Quaternary ammonium COF-based proton exchange membranes for enhanced electrochemical hydrogen compression

Proton exchange membranes (PEMs) with high proton conductivity, excellent mechanical strength, and minimal hydrogen crossover are crucial for the practical implementation of electrochemical hydrogen energy conversion devices, including electrochemical hydrogen compression (EHC). Herein, hydrazone-linked ionic covalent organic frameworks (iCOF) bearing quaternary ammonium (QA) groups were synthesized and introduced into the sulfonated poly (ether ether ketone) (SPEEK) matrix to fabricate hybrid PEMs. Among them, the orderly arrangement of QA and –NH- groups on iCOF not only rearranged the distribution of −SO 3 H groups in the SPEEK polymer matrix, increasing the continuity and connectivity of the proton conduction pathways but also formed acid-base pairs with −SO 3 H groups to facilitate proton dissociation. Additionally, the electrostatic and hydrogen bonding interactions formed between iCOF and SPEEK matrix optimized the microphase separation structure and enhanced the mechanical stability of membranes. As a result, the hybrid PEMs exhibited an enhanced proton conductivity of 469.0 mS cm −1 (80 °C, 100 % RH) with only 2 wt% iCOF content, high mechanical strength of 91.3 MPa, and superior EHC performance with a high outlet pressure of 3.31 MPa (30 °C, 100 % RH) and high-purity hydrogen (>99.9 %) from a 40 % hydrogen–nitrogen mixture.