Concentration polarization in electrodialysis—I. The electrometric measurement of interfacial concentration

Abstract

The value of overpotential measurements in the study of concentration polarization occurring in electrodialytic systems with ion-exchange membranes is considered. With proper allowance made for the liquid junction potentials which arise, it is possible to estimate interfacial concentrations and thereby study events at currents below the limiting value. Experimental difficulties and sources of error are discussed, attention being given to the effect of ohmic resistance in the reference electrode systems used and to the error introduced by measuring overpotential a short time after interruption of the polarizing current. The experimental results obtained are in agreement with simple concepts based on the Nernst idealization for film-controlled mass-transfer operations. This is in contrast to results reported in the literature on the use of pH change as a criterion for the limiting current in the electrodialysis of sodium chloride solutions.