Fundamental Studies of the Construction of Biocatalyst-Based Super-Bio-Fuel Cells

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Basic researches have been done of a bioelectrochemical fuel cells, which is a new fuel cell system utilizing biocatalysts in place of metal catalysts such as Pt.1)We have first demonstrated that bilirubin oxidase is a promising enzyme catalyst to achieve four electron reductions of dioxygen to water at neutral pH in the biocathode reaction with a mediator compound. We have also discovered that bilirubin oxidase directly accept electrons from several kinds of carbon electrodes to produce cathodic current of significan magnitude for the reduction of oxygen to water.2)We have for the first time constructed a bioelectrocatalysis-based dihydrogen/dioxygen fuel cell operating at physiological pH, in which bilirubin oxidase enzyme and desulfovibrio vulgaris bacterial cells are used as biocatalysts.3)Bio-anode reactions using PQQ-dependent glucose dehydrogenase and diaphorase as catalysts, respectively, have successfully combined with the bilirubin oxidase-based bio-cathode reaction to construct bio fuel cells for glucose and NADH.4)A new hydrogen production system has been proposed which uses a scarifying reagent such as glucose or ethanol in electrolytic hydrogen production. Electrolytic production of hydrogen can be achieved with very small overpotential when desulfovibrio vulgaris catalyzed electrocatalytic reduction of proton at a biocathode is combined with e.g. glucose dehydrogenase catalyzed oxidation of glucose at a bioanode.5)Photosynthetic bioelectrochemical cell utilizing cyanobacteria and water-generating oxidase produces photocurrent by the illumination of the anode compartment. This is a kind of ideal photo cell relying on the simple chemical reaction : 2H_2+O_2=2H2O. However, the stability of the biocatalysts and the low conversion efficiency of light energy remain to be serious problems.