Controllable Cross-Linking Anion Exchange Membranes with Excellent Mechanical and Thermal Properties

A new monomer called 2,2′-(4,4′-oxydiphenol-4,4′-diyl)bis(2-methyl-2,3,3a,4,7,7a-hexahydro-1H-4,7-methanoisoindol-2-ium) iodide (d 3 ) is synthesized possessing both cross-linker and functional groups. The membranes are formed by copolymerizing d 3 with norbornene and (3aR,4S,7R,7aS)-2-methyl-2-(3-(trimethylammonio)propyl)-2,3,3a,4,7,7a-hexahydro-1H-4,7-methanoisoindol-2-ium iodide (a 3 ) at varying ratios. The water uptake is 41.35% at 60 °C, and ion exchange capacity is 2.35 mequiv g −1 for a mole ratio of a 3 , norbornene, and d 3 (1:6:3). The conductivity is 12, 37, and 40 mS cm −1 when d 3 is decreased. Meanwhile, the conductivity increases quickly with increasing the temperature. Furthermore, the mechanical properties and thermal properties are improved, attributed to the increased cross-linker. The membrane has a tensile strength of 41.3 MPa and the elongation at break of 38.0 %, and the 5 wt% loss temperature for membrane is ≈159 °C. The H 2 /O 2 single fuel cells with this membrane show a maximum power density of 124 mW cm −2 at 50 °C. The cross-linked membranes demonstrate high-dimensional stability in alkaline solution.