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H2 production from a water–acetonitrile mixed solution containing iodide electron donor was investigated over dye-sensitized Pt/TiO2 photocatalysts under visible light irradiation. Merocyanine and coumarin dyes were utilized as photosensitizers. The rates of H2 evolution, which decreased with the increasing water amount in the mixed solutions, were ascribed to the decrease in energy gap between the redox potential of I3−/I− and the HOMO level of the dye. The observed high rate of H2 production even in an aqueous solution over a coumarin-sensitized Pt/TiO2 photocatalyst shows that the dye has a sufficiently positive HOMO level relative to the oxidation potential of I−. [Copyright &y& Elsevier]

Direct water splitting into H2 and O2 over Pt-loaded semiconductor photocatalysts such as Pt–TiO2 was investigated. We found that addition of a small amount of iodide anion, I−, into the aqueous suspension of Pt–TiO2–anatase photocatalyst significantly improved the splitting into H2 and O2 with a stoichiometric ratio. The iodide anion was adsorbed preferentially onto Pt co-catalyst as iodine atom, I. This iodine layer effectively suppressed the backward reaction of water formation from H2 and O2 to H2O over the Pt surface. [Copyright &y& Elsevier]

Hydrogen production from aqueous mixture of I− and acetonitrile using dye-sensitized Pt/TiO2 photocatalyst was investigated under visible light irradiation. It was found that energetically uphill H2 formation with a high quantum efficiency (∼2%) took place using a merocyanine dye-sensitized Pt/TiO2 photocatalyst and an I− electron donor in an acetonitrile–water mixture (AN:H2O=95:5 by volume) under visible light irradiation (λ>440 nm). Addition of acetonitrile, which is a good solvent for I− and merocyanine dye, significantly improved H2 evolution. [Copyright &y& Elsevier]

Anodic photocurrent loss processes have been investigated for dye sensitized nanocrystalline SnO2 and TiO2 solar cells by means of electrical bias dependent photocurrent spectroscopy. Electron injection efficiency is not dependent on visible excitation wavelengths under electrical bias application for both films. Under an identical cell configuration, the unsensitised SnO2 film exhibited cathodic photocurrent generation while no cathodic photocurrent was detected for the TiO2 film. The origins of these observations are discussed. The experimental results suggest that the electron transfer reaction from the SnO2 to the electrolyte must be accelerated at the SnO2 surface by the bias application. [Copyright &y& Elsevier]