Oxygen-doped　graphene　(O-G)　derived　from　sodium　gluconate　is　identified　as　a　promising　candidate　to　effectively　catalyze　ambient　electrohydrogenation　of　N-2　to　NH3.　Electrochemical　tests　on　O-G　in　0.1　M　HCl　suggest　a　large　NH3　yield　of　21.3　mu　g　h(-1)　mg(cat.)(-1)　and　a　high　faradaic　efficiency　of　12.6%　at　-0.55　and　-0.45　V　vs.　reversible　hydrogen　electrode,　respectively,　with　strong　electrochemical　and　structural　stability　in　0.1　M　HCl.　Density　functional　theory　calculations　reveal　the　NRR　catalytic　mechanism　and　suggest　that　both　the　C　=　O　and　O-C　=　O　groups　contribute　more　greatly　to　the　NRR　compared　with　the　C-O　group.