First-principles screening of single transition metal atoms anchored on two-dimensional C 9 N 4 for the nitrogen reduction reaction.

Compared to the Haber-Bosch process, the electrochemical nitrogen reduction reaction (NRR) can convert N ₂ into NH ₃ 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 C ₉ N ₄ (M@C ₉ N ₄ ) 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@C ₉ N ₄ , 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 N ₂ , which activates the N ₂ 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.