Influence of Coexisting Electron Donor Species on Charge Transfer in Dye-Sensitized Nanocrystalline TiO2 for H2 Evolution under Visible Light

Water splitting under visible irradiation is of significant importance for the ultimate purpose of producing fuel from abundant water and sunlight for a sustainable future society. The efficient photon collection in the visible region and proper construction of the reaction site on the semiconductor surface have been desired and studied to provide an efficient system to create a photoexcited hole-electron pair to proceed toward surface chemical reactions. In this paper, a dye-sensitized nanocrystalline TiO2 colloidal suspension in an aqueous system is applied for H-2 evolution under visible light (>390nm). The efficiency of H-2 evolution is strongly influenced by the dye-sensitizers, Ru complex (N719) and porphyrin derivatives, and the combination with coexisting electron donor species, methanol (MeOH) and triethanolamine (TEOA), in the suspension system. The analysis of fluorescence quenching of the porphyrin dye-sensitized nanocrystalline TiO2 in the colloidal suspensions and photoelectrochemical studies of dye-sensitized nanocrystalline TiO2 porous films reveal that the charge-transfer kinetics of the electron injection from the excited dye-sensitizers into TiO2 is strongly influenced by the surroundings, especially the concentration of coexisting electron donor species rather than the pH values of the surrounding solution, resulting in significant differences in the efficiencies of the proton reduction into H-2.