(453d) Homogeneous Reaction Kinetics of Carbohydrates with Viologen Catalysts in Biofuel Cell Applications

Renewable resources, which continue to grow in utilization, still have many sustainability challenges related to economics, efficiency, supplies, and storage. Thus, continued efforts are needed to address these and other challenges to optimize the use of renewable energy. One area of exploration is the development of fuel cells, which includes biofuel cells that utilize biomass as the feedstock. This work focuses on utilizing carbohydrates, a biomass constituent, as the feedstock.

Catalysts are used in biofuel cells to enhance the energy extraction efficiency by facilitating the transfer of electrons from the carbohydrate to the anode of the biofuel cell. Based on early work in our research group, viologens have been shown to be effective catalysts in facilitating the electron transfer. However, process optimization of the catalyst is needed to provide the greatest electron transfer rates and associated efficiency. Thus, it is important to characterize how the process environment affects the rate of electron transfer.

Characterization of the homogeneous rate of electron transfer from the carbohydrate to the viologen will be presented. The heterogeneous rate of electron transfer from the viologen to the electrode will only be briefly discussed. Initial reaction rates of electron transfer from the carbohydrate to the viologen were studied in an anaerobic system as a function of pH, temperature, incubation time, type and concentration of carbohydrate (ranging from C3 to C6 carbohydrates), viologen concentration, and carbohydrate incubation time. A mechanistic model was developed to characterize the reaction rate. Model and experimental measurements showed excellent agreement. Studies were also performed to measure the rate at which different viologens decompose since decomposition can reduce process efficiencies. Decomposition rates were experimentally determined and fit to a mechanistic model. The electron transfer rates and decomposition rates were combined to show process conditions that would minimize the impact of decomposition on the biofuel cell process. With knowledge of these mechanistic models, estimates on the potential energy production of biofuel cells utilizing carbohydrates and viologens will be presented.