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 cm(3), 39.7 g). Our biofuel cell, in which two-electron oxidation of glucose and four-electron reduction of O-2 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 O-2 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.