Cyclic water splitting system

Figure 10. An hypothetical model for a cyclic water splitting system, based on a semiconductor particle immobilized in a polymerized membrane and having access to both aqueous solutions on each side of the membrane. Specific and selective coating by catalysts leads to simultaneous and separate hydrogen and oxygen generation on each side of the polymerized membrane.

These data are corroborated by results obtained from continuous photolysis experiments. Cabowax-20M protected Pt catalyst when coupled to Ru02 fails to split water under illumination of a cyclic system containing Ru(bipy)3+ as a sensitizer and methylvio-logen as an electron relay. By contrast, if the Pt microspheres are protected by PVP-Ci6 simultaneous H2 and 02 productions are observed. The lack of specificity of the Carbo-wax 20 M protected particles is attributed to the strongly hydrophylic nature of this protective polymer providing facile access of the Ru(bipy)3+ cation to the platinum surface. Uncharged hydrophylic polymers appear thus unsuitable for Pt protection in this cyclic water decomposition system. 

Cyclic water cleavage by visible light was also achieved in electron relay free systems (48). In this case the fraction of sensitizer that Is absorbed onto the particle surface is photoactive and electron injection occurs directly from its excited state into the Ti02 conduction band. Using the surfactant ruthenium complex depicted in Figure 10, a quantum yield of 7% was obtained for the water splitting process. 

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