A study on electrochemical behavior of Polypyrrole films in differently concentrated Nacl electrolytes

Abstract

Polypyrrole films doped with large surfactant anion dodecyl benzene sulfonate, PPy (DBS), have been electro polymerized in galvanostatic condition and characterized in highly concentrated NaCl aqueous solution (5 M) using Cyclic voltammetry, electrochemical microbalance (EQCM) and UV-visible absorption spectroscopy. In order to compare (property) similar experiments were carried out in 0.1 M NaCl (aq) electrolyte, as well. The EQCM studies show that the mass change occurring in the film during the first cycle, in 0.1 M electrolyte, is comparatively higher than that is observed in the 5 M electrolyte. This is because of many water molecules go in and out of the polymer accompanying the counter ions, when PPy(DBS) film cycled in dilute electrolytes, due to osmotic effect. On the other hand, during the redox process in highly concentrated electrolytes, the mass change is mainly due to moving counter ions where there is less amount of water molecules present in the electrolyte. A large number of continuous cycles were carried out to test the cycling stability of PPy(DBS) films. Cyclic voltammograms are almost unchanged after first few cycles in both higher and lower concentrations. But, on further cycling, the shape and capacity of the cyclic voltammograms change significantly in 0.1 M NaCl (aq) electrolyte while only a minor change is observed in 5 M NaCl (aq) electrolyte. It reflects that the PPy(DBS) films have better cycle life in concentrated electrolytes. The optical absorption spectra obtained at various reduction potentials in both electrolytes looks most identical to each other. This results shows that the PPy(DBS)films do not undergo any noticeable structural or conformational changes during the redox processes.