Evaluating Enzyme Cascades for Methanol/Air Biofuel Cells Based on NAD+-Dependent Enzymes

Previous work by the group has entailed encapsulating enzymes in polymeric micelles at bioelectrode surfaces by utilizing hydrophobically modified Nafion membranes, which are modified in order to eliminate the harsh acidity of Nafion while tailoring the size of the polymer micelles to optimize for the encapsulation of an individual enzyme. This polymer encapsulation has been shown to provide high catalytic activity and enzyme stability. In this study, we employed this encapsulation technique in developing a methanol/air biofuel cell through the combined immobilization of NAD(+)-dependent alcohol dehydrogenase (ADH), aldehyde dehydrogenase (AldDH) and formate dehydrogenase (FDH) within a tetrabutylammonium bromide (TBAB) modified Nafion to oxidize methanol to carbon dioxide with poly(methylene green) acting as the NADH electrocatalyst electropolymerized on the surface of the electrode. The methanol biofuel/air cell resulted in a maximum power density of 261 +/- 7.6 mu W/cm(2) and current density of 845 +/- 35.5 mu A/cm(2). This system was characterized for the effects of degree of oxidation, temperature, pH, and concentration of fuel and NAD.