Oxygen reduction to hydrogen peroxide on oxidized nanocarbon: Identification and quantification of active sites

Two-electron electrochemical oxygen reduction reaction (ORR) on non-metallic nanocarbon catalysts yielding hydrogen peroxide (H₂O₂) has attracted considerable research attentions in the field of electrochemistry, catalysis and material science. Here, oxidized carbon black (OCB) with different amounts of surface oxygen functional groups were synthesized for ORR. OCB catalysts exhibited a significant activity improvement for the two-electron pathway comparing with non-oxidized ones. Identification and quantification of active sites for two-electron pathway of ORR process were further realized via linking the activity to structural compositions of OCB, and both carboxyl (-COOH) and carbonyl (-CO) groups were proved responsible for two-electron pathway ORR to produce H₂O₂. The intrinsic activity of -COOH (k_-COOH = 1.34 × 10^-7 mol^-1) was found higher than that of -CO (k_-CO = 0.25 × 10^-7 mol^-1). The present work provides new physical-chemical insights on the mechanism of oxygen reduction reactions on carbon-based catalysts, paving the way for the establishment of structure-function relations and further development of novel non-metallic catalytic systems.