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

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.