Poly(hydrazide–imide) Membranes with Enhanced Interchain Interaction for Highly Selective H₂/CO₂ Separation

Abstract

Membrane-based H 2 /CO 2 separation plays a significant role in sustainable hydrogen production. However, due to the similar diffusion speed of H 2 and CO 2 in polymers, very few polymer membranes can effectively separate them, which largely limits the application of membrane technology in the hydrogen production process. In this work, a new polymer named poly(hydrazide–imide) (PHI) is synthesized by the polycondensation reaction of aromatic dianhydride with isophthalic dihydrazide and is used for H 2 /CO 2 separation. Hydrazide, a typical polar molecule, is introduced into the polyimide backbone to induce the formation of a hydrogen bond network inside the polymer as confirmed by temperature-dependent infrared reflection spectroscopy. With further thermal annealing, intermolecular π–π interaction is simultaneously strengthened as proved by fluorescence emission spectroscopy, UV–vis absorption spectroscopy, and wide-angle X-ray diffraction (WAXD) characterization. The synergistic effect of the H-bond and π–π interaction efficiently enhances the interchain interaction and optimizes the polymer packing state. The obtained membranes demonstrate greatly improved H 2 permeabilities and H 2 /CO 2 selectivity with the comprehensive separation performance surpassing the 2008 Robeson upper bound. The membranes also exhibit excellent CO 2 plasticization resistance up to 40 bar and stability in the long-time (>100 h) mixed gas separation test. The design of hydrazide-based polyimide polymer membrane provides a new route for preparing polymer materials for H 2 /CO 2 separation.