Complete Phase Transformation of Ir Nanowire Network into Defect‐Rich Oxide Catalyst for High‐Performance PEM Water Electrolysis

ABSTRACT Iridium‐based catalysts remain the most reliable option for the oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWEs). However, their high cost and limited performance represent critical barriers to the commercialization of this green hydrogen production technology. Herein, we report the creation of a metallic Ir nanowire network (IrNWN), which exhibits superior OER performance through its in situ transition into an oxide structure with high intrinsic activity. At a low loading of 0.25 mg Ir /cm 2 in PEMWEs, IrNWN achieved a current density of 3.13 A/cm 2 at a cell voltage of 1.8 V, outperforming the commercial Ir‐based catalyst and surpassing the Department of Energy (DOE) 2026 technical target. Moreover, the high activity of IrNWN was maintained for 900 h in a durability test at 2 A/cm 2 , showing a low degradation rate of 0.042 mV/hour. Structural analysis of the electrochemically oxidized IrNWN revealed the presence of mixed Ir oxidation states and a high density of surface terminal oxygen groups (µ1‐O), which contributed to a reduced energy barrier for the rate‐determining O‐O coupling step.