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

Abstract

PPy|SO 4 and PPy|ClO 4 films have been synthesized and investigated in K 2SO 4, ZnSO 4 and NaClO 4 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|SO 4 in ZnSO 4. This phenomenon is related with strongly aggravated film reduction process in the solution of double-charged cations. In the case of PPy|ClO 4 in NaClO 4 and PPy|SO 4 in K 2SO 4,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|ClO 4 system at oxidized state. The calculated effective diffusion coefficients of ions D remain inside the range from n × 10 −12 to n × 10 −14 cm 2 s −1 for PPy|SO 4 in 0.1 M K 2SO 4 and PPy|ClO 4 in 0.1 M NaClO 4 aqueous solution. In the case of PPy|SO 4 film in ZnSO 4 solution the D values are essentially lower.