Fabrication of efficient CdS nanoflowers-decorated TiO₂ nanotubes array heterojunction photoanode by a novel synthetic approach for solar hydrogen production

A nanocomposite heterojunction photoanode involving CdS nanoflowers (NFs) and one-dimensional TiO₂ nanotube (NT) arrays was reported. The self-assembled TiO₂ NT arrays were fabricated by an anodization method and the surface of TiO₂ NT arrays was decorated with CdS NFs by employing hydrothermal method for the first time. The CdS NF morphology was optimized by controlling the hydrothermal reaction time from 0 to 72 h. Field-emission scanning electron microscopy (FESEM) study of the CdS-NF/TiO₂-NT photoanode revealed good coverage of hydrothermally grown CdS NFs on the surface of TiO₂ NT arrays. The photoelectrochemical measurements were performed under 100 mW cm⁻² illumination using polysulfide electrolyte. A 5.5-fold photocurrent enhancement was observed for the CdS-NF/TiO₂-NT array photoanode synthesized with a 48 h CdS hydrothermal reaction compared to a pristine TiO₂ NT array film. Annealing of TiO₂ NTs as well as CdS NFs led to further improvement in the photocurrent on account of greater crystallinity, significantly higher visible light photon absorption and improved interface properties between CdS and TiO₂. These findings were supported by optical absorption, electrochemical impedance spectroscopy and Mott–Schottky analyses.