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/m2, followed by semi-coke (376 ± 47 mW/m2), graphite (122 ± 14 mW/m2) and carbon felt (60 ± 43 mW/m2). 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 (∼3 or ∼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.