Arming Ru with Oxygen‐Vacancy‐Enriched RuO2 Sub‐Nanometer Skin Activates Superior Bifunctionality for pH‐Universal Overall Water Splitting

Abstract Water electrolysis has been expected to assimilate the renewable yet intermediate energy‐derived electricity for green H 2 production. However, current benchmark anodic catalysts of Ir/Ru‐based compounds suffer severely from poor dissolution resistance. Herein, an effective modification strategy is proposed by arming a sub‐nanometer RuO 2 skin with abundant oxygen vacancies to the interconnected Ru clusters/carbon hybrid microsheet (denoted as Ru@V‐RuO 2 /C HMS), which can not only inherit the high hydrogen evolution reaction (HER) activity of the Ru, but more importantly, activate the superior activity toward the oxygen evolution reaction (OER) in both acid and alkaline conditions. Outstandingly, it can achieve an ultralow overpotential of 176/201 mV for OER and 46/6 mV for the HER to reach 10 mA cm −2 in acidic and alkaline solution, respectively. Inspiringly, the overall water splitting can be driven with an ultrasmall cell voltage of 1.467/1.437 V for 10 mA cm −2 in 0.5 m H 2 SO 4 /1.0 m KOH, respectively. Density functional theory calculations reveal that armoring the oxygen‐vacancy‐enriched RuO 2 exoskeleton can cooperatively alter the interfacial electronic structure and make the adsorption behavior of hydrogen and oxygen intermediates much close to the ideal level, thus simultaneously speeding up the hydrogen evolution kinetics and decreasing the energy barrier of oxygen release.