Fine-tuning ultramicroporosity in PIM-1 membranes by aldehyde functionalization for efficient hydrogen separation

Polymers of intrinsic microporosity (PIMs) have shown great potential for membrane-based hydrogen separations. The archetypal PIM, PIM-1, features hydrogen permeability that is 2-3 orders of magnitude higher than that of conventional polymers. However, the hydrogen selectivities of PIM-1 still need to be improved to meet the purity required for hydrogen production and distribution processes. Herein, we report a facile approach to fine-tune the microstructure of PIM-1 films by converting the nitrile groups of PIM-1 into aldehyde groups at room temperature. The aldehyde-functionalized PIM-1 (PIM-CHO) has a significantly higher concentration of ultramicropores (<7 Å) compared to PIM-1 as confirmed by gas sorption and X-ray scattering analyses. Ultimately, this feature results in excellent H₂/N₂ and H₂/CH₄ separation performance for PIM-CHO, approaching the most recent 2015 upper bound and outperforming all post-synthetically modified PIM-1 membranes reported to date. Mixed-gas transport studies also demonstrate the excellent potential of PIM-CHO for its deployment in practical applications.