Network‐Nanostructured ZIF‐8 to Enable Percolation for Enhanced Gas Transport

Membrane‐based separations offer energy‐efficient solutions for various applications, but commercial polymer membranes show limited performance and stability. Mixed‐matrix membranes (MMMs), incorporating nanoporous inorganic materials in polymer matrices, have been of great interest to circumvent these polymer‐specific issues. However, reaching the percolation threshold is crucial to leverage high‐performing inorganic phases fully, yet the traditional sphere‐like nanofillers require high loadings that easily result in agglomerations and non‐selective defects. Here, a branch‐shaped zeolitic imidazole framework‐8 (ZIF‐8) nanoparticle is synthesized where its unique morphology automatically interconnects, readily forming percolated networks within the polymer matrix at loadings as low as 20 wt.%. Because of the high surface‐area‐to‐volume ratios of branched ZIF‐8 (BZ), strong polymer–particle interactions suppress polymer chain dynamics and the rotation of the ZIF‐8 ligand. This interphase confinement results in enhanced membrane stability and a smaller diffusion cut‐off than traditional ZIF‐8. With pre‐connected diffusion pathways and confined ZIF pores, BZ MMMs significantly outperformed MMMs with sphere‐like ZIF‐8 for H2‐based separations. Overall, the findings provide a novel approach to enhance filler effects in MMMs even at low loadings without any alignment, which can enable the development of advanced membranes in fields where percolation is desired, including separations, sensors, conductors, and batteries. Branch‐shaped ZIF‐8 (BZ) is synthesized for the first time. Compared to the typical sphere‐like ZIF‐8 nanoparticles, BZ readily forms percolated networks when incorporated into mixed‐matrix membranes. Moreover, strong BZ–polymer interactions confine metal–organic framework ligand rotation and reduce polymer chain mobility resulting in more selective hydrogen‐based separations and exceptional plasticization resistance.