(619ag) Viologen-Catalyzed Carbohydrate Oxidation for Biofuel Cell Applications

Biomass has potential as a renewable source of electricity, but currently faces a number of challenges that inhibit its suitability for widespread use. One method of converting carbohydrates to electricity is with a biofuel cell. However, such fuel cells have been plagued by low reaction rates and incomplete conversion of the carbohydrate. Viologens are stable, non-biological catalysts that appear to enable nearly complete carbohydrate conversion. The process consists of a homogeneous reaction between viologen catalyst and the carbohydrate in solution, coupled with a second reaction (electrochemical or with oxygen) for re-oxidation of the catalyst. The purpose of this study is to investigate and quantitatively describe the reaction between the catalyst and the carbohydrate. To do so, experiments were performed as a function of temperature for a variety of carbohydrates obtainable from cellulose and hemicellulose at different molar ratios of viologen to carbohydrate. The rate of the reaction was tracked by spectroscopic measurement of the viologen concentration as a function of time. In addition, the extent of carbohydrate conversion was determined from the reaction products with use of 13C NMR. The reaction was observed to proceed rapidly for all of the biofuels tested; the most rapid rates measured were for the carbohydrates with fewer carbons. Of particular note is the observation of carbohydrate conversion >80% complete (i.e., ~20 of 24 electrons released from glucose). Finally, a comprehensive kinetic model was developed for the oxidation of carbohydrates by a viologen catalyst under anaerobic conditions. The results of this study support the feasibility of using viologen-catalyzed carbohydrate oxidation in a biofuel cell for power generation, and provide quantitative data needed for initial reactor design.