Frequency dispersion in electrochromic devices and conducting polymer electrodes: A generalized transmission line approach

This paper is concerned with the characterization of thin film electrodes by electrochemical impedance. The main problem addressed is the quantitative description of microscopic processes giving rise to frequency dispersion. Models are suggested for the identification and analysis of transport and capacitive processes occurring either at the bulk of the diffusion layer, or at its boundaries. Suitable representations in terms of transmission lines with generalized and distributed elements are provided. The main result is the possibility of the models to provide hints on the origin of the frequency dispersion and therefore correlating the response to structural elements. An application of the method is examined by analysis of impedance measurements of a WO₃ electrochromic layer and a conducting polymer electrode.