Abstract
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•N-CNOs used first-time in MFC as a low-cost and energy-efficient cathodic catalyst.•ORR mechanism on N-CNO exhibits a direct four-electron transfer pathway like Pt/C.•N-doping improved electrical conductivity, ORR activity, and MFC performance.•The cost of N-CNO catalyst is approximately 520 times lower than that of Pt/C.•The cost per power for N-CNO is approximately 310 times lower than that for Pt/C.
In this study, highly graphitic nitrogen-doped carbon nano-onions (N-CNOs) were prepared by a one-step, direct, in situ flame synthesis technique and their potential applications as catalysts for oxygen reduction reaction (ORR) in a microbial fuel cell (MFC) were evaluated for the first time. The ORR activity of the CNO, N-CNO, and the commercial Pt/C were measured using a rotating ring-disk electrode (RRDE). The reaction mechanism for the N-CNO was found to follow a four-electron transfer pathway and possess a higher onset potential in RRDE measurement than CNOs. The ORR activity of N-CNO was 5.4 times better than that of CNO, which was attributed to the introduction of nitrogen to the carbon faramework. The MFC fabricated with the N-CNO cathode produced a maximum power density of 49.6mWm–2, which was approximately double the performance of the CNO-based MFC. The performance of N-CNO was low compared to Pt/C but the cost per power was only 1/310th. These results confirmed that N-CNOs could be used as a low-cost alternative and an energy-efficient metal-free ORR catalyst for practical MFC applications.