Interfacial electron transfer triggered reversible hydrogen spillover effect boosts high-efficient hydrogen evolution.

The mechanistic role of interfacial electron transfer in enabling reversible hydrogen spillover for enhanced hydrogen evolution reaction (HER) kinetics remains fundamentally unexplored. Herein, we report a lattice-matched PtCoNiCuZn/ WCN heterostructure electrode, where interfacial electron transfer triggers reversible hydrogen spillover, thereby achieving exceptional HER performance. Advanced characterization reveals coherent and semicoherent interfaces that induce charge redistribution, creating electron-deficient Pt sites with optimally downshifted d-band centers. The electrode exhibits a remarkable mass activity of 4.63 A mgPt, which is 22 times higher than that of commercial Pt/C, and demonstrates exceptional stability for over 300 h at 10 mA cm, attributed to strong metal-support interactions (SMSI). Density functional theory (DFT) calculations confirm a reversible hydrogen spillover mechanism driven by a built-in electric field at the heterojunction. This electric field facilitates *H migration from WCN to the alloy, alleviating hydrogen accumulation on the support and enhancing metal-site desorption, thus accelerating HER kinetics. This study provides critical insights into the role of interfacial electron transfer in hydrogen spillover and establishes a rational design strategy for highly active and stable self-supported electrodes in sustainable hydrogen production.