HighlightsA hybrid electrocatalyst consisting of PtNi-W alloy nanocrystals loaded on carbon surface with atomically dispersed W sites was realized.Single-atomic W formed protonic acid sites and established an extended proton transport network at the catalyst surface.Peak power density is enhanced by 64.4% compared to that with the commercial Pt/C catalyst in fuel cell as cathode at ultra-low loading of 0.05 mgPtcm−2.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40820-023-01102-9.