Membrane electric conductivity: A study of the effect of the concentration and nature of the electrolyte and of the structure of the membrane

We have studied the variation of the membrane electric conductivity measured under alternative current, as a function of the equilibrating concentration, C-e, of the counter-ion nature and of the membrane type. Seven cation exchange membranes, distributed into three categories, were used: CM1, CM2 and CMx; nafion(R)117 and Nafion(R)324; MK-40 and CRP. The measurements were achieved with three different electrolytes (NaCl, KCl and LiCl), the concentration varying generally from 0,01 to 2 M. The experimental results show that the MK-40, CRP, Nafion(R)117 and Nafion(R)324 membranes present a particular behaviour specific to their categories. In high ranges of concentration, the conductivities of MK-40 and CRP membranes continue to increase in a sensitive way with concentration. This phenomenon can be interpreted by the structural characteristics of the membranes. On the other side, the Nafion(R)117 and Nafion(R)324 membranes present the particularity of their given conductivity ratios kappa(K+)/kappa(Li+) which are lower than their equivalent ionic conductivitie ratios in solution. We have shown that this behaviour can be explained by their internal structure as described by the Gierke model. (C) 1999 Elsevier Science Ltd. All rights reserved.