Theoretical Establishment and Screening of an Efficient Catalyst for N2 Electroreduction on Two-Dimensional Transition-Metal Borides (MBenes)

Electrochemical nitrogen reduction reactions (NRRs) produce ammonia under ambient conditions, and it is necessary and efficient to explore a high-activity and -selectivity catalyst for NRR activity from the view of the energy change profile and electrical structure. Herein, we utilized a theoretical screening approach to systematically design two-dimensional (2D) transition-metal borides (MBenes) as promising electrocatalysts for NRRs. Density functional theory (DFT) calculation results reveal that Ta3B4, Nb3B4, CrMnB2, Mo2B2, Ti2B2, and W2B2 MBenes have an excellent catalytic activity to reduce N-2 to NH3 under ambient conditions. These materials strongly attract N-2 and H around the metal activity center, while the competing hydrogen evolution reaction (HER) can be well suppressed. NRRs occur along the favorite pathway with a low limiting potential of -0.24 V on W2B2, indicating that the W2B2 monolayer provides a new candidate catalyst for NRRs. In addition, the low limiting potentials of Nb3B4 (0.50 eV), Ta3B4 (0.39 eV), and Ti2B2 (0.37 V) are suitable for NRRs due to strong backdonation between the hybridized d orbital of the metal atom and the 2p orbital in N-2. The improved catalytic activity of NRRs, with limiting potentials ranging from -0.7 V < U-L < -0.2 V, depends on theoretical screening criteria: the descriptor Delta G(*N) is proposed to establish the relationship between the different NRR intermediates, and the rate-determining step (PDS) was confirmed by the limiting potential of the volcano plot. The energy barrier for reducing O*/OH* to *H2O is defined as the redox potential, and the difference in U-R - U-L values acts as a descriptor to study the catalytic activity. Theoretical screening work can provide a highly effective approach to investigate the reaction mechanism and can aid in designing novel catalysts for the reduction of N-2 to NH3 on MBenes.