Three types of manganese dioxide, α-MnO(2), β-MnO(2), γ-MnO(2) were tested as alternative cathode catalysts for oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). Prepared by solution-based methods, the MnO(2) 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 MnO(2) species could catalyze ORR in neutral NaCl solution with different catalytic activities. β-MnO(2) had the highest catalytic activity due to its intrinsic structure and better interaction with CNTs. Three MnO(2) 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 β-MnO(2) based MFC yielded the best performance with a power density of 97.8 mWm(-2) which was 64.1% that of the Pt-based MFC, and a lower internal resistance of 165 Ω. Furthermore, the COD removal efficiency of β-MnO(2) based MFC was estimated as 84.8%, higher than that of the Pt-based MFC. This study demonstrated that using β-MnO(2) 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.
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