Electropolymerization of pyrrole on iron electrodes. influence of solvent and electrolyte on the nature of the deposits

Electropolymerization of pyrrole on an iron electrode was carried out in different organic solvents such as ACN (acidic), PC (neutral), MeOH, THF, DMF and DMSO (basic) in the presence of 0.1 M N(Bu),PF, or N(Et),Tos. Two different types of behavior were observed. In the absence of pyrrole and in the case of ACN the rate of corrosion of iron is increased, whereas in a basic solvent it is decreased. The pyrrole electropolymerization process was also found to depend drastically on the acidity of the medium. In the case of ACN the film is a mixture of polypyrrole and ferric oxides, as shown by XPS. In contrast, with basic solvents, the deposits are made of polypyrrole only. In both cases, the structure of the films, analysed by IR spectroscopy, appeared to be quite similar to that of polypyrrole films obtained on a noble metal electrode. The anion of the salt was also found to play an important role. Electroactive films were thus obtained in THF with N(Bu),PF,, while non-electroactive films were formed with N(Bu),ClO, in the same solvent