Photoelectrochemical and Electrochemical Activity of Anodic Semitransparent Aligned and Spaced Titania Nanotubes Formed out of Titanium–Silver Alloys

Two titania nanotube (TNT) architectures, namely, aligned and spaced, have been synthesized by anodizing titanium–silver (TiAg) alloy films (i.e., 1.7, 3.5, and 5% Ag content) sputtered onto indium–tin oxide. The Raman spectra showed that the anatase phase is obtained for the aligned TNT up to 5% Ag content, whereas no anatase peak is observed for the spaced TNT above 1.7% Ag content in the deposited TiAg alloys. The electrochemical studies carried out in the presence of redox species showed that, among others for 5% Ag content in the deposited TiAg alloy used for anodization, a reversible redox reaction of ferricyanide species occurs that was not found for bare TNT. Moreover, irrespective of the titania arrangement, an increase of the Ag content in the TiAg films to 5% leads to a very efficient electron-transfer rate of 3.84 × 10 –3 cm s –1 for aligned and 7.98 × 10 –3 cm s –1 for spaced titania. In addition, the photoelectrode based on aligned TNT grown out of the TiAg alloy films containing 3.5% Ag exhibited a photocurrent density of about 3 times higher with respect to the aligned TNT obtained from the pure titanium film.