Atomic Fe–N5 catalytic sites embedded in N-doped carbon as a highly efficient oxygen electrocatalyst for zinc–air batteries

Abstract

Atomically dispersed transition metal–N_x–C-based catalysts with abundant Fe–N_x active sites have demonstrated good prospects for the oxygen-reduction reaction (ORR) and are promising alternatives to Pt-based electrocatalysts. However, further improving their ORR activity by precise modulation of the Fe–N_x site structure remains challenging. Herein, we synthesize a single-iron-atom electrocatalyst embedded in N-doped carbon with active and robust five-coordinated Fe–N₅ moieties by a simple synthetic approach. The FeN₅–C/G catalyst is obtained through prolonged calcination of melamine and hemin co-adsorbed on oxide graphene. The catalyst exhibits enhanced ORR activity in alkaline mediums with an admirable half-wave potential of 0.84 V, outperforming FeN₄–C, which has four-coordinated Fe–N₄ moieties. Zn–air batteries with a FeN₅–C/G air cathode further demonstrate the excellent ORR performance and stability of the catalyst, outperforming the commercial Pt/C catalyst. The remarkable ORR performance demonstrates the significant roles of mono-dispersed FeN₅ active sites embedded in N-doped carbon, in which N-doped graphene supplies enough N sites to axially coordinate with FeN₄.