Anion exchange membranes with fast ion transport channels driven by cation-dipole interactions for alkaline fuel cells

Abstract

Polyethylene glycol (PEG)-grafted imidazolium-containing flexible-side-chain type anion exchange membrane (AEM) has been designed and fabricated for efficient anion exchange membrane fuel cells (AEMFCs). The cation-dipole interactions between electronegative alkoxy and imidazolium drive the spontaneous self-assembly of the cationic side chains, thus boosting the formation of continuous ion-conducting channels with enhanced OH− conduction kinetic. The PEG's H-bonding with H2O molecules improves the hydrophilicity of the AEMs, thereby reducing the dependence of OH− transport on relative humidity (RH). Meanwhile, the alkaline stability of PEG-grafted AEMs has been improved since the electrostatic interactions reduce the electrophilicity of imidazolium for potential hydroxide attack. Compared with OBImPPO26-PEG0, the designed OBImPPO26-PEG0.5 (with 0.5% PEG grafts) membrane exhibits higher OH− conductivity (93.8 mS cm−1vs. 80.9 mS cm−1, 80 °C) and conductivity remaining (80.4% vs. 51.0%, treated by 2 mol L−1 aqueous NaOH for 216 h at 60 °C). The peak power density of an H2/O2 single-cell employing OBImPPO26-PEG0.5 membrane reaches up to 407 mW cm−2 at 60 °C.