Structure of Iridium Oxide Catalysts Dictates Performance Differences for Proton Exchange Membrane Water Electrolyzers

Abstract

Proton exchange membrane water electrolyzers (PEMWEs) are promising zero-emission technologies. However, their high cost remains a barrier to widespread adoption. Iridium oxide is commonly used as an oxygen evolution reaction (OER) catalyst, and its cost and scarcity make it essential to reduce its loading while increasing its activity. Evaluation of iridium oxide activity should be carried out in the membrane electrode assembly (MEA) configuration to replicate realistic operating conditions. Herein, we present a comprehensive benchmarking framework to accurately evaluate the amorphous and crystalline iridium oxides at the MEA level. By systematically varying the catalyst loading, electrochemical testing elucidated intrinsic surface charge density and mass activity for each of the catalysts. The study establisehed two electrochemical descriptors that evaluated catalyst redox reactions. The effect of the porous transport layer on OER activity was discussed, identifying a 'background' current at zero-loading. This study highlights potential pitfalls in MEA-level catalyst screening and underscores the importance of the loading study for reliable results.