Covalent Organic Polymer Membranes with Exceptional Selectivities for Advanced High‐Pressure Stable Gas Separations

The long-standing challenge in fabricating advanced gas separation membranes lies in overcoming the trade-off between precise pore size control and the formation of defect-free layers. Herein, a high-performance covalent organic polymer (COP) membrane is reported, fabricated via a modulated interfacial polymerization strategy. The COP structure is rationally designed using tetra-amine and tri-aldehyde monomers to enhance cross-linking density and reduce effective micropore size. Analysis of CO₂ adsorption isotherms confirms a narrow pore size distribution centered around ≈0.34 nm, indicative of molecular sieving capability. The incorporation of ionic liquid combined with acetic acid at the interface enables precise regulation of amino monomer concentration, resulting in a controlled polymerization kinetic and facilitating the formation of a continuous, defect-free membrane. The resulting membrane exhibits exceptional H₂/CH₄ separation performance, achieving an ideal selectivity of 297.6 and H₂ permeance of 203.4 GPU. Remarkably, both permeance and selectivity remain stable under high feed pressures up to 2 MPa, attributed to the highly cross-linked and robust polymer networks. This work demonstrates a feasible strategy for designing high-pressure stable COP membranes with outstanding molecular sieving properties for energy-efficient gas separations.