Solar photochemical and thermochemical splitting of water

Abstract

Artificial photosynthesis to carry out both the oxidation and the reduction of water has emerged to be an exciting area of research. It has been possible to photochemically generate oxygen by using a scheme similar to the Z -scheme, by using suitable catalysts in place of water-oxidation catalyst in the Z -scheme in natural photosynthesis. The best oxidation catalysts are found to be Co and Mn oxides with the e 1 g configuration. The more important aspects investigated pertain to the visible-light-induced generation of hydrogen by using semiconductor heterostructures of the type ZnO/Pt/Cd 1− x Zn x S and dye-sensitized semiconductors. In the case of heterostructures, good yields of H 2 have been obtained. Modifications of the heterostructures, wherein Pt is replaced by NiO, and the oxide is substituted with different anions are discussed. MoS 2 and MoSe 2 in the 1T form yield high quantities of H 2 when sensitized by Eosin Y. Two-step thermochemical splitting of H 2 O using metal oxide redox pairs provides a strategy to produce H 2 and CO. Performance of the Ln 0.5 A 0.5 MnO 3 (Ln = rare earth ion, A = Ca, Sr) family of perovskites is found to be promising in this context. The best results to date are found with Y 0.5 Sr 0.5 MnO 3 .