High H 2 Recovery Properties of Carbon Molecular Sieve Membranes with Sub‐Nanometer Precision Derived from Dual Cross‐Linked Polyimide Precursor

Energy-efficient purification technologies are essential for advancing a sustainable hydrogen economy. Carbon molecular sieve membranes (CMSMs) have emerged as promising candidates; however, achieving precise sub-Angstrom micropore control and ensuring structural stability remain significant challenges. Here, we introduce a dual cross-linked strategy to engineer microporosity of the resulting CMSMs by utilizing a decarbonylated 3,5-diaminobenzoic acid (DABA)-induced rigid network (Type A) in conjunction with a sulfur bond-induced flexible network (Type B). The 6F-D-S-CMS membrane exhibits a record-high H₂ permeability of 3464 Barrer with H₂/CH₄ selectivity of 3807, surpassing the Robeson upper bound. Upon pyrolysis at 850 °C, the 6F-D-S-CMS-850 membrane achieves exceptional selectivity values: H₂/CH₄ at 6538, H₂/N₂ at 1634, and H₂/CO₂ at 149-outperforming most reported CMS membranes. Molecular dynamics simulations revealed that the Type B network suppressed CH₄ adsorption (3.6 cm³ g^-1 versus 6.2 cm³ g^-1) and significantly enhanced the small pore volume ratio (V_H2/V_CH4: 10.3 versus 2.1) during carbonization, thereby eliminating non-selective pathways and reducing inter-skeletal spacing (4.09 Å versus 3.78 Å), which enables precise molecular sieving. This rigid-flexible cross-linked strategy for CMSMs establishes a scalable blueprint for next-generation hydrogen production.