Preformed covalent organic framework network‐based polyimide mixed matrix membranes for high‐flux hydrogen separation

Abstract Mixed matrix membranes (MMMs), combining the processability of polymers with the separation performance of fillers, have attracted significant attention for industrial gas separations. Nevertheless, achieving a uniformly distributed, highly connected filler phase remains a major obstacle, limiting the separation performance enhancement of MMMs. Herein, we report a family of preformed covalent organic framework (COF) network‐based MMMs, which are fabricated by preforming a continuous COF network followed by infiltration of a polyimide matrix. This preforming‐filler‐network (PFN) method constructs a three‐dimensional (3D) interconnected transport scaffold within the membrane. This unique structure eliminates filler agglomeration, a key challenge that has not been resolved by conventional MMM fabrication methods. Consequently, the membranes achieve a 707.7% enhancement in H 2 permeability (to 366.7 Barrer) and a 121.7% increase in H 2 /CH 4 separation factor (to 100.2) compared to pristine polyimide membranes. The COF‐network MMM also exhibits excellent stability and plasticization resistance, further highlighting its potential for real‐world hydrogen purification.