Advancing Anion-Exchange-Membrane Water Electrolyzer Devices: Catalyst Layer Interactions, Degradation Pathways, and Operational Development
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Date
2024-01-09
Authors
Lindquist, Grace
Journal Title
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Publisher
University of Oregon
Abstract
Water electrolyzers (WEs) are a key technology for a sustainable economy. When powered by renewable electricity, WEs produce green hydrogen, which can be used for energy, fertilizer, and industrial applications and thus displace fossil fuels. Pure-water anion-exchange-membrane (AEM) WEs offer the advantages of commercialized WE systems (high current density, low cross over, output gas compression, etc.) while enabling the use of less-expensive components and catalysts. However, current systems lack competitive performance and durability needed for commercialization, largely limited by the poor stability of anion-exchange polymers used in the membrane and catalyst layers. Further, while non-platinum-group-metal oxygen-evolution catalysts show excellent performance and durability in alkaline electrolyte, this has not transferred directly to pure-water AEMWEs. The following dissertation is a comprehensive analysis of the fundamental processes that dictate pure-water AEMWE performance and stability. Chapter I introduces AEMWEs in the context of industry-scale devices. Chapter II reports AEMWE cell performance comprising entirely of commercially available materials, detailing the key preparation, and operation techniques. In Chapter III, the structural stability and ionomer interactions of non-platinum-group-metal (non-PGM) anode catalysts are characterized. The results show catalyst electrical conductivity is key to obtaining high-performing systems and that many non-PGM catalysts restructure during operation, resulting in lower lifetimes. Chapter IV investigates ionomer degradation during device operation, revealing anode ionomer oxidation is the dominant degradation mechanism for all AEM-based electrolyzers tested. Improved device stability using oxidation-resistant catalyst layer binders is shown and new design strategies for advanced ionomer and catalyst layer development are provided. Chapter V provides a summary of the findings in Chapters III and IV and describes the future outlook for advanced catalyst layer development. Lastly, Chapter VI introduces advanced applications for AEMWE systems, detailing technical barriers and possible research approaches to developing AEM electrolyzers for impure-water splitting.
These results significantly improve upon past understanding of pure water AEMWE devices by revealing the fundamental catalyst layer processes resulting in AEMWE device failure under relevant conditions, demonstrating a viable non-PGM catalyst for AEMWE operation, and illustrating underlying design rules for engineering anode catalyst/ionomer layers with higher performance and durability. This dissertation contains previously published and un-published co-authored materials.
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Keywords
anion exchange ionomer, anion exchange membrane, electrochemistry, materials chemistry, membrane electrolysis, water electrolysis