Optimised heterojunctions between [100]-oriented rutile TiO2 arrays and {001} faceted anatase nanodomains for enhanced photoelectrochemical activity

Abstract

We report in this work the hydrothermal synthesis of [100]-oriented rutile TiO₂ rods on FTO substrates. The presence of [100]-oriented rutile TiO₂ nanorod arrays was confirmed using HRTEM and EBSD. It was found that by adjusting the concentration of HF, the growth of [100] oriented rutile TiO₂ nanorod arrays and their heterojunctions with {001} faceted anatase TiO₂ crystals can be achieved in a one-step synthesis procedure. The photoelectrochemical activity of the resulting thin films was tested in dihydrogen phosphate buffer (pH 7) and showed a dramatically increased activity. The photoelectrochemical activity, characterised using electrochemical impedance spectroscopy (EIS), revealed that contrary to the behaviour of the analogue anatase TiO₂ phase, the presence of surface fluorine (F⁻) has a beneficial effect in the photoelectron transport properties within the rutile TiO₂ phase. The methodology developed in this work also showcases the reliability of using Raman microscopy and EBSD in the detailed characterisation of surface defects which provides a new insight for the creation of new and improved photoanodes with enhanced photoelectrochemical activity for photoelectrochemical driven reactions.