Competition between the electrotransports of acetate and chloride ions through a polymeric anion exchange membrane

Abstract

The transport numbers of chloride and acetate ions in an anion exchange membrane are measured using radiotracers under different current densities. The membrane (AMV Selemion) is maintained between two identical solutions containing both NaCl (10 −1 M) and CH 3COONa (10 −1 M). The pH of each solution is maintained at a constant value (pH 8.1). The transport number of the acetate ions ranges from 0.1 for 2 mA-cm −2 to 0.3 for 20 mA-cm −2. By applying the Nernst-Planck electrodiffusion equation to analysis of the transport of each ion in the unstirred layer, it is possible to determine the value of the ionic concentration in the aqueous layer in contact with the membrane surface. From this result it is possible to determine the rate constant of ion transfer at the membrane-solution interface. The observed results can be ascribed to a greater variation of the rate constant with voltage for the acetate ion than for the chloride ion.