| Two approaches for production of renewable energy, dye-sensitized photoelectrochemical solar cells and biofuel cells, have been combined into a single hybrid cell. First, porphyrin monomers and dyads were studied as sensitizers of nanoparticulate tin dioxide electrodes in photoelectrochemical cells. These photoanodes form part of the hybrid cell. Key to the operation of the cell is the coupling of the anode photoreactions to the oxidation of biological fuels such as glucose or alcohols by a nicotinamide adenine dinucleotide (NAD(P)HINAD(P) +) redox carrier. When the photoanode is irradiated, porphyrin molecules absorb light and generate an excited state energetic enough to inject electrons into the nanoparticulate tin dioxide, thus generating the oxidized form of the sensitizer. Electron donation to the oxidized sensitizer by NAD(P)H is facile, generating NAD(P)+, which is not reduced by charge recombination reactions at the photoanode. Enzymes oxidize the biological fuel, reducing the NAD(P)+ coenzyme back to NAD(P)H. These reactions are coupled to cathodic redox reactions through an ion-permeable membrane in a two-compartment electrochemical cell. The cell design overcomes problems due to high overpotentials for NADH oxidation at the anodes more commonly employed in biofuel cells and does not suffer from energy-wasting reduction of NAD+ at the photoanode. Hybrid cells of this general type have several potential advantages over either the dye-sensitized photoelectrochemical cell or biofuel cells alone. Finally, the redox potentials of several porphyrin and other chromophore components of supramolecular compounds for artificial photosynthesis are reported herein. |
