Theoretical Insight into the Transition-Metal-Embedded Boron Nitride-Doped Graphene Single-Atom Catalysts for Electrochemical Nitrogen Reduction Reaction

Single-atom catalysts (SACs) have become attractive options for the efficient nitrogen reduction reaction (NRR) because of their unique properties in the activation of nitrogen molecules. As a novel two-dimensional material, boron nitride (BN)-doped graphene has attracted much attention due to its electronic structure, which can be regulated with boron nitride coverage. In the current work, we first screened potential SACs for NRR from various single transition metal atoms embedded in BN-doped graphene (BNC) by using density functional theory (DFT) calculations. Excellent catalytic activity for NRR is demonstrated by the V, Mo, Ru, and Os anchored on the B vacancy and generated SACs, with overpotentials of −0.56, −0.52, −0.60, and −0.61 V vs the standard hydrogen electrode (SHE). Taking advantage of BN-doped graphene electronic structures that can be modified, we further investigated the effect of boron nitride coverage on the SACs’ NRR performance. The electronic structure of the metal center can be altered by controlling the boron nitride coverage, which can further affect the catalytic performance. The potential determining step (PDS) and also the maximal free energy difference vary by modulating the boron nitride coverage. A larger energy range than the hydrogen evolution reaction (HER) is covered by the maximum energy shift between the PDSs, which can reach 0.29 eV. This indicates that by changing the coverage of the BN of the substrate, it is expected to improve the SACs’s catalytic activity and selectivity of NRR. Moreover, it is possible for a pathway to change from one that is adsorption favorable to another one that is thermodynamically favorable of the intermediate NNH. Our results help to clarify the structure–performance correlations and expedite the creation of SACs for ammonia synthesis.