Electrochemical mechanisms of the reduction of N2 to NH3 catalyzed by TM anchored on Nvs-g-C3N4/graphene van der Waals heterostructure: Insights from a first-principles study

•21 single-atom heterostructures (TM@Nvs-g-C3N4/graphene) are constructed to study the reduction of N2 to NH3.•The comparison between cohesive and binding energies shows that TM atom can be stably anchored in nitrogen vacancy.•AIMD results show that all heterostructures possess high thermodynamic stability.•PDOS and Bader charges are used to probe the adsorption behavior of N2 on TM@Nvs-g-C3N4/graphene.•Mo@Nvs-g-C3N4/graphene has the highest NRR performance with the limiting potential value of −0.17 V and lowest overpotential value of 0.01 V.•Mo@Nvs-g-C3N4/graphene is more favorable to HER inhibition than Mo@Nvs-gC3N4.