Development and characterization of polyvinylidene fluoride-imidazolium functionalized polysulfone blend anion exchange membrane

Anion exchange membrane (AEM) is one of the core components of an alkaline fuel cell influencing the fuel cell’s performance, durability and stability. Out of the many anion exchange membranes reported so far, imidazolium functionalized polysulfone (PSf-ImOH) membrane has been identified to have high hydroxide ionic conductivity, reaching up to 50 mS cm at 20C. However, at high levels of ion exchange capacity, the membrane’s water uptake and swelling ratio increases significantly with temperature thus destabilizing it and making it unfit for potential use in high temperature alkaline fuel cells. This limitation of PSf-ImOH membranes has been overcome by blending it with polyvinylidene fluoride (PVDF) polymer, which is a thermally stable and highly hydrophobic polymer. PSf-ImOH membrane with a high degree of chloromethylation (180%) was synthesized and blended with PVDF at different weight ratios (PVDF / PSf-ImOH: 30/70, 50/50 and 70/30) to create a series of novel anion exchange membranes. The prepared membranes were characterized to study their structure, water uptake, swelling ratio, solubility in low boiling water soluble solvents, thermal stability, ion exchange capacity (IEC) and ionic conductivity (IC) at different temperatures. The 70% PVDF blend membrane demonstrated the better performance in terms of IEC, IC and water uptake properties compared to other membranes. Comparative studies on the water uptake and IC variation between the 70% PVDF blend membrane and pure PSfImOH membrane (having the same IEC as that of the blend membrane), clearly indicated the superiority and the promising use of the blend membrane in alkaline fuel cell especially for high temperature working condition.