Oxygen reduction reaction (ORR) is the key reaction at the cathode of proton exchange membrane fuel cells (PEMFCs)and metal-air batteries [1].To address the challenges associated with Pt-based electrocatalysts having prominent activity for ORR,e.g.scarce abundance,prohibitive cost,poor stability,and vulnerability to reaction intermediates,it is necessary to explore other cost-effective ORR electrocatalysts with competitive or even superior performance to promote the commercialization of the energy conversion devices.Among a number of candidates to substitute for Pt-based catalysts,nitrogen-coordinated transition metals (TMs) anchored on carbon (TM-N-C) nanomaterials,especially Fe-N-C,have been emerging as a class of appealing ORR alteatives due to their earth abundance,tunable surface chemistry,modified electronic structure,and optimal O2 adsorption [2,3].On the other hand,single-atom catalysts (SACs) have gaered sustained research interest for their maximum atom utilization efficiency,homogeneity of the catalytically active sites,and unsaturated metal coordination [4].Therefore,the combination of TM-N-C nanomaterials with atomic metal dispersion would be an effective strategy to further boost their electrocatalytic performance for ORR yet still remains greatly challenging.