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 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.