy and FE-SEM microscope. XRD patterns correspond to hexagonal wurtzite structures of ZnO with a P6₃mc space group, according to JCPDS no. 57450. The Rietveld refinements were performed through the general structure analysis (GSAS) program and indicating the structural refinement and numerical results were of a good quality and in good agreement with those published in the literature. Micro-Raman spectroscopy showed the presence of the characteristics vibrational modes of the hexagonal ZnO structure in all samples. FE-SEM images showed ZnO flowers-like nanoparticles morphology in all samples. The ZnO flowers-like was applied in the photodegradation of Rhodamine B dye for their photocatalytic propertie study. Photocatalytic of Rhodamine B was performed in a typical heterogeneous process with a mixture of ZnO (5 mg) dispersed in 50 mL of the the Rhodamine solution (1x10^-5 mol). The suspensions were irradiating by six lamps (PHILIPS TL-D, 15 W). After the reaction, the mixture was centrifuged to completely remove the catalyst nanoparticles. The remaining solution was analyzed by UV-Vis absorption spectroscopy and the absorption band (maximum λ at 554 nm) were monitored. The result revealed that the ZnO processed at 140^oC for 32 minutes have higher photocatalytic efficiency degradation with completely dye degraded in 30 minutes. The pseudo-first order model to obtain the rate constant (k) of catalyst crystals was applied. We can be verifies an increasing in the (k) values with the increase microwave processing time that consequently improve of the ZnO photocatalytic property. In this work we reported a low-temperature way to prepare an photocatalytic ZnO flowers-like structures and the photocatalytic measurements showed the great potential of the ZnO processed at 140^oC at 32 minutes.

The reduction of carbon dioxide to useful chemicals has drawn a great deal of attention as an alternative to the depletion of fossil resources without altering the atmospheric CO₂ balance. As the chemical reduction of CO₂ is energetically uphill due to its remarkable thermodynamic stability, this process requires a significant transfer of energy. In the last decade, achievements in the fields of photocatalysis sparked increased interests in the possibility of using sunlight to reduce CO₂. In this study, we develop the highly efficient photocatalyst for CO₂ reduction on basis of graphene oxides (GOs) and conjugate polymers. This nanocomposite photocatalyst shows a significant improvement of the efficiency, arising from an efficient charge transfer cross the heterojunctions between the two components. We also extend the photocatalyst to PC₆₁BM and C₆₀ for the further improvement of photo-reduction efficiency through tuning the compatibility of photocatalysts and the electronic structures of hydrophilic conjugate polymers. The relationship of co-photocatalyst for electron reduction reaction to form the morphologies is determined by in situ X-ray scattering. Using this approach, we shed light on how to rational design an efficient CO₂ photo-reduction system through manipulating the band gap, compatibility, interaction and morphologies of photocatalysts.

We report on the electrochemical reduction mechanisms of nitrogen dopants in nano carbons used for fuel cell cathode catalysts. Among various dopants, e.g. sulphur, phosphorous and boron, nitrogen has been the most popular due to the beneficial effects on the electrochemical activity of graphene and/or CNTs in both alkaline and acidic media. Multiple research groups have been investigating the electrochemical activity of CNTs, graphene and other carbon nanomaterial containing electrodes with the aim to elucidate the key active site. However, long-term stability of these materials, especially in acidic environment, is rarely mentioned.

Here, nitrogen plasma functionalized carbon nanotubes (NCNTs) are used as solid acid fuel cell (SAFC) cathodes. Plasma treatment of carbon nanomaterials allows us to change the concentration of surface functional groups in a controllable, repeatable manner and we characterise the long term stability of the surface functional groups with X-ray photoelectron and impedance spectroscopy in a humidified oxygen environment at 240°C. Electrochemical results show a significantly improved performance of NCNTs compared to as-synthesized CNTs, but a dramatic drop in the activity after 15 days and depletion of nitrogen dopants. It can be considered that surface functional groups interact with charge carriers at the cathode triple phase boundary and become electrochemically reduced during measurements.

To analyse possible reaction pathways of nitrogen reduction, quantum chemical calculations were performed using Density Functional Theory (DFT) B3LYP method on different nitrogen containing graphene structures at SAFC operating conditions. Nitrogen dopants are likely to be reduced by NH₃ scission after the interaction of the N functionalised graphene sheet with e^- and H⁺

We will present results from a study on the concurrent evolution of the atomic structure and Oxygen Reduction Reaction (ORR) activity of Pd-Cu nanoalloys taking place at the cathode of an operating proton exchange membrane fuel cell (PEMFC). The study involved high-energy x-ray diffraction (HE-XRD) carried out while the PEMFC was cycled between 0.6 V and 1.2 V for 2000 times. Experimental HE-XRD data are analyzed in terms of atomic pair distribution functions and the ORR activity of Pd-Cu nanoalloys is assessed in terms of the current output of the PEMFC. We find that the leaching of Cu species from Pd-Cu nanoalloys and so the ORR activity losses they suffer during the PEMFC operation are highly dependent on the initial Pd:Cu ratio in the nanoalloys and the degree of their chemical ordering. Clues for improving the stability of Pd-Cu nanoalloys under PEMFC operating conditions will be provided and avenues for developing ORR catalysts delivering more with less noble metal involved will be outlined.

Multimetallic materials in which an alloying element is present at or near the surface of a parent metal exhibit enhanced functional properties compared to parent metals alone. They have a wide range of applications in areas such as hydrogen storage, catalysis, and electrocatalysis. Examples include a dramatic increase in the oxygen reduction activity of Pt catalysts in the presence of subsurface alloy layers, Pd overlayers on Pt directing formic acid oxidation pathways to avoid surface-poisoning, and improved kinetics of hydrogen sorption by formation of surface and subsurface alloys. Further, the topology exhibited by nanoparticles and nanoporous metals (NPM) plays an important role in determining functional properties. Much effort has been made to develop approaches to synthesize multimetallic materials with well-controlled surface morphology and composition, but this remains a challenge, particularly at large scale, and when using high surface area powders and nanomaterials as substrates.

Atomic Layer Electroless Deposition (ALED) is a scalable approach to surface-modified metal powders in which deposition of adlayer elements on substrate metals is carried out. In this method, elements more noble than the surface hydrides of the substrate metal are deposited layer-by-layer in surface-limited fashion. The substrate is first charged with a controlled partial pressure of H₂ gas to chemically form a surface hydride. After terminating the flow of reagent gas, surface-limited reduction of an adlayer of a different metal is carried out by galvanic exchange of the surface hydride.

We report herein the results of ALED on NPM substrates that have been synthesized by chemical reduction of metal salts in the presence of a nonionic surfactant. ALED materials have been characterized by nitrogen porosimetry, X-ray photoelectron spectroscopy, electron microscopy and atomic absorption spectroscopy. Surfaces were further characterized by measuring the vibrational spectroscopy of adsorbates to probe fractional coverage of adlayer metals. We will also demonstrate strategies to alter adlayer morphology by controlling particle nucleation and growth rates during the ALED process.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

CO₂ capture and sequestration (CCS) is regarded as a key technology to reduce the concentration of CO₂ generated by large anthropogenic point source. CCS technology involves capture, transport and sequestration of CO₂. In capture process, post-combustion technology appears to be the most feasible at present because its implementation requires least cost. CO₂ absorbents for the post-combustion process are divided into three types depending on the operating temperatures; low (-200 °C), intermediate (200-500 °C) and high (above 500 °C). In view of the energy efficiency in operating post-combustion process, CO₂ absorption in the temperature ranges from 200-500°C is highly desirable. Currently, materials based on MgO are widely investigated for intermediate temperature absorbents.
Mg²⁺ ion is unique in that regard as its carbonate decomposes into oxide at the lower temperature among all of the alkali and alkaline earth metal ions. In addition, the theoretical absorption capacity of MgO (for the reaction MgO + CO₂ -> MgCO₃) is the highest among all of the absorbents investigated so far. However, very large lattice energy of MgO originating from the large charge density of Mg²⁺ makes both absorption and desorption kinetics sluggish.
In order to accelerate the sluggish absorption and desorption kinetics of MgO, NaNO₃-M₂CO₃ (M=Na, Li) promoted MgO was investigated as an absorbent material. Our study indicates that CO₂ absorption occurs through formation of double carbonate (i.e., MgO + M₂CO₃ (M=Na, Li) + CO₂ -> M₂Mg (CO₃)₂) and desorption through reverse reaction. The reaction kinetics of this absorbent is faster than that of MgO + CO₂. NaNO₃ and M₂CO₃ (M=Na, Li) play an important role in this absorbent when this absorbent absorbs and desorbs CO₂. In operating condition at around 330-400 °C, phase change occurs in NaNO₃ turning it from solid to liquid. MgO and M₂CO₃ (M=Na, Li) dissolves in the liquefied NaNO₃ and Na₂CO₃ provides CO₃^2- seed to MgO turning it into carbonate. In this process, Li₂CO₃ enhances its absorption and desorption kinetics. Throughout FT-IR data of NaNO₃-M₂CO₃ (M=Na, Li) promoted MgO, we analyze that Li⁺ ions can affect to this absorbent when it operated. Furthermore, this absorbent can absorb CO₂ even at low partial pressure. As a result, this absorbent can be a promising candidate for the post-combustion CO₂ capture technology.

The sluggish kinetics of the oxygen evolution reaction (OER) remains one of the limiting processes in developing energy storage and conversion processes such as (photo)electrochemical water-splitting and battery cathodes.¹ Thus, structural studies to understand catalyst structure-property relations are useful for the design of new catalyst chemistries for improved kinetics and stability under electrochemical conditions. Perovskite oxides such as LaCoO₃ and the brownmillerite (BM) phase SrCoO_2.5 are such catalysts, with oxygen exchange in SrCoO_2.5 coupled to high OER activity.²

In this study, we determined the atomic stability of LaCoO₃ and SrCoO_2.5 thin films under an alkaline environment with Coherent Bragg Rod Analysis (COBRA), a technique that provides atomic resolution of structure in epitaxial thin films.^3-5 Films of 4 nm LaCO₃ and 4 nm SrCoO_2.5 were deposited on a 4 nm La_0.7Sr_0.3MnO₃ buffer layer on an SrTiO₃ substrate. Using a custom-designed cell at the Advanced Photon Source, we conducted COBRA to determine averaged atomic positions of epitaxial thin films under 1) pristine conditions and 2) open circuit voltage (OCV) conditions in O₂-saturated alkaline solution “in-situ.” We find that 1) the LaCoO₃ perovskite is stable under both conditions, with nearly identical atomic positions under pristine and OCV conditions 2) the BM-SrCoO_2.5 film exhibits a loss of coherency to the brownmillerite structure upon exposure to the OCV conditions 3) electrolyte radiation effects are minimized, demonstrating promise for further aqueous electrochemical studies.

References

¹ Hong, W. T., et al., Energy & Environmental Science, 2015. 8: p. 1404-1427.
² Matsumoto, Y., et al., J. Electrochem. Soc., 1980. 127: p. 2360-2364.
³ Sowwan, M., et al., Physical Review B, 2002. 66(205311): p. 1–12.
⁴ Yacoby, Y., et al., Nat Mater, 2002. 1(2): p. 99-101.
⁵ Feng, Z., et al., Energy & Environmental Science, 2014. 7: p. 1166-1174.

Recently, nanostructured materials such as nanoparticles, wires, and tubes have attracted much attention due to their unique potential applications for solar cells, water splitting, and environmental remediation. The electrocatalytic splitting of water, hydrogen or oxygen evolution reaction (HER or OER), by nanostructured materials has been considered a promising candidate and useful procedure, especially. The metal oxides (Ru, Co, Ir, Ni and Fe) and metal-free carbon materials (CNT and Graphene) have been made great efforts to study for non-precious metal catalysts as substitutes for Pt-catalysts. Among different OER catalysts, metal oxide nanostructures would be desirable to develop electrocatalysts based on considerably cheaper metals such as Ni and Fe. Furthermore, developing mesoporous catalysts materials on high-surface-area is very useful strategy in order to achieve high-efficiency hydrogen and oxygen gas evolution. The monodispersed and mesoporous Ni-Fe multi-composite hollow nanocages (NCs) based on simple calcination via Prussian blue analogue (PBA) of Ni₃[Fe(CN)₆]₂ nanocube precursors. We report the synthesis and characterization of mesoporous Ni-Fe multi-composite hollow NCs under controlled several experiment condition. Also, the mesoporous Ni-Fe multi-composite hollow NCs electrode shows significantly enhanced OER performance compared to RuO2 and Pt/C electrodes. The overpotential and Tafel plot of mesoporous NiO/NiFe₂O₄ multi-composite hollow NCs were as low as 261 mV at the current density of 10 mA cm^-2 and 50.6 mV dec^-1, respectively.

The importance of nanoscale platinum catalysts is well-established for a wide variety of environmental, industrial, and synthetic applications. Platinum nanoparticles (Pt NPs) are highly efficient catalysts for photocatalytic water splitting and the redox reactions of oxygen, hydrogen, methanol, and other fuels. The shape and size of Pt NPs can be controlled to select for specific catalytic reactions, and can also influence interparticle interactions, self-assembly, dielectric properties, and light interactions. Well-dispersed colloidal Pt NPs offer great flexibility for the construction of catalytic nanoarchitectures, functionalization of supports, dispersion for photodegradation of organic pollutants, and integration into sensors and fuel cells. Platinum@hexaniobate nanopeapods (Pt@HNB NPPs) are new nanocomposites that are formed by encapsulating dispersible Pt NPs into ordered one-dimensional arrays inside the scrolled nanosheets of the wide band-gap semiconductor H_xK_4-xNb₆O₁₇. Pt@HNB NPPs offer an isolated environment for catalysis by the Pt NPs, and initial results suggest the presence of interesting optical properties similar to those observed in Ag- and Au@HNB NPPs recently synthesized by our group.

The great potential of well-dispersed, morphologically selected Pt NPs and well-formed Pt@HNB NPPs for advanced optical and catalytic applications demonstrates the need for efficient and reliable synthetic strategies with reduced safety and environmental risks. Despite the widespread use of nanoscale platinum, facile synthetic strategies for producing dispersible Pt NPs are rarely seen. A similar problem exists for the Pt/HNB nanocomposite, which has been well-established in literature as a promising system for photocatalytic water splitting but lacks published synthetic strategies that give good control over placement of the platinum catalyst. Hereafter we describe a novel, facile, and repeatable synthesis of Pt NPs and Pt@HNB NPPs using microwave heating. The highly-dispersible Pt NPs offer size and shape tunability produced via synthesis from common, cost-effective reagents. By eliminating the need for toxic and dangerous Fe(CO)₅ for synthesis of highly monodisperse, size and shape-controlled Pt NPs, our method can rapidly produce large quantities of high-quality Pt NPs at significantly lower risk. Microwave heating was also used to produce Pt@HNB NPPs that showed good loading and morphology. Microwave (MW) heating allows the rapid transfer of energy directly to the reaction, utilizing localized instantaneous superheating of solvents. This results in a significant reduction in reaction times and increased tunability of reaction parameters. While comparable solvothermal syntheses had reaction times ranging from 6-18 hours, synthesis of Pt NPs via MW heating can be achieved in as little as 30 minutes. Similarly, Pt@HNB NPPs superior to those produced solvothermally in 6-18 hours can be achieved in 30 minutes using MW heating.

Recently, primary and secondary zinc-air batteries have attracted considerable attention due to their high energy density, safety, availability and low cost. Zinc-air batteries consist of zinc anode, porous air electrode, alkali aqueous electrolyte and separator. Zinc-air batteries generate electricity through a redox reaction between zinc and oxygen in air. Oxygen diffuses through the air cathode and reduction of oxygen to hydroxide ion occurs while zinc is oxidized at the negative electrode during discharging. Zinc-air batteries have higher theoretical energy density due to abundant supply of oxygen from the atmosphere. However, using oxygen reduction and evolution reactions have also negative effects. Poor efficiency of the oxygen reduction and evolution reactions taking place at the cathode limits the use of zinc-air battery in demanding applications. In literature, many studies focus on the development of catalyst materials to improve these reactions. Some catalyst materials such as Pt, Ag, MnO₂, spinel and perovskite oxides are studied to enhance the performance of zinc-air battery. MnO₂ powders have drawn considerable scientific and technologic interests due to its activity for both oxygen reduction and evolution reactions. The aim of this study is to produce and characterize a novel bifunctional catalyst material to be used in the cathode. In this regard, doped and undoped manganese dioxide catalysts were produced for zinc-air batteries. Prior to the application of produced catalysts, structural characterization of catalyst were performed by XRD and SEM. The effect of processing parameters, doping element and amount on the oxygen reduction and evolution reactions at the catalyst loaded cathode were investigated by constructing an air-cell and electrochemical characterization techniques such as three-electrode half-cell test. The ORR and OER activities of catalysts in the aqueous electrolyte (0.1 M KOH) were tested in a three-electrode electrochemical cell using rotating disk electrode (RDE) voltammetry. All these experiments were performed at room temperature using a Hg/HgO (1 M) as a reference electrode. Graphite rod was used as the counter electrode. A glassy carbon electrode (5 mm OD) coated with 10 µl of solution made by mixing catalyst, carbon support (Printex L6) and a solution of 5 wt% Nafion (LIQUion^TM solution) in water and isopropanol solution was used as the working electrode. Catalytic activity of catalyst materials were compared with the benchmark Pt/C catalyst.

The unchecked burning of fossil fuels is unsustainable, and it is becoming progressively important to investigate strategies to increase the value of waste CO₂. One strategy is to use thermocycling of solid oxides as catalytic materials to reduce CO₂ and H₂O to CO and H₂, respectively, to utilize the Fischer-Tropsch process to produce usable fuel in the form of liquid hydrocarbons. Nanoparticles with the potential to facilitate oxygen transfer show a promising capacity in increasing the efficiency and reducing temperature needed for the thermocycling process. Manganese perovskites, with crystal structure ABO₃, has favorable and applicable properties, such as efficient transition between redox states, and is also amenable to chemical doping and substitution. Reducing particle size has also been shown to have significant effects on catalytic behavior. We synthesized manganese perovskites with various metals and measured their potentials as catalytic materials in thermocycling oxygen exchange experiments.

Formaldehyde is one of the major indoor air pollutants, usually generated from furnishing and construction materials¹. There has been a major thrust in recent times for elimination of formaldehyde using adsorptive¹, photocatalytic² and thermal oxidative strategies³. Manganese oxide, being an earth abundant material, is a potential economic solution via catalytic conversion. However, complete room temperature catalytic conversion remains a challenge⁴. In this study, a simultaneous catalytic oxidation and storage/chemisorption behavior for manganese oxide polymorphs is identified at room temperature while at higher temperatures complete conversion to CO2 is reported. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and X-ray Photoelectron Spectroscopy (XPS) are used to provide new insights into the formation of intermediate species for both the storage and oxidative routes. A mechanistic understanding for the storage and catalytic capacities is developed.

References:
1. Sekine, Y. Atmospheric Environment 2002, 36, 5543.
2. Shie, J.-L., Lee, C.-H., Chiou, C.-S., Chang, C.-T., Chang, C.-C., Chang, C.-Y. Journal of Hazardous Materials 2008, 155, 164.
3. Zhang, C., Liu, F., Zhai, Y., Ariga, H., Yi, N., Liu, Y., Asakura, K., Flytzani-Stephanopoulos, M., He, H. Angewandte Chemie International Edition 2012, 51, 9628.
4. Zhang, J., Li, Y., Wang, L., Zhang, C., He, H. Catalysis Science & Technology 2015, 5, 2305

The enhancement of catalytic performance for methanol oxidation reaction still remains a huge challenge in the field of developing direct methanol fuel cell. Although numerous methods of designing new catalysts based on PtPd nanoalloys have been suggested, their complicated synthesis procedures have been a drawback yet. In this study, we report a simple reduction route for the synthesis of PtPd nanoalloys/carbon dots composite using a formic acid as a reducing reagent at room temperature. To date, conventionally, tiny PtPd nanoalloys have been immobilized only on the surface of relatively larger carbon black, resulting in the limited use of catalytically active sites. In contrast, our synthetic route offers stable and uniform interconnection between PtPd nanoalloys and carbon dots in a nanoscale, thus forming a complete composite material. The resulting composite shows a great enhancement of electrocatalytic activity for the electro-oxidation reaction of methanol as a chemical fuel. We attributed this improvement to the presence of carbon dots in the composite material. Furthermore, the PtPd nanoalloys/carbon dots composite shows hydrophilic property, excellent stability and high catalytic activity for electro-oxidation reactions at room temperature. We expect that this composite can be further utilized for a wide range of electrocatalytic applications. In this regard, research efforts are currently underway in our group.

Nitrogen doped multi-walled carbon nanotubes (NCNTs) were fabricated from the oxidized multi-walled carbon nanotubes (OCNTs) and urea by a pyrolysis process. The OCNTs containing various amounts of oxygen were prepared by reacting multi-walled carbon nanotubes with hydrogen peroxide by controlling reaction time and temperature. Functional groups containing oxygen in the OCNTs were reacted with the amino groups originated from urea and then transformed to the pyrrole and pyridine species. Formation of the NCNTs and their compositions were confirmed by X-ray photoelectron spectroscopy (XPS) and changes in the morphology with nitrogen doping were explored with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrocatalytic activities of the NCNTs towards oxygen reduction reaction (ORR) were investigated by using rotating disk electrode (RDE) and cyclic voltammetry (CV). As the oxygen content in OCNTs increased, nitrogen content in the NCNTs increased. The ORR activity of the NCNTs as non-precious electrode was improved by increasing nitrogen content in the NCNTs.

TiO₂ is a well-studied photocatalyst due to its several advantages such as stability, low cost, non-toxicity and chemical inertness. The polymorph of TiO₂ known to be photocatalytically active is anatase TiO₂. An efficient photocatalyst should have high surface area and a narrow band gap for solar energy conversion. Surfactant-assisted synthesis regulates the shape and size of the nanocrystals and doping with impurities manipulates the band gap. The coupling of impurity ion doping and hydrothermal synthesis has not been explored previously. In this work, we employ hydrothermal synthesis for obtaining uniform monodisperse nanocrystals of TiO₂ as well as dope with different Iron (Fe) concentration. X-Ray diffraction studies performed is in agreement with Raman spectroscopy determining the formation of phase pure anatase TiO_2. Electron microscopy is used to monitor the shape and size of the particles as a function of increasing dopant ions concentration. Diffuse Reflectance spectroscopy (DRS) is employed to understand the effect of dopant ion on the band structure of TiO₂. BET studies will be used for surface area analysis. Fe-doped monodisperse TiO₂ nanocrystals will be analyzed for its photocatalytic activity with the aid of UV-Vis spectroscopy. With uniform morphology and phase composition of TiO₂ obtained, the effect of doping at nanoscale needs to be understood in detail.

Cobalt-doped Zinc oxide (CZO) thin film nano-composites are considered viable catalytic materials for future energy intensive processes. In this study, the structural and surface morphological characteristics of CZO thin film have been investigated as a function of electron beam repetition frequency (1 Hz, 2 Hz, 4 Hz, 6 Hz, 8 Hz). The films have been grown from a single target containing 20 wt.% Co on c-sapphire (0001) and silicon (100) substrates via pulsed electron beam ablation (PEBA). The deposition temperature and accelerating voltage have been kept constant at 450 0C and 14 kV, respectively, and Argon background process gas pressure has been set to ~3 mtorr. To our knowledge, no attempt has been reported on the deposition of CZO films via PEBA using different pulsed electron beam frequencies. Significant modifications in crystallinity, grain size and roughness of CZO films have been observed owing to changes in beam frequency. The structural properties have been assessed by x-ray diffraction (XRD). The results reveal that the crystallinity quality of the films worsens with the increase in beam frequency. The surface morphological characteristics have been examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The findings show that the higher the frequency, the lower the roughness and globule size of the films. Energy dispersive x-ray spectroscopy (EDX) confirms that deposition is nearly congruent as the films contain ~20wt.% cobalt. Based on X-ray photoelectron spectroscopy (XPS) data, the major elements in the condensed films are Zn, O and Co, whereas Co 2p core-level peaks reveal that the deposited films contain metallic Co (binding energy = 778.1-778.5 eV) as well as CoO (binding energy = 780.5 eV). The reported findings bring up new opportunities to produce nano-structured CZO thin films for practical applications.
Keywords: Co:ZnO nano-composites, pulsed electron beam ablation, electron beam repetition frequency, structure, morphology, model catalyst.

In recent years, extensive research have been done on developing high performance electocatalysts for direct methanol fuel cell (DMFC) applications due to its high efficiency and environmental friendly benefits. However, most of the catalysts require alloying between different metals or metal oxides such as palladium/nickel oxide, or complex structures such as carbon nanotubes coated with noble metals. Both approaches involve with complicated preparation methods, and may encounter severe catalyst poisoning. In this work, a highly efficient electrochemical catalyst towards methanol oxidation has been developed based on vertically aligned platinum (Pt) nanowire array. The Pt nanowire array is prepared by electrodeposition method using AAO membrane. Nanowires with different surface roughnesses were synthesized by varying the deposition current density, and the length of nanowires were controlled by the deposition time. This well aligned nanowire array structure makes it possible for every nanowire to have full contact with the analyte without the nanowire overlapping; furthermore, with the assistance of rough surfaces, each individual nanowire is able to have a higher surface to volume ratio that further facilitates the reaction. This novel 3D structure showed several advantages, e.g., being able to avoid the CO poisoning, fully oxidizing the reactants to the desired products, increasing the electrochemical activity and sustainability, and decreasing the electrical resistances between the solution and the electrode surface. The results indicate that this innovative 3D electrocatalyst is able to achieve very high performance for generating electron sources for the direct methanol oxidation reaction. It may also be a very promising catalyst for reactions taking place in a different analyte such as using ethanol as the fuel in basic environment.

The κ-Ce₂Zr₂O₈ phase is an active oxidation catalyst with an extraordinarily high oxygen storage capacity (OSC). High OSC is an important feature in automotive catalysts to balance the oxygen supply in the exhaust gas stream between lean and rich operation of the engine by buffering and releasing oxygen, respectively. The underlying mechanism of the OSC is closely associated with the superb redox chemistry of Ce that can readily switch its oxidation state between Ce³⁺ and Ce⁴⁺.
The κ-Ce₂Zr₂O₈ phase is synthesized starting from t-Ce_0.5Zr_0.5O₂ solid solution which is reduced by hydrogen at high temperatures to form the pyrochlore Ce₂Zr₂O₇ phase (pyr-Ce₂Zr₂O₇) with a high degree of ordering of the cationic sublattice. The final step in the synthesis of the κ-Ce₂Zr₂O₈ phase includes a mild re-oxidation of pyr-Ce₂Zr₂O₇ at around 600 °C under atmospheric conditions.
In this work the structural transformation of the pyr-Ce₂Zr₂O₇ to the κ-Ce₂Zr₂O₈ phase was followed in-situ as the temperature is increased from room temperature to 600°C under ambient atmosphere. Raman spectroscopy is shown to be very sensitive to the process of oxygen incooperation into the structure. The interpretation of the Raman data is supported by state-of-the-art density functional theory (DFT) calculations.

Biomass derived transportation fuels has become a key element in the transportation industries since the petroleum-based gasoline (C₅ – C₁₂), jet (C₈ – C₁₆), and diesel (C₈ – C₂₄) fuels have been recognized as a representative emission source of greenhouse gases and the biomass derived fuels can reduce more than 50% of greenhouse gases compared to the petroleum-based ones. Bioalcohols can be easily converted to light olefins such as ethylene and butenes by an acid catalyzed reaction and the oligomerization of light olefins is of considerable academic and industrial interest because it is one of the major processes for the production of linear and branched higher olefins and ultimately to the transportation fuels. Here we report the synthesis and characterization of Ni- and/or H-forms of SBA-15 with diverse crystal sizes and morphologies and acid functionalized polystyrene coated SBA-15 materials and their catalytic oligomerization of ethylene and 1-hexene over a high pressure (35 bar) continuous fixed-bed reactor. Furthermore, we also compare the catalytic results of nanocrystalline and nanosponge Ni- and/or H-forms of ZSM-5 and beta zeolites. Although the polymer coated H-SBA-15 catalyst was less active for the oligomerization of 1-hexene than the commercial ion-exchange resin (dry form of Amberlyst-35), the nanocrystalline SBA-15, ZSM-5, and beta catalysts showed increased selectivity to hydrocarbons higher than C₁₀ which should be due to the enhanced mass transfer limitation. From the overall results of this study, it is clear that the proper controls of both active sites and diffusivity of the nanoporous materials are the major factors for the oligomerization of light olefins.

For economically feasible electrochemical water splitting, both efficient and low-cost hydrogen evolution and oxygen evolution reaction (OER) catalysts are needed. Transition metal hydroxides are one promising class of materials as a more earth-abundant alternative to precious metal oxide-based OER catalysts (IrOx, RuOx). Layered double hydroxides have a well-defined layer structure that can be tuned by both metal substitution and anion exchange. First, we synthesized well-defined nanoplates of NiCo [1] and NiFe [2] layered double hydroxides by (continuous flow) hydrothermal reactions by using ammonia and triethanolamine as Co- and Fe-chelating agents respectively. We further developed a method for the direct synthesis of non-carbonate NiFe layered double hydroxide under ambient atmosphere. We note that over time the non-carbonate catalysts convert to carbonate-containing layered double hydroxides when submerged in the electrolyte under ambient conditions. Lastly, the non-carbonate layered double hydroxide catalysts can also be grown directly onto conductive carbon substrates for simultaneous catalyst synthesis and working electrode fabrication. These electrodes with their higher surface area and increased mass loading require lower overpotentials (250-300 mV after iR-correction) to achieve similar current densities as the powder catalysts deposited on glassy carbon. Further tuning of the catalysts by exploring the different components of the LDH structures can enable even higher catalytic activity.
[1] H. Liang et al., Nano Letters, 2015, 15 (2), 1421-1427.
[2] J. Y. C. Chen et al., J. Am. Chem. Soc., 2016, 137 (27), 15090-15093.

Recently, noble low-cost alloys have been predicted by computational materials science in order to replace noble metals such as Pd and Pt, known as excellent catalytic materials. For example, Ag₅₀Rh₅₀ alloy nanostructures have been theoretically designed to replace Pd and successfully synthesized via nanoscale effects, even in immiscible in bulk phase. Furthermore, Ag₅₀Rh₅₀ alloy nanostructures have shown excellent catalytic properties, equivalent to Pd, even though, by themselves, neither Ag nor Rh exhibit such catalytic activities. More recently, it has been theoretically suggested that an Ir₅₀Au₅₀ alloy exhibits excellent catalytic activity for dissociating hydrogen, equivalent to Pt. However, Ir and Au atoms are known to be thermodynamically immiscible in bulk form. In this study, we have produced the solid solution alloy of Ir and Au using a filamentary electrochemical deposition, which is facile and cost effective without any surfactants. It is presented that, interestingly, Ir and Au atoms are fully miscible at a nanoscale, as confirmed by high-resolution TEM and XRD analyses. The mechanism of solid-solution alloying of Ir and Au at a nanoscale is discussed.

Laser ablation synthesis in solution in tandem with galvanic replacement reaction (LASiS-GRR) is a newly-developed, facile and environmental friendly synthesis technique for manufacturing a variety of complex nanostructures including hydroxides, metal/metal oxides nanocomposites (NCs), metal-metal nanoalloys (NAs), core-shell nanostructures, etc. This synthetic technique incorporates both “top-down” pulsed laser ablation synthesis in solution approach (LASiS) and the “bottom-up” chemical reduction method (CRM). The setup houses a Q-switched Nd:YAG pulsed laser (1064 nm) with the laser beam focused at a metal target in liquid medium inside a sealed stainless steel reactor cell. The cell is mounted with a gas inlet/outlet, viewing windows, a stepper motor, thermocouple, injection unit, heating coils, and an ultrasonic dismembrator, which enables accurate laser beam focusing status tuning, temperature, pressure and chemical injection rate control, as well as uniform ablation and real-time de-aggregation. Therefore, the unique advantage of combining CRM with the specific condition inside the liquid-confined plasma plume provided by LASIS to generate novel NPs with tailored morphology and metastable phases is realized. In this study, by carrying out LASiS-GRR on Ni in K2PtCl4 solution, we first produced the nanocomposites composed of PtCuCo alloy embedded in NiO nanomatrices. While after acid wash using HCl at pH2, we successfully removed NiO and produced pure PtCuCo ternary alloy. Both products are potential catalysts for the oxygen evolving reactions. The structures of the aforementioned nanocomposites and nanoalloys were confirmed by transmission electron spectroscopy (TEM) and energy dispersive X-ray spectrum (EDX) element mapping. Furthermore, the detailed composition for the PtCuCo alloys were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) and characterized by laser-induced breakdown spectroscopy (LIBS).

Methanol, containing 12.6 wt% hydrogen, is a good hydrogen storage medium because it is a liquid at room temperature. However, traditional catalytic fuel reforming, which is needed to release the stored hydrogen, generated with unavoidable undesirable CO and/or CO2 byproducts. We show here that by controlling the colloidal chemistry strategy, unique MgO nanostructures exhibit ultra-endurable photocatalytic activity for CO/CO2-free proton to hydrogen reduction from liquid methanol at room temperature. The nano-catalyst endurance study and finding in this research shed some light on industrialization avenue for laboratory’s research on nano.

Clusters of MnO_x and CeO_y were modified onto TiO₂ (rutile) surface by chemisorption calcination cycle processing. Then the decomposition activity on 2-naphthol in water was evaluated at 50°C under visible light illumination or in the dark. The modification of MnO_x and CeO_y clusters provided decomposition activity on 2-naphthol in the dark and it was increased by visible light illumination. The decomposition activity in the dark depended on the reaction temperature. The synergy effect in the co-modification of these two clusters was inferred from the reaction constants on the decomposition activity in the dark. Although the decomposition activity in the dark decreased gradually through repeated use and resultant reduction of MnO_x and CeO_y clusters, it recovered by UV illumination and subsequent heating at 80°C in ambient air.

In polymer electrolyte fuel cells (PEFCs), platinum nanoparticles supported on carbon black (Pt-C) have been regarded as the standard catalyst for oxygen reduction reaction (ORR) on the cathode. However, the high price and poor durability of Pt lead to the increase of the cost of PEFCs and shorter cell lifetime. In recent years, nitrogen-doped single-walled carbon nanotubes (N-SWCNTs) have been reported to exhibit excellent electrocatalytic activity for the ORR. The structural factors such as the levels and chemical bonding states of the doped nitrogen of N-SWCNTs are key points on their catalytic activities. Existing methods for nitrogen doping to SWCNTs are generally categorized into “direct-doping” and “post-doping” syntheses. In direct-doping synthesis, it is hard to control the structural factors mentioned above. Meanwhile, post-doping synthesis, in which nitrogen atoms are introduced to the formed SWCNT frameworks, allows one to control the structural factors. However, the preparation of N-SWCNTs with high levels of nitrogen doping using the post-doping approach has not been reported. Here, we report a new and facile post-synthesis method to prepare N-SWCNTs by defluorination-assisted nanotube-substitution reaction. Also, we evaluate the ORR catalytic activity of the prepared N-SWCNTs and assess their catalytic durability compared to that of Pt-C.
Highly crystalline SWCNTs (hc-SWCNTs) were synthesized by the arc-discharge method. The hc-SWCNTs were fluorinated at 250 °C using a gas mixture of F₂ (20%) and N₂ (80%) for 4 h. The fluorinated SWCNTs (F-SWCNTs) were reacted with a gas mixture of NH₃ (1%) and N₂ (99%) at temperatures of 300-600 °C for 30 min. The elemental composition and chemical bonding state of the resulting samples were characterized using X-ray photoelectron spectroscopy (XPS). Linear sweep voltammetry was used to evaluate the ORR catalytic activity of the sample catalysts, using the RDE technique in N₂- and O₂-saturated 0.5 M H₂SO₄ electrolyte. The catalytic durability of the sample was examined by a load-potential cycle test.
The concentration of nitrogen doping estimated from the XPS results was in the range of 1.38-3.04 at%, indicating that this method is effective for introducing nitrogen atoms at high concentrations. The N_1s XPS spectra of the resulting samples also indicated that they contained enriched pyridinic- and pyrrolic-type nitrogen species. The onset potential values and the numbers of electrons transferred per oxygen molecules in ORR of the N-SWCNTs synthesized at 500 °C (N_500°C-SWCNTs) were +0.51 V and 3.38 while those of hc-SWCNTs were +0.16 V and 2.32, respectively. After 11000 cycles in the load-potential test, the current density of N_500°C-SWCNTs remained at 93% of the initial value while that of Pt-C was only 67% of its initial value. These results clearly show that the N-SWCNTs synthesized by our post-doping method demonstrate excellent ORR catalytic activity and long-term catalytic durability.

Creation of high efficiency and safe air cleaning systems is the important task caused by their wide use in living quarters, medical institutions and industrial facilities. The most effective cleaning systems are the ones based on ozone forming as the result of a corona or barrier discharge. The main disadvantage of these cleaning systems is high ozone concentration on electrode system output.
The paper presents experimental studies of the properties of catalytically active coatings on the basis of nanoporous titanium oxide for effective ozone decomposition inside air cleaning systems. For research of coatings catalytic properties a specialized model has been made. It consists of axially symmetrical “needle-cylinder” system in which there was a high-voltage corona discharge with the voltage of up to 12 kV and current of up to 50 µA. The internal diameter of titanium cylinder was 20 mm, the length varied in the range of 100-200 mm. On the internal surface of the titanium cylinder the coating samples of nanoporous titanium oxide with the pore diameter of 20-60 nm and the thickness of 1-20 µm were grown using a standard technique of anodizing in electrolyte on the basis of the mixture of 0.3% NH₄F (masses.), 0.5% H₂O (masses.) and ethylene glycol covering were up. The laminar air flow was pumped through the cylinder and output ozone concentration forming as a result of plasma chemical reactions of the corona discharge was measured.
The experimental research resulted in obtaining the dependencies of influence of titanium oxide parameter structure on the ozone concentration on electrode system output. It is established that the use of catalytic coating leads to decrease of ozone concentration on electrode system output by 25-30% (at low currents - up to 50%). It is shown that with the coating thickness rise within 1-5 µm the catalytic activity increases and then achieves saturation at the thickness of 7-10 µm. It is established that with the tube length growth the reduction rate of ozone concentration decreases significantly. On the basis of the obtained experimental data the requirements to the coating structure providing high efficiency of catalytic ozone decomposition are determined.
The obtained experimental data of catalytic activity of nanoporous titanium oxide coatings can be used for creation of new types of safe plasma air filters.

Recently, wide-ranging of physical studies have been accomplished in both nanoparticle & nanowire forms of zinc oxide (ZnO) photocatalyst, and such nanostructures are used for remediation of organics (methyl orange (MO), naphthalene etc.) in water [1, 2]. Various nanostructures of ZnO were synthesized using hydrothermal and sol methods [3-5]. It is challenging to control the size, shape and quality of the ZnO nanowires for effective remediation of organics in visible light. However recent success of organics remediation by silver doped ZnO and graphene (G) doped titanium oxide (TiO₂) structures have been studied in our group[ 6, 7]. Currently, we are also growing nanowires and nanoparticles forms of graphene doped tungsten oxide (WO₃).
In present work, G-ZnO nanowires & nanoparticles have been compared with undoped ZnO nanowire and nanoparticle and nanostructures forms of graphene doped tungsten oxide (WO₃). The comparative remediation properties of G-ZnO and G-WO₃ for organics (methyl orange (MO), naphthalene etc.) in water with and without the use of surfactants have been studied under visible light.
1. Udom, I., et al., One dimensional-ZnO nanostructures: Synthesis, properties and environmental applications. Materials Science in Semiconductor Processing, 2013. 16(6): p. 2070-2083.
2. Udom, I., et al., A simple photolytic reactor employing Ag-doped ZnO nanowires for water purification. Thin Solid Films, 2014.
3. Ladanov, M., et al. Novel Aster-like ZnO Nanowire Clusters for Nanocomposites. in MRS Proceedings. 2011. Cambridge Univ Press.
4. Becheri, A., et al., Synthesis and characterization of zinc oxide nanoparticles: application to textiles as UV-absorbers. Journal of Nanoparticle Research, 2008. 10(4): p. 679-689.
5. Espitia, P.J.P., et al., Zinc oxide nanoparticles: synthesis, antimicrobial activity and food packaging applications. Food and Bioprocess Technology, 2012. 5(5): p. 1447-1464.
6. Zhang, Y., et al., Enhanced photocatalytic activity of iron doped zinc oxide nanowires for water decontamination. Surface and Coatings Technology, 2013. 217: p. 119-123.
7. Gunti, S., A. Kumar, and M.K. Ram, Comparative Organics Remediation Properties of Nanostructured Graphene Doped Titanium Oxide and Graphene Doped Zinc Oxide Photocatalysts. American Journal of Analytical Chemistry, 2015. 6(8): p. 708.

ZnO /SnO₂ nanocomposite has been successfully synthesized by co-precipetation method. The effect of ZnO/SnO₂ molar ratios on the crystal structure, microstructure, optical and photocatalytic properties has been investigated. The synthesized samples are characterized by X-ray diffraction, transmission electron microscopy, N2 physical adsorption and UV–Vis spectroscopy. XRD results revealed that all diffraction peaks positions agree well with the reflection of a hexagonal wurtzite structure of ZnO phase with extra one peak at 0.95ZnO:0.0.5SnO₂ , 0.9ZnO:0.1SnO₂ and 0.8ZnO:0.2SnO₂ molar ratios. SEM and TEM images revealed that the shape of ZnO and Zn₂SnO₄ particles were spherical and the particle sizes of ZnO, 0.95ZnO:0.0.5SnO₂, 0.9ZnO:0.1SnO₂ and 0.8ZnO:0.2SnO₂ molar ratios were 25 and ~15 nm, respectively. The newly prepared samples have been tested by the determination of photocatalytic degradation of methylene blue (MB). The results indicated that Sn²⁺ doping at 0.95ZnO:0.05 SnO₂ molar ratio showed the highest photocatalytic activity for the MB photodegradation. The heightened photocatalytic activity of ZnO/SnO₂ could be ascribed to the enhanced charge separation derived from the coupling of ZnO with SnO₂ due to the potential energy differences between SnO₂ and ZnO.

The functional graphene (FG) nanocomposite was prepared by an environmentally friendly hydrothermal method the predecessor functional graphene oxide (FGO) was prepared by covalent functionalization of graphene oxide (GO) with Adenine. The attachment of functional groups on the GO surface maintained the aqueous stability of the FG nanocomposite even after the hydrothermal reduction. The prepared samples have been branded by X-ray diffraction (XRD), IR spectroscopy, scanning electron microscopy (FESEM) images, Raman spectroscopy, thermogravimetric analysis (TGA), UV−vis absorption spectroscopy, transmission electron microscopy (TEM), Application of the prepared samples has been evaluated asupercapacitor material in 0.5M H₂SO₄ electrolyte using cyclic voltammetry (CV) at different potential scan rates , and galvanostatic charge/discharge tests at different current. Results show a maximum specific capacitance of 333F/g at scan rate of 1 mV/s and exhibit excellent cycling retention 105% after 1000 cycles at 200mV/s by using aqueous electrolyte (0.5 M H₂SO₄) at room temperature.

Hydrogen production by water electrolysis is a promising route for green energy production and the development of low-cost electrocatalysts is desirable for replace platinum (Pt), an expensive material for Hydrogen Evolution Reaction (HER). One non-precious-metal alternative to Pt is nickel sulfide that has good catalytic activity for HER. In this work, we synthesized Ni₇S₆ nanoparticles in a reaction assisted by microwave (MW) at milder conditions. The reaction was performed in a microwave oven and the solution was heated at 230 °C during 60 min. X-ray diffraction analysis of the as-prepared material showed the Ni₇S₆ phase formation. We have investigated also the electrocatalytic HER activities of the Ni₇S₆. A primary and qualitative analysis reveals an overpotential of 270 mV at cathodic current densities of 10 mA/cm² for Ni₇S₆ obtained by microwave heating. In conclusion, we have developed a synthetic route to process nickel sulfide (Ni₇S₆) under milder conditions, by using MW heating. In addition, we have shown the high electrocatalytic activity of the Ni₇S₆ in HER.

We report the synthesis of a hybrid material comprising a carbon nanotube conductive support decorated with platinum nanoparticles coated by a thin layer of a zirconium metal-organic framework (MOF) and its performance in oxygen reduction reaction (ORR) catalysis in acidic media. Through rotating disk electrode (RDE) studies, we demonstrate that the MOF coating stabilizes the Pt electrocatalysts against deactivation upon sustained cycling. Parameters such as MOF shell thickness and MOF pore functionality were tuned and their effects on catalyst performance assessed by RDE studies including the influence of the MOF shell on mass transport by Koutecky-Levich analysis. MOF pore functionality was tuned by using the Zr₆O₄(OH)₄(terephthalate)₆ (UiO) MOF as the parent structure for generating daughter frameworks by exchange of the terephthalate linkers with functionalized terephthalate derivatives. Catalysts with MOF shells resulting from exchange with terephthalate linkers functionalized with strong acid groups demonstrate behavior consistent with the framework serving as a proton shuttle during catalysis.

Hydrogen is considered one of the most promising fuels for the future. The generation of hydrogen from water using sunlight could potentially form the basis of a clean and renewable source of energy. However, renewable energy contributes only about 5% of the commercial hydrogen production via water splitting, while other 95% hydrogen is mainly from fossil fuels. The present work aims to develop new catalyst that is able to carry out overall water splitting with large scale H₂ production, The proposed catalyst, TiO₂ hollow porous spheres / graphene nano composites should be nontoxic, cheap in price, highly efficient, carry out over all water splitting, visible light responsive and stable in prevailing conditions, These requirements are achieved by nano sized materials which show good response towards water splitting. TiO₂ hollow porous spheres / graphene nano composites was synthesized by hydrothermal method, and was characterized by X-ray diffraction, N₂ physisorption, transmission electron microscope (TEM), scanning electron microscope (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy(XPS), The results showed high photocurrent and IPCE values.

The industrial development is associated with several environmental problems such as global warming. The raise in the concentration of gases that absorb thermal infrared light, such as carbon dioxide (CO₂), results in a temperature increase on Earth’s surface. Therefore, the development of new technologies aimed at environmental preservation has received special attention from the scientific community. Recently, CO₂ photoreduction has attracted considerable attention due to possibility of transforming a pollutant gas into high added value products, using solar light as an energy source. CuO nanoparticles have been used in the present work for the UV photoconversion of CO₂ into CO and CH₄ under UV radiation. CuO has been synthesized by a simple solvothermal method. Several characterization techniques such as X-ray diffraction (XRD), high resolution electron microscopy (HRTEM), diffuse reflectance spectra (DRS), and N₂ physissorption have been used to characterize the as-synthesized photocatalysts. XRD results confirmed the formation of monoclinic structure of CuO. HRTEM images reveal the presence of aggregates with coral-like morphology built by several CuO nanospheres. Photocatalytic activity evaluation of the CuO in relation to the CO₂ photoreduction was performed under UV irradiation in three different conditions: (i) in sodium oxalate aqueous solution; (ii) in sodium hydroxide aqueous solution; and (iii) in pure water. Gaseous aliquots were taken from the photoreactor’s headspace and analyzed by gas chromatography. The results indicated the formation of CH₄ and CO as the only products of CO₂ photoreduction reaction. An increasing in the formation of CH₄ was observed during 24 h in the presence of NaOH aqueous solution and continuous irradiation. During the photocatalytic process, the CO₂ adsorbed on the CuO surface reacts with electrons to produce carbon dioxide radicals (^*CO₂^-) that is the first step, then react with H⁺ to form surface ^*CH₂ radicals that ultimately form CH₄ or react with H⁺ to form HCOO_ads⁻ further formed CH₄. Similar trends were also observed for the photoreduction of CO₂ in H₂O. However, further results indicated that the formation of CH₄ in water was superior compared to that obtained in NaOH aqueous solution. The total CO formation over CuO for sodium oxalate aqueous solution was approximately 17 times higher than the observed for the reactions using water or NaOH aqueous solution. The high photocatalytic selectivity to CO is due to the excellent hole trapping ability of sodium oxalate. It is known that during the photoreduction process H₂O reacts with hole to form H⁺ and O₂. Thus, the H₂O could not supply H⁺ to reduce the CO₂ to CH₄. In summary, from the results presented in this work, it is possible to conclude that CuO is a promising material for CO₂ photoreduction processes, and that the electrolytes affect significantly the selectivity.

Work supported by EMBRAPA, Fapesp (2014/09014-7),CNPq and CAPES.

Proton exchange membrane fuel cells have been taken as a promising alternated energy source because of the high power output density, low operation temperature and none pollution emission. In commercial market, the catalytic poison effect from the impurity of the gas flow, like CO, is one of the reasons that decrease the performance and stability of PEM fuel cell. Previous work have reported that gold nanoparticles that are platelet shaped and have direct contact with the metal oxide substrate to be the perfect catalysts of the CO oxidization.
In this approach, hydrophobic, thiol-functionalized Au/Pt and Au/Pd nanoparticles were synthesized through two-phase method developed by Brust et al. We previously developed a technique to reproducibly form an Au nanoparticles layers with three atomic layers thick at the air water interface. Then we use the same method to deposit these alloy particles with stepped surface directly onto the Nafion membrane in the PEM fuel cell by Langmuir–Blodgett trough, resulting in over 50% enhancement of the efficiency of the fuel cell. Furthermore, DFT calculation demonstrate this kind of enhancement occurs only when the particles are in direct surface contact with the membrane, where they work together with sulfonic groups to oxidize CO back to CO₂, and does not occur when the nanoparticles are incorporated into the electrodes.

We study the effect of post treatment of galvanic replacement reactions on the ligand-exchanged silver nanocrystal thin films (Ag NCs). For this study, oleylamine-coated colloidal Ag NCs are spin-coated on the substrates and the ligand exchange process is performed at room temperature to fabricate ligand-free, highly conductive Ag NC thin-films. Then, the galvanic replacement reaction is conductive for the electroless deposition of gold (Au) or platinum (Pt) on Ag NC surfaces. We demonstrate that the noble metals are successfully coated on Ag NC surface by one-step electroless galvanic replacement reaction, which is corroborated by X-ray diffraction measurement, microscopic analysis, ultraviolet photoelectron spectroscopy (UPS), and optical characterization. In the case of Au, uniform Au shell are deposited on the surface of Ag NC thin films. However, in the case of Pt, small Pt nanoparticles were observed on the surface of Ag NCs, increasing the surface area of Pt, which may be attributed to the different surface energy, bonding energy as well as the interdiffusion coefficient. We perform the electrocatalytic activity test of the highly conductive Pt-deposited Ag NC thin-films. It is observed that the thin-Pt layer deposited Ag NCs exhibit higher catalytic activity on hydrogen evolution reaction (HER) than the electrodeposited Pt thin-films, which indicate that our low temperature, solution-based approach provides a promising route to achieve high-activity catalyst with minimal noble metal usage.

Proton exchange membrane fuel cell (PEMFC) can covert chemical energy stored in hydrogen fuels to electricity and produce environmentally benign product water. However, the commercialization of PEMFCs is hindered by the present requirement of expensive Pt group metals as their electrocatalysts. To advance PEMFC technology, it is of great interests to develop earth-abundant, non-precious metal based catalysts in replacement of Pt, especially for oxygen reduction reaction (ORR) occurring at the cathode of PEMFCs. Recently, non-precious transition metal/nitrogen doped carbon (TM-N-C) catalysts have drawn much attention since they exhibit promising ORR activity close to Pt. However, the chemical structure of the active sites in these TM-N-C catalysts and their catalytic mechanism for ORR have not been fully understood. To gain insight into the nature of the active sites in the TM-N-C catalysts, we have performed density functional theory (DFT) calculations to investigate the progression of ORR on various types of TM-N₄ (TM = Fe, Co) moiety substitutionally embedded into a graphene layer. On each possible TM-N₄ active site, we calculated the adsorption energies of all the relevant chemical species, namely, O₂, O, OH, OOH, HOOH and H₂O, and the activation energies for O-O dissociation reactions involved in ORR using the DFT method. On FeN₄ and/or CoN₄ embedded in an intact graphene plane, our DFT calculations predicted that the ORR could happen through 4e^- associative pathway on the FeN₄ site, whereas follow a 2e^- pathway on the CoN₄ site due to high activation energy for O-O bond splitting and extremely weak adsorption of H₂O₂ on the CoN₄ site. These theoretical results are in agreement with experimental observations. In addition, we studied the ORR on a FeN₄ moiety bridging two adjacent armchair like graphene edges as well as a FeN₄ moiety bridging two adjacent zigzag graphene edges with a porphyrinic architecture. Among the three FeN₄ moieties, the porphyrin-like FeN₄ moiety was predicted to catalyze ORR with the highest onset potential. Moreover, we found that the O-O bond scission had lower activation energy on the FeN₄ moieties bridging graphene edges than on the FeN₄ moiety embedded in an intact graphene layer. Consequently, our computation results suggest that introduction of micropores in the TM-N-C catalysts would enhance their catalytic activity for ORR through improving not only the specific area but also the intrinsic activity of the active sites.

In this talk, microstructural, chemical, and electrochemical property measurements, for (111) crystallographically oriented Pt_100-xM_x (M = Zr, V) sputtered thin films are presented, with electronic structure calculations. These low-PGM alloys are candidates for use as the electrode materials in H₂-Air PEMFCs.

The electrochemical properties for the Pt_100-xM_x thin films were obtained with a custom multi-electrode cell, in 0.1 N perchloric acid electrolytes, vs. a 2 M Hg/Hg₂SO₄ electrode. Surfaces for all measurments (HOR/ORR) were prepared with CV scans at 200 mV/s scan rate (100 cycles, 0.0 - 0.40 V vs. NHE). Double-layer capacitance corrected HOR active areas were obtained from a final CV scan at 100 mV/s scan rate, over the same potential range. All CVs were done in still, UHP Ar-gas de-aerated cells. Anodic ORR measurements used a stirred, oxygenated cell (UHP O₂) with scan rate of 1 mV/sec (0.0 – 1.0 V vs. NHE), with ORR currents reported at 0.9 V vs. NHE.

The results show that (111) Pt-Zr and (111) Pt-V surfaces are stable in 0.1 N perchloric acid, and exhibit (111) Pt-like CVs and polarization curves. After ½-CV scans, the alloy surfaces retain a (111) orientation. On potential cycling above 0.9 V, (110) and (100) surface reconstructions are observed at the same potential values known for Pt.

Each alloy exhibits a composition-dependent HOR and ORR activity, and each are enhanced compared to (111) Pt examined in the same cell. The Pt₆₈Zr₃₂ HOR Pt-active area peaked at 144.9 μC/cm², 1.17X larger than (111) Pt). While on Pt_86.7V_13.3, the HOR Pt-active area peaked at 343.2 μC/cm², 2.77X larger than (111) Pt. On Pt₉₀Zr₁₀, the ORR currents peaked at 10.71 μA/cm², 1.54X larger than (111) Pt). While on Pt_86.7V_13.3, the ORR currents peaked at 99 μA/cm², 10X larger than (111) Pt).

The Pt_100-xM_x ORR currents peak for 10 < x < 13 At. %, so local chemical-short-range-order, may exist; commensurate with the strong ordering in Pt₈M (M = Ti, V, Zr). The HOR and ORR reaction kinetics on the alloyed surfaces are composition dependent, and suggest two possible effects: 1) charge transfer process from V-(3d)³ [or Zr-(4d)²] states, to the hole in the top of the Pt-(5d)⁹ band, and 2) the alloyed surfaces take on a bi-functional character. To confirm the first hypothesis, we will calculate results for the electronic structure of Pt₈Ti, Pt₈Zr, and Pt₈V, using the WIEN2k program package. The calculated Pt₈Ti DOS, found using the Pt₈Ti atomic structure data in Pearson's Handbook, are given below.

For the Pt₈Ti DOS, on alloying with Ti, the calculated DOS at the Fermi level increases from ~0.6 states/eV.Atom in pure Pt, to ~0.75 states/eV.Atom in Pt₈Ti. The calculated DOS at the Fermi level in pure Ti is ~0.275 states/eV.Atom. So, a Ti-(3d)² band appears across the Fermi level with center-of-gravity energy higher than the host Pt. Thus, in Pt₈Ti charges from the Ti-3d band are transferred to the hole in the top of the Pt-5d band. Proving in part, our 1st hypothesis.

Zn-air batteries have been extensively studied because of their high energy densities and low cost. One of the main challenges associated with Zn-air batteries is the development of an effective air electrode for oxygen reduction reaction. We report the synthesis of free-standing structure of vertically aligned carbon nanotubes (VACNTs) supported by graphene foam, which later went through surface modification to create active sites that catalyze oxygen reduction reaction. Besides the activity of catalyst, the structure of the air electrodes is also extremely important for Zn-air batteries. Due to the low solubility and diffusivity of oxygen in the electrolyte, oxygen reduction in Zn-air batteries are designed to take place in tri-phase interfaces in which the catalyst, electrode and air come in contact. The free-standing electrode has a well-engineered hierarchical structure which contains both larger pores that acts as highways for oxygen diffusion and mesopores that increases the surface area and creates more three-phrase interfaces for the reaction. Moreover, the VACNT-graphene foam structure also processes excellent electrical conductivity. In conventional electrode preparation the large PTFE content (typically about 30%) in gas diffusion layer severely hinders the electric conductivity of the electrode, reducing battery performance. With the conductive backbone formed by VACNTs and graphene foam providing pathway for fast electron transportation we were able to overcome the problem. Overall, this electrode demonstrates excellent electrochemical oxygen reduction reaction (ORR) activity. Zn-air battery assembled by this free-standing electrode exhibits higher performance than commercial Pt/carbon black (Pt/C) electrocatalyst prepared similarly.

Copper (I) oxide (Cu₂O) is a highly attractive photoelectrode material for solar water splitting. Here, we report the fabrication of p-type Cu₂O films, via electrodeposition. The Cu₂O films were deposited on indium doped tin oxide (ITO) substrates, using an alkaline copper (II) sulfate bath containing lactic acid and potassium hydroxide. The influence of process parameters like pH, reaction time, temperature and current density on the properties of the deposited films was studied. The deposited films were characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and PEC measurements. It was observed that with increase in pH from 9 to 13 the orientation of the deposited film changed from (200) to (111). In addition, the photocurrent density during PEC measurements increased from 0.7 mA/cm² to 1.6 mA/cm² for films deposited at higher applied current densities. Stability measurements were also carried out. Further, Cu₂O-ZnO multilayered films were electrodeposited to improve stability of the photoelectrode.

Hydrogen is an alternative energy resource that is renewable and produces little to no pollution during combustion, but its use is limited by efficiency, generating a need for high-performance catalysts. Although the most effective catalyst is well known to be Pt, this metal is expensive to use commercially. One of the materials of interest for hydrogen production are transition-metal dichalcogenides (TMDs), including MoS₂ and WS₂ through the Hydrogen Evolution Reaction (HER). The HER catalysis occurs around the sulfur edges of TMD crystals, making 2-D TMDs an excellent option for the HER catalysis. MoS₂ can be grown as single layer crystals via CVD, but by using graphene oxide (GO) or reduced graphene oxide (rGO) as a substrate, one can avoid the growth of 3-D MoS₂ aggregates and instead grow thin film MoS₂ when using (NH₄)₂MoS₄ as a precursor. In the instance of GO deposition, thermal reduction conditions for GO should also be sufficient to reduce TMD precursors into the desired materials. Among the key factors that affect the HER activity of TMDs is the electron transport from the active sites of TMDs to the electrodes. The use of graphene oxide as a substrate for TMD precursors provides the additional benefit of an excellent cocatalyst. TMDs are not the most conductive material, which could hamper the HER behavior. Using rGO as a substrate allows for facile transfer of electrons to the TMD active sites. Our group has recently been focusing on the development of graphene oxide fibers through the wet-spinning of graphene oxide in ionic coagulation baths. We have shown that these fibers can be reduced so that they have a high degree of graphene character, including graphene-like crystallinity and conductivity. Initially, non-conductive GO fibers are annealed to remove oxygen groups and induce partial graphene character. Further reduction is induced via microwave heating of the graphene portions of the rGO fiber, a process which causes a cascade heating effect to heavily reduce the rGO fiber. This microwave reduction is rapid and can preserve the fiber structure while enhancing internal porosity for catalysis. Utilizing the high conductivity and high surface area of these microwaved rGO, the catalytic efficiency of the MoS₂ can be enhanced for the HER.

The scarcity and high cost of Pt as well as durability issue remains as barriers towards widespread commercialization of proton exchange membrane fuel cells (PEMFC). The US department of energy set a platinum-group-metal (PGM) target of 0.125 g_Pt kW by the year 2020, requiring Pt loading to be reduced to 0.025 and 0.1 mg/cm² for the anode and cathode, respectively. The Pt/C catalyst durability at such low Pt loading remains challenging [1]. In this study, we demonstrate the improvement of Pt/C durability in simulated drive cycles (DOE protocol, [2]) through gradient cathode catalyst layer fabricated by a one-step dry deposition process: reactive spray deposition technology (RSDT). Using solution-based Pt precursor, RSDT is able to eliminate the energy-intensive process of commercial Pt/C catalyst and catalyst-coated membrane (CCM) production, while allowing independent control of different catalyst components, suitable in making gradient layer. [3].
Herein, low Pt loading CCMs (Anode/Cathode 0.05/0.1 mg/cm²) were made with Pt supported on Ketjen Black EC-600JD, Vulcan XC-72R, and graphitized carbon. The average Pt particle size were controlled to be 2, 3 and 5 nm (nominal). Two types of gradient cathode catalyst layer were considered: the first type consisted of a 6 μm layer with mixed Pt particles of 5 and 2 nm toward the membrane and another 6 μm layer with uniform Pt particles of 2 nm toward the gas diffusion layer (GDL); the second type, keeping Pt particle size at 2 nm, consisted of a ~3 μm layer of high Pt wt.% catalyst (~60 wt%) adjacent to the membrane and a 9 μm layer of ~45wt% Pt/C catalyst toward GDL. Preliminary results after durability tests showed that the loss of electrochemical surface area and PEMFC performance were reduced compared to cathode with uniform Pt size [4]. Electron microscopy analysis suggested two possible mechanisms of durability improvement: 1) reduction of the amount of Pt lost in the membrane, and 2) preservation of Pt particles at the cathode/membrane interface [4]. A one-dimensional macro model [5] was employed to elucidate the Pt dissolution and transport process in the gradient catalyst layer.
References:
[1] A. Kongkanand and M.F. Mathias, J. Phys. Chem. Lett., 7, 1127 (2016).
[2] http://energy.gov/sites/prod/files/2014/02/f8/fctt_roadmap_june2013.pdf
[3] H. Yu, J.M. Roller, W.E. Mustain, R. Maric J. Power Sources, 283, 84 (2015).
[4] H. Yu, A. Baricci, A. Casalegno, L. Guetaz, and R. Maric, ECS Trans., accepted (2016).
[5] T. Takeshita, H. Murata, T. Hatanaka and Y. Morimoto, ECS Trans., 16, 367 (2008).

Molybdenum disulfide (MoS₂) has been extensively explored as a promising catalyst for hydrogen evolution. The catalytic performance, however, is limited by low intrinsic electrical conductivity and a low density of active edge sites for the hydrogen evolution reaction. In this work, we demonstrate that seeded growth of MoS₂ via a scalable hydrothermal process can alleviate both of these issues. Raman spectra of the obtained MoS₂ reveal an increased proportion of the metallic phase and x-ray diffraction (XRD) indicates a higher degree of crystallinity. MoS₂ produced via the seeded growth process exhibits improved dispersion in water, likely the result of an increased number of exposed hydrophilic molybdenum atoms. This is confirmed by scanning electron microscopy (SEM) images in which recrystallized flower-like MoS₂ particles are comprised of thinner flakes and more abundant edge sites than the seed particles. Therefore, the hydrothermal seeded growth process increases the proportion of the metallic phase, the crystallinity, and the density of exposed active sites of MoS₂. The catalytic activity of MoS₂ grown from metallic, semiconducting, and hybrid phase seed crystals was evaluated, and it was found that the hybrid phase samples performed best. The overpotential decreased by 10% to 226 mV at current density 10 mA.cm^-2 and the Tafel slope decreased by 20% to 81 mV.dec^-1 with reference to the original MoS₂ seed crystal. An even greater improvement is seen when these values are compared to MoS₂ grown without a seed crystal. The utilization of phase-engineered seed crystals could be a robust and versatile method to refine the quality of MoS₂ and promote catalytic performance for hydrogen evolution.

IrO₂ nanoclusters used in solar fuels are one of the most efficient electrocatalysts for the oxygen evolution reaction (OER) and water splitting process, for efficient conversion and storage of solar energy in fuel (H₂). The electrocatalytic activity of IrO₂ strongly depends on the size and shape of nanoclusters. Predictive modeling of IrO2 nanoparticles including sizes and shapes, catalytic activity, and thermodynamic stability, can enable fundamental understanding of catalytic processes at nanoparticle surfaces and provide insights into catalyst design. Here, we used density functional theory (DFT) and variable charge force field calculations to study catalytic activity changes at the surfaces, edges and corners on the nanoclusters. We used O adsorption energy as a descriptor for the catalytic activity of water splitting reaction and determined the activity changes with respect to atomic coordination and charge transfer at different active sites on the nanoparticle. Calculations with a variable charge force field parameterized using machine learning enable investigation of thermodynamic stability of relatively large IrO₂ nanoparticles with different shapes. We construct a metric to describe the overall catalytic activity of a nanoparticle and describe the effects of nanoparticle shape and size on the catalytic activity in terms of surface coordination changes, charge transfer and structural stability. By incorporating solvation models into DFT, we investigate the changes in the nanocluster shape and catalytic properties upon immersion in water environment. Our results will shed light on the design and development of stable nanoscale IrO₂ nanoparticle electrocatalytsts that efficiently utilize solar energy for water splitting reaction. ACKNOWLEDGEMENT: Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The submitted abstract has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”).
Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

Frictional losses at sliding mechanical interfaces are responsible for a significant fraction (about one-third) of energy consumption in automobiles. With transportation vehicles accounting for ~19% of the world energy consumption as well as ~23% of the total greenhouse gas emissions annually, reducing energy losses due to friction remains a grand energy/materials science challenge. Until now, much of the efforts have been focused on enhancing the anti-wear properties of lubricating oils by using environmentally hazardous additives (e.g., zinc dialkyldithiophosphate), or more friendly alternatives, including inorganic nanoparticles and ionic liquids. Here, we depart from the state-of-the-art and introduce a catalytically active composite coating (made of transition metal nitride and transition metal catalyst, e.g., MoN_x-5% Cu), which eliminates the need for harmful additives while providing enhanced wear-resistance with base lubricating oil (25% lower friction than the best blended lubricants). Our electron microscopy, and spectroscopic measurements indicate the formation of a carbon tribofilm whose structure is similar to that of diamond-like carbon (DLC). Using ab-initio and large-scale reactive (classical) molecular dynamics, we traced the origin of exceptional anti-wear properties of the coatings to catalytic phenomena possible only under the extreme conditions (high temperature/pressure) provided by friction at the sliding interfaces. Under these conditions, the transition metal catalyzes breakdown of the lubricating oils (long-chain alkenes) via: (a) dehydrogenation, followed by (b) backbone scission of long chain alkenes to form short fragments, and (c) their subsequent polymerization into DLC-like carbon. In addition, our atomistic simulations showed that the formation of DLC-like tribofilm is crucially linked to the propensity of the transition metal catalyst to form carbides; carbide forming metals, e.g., V preclude the formation of DLC tribofilm. These results open up new avenues to exploit extreme conditions to promote catalytic reaction pathways that are inaccessible in ambient environment.

Catalysts provide enormous potential in enabling low cost, efficient, sustainable fabrication processes to meet the energy demands of tomorrow. Processes such as hydrogen and oxygen evolution reactions have the potential to decrease environmental impact and increase energy security by providing a key coal, oil and natural gas alternative. Other electrocatalytic processes such as carbon dioxide reduction or glycerol oxidation have the potential to directly reduce unwanted byproducts of energy production and simultaneously generate low-carbon fuels or desired chemicals in the process. Before these electrocatalysts can be implemented, however, cells must exhibit high faradaic efficiency and energetic efficiency at reasonable current densities. Additionally life cycles of catalysts need to be lengthened and the cost of catalysts must be reduced.
Despite the importance of both electrocatalyst composition and structure to catalyst performance, few studies to date have focused on the effects of electrode structure on performance. Even fewer studies have focused on the synergy between composition and structure on electrode performance [1]. To this end, biotemplating provides unique control in materials synthesis enabling control over nanoscale structural features as well as material composition. The M13 bacteriophage (M13) in particular, has been utilized as a material template for the synthesis of 3D networks as well as specific compositions of metal oxide nanowires [2].
To date, we have demonstrated the ability of the M13 phage to serve as a synthetic functional handle to simultaneously tune several variables affecting the activity of an electrocatalyst; these variables include surface area, composition, and porosity. Specifically, the M13 mediated fabrication process results in metallized nanofoams. The process has demonstrated synthetic control over the strut thickness from 50-200nm as well as control over the nanofoam porosity. With respect to composition, separate nanofoams of copper, cobalt, and nickel have been successfully fabricated. Each of these materials have been further modified to produce alloys and/or composites on a continuum of ratios of the former listed transition metals and one or more of the following materials: Copper, Nickel, Gold, and Zinc Oxide. Through a secondary DNA mediated biotemplating process, the surface area and morphology can be further controlled and altered. Electrocatalytic processes currently being explored with this catalytic system include electro-oxidation of glycerol, oxygen reduction reaction, and electro-reduction of carbon dioxide.
[1] Ma, Sichao, and Paul JA Kenis. "Electrochemical conversion of CO 2 to useful chemicals: current status, remaining challenges, and future opportunities."Current Opinion in Chemical Engineering 2.2 (2013): 191-199.
[2] Oh, Dahyun, et al. "M13 Virus-Directed Synthesis of Nanostructured Metal Oxides for Lithium–Oxygen Batteries." Nano letters 14.8 (2014): 4837-4845.

Core@shell NPs composed of various core and shell materials are known to possess high catalytic activities towards several reactions, with a few reports on supported and unsupported core@shell NPs for methanol oxidation reaction (MOR) ^{1, 2}. In our previous work on Ru_core@Pt_shell NPs activity towards MOR, we were able to show that the rate of methanol adsorption/dehydrogenation can be accelerated either by compression of the Pt_shell (by making the Ru_core larger) when it is less than one monolayer in thickness, or by decreasing the electronic effect of the Ru_core on the Pt_shell (achieved by adding a second Pt layer to the Pt_shell)³.
In this work, 2 or 3 nm-diameter Ru_core NPs were synthesized using a simple polyol method, in which ethylene glycol (EG) or pentamethylene glycol (PMG) were used, respectively, both as the solvent and the reducing agent. Ru_core@Pt_shell NPs with a monolayer Pt-Ir coverage and different Pt:Ir ratio were fabricated in order to determine the effect of Ir on enhancing the Pt activity and on modify the Ru effect. X-ray diffraction (XRD), transmission electron microscope (TEM) coupled with energy dispersive spectroscopy (EDS) were employed to characterize the prepared catalyst. In the case of 2 nm Ru core, in the absence of Ir, Pt is found to lose the compression effect imposed by the Ru core with increasing the Pt coverage from sub- to full monolayer³. However, with adding Ir to the shell, Pt maintained the compression effect, which resulted in a significant enhancement in the overall methanol oxidation rate. In the case of 3 nm Ru core, Pt maintained the compression effect imposed by Ru in the presence and absence of Ir. Even though Ir in this case has no contribution to the strain effect, it found to enhances the Pt activity towards MOR by enhancing the CO oxidation at low potentials.

Carbon nanotubes are a potential replacement for carbon black as a catalyst support in proton

exchange membrane fuel cells (PEMFC)¹. However, significant safety concerns are associated with

manufacturing using nanoscale materials². Assembling carbon nanotubes into micron-scale

particles would avoid hazards associated with small particle size. Here, carbon nanotubes and

TiO 2 , a highly corrosion resistant material¹. were self-assembled into composite microparticles

using low-power ultrasound³. Since low electrical conductivity of catalyst supports can have a

deleterious effect on fuel cell performance¹, electrical conductivity was tested using a new

benchmarking protocol. Powder conductivity measurements must be performed under

compression since electrical conductivity depends on the degree of contact between particles⁴.

Conventional two-probe methods are not suitable for measuring materials with low conductivity

due to high contact resistance between the probes and the sample⁵. We designed and 3D-printed

a new probe that measures the electrical conductivity of small sample volumes (<0.005 cm³)

under compression using the van der Pauw technique⁶. This device, made from inexpensive

robust materials, can be turned into a two-probe device, enabling comparison between the two

techniques. We verified the performance of the device with TiO₂ and carbon black, the gold

standard electrocatalytic support for PEMFC¹. We compared

conductivity of these materials measured with both techniques to literature values.

Conductivity measurements on the very conductive carbon black were similar

for both techniques and matched literature values, validating our device. The van der Pauw

method showed superior performance with the poorly conductive TiO₂. Although there is little

difference between the two methods for conductive materials, for resistive materials

the van der Pauw technique yielded results approaching the bulk conductivity, confirming that

it is a preferable screening technique. The van der Pauw technique was then used to

test different compositions of composite microparticles. The composites were found to be

sufficiently conductive to be incorporated into fuel cells. Future work will focus on testing

electrocatalytic performance and corrosion resistance.

1. Debe, M. K. Electrocatalyst approaches and challenges for automotive fuel cells. Nature 486,

43–51 (2012).

2. Sharifi, S. et al. Toxicity of nanomaterials. Chem Soc Rev 41, 2323–2343 (2012).

3. Bassett, D. C. Ultrasonic phosphate bonding of nanoparticles. Adv. Mater. 25, 5953–5958

(2013).

4. Celzard, A., Marêché, J. F., Payot, F. & Furdin, G. Electrical conductivity of carbonaceous

powders. Carbon 40, 2801–2815 (2002).

5. Webster, J. G. Electrical measurement, signal processing, and displays. (CRC Press, 2004).

6. van der Pauw, L. J. A method of measuring the resistivity and Hall coefficient on lamellae of

arbitrary shape. Phillips Tech. Rev. 20, 220–224 (1958).

This study reports the effects of the applied pressure on cathodic deposition of metal oxides, such as TiO₂ and ZnO, thin flms in an aqueous solution and the performance of the metal oxides thin films in the photoelectrochemical water splitting reaction. The applied pressure is usually assumed to have insignificant influence on the properties of the materials fabricated in aqueous solution environment. However, morphology and crystallinity of the TiO₂ and ZnO thin films cathodically deposited at 35 MPa were found to be different from those deposited at atmospheric pressure. Especially, the crystallinity was improved with an increase in the applied pressure from atmospheric pressure to 35 MPa, and the as-deposit TiO₂ was found to have anatase crystal phase without any heat treatment process. Because of the effects on the crystallinity, both TiO₂ and ZnO thin films deposited under high applied pressure exhibited significantly enhanced photocurrent densities of water oxidation reaction under white light illumination. The electrochemical impedance spectra and photovoltage decay data illustrated that the enhanced photoactivity can be attributed to the facilitated charge transfer as a result of the improved crystallinity. Here, “hydrobaric effect” is defined to describe the phenomenon observed from the effect of the high pressure (baric) on the properties of the metal oxides since the cathodic deposition mainly takes place in aqueous solutions (hydro), analogous to the derivative origin of “hydrothermal”. This work delivers a sophisticated but efficient preparation method of highly crystalline TiO₂ and ZnO for photoelectrochemical water oxidation. The effects of the pressure on electrochemical deposition conducted in an aqueous electrolyte can be extended to other solution-phase synthetic systems especially in aqueous solutions, from which highly crystalline metal oxides can be utilized as-prepared without further complicated processing such as post heat treatment or surface modification.

Adsorption and dissociation of hydrocarbons on metallic surfaces represent crucial steps to carburization of metal. Here, we use density functional theory (DFT) and molecular dynamics (MD) to understand the role of structural defects on the Fe-110 surface on the carburization process of α-Fe by reacting with CO. It is well-known that the C interstitials in bulk Fe bind strongly with vacancy defects and grain boundaries. Therefore it is postulated that the carburization of the Fe surface by adsorption and dissociation of CO may be accelerated in the vicinity of a defect.
Single Fe vacancies on surface may occur at high concentrations due to a low formation energy. We find that in the presence of a vacancy defect, the adsorption and dissociation of CO is affected by two competing phenomena, first, a strong C-vacancy attraction that decreases the energy barriers for dissociation and diffusion and second, the O adatom, resulting from the dissociation of CO, is unstable in the electron-deficit neighbourhood of the vacancy and raises these energy barriers. However, the first phenomenon was found to strongly dominate over the second and we predict that the entire process of carburisation by CO, i.e. starting from the adsorption of CO to subsurface diffusion of C, is more favourable in the vicinity of a vacancy defect. As the single vacancy defect assists carburization, it is likely that a grain boundary (GB), exposed to the surface, would help also by channelling the C atoms deep into the metal. To check this hypothesis, we explored the effect of two symmetrical tilt grain boundaries, namely ∑3 (111) and ∑5 (210) GBs exposed to the free surface. We found that adsorption in certain sites for C atoms on the surface grooved area of a grain boundary is energetically favourable than that on a clean surface. Furthermore, molecular dynamics (MD) study shows that, at a temperature of 1180K, dissociation of CO and diffusion of C atoms in Fe is more preferable in a region where the grain boundary emerges at the surface and that the C atoms prefer the diffusion through ∑5 (210) GB rather than ∑3 (111).

Solid oxide fuel cells (SOFCs) are capable of utilizing diverse fuels due to oxygen ions, which enables the direct utilization of hydrocarbon fuels without external reformers increasing total system efficiency and cost. In particular, utilization of methane, the most abundunt and renewably generated, with high efficiency could allow for constituting a cost-effective SOFC system. For this approach, a catalyst in the anode plays a pivotal role of chemical reforming and electrochemical oxidation of reformed fuels. Ni is the most active material known for the catalyst, nonetheless, carbon coking on nickel-based anodes and low efficiency with hydrocarbon fueling relegate these systems to immature technologies. Herein, we present new methane fuelled SOFCs operated by catalytic partial oxidation (CPOX). Utilizing CPOX of methane by co-fed O2 with methane-to-oxygen ratio of 2 eliminates the carbon coking on Ni fundamentally and increases the conversion of methane into H₂ and CO by 123% as compared to operation without O₂. Ni-gadolinium doped ceria (GDC) cells exhibits the power density of 1.31 at 650 ^oC and 0.74 W cm^-2 at 550 ^oC, which remains stable over 500 h. In addition, a stainless steel current collector exhibits long-term stability under the CPOX operation, while it is disrupted totally under the operation without O₂. On the other hand, similarly prepared Ni-yttria stabilized zirconia cells exhibit only 0.27 W cm^-2 at 650 ^oC and gradual degradation. Chemical analyses on Ni suggest that juxtaposing GDC with Ni anode prevents Ni from oxidation due to GDC’s oxygen exchange ability. Our results demonstrate that durable and high-performance SOFC utilizing methane via CPOX can be achieved without deterioration of Ni catalysts.

Minimizing the cost of ORR reaction without compromising stability and efficiency can be achieved both on the support or the catalyst level or/and combination. Processing 2D carbon nanotubes into 3D materials is highly attractive for the development of electrocatalytic support. The 3D carbon nanotube microspheres exhibit high surface area (ca. 250m² g^-1) and highly porous architecture, providing paths for reactant molecules and ions get through. However, it is still a major challenge to self-assemble 3D carbon nanotube microspheres through a template-free and facile method.

Carbon nanotubes have attracted excessive attentions over the past few decades due to its excellent corrosion resistance, thermal stability and high electrical conductivity. However, a great concern for carbon nanotubes entering working environment is its extremely light property could make it suspended particulate matter (PM), which could cause inhalation problems. Therefore, a method which could reduce the risks to work with CNTs without compromising the properties of CNTs is highly desired.

To the best of our knowledge, this is the first time that using the low-intensity sonication to self-assemble carbon nanotube to 3D microspheres, and this inexpensive and non-toxic method could produce highly reproducible around 100 um microspheres. To reach a better ORR catalytic activity, we doped nitrogen atoms into carbon nanotube microsphere networks in order to enhance Oxygen Reduction Reaction (ORR) activity. Briefly, N-CNM was fabricated by heating urea and CNM together to 800 °C under nitrogen atmosphere and maintained at 800 °C for another 30 min. Bearing in mind that N contains one additional electron as compared to C, C atoms in the graphitic lattice of the microspheres have been substituted with N atoms to generate an increased n-type carriers to accelerate ORR [1]. Then, a double-pulse electrochemical deposition method was used to produce Pt nanoparticles of 2-5 nm. Three different nucleation time (t=50ms, 100ms and 200ms) were applied to create the increasing density of Pt loading at the nucleation potential of -1.0V (vs SCE) while just one fixed growth time was applied at 0V (vs SCE) to ensure a similar size of Pt nanoparticles.

In this work, we demonstrated that this novel Pt based N-CNM catalyst increased by 44% the mass activity towards ORR (up to 137 mA mg^-1 _Pt) in comparison with commercial Pt/C catalysts. Furthermore, this catalyst exhibits four electrons transfer mechanism and excellent operational durability without any decrease of electrocatalytic activity after 12,000th cycles.


Ref.
1. Lee, W.J., et al., Nitrogen-doped carbon nanotubes and graphene composite structures for energy and catalytic applications. Chem. Commun. (Cambridge, U. K.), 2014. 50(52): p. 6818-6830.

Oxy-apatites based on rare earth silicates (A10x(SiO4)6O2±x, A=rare earth cation) are of interest for solid oxide fuel cell (SOFC) applications due to the high conductivity at moderate temperatures (<1000 K). Atomistic scale simulations on this materials system in literature suggest dominant interstitial conduction mechanism. Limited experimental studies exist to date due to the extreme conditions needed for their synthesis, and have focused on preparation of bulk forms with emphasis on applications as solid electrolytes. However, the open structure allows a range of substitutional doping leading to exquisite tuning of electronic and ionic transference. We will present results on synthesis of thin film oxy-apatites: Ce_4.67(SiO₄)₃O-based apatites (~80 nm-thick) were synthesized at 973 K at low oxygen partial pressure (p(O2)<10^-17 atm) and the incorporation of ZnO into the cerium silicate system leads to the high mixed conductivity of ~0.05-0.2 S/cm. The formation of oxy-apatites was identified by in-situ conductivity measurements as a function of p(O2), x-ray diffraction analysis and x-ray photoelectron spectroscopy. The in-situ conductivity measurements show unique oxygen partial pressure dependence indicating dominant interstitial mechanism in the range of phase stability. In order to evaluate the performance of the apatite anode in SOFCs, thin film apatites were grown on Sc-stabilized ZrO₂/LSCF electrolyte/cathode substrates. Bilayer apatite/Pt and Ni-apatite composite anodes were utilized in identical electrolyte/cathode system and their performance will be discussed in this presentation.

Ref. S. Lee, X Guan, S. Ramanathan, J of Electrochemical Society 163(7), 2016

Since the beginning of catalysis research, recovery and reusability of catalysts are important issues for sustainable process management. Owing to recent breakthroughs, green nanotechnology has tremendous potential to transform homogeneous catalyst with magnetically retrievable nanocatalyst. This approach is much greener, economical, and sustainable. The application of magnetically retrievable nanocatalyst not only overcomes the problem of separation, but also provides very large surface areas and good surface activities. Hence, these nano-particles are strong contenders for catalysis. But, unfortunately these iron oxides nano-derivatives have a strong tendency for aggregation and decomposition. In order to resolve this problem, our group has synthesized silica based organic-inorganic hybrid magnetic nanocatalysts. The salient features of the synthesized catalyst such as its stability, rigidity, economic feasibility, effortless recoverability and reusability, make it a valuable green catalyst compared to the other non-magnetic heterogeneous catalytic system. The obtained nanocomposites have been characterized using various physico-chemical techniques such as FT-IR, XRD, XPS, SEM, TEM, EDS, VSM, AAS and ED-XRF. Furthermore, their applications have been investigated for different organic transformations which include oxidation of aromatic amines, Friedel-crafts, Knoevnagel, Pechmann condensation reaction, synthesis of secondary amines, reduction of nitro amines and C-H activation of formamides, C-C, C-S, C-N, C-O coupling reactions. In the foreseeable future, the design of novel magnetic nanostructured catalysts with multiple components and their use is potentially a “double green dream”.
References:
1. R.K. Sharma, M. Yadav, Y. Monga, R. Gaur, A. Adholeya , R. Zboril, R. S. Varma and M. B. Gawande, ACS Sustainable Chemistry and Engineering, 2016, 4, 1123-1130.
2. R.K. Sharma, S. Dutta and S. Sharma, New Journal of Chemistry, 2016, 40, 2089-2101.
3. R.K. Sharma, S. Dutta, S. Sharma, R. Zboril, R.S. Verma and M.B. Gawande, Green Chemistry 2016, 18, 3184-3209.
4. R. K. Sharma, M. Petr, R. Gaur, R. Zboril, M. Yadav, M. B. Gawande, A. K. Rathi, J. Pechousek, ChemCatChem, 2015, 7, 3495.
5. M. B. Gawande, Y. Monga, R. Zaboril, R. K. Sharma, Coordination Chemistry Reviews, 2015, 288, 118-143.
6. R. K. Sharma, M. Yadav, R. Gaur, Y. Monga, A. Adholeya, Catalysis Science and Technology, 2015, 5 2728.
7. R. K. Sharma, S. Dutta, S. Sharma, Dalton Transactions, 2015, 44, 1303–1316.
8. R. K. Sharma, Y. Monga, A. Puri, G. Gaba, Green Chemistry, 2013, 15, 2800–2809.

Nanostructured semiconductors are taking a centre stage in the continuous miniaturisation of optoelectronic devices due to large surface area and size dependent quantum effects with enhanced properties as compared to the bulk. Towards this end, deliberate engineering to control the shape and size of nanostructures is becoming a unique field of materials science and technology. Cupric oxide (CuO) is a p-type semiconductor material with diverse applications in photovoltaic and photo-thermal energy conversion, catalysis, gas sensing, dye sensitised solar cells, lithium ion battery technologies and magnetic storage. CuO nanostructures were synthesised by a simple, low cost and facile chemical bath deposition method. Ammonia solution was used as a complexing agent and ethylene glycol (EG), Hexadecyltrimethylammonium bromide (HCTAB) as surface assisting agents and water (H₂O) medium as a reference. The structural, optical and photocatalytic properties of the products were investigated. X-ray diffraction (XRD), Raman spectroscopy and Energy dispersive spectroscopy confirmed formation of CuO. All the XRD peaks observed were indexed to pure monoclinic phase of CuO and no peaks corresponding to other crystalline phases or Cu and Cu(OH)₂ impurities were observed. The average crystallite sizes evaluated on the basis of Debye-Scherrer method were found to be 21.5 nm (H₂O), 13.4 nm (EG) and 14.2 nm (HCTAB). The shape, orientation and nature of the nanostructures formed depended very much on the type of medium used. HCTAB surfacant did not produce free-standing nanorods like EG and H₂O, but rather nanostructured sheafs piled horizontally. Although EG and H₂O additives resulted in the growth of nanorods, the shape of the nanorods differed. The films were mainly absorbing in the UV and Vis spectral regions. The photocatalytic activity of the samples were investigated via photodegradation of methylene blue under UV-Vis light (350 - 800 nm) and it was observed that the degradation rate was influenced by the morphology of samples.

Efficient and low cost electrocatalysts are indispensable for electrochemical oxygen reduction reactions (ORR) during proton exchange membrane fuel cell (PEMFC) operations. Yet, the challenge for solution phase synthesis of nanocatalysts with low precious metal loading, high durability and catalytic activities remains in tailoring their architectures and compositions without using unwanted chemicals and surfactants/ligands that are known to impede their active catalytic sites. We present tandem laser ablation synthesis in solution-galvanic replacement reaction (LASiS-GRR) as a recently developed facile, green yet, efficient route for the synthesis of binary (PtCo) and ternary (PtCuCo) nanoalloys (NAs) with varied sizes, compositions and degrees of alloying. The transformative concept here is the ability to design these NAs by tuning the high-energy physico-chemical conditions emerging from liquid-confined, laser-induced plasma, and the GRR pathways dictated by solution-phase pH and precursor metal salt concentrations. Electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDX) mappings indicate that the resultant NAs exhibit uniformly alloyed cores with Pt-rich shells for the PtCo NAs and PtCu-rich shells with minor Cu contents for the PtCuCo ternary NAs. Our recent results have shown that the PtCo NAs with high degrees of alloying promote their outstanding electrocatalytic ORR activities in acid electrolytes while enabling a reduction in Pt content. Furthermore, compared to commercial Pt/C catalysts, the Pt₇₀Cu₂₁Co₉ ternary NAs indicate a c.a. 4 and 6-fold increase in mass and specific activities respectively along with a 25-30% (at.) reduction in Pt. Such enhanced ORR activities are attributed to the efficacy of tandem LASiS-GRR route to rationally tune size distributions, compositional ratios and alloying degrees of the NAs without the use of any detrimental surfactants or reducing agents.

The study of the electrochemical behavior of size-controlled bare Cu nanoclusters has been performed to elucidate the redox behavior of sub – nm copper particles and the effect of CO₂ on them. Cu₅ and Cu₂₀ cluster impregnated glassy carbon samples are prepared in high vacuum chamber by a combination of magnetron sputtering source (for producing pure clusters in gas phase), mass spectrometry and softlanding techniques. The average valence state and the chemical composition of the clusters are determined by grazing incidence X-ray absorption near edge structure (GIXANES) measurement. Simultaneous grazing incidence small angle X-ray scattering (GISAXS) results confirms that the naked clusters stay as isolated particles on the electrode surface. A custom made electrochemical setup has been used for sample investigation with highly sensitive square wave voltammetry (SWV) and cyclic voltammetry (CV) techniques.
Cu₂₀ nanoclusters show anodic redox processes occurring at much lower potential with respect to Cu₅ nanoclusters, which behave relatively similar to much larger Cu particles. However, Cu₅ nanocluster coordinate effectively CO₂ (hydrogen carbonate) in solution differently from Cu₂₀ nanoclusters and larger Cu particles. This effect, rather than the redox behavior, is apparently connected to the ability of Cu₅ nanoclusters to reduce CO₂ under cathodic conditions at low overpotential. Although preliminary, these results provide rather exciting indications on the possibility to realize low overpotential electrocatalytic conversion of CO₂.

References:

[1] Rosalba Passalacqua, Siglinda Parathoner, Gabriele Centi, Avik Halder, Eric. C. Tyo, Sönke Seifert, and Stefan Vajda. Electrochemical behavior of naked sub-nanometre sized copper clusters and effect of CO₂ (submitted).

Polymer electrolyte fuel cells have attracted much attention because of their great potential as a low-emission power generator. One of the major investigations in this field has been developing a low-cost alternative to Pt-Carbon (Pt-C) to catalyze the oxygen reduction reaction (ORR). As a candidate catalyst, Iron-Nitrogen-Carbon (Fe-N-C) catalysts composed by environmentally friendly elements are intensively studied. However, the true potential of Fe-N-C for ORR has not been fully understood yet.
In this study, we carried out the electrochemical measurement under unconventional conditions (using much higher catalyst loading amount, or under high pressure) to understand their catalytic behaviors from a larger perspective. Firstly, we demonstrated that how the ORR current-density behave by marginally increasing the density of activation-site using Rotating Disk Electrode (RDE). The control parameter of the catalyst loading amount on a working electrode can be widely increased by adopting Bonjet (CW-1s, Orient Chemical Industry Corp.) as a supporting material instead of the well-studied Ketjen Black (EC600JD, Lion Corp.). The current density monotonically increased with the increment of the activation-site of Fe-N-C catalysts. The obtained maximum current density was almost the same as that of Pt-C which is no relevance to the Pt loading amounts. Second, we carried out the electrochemical experiment under O₂ pressurized condition up to 10 atom to examine the limit of current density by the oversupply of reactant. A saturated behavior of current-density with increasing O₂ pressure were observed, whereas that of Pt/C linearly increased within whole measured conditions. This result directly indicates that, in the Fe-N-C catalyst, the number of activation site is rate-limiting to determine the whole reaction when O₂ supply is sufficient. The further increase of activation-site density in Fe-N-C is one of the key factors to realize the alternative to Pt-C for ORR. We believe obtained results partly contributes to the understanding the potential for Fe-N-C catalyst and leads to the next strategies for design of more effective Fe-N-C based catalysts.

Post-combustion CO2 capture and the conversion of captured CO2 into value added chemicals are integral part of today`s energy industry mainly due to their economic and environmental benefits arising from the direct utilization of CO2 as a sustainable source. Sterically-confined N-heterocyclic carbenes (NHCs) have a played a significant role in organocatalysis due to their air-stability, super basic nature and strong ability to activate and convert CO2 gas. Here we report a new class of nanoporous polymer incorporating sterically-confined N-heterocyclic carbenes (NP-NHCs) that exhibit exceptional CO2 capture fixation efficiency of 97% at room temperature, which is the highest ever reported for carbene based materials measured in the solid state. The NP-NHC can also function as a highly active, selective, and recyclable heterogeneous porous organocatalyst for the conversion of CO2 into cyclic carbonates at atmospheric pressure with excellent yields up to 98% along with 100% product selectivity through an atom economy reaction by using epoxides. Narrow pore size distribution of NP-NHC also allowed us to introduce substrate selectivity based on size, just like enzymes, for the corresponding epoxides. This two in one approach for the CO2 gas fixation/release and conversion provides a new direction for the cost-effective, CO2 capture and conversion processes.

We demonstrate the evaluation of the solar-to-fuel conversion efficiency of ceria-zirconia mixtures in a solar thermochemical water splitting system. Energy balance calculations were performed to study the effect of different process conditions on the thermodynamic efficiency of the system. Zirconium-doped ceria showed an enhanced efficiency compared to pure ceria when used in thermochemical water splitting system. A significant enhancement in solar-to-fuel efficiency was shown in case of isothermal redox cycles, at temperature approaches 1800 K with 90% gas heat recovery efficiency, 5% Zr-doped ceria gives an efficiency of 0.032% compared to an efficiency of 0.005% given by pure ceria. However, negative effects were observed upon their use in two-temperature redox cycles at normal oxidation temperatures (900 K -1200 K). Higher or lower oxidation temperatures resulted in significant enhancement in the conversion efficiency. At oxidation temperature approaching 1600 K and reduction temperature approaching 1773 K with 90% and 80% gas and solid heat recovery efficiency respectively, an efficiency of 0.762 % is obtained upon using 5% Zr-doped ceria compared to an efficiency of 0.34% when using pure ceria. At oxidation temperature of 600 K and at the same reduction temperature and heat recovery efficiencies to the previous case, an efficiency of 6.4% is obtained upon using 15% Zr-doped ceria compared to an efficiency of 5.2% when using pure ceria. The optimum conditions for operating a thermochemical water splitting reactor using 5 %, 10%, 15 % and 20% Zr-doped ceria were investigated and identified.

To date, most studies on the fabrication and development of photoelectrodes for solar-fuel generation have been based on simple binary systems with limited success. However, ternary systems have not been explored extensively although they can offer more possibilities for band gap and band alignment tuning that allow the development of more efficient photoelectrochemical systems. Herein, we report on the growth of a novel ternary oxide photoanode material composed of self-ordered, vertically oriented nanotube arrays of titanium–molybdenum–nickel mixed oxide films via the anodization of a Ti–Mo–Ni alloy in an electrolyte solution of formamide containing NH₄F at room temperature, followed by annealing in an air atmosphere. The nanostructure topology was found to depend on both the anodization time and the applied voltage. Our results demonstrate the ability to grow mixed oxide nanotube array films that are several microns thick. The Ti–Mo–Ni mixed oxidenanotube array films were utilized in solar-spectrum water photoelectrolysis, demonstrating a photocurrent density of 2.1 mA cm⁻² and a ∼10 fold increase in the photoconversion efficiency under AM 1.5 illumination (100 mW cm⁻², 1 M KOH) compared to pure TiO₂ nanotubes fabricated under the same conditions. This enhancement in the photoconversion efficiency can be related to the synergistic effects of Ni and Mo alloying and the unique structural properties of the fabricatednanotube arrays.

Control of the amounts of exposed edge sites of molybdenum disulfide (MoS₂) is the key to develop the efficient catalyst for hydrogen evolution reaction (HER). Atomic layer deposition (ALD) method has been well-known for conformal coating of desired materials. However, application of ALD to control the amount of edge site of MoS₂ remains exclusive. Here, we demonstrate that ALD was successfully applied to grow MoS₂ films together with control the amount of edge sites and high porous morphology. Our data show that the non-ideal mode of ALD growth on planar surfaces could be used in controlling the relative fractions of active-edge sites of MoS₂. In addition, the effect of amount of edge sites to the Tafel slopes and current densities in HER performance was also investigated. We achieved the best catalytic performance of the current densities up to 20 mA cm^-2 at -0.3 V versus reversible hydrogen electrode, Tafel slope of 50 to 60 mV/decade, and onset potential of 143 mV vs RHE. Our results are indicative for the first time that ALD approach is a potential strategy in designing HER materials.

With increasing environmental concerns and depletion of fossil fuel-based resources, the development of efficient energy conversion and storage technologies has attracted growing interest as one of the major scientific challenges of the 21th century. In this regard, a high level of activities in materials science and engineering research has been made to realize its potential application and to develop sustainable energy technologies by lowering our dependence on fossil fuels. A polymer electrolyte membrane fuel cell (PEMFC) has been developed as a clean and efficient energy source at a range of scale for stationary, automotive, and backup power systems because of high efficiency and power density, low operating temperature, and environmental friendliness relative to conventional energy conversion devices. The development of a carbon supported Pt catalyst that has both high oxygen reduction activity and high durability would significantly contribute to the commercialization of automotive PEMFC. We report a diazonium-functionalized graphitized carbon (DFGC) support prepared via simple diazonium chemistry that can improve the dispersion of Pt nanoparticles and reduce their sintering phenomena, resulting in higher electrochemical durability with enhanced activity as compared to the unmodified GC support. High electrochemical performance of the Pt/DFGC is attributed to the uniform distribution of Pt nanoparticles as well as strong interaction between Pt nanoparticles and DFGC, which can be enhanced by the surface modification of the GC supports with the diazonium-based functional groups. The membrane electrode assembly (MEA) fabricated with the Pt/DFGC as the cathode catalyst exhibited a power density higher than 1 W cm^-2 under an automotive operating condition at a low catalyst loading of 0.25 mg_-Pt cm^-2 and excellent voltage holding and cycling durability. The durability of the MEA with the Pt/DFGC catalysts confirms the increase by 3 and 6 times, respectively, in the voltage cycling and voltage holding durability even at 30% lower catalyst loading as compared a commercial MEA. These results demonstrate that the catalyst design strategy based on diazonium chemistry provides a high performance MEA for automotive applications.

Non precious metal derived nitrogen co-doped nanostructured carbon materials have gathered intense attention due to their highly improved activity towards oxygen reduction reaction (ORR) in both acidic and alkaline media. In this study we have selected polyaniline (PANI), dicyandiamide (DCDA) and melamine as the carbon nitrogen (C-N) precursors, Ketjenblack 300J as the carbon template and Fe as the metal catalyst to synthesize Fe, N doped highly graphitized nanocarbon. The concentration of dopants (Fe, O, N (pyridinic, graphitic and oxidized pyridinic)) in the final catalysts was found to depend on the type of C-N precursor used. The highest and which is also the optimal dopant concentration was achieved when both PANI and DCDA in optimized molar ratio were used as the C-N precursors. Quite interestingly this combination also generated the highest number of graphene layers in the graphitized nanocarbon with high mesoporosity and surface area of 1136.2 m²/g. In addition to the total nitrogen content and Fe content, pyridinic nitrogen was found to significantly improve the ORR activity in both acidic and alkaline electrolytes. As a result, the best catalyst in the group achieved an ORR onset (~ 0.97 V) and half wave potential (~0.804 V) just 60 mV and 44 mV short of benchmark Pt/C, respectively, in acidic media. However, the same catalyst surpassed the onset (~1.035 V) and halfwave potential (~0.901) of Pt/C with a difference of 37 mV and 10 mV, respectively, in alkaline media. This systematized study aims to demonstrate that careful selection of C-N precursors and their fine tuning can greatly modulate the dopants’ concentration affecting the ORR activity.

It is of great significance to design a platform with large surface area and high electrical conductivity for poorly conductive catalyst for hydrogen evolution reaction (HER), such as molybdenum sulfide (MoS_x), a promising and cost-effective non-precious material. Carbon materials are ideal candidates to be combined with poorly conductive catalysts for enhanced HER performance. There are two main forms for using composite catalyst containing poorly conductive catalyst and graphene or carbon nanotubes. For one thing, these composite catalysts were fabricated in solution and then loaded on a glassy carbon (GC) rotating disk electrode for testing. For another, the composite catalyst was prepared as self-supported and free-standing electrode, which could be used directly in the electrocatalysis process. For the second form, some substrates as conductive electrodes have been utilized, such as Ni Foam, graphene-protected 3D Ni Foams, carbon cloth, and reduced graphene oxide paper. However, none of these platforms was carefully designed to provide large deposition surface area for catalyst, thus hinder the full expression of their HER performance.
Here, a free-standing and binder-free hybrid membrane composed of graphene mesoporous structure (GMS) and single-walled carbon nanotubes (SWCNTs) was prepared through templating with Pluronic F127 micelles. Amorphous MoS_x is electrodeposited on this platform via a wet chemical process under mild temperature. For MoS_x@GMS/SWCNT hybrid electrode with a low catalyst loading of 32 μg cm^-2, the onset potential was near 113 mV vs reversible hydrogen electrode (RHE) and a high current density of ~71 mA cm^-2 was achieved at 250 mV vs RHE. The excellent HER performance can be attributed to the large surface area for MoS_x deposition, as well as the efficient electron transport and abundant active sites on the amorphous MoS_x surface. This novel catalyst is found to outperform most previously reported MoS_x-based HER catalysts. In addition, the MoS_x@GMS/SWCNT composite electrode could be tuned by adjusting the interaction of templates with raw materials, the content of SWCNTs, as well as the loading amount of MoS_x. Moreover, the flexibility of the electrode facilitates its stable catalytic performance even in extremely distorted states. This strategy is simple, cost-effective and scalable. We also believe the GMS/SWCNT hybrid architecture can serve as an excellent platform for other catalytic processes and pave a new way for designing novel electrodes for other gas evolution reactions.

With recent developments in anion exchange membranes and mitigated cathode losses in alkaline electrolytes, Anion exchange membrane fuel cells (AEMFCs) have gained importance in the electrical power market. However, the major hindrance to commercialize these fuel cells lies in the higher overvoltage losses for hydrogen oxidation reaction (HOR) in alkaline electrolyte.[1] Such high overpotential (two order of magnitude higher than in acid electrolyte) can be alleviated by employing Pt-M systems as HOR electrocatalysts, where M is a transition metal existing either as an alloy component or as an ad atom. The mechanistic origin of such activity enhancements remains unclear and there are two different theories that have evolved in order to explain such phenomenon. The first theory is based on bifunctional effects offered by Pt-M systems whereby optimal interaction energies of adsorption/dissociation of H₂ and adsorption of hydroxyl species (OH_ad) on metal surfaces are achieved;[2] whereas the second theory emphasizes on the effect of Pt-H binding energy values, and believes this factor to be dominant in determining the HOR activity of Pt-alloys in alkaline media.[3]
We have extensively studied a series of Pt alloys such as PtRu/C, PtNb/C and PtCo/C using rotating disk electrode (RDE) and surface sensitive in situ X- ray absorption spectroscopy (XAS) methods. Herein, we propose a novel depiction of the electrochemical double layer structure and use it as the foundation to support our theory explaining the enhanced activity of the aforementioned Pt-M alloy electrocatalysts. When M is a non-precious, oxophillic metal, the OH_ad is supplied from Inner Helmholtz Plane of the double layer, whereas in the case when M is a precious metal, the OH_ad is furnished from the Outer Helmholtz Plane of the double layer. A complex relationship which exists at the electrocatalytic interface will be discussed in details along with experimental and theoretical results.

Acknowledgements:
The authors gratefully acknowledge the financial support from Arpa-e, US DOE under a grant lead by Proton On-Site, Walingford, CT. Use of the Stanford Synchrotron Radiation Light-source, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) .

References
1. Durst, J., et al., Hydrogen Oxidation and Evolution Reaction (HOR/HER) on Pt Electrodes in Acid vs. Alkaline Electrolytes: Mechanism, Activity and Particle Size Effects, in Polymer Electrolyte Fuel Cells 14, H.A. Gasteiger, et al., Editors. 2014. p. 1069-1080.
2. Strmcnik, D., et al., Improving the hydrogen oxidation reaction rate by promotion of hydroxyl adsorption. Nature Chemistry, 2013. 5(4): p. 300-306.
3. Durst, J., et al., New insights into the electrochemical hydrogen oxidation and evolution reaction mechanism. Energy & Environmental Science, 2014. 7(7): p. 2255-2260.

Urea is widely used as the ammonia storage compound for selective catalytic reduction (SCR) of nitrogen oxides in automobiles. However, the observable problems with urea have fostered immense interests in replacing this compound with alternative ammonia precursors, such as concentrated guanidinium formate, ammonium formate (AmFo) and methanamide solutions, that are more thermally stable, freeze at lower temperatures, have higher ammonia storage capacities and decompose more selectively.^1,2 Most of these precursors decompose in the hot exhaust to produce formic acid in the gas phase.³ Hence, their successful adoption in the SCR process requires that the generated formic acid is rapidly and selectively decomposed to CO₂ while the co-evolved ammonia remains unreacted. We identified Au/TiO₂ as a uniquely selective catalyst that converts formic acid to CO₂ without oxidizing the co-evolved ammonia even under highly oxidizing conditions prevalent in the exhaust gases.⁴ Moreover, the presence of gas phase ammonia lead to enhanced CO₂ production.⁵ Such a promotional effect was transformed into a catalytic effect by incorporating a base metal oxide into the catalyst.⁶ In-depth mechanistic investigations employing kinetic and spectroscopic measurements revealed that an oxidative dehydrogenation pathways proceeds under SCR-relevant conditions, which is markedly different from stoichiometric formic acid dehydrogenation that is commonly reported in literature.⁷ These findings are important on a fundamental level as well as in practice for the design of a dedicated hydrolysis catalyst for the decomposition of alternative formate-based ammonia precursors in the SCR process.

References:
1 T. V Johnson, Int. J. Engine Res., 2009, 10, 275–285.
2 C. Gerhart, H.-P. Krimmer, B. Hammer, B. Schulz, O. Kröcher, D. Peitz, T. Sattelmayer, P. Toshev, G. Wachtmeister, A. Heubuch and E. Jacob, SAE Int.J.Engines, 2012, 5, 938–946.
3 O. Kröcher, M. Elsener and E. Jacob, Appl. Catal. B Environ., 2009, 88, 66–82.
4 M. Sridhar, D. Peitz, J. A. van Bokhoven and O. Kröcher, Chem. Commun. (Camb)., 2014, 50, 6998–7000.
5 M. Sridhar, J. A. van Bokhoven and O. Kröcher, Appl. Catal. A Gen., 2014, 486, 219–229.
6 M. Sridhar, D. Ferri, M. Elsener, J. A. van Bokhoven and O. Kröcher, ACS Catal., 2015, 5, 4772–4782.
7 M. Sridhar, D. Ferri, J. A. van Bokhoven and O. Kröcher, In preparation.

Electrochemical reduction of carbon dioxide (CO₂) to carbon monoxide (CO) offers a renewable-electricity-powered path to value-added carbon-based fuels and feedstocks. Unfortunately, because of the low local concentration of CO₂ surrounding typical CO₂ reduction reaction (CO₂RR) catalysts, the reaction suffers from slow kinetics. The competing off-pathway reduction of water to hydrogen produces poor selectivity as a result. Here we report field-induced reagent concentration (FIRC), wherein a nanostructured electrode produces a local high electric field at low applied overpotential. The high field concentrates electrolyte cations, and the cations bring with them a high local concentration of CO₂ proximate the active CO₂RR surface. Simulations reveal that nanometrically sharp tips on metallic electrodes achieve 10-fold higher electric fields compared to quasi-planar regions. We then use bottom-up nanomaterials chemistry to synthesize gold nanoneedle electrodes that achieve a CO₂RR with record-low onset potential (η_CO = 0.07 V) and record-high geometric current density (j_CO) of 22 mA cm⁻² at the low potential of −0.35 V (η_CO = 0.24 V) with nearly quantitative (>95%) Faradaic efficiency for CO₂ to CO conversion. We prove robust continuous reactions over 8 hours in an inorganic aqueous electrolyte. The geometric density surpasses by an order of magnitude the performance of the best gold nanorods, nanoparticles, and oxide-derived noble metal catalysts. Furthermore, we have leveraged the FIRC concept to build palladium nanoneedles that also exhibit record breaking geometric current density (j_formate) of 10 mA cm⁻² at a low potential of −0.2 V over 20 h with >91% Faradaic efficiency for CO₂ to formate conversion, proving the wider application of the FIRC concept.

Direct Methanol Fuel Cell (DMFC) is a promising technology to power small, portable applications due to its versatility and the easy of fuel transportation. On the other hand, the cost of the materials is high, especially weighted on the performances of the device, which is very low with respect to the traditional hydrogen fuel cells. To overcome this limitation, research is moving towards the reduction of the Pt loading in the electrodes by increasing its utilization, tuning the morphology of the metal catalyst and the relative support. To date, the state of the art of catalyst supports is dominated by mesoporous carbon. It shows high conductivity but suffer from stability issues especially on long term operation. As shown in various literature works, titanium nitride (TiN) has a metal-like conductivity with an outstanding chemical stability, making it an excellent candidate to replace carbon.
In this contribution, we report about a novel TiN catalyst support with a self-assembled, quasi-1D hierarchical mesoporous nanostructure, grown by Pulsed Laser Deposition. With this approach, by controlling the gas dynamics of the nanoclusters-inseminated supersonic jet, the resulting impaction deposition can be oriented and differentiated, affecting the growth of the film. We demonstrate that with our technique, morphology can be tuned at the nanoscale. Platinum nanoparticles are deposited on the tree-like structures by means of pulsed electrodeposition. Upon potential cycling in acidic medium, the Pt re-organizes into high-surface nano-lamellae guided by the local electric fields generated in the scaffold.

Catalysts comprising the unique combination of the TiN quasi-1D hierarchical mesoporous scaffold and the Pt nano-lamellae are electrochemically characterized towards the reactions of interest for DMFC, namely Methanol Oxidation Reaction (MOR) and Oxygen Reduction Reaction (ORR). We obtain high values of the Electrochemical Surface Area while controlling the porosity and the morphology of the material down to the nanoscale, reaching performances comparable to state of the art carbon-based catalysts. Moreover, we show how for MOR, the TiN scaffold is active towards the CO removal from the Pt active sites, making it suitable for replacing the Ru co-catalyst. For ORR on the other hand, we show an outstanding stability after thousands of CV cycles.
These results show how a carefully nano-engineered catalyst has the potential to reach and, possibly in the future, overcome the limitations of the current state of the art catalysts for fuel cell technology.

Recently, the development of anion-exchange membranes (AEMs) as analogues to proton-exchange membranes (PEMs) has received lots of attention. To gain higher efficiency in electrochemical water splitting, NUCRET has successfully developed high performance non-PGM catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) that work well for AEM solid polymer electrolytes (A-201 specifically). These catalysts are 60% Ni-Cr/C for HER and 40% Ni-Fe/Raney-PANI for OER. It is well known that the major challenge when dealing with alkaline environments is the reaction of OH^- ions with atmospheric carbon dioxide leading to a mixture of carbonate/ bicarbonate in the membrane. There is a controversy about the exact composition of anion inside the membrane. However, reports suggest that carbonate ion enrichment is feasible in fuel cell operating conditions. Selectivity of AEMs for carbonate ions is explained by the Donnan exclusion effect where the H⁺ ions are excluded from the membranes. Prior reports have shown that the pore solution pH increases hence becomes rich in multi charged anions. Hence, towards higher current densities, the anion composition inside the AEM becomes a mixture of only carbonate/hydroxide ions due to the progressive production of hydroxide ions at the cathode. Detection of carbon dioxide in the anode exhaust in such conditions further suggests the presence of carbonate ions as charge carriers and supports equation (1) over equation (2) as the anode reaction.
H₂+CO₃^2- →CO₂+H₂O+2e (1)
H₂+CO₃^2- →2HCO^3- +2e (2)
However, during testing under single cell conditions using a commercially available AEM (Tokuyama Corp., Japan, A201 membrane), it was determined that feeding the anode side (OER side) with 1% K₂CO₃ instead of DI water resulted in lowering of overpotential by up to 400 mV enabling overall cell potential to be below 2 V at current densities in excess of 200 mA/cm². In addition this performance was found to be stable for prolonged operation for several hundred hours. This test conducted by our validation partner Proton On-Site (Wallingford, CT) is in variance to conventional thinking on the negative effect of carbonate formation. The baseline GDLs comprised of Pt as HER catalyst and Ir as OER catalyst were compared with newly formulated non noble metal catalysts, Ni-Cr/C catalyst (HER) and Ni-Fe/Raney-Ni-PANI (OER). Both half cell studies with Ir catalyst as OER and Pt as HER and full cell data was obtained with and without carbonate feed. This presentation will provide detailed interfacial perspective( solid vs. liquid) in the context of three different studies. First study will comprise RDE experiment with various electrolytes containing KOH, K₂CO₃ and mixtures thereof. Second study will be shown using a unique cell design to understand catalyst ionomer and membrane interface. Third study will be done using a micro-electrode to combine simultaneous mass transport and kinetics at the membrane interface.

The mild synthesis route, as a green and energy-efficient chemical process, becomes increasing significant in inorganic or organic synthesis, especially for preparing some functional inorganic porous materials with great potential/practical values. The porous structure and surface area are apt to be protected through room-temperature synthetic route, which may beneficial for the related property and function of materials. Titania is believed to be one of the most widely used and studied inorganic functional oxide semiconductors.¹ Especially, porous titania materials with large surface area exhibit many promising properties and applications in photocatalysis, photovoltaics, self-cleaning techniques, sensors, etc. For most of the existing synthetic routes to porous titania, a final thermal treatment of at elevated temperatures (400 ^oC or higher) is necessary to remove the template, surfactant or other organic remnants, and/or improve the crystallinity.

Herein, a mild room-temperature crystallization of anatase titania (An-TiO₂) with porous structure and large surface area is developed.²After about 80 d, a high-surface-area (400 m² g^-1,) porous anatase titania would be obtained under ambient conditions in the absence of any solvents, additives and catalysts. Through the surface photovoltage (SPV) technique, the as-obtained An-TiO₂ exhibited high separation efficiency of photogenerated charges. In addition, the photocatalytic performance of An-TiO₂ for H₂ evolution in an aqueous solution containing methanol (50 vol%) under UV light. For comparison, An-TiO₂ exhibited excellent photocatalytic activity which is more than twice that of the benchmark P25 TiO₂. The key to realize such room-temperature crystallization process is the development of amorphous porous titania through photochemical approach. Such amorphous porous titania is quite unique due to its excellent electron-storing, ferromagnetism and activation of urea for g-C₃N₄ formation. Both its large surface area and rich surface hydroxyl groups increase the opportunities of TiO₆-bridging in the form of face-sharing.



Keywords: porous titania; Room-temperature crystallization; photochemical synthesis

References
[1] X. Chen and S. S. Mao, Chem. Rev. 2007, 107, 2891.
[2] Su, J. Zou, X. X. Li, G. D. Jiang, Y. M. Cao, Y. Zhao, J. Chen, J. S. Chem. Commun. 2013, 49, 8217.

The origin of the strain effect on metallic catalytic activity has been widely studied and attributed to strain-induced changes in the catalyst electronic structure. In this study, we directly and systematically verify this idea by using a PdCuSi metallic glass thin film, which is capable of elastic strains up to ~2%. We demonstrate that, during oxygen reduction reaction (ORR), the compressive strain applied on the metallic glass film can increase the catalytic activity, while the tensile strain can suppress it. Also, X-ray photoelectron spectrometry (XPS) results for unstrained and strained specimens to confirm the valence electron band shifts. The experimental findings are complemented by electronic structure calculations on single crystal Pd, as well as alloys with Cu and Si. The electrochemical and XPS results observed in the experiments are consistent in both direction and magnitude to those predicted by theory for single crystal Pd.

Understanding the interfacial properties between catalysts and semiconductor light absorbers is crucial to the study of solar-driven hydrogen evolution reaction (HER). Electroless metal plating is a facile and economic way to deposit catalyst nanoparticles (like Pt) onto semiconductor electrode surfaces (like Si). This contribution investigates the interfacial properties of Pt/p-Si HER cathodes prepared with electroless deposition.

Atomic force microscopy (AFM) and scanning electron microscopy (SEM) studies show that these nanoparticles are highly-dispersed and randomly-distributed on the electrode surface. In addition, some nanoparticles were spontaneously removed by repeated electroless deposition procedures, providing direct observation of the structure of the underlying interface.

We also used conductive AFM based on PeakForce tapping mode (PeakForce Tunneling AFM, PF-TUNA) to image the topography of the surface and electrical properties of the interface at the same time. The result showed that electrical contact at the electroless deposited Pt/p-Si interface is highly resistive compared to Pt thin film grown on p-Si using physical vapor deposition. The mapping also revealed that the electroless sample had inhomogeneous conductivity from one nanoparticle to another. Local current-voltage measurement indicated a rectified junction at the electroless Pt/p-Si interface, which is different from the conventional assumption of a Pt/p-Si ohmic contact.

In addition to ex situ measurements, PeakForce scanning electrochemical microscopy (SECM) was employed for in situ investigation of the interfacial mechanical, electrical and electrochemical properties. For these studies, we first found that the catalyst particles only loosely attached to the p⁺-Si substrate when in liquid. PeakForce imaging with its off-resonance tapping mechanism (typically, 1~2 kHz) allows using ultralow and stable imaging force (< 500 pN for this study) in liquid and is well-suited for mapping these electrodes. The AFM-SECM probes are batch-fabricated, high-quality and robust nanoelectrodes with the exposed Pt-coated tip apex of ~200 nm height and the end tip diameter of ~50 nm. These characteristic dimensions allows for sub-100 nm spatial resolution for electrochemical imaging, which resolves catalytic activities on the single-particle level. Furthermore, PeakForce SECM is also capable of simultaneously capturing interfacial conductivity information. SECM also showed a broad distribution of interfacial conductivities together with the heterogeneity in electrochemical activities. Interestingly, for some of the particles, these two properties are not directly correlated.

WIth both the ex situ studies and the in situ, simultaneously captured, correlated multi-dimensional information (topography, conductivity and electrochemistry), one can explore the influential interfacial factors for electrode performance in solar fuels production.

Cutting-edge breakthroughs in the development of cheap, sustainable and efficient materials for the production of hydrogen through water splitting as a renewable energy storage system are considered key for the meeting future energy requirements. Oxygen evolution reaction (OER), a key challenge in water splitting, involves the creation of a double O-O bond from two water molecules with the concomitant release of four protons and four electrons (vs. 2e⁻ for HER) and requires a large overpotential^1,2. Although metallic platinum and oxides/hydroxides of iridium and ruthenium exhibit excellent activity towards OER, their high costs^3,4 prohibit their widespread utilization. Cobalt/phosphate^5,6 and related catalysts including Mn, Co, Ni and Fe^7,8 have generated much interest because of their low cost and their promising catalytic activity for water oxidation in alkaline as well as neutral condition. However, these oxides materials do not yet fulfilled all the requirements for becoming a successful promising electrocatalytic element for developing a practicable conversion system. Here, we discovered a novel synthetic approach highly similar with the Pechini process, to prepare robust amorphous mixed metal oxide compounds. These mixed oxide electrocatalysts exhibit an unprecedentedly low overpotential and enhanced current density for the O₂ evolution reaction both at alkaline (pH 13-14) and neutral (pH 7.4) condition reported to date, outperforming the commercial IrO₂ catalyst in both OER activity and stability as well as the recently discovered cobalt phosphate catalyst. Furthermore a change in temperature from 20C to 70C increases the conductivity by a factor of 1.2 and a 100mV shift of the onset potential to the more negative value, compared to unmodified metal oxide that only showed a modest increase in current density by a factor of 0.4 and no significant change in onset potential at the same conditions. This finding potentially removes one of the remaining obstacles to high efficiency water-oxidation using inexpensive and earth-abundant materials.

1 Meyer, T. J. Nature 451, 778-779 (2008).
2 Smith, R. D. L. et al. Science 340, 60-63, (2013).
3 Carmo, M., Fritz, D. L., Mergel, J. & Stolten, D. International Journal of Hydrogen Energy 38, 4901-4934, (2013).
4 Frame, F. A. et al. Journal of the American Chemical Society 133, 7264-7267, (2011).
5 Kanan, M. W. & Nocera, D. G.Science 321, 1072-1075, .1162018 (2008).
6 Kanan, M. W., Surendranath, Y. & Nocera, D. G. Chemical Society Reviews 38, 109-114, (2009).
7 Burke, M. S., Enman, L. J., Batchellor, A. S., Zou, S. & Boettcher, S. W. Chemistry of Materials, (2015).
8 McCrory, C. C. L., Jung, S., Peters, J. C. & Jaramillo, T. F. Journal of the American Chemical Society 135, 16977-16987, (2013).

Improving the performance of electrochemical energy devices such as fuel cells rests on the development of electrocatalysts with enhanced performance and stability. In this respect, preparation routes allowing a fine-tuning of surface composition and orientation serve a pivotal role, as most electrocatalytic reactions are surface-sensitive processes. Among others, pulsed laser deposition (PLD) has recently come to the fore as a gateway to obtaining thin films of kinetically stable alloys, predicted to phase-segregate^1,2. Additionally, well-ordered substrates can be employed to grow metallic films or metastable alloys epitaxially, thus avoiding the use of expensive and cumbersome single-crystal electrodes³.
In this work, the electrochemistry of thin films prepared with PLD is investigated with an eye to electrochemical applications in the domains of environmental remediation (nitrate and nitrite reduction), electroanalysis (ammonia detection) and energy conversion (CO and dimethylether oxidation; water splitting reactions).
Particular focus is directed towards Pt thin films having a preferential (100) orientation. The voltammetric characterisation was carried out following standard methods developed for Pt single crystals and nanoparticles. It is crucial to establish the actual distribution of sites with different surface orientation, because the catalytic activity towards nitrite reduction and ammonia oxidation depends on the presence of long, well-ordered (100) terraces. The voltammetric features of short terraces and step sites of (100) orientation in H₂SO₄ are highlighted in all cases, while those of long (100) terraces become predominant for thicker films, and for those deposited at higher temperatures. The effect of the adsorption and subsequent oxidative stripping of CO is also investigated. This reaction offers additional insight into the orientation of the Pt surface. On the other hand, nitrite reduction in NaOH, a well-known surface-sensitive reaction⁴, is specifically employed to quantify the ratio between (100) surface sites and defects, while also corroborating the presence of long (100) terraces. In all cases, evidence from electrochemical techniques is correlated with data from ancillary methods (XPS, XRD, AFM). The pretreatment step required to “electrochemically anneal” the surface will also be discussed.

Bibliography
(1) Irissou, E.; Laplante, F.; Garbarino, S.; Chaker, M.; Guay, D. J. Phys. Chem. C 2010, 114, 2192.
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Operando characterization of gas–solid reactions at the atomic scale is of great importance for determining the mechanism of catalysis. This is especially true in the study of heterostructures because of structural correlation between the different parts. However, such experiments are challenging and have rarely been accomplished. In this work, atomic scale redox dynamics of Ag/AgCl heterostructures have been studied using in situ environmental transmission electron microscopy (ETEM) in combination with density function theory (DFT) calculations. The reduction of Ag/AgCl to Ag is likely a result of the formation of Cl vacancies while Ag⁺ ions accept electrons. The oxidation process of Ag/AgCl has been observed: rather than direct replacement of Cl by O, the Ag/AgCl nanocatalyst was first reduced to Ag, and then Ag was oxidized to different phases of silver oxide under different O₂ partial pressures. Ag₂O formed at low O₂ partial pressure, whereas AgO formed at atmospheric pressure. By combining in situ ETEM observation and DFT calculations, this structural evolution is characterized in a distinct nanoscale environment.

Reference: Wu, Y. A. et al. ACS Nano, 2016, 10 (3), pp 3738–3746

In doped bismuth vanadate (BiVO₄), a promising photoelectrochemical water splitting anode, ‘small-polaron’ formation means that electrons are forced to hop slowly through the lattice instead of flowing freely under an applied bias. This limits charge transport and places a severe bottleneck on the materials PEC performance. Hybrid computational methods and electronic transport studies and have been used to understand the nature of trapped charge carrier states and their influence on electronic transport in BiVO₄, respectively. Here we expand on this understanding by using a set of synchrotron x-ray spectroscopic methods to examine the electronic structure of Mo or W doped BiVO₄, and the nature of the localized electron states formed upon doping. In addition, using the polarized nature of the x-rays, we probe variations in the electronic structure along the crystal axes. Thus, we reveal aspects of the electronic structure related to electron small-polaron formation and observations consistent with conductivity anisotropy between the ab-plane and c-axis. We verify that tungsten and molybdenum substitute as M⁶⁺ for V⁵⁺ in BiVO₄. This results in the presence of inter-band gap states linked to localized electrons at V⁴⁺ sites of e_g symmetry (consistent with the existence of small-polarons). The sites are identified as lying ~1.8 eV below the conduction band and may act as recombination centres. Polarization dependent x-ray absorption spectra reveal anisotropy in the electronic structure between the ab-plane and c-axis. Results reveal greater hybridization between V 3d-O 2p states, higher V wavefunction overlap and broader conduction bands in the ab-plane relative to the c-axis - highlighting the lattice influence on charge transport. The insights are discussed in the context of current theories concerning electron small-polaron transport in BiVO₄.

Titanium dioxide still represents the most active and suitable semiconductor oxide for heterogeneous photocatalysis environmental applications. However, this material presents two main limitations: i) due to its relatively high energy band gap (i.e. 3.2 eV), only a small fraction (5%) of the sunlight can be exploited for the activation of photocatalytic processes; ii) the quite rapid electron-hole pairs recombination may compete with an efficient transfer of charge carriers to substrate molecules adsorbed on the photocatalyst surface.
In recent years, different strategies have been exploited to activate TiO₂ under visible light irradiation, including anion doping with p-block elements. A systematic investigation was performed on an extended series of singly doped or co-doped TiO₂ photocatalysts prepared by the sol-gel method starting from different amounts of N and F dopants and calcined at different temperature in the 500-700 °C range. Their photocatalytic behavior was investigated in both thermodynamically down-hill reactions, such as formic and acetic acid degradation in aqueous suspension and gas phase mineralization of acetaldehyde, and up-hill reactions for solar fuels production, such as hydrogen production from methanol-water vapor mixtures.
In the present work home-prepared TiO₂-based doped photocatalytic materials were characterized by time resolved photoluminescence (PL) spectroscopy with UV light excitation, either in the picosecond or nanosecond regimes, aiming at obtaining a better, direct insight on the effects that doping TiO₂ with N and/or F elements has on the dynamics of the charge carriers generated upon band gap excitation, in relation to the photocatalytic activity of these materials.
The PL experiments were performed under different conditions, including vacuum and low temperature (at 77 K), in addition to room temperature and atmospheric pressure. The relaxation dynamics of the UV induced luminescence was separated in different lifetime components.
Interestingly, both the PL spectral shapes and lifetimes were found to be strongly affected by the presence of dopants, as well as by the calcination temperature. In particular, a clear correlation can be outlined between the long-lasting PL decay component and the photocatalytic performance of fluorine doped TiO₂-based materials in formic acid mineralization [1]. This suggests that PL provides valuable insight to investigate the fate of photoproduced trap states originating the long-lasting PL component, which is relevant in relation to electron transfer paths originating the photocatalytic activity of TiO₂. The effects induced on the PL response by combining fluorine doping with noble metals (Au or Pt) nanoparticles, deposited on TiO₂ to mitigate the detrimental photoproduced charge carriers recombination process, will also be discussed.

[1] M.V. Dozzi, C. D’Andrea, B. Ohtani, G. Valentini, E. Selli. Journal of Physical Chemistry C, 2013, 117, 25586.

Photocatalyst for hydrogen evolution reaction (HER) is a key object for realizing solar energy conversion.¹ However, despite tremendous efforts, the synthesis of HER catalysts with high activity and long-term stability remains an ongoing challenge. Recently, the synthesis of highly crystalline mesoporous semiconductors has been the focus in the field of photo- and electrocatalysis.^2,3 This is because by combining the high reactivity of semiconductor nanocrystals (NCs) with mesoporosity into the same material it is possible to design novel photocatalysts with improved efficiency and reliability. Such materials are expected to benefit from the large accessible surface area and enhanced light-harvesting efficiency arising from multiple scattering of light inside the pores. Furthermore, the 3D nanostructured configuration of this system would allow photogenerated carriers to diffuse to the semiconductor/electrolyte interface within a short distance, resulting in a high quantum yield (QY) for the photocatalytic process.
In this work, we report the design and fabrication of mesoporous Pt-decorated CdS nanocrystal assemblies (NCAs) and demonstrate their excellent performance for the photocatalytic hydrogen production. To produce these materials, we utilized an oxidative polymerization of thiol-capped CdS NCs in the presence of an amphiphilic polyoxoethylene-b-cetyl ether (Brij-58) block copolymer, as template.⁴ The mesoporous structures obtained after template removal were decorated with ultrasmall Pt nanoparticles (ranging from 1.8 to 3.3 nm) by a straightforward photo-deposition method and used as catalysts for the photocatalytic HER. Catalytic studies along with UV–vis/NIR optical absorption, photoluminescence (PL) and electrochemical impedance spectroscopy measurements suggest that the particle size of Pt greatly effects the photocatalytic activity of these assemblies by altering the band-edge positions and carrier density of CdS NCs. Our findings indicated that Pt-CdS NCAs catalyst, containing 5 wt. % of Pt with 2.5–3 nm diameter, exhibit the highest activity. The apparent QY for this catalyst reached ~70% (1.2 mmol h^-1 H₂-production rate) under irradiation of l = 420 ± 10 nm light, which is higher than that obtained with any other CdS-based photocatalyst system operated without the use of additional oxidation co-catalysts. These results demonstrate the potential of the present Pt/CdS photocatalytic system for sustainable hydrogen production.

Recently, Pt single-atom catalysts (Pt-SACs) have attracted considerable attention not only because they can maximize the efficiency of Pt atom utilization but also because they exhibit peculiar adsorption characteristics for small molecules, resulting in high activity and unique selectivity. However, Pt atoms of these Pt-SACs easily aggregate with the increase in Pt content. Covalent triazine frameworks (CTFs), which are microporous conjugated polymers linked together with 1,3,5-triazine units, are promising candidates to immobilize Pt-SACs because they possess the high density of nitrogen (N) atoms in their organic pore.
In the present work, we successfully synthesized the single Pt-atom modified CTF (Pt-CTF), which exhibited oxygen reduction reaction (ORR) activity in acidic solutions with a high methanol tolerance, a unique property that was attributed to the atomic dispersion of the Pt atoms. In addition, we demonstrated that 2.8 wt% Pt-CTF exhibited efficient hydrogen oxidation (HOR) electrocatalytic activity comparable to the commercial 20 wt% Pt/C. The methanol tolerant ORR and the high HOR activity with the low loading amount of Pt are very attractive properties for the cathode of direct methanol fuel cells and the anode of polymer electrolyte fuel cells, respectively.

References
K. Kamiya et al. Nat. Commun. 5, 5040, (2014)
K. Iwase, K. Kamiya et al., Angew. Chem. Int. Ed. 2015, 38, 11068.
T. Yoshioka, K. Kamiya et al., J. Phys. Chem. C in press.

Metal-insulator-semiconductor (MIS) structures are promising candidates for integrated solar driven water splitting. In recent years, incorporation of protection layers into the MIS junction has made it possible to use semiconductor materials, such as silicon, that would normally be unstable under the conditions required for water oxidation. The metal traditionally serves a dual purpose, catalyzing water oxidation while also setting the built-in field for extracting photogenerated carriers from the semiconductor. A sufficiently thin insulator, such as 1-3 nm SiO₂, enables defect passivation and charge transport by tunneling.¹ The theoretical maximum photovoltage for silicon photovoltaics is 700-800 mV,² but previous reports of MIS photoanodes have fallen well below this benchmark. For example, maximum photovoltages of ~400 mV have been reported for nSi / TiO₂ / metal photoanodes protected by highly conductive TiO₂ layers,³ with some devices achieving only 200-250 mV.⁴

We investigate a strategy for isolating the photovoltaic junction and maximizing the photovoltage using highly conductive, high work function transition metal oxide-titania alloys grown by atomic layer deposition (ALD). Isolating the photovoltaic junction from the electronic characteristics of catalysts and protection layers allows for optimization of the individual layers for catalytic efficiency and stability without compromising the photovoltage or photocurrent of the device. We have shown that TiO₂-RuO₂ alloys comprised of 13-46% Ru consistently achieve photovoltages >525 mV without any post-processing anneals. The films show no significant Ohmic loss as film thickness is increased from 3 nm to 45 nm. The built-in field is set by the TiO₂-RuO₂ alloy, not by an overlying catalyst, and as a result, the photovoltage is independent of catalyst identity. TiO₂ protection layers can also be added in series with the isolated MIS junction without photovoltage loss. Thus, TiO₂-RuO₂ alloys function as Schottky contacts to nSi, creating a more ideal MIS junction in series with stable protection layers and efficient catalysts. This strategy is particularly significant for semiconductors that do not form high quality homojunctions. In principle, the alloy components could be optimized for any semiconductor absorber. Overall, this work illustrates the significant opportunity presented by ALD to tune the conductivity and work function of metal oxide Schottky contacts.

1. Singh, R., Green, M. A. & Rajkanan, K., Sol. Cells 3, 95–148 (1981).
2. Green, M. A., IEEE Trans. Electron Devices ED-31, 671–678 (1984).
3. Hu, S. et al., Science (80-. ). 344, 1005–1009 (2014).
4. McDowell, M. T. et al., ACS Appl. Mater. Interfaces 7, 15189–15199 (2015).

Here we promote BiCuSeO as a new type of candidate photocatalytic material. This material shows promising solar lights-photocatalytic properties over other narrow band-gap materials experimentally. Through DFT calculation, we not only clarified that its superior properties stem from the intrinsic hetero-layered structure of the material itself, but also regard this structure as a “good” descriptor from the materials genome point of view. In this kinds of materials, electrons and holes will be excited and limited in different layers in the following transportation. Moreover, a narrow band gap ensures the full-spectrum absorption capability. In our analysis, the partial density of states, charge density difference and effective mass anisotropy provide evidences for the hierarchy transport behavior. The dielectric constant and optical absorption are calculated for further confirmation of the high transition rate and full-spectrum absorption. The defect states are also investigated for the transport properties.

Monoclinic bismuth vanadate (m-BiVO₄) has attracted attention as a photoelectrode material for water splitting due to its suitable band gap energy of about 2.5 eV and remarkable photocurrent densities of more than 4 mA/cm¹. If such a material is to be used in practical water splitting applications, scale-up is one of the main challenges to be addressed². Specifically, a large-scale and cost-effective deposition technology for the preparation of efficient photoelectrodes is needed. Reactive sputtering is one of the techniques that can, in principle, meet these requirements. Our first attempts to sputter BiVO₄ using metallic Bi and V targets with separate direct current power supplies illustrates that sputter deposition of photoactive BiVO₄ is indeed viable, but the efficiencies still need to be improved³. One crucial factor is the stoichiometry of the films. To investigate this in more detail, photoactive BiVO₄ thin films were prepared by direct current reactive magnetron sputtering from Bi and V targets with V-to-Bi ratios from 0.7 to 1.5. The highest photoactivity occurs under slightly V-rich deposition conditions (j_ph,AM1.5 ≥1.5 mA/cm²) while the Bi-rich BiVO₄ films (V/Bi≤1) showed relatively low photoactivity (j_ph,AM1.5 ≤0.5 mA/cm²). Charge carrier dynamics and recombination processes were investigated by time-resolved microwave conductivity (TRMC) measurements. A strong dependence of carrier mobility and lifetime on the V-to-Bi ratio was observed. Furthermore, TRMC measurements at different light intensities revealed initial trap filling and recombination effects. Moreover, the monoclinic BiVO₄ phase became more prominent with increasing V-to-Bi ratio. Raman spectroscopy and chemical mapping by EDX showed that at a high V-to-Bi ratio a phase separation into BiVO₄ and V₂O₅ occurs. The improved crystallinity and the increased grain size at higher V-to-Bi ratios seem to be responsible for the improved electronic properties and hence increased photocurrents of the BiVO₄ films.

(1) Abdi, F. F.; Han, L.; Smets, A. H. M.; Zeman, M.; Dam, B.; Krol, R. v. d. Nat. Commun. 2013, 4, 2195.
(2) Pinaud, B. A.; Benck, J. D.; Seitz, L. C.; Forman, A. J.; Chen, Z.; Deutsch, T. G.; James, B. D.; Baum, K. N.; Baum, G. N.; Ardo, S.; Wang, H.; Miller, E.; Jaramillo, T. F. Env. Sci. Techn. 2013, 6, 1983.
(3) Gong, H.; Freudenberg, N.; Nie, M.; van de Krol, R.; Ellmer, K. AIP Advances 2016, 6, 045108.
Key words: BiVO₄, water splitting, Direct current, reactive magnetron sputtering, stoichiometry, grain size, charge carrier mobility, carrier lifetime, phase separation

Over the past a few decades, semiconductor-based photocatalysts have been widely explored for both solar energy conversion and environmental applications. Most of these photocatalysts only functioned under illumination because their production of ROSs relied on continuous illumination to generate electron-hole pairs. However, many potential applications require the continuous activity in the dark for an extended period of time. Recently, an interesting post-illumination photocatalytic “memory” effect was found in several photocatalytic material systems, which could be active in the dark after the illumination was switched off. Till now, photocatalysts with the post-illumination photocatalytic “memory” effect required that photogenerated electrons were trapped on decoration components with the conduction band potential negative than the one-electron reduction potential of O₂ (−0.05 V vs NHE) to react with O₂ in the dark to produce ^.O₂^– and subsequently ^.OH, which largely limited the selection of decoration components.

In this work, a novel composite photocatalyst composed of Cu₂O nanocubes decorated with SnO₂ nanoparticles was successfully created, in which Cu₂O served as the main visible light absorber, while SnO₂ nanoparticle decoration formed p-n heterojunction of good contact with Cu₂O nanocubes. The combined effect from both their large conduction band potential difference and the inner electric field provided a strong driving force for photogenerated electrons to transfer from the conduction band of Cu₂O to that of SnO₂ and be trapped there under visible light illumination. Thus, a largely enhanced photocatalytic performance was observed on these Cu₂O/SnO₂ photocatalysts as demonstrated by its disinfection of S. aureus cells and degradation of SMX, compared with pure Cu₂O nanocubes. When the visible light illumination was turned off, trapped electrons could be released from SnO₂ and react with O₂ to produce H₂O₂ in the dark for more than 24 h, and the Cu₂O/SnO₂ sample demonstrated a strong post-illumination photocatalytic “memory” disinfection of S. aureus cells in the dark. This work demonstrated that the selection of potential decoration components to construct photocatalyst systems with the post-illumination photocatalytic “memory” effect could be largely expanded to semiconductors with conduction band potentials less positive than the two-electron reduction potential of O₂. With high efficiency and relatively low cost/energy consumption, photocatalysts with the post-illumination photocatalytic “memory” effect could have the potential for a broad range of environmental applications which require the continuous activity in the dark for an extended period of time.

Intermetallic compounds are a particular class of alloyed metals with distinct, ordered lattices. Due to their ordered nature, the sorption/desorption properties are similar for each active site, increasing the activity as well as decreasing the likelihood of CO poisoning for energy sustainability. During the ordering process, high temperature annealing or synthesis conditions are necessary to obtain the correct ratio and metal atom alignment in the final structure, making shape controlled particles very difficult. In this research we have synthesized core-sandwich-shell structures with both three and five intermittent Ni and Pt layers to shorten the diffusion path length of the metal atoms. By maintaining a cubic core material and layered Ni and Pt, the shorter diffusion length allows for lower temperature annealing to form the final intermetallic phase while keeping the general atom alignment and faceting. These nanoparticle precursors to the intermetallic phase were tracked through various temperature profiles and their activities compared using methanol oxidation. The thicker three layered particle activity and lattice measurements were compared to those of the five layered particles with each showing altered metal mixing capabilities. .