Lithium ion-coordinated polybenzimidazole/polyethylene glycol blend membranes: Synthesis, characterization, and application in H2/CO2 separation

Polybenzimidazole (PBI) and its derivatives have excellent thermal stability, mechanical robustness and is suitable for fabricating H 2 /CO 2 separation membranes. However, the H 2 /CO 2 selectivity of the membranes made from commercial PBI are not sufficiently high for practical use. Current post-cross-linking of PBI membranes can raise H 2 /CO 2 selectivity by enhancing the sieving effect, while prone to creating a discrepancy in cross-linking density between the surface and interior of a membrane, which induces internal stress and deformation. In this study, the OPBI-LiCl-PEG ternary component membranes were constructed by solution casting method. XRD and XPS analyses confirmed that metal coordination of Li + with imidazole nitrogen/ether oxygen cooperates with N–H⋯O hydrogen bonds to construct supramolecular networks. The rigid OPBI backbone provides a three-dimensional scaffold, traversed by flexible PEG segments, while Li + coordination enhances multi-component synergy and fundamentally inhibits phase separation. Gas permeation experiments showed that H 2 /CO 2 selectivity of OPBI-LiCl(1)-PEG(1) membrane reached 15.4 ​at 5 ​bar and 35 ​°C, significantly higher than the OPBI-LiCl(1) and OPBI-PEG(1) membranes. This result indicates that the components form a significant synergistic effect rather than undergoing simple physical mixing. On the other hand, the H 2 /CO 2 selectivity of OPBI-LiCl(1)-PEG(1) membrane remains 10.9 even at 150 ​°C. Compared to previous post-crosslinking modification methods for PBI, this one-step crosslinked OPBI membrane fabricating approach is more suitable for industrial applications. • A stable supramolecular polymer network was successfully constructed in polybenzimidazole (PBI) through an in-situ coordination cross-linking strategy. • The incorporation of PEG enhances membrane performance synergistically by suppressing phase separation and promoting structural densification. • The modified membrane demonstrated superior H 2 /CO 2 selectivity.