Raman spectroscopy analysis of polypyrrole films as protective coatings on iron

In situ Raman spectroscopy was used to study the redox modifications of electropolymerized polypyrrole (Ppy) films used as protective coatings on iron. A preliminary study of the redox behavior of Ppy on platinum was carried out for highlighting the most sensitive bands to potential variations: the 1560–1620 cm −1 as well as the 930 and 980 cm −1 peaks show a strong dependence on the applied potential. In situ Raman spectra of Ppy on iron were recorded at different times after immersion in a 3% NaCl solution. They formally display the same peaks as those found for platinum, allowing to characterize the redox state of the Ppy film at the solution/film interface. Additional ex situ Raman spectra allowed to identify the corrosion products at the Ppy/metal interface. These results complement kinetics analysis early developed to understand the protection mechanism and its loss.