(Invited) Catalyst and Anode Design for Durable Alkaline-Membrane 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 IrO 2 and Pt that are nominally stable under 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 highlight our fundamental work in understanding the chemical and electrochemical processes in earth-abundant water-oxidation catalysts over the past decade and we are using that understanding to drive progress in high-performance AEM electrolyzers. Baseline systems operate at 1 A·cm -2 in pure water feed at < 1.9 V at a moderate temperature of ~70 °C using either IrO 2 or Co 3 O 4 anode catalyst layers, PiperION alkaline ionomers, and stainless-steel porous transport layers. These devices, however, degrade rapidly compared to PEM electrolyzers which we link to chemical and structural changes in the ionomer-catalyst reactive zone using a combination of integrated reference-electrode device architectures, impedance, and cross-sectional and post-mortem materials analysis. 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. Given this baseline understanding, I will end with new chemical strategies we have developed to mitigate degradation and enhance performance using novel ionomers, passivated electrolyte-catalyst interfacial architectures, and specifically designed multicomponent anode oxygen catalysts to target stable performance without supporting soluble electrolyte: <10 μV/h degradation at currents > 2 A cm -2 and cell voltages < 2V.