Non‐selective Defect Minimization towards Highly Efficient Metal‐Organic Framework Membranes for Gas Separation

Abstract The persistence of defects in polycrystalline membranes poses a substantial obstacle to reaching the theoretical molecular sieving separation and scaling up production. The low membrane selectivity in most reported literature is largely due to the unavoidable non‐selective defects during synthesis, leading to a mismatch between the well‐defined pore structure of polycrystalline molecular sieve materials. This paper presents a novel approach for minimizing non‐selective defects in metal–organic framework (MOF) membranes by a constricted crystal growth strategy in a confined environment. The in situ ZIF formation using the densely packed seeding array between the substrate and the pre‐grown top ZIF layer yields a confined membrane interlayer, which is highly uniform with a tightly packed crystalline structure. Unlike uncontrolled crystal growth, we purposely regulate the interlayer membrane growth in the direction parallel to the substrate. A notable 99 % decrease in defects in the confined interlayer was achieved compared to the random‐grown top layer, leading to a ~353 % increment in H 2 /N 2 selectivity over the non‐confined reference MOF membrane. The performance of this new membrane sits in the optimal range above the Robeson upper bound. The membrane boasts a balanced high H 2 permeability (>5000 Barrer) and selectivity (>50), significantly surpassing peer ZIF membranes.