▎ 摘　　要

Electrochemical nitrate reduction reaction (NO3RR) is an advantageous conversion technology for nitrate removal and ammonia synthesis. Single-atom catalysts, owing to their utmost metal atom utilization efficiency, are promising electrocatalysts for NO3RR but are rarely investigated in systematic ways. In this study, a theoretical screening is performed on transition metal-N-4-doped graphene (TM-N-4/C) as active and selective electrocatalysts for NO3RR, where detailed reaction mechanisms and activity origins are explored. Volcano plots of activity trends show that Cu- and Pt-N-4/C are highly active for NO3RR following the NH3 and N-2 formation pathways, respectively, whose activities can be attributed to the optimal NO and N adsorptions. In addition, a contour plot of selectivity trend shows that Re- and Pt-N-4/C are highly selective toward NH3 and N-2 formations, respectively. This work provides theoretical insights into the rational design of TM-N-4/C catalysts for NO3RR and opportunities for efficient nitrate removal and ammonia synthesis strategies.