Manganese dioxide-coated carbon nanotubes as an improved cathodic catalyst for oxygen reduction in a microbial fuel cell

摘要

To develop an efficient and cost-effective cathodic electrocatalyst for microbial fuel cells (MFCs), carbon nanotubes (CNTs) coated with manganese dioxide using an in situ hydrothermal method (in situ MnO_2/CNTs) have been investigated for electrochemical oxygen reduction reaction (ORR). Examination by transmission electron microscopy shows that MnO_2 is sufficiently and uniformly dispersed over the surfaces of the CNTs. Using linear sweep voltammetry, we determine that the in situ MnO_2/CNTs are a better catalyst for the ORR than CNTs that are simply mechanically mixed with MnO_2 powder, suggesting that the surface coating of MnO_2 onto CNTs enhances their catalytic activity. Additionally, a maximum power density of 210mWm~2 produced from the MFC with in situ MnO_2/CNTs cathode is 2.3 times of that produced from the MFC using mechanically mixed MnO_2/CNTs (93 mW m~(-2)), and comparable to that of the MFC with a conventional Pt/C cathode (229mWm~(-2)). Electrochemical impedance spectroscopy analysis indicates that the uniform surface dispersion of MnO_2 on the CNTs enhanced electron transfer of the ORR, resulting in higher MFC power output. The results of this study demonstrate that CNTs are an ideal catalyst support for MnO_2 and that in situ MnO_2/CNTs offer a good alternative to Pt/C for practical MFC applications.