Molecular catalysts for water oxidation and hydrogen generation inspired by the active sites of respective OEC in Photosystem II and [FeFe]- or [NiFe]-Hydrogenases have been developed in our group during the past two decades. These molecular catalysts are based on Mn, Ru, Fe, Cu, Ni and Co, with some water oxidation catalysts showing record high turnover frequency (TOF) of >1000 s-1 in pH 1 solutions. With the deep understandings of O-O bond and H-H bond formation mechanisms from the molecular catalysts, we have recently developed a series of nanostructured first row transition metal oxides/hydroxides as efficient electrocatalysts for water oxidation and hydrogen generation with low overpotentials. Photoelectrochemical (PEC) cells have been assembled in our group by immobilizing molecular water oxidation catalyst on dye sensitized n-type semiconductor (such as TiO2) as photoanode, and molecular water reduction catalyst on dye sensitized p-type semiconductor (such as NiO) as photocathode. Light driven total water splitting by using these PEC cells will be demonstrated during the lecture.