The photocatalytic overall water splitting under visible light irradiation is an attractive reaction from the viewpoint of a solar energy conversion. The authors have recently succeeded in the construction of two-step photocatalysis systems (called as Z-scheme systems) constituted of two visible-light-driven photocatalysts, Pt/SrTiO₃:Rh and BiVO₄, and an iron ion redox couple of an electron mediator. However, low activity of SrTiO₃:Rh, which functions as a hydrogen evolution photocatalyst in the Z-scheme systems, limits the overall quantum yields of the Z-scheme systems to 0.4%. In the present research, the authors investigated in preparation of the SrTiO₃:Rh photocatalyst via a soft chemical root using a polymerizable complex method to improve the activity.
Powder of the SrTiO₃:Rh photocatalyst was prepared using a polymerizable complex method or a conventional solid state reaction. The photocatalytic reactions were conducted in a gas-closed circulation system connected to an on-line gas chromatograph. A Xe-arc lamp (300-W) was used as a visible light source.
SrTiO₃:Rh photocatalyst prepared by the polymerizable complex method showed higher activity for hydrogen evolution with Fe²⁺ as an electron donor in one order of magnitude than that prepared by the solid state reaction. The overall quantum yield of the Z-scheme system with an Fe³⁺/Fe²⁺ electron mediator was improved to 4% when SrTiO₃:Rh prepared by the polymerizable complex method was used. Thus, the improvement of overall efficiency of the present Z-scheme system has been achieved by the efficient SrTiO₃:Rh photocatalyst prepared by the polymerizable complex method.