From the multi-ionic to the bi-ionic potential

When an ion exchange membrane separates two electrolyte solutions, an electric potential is set up. In the particular case where the two solutions contain the same co-ion and different counter-ions at the same concentration, C-0, this potential is named the bi-ionic potential (BIP). The ion interdiffusion fluxes transform every bi-ionic system to a multi-ionic one. We have set up an experimental device which permits us to obtain reliable measurements of BIPs. A cation exchange membrane (CM(2)) has been used to study the BIP as a function of C-0. The comparison of experimental results with the Helfferich equations shows that the former is only confirmed at high or low concentrations. The important role of diffusion layers, co-ion flux and/or influence of membrane structure are proved. Copyright (C) 1996 Elsevier Science Ltd