Connection of the electrochemical impedance of conducting polymers with CVand other experiments

Recently developed theoretical descriptions for the electrochemical impedan ce spectra (EIS) and combined cyclic voltammogram-electron spin resonance ( CV-ESR) of conducting polymers are extended and the connections between the m are established. For the EIS of porous layers a two-phase model with a di ffusive hindrance of the distributed charge transfer resistance is used. Th e redox process is described by two successive one-electron steps followed by comproportionation and leading to polarons and bipolarons as charged sta tes of the polymer chains. Physical models for the bipolaron lattice format ion at high densities lead to an increase of the polaron and bipolaron form ation energies and hence an increase of the newly introduced modified forma l potentials which, as an approximation, are used in the Nernst equations f or the two processes. The usually observed capacitive CV current plateau ab ove the redox potential, the asymmetric ESR intensity with a tail and the c onstant and low EIS charge transfer resistance follow already in an equilib rium description. In the extension to a finite sweep rate these peculiariti es are combined with the peak separation and one obtains the qualitative de pendence of the corresponding electrochemical quartz crystal microbalance s ignals. The potential dependence of the EIS is described by using the micro scopic definition of the parameters. At first the charge transfer resistanc e following from the description of the redox process is taken into account and secondly the concentration dependence of the polymer resistivity. The potential dependence in the oxidized region can be described but for the tr ansition into the reduced potential range further extensions are needed. He re the layer becomes highly inhomogeneous. The EIS of such layers is mathem atically described by transfer matrix methods. Conductivity gradients lead to qualitative modifications of the impedance. This leads especially in the capacitive If region to a CPE like dependence.