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

Abstract 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 H 2 permeability of 3464 Barrer with H 2 /CH 4 selectivity of 3807, surpassing the Robeson upper bound. Upon pyrolysis at 850 °C, the 6F‐D‐S‐CMS‐850 membrane achieves exceptional selectivity values: H 2 /CH 4 at 6538, H 2 /N 2 at 1634, and H 2 /CO 2 at 149—outperforming most reported CMS membranes. Molecular dynamics simulations revealed that the Type B network suppressed CH 4 adsorption (3.6 cm 3  g −1  versus 6.2 cm 3  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.