On tuning and understanding electrocatalysts for hydrogen and carbon-based energy storage
- The following thesis is a composition of published and soon-to-be published works. All works use density functional theory (DFT) calculations and descriptor-based mechanistic models to tune and screen catalytic materials for the hydrogen evolution reaction (HER) and the CO2 reduction reaction (CO2RR). In several works, experiments are included to substantiate predictions. The early sections focus on elucidating the role of key descriptors in the HER and CO2RR, specifically the H* and CO* adsorption state. It was found that nickel-gallium intermetallic systems can alter the CO* adsorption energy to achieve an early onset potential for C1 and C2 product distributions. With regards to system stability, CO* adsorption was found to induce surface refaceting towards stepped motifs on three commonly used metal catalysts, Cu, Ni, and Pt. In the latter sections, the thesis builds upon past mechanistic models to develop a multi-descriptor model that suggests new strategies to screen for better catalysts for CO2RR. It is found that not all steps may be necessarily electrochemical steps; some key intermediate steps may be surface driven, which dramatically simplifies the selectivity picture of products formed in CO2RR. As such, OH* and C* are noted as possible descriptors to use in conjunction with CO* to build potential-dependent selectivity maps that describe how the competition from the HER may affects product selectivity in CO2RR. Finally, the thesis dives into the mechanistic trends of HER, where kinetic scaling relations are calculated explicitly with a metal-water interface across multiple transition metals. It was found that the Volmer-Heyrovsky route can produce an optimal peak at ∆G_H* = ~0eV, where ∆G_H* is the free binding energy of hydrogen. The active species of H* has also been elucidated to be any adsorbed hydrogen, and not strictly H* adsorbed on weaker binding, atop sites. Tafel plots indicate that although electrochemical barriers vary with potential, the overall HER rate stays governed by the surface coverage of hydrogen. Lastly, we find that CO* and OH* adsorbate-adsorbate interactions can either hinder or promote HER by leaving only weaker binding sites to H*. Prior to presenting the findings, this thesis attempt at a short primer on the physical chemistry concepts behind computational catalysis, as well as the conceptual tools used in computational catalysis. The section is aimed at theoretical or experimental researchers with an interest in computational science and catalysis. This is in part because the technical jargon used herein may seem vague or less familiar to those not in the field of computational catalysis, such as the term 'free energetics', 'atomic orbitals', 'descriptor', 'scaling relations'. The reader is welcomed to bring themselves up to speed in the background and concepts section
|Type of resource
|electronic resource; remote; computer; online resource
|1 online resource
|Tang, Michael T
|Reed, Evan J
|Reed, Evan J
|Degree committee member
|Stanford University, Department of Materials Science and Engineering.
|Statement of responsibility
|Submitted to the Department of Materials Science and Engineering
|Thesis Ph.D. Stanford University 2020
- © 2020 by Michael T Tang
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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