Improved fuel cell and electrode designs for producing electricity from microbial degradation

Abstract

Abstract A new one‐compartment fuel cell was composed of a rubber bunged bottle with a center‐inserted anode and a window‐mounted cathode containing an internal, proton‐permeable porcelain layer. This fuel cell design was less expensive and more practical than the conventional two‐compartment system, which requires aeration and a ferricyanide solution in the cathode compartment. Three new electrodes containing bound electron mediators including a Mn 4+ ‐graphite anode, a neutral red (NR) covalently linked woven graphite anode, and an Fe 3+ ‐graphite cathode were developed that greatly enhanced electrical energy production (i.e., microbial electron transfer) over conventional graphite electrodes. The potentials of these electrodes measured by cyclic voltametry at pH 7.0 were (in volts): +0.493 (Fe 3+ ‐graphite); +0.15 (Mn 4+ ‐graphite); and −0.53 (NR‐woven graphite). The maximal electrical productivities obtained with sewage sludge as the biocatalyst and using a Mn 4+ ‐graphite anode and a Fe 3+ ‐graphite cathode were 14 mA current, 0.45 V potential, 1,750 mA/m 2 current density, and 788 mW/m 2 of power density. With Escherichia coli as the biocatalyst and using a Mn 4+ ‐graphite anode and a Fe 3+ ‐graphite cathode, the maximal electrical productivities obtained were 2.6 mA current, 0.28 V potential, 325 mA/m 2 current density, and 91 mW/m 2 of power density. These results show that the amount of electrical energy produced by microbial fuel cells can be increased 1,000‐fold by incorporating electron mediators into graphite electrodes. These results also imply that sewage sludge may contain unique electrophilic microbes that transfer electrons more readily than E. coli and that microbial fuel cells using the new Mn 4+ ‐graphite anode and Fe 3+ ‐graphite cathode may have commercial utility for producing low amounts of electrical power needed in remote locations. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 81: 348–355, 2003.

Key findings

• ▸The new one-compartment fuel cell design is less expensive and more practical than the conventional two-compartment system.
• ▸The new electrodes with bound electron mediators (Mn4+-graphite anode, NR-covalently linked woven graphite anode, and Fe3+-graphite cathode) greatly enhanced electrical energy production compared to conventional graphite electrodes.
• ▸The maximal electrical productivities obtained with sewage sludge as the biocatalyst were 14 mA current and 0.45 V using a Mn4+-graphite anode and a Fe3+-graphite cathode.

Keywords

Identifiers

DOI

10.1002/bit.10501

Journal

Biotechnology and Bioengineering

Year

2002