pH, pOH shift and electroconvection of strong and weak electrolytes under ion concentration polarization.

This article focuses on the effects of water dissociation and buffer (acid dissociation) reactions on ion concentration polarization (ICP) phenomena near permselective membranes, specifically examining pH variations and electroconvection in strong (NaCl) and weak (Na₂HPO₄) electrolytes through numerical simulations. The study finds that chemical reactions producing free ions enhance electrical conductivity, significantly increasing current (by about 14.82%) and doubling electroconvection velocity at the overlimiting current regime in weak electrolytes, while effects are minor in strong electrolytes. pH changes are most pronounced in the quasi-equilibrium electric double layer (QE-EDL) and extended space charge (ESC) regions, with water dissociation moderating pH surges in strong electrolytes and acid dissociation buffering pH variations in weak electrolytes, maintaining stability in the diffusion boundary layer (DBL). These findings have implications for optimizing ion transport and pH control in applications such as electrodialysis and membrane-based microfluidic systems involving pH-sensitive species.