Imidazolium functionalized polysulfone electrolyte membranes with varied chain structures: a comparative study

Abstract

The alkaline electrolyte membrane (AEM) is one of the key materials for alkaline electrolyte membrane fuel cells. While most studies focus on AEM performance in relation to cation structure, ion exchange capacity (IEC) and membrane architecture (cross-linking, composite, microphase separation), herein we report that AEMs of varied backbone structures and comparable IEC show remarkably different conductivities and alkaline stability. In particular, the AEM of imidazolium functionalized, isopropylene-containing polysulfone exhibits higher conductivity, but lower swelling- and alkali tolerance than those without such a unit. To confirm and mitigate the backbone influence, we grafted the isopropylene-containing polysulfone with imidazolium functionalized side chains. The resulting grafted membrane shows conductivity of 64 mS cm⁻¹ at 80 °C, which is higher than that of the un-grafted AEMs; its stability against water swelling and hydroxide attack is also improved. Our study provides a new understanding on the structure–property correlation of AEMs, and thus is beneficial for designing high-performance electrolyte membranes for an alkaline fuel cell.