Long-term evaluation of deposited polyaniline on commercial carbon felt used as anode in Microbial Fuel Cells

Microbial Fuel Cell (MFC) are bio-electrochemical systems that directly convert chemical energy of organic compounds into electricity via microbial metabolism. To date, the process of electron transfer from bacteria to anode represents a bottleneck for efficient energy generation from MFC. Recently, conductive polymers in combination with carbon materials showed remarkable improvement on power densities; however many of those studies have been done in a short-term evaluation of MFC performances. Focused on this, the aim of this study is to evaluate the effects of polyaniline deposition on carbon felt called C-PANI as anode material in a long-term period on the increase of the electrical conductivity and the capacity to harvest electrons; in otherwords the possibility of the MFC to generate electrical energy, not only to have an higher electrical power device. Tests were conducted in a two-compartment laboratory prototype MFC in continuous mode for more than 3 months at room temperature (22 ± 2 °C). In the anodic chamber, a mixed microbial population naturally present in sea water was employed as active microorganisms and sodium acetate (1 g.L-1 per day) in buffer solution was continuously fed as substrate. In the cathodic chamber, carbon felt was used as electrode material and potassium ferricyanide in buffer solution as an electron acceptor. Conductivity, redox potential and pH were continuously measured in the anodic solution. Electrochemical characterization were performed as a follow: (i) polarization curves: Linear Sweet Voltammetry, Current Interrupt and Electrochemical Impedance Spectroscopy and (ii) current and voltage under an external resistance of 1000 Ω were recorded to evaluate the electrical energy produced. Results showed that initially C-PANI given a power of 520 mW•m-2 compared to the pristine carbon felt of 60 mW.m-2 induced an important increase on the maximum power density, while the energy production were of 1740 J and 1640 J, respectively. However, the performances of C-PANI anode decreased continuously and comparable results were obtained either for treated or no-treated anode after 3 months of operation suggesting a possible degradation due to physical and/or biological attack of polyaniline during the time course of test.