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Recently, hydrogen spillover based binary (HSBB) catalysts have received widespread attention due to the sufficiently utilized reaction sites. However, the specific regulation mechanism of spillover intensity is still unclear. Herein, we have fabricated oxygen vacancies enriched Ru/NiMoO4‐x to investigate the internal relationship between electron supply and mechanism of hydrogen spillover enhancement. The DFT calculations cooperate with in situ Raman spectrum to uncover that the H* spillover from NiMoO4‐x to Ru. Meanwhile, oxygen vacancies weakened the electron supply from Ru to NiMoO4‐x, which contributes to dilute the resistance of built‐in electric field (BEF) for hydrogen spillover. In addition, the higher ion concentration in electrolyte will promote the H* adsorption step obviously, which is demonstrated by in situ EIS tests. As a result, the Ru/NiMoO4‐x exhibits a low overpotential of 206 mV at 3.0 A cm−2, a small Tafel slope of 28.8 mV dec−1, and an excellent durability of 550 h at the current density of 0.5 A cm−2 for HER in 1.0 M KOH seawater. [ABSTRACT FROM AUTHOR]

Currently, hydrogen evolution reaction (HER) in alkaline seawater still faces problems such as low catalyst activity and Cl - poisoning of active sites. In this work, an electron transfer facilitator of oxygen vacancies is introduced as a driving force for electronic transmission, which enhances the electron-metal-support interactions (EMSI) effect while introducing a charge protective layer, realizing killing two birds with one stone. In situ characterizations and density functional theory (DFT) calculations demonstrate that the EMSI effect enhances the H * transfer step at the interface. At the same time, due to oxygen vacancies for the enhanced EMSI, Ru forms an electron-rich layer, avoiding the poison of Cl - on active sites in seawater for HER. As a result, the Ru/Ni(OH) 2-x has an overpotential of only 156 mV at a current density of 1.0 A cm -2 in alkaline seawater. After assembling anion-exchange-membrane water electrolyzers (AEMWE), the Ru/Ni(OH) 2-x has a flat efficiency of ≈70% at different current densities, low energy consumption and price of per gallon gas equivalent (GGE) H 2 produced. Owning to the well Cl - tolerance, the catalyst also maintains long-term stability at 0.5 A cm -2 , indicating its great potential for industrial feasibility., (© 2024 Wiley‐VCH GmbH.)