Analysis of electrochemical impedance of polypyrrole|sulfate and polypyrrole|perchlorate films

PPy|SO4 and PPy|ClO4 films have been synthesized and investigated in K2SO4, ZnSO4 and NaClO4 aqueous solutions by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and electron probe microanalysis (EPMA) methods. On the basis of obtained data and calculated impedance parameters as the potential functions, the role of different processes (diffusion of ions, double-layer charging, adsorption and charge transfer) in oxidized, partially reduced and reduced PPy films is estimated. The lowest pseudocapacitance values (from n × 10−6 to n × 10−4 μF cm−2 for 1 μm film), independent of solution concentration, were established for PPy|SO4 in ZnSO4. This phenomenon is related with strongly aggravated film reduction process in the solution of double-charged cations. In the case of PPy|ClO4 in NaClO4 and PPy|SO4 in K2SO4,where the mono-charged cations participate in redox process, the capacitance values are in the range from: n × 10−3 to n × 10−2 μF cm−2 and even somewhat higher for PPy|ClO4 system at oxidized state. The calculated effective diffusion coefficients of ions D remain inside the range from n × 10−12 to n × 10−14 cm2 s−1 for PPy|SO4 in 0.1 M K2SO4 and PPy|ClO4 in 0.1 M NaClO4 aqueous solution. In the case of PPy|SO4 film in ZnSO4 solution the D values are essentially lower.