Abstract: Room-temperature electrocatalytic nitrogen reduction reaction (NRR) is of paramount significance for the fertilizer industry and fundamental catalysis science. However, many NRR catalysts were based on the use of metals. Herein, we focus on exploring boron-based, metal-free, efficient catalysts for NRR by density functional theory calculations with van der Waals corrections (DFT+D3). Our results show that the NRR performance of the boron active site can be improved by tuning the N-coordination environment in a graphene sheet, and the B-N-C structures show excellent stability. By considering the correlation between the Bader charges of the boron dopant over N-decorated graphene and their NRR activities, the rational design principle of a boron-based catalyst for NRR is developed. The boron-site with one pyridinic nitrogen in a double-vacancy structure is found to be a highly active center, with low reaction energy (0.53 eV) and kinetic barrier (0.84 eV) through the distal mechanism. We also found that the charge loss of boron considerably hampers hydrogen adsorption, which in turn promotes the NRR efficiency by hindering the competing hydrogen evolution. This work offers new insights into developing low-cost, highly effective boron-based materials as promising electrocatalysts for green ammonia synthesis.

Key words: B-based metal-free materials, Nitrogen reduction reaction, Ammonia synthesis, Density functional theory, Catalyst design