Growth of anatase and rutile TiO₂@Sb:SnO₂ heterostructures and their application in photoelectrochemical water splitting

We report three-dimensional (3D) nanostructures based on shape- and phase-controlled TiO₂ coated transparent conducting oxide (TCO) nanowire array. Core-shell and branched nanostructures were obtained using an aqueous chemical bath deposition (CBD) method at room temperature. Adjusting the pH of a TiCl₄ solution is a key factor that determines the morphology of the nanostructure. Spherical TiO₂ anatase covered a Sb-doped SnO₂ (ATO) nanowire when pH was maintained at a high level. In contrast, branched nanostructures with TiO₂ rutile nanorods were synthesized by keeping a TiCl₄ solution going down to a low pH. Nanorods were grown epitaxially along the [001] direction on ATO nanowires. Morphological and structural analysis indicates that phases and shapes of the 3D hybrid nanostructure are determined by the pH of the solution and the reaction time. A two-fold higher photoconversion efficiency of rutile TiO₂ rod@ATO was obtained under simulated solar illumination compared to that of the anatase TiO₂ nanoshell@ATO. These 3D hybrid nanostructures can offer (i) a large surface area and efficient charge transport in the TiO₂ nanostructure, and (ii) an effective charge collection path through one-dimensional TCO, which is promising for various areas, including photoelectrochemical water splitting, as well as for application in electronic and photonic nanodevices.