New insights in the anticorrosive performance of MoO42--doped PPy conductive polymer on iron in 3% NaCl solution

Polypyrrole (PPy) and polypyrrole doped with molybdate (PPy/MoO₄^2-) coatings were prepared in oxalic medium on iron at a current density of 1.5 mA.cm^-2. The presence of anions doped inside PPy coating was identified by SEM/EDS analysis, and the morphology of the coating was analyzed by scanning electron microscopy. The corrosion protection performance of the coatings was investigated with both electrochemical impedance spectroscopy (EIS) and open-circuit potential (OCP) in 3% NaCl solution. OCP results show that the protection time is improved up to 84 h for PPy/MoO₄^2- coating while it was only 42 h for PPy coating. A self-healing property of PPy/MoO₄^2--based films was observed on the OCP measurement with the fluctuation of the rest potential. EIS results show that the film capacitance C_f of the PPy/MoO₄^2- coating decreases continuously when immersion time increases to reach a value of 53.84 10^-6 F after 24 h and then increases. In parallel, the film resistance R_f increases when immersion time increases indicating better corrosion resistance of the iron by the PPy/MoO₄^2- coating.