Photodecomposition of Water over Pt/TiO₂ and Ni0x/TiO₂

Abstract

Photodecomposition of water over TiO₂ powders loaded with Pt or NiOx was carried out in a top-illumination type flat cell. TiO₂ samples used were commercial anatase (TP-2 and P-25). Stoichiometric water photosplitting over Pt/TiO₂ (TP-2) was observed when the amount of NaOH solution was reduced to less than ca.0.3 ml (less than O.2 mm solution thickness), and the formal yield was maximized at ca.0.12 ml of solution volume. A similar dependence on solution volume was also observed on NiOxiTiO, (TP-2), but the stoichiometric formation of H₂2and O₂ was observed even in a large amount of solution. These results can be explained in terms of the recombination of H₂ and O₂ in bubbles formed on the catalyst immersed in solution. In H₂SO₄ solution, stoichiometric water photolysis over Pt/TiO₂ (TP-2)was declined rapidly and evantually stopped. Pt-loaded fine powdered TiO₂ (P-25) showed no activity for water photolysis in NaOH solution, but NiOx-loaded one as well as oxidized Pt-loaded one did. To explain these results, a mechanism was proposed in which hydrogen spillover from, the Pt to the TiO₂ surface occurs, leading to the recombination of hydrogen adatoms with oxygerr species produced by the photooxidation of water.