Development of alcohol/O2 biofuel cells using salt-extracted tetrabutylammonium bromide/Nafion membranes to immobilize dehydrogenase enzymes

Quaternary ammonium bromide salt-treated Nafion membranes provide an ideal environment for enzyme immobilization. Because these quaternary ammonium bromide salt-treated Nafion membranes retain the physical properties of Nafion and increase the mass transport of ions and neutral species through the membrane, they are also ideal for modifying electrodes. Therefore, high current density bioanodes are formed from poly(methylene green) (an electrocatalyst for NADH) modified electrodes that have been coated with a layer of tetrabutylammonium bromide salt-treated Nafion with dehydrogenase enzymes immobilized within the layer. Ethanol/O2 biofuel cells employing these bioanodes have yielded power densities of 1.16 mW/cm2 with a single-enzyme system (alcohol dehydrogenase) and 2.04 mW/cm2 with a double-enzyme system (alcohol dehydrogenase and aldehyde dehydrogenase) in the polymer layer. Methanol/O2 biofuel cells employing these bioanodes have yielded power densities of 1.55 mW/cm2 and open circuit potentials of 0.71 V.