Water　dissociation　process　is　generally　regarded　as　the　rate-limiting　step　for　alkaline　hydrogen　evolution　reaction　(HER),　and　severely　inhibits　the　catalytic　efficiency　of　Pt　based　catalysts.　To　overcome　this　problem,　the　in-situ　constructed　interfaces　of　Pt-Co　alloy　and　amorphous　cobalt　oxide　(CoOx)　on　the　carbon　powder　are　designed.　The　amorphous　CoOx　at　Pt-Co/CoOx　interfaces　not　only　provide　active　sites　for　water　dissociation　to　facilitate　Volmer　step,　but　also　produce　the　strong　electronic　transfer　with　Pt-Co.　Accordingly,　the　obtained　interfacial　catalysts　exhibit　outstanding　alkaline　HER　performance　with　a　Tafel　slope　of　29.3　mV·dec−1　and　an　ultralow　overpotential　of　only　28　mV　at　10　mA·cm−2.　Density　functional　theory　(DFT)　reveals　that　the　electronic　accumulation　on　the　interfacial　Co　atom　in　Pt-Co/CoOx　constructing　the　novel　active　site　for　water　dissociation.　Compared　to　the　Pt-Co,　all　of　the　energy　barriers　for　water　adsorption,　water　dissociation　and　hydrogen　adsorption/desorption　are　reduced　in　Pt-Co/CoOx　interfaces,　suggesting　a　boosted　HER　kinetics　for　alkaline　HER.　[Figure　not　available:　see　fulltext.]　©　2022,　Tsinghua　University　Press.