Photocatalytic Water Oxidation By Homogeneous Ruthenium And Copper Catalysts

Utilization of sunlight to split water into oxygen and hydrogen, is a potential approach to solve the problems such as global warming and environmental pollution. Due to the complexity for4H+/4e-process, the water oxidation reaction has been considered to be more demanded with respect to the proton reduction reaction. In this regard, development of hihgly efficient photocatalyst towards water oxidation is of great importance.In order to realize overall water splitting, a promising way to combining water oxidation and proton reduction is to build photoelectrochemical (PEC) cells, where photoanodes loaded with water oxidation catlayst is needed. In this thesis,visible light-driven water oxidation was carried out in a three-component system with [Ru(bpy)3]Cl2as the photosensitizer, Na2S2O8as the sacrificial electron acceptor, and ruthenium dimer26as the catalyst in CH3CN/H2O mixed solvent. Increasing the proportion of acetonitrile, greatly enhanced photocatalytic activity for oxygen evolution were found for both9and26. High TONs of204and215were observed for9and26, respectively. Moreover, with the proportion of acetonitrile lower than40%, the dinuclear ruthenium catalyst26exhibits three-fold increases in activity relative to that of monomeric9; however, the activities for both catalysts turn to comparable when over40%CH3CN containing in the reaction solution, leading to the postulation that the reaction mechanism may be changed by tuning the solvents.A composite photoanode was fabricated by immobilization of Ni(CH3COO)2, Cu(NO3)2and Cu complex28onto visible light-absorbing BiVO4thin film. The composite anode exhibites high catalytic activity and stability with overpotential reduced by300mV. Cyclic voltammetry shows that Ni2+converts to nickle oxide which is the true catalyst in photoelectrochemical experiments. In contrast, Cu2+was found to remain its ironic nature, and the copper complex28remians its molecular nature in photoelectrochemical water oxidation.