Lithium‐mediated Reconfiguration Activates Oxygen Radical Coupling in Iridium Oxide for Efficient Acidic Water Oxidation

ABSTRACT Activating robust oxygen evolution reaction (OER) pathways in acidic media remains a major challenge for scalable hydrogen production via proton‐exchange membrane water electrolysis (PEMWE). Here, we report a lithiation/delithiation (L/D) engineering strategy that enables a mechanistic switch in IrO 2 from the conventional adsorbate evolution mechanism (AEM) to a radical oxygen coupling pathway. This transition is driven by two cooperative effects: shortened Ir–Ir distances that geometrically favor O–O coupling; and enhanced oxygen hole formation on adsorbed oxygen species ( * O ads ), promoting the generation of reactive O ads 2−x like intermediates. Operando spectroscopy and density functional theory (DFT) calculations corroborate that these geometric and electronic modulations synergistically activate direct ( * O ads – * O ads ) coupling. The L/D‐IrO 2 catalyst achieves an ultralow OER overpotential of 204 mV at 10 mA cm −2 and delivers outstanding durability over 1200 h in 0.5 m H 2 SO 4 . Integrated into a PEMWE device, it enables a current density of 3 A cm −2 at only 1.799 V, and stable operation at 500 mA cm −2 for 1200 h, with extended high‐current durability from 1 to 3 A cm −2 . These findings establish a clear structure‐activity correlation for oxygen coupling activation and provide a generalizable strategy for designing efficient and durable acidic OER electrocatalysts.