Energy Storage of TiO₂−WO₃ Photocatalysis Systems in the Gas Phase

Abstract

Reductive energy generated at a TiO 2 photocatalyst under UV light can be stored in WO 3 by coupling them together, and the stored energy can be used after dark. However, the reduction of WO 3 requires cation intercalation for charge neutralization. Thus, behavior of the TiO 2 −WO 3 composite on an ITO electrode was examined in nonelectrolytic media. When the TiO 2 and WO 3 were close to each other (less than 1 mm), WO 3 could be reduced even in pure water or humid air (relative humidity ≥25%), by irradiating the composite with UV light. In dry air, WO 3 was not reduced efficiently, even if the TiO 2 and WO 3 nanoparticles were mixed well. These results suggest that protons generated at the TiO 2 surface as a result of photocatalytic oxidation of water are intercalated into WO 3, and therefore ionic conductivity of the medium or the composite film surface is important. The composite film charged in air exhibited almost the same electrode potential as that of the film charged in aqueous NaCl.