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.