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

Abstract

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.