Influence of the formed interface during preparation of poly(vinylidene fluoride) blend cation exchange membrane on the electro-chemical properties and performance

Abstract

Cation exchange membrane containing low fraction of charge moiety is beneficial as it minimizes the water swelling and back diffusion of ions, increases the mechanical property and lowers the cost. However, moderate to high extent of ion conducting group in a membrane is necessary for the effective ion exchange and good electrodialysis performance. To address this issue, we report a non-solvent (water) induced phase separation process where solid-water interface is generated and helps to migrate the ionic moieties on the surface and transport of ions, while a solid-air interface is formed in the solvent evaporation process which partially hinders the migration of the ionic moieties (high surface energy) on the membrane surface and ion transport property. Cation exchange membranes of the blend of poly(vinylidene fluoride) and poly(methyl methacrylate)-co-poly(styrene sulfonic acid sodium salt) have been prepared by both non-solvent induced phase separation and solvent evaporation process. Membrane containing about 5% (w/w) anionic polymer and prepared by non-solvent induced phase separation process exhibits high transport number (t+ = 0.93), good water desalination performance with power consumption of 1.15 KWhKg−1 and current efficiency of 90% than that of the membrane prepared by solvent evaporation process (power consumption = 1.58 KWhKg−1 and current efficiency = 58%).