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Photocathodic protection technology has presented great potential for protecting stainless steel; however, due to the higher electrochemical activity and more negative corrosion potential of carbon steel, most of them are not applicable to carbon steel. This study has fabricated a series of TiO2/Au/CdS nanostructured coating. The prepared samples have extended light absorbance to the visible light region. Among then, the TiO2/Au10/CdS nanostructured coatings have successfully offered cathodic protection to carbon steel. The maximum photogenerated potential drop value is −0.591 V, and the photocurrent density is 1.253 mA·cm–2, which is about 4 times higher than that of TiO2. The active species trapping tests have been performed to reveal that the nanostructured coatings possess a Z-scheme heterojunction property, which supplies an efficient charge separation and demonstrates strong reduction and oxidation abilities. The photocathodic protection mechanism is discussed in detail in the paper.

Photocathodic protection has evoked great attention in stainless steel protection; however, it has not been fully studied on carbon steel. This study has prepared a series of TiO 2 /Zn 3 In 2 S 6 nanocomposite films by combining anodic oxidation with hydrothermal methods, in which composition and morphology together with optical properties have been characterized. This heterojunction TiO 2 /Zn 3 In 2 S 6 has allowed access to visible-light absorbance. Photoelectrochemical tests suggest that this film can supply effective photocathodic protection to carbon steel. The maximum photogenerated potential drop achieved on TiO 2 / Zn 3 In 2 S 6 -30 coupled to carbon steel is about −0.49 V even after 80 h of illumination, and the corresponding photocurrent is 1.91 mA•cm −2 , which is about 5 times higher than that of pure TiO 2 . This is benefited from the effective photogenerated charge separation by the built-in electric field in the heterojunction. The detailed mechanism has been discussed in the paper.