The　design　of　economically　feasible　and　effective　platinum　(Pt)-based　single-atom　electrocatalysts　for　hydrogen　evolution　reaction　(HER)　is　critical　to　the　realization　of　a　clean　hydrogen　energy　infrastructure　but　is　hindered　by　a　lack　of　sufficient　understanding　to　overcome　kinetically　adverse　hydrogen　spillover.　Herein,　we　confine　Pt　single　atoms　into　the　lattice　of　nitrogen-doped　MoC　nano-sheets　(MoC-NNs)　to　activate　the　dual　hydrogen　spillover　effect　and　outline　the　design　guidelines　between　electronic　metal-support　interaction　and　spillover　kinetics.　Constrained　Pt　single-atom　causes　MoC-NNs　local　lattice　distortion　and　gives　rise　to　the　emergence　of　Mo–O　coordination,　resulting　in　simultaneous　manipulation　of　electronic　structure　on　Pt　single　atom　and　MoC-NNs.　Thus,　PtSA/MoC-NNs　exhibited　outstanding　HER　performance　with　a　70-fold　higher　mass　activity　than　commercial　Pt/C.　DFT　calculations　revealed　that　the　enhanced　HER　performance　originated　from　the　charge　delocalization　between　the　Pt　single-atom　and　MoC-NNs,　which　reduced　the　Mo-to-Pt　hydrogen　migration　barrier　and　subsequently　activated　the　Mo-to-Mo　hydrogen　spillover　on　the　support.　Furthermore,　it　suggests　that　the　difference　(ΔΕd)　between　the　d-band　center　of　Pt　(Εd-Pt)　and　support　(Εd-support)　can　serve　as　a　descriptor　for　designing　kinetically　efficient　Pt-based　single-atom　HER　electrocatalysts.　©　2025　Elsevier　Ltd