Boettcher, ShannonTwight, Liam2025-02-242025-02-242025-02-24https://hdl.handle.net/1794/30447Renewable electricity-driven alkaline water electrolysis is poised to be a key technology for reducing the CO2 emissions from combustion of fossil fuels in industrial sectors like aviation and fertilizer manufacturing. One of the largest costs of operating water electrolyzers is that of the electricity needed to drive the liberation of hydrogen and oxygen gases. Therefore, improving electrolyzer efficiency – lowering the electrical power needed per kilogram of H2 generated – is essential to their widespread deployment. The anodic oxygen evolution reaction (OER) is a process with intrinsically slow kinetics that makes large contributions to electrolyzer inefficiency. The kinetics of OER can be hastened with the proper choice of catalyst the best of which are based on Ni and Co oxides or hydroxides with a minority component of incorporated Fe. Decades of research involving Ni/Co/Fe OER catalysts have been done, but there is still debate about the nature of the active sites in these materials. The complexity of these systems is to blame; the formation and maintenance of high OER activity sites depends on highly dynamic processes involving surface iron site dissolution-redeposition and catalyst structural change both of which are likely functions of the electrolyte pH, iron concentration in electrolyte, applied electrical bias, and catalyst chemical composition. This dissertation advances understanding of the nature of extremely high activity Fe active sites which form in-situ on nickel and cobalt hydroxide and lanthanum nickel oxide, three technologically promising catalysts. In Chapter I, I describe from a broad perspective the areas where high efficiency alkaline electrolyzers could serve to eliminate CO2 emissions and the role that OER catalysts will play in accomplishing this goal. In Chapter II, I report the results of fundamental investigations which reveal that Fe active sites are not of one, but two kinds: one that forms by surface adsorption of electrolyte Fe and another that substitutes for host metal atoms. In Chapter II, I describe the results of a deeper mechanistic investigation into the thermodynamic parameters that govern the activity of these surface Fe sites. Chapter III extends the methods used to understand Fe-sites on nickel hydroxides to an understudied perovskite oxide, lanthanum nickelate (LaNiO3). Together, these studies deepen our understanding of why Fe is a ubiquitous activator of OER catalysts and broaden the family of catalysts for which Fe activation is integral. As a result, new design principles for high performance alkaline electrolyzer anodes become evident. Catalysts should have a high density of sites for cooperative surface Fe site adsorption such that the activation energy and pre-exponential factors are optimized. Surface restructuring should be purposefully induced for those that need it for high OER activity to maximize active site formation. Where restructuring is required for high activity, surface chemical descriptors should be developed and utilized instead of bulk ones which may not directly connect to the relevant physical picture of catalysis. This dissertation contains previously published and un-published co-authored materials.en-USAll Rights Reserved.electrocatalysiselectrochemistryelectrolysishydrogenOERElectronic Thesis or Dissertation