Enhanced hydroxide conductivity and dimensional stability in quaternized polybenzimidazole-based nanocomposite membranes containing ionic liquid-impregnated covalent organic framework for anion exchange membrane fuel cells

Abstract

Anion exchange membrane fuel cells (AEMFCs) offer a cost-effective alternative to proton exchange membrane fuel cells (PEMFCs), but their performance is often constrained by the low ionic conductivity of anion exchange membranes (AEMs). In this study, we developed a high-performance nanocomposite AEM by incorporating covalent organic framework particles impregnated with imidazolium ionic liquid (Im@COF-LZU1) into a quaternized polybenzimidazole with imidazolium side chains (PBI-Im). The interconnected nanochannels of Im@COF-LZU1 provided additional ion transport pathways, while its rigid framework restricted polymer side-chain mobility, enhancing both hydroxide conductivity and dimensional stability. At an optimal filler content of 5 wt %, the nanocomposite membrane exhibited a hydroxide conductivity of 0.0592 S/cm at 80°C—an 183 % increase over the pristine membrane—along with a high ion exchange capacity (2.89 mmol/g) and a low swelling ratio (3.8 %). Additionally, the membrane demonstrated superior oxidative stability and improved fuel cell performance. These findings suggest that Im@COF-LZU1 is a promising filler for high-performance AEMs used in fuel cell applications.