Electric‐Field‐Driven Assembly of Ultrathin and Crystalline iCOF Membranes for High‐Performance Molecular Sieving

ABSTRACT The fabrication of high‐performance ionic covalent organic framework (iCOF) membranes is fundamentally constrained by the kinetic conflict between the slow crystallization required for structural order and the rapid film formation needed for defect‐free continuity. Here, we introduce an electric‐field‐driven assembly (EFDA) strategy that actively overcomes this limitation. By applying a directional electric field across the liquid–liquid interface, we create a steep field gradient that electrophoretically pumps ionic monomers against diffusion barriers, achieving rapid and focused interfacial enrichment. This active supply enables the fast (∼4 h) growth of an ultrathin (∼45 nm), continuous, and highly crystalline iCOF layer—a combination unattainable by passive diffusion methods. The resultant membrane exhibits an exceptional water permeance of ∼70 L m −2 ·h −1 ·bar −1 coupled with precise charge‐selective separation (>98% rejection of anionic dyes), outperforming most reported nanofiltration membranes. Demonstrated with various ionic monomers, the EFDA strategy presents a universal platform for the rational construction of advanced molecular sieving membranes.