▎ 摘　　要

Single atom catalysts (SACs) with atomically dispersed transition metals on nitrogen-doped carbon sup-ports have recently emerged as highly active non-noble metal electrocatalysts for oxygen reduction reac-tion (ORR) and oxygen evolution reaction (OER), showing great application potential in Zn-air batteries. However, because of the complex structure-performance relationships of carbon-based SACs in the oxy-gen electrocatalytic reactions, the contribution of different metal atoms to the catalytic activity of SACs in Zn-air batteries still remains ambiguous. In this study, SACs with atomically dispersed transition metals on nitrogen-doped graphene sheets (M-N@Gs, M = Co, Fe and Ni), featured with similar physicochemical properties and M-N@C configurations, are obtained. By comparing the on-set potentials and the maxi-mum current, we observed that the ORR activity is in the order of Co-N@G > Fe-N@G > Ni-N@G, while the OER activity is in the order of Co-N@G > Ni-N@G > Fe-N@G. The Zn-air batteries with Co-N@G as the air cathode catalysts outperform those with the Fe-N@G and Ni-N@G. This is due to the accelerated charge transfer between Co-N@C active sites and the oxygen-containing reactants. This study could im-prove our understanding of the design of more efficient bifunctional electrocatalysts for Zn-air batteries at the atomic level. (c) 2023 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.