First-principles screening of single transition metal atoms anchored on two-dimensional C9N4 for the nitrogen reduction reaction

Abstract

Compared to the Haber–Bosch process, the electrochemical nitrogen reduction reaction (NRR) can convert N₂ into NH₃ under ambient conditions, and thus has attracted considerable attention in recent years. However, it remains a challenge to fabricate NRR catalysts with high faradaic efficiency and yield rate. In this work, by systematic first-principles calculations, we investigate the structure, stability and catalytic performance of single metal atoms anchored on porous monolayer C₉N₄ (M@C₉N₄) for the electrochemical NRR. A total of 25 transition metals (Sc–Zn, Zr–Mo, Ru–Ag, Hf–Au) were explored, and we screened out four promising systems, i.e., Nb, Ta, Re and W@C₉N₄, which not only exhibit high catalytic activity with low limiting potentials of −0.3, −0.42, −0.49 and −0.25 V, respectively, but also have superior selectivity that suppresses the competitive hydrogen evolution reaction. The physical origin lies in the coupling between the d orbitals of the transition metals and the 2π* orbital of N₂, which activates the N₂ molecule and facilitates the reduction process. Our proposed systems are kinetically and thermodynamically stable, which may shed light on future design and fabrication of high-efficiency single atom catalysts for various technologically important chemical reactions.