Electrochemical impedance spectroscopy evaluation on the protective properties of epoxy/DBSAdoped polyaniline-TiO2 nanocomposite coated mild steel under cathodic polarization

The dodecyle benzene sulphonic acid doped polyaniline (DBSA doped PANI) and dodecyle benzene sulphonic acid doped polyaniline-TiO2 (DBSA doped PANI-TiO2) nanocomposite were synthesized via in situ oxidative polymerization and characterized by Fourier transform infrared (FTIR) spectroscopy, ThermoGravimetric/differential ThermoGravimetric analysis (TGA/DTA), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The protective properties of epoxy/DBSA doped PANI and epoxy/DBSA doped PANI-TiO2 coated mild steel were evaluated by electrochemical impedance spectroscopy (EIS) in NaCl 3.5 wt% at 65 °C with and without cathodic protection (CP). Cathodic protection was applied at − 500, − 750, − 1000, − 1250 and − 1500 mV vs. Ag/AgCl. The application of cathodic protection at more negative potentials than − 750 mV affected the performance of the both coatings causing the decreasing of coating resistance (Rcoat). The coating resistance of epoxy/DBSA doped PANI and epoxy/DBSA doped PANI-TiO2 are in the order of 1 × 104 Ω cm2 and 1 × 105 Ω cm2, respectively. Accordingly, the coating capacitance and water uptake of epoxy/DBSA doped PANI is greater than epoxy/DBSA doped PANI-TiO2 at whole applied potentials. The protective performance of epoxy/DBSA doped PANI coating is improved in the presence of TiO2 nanoparticles under different cathodic potentials.