Fabrication of TiO2/Ti nanotube electrode and the photoelectrochemical behaviors in NaCl solutions

Titanium oxide nanotube electrodes were successfully prepared by anodic oxidation on pure Ti sheets in 0.5 wt.% NH₄F + 1 wt.% (NH₄)₂SO₄ + 90 wt.% glycerol mixed solutions. Nanotubes with diameter 40–60 nm and length 7.4 μm were observed by field emission scanning electron microscope. The electrochemical and photoelectrochemical characteristics of TiO₂ nanotube electrode were investigated using linear polarization and electrochemical impedance spectroscopy techniques. The open-circuit potential dropped markedly under irradiation and with the increase of Cl⁻ concentrations. A saturated photocurrent of approximately 1.3 mA cm⁻² was observed under 10-W low-mercury lamp irradiation in 0.1 M NaCl solution, which was much higher than film electrode. Meanwhile, the highest photocurrent in NaCl solution implied that the photogenerated holes preferred to combine with Cl⁻. Thus, a significant synergetic effect on active chlorine production was observed in photoelectrocatalytic processes. Furthermore, the generation efficiency for active chlorine was about two times that using TiO₂/Ti film electrode by sol–gel method. Finally, the effects of initial pH and Cl⁻ concentration were also discussed.