Enzyme Electrodes — A Prelude to Utilizing Hydrogen or Hydrogen Rich Fuels in Biochemical Fuel Cells

Abstract

Hydrogen and hydrogen rich compounds such as methane, methanol, ethanol, etc. are used as fuels in fuel cells for generation of electricity. The generally high temperatures of operation of fuel cells limit the half-lives of the electrodes and as a result, the magnitude and stability of the power output. The problem becomes more severe with the realization that attainment of higher fuel cell efficiency may require the use of even higher cell temperatures. With enzymes, it is possible to bring down the operating temperatures and pressures to ambient conditions. Hydrogenase, the enzyme that catalyzes the oxidation of hydrogen, seems to be an ideal candidate for most of hydrogen-oxygen type of fuel cells. However, since the study of hydrogenase is still a subject of basic research, it is essential that a well studied system may be used as a model. Glucose oxidase (GOD) is one such system which has been well characterized otherwise. In our laboratory, the enzyme has been immobilized on carbon electrodes, a conjugated double bond chain serving as a spacer between FAD — its coenzyme, and the electrode. This GOD immobilized electrode serves as a bioanode. At the cathode, where oxygen is reduced, the cytochrome C oxidase (COD) system has been chosen as the catalyst. This enzyme was copolymerized on carbon electrodes along with bovine serum albumin. The half-cell potentials of the GOD and COD are found to be −0.75 V and +0.1 V respectively. We are, at present, attempting to use these enzyme electrodes in biochemical fuel cells.