HighlightsUltrathin P and Fe co-doped NiSe2nanosheets supported on modified Ni foam are synthesized, which shows desirable bifunctional electrocatalytic hydrogen evolution reaction (HER)/hydrazine oxidation reaction (HzOR) performance in hydrazine-assisted water electrolysis and Zn-Hz battery.The coexistence of P and Fe heteroatoms induces an accelerated “2 + 2” reaction mechanism with a two-step HER process and a two-step HzOR step.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40820-023-01128-z.