Performance of photocatalytic cathodic protection of 20 steel by α-Fe2O3/TiO2 system

Abstract

Photocathode protection is widely used in carbon steel for corrosion protection owing to its energy saving, environmental friendliness, convenience and high efficiency. In this work, α-Fe2O3 was used as a transition layer between 20 steel and TiO2 film, this structure is designed to improve the photocathode protection performance of TiO2 by hindering iron diffusion from matrix to TiO2 layer. Two different types of α-Fe2O3 were obtained by thermal and anodic oxidation on 20 steel. Then, TiO2 layers were prepared by spin-coating method on α-Fe2O3 transition layers. The effect of different α-Fe2O3 layer on the photocatalytic properties of TiO2 films was investigated. The photoelectric conversion properties of α-Fe2O3/TiO2 heterojunction films were evaluated by UV–vis absorption spectra, surface photovoltage spectroscopy (SPV), photoluminescence spectra (PL) and photocurrent density-time curves (I-t). Electro-chemical impedance spectroscopy (EIS) and potentiodynamic polarization curves were used to measure the corrosion resistance of 20 steel coupled with different α-Fe2O3/TiO2 film photoanodes. The samples pretreated by anodic oxidation demonstrate better photoelectric conversion efficiency than the samples obtained by thermal oxidation. Under sunlight irradiation, the α-Fe2O3/TiO2 film sample pretreated by anodic oxidation, as a photoanode, reduced the corrosion current density and corrosion potential of 20 steel in 0.5 M NaCl solution by 0.149 mA∙cm−2 and 297 mV, respectively, exhibiting superior photoelectro- chemical cathodic protection over the samples pretreated by thermal oxidation.