title: One sign ion mobile approximation.
abstract: The electrical response of an electrolytic cell to an external excitation is discussed in the simple case where only one group of positive and negative ions is present. The particular case where the diffusion coefficients of the negative ions, D(m), is very small with respect to that of the positive ions, D(p), is considered. In this framework, it is discussed under what conditions the one mobile approximation, in which the negative ions are assumed fixed, works well. The analysis is performed by assuming that the external excitation is sinusoidal with circular frequency ω, as that used in the impedance spectroscopy technique. In this framework, we show that there exists a circular frequency, ω*, such that for ω > ω*, the one mobile ion approximation works well. We also show that for D(m) ≪ D(p), ω* is independent of D(m).
authors.affiliation: Dipartimento di Fisica del Politecnico, Corso Duca degli Abruzzi 24, 10129 Torino, Italy. giovanni.barbero@polito.it
authors.forename: G
authors.initials: G
authors.lastname: Barbero