Electrode covering effect on the electric response of a cell to external stimulus

• Role of the surface non-uniformity on the electric response of an electrolytic cell.
• Partial coverage of an electrode may modify the impedance spectra.
• Deviation from Poisson–Nernst–Planck model prediction in the low frequency region is observed.
• A new interpretation of the low frequency impedance behavior is suggested.

The covering effect of the electrode on the electric response of a cell is investigated. We assume that this effect is responsible for the variation of the electrode impedance due to the surface deposition of particles or gas bubbles. From the spectrum of the resistance we predict the presence, in the low frequency region, of a new plateau and from the spectrum of the reactance, in the same frequency region, a new peak related to the covering effect. In this region the slope of the logarithm of the reactance versus the logarithm of the frequency differs from −1, as predicted by Poisson–Nernst–Planck model and experimentally observed. These effects have been described previously using the anomalous diffusion approach with the non-validity of the Fick law near the electrodes. According to our point of view an alternative interpretation could be the one related to a material deposition on the electrode surface responsible for the changes of the surface properties of the electrode itself.