Electrocatalytic　nitrogen　reduction　reaction　(eNRR)　is　a　new　method　for　sustainable　NH3　production,　which　has　attracted　much　attention　in　recent　years.　However,　the　low　Faradaic　efficiency　due　to　the　competitive　hydrogen　evolution　reaction　(HER)　and　inert　NN　triple　bond　activation　hinders　its　practical　application.　To　find　highly　efficient　electrocatalysts　with　excellent　activity,　stability　and　selectivity,　we　have　studied　a　series　of　transition　metal　dimers　(TM2)　loaded　on　poly　triazine　imide,　(PTI)　a　crystalline　carbon　nitride,　by　density　functional　theory　calculations.　The　results　show　that　most　of　the　metal　dimers　have　good　stability.　Finally,　among　26　homonuclear　diatomic　catalysts,　Mo2@PTI,　Re2@PTI,　and　Pt2@PTI　exhibit　strong　capability　for　suppressing　HER,　with　a　favorable　limiting　potential　of　-0.53,　-0.36,　and　-0.63　V,　respectively,　and　hence,　can　be　used　as　efficient　electrocatalysts　for　NRR.　In　this　study,　a　homonuclear　diatomic　eNRR　catalyst　was　designed　and　screened　to　provide　not　only　a　theoretical　basis　for　the　experiments　but　also　an　alternative　approach　for　sustainable　synthesis　of　ammonia.　©　2022　Author(s).