Long-Term Photoelectrochemical Cathodic Protection by Co(OH)₂-Modified TiO₂on 304 Stainless Steel in Marine Environment

The long-term photoelectrochemical cathodic protection by Co(OH) 2 -surface modified TiO 2 of anatase nanotubes and rutile type, prepared by anodic oxidation has been studied in aqueous 3.5 wt% NaCl solution. Electrochemical measurements have been used to evaluate the photoelectrochemical protective properties of both Co(OH) 2 -modified TiO 2 coupled with 304 stainless steel in 3.5 wt% NaCl solution under illumination and in the dark. Morphologies, crystal structures, surface compositions, and light response range of both Co(OH) 2 -surface modified TiO 2 films before and after immersion were characterized, respectively, by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis spectrophotometry. The results show that the photogenerated electrode potential of both types of TiO 2 films modified with Co(OH) 2 is more negative affording protection of 304 stainless steel than that of the non-modified TiO 2 under illumination. These TiO 2 films provide a long period (12 h) of protection. The anatase-TiO 2 nanotube film always shows a better protection performance than rutile-TiO 2 film.