Ion exchange membrane cathodes for scalable microbial fuel cells

One of the main challenges for using microbial fuel cells (MFCs) is developing materials and architectures that are economical and generate high power densities. The performance of two cathodes constructed from two low-cost anion (AEM) and cation (CEM) exchange membranes was compared to that achieved using an ultrafiltration (UF) cathode, when the membranes were made electrically conductive using graphite paint and a nonprecious metal catalyst (CoTMPP). The best performance in single-chamber MFCs using graphite fiber brush anodes was achieved using an AEM cathode with the conductive coating facing the solution, at a catalyst loading of 0.5 mg/cm2 CoTMPP. The maximum power densitywas 449 mW/ m2 (normalized to the projected cathode surface area) or 13.1 W/m3 (total reactor volume), with a Coulombic efficiency up to 70% in a 50 mM phosphate buffer solution (PBS) using acetate. Decreasing the CoTMPP loading by 40-80% reduced power by 28-56%, with only 16% of the power (72 mW/m2) generated using an AEM cathode lacking a catalyst. Using a current collector (a stainless steel mesh) pressed against the inside surface of the AEM cathode and 200 mM PBS, the maximum power produced was further increased to 728 mW/m2 (21.2 W/m3). The use of AEM cathodes and brush anodes provides comparable performance to similar systems that use materials costing nearly an order of magnitude more (carbon paper electrodes) and thus represent more useful materials for reducing the costs of MFCs for wastewater treatment applications.