Enhanced hydroxide conductivity of imidazolium functionalized polysulfone anion exchange membrane by doping imidazolium surface-functionalized nanocomposites

Abstract

A new method was proposed to prepare a membrane with regional aggregation of functional groups by incorporating nanocomposites surface-functionalized with a large number of functional groups. Imidazolium surface-functionalized SiO₂ (SiO₂-Im) nanocomposites were synthesized by the reaction of 1,2-dimethylimidazole, γ-chloropropyl triethoxysilane and SiO₂ nanocomposites. The obtained SiO₂-Im nanocomposites were incorporated into imidazolium functionalized polysulfone (PSf-Im) to fabricate composite alkaline anion exchange membranes. The uniform dispersion of nanocomposites in the membrane was demonstrated by SEM. With increasing mass ratio of SiO₂-Im from 0% to 20%, hydroxide conductivity of composite membrane dramatically increases at first and then decreases. The composite membrane with 12 wt% of SiO₂-Im shows the highest conductivity, e.g., the hydroxide conductivity of the composite membrane based on PSf-Im with functionalization degree of 76% reaches 32 mS cm⁻¹ (at 20 °C) that is 68% higher than the membrane's without doping SiO₂-Im (19 mS cm⁻¹). In addition, adding SiO₂-Im has a slight effect on water uptake and swelling ratio of composite membrane. It indicates that doping surface-functionalized nanocomposites is a simple and effective method to enhance the hydroxide conductivity without increasing swelling.