Hydrogen evolution from water splitting on nanocomposite photocatalysts

Wenfeng Shangguan
Research Center for Combustion and Environment Technology, Shanghai Jiao Tong University, Shanghai 200030, PR China

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     Last modified: May 9, 2006

Abstract
The production of renewable and non-polluting fuels by the direct conversion of solar energy into chemical energy remains a fascinating challenge for this 21st century. Among various interesting reactions, the cleavage of water into hydrogen and oxygen by sunlight is potentially one of the most promising ways for the photochemical conversion and storage of solar energy. Up to now, various metal oxide semiconductors were intensively studied. However, most of them showed low activity, and are only active under UV light, which accounts for only 3 ~ 4% of the solar spectrum at the earth’s surface. Therefore, the development of visible light responsive photocatalysts for water splitting is currently attracting much attention as a potentially efficient utilization of solar energy.
Here, our recent studies on the photocatalysts splitting water into hydrogen under irradiation are presented. The attention is mainly focused on the promotion effects of nanosized modifications in the interlayer and surface of photocatalysts for photocatalytic hydrogen evolution with visible light. It was found that the photocatalytic activity depends significantly on modification techniques, such as loading, proton exchange, and intercalation. The activity was enhanced by loading nanosized Pt and RuO2 for various mixed metal oxides. The higher activity of catalysts having tunnel structures might be attributed to the formation of a ‘nest’ on the particle surface, which promotes a uniform distribution and strong combination of the nanosized particles on the surface of catalysts. By the methods of intercalation and pillaring as well as by selecting both host and guest, a large variety of molecular designed host-guest systems were obtained. CdS, which can response visible light, was intercalated into KTiNbO5, K2Ti4O9 and K2Ti3.9Nb0.1O9 through interaction in interlayer and a sulfurization process. The intercalated composites showed higher activity and stability. This improvement might be attributed to the formation of microheterjunctions and the quicker transference of the photogenerated electrons and holes. K4Ce2M10O30 (M=Ta, Nb) evolving H2 under visible light irradiation was presented. This activity was enhanced by the incorporation of Pt, RuO2 and NiO as co-catalysts. Especially, the nanosized NiOx (double layer structure of Ni and NiO) prompted the photocatalytic H2 evolution significantly.
The photocatalytic production of H2 in one step is very attractive, and there are some barriers to be overcome for its application.