Effect of nitrogen doping on the catalytic activity of carbon nano-onions for the oxygen reduction reaction in microbial fuel cells

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 49.6 mW m(-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. (C) 2019 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.