One　way　to　efficiently　store,　transport,　and　utilize　hydrogen　is　to　convert　it　into　liquid　ammonia　(NH3).　Exploring　low-cost　and　high-efficiency　electrocatalysts　for　liquid　ammonia　oxidation　reaction　(AOR)　is　critical　in　developing　hydrogen　production　fuel　cells.　Here,　we　have　investigated　the　catalytic　electro-oxidation　of　liquid　ammonia　on　surfaces　of　transition　metal　dimer　anchored　in　g-CN　(TM2@g-CN)　monolayer　to　derive　insights　into　the　reaction　mechanism　and　evaluate　the　catalystic　activity.　Our　results　show　that　the　mechanism　proposed　by　Gerischer　and　Mauerer　is　kinetically　preferred.　Furthermore,　Fe2,　Co2,　Ru2,　Rh2,　and　Ir2　anchored　in　g-CN　monolayer　exhibit　high　AOR　catalytic　activity.　In　particular,　Rh　and　Ir　atoms　exhibit　excellent　performance　for　hydrogen　evolution　reaction　(HER),　indicating　that　they　can　be　used　as　the　efficient　bifunctional　catalysts　towards　ammonia　splitting　for　production　H2.　Remarkably,　by　regulating　TM　atoms　with　different　d-electron　numbers,　the　d-band　center　(εd)　of　TM　atoms　on　TM2@g-CN　can　be　turned　and　utilized　to　predict　AOR　performance,　which　provides　a　theoretical　guideline　for　the　design　of　advanced　AOR　electrocatalysts.　©　2022　Elsevier　B.V.