Suppressing Catalyst Deactivation in Cu-α-MnO2 Cathodes for High-Performance Anion Exchange Membrane Fuel Cells

Abstract Hydrogen is a promising energy carrier for reducing greenhouse gas emissions in mobile and on-site power applications. However, today's dominant acidic proton exchange membrane fuel cells rely on rare platinum group metal (PGM) catalysts and ionomer materials linked to the emissions of possibly toxic per- and polyfluoroalkyl substances (PFAS). Anion exchange membrane fuel cells (AEMFC) offer a pathway to low-PGM and non-PGM operation. However, the use of manganese oxides as catalysts is limited by stability issues under harsh electrochemical conditions. Cu-α-MnO2 catalysts have emerged and were demonstrated as highly active oxygen reduction reaction (ORR) catalysts in alkaline environments, yet without sufficient consideration of their catalytic and geometric stability. Here, we elucidate the structural dynamics of Cu-α-MnO2 using operando X-ray absorption spectroscopy and wide-angle scattering, revealing significant changes in electronic and crystal structures during fuel cell operation. Our findings indicate that the material undergoes irreversible transformations that affect its electrochemical performance at potentials below +0.6 V. These insights are crucial for designing stable, high-performing catalysts for anion exchange membrane fuel cells, informing strategies to reduce reliance on platinum group metals in next-generation fuel cell technologies.