Manganese as Electron\nReservoir Stabilized RuMnO<sub><i>x</i></sub>@RuO<sub><i>x</i></sub> with Enhanced\nActivity and Robust Durability for Acidic Water Oxidation

Designing\nhighly active and durable electrocatalysts\nwith low noble-metal\nmass-loading to boost the sluggish oxygen evolution reaction is crucial\nfor hydrogen production. Herein, a Ru-enriched surface and oxygen-defective\nRuMnO<sub><i>x</i></sub>@RuO<sub><i>x</i></sub>-1.5 catalyst is developed with enhanced activity and robust stability\nthrough MnO<sub><i>x</i></sub> serving as an electron reservoir.\nThis RuMnO<sub><i>x</i></sub>@RuO<sub><i>x</i></sub>-1.5 catalyst with an ultralow mass-loading of 91.2 μg<sub>Ru</sub> cm<sup>−2</sup> delivers 1645 A g<sub>Ru</sub><sup>−1</sup>@1.5 V versus RHE and long-term operational stability\nexceeding 240 h with a high stability number (6.22 × 10<sup>4</sup>) in 0.5 M H<sub>2</sub>SO<sub>4</sub>. Characterizations and theoretical\ncalculations reveal that the sacrificial spaced Mn dissolution makes\nthe adjacent Mn serve as an electron reservoir to replenish electrons\non active Ru sites and suppress the overoxidation of Ru extending\nthe robust stability. The crystalline−amorphous heterointerfaces,\nabundant oxygen vacancies, and stable Ru−O−Mn motifs\nsimultaneously facilitate superior activity. The weaker adsorption\nbetween Ru sites and oxo-intermediates lowers the energy barrier from\nO* to *OOH following the adsorbate evolution mechanism (AEM) pathway.\nThis work provides a promising perspective on designing cost-effective\nOER electrocatalysts for proton exchange membrane water electrolysis.