CONCENTRATION POLARIZATION AND WATER-SPLITTING AT ELECTRODIALYSIS MEMBRANES

The factors influencing three major phenomena in an investigation of the concentration polarization and the water splitting at anion and cation exchange electrodialysis membranes were studied. Firstly, a plateau formation in the current versus voltage curve; secondly, the formation of acid and base at current densities above that at which the plateau forms; thirdly, the change of the temperatures in the boundary layers at the polarized and non-polarized membrane surfaces, as well as the 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 membrane side. The results of several experiments investigating the nature of the acid and base generation reaction indicate that water splitting occurs in the reaction layer at the polarized membrane surface of both cation and anion exchange membranes and not within the membrane, and is not bound to the presence of fouling materials, amino groups, catalytic 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.