Progressive Pore‐Narrowing in Ultramicroporous Polymeric Membranes for High‐Throughput H₂/CO₂ Separation

Abstract Efficient H 2 /CO 2 separation using membrane technology is crucial for energy‐efficient hydrogen production. However, due to the similar transport rates of the two gases, existing polymeric membranes face significant challenges in H 2 /CO 2 separation. In this work, the microporous structure of polymer membranes is designed by a two‐step collaborative cross‐linking strategy to achieve ultra‐permeable mixed‐gas H 2 /CO 2 separation, where rigid molecular cross‐linking sites are incorporated into the polymer chains to stabilize the pore structure and the flexible molecular cross‐linking sites are subsequently incorporated to finely tune the pore size of the membranes. Through this two‐step collaborative cross‐linking‐based structure reconstruction (TSC‐SR) strategy, a membrane derived from an amidoxime‐functionalized polymer precursor achieves a H 2 permeability of 1117.4 barrer and a H 2 /CO 2 selectivity of 34.1, and a membrane derived from a nitrile‐functionalized polymer precursor achieves a H 2 permeability of 237.0 barrer and a H 2 /CO 2 selectivity of 107.3. The performance of the two membranes is superior to all reported polymer membranes and even surpasses most inorganic membranes. The work not only demonstrates that polymeric membranes can effectively separate H 2 /CO 2 but also represents a significant advancement in the design of polymeric membranes for gas separation.