Effect of the resin content in cation-exchange membranes on development of electroconvection

Comparative analysis of the effect of ion-exchanger content in heterogeneous sulfonated ion-exchange membranes Ralex CM Pes produced by MEGA a.s. (Czech Republic) on their microstructure, current-voltage characteristics and intensity of electroconvective instability was carried out. Using the SEM method, it has been found that with an increase in resin content from 45 to 70 wt%, fraction of the ion-exchanger on the surface of swollen membranes increases 1.8 times, and the distance between them is halved. At the cross-section of membranes, the growth of fraction of ion-exchange regions is 46%. An increase in the resin loading into the membrane causes a 1.7-fold and a twofold increase in the fraction of macropore on the surface and on the cross-section, respectively. With an increase in the ion-exchanger content in membranes, a decrease in the potential of the onset of the overlimiting state and a decrease in the plateau length of the limiting current on the current-voltage curve were revealed. It is shown that a change in resin/inert binder ratio determines the occurrence and development of heteroelectroconvection. Using laser interferometry and flicker noise spectroscopy, evidences of more intense electroconvective mixing of the solution at the boundary with the Ralex cation-exchange membrane with maximum resin loading were obtained.