Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B47: Catalytic Energy GenerationFocus
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Sponsoring Units: GERA Chair: Filip Podjaski Room: BCEC 213 |
Monday, March 4, 2019 11:15AM - 11:27AM |
B47.00001: Mechanism of water oxidation catalyzed by cobalt-intercalated layered MnO2: confinement and intercalant local ordering Jinliang Ning, James Furness, Yubo Zhang, Akila C. Thenuwara, Richard C Remsing, Michael L Klein, Daniel R. Strongin, Jianwei Sun To lower the overpotential is a persistent goal for (photo)electrochemistry reactions, which can be facilitated by selectively stabilizing one reaction intermediate over another. In this mechanistic SCAN+rVV101,2 study of the oxygen evolution reaction (OER) catalysed by cobalt-intercalated layered MnO2, we show that confinement effects and local cobalt atomic ordering in the interlayer space can be used to tune the adsorption energies of O, OH, and OOH reaction intermediates and the scaling relationship between them. Interlayer confinement destabilizes the OER intermediates, but clustering Co atoms can selectively stabilize OOH. With considering both effects, our model predicts an overpotential of 0.30 V, in excellent agreement with the experimental result of 0.36 V3. In addition to giving mechanistic explanation for experimental findings, these insights illuminate a route for engineering non-toxic precious-metal-free catalysts through designed layered materials. |
Monday, March 4, 2019 11:27AM - 11:39AM |
B47.00002: Photocatalytic oxygen evolution reactivity at surface edges and corners of anatase TiO2 nanoparticles revealed by coupled quantum mechanical and molecular mechanical simulations Lixin Sun, Bilge Yildiz Coupled quantum mechanical and molecular mechanical (QM/MM) method is applied to investigate the oxygen evolution reactions (OER) on a realistic 9.5-nm long anatase TiO2 nanoparticle. The nanoparticle surface has easier electron and hole localization behavior on some of the corners and edges, compared to flat surfaces. As a result, OER reaction energy can be reduced by 0.1 - 0.5 eV at the corners and edges. However, since some of the structures with low reaction energies are also prone to form electron polarons, its high OER activity can be compromised due to electron-hole recombination. By considering both factors, the (101) facet and the edge between (101) and (011) facets are found to be the most active for OER, while the remaining corners and edges can be active for reduction reactions. Unlike early works where four-fold coordinated Ti4c was attributed to the only reason for active corners and edges, this work shows that Madelung potential, surface relaxation can also be the cause of active surface. |
Monday, March 4, 2019 11:39AM - 11:51AM |
B47.00003: Operando studies of carbon removal and contaminants in solid oxide fuel cells Jeffrey Owrutsky, William A. Maza, Daniel Steinhurst, Stanislov Tsoi, Bryan Eigenbrodt, Robert Walker Solid oxide fuel cells (SOFCs) are attractive devices for power generation due to their fuel flexibility. These devises present challenges for real time, direct observations because they operate at high temperatures (> 700 °C). We have developed and used several methods for real-time, operando studies, including infrared emission, near infrared thermal imaging and Raman spectroscopy which are combined with ex situ infrared spectroscopy and mass spectrometry of the products and concurrent electrochemical measurements for comprehensive investigations of the effects of contaminants and remediation approaches. We characterized the products, primarily CO and CO2, as well as anode temperature changes to explore the effects of various mixtures of H2 and O2 on carbon removal from Ni-YSZ anodes as well as during partial methane oxidation for SOFC operation. The prevalent processes effectively reduce to steam reforming with hydroxyl as a primary reaction intermediate. We also report initial studies of sulfur effects based on SOFC operation with methane and compare the results to similar studies for chlorine degradation to identify whether there are common themes. |
Monday, March 4, 2019 11:51AM - 12:03PM |
B47.00004: Characterization of Platinum Nanoparticles Utilized in Photocatalytic Hydrogen Synthesis Daniel Boyce, John Colton, Matthew Richards Hydrogen (H2) gas is a possible alternate fuel to help meet increasing worldwide energy needs, but a major obstacle in the use of H2 for green, environmentally-friendly fuel is the energetic and chemical requirements to synthesize the gas. We are studying the use of photocatalytic reactions to produce H2, where a light-absorbing substance acts as a catalyst in shuttling electrons from a donor to protons that are reduced into H2. Previous research conducted at BYU showed that platinum nanoparticles bound to ferritin catalyzed the photoreaction of methyl viologen to reduce protons in an organic acid offered an increase in hydrogen production efficiency by up to 100 times over platinum black (a commonly available platinum-based catalyst). We are reporting on our efforts to optimize the synthesis of the platinum nanoparticles bound to ferritin that are used in this photocatalytic system and how we characterize these nanoparticles, as well as how these characteristics affect H2 production. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B47.00005: First-principles Studies on the Structural and Electronic Modifications of Nitrogen Electrochemical Reduction on Anatase TiO2(101) Surface Yanning Zhang, Tongwei Wu The conversion of dinitrogen (N2) to ammonia (NH3) through an electrochemical reduction process is attracting increasing attentions due to its great importance in both the biosphere and the fertilizer industry. In this work, we performed systematic density functional theory (DFT) studies on the nitrogen reduction reaction (NRR) mechanisms on both clean and O-decorated TiO2(101) surfaces at an atomic scale.Our calculation results showed that the Ti4C,VO2c site most likely serves as the active site for NRR process, and the VO2c-decorated TiO2(101) surface exhibits outstanding NRR catalytic activity through a mixed mechanism compared with the clean anatase TiO2(101) surface. We further studied the effect of structural and electronic features on N2 fixation and activation on TiO2(101) surface. The introduction of surface oxygen vacancy should enhance the nitrogen adsorption obviously with an adsorption energy of -0.46 eV, and the tuning of Ti3+ concentration further changes the adsorption energy, such as to -0.65 eV if the concentrations of Ti3+ can be decreased to 4%. Our calculation results may provide some guidelines in the design of new catalysts for NRR. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B47.00006: Optimizing proton conductivity in alkaline-earth zirconates through defect engineering Andrew Rowberg, Leigh Weston, Chris Van de Walle The alkaline-earth zirconates (AeZrO3; Ae = Sr, Ca, Ba) are among the best solid-state proton conductors and as such have energy applications in solid-state hydrogen fuel cells. They crystallize as perovskite oxides of the form ABO3. Oxygen vacancies form readily in these systems, and upon exposure to water, these vacancies are filled and the materials are populated with protons. To incorporate oxygen vacancies, acceptor dopants such as Sc and Y substituting on the Zr-site are used; however, these dopants can simultaneously incorporate as A-site donors and self-compensate. We study the properties of these dopants using first-principles calculations with a hybrid functional. We characterize the bulk properties and study the formation of native and extrinsic point defects. We examine the propensity for self-compensation of Sc and Y, as well as possible A-site and O-site acceptors. We find that certain alkali metal A-site dopants (Na in CaZrO3, K in SrZrO3, and Rb in BaZrO3) incorporate oxygen vacancies in higher concentrations than Sc and Y, while also circumventing the problem of self-compensation. Furthermore, these acceptors have low proton binding energies, making them good choices to improve proton conductivity in the zirconates. |
Monday, March 4, 2019 12:27PM - 12:39PM |
B47.00007: High throughput screening of semiconductor photoelectrodes for renewable hydrogen generation Quinn Campbell, Jared Mondschein, Haiyu Wang, Kriti Seth, Julian Fanghanel, Héctor Abruña, Venkatraman Gopalan, Raymond Schaak, Ismaila Dabo The need to produce carbon-neutral chemical fuels for transportation provides a strong motivation to develop semiconductor photoelectrodes that can split water molecules to renewably generate hydrogen fuels. Available photocatalytic electrodes exhibit low efficiencies due to limited solar absorption, misaligned electronic levels, and short-lived stability in water. We develop a high-throughput screening protocol based on self-interaction-corrected semilocal density-functional theory to identify semiconductor photoelectrodes for hydrogen production. We further introduce a quantum–continuum method for predicting charge accumulation at the semiconductor electrode under applied bias to examine how surface states affect efficiency and stability. We predict 30 candidate materials, which have been synthesized and characterized by experimental collaborators, showing promising solar-to-hydrogen performance. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B47.00008: Role of diffusivity in hydrogen evolution reaction Jiang Zeng, Leiqiang Li, Ping Cui, John P Perdew, Zhenyu Zhang The hydrogen binding strength on a catalyst is known to be an important factor in electrochemical hydrogen evolution. Although much effort has been exerted to improve the binding strength to exploit precious-metal-free catalysts, their performance is still inferior to that of platinum. Based on first-principles calculations, here we investigate the role of a different physical property, namely, the diffusivity, in hydrogen evolution reaction. On typical catalytic metal surfaces, the diffusivity of hydrogen is high, and the binding strength is the dominant controlling factor. In contrast, the diffusion barrier on the surfaces or edges of two-dimensional catalytic materials such as MoS2 is found to be inversely proportional to the binding strength. This relatively large diffusion barrier may serve as another important factor on such surfaces. Moreover, the charge density wave of a catalytic surface can also significantly modulate the diffusion barrier. These findings provide important insights into how to design efficient catalysts for enhanced hydrogen evolution reaction. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B47.00009: ABSTRACT WITHDRAWN
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Monday, March 4, 2019 1:03PM - 1:15PM |
B47.00010: Influence of Sr leaching on the catalytic activity of reconstructed SrTiO3 photoelectrodes Yihuang Xiong, Ismaila Dabo Perovskite photoelectrodes are being extensively studied in the search for photocatalytic materials for hydrogen production through water splitting. The solar-to-hydrogen efficiency for these materials is critically dependent on the electrochemical state of their surface. Here, we develop an embedded quantum-mechanical approach using the self-consistent continuum solvation (SCCS) model to predict the relation between electrochemical stability, band alignment, and photocatalytic activity taking into account the long-range polarization of the semiconductor electrode under electrical bias. Using this comprehensive model, we calculate the charge-voltage response of various reconstructions of a solvated SrTiO3 surface, revealing that interfacial charge trapping exerts primary control on the electrical response, electronic structure, and surface stability of the photoelectrode. Our results provide a detailed molecular-level interpretation of the enhanced photocatalytic activity of SrTiO3 upon the voltage-induced restructuring of the semiconductor–solution interface. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B47.00011: Adsorption characteristics of small aromatic molecules on silica/Ru(0001) Muhammad Sajid, William Kaden, Abdelkader Kara Organic molecules are part of future materials for electronic devices. The performance of these devices depends strongly on the atomic and electronic characteristics at the organic-substrate interface, which is necessary to provide support and/or conduction for the device. To develop a catalogue of anchor-group-dependent trends in these characteristics, we have undertaken a joint computational/experimental study of aromatic molecules (benzene, pyridine and thiophene) bound to Ru(0001), both with and without silica sheets inserted between the two. The silica sheets have been chosen to provide an experimentally accomplishable means of varying the separation between the adsorbate molecules and metal by growing them as monolayer or bilayer. Using DFT with vdW corrections, the models of above-mentioned systems will be presented along with their electronic properties (workfunction, charge transfer etc.). Accompanying, XPS measurements will provide complementary experimental data to compare electronic predictions. These will include changes in workfunction, valence-band measurements, and core-level XPS analysis with Auger Parameter analysis for improved deconvolutions of initial and final-state contributions to binding energy shifts. |
Monday, March 4, 2019 1:27PM - 1:39PM |
B47.00012: Understanding the role of vacancy-vacancy interaction and hydrogen-hydrogen coupling in hydrogen bonding on MoS2 surfaces Liping Yu, Adrienn Ruzsinszky, Qimin Yan MoS2 is a promising nonprecious electrochemical catalyst for catalyzing hydrogen production from water. It has been found that (i) the catalytic reaction activity depends on the concentration of sulfur vacancies, and (ii) the free energy of hydrogen adsorption varies with the coverage of hydrogen adsorbates. However, microscopically, the physical factors responsible for such finding remain unclear. In this talk, we will present a microscopic model to understand the effects of vacancy-vacancy interaction and hydrogen-hydrogen coupling. We find that the effect of vacancy-vacancy interaction on hydrogen-surface bonding becomes considerable only when they are separated by less than 1.1 nm. When one hydrogen atom is adsorbed at a sulfur vacancy, the interaction between this sulfur vacancy and others nearby will be largely disabled. Such disabling decreases the adsorption energy and hence strengthens the binding. Similarly, the hydrogen-hydrogen interaction also becomes important only when they are close enough. However, instead of being disabled, such interaction is introduced upon hydrogen adsorption, which increases the adsorption energy and weakens the binding. The generation of those results will also be briefly discussed. |
Monday, March 4, 2019 1:39PM - 1:51PM |
B47.00013: Defect-mediated charge and mass transport in energy materials Khang Hoang Conventional solid-oxide fuel cells (SOFCs) based on yttria-stabilized zirconia (YSZ) electrolytes and Ni-YSZ cermet anodes suffer performance degradation due to problems associated with the Ni-based anodes such as redox cycling instability, nickel agglomeration, carbon deposition, and sulfur poisoning. It is thus necessary to search for new, Ni-free materials that may hold potential for overcoming these problems. Recently, Ba3Ti3O6(BO3)2 has been identified as a possible candidate for SOFC anodes or anode composites [1]. The oxyborate material undergoes a change from ionic under oxidizing and soft reducing conditions to mainly electronic transport under an extreme reducing atmosphere typical of anode environment, leading to a drastic enhancement in the electrical conductivity. In this talk, we introduce a theoretical framework, based on defect physics, to understand changes in the electrical transport mechanism caused by changes in the environment and to explore and design new materials for SOFC applications. [1] Doux et al., ACS Appl. Energy Mater. 1, 510 (2018). |
Monday, March 4, 2019 1:51PM - 2:03PM |
B47.00014: Uncovering Biaxial Strain Effect on Nanoparticle Exsolution for Thin-film Perovskites Jiayue Wang, Alexander Opitz, Roland Bliem, William Bowman, Xiahui Yao, Andreas Nenning, Georgios Dimitrakopoulos, Iradwikanari Waluyo, Adrian Hunt, Jean-Jacques Gallet, Bilge Yildiz Environment-friendly approaches are being advanced to synthesize carbon-neutral fuels. Many of these technologies rely on catalytically highly active nanoparticles that are supported on oxides. A recent advance in such catalyst design is to exsolve catalytic metal nanoparticles at the surface of a supporting oxide. Unlike traditional deposition techniques, the nanoparticle catalysts from exsolution are anchored in the parent oxide. This strong metal-oxide interaction makes the exsolved nanoparticles more resistant against particle agglomeration. In addition, the exsolved particles also open up the possibility of regeneration of catalysts. |
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