Revisiting Active Sites for Nitrogen Reduction Reaction on 2D Materials Supported Metal Atoms: A Theoretical Investigation

Single atom catalysts supported by two-dimensional (2D) materials, including graphene, g-C₃N₄, and graphdiyne, exhibit promising electrocatalytic nitrogen reduction reaction (NRR) activity. Nevertheless, sometimes theoretical works failed to predict the high activity of NRR of single atom catalysts, especially for Fe, Co, Mn, Cu, Ru. In this work, based on DFT calculations, it is suggested that dual-atom sites on N doped graphene (M₂@N-graphene) rather than single-atom sites are more likely to be the active sites for NRR. Notably, Fe₂@N₃, Co₂@N₂, Mn₂@N₂, Cu₂@N₁, and Ru₂@N₃ endow the best catalytic activity with corresponding limiting potentials of −0.26, −0.18, −0.17, −0.39, and −0.30 V, respectively. Furthermore, on g-C₃N₄ and graphdiyne, triple-atom sites (TAS, M₃) such as Ru₃(Co₃)@g-C₃N₄ and Ru₃(Rh₃)@graphdiyne are expected to exhibit higher stability and NRR catalytic performance than single-atom sites (SAS) and dual-atom sites (DAS), with corresponding limiting potentials of −0.28, −0.48, −0.24, and −0.23 V. The calculated results with the corresponding experimental potentials indicate that the origin of superior NRR activity observed in experiments may be contributed by M₂ or M₃ on 2D materials. This study provides an in-depth investigation into real active NRR sites of metal atoms supported on 2D materials and contributes to the design of effective NRR catalysts.