Investigation on Electron Transfer Process of Oxygen Reduction Reactions Catalyzed by Nitrogen-doped Graphitic Carbon in Acidic and Alkaline Media

The electron transfer number is an important parameter to illustrate oxygen reduction reaction (ORR) pathway and explore reaction processes, which can be obtained by the rotating ring-disk electrode (RRDE) method and the Koutecky−Levich equation. However, the two approaches sometimes lead to different and confusing conclusions. Herein, graphitic carbon, nitrogen-doped graphitic carbon and Pt/C are respectively used as carbon and precious metal catalysts to evaluate the reliability of these two methods to calculate electron transfer numbers in acidic and alkaline media. Furthermore, density functional theory (DFT) calculations are employed to reveal effects of electrical potentials on the 4-electron ORR process in acidic and alkaline media. The results show that the electron transfer number varies with potentials and the RRDE method can provide more objective and actual electron transfer numbers in alkaline and acidic electrolytes from the perspective of experiments and theoretical calculations.