Tokuji Ikeda

A high-power glucose /oxygen biofuel cell operating under quiescent conditions

Biofuel cells are a next-generation energy device because they use renewable fuels with high energy density and safety. We have developed passive-type biofuel cell units, which generate a power over 100 mW (80 cm3, 39.7 g). Our biofuel cell, in which two-electron oxidation of glucose and four-electron reduction of O2 occurs at pH 7 in mediated bioelectrochemical processes under quiescent conditions, accomplished the maximum power density of 1.45 ± 0.24 mW cm−2 at 0.3 V. This performance was achieved by introducing three technologies: (1) Enzymes and mediator are densely entrapped on carbon-fiber electrodes with the enzymatic activity retained, (2) the concentration of buffer in electrolyte solution was optimized for the immobilized enzymes, and (3) the cathode structure was designed to supply O2 efficiently. The cell units with a multi-stacked structure successfully operate a radio-controlled car (16.5 g), which demonstrates the potential of biofuel cells in practical applications.

Kinetic Analysis of Glucoamylase-Catalyzed Hydrolysis of Starch Granules from Various Botanical Sources

The kinetics of glucoamylase-catalyzed hydrolysis of starch granules from six different botanical sources (rice, wheat, maize, cassava, sweet potato, and potato) was studied by the use of an electrochemical glucose sensor. A higher rate of hydrolysis was obtained as a smaller size of starch granules was used. The adsorbed amount of glucoamylase on the granule surface per unit area did not vary very much with the type of starch granules examined, while the catalytic constants of the adsorbed enzyme (k 0) were determined to be 23.3±4.4, 14.8±6.0, 6.2±1.8, 7.1±4.1, 4.6±3.0, and 1.6±0.6 s−1 for rice, wheat, maize, cassava, sweet potato, and potato respectively, showing that k 0 was largely influenced by the type of starch granules. A comparison of the k 0-values in relation to the crystalline structure of the starch granules suggested that k 0 increases as the crystalline structure becomes dense.