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 (Rint) using two methods (polarization curve, PolC, and impedance spectroscopy, IS); and (ii) to evaluate the effect of operation temperature (35 and 23°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 ξ, 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 Rint of MFC-A was consistently lower than that of MFC-B at 23oC, irrespective of the method, indicating the advantage of the design A. Rint 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. Rint of MFC-A determined by PolC at 35oC resulted 65% lower than that of MFC-A. The effect of temperature on Rint was distinct, depending upon the type of cell; decrease of temperature was associated to an increase of Rintin 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 PV 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 PV was ascribed to the combined effects of increased ξ and decrease of Rint. In spite of opposing trends in cells’ Rint, performance of both cells in terms of PVave 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°C could be saved by operation at ambient temperature
internal resistance; impedance spectroscopy; microbial fuel cell; polarization curve; temperature
ICYTDF and CINVESTAV-IPN (Mexico) partial financial support to this research is gratefully acknowledged. ALV-L received a graduate scholarship from CONACYT, Mexico. The authors wish to thank the Editor, Associate Editor, and Referees, for their proactive comments that allowed for significant improvement of the manuscript. The excellent help with chromatographic analysis of Mr. Cirino Rojas of Central Analítica, Dept. Biotechnology and Bioengineering, CINVESTAV del IPN, the technical assistance of Mr. Rafael Hernández-Vera from the Environmental Biotechnology and Renewable Energy R&D Group and personnel from the Fuel Cell and Hydrogen Group of CINVESTAV is much appreciated.
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