Side-chain type PPO based anion exchange membrane with steric hindrance containing dual conduction sites

Abstract

Appropriate addition of cation transport sites while maintaining the good mechanical properties of anion exchange membranes (AEMs) can effectively improve the hydroxide ion conductivity. Therefore, a series of poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) based side-chain type AEMs containing dual conduction sites are successfully prepared. The 4-(4-dimethylaminostyryl)-1-methylpyridinium (DASP) side chains are grafted to brominated PPO at different ratios, which is confirmed by Fourier transform infrared spectroscopy (FT-IR). Analysis of the microscopic morphology reveals a distinct microscopic separation pattern of hydrophilic/hydrophobic regions, which provides efficient channels for the transport of hydroxide ions. The ionic conductivity of the PPO-DASP13 membrane reaches 89.97 mS/cm at 80 °C, which is benefited from the double cationic groups contained in the side chains, providing more conduction sites for hydroxide ions. Meanwhile, the tensile strength of membranes range from 17.83 MPa to 29.38 MPa, which have good mechanical properties. The ionic conductivity of all membranes retain about 70 % after a 800 h long-term alkali resistance test, which is related to the steric hindrance contained in the side chain structure and the conjugated system. Furthermore, the single cell based on PPO-DASP13 membrane with the highest ionic conductivity achieves a peak power density of 347.7 mW/cm2 in H2-air (CO2-free) at 60 °C.