Comprehensive Analysis of the Degradation Phenomena of Proton Exchange Membrane Water Electrolyzers with Iridium on Antimony Tin Oxide Anodes

Proton exchange membrane water electrolysis (PEMWE) has emerged as one of the most promising technologies for large hydrogen (H 2 ) production from renewable electricity. However, using iridium (Ir) in large quantities is a roadblock in the widespread expansion of this technology. One strategy to reduce Ir loading in the anode is the use of an electroceramic support material. This study examines the structural and electrochemical evolution of Ir on antimony tin oxide (Ir/ATO) anodes under extended operation. Initial electrochemical performance demonstrates that low‐loaded Ir/ATO (0.2 mg Ir cm −2 ) can achieve a competitive current density of 2.82 A cm −2 at 2 V, comparable to state‐of‐the‐art PEMWE catalysts. However, extended operation leads to a minimal but gradual decline in catalytic activity. Postmortem analysis reveals changes in porosity and pore distribution, while atomic force microscopy (AFM) studies indicate ionomer degradation in the anode catalyst layer (ACL). Transmission electron microscopy (TEM) reveals the dissolution of oxides of Sb and Sn from the support material. Furthermore, X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption spectroscopy (XAS) confirmed the oxidation of metallic Ir (Ir 0 ) to IrOx x ·OH y species before and after operation. Understanding degradation in low‐Ir PEMWEs is key to improving long‐term stability. These results highlight the need for support stabilization and catalyst structuring to ensure durable performance.