Tuning the selectivity of oxygen reduction reaction to 2 e(-) pathway is of significant importance for hydrogen peroxide electrochemical generation. C-800 with superior 2 e(-) oxygen reduction reaction activity and inferior peroxide reduction reaction and peroxide disproportionation reaction activity is the most promising catalyst for hydrogen peroxide electrochemical generation. The thorough understanding of oxygen reduction reaction mechanism provides great insights into the catalyst design. Different pi-electron delocalization degree of carbon can tune the electron transferring ability out of catalyst surface and the density of active sites. A plausible volcano relationship of oxygen reduction reaction activity vs. pi-electron delocalization degree of carbon is established. High pi-electron delocalization degree benefits the electron transfer from catalyst surface to hydrated O-2 in outer Helmholtz plane but is unfavorable to the increase of active sites for the further adsorption and reduction of intermediate OOH. This work provides a new insight into the design of carbon materials for effective hydrogen peroxide electrochemical generation. (C) 2020 Elsevier Inc. All rights reserved.