Solar hydrogen production by photoelectrochemical cell composed of semiconductor photoelectrode

Firstly, general intoduction of solar hydrogen producition systems such as the combination process of solar cell & water electrolysis and one-step photoelectrochemical water splitting using a p-GaAs-n-GaAs//p- GaInP2 photoelectrode was described. Then, 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 aaueous solution, solar energy conversion efficiency to H2 and O2production (STH efficiency) was only 0.016%. In addition, STH efficiency of visible light responding photocatalyst, NiOx/ promoted In0.9Ni o.1TaO4, was estimated as 0.03%. On the other hand, in photoelectrochemical system using an oxide semiconductor film photoelectrode, STH efficiencies of meosporous TiO2 (Anatase) and WOa film were 0.32-0.44% at applied potential of 0.35 V vs NHE and 0.44% at 0.9 V, respectively. Finally, solar hydrogen production by tandem cell system composed of and oxide semiconductor photoelectrode, a Pt wire counter electrode and a dye-sensitized solar cell (DSC) was investigated. As photoelectrodes, meosporous TiO2 (Anatase), WO3 were investigated. STH efficiency of tandem cell system composed of a WO3 film photoelectrode, and a two-series-connected DSC (Voc=1.4 V) was 2.5-3.3%, which is very attractive for practical H2 production process. It is speculated that more than 4% 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.