Developing efficient electrocatalysts for nitrogen reduction reaction(NRR)is crucial to replace the both energy-intensive and environment-malignant Haber-Bosch process.Here using density functional the-ory calculations,we systematically studied the potential of the heteronuclear 3d transition metal dimers anchored graphdiyne monolayers(FeM@and NiM@GDY,M = Ti,V,Cr,Mn,Fe,Co,Ni,and Cu)as efficient NRR catalysts.Among all the studied double-atom catalysts(DACs),FeCo@and NiCo@GDY are the most promising with excellent NRR catalytic activity,high ability to suppress the competing hydrogen evolu-tion reaction(HER),and good stability.For both FeCo@and NiCo@GDY,NRR prefers to the distal pathway with the calculated onset potentials of-0.44 and-0.36 V,respectively,which are comparable and even better than their homonuclear counterparts.Moreover,FeCo@and NiCo@GDY have higher ability to sup-press HER than Fe2@and Co2@GDY,which may result from the modulated d state electronic structure due to the synergy effect of the heteronuclear atoms in the DACs.Our work not only suggests that FeCo@and NiCo@GDY hold great promises as efficient,low-cost,and stable DACs for NRR,but also further provides a strategy,i.e.alloying the atomic metal catalysts,to improve the NRR catalytic activity and/or selectivity.