Charge Transport and Catalysis by Molecules Confined in Polymeric Materialsand Application to Future Nanodevices for Energy Conversion

Abstract

Polymeric materials confining functional molecules are one of the most promising materials for designing nanodevices for energy conversion, e.g., solar cells, fuel cells, and artificial photosynthetic devices that are expected to provide a renewable energy resource. Charge transport (CT) and catalysis by redox molecules in polymeric solid materials are reviewed with a focus on a polyanion film, typically Nafion and other polymeric materials, containing excess water. CT in a polyanion film is evaluated based on the physical displacement (physical diffusion) and charge hopping mechanisms between redox molecules. The mechanism of CT is exhibited to depend on the structure and redox reaction of the center molecules, and the influencing factor on CT is discussed. For the polymeric solid reactor containing excess water, the physical data of CT and molecular transport in the bulk matrix are summarized to demonstrate that the electrochemical reaction in the solid reactor occurs similarly as in an aqueous solution. Recent progress in molecular catalysis for multielectron redox reactions with a focus on water oxidation, reduction of proton, and carbon dioxide is introduced, and the catalytic activity and mechanism in solution and polymeric matrixes are reviewed. A dye-sensitized solar cell was fabricated using polymeric solid materials containing excess organic solution as an electrolyte layer, and its performance similar to a liquid-type solar cell is discussed based on the physicochemical data in the polymeric solid materials. Recent approaches toward construction of an artificial photosynthetic system are reviewed, and, finally, concluding remarks and directions for future research are given.