Morphology-dependent Performance of Nanostructured MnO2 as an Oxygen Reduction Catalyst in Microbial Fuel Cells

Different nanostructures (nanoflowers, nanorods and nanotubes) of manganese dioxide (MnO2) were successfully synthesized using hydrothermal methods with different dwell times and were demonstrated to be efficient and stable cathode catalysts for the oxygen reduction reaction (ORR). Subsequent examination of these nanostructures using field-emission scanning electron microscopy and transmission electron microscopy revealed a strong correlation between the dwell time and the resulting morphology of the nanostructures and confirmed the successful synthesis of nanotubes. The electrocatalytic activities of the different nanostructures were investigated using cyclic voltammetry and linear sweep voltammetry, and the results indicated that all of the MnO2 nanostructures can catalyze the ORR with different catalytic activities. The nanotubes appeared to possess the highest catalytic activity, with a more positive peak potential and a larger ORR peak current. Additionally, a maximum power density of 11.6 W/m(3) was produced by the microbial fuel cell (MFC) with the nanotube cathode, which was higher than that of the other nanostructures and comparable to that of Pt/C (14.1 W/m(3)). The results of this study demonstrate that nanotubes are ideal crystal structures for MnO2 and that they offer a good alternative to Pt/C for practical MFC applications.