Water splitting using a large portion of solar spectrum will be a major advance in solar energy conversion and the critical breakthrough with respect to the rising concern of environmental pollution caused by the use of fossil fuels. Recent efforts have been devoted to achieve the water splitting using photocatalysts under visible light irradiation, in addition to the combination of the active photocatalysts for H₂ and O₂ production in the presence of redox couples. However, there are only a few reports so far on the use of metal salts as electron mediators. We report our recent development of copper complexes as biomimetic electron mediators for water splitting by a Z-scheme photocatalysis system.The Ru-loaded SrTiO₃ doped with Rh (Ru/SrTiO₃:Rh) and BiVO₄ were prepared by previously reported procedures. The complex ([CuCl₂(bpy)]) was obtained by mixing the copper(II) chloride with the stoichiometric amount of 2,2'-bipyridine in methanol. Electron transfer occurs from BiVO₄ to [CuCl₂(bpy)], and then to Ru/SrTiO₃:Rh under visible light irradiation (? > 420 nm) to afford the H₂ and O₂ evolution with high efficiency from pure water, although the photocatalytic activity decreases as a reaction time. This may arise from the intrinsic photoresistance of the complex. To overcome this problem, we have examined the photocatalytic activities using coordination polymers given by the copper (I) halide and bidentate ligands, and the results will also be presented. In summary, we have constructed the Z-scheme type water splitting systems which are combined by using the copper complexes affording efficient H₂ and O₂ evolution.