Oxo transition metal anchored on C3N4 with constructing a high-activity bifunctional electrocatalyst for rechargeable metal-air batteries.

It is urgent to find efficient bifunctional electrocatalysts of oxygen reduction and evolution reactions to catalyze the oxygen electrode reaction of metal-air batteries. Herein, oxo transition metal anchored on C3N4 as bifunctional oxygen electrocatalyst is investigated using density functional theory calculations. Various stability analysis results show that all catalysts in this study have excellent stability. In particular, for the two sites of the catalyst, the calculated results show that the effect of the β site on the reaction species is generally stronger than that of the α site, while the catalytic activity of the α site is slightly better than that of β site. In particular, the α site on Ni2@C3N4 has the lowest overpotential (ηORR = 0.44 V, ηOER = 0.51 V) and bifunctional index value (BI = 0.95 V). Finally, the linear relationships between eight activity descriptors and the adsorption strength of reaction intermediates are used to analyze the influencing factors of the effective activity of the catalyst. The results reflect that the activity descriptors can well describe the change in adsorption strength of intermediates on the catalyst. Thus, this work provides a good idea for designing excellent bifunctional catalysts for rechargeable metal-air batteries.