Power generation by packed-bed air-cathode microbial fuel cells

Catalysts and catalyst binders are significant portions of the cost of microbial fuel cell (MFC) cathodes. Many materials have been tested as aqueous cathodes, but air-cathodes are needed to avoid energy demands for water aeration. Packed-bed air-cathodes were constructed without expensive binders or diffusion layers using four inexpensive carbon-based materials. Cathodes made from activated carbon produced the largest maximum power density of 676 +/- 93 mW/m(2), followed by semi-coke (376 +/- 47 mW/m(2)), graphite (122 +/- 14 mW/m(2)) and carbon felt (60 +/- 43 mW/m(2)). Increasing the mass of activated carbon and semi-coke from 5 to >= 15 g significantly reduced power generation because of a reduction in oxygen transfer due to a thicker water layer in the cathode (similar to 3 or similar to 6 cm). These results indicate that a thin packed layer of activated carbon or semi-coke can be used to make inexpensive air-cathodes for MFCs. (C) 2013 Elsevier Ltd. All rights reserved.