Electron delocalization during the oxidation-reduction cycle of FAD and NAD: a quantum chemical approach to the design of coenzyme-immobilized bioanode for biochemical fuel cells

Abstract

A biochemical fuel cell (BFC) is an electrochemical power-generating device which converts the chemical energy of a hydrogen-rich fuel (alcohol, glucose, hydrocarbons, or hydrogen itself) into electrical energy through enzyme-catalyzed oxidation-reduction reactions. The major bottleneck in the design of such systems is the slow electron transport from the substrate to the electrode. Biochemical systems that use coenzymes such as flavin adenine dinucleotide (FAD) or nicotinamide adenine dinucleotide (NAD) seem to be promising in circumventing these difficulties. We have made systematic molecular orbital calculations at the indo level on the electron flow diagrams of flavin and nicotinamide rings during their oxidation-reduction cycle. We observe from such calculations that it is possible to obtain very efficient electron transport from the coenzyme to the electrode surface by immobilizing FAD or NAD through semiconducting side chains at certain selected positions to the electrodes such as graphite. The theoretical studies have helped in the design of coenzyme-immobilized anodes which show the expected redox cycles in cyclic voltammetric studies.