Solar hydrogen production by tandem cell system composed of metal oxide semiconductor film photoelectrode and dye-sensitized solar cell

Photocatalytic and photoelectrochemical approaches to solar hydrogen production in our group were introduced. In photocatalytic water splitting system using NiOx/TiO2 powder photocatalyst with concentrated Na2CO3 aqueous solution, solar energy conversion efficiency to H-2 and O-2 production (STH efficiency) was 0.016%. In addition, STH efficiency of visible light responding photocatalyst, NiOx/promoted In0.9Ni0.1TaO4, was estimated at 0.03%. In photoelectrochemical system using an oxide semiconductor film phptoelectrode, STH efficiencies of meosporous TiO2 (Anatase), mesoporous visible light responding S-doped TiO2 (Anatase) and WO3 film were 0.32-0.44% at applied potential of 0.35 V vs NHE, 0.14% at 0.55 V and 0.44% at 0.9 V, respectively. Finally, solar hydrogen production by tandem cell system composed of an oxide semiconductor photoelectrode, a Pt wire counter electrode and a dye-sensitized solar cell (DSC) was investigated. As photoelectrodes, meosporous TiO2 (Anatase), mesoporous S-doped TiO2 (Anatase), WO3, BiVO4 and Fe2O3 film were tested. STH efficiency of tandem cell system composed of a WO3 film photoelectrode, and a two-series-connected DSC (Voc=1.4 V) was 2.5-2.8%. In conclusion, it is speculated that more than 5% STH efficiency will be obtained by tandem cell system composed of an oxide semiconductor photoelectrode and a two-series-connected DSC in near future. This suggests a cost-effective and practical application of this system for solar hydrogen production.