Study of the electrochemical impedance and the linearity of the current–voltage relationship in inhomogeneous ion-exchange membranes

The electrochemical impedance and the linearity of the current–voltage relationship in inhomogeneous ion-exchange membrane systems, have been investigated. The system under study is constituted by a membrane with negative fixed charge varying linearly with position inside the membrane and two diffusion boundary layers on both sides of the membrane, ionic transport being described by the Nernst–Planck and Poisson equations. The electrochemical impedance and a decomposition into Fourier components of the current–time response of the system to a sine electric potential, have been obtained by using the network simulation method. The influence of the degree of inhomogeneity of a membrane on the electrochemical impedance and the linearity of the current–voltage relationship of ion-exchange membrane systems, is analyzed and discussed.