Performance and Degradation Mitigation by Ionomer Gradient Engineering in the Anode Catalyst Layer of Proton Exchange Membrane Electrolysis

Abstract Ionomer content and its distribution in the anode catalyst layer (ACL) is critical to optimizing the triple-phase boundary for high performance and stability in proton exchange membrane (PEM) electrolysis. This understanding, however, is lacking particularly with low catalyst loadings, and high performance and durability together have not been achieved through traditional electrode designs with a single ionomer content. This work investigates ionomer distribution with respect to oxygen evolution reaction (OER) kinetics and durability, starting with bilayered designs. Performance-durability tradeoffs are observed in bilayer electrodes using ionomer contents 10–40 wt %, related to the inhomogeneous distribution of catalyst sites and Ir band formation. Multi-layered ACLs with 5, 10 and 40 wt % equally layered from the membrane to transport layer interfaces are found to achieve superior OER kinetics and enhanced durability simultaneously, showing 392 mV of kinetic overpotential at 3 A/cm2, a decay rate of 26.6 µV/h, and smaller Ir band formation after 1000 h. As a comparison, traditional electrodes show either high degradation (60.5 µV/h) with 10 wt % ionomer or high kinetic overpotential (440 mV) with 40 wt % ionomer. This work advances an understanding of ACL degradation through multimodal characterization and enables mitigation strategies through electrode architecture optimization.