Constructing a rigid crosslinked structure for enhanced conductivity of imidazolium functionalized polysulfone hydroxide exchange membrane

A series of novel bis-imidazolium crosslinked polysulfone membranes (CL-PSf-ImOHs) membranes were prepared through simultaneous quaternization and crosslinking reactions of 4,4′-bis(2-methylimidazole-1-ylmethyl)diphenyl (bis-Im-diPh) and chloromethyl groups on the polymer during the membrane formation. The novel bis-Im-diPh crosslinker possesses a rigid bis-phenyl structure, which creates large free volume and leads to the formation of continuous hydroxide conducting channels in the membrane as demonstrated by TEM . The properties of the crosslinked membrane were controlled by varying the molar ratio ( R d/c ) of bis-Im-diPh and chloromethyl groups from 0.18 to 0.33. With increasing R d/c , the swelling ratio decreases, and the hydroxide conductivity increases. The CL-PSf-ImOH membrane with R d/c of 0.33 exhibits the conductivity of 112 mS cm −1  at 60 °C, much higher than that of non-crosslinked membrane (83 mS cm −1 , losing its morphology at 60 °C) and those of other crosslinked membranes (17–68 mS cm −1 ) prepared with the similar methods. In addition, the CL-PSf-ImOH membranes show good dimensional stability at elevated temperatures.