In-situ odd random phase electrochemical impedance spectroscopy study on the electropolymerization of pyrrole on iron in the presence of sodium salicylate - The influence of the monomer concentration

In this work, the potentiostatic electropolymerization of polypyrrole (PPy) on iron in aqueous solution of sodium salicylate and pyrrole is studied in situ by odd random phase electrochemical impedance spectroscopy (ORP-EIS). The influence of the pyrrole concentration on the electrosynthesis process is investigated. The ORP-EIS technique ensures a reliable analysis of the PPy electrosynthesis on iron by means of an advanced data analysis of the non-linear and non-stationary behaviour and the signal-to-noise ratio of the system. Additionally, the structure and the chemical nature of the PPy film on iron are studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and glow discharge optical emission spectroscopy (GDOES). The results of the characterization confirm the presence of the passivation layer at the PPy/iron interface formed prior to the polymer deposition. The modelling of the impedance evolution over time provides the quantitative analysis of the electropolymerization of PPy on iron. The results show that the electrosynthesis of pyrrole on oxidizable iron in the presence of sodium salicylate is a complex process, which includes not only the pyrrole oxidation reactions but also reactions such as the oxidation/reduction of the iron surface and/or reactions between the iron, formed interlayer and polypyrrole.