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

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.