Sensitisation of semiconducting electrodes with ruthenium-based dyes

Abstract
Practical photoelectrolysis of water by sunlight requires the development of suitable semiconductor electrodes. One approach is the photosensitisation of wide-bandgap oxide semiconductors by the chemical attachment of a suitable dye to the surface. We report on the photosensitisation of n-TiO2, n-SrTiO3 and n-SnO2 with chemically attached Ru(bipy)2(bpca) in which the 2,2′-bipyridine-4,4′ dicarboxylic acid (bpca) is chemically attached to the semiconductor surface by two ester linkages. Kinetic analysis reveals a surprisingly low quantum efficiency (ηe≈ 0.25%) for electron injection from the photoexcited dye into the semiconductor and a low rate constant for reoxidation of the dye. A suggestion is made how the dye molecule might be designed to improve the situation radically. Some deterioration in performance was observed after illumination of the sensitised electrode for many hours.

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