Photocathodic protection of 304 stainless steel by coating muscovite/TiO2 heterostructure

Abstract

The sol-gel method was used to prepare a series of muscovite/TiO2 heterostructures for photocathodic protection of 304 stainless steels (304SS). The effects of different mass ratio of muscovite to TiO2 (1:0.5, 1:1 and 1:1.5, denoted as MT-0.5, MT-1 and MT-1.5, respectively) on the crystal phase, grain size, light absorption properties and photoelectrochemical properties of TiO2 and muscovite/TiO2 heterostructures were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–visible diffuse reflection spectroscopy (UV–vis DRS). The corrosion resistances and photoelectrochemical properties of the 304SS coated with muscovite/TiO2 heterostructures (304SS/MT) were studied through corrosion immersion test and electrochemical workstation in 3.5 wt% NaCl solution, respectively. In addition, Tafel curves and the electrochemical impedance spectroscopy (EIS) measurements were carried out to evaluate the photogenerated electron separation and transfer efficiency, and the interfacial charge transfer resistance of the 304SS and 304SS/MT electrodes, respectively. The time-dependent photocurrent responses of the MT-1 heterostructures demonstrated an enhanced photo-generated cathodic protection performance for 304SS substrates under visible light irradiation compared to TiO2. A photoinduced potential drop value for 304SS coated with MT-1 in 3.5 wt% NaCl solution was −0.54 V (vs. SCE). After immersion test, the corrosion image analyses of the 304SS, 304SS-MT, and 304SS coated with physically mixed muscovite/TiO2 samples showed that the 304SS/MT-1 exhibits the best corrosion resistances. After connecting with 304SS/MT-1 in 3.5 wt% NaCl solution, the corrosion current densities (icorr) of 304SS increased significantly under the white light illumination, indicating more photoinduced electrons were migrated from the muscovite/TiO2 heterostructures to the 304SS compared with that from pure TiO2. Furthermore, the simulated charge transfer resistance (Rct) of 304SS/MT-1 electrode is smaller than that of the 304SS electrode coated with TiO2, indicating that there exists an effective separation of the photogenerated electrons and holes, and a fast interfacial charge transfer after coating muscovite/TiO2 heterostructures.