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A combined hydroxyl-functionalized and NH 4 Cl-assisted etching strategy is developed to effectively promote the yield of edge-hosted single-atomic Cu-N4 sites. The developed CuSAs@DCSs renders outstanding ORR activity (E onset =1.02 V, E 1/2 = 0.90 V), and excellent stability. CuSAs@DCSs-based Zn-air battery achieves ultralong cycle life and large power density. Rich edge-hosted active sites are responsible for the remarkable ORR performance. [Display omitted] • A hydroxyl-functionalized and NH 4 Cl-assisted etching strategy is developed to promote the yield of edge-hosted Cu-N4 sites. • Rich accessible edge-hosted Cu-N4 sites are responsible for the remarkable ORR performance. • CuSAs@DCSs exhibits extraordinarily ORR activity and excellent stability in both alkaline and acid solution. • CuSAs@DCSs exhibits superb performance when used as air cathode for Zn–air battery. • This strategy can be extended to fabricate other single atoms catalyst with controlled electronic structure. Single-atom electrocatalysts with metal-nitrogen-carbon (M N C SACs) moieties in carbon support display outstanding electrocatalytic performance towards oxygen reduction reaction (ORR) and have received widespread attentions. Only active sites on the edges of pores in carbon support are electrochemically accessible and contribute to ORR. Herein, we report a combined hydroxyl-functionalized and NH 4 Cl-assisted etching strategy to effectively promote the yield of edge-hosted Cu SAs. Thus, well-defined SAs with Cu-N 4 configuration are generated into the defect of carbonaceous nanospheres (CuSAs@DCSs). Impressively, the obtained SACs renders outstanding electrocatalytic ORR activity with onset, half-wave potentials of 1.02 V, 0.90 V, and extremely high stability, which transcends the noble-metals and most of the previously reported catalysts. When used in rechargeable Zn-air batteries, CuSAs@DCSs achieves ultralong cycle life at the large current density of 10 mA cm−2 (over 260 h) with low charge–discharge potential gap. Our study demonstrates that the creation of abundant micropores enriches the electrochemically accessible SAs, which locate at the edge-defects and are responsible for the remarkable ORR performance. This work sheds a facile strategy for designing and developing efficient electrocatalyst for various energy-related electrocatalytic reactions. [ABSTRACT FROM AUTHOR]