Coordination crosslinking engineering of alkynyl-based polyimide membranes for H2/CO2 separation

Polyimide membranes, owing to their robust polymer backbone and facile structural tunability, are extensively used for H₂/CO₂ separation. However, efficient H₂ separation remains challenging because of the wide pore size distribution within the chain-packed structure of conventional polyimides. Here, we propose a coordination crosslinking engineering strategy, where Pd²⁺ is incorporated into an alkynyl-based polyimide containing carboxyl groups to generate coordination cross-linked networks in situ. The formed coordination bonds significantly reduce the interchain d-spacing and restrict the mobility of the polymer chains, thereby enhancing size-sieving ability. Additionally, the presence of Pd²⁺ significantly increases the affinity of membrane for H₂. Based on their synergistic effect, the optimized EBPA-TB-COOH@Pd²⁺-6 membrane (EBPA: 4,4′-(ethyne-1,2-diyl) diphthalic anhydride; EBPA-TB-COOH: alkynyl-based polyimide polymer) exhibits an unprecedented combination of high H₂ permeability (512.5 bar) and excellent H₂/CO₂ selectivity (30.4), surpassing most polyimide membranes reported to date. Furthermore, the coordination crosslinking networks endow the membranes with high and stable H₂/CO₂ separation performance under a wide operating pressure range (1 to 6 bar). This coordination crosslinking engineering strategy offers an effective approach for designing next-generation polyimide membranes for hydrogen recovery and purification.