Decomposition of water in the separate evolution of hydrogen and oxygen using visible light-responsive TiO2 thin film photocatalysts: Effect of the work function of the substrates on the yield of the reaction

The development of visible light-responsive TiO2 thin films (vis-TiO2) was successfully carried out by applying a radio-frequency magnetron sputtering (RF-MS) deposition method. The Pt-loaded vis-TiO2 thin films clearly showed high potential for the decomposition of water into H2 and O2 by the evolution of H2 from methanol/water as well as O2 from a silver nitrate/water system under both UV and visible light irradiation (λ ≥ 420 nm). These thin films were found to decompose pure water into H2 and O2 stoichiometrically under light irradiation of wavelengths longer than 390 nm. Next, a novel TiO2 thin film photocatalyst was prepared on various metal substrates such as Al, Fe, Pd, Pt, Ti and Zr, while nanoparticles of Pt were deposited on the other side of these substrates. The reaction rate was revealed to increase with a decrease in the work function (ϕ) of the substrate. Moreover, the separate evolution of H2 and O2 could be successfully achieved under solar light irradiation by applying these thin film photocatalysts in an H-type glass container consisting of two water phases separated by a TiO2 thin film and proton-exchange membrane.