Construction of Ti3C2/TiO2/TiN/polyaniline quaternary composite and its application in photocathodic protection coating for 304 stainless steel

A quaternary composite of Ti3C2/TiO2/TiN/polyaniline was synthesized by doping TiN nanoparticles on the calcined Ti3C2 MXene nanosheets, and then polyaniline was deposited through chemical oxidation. The bandgap and flat band potential of composite were determined by X-ray diffraction and ultraviolet–visible spectroscopy. In order to prepare photoanode and photocathodic protective coating, the quaternary composite was added to the polyvinyl alcohol solution and epoxy resin to. Photoelectrochemical results indicated that photoanode and relevant photocathodic protective coating had similar photocurrent with about 5 μA cm−2, but open circuit potential of the photocathodic protective coating was more negative than that of photoanode. The Rct of photoanode with illumination was 5.5 kΩ, while that of photocathodic coating was 136 kΩ. The 304 stainless steel could be well protected by the photoanode and photocathodic protective coating whether illumination or not, due to synergistic effect of local surface plasmonic resonance of TiN, “electron pool” of polyaniline and non-interfacial contact of TiO2 and MXene. Moreover, the epoxy resin in the photocathodic coating could act as a kind of physical barrier in the dark environment. Additionally, results of long-term protection test indicated that the photocathodic protective coating under intermittent illumination had better protection property than that of the coating without illumination.