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Improving the performance of a direct photosynthetic/metabolic bio-fuel cell (DPBFC) using gene manipulated bacteria

In our laboratory, we have developed a mediator-less direct photosynthetic/metabolic bio-fuel cell (DPBFC) in which microparticles of polyaniline were adopted as the electrode material to extract reducing equivalents from bacteria. In this paper, we selected purple photosynthetic bacteria Rhodopesudomonas palustris as a new fuel source which requires organic compounds for photosynthesis and emits hydrogen as a result of nitrogenase activity. To improve the electron generation efficiency of R. palustris, gene manipulation was applied so as to suppress hydrogen emission. We assumed that if hydrogen emission was suppressed, more reducing equivalents would be stored inside R. palustris. As a result, the power density obtained for the mutant was 18.3 µW cm−2, which was higher than for the wild type. In addition, we have prototyped a replaceable medium-type DPBFC for activating R. palustris by replacing the old medium with a fresh one which extended the fuel cell life to 8 h, four times longer than without medium replacement.