Electrochemical and X-ray diffraction studies on polypyrrole films

The redox behaviour of polypyrrole (PPY) films doped with perchlorate (ClO4-) or p-toluene sulfonate (TsO(-)) anions was studied by cyclic voltammetry. The values of the kinetic parameters I-0, alpha(A) and alpha(C) (exchange current density, anodic and cathodic transfer coefficients) were obtained using Tafel equations. We report a decrease in the I-0 value after each redox scan, in contrast with the alpha(A) and alpha(C) values, which remain almost constant. We attribute this variation of the I-0 value to the irreversible trapping of cations (Li+ or H+) in the polymer layer, after the reduction process. X-ray diffraction measurements evidenced an anisotropic molecular organization of PPY (TsO(-)), in contrast with PPY( ClO4-), which exhibits an isotropic structure.