Engineering Stable Mutliscale Electrocalyst Architectures for Efficient Alkaline-Membrane Water Electrolysis

Commercialized membrane electrolyzers use acidic proton exchange membranes (PEMs). These systems offer high performance but require the use of expensive precious-metal catalysts such as IrO₂ and Pt that are nominally stable under the locally acidic conditions. Alkaline-exchange-membrane (AEM) electrolyzers in principle offer the performance of PEM electrolyzers with the ability to use earth-abundant catalysts and inexpensive bipolar plate materials. I will present our work in understanding the chemical and electrochemical processes in earth-abundant water-oxidation catalysts, including the use of integrated reference-electrode device architectures and cross-sectional materials analysis, as well as progress in building high-performance AEM electrolyzers. Baseline electrolyzers operate at 1 A cm^-2 in pure water feed at < 1.9 V at a moderate temperature of ~70 °C using either IrO₂ or Co₃O₄ anode catalyst layers, PiperION alkaline ionomers, and stainless-steel porous transport layers. These devices, however, degrade rapidly compared to PEM electrolyzers. The voltage profile corresponding to degradation has initial fast (~10 mV/h) and steady-state slow components (~1 mV/h), which we link to chemical and structural changes in the ionomer-catalyst reactive zone. We further discover that dynamic Fe-based OER catalysts – that have world-record performance in traditional liquid alkaline electrolyzer systems – perform poorly with enhanced degradation rates in alkaline membrane electrolysis, illustrating fundamentally different chemical design principles for OER catalysts. We use these principles to created advanced catalysts with surface and bulk properties tuned for AEM electrolysis applications leading to enhanced performance. I will also highlight promising new chemical strategies to mitigate degradation using novel ionomers and passivated electrolyte-electrode-catalyst compositions and interfacial architectures.