Lewis acid‐driven interlayer shifting in sub‐nm <scp>2D</scp> covalent organic framework membranes for hydrogen purification

Abstract Covalent organic framework (COF) membranes are promising for eco‐friendly separations, but precise control of pore size at the angstrom level has been challenging, limiting their application in gas separation. This study introduces a pore redistribution method to reduce pore size to the sub‐nanometer range in single‐phase COF membranes. Using a Lewis acid (YbCF 3 (SO 3 ) 3 ) as the catalyst, interlayer shifting in 2D COFs was observed, which accelerates imine formation and weakens interlayer stacking forces. The pore size was engineered from &gt;1.0 to ~0.6 nm. The optimal membrane achieves a competitive H 2 permeance of 2253 gas permeation units (GPUs) and a high H 2 /CO 2 selectivity of 21.6 in a binary equimolar gas test at room temperature, outperforming other one‐phase COF membranes and exceeding the 2008 Robeson upper bound. This approach offers an effective strategy for engineering microporous materials for gas separation and other applications.