Enhancing Acidic Water Electrolysis via Local Electronic Regulation of Ru/TiO_<i>x</i> Catalyst with Oxygen Coordination Unsaturated Ti Sites

Effective local electron regulation in ruthenium-based catalysts in acidic oxygen evolution reactions (OER) remains a key challenge. The lack of a unified understanding of catalyst activity and stability based on electron regulation limits the further development of proton exchange membrane water electrolysis (PEMWE). In this study, we develop the concept of oxygen coordination unsaturated Ti (TiOCU) sites. Based on the constructed local dual-oxide heterojunction interface in the Ru/TiOx catalyst, we achieve precise modulation of the d-electron orbitals of Ru sites. The charge redistribution between the Ru–Obridge–TiOCU local coordination units and the strengthened Ru–O bonds suppresses the formation of high-valence species and deactivation of catalyst. Combined with density functional theory (DFT) calculations and in situ spectroscopic experiments, we confirm that the modulation of the dz2 orbital charge significantly optimizes the deprotonation process of interfacial water and the formation of a hydroxyl-rich interface, thereby enhancing the OER kinetics and the dominance of the adsorbed evolution mechanism (AEM). Consequently, the Ru/TiOx catalyst exhibits superior OER performance, achieving a current density of 10 mA/cm2 at an overpotential of only 237 mV in 0.5 M H2SO4, and demonstrates stability for over 160 h. This work reveals the application of interfacial TiOCU, providing a perspective for the development of transition metal defect materials in water electrolysis.