Photocathodic Protection of 316L Stainless Steel by Surface Coating of Photocatalytic Mesoporous TiO2-WO3 Nanocomposite

The photocathodic performance of 316 low-carbon stainless steel coated with mesoporous TiO2-WO3 nanocomposites of high specific surface area is reported. The tungsten oxide (WO3) contents ranged from 2 to 6 wt.%, and 3, 5, and 7 layers of the nanocomposite were investigated at visible wavelengths using electrochemical impedance spectroscopy (EIS), and their relative bandgaps were determined by diffuse reflectance spectroscopy-ultraviolet (DRS-UV). The nanocomposites were formed by dipping the 316 stainless steel substrates in sol-gel solutions, and phase analysis of the coatings was by x-ray diffractometry, scanning electron microscopy and transmission electron microscopy. The corrosion resistance of the samples was determined by polarization measurements and electrochemical impedance spectroscopy (EIS). Polarization and DRS-UV measurements showed the greatest degree of corrosion resistance in the 5-TiO2/WO3-4% sample (6.2 x 10(-4) mm/year), compared with the uncoated control sample (0.47 mm/year). The coated sample had a bandgap of 2.85 eV in visible light. The corrosion current densities of 5-layer TiO2 films without WO3 were shown by polarization measurements to be 15.4 times higher in mesoporous TiO2 and 263.6 times higher in nanoparticle TiO2, indicating a significant capability of this novel nanocomposites for photocathodic corrosion protection applications.