Fuel Cell Technology: Reaching Towards Commercialization

Chapter 9: Microbial Fuel Cells

Ken Noll

9.1 Microbial Fuel Cells

9.1.1 Introduction

Cellular life exists at the interface between electrochemical extremes. The energy of most living cells depends on the transfer of electrons from intracellular, electrically reduced biochemicals to oxidized extracellular acceptors. For almost one hundred years investigators have tried to tap into these processes in microbes for electrical power generation. Efforts have been made to use microbes as complex catalysts to oxidize relatively inexpensive organic and inorganic substrates as fuels in compact spaces in microbial fuel cells (MFCs). However, natural selection does not favor microbial metabolism under such conditions. Evolution has shaped microbes to use their growth substrate efficiently to reproduce under changing environmental conditions. Consequently, they are not optimized for use in MFCs, where electrons derived from substrate oxidation go only to the anode and not to cell growth.

In contrast to conventional fuel cells, MFCs operate under relatively mild conditions, use a wide range of organic fuels, and do not use expensive precious metals as catalysts. However, MFC technology is still rudimentary and there are several areas for improvement [28]. For example, typical MFCs exhibit low coulombic efficiencies due to inefficient electron transfer between the microbial cells and the anode. This inefficiency results in incomplete oxidation of the fuel [7], [14], [50] and undesired assimilation of some of the fuel carbon into biomass [42], [50]. Power output from MFCs may also be limited by the rates of intracellular substrate oxidations [48]. Even though there...

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