Programming Permeation Inversion in Nanoconfined Ionic Liquid Membranes for Ultra-Selective CO ₂ /H ₂ Separation

To bypass the enduring limitations intrinsic to traditional size-sieving separation, alternative materials for CO 2 /H 2 separation need to be developed. Here, we program a permeation inversion in CO 2 /H 2 transport by constructing a nanoconfined ionic liquid membrane through the synergistic engineering of graphene oxide nanosheets and ionic liquids. A substrate-assisted size-selection strategy enables the preferential incorporation of large nanosheets, which form ordered laminates, while short-chain CO 2 -philic ionic liquids are precisely confined within the interlayer galleries. The resulting membrane exhibits inverted transport behavior, achieving an ultrahigh CO 2 permeance of 358.2 GPU and a mixed-gas CO 2 /H 2 selectivity of 201.9 under a 10:90 CO 2 /H 2 feed─surpassing the upper bounds of conventional polymeric and mixed-matrix membranes. Scalability is demonstrated using a five-cell module, in which CO 2 flux increases linearly without selectivity loss. Molecular dynamics simulations and spectroscopic studies reveal that the nanoconfined ionic liquid phase creates a continuous, high-solubility pathway for CO 2, whereas H 2 is largely excluded from the graphene oxide interfaces. This study establishes nanosheet–ionic liquid synergy as a programmable design platform to engineer permeation inversion, offering a scalable route to advanced CO 2 /H 2 separation membranes.