A photoelectrochemical study of n-doped TiO2 nanotube arrays as the photoanodes for cathodic protection of SS

In order to improve the characteristics of TiO2-based cathodic protection coatings, including the visible light response and the protection performance in the dark conditions, the n-doped TiO2 nanotube layers with a highly ordered structure on titanium were prepared by a self-organized electrochemical anodization in fluorinated electrolyte. The structure and composition of the as-prepared nanotubes were characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The n-doped TiO2 nanotubes show a stronger absorption in the 400-550 nm range. The performances of photogenerated cathodic protection and the photoelectrochemical response for the n-doped TiO2 nanotube layers coupled with 316L stainless steel (SS) under illumination and dark conditions were evaluated through the electrochemical measurements. It is found that the open-circuit potentials of 316L SS coupled with the n-doped TiO2 nanotube layers shift negatively under visible light irradiation (lambda>400 nm). It is indicated that the n-doped TiO2 nanotube layers are able to function effectively to provide a photogenerated cathodic protection for metals under regular sunlight conditions.