AbstractImpedance spectroscopy was used to study the effect of solution pH on the electrochemical behavior of poly(o-aminophenol) (POAP) modified electrodes. An a.c. impedance expression was derived on the basis of a model which considers a chemical reaction influencing the dynamics of the charge transport process by electron hopping between redox sites. Experimental impedance spectra of POAP films at different pH values of the bathing electrolyte were fitted by means of this theoretical equation. A pKa value for the proposed protonation reaction could be estimated from the model.
AbstractThe effects of ionic strength and film thickness on the transport properties of poly(o-aminophenol) (POAP) film electrodes were studied by impedance spectroscopy. The dependences of the characteristic impedance quantities (Warburg coefficient, resistance and redox capacitance at low frequency) on these external variables were interpreted on the basis of two models: a transmission line and a modified electron hopping model. Analysis of experimental data by means of the transmission line model allowed us to separate the charge transport process within the film in terms of electronic and ionic contributions represented by the diffusion constants. Dc and Dx, respectively. Application of the electron hopping model only gave an effective diffusion coefficient, Dcff. The diffusion coefficients Dc and Dx, in the first case, and Deff in the second case, depend upon the ionic strength and film thickness. Moreover, Deff is very close to Dc. This proves that charge propagation is dominated by electron transport in this polymer.