Electrochemical　water　splitting　to　produce　hydrogen　is　a　key　technology　for　converting　sustainable　energy　into　chemical　fuels.　The　high　overpotential　and　sluggish　kinetics　for　the　electrocatalytic　hydrogen　evolution　reaction　(HER)　lead　to　low　energy　conversion　efficiency.　Herein,　we　report　a　new　electrocatalyst　of　RuCu　supported　on　guanine-derived　carbon　nanosheets　for　highly　efficient　HER,　in　which　the　trace　Cu　of　0.1　wt%　loadings　can　significantly　boost　the　electrocatalytic　activity　during　the　whole　pH　range.　Specifically,　the　0.5Ru0.1Cu-GN1000　can　release　a　current　density　of　10　mA/cm(2)　at　68　mV　and　157　mV　in　1.0　M　KOH　and　0.5　MH2SO4,　respectively.　This　catalyst　still　delivers　a　high　HER　activity　even　in　the　actual　seawater.　The　improvement　of　HER　activity　can　be　ascribed　to　the　strong　interaction　between　Ru　and　Cu,　resulting　in　the　formation　of　an　electron-rich　state　of　Ru　nanoparticles　at　the　surface　for　series　of　HER　at　low　overpotential.　This　research　has　opened　up　a　promising　pathway　towards　electrocatalytic　water　splitting　through　the　innovation　of　carbon　support　and　the　modulation　of　metal　interactions.