Electrochemical characteristics and concentration polarization of perfluorinated cation-exchange membranes

Equilibrium parameters (ion-exchange capacity, moisture content) and transport characteristics (electroconductivity, ion transport numbers, liquid filtration coefficient, and streaming potential) of perfluorinated sulfonated (MF-4SK) and carboxylated (MF-4CK) cation-exchange membranes in NaCl and KCl solutions were measured. Experimental data were used for calculation of the electrochemical membrane characteristics: concentration of fixed ions, counter- and coions, efficiency coefficients and structural resistance coefficients, ion mobilities in membranes, electroosmotic mobility and convective part of specific conductivity of intramembrane liquid, Donnan's potentials and water transport numbers in membranes.Concentration polarization of the membrane systems was also investigated. Method of limiting current determination – using polarization potential measurements after current interruption (ΔEj=0) – was proposed and compared with usual (from current–voltage curve) method. Two components of ΔEj=0 potentials — connected with electrolyte diffusion (slow part) and connected with volume charge in diffusion layer (fast part) were determined. Electrolyte concentrations near membrane surfaces were calculated from the slow part of membrane polarization potentials in dependence on current density values.