High proton conductivity of sulfonate-amine ionic HOFs and enhancement of SPEEK composite membranes.

ABSTRACT

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 introduction of ionic bond based on the weak hydrogen-bonding force was employed to enhance the stability of ionic HOFs (iHOFs). 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 (Ea) 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.