Enhancing Acidic\nWater Electrolysis via Local Electronic\nRegulation of Ru/TiO<sub><i>x</i></sub> Catalyst with Oxygen\nCoordination Unsaturated Ti Sites

Effective local electron regulation in ruthenium-based\ncatalysts\nin acidic oxygen evolution reactions (OER) remains a key challenge.\nThe lack of a unified understanding of catalyst activity and stability\nbased on electron regulation limits the further development of proton\nexchange membrane water electrolysis (PEMWE). In this study, we develop\nthe concept of oxygen coordination unsaturated Ti (Ti<sub>OCU</sub>) sites. Based on the constructed local dual-oxide heterojunction\ninterface in the Ru/TiO<sub><i>x</i></sub> catalyst, we\nachieve precise modulation of the d-electron orbitals of Ru sites.\nThe charge redistribution between the Ru–O<sub>bridge</sub>–Ti<sub>OCU</sub> local coordination units and the strengthened\nRu–O bonds suppresses the formation of high-valence species\nand deactivation of catalyst. Combined with density functional theory\n(DFT) calculations and in situ spectroscopic experiments, we confirm\nthat the modulation of the d<sub><i>z</i><sup>2</sup></sub> orbital charge significantly optimizes the deprotonation process\nof interfacial water and the formation of a hydroxyl-rich interface,\nthereby enhancing the OER kinetics and the dominance of the adsorbed\nevolution mechanism (AEM). Consequently, the Ru/TiO<sub><i>x</i></sub> catalyst exhibits superior OER performance, achieving a current\ndensity of 10 mA/cm<sup>2</sup> at an overpotential of only 237 mV\nin 0.5 M H<sub>2</sub>SO<sub>4</sub>, and demonstrates stability for\nover 160 h. This work reveals the application of interfacial Ti<sub>OCU</sub>, providing a perspective for the development of transition\nmetal defect materials in water electrolysis.