▎ 摘　　要

Achieving an effective nitrogen reduction reaction (NRR) under mild conditions is a great challenge for industrial ammonia synthesis. NRR is often accompanied by a competing hydrogen evolution reaction (HER), which causes an extremely low Faraday efficiency. We systematically investigated the NRR reactivity of atom-pair catalysts (APCs) formed by 20 transition metal (TM) elements supported by N-doped graphene via three reaction pathways. By analyzing the correlation among the limiting potential, Gibbs free energy, and d-band center, we evaluated the activity trends of the TM APCs. Our computations revealed that the enzymatic pathway is the most suitable reaction pathway for the TM APCs, and the intrinsic activity trend of these APCs can be determined by the d-band center-based descriptor, which has a simple linear correlation with the bonding/antibonding orbital population. In addition, the NRR APCs with excellent performance have been screened out through selective analysis of the competing HER in the electrocatalytic NRR process.