Nafion/ Clay Nanocomposites as BioFuel Cells Membranes

Biofuel cells (BFCs) are a mimic of biological systems that use bacteria as the catalysts to oxidize organic and inorganic matter and generate green electricity. Proton exchange membranes (PEMs) are often used in BFCs to provide protonic communications between anode and cathode chambers and acts as a separator. Nafion is presently an important candidate as a fast proton transporting membrane in fuel cells. Nafion has been applied also in BFCs. However, application of Nafion in BFCs has been confronted with operational problems. Nafion transports cation species other than protons as well, and in BFCs concentrations of other cation species are about five orders of magnitude higher than the proton concentration. Thus during operation of an BFC mainly cation species other than protons were transport through the membrane, which resulted in accumulation of these cations and increased conductivity in the cathode side. Furthermore, protons are consumed in the cathode reaction and resulted in a decreased fuel cells performance. In order to architecture of Nafion nanochannels for confined cations cross-over, we seek to create Nafion/ organically modified montmorillonite (OMMT) nanocomposite membranes and report structure–property information that will be of use to the membrane community in consideration of applications in BFCs. To prepare a composite membrane, a desired amount of prepared OMMT (Closite^®15A, Southern Clay Product Inc.) was added to a 5 wt% Nafion solution (DuPont), and then stirred and degassed by ultrasonication. The contents of OMMT were varied in 0.5–10wt%. The membranes prepared using the solution cast technique. X-Ray Diffraction spectra approved producing of exfoliated nanocomposite. Water uptake and proton conductivities of these membranes were investigated in terms of various OMMT loading weight. Then two-chambered microbial fuel cell were constructed using two media bottles joined with a glass tube containing a PEM as a separator. Anode and cathode electrodes were made of Toray carbon paper (TGPH-120, E-TEK), the cathode contained a Pt catalyst, Pt ink is painted directly onto a Na⁺ form of dry membrane and then hot-pressed. The bottles were inoculated using anaerobic sludge  and acetate in a nutrient medium containing (g/L in deionized water, pH7): NH₄Cl, KCl, NaH₂- PO₄.H₂O, Na₂HPO₄ and a trace mineral and vitamin solution. Performances of fabricated nanocomposite membranes are evaluated by using of MFCs' polarization curve to compare the performance of fabricated membranes. Results showed significant increment in power density in compared with unfilled Nafion and consequently, confirmed the utilization of nanocomposite membranes in MFCs application.