View of Saccharide Fuel Cells for Power, Capacity and Energy Densities

Carbohydrates such as glucose and saccharides are attractive as sustainable energy sources for use in fuel cells.Output characteristics, that is, power density, specific discharge capacity and energy density of various saccharide fuel cells were summarized and comprehensively explained.Fuel cell performances of monosaccharides (D-and L-glucose, D-galactose, and D-fructose), disaccharides (maltose, isomaltose, cellobiose, lactose, melibiose, sucrose and trehalose), oxidized-glucoses (gluconic, glucaric, glyoxylic, and oxalic acids), glucitol (sorbitol), and artificial sweetener (sucralose) were examined using PEDOT: PSS, SWCNT and PtRu composite anode/Pt cathode.D-glucose's maximum power density (Pmax) was 30.8 mW cm -2 , the largest value, and that of L-glucose and D-galactose was approximately the same.The Pmax of D-fructose was half that of D-glucose.The Pmax of oxidized glucose acids and sorbitol was comparable to or slightly less than that of glucose.By contrast, the Pmax of disaccharides was less than half that of glucose, indicating a lower diffusion rate of disaccharides in the fuel solution.The Pmax of sucrose and trehalose was less than one-hundredth that of glucose, consistent with the property of non-reducing sugar.The specific discharge capacities (Qout) of D-glucose and oxidized-glucoses indicated a multi-electron cascade reaction of glucose to generate CO2.The amount of CO2, which was evaluated from the reaction products, was consistent with the number of C atom in fuel molecules.The specific energy density ( out) of glucose was observed to be 803 Wh kg -1 upon slow rate discharge, which is approximately 19 % of the theoretical energy density (4,430 Wh kg -1 ).Qout and out of the disaccharides were less than half as high as those of monosaccharide, indicating that only a single glucose unit of disaccharides was oxidized.Driving solar motor and LED by glucose fuel cell was demonstrated, and the performance was discussed based on the current-voltage characteristics.