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

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 produced increased photocurrent from 4.9 µA cm−2 to 56.8 µA cm−2 under illumination at 0.7 V vs. SHE. Modification of the nanotubes was carried out by electroreduction on both heat treated and untreated samples and its photoactivity evaluated. The spectral response showed increased photocurrent for the reduced material (black titania), although no appreciable change was detected in the absorbed spectra for the visible 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) showing the potential for cheap commercialization.