Surfactant-free pH-assisted facile engineering of hierarchical rutile TiO2 nanostructures by a single step hydrothermal method for water splitting application

Abstract

A photoanode of distinct hierarchical pure rutile phase TiO₂ nanostructures was successfully prepared by a surfactant and template-free, single-step hydrothermal route. Tuning of the morphology from compact broccoli-like structures of ∼4 μm in diameter to outsized round bottle brush flower-like structures of ∼12 μm in diameter was achieved only by varying the pH (concentration of HCl) of the solvent. The subsequent growth mechanism of the different hierarchical structures was thoroughly illustrated using appropriate schematics. The structural, optical and morphological properties of all the rutile TiO₂ photoanodes have been studied by using an X-ray diffractometer, X-ray photoelectron spectrometer, UV-vis spectrophotometer, scanning electron microscope and transmission electron microscope. The deposited TiO₂ nanostructures were directly used as a photoanode in a photoelectrochemical cell. The photocurrent showed an increasing trend with decreasing theoretical pH up to −0.76 (corresponding to a HCl concentration of 5.7 M) of the solvent used for preparing the nanostructures. However, further decrement in the pH resulted in lowering of the photocurrent. The best photoelectrochemical performance is observed for the rutile TiO₂ photoanode with a well-arranged microflower-like structure corresponding to pH −0.76.