The Impact of Long-Time Operation of an Anion-Exchange Membrane AMX-Sb in the Electrodialysis Desalination of Sodium Chloride Solution on the Membrane Current–Voltage Characteristic and the Water Splitting Rate

Abstract

Long-term (over 20 h) operation of the AMX-Sb membrane in the electrodialysis desalination of 0.02 M NaCl solution in overlimiting current regimes can lead to an increase in experimentally determined limiting current by more than 30% compared to the pristine membrane. This growth is caused by electrochemical degradation of the ion-exchange material at the AMX-Sb/solution interface, which leads to (1) a decrease in hydrophilicity of the membrane surface and (2) the formation of membrane cavities with linear dimensions of 2–3 μm. Both of these effects stimulate electroconvection, which develops in underlimiting current regimes via the mechanism of electroosmosis of the first kind. The resulting microvortex structures deliver a more concentrated solution to the AMX-Sb surface, shifting the limiting state and the onset of the intense generation of H⁺ and OH⁻ ions to higher currents. The study has been carried out using the techniques of voltammetry and impedance spectroscopy, as well as contact angle measurements and optical visualization of the membrane surface.