Not only high efficiency but also high selectivity of the electrocatalysts is crucial for high-performance, low-cost, and sustainable energy storage applications. Herein, we systematically investigate the edge effect of carbon-supported single-atom catalysts (SACs) on oxygen reduction reaction (ORR) pathways (two-electron (2 e−) or four-electron (4 e−)) and conclude that the 2 e−-ORR proceeding over the edge-hosted atomic Co−N4 sites is more favorable than the basal-plane-hosted ones. As such, we have successfully synthesized and tuned Co-SACs with different edge-to-bulk ratios. The as-prepared edge-rich Co−N/HPC catalyst exhibits excellent 2 e−-ORR performance with a remarkable selectivity of ≈95 % in a wide potential range. Furthermore, we also find that oxygen functional groups could saturate the graphitic carbon edges under the ORR operation and further promote electrocatalytic performance. These findings on the structure–property relationship in SACs offer a promising direction for large-scale and low-cost electrochemical H2O2 production via the 2 e−-ORR.