Reversed Hydrogen Spillover via Oxygen Vacancy Concentration Modulation for Enhanced Interfacial Hydrogen Transfer Kinetics

Utilizing the hydrogen spillover effect as a metal–support interfacial engineering strategy can enhance the hydrogen evolution efficiency. However, conventional hydrogen spillover suffers from interfacial H* transfer energy barriers. To address this, we designed an O_v-concentration-gradient WO_x support using Dawson-type polyoxometalates (POMs) to spatially separate H* adsorption sites. Herein, we show that a reversed hydrogen spillover effect, where the WO_x support stores and transports H* to surface Pt active sites, drastically enhances the hydrogen spillover kinetics and improves the hydrogen evolution stability. Combined experimental investigations and theoretical calculations demonstrate that increasing the O_v concentration enhances the electronic metal–support interaction (EMSI) and reduces the energy barrier for H* migration from WO_x to Pt, thereby optimizing the reverse hydrogen spillover efficiency. The O_v-rich 12-Pt/WO_x catalyst exhibits exceptional HER performance (η₁₀ = 3 mV) and 1800 h stability at 200 mA cm^–2. Furthermore, the entire reversed hydrogen spillover process (adsorption–migration–desorption) was dynamically tracked via complementary in situ techniques. This study elucidates the quantitative correlation between O_v concentration and reversed hydrogen spillover kinetics, providing a universal defect-engineering strategy for high-performance low-platinum HER catalysts for industrial applications in acidic media.