Concentration polarization and conductance of cation exchange membranes in sulfuric acid and alkaline sulfate media

Ion-transport investigations are performed on systems of CMV and CMS commercial cation exchange membranes in contact with H2SO4 or various alkaline sulfates M2SO4 (with M = Li+, Na+, K+). The voltametric study at constant current of the transient transport process enables to characterize the membrane surface homogeneity. This method leads also to determine the ion and electrolyte diffusion coefficients values and allows assessing the validity of their use in the diffusion-migration flux equations at the membrane interface. Current–potential polarization curves are further recorded with these systems at steady state conditions in absence of stirring. In conjunction with these measurements, impedance spectrometry is supplying the value of the membrane internal resistance in sulfuric acid solution. Altogether these results provide the respective contributions brought forward by concentration polarization and ion migration in the membrane to the overall membrane resistance as derived from current–potential measurements. With sulfuric acid no significant difference of these contributions between the CMV and CMS membranes is observed. In sulfate salt media the membrane ion conductance in CMS remains smaller than in CMV. The specific conductance of both membranes increases as a function of the electrolyte along the sequence Li+

► Membrane surface homogeneity was characterized by chronopotentiometric method. ► Diffusion coefficients of electrolytes and ions in bulk solutions were determined. ► Validity of the values in the diffusion-migration flux equations was confirmed. ► Concentration polarization contributed a considerable resistance. ► Membrane conductance increased as a function of the electrolyte along the sequence Li+