Manganese–polypyrrole–carbon nanotube, a new oxygen reduction catalyst for air-cathode microbial fuel cells

A novel manganese–polypyrrole–carbon nanotube (Mn–PPY–CNT) composite is synthesized and demonstrated as an efficient and stable cathode catalyst for oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). The Mn–PPY–CNT composite is prepared by solvothermal method and comprehensively characterized. Subsequently, electro-catalytic capability of this novel catalyst in neutral electrolyte has been investigated by cyclic voltammetry, showing that Mn–PPY–CNT can catalyze ORR in neutral medium with quite good activity, possibly due to manganese–nitrogen (Mn–N) active sites. To further verify catalytic capability of the Mn–PPY–CNT composite, it has been utilized as the cathode catalyst in air-cathode MFCs. It has been found that Mn–PPY–CNT-based MFCs yield efficient and stable performance with maximum power density of 169 mW m−2 at the loading of 1 mg cm−2, and 213 mW m−2 at the loading of 2 mg cm−2, comparable to MFCs with the benchmark platinum/carbon black (Pt/C) catalyst. Furthermore, the catalyst shows good long-term stability which is essential for MFC study. This is the first study regarding the manganese–heterocycle polymer composite as a new ORR catalyst, and it has successfully demonstrated that using cheap Mn–PPY–CNT catalyst instead of Pt/C could improve the feasibility of scaling up MFCs for practical applications.