Electrosynthesis of hydrogen peroxide (H 2 O 2 ) through oxygen reduction reaction (ORR) is an environmentfriendly and sustainable route for obtaining a fundamental product in the chemical industry. Co−N 4 single-atom catalysts (SAC) have sparkled attention for being highly active in both 2e − ORR, leading to H 2 O 2 and 4e − ORR, in which H 2 O is the main product. However, there is still a lack of fundamental insights into the structure−function relationship between CoN 4 and the ORR mechanism over this family of catalysts. Here, by combining theoretical simulation and experiments, we unveil that pyrrole-type CoN 4 (Co−N SAC Dp ) is mainly responsible for the 2e − ORR, while pyridine-type CoN 4 catalyzes the 4e − ORR. Indeed, Co−N SAC Dp exhibits a remarkable H 2 O 2 selectivity of 94% and a superb H 2 O 2 yield of 2032 mg for 90 h in a flow cell, outperforming most reported catalysts in acid media. Theoretical analysis and experimental investigations confirm that Co−N SAC Dp �with weakening O 2 /HOO* interaction�boosts the H 2 O 2 production.