Characterization of titania self-aligned nanotubes prepared under various conditions for the photoelectrochemical water splitting

Abstract TiO₂ nanotubes were grown by anodization of Ti sheets in an ethylene glycol solution. The then prepared nanotubes were tested with and without heat treatment at 450 ºC, for the water splitting process. The heat treatment was shown to increase the photocurrent from 4.9 µA cm⁻² to 56,8 µA cm⁻² while being illuminated at 0.7 V vs. SHE. Modification of the nanotubes was carried out by electroreduction on both, the heat treated and untreated samples and its photoactivity evaluated. A comparison of photon-to-current was made between the nanotubes before and after reduction. It was found that after reduction (black titania), an increase in photocurrent was observed, although there was no change detected in the absorbed wavelengths. Finally, high-purity (>99.6%) and commercially pure (99%) Ti sheets were used to grow TiO₂ nanotubes with no clear difference in photocurrents (61.5 µA cm⁻² vs 65.4 µA cm⁻² while illuminated at 0.7 V vs. SHE).