Unveiling the Cationic Promotion Effect of H2O2 Electrosynthesis Activity of O-Doped Carbons

Abstract

H2O2 electrosynthesis is an emerging clean chemical technology, whose efficiency critically depends on the activity and selectivity of electrocatalysts for two-electron oxygen reduction reaction (2e(-) ORR). Here, we demonstrate that 2e(-) ORR activity of oxygen-doped carbons, which have been one of the most promising catalysts for this reaction, can be substantially influenced by the types and concentrations of cations in electrolytes. Heat-treated carbon comprising active oxygen functional groups exhibits cation-dependent 2e(-) ORR activity trends in alkaline media, following the order Cs+ > K+ > Li+. Importantly, an electrolyte with a high cation concentration (0.1 M KOH + 0.5 M KCl) afforded the highest 2e(-) ORR mass activity (250 +/- 30 A gcat(-1) at 0.70 V vs reversible hydrogen electrode) ever reported. We have established that the cation promotion effect correlates with cation-dependent electron-transfer kinetics, which regulates the rate-determining first electron transfer to O-2.