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

• Crosslinked membranes with a rigid crosslinked structure were prepared.
• The continuous hydroxide conducting channels were formed in the membrane.
• The membrane shows high conductivity of 112 mS cm-1.

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 (Rd/c) of bis-Im-diPh and chloromethyl groups from 0.18 to 0.33. With increasing Rd/c, the swelling ratio decreases, and the hydroxide conductivity increases. The CL-PSf-ImOH membrane with Rd/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.

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