CONCENTRATION POLARIZATION AND WATER-SPLITTING AT ELECTRODIALYSIS MEMBRANES

The factors influencing three major phenomena in an investigation of t he concentration polarization and the water splitting at anion and cat ion exchange electrodialysis membranes were studied. Firstly, a platea u formation in the current versus voltage curve; secondly, the formati on of acid and base at current densities above that at which the plate au forms; thirdly, the change of the temperatures in the boundary laye rs at the polarized and non-polarized membrane surfaces, as well as th e temperature difference across the membrane. It has been proved that the plateau forms as a result of increasing resistance associated with concentration polarization in the boundary layer at the polarized mem brane side. The results of several experiments investigating the natur e of the acid and base generation reaction indicate that water splitti ng occurs in the reaction layer at the polarized membrane surface of b oth cation and anion exchange membranes and not within the membrane, a nd is not bound to the presence of fouling materials, amino groups, ca talytic reactions, etc. The recombination reaction of H+ and, OH- ions within the membrane or within the boundary layer adjacent to the non- polarized surface of the membrane was also established.