Electroreduction of O2 is a promising method for decentralized H2O2 production. Due to their high selectivity, low cost, and highly tunable properties, O- and N-doped carbon catalysts are appealing for this process. However, the relative effects of O and N dopants on the catalytic performances of carbon are not well understood. In this work, we present highly active and selective 2e– O2 reduction catalysts based on doped carbon nanohorns (CNH) synthesized by the gas-injected arc-in-water (GI-AIW) method. The effects of O and N dopants incorporated during the synthesis and the post-treatment are investigated. We discovered that the selectivity of CNH may be more sensitive to changes in N dopant than to changes in O dopant. Our doped CNH catalyst exhibits an early onset potential of 0.85 V vs RHE, >80% selectivity, and excellent stability even after 5,000 cycles and 12 h of flow electrolysis. Our gas diffusion device can generate H2O2 at a practical concentration of 56 mM per hour, corresponding to a production rate of 0.74 mol h–1 gcat –1. These results suggest that regulating both O and N dopants is an effective design strategy for an efficient carbon catalyst, which is essential in the electrosynthesis of H2O2 from O2.