Deriving electrical energy from glucose and other carbohydrates under mild conditions is an important research objective because these biomolecules are abundant, renewable, have high energy density, and are convenient as fuels. This rich promise has not been realized because stable, inexpensive, and efficient catalysts are not available to oxidize carbohydrates and transfer all or nearly all of their electrons to fuel cell anodes. We report here that viologen catalysts meet these demanding criteria by catalytically oxidizing glucose and other carbohydrates in a mildly alkaline solution, making possible a direct carbohydrate fuel cell. Formate and carbonate are major products of carbohydrate oxidation, demonstrating that extensive carbon–carbon bond breaking has occurred. A rudimentary fuel cell utilizing viologen catalysts and glucose or dihydroxyacetone as fuels demonstrated electrical power production at up to 20mA/cm2 superficial current density. Improved catalyst function and cell design should significantly advance the efficiency and viability of direct carbohydrate fuel cell technology as a means of generating electrical energy from renewable biomass.

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Dialkyl viologens are known to be effective catalysts in the oxidation of carbohydrates under alkaline conditions and are being investigated for use in direct-carbohydrate fuel cells (DCFCs). However, dialkyl viologens hydrolyze to more stable monoalkyl viologens under alkaline conditions. It has been reported that monoalkyl viologens also act as catalysts for the oxidation of carbohydrates, but little was known about the electrochemistry of monoalkyl viologens. Other researchers have investigated the redox dyes indigo carmine and methylene blue for use in DCFCs. In the present report monoalkyl, aminoalkyl, and dialkyl viologens, as well as indigo carmine and methylene blue, were examined using the method of cyclic voltammetry. These species were tested in acetonitrile, dimethyl sulfoxide, and water. Redox potentials, diffusion coefficients, and heterogeneous electron-transfer rate constants are all reported. Stability in alkaline solution and aqueous solubility are also examined in a semi-quantitative fashion. A comparison between viologens and the other redox dyes is made and recommendations are given on the use of viologens as catalysts.

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Investigation of viologen-based organic catalysts has shown them to be capable of directly oxidizing various sugars. Methyl viologen has been studied using oxygen uptake vial experiments, NMR analysis, and electrochemical methods. We have found that under appropriate conditions this catalyst is capable of completely oxidizing glucose to form carbonate. The preliminary performance of this catalyst in an alkaline fuel cell is also demonstrated.