Insights into electrochemical nitrogen reduction reaction mechanisms: Combined effect of single transition-metal and boron atom

Abstract Developing single-atom catalysts (SACs) for electrochemical devices is a frontier in energy conversion. The comparison of stability, activity and selectivity between various single atoms is one of the main research focuses in SACs. However, the in-depth understanding of the role that the coordination atoms of single atom play in the catalytic process is lacking. Herein, we proposed a graphene-like boron–carbon-nitride (BCN) monolayer as the support of single metal atom. The electrocatalytic nitrogen reduction reaction (eNRR) performances of 3d, 4d transition metal (TM) atoms embedded in defective BCN were systematically investigated by means of density functional theory (DFT) computations. Our study shows that the TM-to-N and B-to-N π-back bonding can contribute to the activation of N2. Importantly, a combined effect is revealed between single TM atom and boron atom on eNRR: TM atom enhances the nitrogen reduction process especially in facilitating the N2 adsorption and the NH3 desorption, while boron atom modulates the bonding strength of key intermediates by balancing the charged species. Furthermore, Nb@BN3 possesses the highest electrocatalytic activity with limiting potential of −0.49 V, and exhibits a high selectivity for nitrogen reduction reaction (NRR) to ammonia compared with hydrogen evolution reaction (HER). As such, this work can stimulate a research doorway for designing multi-active sites of the anchored single atoms and the innate atoms of substrate based on the mechanistic insights to guide future eNRR research.