Enhanced Proton Spillover at Pt‐Cluster/NiO Interface Reduces the Acidic–Alkaline Hydrogen Evolution Activity Gap

The sluggish hydrogen evolution reaction (HER) kinetics in alkaline media, primarily attributed to the additional water dissociation step, has led to a significant activity gap between acidic and alkaline conditions. Metal‐supported electrocatalysts leveraging hydrogen spillover have garnered significant attention due to sufficiently utilized reaction sites; however, designing active catalysts remains a formidable challenge, primarily due to the limited understanding of the specific regulatory mechanisms governing proton spillover. Herein, a facile strategy is reported for the fabrication of Pt nanoclusters (Pt NC ) on oxygen‐defect‐rich NiO nanowires (Pt NC ‐D‐NiO). The electrocatalyst demonstrates excellent intrinsic and mass‐normalized HER activity and remarkable long‐term stability, outperforming Pt NC on pristine NiO nanowires and commercial Pt/C. Notably, its alkaline HER activity is fairly close to its acidic counterpart, significantly narrowing the activity gap compared to commercial Pt/C. Advanced ex situ / operando physicochemical characterizations, including in situ electrochemical impedance spectroscopy, reveal that oxygen defects substantially lower the water dissociation energy barrier. This facilitates rapid H* spillover and enhances local H* coverage on Pt NC , thus accelerating subsequent H* recombination to boost alkaline HER. This work not only offers a cost‐effective catalyst design strategy but also provides fundamental insights into the role of hydrogen spillover in optimizing electrocatalytic performance.