Fabrication of CdS quantum dots sensitized ZnO nanorods/TiO2 nanosheets hierarchical heterostructure films for enhanced photoelectrochemical performance

Abstract

A novel CdS/ZnO/TiO2 hierarchical heterostructure for photoelectrochemical (PEC) application was fabricated by growing ZnO nanorods (NRs) onto TiO2 nanosheets (NSs) with dominant high-energy {001} facets via hydrothermal method, subsequently coated CdS quantum-dots (QDs) sensitized layer via successive ionic layer adsorption and reaction (SILAR) technique. The as-prepared TiO2, ZnO/TiO2 and CdS/ZnO/TiO2 films were characterized by XRD, SEM, TEM, UV–vis absorption spectrum and EIS techniques to investigate the effects of ZnO NRs and CdS QDs on the structure, morphology, optical property and charge carrier transmission characteristics. The results demonstrated that the growth of ZnO NRs obviously enlarges the specific surface area, while the deposition of CdS QDs significantly enhances the light harvesting ability. And the heterojunctions formed among TiO2 NSs, ZnO NRs and CdS QDs effectively promote the photogenerated charge carrier transport and separation, simultaneously inhibit the photogenerated electron-hole recombination. Moreover, it is notable that ZnO NRs trend to grow on the low-energy {101} facets of TiO2 NSs due to the impact of crystal facet controlling agent, which can effectively shorten the electron conduction path-ways and facilitate the photogenerated electron-hole separation due to the lower band edge position of {101} facets than that of {001} facets. As a result, the photocurrent density of the optimized CdS/ZnO/TiO2 composite film enhances to an excellent value of 12.1 mA/cm2 at a potential of 0 V vs SCE, which is more than 27 times higher than that of bare TiO2 NSs films. In addition, the corresponding optimal condition and physical mechanism were also discussed in the paper.