Unraveling Compressive Strain and Oxygen Vacancy Effect of Iridium Oxide for Proton‐Exchange Membrane Water Electrolyzers

Abstract Iridium‐based electrocatalysts are commonly regarded as the sole stable operating acidic oxygen evolution reaction (OER) catalysts in proton‐exchange membrane water electrolysis (PEMWE), but the linear scaling relationship (LSR) of multiple reaction intermediates binding inhibits the enhancement of its activity. Herein, the compressive strain and oxygen vacancy effect exists in iridium dioxide (IrO₂)‐based catalyst by a doping engineering strategy for efficient acidic OER activity. In situ synchrotron characterizations elucidate that compressive strain can enhance Ir─O covalency and reduce the Ir─Ir bond distance, and oxygen vacancy (O_v) as an electronic regulator causes rapid adsorption of water molecules on the Ir and adjacent Ov (Ir─O_v) pair site to be coupled directly into ^*O─O^* intermediates. Importantly, hence, volcano‐shape curves are established between the compressive strain/oxygen vacancy and OER current using OER as the probe reaction. Theoretical calculation reveals Ni dopant can modulate Ir 5d‐ and O 2p‐band centers for increasing overlap of Ir 5d and O 2p orbits to trigger a continuous metal site‐oxygen vacancy synergistic mechanism (MS‐O_VSM) pathway, successfully breaking the LSR of intermediates binding during OER. Therefore, the resultant proton‐exchange membrane water electrolysis (PEMWE) device fabricated using T‐0.24Ni/IrO₂ delivers a current density of 500 mA cm⁻² and operates stably for 500 h.