Advanced cross-linked anion exchange membranes from acetal ethylene vinyl alcohol copolymer and quaternary ammonium poly(vinyl benzyl chloride) for fuel cell application

Based on rigid poly (vinyl benzyl chloride) (PVB) and flexible ethylene vinyl alcohol (EVOH) main chains, anion exchange membranes (AEMs) are prepared using the acetal reaction and the Menshutkin reaction. The crosslinking of rigid and flexible backbones, along with the regulation of hydrophilicity/hydrophobicity by fluorinated side chains on EVOH, endows the resulting AEMs with good mechanical properties. The high ionic conductivity of AEMs originates from the effective ionic aggregation morphology, which is generated from the differences between the two main chains and the fluorinated side chains. Their non-polar main chains with stable acetal groups and β-H-free cations contribute to high alkaline stability of AEMs. Specifically, cIM25-TFBA75-EVOH-PVB possesses an ionic conductivity of 148.5 mS cm−1 at 80 °C, with a swelling degree of 12.3 %. The tensile strength and elongation at break of the sample in a fully hydrated state at 25 °C are 7.0 MPa and 12.2 %, respectively. After immersion in 1 M KOH at 80 °C for 1080 h, it almost retains 90 % of its mass, ion exchange capacity, and conductivity. In fuel cells, it achieves peak power densities of 895 mW cm−2 with H2/O2 and 692 mW cm−2 with H2/CO2-free air at 80 °C.