The active site exploration of Co-based non-precious metal electrocatalysts for oxygen reduction reaction

A kind of cobalt and nitrogen co-doped carbon catalyst for oxygen reduction reaction (ORR) is synthesized by pyrolyzing cobalt-melamine complexes supported on carbon at high temperature from 600 to 1000 °С. The optimum activity is obtained on Co0.25-N0.32/C-800 catalyst heat-treated at 800 °С, with the peak potential and onset potential of 0.826 and 0.930 V (vs. RHE), respectively. From the rotating disk electrode measurement using linear sweep voltammetry (LSV) and Koutechy-Levich analysis, the overall electron number transferred for ORR catalyzed by the optimum catalyst Co0.25-N0.32/C-800 is determined to be 3.43–3.87, suggesting that the ORR catalyzed by Co0.25-N0.32/C-800 is dominated by a four-electron transfer process. The catalytic active site of the catalysts is explored by Fourier transform infrared spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. The Co-N-C unit is the most efficient active site and responsible for the ORR activity enhancement in alkaline electrolyte. Accordingly, a possible ORR mechanism on the cobalt and nitrogen co-doped carbon catalyst is proposed.