Contribution of the electrode-electrolyte interface to the impedance of an electrolytic cell

We analyze the experimental data relevant to samples of solutions of water and KCl, in the shape of slabs of different thicknesses, with electrodes in gold. The experimental data show an increase in the real part of the electrical impedance of the samples in the low frequency region (f similar to 5 Hz). We compare the theoretical predictions of the models proposed to interpret the anomalous behavior of the resistance of the sample in the dc limit with the experimental data. We show that the theoretical predictions of the models based on the adsorption of ions at the interface and on the Ohmic character of the electrodes are in good agreement with experimental data. The model based on the constant phase element is also considered. However, its agreement with the considered experimental data is very good for what concerns the real part, whereas it is poor for the imaginary part of the electrical impedance. The equivalence between the models based on the adsorption on the electrodes and on the Ohmic character of the electrodes is analyzed. From the good agreement between the two descriptions, a mechanism for the conduction across the electrodes is proposed, according to which the exchange of charge on the electrode takes place in two steps: one related to the adsorption of the ions, and the other connected with their neutralization from the external charges. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.3033392]