Pt　catalysts　are　the　best　potential　hydrogen　evolution　reaction　(HER)　electrocatalysts　for　industrial　applications,　but　the　development　of　efficient　Pt　catalysts　with　low　Pt　loading　and　high　utilization　efficiency　remains　challenging.　Herein,　sub-nanometer　PtCo　clusters　confined　into　the　small　pores　of　ZIF-8　derived　N-doped　nanomaterials　are　fabricated　through　the　galvanic　replacement　method.　Benefiting　from　the　formation　of　sub-nanometer　PtCo　clusters　confined　in　small　pores　and　the　synergic　effect　of　bimetallic　components,　the　optimal　sub-nanometer　PtCo　clusters　with　only　1.2%　Pt　loading　(1.2%PtCo/NPC)　achieve　an　extraordinary　HER　catalytic　activity　and　durability　with　a　mass　activity　of　13.83　A　mg−1at　an　overpotential　of　20　mV,　which　is　more　than　65　times　greater　than　that　of　the　commercialized　Pt/C　catalyst.　Density　functional　theory　(DFT)　calculations　reveal　that　the　outstanding　HER　activity　on　the　1.2%PtCo/NPC　electrocatalyst　is　attributed　to　the　charge　redistribution　and　the　lower　d-band　center　on　Pt　due　to　the　enhanced　coupling　of　electrons　in　the　d　orbitals　between　Pt　and　Co,　which　decreases　the　Gibbs　free　energy　of　H*　adsorption　and　increases　the　HER　kinetics　and　activity.　©　The　Royal　Society　of　Chemistry　2021.