Effect of doping anions on corrosion protection of polypyrrole coating on steel substrate

Electropolymerization of Pyrrole on metals has been carried out in different electrolytes despite shortcomings prevailing due to defects formed in the coating during polymerization. Surface passivation before polymerization may reduce such defects but optimization of the effects and elucidation of its mechanism await further research. Conflicting reports exist on the mechanism of protection by Polypyrrole coating because of differences in its behavior due to structural variations in the presence of different ions in the polymerization solution. In this study, the effect of molybdate as a doping anion on the corrosion protection of Polypyrrole is investigated. The polymerization solution was 0.1M Pyrrole plus 0.1M Molybdate at pH5. Pretreatment in nitric acid improved coating integrity so that the defects, active pits appearing during polymerization, disappeared. Surface morphology showed a perfect defect-free surface and exhibited a remarkable resistance in electrochemical corrosion test. It was found that pretreatment of the substrate and introduction of molybdate doping ions improve corrosion protection of Polypyrrole conducting polymer on steel.