Tandem Structure of QD Cosensitized TiO₂ Nanorod Arrays for Solar Light Driven Hydrogen Generation

One-dimensional (1D) TiO₂ nanorod arrays as photoelectrode have great potential for solar photoelectrochemical (PEC) hydrogen generation. However, the large band gap and Ti-growth unit preference of rutile TiO₂ limit its solar light utilizing and multijunction nanostructure photoelectrode design. This paper presents a double-sided tandem structure for quantum dot cosensitized photoelectrodes with excellent solar PEC hydrogen generation. TiO₂ nanorod arrays were grown directly on transparent and conductive glass substrates by hydrothermal method and then coated with CdS or CdSe as photosensitizer to extend successfully their photoresponse to visible light. Given the transparent substrate, TiO₂ nanorod arrays could be grown on both sides, allowing the formation of the tandem structure of cosensitized CdS and CdSe with high reactivity under visible light. The double-sided CdS and CdSe cosensitized 1D TiO₂ photoelectrode exhibited the highest solar-to-hydrogen conversion efficiency of 2.78% and pronounced enhancement of simulated photoconversion efficiency. This success in fabricating a double-sided tandem structure 1D TiO₂ photoelectrode provides the opportunity for composite material design based on different band gaps, and this photoelectrode could be applied to other PEC applications.