Optimizing the NRR activity of single and double boron atom catalysts using a suitable support: a first principles investigation

Abstract

Designing cost effective transition-metal free electrocatalysts for nitrogen fixation under ambient conditions is highly appealing from an industrial point of view. Using density functional theory calculations in combination with the computational hydrogen electrode model, we investigate the N₂ activation and reduction activity of ten different model catalysts obtained by supporting single and double boron atoms on five different substrates (viz. GaN, graphene, graphyne, MoS₂ and g-C₃N₄). Our results demonstrate that the single/double boron atom catalysts bind favourably on these substrates, leading to a considerable change in the electronic structure of these materials. The N₂ binding and activation results reveal that the substrate plays an important role by promoting the charge transfer from the single/double boron atom catalysts to the antibonding orbitals of *N₂ to form strong B–N bonds and subsequently activate the inert NN bond. Double boron atom catalysts supported on graphene, MoS₂ and g-C₃N₄ reveal very high binding energies of −2.38, −2.11 and −1.71 eV respectively, whereas single boron atom catalysts supported on graphene and g-C₃N₄ monolayers bind N₂ with very high binding energies of −1.45 and −2.38 eV, respectively. The N₂ binding on these catalysts is further explained by means of orbital projected density of states plots which reflect greater overlap between the N₂ and B states for the catalysts, which bind N₂ strongly. The simulated reaction pathways reveal that the single and double boron atom catalysts supported on g-C₃N₄ exhibit excellent catalytic activity with very low limiting potentials of −0.67 and −0.36 V, respectively, while simultaneously suppressing the HER. Thus, the current work provides important insights to advance the design of transition-metal free catalysts for electrochemical nitrogen fixation from an electronic structure point of view.