Anion exchange membrane with a novel quaternized ammonium containing long ether substituent

The anion exchange membranes (AEM) is one of the key components for alkaline electrolyte membrane fuel cells. However, poor alkaline stability and conductivity of the membrane greatly hinders its practical application. Herein, we report a novel 4-(dimethylamino)butyraldehyde diethyl acetal (DABDA) quaternized polysulfone AEM, or PSf-DABDA, which shows improved conductivity and alkaline stability due to the better hydrophilicity and the electron donating effect imparted by the long alkyl substituent with two ether-containing moieties in the cation structure. Its room temperature conductivity reaches 21 mS/cm while that of trimethylamine (TMA)- and dimethylbutylamine (DMBA) quaternized AEMs with comparable ion exchange capacity (IEC) is 11.8 and 13.2 mS/cm, respectively. When treated 150 h in 1 M NaOH at 60 °C, the PSf-DABDA membrane experiences a slight conductivity decrease of 5% while the PSf-TMA and PSf-DMBA membranes with a comparable IEC suffer a more serious conductivity decay of 19 and 13.5%, respectively. The better alkali stability of PSf-DABDA over its counterparts is further confirmed by a density functional theoretical study and a structural characterization before and after the alkali treatment. Our work demonstrates the advantage of the DABDA cation by both experimental and computational study; it presents a new possibility of improving AEM conductivity and stability.