Carbon nanotube supported MnO₂ catalysts for oxygen reduction reaction and their applications in microbial fuel cells.

Three types of manganese dioxide, alpha-MnO2, beta-MnO2, gamma-MnO2 were tested as alternative cathode catalysts for oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). Prepared by solution-based methods, the MnO2 nanomaterials were comprehensively characterized, and their electrocatalytic activities in neutral electrolyte were investigated with the supporting material of carbon nanotubes (CNTs) by cyclic voltammetry (CV). The CV results showed that all MnO2 species could catalyze ORR in neutral NaCl solution with different catalytic activities. beta-MnO2 had the highest catalytic activity due to its intrinsic structure and better interaction with CNTs. Three MnO2 species were further used as cathode catalysts under optimized conditions in air-cathode cubic MFCs, in which mixed culture was inoculated as biocatalysts and domestic wastewater was used as the substrate in the anode chamber. It was also found that beta-MnO2 based MFC yielded the best performance with a power density of 97.8 mW m(-2) which was 64.1% that of the Pt-based MFC, and a lower internal resistance of 165 Omega. Furthermore, the COD removal efficiency of beta-MnO2 based MFC was estimated as 84.8%, higher than that of the Pt-based MFC. This study demonstrated that using beta-MnO2 on CNT support instead of Pt could potentially improve the feasibility of scaling up air-cathode MFCs for practical applications by lowering the material cost. (C) 2011 Elsevier B.V. All rights reserved.