Electrochemical oxygen reduction reaction (ORR) with 2-electron process is an alternative for decentralized H₂O₂ production, but it remains high challenging to develop highly active and selective catalysts for this process. In this work, we present a selective and efficient nonprecious electrocatalyst, prepared through an easily scalable mild oxidation of single-walled carbon nanotubes (SWNTs) with different oxidative acids including sulfur acid, nitride acid and mixed sulfuric/nitric acids, respectively. The high-degree oxidized SWNTs treated by mixed acids exhibit the highest activity and selectivity of electroreduction of oxygen to synthesize H₂O₂ at low overpotential in alkaline and neutral media. Spectroscopic characterizations suggested that the C–O is vital for catalyzing 2-electron ORR, providing an insightful understanding of defected carbon surface as the active catalytic sites for 2-electron ORR.