Symposium Organizers
Yu Han, King Abdullah University of Science and Technology
Phillip Christopher, Univ of California-Riverside
Zili Wu, Oak Ridge National Laboratory
Ning Yan, National University of Singapore
Symposium Support
King Abdullah University of Science and Technology
NM4.1: Novel Catalysts and Reaction Mechanisms I
Session Chairs
Tuesday PM, April 18, 2017
PCC West, 100 Level, Room 104 B
11:30 AM - *NM4.1.01
Structure-Property Relationships and Reaction Pathways in CO Hydrogenation Reactions over Supported K/MoS2 Catalysts in Higher Alcohol Synthesis from Syngas
Micaela Taborga Claure 1 , Michael Morrill 1 , Song-Hai Chai 2 , Sheng Dai 2 , Pradeep Agrawal 1 , Christopher Jones 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe use of supports as a means of enhancing the reactivity of K/MoS2 catalysts in higher alcohol synthesis from syngas has been widely investigated. In this work, we show that Mo-support interactions significantly affect the product distribution. At low Mo, and K loadings, carbon supports are predominantly hydrocarbon selective, whereas hydrotalcite-derived mixed MgAl oxide (MMO) supports yield high C2+OH selectivity.[1] These differing reactivity patterns are connected with different types of MoS2 domains on the two catalyst surfaces. [2] Subsequently, we evaluated the effect of the support on the specific reaction pathways by evaluating changes in product distribution via alcohol and olefin co-feed experiments. Specifically, the importance of (i) CO insertion and (ii) Guerbet coupling pathways were investigated. Early studies by Santiesteban et al. demonstrated that higher alcohols and hydrocarbons were formed via classical CO insertion pathways over K/MoS2 catalysts.[3] However, recent studies showed that coupling reactions may also be important.[4-5]
We have explored changes in product distribution in carbon and MMO supported K/MoS2 catalysts via MeOH, EtOH and Ethylene co-feed experiments, including use of 13C labeled cofeeds.[6-7] Alcohol co-feed experiments were specifically targeted toward elucidating Guerbet coupling reactions as well as providing insight into the importance of CO insertion pathways. The dominant pathway is determined from the product distribution by the prominence of either the expected coupled product or the decrease in production of longer chain products as the carbon chain increases. Similarly, ethylene co-feed experiments were used to investigate CO insertion pathways, with an increase in the next carbon chain product indicating a dominant hydroformylation pathway. Experiments over bulk MoS2 were used as a control to investigate the role of the supports.
References
[1] M.R. Morrill, N.T. Thao, H. Shou, R.J. Davis, D.G. Barton, D. Ferrari, P.K. Agrawal, C.W. Jones, ACS Catal. 2013, 3, 1665.
[2] M. Taborga Claure, S.-H. Chai, S. Dai, K.A. Unocic, F.M. Alamgir, P.K. Agrawal, C.W. Jones, J. Catal. 2015, 324, 88.
[3] J.G. Santiesteban, C.E. Bogdan, R.G. Herman, K. Klier, in: M.J. Philips, M. Ternan (Eds.), 9th Congress on Catalysis, vol.2, Chem. Inst. Can, Ottawa, 1988, p. 561.
[4] V.P. Santos, B. van der Linden, A. Chojecki, G. Budroni, S. Corthals, H. Shibata, G.R. Meima, F. Kapteijn, M. Makkee, J. Gascon, ACS Catal. 2013, 3 1634.
[5] J.M. Christensen, P.A. Jensen, N.C. Schiødt, A.D. Jensen, ChemCatChem 2010, 2 523.
[6] M. Taborga Claure, M. R. Morrill, S.-H. Chai, S. Dai, P. K. Agrawal, C. W. Jones, Catal. Sci. Technol. 2016, 6, 1957-1966.
[7] M. Taborga Claure, L.-C. Lee, J. W. Goh, L. T. Gelbaum, P. K. Agrawal, C. W. Jones, J. Mol. Catal. A. Chem. 2016, 423, 224-232.
12:00 PM - NM4.1.02
Pt Single-Atom Catalysts—Structure, Stability and Reactivity
Bin Zhang 1 , Zailei Zhang 1 , Yunzhu Wang 1 , Ning Yan 1
1 Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore Singapore
Show AbstractSingle-atom catalyst (SAC) has recently emerged as a new frontier in heterogeneous catalysis and is considered to bridge the gap between homogeneous and heterogeneous catalysis due to their unique features: each metal atom in the SACs experiences a similar environment and thus resulting in an identical geometric structures, analogous to that of a homogeneous catalyst.1-3 Two big challenges in synthesizing SACs are to stabilize single atom species when metal loading increases, and to maintain its catalytic stability under high reaction temperature.
In coordination chemistry, catalytically active metal complexes in zero or low valent state often adopt four-coordinate square-planar or tetrahedron geometry. By applying this principle, we have developed stable, high loading (close to 1 wt%), Pt1 single-atom catalyst on phosphomolybdic acid (PMA) modified active carbon, by anchoring Pt atoms on the four-fold hollow sites on PMA. Each Pt atom is stabilized by four surrounding oxygen atoms in a distorted square-planar geometry, with Pt slightly protruding from the oxygen planar surface. Pt is positively charged, easily absorbs hydrogen, and exhibits excellent activity and selectivity in the hydrogenation of nitrobenzene and cyclohexanone. This system describes here is likely to be extended to a number of stable SACs with superior catalytic activities.4
Besides, atomically dispersed Pt catalysts are often used in low-temperature catalytic reactions to avoid formation of nanoparticles at high temperature. We designed a thermally stable catalyst that consists of Pt atoms on the surface of coordinatively unsaturated pentahedral Al3+ centers, which are embedded in mesoporous Al2O3. After calcination and reduction at 400 °C, the obtained 0.2Pt/m-Al2O3-H2 is applied in CO oxidation, 1,3-butadiene hydrogenation and n-hexane reforming, which exhibits higher stability than commercial Pt/Al2O3 catalysts against the aggregation or deformation. No deactivation is observed for 0.2Pt/m-Al2O3-H2 with CO oxidation after 60 cycles, with temperature increasing from 100 °C to 400 °C and staying at 400 °C for 220 h. Noticeably, the 0.2Pt/m-Al2O3-H2 catalyst is also able to afford better stability than commercial Pt/Al2O3 catalysts, in n-hexane reforming and hydrogenation of 1,3-butadiene, at high temperature and in H2 atmosphere.
[1] Flytzani-Stephanopoulos, M.; Gates, B. C. Annu. Rev. Chem. Biomol. Eng. 2012, 3, 545-574.
[2] Yang, X.-F.; Wang A.; Qiao B.; Li J.; Liu, J.; Zhang, T. Acc. Chem. Res. 2013, 46, 1740-1748.
[3] Thomas, J. M. Nature 2015, 525, 325-326.
[4] Zhang B.; Asakura H.; Zhang J., Zhang J.; De S.; Yan, N. Angew. Chem. Int. Ed. 2016, 55, 8319-8323.
12:15 PM - NM4.1.03
Impact of Dislocations on Water-Gas Shift in Cu-Doped Ceria
Lixin Sun 1 , Bilge Yildiz 1 2
1 Department of Nuclear Science and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Material Science and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractCeria-based materials are promising for catalysts because of their low cost and high performance. A high density of dislocations, up to 1013/cm2, can be found in the nanostructured ceria, including thin films and nano particles. However, the role of dislocations on catalytic properties in ceria has not been systematically studied, compared to other surface defects like surface oxygen vacancies and surface steps.
Dislocations can greatly affect the catalytic performance of ceria via their interaction with surface metal additions and surface oxygen vacancies. Our previous research shows that edge dislocations in ceria can trap charged point defects via the elastic interaction with cation defects and the coulombic interaction with oxygen vacancies: larger trivalent cations, such as Ce3+ and Gd3+, can attract oxygen vacancies to the tensile region around dislocations, while smaller trivalent cations, such as Sc3+ can attract oxygen vacancies to the compressive region around dislocations. Meanwhile, transition metal atoms can strongly interact with dislocations in ceria. Using density functional theory calculations, we found that Cu interstitials segregate to the core of an edge dislocation with a segregation energy of 1.2 eV, changing their preferential oxidation state from 2-3+ to 1+, which is a more active oxidation state for surface reactions.
Based on this, we believe that dislocations can impact ceria surface reactivity by increasing the local oxygen vacancy concentration and anchoring single Cu atoms at the surface. Currently, we employ the QM/MM technique, combining classical force fields and density functional theory, to investigate the direct impact of dislocations on the catalytic reaction kinetics of water gas shift, especially the adsorption and desorption behavior of CO and CO2 molecules.
12:30 PM - *NM4.1.04
A DFT Rationalization of a Two Metals Strategy to Tune Selectivity in Catalysis
Luigi Cavallo 1 , Kazuhiro Takanabe 1 , Abdesslem Jedidi 1
1 , KAUST, Thuwal Saudi Arabia
Show AbstractSelectivity is among the most important properties of an effective catalyst. In homogeneous transition metals catalysis this can be achieved by appropriate design of the ligand wrapped around the metal. In heterogeneous catalysis this is a more complex issue, since selectivity is often associated with different reactivity at different surfaces of the catalyst, as well as at steps, edges, and any type of defects that almost inevitably are present in any heterogeneous catalyst. Indeed, the less selective sites on a metallic catalyst are usually associated with low coordinated metals, such as those of rugged surfaces or defects, since these sites are considered as the most reactive. Under these conditions, a promising strategy to improve the selectivity of a metallic catalyst is alloying a second metal, less reactive and capable to occupy preferentially sites corresponding to low coordinated metals.1 In this communication we will present some DFT insights supporting this scenario in the conversion of methylcyclohexane to toluene promoted by Ni/Zn catalysts,2 as well as in the dry reforming of methane promoted by Ni/Co catalysts.3
References.
1. Laesgaard, E.; Clausen, B. S.;. Nørskov, J. K.; Besenbacher, F. Nature Mat. 2005, 4, 160.
2. Al-ShaikhAli, A. H.; Jedidi, A.; Cavallo, L.; Takanabe, K. Chem. Commun. 2015, 51, 12931.
3. AlSabban, B.; Falivene, L.; Kozlov, S.; Aguilar-Tapia, A.; Ould-Chikh, S.; Lahera, E.; Delnet, W.; Hazemann, J. L.; Prat, A.; Cavallo, L.; Takanabe, K.; Basset J. M. Submitted
NM4.2: Novel Catalysts and Reaction Mechanisms II
Session Chairs
Yu Han
Zili Wu
Xueyi Zhang
Tuesday PM, April 18, 2017
PCC West, 100 Level, Room 104 B
2:30 PM - *NM4.2.01
Single-Atom Pt Catalysts for Electrochemical Reactions
Hyunjoo Lee 1 , Jiwhan Kim 1 , Sungeun Yang 1
1 , KAIST, Daejeon Korea (the Republic of)
Show AbstractAs a catalyst, single-atom platinum may provide an ideal structure for platinum minimization. The single-atom catalyst of platinum supported on titanium nitride nanoparticles were successfully prepared with an aid of chlorine ligands. Unlike platinum nanoparticles, the single-atom active sites predominantly produced hydrogen peroxide in the electrochemical oxygen reduction with the highest mass activity reported so far. The electrocatalytic oxidation of small organic molecules, such as formic acid and methanol, also exhibited unique selectivity on the single-atom platinum catalyst. A lack of platinum ensemble sites changed the reaction pathway for oxygen reduction reaction toward two electrons pathway and formic acid oxidation toward direct dehydrogenation, and also induced no activity for methanol oxidation. The single-atom platinum showed high mass activity and unique selectivity for the electrochemical reactions. Additionally, the role of the support may have a significant impact on the catalytic properties similar to that of the ligand molecules in homogeneous catalysts. The support effect was demonstrated by preparing the single-atom platinum catalyst on two different supports, titanium carbide and titanium nitride. The formation of single-atom Pt was confirmed by STEM, EXAFS, and in-situ IR spectroscopy. Pt1/TiC showed higher activity, selectivity, and stability for electrochemical H2O2 production than Pt1/TiN. Density functional theory calculation presented that oxygen species have strong affinity into Pt1/TiN possibly acting as surface poisoning species, and Pt1/TiC preserves oxygen-oxygen bond more with higher selectivity towards H2O2 production. The support in single-atom catalysts actively participates in the surface reaction, not just acting as anchoring sites for single-atoms.
3:00 PM - NM4.2.02
Catalytic Role of Ligands in Supported AunRm Nanoclusters for Gas Phase Reactions
Zili Wu 1 , David Mullins 1 , De-en Jiang 2
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , University of California, Riverside, Riverside, California, United States
Show AbstractLigand-protected gold nanoclusters, AunRm, with atomic precision and monodispersity have recently attracted much attention due to their well-defined structures and excellent catalytic performances in various reactions. The atomically precise Au nanoclusters are ideal model systems for understanding the structure-catalysis relationship of Au-based nanocatalysts. To elucidate how the organic ligands may affect the catalytic properties of gold catalysts, We compared two different AunRm nanoclusters supported on ceria for gas phase CO oxidation: thiolate ligands protected Au25(SR)18 (SR = -SCH2-CH2-Ph) with all surface Au atoms being coordinated and phosphine protected Au22(L8)6 (L8 = 1,8-bis(diphenylphosphino) octane) with coordination unsaturated (cus) Au atoms. Reaction kinetic tests, in situ IR and X-ray absorption spectroscopy (XAS), electron microscopy and density functional theory (DFT) were employed to understand how the different ligands affect the activation of CO and O2 and thus the reaction mechanisms. The results clearly suggest that the type of organic ligands determines how Au clusters perform in the gas phase catalysis. Namely, the ligands such as thiolates can act as a double-edged sword for the AunRm nanoclusters in gas phase reactions while the phosphine ligands-protected Au clusters are readily active for gas phase catalysis without the need of ligands removal. We conclude that the essence comes down to the availability of cus Au sites when the organic ligands are in place.
Furthermore, when the organic ligands are removed, the Au clusters would be ligated with the oxide support (inorganic ligand). Therefore the surface structure of the oxide support is deemed important for catalysis by the Au clusters. We employed two different ceria nanoshapes to support the Au clusters and explored how the shape of the support impact the removal of the organic ligands, the nature of the exposed Au sites, and consequently the catalytic performance.
Our work on understanding the role of both the organic and inorganic ligands on the catalysis of Au clusters paves the path forward for utilizing the model metal clusters for efficient catalysis.
Acknowledgements: This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. Part of the work was conducted at the Center for Nanophase Materials Sciences, which is U. S. Department of Energy Office of Science User Facility.
3:15 PM - *NM4.2.03
Cellulose Nanocrystals as Catalysts Supports and Chiral Inducers and Silver Nanoparticles for Plasmonic Induced Reductive Catalysis
Audrey Moores 1 , Madhu Kaushik 1 , Michael Landry 1 , Chris Barrett 1 , Hava Friedman 1 , Alain Li 1
1 , McGill University, Montreal, Quebec, Canada
Show AbstractNanomaterials are intensely researched for their powerful properties applicable in the broad fields of medicine, electronics, optics and catalysis.
We first explored the use of cellulose nanocrystals (CNCs) as a non-innocent support to generate metal/cellulose nanohybrids.1 CNCs are easily harvested from cellulose by strong acid hydrolysis and have been extensively researched as key components in the design of super capacitors, pH-responsive reversible flocculants, aerogels, sensors, coatings, chiral materials and catalysts. We showed that, with Pd, we could afford active and enantioselective hydrogenation catalysts,2,3 while with Ru, extremely active and recyclable catalysts were accessed for the difficult reduction of arenes under mild conditions.4 These nanocrystals in suspension could allow the direct synthesis of silver nanoparticles without the use of any additional oxidizing or reducing chemical.5
Besides, we have employed silver nanocubes for hydrogen activation and hydrogenation of ketones and aldehydes via irradiation at 405 nm, corresponding to the position of the plasmon band of the nanocubes. Exposure to other wavelengths, or absence of light failed to provide activity thus proving the plasmonic effect. Compared to other catalytic systems, the plasmonically activated catalyst provides access to primary and secondary alcohols using milder conditions, in a highly atom economical fashion.6
(1) Kaushik, M.; Moores, A. Green Chem. 2016, 18 (3), 622–637.
(2) Cirtiu, C. M.; Dunlop-Brière, A. F.; Moores, A. Green Chem. 2011, 13 (2), 288–291.
(3) Kaushik, M.; Basu, K.; Benoit, C.; Cirtiu, C. M.; Vali, H.; Moores, A. J. Am. Chem. Soc. 2015, 137 (19), 6124–6127.
(4) Kaushik, M.; Friedman, H. M.; Bateman, M.; Moores, A. RSC Adv. 2015, 5 (66), 53207–53210.
(5) Kaushik, M.; Li, A. Y.; Hudson, R.; Masnadi, M.; Li, C.-J.; Moores, A. Green Chem. 2016, 18 (1), 129–133.
(6) Landry, M.; Barrett, C. J.; Moores, A. 2016, In preparation.
3:45 PM - NM4.2.04
Plasmon-Enhancement of the Electro-Oxidation of C2 Molecules in Alkaline Media with Metal-Semiconductor Embedded, Sandwich and Surface Configurations
Joshua McClure 1 , Kyle Grew 1 , Naresh Das 1 , Deryn Chu 1 , David Baker 1 , Nicholas Strnad 1 , Eric Gobrogge 1
1 , U.S. Army Research Laboratory, Adelphi, Maryland, United States
Show AbstractThe electrochemical oxidation of hydrocarbon fuels requires breaking carbon-carbon (i.e., C-C) bonds for maximum efficiency, which is difficult at low temperatures. We discuss experimental and theoretical efforts dedicated to developing plasmonic-enhanced arrays for the photo-electrochemical oxidation of C2 molecules (e.g. ethanol) at room temperature in alkaline media. However, the mechanism of plasmon-enhanced electrocatalytic reactions is not well understood and decoupling the electrocatalytic dark response from the plasmon-enhanced improvement is a difficult challenge. Mechanistically, validation of the C-C bond breakage facilitated by plasmonic-enhancement requires exploring various materials design configurations, in-situ monitoring of products/byproducts and tracking incident-current-to-photon efficiencies specifically related to enhanced UV-Vis absorption. As a contribution to understanding the mechanistic behavior of the C2 photo-electrooxidation, multiple semiconductor-metal combinations were fabricated and evaluated in parallel with discrete dipole approximation (DDA) modeling. The incorporation of plasmonic nanoparticles/arrays in semiconductor-metal composites is believed to allow for direct-electron transfer and/or plasmon-induced resonance energy transfer processes at the band-edge of the adjacent semiconductor. Therefore, semiconductor materials (i.e., TiO2 and Fe2O3) either alone or in combination were deposited by electron-beam evaporation and/or atomic layer deposition (ALD). Variable thicknesses and different configurations including embedded, surface and sandwich layers with and without the addition of plasmonic nanoparticles/arrays are discussed. In addition, the configurations are investigated with the addition of Pt nanoparticles deposited by ALD as a co-catalyst. The design strategies were guided by DDA simulations to assess absorption, scattering, and near-field enhancement/damping within or near the semiconductor boundary. The arrays (i.e., composites with and without co-catalyst) were studied using a custom-made in-situ apparatus containing a light source with a 300 W Xe bulb, AM1.5 filter, cut-off filters and high-resolution monochromator in combination with a gas chromatograph-mass spectrometry (GC-MS) and potentiostat. The in-situ technique allows for a systematic investigation of the materials designs in the presence and absence of C2 molecules (e.g., ethanol) and light/dark measurements. We report the over-potential and selectivity (i.e., number of e- per C2 molecule) measured for the different samples with select configurations considered for full product analysis by GC-MS equipped with a head-space analyzer. Finally, we discuss the best configurations for C2 electro-oxidation in terms of the positive steady-state current enhancement for potential regions relevant for the electrocatalytic oxidation of C2 molecules, as well as future design considerations for enhancing C-C breaking rates.
4:30 PM - *NM4.2.05
Tuning Surface Structure of Transition Metal Oxide for Higher Selectivity in Partial Oxidation of Hydrocarbon
Franklin (Feng) Tao 1
1 , University of Kansas, Lawrence, Kansas, United States
Show Abstract
Tuning catalytic selectivity is crucial in the design of catalysts for green chemistry processes that minimize the production of undesired byproducts. We found that selectivity for production of ethylene through oxidative dehydrogenation (ODH) of ethane on Co3O4 nanorods strongly depends on surface structure of Co3O4 formed through annealing at different temperatures in O2 before catalysis. Co3O4 annealed at 800oC in air (Co3O4-800oC) exhibit obviously higher selectivity than those annealed at 350 - 700oC (Co3O4£700oC) by 30%-40%. Environmental TEM studies uncovered that surfaces of Co3O4-800oC and Co3O4£700oC exhibit mainly high Miller index including (311) and low Miller index including (111), respectively. In situ/operando characterizations show that the selectivity for production of ethylene from ethane through ODH on Co3O4 nanorods strongly depends on the surface faceting of Co3O4 nanorods. The transition of high Miller index surface to lower Miller index surface through annealing Co3O4 nanorods leads to significant change of chemical environment of surface lattice oxygen and oxygen vacancies. Isotope-labelled temperature-programmed oxygen exchange and in situ studies using ambient pressure X-ray photoelectron spectroscopy suggested distinctly different activity of surface lattice oxygen of (311) and (111). Our correlation of surface structures of Co3O4 nanorods and their catalytic performances showed that activity of surface lattice oxygen atoms in terms of surface structure of transition metal oxide is closely relevant to or even determine a further oxidation of intermediate or product of a partial oxidation and thus control selectivity for formation of a production of a partial oxidation. It further suggested that tuning surface structure of a transition meal oxide is a new approach to tune catalytic performance of partial oxidation on a transition metal oxide.
5:00 PM - *NM4.2.06
Understanding Catalysis by Transition-Metal Oxides from First Principles
Victor Fung 1 , Guoxiang Hu 1 , De-en Jiang 1
1 , University of California, Riverside, Riverside, California, United States
Show AbstractAlthough many insights have been obtained into catalysis by transition metals, there have relatively few general trends guiding our understanding of catalysis by transition-metal oxides. On one hand, this is due to the complexity of electronic structure associated with many transition-metal oxides; on the other hand, their complicated surface chemistry and reconstruction also hampers the surface-science studies. In this talk, I will discuss our recent computational efforts to correlate the structural, energetic, and electronic features of typical transition-metal oxides and their surfaces to activation energies and catalysis. We will show that a simple geometric descriptor can be used to describe the activity of lattice oxygen sites on transition-metal oxides. Detailed reaction pathways of some catalytic chemistry will also be discussed, in combination with the exprimental results.
5:30 PM - NM4.2.07
Surface Reactivity of Pt-Cu(111) Single Atom Alloys—Model Studies that Guide the Design of Atom Efficient Pt Nanoparticle Catalysis
Felicia Lucci 1 , Charles Sykes 1
1 , Tufts University, Medford, Massachusetts, United States
Show AbstractPt is an ubiquitous catalyst in the chemicals and energy production sectors, however, its scarcity in nature and high price will limit future proliferation of current and new Pt-catalyzed reactions. We show by reducing the catalytic element to the minimum atomic ensemble, the catalytic reactivity, selectivity and stability can be optimized while using a reduced concentration of precious metal. Using atomic scale microscopy and desorption studies, we developed atom efficient Pt-Cu catalysts that exhibit enhanced reactivity and selectivity compared to monometallic surfaces. The mechanistic details determined though surface studies on model catalysts guided the design of a new generation of Pt based catalysts for hydrogenation reactions under realistic reaction conditions. An isolated Pt atom geometry enables H2 activation and spillover but is incapable of C-C scission that leads to loss of selectivity and catalyst deactivation. Furthermore, isolated Pt atoms exhibit weak binding strength of CO. Thus, Pt-Cu single atoms alloys maintain high hydrogenation activity even in the presence of poisonous CO.
5:45 PM - NM4.2.08
Tailoring Reaction Enthalpies and Activation Energies in Complex Metal Hydrides Doped with Reactive Metal Ions
Vitalie Stavila 1 , James White 1 , Rob Kolasinski 1 , Lennie Klebanoff 1 , Farid El Gabaly 1 , Xiao Zhou 1 , Tae Wook Heo 1 , Brandon Wood 1 , Jinghua Guo 1 , David Prendergast 1 , Jonathan Lee 1 , Mark Allendorf 1
1 , Sandia National Labs, Livermore, California, United States
Show AbstractMetal hydrides are promising materials for hydrogen storage applications, as they can potentially store large quantities of hydrogen in a small volume at moderate temperatures and pressures. However, most of the metal hydrides are thermodynamically too stable and release and absorb hydrogen at temperatures that are too high for practical applications. Furthermore, kinetics are often slow, which leads to hydrogen release/uptake at insufficient rates. In a few cases the kinetics can be improved by addition of early transition metals or alkali metal ions; however, for most hydride systems no effective additives have been found. Unfortunately, the role of these additives is often very unclear; are they catalysts, or do they form new phases that alter the reaction pathway? In this study, we investigated the effects of titanium(III) ions on the Na-Al-H system and of potassium(I) ions on the Li-Mg-N-H system using new surface-sensitive tools that have not been previously applied to hydrogen storage materials. Local structural changes, as well as surface and bulk composition of the doped hydrides before/after hydrogenation, were probed using ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and low-energy ion scattering (LEIS), as well as conventional in situ X-ray absorption spectroscopy (XAS). Hydrogen uptake was also measured using thermally programmed desorption (TPD) and gravimetric and volumetric H2 sorption measurements. Surprisingly, we find that in addition to the reaction rate, these two additives also affect the equilibrium plateau pressures of the Na-Al-H and Li-Mg-N-H hydride systems through alloying processes. The reaction enthalpies and activation energies can be tailored by controlling the amount and chemical states of titanium or potassium additives. Examples of successful interplay between theory and experiment to identify the reaction steps affected by dopants and provide fundamental insights into their properties will be also presented.
NM4.3: Poster Session I
Session Chairs
Phillip Christopher
Yu Han
Zili Wu
Ning Yan
Wednesday AM, April 19, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - NM4.3.01
LED-Assisted Degradation of Aromatic Organics Using Cu2O Photocatalysts
Yang Su 1 , Hanbin Ma 1 , Arokia Nathan 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractAromatic organic compounds widely exist in industrial wastewater at high toxicity levels, causing serious ecological pollution. Conventional biological treatment methods are not suitable for industrial wastewater because of the high concentration of aromatic compounds. Photocatalysis has shown great potential to purify this kind of wastewater at minimal costs. However, conventional photocatalyst materials e.g. TiO2, needs to be activated by UV light in view of its large bandgap thus limiting its application. In this work, we successfully synthesized rhombic dodecahedral Cu2O nanocrystals with a size of 300 – 400 nm using a facile hydrothermal method. The as-prepared photocatalyst with narrow bandgap is able to be activated using low-power visible LED light sources and shows high efficiency in degrading aromatic organic compounds e.g. toluene. The HO substitution leads to oxidation/ionization potential drops while the nature of the p-type Cu2O contributes to an effective single electron transfer reaction. No organics were detected after the photocatalytic degradation of toluene, indicating that the pollutants were completely degraded into carbon dioxide and water. In this work, we also demonstrate the capability of decontaminating a wide range of aromatic organics in industrial wastewater that comes from an oil company. Such high efficiency of ring-opening reactions and degradation of aromatic contaminants using Cu2O irradiated by LED demonstrates its potential as a green, economic method for industrial wastewater treatment.
9:00 PM - NM4.3.02
Nanoscale Characterization of Carbon Nitride Powders and Correlations to Photocatalytic Activity for Solar Hydrogen Production
Diane Haiber 1 , Toshihiro Aoki 1 , Peter Crozier 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractCarbon nitride powders are polymer-based semiconductors with band gap energies ranging from 2.7-3 eV, which have been recently discovered as active photocatalysts for the water reduction half-reaction under visible light [1,2]. Both graphitic carbon nitrides (g-CNxHy), which are based on heptazine (C6N7) building blocks, and poly(triazine imides) with intercalated Li and Cl ions (PTI/LiCl), based on triazine (C3N3) units, are layered materials with dissimilar morphologies. To enhance the hydrogen evolution rate, these materials are often functionalized with Pt via photodeposition. Less emphasis has been placed on Pt-support interaction effects such as particle-size distributions and interface characteristics. Aberration-corrected transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS), including in-situ approaches, are powerful tools and will be applied to this photocatalytic system to elucidate structure-reactivity relationships.
Reactivity will be determined with photocatalytic half reactions on Pt-supported g-CNxHy and PTI/LiCl in aqueous solutions of methanol and triethanolamine electron donors under UV and visible illumination. Decreases in photocatalytic activity are expected to occur in PTI/LiCl-Pt material, even with replenishment of electron donor [2]. Previously, we have demonstrated using monochromated EELS that heptazine and triazine-based carbon nitrides can be differentiated based solely on their vibrational spectra [3]. In addition, the band gap energies can be reliably measured using an aloof-beam geometry which minimizes specimen damage while maintaining sufficient signal. Ultimately, by combining EELS and TEM imaging with ex-situ photoreactions, we will identify key aspects of nanoscale morphology and electronic structure that will provide fundamental insights into the activity and potential deactivation mechanisms of carbon nitride photocatalysts.
[1] Wang et al. Nat. Mater. 2009, 8, 76-80.
[2] Schwinghammer et al. J. Am. Chem. Soc. 2014, 136, 1730-1733.
[3] The support from the US Department of Energy (DE-SC004954), the use of TEM’s at the John M. Cowley Center for High Resolution Microscopy at Arizona State University, and the use of facilities within the Center for Solid State Science at Arizona State University are gratefully acknowledged.
9:00 PM - NM4.3.03
Novel Catalytic Hybrid Materials Based on Nitroxide Grafted on Transition Metal Oxide for Sugar Oxidation
Mehdi Omri 1 2 3 , Matthieu Becuwe 2 3 , Gwladys Pourceau 1 3 , Anne Wadouachi 1 3
1 , Laboratoire de Glycochimie, des Antimicrobiens et des Agroressources, UMR CNRS 7378, Amiens France, 2 , Laboratoire de Réactivité et Chimie des Solides, UMR CNRS 7314, Amiens France, 3 , Institut de Chimie de Picardie FR 3085 - Université de Picardie Jules Verne, Amiens France
Show AbstractNowadays, the use of carbohydrates as biomass feedstock to prepare environmentally friendly products is very attractive. In fact, many of high-value products such as detergents, pharmaceuticals, polymers and cosmetics can be easily obtained by different modifications of carbohydrates (oxidation, hydrogenation, isomerization, glycosylation…). Among these transformations, selective oxidation of primary position of free carbohydrates is particularly interesting since it leads to sugar acids. These biocompatible and biodegradable chemicals are considered as important platform molecules from biomass: glucaric acid, as example, obtained from the oxidation of glucose, is one of the top 12 platform chemicals from biomass and is a promising alternative to provide adipic acid, widely used in the plastics and textile industries. Generally, the conventional oxidation methods to obtain sugar acids employ homogenous chromium catalysts and exhibits several disadvantages such as toxicity and limited selectivity, requiring multistep strategies with protection/deprotection steps. Otherwise, a more selective homogenous catalytic system based on free nitroxide/co-oxidant has also been developed but reaction time is generally long and separation of the products from the oxidant/co-oxidant mixture is a great drawback. With the aim to develop a greener sugar oxidation protocol, a promising alternative should be to covently anchor the nitroxide onto insoluble material to improve the catalytic properties and the recovering of the catalyst.
We present herein the design of novel hybrid catalyst, based on supported nitroxide, for selective oxidation of sugar. Firstly, nitroxides holding different anchoring functions (carboxylic, phosphonic, catechol..) were grafted on the surface of different transition metal oxides and were tested for the oxidation of methyl-D-glucoside. Significant differences were observed depending on the grafting function and the metal oxide support and will be discussed. In particular, a new nitroxide bearing the phosphonic acid function showed a very good stability as well as interesting catalytic properties. In brief, new hybrid catalysts showing good efficiency for the catalytic oxidation of sugars were developed and promising properties of this material may lead to other applications in different fields.
9:00 PM - NM4.3.04
In Situ Growth of TiO2 on TiN Nanoparticles for Non-Noble-Metal Plasmonic Photocatalysis
Chao Li 1 , Weiyi Yang 1 , Lingmei Liu 1 , Wuzhu Sun 1 2 , Qi Li 1
1 , Institute of Metal Research, Chinese Academy of Sciences, Shenyang China, 2 School of Materials Science and Engineering, Shandong University of Technology, Zibo, Shandong Province, China
Show AbstractThe creation of plasmonic photocatalysts had been demonstrated as a promising approach to largely enhance the photocatalytic performance for various applications. By introducing nanostructure components (mostly noble metal nanoparticles, like Au and Ag) that could possess a localized surface plasmon resonance (LSPR) effect into semiconductor photocatalysts, both the photo-induced electron-hole pair separation efficiency could be enhanced and the responsive illumination range could be expanded to visible and near-infrared light regions. Till now, most plasmonic photocatalysts relied on noble metal nanostructures of Au or Ag due to their easy synthesis and efficient absorption of visible light. However, their rarity, high cost, low melting point, low thermal stability, and easy dissolution (especially for Ag) upon the exposure to air or humidity largely limited their potential for practical applications. Thus, novel plasmonic photocatalysts without noble metal components should be developed to overcome these problems, which could have great potentials for various environmental applications.
Titanium nitride (TiN) is a hard material with gold-like optical properties, which is commonly used as coatings for various substrates due to its high melting temperature, strong corrosion resistance, and non-toxicity/bio-compatibility. Recently, it was reported that TiN could possess a plasmonic resonance absorption peak located in the visible and near-infrared light range. Thus, a novel plasmonic photocatalyst without noble metal components could be developed if nanostructured TiN/TiO2 composite with good contact could be created. In this work, TiN/TiO2 was created by in-situ growth of TiO2 nanoparticles on TiN nanoparticles with a fluorine-free vapor-phase hydrothermal (VPH) process. In our approach, TiN nanoparticles were synthesized through a chemical vapor deposition (CVD) process, and TiO2 was grown in-situ based on these TiN nanoparticles to form TiN/TiO2 nanocomposite by a VPH process with HNO3 as the oxidant. By replacing the commonly used oxidant of HF in the VPH technique to create various metal oxide nanostructures, a fluorine-free VPH approach was developed which avoided the use of highly corrosive chemicals. TiN/TiO2 composite photocatalyst demonstrated the desirable visible light absorption, and their good visible light photocatalytic activity was demonstrated by both the photodegradation of organic pollutants and the disinfection of microorganism. The mechanism of the visible light photocatalytic activity of the TiN/TiO2 composite photocatalyst was verified to the LSPR effect of nanostructured TiN, while no energy barrier was found to exist between TiN and TiO2. Once electrons in TiN are excited above the Fermi energy level, these hot electrons could be completely injected to TiO2, resulting in better electron injection efficiency than previous reported noble-metal-based plasmonic photocatalysts.
9:00 PM - NM4.3.05
Structural Evolution and Fluxionality of Sub-Nanometer Pt and Pt-Sn Clusters from First Principles
Victor Fung 1 , De-en Jiang 1
1 , University of California, Riverside, Riverside, California, United States
Show AbstractSub-nanometer transition metal clusters are a class of materials of considerable research interest and potential. Possessing very different properties from bulk metals, small changes in size and composition can have a significant effect on its geometric and electronic structure and by extension its catalytic performance. We use global minimization with density functional theory to study the structural evolution and properties of sub-nanometer pure Pt and Sn-doped Pt clusters. We study how changing cluster size by adding or removing Pt atoms, or by the addition of Sn atoms can have on coordination, shape, and cluster fluxionality. These results provide additional insights into the nature of cluster structure and energy relations, and its effects on catalytic performance.
9:00 PM - NM4.3.06
La-Based Perovskites as Oxygen-Exchange Redox Materials for Solar Syngas Production
Rahul Bhosale 1 , Anand Kumar 1 , Anchu Ashok 1 , Parag Sutar 1 , Fares AlMomani 1 , Majeda Khraisheh 1
1 Department of Chemical Engineering, Qatar University, Doha Qatar
Show AbstractIncreasing oil prices due to the extreme dependency on fossil fuels is one of the major challenges the world is facing today. Metal oxide based solar thermochemical H2O and CO2 splitting cycles are an attractive and sustainable route for the production of clean and carbon-neutral chemical fuels such as H2 or syngas. Non-stoichiometric oxides, such as ceria, doped ceria, doped ferrites and perovskites have been recently considered as the promising catalytic redox materials for the production syngas via splitting of H2O and CO2 due to their excellent oxygen conductivity through the lattice. It was also observed that the La-based perovskite materials are better as compared to other non-stoichiometric materials due to the higher reduction extent at lower temperatures which automatically results into higher fuel yield. However, most of the La-based materials investigated in past are directly purchased from the commercial supplier. To improve the redox reactivity, it is highly important to study the effect of different synthesis approaches and also the effect of various dopants added in different concentrations in the crystal structure of the La-based perovskites. Therefore, in this study, several kinds of La-based perovskites such as La-Mn-O, La-Sr-O, La-Sr-Mn-O, La-Sr-Mn-M-O (where M = Ni, Co, Zn, Cu, Fe, etc), and others were synthesized via sol-gel method, co-precipitation method, Pechini method, solution combustion synthesis, cellulose assisted combustion synthesis, and sol-gel auto combustion method. The derived materials were characterized using XRD, BET, SEM, TEM, EDX, ICP, and XPS. After characterization, the redox reactivity and thermal stability of these materials were tested by performing H2O and CO2 splitting reactions using a TGA and a packed bed reactor set-up. The effluent gases coming out from these two equipments were tested by using a GC and MS. At first, all the above mentioned materials were synthesized via co-precipitation method and then the derived materials were compared with each other based on their physico-chemical properties, redox reactivity and thermal stability by performing multiple thermochemical H2O and CO2 splitting cycles. The best La-based perovskite was selected for the next study and it was synthesized by various synthesis methods to study the effect of synthesis approach. Again the same criteria was used to decide the best synthesis method for the production of La-based perovskites with improved redox reactivity and thermal stability towards thermochemical H2O and CO2 splitting cycles. All the results obtained in this study will be presented in detail.
9:00 PM - NM4.3.07
Synergism of Porous-Organic Polymers and Graphene—Opportunities in Electrocatalytic Reduction of CO2
Mohamed Alkordi 1 , Ahmed Soliman 1 , Rana Haikal 1 , Youssef Sayed 1
1 Center for Materials Science, Zewail City of Science and Technology, 6th of October, Giza, Egypt
Show AbstractWe report a composite of Graphene and Porous-Organic Polymer containing the pyrimidine ring (PyPOP) through a one-pot, bottom-up assembly on top of commercial, unmodefied graphene. The reported synthesis resulted in homogenous deposition of the PyPOP atop unmodefied graphene sheets, as evident from several structural characterization techniques including FTIR, solid state 13C-CPMAS NMR, SEM, and TEM. The PyPOP, with its abundant Lewis base sites, demonstrated an appreciable affinity toward CO2 capture but as commonly encountered in POPs, was found to be largely insulating, thus prevented its useful utilization as active element in electrochemical conversion of CO2. Once composited with graphene, the composite demonstrated a mix of desirable properties from both of its two components. The composite demonstrated enhanced microporosity, maintained affinity to CO2, and, most significantly, demonstrated significant electrochemical activity toward CO2 reduction (5 mA/cm2 at -1.6 V), not observed in either of its two components separately.
9:00 PM - NM4.3.08
Ultrathin Ag-Pd Nanoframes and Their Catalytic Properties
Xiaojun Sun 1 , Jumei Li 1 , Dong Qin 1
1 MSE, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractNoble-metal nanoframes with highly open structure and high specific surface area are great candidates as new catalysts. In this talk, we will present a facile synthesis of Ag-Pd bimetallic nanoframes with the ridges as thin as 1.7 nm. Specifically, we co-titrated aqueous AgNO3 and Na2PdCl4 into an aqueous suspension containing 40-nm Ag nanocubes, ascorbic acid, and poly(vinylpyrrolidone). The Ag and Pd atoms derived from co-reduction would be preferentially deposited onto the edges and corners of Ag nanocubes for the generation of Ag@Ag-Pd core-frame nanocubes. Upon the removal of Ag interior by H2O2 etching, we obtained Ag-Pd bimetallic nanoframes made of ultrathin ridges enriched in Ag. These nanoframes demonstrated the remarkable catalytic activity in catalyzing the reduction of 4-nitrophenol by NaBH4. More significantly, the nanoframes inherited exceptional mechanical stability and shape durability.
9:00 PM - NM4.3.09
CO2 Reduction to Renewable Hydrocarbon Fuel—Mimicking Natural Photosynthesis
Sherin Alfalah 1 , Walid Hassan 4 , Amit Verma 2 , M.P. Anantram 3 , Mahmoud Khader 1 , Reza Nekovei 2
1 , Qatar University, Doha Qatar, 4 , King Abdulaziz Univeristy, Jeddah Saudi Arabia, 2 , Texas A&M University, Kingsville, Texas, United States, 3 , University of Washington, Seattle, Washington, United States
Show AbstractNatural photosynthesis in green plants changes sunlight into chemical energy using chlorophyll molecules. This is achieved by converting CO2 into energy storing products. This is accomplished by splitting water to liberate O2 and fixing CO2 into sugar; producing a clean and sustainable power source. Mimicking natural photosynthesis has been the goal of many research activities. However, many academic and technological challenges have to be addressed and solved until this process is maintained at large scale and low cost. g-C3N4 has been used as a base photocatalysts for artificial photosynthesis [1]. In recent years, g-C3N4 has been successfully used as effective photocatalyst to enable CO2 reduction due to its high conduction band minimum favoring the reduction half-reaction. CO2 is being reduced in multi-step reaction involving proton assisted multielectron process leading to diverse products. However, the current apparent quantum efficiency is still low for commercial applications. Moreover, exact reaction mechanism for the CO2 reduction is still unclear. Wang et al have studied the effect of C5 and C6 rings on the structural and optical properties of nanographene using DFT and TDDFT [2]. The authors shed some light on how multiple carbon rings affect the optical absorption of nanographenes. Such findings create questions about the effect of enhancing the optical absorption and photocatalytic activity of g‑C3N4 by altering the C6 rings with C5 rings, similar to those in chlorophyll.
This study theoretically investigates g-C3N4 photocatalysis systems combined with earth abundant environment friendly metals/nonmetals, especially those available in plants and involved in the natural photosynthesis process, such as K, Mg, Mn, Mo, Fe, Co, Cr, S and B. The work aims to investigate the effect of changing the ring size on g-C3N4 photocatalytic activity trying to mimic the superior activity of natural photosynthesis process. It is found that doping increases the range at which light absorption occurs to regions beyond that of the visible light. These findings suggested that the g-C3N4 can be a promising system for the photosynthesis process. Next, the modified g-C3N4 system is used to build better photocatalyst that can be used for artificial photosynthesis including CO2 reduction and water splitting. Accordingly, a deeper understanding of the photocatalytic reaction steps and mechanism are highlighted.
References:
[1] Ong, W.-J.; Tan, L.-L.; Ng, Y. H.; Yong, S.-T.; Chai, S.-P.; Chem. Rev., 2016, 116 (12), 7159–7329.
[2] Wang, X.; Yu, S.; Lou, Z.; Zeng, Q.; Yang, M.; Phys. Chem. Chem. Phys., 2015, 17, 17864-17871.
9:00 PM - NM4.3.10
Sulfonated High Surface Area Carbons for Waste-to-Fuel Conversion
Shiba Adhikari 1 , Abdou Lachgar 1 , Zachary Hood 2
1 , Wake Forest University, Winston Salem, North Carolina, United States, 2 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractDifferent carbon derived materials have been used as heterogeneous solid acid catalysts for waste-to-biofuel conversion. Many cheap biofuel feedstocks, including those that contain high concentrations of free fatty acids (FFAs), are typically disposed of due to the inability to efficiently convert them into usable biofuels. Herein, a sulfonated (SO3H-bearing) carbon catalyst with high specific surface area was successfully prepared from chemical activation method of hydrothermally prepared carbon (HTC) (Scheme 1). In particular, KOH activated HTC carbon has been converted into high surface area carbon containing catalytically active -SO3H functional groups using a novel, environmentally benign process involving the use of L-cysteine followed by reduction with NaBH4 and oxidation with H2O2 Its activity for formation of fatty acid methyl ester (FAME) from FFA was compared with similar sulfonated HTC with low surface area.
Scheme 1: Synthesis of sulfonated high surface area carbon from KOH activated HTC using L-cysteine followed reduction and oxidation steps
9:00 PM - NM4.3.11
Multi-Metal Oxide for Low Temperature Thermochemical Water Splitting
Shang Zhai 1 , Hyungyu Jin 1 , Nadia Ahlborg 1 , William C. Chueh 1 , Arun Majumdar 1
1 , Stanford University, Stanford, California, United States
Show AbstractThermochemical water splitting (TWS) process has been long pursued for H2 production, but the need for high operating temperature (>1500oC) makes it incompatible with the chemical industry infrastructure. A thermodynamic analysis helped identify the enthalpy and entropy ranges for TWS at temperatures ~1000oC or below. Based on this framework, we designed and synthesized a new class of metal oxides and experimentally demonstrated O2 evolution reaction at temperatures as low as 1100oC and the H2 evolution reaction at 600oC. The experiments also showed unusually fast kinetics for O2 evolution rate. Thermodynamic, chemical and structural characterization is being conducted to investigate the reaction mechanism of this new class of materials. The large design space of such materials offers the promising prospects of TWS at temperatures < 1000oC.
9:00 PM - NM4.3.12
Preparation and Properties of Alkylated and Perfluorinated ZnPc-Modified Carbon Nanotubes Derivatives
Sunmi Hong 1 , Anil Kumar Mutyala 1 , Da-Hye Kim 1 , Jong Seung Park 1
1 , Department of Organic Material Science and Engineering, Busan Korea (the Republic of)
Show AbstractCarbon nanotubes (CNTs) have superior electrical and thermal conductivities, along with excellent mechanical properties, which have been found to be useful for diverse electronic and industrial applications. However, the molecular-level interaction among CNTs is too strong, which makes it difficult to break them up into individual entities. In order to make the most of their inherent properties, various covalent and non-covalent approaches, which allow to efficiently modify the surface properties of CNTs, have been suggested. We have long been interested in covalent attachment of electro-active materials on the surface of CNTs as a measure to obtain novel electrically conductive materials. Recently, Pc-grafted CNTs have been reported to exhibit outstanding electrical properties as conductive fillers for composite dielectrics. With the end in mind, herein we present the preparation and properties of CNT complexes covalently functionalized by substituted phthalocyanine (Pc) derivatives. Effective manipulation had been achieved by incorporating either alkyl or perfluorinated substituents at peripheral positions of Pcs. In their actual synthesis, a –COOH group was generated on the surface of CNTs through acid treatment, and 2-amino-zinc-phthalocyanine and 2-Amino-9,16,23-tris(perfluorohexyl)-zinc-phthalocyanine were combined with CNTs by way of DCC coupling. The properties of resulting CNT-Pc complexes were thoroughly investigated using various analytic techniques such as SEM, EDS, conductivity, UV-vis, photoluminescence, and etc. The prepared alkylated and perfluorinated Pc-modified CNTs provide good compatibility and associated interaction with the host polymers. Hence, by taking advantage of such improvement, we have prepared composite dielectrics with poly(vinylidene fluoride), which are found to exhibit improved dielectric properties with a high dielectric constant and reduced dielectric loss. Furthermore, the oxygen reduction reaction (ORR) activity of the Pc-CNT complexes has been investigated, and their promising applications as non-precious metal catalysts are also addressed.
Keywords: carbon nanotubes; zinc phthalocyanine; alkyl or perfluorinated substituents
9:00 PM - NM4.3.13
High Efficient Ag2O/Bi24O31Br10 Hybrid Photocatalyst for Enhanced Photocatalytic Activity
Yonglei Xing 1 , Wenxiu Que 1 , Xingtian Yin 1 , Qinghe Que 1
1 , Xi’an Jiaotong University, Xi'an China
Show AbstractRecently, bismuth-based compounds are identified as a significant class of photocatalyst due to their unique electronic structures. Among these, Bi24O31Br10 has been reported to be a novel bismuth oxyhalide with high photocatalytic activity. However, very few studies on Bi24O31Br10 heterojunction coupled with noble metallic oxide are reported so far. In this presentation, Ag2O/Bi24O31Br10 hybrid photocatalyst was successfully prepared by a chemical deposition method. The prepared 3Ag2O/Bi24O31Br10 hybrid photocatalyst exhibited a much higher photocatalytic activity for the degradation of Rhodamine B (RhB) under visible light, as compared with Bi24O31Br10 nanosheets. What’s more, Ag/Bi24O31Br10 was obtained at 300 C. Based on active species detection, a proper mechanism was proposed. The improvement in photocatalytic performance is due to the extended absorption in the visible light region resulting from the loading of Ag2O, which can also act as a high active center for degrading the RhB solution.
9:00 PM - NM4.3.14
The Surface Plasmon Resonance Effect on the Enhancement of Photodegradation Activity by Au/ZnSn(OH)6 Nanocubes
Yu Ting Chang 1 , Jyh Ming Wu 1
1 , National Tsing Hua University, Hsinchu Taiwan
Show AbstractWe demonstrated Au/ZnSn(OH)6 hollow nanocubes that exhibited extremely high photodegradation activity under ultraviolet and visible-light illumination. The pristine ZnSn(OH)6 hollow nanocubes can achieve a 100% photodegradation ratio within 20 min under ultraviolet-light illumination. The high photodegradation activity of ZnSn(OH)6 can be attributed to plenty of OH groups present in the polyhedral corner of the ZnSn(OH)6 that generate a large number of reactive hydroxyl radicals for degradation of dye molecules. High resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) images revealed that the size of the ZnSn(OH)6 and Au/ZnSn(OH)6 hollow nanocubes is ∼30–80 nm. After ZnSn(OH)6 nanocubes were decorated with Au, the heterostructures exhibited a significantly strong and widened absorption peak in the range 450–750 nm because of the surface plasmon resonance (SPR) effect, and therefore showed an excellent photodegradation activity under visible-light illumination. The rate constant k of Au/ZnSn(OH)6 is as high as 51.8 L mol−1 min−1 under UV-light illumination. This value is much higher than those reported so far. The hydroxyl groups essentially enhance the reaction rate and enable the active radicals to participate in the reaction for destruction of the Rhodamine B (RB) solution. Au/ZnSn(OH)6 has been successfully applied for preparing hybrid coating screens with polydimethylsiloxane (PDMS), which exhibited an excellent mechanical desirable durability and extended its feasible application in our daily lives.
9:00 PM - NM4.3.15
Durable Pt-Based Alloy Nanoparticle Design for Fuel Cells Electrocatalyst
Yung-Eun Sung 2 1 , Heock-hoi Kwon 3 , Wansoo Huh 3 , Ji Mun Yoo 2 1 , Dong Young Chung 2 1
2 Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul Korea (the Republic of), 1 , Seoul National University, Seoul Korea (the Republic of), 3 Department of Chemical Engineering, Soongsil University, Seoul Korea (the Republic of)
Show AbstractFuel cell is one of the most promising energy conversion devices due to its high efficency. However, big hurdles to commercialize the fuel cells are still remained including activity and stability. Recently, Pt based alloy and core shell structures have been reported to be promising in terms of activity. Developments achieved by tailoring the activity of catalyst through alloying at the nanoscale level was suggested. However, low durability of transition metals such as nickel, cobalt and iron is a big issue to utilize transition metal alloy nanoparticles. Considering that even Pt is not stable in fuel cell operation condition at nanoscale, new and efficient design of nanoscale alloy materials is timely important. Here, we suggest efficient strategies to develop highly active and durable nanoscale electrocatalyst for oxygen reduction reaction. Various electrochemical and physical analysis verified its superior long-term stability. Finally we will discuss the general design principles to develop durable nanoscale electrocatalyst based on our results.
9:00 PM - NM4.3.16
Study of Catalytic Activity of Titanium Oxide Coatings for Ozone Decomposition
Sergey Karabanov 1 , Dmitry Suvorov 1 , Gennady Gololobov 1 , Maria Serpova 1 , Yulia Stryuchkova 1 , Evgeny Slivkin 1
1 , Ryazan State Radioengineering University, Ryazan Russian Federation
Show AbstractCreation of high efficiency and safe air cleaning systems is the important task caused by their wide use in living quarters, medical institutions and industrial facilities. The most effective cleaning systems are the ones based on ozone forming as the result of a corona or barrier discharge. The main disadvantage of these cleaning systems is high ozone concentration on electrode system output.
The paper presents experimental studies of the properties of catalytically active coatings on the basis of nanoporous titanium oxide for effective ozone decomposition inside air cleaning systems. For research of coatings catalytic properties a specialized model has been made. It consists of axially symmetrical “needle-cylinder” system in which a high-voltage corona discharge with the voltage of up to 12 kV and current of up to 50 µA. The internal diameter of titanium cylinder was 20 mm, the length varied in the range of 100-200 mm. On the internal surface of the titanium cylinder the coating samples of nanoporous titanium oxide with the pore diameter of 20-60 nm and the thickness of 1-20 µm were grown using a standard technique of anodizing in electrolyte on the basis of the mixture of 0.3% NH4F (masses.), 0.5% H2O (masses.) and ethylene glycol covering were up. The laminar air flow was pumped through the cylinder and output ozone concentration forming as a result of plasma chemical reactions of the corona discharge was measured.
The experimental research resulted in obtaining the dependencies of influence of titanium oxide parameter structure on the ozone concentration on electrode system output. It is established that the use of catalytic coating leads to decrease of ozone concentration on electrode system output by 25-30% (at low currents - up to 50%). It is shown that with the coating thickness rise within 1-5 µm the catalytic activity increases and then achieves saturation at the thickness of 7-10 µm. It is established that with the tube length growth the reduction rate of ozone concentration decreases significantly. On the basis of the obtained experimental data the requirements to the coating structure providing high efficiency of catalytic ozone decomposition are determined.
The obtained experimental data of catalytic activity of nanoporous titanium oxide coatings can be used for creation of new types of safe plasma air filters.
9:00 PM - NM4.3.17
Novel Very High Surface Area, Mesoporous Films of SrTiO3 Using Pulsed Laser Deposition and Their Application in Photoelectrochemical Water Splitting
Abhijeet Sangle 3 , Simrjit Singh 2 , Jie Jian 1 , Sneha Bajpe 3 , Haiyan Wang 1 , Neeraj Khare 2 , Judith MacManus-Driscoll 3
3 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Department of Physics, Indian Institute of Technology Delhi, New Delhi India, 1 Electrical and Computer Engineering, Texas A & M University, College Station, Texas, United States
Show AbstractA method to develop very high surface area, epitaxial, highly crystalline, oriented mesoporous SrTiO3 films from self-assembled columnar nanocomposite films of SrTiO3 with other oxides is described. The columnar oxide phase of MgO or Sm2O3 is etched out selectively, leaving behind very high surface area (estimated increase in area ~ 2400% over substrate surface area in films of thickness 250 nm), highly oriented and crystalline mesoporous SrTiO3 matrix phase. Furthermore, the electronic charge carrier density is tuned by post-annealing in different oxygen atmospheres. The films are shown to give highly enhanced photoelectrochemical water splitting performance due to tuned charge carrier concentration and high surface area.
9:00 PM - NM4.3.18
Enhanced Photocatalytic Activity of Monodispersed TiO2 Quantum Dots Decorated g-C3N4 as a Z-Scheme Photocatalyst
Xue Ding 1 , Lei Zeng 1 , Yun Zhao 1 , Limin Huang 1
1 , South University of Science and Technology of China, Shenzhen China
Show AbstractInspired by the fact that carbon nanodots decorated g-C3N4 has recently demonstrated significant enhancement of photocatalytic activity for hydrogen generation[1], a nanocomposite composed of monodispersed TiO2 quantum dots and g-C3N4 nanosheets was prepared by a simple interfacial reaction, and it shows a 1.5-fold enhancement of photocatalytic activity compared with g-C3N4/P25 in terms of degradation of methyl orange (MO). The photocatalytic activity for hydrogen generation is also significantly improved after the decoration with TiO2 quantum dots. The blue-shift of optical absorption edge was observed in the monodispersed TiO2 nanodots (<10nm), suggesting the existence of quantum size effect. The enhancement of photocatalytic activity after decorating with TiO2 quantum dots can be illustrated with the mechanism of Z-scheme photocatalyst [2]. Both photo-generated holes and superoxide anion radicals are the predominant reactive species that are responsible for the efficient degradation of MO. The participation of the photo-generated holes originating from the TiO2 quantum dots significantly accelerates the photocatalytic degradation reaction. This paper provides an accessible strategy to improve the photocatalytic activity of g-C3N4 for environment remediation.
Keywords: TiO2 quantum dots, g-C3N4, photocatalysis
Reference:
[1] J. Liu, Y. Liu, N. Liu, Y. Han, X. Zhang, H. Huang, Y. Lifshitz, S.-T. Lee, J. Zhong and Z. Kang, Science, 2015, 347, 970–974.
[2] W. Ong, L. Tan, Y. Ng, S. Yong, S. Chai, Chemical Reviews, 2016, 116, 7159-7329.
9:00 PM - NM4.3.19
Functional Group Modified g-C3N4 Nanosheets as an Excellent Photocatalyst
Lei Zeng 1 2 , Xue Ding 1 , Yun Zhao 1 , Limin Huang 1
1 Department of Chemistry, South University of Science and Technology of China, Shenzhen China, 2 Department of Chemistry, Fudan University, Shanghai China
Show AbstractGraphitic carbon nitride (g-C3N4) is a rising star in photocatalytic field due to its excellent physicochemical property, unique electronic structure, suitable bandgap and superior photochemical stability [1]. The photocatalytic activities of g-C3N4 modified by carbon-dots, metals or metal oxides have been widely reported. However, as a general method used in chemistry, the modification of functional groups in g-C3N4 is rarely reported, Here, functional group modified g-C3N4 nanosheets can be designed and prepared via a simple refluxing method. The modified g-C3N4 exhibits enhanced photocatalytic oxidation ability which originates from the positive shift of valence band. It is demonstrated that the photocatalytic degradation mechanism is changed from a superoxide anion radical oxidation path to a direct h+ oxidation path after the modification, and the recombination of photogenerated charges is also significantly suppressed. Moreover, the photocatalytic activity (including photocatalytic antibacterial property) can be further improved after the formation of heterojunction with TiO2 nanoparticles or quantum dots. The methyl orange (MO) solution can be completely degraded by the nanocomposite within one hour visible light irradiation, and the degradation rate of methyl orange (MO) increases by three times after the modification (g-C3N4) and by six times after further loading TiO2 nanoparticles (g-C3N4/TiO2). The photocatalytic activity for hydrogen generation was also investigated. The modification of functional groups in g-C3N4 is a simple and efficient method that can effectively boost the photocatalytic activities and expand the applications of g-C3N4 nanosheets and the related hybrids.
Keywords: g-C3N4, photocatalysis
Reference:
[1] W. Ong, L. Tan, Y. Ng, S. Yong, S. Chai, Chemical Reviews, 2016, 116, 7159-7329.
9:00 PM - NM4.3.20
Oxygen Evolution Catalysis Based on d-Band Tuned p-Band Center Principle
Yingfang Yao 1 2 , Shicheng Yan 1 3 , Zhigang Zou 1 2
1 Ecomaterials and Renewable Energy Research Center, Nanjing University, Nanjing, Jiangsu, China, 2 College of Physics, Nanjing University, Nanjing, Jiangsu, China, 3 the College of Engineering and Applied Sciences, Nanjing University, Nanjing, Jiangsu, China
Show AbstractThe merits of high surface areas, high conductivity, the facility of doping, etc. make carbon based electrocatalysts widely applied in various energy conversion and storage systems. However since their low electrochemical window of oxidation, they showed few application opportunities in oxygen evolution reaction (OER) catalysis. In our work, we applied a d-band of earth-abundant first row (3d) transition metal ion tuned carbon p-band center principle to resolve the deficits of p-band center principle for carbon based OER catalysts, which could not offer sufficient electronegativity to trigger high-performance OER; and d-band center principle for 3d transition metal oxides, which was limited by the low activity on the superficial active sites and low conductivity of the catalysts. Our major research contents contain: 1) to investigate the law of metal ions d-band tuning the p-band catalytic efficiency of Carbon materials, and to find out the proper activity descriptor; 2) to direct the material design of 3d transition metal ions embedded in nonmetal doped graphene as the electrocatalysts; 3) to optimize and develop new OER electrocatalysts accordingly, and to testify the tuning mechanism of OER electrocatalysis in practical applications. These research results will be further used to setup the general principle for the material design and syntheses of OER catalysts that aim to provide experimental foundation and theoretical guidance for future material design and performance improvements.
Here we proposed a new design principle of tuning p-band of graphene by d-orbitals of transition metal ions. This principle was first examined by density functional theory (DFT) calculations. Comparing with pristine carbon catalysts (or doped with N), our calculations revealed that the embedded Cr6+ cations induced Cr d-band to hybridize with the neighboring carbon atoms that narrow the relative position of C p- and O p-levels by lowering C p-orbitals. The resultant C p-orbitals enter the O p-orbitals, triggering increased σ*-filling via effective anodic electron transfer from O to C atoms. And then we demonstrated the catalyst design principle by OER tests of the 3d transition metal Cr6+ ions encapsulated in graphene (Cr6+@G) catalysts, which achieved a low OER overpotential of η = 197 mV at j = 10 mA cm-2. The synthesized catalysts was one of the leading OER catalysts and notably apposed the most recent state-of-the-art gelled FeCoW oxyhydroxides (η = 192 mV at j = 10 mA cm-2).
9:00 PM - NM4.3.21
Carbon Deposition on a Ni/CeO2 Catalyst from Hydrocarbon Gases
Ethan Lawrence 1 , Peter Crozier 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractInternal reforming of hydrocarbons in solid oxide fuel cells (SOFCs) can enhance electrochemical conversion efficiencies by eliminating the need for an external fuel reforming process [1]. Several issues remain that hinder long-term stability and performance. One major problem is carbon deposition onto the active anode catalyst which can deactivate the catalyst or destroy the ceramic-metal (cermet) composite structure. Natural gas consists primarily of methane (~90%) but also contains several percent of higher hydrocarbons such as ethane, which motivates our choice for hydrocarbon gases. Ni/ceria cermets have been used to provide favorable catalytic properties while discouraging carbon deposition [3]. In the cermet, Ni catalyzes the decomposition of the fuel molecule and ceria enables oxygen transport from the electrolyte and cathode. Ceria has also been shown to inhibit carbon deposition due to its ability to oxidize carbon on its surface by quickly exchanging oxygen from its lattice [2].
Reforming of methane and ethane with oxygen were performed in a microreactor, and products were analyzed via gas chromatography (GC). The resulting catalysts were examined using transmission electron microscopy (TEM) to determine the spatial distribution of deposited carbon. To determine the hydrocarbons most responsible for carbon deposition, experiments were performed using methane, ethane, and ethylene as the carbon source. To simulate SOFC anode conditions, a Ni/ceria catalyst was heated to 550° and exposed to one of the three hydrocarbon gases. Temperature-programmed oxidation (TPO) was employed to quantify the amount of carbon deposited by each carbon source gas. These ex situ results indicated that ethylene and ethane yielded the most deposited carbon, thus in situ experiments using an FEI Titan environmental TEM were performed using these gases to observe carbon deposition under near reactor conditions. Results highlighting the relationship between the metal-support interaction and carbon deposition will be presented.
[1] Gür, T.M., et al, Progress in Energy and Combustion Science 54 (2016), p. 1-64.
[2] Zhou, Y., et al, The Journal of Physical Chemistry Letters 1 (2010), p. 1447-1453.
[3] Wang, W., et al, Chemical Reviews 113 (2013), p. 8104-8151.
[4] We gratefully acknowledge support of NSF grant DMR-1308085 and ASU’s John M. Cowley Center for High Resolution Electron Microscopy.
9:00 PM - NM4.3.22
Graphene/Ni Wire Foam with Multivalent Manganese Oxide Catalysts for Li-O2 Battery Cathode
Chueh Liu 1 , Changling Li 1 , Mihri Ozkan 1 , Cengiz Ozkan 1
1 , University of California, Riverside, Riverside, California, United States
Show AbstractHerein, commercial Ni foam coated with self-assembled and linearly-aligned Ni wires is utilized as a cost-effective current collector for application in Li-O2 battery. The Ni wires are furthered deposited with graphene layers (g-Ni wire) to improve electrical conductivity. Multivalent Mn oxides consisting of Mn3O4, Mn2O3 and MnCO3 are used as effective oxygen reduction (ORR) and evolution reaction (OER) catalysts deposited on g-Ni wire current collectors. Specific capacities are respective ~100 and ~170 mAh g-1 without or with O2 introduction into the cell. The relative facile synthesis process requiring merely solution-based synthesis at ambient pressure, low temperature and short process time renders the Mn oxides/g-Ni wire electrode promising for Li-O2 battery application.
9:00 PM - NM4.3.23
A Research Study on Transition Metal Catalyzed Utilization of Reversible Conversion and Alloying Reactions
Hui Ying Yang 1
1 , SUTD, Singapore Singapore
Show AbstractThe alloying-dealloying reactions of SnS2 proceeds with the initial conversion reaction of SnS2 with Lithium that produces Li2S. Unfortunately, due to the electrochemical inactivity of Li2S, the conversion reaction of SnS2 is irreversible, which significantly limit its potential applications in Lithium-ion batteries. Herein, a systematic understanding of transition metal molybdenum (Mo) as a catalyst in SnS2 anode is presented. It is found that Mo catalysts is able to efficiently promote the reversible conversion of Sn to SnS2. This leads to the utilization of both conversion and alloying reactions in SnS2 that greatly increases Lithium storage capability of SnS2. Mo catalyst is introduced in the form of MoS2 grown directly onto self-assembled vertical SnS2 nanosheets that anchors on three-dimensional graphene (3DG) creating a hierarchal nanostructured named as SnS2/MoS2/3DG. The catalytic effect results in a significantly enhanced electrochemical properties of SnS2/MoS2/3DG; a high initial Coulombic efficiency (72.3%) and high discharge capacities of 960.5 and 495.6 mA h g-1 at current densities of 50 and 1000 mA g-1, respectively. Post cycling investigations using ex situ TEM and XPS analysis verifies the successful conversion reaction of SnS2 mediated by Mo. The successful integration of catalyst on alloying type metal sulfide anode creates a new avenue towards high energy density lithium anodes.
9:00 PM - NM4.3.24
Catalytic Synthesis of Highly Mesoporous Carbon Nanotubes/Nanowires for Catalysis and High Performance Energy Storage Devices
Honglu Wu 1 2 , Yian Song 1 , Yongsheng Wang 2 , Jingyue Liu 1
1 Department of Physics, Arizona State University, Tempe, Arizona, United States, 2 Institute of Photoelectronic Technology, Beijing Jiaotong University, Beijing, Beijing, China
Show AbstractPorous carbon nanostructures are of great interest because of their practical applications in catalysis, gas absorption/separation, and energy storage and conversion [1]. The unique properties of porous carbons, such as high surface area, electronic conductivity, resistance to acid and basic environment, etc. make them ideal and promising materials in those applications. Porous carbon nanostructures can be synthesized via the template approach [2]. We have developed a new catalytic process for synthesizing mesoporous carbon tubes, carbon nanowires, or other types of carbon nanostructures. The synthesis strategy involves the use of ZnO nanostructures as templates for deposition of carbonaceous species via catalytic steam reforming or decomposition of ethanol. Due to the templates, mesoporous carbon hollow tubes with controllable wall thicknesses can be fabricated. Moreover, the ZnO nanowire template can be removed by a hydrogen-based reduction process after the carbon deposition. We recently discovered that partial removal of the ZnO nanowire template can be accomplished by controlling the reduction temperature and time. With the partial removal of the ZnO, another cycle of catalytic carbon deposition can be realized, during which the carbonaceous species deposit into the interior regions of the hollow carbon. Such a deposition-reduction cycling process can be repeated many times until the ZnO nanowire is completely removed. The resultant mesoporous carbon nanostructures can be functionalized with nitrogen doping to further improve their catalytic or electrochemical properties. Our design and synthesis process is general and can be used to produce various types of mesoporous carbon nanostructures for practical applications in liquid catalysis and electrocatalysis, and for electrochemical energy storage devices such as supercapacitors and batteries. The electrochemical and catalytic properties of the synthesized mesoporous carbon nanostructures will be discussed [3].
1. Y. Gong et al. Scientific Reports 4 (2014) 6349.
2. M. Taubert et al. Microporous and Mesoporous Materials 197 (2014) 58.
3. This work was supported by the College of Liberal Arts and Sciences of Arizona State University. H. Wu acknowledges the financial support from the China Scholarship Council. The authors gratefully acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science at Arizona State University.
9:00 PM - NM4.3.25
Synthesis and Performance of Non-Precious Metal Oxygen Evolution Catalysts for Anion Exchange Membrane Electrolyzer
Kyu Hwan Lee 1 , Sung Mook Choi 1 , Myung Je Jang 1
1 , KIMS, Gyeong Nam Korea (the Republic of)
Show AbstractHydrogen has recognized as a high energy density, efficient, and environmentally clean in a variety of renewable energy sources. It can be produced by an anion exchange membrane electrolyzer that has several advantages as use of non-precious metal oxide catalysts, high pressure operation, and high efficency compared with ther type electrolyzers.
The target of this study is the development of CoCu oxide based non-precious catalysts with high activity via simple coprecipitetion synthesis method. The prepared OER electrocatalysts were characterized by various physicochemical analyses such as -ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Furthermore, to investigate electrocatalytic properties of prepared catalysts, we carried out electrooxidation actiity measurement such as cyclic voltammetry (CV), linear sweep voltammetry (LSV), long-term stability test, and electrochemical impedance spectroscopy (EIS). The synthesized CuCoO4 series catalysts show a different tendency in physicochemical properties and OER activity with synthesis conditions as pH, heat treatment temperature, ad drying method.
9:00 PM - NM4.3.26
Quantitative Spectrochemical Characterization of Nanoalloy/Nanocomposite Catalysts via Calibration-Free Laser Induced Breakdown Spectroscopy (LIBS)
Seyyed Ali Davari 1 , Sheng Hu 1 , Dibyendu Mukherjee 1
1 , University of Tennessee, Knoxville, Tennessee, United States
Show AbstractIntermetallic nanoalloys (NAs) and nanocomposites (NCs) have gained prominence in recent years as efficient catalytic materials in electrochemical energy conversion and storage systems. However, the structure and chemical compositions of NAs and NCs play critical roles in tailoring their catalytic activities, and precious metal contents. Advanced microscopy techniques have facilitated morphological characterizations, but traditional chemical characterizations largely remain qualitative or extremely involved. We present here Laser Induced Breakdown Spectroscopy (LIBS) for quantitative compositional analysis of NAs and NCs synthesized via in-house pulsed laser ablation-based technique. Specifically, elemental ratios of binary PtNi, PdCo (NAs) and PtCo (NCs) with different compositions are spectrochemically analyzed by LIBS using an internal calibration technique that employs bulk matrix species as internal standards. Transmission Electron Microscopy (TEM) images and Energy Dispersive X-ray Spectroscopy (EDX) measurements corroborate the morphology and qualitative elemental compositions of the aforesaid NAs and NCs. LIBS experiments are carried out in ambient conditions with the NA and NC samples drop cast on silicon wafers after centrifugation to increase their concentrations. Thus, the LIBS measurements are devoid of the burdensome sample preparations such as acid digestions and external calibration standards commonly required in Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). And yet, the quantitative LIBS results show good agreement with those from corresponding ICP-OES measurements. The results presented here indicate the future feasibility of LIBS for rapid and in-situ quantitative chemical characterizations of wide classes NAs and NCs synthesized as novel catalytic materials.
9:00 PM - NM4.3.27
Facile Synthesis of PdSx/C Porous Nanospheres and Their Applications for Ethanol Oxidation Reaction
Shifeng Hou 1 , Qiang Zhang 1 , Yiqun Zheng 1
1 , Shandong University, Jinan China
Show AbstractA facile approach for the synthesis of carbon-supported palladium polysulphide porous nanospheres (PdSx/C) had been developed, palladium/poly (3,4-ethylenedioxythiophene) (Pd/PEDOT) nanospheres were prepared first, then a calcination process at an optimized temperature to form PdSx/C, with an average diameter of 2.47 ± 0.60 nm of PdSx, and an average diameter of 50 nm of carbon nanophere. Various techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) and electrochemical techniques were performed to characterize its morphology, composition and tstructures. In contrary to most Pd-based electrochemical catalysts, which are easily poised with trace sulfur and monoxide during the catalytic oxidation process, the as-prepared PdSx/C porous nanospheres perform high electrocatalytic activities and extreme stabilities for the electrochemical catalytic oxidation of ethanol in alkaline medium. In particular, the forward peak current intensity achieved 162.1 mA mg-1 and still kept at 46.7 mA mg-1 even after 1000 cycles. This novel material shows potential applications as an ideal fuel cell catalyst.
Symposium Organizers
Yu Han, King Abdullah University of Science and Technology
Phillip Christopher, Univ of California-Riverside
Zili Wu, Oak Ridge National Laboratory
Ning Yan, National University of Singapore
Symposium Support
King Abdullah University of Science and Technology
NM4.4: ORR and CO<sub>2</sub>RR
Session Chairs
Phillip Christopher
Ning Yan
Wednesday AM, April 19, 2017
PCC West, 100 Level, Room 104 B
9:30 AM - *NM4.4.01
Atomistic Engineering of Efficient Oxygen Reduction Electro-Catalysts by Tailoring Local Chemical Environment of Pt Surface Sites
Suljo Linic 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractOxygen reduction reaction is the limiting half-reaction in hydrogen fuel cells. While Pt is the most active single component electro-catalyst for the reaction, it is hampered by high cost and low reaction rates. Most research to overcome these limitations has focused on Pt/3d alloys, which offer modest activity enhancements but have poor long-term stability.
Herein, we synthesized, characterized and evaluated the performance of a series of alloy materials belonging to a new family of electro-catalysts. These multilayer nanoparticles contain an internal AuxCu100-x alloy core of precise composition, surrounded by two Au monolayers and covered by a catalytically active Pt surface monolayer. Their performance relative to that of the commercial Pt standards reaches up to four times improved area-specific activity. The AuxCu100-x@Au2ML@PtML electro-catalysts were initially identified with quantum chemical calculations and then synthesized in nanoparticle form using a combination of colloidal and electrochemical methods. Characterization studies support the hypothesis that the activity improvement originates from a combination of Au-Pt ligand effect and local strain effect induced by the AuCu alloy core. We demonstrate that tuning the molar composition of the internal AuCu alloy core can directly modify the oxygen reduction activity of these electro-catalysts.
10:00 AM - NM4.4.02
Designing Better Platinum Alloys for the Oxygen Reduction Reaction
Jakob Schiotz 1 , Maria Escudero-Escribano 1 , Paolo Malacrida 1 , Martin Hansen 2 , Ulrik Vej-Hansen 3 , Amado Velazquez-Palenzuela 1 , Vladimir Tripcovic 2 , Jan Rossmeisl 2 , Ifan Stephens 1 , Ib Chorkendorff 1
1 , Technical University-Denmark, Lyngby Denmark, 2 Department of Chemistry, Copenhagen University, Copenhagen Denmark, 3 , QuantumWise A/S, Copenhagen Denmark
Show AbstractPlatinum is the commonly used catalyst for the Oxygen Reduction Reaction (ORR) in polymer-electrolyte-membrane fuel cells. However, it is known that alloying Platinum with some transition metals increase the activity dramatically, although stability becomes an issue in the harsh environment of a fuel cell.
A new class of ORR catalysts has been discovered through an interplay between
Density Functional Theory calculations, simple theoretical models, and experiments. These alloys between Platinum and either a rare earth or an alkaline earth are up to ten times more active than pure platinum, and stable for 10000 cycles under accelerated stability testing. According to the theoretical models the crystal structure and the size of the alloying atoms play a central role in explaining this activity. This is demonstrated experimentally by leveraging the “lanthanide contraction”: the systematic variation of atomic radii through the lanthanide series.
Reference:
M. Escudero-Escribano, P. Malacrida, M.H. Hansen, U.G. Vej-Hansen, A. Velazquez-Palenzuela, V. Tripkovic, J. Schiøtz, J. Rossmeisl, I.E.L. Stephens, and I. Chorkendorff, Science 352, 73 (2016).
10:15 AM - NM4.4.03
Controlling Nanoscopic and Atomic Segregation of Pt within Pt-Ni Rhombic Dodecahedra and Nanoframes for Fuel Cell Catalysis
Nigel Becknell 1 , Zhiqiang Niu 1 , Yoonkook Son 1 , Peidong Yang 1
1 , University of California, Berkeley, Berkeley, California, United States
Show AbstractNanoparticle catalysis plays a crucial role in the development of renewable energy cycles, such as splitting water into hydrogen and oxygen and storing the hydrogen for on-demand power generation in a proton exchange membrane fuel cell (PEMFC). Though PEMFCs are entering commercialization, primarily in passenger vehicles, major challenges face this technology in cost and durability of the fuel cell stack. In particular, the oxygen reduction catalyst, typically platinum, contributes significantly to these cost and durability issues, with Pt being one of the most expensive metals and Pt dissolution occurring at the oxidizing potentials of the oxygen reduction reaction. Therefore, advanced designs for oxygen reduction nanocatalysts must be developed to obtain higher levels of activity and stability required for cost-effective commercialization of PEMFCs. Common strategies include composition and shape control and have demonstrated improvement over state-of-the-art Pt electrocatalysts, but these approaches do not obtain the level of atomic precision necessary to make significant improvement in catalyst activity and durability. We present nanoscopic and atomic segregation of the elements in Pt-Ni nanoparticles as next-level variables that can be controlled to create a three-dimensional Pt3Ni nanoframe composed of highly active interconnected one-dimensional struts. Starting from solid Pt-Ni rhombic dodecahedra with a Pt-rich phase segregated to their edges, selectively removing the interior Ni-rich phase results in hollow nanoframes. The synthesis of the rhombic dodecahedra is revealed as a complex concurrent evolution of their composition, element spatial distribution, and morphology. It can be summarized as a series of fundamental chemistries including unmatched reduction potentials of Pt and Ni precursors, anisotropic overgrowth on preformed seeds, step-induced metal deposition, and site-dependent phase segregation and migration. Once evolved to Pt3Ni nanoframes, in situ EXAFS analysis illustrates that these catalysts exhibit excellent oxygen reduction activity due to atomic-level segregation of Pt from Ni, forming a Pt-skin on the nanoframe surface. Ultimately, we demonstrate how nanoscopic and atomic level segregation of Pt and Ni can be used to innovate new catalyst morphologies with unprecedented levels of activity and stability for the oxygen reduction reaction.
10:30 AM - NM4.4.04
Catalytic Reduction of CO2 into Solar Fuels via Ferrite Based Thermochemical Redox Reactions
Rahul Bhosale 1 , Anand Kumar 1 , Fares AlMomani 1 , Majeda Khraisheh 1 , Ivo Alxneit 2
1 Department of Chemical Engineering, Qatar University, Doha Qatar, 2 Bioenergy and Catalysis Laboratory, Paul Scherrer Institute, CH-5232, Villigen-PSI Switzerland
Show AbstractCO2 is considered as the major greenhouse gas and its continuous emission from various sources such as chemical industry, automobile exhaust, combustion of fossil fuels and others leads to one of the major environmental issues i.e. global warming. It is highly important to work towards the reduction in the excessive discharge of CO2 and also the utilization of the liberated CO2 towards value added products. In this regard, one of the promising options is to reduce the CO2 into CO via ferrite (doped iron oxide) based thermochemical redox cycles performed using concentrated solar energy. This produced CO can be combined with the H2 produced from the water splitting reaction via similar ferrite based thermochemical cycle to yield into syngas which can be further processed to liquid fuels such as Methanol, Diesel, and Kerosene via the Fischer-Tropsch process. It is highly important to note that the ferrite materials were considered as the bench-mark for the production of hydrogen via water splitting cycle, however; their utilization towards the CO2 splitting reactions is not yet investigated in detail. Hence, in this study, various ferrite based materials (transition metal doped iron oxides) such as Ni-, Zn-, Co-, Mn-, Mg-, and Cu-ferrite were synthesized via sol-gel method. After characterizing the composition, morphology, surface area, and other physico-chemical properties, the derived ferrite materials were tested towards thermochemical CO2 splitting using a thermogravimetric analyzer (TGA). The ferrite powder was thermally reduced at 1400oC, while the CO2 splitting reaction was performed at lower temperatures (800 to 1100oC). O2 and CO release was further monitored by gas chromatography. The synthesized ferrite materials were compared with each other and also with the ceria based materials based on their redox reactivity and thermal stability by performing multiple thermochemical thermal reduction and CO2 splitting steps.
10:45 AM - NM4.4.05
3D Free Standing RGO-Cu2O Electrode for the Electrochemical Reduction of Carbon Dioxide
Rini Ravindranath 1 2 , Huan-Tsung Chang 1
1 Department of Chemistry, National Taiwan University, Taipei Taiwan, 2 Nanoscience and Technology Program, Academia Sinica, Taipei Taiwan
Show AbstractCarbon dioxide (CO2) is a nefarious greenhouse gas, released by both natural and artificial processes. It is also an indispensable material for the growth of all earth’s plants and for many industrial processes. Ideally, the CO2 produced on earth ought to be balanced with that consumed, in order for the level of CO2 to remain constant and maintain environmental stability. However, rapid growth and industrialization has caused a great imbalance leading to more CO2 production and making global warming a pressing issue. Therefore, reducing CO2 production and conversion of CO2 into useful materials is the mother of all necessity for environmental protection and economical sustainability. In this regard, we have for the first time prepared a free standing 3D electrode based on reduced graphene oxide-copper oxide (RGO-Cu2O) that has been successfully utilized for the electrochemical reduction of CO2 in aqueous 0.1 M KHCO3 electrolytes. The RGO-Cu2O films of different thicknesses were formed by a special vacuum based rotary deposition. In addition to scanning electron microscopy and X-ray diffraction, Raman spectroscopy was used for the first time, to probe changes in the chemical and structural composition of the Cu2O films during the CO2 reduction. The presence of Cu2O increased the current density when compared to the activity seen for RGO. The addition of counter ions further increased the electrochemical performance of the film. Effects and properties of different counterions on the formation of Cu2O and the electrochemical performance was also thoroughly investigated.
Methanol was substantially formed on these films while methane production was practically suppressed. The film also exhibited enhanced selectivity towards methanol while the formation other minor byproducts were not seen. We were thus able to increase the Faradaic efficiency and production rate of methanol. The films were extremely stable and durable. It performed well during reproducibility tests maintaining high production rate of methanol while remaining reusable for further cycles. We believe that this type of 3D free standing electrode has the potential to revolutionize the CO2 reduction process.
11:30 AM - *NM4.4.06
Material Designs of High-Performance Electrocatalysts for Oxygen Reduction and Evolution Reactions
Hong Yang 1
1 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractRequirements of high activity, stability and low cost post new challenges for the design of advanced catalysts and electrocatalysts. In this talk, I will present recent approaches to the design of two classes of catalyst materials, that is, core-shell bimetallic catalysts for electrochemical reduction of oxygen and selective thermal reactions, and AxByOz catalysts for oxygen evolution reaction (OER). In all cases, design and processing of catalysts with optimal surface atomic structures and favored dynamics under reactive environments are important. In situ, variable-temperature environmental transmission electron microscopy (TEM) techniques thus can be quite useful for understanding the processing conditions to obtain designed structures, such as regioselective atomic distributions at surface regions. Such information helps in the control of catalyst facet, composition and structure with high-level of accuracy, such as, site and composition specificity. Specific discussions will be on the solution phase design and post-synthesis treatment of nanoparticle catalysts, which include theoretical and experimental understanding on the design and controlled synthesis of catalysts; in-situ environmental TEM (ETEM) in studying the dynamics of structural behaviors under reactive environments for both electro- and thermal catalysts; and structure-electrocatalytic property relationships for bimetallic ORR and AxByOz OER catalysts.
12:00 PM - NM4.4.07
Electrochemical Synthesis of Hydrogen Peroxide Using Cost-Effective Materials, Challenges and Opportunities
Samira Siahrostami 1 , Zhihua Chen 1 , Shucheng Chen 1 , Zhenan Bao 1 , Thomas F. Jaramillo 1 , Jens Norskov 1
1 , Chemical Engineering, Stanford, California, United States
Show AbstractHydrogen peroxide (H2O2) is an important chemical with wide range of applications in industry such as paper and textile manufacturing and most importantly environmental protection for the detoxification and color removal of wastewater.1 Currently, H2O2 is produced indirectly via anthraquinone oxidation process in a large scale which is an energy demanding multi-electron process and requires large plants.1 Two-electron electrochemical reduction of oxygen to H2O2 using fuel cells provides a direct route to locally produce this chemically valuable product with simultaneous generation of electricity. Moreover, this process offers unique opportunities for sanitization applications and purification of drinking water. One of the major challenges however, is the competing four-electron reduction of oxygen, which generates water. Recent understandings indicate that catalysts capable of preserving the O-O bond in the electrochemical O2 reduction are selective for H2O2 production over water. Some of the promising examples are mercury alloys of Pt and Pd2,3 and PdAu alloy.4 Alloys of mercury have been proven to be the most active, selective catalyst for H2O2 synthesis.2,3 However, the fact that they are made of toxic mercury and costly metals such as Pd and Pt hinders their widespread application. PdAu alloy is not economically viable either and suffers from low intrinsic activity.4 Carbon-based materials are alternatives that have been recently studied for the electrochemical reduction of O2 to H2O2.5,6 However, their efficiency is very low and development of inexpensive, efficient and selective catalysts for this reaction remains a challenge. In this work we use combined density functional theory (DFT) and experiments to identify the active sites in carbon-based materials as well as exploring alternatives for this reaction. Using facile synthetic approaches the targeted promising structures are synthesized with optimized surface motifs. The catalytic activity and selectivity of the synthesized materials are measured for the two-electron reduction of O2 to H2O2. Using this comprehensive approach we find active and selective catalysts, which are made of only cost-effective materials.
12:15 PM - NM4.4.08
Nanoscale Compositions and Structures of Non-Precious Metal Mesoporous Carbon Electrocatalysts
Niels Zussblatt 1 , Nina Fechler 2 , Markus Antonietti 2 , Bradley Chmelka 1
1 Department of Chemical Engineering, University of California, Santa Barbara, California, United States, 2 Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Potsdam Germany
Show AbstractNitrogen- and transition-metal-containing carbon materials have been the subject of intense recent research interest, due to their desirable properties, including high stabilities, high conductivities, and high electrocatalytic activities, which make them promising for use as replacements for platinum-based oxygen reduction reaction (ORR) catalysts in fuel cells. Previous studies have shown that the catalytic activities of these materials depend on their N or transition-metal contents. However, significant fractions of non-carbon atoms, particularly nitrogen, usually result in dramatically reduced electrical conductivities, and correspondingly reduced suitabilities, for use of heteroatom-containing mesoporous carbons as electrode materials. Recently, we demonstrated that mixtures of urea and poly-quinones form a low-viscosity eutectic melt at moderate temperatures (68-130 °C) which allow uniform incorporation of Fe species and preparation of mesoporous carbon materials. The resultant materials, which exhibit high Fe and N contents (up to 6 and 11 atom%, respectively), high electrical conductivities (2.0 S/cm), and surface areas in excess of 900 m2/g, have been found to exhibit high ORR activities, as indicated by half-wave potentials up to 0.89 V vs. RHE under alkaline conditions. Solid-state 15N nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements demonstrate that the surface N moieties present in these materials are strongly influenced by inclusion of transition-metal codopants, as well as local interactions with the surfaces of structure-directing silica and soluble salt materials. Combined analyses by XPS, NMR relaxometry, 57Fe Mössbauer spectroscopy, and catalytic measurements reveal the proximities of Fe and N species and the importance of surface Fe sites to the catalytic activity of the materials. Of particular interest are synthesis choices, such as short-duration thermal treatments under reactive atmospheres, which selectively alter surface chemistry without changing pore structure, as these can be correlated with electrocatalytic activities to provide insight into the identity of the ORR active sites. By comparing and correlating the molecular compositions with the electrocatalytic activities, we establish optimal material compositions for a non-precious metal carbon catalyst to exhibit ORR activities that are comparable to current Pt-based materials.
12:30 PM - NM4.4.09
Composition Tunable Ternary Pt-Ni-Co Octahedra for Optimized Oxygen Reduction Activity
Zipeng Zhao 1 , Yu Huang 1
1 , University of California, Los Angeles, Los Angeles, California, United States
Show AbstractPt-based alloy is a class of promising oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cell. Introducing a third element to the binary Pt-Ni alloy has been demonstrated to be effective in further optimizing ORR performance. However, composition correlated ORR performance study for ternary alloys is absent due to considerable difficulty in systematically tuning the alloy composition while maintaining morphology. Herein, we report a one-step synthesis method for octahedral Pt-Ni-Co ternary catalysts with tunable compositions and fixed shapes. Impressively, the composition optimized octahedral PtNi0.55Co0.1/C demonstrated significant improvement in ORR activity compared to those of previously reported Pt-Ni-Co alloy octahedra, showing outstanding specific activity of 5.05 mA/cm2 and mass activity of 2.80 mA/μgPt, which are around 20.2 times and 14.7 times higher than those of the commercial Pt/C catalyst (0.25 mA/cm2 and 0.19 mA/μgPt).
12:45 PM - NM4.4.10
Large Scale Synthesis of Porous Carbon Nanotubes for High Performance Electrocatalysts
PengXiang Hou 1 , JinCheng Li 1 , Chang Liu 1 , Hui-Ming Cheng 1 , Jinhong Du 1
1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang, Liaoning, China
Show AbstractThe oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are the most important processes in a wide range of renewable energy technologies, such as in fuel cells, metal-air batteries, and water splitting devices. In this study, a flexible, large area three-dimensional (3D) porous N-doped carbon microtube (NCMT) sponge was prepared via a simple and low-cost process of pyrolyzing facial cotton under NH3 atmosphere. The NCMTs possess a dictyophora-like structure with a micron-scale hollow core and porous well-graphitized and intimately interconnected tube walls, together with a high content of pyridinic and quaternary nitrogen. Their unique structural characteristics endow the NCMT sponge with high density active sites, fast electron transfer capability and sufficient mass transport pathways. Therefore, the NCMT sponge demonstrates incomparable electrocatalytic activity for the ORR and the OER with a small potential difference of 0.63 V between the OER current density at 10 mA cm-2 and the ORR current density at -3 mA cm-2, which is the best to date. Considering its low cost, simple fabrication process, and excellent catalytic performance, the 3D NCMT sponge can act as both a high-efficiency bi-functional electrocatalyst and a gas diffusion layer in electrochemical cells, showing great potential for use in flexible energy conversion and storage systems. Recently, we developed a new, facile and scalable strategy for achieving high content of Fe single atoms on porous N-doped carbon nanotube film through atomic isolation technique, which exhibited ultrahigh ORR activity superior to Pt/C in acidic medium.
NM4.5: <i>In Situ</i> and <i>Operando</i> Characterization
Session Chairs
Wednesday PM, April 19, 2017
PCC West, 100 Level, Room 104 B
2:30 PM - *NM4.5.01
In Situ and Operando Electron Microscopy Imaging and Spectroscopy of Catalysts
Peter Crozier 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractUnderstanding the fundamental relationships between catalyst activity and structure at the nanoscale will enable the improved design of novel catalytic materials. In-situ or operando environmental transmission electron microscopy (ETEM) is a powerful technique for the investigation of structure-reactivity relationships in high surface area catalysts under reaction conditions. With new instruments, atomic resolution imaging and spectroscopy can be carried out in the presence of gas, liquid, light and thermal stimuli [1-5]. The combination of mass spectrometry and electron energy-loss spectroscopy (EELS) allow catalytic products to be detected and quantified directly in the electron microscope. With aberration corrected TEM, the positions of atomic columns on nanoparticles surfaces can be observed and correlated with changes in conversion. New developments in monochromated EELS allow the electronic and vibrational structure of catalyst surfaces to be probed with focused electron beams [6]. Using the so-called “aloof beam” approach to EELS, radiation damage is controlled which should allow local electronic surface and defect states to be observed and correlated with catalytic properties [7,8]. Recent applications of these novel approaches will be illustrated to elucidate the structure and electronic properties of catalytic nanoparticles surfaces relevant to a variety of energy conversion processes such as water splitting, CO oxidation and reforming. The challenges associated with correlating reaction kinetics with local structure and properties will be discussed and evaluated.
References
1. S. Chenna and P.A Crozier, ACS Catal. 2 (2012) 2395.
2. B.K Miller et al, Ultramicroscopy 2015. 156: p. 18-22.
3. Miller, B.K. and P.A. Crozier, Microscopy and Microanalysis, 2014. 20(3): p. 815-824.
4. L. Zhang et al, Nano Letters, 2013. 13(2): p. 679-684.
5. F. Tao, and P.A. Crozier, Chemical Reviews, 2016. 116(6): p. 3487-3539.
6. O. L. Krivanek et al, Nature 514, 209 (2014).
7. P.A., Crozier et al, Ultramicroscopy, 2016. 169: p. 30-36..
8. Q. Liu et al, Ultramicroscopy (in press), 2016.
9. The support from the National Science Foundation (NSF-CBET 1134464, DMR-1308085 CHE-1508667), US Department of Energy (DE-SC0004954) and the use of TEMs at the John M. Cowley Center for High Resolution Microscopy at Arizona State University are gratefully acknowledged.
3:00 PM - *NM4.5.02
High-Resolution and In Situ/Operando (S)TEM Imaging of Catalysts
Nigel Browning 1 , B. Layla Mehdi 1 , Libor Kovarik 1 , Andrew Stevens 1 , Yuanyuan Zhu 1
1 , Pacific Northwest National Lab, Richland, Washington, United States
Show AbstractThe last few years have seen a paradigm change in scanning transmission electron microscopy (STEM) with aberration correctors generating an unprecedented improvement in both the spatial resolution and the compositional sensitivity of Z-contrast images. These images can now be routinely used to observe and quantify the sizes, shapes, and compositions of supported mono-, bi-, and multi-metallic metal clusters and even image the metal atoms in single-metal-atom complexes, as well as providing direct structural information characterizing the structure of the support and the metal–support interface. However, quantitative and reproducible atomic resolution observation of catalysts is actually harder with these new instruments, as the increase in beam current (which increases sensitivity) also brings with it the potential for electron beam modification of the specimen during image acquisition and the larger apertures used with aberration correctors decreases the depth of focus, making image interpretation less straightforward. Therefore, to fully realize the potential of aberration corrected microscopes to quantify catalyst heterostructures it is important to develop a low-dose methodology that allows resolution and sensitivity to be quantitatively defined as a function of the beam current for each particular system being studied. Here we assess the major experimental challenges associated with obtaining atomic resolution Z-contrast images of these highly beam-sensitive materials — individual atoms and clusters can readily migrate and sinter, and the motion of atoms within the structure can radically change the experiment. Such control over the imaging conditions assumes even more importance when using in-situ stages or environmental microscopes to study the dynamics of catalyst interactions in the presence of gases, in liquids or at elevated temperatures. In this presentation, how the application of STEM imaging for high-resolution structure determination is modified to observe dynamics in liquids and gases will be discussed, along with the control parameters that are needed. In particular, emphasis will be placed on optimized sampling procedures that allow for the use of compressive sensing/inpainting algorithms to extract quantitative measurements. Examples of the application of these methods will include sub-nm metallic clusters on a range of supports, MoVNbTe catalysts for oxidative dehydrogenation and metal-organic frameworks.
4:30 PM - *NM4.5.03
New Aspects in Applying Environmental TEM to Catalyst Chemistry
Seiji Takeda 1 , Naoto Kamiuchi 1 , Ryotaro Aso 1 , Kentaro Soma 1 , Hideto Yoshida 1
1 , Osaka University, Ibaraki Japan
Show AbstractApplications of environmental TEM (ETEM) were already described in various aspects, for instance atomic resolution observation in reaction environments and imaging and spectroscopy combined with simultaneous catalytic measurements. Most of previous studies, however, focused on the characterization of established catalyst materials. To advance atomic resolution ETEM, we report a couple of new applications to catalyst materials utilizing the large space available around a sample in our ETEM apparatus such as direct observation of the formation process of model catalysts by using sputter guns in a ETEM apparatus and nearly electron-irradiation free characterization of solid catalysts in reaction environments with a fast detection camera.
5:00 PM - *NM4.5.04
Probing Catalytic Conversion of Biomass-Derived Molecules at Solid-Liquid Interfaces Using Operando Solid-State NMR Spectroscopy
Susannah Scott 1 , Long Qi 1 , Ali Chamas 1 , Marcus Foston 2
1 , University of California, Santa Barbara, Santa Barbara, California, United States, 2 , Washington University St. Louis, St. Louis, Missouri, United States
Show AbstractReactions of biomass-derived carbohydrates and phenolics catalyzed by solid materials often take place at solid-liquid interfaces, where the local composition of the fluid phase can be very different from that of the bulk solution. Many such reactions take place in semi-aqueous solvent mixtures whose micro-heterogeneity is enhanced inside the catalyst pores. Solid-state NMR spectroscopy is a powerful tool to probe the composition and dynamics of molecules at solid-liquid interfaces. However, the demanding reaction conditions used in hydrothermal biomass transformations are particularly challenging for NMR methods. Customized chemically-resistant high pressure rotors adapted to withstand elevated temperatures and pressures were used to acquire magic-angle-spinning spectra which follow the populations of adsorbed molecules and report the kinetics of their transformations. Selective isotope labeling (13C, 2H) was used to enhance sensitivity, provide mechanistic information, and study mobility effects. Initial results involving carbohydrate isomerization catalyzed by basic zeolites and hydrogenolysis of aryl ethers catalyzed by nickel aluminates will be presented.
5:30 PM - NM4.5.05
Accelerating Nanoparticle Synthetic Design Using In Situ Synchrotron-Based Small Angle X-Ray Scattering
Liheng Wu 1 2 , Joshua Willis 1 , Matteo Cargnello 1 , Christopher Tassone 2
1 , Stanford University, Menlo Park, California, United States, 2 , SLAC National Accelerator Laboratory, Menlo Park, California, United States
Show AbstractIn the past two decades, significant developments have been achieved in the colloidal synthesis of monodisperse nanoparticles (NPs) with fine control over their size, shape, and structure, which have allowed better understanding of their properties, especially catalytic properties. However, synthesizing well-defined NPs in a predictable way is still challenging. Here, we use synchrotron-based small-angle X-ray scattering (SAXS) to experimentally probe the formation of NPs during solution phase synthesis. We choose Pd NPs as an example. Through real-time SAXS measurements, we can quantitatively determine the size, size distribution, and concentration of Pd NPs during the synthesis. We systematically study the effects of different surfactants (e.g., oleylamine, trioctylphosphine) on the kinetics of Pd NP nucleation and growth. Based on the in situ SAXS data, we are able to better understand the growth mechanism of Pd NPs and as a result optimize the synthetic parameters to precisely control their size from 2 to 10 nm with sub-1 nm control, and these well-controlled Pd NPs serve as a model system for studying the size-dependent catalysis for methane combustion reaction.
5:45 PM - NM4.5.06
Chemical Composition-Phase State-3D Atomic Structure and Catalytic Activity Relationship in Metallic Nanocatalysts inside Fuel Cells by in Operando Energy Dispersive X-Ray Spectroscopy and Atomic Pair Distribution Studies
Valeri Petkov 1
1 , Central Michigan University, Mt Pleasant, Michigan, United States
Show AbstractThe fuel cell technology may not become commercially viable unless affordable, highly active and durable nanocatalysts for speeding up the sluggish chemical reactions driving cells’ operation, such as the oxygen reduction reaction (ORR), are developed. Indeed, a number of excellent nanocatalysts for ORR, for the most part metallic nanoparticles, were developed recently. Despite real progress, fuel cells are not yet on the market. This is so, mostly, because metallic nanocatalysts proven excellent in a Lab, i.e. ex situ, do not necessarily deliver the expected high performance inside operating fuel cells. The underperformance reflects the fact that under actual operating conditions, metallic nanocatalysts undergo particular atomic-level changes, ranging from order-disorder transitions and gradual growth to phase segregation and even complete disintegration, and so suffer a substantial loss in ORR activity. To be successful, efforts to limit the losses need precise knowledge of the concurrent evolution of the chemical composition, phase state, 3D atomic structure and ORR activity of the nanocatalysts taking place while they function inside fuel cells. We will present results from recent in-operando energy dispersive x-ray spectroscopy and atomic pair distribution studies on binary and ternary noble-transition metal NPs used as ORR catalysts at the cathode of an operating proton exchange membrane fuel cell. Also, we will show examples how the knowledge obtained helps bring fuel cells a step closer to commercialization.
NM4.6: Poster Session II
Session Chairs
Phillip Christopher
Yu Han
Zili Wu
Ning Yan
Thursday AM, April 20, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - NM4.6.01
Pt/TiO2 Nanocomposites for Active Chemical-Electrical Signal Transduction
Nathan Ray 1 , Eduard Karpov 1
1 , University of Chicago, Chicago, Illinois, United States
Show AbstractInvestigation of heterogeneous catalysis using bifunctional systems of nanodispersed Pt on porous oxide substrates is important for a broad range of applications including photocatalysis, fuel cells, solid state chemical sensors, and many others. Active transducers exhibit great potential through their ability to convert excessive surface-released chemical energy into an electric current in an electrolyte-free system. We report on a mesoporous TiO2 system that has been synthesized by a plasma electrolytic oxidation process. The porous TiO2 structure is then decorated with an electrically continuous array (mesh) of Pt nanoparticles; this nanocomposite generates an electrical signal when subjected to catalytic oxyhydrogen reactions on its surface. We discuss the water turnover frequency during generation of stationary current under a room temperature regime. A correlation between water production and reaction current generation will be outlined, providing evidence for the production of water as the dominant force behind the generated electromotive force under steady-state conditions. The impact of Pt phase microscopic structure on the reaction current magnitude is also investigated. These results shed light on the underlying and competing processes within the Pt/TiO2/Ti system during the oxidation of hydrogen and the generation of a room temperature stationary reaction current with a potential for novel, one-compartment hydrogen fuel cell devices.
9:00 PM - NM4.6.02
Stationary Reaction Current Generation in Mesoporous Pt/ZrO2 under Oxyhydrogen Conditions
Nathan Ray 1 , Eduard Karpov 1
1 , University of Chicago, Chicago, Illinois, United States
Show AbstractWe advocate on the existence of a large class of surface-driven functional nanocomposite mesoporous systems adept at converting surface-released chemical energy into a stationary reaction current when subjected to oxyhydrogen conditions at room temperature. Recently, there has been a large interest and amount of work studying thermionic currents and chemicurrents generated by Pt/TiO2 systems under exposure to oxyhydrogen environments; we now report on mesoporous ZrO2 (synthesized via plasma electrolytic oxidation) with Pt deposition exhibiting similar properties. Through the adjustment of anodization parameters, ZrO2 pore diameter and pore density can be controlled. Substrates oxidized at 2.2 mA×cm-2 result in a fractional surface area of 0.49% pores, while a fractional surface area of 3.35% pores corresponds to an anodization current of 55 mA×cm-2. Increase in pore density leads to reaction current enhancement, as well as an initially heightened H2 sensitivity. The low current densities make this a very cost-effective technique to produce electrolyte-free nanosystems able to generate electrical power under oxyhydrogen environments at room temperature.
9:00 PM - NM4.6.04
Cobalt Oxide Nanoplates with Enriched Oxygen Vacancies for Oxygen Evolution Reaction
Wenjing Xu 1 , Yadong Yin 1
1 , University of California, Riverside, Riverside, California, United States
Show AbstractElectrochemical water oxidation, also known as oxygen evolution reaction (OER), has been regarded as a promising approach for conversion and storage of sustainable and efficient energy. However, OER is kinetically sluggish, which requires a high overpotential, owing to the stepwise four-electrons oxidation process. Although noble metal and noble metal oxides such as Pt, RuO2 and IrO2 are currently regarded as the most active electrocatalyst, their scarcity and high cost have seriously impeded the large-scale applications. Accordingly, the exploration of abundant, highly efficient and economic alternatives for water splitting is crucial in terms of solving global energy crisis and environmental challenges. Recently, earth-abundant and environmental friendly transition-metals-based oxides (Co, Ni, Fe) have exhibited superior performance in OER catalysis due to high conductivity and stability. However, their electrocatalytic activity still underperforms those benchmark IrO2 and RuO2. Therefore, the proposal of simple and economic routes to significantly improve the activity of transition-metal-based catalyst is of great importance for the development of OER. In this presentation, we report the synthesis of oxygen-vacancies-enriched ultrathin cobalt oxide nanoplates using a surface protected reduction method, which enables large-scale production with good uniformity, dispersity and controllable concentration of oxygen vacancies. Benefiting from the large surface area and the high concentration of oxygen vacancies, cobalt oxide nanoplates provide more active sites, promoting faster exchange of intermediates and more efficient electron transfer. Therefore, the as-prepared cobalt oxide manifests an OER overpotential as low as 306 mV at 10 mA/cm2 in 1 M KOH, which is superior to the values of its bulk counterparts as well as those of the most reported Co-based catalysts.
9:00 PM - NM4.6.05
Novel Humic Acid Derivatives and Potential Applications
Mark Riggs 1
1 , Texas State University, San Marcos, San Marcos, Texas, United States
Show AbstractHumic acid refers to a class of molecules composed primarily of a mixture of aromatic and partially saturated carbon rings with pendant functional groups including phenols, carboxylic acids, and epoxides. This naturally occurring molecule is commonly found in brown coal deposits near lignite formations. Applications for humic acid reside commonly in soil remediation but it has also been used as a precursor for graphene, which has exceptional material properties with respect to electron mobility, Young's modulus, and thermal conductivity. Graphene’s incredible properties have been effectively matched by the difficulty associated with reproducibly manufacturing it on a large scale, limiting the use of graphene for commercial applications. Usage of humic acid for similar enhanced applications warrants investigation due to the similarities of humic acid to graphene in addition to the inexpensive nature and availability of humic acid. The polar functional groups of humic acid reduce its solubility in organic solvents. Surfactants containing long alkyl chains can succesfully improve the miscibility of humic acid in an organic solvent, but are often difficult to remove after being incorporated into a system. It is theorized that through performing various chemical reactions at the terminal sites of humic acid, the aqueous affinity of humic acid can be altered thus enabling incorporation of humic acid into organic solvents without the negative side effects of surfactants. This research addresses varying degrees of esterification, amidation, and oligimerization of humic acid molecules with the intention of identifying the resulting change in solvent affinity. The novel molecules are characterized to confirm successful chemical reaction through microscopy, thermo gravimetric analysis, fourier-transform infrared spectroscopy, and X-ray diffraction. Effective dispersion of humic acid into multiple organic solvents will be verified using light scattering and microscopy. Humic acid derivatives will be incorporated into organic solvents commonly used as fuel sources to identify the resulting influence on combustion properties of the solvents.
9:00 PM - NM4.6.06
Formation of Highly Dense, Monodispersed, Metal and Transition Metal Nanoparticles by Electroless Deposition
Minh Tran 1 , Sonal Padalkar 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractMetal and transition metal nanostructures are of great interest due to their applicability in various areas such as catalysis, sensing and optoelectronics. We report the formation of highly dense and monodispersed metal and transition metal nanoparticles including silver, platinum, nickel and cobalt by electroless deposition technique. The synthesis method consists of immersing a silicon (Si) substrate in hydrofluoric (HF) acid for 2 min., followed by immersing the substrate in metal or transition metal precursor solution for 5 min. These steps are repeated several times to obtain the desired density of the nanostructures. A series of experiments were performed to monitor the density of the synthesized nanostructures and the results were correlated to the number of times the above step was repeated. Thus a good control over the nanostructure density was obtained. Further, to improve the dispersity of the nanostructures, surfactants like L-cysteine and cetyltrimethylammonium bromide (CTAB) were used in the synthesis process. The inclusion of surfactants provided a uniform morphology to the synthesized nanostructures. The characterization of all the above nanostructures was performed by using scanning electron microscope (SEM), X-ray diffractometer (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS).
9:00 PM - NM4.6.07
Facile Method to Synthesize Au Nanostructures of Controlled Morphology
Minh Tran 1 , Sonal Padalkar 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractGold (Au) nanostructures have been the subject of intense scientific research for their value in several new technological applications, including biosensing, catalysis, optics, and electronics. Many novel properties of Au nanostructures can be explored or enhanced by our ability to obtain certain Au nanostructure morphologies. In this investigation, we report a facile seed-mediated method to obtain Au nanostructures of different shapes. Specifically, in the first step dense quasi-spherical Au seeds were obtained in situ by galvanic displacement method. Then, Au nanostructures were grown on the existing seeds by controlling the reduction kinetics of HAuCl4 in the growth solution. Different morphologies of Au nanostructures were obtained. Our method is versatile and can be applied for other metals. Scanning electron microscopy (SEM), X-ray diffractometer (XRD), transmission electron microscopy (TEM), and Raman spectroscopy were used to characterize the resulting nanostructures.
9:00 PM - NM4.6.08
Fabrication of Size Controlled Copper (I) Oxide Nanostructured Film by Electrodeposition
Tian Lan 1 , Minh Tran 1 , Sonal Padalkar 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractCopper (I) oxide (Cu2O) nanostructures are favorable for applications in several areas including, catalysis, sensing and biosensing. Here we report the size controlled synthesis of Cu2O nanostructures by electrodeposition. The Cu2O nanostructures were deposited on indium doped tin oxide (ITO) substrates, using an alkaline copper (II) sulfate bath containing lactic acid and potassium hydroxide. The size control of the deposited Cu2O was carried out by the addition of ethylenediamine (EDA) in the electrolytic bath. The size of Cu2O nanostructures was varied by changing the concentration of EDA in the electrolytic bath during electrodeposition. The deposited nanostructures were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction.
9:00 PM - NM4.6.09
Morphology Dependence of the Photocatalytic Activity of Bismuth Oxide and Bismuth Oxychloride Films
Laura Gomez-Velazquez 1 , Maeve O'Brien 2 , Valerie Leppert 2 , Monserrat Bizarro 1
1 , Instituto de Investigaciones en Materiales, UNAM, Mexico City Mexico, 2 , University of California, Merced, Merced, California, United States
Show AbstractHeterogeneous photocatalysis has been considered as a successful alternative for removing organic pollutants in aqueous phase. One of the advantages of this process is the ability to convert the organic compounds into CO2 and water using light. Bismuth compounds are recently receiving attention as photocatalysts due to a high mobility of the photogenerated charge carriers. Materials containing Bi have a largely dispersed Bi 6s orbital that is beneficial for photocatalytic activity. In this work, we obtained β-Bi2O3 thin films by spray pyrolysis using bismuth acetate as a precursor salt and converted it into BiOCl by a chemical bath with HCl. Bi2O3 and BiOCl films were characterized by XRD, FESEM and UV-Vis diffuse reflectance. The photocatalytic activity was tested for the degradation of acid blue 113 dye, indicating that BiOCl was three times more efficient than β-Bi2O3. FESEM images indicated that the morphology of BiOCl films is composed of 100-200 nm diameter crenulated flakes with orientations ranging from the horizontal to vertical, while the β-Bi2O3 films are composed of embedded, horizontally oriented flakes of 200-800 nm in diameter. The higher photocatalytic activity can in part be attributed to a higher surface area available in the BiOCl films.
9:00 PM - NM4.6.15
Study of Surface Chemistry of Ni(111) in the Presence of CO2 and H2O
Jun Cai 3 2 1
3 , ShanghaiTech University, Shanghai China, 2 , Shanghai Institute of Microsystem and Information Technology, Shanghai China, 1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe electrochemical reduction of CO2 using various metal electrodes has been studied extensively by many workers, and it has been found that the reduction products depend strongly on the electrode material. To gain the improved catalysts with better performance, less cost and environment impact, a more thorough understanding of the species formed during the early steps of electrochemical reduction under operating conditions, i.e., while exposed to realistic gas pressures of CO2 and under condensed films of water, is essential. In this study, we reported the adsorption and reactions of CO2 and CO2+H2O at the pressure of 400mTorr on the Ni(111) surface to identify the surface chemical state and the nature of the adsorbed species using ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). We found that NiO is formed from CO2 dissociation into CO and atomic oxygen. Additionally, carbonate and surface carbonate are present on the surface from further reaction of CO2 with NiO. The addition of H2O into the reaction environment leads to the reaction intermediates such as formate.
9:00 PM - NM4.6.16
Design and Synthesis of Functionalized Organic-Inorganic Hybrid Nanomaterials and Its Application in Biomass Conversion Process
Poonam Bhargava 1 , Shivani Sharma 2 , Rakesh Kumar Sharma 2
1 Department of Chemistry, Miranda House, University of Delhi, Delhi India, 2 Department of Chemistry, University of Delhi, Delhi, India, India
Show AbstractCatalytic technologies play a key role in the design and development of greener routes for the production of industrially significant chemicals to address ecological and environmental concerns. In recent years, substantial progress has been made to explore novel approaches for the fabrication of organic-inorganic hybrid nanostructures that offers excellent prospects in designing highly selective and versatile catalytic systems. Recently, heterogenization of active catalytic species has emerged as an elegant and ingenious methodology to generate catalytic materials that possess immense potential to accelerate chemical transformations with enhanced selectivity, excellent durability and recyclability. In this perspective, silica nanospheres have captivated the interest of scientific community as exceptional support matrices since they display numerous unique physiochemical properties such as high surface area, good accessibility, and nanometre size, excellent thermal and mechanical stability. Within this framework, we have developed silica based functionalized organic-inorganic hybrid nanomaterials and their structure have been affirmed using several characterization tools such as TEM, SEM, XRD, FT-IR, BET and elemental analysis.
Subsequently, the catalytic efficacy of these nanostructures has been explored in the biomass conversion process. Cellulose is the most abundant biomass resource on the earth and its utilization is important, owing to increasing attention on energy resource consumption for a sustainable society and development. The conversion of glucose/fructose obtained from cellulosic biomass into useful chemicals in the presence of functionalized organic-inorganic hybrid nanomaterials as catalyst is the most promising and sustainable route to solve the crisis of fossil fuel resources. The interesting results will be presented.
9:00 PM - NM4.6.17
Complete Reaction Mechanisms of H2S Decomposition on Anatase TiO2(001) Surface—Density Functional Theory Calculations
Anchalee Junkaew 1 , Supawadee Namuangruk 1
1 Nanoscale Simulation Laboratory, National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency (NSTDA), Pathumthani Thailand
Show AbstractAn anatase TiO2 (001) has been reported as the active facet for many catalytic reactions. In this work, the complete mechanisms of H2S decomposition on the anatase TiO2 (001) facet were determined by using the plane wave based Density Functional Theory (DFT) method. The adsorption of intermediates and the reaction mechanisms on the surface were investigated systematically. The dissociation of H2S on the TiO2 surface requires a low activation energy (Ea~8.4 kcal/mol). Subsequently, two possible pathways, H2 formation and H2O formation, were proposed. The activation barriers for H2O formation ranging from 11-13 kcal/mol, while those for the H2 formation are extremely high in the range between 67-87 kcal/mol. On the (001) surface, the hydrogen transfer between two oxygen sites can be proceeded by the moderate energy, which facilitates the H2S reaction on the surface. As a result, the H2S dissociation over the anatase TiO2 (001) prefers the H2O formation path and yields the S-substituted O vacancy on the surface. This S-modified surface can enhance the photocatalytic reactivity due to reducing of the band gap compared to the perfect TiO2 (001) surface. Therefore, the TiO2 (001) catalyst is proposed as a potential catalyst for H2S desulfurization. Nonetheless, this facet is less favorable for H2 production application.
9:00 PM - NM4.6.18
Synthesis of NiCoP for Efficient Overall Water Splitting
Hanfeng Liang 1 , Appala Gandi 1 , Dalaver Anjum 1 , Xianbin Wang 1 , Udo Schwingenschlogl 1 , Husam Alshareef 1
1 , King Abdullah University of Science and Technology, Thuwal Saudi Arabia
Show AbstractEfficient water splitting requires highly active, earth-abundant, and robust catalysts. Monometallic phosphides such as Ni2P have been shown to be active toward water splitting. Our theoretical analysis has suggested that their performance can be further enhanced by substitution with extrinsic metals, though very little work has been conducted in this area. Here we present the synthesis of ternary NiCoP and further its application for water splitting. The obtained NiCoP nanostructure supported on Ni foam shows superior catalytic activity toward the hydrogen evolution reaction (HER) with a low overpotential of 32 mV at -10 mA cm-2 in alkaline media. Moreover, it is also capable of catalyzing the oxygen evolution reaction (OER) with high efficiency though the real active sites are surface oxides in situ formed during the catalysis. Specifically, a current density of 10 mA cm-2 is achieved at overpotential of 280 mV. These overpotentials are among the best reported values for non-noble metal catalysts. Most importantly, when used as both the cathode and anode for overall water splitting, a current density of 10 mA cm-2 is achieved at a cell voltage as low as 1.58 V, making NiCoP among the most efficient earth-abundant catalysts for water splitting.
9:00 PM - NM4.6.19
Preparation of Nitrogen Doped Porous Carbon Nanotubes for Highly Enhanced Electrocatalytic Activity toward Oxygen Reduction Reaction
Eun yeob Choi 1 , So-Hyeon Hong 1 , Hyejin Park 1 , Chang Keun Kim 1
1 , Chung-Ang University, Seoul, SE, Korea (the Republic of)
Show AbstractNitrogen doped porous carbon nanotubes (N-PCNTs) were prepared as a non-precious and effective electrocatalytic material for oxygen reduction reaction (ORR). The porous carbon nanotubes (PCNSs) containing high amount of oxygen functional groups were fabricated by reacting carbon nanotubes (CNTs) and hydrogen peroxide. To introduce the electrocatalytic activity into PCNTs, nitrogen impurities were doped on the surface of PCNTs by a pyrolysis reaction between the oxygen functional groups of PCNTs and urea. Formation of the N-PCNTs was confirmed by X-ray photoelectron spectroscopy (XPS), and their morphologies were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The changes in the surface area and pore size distribution of the N-PCNTs versus pristine CNTs were explored by Brunauer-Emmett-Teller (BET) analysis. The ORR activity of the N-PCNTs in alkaline media was investigated by using rotating ring disk electrode (RRDE). As a result of improved surface area and highly introduced nitrogen content, N-PCNTs exhibited remarkable performance of electrocatalytic activity toward ORR.
9:00 PM - NM4.6.21
Low Cost Cu-Based Electrocatalysts for Carbon Dioxide Reduction
Aditi Halder 2 , Shifali Bajaj 2 , Rohit Kaundal 2 , Himmat Kushwaha 1
2 School of Basic Science, Indian Institute of Technology, Mandi, Mandi India, 1 School of Engineering, Indian Institute of Technology, Mandi, Mandi, HP, India
Show AbstractThe primary goal of our research is based upon the electrochemical conversion of carbon dioxide to carbon monoxide (an important component of syn gas - a mixture of hydrogen and carbon monoxide).Electrochemical conversion of carbon dioxide has a large kinetic barrier and involves large number of products. The proposed electrocatalysts selectively converts carbon dioxide into carbon monoxide by preventing the uncontrolled formation of competitive reaction product and selectivity at low overpotential.We have synthesized low-cost cu-based electrocatalysts which can selectively convert carbon dioxide in to useful products depending upon the potential chosen for conversion. We have simultaneously carried out the in situ gas chromatography analysis to analyze the conversion products. We have synthesized four different Cu-based catalysts and carried out microstructural characterization of the same . These four catalyts have been studied for electrochemical conversion of carbon dioxide into different bye-products and in situ gas chromatography was done to understand the mechanistic pathways of product formation.
9:00 PM - NM4.6.22
Amphiphilic Dipyridinium-Phosphotungstate Complex as an Active, Selective and Recyclable Catalyst for the Epoxidation of Oils and Fatty Acids with Hydrogen Peroxide
Luis Carlos de la Garza Becerra 1 , Audrey Moores 1
1 , McGill, Montreal, Alberta, Canada
Show AbstractA new amphiphilic dipyridinium peroxo-phoshotungstate catalyst was developed as a selective and recyclable catalyst for the biphasic epoxidation of oils and fatty acids with hydrogen peroxide. The oxidation of vegetable oils is of prime importance for the production of lubricants, plasticizers, polymer stabilizers and other olefinic compounds. Vegetable oils also represent the largest share of renewable raw materials currently in use by the chemical industry. Based on the oxidizing activity of peroxophosphotungstates known as Venturello’s catalyst, we designed a lipophilic phase transfer agent that renders the active complex insoluble in the reaction media, without having to support it on a matrix. This results in a catalyst that bridges the gap between the activity of homogeneous catalysts and the recyclability of heterogeneous systems. The catalyst is effective at room temperature without the need of any additional solvents, which simplifies the purification of the product, it’s more active than other reported supported oxidation catalysts, and it may be recycled by simple filtration.
9:00 PM - NM4.6.23
Heteroatoms-Doped Carbon Nanowire Aerogels with Enhanced Electrocatalytic Performance for Oxygen Reduction
Shaofang Fu 1 , Chengzhou Zhu 1 , Junhua Song 1 , Yuehe Lin 1
1 , Washington State University, Pullman, Washington, United States
Show AbstractAs a result of the inherently sluggish reaction kinetics of oxygen reduction reaction (ORR) in many technologies (e.g. fuel cells, metal-air batteries), development of efficient catalysts for ORR becomes one of the major challenges for the extensive application of these devices. Even though carbon supported Pt nanomaterials are the widely utilized catalysts, the high cost and scarcity of Pt limit their large-scale production. In addition, these Pt-based catalysts are also subject to cross-over effect of methanol, CO poisoning, Pt aggregation and carbon corrosion, which will compromise the activity and long-term stability of the catalysts. In order to overcome these issues, substantial efforts have been made on developing other cost-effective electrocatalysts with high catalytic activity, including metal oxides, and metal-doped or metal-free carbon materials.
Apart from the compositional adjustment, the rationally designed morphology of the carbon materials can provide the structural benefits in improving their electrocatalytic performance. For instance, carbon-based three-dimensional (3D) networks have attracted increasing attentions because of their low density, large surface area and pore volume, as well as good conductivity. For electrocatalysis, the application of these 3D carbon materials is also favorable for the enhanced ORR performance because they are expected to provide better electrolyte permeability, faster electron transfer and mass transport.
Combining compositional advantages and morphological features, we a facile template-directed procedure was used to synthesize heteroatoms-doped (N, S, and F) carbon nanowire aerogels (CNWAs). By virtue of the precisely controlled composition and unique interconnected 3D morphology, the as-synthesized CNWAs reveal good electrocatalytic activity for ORR in alkaline solution. Significantly, the catalysts obtained under optimized condition exhibit remarkable stability, which is even better than that of commercial Pt/C catalysts. This synthetic method might be promising to design novel nanomaterials with the potential application in fuel cells.
9:00 PM - NM4.6.24
Electrodeposition of Size Controlled Ceria Nanostructures for Solar Water Splitting
Ahmad Fallatah 1 , Sonal Padalkar 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractCeria nanostructures have emerged as important contenders in the areas of photocatalysis. This is mainly attributed to their unique properties and the ease of fabrication. Here we report the electrochemical synthesis of ceria nanostructures for solar water splitting. The deposition of size controlled ceria nanostructures was possible by varying the process parameters. In a typical deposition, ceria nanostructures were deposited on fluorine doped tin oxide (FTO) substrate. The electrolytic bath contained cerium nitrate and dimethyl sulfoxide. The reaction temperature was kept between 70 – 90 °C. The process parameters including deposition time, temperature, applied potential and pH of the electrolyte was varied to obtain the size controlled ceria nanoparticles. These samples were utilized for photoelectrochemical water splitting. The obtained results were analyzed. The samples were characterized by scanning electron microscope, UV-Visible spectroscopy, gas chromatography, FT-IR and the incident photon to current conversion efficiency (IPCE)
9:00 PM - NM4.6.25
Photocatalytic Hydrogen Generation from 2D CdS Heterostructures
Maksym Zhukovskyi 1 , Masaru Kuno 1
1 , University of Notre Dame, Notre Dame, Indiana, United States
Show AbstractHigh quality ultrathin CdS nanosheets and corresponding Ni nanoparticle decorated counterparts represent efficient systems for photocatalytic hydrogen generation. Long time apparent quantum yields of 25% and transient yields as large as 64% have been found during the initial stages of H2 generation. Ensemble TDA spectroscopy illustrates that the high efficiency of Ni NP coated CdS NSs stems from efficient electron transfer from CdS to Ni. The metal/semiconductor heterojunction is therefore seen to be critical in dissociating strongly bound excitons in CdS NSs and play role in introducing an effective pathway for creating free carriers needed to carry out relevant reduction chemistries.
9:00 PM - NM4.6.26
Gas Sensing of ZnO/SnO2 Macro Porous Silicon Composite—Highly Sensitive CO2 Detection for Monitoring Air Quality
Venkata Krishna Karthik Tangirala 1 , Lizeth Martinez 2 , Vivechana Agarwal 2 , Ventura Lugo 1
1 , Universidad Autonoma de Estado Hidalgo, Hildago Mexico, 2 CIICAP, UNIVERSIDAD AUTONOMA DE ESTADO MORELOS, CUERNAVACA, MORELOS, Mexico
Show AbstractIn this work, we report the preparation of tin oxide (SnO2) and zinc oxide (ZnO) thin films onto crystalline (cSi) and macro - porous silicon (PS) substrates and their comparative carbon dioxide (CO2) gas sensing properties. An excellent sensitivity around 19 was obtained with SnO2/PS, whereas, ZnO/PS possess relatively faster response time ~ 65s. PS was developed by electrochemical etching of p-type monocrystalline silicon and the metal oxide thin films were deposited using homogenous precipitation deposition. All the obtained nanostructured films were characterized by X-ray diffraction (XRD), which confirms the presence of tetragonal and wurtzite phases of SnO2 and ZnO respectively. Scanning electron microscopy (SEM) reveals the formation of substrate porosity dependent porous metal oxide composite nanostructures. The CO2 sensing properties of SnO2/cSi and ZnO/cSi, SnO2/PS and ZnO/PS were studied as a function of deposition time, gas concentration and operation temperature (up to 3000C). Porous silicon templates greatly improve the gas-sensing properties of both SnO2 and ZnO films with respect to the films over cSi substrates due to increase in specific surface area. Irrespective of substrate type, the SnO2 films showed higher sensitivity than ZnO films due to the excellent association and dissociation reactions of SnO2 with adsorbed atmospheric oxygen. Additionally, the faster response times were achieved for all films using PS substrates. Therefore, these composite devices can be used as cost effective, VLSI integrable CO2 sensors operational at relatively low temperatures for indoor air quality and in mining applications.
Symposium Organizers
Yu Han, King Abdullah University of Science and Technology
Phillip Christopher, Univ of California-Riverside
Zili Wu, Oak Ridge National Laboratory
Ning Yan, National University of Singapore
Symposium Support
King Abdullah University of Science and Technology
NM4.7: OER and HER
Session Chairs
Thursday AM, April 20, 2017
PCC West, 100 Level, Room 104 B
9:30 AM - *NM4.7.01
Oxygen Evolution Reaction Electrocatalysis—Redefining Intrinsic Activity Trends and lIlustrating Design Principles
Shannon Boettcher 1
1 , University of Oregon, Eugene, Oregon, United States
Show AbstractPoor oxygen evolution reaction (OER) catalysis limits the efficiency of H2 production from water electrolysis and photo-electrolysis—clean routes to large-scale energy storage. Despite nearly a century of research, the factors governing the activity of OER catalysts are not well understood. I will discuss our recent advances in understanding the OER in alkaline media for earth-abundant, first-row, transition-metal oxides and (oxy)hydroxides.1 We find that the most-relevant structures for study are thermodynamically stable (oxy)hydroxides and not crystalline oxides. We show how thin-film electrochemical microbalance techniques2 allow for accurate quantification of intrinsic activity and how in situ conductivity measurements illustrates how materials are limited by electronic transport.3 We highlight the dramatic effect that Fe cations—added either intentionally or unintentionally from ubiquitous electrolyte impurities—have on the activity of most OER catalysts.4 In the absence of Fe we find activity trends across the first-row transition metals that are opposite of the established ones.5 We propose a new view of OER on mixed-metal (oxy)hydroxides where Ni or Co host-structures support active sites that contain Fe. By rationally combining cations6 we tune intrinsic activity and electrical conductivity. The work thus illustrates design principles for electrocatalysts that may speed advanced hydrogen production applications.
(1) Burke, M. S.; Enman, L. J.; Batchellor, A. S.; Zou, S.; Boettcher, S. W. Oxygen Evolution Reaction Electrocatalysis on Transition Metal Oxides and (Oxy)hydroxides: Activity Trends and Design Principles. Chem. Mater. 2015, 27, 7549-7558.
(2) Stevens, M. B. et. al.; Boettcher, S. W. Measurement Techniques for the Study of Thin Film Heterogeneous Water Oxidation Electrocatalysts. Chem. Mater. 2016.
(3) Burke, M. S.; Kast, M. G.; Trotochaud, L.; Smith, A. M.; Boettcher, S. W. Cobalt-Iron (Oxy)hydroxide Oxygen Evolution Electrocatalysts: The Role of Structure and Composition on Activity, Stability, and Mechanism. J. Am. Chem. Soc. 2015, 137, 3638-3648.
(4) Trotochaud, L.; Young, S. L.; Ranney, J. K.; Boettcher, S. W. Nickel-Iron Oxyhydroxide Oxygen-Evolution Electrocatalysts: The Role of Intentional and Incidental Iron Incorporation. J. Am. Chem. Soc. 2014, 136, 6744-6753.
(5) Burke, M. S.; Zou, S.; Enman, L. J.; Kellon, J. E.; Gabor, C. A.; Pledger, E.; Boettcher, S. W. Revised Oxygen Evolution Reaction Activity Trends for First-Row Transition-Metal (Oxy)hydroxides in Alkaline Media. J. Phys. Chem. Lett. 2015, 6, 3737-3742.
(6) Enman, L. J.; Burke, M. S.; Batchellor, A. S.; Boettcher, S. W. Effects of Intentionally Incorporated Metal Cations on the Oxygen Evolution Electrocatalytic Activity of Nickel (Oxy)hydroxide in Alkaline Media. ACS Catalysis 2016, 2416-2423.
10:00 AM - NM4.7.02
Oxygen Evolution Reaction on α-Fe2O3 (0001)—A First-Principles Study of the Impact of Surface Hydroxylation and Hydration
Junghyun Noh 1 2 3 , Osman Abdelkarim 4 , Saadullah Aziz 4 , Paul Winget 5 , Jean-Luc Bredas 2 3
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal Saudi Arabia, 4 Department of Chemistry, King Abdulaziz University, Jeddah Saudi Arabia, 5 , The Coca-Cola Company, Atlanta, Georgia, United States
Show AbstractAmong the various iron oxide phases and polymorphs, hematite (α-Fe2O3) has been explored extensively in the field of heterogeneous catalysis, in particular, as a catalytic anode material for photo-electrochemical (PEC) water splitting. The reasons are its outstanding thermodynamic stability and the characteristics of its electronic structure, which facilitate the oxygen evolution reaction (OER). In aqueous solution, the oxide surface easily binds water molecules, in both molecular and dissociative fashions, which leads to the appearance of hydrated/hydroxylated surface configurations. Since this process involves charge transfer between the surface and the water/hydroxyl complexes, the surface chemistry of hydrated/hydroxylated domains is different from that of clean, unmodified domains. Thus, the OER thermodynamics and kinetics as well as the charge separation processes are expected to be affected. Here, we determine the surface configurations in given PEC conditions and establish a fundamental understanding of the impact of adsorbates on the hematite catalytic activity.
To this end, we perform DFT calculations at the PBE+U level to predict the most energetically favorable surface domains of α-Fe2O3 (0001) based on surface Pourbaix diagrams constructed in the framework of first-principles thermodynamics. The relative surface stabilities are investigated both for perfect bulk terminations and for defect-containing surfaces with various degrees of hydroxylation and hydration. Overall, fully saturated models exhibit the lowest surface free energies in the low potential regime; at higher electrode potentials, which correspond to the conditions reached when photoinduced holes are generated in hematite upon illumination, partially hydroxylated surfaces become more favorable.
The thermodynamics of the four-step OER mechanism are examined for different surface models in order to unravel the impact of adsorbed water molecules or/and hydroxyls on the redox reactions. The theoretical overpotential are in the range of 0.5-0.7 V for O3 terminations while 1Fe terminations require a higher electrode bias of 0.6-1.1 V. Our findings underline that the nature of surface termination as well as the degree of near-surface hydroxylation can give rise to a significant variation in the OER overpotentials. The best performance is predicted for the reaction cycle which deprotonation step occurs at moderately hydroxylated surfaces.
10:15 AM - NM4.7.03
Investigating Transition Metal Chalcogenides for Efficient Oxygen Evolution Electrocatalysis—The Effect of Covalency and Lattice Directionality
Manashi Nath 1 , Jahangir Masud 1 , Abdurazag Swesi 1 , Siddesh Umapathi 1 , Bahar Golrokhamen 1
1 , Missouri S&T, Rolla, Missouri, United States
Show AbstractWater electrolysis leading to generation of oxygen and hydrogen, has been one of the most promising routes towards sustainable alternative energy generation and storage, with applications ranging from metal-air batteries, fuel cells, to solar-to-fuel energy conversion systems. Oxygen and Hydrogen evolution reaction (OER and HER respectively) are the two half reactions for water electrolysis, amongst which OER is the most challenging uphill process with a high electron count. Hence, designing efficient catalysts for OER process from earth-abundant resources has been one of the primary concerns for advancing this field. Recently transition metal chalcogenides has been identified as efficient OER electrocatalysts. We have synthesized a plethora of transition metal selenides including those based on Ni, Ni-Fe, Co, and Ni-Co, which show high catalytic efficiency characterized by low onset potential and overpotential at 10 mA/cm2 [Ni3Se2 - 200 - 290 mV; Co7Se8 - 260 mV; FeNi2Se4-NrGO - 170 mV (NrGO - N-doped reduced graphene oxide); NiFe2Se4 - 210 mV; NiCo2Se4 - 190 mV]. We have proposed the idea that one of the primary reasons these selenides show a much better OER catalytic activity is due to increasing covalency in the metal-selenium bond compared to the oxides caused by decreasing electronegativity of the anion, which in turn leads to variation of chemical potential around the transition metal center, specifically, lowering the Ni2+ --> Ni3+ oxidation potential (Ni3+ being the actually catalytically active species). In this presentation we will highlight the importance of this increasing covalency in enhancing the catalytic activity with the help of experimental evidence in selenide compositions ranging from binary Ni-selenides (Ni3Se2, NiSe2, NiSe), ternary mixed metal selenides (Ni-Co-Se, Ni-Fe-Se) as well as seleno-based molecular complex containing NiSe4 tetrahedral core. We will illustrate how the Ni(II) --> Ni(III) oxidation potential is indeed lowered within the selenide coordination compared to the oxide, in pure single crystals of the seleno-based coordination complex which is devoid of any surface impurities and adsorbates. We will also emphasize the lattice-plane-dependent catalytic activity through the example of electrodeposited NiSe2 which shows that if grown along the <311> direction exposing the Ni-rich terminating lattice plane, this catalyst can exhibit lowest overpotential at 10 mA/cm2 (140 mV) that has been reported so far for OER in alkaline medium. All of these selenide electrocatalysts has been characterized with pxrd, SEM, TEM, Raman, XPS, EDS and detailed electrochemical studies including LSV, CV, chronoameprometry, chronopotentiometry, determination of Faradaic efficiency, and ECSA. Through this presentation we will offer insight into possible reasons these selenides outperform most of the known OER electrocatalysts, which will hopefully initiate discussion and efforts to fully understand and utilize their full potential.
10:30 AM - NM4.7.04
Electrochemical Tuning of Catalysts for Improved Water Splitting and Fuel Cell Electrocatalysis
Haotian Wang 1 , Yi Cui 2
1 , Harvard University, Cambridge, Massachusetts, United States, 2 , Stanford University, Stanford, California, United States
Show AbstractEmploying battery technologies into electrocatalysis can provide powerful tools and great opportunities to systematically and controllably tune the electronic structures of catalytic materials for improved performance. Here we present a few representative examples including the Li electrochemical tuning of MoS2 and LiCoO2 for improved hydrogen evolution reaction and oxygen evolution reaction respectively, and the Li cycled transition metal oxides for highly efficient bifunctional water-splitting catalyst. In addition, by taking the advantages of the volume changes in battery electrodes, we controllably induce lattice tension and compression in Pt nanoparticles on LiCoO2 supports, and thus continuously tune the oxygen reduction reaction activity of Pt.
11:15 AM - *NM4.7.05
Sub-Particle Reaction and Photocurrent Mapping on Single-Particle Photoanodes
Peng Chen 1
1 , Cornell University, Ithaca, New York, United States
Show AbstractPhotoelectrochemical solar energy conversion to electricity or fuels is often limited by the activity of photogenerated holes and electrons on photoelectrode surfaces, requiring modification with catalysts to improve efficiency. It is unclear, however, on what surface sites to optimally deposit catalysts, and to what extent the same surface sites, responsible for fuel-forming reactions, also cause recombination. Here we use charge-carrier-selective single-molecule super-resolution photoelectrocatalysis imaging to quantify the correlation between photogenerated hole and electron activities on single semiconductor photoanodes under photoelectrochemical water oxidation conditions. We further use sub-particle-level photocurrent measurements to define the relationship between water oxidation photocurrent and charge-carrier surface activities. Guided by hole and electron activity maps, site-selective catalyst deposition on individual semiconductor particles reveals the optimal sites for oxygen evolution catalysts, leading to a strategy for rationally engineering photoanodes with catalysts.
11:45 AM - NM4.7.06
Highly Active Non-Noble Nanocatalysts for Fuel Cell Applications
Jinsong Hu 1
1 , Institute of Chemistry, Chinese Academy of Sciences, Beijing China
Show AbstractThe rapidly increasing energy demand for human activities stimulates the lasting research interests to develop renewable energy alternatives worldwide. The development of low-cost high-performance electrocatalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) to replace the precious metal-based catalysts would be essential and important for the commercialization of various fuel cell applications.
This presentation will talk about several reasonable ways for designing new non-precious metal nanocatalysts with high electrocatalytic activities and superior stability for ORR and HER. By focusing on the creation and the enrichment of highly active sites for ORR and simultaneously considering the mass transfer and electron transportation, we have developed several efficient metal-free ORR catalysts.1-3 The further improvement of the performance can be achieved by introducing transition metal or nanostructures into these nanocatalysts.4-6 Furthermore, understanding the origin of high activity of these electrocatalysts in ORR is also critical for developing efficient non-precious metal catalysts but still challenging. We developed a new highly active Fe-N-C ORR catalyst containing Fe-Nx coordination sites and Fe/Fe3C nanocrystals, and revealed the origin of its activity by intensively investigating the composition and the structure of the catalyst and their correlations with the electrochemical performance. Based on our experimental and theoretical results, it can be concluded that the high ORR activity in this type of Fe-N-C catalysts should be ascribed to that Fe/Fe3C nanocrystals boost the activity of Fe-Nx. Last, the presentation will also discuss the design and several examples for highly active HER catalysts.7-8 These new findings open an avenue for the rational design and bottom-up synthesis of low-cost highly active ORR electrocatalysts.
1.W.J. Jiang, J.S. Hu, X. Zhang, Y. Jiang, B.B. Yu, Z.D. Wei, and L.J. Wan, J. Mater. Chem. A. 2014, 2, 10154-10160.
2.W. Ding, Z.D. Wei, S.G. Chen, X.Q., T. Yang, J.S. Hu, D. Wang, L.J. Wan, S.F. Alvi, and L. Li, Angew. Chem. Int. Ed., 2013, 52, 11755.
3.Y. Zhang, W.J. Jiang, X. Zhang, L. Guo, J.S. Hu, Z.D. Wei, and L.J. Wan, Phys. Chem. Chem. Phys., 2014, 6, 13605-13609.
4.W.J. Jiang, L. Gu, L. Li, Y. Zhang, X. Zhang, L.J. Zhang, J.Q. Wang, J.S. Hu, Z.D. Wei, and L.J. Wan, J. Am. Chem. Soc., 2016, 138, 3570-3578.
5.Y. Zhang, W.J. Jiang, X. Zhang, L. Guo, J.S. Hu, Z.D. Wei, and L.J. Wan, ACS Appl. Mater. Interfaces, 2015, 7, 11508−11515.
6.Y. Zhang, L.B. Huang, W.J. Jiang, X. Zhang, Y.Y. Chen, Z.D. Wei, L.J. Wan, and J.S. Hu, J. Mater. Chem. A, 2016, 4, 7781-7787.
7.X. Zhang, Y. Zhang, B.B. Yu, X.L. Yin, W.J. Jiang, Y. Jiang, J.S. Hu, and L.J. Wan, , J. Mater. Chem. A, 2015, 3, 19277-19281.
8.Y.Y. Chen, Y. Zhang, W.J. Jiang, X. Zhang, Z.H., Dai, L.J. Wan, and J.S. Hu, ACS Nano, 2016, 10, 8851–8860.
12:00 PM - NM4.7.07
The Catalytic Sites of MoS2 for Hydrogen Evolution
Guoqing Li 1 , Linyou Cao 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractMoS2 presents a promising low-cost catalyst for the hydrogen evolution reaction (HER), but the understanding about its active sites has remained to be limited. Here we present an unambiguous study for the catalytic activities of all possible reaction sites of MoS2, including edge sites, sulfur vacancies, and grain boundaries. We demonstrate that, in addition to the well-known catalytically active edge sites, sulfur vacancies provide another major active site for the HER while the catalytic activity of grain boundaries is much weaker. The intrinsic turnover frequencies (Tafel slopes) of the edge sites, sulfur vacancies, and grain boundaries are estimated to be 7.5 s-1 (65-75 mV/dec), 3.2 s-1 (65-85 mV/dec), and 0.1 s-1 (120-160 mV/dec), respectively. We also demonstrate that the catalytic activity of sulfur vacancies strongly depends on the density of the vacancies and the local crystalline structure at the proximity of the vacancies. Unlike edge sites, whose catalytic activity linearly depends on the length, sulfur vacancies show optimal catalytic activities when the vacancy density is in the range of 7-10%. And the sulfur vacancies in the MoS2 whose crystalline quality is otherwise high tends to show better catalytic activities.
12:15 PM - NM4.7.08
Computational Screening of Two-Dimensional Metal Dichalcogenides with Anion Vacancies for Hydrogen Evolution Reaction
Joohee Lee 1 , Kye Yeop Kim 1 , Seungwu Han 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractHydrogen has been a strong candidate for a clean energy source that may replace fossil fuels. For clean production of hydrogen by splitting water, the catalyst is necessary to reduce the large overpotential during the hydrogen and oxygen evolution. Pt catalyst, which is known to be the best catalyst for water splitting, is very expensive and it limits large scale applications, so novel materials are actively studied as water splitting catalyst. Recently, transition metal dicalcogenides (TMDs), most notably MoS2, are receiving much attention as a novel catalyst for water splitting due to their earth abundance, stability in the acidic media, and their 2D nature which provides largely exposed active sites. Although basal planes of many stable TMD phases are known to be inert and edges are considered as the active sites, it was recently found that the basal plane of MoS2 can also be active for hydrogen evolution reaction (HER) by introducing sulfur vacancies and strain.
In this presentation, we try to find other defective TMD materials for HER catalyst by means of computational screening based on the density functional theory. We first identify the stable phase of 40 TMDs. Then, we explore the HER efficiencies of basal planes and anion vacancy sites of the TMD materials by using the hydrogen binding free energy as the descriptor for the exchange current density. As a result, we were able to select TMD candidates that may show high HER performance in experiment. The candidate TMDs can be classified in four types according to how the hydrogen binding energy depends on the vacancy density. In addition, through the backward elimination of factors for multiple linear regression, we identify the key physical quantities that affect the hydrogen adsorption energy.
12:30 PM - NM4.7.09
Photoluminescence Imaging as a Tool to Surface Reactions on MoS2
Koichi Yamaguchi 1 , Sahar Naghibi 1 , Gretel Von Son 1 , Emma Bryan 1 2 , Aimee Martinez 1 , Raymond Acosta 1 , Wiliam Coley 1 , Alison Guan 1 , Ariana E. Nguyen 1 , Joseph Martinez 1 , Michael Valentin 1 , Miguel Isarraraz 1 , Ludwig Bartels 1
1 , University of California, Riverside, Riverside, California, United States, 2 , University of Cambridge, Cambridge United Kingdom
Show AbstractMoS2 is a key industrial catalyst for hydrodesulfurization (HDS) of crude oil and it also has potential applications in the formation of (higher) alcohols from syngas as well as in facilitating electrochemical reactions. The industrial catalyst material consists of few-layer platelets of MoS2 and arguably resembles single-layer MoS2 flakes sufficiently well so that the latter can be used as a meaningful model system. We report on the development of a new experimental approach that relies on strong photoluminescence (PL) of monolayer MoS2 (peak @ 670-690 nm). PL imaging and spectroscopy is possible even at elevated temperatures and pressures, allowing the investigation of MoS2 surface reactivity under near-realistic conditions. Our experimental approach makes use of PL mapping generated by use of wide field PL imaging to drastically reduce the data acquisition time. Via this experimental approach, we can measure changes in PL intensity and use this to determine the formation/density of defects as caused in the single-layer material as caused by the MoS2 sulfur being activated in the cause of surface reactions. MoS2 is known to be catalytically active between temperatures from 200 °C to 400 °C; in this regime, we have confirmed gradual redshift of the PL spectrum from 670nm to 750nm under Hydrogen and Methanol-Hydrogen atmosphere for both edge and basal plane of MoS2. This redshift persists to a certain degree even if the MoS2 substrate is subsequently brought to cryogenic temperatures. Introduction of sulfur-containing species reverses this effect allowing the real-time monitoring of HDS activity. We present results that correlates PL mapping under and immediately following reactive conditions to the reaction product distribution as measured by mass spectrometry. These findings highlight the involvement of the basal plane in MoS2 catalytic activity.
12:45 PM - NM4.7.10
A Precise and Scalable Post-Modification of Metal-Organic Framework NU-1000 via Atomic Layer Deposition for Catalysis
Alex Martinson 1 , In Soo Kim 1 , Omar Farha 2 , Joseph Hupp 2 , Laura Gagliardi 3 , Karena Chapman 1 , Chris Cramer 3
1 , Argonne National Laboratory, Argonne, Illinois, United States, 2 , Northwestern University, Evanston, Illinois, United States, 3 , University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractThe connectivity of NU-1000, a metal-organic framework, gives rise to Zr6 nodes with hydroxyl-containing functional groups pointing into the large 1D mesoporous hexagonal channels of the framework. These free and exposed –OH groups are ideal grafting sites, and they can be tailored to serve a specific function. Through atomic layer deposition in MOFs (AIM), we demonstrate the ability to form several oxides and noble metals with atomic precision . Importantly, this process occurs without significantly changing the overall structure of the framework. Recent progress in scaling AIM process of the ultrahigh surface area (2300 m2/g) framework as well as progress in pinpointing the location and mechanism of surface chemical reactions of catalytically relevant metals is discussed. Computational, synchrotron, and in-situ analytical methods including DFT, differential electron diffraction, and in situ FTIR are brought to bear on several new metal systems, many of which show remarkably self-limiting behavior and exhibit unique activity for alkane catalysis.
NM4.8: Photocatalysis and PEC
Session Chairs
Phillip Christopher
Zili Wu
Thursday PM, April 20, 2017
PCC West, 100 Level, Room 104 B
2:30 PM - *NM4.8.01
Photocatalytic Overall Water Splitting Using Semiconductor Particulate—Essential Role of Electrocatalyst Decoration
Kazuhiro Takanabe 1
1 , KAUST, Thuwal Saudi Arabia
Show AbstractSolar energy is abundant and renewable energy: however, extensive conversion of the solar energy can only be achieved by large-scale collection of solar flux. The technology that satisfies this requirement must be as simple as possible to reduce capital cost. Overall water splitting (OWS) by powder-form photocatalysts directly produces H2 as a chemical energy in a single reactor. Because of its simplicity and low capital cost, it has tremendous potential to become the major technology of solar energy conversion. During the OWS, the hydrogen evolution reaction (HER) should take place efficiently, which requires an efficient electrocatalyst. Platinum-group metals (Pt, Rh, Pd, etc.) are excellent HER electrocatalysts, but the surfaces of the catalysts should be insensitive to the back-reaction of the produced H2 and O2 that produces H2O as well as the oxygen reduction reaction (ORR) that may concurrently occur during the OWS. Here some successful OWS was achieved using core-shell metal-CrOx electrocatalyst configuration. This shell material funcitions as selective permiation membrane where proton and H2 can permiate but O2 cannot. It also remains challenging to develop highly active HER cocatalysts that have a low cost and utilize abundant materials. Some recent progress in our group will be discussed including electrochemical understanding of non-noble metal electrocatalyst for OWS, as well as of novel shell material for the selective H2 production during OWS.
3:00 PM - *NM4.8.02
Efficient Water Splitting by Metal Oxide Multi-Shelled Hollow Microspheres
Yu Yang 1 , Yanze Wei 3 , Muhammad Waqas 1 , Ranbo Yu 3 , Huijun Zhao 2 , Dan Wang 1 2
1 , Institute of Process Engineering, Beijing China, 3 , University of Science and Technology Beijing, Beijing China, 2 , Griffith University, Gold Coast, Queensland, Australia
Show AbstractOverall water splitting has been a difficult task in photocatalysis during the past decades. Substituting for noble-based photocatalysts with earth abundant element based metal oxide is crucial for large-scale manufacture and application of above technics. Herein, we prepared composite metal oxide multi-shelled hollow microspheres, which present either excellent hydrogen or oxygen evolution performance. Secondly, in order to achieve the overall water splitting, we fabricated an photoelectrochemical (PEC) water splitting system using the TiO2-CuxO multi-shelled hollow microspheres (TCMSHMS) as the photocathode and CeO2-CeFeO3 multi-shelled hollow microspheres (CCFMSHMS) as the photoanode. The PEC cell exhibited a stable photocurrent of 1mA/cm-2 with an external bias less than 0.7 VRHE under direct irradiation of AM 1.5G. The excellent performance of overall water splitting using multi-shelled hollow microspheres provide a huge potential of achieving effective conversion of clean energy in a large scale.
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3:30 PM - NM4.8.03
Enhancing Photocatalytic Activity of Titanium Dioxide Nanoparticles by Internal Polarization of a Hydroxyapatite Support
Xuefei Zhang 1 , Matthew Yates 1
1 , University of Rochester, Rochester, New York, United States
Show AbstractThe fast recombination of photogenerated charge carriers in titanium dioxide (TiO2) remains a challenging issue limiting the photocatalytic efficiency. Although some reports have used spontaneous internal polarization of ferroelectric photocatalyst supports to enhance photoinduced carrier separation, very few studies have investigated the effects of built-in polarization of non-ferroelectric supports which may possess tunable and much larger electrical polarization than ferroelectric materials do. This study describes a method for increasing the photocatalytic performance of TiO2 nanoparticles by utilizing giant internal electrical polarization of hydroxyapatite supports to promote the separation of photogenerated electron-hole pairs. Dense and thermally stable yttrium and fluorine co-doped hydroxyapatite films with giant internal polarization were synthesized as photocatalyst supports. TiO2 nanoparticles were deposited on the supports. The TiO2 nanoparticles were then used to catalyze the photochemical reduction of aqueous silver ions to produce silver nanoparticles. It was found that significantly more silver nanoparticles were produced on polarized hydroxyapatite supports than on depolarized hydroxyapatite supports. It is proposed that photogenerated electrons and holes in TiO2 nanoparticles are driven to different directions by the internal polarization of the hydroxyapatite support, and consequently, the recombination of charge carriers is mitigated. The results imply that materials with tunable internal polarization can be designed as a new strategy for enhancing quantum efficiency of photocatalysts.
3:45 PM - NM4.8.04
Harnessing Hot Electrons from Near IR Light for Hydrogen Production Using Pt-End-Capped-AuNRs
Nathalia Ortiz 1 , Brandon Zoellner 1 , Soung Young Hong 1 , Yue Ji 1 , Tao Wang 1 , Yang Liu 1 , Paul Maggard 1 , Gufeng Wang 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractGold nanorods show great potential in harvesting natural sun light and the generation of hot charge carriers that can be employed to produce electrical or chemical energies. We show that photochemical reduction of Pt(IV) to Pt metal mainly takes place at the ends of gold nanorods (AuNRs), suggesting photon-induced hot electrons are generated, or localized in a time-averaged manner, at AuNR ends. To use these hot electrons efficiently, a novel synthetic method to selectively overgrow Pt at the ends of AuNRs has been developed. These Pt-end-capped AuNRs show relatively high activity for the production of hydrogen gas using artificial white light, natural sun light, and more importantly, near IR light at 976 nm. Tuning of the surface plasmon resonance (SPR) wavelength of AuNRs changes the hydrogen gas production rate, indicating that SPR is involved in hot electron generation and photo-reduction of hydrogen ions. This study shows that gold nanorods are excellent for converting low energy photons in to high energy hot electrons, which can be used to drive chemical reactions at their surfaces.
4:30 PM - *NM4.8.05
Highly Concentrated CO Evolution for Photocatalytic Conversion of CO2 by H2O as an Electron Donor
Kentaro Teramura 1
1 , Kyoto University, Kyoto Japan
Show AbstractThe reduction in human-induced emissions of CO2 from automobiles, factories, power stations etc., over the next 15 years is currently one of the most important issues facing the planet. We should therefore attempt to develop industrial processes using CO2 as a feedstock in order to build a sustainable society in the near future. Linear CO2 molecules adsorbed on the surface of the solid bases are converted into unique structures, such as bicarbonate and carbonate species possessing lattice oxygen atoms. We believe that the process involves the capture and distortion of CO2 upon adsorption on a solid base through activation by photoirradiation. Unstable CO2 species adsorbed onto the surface can then be reduced by electrons with protons derived from H2O (CO2 + 2e− + 2H+ → CO + H2O). These days, we succeeded in designing highly selective photocatalytic conversion of CO2 by H2O as the electron donor, by the simultaneous use of an inhibitor of the production of H2 and a material for CO2 capture and storage, such as ZnGa2O4/Ga2O3, La2Ti2O7, SrO/Ta2O5, ZnGa2O4, ZnTa2O6, and Sr2KTa5O15 with the modification of Ag cocatalyst. An isotope experiment using 13CO2 and mass spectrometry clarified that the carbon source of the evolved CO is not the residual carbon species on the photocatalyst surface, but the CO2 introduced in the gas phase. In addition, stoichiometric amounts of O2 evolved were generated together with CO.
5:00 PM - NM4.8.06
Complete Splitting of Carbon Dioxide Using Amorphous Oxide Semiconductor under Light Irradiation
Shicheng Yan 1
1 College of Engineering and Applied Sciences, Nanjing University, Nanjing, Jiangsu, China
Show AbstractA natural method to fix carbon dioxide molecular (CO2) into solid products and releasing oxygen is photosynthesis, mainly achieving by plants, which is the most important chemical reaction to transfer CO2 in atmosphere and H2O into energy and foods for lives on the earth.1 Learning from nature, artificial photosynthesis can be constructed based on semiconducting photocatalysis by using H2O as reductant to convert CO2 into gaseous or liquid reduced carbon-based products and oxygen 2, 3, 4, 5. However, it is difficult to produce easily storable and more stable solid products by utilizing artificial photosynthesis. Recently, experimental evidence indicated that CO2 can be resolved into C and O2 at least vacuum ultraviolet irradiation of 11.44 eV 6, which is 10.4 eV higher than the thermodynamic requirement of 1.04 eV for CO2 splitting into C and O2 (as the heat of formation of CO2 from C is -393.5 kJ mol-1), meaning that light driven splitting of CO2 is feasible and needs to decrease the reaction activation energy by catalysis. Here, we achieved splitting of CO2 into C and O2 over amorphous zinc germanate (α-Zn-Ge-O) semiconductor photocatalyst under 300 W Xe lamp irradiation. Electron paramagnetic resonance (EPR) and 18O isotope labeling indicated that the splitting of CO2 was achieved via photogenerated holes induced oxygen vacancies (OVs ) on α-Zn-Ge-O reacting with O of CO2 to fill the oxygen vacancies of α-Zn-Ge-O, while the photogenerated electrons reduce the carbon species of CO2 to solid carbon. Under light irradiation, such a defects reaction is sustainable by continuous photogenerated hole oxidation of surface oxygen atoms on α-Zn-Ge-O to form oxygen vacancies and release O2. Our findings offer a new method for transcending nature to directly split CO2 into solid carbon and O2 without using reductant based on a well-known photocorrosion mechanism of oxide semiconductor.
Reference
[1] Lewis, N. S.＆Nocera, D. G. Powering the planet: Chemical challenges in solar energy utilization. Proc. Natl. Acad. Sci. U.S.A. 103, 15729-15735 (2006).
[2] Halmann, M. Photoelectrochemical reduction of aqueous carbon dioxide on p-type gallium phosphide in liquid junction solar cells. Nature 275,115-116 (1978).
[3] Kumar, B. et al. Photochemical and photoelectrochemical reduction of CO2. Annu. Rev. Phys. Chem. 63, 541-569 (2012)
[4] Yan, S. C. et al. A room-temperature reactive-template route to mesoporous ZnGa2O4 with improved photocatalytic activity in reduction of CO2. Angew. Chem. Int. Ed. 49, 6400 -6404 (2010).
[5] Liu, C. et al. Water splitting-biosynthetic system with CO2 reduction efficiencies exceeding photosynthesis. Science 352,1210-1213 (2016).
[6] Lu, Z. et al. Evidence for direct molecular oxygen production in CO2 photodissociation. Science 346 , 61-64 (2014)
5:15 PM - NM4.8.07
Coaxial Tubular TiO2-PtPd Nanomachines for Efficient Water Purification under Sunlight
Fajer Mushtaq 1 , Agim Asani 1 , Marcus Hoop 1 , Xiang-Zhong Chen 1 , Daniel Ahmed 1 , Bradley Nelson 1 , Salvador Pane i Vidal 1
1 , ETH Zurich, Zürich Switzerland
Show AbstractRapid industrialization and population growth are imposing an increasing demand on clean water sources worldwide.1 Industries are the biggest polluters of water bodies, with the textile industry discharging more than 200,000 tons of toxic, synthetic dyes every year into effluents.2,3 This has led to a growing interest in studying photocatalysis as a potentially cheap and green technique to convert hazardous organic pollutants into harmless by-products using abundantly available sunlight. In this work, we report the fabrication of coaxial, titanium dioxide- platinum palladium (TiO2-PtPd) nanotubes (NTs) with nickel (Ni) nanowire segments for photocatalytic water remediation under UV, visible and natural sunlight. Electrochemical synthesis route was chosen to fabricate these multicomponent nanostructures by sequential template-assisted electrodeposition. Using this approach, two different architectures of coupling noble metals to TiO2 (either as nanoparticles and as nanotubes) were compared for their photocatalytic efficiency. Apart from this, the photocatalytic efficiency of monometallic vs. bimetallic noble metal coupling was also compared.
The composition, morphology and crystalline structure of these hybrid nanotubes were studied by energy-dispersive X-ray spectroscopy, SEM, TEM and X-ray diffraction. Experiments on photocatalytic degradation of organic pollutant rhodamine-B were performed and displayed a 100% degradation efficiency in 50 and 30 min under visible light and natural sunlight, respectively. Cytotoxicity experiments performed on these hybrid nanostructures showed a good biocompatibility allowing their potential use to clean water with aquatic life. Additionally, these hybrid NTs were tested for their actuation mechanisms and owing to their unique design, demonstrated versatile motions such as autonomous, fuel-powered actuation in a 5% hydrogen peroxide solution as well as a fuel-free, magnetic, and acoustic field guided swimming behavior. These different propulsion mechanisms render these hybrid nanomachines cost-effective photocatalysts that can be precisely guided and collected for re-use, making them attractive candidates for designing future, visible-light active water remediation and water splitting photocatalysts.
References:
(1) Farah Maria Drumond Chequer, G. A. R. d. O., Elisa Raquel Anastácio Ferraz, Juliano Carvalho Cardoso, Maria Valnice Boldrin Zanoni and Danielle Palma de Oliveira Eco Friendly Textile Dyeing and Finishing; InTech, 2013.
(2) Padhi, B. International Journal of Environmental Sciences 2012, 3, 940.
(3) Kant, R. Natural Science 2012, 4, 22.
5:30 PM - NM4.8.08
Hybrid Organic-Inorganic Electrochemical Systems for Photo-Catalytic Hydrogen Production
Maria Rosa Antognazza 1 , Hansel Comas 2 , Sebastiano Bellani 1 , Francesco Fumagalli 1 , Fabio Di Fonzo 1
1 , Istituto Italiano di Tecnologia, Milano Italy, 2 , Higher Institute for Applied Sciences and Technologies, La Habana Cuba
Show AbstractThe direct conversion of solar energy into fuels, H2 in particular, at a simple and low cost semiconductor/water junction is still a challenge. Despite the theoretical simplicity of such a device, limitations in suitable semiconductor materials have hindered its development. Recently, few authors started exploring the potential of organic and hybrid organic-inorganic semiconductors, as an alternative to the usual transition metal oxides or more costly III-V semiconductors, in photoelectrochemical systems. Most reports described performances in the order of 1 mA/cm2 at the reversible hydrogen electrode potential (RHE), relatively low onset potentials and limited stability. Here we report our recent results on the optimization of a hybrid organic-inorganic photocathode for the direct conversion of solar light into chemical energy. Starting from a prototypical P3HT:PCBM blend as photoactive element, we focused our attention on different interfacial layers and their influence on the photocathode performances. The photocatalytic activity and long-term stability of a simple, catalysed, bulk heterojunction is proven and the specific effect on hydrogen generation performances of electron- and hole- selective contacts is investigated. The relevance of our findings can be summarized in few key points: (i) high performances with a maximum photocurrent of 8 mA/cm2 at RHE and 50% IPCE; (ii) optimal process stability with 100% faradaic efficiency along the whole electrode’s lifetime; (iii) excellent energetics with onset potential as high as +0.7 V vs RHE; (iv) promising operational activity of several tens of hours and (vi) by-design compatibility for implementation in a tandem architecture. In addition, we realized a large area, all-solution processed device as the first proof of concept of the high versatility and up-scaling potential of our approach. Collectively, this set of features establish the hybrid architecture we developed well ahead of existing reports on organic photoelectrochemical systems and suggest the potential of the hybrid organic-inorganic photoelectrochemical (HOPEC) concept as real contender to the traditional inorganic counterpart.
5:45 PM - NM4.8.09
Porous Carbon-Doped TiO2 on TiC Nanostructures for Enhanced Photocatalytic Hydrogen Production under Visible Light
Jiaqian Qin 1
1 , Chulalongkorn University, Bangkok Thailand
Show AbstractTitanium dioxide (TiO2) as a photocatalyst material has been widely investigated because of its stabilization and hypotoxicity. However, photocatalytic activity of TiO2 is suppressed by the large band gap and the high recombination rate of charge carrier, which leads to a confined application. Moreover, how to improve the photocatalytic H2 production without any co-catalyst also remains a big challenge. Here, we report a conceptual strategy in a core-shell nanostructure to simultaneously reduce band gap and charge carrier recombination rate by introducing carbon-doped porous TiO2 layer on metallic TiC nanostructure using a facile in situ thermal growth method. TiC@C-TiO2 core-shell nanostructure materials have a higher photocatalytic activity compared with pure P25 and the carbon-doped TiO2, which result from the enhanced visible light absorption, drastic charge transfer and the large surface area. Notably, the novel core-shell nanostructures still exhibit an excellent photocatalytic H2 production without Pt co-catalyst. The results demonstrate that TiC is an ideal support for TiO2 photocatalyst, and this novel core-shell nanostructure can significant shift the position of the band edge of the obtained material. This study presents a design principle for photocatalytic materials towards the highly efficient visible light photocatalysts.
Symposium Organizers
Yu Han, King Abdullah University of Science and Technology
Phillip Christopher, Univ of California-Riverside
Zili Wu, Oak Ridge National Laboratory
Ning Yan, National University of Singapore
Symposium Support
King Abdullah University of Science and Technology
NM4.9: Nanoparticles for Catalysis
Session Chairs
Phillip Christopher
Yu Han
Friday AM, April 21, 2017
PCC West, 100 Level, Room 104 B
9:30 AM - NM4.9.01
Dual Catalyst: Ag@Pd Core-Frame Nanocubes for Monitoring Stepwise Reduction and Oxidation Reaction by Surface-Enhanced Raman Scattering
Dong Qin 1 , Yiren Wu 1 , Jumei Li 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractAmong all noble metals, palladium has the lowest energy barrier to the dissociation of H2 into atomic hydrogen for the hydrogenation reaction of unsaturated compounds. In comparison, silver is a well-known component of the industrial catalysts used for the epoxidation of ethylene by O2. Conceptually, a combination of Pd with Ag would build a promising dual-catalytic system. In this talk, we will report such a dual catalyst based on Ag@Pd-Ag core-frame nanocubes for the stepwise conversion of 4-nitrothiophenol to trans-4,4’-dimercaptoazobezene under ambient conditions. Our in-situ surface-enhanced Raman spectroscopy study reveals three sequential processes that include the Pd-catalyzed reduction of 4-nitrothiophenol to 4-aminethiophenol by hydrogen, a period during which the 4-aminothiophenol remain unchanged until all hydrogen has depleted, and the Ag-catalyzed oxidation of 4-aminothiphenol to trans-4,4’-dimercaptoazobezene by the O2 from air.
9:45 AM - NM4.9.04
Nanocarbon and Nanocarbon Supported Metal Catalysts for Heterogenous Catalytic Reactions
Hongyang Liu 1
1 Shenyang National Lab of Material Sciences, Institute of Metal Research Chinese Academy of Sciences, Shenyang China
Show AbstractNanocarbon is a term increasingly used to indicate the broad range of carbon materials having a tailored nanoscale dimension and functional properties that significantly depend on their nanoscale features. Recently, lots of studies have demonstrated that nanocarbons, such as carbon nanotube (CNT), porous graphene and nanodiamond (ND) can be used as metal free catalysts for the light alkanes dehydrogenation reactions, showing their potential applications to replace the traditional metal oxide catalysts. In this report, we will not only present our recent studies about the exploration of nanocarbons as metal free catalysts for the industrial dehydrogenation reactions, but also we will introduce the fabrication of nanocarbon materials (carbon nanotube, hollow carbon sphere and hollow graphene nanoshell) embedded by Au and Pd NPs used in catalytic oxidation and hydrogenation reactions, and the stabilization of Pd and Pt NPs on novel nanodiamond–graphene with core–shell supports for CO oxidation. The detailed preparing process, characterization, catalytic performance and mechanism will be carefully discussed in the report.
References
1. H.Y. Liu, L.Y. Zhang, N. Wang, D. S. Su, Angewandte Chemie International Edition, 2014, 53(46), 1263; L.Y. Zhang, H.Y. Liu, Z. Jiang, D.S. Su, Angewandte Chemie International Edition, 2015, 54(52), 15823.
2. H.Y. Liu, J. Wang, D.S. Su, Small, 2015, 11(38), 5059; J.Y. Diao, R. Huang, H.Y. Liu and D.S. Su, ChemSusChem. 2016, 9, 662; X. R. Zhang, Z.S. Meng, H.Y. Liu and R.F. Lu, Energy & Environmental Science, 2016, 9(3), 841.
10:00 AM - NM4.9.05
Combinatorial Synthesis of Multimetallic Nanoparticles
Pengcheng Chen 1 , James Hedrick 1 , Chad Mirkin 1
1 , Northwestern University, Evanston, Illinois, United States
Show AbstractThe emerging potential of multimetallic nanoparticles has led to an increased demand for combinatorial and high-throughput synthesis of particles that encompass an enormous compositional and structural parameter space that can be rapidly screened for desired properties. Here, we report the combinatorial synthesis of multimetallic particles by scanning probe block copolymer lithography. The scope of this method was demonstrated by creating combinations of Au, Ag, Pd, Ni, Co, Cu, and Pt nanoparticles. Particularly, a library of particles consisting of five elements, i.e., Au, Ag, Co, Cu, and Ni, was developed through polymer nanoreactor mediated synthesis. We show that all combinations of binary, ternary, quaternary, and quinary particles can be independently synthesized in a site-isolated manner and characterized by STEM and EDS. The structure of the nanoparticle is tailorable based on particle composition and metal compatibility. The ability to systematically synthesize and characterize such structures provides important insight into the factors that lead to alloy formation and phase segregation on the nanoscale as well as a route to combinatorial libraries of complex nanostructures that are promising for a broad range of fields, such as catalysis, plasmonics, and magnetics.
10:15 AM - NM4.9.06
Encapsulating PdZn and Pd Nanoparticles into the Porous Walls of Hollow Carbon Tubes for CO2 Conversion
Jia Xu 1 , Honglu Wu 2 3 , Yang Lou 2 , Jingyue Liu 2
1 School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona, United States, 2 Department of Physics, Arizona State University, Tempe, Arizona, United States, 3 Institue of Photoelectronic Technology, Beijing Jiaotong University, Beijing China
Show AbstractCarbon supported metal nanoparticle (NP) catalysts are extensively used for aqueous phase catalytic reactions and as electrocatalysts for fuel cells. A critical question for the broad applications of carbon supported catalysts is to prevent leaching and/or sintering of the metal NPs. Extensive research have been conducted to encapsulate metal NPs for desired catalytic reactions or for developing sintering-resistant catalysts [1-2]. We recently developed a unique catalytic process for synthesizing mesoporous hollow carbon nanostructures with controllable wall thicknesses and the growth of carbon structures in the interior regions of the hollow carbon tubes. This synthesis process has been adapted to incorporate metal or alloy NPs into the mesoporous walls of the carbon hollow tubes of other types of carbon hollow nanostructures. We have developed catalysts that consist of Pd or PdZn NPs encapsulated in the interior regions of the walls of carbon tubes and tested their catalytic performances for hydrogenation reactions including the hydrogenation of CO2 to methanol [3]. Since the Pd or PdZn NPs are encapsulated in the interior regions of the hollow carbon nanostructures these NPs are stable during high temperature treatments or during catalytic reactions such as hydrogenation of CO2 or CO to methanol. The unique encapsulation of the metal NPs by the mesoporous hollow carbon tubes with controllable wall thicknesses and structures provides a general strategy to anchoring metal or alloy NPs for catalytic reactions including electrochemical reactions. The synthesis processes, detailed atomic scale characterization of the encapsulated Pd and Pd alloy NPs, the stability evaluations, and the structure-performance relationships will be discussed [4].
[1] Q. Zhang et al. Acc. Chem. Res., 2013, 46, pp 1816–1824.
[2] C. Galeano et al. ACS Catal., 2014, 4, pp 3856–3868
[3] X. L. Liang et al. Appl. Catal. B: Environ., 2009, 88, pp 315-322.
[4] Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research. This work was partially supported by the College of Liberal Arts and Sciences of Arizona State University. The authors gratefully acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science at Arizona State University.
NM4.10: Porous Materials for Catalysis
Session Chairs
Friday PM, April 21, 2017
PCC West, 100 Level, Room 104 B
11:30 AM - *NM4.10.02
Nanoscale Structural Characterization of Beam-Sensitive Materials for Gas Separation
Jim Ciston 1
1 , Lawrence Berkeley National Lab, Berkeley, California, United States
Show AbstractThe discovery of single-layer graphene has led to a surge of research interest in clean energy applications and novel electronic devices. Tailoring the sheet structure of graphene by pore insertion, especially in the single digit nanometer region, has been predicted as an effective route to engineer multifunctionality. In contrast to the advancement in theory, very limited success has been made in realizing multifunctional porous graphitic materials (PGMs) with sub-10 nm pore features. Top-down methods, such as ion milling or other energy-intense physical routes, often result in poor control over pore size and homogeneity. There is therefore a huge opportunity for bottom-up, chemically derived structures to provide significantly enhanced selectivity and robustness. Only a handful of nanoporous network structures, known as covalent organic frameworks (COFs) and cyanimide-based C3N4 polymer, are reported. Materials exhibiting fully fused aromatic sheets are rare, due to the presence of large proportions of single bonds bridging the aromatic rings obtained using previous synthetic routes. Another attribute of these materials is their potential to be exfoliated and incorporated into test membranes on a support structure – this enables both direct property measurements and the microscopy studies. High-resolution TEM studies on exfoliated layers of the PGM framework for enables direct visualization of the lattice and local spectroscopic bonding information. Initial attempts to characterize these materials in a gas cell environment will also be discussed.
12:00 PM - NM4.10.03
Correlated Atomic-Scale Compositions, Structures and Reaction Properties of Heterogeneous Aluminosilicate Zeolite Catalysts
Zachariah Berkson 2 , Subramanian Prasad 1 , Bradley Chmelka 2
2 Chemical Engineering, University of California, Santa Barbara, Santa Barbara, California, United States, 1 Catalysis Division, BASF Corporation, Iselin, New Jersey, United States
Show AbstractThe macroscopic reactivities and selectivities of heterogeneous zeolite catalysts depend strongly on atomic-scale order and disorder that develop during their initial synthesis/crystallization or subsequent exposure to reactor conditions. For example, nanoporous aluminosilicate zeolites, such as zeolite H+-Y, H+-ZSM-5, and Cu2+-chabazite, are of considerable interest for conversion of hydrocarbons or removal of nitric oxides from automotive exhaust. These technological applications are enabled by the adsorption and catalytic reaction properties of zeolites, which are strongly influenced by the distributions and local environments of non-stoichiometric framework aluminum atoms and their associated exchangeable cations. Measuring the atomic-scale aluminum environments has been challenging, due to the complicated distributions of the framework aluminum atoms to which scattering techniques are insensitive. Complementary analyses by X-ray diffraction, solid-state nuclear magnetic resonance (NMR) spectroscopy, and electron microscopy provide detailed information on both the long-range structural order and distributions of atomic environments in aluminosilicate zeolites. Notably, new dynamic-nuclear-polarization-enhanced NMR techniques provide dramatically enhanced signal sensitivity (ca. x100) and resolution that enable detection of distinct 29Si, 27Al, and 13C species in aluminosilicate zeolites that are altered by exposure to catalytic reaction conditions, which until now have been infeasible to characterize. The analyses establish the types, distributions, and relative proximities of different silicon and aluminum atoms, the latter of which account for the macroscopic reaction properties of the catalysts. The results yield new insights on zeolite catalysts and their complicated atomic-scale structures, which are correlated with technologically important (e.g., methanol-to-olefin) reaction properties.
12:15 PM - NM4.10.04
Fabricating Hierarchical Zeolites Using Polymer-Based Dual-Function Templates
Qiwei Tian 1 , Yihan Zhu 1 , Yu Han 1
1 , KAUST, Thuwal Saudi Arabia
Show AbstractHierarchical zeolites (also referred to as “mesoporous zeolites” or “mesostructured zeolites”) that contain both mesopores to allow for the rapid diffusion of bulky molecules and zeolitic micropores to provide catalytic activity and selectivity are highly desirable, because they circumvent the diffusion limitation and coke formation of conventional zeolites, and enable the preparation of multifunctional catalysts. Direct synthesis of hierarchical zeolites currently relies on the use of surfactant-based templates to produce mesoporosity by the random stacking of 2D zeolite sheets or the agglomeration of tiny zeolite grains. The benefits of using nonsurfactant polymers as dual-function templates in the fabrication of hierarchical zeolites are demonstrated. First, the minimal intermolecular interactions of nonsurfactant polymers impose little interference on the crystallization of zeolites, favoring the formation of 3D continuous zeolite frameworks with a long-range order. Second, the mutual interpenetration of the polymer and the zeolite networks renders disordered but highly interconnected mesopores in zeolite crystals. These two factors allow for the synthesis of single-crystalline, mesoporous zeolites of varied compositions and framework types. A representative example, hierarchial aluminosilicate (meso-ZSM-5), has been carefully characterized. It has a unique branched fibrous structure, and far outperforms bulk aluminosilicate (ZSM-5) as a catalyst in two model reactions: conversion of methanol to aromatics and catalytic cracking of canola oil. Third, extra functional groups in the polymer template can be utilized to incorporate desired functionalities into hierarchical zeolites. Last and most importantly, polymer-based templates permit heterogeneous nucleation and growth of mesoporous zeolites on existing surfaces, forming a continuous zeolitic layer. In a proof-of-concept experiment, unprecedented core–shell-structured hierarchical zeolites are synthesized by coating mesoporous zeolites on the surfaces of bulk zeolites.
12:30 PM - NM4.10.05
Chemistry in Confined Spaces—Reactivity of the Zn-MOF-74 Channels
Kui Tan 1 , Yves Chabal 1 , Erika Fuentes-Fernandez 1 , Hao Wang 2 , Sebastian Zuluaga 3 , Timo Thonhauser 3 , Jing Li 2
1 , University of Texas at Dallas, Plano, Texas, United States, 2 , Rutgers University, Piscataway, New Jersey, United States, 3 , Wake Forest University, Winston-Salem, North Carolina, United States
Show AbstractWater dissociation represents one of the most important reactions in catalysis, and is relevant to both surface and nano sciences. It has been difficult to fully understand the dissociation mechanism on oxide surfaces due to experimental challenges. To remedy this problem, we propose the metal organic framework materials MOF-74 [M2(dobdc), M=Mg2+, Zn2+, Ni2+, Co2+, and dobdc=2,5-dihydroxybenzenedicarboxylic acid] as a model system to study water reactions since its crystalline structure is well characterized and the metal-oxide pyramid clusters node mimics the oxides surfaces with exposed cations.1 Combining in situ IR spectroscopy and first-principles calculations, we have recently been able to show direct evidence of a water dissociation reaction H2O→OH+H occurring at the metal centers of MOF-74 above 150 oC. Interestingly, the latter O-H bond is only detected when D2O is used due to the strong vibrational coupling of the O-H bending vibration to the dobdc linker vibrations. In contrast, the O-D bending vibration is fully decoupled from the linker vibrations (i.e. behaves as a local vibrational mode) leading to a strong, sharp and detectable absorption band. We further demonstrate that the formation of a water network and resulting interaction among several water molecules is critical to lower the reaction barrier at the metal centers.2 Taking advantage of the water dissociation inside the MOF channels, we investigate the interaction of CO molecules in MOF-74 after water dissociation (H2O→OH+H) at the metal centers, and find that addition of 40 Torr of CO at 200 oC starts a catalytic reaction with production of formic acid via OH+H+CO→HCO2H.3 A detailed analysis shows that the overall reaction H2O+CO→HCO2H takes place within the MOF-74 pore, in the vicinity of the metal center, without an external catalyst, which would be needed for the same reaction on flat surfaces. These findings open the door for detailed studies of catalytic reactions in confined environments (e.g. MOF pores) and provide an alternative means to produce an important industrial feedstock such as formic acid.
References:
1. Tan K, et al. Water Reaction Mechanism in Metal Organic Frameworks with Coordinatively Unsaturated Metal Ions: MOF-74. Chemistry of Materials 26, 6886-6895 (2014).
2. Zuluaga S, Fuentes-Fernandez EMA, Tan K, Li J, Chabal YJ, Thonhauser T. Cluster assisted water dissociation mechanism in MOF-74 and controlling it using helium. Journal of Materials Chemistry A 4, 11524-11530 (2016).
3. Zuluaga S, et al. Chemistry in confined spaces: reactivity of the Zn-MOF-74 channels. Journal of Materials Chemistry A 4, 13176-13182 (2016).