Influence of the Cathode Platinum Loading and of the Implementation of Membranes on the Performance of Air-Breathing Microbial Fuel Cells

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The use of catalysts and membranes in microbial fuel cells (MFCs) is rather controversial. Platinum is the best catalyst to improve the oxygen reduction reaction and the implementation of an ion exchange membrane may help to avoid the oxygen leakages from the cathode to the anode compartments and, therefore, the losses of efficiencies associated to the use of oxygen by microorganisms as the immediate electron acceptor. In this work, it is studied the influence of the platinum loading in the cathode and the implementation of membrane on the performance of an air-breathing MFC. To do this, four cells were operated for 50 days in order to clarify the effect of the platinum loading contained in the cathode (0.25, 0.50, 1.00, and 2.00 mg Pt cm−2) and two additional MFCs for more than 100 days in order to evaluate the effect of the membrane on the performance of the MFC. The results obtained point out that the performance of the MFC, in terms of maximum current density and power density from the polarization curves, depends strongly on the Pt content of the cathode. This indicates that under open-circuit conditions the cathode controls the performance. Nonetheless, during the closed-circuit operation (under 120 Ω resistance), the performance is not cathodically limited as there are no significant changes between the four cells. This suggests that the performance of the MFC is limited by the anodic process. Likewise, the separation of the anode and cathode by a membrane attains a faster stabilization of the MFC and a slight improvement in the production of electricity, although for air-breathing MFC, this element does not seem to be as crucial as for other types of MFCs.