Trimetallic single-cluster catalysts for electrochemical nitrogen reduction reaction: Activity prediction, mechanism, and electronic descriptor

Electrochemical nitrogen reduction reaction (NRR) for ammonia synthesis remains a long-standing challenge owing to unsatisfactory activity and low selectivity of electrocatalysts. By employing the density functional theory calculations, we designed a series of trimetallic single-cluster catalysts including group IVB to IIB transition metals supported on N-doped porous graphene (M₃-NG) for electrochemical NRR. Based on the analysis of the thermodynamic and electrochemical stability, activity, and selectivity, Ni₃-NG, Ru₃-NG, and Ir₃-NG were predicted as promising electrocatalysts for NRR with extremely low limiting potential of −0.31 ~ −0.33 V. The detailed mechanistic study revealed that they can effectively activate the inert N₂ by multiple “pull–push effect” according to the tunable electronic structure. An electronic descriptor was proposed to effectively estimate the NRR activity of M₃-NG by considering the number of relevant electrons and the first ionization energies for metal and nitrogen atoms, and it is expected to be widely applicable for other similar catalysts and beyond.