Converting Low-grade Biomass to Produce Energy Using Bio-fuel Cells

Aerobic and anaerobic respiration of microorganisms involves redox reactions that provide energy for cell growth or maintenance. The energy comes from breaking up chemical bonds during the oxidation of organic carbons by the microorganisms. The electrons released from the oxidation are taken up by the reduction of an oxidant such oxygen, sulfate, nitrate, etc. If the oxidation and reduction reactions occur at the same place, for example, the cytoplasm of microbial cells, no electricity is produced. The energy produced will be used for cell growth or maintenance. The rest will be released as low-grade heat that cannot be harvested cost-effectively. Electrochemically, digestion of organic carbons can be split into anodic (organic carbon oxidation) and cathodic (proton reduction) reactions to produce an electric current that can be harvested when electrons from the oxidation reaction is donated to the anode and fl ow through an external circuit before be utilized by the reduction reaction at the cathode. Bio-fuel cells are classifi ed into two different categories. One is the so-called microbial fuel cell (MFC) that relies on a microbial biofi lm to provide enzyme catalysis to the anodic reaction while the other utilizes a cell-free enzyme system for catalysis. The recent energy crisis and concerns over global warming have reinvigorated interests in Y. Zhou (ed.), Ecoand Renewable Energy Materials © Science Press Beijing and Springer-Verlag Berlin Heidelberg 2013 Ecoand Renewable Energy Materials 74 bio-fuel cells because their potential applications in electricity generation and biohydrogen production from renewable sources that are often low-cost or zerocost wastes. Currently, the bottleneck of real-world applications of bio-fuel cells in harnessing energy lies in their low power density and high costs, thus limiting their uses to powering small sensors or devices that require very little power. Numerous interesting and innovative approaches have been reported to increase the performances and to reduce reactor construction and operating costs of biofuel cells. Although signifi cant hurdles remain ahead, new progresses are making bio-fuel cells closer to eventual practical applications utilizing low-grade biomass. This book chapter reviews various recent advances in bio-fuel cell research using various biomass feed stocks.