Bi-ionic potential through a cation exchange membrane separating two electrolyte solutions at different concentrations

Abstract

We have studied the bi-ionic potential (BIP) through an ion-exchange membrane separating two electrolyte solutions having the same co-ion, different counter-ions and different concentrations. This study is carried out for a cation exchange membrane (CM1: a polystyrene and divinylbenzene sulfonated membrane), for three electrolyte pairs (ACl—BCl where A, B ∈ {K, Na, Li}) and for two stirring rates (ω 0 = 0 rpm and ω max = 900 rpm). Our experimental results show that the higher the concentration of the more mobile counter-ion (A) the higher the BIP, and conversely for B. The BIP variation versus the logarithm of the concentration of one solution is almost linear until 0.1 M for all the systems studied. The stirring rate, ω, has no influence on the BIP values if the concentration of A or B is very small (of the order of 0.001 M). However, if the concentrations of A and B are greater than 0.01 M, ω has a non-negligible effect which is attributed to the existence of diffusion boundary layers. The influences of the co-ion flux, of the solvent flux and of the counter-ion hydrated volumes have been examined.