Enhanced Oxygen Coupling via Regulated Interfacial Water and *OH Adsorption by Cr─O─Ir Motif to Enable Efficient Acidic Water Oxidation.

Highly active and durable anode electrocatalysts are crucial for acidic oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWE), yet IrO2-based catalysts often face a trade-off between activity and stability. In this study, a Cr-IrO2 catalyst is developed through partial substitution of Ir by Cr atoms in the IrO2 framework to overcome this limitation. Experimental and theoretical calculations reveal that the resulting Cr─O─Ir motifs amplify the orbital overlap the lone electron pair of O in H2O and the empty orbitals of Ir, thereby enhancing initial H2O adsorption. Meanwhile, Cr doping reduces the positive charge of H atoms in adsorbed H2O, thereby regulating the interfacial water structure and disrupting the hydrogen-bond network, which facilitates water dissociation and consequently increases the *O coverage for OER. Furthermore, the introduction of Cr atom into IrO2 weakens *OH adsorption at the second active site and shortens the dual-site distance, synergistically promoting the direct O-O radical coupling and enabling the oxide path mechanism (OPM). Consequently, Cr-IrO2 achieves 10 and 1000 mA cm- 2 at overpotentials as low as 233 and 348 mV, respectively, and demonstrates exceptional durability for over 2000 and 400 h in a practical PEMWE operating at 0.1 and 1 A cm-2, respectively.