A new lateral method for characterizing the electrical conductivity of ion-exchange membranes

Abstract

A new method for determining the electrical conductivity of ion-exchange membranes was implemented with four commercial membranes (AMX, CMX, MK-40 and MA-41). It is based on lateral resistance measurements without direct contact between electrodes and membranes. The cell configuration made it possible to determine the membrane conductivity over a wide range of electrolyte concentrations (measurements were carried out in the range 10-5 - 5x10-1 M). The structural parameters of the different membranes were inferred from AC conductivities and the microheterogeneous model. They were found in good agreement with literature results obtained by normal measurements (i.e. with current lines oriented normally to the membrane surface), thus confirming the reliability of the proposed method. The main advantage of our method is the possibility to characterize ion-exchange membranes even at low salt concentration unlike usual non-contact methods based on normal measurements.Counterion diffusion coefficients and transport numbers within the membrane gel phase were estimated. The inter-gel phase volume fraction of an anion-exchange membrane (AMX) was also determined for the first time from membrane DC conductivity inferred from streaming potential and streaming current measurements. An excellent agreement was found with structural parameters obtained from AC measurements. Keywords: Ion-exchange membranes, Electrical conduct