High Proton Conductivity of Sulfonate-amine Ionic HOFs and Enhancement of SPEEK Composite Membranes.

Hydrogen-bonded organic frameworks (HOFs) are crystalline materials assembled by intermolecular hydrogen-bonding interactions, and their hydrogen-bonding structures are effective pathways for proton transport. Herein, we synthesize iHOF-45 using 4,4'-diaminodiphenylmethane and 1,3,6,8-pyrenetetrasulfonicacid sodium salt with 2D hydrogen-bonding networks. The stability of ionic HOFs (iHOFs) can be enhanced by introducing ionic bonds in addition to hydrogen-bonding forces. Thermal analyses demonstrated that iHOF-45 exhibited excellent thermal stability up to 332 °C. The proton conductivity of iHOF-45 was evaluated, demonstrating a notable increase with rising temperature and RH. At 100 °C and 98 % RH, the conductivity reached 5.25×10 ^-3  S cm ^-1 . The activation energy (E _a ) of iHOF-45 was calculated to be 0.281 eV for 98 % RH, and the proton conduction was attributed to the Grotthuss mechanism, whereby the protons were transported in 2D hydrogen-bonding networks. Moreover, iHOF-45 was doped into SPEEK to prepare composite membranes, the proton conductivity of the 15 % iHOF-45/SPEEK membrane reached 9.52×10 ^-2  S cm ^-1 at 80 °C and 98 % RH, representing a 45.1 % increase over that of the SPEEK. This suggests that doping enhances the proton conductivity of SPEEK and providing a reference for the development of high proton conductivity materials.
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