Evaluation of Microbial Fuel Cells with Graphite Plus MnO2 and MoS2 Paints As Oxygen Reduction Cathode Catalyst

Abstract

For the improvement of microbial fuel cell (MFC) performance in real wastewater it is necessary to implement catalysts on the cathode. Graphite, MnO2 and MoS2 fulfill the requirements with respect to costs and activity and were evaluated in this work. These materials were prepared by dispersion of MnO2 and/or MoS2 and graphite in a solution of celluloid using butanone as solvent. The mixture is than painted on the surface of stainless steel cathode carriers. The individual maximum output power densities of MFCs were evaluated in dependence of time, see figure (left). Comparing with graphite plus MnO2 coating, the graphite plus MoS2 paint shows a lower power density but much higher long-term stability than graphite plus MnO2 coating. Therefore, the combination of different catalysts (MnO2 and MoS2) is necessary for further improvement of power density. The power density performance of MFCs with different MnO2 plus MoS2 proportions is shown in figure (right). The data suggested that the MFC with mixed catalysts with graphite plus MnO2 plus MoS2 proportion of 20:1:1 possessed the highest power density during experiments (125 mW/m2 at 5th day). The power density of a MFC with mixed catalysts with graphite plus MnO2 plus MoS2 proportion of 30:1:2 possessed the value of 85 mW/m2 at the beginning and descended rapidly after starting operation. By comparing the MFC with mixed catalysts with graphite plus MnO2 plus MoS2 in proportion of 30:2:1, with the power density of the MFC with graphite plus MnO2 plus MoS2in proportion of 20:1:1 it was shown, that the later one is the optimal mixing proportion in our experiments. A RHE is also used in our experiments for measuring the potential of single electrodes. The data are shown in figure (right). It can be seen that the cathode potential of the cell descended significantly during the measurement, while the potential of the anode changed only slightly. These reveals clearly, that the cathode is the rate limiting electrode. Therefore, new forms of cathodes have to be further developed to improve the performance of MFC. Figure 1