H₂O₂ electrosynthesis by 2e⁻ oxygen reduction reaction (ORR) is an emerging eco-friendly chemical technology, whose efficiency critically depends on the activity and selectivity of electrocatalysts. In this presentation, it is demonstrated that the 2e⁻ ORR activity of oxygen-doped carbons, which has exhibited high 2e⁻ ORR performance in alkaline solutions, can be promoted by the types and concentrations of cations in electrolytes. The O-doped carbon including active oxygen functional groups could be prepared by facile one-step heat-treatment. The catalyst exhibited cation-dependent 2e⁻ ORR activity trends following the order: Li⁺ < K⁺ < Cs⁺. Along with the effect of cation type, 2e⁻ ORR activity of the heat-treated carbon was further improved under high cation concentration conditions. Importantly, a record high 2e⁻ ORR mass activity was obtained in 0.1 M KOH + 0.5 M KCl electrolyte (250 ± 30 A g_cat⁻¹ at 0.70 V vs. reversible hydrogen electrode). The cation promotion was applicable to a more practical bulk H₂O₂ electrosynthesis system. The origin of cation promotion was attributed to cation-dependent electron transfer kinetics, which affected the rate-determining first electron transfer to O₂.