3D ZnIn2S4 nanosheets/TiO2 nanotubes as photoanodes for photocathodic protection of Q235 CS with high efficiency under visible light

A 3-dimensional ZnIn₂S₄/TiO₂ nanotubes composite was prepared by a combined hydrothermal reaction and electrochemical anodization method. Photogenerated open circuit potential, photogenerated current density, electrochemical impedance spectra, Tafel curves, and i-V curves were measured to investigate the photoelectrochemical activities and photocathodic protection properties for Q235 carbon steel. The results showed that the photocurrent density of the ZnIn₂S₄/TiO₂ composite was greatly increased compared with pure TiO₂. Under visible light irradiation, the photocurrent density of the ZnIn₂S₄-0.25/TiO₂ composite can reach 400 μA cm⁻², which was two times that of TiO₂. The photogenerated potential drop of the composite photoanode was about 0.36 V, which was greater than that of TiO₂ (about 0.16 V). The introduction of the ZnIn₂S₄ improved the visible light absorption ability and photogenerated charge separation efficiency of TiO₂. The loading of ZnIn₂S₄ onto the TiO₂ surface led to a negative shift of the Fermi level of TiO₂. The generation of adsorbed oxygen can facilitate the separation of photogenerated charges.