It is highly desirable to access to well defined nanoparticles in catalysis research as the polydispersity and unknown surface structure of conventional nanocatalysts pose major challenges to fundamental catalysis. We have recently developed the wet chemistry for attaining atomically precise nanoclusters (e.g. thiolate-protected gold nanoclusters). These molecularly pure nanoclusters allow total structure determination by X-ray crystallography. Such structurally characterized, size-specific Aun(SR)m nanoclusters provide unique oppornities in catalytic application. We will present catalytic examples of selective oxidation and hydrogenation reactions, as well as insight into surface adsorption of reactants and catalytically active site on nanoclusters. Bimetallic nanoclusters have also been explored for catalytic application, which demonstrates tuning of catalytic properties truly on an atom-by-atom basis. Overall, the atomically precise nanoclusters may serve as new model catalysts and are expected to contribute to fundamental catalysis and future design of selective catalysts for specific chemical processes.

Carbon black nanoparticles localized in-between liposomal bi-layers provide a unique reaction environment that permits one-step synthesis of carbon-supported foam-like platinum (Pt foam/C) in aqueous solution under ambient conditions. The obtained Pt foam/C was readily purified by simple washing with water and chloroform at room temperature. Unlike commercial Pt/C composed of semi-spherical nanoparticles, Pt foam/C consists of convoluted dendritic nanosheets. Interestingly, Pt foam/C demonstrated both improved durability and activity toward oxygen reduction reaction (ORR). The improved durability is because of the formation of metastable nano-holes among dendritic branches of Pt foam/C under ripening, preserving the surface area. The activity enhancement of Pt foam/C can be contributed to predominantly exposed Pt {1,1,0} planes that possess the highest ORR activity among all low-indexed Pt crystalline planes. Nano-scale Pt primarily enclosed by {1,1,0} planes has not been reported previously.This work was supported by National Key Basic Research Program of China (973 project, No. 2012CB215500).
References
1. M. C. Orilall and U. Wiesner, Chem. Soc. Rev., 2011, 40, 520.
2. J. Zhang, K. Sasaki, E. Sutter and R. R. Adzic, Science, 2007, 315, 220.

Soft- and reactive landing of mass-selected ions onto surfaces is a powerful approach for the highly controlled preparation of materials that are unobtainable using conventional techniques. A non-thermal physical synthesis method, DC magnetron sputtering combined with inert gas-aggregation, has been employed to produce anionic metal nanoparticles in the gas-phase across a wide range of sizes, shapes and elemental compositions for deposition onto selected surfaces. Simultaneous sputtering of multiple targets employing up to three independent magnetrons in the same aggregation region is demonstrated to produce complex binary and ternary alloy nanoparticles with well defined elemental composition and morphology. Mass-selection of the anionic nanoparticles employing a quadrupole mass-filter prior to deposition is shown to provide effective control over the size of nanoparticles delivered to surfaces. A suite of cutting edge analytical techniques including atomic force microscopy, scanning and transmission electron microscopy, and x-ray photoelectron spectroscopy is utilized to determine how the size, shape, elemental composition and surface density of the deposited nanoparticles may be adjusted to promote the catalytic reduction of oxygen.

Au-Pd/TiO2 catalysts prepared by different methods were studied by HAADF imaging and XEDS analysis in an aberration corrected JEOL 2200FS STEM. Developing preparation-structure-performance correlations in this way has allowed us to rationally devise a novel catalyst preparation method for Au-Pd/TiO2 catalysts, which display a 3-fold improvement in catalytic performance for the direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen.
We first studied two commonly used synthesis methods for preparing Au-Pd/TiO2 catalysts, namely conventional impregnation (CIm) and sol-immobilization (SIm): The CIm method involves adsorption of aqueous HAuCl4 and PdCl2 solutions onto the TiO2 support, followed by drying and a calcination treatment in air. ~10 nm Pd-rich shell/Au-rich core particles, along with mu;m scale Au-rich particles as well as sub-nm Pd-rich clusters. The CIm method mainly has the important merit of simplicity. In the case of the SIm method, Au-Pd nanoparticles were pre-formed in the aqueous phase by simultaneously reducing HAuCl4 and PdCl2 in the presence of PVA surfactants, and subsequently immobilized onto the TiO2 support. This results on the formation of 1-6 nm homogeneous Au-Pd alloy particles, which display a superior catalytic performance to the CIm materials. However a systematic size-dependent composition variation was identified in SIm materials, indicating that the composition control by SIm is limited. Furthermore, the SIm method is not easy to scale up for mass production.
Our goal was to develop a new synthesis method that is as simple as CIm, yet provides even better size and composition control than SIm. We achieved this by first adding an excess amount of Cl- into the precursor solutions utilized in the original CIm route, and then replacing the air calcination treatment with a heat treatment in a reducing 5% H2/Ar atmosphere. Catalyst characterization revealed that firstly the heat treatment in a reducing atmosphere shrinks the mean particle size and also eliminates core-shell morphology structures. The reduced MIm catalyst has a 1-6 nm particle size and a homogeneous alloy structure, while in contrast, particles in the calcined MIm material are ~10 nm in size and have a distinctive Pd-rich shell/Au-rich core structure. Secondly, the effect of the excess Cl- was found to better disperse the Au into the nanoparticles therefore more uniform alloyed particles were formed. It is remarkable that with this simple MIm technique, the size, structure and composition of Au-Pd alloy particles could all be successfully controlled to a much higher degree of precision than the CIm or SIm methods. Our optimized MIm material reached 99 mol H2O2/kgcathr in the direct hydrogen peroxide synthesis reaction, which is at least a factor of three better than material prepared by the more conventional methods (32 mol H2O2/kgcathr for SIm material and 23 mol H2O2/kgcathr for CIm material).

Organic capping agent is considered essential for colloidal nanoparticle synthesis to maintain the particle shape and prevent aggregation. However, this capping agent are difficult to be removed and may cause the loss of catalytic activity of the nanoparticles. Here, we report a one-pot method to encapsulate capping agent free nanoparticles into metalminus;organic frameworks (MOFs). The synthesized nanoparticles are monodispersed and size controllable within the MOF crystals. This one-pot encapsulation strategy is applicable not only for variable metal nanoparticles (Pt, Pd and Au) but also for different MOF subfamilies. The nanoparticle/MOF composites represent size selective catalytic properties due to the uniform microporous of MOF structure. The results imply the nanoparticles are fully confined and stabilized within the MOF crystals.

This paper discusses the size-dependent performance of subnanometer cluster based catalysts in electrochemical processes of water splitting and Li-air batteries.
In the first part of the presentation, water oxidation under alkaline conditions will be discussed on the example of size-selected palladium clusters deposited on ultrananocrystaline diamond (UNCD), with the goal to probe the relationship between cluster size and efficacy of the water oxidation reaction. The support electrode chosen for these investigations is UNCD, a material thin enough to be electrically conducting, and chemically/electrochemically very stable. Even under the harsh experimental conditions (basic, high potential) typically employed for water oxidation catalysts, UNCD demonstrates a very wide potential electrochemical working window and shows only minor evidence of reaction. We find that while Pd4 clusters show no reaction, Pd6 and Pd17 clusters are among the most active catalysts known (in in terms of turnover rate per Pd atom). The system (soft-landed Pd4, Pd6, or Pd17 clusters on an UNCD Si coated electrode) shows stable electrochemical potentials over several cycles, and synchrotron studies of the electrodes show no evidence for evolution or dissolution of either the electrode material or the clusters, found to be present in oxidized PdnOn form. 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 (OER) in Pd6O6.
As time allows, examples of support and light effects on the performance of select cluster-based systems in water splitting will be shown, along with the demonstration of the effect of the cluster size and catalyst loading in lithium air batteries. In the latter case, dramatic size effects on the overpotential are observed, accompanied by changes in the morphology of the lithium peroxide particles formed.
References:
(1) G. Kwon, G. A. Ferguson, C. J. Heard, E. C. Tyo, C. Yin, J. DeBartolo, S. Seifert, R. E. Winans, A. J. Kropf, J. Greeley, R. L. Johnston, L. A. Curtiss, M. J. Pellin, and S. Vajda, ACS Nano, accepted
(2) S. Riha, E. C. Tyo, G. Kwon, M.J. Pellin, S. Vajda et al., in preparation
(3) J. Lu, E.C. Tyo, J. G. Wen, D. J. Miller, L. A. Curtiss, S. Vajda, K. Amine, et al. , in preparation

Core-shell architectures have been proven beneficial in enhancing nanocatalysts&’ activity, selectivity and durability while increasing utilization of precious metals such as platinum, an expensive noble metal but also the most active catalyst for various electrochemical and chemical reactions. To meet the performance/cost requirements for commercializing renewable-energy products, for example, proton exchange membrane (PEM) fuel cell cars utilizing hydrogen as the fuel, a vital factor is the catalysts&’ structural perfection at the atomic level. While the hydrogen produced via steam reforming followed by water gas shift (WGS) reaction contains about 1% of carbon monoxide (CO) which can severely deactivate the current fuel-cell catalysts, advances have been made in removing CO to ~ 10 ppm via preferential oxidation of CO in hydrogen feeds (PROX)[1], renewing the interest in developing CO-tolerant catalysts for using reformate that is less expensive than pure hydrogen as the fuel.
Here we report that ordered ruthenium-platinum (Ru-Pt) core-shell nanocatalysts with enhanced CO tolerance and dissolution resistance are achieved via an ethanol-based synthesis method. The interlayer mixing of the two metals is avoided by minimizing lattice defects in Ru cores before coating them with Pt at a moderate temperature. In addition, single crystalline particles are formed though Ru and Pt have distinctly different crystal structures, hexagonal close-packed (hcp) for Ru, and face-centered cubic (fcc) for Pt. Ordered lattice structural transition from Ru(hcp) to Pt(fcc) at the core-shell interface is verified by X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM), coupled with density functional theory (DFT) calculations. Furthermore, the Ru-Pt electrocatalysts with optimized structures and improved Pt utilizations exhibit significantly enhanced CO tolerance and excellent dissolution resistance at ultra-low catalyst loadings for the hydrogen oxidation reaction (HOR) in fuel-cell tests. This new level of atomic control also solves the dilemma in using a dissolution-prone metal (Ru) for alleviating the deactivating effect of CO. Our results demonstrate how a new level of atomic control in syntheses enables the atomic perfection ordering of core-shell nanoparticles, and therefore results in the superior catalytic performances for renewable energy applications.
[1] K. Liu, A. Wang, T. Zhang, ACS Catalysis 2012, 2, 1165-1178.

A particular interest in graphene for developing advanced energy materials is to use it as an efficient component in catalyzing oxygen reduction and evolution reactions, a pair of the most important electrochemical reactions crucial to a variety of electrochemical energy storage and conversion technologies (e.g. fuel cells and metal-air batteries).1-4 The promising application of graphene is primarily due to its unique physical and chemical properties, such as high surface area, very good chemical stability, excellent conductivity, unique graphitic basal plane structure, and the easiness of functionalization. Chemical doping with heteroatoms (e.g. N, B, P, or S) into graphene planes can tune the electronic properties, provide more active sites, and enhance the interaction between carbon structure and oxygen molecules. It was experimentally found that the nitrogen atoms can be incorporated into the graphene basal plane, replacing carbon atoms at different locations and leading to the formation of various defects.5 Theoretical studies have shown that nitrogen can be viewed as an n-type carbon dopant that assists in the formation of disordered carbon nanostructures and donates electrons to carbon, thus enhancing the ORR activity.6 In addition, there is growing evidence that transition metal cations such as Fe and Co are able to bond with nitrogen and embed into the graphene lattice, offering much improved activity compared to metal-free nitrogen-doped graphene structures. At Los Alamos, cost-effective nitrogen-doped graphene composite was developed via graphitization of heteroatom polymers such as polyaniline using transition metals (Co or Fe) as catalysts and carbon nanotubes as a template. The graphene-rich composite catalysts exhibit substantially improved activity for oxygen reduction in nonaqueous lithium-ion electrolyte compared to the currently used carbon blacks and Pt/carbon catalysts. The synthesis-structure-activity correlations for the graphene nanostructures were further established by tuning their synthetic chemistry (supports, nitrogen precursors, heating temperature, and transition metal types and contents). This will allow us to investigate how the resulting morphology and nitrogen-doping functionalities influence the catalyst activity.2,7 The in situ formation of nitrogen-doped graphene directly from heteroatom polymers provides a new route for the preparation of graphene nanocomposites with enhanced oxygen reduction catalytic activity for Li-O2 battery cathodes.
Reference
1. G. Wu, P. Zelenay, Acc. Chem. Res., 2013.
2. G. Wu, K.L. More, C.M. Johnston, P. Zelenay, Science, 332, 443, 2011.
3. G. Wu, et al., Chem. Commun., 49, 3291, 2013.
4. G. Wu, et al., ACS Nano. 6, 9764, 2012.
5. P.H. Matter, L. Zhang, U.S. Ozkan. J Catal., 239:83, 2006.
6. J.R. Pels, F. Kapteijn, J.A. Moulijn, Q. Zhu, K.M. Thomas. Carbon, 33:1641, 1995.
7. G. Wu, et al., J. Mater. Chem., 21, 11392, 2011.

In efforts to reduce the Pt content in oxygen reduction-active nanoparticles, a common strategy has been to coat non-precious metal nanoparticles with nanoscopically thin layers of Pt. In some cases, after potential oxidative/reductive potential cycling, the core of the particles is observed to be hollow, indicating the non-precious metal has dissolved away. This effect has been attributed to a room-temperature Kirkendall effect, in which interdiffusion of the core and shell provides mass transport of the core to the corrosive surrounding electrolyte. Here, we discuss how the kinetics of thermodynamics of this process in Pt-shell nanoparticles is far too slow to explain the observed behavior. Instead, we present analytical theory and kinetic Monte Carlo simulations that show the likely explanation of hollow cores has the following components: (i) morphological fluctuations in the shape of the particle expose the core, (ii) the core is dissolved away, leaving a shell with a pinhole, (iii) surface diffusion closes the pinhole, leaving the hollow core.

There are two central issues regarding polymer electrolyte membrane fuel cells (PEMFCs): the poor catalytic performance of a pure platinum cathode catalyst for the oxygen reduction reaction, and the propensity of a pure platinum anode catalyst to become easily poisoned and rendered inactive. For this reason, bimetallic Pt/M nanoparticles, where M is a cheaper metal, with higher catalytic activity are desirable. A block copolymer templating method is presented to yield more efficient nanoparticle catalysts for implementation into PEMFCs. Three different Polystyrene-blocknot;-poly(4-vinylpyridine) (PS-b-P4VP) block copolymers of block ratio ~3:1 were used to synthesize the nanoparticles. The templating method is used to control size, morphology, structure, and composition. A full study was done on a platinum/gold system utilizing scanning force microscopy, cyclic voltammetry coupled with a rotating ring-disk electrode, x-ray photoelectron spectroscopy, and laser ablation-inductively coupled plasma-mass spectrometry. The catalysts were all subjected to testing for activity in the oxygen reduction reaction, which takes place at a fuel cell cathode, and the methanol oxidation reaction, which takes place at the anode, with favorable results.

Using catalysts with high-activity to replace the prohibitive and precious platinum for the cathodic oxygen reduction reaction (ORR) is one of the key factors for the widespread use of renewable-energy technologies like polymer electrolyte fuel cells. Here we report a fast and facile synthesis of palladium doped tungsten nanoparticle-decorated ordered mesoporous carbon (Pd-W/OMCs) catalyst for oxygen reduction reaction using simple microwave method. The catalyst powder was prepared by the mixture of Pd acetate with tungsten hexacarbonyl in toluene, followed by the addition of ordered mesoporous carbon (OMC) and then polished in a mortar. The mixture was then given a microwave treatment in argon for one minute and the bimetallic Pd-W OMCs can be formed. In order to explore its ORR catalytic activity towards oxygen reduction, cyclic voltammetry was employed to compare the Pd-W/OMCs with W/OMC and Pt-Vulcan. It was found that Pd doping can positively shift the reduction potential of oxygen at W-OMCs composite and increases current intensity of ORR, but it is still little lower than the commercial Pt-Vulcan.
The scanning transmission electron microscope (STEM) was employed to study the microstructure of the Pd-W/OMC. The atomic resolution Z-contrast imaging was achieved by JEOL ARM 200F electron microscope with probe spherical aberration corrector. It was found that nano-sized particles (below 5nm) were homogeneously distributed in the WC matrix and most particles exhibit bcc structures (similar to W structure) while twin boundaries or other crystalline defects are commonly observed, which were formed possibly due to the fast synthesis. The energy dispersive x-ray spectroscopy (EDS) analysis was also used to investigate the elemental distribution of the catalysts. It is found that both W and Pd were homogeneously spread inside the nano-particles, which confirms that Pd-W particles are alloys rather than having core-shell structure.
Although the Pd loading in the as-prepared material is less than 2%, the catalytic current of oxygen reduction at the hybrid exhibits similar to the commercial 60% Pt-Vulcan catalyst, making it a promising candidate to replace Pt catalysts for ORR with three-hundredth level of commercial catalyst cost.

Layered Transition Metal Dichalcogenides (LTMD) are a source of exfoliable materials, which have various interesting properties for optoelectronics, composites or catalysis. In particular, MoS2 have demonstrated promising activity towards the hydrogen evolution with remarkably low overpotential and high exchange current density [1]. Chemically exfoliated TMDs obtained via lithium intercalation have revealed unique properties induced by the change of the atomic structure from 2H to 1T phase [2]. We have recently reported that the outstanding HER activity of the chemically exfoliated WS2 is originated from strain in the 1T regions of the nanosheets [3]. Similar enhancement has been observed from chemically exfoliated MoS2. Interestingly the activity can be further improved by inducing chemical modifications on the surface of the MoS2 nanosheets. This leads to an overpotential of ~150 mV coupled with Tafel slope as low as ~40 mV/dec. Such low Tafel slope, one of the lowest reported so far for TMDs, demonstrates the importance of the surface condition of the MoS2 nanosheets on the HER performances.
[1] Jaramillo, T. F. et al. Science 317, 100-102 (2007).
[2] Eda, G. et al. Nano Lett. 11, 5111-5116 (2011).
[3] Voiry, D. et al. Nature Mater, Accepted (2013).

Solid oxide fuel cells (SOFC) have recently emerged as a serious high temperature fuel cell technology. Ceria based oxides have been found to be promising as solid electrolyte for fuel cells due to their high ionic conductivity. Two co-doped ceria systems have been studied in this work viz. Ce0.8Sm(0.2-x)YxO2 (x=0-0.2) and Ce0.8Sm(0.2-x)NdxO2 (x=0-0.2) systems. These materials were prepared using the Sol-Gel process at a temperature of 300-400C followed by pelletization. Obtained oxides have been characterized using various measurement techniques such as SEM, XRD, Thermal expansion, DC Conductivity and AC impedance to understand its underlying properties.
For all the materials, grain size was obtained using XRD and is found to be in the range of nanometers. All materials were formed in cubic structure with single phase. Density measurements have shown a steady decrease from 5.8 to 4.6 gm/cm3 with addition of Yttrium and this is confirmed by calculation of XRD density from bond length measurements. Density of the all samples was more than 90% of theoretical density indicating that the material is tightly packed. SEM measurements show separate grains and by addition of Y & Nd, the material changes its structure significantly. Thermal expansion coefficient (TEC) measured using a dilatometer showed that it increased linearly with increasing temperature for all the samples. The average linear TEC was found to increase with Y doping and Nd doping respectively. The TEC values for all the compositions are in the range of 1.2-1.5 x 10^-5 /degrees C which makes it compatible with the coefficient of thermal expansion of cathode and anode materials of solid oxide fuel cells. DC conductivity and Impedance measurements are also presented to understand the ion conduction properties in the material.

The selection of the size of nanoclusters created in the beam currently permits the investigation of their size-dependent properties, e.g. in catalysis [1]. However, even for a specific size, metal nanoclusters exhibit a range of geometric structures [2], The ability to control the isomer popultaions during formation would enable their properties to be correlated with their atomic structure. Indeed, one could argue that the combination of size-selection and atomic structural conclusion would represent an “ultimate limit” of making control at the nanoscale. Our recent work has shown, for size-selected Au923 clusters prepared using a gas condensation source, that three main high sysmetry structures observed -- decahedral (Dh), icosahedral (Ih) and fcc structure such as the cuboctahedron [3]. Transformations between the structures driven by the electron beam were observed in real time at atomic resolution in the aberration-corrected electron microscope, demonstrating efficient conversion of Au abundant but metastable icosahedral nanoclusters to Dh or fcc. Here we report the control of the nanocluster structure at the formation stage by controlling the gas phase cluster preparation parameters to explore the potential energy landscape of the Au923.
The size-selected Au923 clusters were prepared using a magnetron sputtering gas condensation cluster beam source incorporating a lateral time-of-flight mass selector [4][5]. Parameters including magnetron power, condensation length, gas pressure and gas flow were varied systematically during synthesis. The structures of the clusters were imaged in a spherical aberration-corrected scanning transmission electron microscope (STEM) equipped with an HAADF detector, and compared with the multi-slice simulated images obtained from the standard atomic models of the Ino-Dh, fcc and Ih isomers. Over 100 clusters from each sample were studied to provide the statistical distribution of isomers within a given population. Preliminary results show the Dh and fcc structures are dominant with long condensation length and low magnetron power. And their proportion can be controlled respectively by gas flow and gas pressure in the preparation chamber. The Ih structure appears and its proportion is increased significantly, with high magnetron power and short condensation length. These results open the way to investigating nanocluster properties as a function of both size and atomic configuration.
[1] V. Habibpour, M. Y. Song, Z. W. Wang, J. Cookson, C. M. Brown, P. T. Bishop and R. E. Palmer, J. Phys. Chem. C, 116, No. 50, 26295 - 26299, (2012)
[2] M. C. Daniel and D. Astruc, Chem. Rev. 104, 293 (2004).
[3] Z. W. Wang and R. E. Palmer, Phys. Rev. Lett, 108, No. 24, 245502, (2012)
[4] S. Pratontep, S. J. Carroll, C. Xirouchaki, C. M. Streun and R. E. Palmer, Rev. Sci. Instrum. 76, 045103 (2005).
[5] B. von Issendorff and R. E. Palmer, Rev. Sci. Instrum. 70, 4497 (1999).

Oxygen Reduction Reaction (ORR) is a critical process in fuel cells, which is normally catalyzed on cathode by Pt-based catalysts. Its sluggish reaction kinetics requires the high Pt loading to ensure the efficiency of the whole system. The limited nature reserves and high price of Pt, together with the issues of instability and deactivation by CO poisoning and crossover effect, have hindered the large-scale application of fuel cells. Therefore, great efforts have been devoted to reducing Pt consumption by alloying or structural regulation, and searching for non-precious metal or even metal-free catalysts for ORR. The sp2 carbon materials have abundant free-flowing π electrons, which should be the potential catalysts for the reactions needing electrons, such as ORR. However, these π electrons are too inert to be directly used in ORR. Recently, it has been found that doping with electron-rich nitrogen and electron-deficient boron can turn sp2 carbon into metal-free ORR electrocatalysts.[1,2] Intuitively, co-doping with B and N could also be a possible route to further optimize the carbon-based metal-free ORR electrocatalysts. But, there arises a fundamental issue when B and N co-exist in sp2 carbon, i.e., B and N are bonded together or located separately. Due to the compensation effect between the p and n type dopants, these two cases correspond to totally different electronic structures thereof the different conjugation effects with carbon π system, which eventually leads to distinct ORR activities. Based on this consideration, we have synthesized two kinds of B&N co-doped CNTs by different procedures, which are dominated by bonded or separated B and N respectively. The electrochemical measurements show that the ORR performance for the bonded case gradually drops to the inert level of the pristine CNTs with increasing the B/N ratio, while the onset potential and current density for the separated case gets better and better with increasing B and N contents. Theoretical calculations reveal that the neutralization occurs between the extra electron from N and the vacant orbital from B for the bonded case, leading to the unfavorable chemisorption of O2 on the co-doped CNTs. The experimental and theoretical results jointly indicate that the bonded case can hardly break the inertness of CNTs, while the separated case can turn CNTs into excellent ORR electrocatalysts. These results demonstrate the crucial role of the doping microstructure on ORR performance, which is of significance in designing and optimizing the advanced metal-free electrocatalysts by multi-doping sp2 carbon nanostructures.[3]
References
[1] Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L. Science 2009, 323: 760.
[2] Yang, L.; Jiang, S.; Zhao, Y.; Zhu, L.; Chen, S.; Wang, X.; Wu, Q.; Ma, Y.; Hu, Z. Angew. Chem. Int. Ed. 2011, 50: 7132.
[3] Zhao, Y.; Yang, L.; Chen, S.; Wang, X.; Ma, Y.; Wu, Q.; Jiang, Y.; Qian, W.; Hu, Z. J. Am. Chem. Soc. 2013,135 :1201.

Direct methanol fuel cells (DMFC) that exhibit high energy density have attracted considerable interest for portable applications. However, during the electro-oxidation process, methanol is dehydrogenated to the adsorbed carbonaceous intermediates on Pt atoms, which are unavoidably poisoned by the formation of strong Pt-CO bonds that lead to the degradation of catalytic activity. These issues have been addressed by combining Pt with other transition metals in various forms, known as the bi-functional catalytic mechanism, which is responsible for the annihilation of intermediate carbonaceous molecules generated in the process.
Conventional routes for maximizing catalytic activity, either by reducing particle size or by constructing high-index facets have proven effective. However, the reduction of particle size results in poor catalytic lifetimes caused by surface energy-driven Gibb-Thomson effects. Improved catalytic stability has been achieved using nanoporous structures prepared by chemical/electrochemical dealloying procedures. Although these approaches lead to significant improvements, the composition of nanoporous alloys cannot be well controlled due to the restricted selectivity of the precursors being used. These limitations hinder the ability to design and fabricate optimized compositions for simultaneously maximizing catalytic activity and stability.
To overcome this limitation, we developed a thermal-decomposition strategy for the synthesis of component-controllable nanoporous PtPd composed of 2.3±0.6 nm sawtooth-like ligaments induced by a high density of twinning boundaries. Such twinned and ultrathin ligaments exhibit large curvatures between concave and convex regions, associated with abundant low-coordination surface atomic steps and kinks. These low-coordination atoms corroborated by theoretical simulations are the sites of high catalytic activity. The optimized Pt25Pd75 sample exhibits the best catalytic performance among all the currently reported catalysts, and has a mass activity of 1110 mA/mg Pt and high stability for the electro-oxidation of methanol.

Fuel cells convert chemical energy directly into electrical energy with high efficiency and are extremely attractive as power sources for stationary and portable applications. Ethanol is almost the ideal energy source for fuel cells wherein its chemical energy can be converted directly into electrical energy. For its slow and inefficient oxidation, highly active electrocatalyst is required as anode electrode. In previous studies, addition of Sn to carbon supported Pt has shown good performances for ethanol oxidation. Here we are reporting a novel method for synthesizing carbon supported Pt-SnO2 catalyst using electron beam irradiation method. The electron beam irradiation method is a simple one-pot process, in which a glass vial containing water together with support carbon powder and metal sources (H2PtCl6 and SnCl4) are irradiated with an high energy electron beam (4.8 MeV, 20 kGy) for several seconds. Radiation induced radicals reduces the aqueous ions of Pt and Sn and induces precipitation of composite phases on the support. 2-propanol was added to 1 vol.% as a reduction enhancer. In order to control the structure of the catalysts, tartaric acid and NaOH were also added. Ar gas was bubbled to purge air from the solution as necessary. These samples were characterized by techniques of ICP-AES, XRD, XAFS, TEM, and LSV. ICP-AES experiment revealed that both Pt and Sn were immobilized on carbon support. XRD study showed typical fcc structure of Pt. No PtSn alloy was formed. XAFS study revealed that the composite catalyst consists mainly of Pt metal and SnO2. TEM observation revealed that Pt nanoparticles have particle size of 2-4 nm. These results show that nanoparticles of Pt metal and Sn oxide could be synthesized with the one-pot process. The catalytic activity was evaluated using Linear Sweep Voltammetry. For comparison, activities of Pt/C catalyst synthesized by the same method as Pt-SnO2 sample and commercial Pt catalyst (TEC10E50E, TKK CO. Ltd.), were measured as well. Pt/C made by the electron irradiation showed a better activity than TEC10E50E, which is referred to their particle size; the particle size of TEC10E50E is 3-10 nm and that of Pt/C made by electron irradiation is 2-4 nm. Also, the catalytic activity increased from Pt/C made by the electron irradiation and to Pt-SnO2, which is referred to the existence of SnO2. SnO2 is well known to act as a promoter in ethanol oxidation catalysts. The present study revealed that SnO2 acts as a promoter for oxidizing ethanol in Pt-SnO2/C catalyst prepared using electron irradiation.

Much attention has been paid to the direct methanol fuel cells (DMFCs) as power sources for mobile devices in near future. Bimetallic nanoparticle catalysts of PtRu immobilized on carbon support (PtRu/C) have been reported to show high activity for methanol oxidation reaction. It has also been reported that the control of PtRu structure is one of the key factor for improved catalytic activity. We have been reported successful preparation technique of PtRu/C nanoparticles by using radiochemical process [Ref1], which showed relatively high activity compared with commercial catalyst. In this study, we report on the structure control of radiochemically synthesized PtRu nanoparticle by annealing them under reducing atmosphere to obtain higher methanol oxidation activity.
For the radiochemical synthesis of PtRu/C, a glass vial containing water together with support carbon (Vulcan XC-72R) and metal sources (H2PtCl6 and RuCl3) is irradiated with an electron beam (4.8 MeV, 20 kGy) for several seconds. 2-propanol was added to 1 vol.% as a reduction enhancer. In order to control the structure of the catalysts, tartaric acid and NaOH were also added. Ar gas was bubbled to purge air from the solution. Metal loading weight was adjusted to be approximately 40 wt.%. In the radiochemical process, radicals generated by the water radiolysis reduce the aqueous ions of Pt and Ru and induce precipitation of composite phases on the support. The PtRu/C powder thus obtained was annealed under reducing atmosphere (1%-H2 in N2). The annealing temperature was 200 to 400 degrees C and annealing time was 1 to 5 hours. The samples were characterized by techniques of ICP-AES, XRD, XAFS, TEM, and UPD. The catalytic activity was evaluated by LSV.
Before the annealing process, average diameter of the radiochemically synthesized PtRu particles was 2.2 nm. After the annealing process, the average particle size of PtRu increased to 4-5nm. Despite the increment in particle size, methanol oxidation activities of the annealed PtRu catalysts were significantly enhanced by the annealing process. The methanol oxidation current at 0.45 V (vs. NHE) obtained with annealed sample was about four times higher than that without annealing. The improvement was discussed based on their structural change. Before the annealing process, the structure of the PtRu is considered to possess Pt rich core and Ru rich shell structure. XANES and UPD analysis implied that by the annealing process the Pt atoms inside the PtRu grains migrated to its surface, which resulted in the higher catalytic activities. We have also found that the annealing temperature and time must be carefully controlled to obtain highest catalytic activity.
[Ref1] T. A. Yamamoto et. al., Applied Catalysis A: General 396 (2011) 68-75

With the increasing environmental concerns and depletion of fossil fuels, there has been renewed of great interest in polymer electrolyte membrane fuel cells (PEMFCs) as promising alternative systems to conventional energy conversion devices because of their high efficiency and power density, low operating temperature, and environmental friendliness. In this regard, PEMFC has been developed to date as clean and efficient energy sources for automotive and stationary power systems. For realizing the commercialization of PEMFC, there are still technological hurdles including high cost, performance loss, and poor durability with long-term cycle. In particular, low durability is key barrier to the widespread commercialization of PEMFC.
In the first part, we present the synthesis of the nitrogen-doped graphene (N-doped graphene) composite by polymer wrapping and in situ polymerization of conductive polymer as a nitrogen-containing precursor on the graphene surfaces, thus serving as anchoring sites for binding Pt nanoparticles. The Pt nanoparticles dispersed on the N-doped graphene composite are characterized by small particle size and narrow size distribution, resulting from the polymer-stabilization and the presence of Pt-N-C bonding. As compared to the Pt/unmodified graphene and commercial Pt/C catalysts, higher electrochemical performance of the Pt/N-doped graphene is attributed to the nitrogen doping and the uniform Pt distribution through π-π interaction and Pt-N-C bonding. This strategy is helpful for preparing highly durable Pt/C catalysts with a great potential for PEMFC application.
In the second part, we demonstrate simple approaches to functionalize the graphitized carbons with the benefits of surface modification techniques for preparing high durable Pt catalyst supports in PEMFC applications. One is the covalent modification of graphitized carbons via diazonium chemistry without severely sacrificing their intrinsic properties. The other is the non-covalent modification of carbons with high degree of graphitization by means of π-π stacking interaction and increased interfacial adhesion. The enhanced durability of the Pt/functionalized carbons results from the combined effect of the grafted layers acting as effective barriers for the migration of Pt nanoparticles and their agglomeration on the carbon surfaces and the slow-down of the carbon oxidation kinetics induced by the graphitization. Our results also provide a design guide of highly durable catalyst for automotive application.

Lithium-air batteries offer the tantalizing possibility of a secondary battery with a theoretical gravimetric energy density rivaling that of gasoline, however degradation of the electrolyte and cathode materials due to side reactions with superoxide intermediates severely limit the number of times that a cell can be recharged. Carbon, as used as an electrocatalyst support, a conductive additive, and as an active material in the cathode of a lithium-air cell has been demonstrated to undergo decomposition on charging even in the presence of particularly stable electrolytes. A carbon-free construction of the cathode can dramatically extend the lifetime of the cell by limiting decomposition pathways, but has not yet been demonstrated with nonprecious metals. We demonstrate the synthesis of highly porous pyrite-structured cobalt disulfide using a surfactant template in an aqueous solution and its performance in a carbon-free lithium-oxygen cathode. This crystalline material features large voids for the deposition of solid discharge products, and its high conductivity and interconnected domains allow it to be used in place of carbon as an active catalytic material for the construction of lithium-air cells.

The synthesis of core-shell (shape-controlled) metal@carbon nanostructures is highly desirable in both electrocatalysis and gas phase catalysis as the conductive carbon can aid in carrying current produced in an electrocatalytic reaction from the metal nanoparticle surface to the electrode and the pores inherent to the carbon shell can provide size selectivity of the catalyst to gas phase reactions. Furthermore, the carbon shell provides thermal stability to the shape-controlled metal nanocrystals, maintaining the specific crystal facet expressed in the metal nanostructure. In this work, a one-pot synthesis and two-pot synthesis of metal@carbon core-shell nanostructures have been developed. The use of glucose and the aqueous-based system for the shape-controlled synthesis of metal and metal@carbon core-shell nanostructures is a novel and environmentally-friendly method. This method is being tested on multiple metals capped by alkyl ammonium salts to verify the generality of the synthesis.

Rechargeable Li-air batteries have been of great interest in energy storage technology for advance electronic devices of bleeding-edge technology due to its larger storage capacity than that of state-of-the-art Li-ion battery. The oxygen reduction reaction (ORR) in basic media is an essential reaction for Li-air batteries because it directly relates to efficient energy conversion and storage. A significant development of highly efficient ORR electrocatalysts is thus of great importance. To date, Pt-based catalyst is commonly used as cathode material due to its highest ORR activity. However, large-scale implementation is limited by its high cost and scarcity. Therefore, a grand challenge still widely opens for us to explore and develop the cathode catalysts in order to compete the commercial Pt/C. Heteroatom (N, S, P)-doped carbons have been rapidly gaining interest in recent cathode catalyst for ORR because they can effectively tune the physical and electrochemical characteristics. They are also low cost and high stability. In this study, we present the preparation of N-doped carbon nanoballs via a simple solution plasma technique. Solution plasma or plasma in liquid is enormously expanding in the fields of nanoparticle and carbon syntheses due to its several advantages such as simplicity, low cost, fast reaction, and atmospheric pressure. The precursor used for synthesizing N-doped carbons is a mixture composed of benzene (C₆H₆) and pyridine (C₅H₅N). The N doping level was controlled by varying the amount of pyridine from 0 to 50 vol%. The plasma discharge was generated in the liquid precursor between two electrode wires (tungsten) by applying bipolar pulse voltage. The pulse width and frequency were set at 0.6 mu;s and 20 kHz, respectively. The influence of N doping level on the structural and morphological properties was investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. From preliminary results, the synthesized N-doped carbons had a ball-like shape with a diameter size of 10-20 nm with high surface area. With increasing N doping level, the size of carbon became larger and the lattice constant decreased. The catalytic activity of carbons with different nitrogen-doping level for ORR was also investigated electrochemically in 0.1 M KOH solution. It was found that proper amount of nitrogen doping could promote the catalytic activity. However, further increase in nitrogen doping lowered the ORR activity, which may be due to the destruction of carbon network. We expect that this work will open up an alternative synthetic pathway for metal-free cathode catalyst in next-generation rechargeable Li-air batteries.

In this study, Platinum and Platinum alloy (PtNi, PtCo, PtNiCo) nanocatalysts with well controlled sizes and shapes have been synthesized using a one pot, facile and surfactant free solvothermal approach. Morphology transformation of Pt nanoparticles (below 10 nm) from truncated octahedral (TO) to cubic shape has been achieved by variation in synthesis parameters such as reaction time, temperature and solvent concentration. A series of Pt alloy nanoparticles with varying alloy compositions and shapes have also been synthesized. The samples were characterized using X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), high-resolution scanning transmission electron microscopy (HR-STEM), energy-dispersive x-ray spectroscopy (EDS) and thermogravimetric analysis (TGA). EDS mapping and line scan coupled with HR-STEM imaging, was utilized to study elemental distribution within individual Pt alloy nanoparticles. Variable shaped Pt nanopartilcles enabled direct comparison of the reactivity on {111} and {100} facets for important electrochemical reactions. Solvothermally prepared Pt alloy nanoparticles on carbon support exhibited ~ 3-10 fold enhancements in oxygen reduction reaction (ORR) compared to commercially available Pt-C in terms of both specific and mass activities.

Nanoparticles (NPs) based on palladium (Pd) have been studied extensively as catalysts for numerous chemical reactions. Combining Pd with early transition metals (TM) is believed to be an important approach for tuning Pd catalysis with desired activity. Here, we present our developments in the nickel palladium (NiPd) NP system. Monodisperse Ni/Pd core/shell nanoparticles (NPs) have been synthesized by sequential reduction of nickel(II) acetate and palladium(II) bromide in oleylamine (OAm) and trioctylphosphine (TOP). The Ni/Pd NPs have a narrow size distribution with a mean particle size of 10 nm and a standard deviation of 5% with respect to the particle diameter. Mechanistic studies showed that the presence of TOP was essential to control the reductive decomposition of Ni-TOP and Pd-TOP, leading to the formation of Ni/Pd core/shell NPs. The composition of the Ni/Pd within the core/shell structure can be readily tuned by simply controlling the initial molar ratio of the Ni and Pd salts. The as-synthesized Ni/Pd core/shell NPs were supported on graphene (G) and used as catalysts in the Suzuki-Miyaura cross-coupling reaction. Among three different compositions of Ni/Pd NPs tested, the Ni/Pd (Ni/Pd = 3/2) NPs were found to be the most active catalyst. These catalysts were found to be stable and reusable, providing 98% conversion after the 5th catalytic run without showing any noticeable Ni/Pd composition change. Furthering our studies on the NiPd system, we also present our recent work on the synthesis of 3.5 nm TM-Pd alloy NPs which also can enhance the catalytic activity of Pd. These NPs were synthesized via a burst nucleation event facilitated by borane tert-butyl amine and subsequently stabilized by oleylamine. Composition control of the NPs was achieved by tuning the starting metal precursor ratios. Because of the simultaneous reduction process of the metal salts, we are able to achieve the alloy form of the NiPd NPs. Preliminary results show once activated by thermal annealing, these NPs showed composition dependent catalysis on the electrochemical oxidation of formic acid and selective hydrogenation of nitrobenzene derivatives. Our studies show Pd-catalysis can indeed be controlled and enhanced through the introduction of nickel.

Catalytic reaction of porous catalysts was severely limited by reaction limitation, pore diffusion limitation, external mass transfer limitation. Among these limitations, pore diffusion limitations result in underutilization of active site located in center of catalyst due to slow transport of reactant through the narrow pores. To enhance catalytic activity, it is important to improve the accessibility of the reactant to the active site. Macropores can greatly enhance the mass transportation of fluids and improve the access of a reactant to active sites located in center of catalyst. Template synthesis method was widely used to synthesis of macroporous material due to the highly ordered macroproe and tunable the pore size.
Pt has a high selectivity and high catalytic activity during the exothermic reaction of hydrogen oxidation. Recently, this catalytic reaction was received more attention for hydrogen sensor, because of increase of hydrogen usage in clean energy source.
In this study, we synthesize macro-mesoporous Pt/alumina composite by using the sol-gel method with polystyrene sphere templates. Macro pore size was controlled by using the various diameter of polystyrene spheres templates from 60 nm to 2.5 um. The diffusion coefficients of hydrogen gas in macro- and mesopores were theoretically calculated. The diffusion coefficient in macropores was about 30 times higher than in mesopores. A high diffusion coefficient in macropores accelerates the diffusion of hydrogen gas into the center of the catalyst and effectively improves the catalytic reaction of hydrogen oxidation. The catalytic activity test was carried out under the flow of hydrogen/air mixture gas and temperature changes was measured by IR thermometer. Pt/alumina composite was characterized by XRD, FE-SEM, BET and TEM analysis.

The delicate alteration of structural anisotropy on metal-γFe3O4 binary nanocrystals was achieved by controlling the nucleation behavior and growth kinetics of Fe on spherical metal NP seeds with different molar ratios of two distinct surfactants, oleylamine and oleic acid. The resulting nanostructures, isotropic Pd@γFe3O4 (Pd-1), anisotropic Pd@γFe3O4 (Pd-2), and dumbbell-like Pd-γFe3O4 (Pd-3) exhibited clear changes of crystallinity, crystal domain size, and magnetic properties of the γ-Fe3O4 component as well as their structural anisotropy. Pd-1 and Pd-3 were employed as heterogeneous catalysts for Suzuki cross coupling reactions. As a result, both catalysts could be easily separated with a magnet for reusing several times, and Pd-3 showed the product yield superior to that of Pd-3, demonstrating the effect of shape anisotropy on the catalytic activity. The research extension to the Au-γFe3O4 system successfully attained well-defined Au-γFe3O4 binary nanocrystals that clearly presented structural anisotropy changes, and offered a general route for the controlled fabrication of binary nanostructures.

The potential applications of metallic nanoparticles (NPs) as light absorbers in solar cells, storage media in technological devices, catalyst in catalytic reactions, and antimicrobials in biological systems have increased efforts in the development of novel methodologies to synthesize NPs with highly controllable sizes, compositions, and morphologies. However, due to the high affinity of metal-to-metal interactions, size control and conglomeration of the formed NPs are difficult to control during the synthesis process. One promising method for the preparation of monodispersed metal NPs is the use of Poly(amido)amine “PAMAM” dendrimers as host templates, which can overcome limitations associated with traditional synthesis methods. In this work, we report the synthesis of monodispersed bimetallic CuNi nanoparticles with highly controllable sizes and composition. Using the chemical reduction approach, UV-Visible Spectroscopy shows that bimetallic CuNi NPs are formed within the interior cavities of the dendrimer structure. X-ray diffraction analysis confirms the presence of both Cu and Ni with a face-centered cubic crystal structure. TEM and SEM will be used to evaluate the size and shape of the bimetallic nanoparticles. In addition, the catalytic activity of the formed bimetallic NPs will be evaluated for potential applications as antimicrobial agents and as enhanced light absorbers for solar cells.
Acknowledgements: The authors gratefully acknowledge the National Science Foundation under Grant Nos. NSF EPS-1158862, NSF HRD-1137681, and Department of Chemistry for support of this research.

The study of alloy catalysts offer scientists the opportunity to better understand how the interplay between different metals in the nanoregime affects the outcome of heterogeneously catalyzed chemical reactions. AuPd catalysts have been of particular interest not only because of the wide range of reactions in which they can be used, but also because of their relative simplicity, being soluble at all compositions and comprising of one active metal, Pd, and one generally inert metal, Au. However, conventional catalysts, typically made by incipient wetness impregnation or co-precipitation, result in catalysts with ambiguous structures that make it difficult to delineate the structure dependence of their catalytic properties. Even among colloidal syntheses that have been published, the degree of uniformity in size and composition falls short of what would be necessary to start making ties between catalyst structure and function. To that end, the work presented here describes the solution-phase synthesis of 4-nm gold nanoparticles with 0.7-atom-thick, 1.9-atom-thick, and 3.8-atom-thick layers of Pd on their surfaces. These well-defined core-shell nanoparticles were deposited on a silica support, calcined, and reduced at 300 °C to create alloyed nanoparticles containing 10.9, 20.2, and 28.5% Pd (w/w). Monometallic Pd nanoparticles sintered during calcination at 300 °C, but no sintering was observed for AuPd nanoparticles. Diffuse reflectance infrared Fourier transform (DRIFT) spectra of adsorbed CO suggests that Au donates d electron density to Pd in the core-shell and alloy structures, and confirms the presence of Au and Pd atoms on the nanoparticle surfaces after calcination and reduction. The properties of the AuPd alloy catalysts were tested in the vapor-phase conversion of α-limonene to p-cymene. AuPd nanoparticles containing 20% or more Pd per particle produced p-cymene yields greater than 80%, equivalent to conventional Pd catalysts prepared by incipient wetness and ion exchange methods. Very low yields of p-cymene were obtained from dehydrogenation of p-menthane under equivalent conditions, suggesting that the production of p-cymene from α-limonene proceeds through terpinene intermediates. Future work will compare the catalytic properties of the core-shell AuPd particles with the properties of the alloys to gain further insights into the relative contributions of ensemble, ligand, and spillover effects to a catalyst's activity and selectivity.

Tungsten trioxide (WO3) and its hydrates (WO3.xH2O, x=0-2) play an important role in many areas of modern science and technology, such as water photosplitting, wastewater treatment, gas sensors, near-infrared absorbent, pronounced photochromism which makes them attractive for applications in many areas, such as smart windows, nonemissive displays, photochromic switches and information storage media. The previous work mainly focuses on the preparation of hierarchical WO3 using hydrothermal method which required autoclaves and long time [1]. In this work, hierarchical mesoporous urchin-like WO3.0.33H2O and flower-like WO3.H2O possessing abundant of O-H groups, were synthesized via a simple ion-exchange route.
Hierarchical urchin-like WO3.0.33H2O with mesoporous structure was synthesized via ion-exchange with 0.01 M Na2WO4.2H2O aqueous solution, while flower-like WO3.H2O could be obtained with 0.05 M Na2WO4.2H2O. It was found that the surface of the as-synthesized WO3.0.33H2O sample was covered by many nanorods. Furthermore, the nanorods possessed porous structure. High resolution transmission electron microscopy image showed that the nanorods grew preferentially along [100] direction. On the other hand, the flower-like architectures were assembled by nanosheets with average thickness of ca. 80 nm. These characteristics result in excellent adsorption performance on both organic dyes and heavy metal ions from wastewater. The maximum adsorption capacities of the urchin-like WO3.0.33H2O for methylene blue and Pb2+ are 247.3 and 248.9 mg/g, respectively and those of the flower-like WO3.H2O are 117.8 and 315.0 mg/g, respectively. Furthermore, the hierarchical WO30.33H2O mesoporous assemblies also exhibit both UV-driven and visible-light-driven photochromic response due to large specific surface area originated from the mesoporous structure. The formation mechanism of such hierarchical mesoporous urchin-like WO3.0.33H2O and adsorption mechanism were studied.

[1] W. Xiao, W. T. Liu, X. H. Mao, H. Zhu and D. H. Wang, J. Mater. Chem. A, 2013, 1, 1261-1269.

Colloidal semiconductor nanocrystals decorated with suitable catalysts are promising materials for solar fuel generation such as hydrogen due to their tunable electronic and optical properties.[1] Previously, it was shown that sub-nanometer Pt clusters show high photocatalytic activity for hydrogen generation when deposited onto colloidal CdS nanorods. [2] This potentially allows for reduced costs of the nanomaterial. Utilizing the non-size-scalable properties of sub-nm-sized Pt clusters we show here, that both the cluster density and the precise number of atoms in the clusters determine the hydrogen generation efficiency of this nanosystem.[3,4] We determine for the first time the minimum cluster coverage necessary to achieve maximum hydrogen generation efficiency and show that, in the cluster size range investigated, clusters with 46 Pt atoms are particularly photocatalytically active.
[1] A. Vaneski et al. Adv. Funct. Mater. 21, 1547-1556 (2011).
[2] M. Berr et al. Appl. Phys. Lett. 97, 093108 (2010).
[3] M.J. Berr et al. Nano Letters 13, 5903-5906 (2013).
[4] F. Schweinberger et al. submitted.

Heterogeneous catalytic chemical reactions are at the core of many energy and environment related challenges. The shape of catalyst nano-particles determines the accessible surfaces, and thus has a significant influence on the catalytic activity. Understanding this structure-reactivity relationship is crucial for the optimization of industrial catalysts.
Recently, Shao-Horn and coworkers have shown that gold-copper (Au/Cu) nanoparticles are stable and efficient electrocatalysts for the reduction of CO2 [1]. Our goal is to understand the structures of the Au/Cu nanoalloy at the atomic scale for further investigations of the mechanism of the catalytic reaction. We report the equilibrium shape of Au/Cu clusters for different alloy compositions and under varying catalytic conditions based on density-functional theory calculations and simulations using atomistic potentials.
[1] Z. Xu, E. Lai, Y. Shao-Horn, and K. Hamand-Schifferli, Chem. Commun. 48, 5626 - 2528 (2012).

Azo dyes are widely used in the textile, food, drug, and other industries to dye products. Some of these toxic, carcinogenic, and mutagenic dyes have been found in food and water supplies. Thus, much attention has been given to eliminating the dyes through photocatalysis.
Many metal oxide semiconductors have been found to be effective photocatalysts, such as the most widely studied, TiO₂. However, TiO₂ has a large bandgap (3.2 eV) that limits light absorption to the small UV portion of the solar light spectrum. Cu₂O has a smaller bandgap than TiO₂, thus allowing utilization of more of the visible light and offering a more effective and cheaper alternative photocatalyst. The photocatalytic activity of Cu₂O can be greatly improved by decoration with Ag nanoparticles due to their surface plasmon resonance (SPR). SPR in the Ag particles can free electrons and send them directly into the Cu₂O surface, or scatter photons into the Cu₂O surface, resulting in a large increase in the population of the Cu₂O conduction band.
The present study details facile synthesis of hollow Cu₂O nanospheres decorated with Ag nanoparticles using a simple microwave technique for enhanced photocatalytic activity. The morphology and structure is studied via XRD, SEM and TEM. Cu₂O hollow nanospheres with a diameter of 300-600 nm were synthesized via Ostwald ripening using CuSO₄ aqueous solution. The catalytic activity of Cu₂O is studied in the presence of UV and visible light using Methylene Blue (MB) as a model pollutant. Various parameters controlling the degradation rate of MB such as Ag loading on Cu₂O, sample weight percent, pH of solution, etc. have been assessed.

Ceria, CeO2, has many hi-tech and energy-related applications, notably in catalysis. The technological importance of ceria is their high oxygen storage capacity (OSC). This property is linked to the high yield of Ce4+/Ce3+ redox reaction which generate oxygen vacancies. Further improvement in OSC has been achieved by introducing metal ions, as Ni2+, into ceria network. Moreover, one-dimensional (1D) ceria nanostructures have remarkable activity and OSC because of their efficient expose of {110} and {100} reactive planes. The aim of this work is to obtain 1D NixCe(1-x)O2 phases via hydrothermal synthesis. Since 1D-arrays and nickel-doping, one at a time, enhance thermal stability and OSC of CeO2 it is expect a superior effect by implementing both conditions. Nickel-ceria solid solution show excellent catalytic activity for the CO and CH4 oxidation; a management of reactivity and selectivity for those oxidative catalysis will be achieved by controlling composition, size and shape of the NixCe(1-x)O2 phases. Also a very carefully analysis of the synthesis and physical chemical properties are presented.

Magnetite nanoparticles were synthesized by an aqueous reaction process at 70 C in the presence of an organic stabilizer to obtain a stable colloidal suspension. Transmission electron microscopy (TEM) showed the particles had a mean diameter of 2.5 nm, with a coefficient of variation of 28%, and a dynamic light scattering revealed a hydrodynamic diameter of 4.9 nm. High-resolution TEM indicated the particles were single crystalline. X-ray diffraction spectra had two prominent peaks that were most closely matched by magnetite. Carbon black was used as a model for soot and was imbibed with the nanoparticles using an incipient wetness technique. The resulting mixture was characterized with HRTEM to study the “soot”-nanoparticle interface. Additionally, the mixture was heated in a fixed bed reactor under flowing air stream and the output gas was analyzed with gas chromatography. A dramatic lowering of the ignition temperature by about 200 C relative to the untreated carbon black was found. Similar tests with larger magnetite nanoparticles showed less reduction in ignition temperature compared to the untreated carbon black. For dosing liquid fuels, the nanoparticles were extracted into a nonpolar medium using an immiscible carboxylic acid. Tests of diesel fuel with 2.5 ppm by weight of the nanoparticles in an electric generator with a portable emission measurement system resulted in more than a 20% reduction in total hydrocarbons, along with a reduction in particulate matter of about 8%. Preparation of these nanomaterials by a highly scalable aqueous precipitation process using earth-abundant resources opens the possibility for a cost-effective combustion of soot by a fuel-borne additive.

Corrosion of the carbon support is one degradation mechanism leading to poor durability and unacceptable lifetimes of Platinum-based catalysts supported on carbonaceous materials (Pt/C). Discovery of a support that offers comparable electrical conductivity, surface area, structure, and Pt activity enhancement that can be manufactured at a competitive price to carbon and possesses a greatly increased corrosion resistance is a major challenge to fuel cell commercialization. Several reviews of potential support materials have recently been published on alternative materials to carbon. Of particular interest are the Ebonex particles the sub-stoichiometric titanium oxides of the general formula TinO2n-1 (Magnéli phases), where n is a number between 4 and 10. These Magnéli phases are characterized by extended planar defects and crystallographic shear planes which vary according to the oxygen deficiency.
The aim of this project is basis research on Pt nano-particles on ball-milled Ti4O7 particles. High-quality characterization of these particles is required to investigate their composition and their structure. A focused ion beam (FIB) was used to prepare cross-section specimens for the transmission electron microscopy (TEM). In order to evaluate the chemical composition, scanning transmission electron microscopy (STEM) and high-angle annular dark field (HAADF) were performed on the specimens to get information on microstructure, atomic structure and atomic number. X-ray Energy dispersive spectroscopy (XEDS) permits sub-nanometer elemental identification and compositional analysis. The addition of electron energy loss spectroscopy (EELS) and energy-filtered imaging allows for the detection of elements at higher spatial resolution, phase identification and bonding information. For structure analysis, the Z-contrast image was particularly suited to imaging catalyst particles with high Z that are often used to grow nanotubes. In the Z-contrast image, the support was seen more clearly in the phase contrast image. Due to the large size of the TinO2n-1 particles, even after ball-milling, imaging in electron transmission modes is challenging.

Photocatalytic hydrogen production from water using semiconducting photocatalysts has attracted attention as a clean solar hydrogen-generation system. A high crystallinity and a large surface area are critical for realizing high-efficiency photocatalysts. Two-dimensional nanocrystals with a thickness of around 1nm satisfy both these requirements. Some oxide nanosheets have been reported to have higher catalytic efficiencies than their parent compounds. However, these nanosheets have large band gaps and are thus not active under visible light irradiation. There have been only a few reports on nanosheet photocatalyst with visible light response. In this study, we report on the photocatalytic activities of nitrogen-doped AE2Ta3O10(AE:Ca, Sr, Ba) two-dimensional nanocrystals, which were prepared by exfoliating layered perovskite compounds, N-doped CsAE2Ta3O10 (AE:Ca, Sr, Ba). N-doped Sr1.5Ba0.5Ta3O10 showed the highest photocatalytic activity for H2 production from the water/methanol system among the AE2Ta3O10 (AE:Ca, Sr, Ba) nanosheets prepared. In addition, Rh-loaded Sr1.5Ba0.5Ta3O9.6N0.3 nanosheet showed the photocatalytic activity for oxygen and hydrogen production from pure water under visible light irradiation. The ratio of hydrogen to oxygen evolved was around two. These results indicate that the Rh-loaded N-doped Sr1.5Ba0.5Ta3O10 nanosheet is a potential catalyst for photocatalytic water splitting.

Nowadays platinum has been widely used as an electrocatalyst for oxygen reduction reaction (ORR). However, because of its high cost and scarcity, alternative catalyst materials that can rival the activity and durability of Pt-based catalyst are highly needed. Nitrogen-doped carbon is an attractive candidate because of its high ORR activity provided by incorporating nitrogen into graphene structure. Moreover, it has selectivity for electrochemical reactions, for example, unlike Pt, it does not suffer from methanol and CO poisoning. Therefore, nitrogen-doped carbon catalysts are being regarded as one of the most promising materials in the application for not only fuel cells but also capacitor, Li-ion battery, Li-Air battery, and electrolysis. But the nature of the nitrogen atoms in nitrogen-doped carbon materials and the most active reaction site for ORR remain unclear.
Herein, we report ORR activity and hydrogen evolution reaction (HER) activity of various catalysts prepared from different precursors of nitrogen-doped carbon.
We have investigated electrochemical property of various nitrogen-doped carbon catalysts:(a)rGO from hydrazine-treated graphene oxide(GO), (b) heat-treated rGO, (c) GO, (d) heat-treated mixture of Fe compounds and nitrogen-containing polymer, and (e) heat-treated polyacrylonitrile. (f) Pt and (g) Ketjen Black were used as references. The ORR activity and HER activity were evaluated in 0.5M H2SO4 solution with a glassy carbon electrode. Carbon paper and Ag/AgCl electrodes were used as the counter and the reference electrode, respectively. The working electrode was prepared by the thin-film electrode method. Cyclic voltammograms were recorded by scanning the potential in nitrogen atmosphere (to obtain the background) and oxygen atmosphere (to obtain oxygen reduction onset potential).
ORR onset potential is significantly increased through introducing nitrogen. Heat-treated mixture of Fe compound and nitrogen-containing polymer possess the highest onset potential at about 0.85Vvs RHE, even though it is still lower than platinum. And the relationship between nitrogen content and ORR onset potential is not clear. HER activity of nitrogen-doped carbon is lower than platinum and it decreases with the growth of nitrogen content, which suggests that nitrogen may act as an inhibitor of hydrogen evolution. The potential range of ORR was estimated from the difference between ORR and HER. The result was that the nitrogen-doped carbon catalysts show wider range of potential window than those of platinum and non-doped carbon catalyst, which indicates that nitrogen-doped carbon has high selectivity for ORR.

Catalysis is among the most important applications within the field of nanoscience [1]. The large surface area of nanoparticles qualifies them naturally to act either as heterogeneous promoters for catalytic reactions or as a support for homogeneous catalysts. Especially magnetic nanoparticles are meant to overcome the most tantalizing drawback in homogeneous catalysis, i.e. reliable separation and recycling of often toxic and expensive transition metal complexes for more sustainability in catalysis. Thus, they simultaneously comply with economical and ecological requirements[2].
We have synthesized highly ferromagnetic, thermoresponsive nanomagnets with a graphene coated cobalt metal core to which amphiphilic N-isopropylacrylamide polymer branches were covalently attached. [3] This novel hybrid material could be further modified with a Pd-phosphine complex to catalyze Suzuki-Miyaura cross-coupling reactions. The heterogenized metal-complex acted as a ‘self-separating&’ catalyst. Thermally triggered switching of poly-NIPAM coated C/Co-nanoparticles in typical biphasic water/toluene reaction systems allowed for a temperature- controlled shift of the catalyst from the organic to water phase and vice versa. This enabled the catalyst to switch in the organic layer at reaction temperature and to return into the aqueous layer once the reaction mixture was cooled (ambient temperature; magnetic removal and reuse of the catalyst). Thus, the product phase was isolated via simple extraction/decantation. Moreover, the supported catalyst was recycled from the aqueous phase by taking advantage of the magnetic cores and reused over ten times.
[1] A. Schaetz, O. Reiser, W.J. Stark, Chem. Eur. J., 2010, 16, 8950.
[2] R. N. Grass, E. K. Athanassiou, W. J. Stark, Angew. Chem., 2007, 119, 4996.
[3] M. Zeltner, A. Schaetz, M.L. Hefti, W.J. Stark, J. Mater. Chem., 2011, 21, 2991

Advanced materials for electrochemical hydrogen evolution reaction (HER) are keys to the utilization and storage of renewable energy. Currently, the most effective electrocatalysts for the HER are platinum group metals (PGM). However, platinum is one of the most expensive metals due to the world&’s limited reserves. It remains challenging to develop highly active catalysts based on materials that are more abundant at low costs. Molybdenum disulfide (MoS2) with particle sizes in the range of 1-100 µm is a common dry lubricant and catalyst for hydrodesulfurization in petroleum refineries. However, MoS2 was not considered as a promising electrocatalyst until Hinnemann et al. reported that MoS2 nanoparticles were active for the HER. Since then, the interest in developing and using MoS2 and related metal chalcogenides such as WS2 and MoSe2 as the HER electrocatalysts has emerged. Here, we present a study using nanostructured MoS2 as electrocatalyst for the HER. Our results indicate that the MoS2 electrocatalysts prepared in this study are highly active for the HER. The MoS2 generates a current density of 10 mA/cm2 at -150 mV with a Tafel slop of 40 mV per decade. A detailed research is in progress to characterize and optimize the MoS2 electrocatalysts.

Catalysis is critically important to energy production and to meeting the environmental quality mission of promoting the development and utilization of clean, efficient, and reliable energy resources. It is essential to understand the relationships between the atomic and nanoscale structure of metal nanoparticles and catalyst supports and the crucial role these play in promoting or altering catalytic pathways. The key focus of this talk lies in the controlled synthesis of metallic catalysts with unique metal-support interactions and nanostructured nonmetallic catalysts for heterogeneous catalysis. Critical issues and emerging science and technology in heterogeneous catalysis will be discussed in context of controlled synthesis.
Acknowledgement: This work was performed at the Oak Ridge National Laboratory and the University of Tennessee and supported by Office of Basic Energy Sciences, U.S. Department of Energy, under contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.

Here we report the homogeneous synthesis of core@shell Pd147@Pt162 dendrimer-encapsulated nanoparticles (DENs) and the subsequent spontaneous reconfiguration of these structures to yield an inverted Pt147@Pd147Pt15 form. The monodispersity and small size of these nanoparticles (2.0 nm) allows for direct comparison to computations. However, for accurate correlation of theory and experiment it is important that the structure of the nanoparticle used for the experimental and theoretical activity determinations be the same. The key finding of this study is that the final inverted structure, determined by in-situ extended X-ray absorption fine structure (EXAFS) spectroscopy, correlates well with first-principles calculations. Specifically, DFT calculations predict that the inverted Pt147@Pd147Pt15 structure is more thermodynamically stable than the original Pd147@Pt162 structure.
The Pd147@Pt162 DENs are prepared through formation of a PdH followed by galvanic exchange, first for Cu and then for Pt. The DENs were examined by electron microscopy, UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), in-situ EXAFS, and X-ray absorption near edge structure (XANES) spectroscopy, and the results of all these analytical methods are consistent with structural inversion in which the more noble Pt partitions to the core and the shell becomes enriched in Pd. Larger Pd@Pt nanoparticles (>3 nm) are known to retain their core@shell structure. However, 1-2 nm nanoparticles tend to be structurally unstable. Therefore we infer that the observations reported here are driven by the energetics of the small number of atoms present in particles having sizes of <2 nm. The increased disorder and high energy edge and corner sites that are present in the smaller DENs help to initiate the structural rearrangement.

A new type of gold nanoparticles-coated composite spheres with chemically reactive poly(glycidyl methacrylate) colloids as cores is synthesized in raspberry-like fashion via a controlled assembly method. The surface coverage of the immobilized gold nanoparticles, which is controlled by the surface charge density of the poly(allylamine hydrochloride)-modified polymer spheres and the conformation of the adsorbed polyelectrolyte chains on the spheres, can be tuned with polyelectrolyte concentration, ratio of polymer spheres to gold nanoparticles, and the pH value of the solution. These composites exhibit an excellent catalytic activity and the fastest reported reduction of 4-nitrophenol with sodium borohydride is achieved within 76 s. Experimental results in all cases of our study revealed an nth order (n>1) of the p-nitrophenol/NaBH4 catalytic reaction by the prepared polymer composite particles. The apparent order of reaction is dependent on the total surface area of the coated gold nanoparticles on the polymer spheres, which can be closely correlated with the tunable gold nanoparticle surface coverage.

Gels and aerogels manufactured from a variety of nanoparticles available in colloidal solutions have recently proven to provide an opportunity to marry the nanoscale world with that of materials of macro dimensions which can be easily manipulated and processed, whilst maintaining most of the nanoscale properties. The materials carry an enormous potential for applications. This is largely related to their extremely low density and high porosity providing access to the capacious inner surface of the interconnected nanoobjects they consist of [1]. We will report on latest developments in this field in our group with respect to a) enzyme encapsulated QD hydrogels as a multi-functional platform in the development of optical biosensors [2], b) the electrocatalytical activity towards the oxidation of ethanol of a freestanding palladium nanoparticle aerogel with extremely high electrocatalytic current density and good durability and on the simple synthesis of bimetallic aerogels with their high performance as a new class of electrocatalysts for the oxygen reduction reaction [3].
1. a) J.L. Mohanan, I.U. Arachchige, and S.L. Brock, Science 307, 397 (2005), b) N. Gaponik, A.-K. Herrmann, and A. Eychmüller, J. Phys. Chem. Lett. 3, 8 (2012), c) P. Simon, E. Rosseeva, I.A. Baburin, L. Liebscher, S.G. Hickey, R. Cardoso-Gil, A. Eychmüller, R. Kniep, and W. Carrillo-Cabrera, Angew. Chemie Int. Ed. 51, 10776 (2012).
2. a) J. Yuan, N. Gaponik, and A. Eychmüller, Anal. Chem. 84, 5047 (2012) 5047, b) J. Yuan, N. Gaponik, and A. Eychmüller, Angew. Chem. Int. Ed. 52, 976 (2013).
3. a) W. Liu, A.-K. Herrmann, D. Geiger, L. Borchardt, F. Simon, S. Kaskel, N. Gaponik, and A. Eychmüller, Angew. Chem. Int. Ed. 51, 5743 (2012) 5743, b) W. Liu, P. Rodriguez, L. Borchardt, A. Foelske, J. Yuan, A.-K. Herrmann, D. Geiger, Z. Zheng, S. Kaskel, N. Gaponik, R. Kötz, T.J. Schmidt, A. Eychmüller, Angew. Chem. Int. Ed., DOI: 10.1002/anie.201303109

Site-Selective Deposition of Twinned Pt Nanoparticles on TiSi2 Nanonets by Atomic Layer Deposition and Their Oxygen Reduction Activities
Jin Xie, Xiaogang Yang, Binghong Han, Xiahui Yao, Ian Madden, Yang Shao-Horn, and Dunwei Wang*
For many electrochemical reactions such as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), catalysts are of paramount importance as they are necessary to minimize the kinetic overpotentials. Often, catalysts are prepared in nanoparticle forms to be dispersed on a conductive substrate to minimize electronic polarization. Presently, porous carbon is the most commonly used conductive support for ORR. But it has been recognized that the application of carbon present issues concerning stability. More important, the poorly defined structure of porous carbon makes it exceedingly difficult to study various electrocatalysts in great details, which is needed to fully understand their working, and more often, their failing, mechanism. To meet this challenge, we recently proposed and tested a carbon free catalyst system. The material platform we chose was a conductive, two-dimensional structure of TiSi2 nanonet. As a proof-of-concept, here we present the growth of Pt nanoparticles by atomic layer deposition (ALD). To our surprise and delight, the growth exhibited a unique selectivity with Pt nanoparticles deposited only on the top/bottom surfaces of the nanonet in nanoscale without mask or patterning. In addition, the as-grown Pt nanoparticles are of 5-fold, multiply twinned structures, preferably exposing {111} surfaces. Electrochemical characterizations showed that the resulting materials were indeed of high performance for ORR in alkaline solutions, opening up new doors to the construction of electrodes for applications such as fuel cells or metal air batteries.

This presentation will describe our work of studying the catalysis on metal nanoparticles at the single-nanoparticle level with single-molecule super-resolution imaging techniques. I will present how we interrogate the catalytic activity, mechanism, heterogeneous reaction pathways, selectivity, and surface-restructuring-coupled temporal dynamics of individual metal nanoparticles. I will also present our latest work in imaging and resolving catalytic reactions on a single shaped nanocatalyst at nanometer resolution, which maps the reactivity of different surface sites and uncovers diverse spatial reactivity patterns at the nanoscale. This spatial resolution of catalysis also enables us to probe communication of catalytic reactions at different locations on a single nanocatalyst, in much relation to allosteric effects in enzymes.

PdCu nanoalloy catalysts are promising alternatives to bulk noble metal catalysts like Pt and Au especially in oxidation reduction reactions (ORR). Thermal annealing and post-synthesis treatment are required for the activation and stability of these catalysts. Synchrotron-based time resolved in-situ x-ray diffraction (XRD) was used to investigate the temperature induced structural transformations in the physical mixture of Pd and Cu nanoparticles. The structural parameters of the nanoparticles probed were size, phase, composition and morphology as a function of temperature. The annealing procedure involved two stages (a) isothermal annealing at 300C (b) ramped annealing from 300C to 700C. Pd and Cu nanoparticle mixtures were dispersed on SiO2/Si, C-black and alumina and were annealed in forming gas and He atmospheres. Surface structure, composition distribution and ordering were also explored using transmission electron microscopy. Alloys of different structure and lattice parameters were formed with different mixing ratios of Pd and Cu nanoparticles (1:1, 1:3, 3:1 and 1:5). The particle sizes of the PdCu alloy nanoparticles were larger when annealed in forming gas than in He gas. The ordered B2-phase of PdCu was present when the mixtures (1:1) dispersed on SiO2/Si and C-black were annealed but this phase was absent in the mixtures dispersed on alumina. We found that the Cu and Pd atoms are randomly dispersed across the nanoparticles and there was no evidence of surface enrichment in the 1:1 binary mixture. The lattice parameter of different alloys as a function of Cu percentage will be discussed. These results are important for the design and nanoengineering of PdCu alloy nanocatalysts.

The lattice strain on the surface of a nanoparticle catalyst plays an important role in catalysis due to its influence on molecule sorption energies. This influence makes multi-metallic nanoparticles a great new tool to control the catalysis because the compressed or expanded arrangement of atoms at the interface of two metals takes place over more than a few atomic layers and generates a lattice strain on the nanoparticle surface. Our work focuses on developing new syntheses for well-defined multi-metallic nanoparticles and using them as model catalysts to study the surface lattice strain governed-catalysis. We demonstrated the relations between the lattice strain and electrochemical oxidation activity. Detailed structure and catalysis studies indicate that the activity enhancement is contributed by the surface lattice strain.

Noble metal nanocrystals (NCs) are useful catalysts for many chemical reactions. Bimetallic NCs can further increase the versatility of noble metal NCs by integrating the properties of different metals and/or by leveraging on specific component interactions to invoke a synergistic outcome. The synthesis of bimetallic NCs is challenging since the size, shape and distribution of components has to be controlled to provide structural diversity and to deliver the desired outcome. This presentation summarizes our recent work on the architectural controlled synthesis of bimetallic NCs in various structures including alloys, core-shell structures and more complex heterostructures.
For the synthesis of alloy NCs, we introduced an epiphytic relationship between the two component metals, where the reduction of the fast-reduced metal (epiphyte) depends on the availability of the fresh surface of the slow-reduced metals (host). In this way the two metals could be co-reduced with highly uniform intermixing. In addition, as the epiphyte-metal usually adsorbs preferentially on specific facets of the host metal, this strategy can be used to promote directional crystal growth. Multi-pot NCs with high-index facets can then be produced.
Using concave Au trisoctahedral NCs as the seeds, polyhedral Au@Pd core-shell NCs with customizable high-index Pd facets were synthesized including concave trisoctahedral, concave hexoctahedral and tetrahexahedral NCs with {hhl}, {hkl} and {hk0} facets respectively. The Miller indices of these NCs were also modifiable. High quality high-index NCs with customizable high-index facets are of strong interest to catalysis since a high density of steps and kinks on high-index facets is deemed to boost catalytic performance.
We have also developed a synthesis strategy capable of fabricating more complex heterogeneous metallic nanocrystals as an ensemble of component NCs. The strategy could program the shape and size of the component NCs and their spatial relationship. E.g. satellite NCs with the desired design (shape and size) may be placed exclusively on the corners and edges of various polyhedral central NCs. Similar to molecular engineering where structural diversity is used to create more property variations for application explorations, the architectural engineering of heterogeneous metallic nanocrystals can likewise increase the versatility of metallic nanocrystals.
We will also discuss how structural parameters such as shape, size and composition affect the catalytic properties of bimetallic nanomaterials.

Polymer electrolyte membrane (PEM) fuel cell performance degradation can be directly correlated with the stability and durability of individual material constituents comprising the membrane electrode assemblies (MEAs), including the electrocatalyst, catalyst support, recast ionomer, and polymer membrane, particularly materials associated with the cathode catalyst layer. The structural and chemical changes of the individual MEA constituents are being quantified via advanced electron microscopy methods to more fully understand the specific degradation mechanisms contributing to performance loss and to determine the interactions of these materials that will impact durability. These studies are used to establish critical processing-microstructure-performance relationships and to elucidate the individual materials changes contributing to measured MEA degradation, performance loss, and failure, e.g., degradation of carbon support structures, ionomer films, and quantifying Pt loss due to dissolution, migration, particle coalescence. Understanding and quantifying the structural and compositional changes of the materials comprising the MEA during electrochemical-aging will allow for the implementation of processing changes and critical materials development that are required for optimizing PEM fuel cell durability and performance.
Research sponsored by (1) the Fuel Cell Technologies Program, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy and (2) Oak Ridge National Laboratory&’s Shared Research Equipment (ShaRE) User Facility, which is sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy.

Hydrogen fuel cells offer potential to diversify the energy supply. Reduction of O2 to water using Pt on the cathode is rate limiting and represents a major cost obstacle. Reducing the Pt and increasing the activity can, in principle, be achieved using core-shell catalysts. In this approach a Pd core is used as a seed particle, produced by a colloidal synthesis, to reduce the amount of Pt; this process also induces a moderate lattice compression that increases the ORR rate [1]. A Pt shell is deposited on the core using galvanic displacement of an underpotentially deposited (UPD) Cu monolayer. Another promising method of producing Pd nanoparticle cores is the decomposition of Pd(II) acetylacetonate in the jet-flame Reactive Spray Deposition Technology (RSDT) process [2,3].
Coverage of the Pt on the Pd is an important parameter for catalysis: non-uniform coverage or segregation should be avoided. To verify Pt surface coverage and atomic structure the spatial distribution of the Pd and Pt is examined using an aberration-corrected STEM. Simultaneous imaging of the nanoparticles and acquisition of the Pd and Pt distribution can be achieved at atomic resolution. The HAADF intensity is proportional to the square of the average atomic number (Z2); the Z values for Pt (Z = 78) and Pd (Z = 46). The image intensity is also a function of the particle thickness and number of atoms aligned in the column parallel to the beam. Other factors affecting the HAADF image intensity are i) that the edges of the nanoparticle contain fewer atoms than the center and ii) there is a Debye-Waller effect. The nanoparticle size and distribution are important for parameters for catalysis. The crystal structure for both Pd (a = 3.890 Å) and Pt (a = 3.920 Å) is FCC.
The HAADF intensity is a function of imaging conditions which must be known to aid in quantitative analysis. The EELS signal can be collected simultaneously with the HAADF image to create line scans and two-dimensional mappings for further elucidation of the size and shape of the Pd cores. Differences in the two intensity profiles of the HAADF, the EELS signals and the XEDS data are examined considering the proposed core/shell structure. The presence of atomic Pd clusters are also monitored.
The authors would like to thank Matthew Janish, Vahid Rastegar and Lichun Zhang for helpful discussion. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
[1] J. Wang, H. Inada, L. Wu, Y. Choi, P. Liu, W. Zhou, and R. Adzic, J. Am. Chem. Soc. 131 17298-17302 (2009).
[2] J. Roller, M. Arellano-Jiménez, R. Jain, H. Yu, C.B. Carter, and R. Maric, J. Electrochem Soc. 160 (6) F716-F730 (2013)
[3] R. Maric, J. Roller, and R. Neagu, J. Thermal Spray Techn., 20(4) (2011) 698.

Promising catalytic activity from molybdenum disulfide (MoS2) in the hydrogen evolution reaction (HER) is attributed to active sites located along the edges of its two-dimensional layered crystal structure, but its performance is currently limited by the density and reactivity of active sites, poor electrical transport, and inefficient electrical contact to the catalyst. Here we report dramatically enhanced HER catalysis from metallic nanosheets of 1T-MoS2 chemically exfoliated via lithium intercalation from semiconducting 2H-MoS2 nanostructures grown directly on graphite. Our metallic MoS2 catalyst reaches an electrocatalytic current density of 10 mA/cm2 at a low overpotential of -187 mV vs. RHE and a Tafel slope of 43 mV/decade, and is among the best of MoS2 HER catalysts. Structural characterization and electrochemical studies confirm that the nanosheets of the metallic MoS2 polymorph exhibit facile electrode kinetics, low-loss electrical transport, and possess a proliferated density of catalytic active sites. These distinct and previously unexploited features of 1T-MoS2 make these metallic nanosheets a highly competitive earth-abundant HER catalyst.

The invention of the proton exchange membrane fuel cell (PEMFC) occurred over a half-century ago and, in spite of extensive developments of its science and its components, its widespread commercialization remains a challenge. Currently, improvements in the durability, performance and manufacturing cost of PEMFCs are required - all of which can be addressed with advances in catalyst function. Platinum (Pt) for example has long acted as the benchmark anodic and cathodic fuel cell catalyst, which makes resulting fuel cell devices less efficient due to Pt poisoning and slow kinetics for the oxygen reduction reaction (ORR). Recent work in our laboratories has shown that a block copolymer template-directed synthesis of mono- and bimetallic nanoparticle catalysts is an attractive method for preparing high performance PEMFCs catalysts. The content of this presentation will describe our investigation of the underlying principles for prescribing the size, spacing and composition of nanocatalysts that can be isolated from self-assembled block copolymers loaded with metallic anions and/or cations.
The approach offers several advantageous synthetic features compared to solvothermal catalyst synthesis. The approach is highly flexible and allows for the preparation and screening of a variety of mono- and bimetallic catalysts particles (Pt/Au, Pt/Ir, Pt/Pd, etc.). The method allows for the fine-tuning of the catalyst activity by selection of the block copolymer template precursor. The equivalent exercise of isolating and refining catalysts by solvothermal or direct metallurgy techniques often requires a vigilant redesign of the experimental conditions (ligands, solvents, temperature, pressure, new metal salt precursors, etc.) that control the growth and reduction kinetics of the reagents that create the nanocatalysts. Accordingly, The electrocatalytic activity of block copolymer template-directed bimetallic catalysts (Pt/Au, Pt/Ir, Pt/Pd) is presented. Details for the methanol and formic acid oxidation reactions and oxygen reduction reaction and tolerance to catalyst poisoning are discussed. Preliminary details on a structure-activity relationship between nanocatalysts and their self-assembled block copolymer templates is also discussed.

Enzyme based biofuel cells convert chemical to electrical energy employing enzymes as biocatalysts, with promising advantages in terms of cost, simple construction, renewable catalysts and fuels, while operating in mild conditions.1,2 The design of electrode materials is critical to overcome mass transport limitations, enzyme-electrode or mediator-electrode electron transfer limitations, and optimisation of enzyme loading on the electrode surface. Overcoming these issues, will eventually lead to an improvement in current (and hence power) generation. Our group is among the firsts to have pioneered the idea of using three-dimensional electrodes for the construction of biofuel cells, as it is already common practice in classical fuel cells.3,4
Here we aim at presenting the synthesis and performances of novel three dimensional macrocellular carbonaceous biofuel cell5 obtained via the Integrative Chemistry synthetic path.6 First, we developed a new synthetic pathway to produce a new carbonaceous foam material with increased porosity both in the meso and macroporous scale. We proved that by increasing the porosity of our three-dimensional foams we could increase the current density in our electrodes. Then, by choosing the right combination of enzyme and mediator, and the right loading of active components, we achieved unprecedentedly high current densities for an anodic system. Finally, we combined the improved cathode and anode to build a new membrane-less hybrid enzymatic biofuel cell consisting of a mediated anode and a mediator-less cathode.
1. S. C. Barton, J. Gallaway and P. Atanassov, Chemical Reviews, 2004, 104, 4867-4886.
2. R. A. Bullen, T. C. Arnot, J. B. Lakeman and F. C. Walsh, Biosensors and Bioelectronics,
2006, 21, 2015-2045.
3. V. Flexer, N. Brun, R. Backov and N. Mano, Energy Environ. Sci., 2010, 3, 1302-1306.
4. V. Flexer, N. Brun, O. Courjean, R. Backov and N. Mano, Energy Environ. Sci., 2011.
5. V. Flexer, N. Brun, M. Destribats, R. Backov, N. Mano, P.C.C.P., 2013, 15, 6437.
6. (a) R. Backov, Soft Matter, 2006, 2, 452-464; (b) N. Brun, S. Ungureanu, H. Deleuze and R. Backov, Chemical Society Reviews, 2011, 40, 771-788.

The main fundamental problems of polymer electrolyte membrane fuel cells (PEMFCs) to date are a low practical efficiency due to the high overpotential for the oxygen reduction reaction (ORR), the high amount of noble metal catalyst in use, and the degradation of the catalyst in a fuel cell during operation.
In order to develop improved catalysts a detailed understanding of the electrochemical interface is required - especially to clarify the relationship between the interface structure and the activity as well as the stability of the employed catalyst. In this study we discuss our recent work to utilize spectroscopic methods, i.e. in-situ FTIR spectroscopy and ex-situ Raman spectroscopy, to probe the interface structure and relate its properties to the performance of the catalysts. The investigated catalysts are synthesised according to a recently developed “tool box principle” that allows for systematic investigations [1].
[1] J. Speder, L. Altmann, M. Roefzaad, M. Bäumer, J.J.K. Kirkensgaard, K. Mortensen, M. Arenz; "Pt based PEMFC catalysts prepared from colloidal particle suspensions - a toolbox for model studies"; Phys. Chem. Chem. Phys., 2013, 15, 3602

Nanoparticles are typically used to catalyze the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) in PEM Fuel cells. They are normally made of non abundant or precious materials but the wide applications of fuel cell devices demand an important cost reduction. Especially a decrease of Pt loading of catalyst layers is desirable and this investigation deals directly with the synthesis and characterization of Ni@Pt core shell nanoparticles as well as the relationship between Pt distribution and catalytic activity for the ORR. Special attention is given to structural characterization by electron microscopy and a special technique to avoid change or damage to the particles under observation. The particle shape together with the elemental distribution of Pt on Ni for different Pt loadings (0-40%) are determined and related to the catalytic activity. Interestingly lower Pt loadings produce a wide distribution o Pt atom pair on the Ni core that activates a rather high catalytic activity. The TEM technique includes analysis of focal series and determination of the electron exit wave to obtain phase and amplitude images. They are used to establish the distribution and chemical nature of the atomic species reliably.

Oxygen reduction reaction (ORR) is one of the most important processes in energy conversion systems, such as fuel cells and lithium-air batteries. Pt-based materials are commonly used electrocatalysts for ORR, but troubled by the issues of performance degradation, resource scarcity, CO poising and methanol crossover. Recently it is found that the doped carbon nanostructures have high ORR catalytic activities and are free from the above listed issues. Thus, a research boom is currently ongoing and various carbon based ORR electrocatalysts have emerged. However, the origin of the ORR activity for the doped carbon materials is not clear, which is important for the exploration of new ORR electrocatalysts. In this study, the B-doped carbon nanotubes (CNTs) are firstly prepared, and are found to have rather good ORR activity in alkaline medium [1]. Theoretical calculations indicate that the vacant 2pz orbital of B conjugates with the carbon π system to extract the electrons. These electrons become quite active due to the low electronegativity of B and thus could be utilized by ORR. Likewise, for N doping, the carbon π electrons can be activated by conjugating with the lone pair electrons from N dopants. According to these experimental results and theoretical calculations, it can be speculated that the origin of the ORR activity for the doped carbon materials is the activation of carbon π electrons for effective utilization by ORR. To test this theory, two kinds of B&N co-doped CNTs dominated by bonded or separated B and N are intentionally prepared, corresponding to the intact or activated carbon π electrons respectively [2]. The experimental and theoretical results indicate that the bonded case can hardly break the inertness of CNTs, while the separated one can turn CNTs into excellent ORR electrocatalysts. This progress not only supports the theory of ‘activating carbon π electrons&’, but also demonstrates the crucial role of the doping microstructure on ORR performance, which is of significance in designing and optimizing the advanced C-based metal-free electrocatalysts.
References:
[1] L. J. Yang, S. J. Jiang, Y. Zhao, L. Zhu, S. Chen, X. Z. Wang, Q. Wu, J. Ma, Y. W. Ma, Z. Hu, “Boron-doped carbon nanotubes as metal-free electrocatalysts for oxygen reduction reaction” Angew. Chem. Int. Ed. 50(2011)7132
[2] Y. Zhao, L. J. Yang, S. Chen, X. Z. Wang, Y. W. Ma, Q. Wu, Y. F. Jiang, W. J. Qian, and Z. Hu, “Can boron and nitrogen codoping improve oxygen reduction reaction activity of carbon nanotubes? J. Am. Chem. Soc. 135 (2013)1201

Oxygen reduction reaction (ORR) is the key process of the cathode reaction of polymer electrolyte fuel cells (PEFCs). For practical fuel cells, platinum (Pt) is used as the ORR electrocatalyst. However, the demand for the replacement of Pt to a non-noble-metal is increasing because of the preciousness of Pt. The catalysts obtained by pyrolyzing organic carbons containing nitrogen are promising candidates. However, the long-period heat treatment caused formation of by-products such as metal carbides and desorption of the doped elements, i.e., the active reaction centers, which decreased the ORR electrocatalytic activity.
In the present work, we developed an instantaneous one-pot synthesis method of graphene doped with Fe and N (Fe-N-graphene) by using graphene oxides (GOs) with defined graphitic structure as a precursor. Although long-time heat treatment is necessary for existing pyrolysis method to form graphitic structure as mentioned above, the use of GOs as the raw materials allow us not to do long-time heat treatment.
GOs are treated in Ar atmosphere under 900 °C for 45s with Fe-N precursors to obtain Fe-N-graphene. The ORR onset potential of the Fe-N-co-doped in 0.5M H2SO4 is better than that of Fe-, N-doped graphenes. Thus, it was revealed that co-doping of Fe and N is necessary for the higher ORR activity. Futhermore, when the heat-treatment period made longer, the Fe-N coordination bond was broken and electron numbers for oxygen reduction reaction decreased.

Hydrogen is recognized as an ideal alternative fuel to the current energy, since it is an environmentally friendly fuel with non-polluting nature. Recently, the direct use of methanol to produce hydrogen has attracted a lot of attention because of the high-energy content of methanol. Here, we report Copper, zinc and gallium oxides (CuZnGaOx) obtained by co-precipitation, which has been identified as a highly active catalyst for the low temperature, direct stream reforming of methanol to supply hydrogen to various applications. However, there is no proper investigation to provide an elucidation of synthesis parameters that controls the performance of the final catalyst. In this study, a CuZnGaOx catalyst for direct hydrogen production at 150oC has been demonstrated, compared to the commercial catalyst, it shows two times enhancement of methanol conversion rate and 40 % decrease of CO formation. In addition, we had systematically study of operational conditions to elucidate the mechanism of this reaction and applied the X-ray diffractomer (XRD) and the temperature programmed reduction (TPR) to discover the correlation between the activity of catalysts, the reducibility of the copper ion, and the crystalline phase of the support oxides. The catalytic activity was found to be dependent on the preparation conditions that caused the changes in the catalyst characteristic, furthermore, we also discovered that aging process, storage of precursors, and heat treatment, all have certain influences on the CuZnGaOx catalyst. For the calcination process, it has been confirmed that the catalytic activity of the calcined catalysts are very sensitive to the calcination temperature. Therefore, to control the heat treatment condition is crucial for producing the desired catalyst. In summary, this work has shown the importance in the preparation of superior CuZnGaOx catalysts, and provided the relationships between the preparation conditions and the catalyst performances with fast differentiation techniques.

Due to its role in climate change, there is great interest in finding ways to take advantage of the vast amount of waste CO₂ we produce by its conversion to useful substances. This approach is currently impractical due to the high temperatures and pressures generally required for the synthesis of compounds using CO₂ as a precursor. To make direct CO₂ capture and conversion economically viable, new materials able to catalyze the conversion reactions at significantly milder conditions will be essential. In this work, we use DFT computations to design a dynamically tunable ferroelectric oxide-supported thin film catalyst that can capture CO₂ directly from the emission stream and convert it into methanol. One promising candidate for a dynamically tunable catalyst of this type is Zn_xO_y/PbTiO₃. We investigate the stability of ZnO grown on the ferroelectric and compare our results with experiment. Further, we demonstrate that switching the polarization of the ferroelectric substrate substantially changes the surface atomic and electronic properties of the heterostructure, thereby alternately encouraging strong CO₂ adsorption and desorbing the products. We also investigate the adsorption of other molecules on this catalyst. Our approach may lead not only to new technologies for reducing emissions, but also to novel catalysts that could decrease energy consumption for industrial-scale synthetic processes.

Oxides, in particular perovskites, have been investigated as replacement of Pt catalysts in oxidation reactions with mixed success. Recently, rare earth Mn-mullite (Sm, Gd)Mn2O5 were shown to surpass perovskite as effective catalysts for NO oxidation and be with 45% higher performance than costly platinum catalysts.[1] DFT calculations have shown that Mn-Mn dimers sites on the (100) step surface of SmMn2O5 along the octahedral Mn4+O6 edge-sharing chain are the active sites for activating O2 molecules.[1] In this work, SmMn2O5 and SmMnO3 were synthesized by a co-precipitation method followed by calcination at high temperatures. The phases were confirmed by XRD analysis. Differential scanning calorimetry and thermogravimetric analysis were employed to probe the solid phase transitions during calcination. To study the elemental composition of surface layer of the oxide compounds, we employ low energy ion scattering (LEIS). The presence of Mn on the surface layer was established for the first time by surface sensitive LEIS measurements as a function or scattering/sputtering cycles. In addition, Raman scattering spectra using both the 532 nm and 780 nm excitation radiation show that the most intense vibrational bands are observed above 600 cm-1 and below 300 cm-1. The high frequency modes (>600 cm-1) correspond to Mn-O stretching vibration of octahedra Mn4+O6 in the edge sharing chain. For mullite compounds, the pronounced band in the low frequency region (< 300 cm-1) collected with 532 nm laser line is composed of a doublet at 212 cm-1 and 197cm-1, which involve a Mn-Mn translation motion along the chain according to lattice dynamics calculations. This mode is absent in the perovskite structure which contains only isolated Mn4+O6 octahedra units sharing vertex O atoms. The assignment of this mode to a Mn-Mn dimer vibration is further confirmed by the observation that the 212 cm-1 band is resonance-enhanced by using an excitation wavelength of 780 nm to excite the Mn(d-d) transition. During the NO oxidation reaction at a temperature of 200°C performed in-situ in the Raman microscope, surface reaction intermediates such as nitrate species were detected on the mullite compound but not on the perovskite samples, which have no Mn dimer units. The Raman intensity of Mn-O stretching and doublet mode of Mn dimers decreased after exposing the catalyst to NO. These spectroscopic data suggest that the high oxidation catalytic activity is correlated to the presence of Mn-Mn dimer units. The detailed structural information obtained in this study and its correlation with the catalytic oxidation reaction open a way for utilizing Mn-mullite metal oxides as a catalyst for various real-world applications.
[1] Wang, W., G. McCool, et al. "Mixed-Phase Oxide Catalyst Based on Mn-Mullite (Sm, Gd)Mn2O5 for NO Oxidation in Diesel Exhaust." Science 337(6096): 832-835.

The water-gas shift (WGS) reaction (CO (g) + H₂O (g) →CO₂ (g) + H₂ (g)) is an integral part of fuel processing for the production of hydrogen. When hydrogen is used in the fuel cell operation, the WGS catalyst should be both active and stable in cyclic operation. Ceria is a superior support for noble metals in the low temperature shift (LTS) reaction. The favorable catalytic enhancement is attributed to high oxidation storage capacity (OSC), multiple oxidation states (Ce⁴⁺/Ce³⁺) that increase oxygen vacancies, metal activity enhancement, dispersion stabilization of the catalytic material and water splitting on oxygen vacancies. The reducibility and catalytic activity of ceria is significantly enhanced by the presence of a small amount of a transition metal. However, complete conversion of CO has not been achieved at sub 250 °C temperatures (1). This work explores three different ceria supports with an identical Pt loading of 5 wt. % to identify the most efficient ceria supported Pt catalysts for the low temperature (200-350 °C) WGS reaction. The Pt is applied by the jet-flame deposition process Reactive Spray Deposition Technology (RSDT). The supports were prepared by a sol gel process, RSDT and one is a commercial ceria prepared by calcination of cerium oxalate. The microstructural properties of the ceria supports were investigated by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area, Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). The prepared catalysts were tested for CO oxidation, Temperature Programmed Reduction (TPR) and CO chemisorption. The processing-structure-properties relationship are correlated to identify the ceria support with the most superior CO conversion efficiency at temperature below 250 °C. The CO oxidation temperature was found to be lowest at 225 °C for the ceria with crystallite size 5.6 nm.
Authors would like to acknowledge support from the University of Connecticut and Materials Genome Initiative for funding this work.
Reference:
Luengnaruemitchai, A., Osuwan, S. and Gulari, E., 2003. Catalysis Communications, 4(5), pp. 215-221.

ZnO nanotetrapod (ZnO-TP) photoanodes have been fabricated by a simple thermal evaporation method followed by characterization of their morphological, structural, optical and photoelectrochemical properties. The reaction time was found to be a critical factor in the synthesis of well-defined tetrapod nanostructures. The crystallinity of the grown tetrapods was investigated using X-ray diffraction as well as Raman spectroscopy. The photoluminescence (PL) spectra of the fabricated ZnO nanostructures showed two peaks; a near-band-edge (NBE) emission in the UV region and a broad deep-level emission (DLE) in the green emission region. Used as photoanodes to photoelectrochemically split water, the 90 min-treated ZnO-TP electrodes showed a photocurrent density of 0.4 mA/cm2 under AM 1.5G illumination (100 mW/cm2, 0.5 M Na2SO4), a significantly greater photocurrent than the bulk ZnO counterpart electrodes. The transient photocurrent measurements revealed exceptional stability of the as-fabricated ZnO-TPs.

The understanding of the design of catalysts for low temperature catalytic CO and alcohol oxidations is important for exploring a wide range of applications in sustainable energy and environment. This report describes recent findings of our investigations of alloy catalysts for catalytic oxidations of CO and alcohols (e.g., methanol and ethanol). For catalytic CO oxidation, selected examples including AuCu, AuAg and AgCu nanoparticles with a size of around 4~5 nm will be discussed, highlighting the structural and composition effects on the catalytic activities. For catalytic alcohol oxidation, selected examples including PtCo and PtNi of 3~5 nm sizes will be discussed, focusing on their comparison with Pt catalysts and their potential use for catalytic heat generation for exploring thermoelectric properties. Structural insights from high energy X-ray diffraction characterization of the alloy catalysts will also be discussed. The findings on the structure-activity correlation have implications for the design of low-temperature catalysts for applications in sustainable energy production, conversion and storage.

Due to their powerful neurotoxic properties, organophosphates (OPs) are potent chemical warfare agents and are among the more toxic organic chemicals produced on an industrial scale. Two strategies for degrading organophosphates have been demonstrated. First, a biochemical approach relies on the enzyme organophosphorus hydrolase (OPH) to catalyze hydrolysis of organophosphates. Second, an inorganic approach utilizes fluorine-doped titania replicas of diatom frustules to degrade organophosphates through both light dependent and independent mechanisms. We have combined these strategies with the aim of developing a novel, highly active multi-modal material for OP degradation. By immobilizing OPH onto the surface of fluorine-doped titania frustule replicas, three modes of OP hydrolysis have be leveraged in a single material: 1) OPs are enzymatically hydrolyzed by titania-bound OPH, 2) titania is able to degrade the OPs in a photocatalytic manner, 3) fluorine associated with the titania frustule replicas is able to induce OP hydrolysis independent of light. Increased thermal stability of OPH is an additional advantage observed with immobilization on titania frustules, allowing the kinetics of both the organic and inorganic based hydrolysis modes to be optimized with increased reaction temperature. Finally, this new material takes advantage of the inherent benefits of diatom frustules, namely their high surface area, complexity, porosity as well as their natural abundance and low cost.

Structural and electronic properties of highly mono-disperse (geometric standard deviation ~1.1) Pd, Pd-Ag and Pd-Cu alloy nanoparticles were studied using the in-situ XRD and XPS, respectively. Structural properties have been studied by varying the temperature from 250K to 350 K in the pressure range of 1x10-4 mbar to 75 mbar. It is observed that Pd makes a transition from α-phase to β-phase depending on the hydrogen pressure and temperature while no such transition is observed in Pd-Cu and Pd-Ag nanoparticles in the whole range of temperature and pressure used in this study. Electronic properties of the Pd-Ag and Pd-Cu confirm the complete alloy formation. Core level and valance band shifts clearly show that both the size and alloying effects are clearly responsible for these shifts. In comparison to Pd, Valance band centroid of Pd-Cu and Pd-Ag alloy nanoparticles shift towards Fermi edge. This indicates less reactivity of Pd-Cu and Pd-Ag in comparison to Pd nanoparticles as is clearly observable in the structural properties. Hydrogen sensing behavior of Pd, Pd-Ag and Pd-Cu alloy nanoparticles will be carried out to confirm the predictions about hydrogen interaction of these Pd, Pd-Ag and Pd-Cu nanoparticles drawn on the basis of the structural and electronic properties. This study may be of potential importance in the hydrogen related industries.

One of the major challenges for vehicle emissions control relates to the deactivation of present day noble metal (Pt/Pd) emissions after-treatment catalysts by sulfur oxides (SO _x (x = 0 - 4)) [1, 2]. Sulfur oxides chemisorb onto and react with the active catalyst sites, preventing reactant access and modifying the surface chemistry. Metal-sulfate formation due to the interactions with SO _x with the catalyst metals and supports are associated with changes in various structural, morphological, and electronic properties [3, 4]. Despite a plethora of experimental and computational studies, SO _x interactions with metal surfaces and their impact on catalytic activity are not clearly understood. In the present study, we attempt to explore the fundamental and molecular level SO _x (x = 0 - 4) chemistry in terms of interactions and oxidation reaction pathways on Pt(111) and Pd(111) surfaces using first principles density functional theory (DFT) [5]. We identified various stable configurations, revealed the charge redistribution patterns, and observed the molecular orbital interactions of SO _x on both surfaces (Pt and Pd) during adsorption. Our study suggests that the metal-sulfate formation is part of a series of successive exothermic processes and favored on both metal surfaces. The possible reaction pathways and estimated activation barriers for various elementary steps are found to be in good agreements with the available experimental results. Pre-exponential factors are estimated for SO _x oxidation reactions, which are in close agreement with the transition state theory (TST) for typical Langmuir-Hinshelwood type surface reactions. This comprehensive and comparative study provides important insights about SO _x chemistry on Pt and Pd surface, which can be useful to design and improve sulfur resistant catalysts materials.
References:
[1] T. Kolli, M. Huuhtanen, A. Hallikainen, K. Kallinen, R. Keiski, Catal. Lett. 127 (2009) 49-54.
[2] A. Russell, W.S. Epling, Catal. Rev. Sci. Eng. 53 (2011) 337-423.
[3] J.A. Rodriguez, J. Hrbek, Acc. Chem. Res. 32 (1999) 719-728.
[4] H.N. Sharma, S.L. Suib, A.B. Mhadeshwar, in: Novel Materials for Catalysis and Fuels Processing, ACS, 2013, In press.
[5] G. Kresse, J. Furthmüller, Phys. Rev. B. 54 (1996) 11169.

Light cycle oil (LCO), which accounts for approximately 10 -20 % of FCC products, is a highly interesting blending stock to diesel pool because of the boiling point range similarity. The major disadvantages of LCO are primarily related to the high content and the structural complexity of mainly bulky multiring polynuclear aromatics. Recently, selective ring opening (SRO) approach has been proposed as an alternative. Yet, none of the studied SRO based catalysts (i.e. zeolites, ordered mesoporous silica, mixed oxides) achieved the great potentials of SRO process, owing to structural instability, diffusion limitations, and fast deactivation. Therefore, metal-containing catalysts of improved acidity and mass transport were synthesized via newly developed synthesis approach. In particular, MCM-41 aluminosilicate mesostructures was assembled from amorphous-silica alumina seeds via mixed-templating mediated hydrolysis using Tetramethylammonium Hydroxide. The novel MCM-41 aluminosilicate was characterized by high surface area (ca. 800 m2g-1), high pore volume, and high surface acidity. In addition, the novel support exhibited well-ordered-highly stable MCM-41 phase. It was found that novel metal-containing MCM-41 aluminosilicate exhibited much better performance in the hydrogenation of naphthalene, compared to corresponding traditional MCM-41 aluminosilicate.

Automobile exhaust contains significant amount of unburned hydrocarbons. Hydrocarbon mixture contains a large variety of hydrocarbons such as ethylene, acetylene, propane and propene. Removal of unburned hydrocarbon requires a catalyst, which can oxidize these hydrocarbons at a considerably lower temperature. Therefore, mixed MoO3-ZrO2 and MoO3-CeO2 of a wide range of molar ratios were synthesized using different methods that include coprecipitation, hydrothermal, and amine assisted hydrothermal. It was revealed by the XRD patterns of MoZr with different Mo/Zr ratios that different crystalline phases coexist upon using preparation methods such as coprecipitation and hydrothermal methods (i.e. ZrO2 (both monoclinic and tetrahedral), MoO3 and MoZr mixed phase). It was also shown that samples obtained by hydrothermal method have much lower crystallite sizes. Thermal treatment at temperature higher than 550 °C up to 900 °C showed that hydrothermal methods significantly stabilized the tetragonal zirconia phase. More importantly, it was found that samples obtained by hydrothermal crystallization method exhibited ordered mesoporous structure.These findings were further supported by Raman spectra. Interestingly, Thermal analysis (TGA/DSC) revealed that hydrothermal method can produce greater stabilization of Mo, as compared to coprecipitation (i.e. there was less weight loss at high temperature). MoO3-CeO2 mixed oxides displayed better stability than Mo-Zr oxide.

Proton exchange membrane fuel cells (PEMFCs) are highly efficient energy systems which can directly convert chemical energy into electrical energy, and most important, produce no emissions except water. However, its relatively low power output compared to that of its price has prevented it from many practical applications. Nanoparticles have been widely known to possess catalytic capabilities. Marvrikakis et al have predicted that gold nanoparticles that are platelet shaped and have direct contact to the substrate to be the “perfect” catalysts. We have shown that such particles can be synthesized by first starting with the standard two phase method, which produces spherical gold (Au) and gold-palladium (Au-Pd) nanoparticles. When a solution containing these particles is spread at the air water interface, X-ray reflectivity and EXAFS spectroscopy indicate that some of the Au or Pd atoms are removed, as the water displaces the hydrophobic thiol chains from the particle surface, resulting in platelet shaped particles. Furthermore, if the particles are spread on a Langmuir trough where surface pressure can be applied to compress them, they form films consisting of monolayers. These monolayer films can then be deposited onto a solid substrate, such as the PEM membrane where the particle surface can make direct electronic contact with the fuel cell membrane, greatly enhancing the efficiency of electron-ion separation and thus increasing the ion current through the membrane.
A series of parallel experiments were done to explore the various factors that may affect the performance of PEM fuel cell, such as hydrogen flow rates, type of nanoparticles, surface pressure of the LB trough etc. We found that under the optimal hydrogen flow rate of 40 ccm (cubic centimeter per minute), the deposition of gold nanoparticles monolayers compressed at 3mN/m resulted in highest increase in the power output of the fuel cell.

Catalytic performance and surface chemistry of Fischer-Tropsch cobalt catalyst supported on silica nanosprings (Co/SiO2-NS) has been evaluated and compared with conventional silica gel supported cobalt (Co/SiO2-gel) catalyst used in the reforming of syngas to higher alkanes. To obtain Co/SiO2-NS catalysts, nanosprings were first grown via a vapor-liquid-solid mechanism and subsequently decorated with Co nanoparticles by thermal assisted reduction of cobalt (III) acetylacetonate in an H2/Ar at 500°C. Traditional Co/SiO2-gel catalysts were prepared by incipient wetness impregnation. Both catalysts were characterized by means of scanning and transmission electron microscopes, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller measurements, and temperature programmed reduction. The performances of the two types of Fischer-Tropsch catalysts were tested in a fixed-bed microreactor at 230°C with atmospheric pressure of 2:1 ratio of H2:CO. Co/SiO2-NS, which had 75 times less gravimetric Co content than the sol-gel catalyst, showed similar selectivity to C5+ hydrocarbons and a higher CO conversion rate of syngas to higher order alkanes. These results were attributed to higher Co dispersion on the nanosprings and greater access to the entire surface of the catalyst.

Synthesis of aromatic amines by selective hydrogenation of aromatic nitro compounds has emerged as one of the most important and, synchronously, challenging task in synthetic organic chemistry. Amines are highly valuable intermediate chemicals particularly used in the manufacture of pharmaceuticals, polymers, dyes and cosmetics [1]. Although various noble metal nanoparticles supported on a metal oxide, such as Au/CeO2, Au/Al2O3, Pt/Al2O3, Au/Fe2O3 and Au/C, have been successfully used to reduce nitroaromatic compounds, these catalysts require harsh reaction conditions and are characterized by poor selectivity [2]. The selective hydrogenation of nitro compounds to produce amines is not trivial because of the unavoidable formation of azo- and azoxy-derivatives during the reaction process. Therefore, exploring new catalytic systems offering high chemoselective production of aromatic amino-compounds is an ongoing research.
Gold supported on TiO2 is the most promising catalyst for hydrogenation or oxidation of alkene, carbonyl and nitro compounds. The reactivity of Au/TiO2 catalysts has been related to the nature of TiO2 support and the small size of Au particles. In this work, we demonstrate novel mesoporous Au-sensitized TiO2 nanoparticle assemblies (Au-MTA) as high-effective catalysts for the selective transformation of nitroaromatics into the corresponding amines. Namely, we utilized deposition-precipitation of gold hydroxides within the pores of mesoporous TiO2 nanoparticle ensembles (MTA) [3]. The obtained materials (Au-MTA) possess a continuous network of interconnected gold and anatase TiO2 (ca. 9 nm) nanoparticles with controllable gold particle size (i.e. ranging from 3 to 10 nm) and exhibit large and accessible pore surface area (ca. 100-160 m2/g), as evidenced by SAXS, XRD, TEM and N2 physisorption measurements. Interestingly, Au-MTA show outstanding performance for the selective reduction of nitro into amine groups using sodium borohydride as reducing agent. We also addressed the role of supported gold particles on the chemoselective response of Au-MTA, showing that the yield and product composition are highly related to the Au loading and particle size. As a result the 2% Au-MTA catalyst associated with 5-nm-sized Au nanoparticles has found to be a prominent catalyst for the reduction of nitroaromatics, not only giving exceptionally high selectivity (>96%) and conversion yield (>92%) to the corresponding amines, but also allowing the efficient synthesis of aromatic amino-compounds at ambient conditions.
References
[1] P. F. Vogt and J. J. Gerulis in Ullmann&’s Encyclopedia of Industrial Chemistry, Aromatic Amines, (Wiley-VCH Verlag GmbH & Co., Weinheim, 2005).
[2] a) X. Ke, X. Zhang, J. Zhao, S. Sarina, J. Barry and H. Zhu, Green. Chem. 15, 236 (2013). b) A. Corma and P. Serna, Science, 313, 332 (2006).
[3] I. Tamiolakis, I. N. Lykakis, A. P. Katsoulidis and G. S. Armatas, Chem. Commun., 48, 6687 (2012).

CO oxidation (2CO+O2->2CO2) on metal surfaces (noble metals: Pt and Au; transition metals: Ni and Cu) is often viewed as an ideal reaction for fundamental investigations of heterogeneous catalysis. CeO2 support plays important roles to disperse the metal catalysts over a high surface area, and also as an oxygen buffer material by a reversible valence change of the cerium ions (2CeO2 ->Ce2O3 + 1/2O2) with formation or elimination of surface oxygen vacancies. Particle shape and especially the type of crystalline faces exposed on the surface of crystallites are believed to play a major role in surface oxygen exchange of CeO2. In this study, we has prepared a set of high surface-area CeO2 nanopowders using low-temperature solution based hydrothermal methods that will allow for control of shape and size of the crystallites. We are testing CO oxidation using CeO2 nanorods and nanocubes-supported metals (Pt, Au, Ni, Cu) clusters. Our preliminary measurements exhibit that CeO2 nanorods-supported metals show superior activity for low temperature CO oxidation. We will present our understanding about the role of CeO2 support in the shape of nanorods, nanotubes, or nanocubes with reactive {110}, {100}, {211} faces on the crystal surface on low temperature CO oxidation.

The generation of catalytic nanostructured materials under mild conditions is a major research thrust given global environmental and energy issues. Inspired by nanomaterial synthesis found in nature, biological material templates have been shown to create various catalytic nanomaterials under ambient conditions. The diatom-based silica precipitating R5 peptide (SSKKSGSYSGSKGSKRRIL) is one prominent example. R5 can also template other nano-scale materials, largely due the sequence&’s cationic nature and its ability to self-assemble into macromolecular templates that arise from amphiphilic segments of the peptide. In this work, R5 is conjugated to the surface of PAMAM dendrimers and used to template Pd nanomaterials. Covalently linking R5 to PAMAM through the N and C termini alters the inherent self-assembly properties of the peptide, resulting in different morphologies of Pd nanomaterials. The assembly of Pd in solution is also substantially altered, as determined using DLS and SAXS. These templated-driven morphological and conformational differences result in Pd nanomaterials with increased catalytic activity for the hydrogenation of allyl alcohol as compared to R5 templated Pd (TOF of ~5000 vs ~3000 mol product*(mol Pd*h)-1). Such results are of the highest reported in the literature for the hydrogenation of allyl alcohol with similar materials. Taken together, the use of peptide-dendrimer conjugates provide a means to alter biotic/abiotic interactions creating materials with alter morphologies and improved properties.

Solid acid catalysts have been widely used in petrochemical industry. Recently, development of acid catalysts suitable for biomass process has been important due to its increased utilization. However, conventional acid catalysts such as zeolite are not proper in converting heavy petroleum fraction and polymeric biomass compounds to fuel and value-added chemicals, due to their difficult accessibility for reactants and poor catalytic stability. In order to overcome these limitations from narrow pore size of conventional catalysts, several research efforts have progressed for the synthesis of large-pore catalysts such as mesostructured materials. Despite these efforts, the catalysts showed insufficient acidity and stability to be applied in practical refinery industry.
Herein we have prepared three dimensionally open-porous acid catalyst for enhanced acidity and stability compared to the conventional catalysts. The catalyst has uniform size (ca. 500nm), wide-open pore (over 10nm) and high surface area (ca. 500m2/g). In addition, acid properties (acid type, strength and amount) of the catalyst are easily adjustable by changing ratio of its components in preparation step. It was also possible to enhance Broslash;nsted acidity by using pH adjusting agent in preparation step. The catalytic activity of the material was tested in cracking reaction of petrochemicals and hydrolysis of biomass-derived materials. In cracking of 1,3,5 triisopropylbenzene, these catalyst showed the highest performance and long-term stabililty compared to conventional catalysts. They also showed good activity in hydrolysis of sucrose. Based on these results, our material is one of promising catalysts for petrochemistry and biomass processes.
This subject is supported by Korea Ministry of Environment as "Converging technology project (202-091-001)”

The incorporation of a metal dopant in TiO₂ structure is known to loose the bonding of neighboring oxygen atoms at the surface. Thus oxygen atoms are readily released from the lattice of the metal-doped TiO₂, and vacancy sites remained on the metal-doped TiO₂ are easily oxidized by gas phase O₂. As a result, metal-doped TiO₂ can be a better oxidant than the undoped one, and it is more likely to engage in an oxidation reaction by a Mars-van Krevelen mechanism in which surface lattice oxygen oxidizes a reagent that is adsorbed on the catalyst surface, and an oxygen vacancy leaving behind on the surface is then oxidized with O₂ gas.
Here, a facile preparation method of Fe-doped TiO₂ nanoparticles was proposed to improve the oxidation characteristics of TiO₂ support over the CO oxidation reaction. Fe-doped TiO₂ nanoparticles were prepared by a gel-hydrothermal method. The method allows one to prepare Fe-doped TiO₂ particles with uniform nanoparticles. The amount of Fe dopant was easily controlled by using different amount of Fe(NO₃)₃. The concentration of Fe dopant into the TiO₂ framework was quantified by inductively coupled plasma-atomic emission spectroscopy. Morphology and microstructure were investigated by high-resolution transmission electron microscopy and X-ray diffraction, Raman spectroscopy, electron paramagnetic resonance spectra analyses. The findings indicate that Fe dopant is substitutionally doped with replacing to Ti⁴⁺ cation. The catalytic activity in CO oxidation reactions showed that Au catalyst supported on Fe-doped TiO₂ containing 6 % Fe dopant showed an outstanding oxidation performance.

Hydrogen (H2), a sustainable and environmentally attractive energy carrier, is a potential secondary energy vector that would enable clean energy storage and transduction. Herein, we introduce a novel heterogeneous catalyst for H2-generation from FA, using a Fe-complex (Diphenylphospine/Fe(BF4)2), covalently immobilized on SiO2 particles. Catalytic H2 production from FA takes place at near-ambient temperatures (60-100 C) with high selectivity and activity. The present data show that a novel heterogeneneous Fe-PPh2@SiO2 catalyst is a remarkable system with regard to H2 generation from FA. The catalyst shows excellent stability and reusability, being able to generate up to 7lt of H2 within 7.5 hours. Advanced Electron Paramagnetic Resonance (EPR) spectroscopic methodologies including Parallel-Mode EPR and 2-dimensional HYSCORE Pulsed EPR spectroscopy allow direct monitoring of the catalytic centers. Detailed thermodynamic data reveal that a synergistic mechanism exists where the particle-oxide surface enhances the H2 generation by lowering the energy-barrier of the Arrhenius activation step by ΔEpsi;=4-6kJ/mole.
Acknowledgements
This research has been co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: THALIS. Investing in knowledge society through the European Social Fund.

Hydrotalcite precursors of La modified Ni-Al2O3 and Ni-SiO2 catalysts prepared by co-precipitation method and the catalytic activities were examined for the production of COx free H2 by CH4 decomposition. Physico-chemical characteristics of fresh, reduced and used catalysts were evaluated by XRD, TPR and O2 pulse chemisorptions, TEM and BET-SA techniques. XRD studies showed phases due to hydrotalcite-like precursors in oven dried form produced dispersed NiO species upon calcination in static air at and above 450°C. Raman spectra of deactivated samples revealed the presence of both ordered and disordered forms of carbon. Ni-La-Al2O3 catalyst with a mole ratio of Ni:La:Al = 2:0.1:0.9 exhibited tremendously high longevity with a hydrogen production rate of 1300 mol of H2 (mol Ni)-1. A direct relationship between Ni metal surface area and hydrogen yields are established.

Nanomaterials have a number of advantages in catalysis when compared to their bulk counterparts. As metal particle size reaches the nano scale, the surface area to volume ratio greatly increases along with the percentage of atoms occupying catalytically active corner and edge sites. Creating bimetallic nanoparticles can enhance catalytic activity, because one metal influences the properties of the second metal through various electronic and geometric effects. An important bimetallic effect is lattice strain, the expansion or compression of a metal&’s lattice due to contact with a second metal, which causes a change in the metal&’s electronic properties through a shift in the d-band center. This electronic shift directly influences catalytic activity by altering the adsorption energy of reactant molecules.
This study focuses on the effect of lattice strain on catalysis for the relatively unstudied rhodium system. A series of bimetallic Pd and Rh nanostructures were synthesized, with varying degrees of lattice strain. Core-shell Pd@Rh nanocubes were synthesized by epitaxially growing a layer of Rh over shape-controlled Pd substrates. Hollow particles comprising Rh were synthesized by treating the Pd@Rh particles hydrothermally, forming hollow Pd-Rh phase-segregated alloy nanocubes and pure Rh hollow porous nanocubes. The crystal structure and extent of lattice strain for these structures was studied with X-ray diffraction and scanning transmission electron microscopy, revealing the largest degree of lattice strain for the heterogeneous-alloyed particles due to the many contact surfaces between Rh and Pd.
In order to determine the effect of lattice strain on catalysis, a series of electrocatalytic reactions was performed with each of the synthesized structures in addition to pure Pd nanocubes for comparison. The model fuel cell reactions of carbon monoxide oxidation (CO stripping), formic acid oxidation, ethanol oxidation in acidic and alkaline solutions, and oxygen reduction were performed, and each of these reactions exhibited unique trends in activity that could not be explained by composition effects alone. Lattice strain was found to alter the reactivity of both Pd and Rh, most notably in the oxygen reduction reaction in which the relation between composition and activity formed a volcano curve. Moving forward, lattice strain can be further tuned for other metal systems to optimize nanocatalysts for use in a variety of energy applications.

The increasing world population and the world dependence on portable energy sources make lithium-air batteries one of the most promising alternative systems. These batteries are good candidates to substitute the current lithium ion technology, because they present high theoretical energy densities compared with gas combustion (13 kW h Kg^-1). Their large energy capacity arise from a continuous reducing atmosphere of oxygen molecules in the cathode, which react with lithium ions during the discharge process, in contrast with the limiting volume of conventional electrodes. However, to deliver high power, some challenges have to be overcome, like poor cyclability, reversibility, and large overpotential for the charge process. According to the literature, the main discharge products in the presence of organic solvents are lithium superoxide (LiO₂), lithium peroxide (Li₂O₂) and lithium oxide (Li₂O). However, these reduction processes are poorly understood, and problems like low oxygen solubility in organic media and sluggish electronic transfer calls for methods that will help elucidate and enhance these processes, to achieve the theoretical energy density. In this context, our study aims to clarify the discharge mechanisms involved in the oxygen reduction reaction (ORR) in organic solvents using fluorine doped tin oxide (FTO) and glassy carbon (GC) electrodes modified with carbon nanoparticles. We applied these mechanisms in a mathematical model based on the work of Henderson et al., to modulate experimental electrochemical impedance spectroscopy (EIS) data. This study used a normal three-electrode electrochemical cell. LiClO₄ (0.1 mol L^-1) dissolved in 1,2-dimethoxyethane with saturated O₂ was used as electrolytic solution. The potentiodynamic profile of ORR in FTO without modified electrodes showed that pristine FTO was active for ORR and the oxygen evolution reaction (OER). However, the performance decreased with the numbers of cycles, because sluggish reaction during the oxidation process contributed to electrode surface passivation. These processes were catalyzed in modified electrodes, because ORR occurred at 200 mV more positive potentials and cyclability increased as compared with FTO alone. The carbon nanoparticles may account for this phenomenon, because they present peroxidase-like behavior, as reported elsewhere. This could facilitate O₂ reduction and oxidation of peroxide products. In the GC electrodes, previous results showed that the carbon nanoparticles effect was more pronounced on the products oxidation than on the discharge process. We adjusted the experimental results using the developed EIS model, to obtain surface coverage degree and kinetic parameters, like rate constants, to investigate the role of the carbon nanoparticles in these effects which can be used to develop specific strategies to increase the rate-determining process.

Catalysis is indispensable to chemical processes and relevant to many aspects of modern life. Owing to the intriguing electronic structures and good ionic properties, multivalent transition metal oxides have attracted attention as key catalysts for various energy and environmental applications. Here, we demonstrate that the brownmillerite SrCoO_2.5 (SCO) can be a good cathode material for sold oxide fuel cells and rechargeable batteries and a catalyst material in catalytic gas converters due to the open oxygen frameworks. We have grown epitaxial SCO thin films by pulsed laser epitaxy with two different crystallographic orientations, i.e. (001) and (114), on (001) and (111) YSZ substrates, respectively, in order to study the oxygen vacancy channel (OVC) orientation dependent oxygen reduction reaction activities. Note that the former film has the OVC running parallel to the substrate surface, while the latter has OVC tilted ~60^o away from the normal to the substrate normal. Temperature and oxygen partial pressure dependent electrochemical characterizations were performed with electrochemical impedance spectroscopy. By comparing the impedance data, we found that one can drastically increase the surface oxygen exchange rate approximately up to two orders of magnitude, when the OVCs are opened to the surface. The improved oxygen reduction kinetics is attributed to a substantial decrease in the thermal activation in the (114)-oriented SCO film. In addition, a preliminarily test with a brownmillerite SCO thin films reveals that the films can catalytically oxidize CO at relatively reduced temperatures (~300 ^oC). Thus, our epitaxial approach can pave a novel pathway to providing precise interpretation of oxygen reduction reactions and to developing oxide-based energy materials.
The work was supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.

Multilayers of thin ceramic and metal films are model systems for applications like the newest generation of micro solid oxide fuel cells and sensors, the emerging field of Redox RAM (RRAM) data memory and electrochemical supercapacitors. Despite increasing interest, the physical laws that control the properties of nanocrystalline materials at metal/ceramic interfaces are far from well understood [1]. In nano-crystalline ceramic/metal multilayers over half of all the atoms participate in or are influenced by defects, i.e. the interface, grain boundaries (GB) and triple junctions (TJ). The presence of these defects significantly alters the thermodynamic free energy of the system, allowing for new physical properties that may not comply with expectations.
In this study, we investigated the model system Pt/ZrO2-multilayers. The investigation focuses on the solubility and diffusion of oxygen in noble metal GB and TJ. This approach is chosen with the objective of introducing a new concept for catalytic materials whose active catalytic site is no longer only at the surface but also at the GB and/or TJ [2]. Rutherford backscattering spectroscopy provided the global composition and individual thickness of the layers in the multilayer, while atom-probe tomography (APT) was used to investigate the GB and TJ. APT is the only characterisation technique that is able to map the location of both the heavy matrix atoms (Pt) and the light oxygen atoms at an atomic level in 3D [3], and is thus the technique of choice to obtain information about local composition at GB and TJ. Using this technique enables us to study the diffusional pathways in nanocrystalline thin film metal/ceramic combinations, revealing both structural and crystallographic influence on the diffusional performance [4, 5]. This approach leads to the first direct experimental observations of the catalytically nanoscopic active three-phase boundary and its oxygen transport mechanisms - information that is essential for the design of functional devices from these films. This knowledge will contribute to the manufacturing of more energy-efficient sensors and fuel cells for portable electrical power generation. As well as in the semi-conductor industry, where the integration of novel electroceramic materials and hence new nano-engineered metal/ceramic interfaces is essential to fulfill the demand for faster, higher and more-reliable computing capacity.
References
[1] Finnis, M.W., Condensed Matter, 1996. 8(32): 5811.
[2] Ryll, T., et al., Advanced Functional Materials, 2011. 21(3): 565.
[3] Kelly, T.F. and D.J. Larson, Annual Review of Materials Research, 2012. 42(1): 1.
[4] Stender, P., Z. Balogh, and G. Schmitz, Physical Review B, 2011. 83(12): 121407.
[5] Araullo-Peters, V.J., et al., Scripta Materialia, 2012. 66(11): 907.

One of key issues in the development of renewable energy production technologies is the discovery of efficient and cost-effective catalysts for use in electrochemical energy conversion processes such as oxygen reduction reaction in fuel cells, and reduction of triiodide ions in solar cells. In fuel cells, and dye-sensitized solar cells, energy conversions need precious metals - primarily Pt - as catalysts to promote electrochemical reactions on the cathode. The limited resources and high cost of noble metal catalysts impede commercialization. Doped carbon nanomaterials are attractive in principle for catalytic applications because their unique molecular structure facilitates the reduction reaction. In addition, there are even more appeals because of their extreme flexibility, the large surface area, excellent mechanical and electrical properties, and highly stability in the extreme environment. A fundamental understanding of carbon-based catalyst design principle that links material structures to the catalytic activity can accelerate the search for highly active and abundant metal-free catalysts to replace platinum. In this talk, we present a first-principles study of reduction reaction on nitrogen-doped graphene. We demonstrate that the catalytic activity primarily correlates to charge and spin densities of the graphene. The nitrogen doping and defects introduce high positive charge densities that facilitate the reduction reaction on graphene surface. The identified active sites are closely related to doping cluster size and dopant-defect interactions.

The polymer electrolyte fuel cell (PEFC) is a promising power source for fuel cell vehicles. Two major issues that are necessary for the wide spread use of PEFC are to reduce the cost and enhance the stability of the electrocatalyst. In order to realize the commercialization of PEFC, it is important to clarify the mechanism of the degradation and improve the stability of the electrocatalyst. In the previous study, we investigated the effect of humidity in the air on the structural change of a commercial Pt/C electrocatalyst. The in situ TEM observation in humidified air revealed that the structural change was caused by the active movement of Pt particles on the carbon support, leading to the coalescence and growth of Pt particles [1,2].
In this study, we investigated the effect of pretreatment of Pt/C on the degradation mechanism in humidified air by in situ TEM. The catalyst sample (commercially available Pt/C) was observed either as received or after washing with ultrapure water. TEM observation was conducted using a Hitachi H-9500 high-resolution 300 kV analytical TEM equipped with an AMT CCD camera system. The procedure for TEM observation was described in the literature [2].
The morphological changes of the catalyst sample were dynamically and statically observed under humidified air condition. In contrast to the previous results with as-received Pt/C with round-shaped Pt particles [2], most of the Pt particles of pre-washed Pt/C were polyhedral-shaped. Also, active movement of the particles was not observed in the pre-washed sample. This morphorogical change was probably caused by the removal of impurities used in the synthesis. Therefore it appears that remaining impurities such as surfactants affect the structural stability of Pt/C electrocatalyst.

Acknowledgments
This work was partly supported by Grant-in-Aid for Scientific Research (C) 23510136 from the Japan Society for the Promotion of Science (JSPS).
References
[1] T. Shimizu, D. Imamura, T. Yaguchi, T. Kanemura, and T. Kamino, JARI Res. J., 2012-03-02 (2012).
[2] T. Shimizu, D. Imamura, T. Yaguchi, T. Kanemura, and T. Kamino, ECS Trans., 50 (2), 1439 (2012).

Numerous studies on the design of catalysts for fuel cells have highlighted how nano-materials enhance the activity and selectivity of catalysts. The nanoparticles supported on the metal oxide surface reportedly exhibit unique catalytic performance. The electronic interaction between the metal nanoparticles and the oxide support induces a change in the charge state of the nanoparticles. The negatively or positively charged nanoparticles were observed depending on the defects of the oxide surface, the morphology of the supported nanoparticles, or the interface between nanoparticles and the support. The excess charge of a nanoparticle affects the activity of a catalytic reaction on the surface of the nanoparticles. Here, the structural stability and charge redistribution of oxide supported nanoparticles with the size were calculated using DFT study. We investigated the details why the catalytic performance can be improved by changing the charge state using a modified kinetic model. By controlling the charge state of nanoparticles, the CO oxidation reactivity of Ag nanoparticles was found to be similar for Au nanoparticles.

Transparent UV protective coatings were developed by incorporating nano-TiO2 into waterborne acrylic systems to provide long-term UV protection for UV sensitive color cool roofing. Water based high crystalline TiO2 nanoparticle suspension was prepared via a gel-sol method at a basic pH. The TiO2 nanoparticles have an average size of 20 nm and are stable against agglomeration. As prepared TiO2 nanosuspension is readily to be well dispersed in commercial waterborne acrylic resin system. The fabricated TiO2/acrylic nanocomposite coating is high transparent with demonstrated UV blocking capability. It is also proved that surface modification of Nano-TiO2 with a SiO2 insulation layer would surpass the catalytic activity of Nano-TiO2 and improve the UV protection for UV and photocatalysis sensitive dyes.

New functional nanocatalyst materials are key to the realization of future sustainable energy storage and conversion technologies. Their successful development and optimization requires insight into the relation between atomic scale structure and macroscopic catalytic activity. Their implementation in viable energy technologies requires knowledge of their interaction with other device or technology components at the mesoscale.
In this talk, we will highlight some of our recent work focused on the preparation, characterization and understanding of electrocatalytic nanomaterials for energy technologies. Our discussions will include metal alloy catalysts for fuel cell cathodes and chemical fuel production, as well as metal oxides for electrolyzer anodes. Topics will touch upon oxygen reduction and evolution, oxidation of organic molecules as well as the electroreduction of CO2.

We have developed a multiscale Quantum Mechanics/Molecular Mechanics (QM/MM) method to study strain effect on the oxygen reduction reaction (ORR) based on Cu-Pt core-shell nanoparticles. The multiscale method allows us to examine particle sizes ranging from 3 nm to 8 nm, far beyond the present capability of QM simulations. We have determined the oxygen adsorption energy - the well-established descriptor for ORR activity - as a function of nanoparticle size and thickness of Pt shell. We find that the Pt-Cu core-shell nanoparticles have higher ORR activities than the flat Pt (111) surface, consistent with experiments. We predict that the optimal size of the nanoparticle should exceed 7 nm to reach the volcano peak of ORR activity. By examining the effects of “ligand”, strain and quantum confinement, we conclude that the enhanced ORR activity of the core-shell particles is entirely due to the strain on the Pt shell. The correlations between the oxygen adsorption energy, strain and d-band center shift are established, from which a simple computational strategy can be envisaged to quickly screen and/or guide the design of core-shell particles for superior ORR performance.

The electrodeposition of Pt alloy films is examined and compared to the characteristics of the constituent elements. Pt deposition at negative potentials revealed an unanticipated self-terminating characteristic that enables controlled deposition of Pt monolayer films from a K2PtCl4-NaCl electrolyte.1 Despite the deposition overpotential being in excess of -1 V, Pt deposition is quenched at potentials just negative of proton reduction by alteration of the double layer structure induced by a saturated surface coverage of underpotential deposited hydrogen, (Hupd).1 The surface may be reactivated for Pt deposition by stepping the potential to more positive values where Hupd is oxidized and fresh sites for adsorption of PtCl42- become available. Periodic pulsing of the potential enables sequential deposition of two dimensional (2-D) Pt layers to fabricate films of desired thickness relevant to a range of advanced technologies in a manner that is tantamount to wet atomic layer deposition (ALD). In the presence of iron group metals, the Hupd induced suppression is lifted by underpotential deposition of the iron group metal as revealed in voltammetric studies of singular surfaces and thin film deposition studies of binary Pt100-xNix and Pt100-xCox alloys.2,3 Bulk alloy formation is facilitated by ongoing Pt deposition that incorporates the iron group metal in accord with the excess enthalpy of alloy formation. The performance of these materials as electrocatalysts will also be briefly detailed.4,5
1. Y. Liu et al., Science, 338, 1327 (2012).
2. J.J. Mallett et al. J. Electrochem. Soc,155, D1 (2008).
3. C.A. Hangarter et al., to be submitted.
4. Y. Liu et al, J. Phys. Chem C., 116, 7848 (2012).
5. T.P. Moffat et al, J. Electrochem. Soc., 156, B238
(2009).

The controlled tailoring of nano-porosity in metallic thin films of several 100 nm thickness using dealloying has gained renewed attention in recent years, as such nanoporous thin films are candidates for applications in sensors, plasmonics, fuel cells and super-capacitors. In this contribution, the physical mechanism of nanoporosity formation during the dealloying process of binary PtAl- and ternary PtYAl-alloy thin films is examined using focused ion beam (FIB) nanotomography and Rutherford backscattering spectrometry (RBS). The selective dissolution of Al from the Pt-alloy compound results in a branched nanoporosity with a mean branch thickness below 10 nm and a pore intercept length of 10 nm.
The dynamics of nanoporosity formation is found to obey to a superposition of a reaction diffusion equation describing the linearly propagating diffusion front ¹ and a secondary slower dissolution process away from the moving interface. An increased Al content as well as a partial substitution of Pt by Y results in a slower dealloying kinetics with a slower linearly propagating diffusion front.
The resulting nanoporous Pt thin films perform exceptionally well as oxygen reduction electrodes in a micro-solid oxide fuel cell setup in the temperature range from 473 to 1073 K² and allow for up to 93% absorption of light in the visible spectrum.
¹ PRL 107, 225503 (2011), ² PRB 84, 184111 (2011)

The proliferation of low-temperature fuel cells is hampered by the large amounts of Pt required to catalyse its electrode reactions. A state-of-the-art fuel cell requires ~0.5 g of Pt per kW of power, meaning that a 100 kW car would require 50 g of Pt. With ~200 tonnes of Pt produced each year, there is not enough available for low-temperature fuel cell cars to be produced on a large scale. In order to overcome this challenge, we need to improve the kinetics for the oxygen reduction reaction (ORR) on the cathode side and thereby allow for a reduction of the Pt loading. The development of more active and stable catalysts could achieve this aim. In particular, alloying Pt with other metals, can improve its activity by up to an order of magnitude [1-3].
Alloys of Pt with e.g. Ni and Co have been investigated for several decades, and show increased activity for the ORR. However they are not adequately stable for long time periods due to the many start up and shut down cycles required of a fuel cell during its operational lifetime [4]. More recently, alloys of Pt and early transition metals and lanthanides, also show significantly improved activity over Pt, as well as high stability [5].
The performance of Pt alloys will be limited by their stability towards corrosion in the hostile environment of a fuel cell. Therefore, it is crucial to understand why some alloys are more stable than others, in order to optimize the stability. We investigate the simplest diffusion mechanisms for the solute metal in the different alloys, using Density Functional Theory to calculate the size of the diffusion barriers in the alloy. This allows us to elucidate the trends, which will then be correlated with the known stability of the alloys, in order to determine the parameters relevant for long-term stability.
[1] H. A. Gasteiger, et al. Appl. Catal. B 2005, 56, 9. [2] J. Greeley, et al. Nature Chem. 2009, 1, 552. [3] I. E.L. Stephens, et al. Energy Environ. Sci. 2012, 5, 6744. [4] Chen et al., J. Electrochem. Soc. 2010, 1571, A82-A97. [5] M. Escudero-Escribano, et al. J. Am. Chem. Soc. 2012, 130, 16476.

Reduction of the usage amount of expensive Pt is a key for the real commercialization of PEFCs. Core/shell structured catalyst is a strong candidate for the reduction and it has been recognized that the ORR activity can be enhanced with the core/shell structured catalysts. In this study, Au and Pd NPs were selected as the core materials and a new process for the Pt shell formation was developed. The newly developed process is a modification of the conventional Cu under potential deposition (Cu-UPD) technique. The modified Cu-UPD process doesn&’t need precise potential control and is easy to shift to mass-production. For example, carbon supported Au NPs (Au/C) are dispersed into water containing sulfuric acid and copper sulfate and stirred with co-existence of Cu mesh under Ar atmosphere. When the Au/C contacts with the Cu mesh, the Cu mesh is oxidized and releases electrons with the difference in the redox potentials between Au and Cu. The released electrons reduce the Cu cations and the Au core surface is covered with the Cu shell. Finally, the Cu shell is replaced with the Pt shell with addition of Pt cations after removal of the Cu mesh.
When the Au NPs were used as the core material, durability of the carbon supported Au core/Pt shell structured catalyst (Pt/Au/C) was inferior to that of the reference carbon supported Pt catalyst (Pt/C). The inferior durability of the Pt/Au/C catalyst was caused from dissolution of the Pt shell into the Au core and the dissolution came to light when smaller Au NPs were used. It was found that, however, addition of Ru into the Pt shell drastically suppresses the dissolution and improves the durability.
In case of carbon supported Pd core/Pt shell structured catalyst (Pt/Pd/C), 30-40 % of the Pd core was dissolved out with the potential cycling durability test (rectangular wave, 0.6-1.0 V vs. RHE, Ar saturated 0.1 M perchloric acid at 333 K and 353 K). The TEM line analysis revealed that the core/shell structure was retained even after the durability test. Interestingly, after the durability test, the Pt/Pd/C catalyst showed three times higher ORR mass activity with respect to the initial ORR mass activity of the Pt/C catalyst. Morphology of the Pt/Pd/C catalyst became rounded shape and the mean diameter of the catalyst decreased after the durability test. The enhanced ORR activity of the Pt/Pd/C catalyst is considered to be due to compressive strain of the Pt shell and reconstruction in the surface Pt atoms with the potential cycling durability test.

Controlling crystal structure of multimetallic alloy nanoparticles (NPs) can provide a great opportunity to tune and optimize NPs catalysis for fuel cells applications, but still lack of systematically study in both synthesis and mechanism. Starting with monodisperse bimetallic FePt NPs that are made in non-aqueous solution synthesis, here we demonstrate the intermetallic ordering in face centered tetragonal (fct) FePt NPs leads to drastic enhancement in oxygen reduction reaction (ORR) catalysis comparing to traditional disordered face centered cubic (fcc) FePt NPs. The fct-FePt NPs shows 200 %-300% activity and much enhanced stability comparing to the fcc-FePt NPs. The atomic-scale structural analysis and theoretical simulation reveal this structure-induced enhancement is contributed to the optimization of surface energetics of FePt NPs for ORR induced by intermetallic structure, which provides the best kinetics for adsorption and desorption of oxygenated intermediated species in the ORR catalysis. Extended fabrication of intermetallic FeMPt (M=Co, Ni and Cu ect.) gives the opportunity to further enhance the ORR catalytic activity and durability due to the combination of intermetallic structure effect and multimetallic composition effect. The related synthetic control and theoretical calculation of FeMPt NPs for ORR will be discussed. By rational tuning of the intermetallic FeMPt NPs composition and structure, the promising catalysts for fuel oxidation reactions with strong CO-tolerance can also be developed, which will also be included in this talk. This structure-control principle presents a new model to advanced NP catalysts with simultaneous enhancement in both activity and durability for practical applications.

Nanoengineering the composition and structure of noble metal containing catalysts is an important pathway for developing active, robust and low-cost catalysts for energy and environment applications, which has been a major driving force for the exploration of various binary and ternary platinum-based alloy catalysts for fuel cells. In comparison with the extensive studies of binary alloy catalysts for oxygen reduction reaction, the exploration of ternary nanoalloy catalysts in the past few years has led to many intriguing discoveries in terms of understanding of the detailed structural effects on the enhanced catalytic activities. This presentation describes findings of the correlation between the atomic scale structure and the electrocatalytic performance of ternary nanoalloy catalysts treated at different conditions for oxygen reduction reaction, aiming at providing a new fundamental insight into the role of the detailed atomic alloying and interaction structures in the electrocatalysis. Major findings in the studies of certain ternary nanoalloys will be discussed to highlight the importance of ternary composition for the design and preparation of the electrocatalysts.

Metal air batteries offer the promise of significantly increased energy density relative to state of the art batteries. However, the slow kinetics of the oxygen reduction reaction are a significant barrier to implementation. Preparation and characterization of a multicomponent composite electrode based on a carbon-based current collector, conducting polymer, and metal nanoparticles will be described. The role of each individual composite component will be independently assessed. The minimum quantity of catalyst needed to maximize oxygen reduction activity will be defined. In addition, mechanistic studies of the entire composite will be undertaken to determine the stoichiometry of the reduction process and to evaluate the role of electrolyte. The results presented here will have relevance toward the future development of nonaqueous metal air batteries.

The use of fuel cells is currently limited by the oxygen reduction at the cathode. The oxygen reduction reaction (ORR) is sluggish and most electrocatalysts are based on expensive and non-renewable materials. On the other hand, doped carbon-based materials have demonstrated promising performance while being relatively inexpensive [1]. Reduced graphene oxide (rGO) aerogels are particularly interesting materials for making electrodes due to their excellent electrical conductivity and high specific surface area [2]. We have developed a simple method for preparing nitrogen-sulfur co-doped rGO aerogels using a nitrogen and sulfur-rich dye molecule. The aerogels can be further doped with boron using solid precursor. Such doped aerogels have demonstrated high activity towards the oxygen reduction with exceptionally low overpotentials. Characterization of the materials and analysis of the catalytic activity will be presented.
[1] Gong, K. et al. Science 323, 760 (2009).
[2] Zhang, X. J. Mater. Chem., 21, 6494 (2011).

Advances in the past decade to synthesize macromolecules and modify structures at the atomic level have enabled significant control in the design of functional materials, including those that are active in catalysis. We have been exploring various methods to exert new forms of control in catalysis.
Because of the relative ease to modify, functionalize, and synthesize polysiloxanes, these compounds offer interesting possibilities to greatly influence the properties of a catalytic system. These potentials are illustrated with three catalytic systems. In the first system, core-shell carbosiloxane nanocages that contain carboxylic acid and silanol in the interior are shown to stabilize cations of uncommon oxidation state, such as Co(I). This stabilized cation can be converted to a selective oxidation catalyst for epoxidaiton. In the second example, polysiloxanes provide a platform to generate a Au-metal oxo interface for selective oxidation catalysis. In the third example, modified spherosiloxanes are shown to modify the catalytic properties of Sn and change the product selectivity in the conversion of glucose.

Mesoporous silica nanoparticles consist of arrays of parallel pores with a uniform length of ~100 nm and uniform effective diameter of ~1.5 nm or above. NMR studies confirm that multi-functionalization enables incorporation not just of catalytic groups within the pore interiors, but also of secondary groups which can tune system thermodynamics and kinetics to enhance yield. For example, addition of hydrophobic groups enhances the yield in the esterification of free fatty acids (a pretreatment step in biodiesel production), noting that H2O is a reaction product. This effect could reflect enhanced intrinsic mobility within the pore, reduced pore loading, and/or a shift of reaction equilibrium. The effect is strongest for highly restricted transport (single-file diffusion). This phenomenon is elucidated by analysis of a spatially coarse-grained model where the pore interior is compartmentalized into cells and diffusion is treated as hopping between cells. This formalism allows efficient analysis of the reaction-diffusion process via both kinetic Monte Carlo simulation and a generalized hydrodynamic theory [Wang et al., J. Chem. Phys. 138 (2013) 134705].

The atomic, nanoscale, and three dimensional (3-D) properties of catalysts play an important role in their ultimate activity and selectivity as industrial materials. However, it is also important for these properties to be ascertained as close to reaction conditions as possible. This study brings together advanced methods in the scanning transmission electron microscope with a series of ex-situ and in-situ treatments to understand the fundamental properties of zeolites and Fischer-Tropsch (FT) catalysts. Zeolites are important due to their wide range of regular pore structures and catalytic site geometries that allows tuning of the catalytic properties. This means that identifying the active site locations and density is important, as well as providing a pore size or surface area large enough for the molecules of interest to enter and react. If a large enough pore size cannot be found, delamination of a layered zeolite may become necessary. In FT catalysis, it is important to understand the size, morphology, and distribution of the active metal species within its support. We will show this can be accomplished using a combination of 3-D electron tomography and ex-situ gas reactions.

The combined focused ion beam/scanning electron microscopy/energy dispersive X-ray spectroscopy (FIB/SEM/EDX) system is a novel tool in the field of automotive catalysis. Automotive emissions such as SOx, NOx, and particulate matter (PM) are regulated throughout the world, requiring the use of multiple aftertreatment components such as the diesel particulate filter (DPF), diesel oxidation catalyst (DOC), three-way catalytic converter (TWC) and selective catalytic reduction (SCR). These aforementioned aftertreatment components consist of robustly designed, multifunctional catalyst nanoparticles supported on ceramic filters which are subject to thermal and chemical aging leading to significantly degraded performance including increased engine emissions levels and decreased fuel economy. Multiscale, multidisciplinary analytical tools are required to investigate this type of sample since the component sizes themselves are generally large (10s of cm to asymp;1/2 m) while component aging mechanisms occur on the nm-µm scales. In particular, this study used the FIB/SEM/EDX system to investigate the aging of the diesel particulate filter (DPF) due to engine lubrication-derived ash accumulation and to explain macroscopic catalyst performance-related data. Ash is comprised of incombustible, inorganic lubrication additives which are carried to the catalytic filter components via carbon nanoparticles (soot), and have been shown in this study to be complex structures of Ca, Zn, and Mg in the form of oxides, sulfates and phosphates. The FIB/SEM/EDX allows for the direct chemical and morphological observation of interfacial and sub-surface/bulk properties of aged catalytic aftertreatment components, where such data is necessary for understanding the complex catalyst aging mechanisms. Successful utilization of the FIB/SEM/EDX system for the automotive aftertreatement field has been shown in this study for the first time with many surprising and significant findings. Although the samples investigated in this study are very different from those typically found in FIB literature, the authors have shown that the FIB/SEM/EDX system is a valuable tool in this field, especially for the investigation of nm-µm size intraparticle structure and nm-µm interfacial details at the aged catalyst surface.

A morphology of hollow, double-shelled submicron particles is generated through a rapid aerosol based process. The inner shell is an essentially hydrophobic carbon layer of nanoscale dimension (20 nm) while the outer shell is a hydrophilic silica layer of approximately 40 nm, with shell thickness being a function of particle size. The particles are synthesized exploiting concepts of salt bridging to lock in a surfactant (CTAB) and carbon precursors together with iron species in the interior of a droplet. This deliberate negation of surfactant templating allows a silica shell to form extremely rapid, sealing in the organic species in the particle interior. Subsequent pyrolysis results in a buildup of internal pressure forcing carbonaceous species against the silica wall to form an inner shell of carbon. The incorporation of magnetic iron oxide into the shells opens up applications in external stimuli responsive nanomaterials. Additionally, these materials can incorporate a number of metal oxides for rattle type geometries in catalysis.

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. Acetylene impurities in ethylene can cause deactivation of the polymerization catalyst if not removed from ethylene. An effective catalyst for this reaction converts all of the acetylene to ethylene without further converting any ethylene to ethane such that there is a net increase in the amount of ethylene. Well-dispersed Pd supported on metal oxides exhibits high activity for acetylene removal, but limited selectivity and long-term stability. 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 the ability of the catalyst to over hydrogenate to form ethane, produce oligomerization products, and form coke on the catalyst surface. Recent efforts have demonstrated that intermetallic Ni-Zn may be a suitable replacement for Pd-based catalysts based on DFT calculations and experimental validation. Replacing Pd-based catalysts with base metal Ni-based catalysts would be highly beneficial in terms of cost. We report on the catalytic selectivity of unsupported bulk intermetallic Ni-Zn and Ni-Ga catalysts for acetylene semi-hydrogenation. Bulk intermetallic Ni-Zn and Ni-Ga catalysts contain little structural and compositional variance, a property that is not easily attainable with supported catalysts. Co-impregnation using nickel and zinc nitrates results in the formation of ZnO, which remains after a high temperature hydrogen treatment. There is no evidence supporting the formation of intermetallic Ni-Zn using a co-impregnation technique. We provide the first report on the catalytic properties of intermetallic Ni-Zn and Ni-Ga for acetylene semi-hydrogenation though the use of a bulk synthesis technique. The difference in activity and reactivity amongst the two Ni catalysts are significant and will be highlighted.

Tuning the composition of bimetallic catalysts as well as controlling their interaction with oxide supports are critical in order to control catalytic properties for hydrogenation and oxidation reactions. In this respect, a tremendous work has been made in recent years to prepare Au-based bimetallic catalysts due to the enhancement of catalytic properties when combining Au with noble metals in nanoalloys [1]. However, up to now, while Au-Pd systems have been widely studied mainly for oxidation reactions, Au-Rh nanoalloys have been rarely envisaged [2, 3].
Similarly, the nature of the interaction between these bimetallic systems and oxide supports is not well understood due to the poorly defined morphology of most of the oxides used. Therefore, using well-defined oxide supports offers opportunities to simplify the nature of the bimetallic particles - support interaction.
The objective of the present study was to prepare Au-M (M = Rh, Pd) bimetallic systems by comparing the efficiency of colloidal or impregnation techniques for obtaining nanoalloys with fine tuning of their composition. These Au-M bimetallic systems were supported on TiO2 nanorods to provide catalytic systems with well-defined metal-support interaction for HRTEM characterization.
Rutile nanorods were obtained first by peptization under acidic conditions using HClO4 and hydrous titania as precursor. Second, a hydrothermal treatment was performed at 200°C for 48 h under strong acidic conditions (pH = 0.8) in the presence of a shape controlling agent, MgSO4 in order to obtain rods.
Results clearly demonstrate the superiority of colloidal techniques, particularly for the Au-Rh case, in comparison to impregnation of the different metallic salts followed by reduction. While impregnation leads to the formation of a high proportion of Au or Rh monometallic particles, precise tuning of colloidal preparation conditions led to Au-Rh nanoalloys with controlled composition. Optimization of colloidal conditions was however found to be critical to avoid redissolution of Rh during preparation and formation of isolated Rh raft-like particles. Similar conditions were obtained for the Au-Pd bimetallic systems. Characterization by HRTEM, XPS, and EDX was performed after deposition on TiO2 nanorods. Finally, in the context of fuel upgrading, the catalysts have been evaluated in benzene hydrogenation in the presence of toluene and tetralin hydroconversion, both at high hydrogen pressure (4 MPa). In this contribution, the effect of gold addition on the hydrotreating and thioresistance properties of rhodium will be presented and discussed on the basis of in-depth structural characterization.
[1] D. Uzio, G. Berhault, Catal. Rev. 52 (2010) 106-131.
[2] E.R. Essinger-Hileman, D. DeCicco, J.F. Bondi, R.E. Schaak, J. Mater. Chem. 21 (2011) 11599-11604
[3] Á. Kukovecz, G. Potari, A. Oszko, Z. Konya, A. Erdohelyi, J. Kiss, Surf. Sci. 605 (2011) 1048-1055.

The structural features of metal nanoparticles such as crystallite size and shape are important to catalytic activity and selectivity. Thus, correlating the performance of metal nanocatalysts to these structural features is important to understanding and designing better catalysts. Here, the size and shape effects of Pd nanocrystals are examined as they are applied as semi-hydrogenation catalysts. Selective hydrogenation is essential in food, pharmaceutical, petrochemical and polymer industries; however the semi-hydrogenated products are often susceptible to isomerization and over-hydrogenation. Since this transformation is sensitive to the structure of the catalysts, this reaction is ideal for examining the role of structural features of Pd nanocatalysts. Seed-mediated growth methods were used to achieve samples composed of different sized {100}-terminated Pd nanocubes and {111}-terminated Pd octahedra, which served as model systems to evaluate the role of surface structure to activity and selectivity. The size of the nanocrystals was easily tuned by controlling the amount of metal deposited per seed. The selection of capping agent provided a means of manipulating the final shape of the nanocrystals. These samples were characterized by SEM and TEM. X-ray photoelectron spectroscopy was used to correlate electron binding energies to the catalytic activities of Pd nanocrystals and also to evaluate the effectiveness of oxygen-plasma treatment as a means of capping agent removal. The catalysis results from this study will facilitate the decoupling of the electronic and geometric parameters of Pd nanocatalysts.

Complex MoVTeNb oxide materials rich in M1 phase catalyze the oxidative dehydrogenation (ODH) of ethane to ethylene with outstanding efficiency [1]. However, the nature of the active site and its position on the surface of M1 crystals is still not completely resolved. It has been observed that the surface of M1 phase undergoes reversible changes when used for the selective oxidation of light alkanes. These changes have been attributed to the formation of a thin active layer upon reaction conditions [2]. In this study, we monitored the surface structure and chemistry for the first time under oxidative atmosphere by in-situ transmission electron microscopy with atomic resolution using environmental transmission electron microscopy (ETEM) and aberration-corrected S/TEM with gas stage holders. In a first step, measurements at room temperature did not show any amorphous layer covering the M1 phase. When heating the material under vacuum, the structure collapses due to reduction-sublimation processes and different binary mixed oxides are segregated. In-situ ETEM studies of M1 in 10 mbar oxygen/argon (23%/77%) at 350 °C showed that after 5 minutes most of the tellurium units disappeared from their position at the center of hexagonal channels of M1, but the crystal framework is not affected. Since the M1 crystal structure is destroyed within a few seconds under vacuum at even lower temperatures, the latter observation suggests that oxygen can be used to stabilize M1 phase. Specific building units of M1 phase are observed on top and lateral of the M1 needles, indicating that active sites can be present in all facets of the M1 particles under reaction conditions. Electron energy loss spectroscopy is underway to determine the V5+ distribution on the surface, which is increasingly believed to play an important role in catalytic performance of the M1 phase in ODH. Further in-situ measurements in ETEM under different atmospheres are planned in order to unravel the surface chemistry of M1 and the relationship with its outstanding activity and selectivity in ethane oxidative dehydrogenation.
References
[1] F. Ivars, P. Botella, A. Dejoz, J.M. Lopez Nieto, P. Concepcion, and M.I. Va zquez, Topics in Catalysis Vol. 38, Nos. 1-3, July 2006
[2] M. Hävecker et al. Journal of Catalysis 285 (2012) 48-60

Lignin is an abundant, alkyl-aromatic polymer found in plant cell walls that is connected by various C-O and C-C linkages. Traditionally, lignin depolymerization has been facilitated with homogeneous acid or alkaline catalysts, which present challenges in recycling. To that end, there has been recently increased interest in the development of heterogeneous catalysts for lignin deconstruction. Here, we report the development, characterization, and screening of a library of heterogeneous, basic catalysts for lignin depolymerization. In particular, we prepare a library of hydrotalcite catalysts, and screen their activity on a model compound that exhibits an aryl-ether linkage typical of lignin at conditions concomitant with reported alkaline depolymerization of lignin. We demonstrate that a 5% Ni/HTC catalyst is particularly effective at C-O bond cleavage in both a non-phenolic and a phenolic model dimer and we examine the regeneration of the Ni-HTC catalyst via calcination and rehydration. Post reaction analysis demonstrates that nickel does not appreciably leach from the catalyst. Subsequently, we characterize the catalyst with several methods including X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, and X-ray diffraction, which suggest that nickel is well dispersed and is primarily present as an oxide, and that the reaction does not significantly alter the catalyst structure or nickel oxidation state. Lastly, we demonstrate that the 5% Ni/HTC catalyst is effective at depolymerization of biomass-derived lignin samples from clean fractionation of corn stover. Overall, this study demonstrates that a nickel oxide on a basic support can function as an effective depolymerization catalyst for lignin.

Researching a two-dimensional transition-metal dichalcogenide (TMDC) has been emerging as a new trend in a wide range of applications such as TFT, gas sensor and solar cell. However, it has not been utilized for energy harvesting and piezoelectric-chemical catalyst until very recently. Here we demonstrate feasibility for using MoS2 nanosheet in piezoelectronics and their application. MoS2 nanosheets were exfoliated by chemical intercalation and oxidation of butyllithium solution, which has an unique property that reveals the coexistence of 1T(octahedral) and 2H(trigonal prismatic) right after Li intercalation. LixMoS2 is changed into 2H structure by annealing above 573K. Here we found that a two-dimensional LixMoS2 sheet has a piezo-electrical potential by simple mechanical bending test. Furthermore, theoretical by COMSOL simulation and experimental study proved the polarity with mechanical bending on flexible substrate. These results could open an advanced 2D-type of Piezo-device such as nano-generators, piezo-phototronic and piezo-catalyst.

Reserves of fossil energies are continuously shrinking. Therefore, alternative, cheap and green ways of energy production must be found. To that point, photo-catalysis is one of the most promising fields due to a quasi-infinite source of energy: the sun. In this study, we report the fabrication of an all solid state z-scheme system able to store solar energy through overall water splitting. We combine the photocatalytic properties of two photoactive electrodes made of TiO2 and Pt-decorated CdS nanocrystals to create a photoelectrochemical cell able to perform overall water splitting without any charge scavengers.
Photoactive TiO2 nanoparticles deposited on transparent conductive oxide substrates are used to oxidize water, when in parallel, Pt-decorated CdS nanorods are applied to generate hydrogen. Using colloidal solutions for the electrode preparation offers the possibility to maintain the tuneable optical and electronic properties of the nanoparticles on macro scale substrates, which increases the chances of better sun light collection. An external circuit connecting both electrodes is used to transfer the electrons from the water-oxidizing TiO2-based electrode to the water-reducing CdS-based electrode. This allows the physical separation of the oxygen and hydrogen production sites, reducing risks and allowing large scale production. Photocurrents between the two electrodes are reported and hydrogen production measurements performed at the cathode are discussed.
The overall water splitting z-scheme built from two photoactive electrodes is a promising beginning for the development of more efficient systems, such as replacing TiO2 (UV absorber) by even more efficient light collectors.

One dimensional core-shell nanostructured electrodes made of aligned TiO2 nanotubes (NTs)/ZnO were fabricated via the thermal sputtering of ZnO layers on anodically fabricated titania NTs. Increasing the ZnO sputtering time resulted in the increase in the shell thickness, which in turn showed different morphological, structural and optical characteristics. The crystallinity of the core nanotubes was found to be a determinant factor in the formation of the NTs/ZnO heterojunctions as revealed by the FESEM, GAXRD, XPS and Raman analyses. Used as a photoanode to photoelectrochemically split water, the TiO2/ZnO heterojunction sputtered for 53 min showed almost 80% increase in the photoconversion efficiency (7.3%) compared to that of pure TiO2 NTs (4.1%) under light illumination (320-400 nm, 100 mW/cm2, 0.5 M Na2SO4). This was confirmed via the IPCE measurements, which showed an enhancement in the charge carriers&’ collection efficiency in the heterojunction electrodes compared to pure titania nanotube films. The decrease in the band gap (3.06 eV), the high surface area as well as the difference in the band positions between ZnO and TiO2 are thought to be the main reasons responsible for the observed enhancement in the photoactivity.
Reference:
B. Saif et al, Physical Chemistry C, in press

Photoactive nanocomposites of coupled semiconductors were synthesized by the sol-gel method. Nanocomposites with two interfaces such as semiconductor-1/semiconductor-2 and semiconductor-1/ceramic were synthesized by using the sol-gel method with non-ionic surfactant template. In particular, coupled ZnO/TiO2 with and without ceramic nanoparticles were prepared and thoroughly characterized for surface area, surface structure, morphology, crystal phase, and elemental identification by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, FT-IR spectroscopy, UV-Vis diffuse reflectance spectroscopy, and nitrogen isotherm. The results of SEM/TEM and diffuse reflectance spectra revealed that the ZnO-TiO2 composite modified with ceramic and sensitized with a co-catalyst were homogeneous and their absorption spectrum was extended in the visible region as compared with the composite without modifying with ceramic material. The effectiveness of these photoactive nanocomposites was examined towards H2 generation from aqueous methanol solution under UV light illumination and results obtained were compared with the activity of Degussa P25, TiO2, ZnO, and coupled ZnO-TiO2 composite. Significant enhancement in H2 generation was noticed with the coupled semiconductor nanocomposites modified with ceramic and other co-catalyst.

In recent years, novel plasmonic photocatalysts has emerged as alternative and promising materials for the development of highly efficient visible-light-driven photocatalyst. Studies revealed that silver on silver halide shows excellent photocatalytic activity under visible light irradiation. Due to the surface plasmon resonance of Ag nanoparticles originated from the partial reduction of silver halides, the Ag-AgX (X=halide ions) system shows enhanced visible light absorption leading to excellent visible light catalysis.
We describe here, a green synthetic route to synthesize Ag-AgCl plasmonic photocatalyst and its visible light electrophotocatalysis. The Ag-AgCl system was synthesized through a sequence of steps. Firstly, polyelectrolyte multilayer films of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were formed on ITO glass slides. The glass slides were then sequentially dipped into the aqueous solutions of silver nitrate (AgNO3) and sodium chloride, under ambient conditions. The composite materials were characterized by several microscopy and spectroscopy techniques. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) proved the presence of Ag+ ions and metallic Ag. In this experiment no separate step was employed to conduct the reduction of AgNO3. Ag+ ions were partially reduced by PAH. UV-visible spectra revealed the presence of surface plasmon resonance band of Ag nanoparticles. The composites found application towards visible light photoelectrocatalytic degradation of the dye methylene blue (MB). Over 94% of MB was degraded by the catalyst after 100 minutes of exposure of visible light under 1.2 V applied potential.

Metal nitrides have been studied for their catalytic activity for some time, in particular for heteroatom removal and hydrogenation reactions where the activity of Mo₂N has been compared with that of platinum metals.¹ More recently Co₃Mo₃N has been found to possess an impressive NH₃ synthesis activity competitive with the best ruthenium systems, and has been shown to able to reversibly deplete and replenish its nitrogen content suggesting the possible operation of a Mars-Van Krevelen type process.²
Previous studies of Ni₂Mo₃N have not shown significant catalytic activity² and the current study was framed to examine whether addition of cobalt would lead to an improvement. Hence a citrate-gel approach was adopted to make low crystallinity mixed oxides that could be converted to nanocrystalline Ni_xCo_2-xMo₃N by heating in ammonia. These solid solutions are single phase with compositions between Ni₂Mo₃N and NiCoMo₃N, with more cobalt-rich compositions containing Co₃Mo₃N-type phases. Interestingly NiCoMo₃N has ammonia synthesis activity comparable with that of Co₃Mo₃N, showing that more than one structure type within this compositional space can exhibit such activity.
1. A. Alexander, J. S. J. Hargreaves and C. Mitchell, Top. Catal., 2012, 55, 1046.
2. D. Mckay, J. S. J. Hargreaves, J. L. Rico, J. L. Rivera and X. L. Sun, J. Solid State Chem., 2008, 181, 325; D. H. Gregory, J. S. J. Hargreaves and S. M. Hunter, Catal. Lett., 2011, 141, 22.

Titanium dioxide is a technologically important material which attracted a considerable interest in various catalytic processes, including hydrosulfurization of hydrocarbon oils, water splitting, epoxidation of propene, CO oxidation and the selective catalytic reduction of nitrogen oxides. The photocatalytic properties of TiO2 reside from its innate structural properties, as it is a semiconductor with a large band gap (Eg=3.2 eV). As such, electron-hole pairs are created by band gap excitations and these electrons can be used in various redox reactions at the surface of the material. The development of efficient TiO2 photocatalysts requires the narrowing of the band gap, so that the light absorption of TiO2 is brought to the visible range, as well as the diversification of the morphology of the material, in order to ensure a high surface contact area with the solution and therefore increase the generation of electrons/holes and their use in various degradation processes.
We discuss here on the fabrication of transition metal-doped TiO2 (M=Mn, Fe, Co, Ni) nanostructures by a novel solution-based process in which alcoholic solutions are converted into of TiO2-based fine powders. The presence of the transition metal ions in solution will hinder the nucleophilic attack of water molecules to the Ti4+ ions, thereby preventing the spontaneous precipitation of the hydroxides and leading to the formation of very uniform gels which can be converted into nanopowders. A systematic comparison of the structure of metal doped TiO2 nanopowders as a function of the chemical identity and concentration of dopant is presented and the results were found to correlate well with the photocatalytic properties of these powders in the decomposition dyes containing azo (N=N) groups, such as methyl red.

Objective assessment of the activity of electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is imperative for the development of solar water-splitting devices. However, testing methods presently employed in catalysis research field are not standardized, making it difficult to cross-compare the activity and stability of these systems. In this presentation, the standard methods used within the Benchmarking facility of the Joint Center for Artificial Photosynthesis (JCAP) to evaluate electrocatalytic performance will be discussed. Specifically, the presentation will focus on standard techniques used for determining electrochemically-active surface areas and measuring electrocatalytic activity and catalyst stability under conditions relevant to an integrated solar-water splitting device. The results of using this benchmarking methodology to study and compare a variety of heterogeneous HER and OER catalysts in both acidic and alkaline solutions will be presented.

Due to it chemical stability, low cost and adequate energy levels for the water splitting, SrTiO3 is a material with great potential for application as photoanode material. Most of the recent works related to the use of SrTiO3 for water splitting are focused on development of photocatalytic material for overall water splitting process. Few are the articles in the literature describing the use of SrTiO3 as photoanode in the thin film shape. In the present study, In this study, we demonstrate an alternative and promising way to produce Nb doped and undoped SrTiO3 photoanodes thin film with good activity under standard solar illumination condition. In this approach, we processed SrTiO3 thin films using a colloidal dispersion of amorphous titanate nanoparticles as the precursor. In this process, the films were deposited by dip coating and subsequently sintered at 600 ° C during 1h. The results of scanning electron microscopy for the doped and undoped films showed similar microstructures with low porosity, thickness of approximately 150nm and a grain size in the range of 30nm. The photoelectrochemical characterization shows that the doped material has a photocurrent of 0.092 mA cm-2, whereas the undoped sample showed a photocurrent of 0.015 mA cm-2 at the potential of 0.5 V RHE. The presence of niobium in the structure of titanate increases the quantum efficiency (IPCE) of the photoanode for water splitting achieving 25% at 300nm.

The photoactivation of bismuth titanate has received attention of scientists in the past decade, owing to its important applications in photocatalysis for environmental clean-up, especially Bi12TiO20 (BTO), a promising candidate for the replacement of TiO2. The BTO has a variable energy gap from 1.5 to 3 eV and it can be excited by light ranging from visible to ultraviolet. In contrast, the band gap of the TiO2 is 3.2 eV, and it only absorbs ultraviolet light (lambda;<400 nm). In the literature, γ-Bi12TiO20 powders showed reaction constant ten times greater than the TiO2 in the visible light region. The γ-Bi12TiO20 degraded acid orange 7 very efficiently and had higher photocatalytic activity than traditional N-doped TiO2. In this work, Bi12TiO20 powders were prepared by state solid reactions by mixing 6-Bi2O3 and TiO2 at different temperatures (500, 600, 700, and 750oC.) The photocatalytic activities of the system Bi2O3/TiO2 was evaluated in the discoloration of Rhodamine B under visible-light irradiation (lambda; > 420 nm). The structural and microstructural properties were analyzed by Diffuse Reflectance Spectra in the ultraviolet-visible region (DRS/UV-Vis), X-ray Diffraction (XDR). The XDR and Raman analysis showed a single phase for the γ-Bi12TiO20 at 750oC. On the other hand, mult-phases from α-Bi12TiO20, Bi2O3 and TiO2 have appeared at temperatures of 500 oC to 700oC. Increasing the temperature from 500oC to 750oC, it was noticed a band gap reduction from 2,68eV to 2.34 eV respectively, for the semiconductor bismuth titanate. The decrease in the band gap with higher temperature can be viewed as a raise of the electrons energy in the material. Among them, powders with an estimated band gap of about 2.34 eV presented the best photocatalytic activity under visible-light irradiation. The system Bi/TiO2 mult-phase at 500oC with narrow band gap energy (2.34 eV) exhibited higher photocatalytic activity than other temperature and Bi2O3, and TiO2. This system showed a Rhodamine B discoloration in a ratio of 50% within 1h 15min, which indicates a better catalytic activity compared to TiO2 , that has the same discoloration within 2h 38 min. The system Bi/TiO2 mult-phase at 500oC could be easily excited by visible light (lambda; > 420 nm, energy less than 2.68 eV) and induce the generation of photoelectrons and holes. Several authors reported the unusual photocatalytic activity, suggesting the synergistic effect between the Bi2O3 and TiO2. The bismuth titanate is promising candidate for various technological applications, mainly photocatalytic property which can respond under visible light.

Enzymatic reduction reactions are well known from biological systems [1]. CO2 is reduced to formate, formaldehyde or methanol by formate dehydrogenase, formaldehyde dehydrogenase and alcohol dehydrogenase respectively with the aid of the coenzyme Nicotinamidadenin dinucleotide (NADH). We present the immobilization [2] of these enzymes in alginate based matrices for a sustainable, reproducable CO2 reduction. Different alginate containing gels were investigated for efficient CO2 conversion [3,4]. Further modification of the gels with PEDOT:PSS increases the conductivity of the material. This offers the opportunity for electrochemical application of the enzyme containing systems and therefore to substitute NADH as electron provider. Production of formate and methanol are shown for the enzymatic CO2 reduction in electrochemical and non-electrochemical experiments. Products were analysed in ion chromatography and gas chromatography. Conductivity of the PEDOT:PSS modified alginate gel was determined by four probe measurement. Electrochemical measurements were performed in a one compartment cell using alginate covered Pt as working electrode. Cyclic voltammograms were recorded for electrochemical characterisation. Results from CO2 saturated samples are compared to N2 purged setups to proof product generation from CO2 reduction.
[1] M. Aresta, A. Dibenedetto, Ref. Mol. Biotechnol., 90, 113-128(2002).
[2] T. Reda, C. M. Plugge, N. J. Abram, J. Hirst, PNAS, 105, 10654-10658 (2008).
[3] O. Heichal-Segal, S. Rapport, S. Braun, Nat. Biotechnol., 13, 798-800 (1995).
[4] Y. Lu, Z.-Y. Jiang, S.-W. Xu, H. Wu, Catal. Today, 115, 263-268 (2006).

Ultra-thin oxide membrane structures have application in fundamental science and reducing the operating temperature of solid oxide fuel cells (SOFCs). We have previously fabricated self-supported electrolyte membranes on the nanoscale, showing high performance at relatively low SOFC temperatures (500 °C). The mechanics of clamped, self-supported membranes is heavily dependent on residual thin film stress (σ_0). Fundamental work on the interplay between physical chemistry, such as anion non-stoichiometry, mechanics, such as membrane fabrication, has yet to be systematically studied. In an effort to broaden the application and utilization of nanoscale membranes, understanding how to control is σ_0 vital. We have utilized radio frequency sputtering to demonstrate aspects towards controlling the chemically and physically induced σ_0. In the former case, we utilize solid state oxide alloys made by co-sputtering to overcome compositional restrictions in forming stable membranes; while in the latter case we show a mechanistic approach for isothermally controlling σ_0. We will discuss our findings in detail and provide a framework with which robust, scalable free standing membrane structures can be fabricated approaching room temperature.

Current photoelectrochemical and photochemical solar water splitting devices are still not efficient enough to make artificial photosynthesis an economically viable route. One of the main reasons is the fast recombination of electrons and holes impeding the photocatalysis. Recombination can be suppressed if electrons are efficiently collected and transported from the photocatalyst to their destination (to a co-catalyst or to a conductive substrate). Graphene can offer a solution to this challenge due to its remarkably high electron mobility, with reported values up to 150,000 cm2Vminus;1sminus;1 and its work function (~4.5 eV) below many semiconductor conduction bands. Recent reports have confirmed that reduced graphene oxide, a chemically derived graphene, collects, stores and shuttles photoinduced electrons from titania. However, the development of graphene-based photocatalysis is still at its infancy because: (1) routes to efficiently couple semiconductors and graphene have not been developed yet, (2) the morphologies and architectures at the nanoscale to microscale are not controlled and (3) the electron transfer mechanism between semiconductors and graphene is not fully understood.
In this work we describe the synthesis and characterization of novel photocatalyst-graphene hybrids for solar water splitting. Graphene is prepared either by reducing graphene oxide via ammonolysis or by exfoliating graphite in organic solvents. Visible-active photocatalysts under study are Ta3N5, TaON, TiO2-xNx and other nitrides. Ammonolysis offers a unique route to either reduce graphene oxide or dope graphene while conserving the nitrogen composition of photocatalysts. Solar water splitting tests show the beneficial effect of graphene which, for example, drastically lowers the potential onset on Ta3N5 photoanodes. The systematic combination of synthesis and characterization is used to identify the effect of graphene, semiconductor chemistry and particle size on the final performance, with special emphasis on the lifetime of photoinduced carriers and electron transfer mechanisms.

Photocatalytic processes require to generate as much as possible electron-hole pairs as well as to have a very high efficient for the electronic transfer. It involves multi-electronic redox reactions, occurring at the near vicinity at the surface of the semiconductor. Therefore a detailed surface engineering of the semiconductor is needed to increase the overall efficiency of the process and be able to explain productivity and selectivity in the photo reduction process.
This contribution is addressed to the analysis of the outermost layers and how the use of different additives can modify the surface chemical structure of the semiconductor, give rise to a local lattice modification, introduce new potential catalysts issues and alter or vary the composition and bond ending which become essential and outstanding for the final photocatalytic properties. Two potential additives, such as magnesium and indium are presented.
A detailed characterization points out that outermost layer of TiO2 is highly affected by the presence of the additive. XPS spectra, especially at the energy zone of oxygen and titanium, show significant evolution of the different detected bonds as the concentration of the additives is increased.
Overall photo catalytic productivity has been found to be straightforward related to the Ti+3 concentration for both of these additives. These states are trapping photo generated electrons preventing their recombination. It defines a competitive pathway to the direct reduction of water. As the density of Ti+3 increases, the production of methane increases while that of the hydrogen decreases. All these data have been correlated below the limit of their solubility for avoiding segregation effects that are generating defects with new recombination via that decrease the overall productivity. These findings confirm that the benefit introduced by the additive is mostly related to the surface states created, being possible to achieve a 5-fold increase in productivity and corroborating the outstanding effects of the surface engineering on the photo catalysis procedures.

The organic and heavy metals removal from water have been performed by combination of physical, chemical and biological, techniques. Recently, we have found organic remediation from water using integrated graphene (G)-titanium oxide materials (TiO2) and G-TiO2-biosurfactant nanocomposite materials. The presence of biosurfactant in G-TiO2 nanocomposite has shown the complete effective organic remediation from water.
Under the present work, we have found the remediation of organic materials using G-TiO2-surfactant and G-Zinc oxide (ZnO)-surfactant using visible light. The G-TiO2 and G-ZnO nanocomposite materials were characterized using FTIR, X-ray diffraction and Scanning Electron microscopy, techniques. Further, we have shown the remediation of toluene, naphthalene, methyl orange, organic oil etc. using G-TiO2-surfactant and G-ZnO-surfactant materials in visible light.

Heterogeneous photocatalysis is a research topic of great importance in view of its applications in energy production and treatment of organic residual. Many oxide semiconductors, such as TiO2, WO3, Nb2O5 and Bi12TiO20, have been employed as photocatalysts in pollutant degradation and water splitting reactions [1]. However, the low electron-hole formation rate of these materials results in low quantum efficiency of photocatalytic reactions, because requires higher energy to activate the semiconductor. Therefore, various strategies have been adopted to enhance visible light absorption by careful design of materials at nanoscale level, including: (i) chemical doping with elements that are able to alter the electronic structure and charge-transfer processes; (ii) coupling metal nanoparticles on semiconductor surface to improve electronic properties. Several authors have reported the synthesis of doped semiconductors materials using numerous techniques. One of the most interesting wet-chemical methods for the synthesis of lead-based nanometric materials was developed by Camargo and Kakihana [2] and called as the oxidant peroxo method, referred to simply as OPM. In this sense, the objective of this study was to evaluate the properties and the catalytic activity of Bi12Ti1-xNbXO20 (x= 0.05, 0.10 and 0.15) prepared by oxidant peroxide method (OPM). First, the hydrogen peroxide is replaced by an inorganic peroxo complex, such as peroxytitanate, which reacts with bismuth ions, leading to the formation of a non-crystalline yellow precipitate. It can be described as a mixture of amorphous Bi2O3 and TiO2 at room temperature, which can be obtained at any desired molar ratio of Bi:Ti and free of contaminants commonly found in materials synthesized by other chemical routes. The morphology and microstructure of the catalysts were characterized using X-ray diffraction, Raman spectroscopy, Diffuse Reflectance Spectroscopy, Scanning Electronic Microscopy and Energy Dispersive X-ray Spectroscopy. The photocatalytic properties of materials calcined at 700 °C were investigated by the rhodamine B (RhB) degradation. X-ray diffraction and Raman spectroscopy show that all samples heat-treated at 700 °C were obtained with single phase. The spectrum of UV-vis absorption indicated that the absorption edge of the Bi12Ti1-xNbxO20 (x=0.05, 0.1 and 0.15) were at 472, 467 and 453 nm respectively, corresponding to the bands gap energies of 2.63, 2.66 and 2.73 eV, which constitute an advantage considering the possibility of using the sunlight radiation. The superior photocatalytic activity observed for all materials doped with niobium was confirmed by the complete degradation of a 10 mg.L-1 RhB solution within 210 minutes using UV light.
Work supported by Fapesp, CMDMC/Cepid, CNPq and CAPES.
[1] J. Hou, et al. J. Hazard. Mater. 217, 177 (2012);
[2] E.R.Camargo, et al. Chem. Mater. 13, 1181 (2001).

Compared to TiO₂ nanoparticles and those decorated with metal nanoparticles, three-dimensional heterostructures composed of TiO₂ nanotubes and noble metal nanodendrites are anticipated to yield a higher SERS and photocatalytic activity, attributable to the large surface areas, the inhibited recombination of photogenerated electron-hole pairs, and the symmetric structures with surface plasmon resonance. However in previous studies using aqueous routes including electrochemical and galvanic reactions, the dendritic structures of noble metals can only be prepared on either conductive substrates or metal plates. Successful aqueous growths of metal nanodendrites on oxide semiconductors in particular TiO₂ nanotubes have never been reported. Interestingly, in the present aqueous synthesis using sacrificial ZnO nanorods, a self non-uniform electric field mechanism was discovered to induce dendritic Pd growths on TiO₂ nanotubes for forming three-dimensional superhydrophobic TiO₂/Pd heterostructures with a high SERS and photocatalytic activity. First, TiO₂/ZnO heterostructures were prepared in a zinc nitrate solution, and then sensitized in a stannous chloride solution and activated in a palladium chloride solution. A symmetric fern leaf-like nanodendrite structure was found to form on the TiO₂ nanotubes; with increasing the concentration of stannous chloride solution and extending reaction time, the nanodendrites transformed into a pine-like, a thorn-like, and ultimately an irregular chained feature constructed from aggregated nanoparticles. Structural analyses (by X-ray diffraction) and elemental mappings (by energy dispersive spectrometry) indicated the minor doping of Zn and Sn in the formed face-centered cubic Pd nanodendrites. Microstructure analyses (by transmission electron microscopy) suggested that the single-crystalline nanodendrites grew along the <111> direction group. Branches were built on the same (111) basal plane of primary arms, but extruded in another direction of the <111> group with an angle of 70° correlated to the lattice of the primary arms, similar to a symmetric twin structure. Sequential formation processes different from the previously reported diffusion-limited aggregation model are suggested for the growth of the present Pd nanodendrites, including the dissolution of ZnO nanorods for forming a self non-uniform electric field, the protruding of primary Pd arms towards a Zn⁺² concentrated zone, and the development of Pd branches through an anion depletion zone. The TiO₂/Pd heterostructures show a hydrophobic surface, very strong SERS, and a high photocatalytic activity in pollutant dye degradations at a rate ten times that by bare TiO₂ nanotubes, and suggest high potential for applications to self-cleaning surface, optoelectronics and photocatalyses.

Grand environmental challenges often require fundamental approaches to the chemistry that best tackles them. Arsenic in drinking water and carbon dioxide in air are the leading molecular contaminants, and in order to be widely applied, technologies that remediate them need to be sustainable by being low cost and accessible. It is likely that nanoscale architectures with tuned surfaces and pores are going to solve these problems. Our research showed that uniform and monodisperse nanocrystals of magnetite (Fe3O4) are the most effective adsorbents for arsenic species [1] and by switching precursors to rust, olive oil and vinegar, one can make highly crystalline magnetic arsenic sponges with very minimal costs. Heavy metals (Hg, Cd, etc.) are also effectively removed by nanoporous systems. For CO2 remediation, physisorption with nanoporous solids, especially the nanoporous covalent organic polymers (COPs) show promise as the most feasible materials since they are robust and inexpensive. We recently reported the syntheses of porous covalent organic polymers (COPs) with record CO2 adsorption capacities and selectivities over N2 and H2 [2].

References
1. Cafer T. Yavuz, et al., Science, 314, 964-967, (2006).
2. Cafer T. Yavuz, et al., Nature Communications, 4, 1357, (2013).

Actinide oxides or actinide doped metal oxides are promising materials as catalysts for visible light driven photo-oxidation of water or organic compounds. Suitable precursors for the material synthesis of these compounds were scarce limiting the use of gas phase or liquid phase material processing from metal organic molecular compounds. The current work describes the synthesis of new volatile uranium and uranyl complexes suitable for gas phase deposition of the respective oxides as pure material or as dopant into different oxide matrices. These complexes show significantly enhanced properties in terms of volatility and stability, which improves significantly their application in CVD processes. The complexes have been used as single source precursor for the chemical vapour phase deposition of uranium oxide thin films using a low pressure, cold wall MOCVD reactor system. The resulting nanostructured films are tested as visible-light photocataslysts for photo-oxidation of organic compounds as well as water-splitting applications for hydrogen production.

Photoelectrochemical (PEC) water splitting has attracted considerable attention because it is a very promising and clean technique to produce carbon-free hydrogen from inexhaustible solar energy and water source. PEC water splitting is a process in which electrons and holes are generated in the semiconductor photoanode by solar radiation to produce both H2 gas and O2 gas from water. Therefore, both optical and electrical properties of photoanode strongly affect the solar-to-hydrogen efficiency for PEC cells. In this study, we present a new type of photoanode consisting of an array of WO3 nano-helixes for much more efficient solar hydrogen production. The unique geometry of the vertically aligned WO3 nano-helixes array, fabricated by a facile and cost-effective method called oblique angle deposition, causes a strong scattering of solar radiation as well as large surface area for chemical reaction to split water into hydrogen ion and electron for much enhanced light harvesting. Furthermore, micro-structural analyses by x-ray diffraction and transmission electron microscopy reveal near-single crystallinity of the WO3 nano-helixes, providing an express way for efficient transport of electrons and holes. The solar-to-hydrogen efficiency for the PEC cells with the WO3 nano-helixes photoanode is enhanced compared to that for the reference cells, which is attributed to the combined effects caused by the unique electrode; (i) enhanced carrier transport through high crystal quality WO3 nano-helixes, and (ii) much higher light scattering by the nanohelix array. The analytic model elucidating the enhanced efficiency will be presented.

The activity of catalysts can be significantly improved by improving its active surface area. Dispersing catalyst nanoparticles on supporting material is a well known method to get highly active catalyst by effectively preventing their agglomeration. Development of highly active catalyst for electrochemical conversion of carbon dioxide into hydrocarbons attains specific importance, particularly in confined atmospheres, like submarines. In this study, we have developed a novel poly(ionic liquid) functionalized graphene supported cathode electrocatalyst for carbon dioxide conversion. It is well reported that poly(ionic liquids) are good CO2 sorbents at low pressures. Hence, poly(ionic liquid) modified graphene (PIL-G) can play a dual role as effective CO2 sorbent and catalyst support. The high affinity of PIL-G towards CO2 improves amount of CO2 in contact with catalyst. As a result, PIL-G based catalyst shows at least one order improvement in current. In this catalyst, amount of PIL loaded on supporting material and synthesis procedure of catalyst play a critical role in performance. A complete electrochemical cell, comprised of Pt/carbon anode, Pt/PIL-G (or Pt/G) cathode and Nafion separator, has been constructed. The cell was operated with various potentials and the products were analyzed. The detailed experimental procedure, characterization and analysis will be discussed at the time of presentation.

In the world today, there is a critical need for utilization of clean and sustainable energy sources. One promising option is photocatalytic fuel production by harvesting sunlight. However, the materials used as photocatalysts have problems such as an overly large bandgap to inefficiently use the solar spectrum for energy, poor conductivity and recombination lifetimes of electrons and holes, and poor reaction kinetics at the interface of the material and electrolyte. Coupling of plasmonic metals (i.e. Au, Ag, Pt) with a semiconductor photocatalyst has been shown to improve the photocatalytic performance previously. This poster presents our new discovery of plasmon-enhanced photocatalysis mechanism and the facile plasmonic metal-semiconductor heterostructures for efficient utilization of plasmon-harvested energy. Our work has shown that the plasmon-induced resonant energy transfer process can induce the charge separation in the semiconductor photocatalyst even though there is a physical gap between the plasmonic metal and the semiconductor, leading to significant photocatalysis enhancement. In addition, the core-shell nanoparticles such as Au@Cu2O, Ag@Cu2O, Au@SiO2@Cu2O have been developed as the efficient plasmonic photocatalysts. The results show that the surface plasmon resonance band can be tuned by varying the shell thickness on the nanometer scale, which results in the plasmonic photocatalysts that absorb the sunlight from the ultraviolet through near infrared region.

Anatase titanium dioxide (TiO2) is an excellent photocatalyst and has been tested for various environmental applications of water and air purification and photochemical solar cells. Nanopowders of TiO2 dispersed in water are one of the most commonly studied photo catalysts for removing organic contaminants. However, having TiO2 immobilized on a substrate eliminates the process of filtration of the catalyst from the treated effluent which can be a tedious and costly process. For this reason, TiO2 films deposited on stainless steel (SS), a widely used material with high mechanical strength and resistance to corrossion, is highly desirable for applications such as photocatalysis and photvoltaics among others. In particular, degradation under solar radiation as opposed to ultraviolet wavelength as required by pure titania would be desirable.
As part of this research three adherent anatase titania systems- nanoporous membranes obtained by anodization, dense films obtained by sputtering and films obtained by sol gel dip coating were synthesized on SS substrates. Contrary to expectation, the dense films obtained by sputtering, 500 nm thick, which has much lesser surface area than the other two systems performed significantly better than the nanoporous titania film in photocatalytic degradation of methyl orange. It also outdid the standard Degussa P-25 benchmark. Examination by XPS indicates that the sputtered films, serendipitously, had a combination of contaminants that potentially extend the absorption range of titania as determined UV-Vis spectrophotometry. The poster will describe the exact nature of these contaminants and the combinatorial chemistry routes currently being investigated to replicate this performance in powder based systems first and then eventually in SS supported systems.

An efficient and cost effective solution for carbon dioxide capture and storage is currently in a high demand due to increasing CO2 concentrations in the atmosphere and potential global climate change as a result. Among many materials previously studied for carbon mitigation, metal organic frameworks (MOFs) were identified to be effective porous adsorbents for CO2 capture from post combustion flue gas. Uniform pore structure on the nanometric scale, large surface area, and framework flexibility are some of the unique characteristics of these materials. Some MOFs demonstrated competitive CO2 adsorption capacities at simulated flue gas conditions of low pressures and low CO2 concentrations in the gas (10-15 %). Nevertheless, while good performance of these materials was observed under dry gas conditions, presence of moisture was shown to decrease their potential as adsorbents under practical conditions. For instance, Mg/DOBDC MOF that reports the highest CO2 adsorption capacity among other MOFs at low pressures in dry gas conditions becomes unstable under humid conditions and adsorbs significantly less CO2, which could be attributed to its strong hydrophilicity. In this work, we present a facile pore modification of MOFs to enhance adsorbent stability and CO2 affinity under practical conditions of humid CO2 capture. In order to prevent direct contact of water molecules with open metal sites of the framework, surface of the nanopores in Mg/DOBDC is decorated with functional groups of ethylene diamine. The post-synthetic functionalization is based on our previously reported technique. The stability of functionalized Mg/DOBDC is assessed via accelerated steam treatments, and the material is characterized by surface area and pore size analyzer, XRD, TGA, IR, etc. Carbon dioxide capture with resulted modified Mg/DOBDC MOF after exposure to humid environment is also evaluated and will be presented.
(1) Choi, S.; Drese, J. H.; Jones, C. W. ChemSusChem 2009, 2, 796.
(2) Sumida, K.; Rogow, D. L.; Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.; Bae, T. H.; Long, J. R. Chemical Reviews 2012, 112, 724.
(3) Kizzie, A. C.; Wong-Foy, A. G.; Matzger, A. J. Langmuir : the ACS journal of surfaces and colloids 2011, 27, 6368.
(4) Choi, S.; Watanabe, T.; Bae, T.-H.; Sholl, D. S.; Jones, C. W. The Journal of Physical Chemistry Letters 2012, 3, 1136.

Herein, we report the preparation, characterization and investigation of previously unexplored W incorporated iron vanadate (FeVO4) electrodes for solar light driven water oxidation in photoelectrochemical cell. The W incorporated FeVO4 films on F-doped SnO2 substrates have been prepared by layer-by-layer deposition of metal-organic precursor and subsequent thermal decomposition at 550 °C in air. The synthesized films with a band gap of about 2.06 eV are responsive to visible light up to wavelength of ~600 nm, i.e. being able to harvest ~45% of the solar spectrum. The W incorporated FeVO4 photoanodes are active materials for photoelectrochemical water oxidation and, yield a significantly enhanced (2.5 fold higher) photocurrent in comparison to pristine FeVO4 photoanodes. This improvement can be attributed to increased n-type conductivity by W6+ ion doping in the FeVO4 lattice. The incident photon to current conversion efficiency achieved with developed photoanodes is as high as 6.5% at 400 nm.

The oxygen evolution reaction (OER) is regarded as a major bottleneck in the overall water splitting process due to the slow transfer rate of four electrons and the high activation energy barrier for O-O bond formation. For the decades, Ir, Ru and Pt based inorganic materials have presented efficient catalytic activity with high turnover frequency (TOF) under mild conditions. However, its scarcity and high cost still inspire to develop inexpensive and sustainable catalysts. In nature, there exists a water oxidation complex (WOC) in photosystem II (PS II) comprised of the earth-abundant elements Mn and Ca. Asymmetric geometry and flexible ligation in biological Mn4CaO5 cluster is one of the important principles in PS II, which can be applied to design a new inorganic water oxidation catalyst.
Here, we identified a new crystal structure, Manganese phosphate hydrate that precipitated spontaneously in aqueous solution at room temperature and demonstrated the superior catalytic performance under neutral pH. Computational analysis showed that phosphate ligations in our crystal make Mn-O bonding longer and more distorted than any other Mn based oxides. Such structural flexibility can stabilize Jahn-Teller distorted Mn(III) and thus facilitate Mn(II) oxidation as monitored by electron paramagnetic resonance (EPR) spectrum. Additionally, we investigated the possible involvement of embedded water molecules in proton coupled electron transfer (PCET). This study can provide a valuable insight to understand the interplay between atomic structure and catalytic activity.

Due to limited amount of energy resources and their depletion as well as environmental concern, the researchers have been seeking for clean and renewable energy sources. In addition, carbon dioxide (CO2) is one of the major greenhouse gases and produced mainly by the consumption of fossils fuels. The managing CO2 emission is one of the major technological as well as political challenges. The photcatlytic reduction of CO2 to value-added chemicals such as methanol, methane and CO using solar energy is an attractive option for capturing greenhouse gas and at the same time to solve the problem of shortage of sustainable energy. Here we have studied the oxide-based photocatalysts for the reduction of CO2. Those oxides include Cu2O, TiO2, titanate, zirconate, and the like. Different products (such as methanol, ethanol, methane, and CO) have been obtained. The heterojunction fabrication has also been used to change/improve the yield of different photoreduction products. Detailed mechanism has been thoroughly studied as well. We envision this would afford a viable approach for the photoreduction of CO2 and a better understanding of the related mechanism, which would facilitate the R&D of the high-efficient photocatalysts for the photoreduction of CO2.

Niobium pentoxide (Nb2O5) is material largely studied as catalyst in several reactions, including in photocatalysis, since it presents a band gap ranging from 3.1 to 4.0 eV and high absorption of light spectrum. Different papers have shown that Nb2O5 presents photocatalytic properties for degradation of organic contaminants, however generally applying this material in the micrometric form. Despite the technological importance of nanoparticulated Nb2O5, few preparation methods have been reported by the literature, since Nb5+ ions are very unstable in aqueous solution. Then, the oxidant-peroxo method (OPM) through hydrothermal treatment is a promising alternative, since the hydrothermal annealing allow the crystallization process in mild conditions, maintaining the hydroxyl groups in as-formed surfaces, which results in a material with high surface area and consequently larger amounts of acid sites. However, the potential of this route to produce Nb2O5 as an active photocatalyst was not properly investigated.
Then, this work evaluates the influence of synthesis variables in OPM method on phase formation, structure and photocatalytic potential of Nb2O5 nanoparticles. A peroxocomplex was formed by the reaction of NH4[NbO(C2O4)2(H2O)2].nH2O with H2O2 (10:1 H2O2:Nb molar ratio) in water, and the Nb2O5 syntheses were performed by the hydrothermal treatment of this complex, during 2 to 12 h at 100, 125, 150 or 175°C. Photocatalytic efficiency and the mechanims of degradation were evaluated by the degradation kinetics of two water contaminants: Rhodamine B dye (RhoB) and Atrazine (a pesticide that absorbs under 222 nm) under UV and visible irradiation. Finally, the detection of the active oxidative species produced on the photocatalyst surface was indirectly investigated by the detection of 2-hydroxyterephthalic acid formed by the reaction of hydroxyl radical with terephthalic acid, through fluorescence spectroscopy (FS).
The obtained materials presented a mixture of recrystallized Nb2O5.nH2O and T/TT phases, with different morphologies, high acidity and specific surface area. It was observed that, under UV light, the main photodegradation mechanism occurred by the attack of .OH radicals on the molecules (RhoB and atrazine) and not by the direct oxidation of adsorbed molecules on the photocatalyst surface. In fact, radical formation was only observed under UV light in FS experiments. On the other hand, sensitized photocatalysis was shown to be an efficient method only for degradation of pollutants that absorbs in visible range: this mechanism was observed as the main mechanism for RhoB degradation under visible light, but this did not take place for Atrazine under the same conditions. For the synthesis performed in lower temperatures the surface hydroxylation was the most influential parameter at photoactivity per unit area of material, whereas for the synthesis performed in higher temperatures the crystallinity became the most influential parameter.

Ab-initio methodologies based on Density Functional Theory has allowed for an increasing predictive ability of materials. In the case of H₂ synthesis, cerium based oxides have garnered signicant interest given their oxygen buering capability that facilitates the creation of active surface defect sites (vacancies). Tailoring the activity and selectivity of these materials towards low temperatures is paramount to improving reactivity. We started investigating the fundamentals governing the surface phases of cerium (IV) oxide under a range of environments. In the case of a pure ceria system in an O₂ environment, it was found that T > 1500 K or P_O2 < 10^-13 atm are required for any appreciable surface reduction. However, exposing the surface to a highly reducing environment such as CO or H₂ could help circumvent these harsh conditions. Given the aforementioned observations we sought to alter surface reducibility by doping with various alkali and transition metal elements. Doping ceria had an eect on the surface vacancy formation; low valence dopants favor defect formation, whilst high valence dopants suppress it. Armed with the insight dopants have on surface vacancy formation, their corresponding impact on the consecutive dissociation of water at these sites was studied. Using a carefully strategized multi-step screening approach abiding with the Sabatiers Principle, we were able to identify a subset of dopants that would promote surface reactivity towards H₂ synthesis. Dopants such as Sc, Au, Co, Pd, La and Y possessed a critical balance in improving surface reducibility while sustaining the dissociation of water, hence are promising candidates in enhancing the two-step water dissociation process.

Photocatalytic hydrogen generation has been recognized as a potential reaction to produce environmentally clean energy from renewable resources. Various materials including TiO2 have been used to study photocatalytic efficiency. Among these materials, cadmium chalcogenides are promising as photocatalysts because of their bandgaps in the visible region of the spectrum. The well-defined morphology and components of the hybrid nanocatalysts provide valuable information pertaining to the photoinduced charge separation and transfer processes during the reaction. In the present work, we focused on geometrical (single- or double-tipped) and compositional (Pt or Au) variations of active metal components in a well-defined CdSe nanorod system. These colloidal nanostructures were employed for photocatalytic hydrogen generation from water under identical reaction conditions with visible light irradiation (lambda; ge; 420 nm). The catalysts exhibited significant dependency of the catalytic activity, both on the catalyst geometry and on the choice of the metal tips. The Pt-tipped CdSe nanorods showed better photocatalytic efficiency than the Au-tipped CdSe nanorods. In particular, the activity of the single Pt-tipped CdSe was found to be better than that of the double Pt-tipped CdSe, although the Pt loading of the former was only half of the Pt amount of the latter. These findings imply that the rational design of photocatalysts with a well-defined geometry and feasible compositions would maximize the photoconversion efficiency in desired reaction pathways. The geometrical and catalytic features of metal-tipped CdS nanorods will also be discussed.

Next generation&’s solar energy conversion calls for new material and structures. Si nanowires (SiNWs) are easy to prepare, more tolerant to impurities than planar Si, and have attracted significant research attention. Devices such as solid junction solar cells and photoelectrochemical cells have been demonstrated based on SiNWs. There has slso been particular interest in using Si for the production of solar hydrogen, because the conduction band edge of Si is more negative than the water reduction potential. To achieve this goal, one important challenge is the application of hydrogen evolution reaction catalysts for the exchange current density of Si for H2 production (j0~10-5 mA cm-2) is insufficient to sustain a significant photocurrent in the absence of large overpotentials. Existing catalyst deposition techniques, however, are either limited by their line-of-sight nature (e.g., evaporation) or diffusion in solution (e.g., electrochemical or electroless deposition) and tend to produce a non-uniform catalyst distribution, with most catalyst particles aggregated on the tips of the NWs, where the space is most accessible for catalyst deposition. Such a catalyst profile is not ideal for solar H2 production by high aspect ratio structures like SiNWs for the long charge diffusion distance required for most photoelectrons which are generated away from the tips of the NWs to reach the catalyst sites. This requirement dictates the need of extremely high purity and high quality crystals to overcome the recombination and obtain high performance, which usually leads to high cost of material preparation.
Herein, we reported a uniform catalyst distribution on SiNWs that ensures effective axial charge collection from high aspect-ratio Si nanowires achieved by atomic layer deposition of Pt nanoparticles. The resulting photoelectrode permits the measurement of high photovoltage, low overpotential and extremely good stability against photo-oxidation of Si nanowires in solar water reduction reactions. The realization of axial charge collection also allows for evaluation of the design advantages and caveats of densely packed Si nanowires for the purpose of solar hydrogen generation.

Recently, the growth of inorganic nanocrystals has aimed at the fabrication of more complex core-shell heterostructures. Some unusual heterostructrures involve two or more materials may exhibit enhanced physical and chemical properties to broaden their potential applications in such as biomedical, magnetic, and optical-electronic fields. However, very few papers have described the preparation of core-shell heterostructures using polyhedral nanocrystal cores to directly grow shells with precise control of morphology and thickness. Cuprous oxide (Cu2O), an attractive p-type semiconductor with a band gap of 2.17 eV, has been used as a visible light-responsive photocatalyst and applied to solar energy conversion. A major advantage of Cu2O is that it is low toxic to environment and cost-effective compared to other semiconductors. However, Cu2O is known to be unstable in water under illumination, and it suffers from photocorrosion due to its oxidation and reduction potentials lying within the band gap. Atomic layer deposition (ALD) is considered as a novel technology to produce precise and highly conformal thin film on various geometric structures. Consequently, in the present study, ALD is introduced to overcome these problems by offering a passivation layer of TiO2 to protect the surface of Cu2O core. We have successfully used Cu2O nanocrystals (cubic, octahedral and rhombic dodecahedral) with diameter of 200-500 nm as the structure-directing cores to synthesize Cu2O-TiO2 core-shell heterostructures. The uniform shell of TiO2 with the thickness of 10-50 nm could be controlled simply by varying the cycle number of ALD. The ALD growth behavior was largely influenced by the exposed surface planes corresponding to different shapes of Cu2O. Furthermore, the successful preparation of these heterostructures with well-defined shapes enabled us to examine their facet-dependent photocatalytic activity. Under light irradiation, Cu2O nanocrystals wrapped with an ultrathin passivation shell of TiO2 could serve as effective and recyclable catalysts without photo-induced corrosion. The photocatalytic activity was in the order of rhombic dodecahedral > octahedral > cubic. Moreover, significant enhancement in photocatalysis performance of the Cu2O-TiO2 core-shell heterostructures was indeed observed. Such an enhanced catalytic activity might be attributed to efficient charge separation occurring at the interface between the core and shell.

Titanium dioxide represents an effective photocatalyst for hydrogen generation in water photolysis that can help to solve the energy problem with conversion of the solar energy into pure, gaseous hydrogen and oxygen. However, it has a wide energy band gap (>3.0 eV) and is activated only under UV light irradiation which accounts for only a small fraction of the solar spectrum compared to the visible region. Many studies focused on improving visible light absorption by reducing the band gap energy of TiO₂ with doping cationic or anionic sublattice [1-3]. Influence of certain metal dopants such as e.g. Cr on structural and optical properties of TiO₂ has already been proved. It is generally accepted that incorporation of Cr or N ions into the TiO₂ lattice leads to a narrowing of the energy gap which increases the visible light response. However, it also affects unfavourably the recombination process, which limits the efficiency of the solar energy conversion. Recently, new doping scheme was proposed, namely simultaneous incorporation of both dopants into TiO₂ cationic and anionic sublattices. Co-doping can promote a separation of the photogenerated electrons and holes which limits recombination process, improves material quality and enhances light absorption.
A study of the co-doped TiO₂ thin films by N and Cr ions obtained by magnetron sputtering is reported. Systematic studies by X-ray diffraction, optical spectrophotometry, photoelectrochemical and synchrotron measurements have been performed. Kβ detected Ti K-edge HERFD-XAFS spectra provide information on the influence of Cr, N dopants on charge distribution in the TiO₂ structure. Quantitative analysis of the RXES Kβ_2,5 and its satellites [4] reveal the information about N dopants distribution and oxygen stoichiometry, enabling a more accurate determination of local structure evolution of co-doped TiO₂. Band gap energies derived from the RXES analysis are compared to the values obtained from optical measurements. Finally, the spectral shift and evolution of the Kβ main emission line are used to determine the valence state (and corresponding average spin) of Ti. The results are related to the diffraction, optical and photoelectrochemical measurements in order to obtain a full interpretation of the changes in local atomic/ionic structure and their influence on the photo-electrical and optical properties.
References:
[1] M. Radecka, et al., J.Nanosci.Nanotechnol. 10 (2010) 1032-42.
[2] A. Trenczek-Zajac, et al., J. Nanosci. Nanotechnol. 12 (2012) 4703-4709.
[3] K. Kollbek, et al., Radiat. Phys. Chem., http://dx.doi.org/10.1016/j.radphyschem.2013.03.035, (2013).
[4] O.V. Safonova, et al., Electrochim. Acta 56, (2010) 145-153.
K.K. has been partly supported by the EU Human Capital Operation Program, Polish Project No. POKL.04.0101-00-434/08-00.
Statutory project of K.Z. is acknowledged.

Photocatalytic and photoelectrochemical water splitting has attracted considerable attention due to the potential for clean production of H₂ from water utilizing abundant solar energy.[1] From the view point of solar energy conversion efficiency, it is indispensable to develop a visible-light-driven photocatalyst. Among a large number of materials that have been studied since the discovery of photocatalytic behavior of TiO₂[2], Rh-doped SrTiO₃ (Rh:STO) has recently been shown to be one of the few useful visible-light-driven oxide photocatalysts for H₂ production.[3] The photocatalytic activity of Rh:STO is dependent on the valence state of the Rh dopant; Rh⁴⁺:STO is photocatalytically inert, while Rh³⁺:STO is active.[3] Based on the photoelectrochemical behavior, Rh:STO appears to be a rare p-type titanate.[4, 5] In the present study, we focus on clarifying the relationship between the photocatalytic activity and the electronic structure of Rh:STO. We also compare Ir:STO with Rh:STO, because Ir is a 5d element and in the same group with Rh (4d element) in the periodic table.
M:STO (M= Rh, Ir) powders were synthesized in a conventional solid-state reaction. Epitaxial thin film samples were fabricated by pulsed laser deposition. The electronic structure of the occupied and unoccupied states of Rh:STO were studied by x-ray emission spectroscopy and x-ray absorption spectroscopy at SPring-8 BL07LSU. The spectroscopy results were compared with first-principles calculations. The photoelectrochemical performance of the epitaxial thin films was measured by cyclic voltammetry in 0.1M K₂SO₄ aq. under light illumination.
The lower photocatalytic activity of Rh⁴⁺:STO compared to Rh³⁺:STO was found to be due to the existence of a mid-gap acceptor level of Rh⁴⁺, which serves as a strong recombination center for the photoexcited carriers.[6] Rh:STO photoelectrodes showed a cathodic photocurrent regardless of the Rh valence. However, it appears that Rh³⁺ is more active and stable in the H₂ evolution reaction than Rh⁴⁺.[5] In contrast, Ir⁴⁺:STO photoelectrodes showed an anodic photocurrent with a lower photocurrent density than Rh:STO, although the light absorption coefficient of Ir:STO is larger than that of Rh:STO. The difference of the electronic structure between Rh:STO and Ir:STO is in the impurity level positions, which is ~0.5 eV higher for Ir than for Rh. These results indicate that the effect of the impurity levels is determined by the degree of the overlap between an impurity-related donor level and the O2p valence band, as has been theoretically suggested in [7].
[1] K.Maeda et al., J.Phys.Chem.Lett. 1, 2655 (2010). [2] A.Fujishima et al., Nature 37, 238 (1972). [3] R. Konta et al., J.Phys.Chem.B 108, 8992 (2004). [4] K. Iwashina et al., J.Am.Chem.Soc. 133, 13272 (2011). [5] S.Kawasaki et al., Appl. Phys .Lett., 101, 033910 (2012). [6] S.Kawasaki et al., J. Phys.Chem.C 116, 24445 (2012). [7] H.C.Chen et al., J.Phys Chem.C 116, 7897 (2012).

Highly crystalline two-phase anatase/brookite TiO2 nanostructures were synthesized from titanium sulfide (TiS2) in sodium hydroxide solutions via a simple hydrothermal method. With variation of sodium hydroxide concentration, the anatase and brookite phase composition can be controlled. From a series of experiments with controlled reaction time, it was determined that anatase and brookite are formed from the direct transformation of sodium titanate. Photocatalytic activities of the as-synthesized two-phase anatase/brookite TiO2, pure anatase nanoparticles and brookite nanoplates were appraised via photocatalytic hydrogen evolution in aqueous methanol solution. Despite having lower surface areas, brookite nanoplates and two-phase anatase/brookite TiO2 exhibit higher hydrogen evolution than anatase nanoparticles. This is attributed to the more cathodic conduction band edge potential of the brookite phase than the anatase phase which was evidenced by Mott-Schottky plots and thus leading to more energetically favorable hydrogen reduction. Furthermore, due to the excited electron transfer from the brookite to anatase phase, the two-phase anatase/brookite TiO2 exhibits higher hydrogen evolution than the single phase TiO2 as a result of effective electron-hole separation. In addition, hydrogen evolution is higher for our as-synthesized two-phase anatase/brookite TiO2 as compared to the highly active P25.

Photochemical water oxidation using solar light is an essential way to provide electrons for artificial photosynthesis. To achieve an efficient artificial photosynthesis system, highly-active and robust water oxidation catalysts are critically required. Iridium oxide (IrO₂) has been considered as a promising candidate material because of its low overpotential for water oxidation, but the poor stability of its colloidal suspension is a crucial issue. In this study, IrO₂ nanoparticles decorated on nanofibrous titanium oxide (TiO₂) scaffold was synthesized as a water oxidation catalyst. Electrospinning technique was introduced to fabricate the nano-sized 1-D structure of TiO₂ scaffold(average diameter ~200 nm), and the scaffold provided stable attachment site to IrO₂ nanoparticles(average diameter 10 and 30 nm) through heat treatment. The size and amount of IrO₂ nanoparticles were successively controlled using the different concentration of iridium precursor solutions. The catalytic effect of IrO₂/TiO₂ hybrid nanofibers on water oxidation was confirmed using cyclic voltammetric analysis and photochemical oxygen evolution test, using Ru(bpy)₃ and Na₂S₂O₈ as a photosensitizer and a sacrificial electron acceptor, respectively. IrO₂ nanoparticles with a diameter of 10 nm on the TiO₂ nanofibers exhibited higher turnover number (TON) than those of 30 nm IrO₂ nanoparticles, and lower iridium contents on TiO₂ nanofiber exhibited higher TON(~300) in photochemical oxygen evolution experiment. The IrO₂ nanoparticles The IrO₂ nanoparticles on titanium nanofiber scaffolds could be used repeatedly without noticeable deactivation due to the high crystallinity of IrO₂ nanoparticles, and XPS analysis revealed that TiO₂ nanofiber can maintain the oxidation state of IrO₂ by self-reduction of TiO₂ scaffold. Our synthetic strategy is a promising route for fabricating efficient and robust catalyst system by immobilizing of metal oxide catalyst on semiconducting scaffold platforms.

Nanostructured ZnO has been the source of great scientific interest, toward both the understanding and exploitation of its intrinsic properties and the performance in optoelectronic applications due to its direct wide band gap of 3.35 eV at 300 K and the high exciton binding energy of 60 meV. Consequently, fabricating ZnO nanostructures with different sizes and morphologies is of great importance for fundamental research and the development of novel devices. To date, various ZnO nanostructures have been successfully synthesized, including quantum dots, nanorods, nanowires, nanobelts, nanorings, nanocups, nanodisks, nanoflowers, nanonails, nanospheres, and hierarchical nanostructures. In particular, one-dimensional (1D) ZnO nanorods have high surface area and good dispersibility in solution rate, which enable them to act as promising photocatalysts for photocatalytic degradation of water pollutants and endocrine disrupting chemicals degradation. Mechanochemical or solid-state reactions are particularly suitable for the large-scale production of nanoparticles because of their simplicity and low cost. Because such reactions do not involve organic solvents, they are attractive from an environmental point of view.
In the present study, ZnO nanorods with good crystallinity were synthesized by michanical assisted thermal decomposition method. The as-synthesized products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) together with an energy dispersion X-ray spectrum analysis (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), Selected area electron diffraction (SAED), and UV-visible spectra. The hexagonal structure of ZnO was confirmed by X-ray diffraction. The nanorods shape and size have been identified through FESEM and TEM. The TEM show that most of the nanorods have straight sides and regular ends. We examined the crystallographic nature of the individual ZnO nanorod using HRTEM observations and SAED. Taking all TEM images, HRTEM and SAED into account, the real shape of the nanorod can be approximately reconstructed, in which the axial direction is [001]. The results indicate that the ZnO nanorod grows along the [001] direction and expose their {10-10} facets.
The photocatalytic activity of ZnO nanorods were evaluated by the methylene blue (MB) degradation in aqueous solution under visible-light irradiation. The photocatalysis experiments demonstrated that high aspect ratio rods showed significantly higher visible light photocatalytic activity when compared to the lower aspect ratio structures. Compared with the HRTEM and photocatalysis experiments, the higher expose fraction of {10-10} facets leading to better visible-light photodegradation. It is proposed that higher activity is due to better charge separation in the elongated 1D structure.

An attractive method to create new molecular level electronic, optical and magnetic devices is to use solid host lattices that serve as templates within which a guest structure of nanometer architecture can be assembled. Zeolites and zeo-type silica structures with nanopores and cavities in 3-dimensional windows are known to represent a “New Frontier” of solid state chemistry with great opportunities for innovative research. Furthermore, zeolites&’ ability to encapsulate nanosized metal and quantum dots inside their channels and pores makes zeolites promising materials where quantum effects due to size confinement become observable. Accordingly, semiconductor photocatalysis has attracted attention recently as an alternative to traditional physical, chemical, or biological technologies for environmental remediation. However, the size of the metal nanoparticles inside this structure is limited by the pore size of that network and thus it is also of great interest to be able to alter the size of these nanoparticles, if possible, in the network [1, 2]. In the current study, ruthenium nanoparticles were synthesized within the cavities of Engelhard Titanosilicate (ETS-10) that possesses semiconductive monatomic hellip;Ti-O-Ti-O-Tihellip; chains and thus makes this material a promising candidate for photocatalysis. Ruthenium nanoparticles were created and controlled in size in a range of 1-7 nm within ETS-10 for the first time. In order to obtain a controlled variation in the size of these nanoparticles, the silica network of ETS-10 was subjected to a controlled structural deformation creating larger mesopores within its structure. It was shown that post-synthesis treatments with aqueous solutions of H2O2 induced structural defects in ETS-10 by partial removal of the structural Ti and Si atoms without a substantial degradation in the crystallinity. Ruthenium nanoparticles were stabilized by ETS-10 network and a new type of photocatalyst for photoreduction of methylene blue in aqueous medium was developed. Moreover, the effect of increasing micropore volume as a function of harshness of H2O2 treatment was investigated to see whether any changes were induced during the formation of such metal nanoparticles.

4-nm Mn2+-doped zinc sulfide nanoparticles at 5% (ZnS:0.05Mn) were fabricated via inorganic chemical method in an aqueous medium at ambient conditions. Upon doping the host semiconductor with Mn2+ions, an additional emission band in the orange region was observed and the material exhibited a ferromagnetic ordering below 30 K, Curie temperature. No ferromagnetic behavior was evidenced for ZnS:0.05Mn bulk. ZnS:0.05Mn nanoparticles showing high photoluminescence efficiency and lifetime shortening were employed as photocatalyst in the photodegradation of 1,3 diphenylisobenzofuran by irradiating the sample with green laser . It was found that degradation efficiency increased remarkably after doping the ZnS host. Also, a singlet oxygen quantum yield of ~ 59 % in water was determined from our photodegradation spectra analyses. Furthermore, the ability of ZnS:0.05Mn to image Gram positive and negative bacteria was studied. The appropriate conditions for the uptake of the nanoparticles by E.coli, P. aeruginosa and S. aureus bacteria will be also presented.

Recent advances in our understanding of alternative active sites for oxygen reduction has provided for the basis of its molecular design. This presentation put these developments in the context of more than two decades of effort devoted to engendering such non noble metal electrocatalysts. In this presentation we will present our latest data on the most active analogs which comprise of a FeNx coordinated sites in close concert with Fe nano-particles either present in some polymer composite or more ideally as edge defects close to the Fe-Nx coordinated structure. We will show how these active sites evolve on carbon supports as graphene defect structures. Such active site determinations are made with the use of a special in situ synchrotron x-ray absorption method using the near edge spectra referred to as x-ray absorption near edge structure (XANES), in a subtractive mode wherein the signal contribution from the bulk is successfully subtracted from the effect of the surface adsorbed species. When combined with our ability to simulate the same signatures using models with specifically adsorbed moieties, a powerful tool emerges to study electrochemical interfaces under actual in situ and operando conditions. This technique, commonly called the ‘Delta Mu (delta mu;) Technique&’ has been applied to a wide variety of transition metal surfaces and alloys (1-2) including non-Pt based metal electrocatalysts with element specificity. EXAFS data taken concurrently provide information on the changes in short range atomic order around the absorber atom thereby providing structural information such as bond distances and coordination numbers (thereby information on average cluster size, homogeneity and surface segregation etc.).
In this presentation among other things we will provide a picture of the electrocatalytic pathways in aqueous (at both the extreme edges of the pH scale) and non-aqueous environments. The technological consequence of such materials in power generation, electrolysis and energy storage will be described.
References
(1) J.M. Ziegelbauer, D. Gatewood, A.F. Gulla, M.J.F. Guinel, F. Ernst, D.E. Ramaker, S. Mukerjee, J. Phys. Chem. C, 113 (2009) 6955-6968.
(2) S. Mukerjee, T. Arruda, Mod. Aspects Electrochem., 50 (2010) 503-572.

The enhancement of the catalytic activity of bimetallic alloys is often affected by the surface composition and geometry of the atoms. Since Pt can catalyze a number of important reactions, Pt-Cu alloys have the potential to sustain activity while reducing the amount of precious metal required to catalyze industrially important reactions; however, the local atomic surface structure and its influence on the observed chemistry is unknown. Using scanning tunneling microscopy (STM), we show that various Pt-Cu surface morphologies can be generated by controlling the preparation conditions. We characterized the atomic arrangement of Pt atoms deposited on Cu(111) as a function of temperature and coverage. Pt atoms readily alloy into Cu(111) at low coverages and moderate temperatures. Depending on the temperature during deposition, the intermixing of Pt-Cu is driven by the negative mixing enthalpy of Pt and Cu, a decrease in surface free energy, and/or a release of elastic strain. As a result, several Pt-Cu metastable states are observed at lower temperatures including isolated Pt atoms, monatomic high islands, and Pt rich regions located at Cu step edges. At higher local concentrations of Pt atoms, the Pt and Cu atoms form small regions of order that maximize the number of stronger Pt-Cu bonds over Pt-Pt or Cu-Cu bonds. Increasing the temperature during the deposition of Pt provides the thermal energy for the direct exchange of Pt atoms into the terraces resulting in an even dispersion of the Pt atoms across the Cu terrace. Surface and subsurface Pt atoms are also observed at higher temperatures. Pt atoms, unlike other catalytic metals such as Pd, are able to directly alloy in the Cu terraces independent of step edges. Hence, Pt atoms exist as isolated atoms that are well separated from one another, unlike Pd atoms that localize at Cu step edges. Due to the improved dispersion of Pt in Cu(111), it is an ideal model system to probe the hydrogenation chemistry of single Pt atoms.

One major goal in electrocatalysis studies is to produce highly active, durable catalysts while minimizing the use of precious noble metals, especially platinum (Pt). This is the key requirement for the large-scale commercialization of proton exchange membrane (PEM) fuel cells. An effective approach is to fabricate core-shell nanoparticles (NPs)with Pt atoms on the surface, and with tunable reactivity through their interactions with other metal cores to assure optimal catalytic performances. In addition to the increase in surface area per Pt mass, high enhancements in the area-normalized specific activity over Pt nanoparticles were found with Pt- or Pd-alloy cores containing 3d transition metals, such as Co, Ni, and Cu. However, a more challenging issue emerged as accelerated durability tests showed a gradual loss of surface area and ORR activity for these advanced ORR catalysts.
It is well known, the catalytic properties of nano-catalysts are directly linked to their structures, e.g. the lattice contraction, facets, surface morphology and compositional ordering. This work will discuss the structure-performance relationship of the Pt based catalysts with various core-shell structures (including nanoparticles, and nanorodes), based on results of the atomic-resolution transmission electron microscopy (TEM) characterization and catalytic performance (mess activity, durability etc.). We mainly use two approaches based on aberration-corrected scanning transmission electron microscopy (STEM): Z-contrast high angle annular dark field (HAADF) imaging and high resolution electron energy loss spectroscopy (EELS) imaging (1D or 2D). With the knowledge of the DFT calculation and synchrotron X-ray techniques, we will discuss three questions: (1) Kirkendall effect and lattice contraction in the hollow Pt nanoparticles, (2) The compositional effect of FePtM (M = Pd, Au) nanoparticles/nanorods (3) The effect of layer-thickness and stacking sequence of Ru@Pt. We believe that the understanding of the structure-performance relationship is essential to develop the new generation of nano-catalysts.

Metal nanoparticle catalysts are commonly supported on metal oxides, but their stability is limited by coalescence. During this process, the surface area, and thus the catalytic activity, decreases. In order to design these systems to inhibit coalescence of the metal nanoparticles, we have carried out a fundamental study of bonding at the metal-oxide support interface. Late transition metal oxide and metal nanoparticles have been deposited on oxides supports and the effects of interfacial bonding, particle migration and coalescence have been studied. Isothermal titration calorimetry (ITC) is used to understand the thermodynamics during the supported nanoparticle synthesis while XAS, TEM, and PDF are used to study the bonding and particle migration and coalescence.

Functional perovskite oxide films and their interfaces have been the subject of active research due to their tunable emergent physical and chemical properties, such as superconductivity, two-dimensional electron gas behavior, and electrocatalytic functionality. New types of tunable electrocatalysts could provide opportunities to overcome the current limits of energy storage and conversion systems related to water dissociation and formation. However, understanding of the electrochemical reaction mechanisms on complex oxide surfaces and interfaces is far from complete, particularly with regards to structure-function relationships of complex oxide surfaces occurring in aqueous solutions under applied electric fields. To elucidate the electrocatalytic properties of oxide surfaces and interfaces, it is necessary to build a model system and to employ in-situ experimental tools. We chose model perovskite-structured SrRuO3 (SRO) ultrathin films, grown on Nb-doped SrTiO3 (001), (110), and (111) substrates to elucidate the structure-function relationships. We performed in-situ synchrotron studies, combining structural, spectroscopic, and electrochemical characterization of the epitaxial thin films. We found that SRO films exhibited large oxygen evolution (OER) activity, but the surfaces examined are not structurally stable under some electrochemical conditions. For the case of (001)-oriented SRO, the c-axis (out-of-plane) lattice parameter was observed to change reversibly with varying electric field at potentials smaller than 1.25 V vs. RHE, but the SRO irreversibly changed under larger voltage electrochemical conditions characteristic of the OER. These changes might be connected to chemical dissociation of SRO during the catalytic reaction. The structural instability correlated with changes observed during in-situ spectroscopic measurements, which showed a change in valence of the active sites (Ru), connected to the loss of perovskite structure. The relationships among activity, stability, and structural properties of the complex oxide surfaces during water dissociation and formation will be described. The possible impact of the results on the development of new strategies for the creation of new stable and active electrocatalysts designed at the atomic level will be discussed.
Work at Argonne, including use of the Advanced Photon Source, is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

Nano-structured and hierarchically structured materials contribute to the enhancement of the catalytic properties of the electrodes, dramatically improve interconnectivity of porous matrixes and revolutionize mass-transport characteristics on micro- and meso-scale. Their main role is in enabling the display of phases of greater catalytic activity, stabilizing “unusual” surface moieties that are not displayed in quantities in bulk phases and in facilitating transport phenomena and through this increasing of volumetric (and in some cases, gravimetric) power density, provide for higher energy density and facilitate increased rate of drain. UNM has developed the Sacrificial Support Method as a main approach for templated synthesis of hierarchically structured electrocatalysts materials. In this method the catalysts precursors are being absorbed on, impregnated within or mechanically mixed with the support (usually mono-dispersed or meso-structured structured silica), thermally processed (pyrolyzed) and then the silica support is removed by etching (in KOH or HF) to live the open frame structure of a “self-supported” material that consists of the catalysts only.
This presentation brings examples from two materials synthesis platforms: aerosol processing in a format of spray pyrolysis and colloidal approach based on sol-gel templating of micro-emulsions. The spray-based process results in formation of unique spherical, micron-sized aggregates consisting of sub-micron electrocatalyst particles where the nanometer sized active phases (PGM and metal alloys, metal oxides, composite and non-noble or graphene metal electrocatalysts) are highly dispersed. Microemulsion-derived materials have three levels of morphology control: nano-pores derived from micellar structure of the surfactant used, meso-pores templated on the microemulsion droplets and meacro-structured particles resulting from sheer mixing. A wide variety of materials can be made by these methods in which not only the composition but also the microstructure can be varied. It is the combination of these attributes - control over microstructure at a number of different length scales and composition, simultaneously - that is extremely important to the performance of the electrocatalyst materials in a fuel cells. This paper will bring examples of successful practical applications of our materials in automotive technologies using both Polymer Electrolyte (PEMFC) and Alkaline Membrane (AMFC) Fuel Cells.

Highly active catalysts for energy storage and conversion are pivotal in the pursuit of sustainable energy. Suntivich et al. have proposed that the occupancy of the transition metal eg orbital can serve as design criterion for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) of perovskite catalysts [1,2], which they used to identify Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) as a highly active OER catalyst. It was later reported that the surface of this material becomes amorphous during OER activity, which increases its specific activity [3,4]. On the other hand, the well-defined surfaces of epitaxial thin films offer great prospects to gain much needed insights into oxygen electrocatalysis [5].
Here, we discuss the OER and ORR activity of epitaxial grown (001)-oriented BSCF thin films and the stability during oxygen electrocatalysis. The epitaxial thin films operate at current densities comparable to those of the ink-casted powders [2-4]. No change of the bulk-like 10 nm film during cyclic voltammetry was observed, which suggests the absence of the previously observed surface modifications [3,4]. While the OER activity of the thin films decreased with film thickness, the trend for the ORR was opposite. This highlights an avenue towards engineering material systems for bifunctionality by tuning the film thickness.
[1] Suntivich, May, Gasteiger, Goodenough, Shao-Horn (2011) Science 334, 1383.
[2] Suntivich, Gasteiger, Yabuuchi, Nakanishi, Goodenough, Shao-Horn (2011) Nat. Chem. 3, 546.
[3] May, Carlton, Stoerzinger, Risch, Suntivich, Lee, Grimaud, Shao-Horn (2012) J. Phys. Chem. Lett. 3, 3264.
[4] Risch, Grimaud, May, Stoerzinger, Chen, Mansour, Shao-Horn (2013), J. Phys. Chem C 117, 8628.
[5] Stoerzinger, Risch, Suntivich, Lü, Zhou, Biegalski, Christen, Ariando, Venkatesan, Yang Shao-Horn (2013) Energy Environ. Sci. 6, 1582.

Transition metal oxides, such as perovskites, are promising non-precious metal catalysts for low-temperature oxygen electro-reduction (ORR) and evolution (OER), and thus of potential value to the development of alkaline fuel cells. Ab-initio modeling of ORR/OER on perovskites is challenging due to the electronic structure of the transition metal, possible surface reconstructions, and potentially complex surface coverages. Previous ab-initio simulations of the ORR and OER on transition metal perovskites have considered only pristine (001)-BO2-terminated surfaces. Although such simplified surfaces may predict correct trends in oxygen catalytic activities with respect to the transition metal, they tend to overestimate the ORR/OER overpotentials by more than ~0.5V compared to the experiments. In this study we use DFT with Hubbard U (GGA+U), to predict the ORR, OER overpotentials. We further include the (voltage-dependent) thermodynamically stable surface coverage in alkaline environment. The results show that the GGA+U and surface coverage effect can play a significant role in the relative binding energies of reactive intermediates of ORR and OER. For the systems studied to date this approach provides overpotentials within 0.3V of accuracy compared to the experimentally reported overpotentials. This study demonstrates a path towards more accurate first-principles predictions of the activities of complex oxides for ORR and OER.

Typically, the electrochemical oxygen reduction reaction (ORR) is assessed using bare metal electrodes in direct contact with an aqueous electrolyte. However, this architecture allows all reactants and products to have equivalent geometric access to the catalyst surface. Here, we discuss results of a survey of ways to bias reactants (oxygen) to the catalyst surface, and bias products (water) away from the catalyst surface, in order to control catalyst activity. We use nanoporous Ni/Pt electrodes fabricated using electrochemical dealloying to create catalytic surfaces with pore and ligament sizes each approximately 3-5 nm in diameter; these pores are then filled with an ionic liquid (IL) that serve as intermediate layer between the catalyst and the electrolyte. In this presentation, we will discuss how the properties of the IL layer affect oxygen reduction in acid electrolyte in rotating disk electrode experiments and the variation of these properties with temperature. Particular properties of the IL that we vary include proton conductivity (protic vs. aprotic), oxygen solubility (higher or lower than the aqueous electrolyte), and IL phase (solid vs. liquid).

Natural photosynthesis harvests the energy in visible light to power chemical reactions and uses CO2 as the carbon source. Because light as an energy source is free and abundant, chemical reactions similar to photosynthesis have major fundamental and practical implications. Indeed, significant efforts have been attracted to this research goal. The majority of attention for photochemical reactions that transform CO2 have focused primarily on conversion into fuels. How to learn from photosynthesis and devise reaction routes for the synthesis of useful organic compounds receives relatively underwhelmed considerations. Drawing inspiration from the mechanisms found in dark reactions of photosynthesis and using p-type Si nanowires as a photocathode, we proposed and demonstrated that highly specific reactions can be readily carried out to produce α-hydroxy acids by photoreduction of aromatic ketones, followed by CO2 fixation. Powered by visible light, this reaction is in close resemblance to natural photosynthesis, and different from its electrochemical analogues. The carboxylation products of two of the substrates examined in this talk serve as precursors to nonsteroidal anti inflammatory drugs (NSAID), ibuprofen and naproxen. Our detailed studies of the photoelectrochemical properties of Si nanowires will be presented as well.

Despite the high thermodynamic stability of CO2, biological systems are capable of both activating the molecule and converting it into a range of organic molecules, under moderate conditions. It is clear that if we were able to emulate Nature and successfully convert CO2 into useful chemical intermediates without the need for extreme reaction conditions, the benefits would be enormous: One of the major gases responsible for climate change would become an important feedstock for the chemical and pharmaceutical industries. Indeed, CO2 conversion is recognised as one of the major challenges in contemporary chemistry.
Iron sulfide membranes formed in the warm, alkaline springs on the Archaean ocean floor are increasingly considered to be the early catalysts for a series of chemical reactions leading to the emergence of life. The anaerobic production of acetate, formaldehyde, amino acids and the nucleic acid bases - the organic precursor molecules of life - are thought to have been catalyzed by small cubane clusters, which are structurally similar to the surfaces of present day sulfide minerals such as greigite (Fe3S4).
Here we present the solvothermal decomposition of metal dithiocarbamate complexes (MDTC) to produce a variety of novel metal sulfide nano particle catalysts. The mechanism of decomposition of MDTC has been followed by in situ XAFS and UV-vis and matched to computational calculations. The phase of the resultant nano particles can be tuned by altering the decomposition variables; in particular the addition of a redox active compound during decomposition promotes the formation of the thiospinel, greigite. This finding can be applied to other metal sulphides leading to a general route for thiospinel synthesis. HRTEM of the greigite catalyst gives full surface characterisation and subsequent computational modelling reveals surface active sites for CO2 reduction. Finally the results for the electro catalytic testing and products from the reduction of CO2 will be shown.

Photoexcited electrons should be efficiently separated from holes in semiconductors, allowing their delivery to specific regions for half-reactions in photocatalysis. In competition with charge transfer is electron and hole recombination, which has been a key process for limiting quantum efficiency in related applications. In order to suppress the recombination, an effective solution is formulation of Schottky junctions by integrating an electron-extracting agent with the semiconductor. In this presentation, I will demonstrate two approaches to efficient electron-hole separation for CO2 reduction and water splitting, respectively, by formulating Schottky barrier in semiconductor-based hybrid structures. In the first approach, a semiconductor-metal-graphene design has been implemented to efficiently extract photoexcited electrons through the graphene nanosheets. Ultrafast spectroscopy characterizations exclusively demonstrate that the accumulation of “hot” electrons at the interface of semiconductor and metal can be substantially avoided, enabling superior efficiency in water splitting. The second approach is to utilize the capabilities of metal-organic frameworks (MOF) in capturing CO2 and transferring electrons, leading to greatly improved activities of semiconductor in CO2 reduction. It is anticipated that this work opens a new window to rationally designing hybrid systems for photo-induced applications.

TiO2 is one of the most popular photocatalysts, and the rutile (110) surface has been widely chosen as a prototype system for studies of fundamental chemical and physical phenomena occurring on oxide surfaces. Photoinduced oxidation of CO to CO2 on TiO2(110), which would be the simplest bimolecular photoreaction, has received considerable attention. A detailed understanding of the underlying mechanisms is of great scientific interest and can also help to improve the performance of existing photocatalytic materials as well as the design and development of new ones. Yates and co-workers determined the existence of two distinct chemisorption states for molecular oxygen on TiO2 (110). That is, one (α state) can photo-oxidize coadsorbed CO and the other (β state) only undergoes fast photodesorption. In addition, a very recent experimental study suggests that an electron-mediated reaction and a hole-mediated reaction are needed for the complete photooxidation reaction. While the photooxidation tends to be associated with different states of adsorbed oxygen and excess charge carriers, the exact adsorption configurations and charge states of O2 and CO as well as the behavior and contribution of holes and electrons still remain unclear. In fact, previous theoretical studies have mainly focused on understanding the nature of O2 interaction with the reduced surface and the reaction of CO with molecularly adsorbed O2 at the oxygen vacancy site. In this talk, we will present the behavior of electrons and holes near surface and how they can catalyze CO oxidation on TiO2(110) based on DFT + U calculations. Our calculations clearly show that both holes and electrons are necessary to significantly enhance CO oxidation to CO2. The underlying mechanisms of the electron/hole-assisted CO oxidation reaction will be discussed based on a detailed analysis of near-surface electron/hole localization as well as its impact on O2 activation followed by O2+CO reaction. Overall, our results explain well recent experimental observations, and also provide some important insight into the photoinduced surface chemistry of TiO2.

To help combat the increased energy demands of society and mitigate the continued environmental impact of fossil fuel depletion, alternative methods of dealing with such issues must be found. The sun provides a viable, clean, and renewable source of energy. Using semiconducting nanoparticles, the energy of the sun can be harnessed and converted into chemical energy to better provide for the world&’s growing energy requirements. In this study, we combine the photocatalytic properties of cadmium sulfide (CdS) nanorods (NRs) with two co-catalysts and show that overall water splitting with visible light can be realized in one structure.
Cadmium sulfide (CdS) is a semiconductor with band energies conducive for effective visible light absorption, along with being well aligned with the redox potentials of water. Combined with platinum (Pt) co-catalysts, electrons can be used for the reduction of H+ into H2. With the addition of adsorbed ruthenium (Ru) molecular catalysts, the system can also be used to produce O2 and help prevent the photo-oxidation of the nanocrystals. Our results indicate that an aqueous suspension of CdS NRs decorated at the tips with Pt nanoparticles in a matchstick configuration and decorated with chemisorbed mononuclear molecular catalysts can be used to produce hydrogen and oxygen. The efficiencies of such hydrogen and oxygen generation will be discussed, and transient absorption measurements will help elucidate the charge transfer dynamics of the system.

Hydrogen is an ideal clean energy and also an important chemical in industries. The hydrogen must be produced from water using a renewable energy source, if one considers the energy and environmental issues. Therefore, photocatalytic water splitting is still a challenging reaction because it is an ultimate solution to these serious problems, even if this research history is long. Photocatalytic CO2 fixation has also attracted attention. These water splitting and CO2 fixation of uphill reactions can be regarded as artificial photosynthesis, because light energy is converted to chemical energy. In the present paper, we introduce various metal oxide and sulfide photocatalysts aiming at artificial photosynthesis [1].
Solar water splitting has been achieved by construction of a Z-scheme photocatalysis system employing visible-light-driven photocatalysts (Ru/SrTiO3:Rh and BiVO4) with and without electron mediators [2]. Photoelectrochemical water splitting without applying external bias under visible light irradiation was also demonstrated using the SrTiO3:Rh photocathode and the BiVO4 photoanode [3,4]. On the other hand, Ag cocatalyst-loaded ALa4Ti4O15 (A = Ca, Sr, and Ba) photocatalysts with 3.79-3.85 eV of band gaps and layered perovskite structures show activities for CO2 reduction to form CO and HCOOH in an aqueous medium without any sacrificial reagents [5].
References
[1] A. Kudo and Y. Miseki, Chem. Soc. Rev., 2009, 38, 253.
[2] A. Kudo, MRS BULLETIN, 2011 36, 32.
[3] K. Iwashina and A. Kudo, J. Am. Chem. Soc. 2011, 133, 13272.
[4] Q. Jia, K. Iwashina, and A. Kudo, Proc. Natl. Acad. Sci. USA, 2012, 109, 11564.
[5] K. Iizuka, T. Wato, Y. Miseki, K. Saito, and A. Kudo, J. Am. Chem. Soc., 2011, 133, 20863.

The photocatalytic oxidation of water is of significant interest as a potential method of hydrogen generation with the use of solar power. Titania is one of the most promising and widely studied catalytic materials proposed for that purpose. We have investigated the initial step of water oxidation on rutile TiO₂ (110) surface - the abstraction of one hydrogen atom from the water molecule adsorbed on the catalyst surface by the photo-generated hole. In order to model the evolution of the excited state of titania-water system, we have carried out real-time simulations using the time-dependent density functional theory. The behaviour of the water molecule and the role of the defects in the photooxidation process are discussed. The results allow to obtain novel insights into the microscopical mechanism of catalyzed water oxidation.

The hydrogen evolution reaction (HER) is an important electrocatalytic process with relevance to renewable fuel production and utilization, such as hydrogen generation through direct semiconductor solar water splitting or through water electrolysis powered by photovoltaics. Since the most efficient electrocatalysts typically used in electrolysis systems are noble metals, the development of less expensive and more abundant non-noble metal based catalysts as alternatives is highly desirable. In this work, we have developed a low temperature synthesis that produces a bimetallic non-noble metal nitride with a high surface area that is an excellent HER catalyst under acidic conditions. A catalytic current density of 10 mA cm-2 is achieved at an overpotential of 200mV. The crystal structure of this nitride was determined through the combined Rietveld refinement of neutron an X-ray diffraction data, and is found to differ from that of Ni-Mo-N, a system in which excellent HER activity was recently discovered. Neutron pair distribution function (PDF) experiments indicate that the local structure does not sufficient differ from the average structure. XANES and XPS measurements provide insights into the valence and stoichiometry in the bulk and at the surface of the phase.

Since the first report of photo-induced water splitting by TiO₂ electrodes was published [1], the potential of this reaction to convert photon energy into H₂ energy using photoelectrodes and powdered photocatalysts has been extensively investigated. Due to its simplicity, water splitting using a powdered photocatalyst is currently a subject of much interest, with most research focusing on the visible light sensitization of catalysts in order to effectively utilize incoming solar energy. However, the number of visible-light-sensitive photocatalysts that are able to split water into H₂ and O₂ in stoichiometric amounts (overall water splitting) is limited. Domen et al. have reported overall water splitting in the presence of GaN-ZnO photocatalyst under visible-light irradiation (one-step photoexcitation) [2]. With respect to the one-step photoexcitation system, we tried to control the conduction band (CB) of AgTaO₃ by introducing Nb at Ta site to be sensitive to visible light because AgTaO₃ is known to absorb only UV light [3]. Then, we prepared NiO-grafted Nb-doped AgTaO₃ (NiO/AgTa_0.7Nb_0.3O₃, NiO/AgTaNbO₃).
The band-gap of AgTaNbO₃ was calculated to be 2.9 eV from the Kubelka-Munk function obtained by a UV-visible absorption spectroscopy. We examined water-splitting over NiO/AgTaNbO₃ under irradiation with visible light generated from a 420 nm-LED lamp. The H₂ and O₂ evolved almost linearly with increasing the irradiation time. More importantly, the ratio of evolved H₂ to O₂ was 2 to 1 (stoichiometric amount). Thus, overall water-splitting in the presence of the photocatalyst was achieved. Detailed investigations will be discussed at the conference.
References: [1] A. Fujishima, K. Honda, Nature, 238, 37 (1972). [2] K. Maeda, K. Teramura, D. Lu, T. Takata, N. Saito, Y. Inoue, K. Domen, Nature, 440, 295 (2006). [3] H. Kato, A. Kudo, J. Phys. Chem. B, 106, 5029 (2002).

Water splitting and CO2 reduction by electrochemical or photoelectrochemical processes have been under intense investigation as a means to store solar energy and reduce the amount of greenhouse emissions in the atmosphere. In order to maximize the efficiency of these processes, catalysts operating with low overpotential and high currents are needed for not only the reductions of water or CO2 but also water oxidation to O2. However, many of the best water oxidation catalysts are too costly because they contain precious metals like Ir or Ru. Therefore, finding a water oxidation catalyst made from earth abundant materials is necessary.
In our previous work, CoWO4 was used as a model system to better understand what properties are necessary to improve water oxidation catalysts made from earth abundant materials. We were able to show that amorphous CoWO4 was able to outperform crystalline CoWO4 as a water oxidation catalyst likely due to the greater number for active sites participating in the water oxidation mechanism. In addition, we were able to show amorphous CoWO4 was capable of outperforming commercially available IrO2 in a photochemical solution system using Ru(bpy)32+ as a photosensitizer and S2O82- as an electron scavenger. These promising results indicate a need to further explore ternary or quaternary cobalt oxide materials and determine what effect the secondary atoms like W in CoWO4 can have on the catalytic ability of a material. With this in mind we have investigated the physical and electrochemical properties of various cobalt oxide based water oxidation catalysts in near neutral conditions to better understand the effect secondary heteroatoms can have on the catalytic efficiency.
1.Jia, H.; Stark, J.; Zhou, L. Q.; Ling, C.; Sekito, T.; Markin, Z. RSC Adv., 2012, 2, 10874-10881.
2.Sekito, T.; Jia, H. Prepr. Pap.-Am. Chem. Soc., Div. Energy Fuels 2012.