The electrochemical synthesis of hydrogen peroxide (H2O2) can provide an attractive alternative to the current anthraquinone redox process, as it combines on-site chemical and electricity productions. A major challenge in the electrochemical H2O2 synthesis is the catalyst design which leads to a selective two-electron pathway in the oxygen reduction reaction (ORR) without dissociation of the O-O bond. In the present work, we report that the partial oxidation of metal-nitrogen-carbon catalysts (Me-N-C, Me = iron, cobalt and manganese) can modify their ORR mechanisms from a fourto a two-electron pathway. Spectroscopic measurements reveal that ex situ H2O2 treatment introduces abundant oxygen functionalities on the Me-N-C surface without considerable changes to their bulk properties, such as crystallinity, degree of defects, surface area, and metal contents. Decreased H2O2 reduction kinetics on the oxidized catalysts confirm that the dissociation of the O-O bond is strongly suppressed by the newly introduced oxygen functionalities. Among the three central metal candidates, the cobalt-nitrogen -carbon catalyst shows the highest H2O2 selectivity of > 85%. This work provides a new simple guideline for designing Me-N-C catalysts for the efficient electrochemical synthesis of H2O2.