Cobalt and nitrogen co-embedded onion-like mesoporous carbon vesicles as efficient catalysts for oxygen reduction reaction

A series of cobalt and nitrogen co-embedded onion-like mesoporous carbon vesicles (Co–NMCVs) were synthesized as non-noble metal catalysts for the first time. Physical characterization indicated that the Co–NMCVs samples all retain the lamellar porous shell structure (accompanying considerable surface areas and pore volumes), except the Co20–NMCV sample. Electrochemical measurements demonstrate that most of the Co–NMCV catalysts exhibit remarkable oxygen reduction reaction (ORR) activity in both acidic and alkaline media. Particularly, the Co10–NMCV catalyst exhibits a more positive onset voltage of −0.13 V (only 50 mV deviation from Pt/C), a higher half-wave potential of −0.18 V (only 20 mV deviation from Pt/C), and better selectivity (electron-transfer number >3.92) for the ORR in alkaline medium. Meanwhile, the Co10–NMCV catalyst also shows higher durability of the ORR catalytic activity and better methanol tolerance than the commercial Pt/C catalyst. The unprecedented performance of the Co10–NMCV catalyst in ORR is attributed to the homogeneous distribution of abundant Co–N active sites (having the dominant effect for the ORR catalytic activity) on the surface of the MCV matrix (which has the onion-like lamellar structure, high specific surface area, and large pore volume), which observably enhance the active site density of the Co10–NMCV catalyst. All experimental results demonstrate that the Co10–NMCV catalyst may be exploited as the potentially efficient and inexpensive non-noble metal ORR catalyst to replace Pt-based catalysts.