Theoretical insight into electrocatalytic nitrogen fixation on transition-metal decorated melon-based carbon nitride

Developing high-efficiency and low-cost single-atom catalysts (SACs) for electrochemical nitrogen reduction reaction (NRR) is becoming increasingly essential, while the problems on activity and selectivity remain a challenge. Herein, by using density functional theory (DFT) computations, we focus on screening out 3d and 4d transition metal (except Tc) decorated melon-based carbon nitride (TM-CN) catalysts for electrochemical ammonia (NH3) synthesis. By evaluating stability, activity, and selectivity of studied TM-CN candidates, Mo-CN is highlighted with low overpotential of 0.26 V along the distal pathway for NRR and has the high selectivity to the competitive hydrogen evolution reaction (HER) with Faraday efficiency close to 100%. A descriptor φ that involves the active site and its coordination environment has a volcano relationship with several factors during N2 reduction process and can be used to reveal the active origin of Mo-CN. The present work not only broadens the application of SACs for NRR but also provides new guidelines for improving the activity and selectivity of catalysts.