Internal Resistance and performance of Microbial Fuel Cells: Influence of Cell Configuration and Temperature

The objectives of this work were (i) to determine the effect of electrode spacing and architecture of microbial fuel cells (MFCs) on their internal resistance (R-int) using two methods (polarization curve, PolC, and impedance spectroscopy, IS); and (ii) to evaluate the effect of operation temperature (35 and 23 degrees C) of MFCs on their internal resistance and performance during batch operation. Two types of MFCs were built: MFC-A was a new design with extended electrode surface (larger xi specific surface or surface area of electrode to cell volume) and the assemblage or "sandwich" arrangement of the anode-PEM-cathode (AMC arrangement), and a standard single chamber MFC-B with separated electrodes. In a first experiment R-int of MFC-A was consistently lower than that of MFC-B at 23 degrees C, irrespective of the method, indicating the advantage of the design A. R-int determined by the two methods agreed very well. The method based on IS provided more detailed data regarding resistance structure of the cells in only 10% of the time used by the PolC R-int, of MFC-A determined by PolC at 35 degrees C resulted 65% lower than that of MFC-A. The effect of temperature on R-int, was distinct, depending upon the type of cell; decrease of temperature was associated to an increase of R-int, in cell A and an unexpected decrease in cell B. In a second experiment, the effect of temperature and cell configuration on cell batch performance was examined. Results showed that performance of MFC-A was significantly superior to that of MFC-B. Maximum volumetric power P-V and anode density power PAn of the MFC-A were higher than those of the MFC-B (4.5 and 2.2 fold, respectively). The improvement in P-V was ascribed to the combined effects of increased and decrease of R-int. In spite of opposing trends in cells' R-int, performance of both cells in terms of P-V ave, improved at ambient temperature; furthermore, MFC-A outcompeted the standard cell B at both temperatures tested. The use of the new cell A would translate into a significant advantage since the power associated to heating the cells at 35 degrees C could be saved by operation at ambient temperature.