Density Functional Theory Study of Triple Transition Metal Cluster Anchored on the C₂N Monolayer for Nitrogen...

The electrochemical nitrogen reduction reaction (NRR) is an attractive pathway for producing ammonia under ambient conditions. The development of efficient catalysts for nitrogen fixation in electrochemical NRRs has become increasingly important, but it remains challenging due to the need to address the issues of activity and selectivity. Herein, using density functional theory (DFT), we explore ten kinds of triple transition metal atoms (M₃ = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) anchored on the C₂N monolayer (M₃-C₂N) as NRR electrocatalysts. The negative binding energies of M₃ clusters on C₂N mean that the triple transition metal clusters can be stably anchored on the N6 cavity of the C₂N structure. As the first step of the NRR, the adsorption configurations of N₂ show that the N₂ on M₃-C₂N catalysts can be stably adsorbed in a side-on mode, except for Zn₃-C₂N. Moreover, the extended N-N bond length and electronic structure indicate that the N₂ molecule has been fully activated on the M₃-C₂N surface. The results of limiting potential screen out the four M₃-C₂N catalysts (Co₃-C₂N, Cr₃-C₂N, Fe₃-C₂N, and Ni₃-C₂N) that have a superior electrochemical NRR performance, and the corresponding values are -0.61 V, -0.67 V, -0.63 V, and -0.66 V, respectively, which are smaller than those on Ru(0001). In addition, the detailed NRR mechanism studied shows that the alternating and enzymatic mechanisms of association pathways on Co₃-C₂N, Cr₃-C₂N, Fe₃-C₂N, and Ni₃-C₂N are more energetically favorable. In the end, the catalytic selectivity for NRR on M₃-C₂N is investigated through the performance of a hydrogen evolution reaction (HER) on them. We find that Co₃-C₂N, Cr₃-C₂N, Fe₃-C₂N, and Ni₃-C₂N catalysts possess a high catalytic activity for NRR and exhibit a strong capability of suppressing the competitive HER. Our findings provide a new strategy for designing NRR catalysts with high catalytic activity and selectivity.