A5035182768- Electrocatalysts for Energy Conversion
- Fuel Cells and Related Materials
- Advancements in Battery Materials
- Electrochemical Analysis and Applications
- Catalytic Processes in Materials Science
- Advanced Battery Materials and Technologies
- Advanced battery technologies research
- Graphene research and applications
- Advancements in Solid Oxide Fuel Cells
- Conducting polymers and applications
- Fiber-reinforced polymer composites
- Molecular Junctions and Nanostructures
- Nanowire Synthesis and Applications
- Machine Learning in Materials Science
- Inorganic Fluorides and Related Compounds
- Semiconductor Quantum Structures and Devices
- Advanced Battery Technologies Research
- Advanced Thermodynamics and Statistical Mechanics
- Supercapacitor Materials and Fabrication
- Nanoporous metals and alloys
- Semiconductor materials and interfaces
- Catalysis and Hydrodesulfurization Studies
- Electron and X-Ray Spectroscopy Techniques
- solar cell performance optimization
- Analytical Chemistry and Sensors
California Institute of Technology
2012-2023
California State University, Long Beach
2013-2020
Institute of Physics
2011-2013
Chinese Academy of Sciences
2013
University of California, Los Angeles
1997-2013
California State University System
2013
Cornell University
2003
University of California, Berkeley
2000
Lawrence Berkeley National Laboratory
2000
Improving the platinum (Pt) mass activity for oxygen reduction reaction (ORR) requires optimization of both specific and electrochemically active surface area (ECSA). We found that solution-synthesized Pt/NiO core/shell nanowires can be converted into PtNi alloy through a thermal annealing process then transformed jagged Pt via electrochemical dealloying. The exhibit an ECSA 118 square meters per gram 11.5 milliamperes centimeter ORR (at 0.9 volts versus reversible hydrogen electrode),...
Abstract Experiments have shown that graphene-supported Ni-single atom catalysts (Ni-SACs) provide a promising strategy for the electrochemical reduction of CO 2 to CO, but nature Ni sites (Ni-N C , Ni-N 3 1 4 ) in Ni-SACs has not been determined experimentally. Here, we apply recently developed grand canonical potential kinetics (GCP-K) formulation quantum mechanics predict as function applied (U) determine faradic efficiency, turn over frequency, and Tafel slope H production all three...
We report here density functional theory (DFT) studies (PBE) of the reaction intermediates and barriers involved in oxygen reduction (ORR) on a platinum fuel cell catalyst. Solvent effects were taken into account by applying continuum Poisson−Boltzmann to bound adsorbates transition states various reactions (111) surface. Our calculations show that solvent change significantly compared with those gas-phase environment (without solvation). The O2 dissociation barrier decreases from 0.58 0.27...
We report results of quantum mechanics (QM) mechanistic studies Nafion membrane degradation in a polymer electrolyte (PEM) fuel cell. Experiments suggest that is caused by generation trace radical species (such as OH●, H●) only when the presence H2, O2, and Pt. use density functional theory (DFT) to construct potential energy surfaces for various plausible reactions involving intermediates might be formed exposed H2 (or H+) O2 Pt catalyst. find barrier 0.53 eV OH formation from HOOH...
We report the reaction pathways and barriers for oxygen reduction (ORR) on platinum, both gas phase in solution, based quantum mechanics calculations (PBE-DFT) semi-infinite slabs. find a new mechanism solution: O2 → 2Oad (Eact = 0.00 eV), Oad + H2Oad 2OHad 0.50 OHad Had 0.24 which is formed by hydration of surface Oad. For (hydrophilic Nafion), we that favored step activation O2ad HOOad 0.30 eV) HOad 0.12 followed 0.23 0.14 eV). This suggests to improve efficiency ORR catalysts, should...
The valence band structures (VBS) of eight transition metals (Fe, Co, Ni, Cu, Pd, Ag, Pt, Au) were investigated by photoelectron spectroscopy (PES) using He I, II, and monochromatized Al Kα excitation. influence final states, photoionization cross-section, adsorption residual gas molecules in an ultrahigh vacuum environment are discussed terms their impact on the VBS. We find that VBSs recorded with radiation most closely comparable to ground state density states (DOS) derived from quantum...
The high cost of proton exchange membrane fuel cells (PEMFCs) comes largely from the use platinum-containing electrocatalysts. Despite significant progress made past decade on reducing platinum catalyst loading in PEMFC electrodes, further substantial reductions require replacement with less expensive nonplatinum electrocatalytic materials. In this study, PdCu alloys have computationally been investigated as possible non-Pt catalysts for oxygen reduction reaction (ORR) PEMFCs. We used...
To facilitate a less empirical approach to developing improved catalysts, it is important correlate catalytic performance surrogate properties that can be measured or predicted accurately and quickly, allowing experimental synthesis testing of catalysts focus on the most promising cases. Particularly hopeful correlating catalysis electronic density states (DOS). Indeed, there has been success in using just center d-electron density, which some cases correlates linearly with oxygen atom...
Proton exchange membrane fuel cells (PEMFCs) have attracted much attention as an alternative source of energy with a number advantages, including high efficiency, sustainability, and environmentally friendly operation. However, the low kinetics oxygen reduction reaction (ORR) restricts performance PEMFCs. Various types catalysts been developed to improve ORR but this problem still needs further investigations improvements. In paper, we propose advanced Os/Pt core–shell based on our previous...
Using density functional theory (DFT) calculations, we have studied structural models of graphite fluorides for five fluorine compositions; C1F (CF1), C2F (CF0.5), C3F (CF0.33), C4F (CF0.25), and C16F (CF0.0625). For each composition, considered several possible calculated heat formation relative to the pristine F2 molecule. We also simulated X-ray diffraction patterns model compared those with experiments. find, in agreement earlier experiments, that most stable structure (CF1) has an...
We use quantum mechanics, density functional theory at the PBE level, to predict binding-site preferences and reaction barriers for all intermediates involved in oxygen reduction (ORR) on low energy surface of Pt3Ni alloy. Here we calculate that layer is Ni depleted (100% Pt) while second enriched (50% as shown by experiment. Even though top pure Pt, find sublayer imposes strong binding sites most intermediates, which turn strongly influences barriers. This preference leads a site dependence...
A simple one‐step process to fabricate three‐ dimensional (3D) microstructures is reported. Based on two‐photon excited‐state chemistry, a chemically amplified positive tone photoresist has been developed and the lithographic investigated. The results, as indicated by fabricated material (see Figure) suggest that 3D microfabrication may be valuable route precision microfluidic microoptical devices.
Based on studies Pt3Co and Pt3Ni, we developed the hypothesis that improved alloy catalysts for oxygen reduction reaction (ORR) at fuel cell cathodes should have a surface layer is noble (e.g., Pt, Pd, or Rh) while second ∼50% electropositive metal to decrease critical barriers ORR, used quantum mechanics (QM) examine 80 binary alloys of composition Y3X, where Y = Rh, X any three rows transition metals (columns 3−11). This study identified Pd3X, good segregating include Re (best), W, Os, Mo,...
Using quantum mechanics calculations, we have studied the segregation energy with adsorbed O and OH for 28 Pt3M alloys, where M is a transition metal. The calculations found surface to become energetically unfavorable Pt3Co Pt3Ni, as well most other Pt binary in presence of OH. However, Pt3Os Pt3Ir remain segregated show best preference among alloys both species on surface. Binding energies various oxygen reduction reaction (ORR) intermediates Pt(111) Pt3Os(111) surfaces were calculated...
Hydrogen fuel cells (FC) are considered essential for a sustainable economy based on carbon-free energy sources, but major impediment the costs. First-principles quantum mechanics (density functional theory including solvation) is used to predict how energies and barriers mechanistic steps of oxygen reduction reaction (ORR) over fcc(111) platinum surface depend dielectric constant solvent. The ORR kinetics can be strongly accelerated by decreasing effective medium polarizability from high...
Using density functional theory (PBE-D2 flavor), we report the mechanism for oxygen reduction reaction (ORR) on graphene sheets. We find that ORR starts with OO chemisorbing onto carbon edges, rather than basal plane face, which is not energetically favorable. The edges were described as one-dimensional periodic ribbons both armchair and zigzag edges. calculated binding energies of products (OO, OOH, O, OH, HOH, HOOH) examining Langmuir–Hinshelwood (LH) Eley–Rideal (ER), to understand how...
To use density functional theory (DFT) to seek improved catalysts for the oxygen reduction reaction (ORR) in a proton exchange membrane fuel cell, we developed systematic way handle barriers of electron transfer reactions (e.g., H+ + e– Oad → OHad) within DFT framework. We report applications this new method determining dependence various ORR steps on operating electrochemical potential Pt-catalyzed cell. This is used estimate optimum potential. In Article, show how change efficiency from...
Long-chain alkanoic acids usually form close-packed monolayer films with alkyl chains highly oriented on substrates. Previous studies have reported the adsorption of stearic acid gold, aluminum, copper, silver, and aluminum oxide. However, there are no reports magnetic metals. In this work, characterization adsorbed Ni(111) surface has been studied experimentally first-principles calculation. The results suggest that is chemically via a bidentate interaction distance about 1.8 Å. Besides...
In this study, we used quantum mechanics (QM) to investigate steam reforming of methane on Ni-alloy catalyst surfaces and examine the effect anode material modifications catalytic processes in a solid oxide fuel cell (SOFC). The conventional Ni suffers from coking, coarsening, sulfur poisoning because decomposition hydrocarbon fuels, particle agglomeration at high operating temperature, impurities contained fuels. Ni-electrode surface modification, such as alloying with other metals (e.g.,...