Electrochemical impedance of ion-exchange systems with weakly charged membranes

The aim of this work was to investigate the effect of the membrane fixed-charge concentration on the electrochemical impedance of ion-exchange membrane systems and the specific properties of the impedance of ion-exchange systems with weakly charged membranes. The systems under study are constituted by a membrane with a homogeneous distribution of negative fixed-charge and two diffusion boundary layers on both sides of the membrane. The ionic transport processes of a binary electrolyte are theoretically described by the Nernst–Planck and Poisson equations not only in the ion-exchange membrane but also in the two diffusion boundary layers. The electrochemical impedance for different values of the anion diffusion coefficients and the direct component of the applied electric current has been obtained by using the network simulation method as a function of the membrane fixed-charge concentration. New results are presented in relation with the evolution of the characteristic frequency of the diffusion impedance and the dc resistance of the system with the uniform concentration of the fixed-charge inside the membrane.