Large‐Area COF Membrane with Hourglass‐Shaped Nanochannels for Enhanced Hydrogen Separation

Abstract Efficient hydrogen purification from methanol steam reforming (MSR) faces challenges due to H 2 /CO 2 kinetic diameter overlap and energy‐intensive traditional methods. Here, we report a biomimetic hourglass‐shaped covalent organic framework (COF) membrane via sequential spray coating of opposite charged COF nanosheets, mimicking aquaporin‐like hierarchical channels. The sandwich structure (large‐pore sulfonated COF outer layers, narrow‐pore guanidinium COF middle layer) enables dual‐functionality: outer TpBD‐SO 3 H layers perform as the diffusion chamber (2.5 nm pores) and protective layer, whereas the middle TpTGCl layer (0.8 nm pores) traps CO 2 via strong electrostatic interactions. The membrane achieves a H 2 permeance of 2833 GPU and H 2 /CO 2 selectivity of 21, surpassing the 2008 Robeson upper bound. Spray coating enables scalable fabrication of 5000 cm 2 defect‐free membranes on porous substrate with high mechanical stability and chemical resistance (mass loss < 0.3% in 150 °C methanol). Separation process simulations show a two‐stage system boosts H 2 purity to 96.7% with 94.3% recovery, outperforming pressure swing adsorption (PSA) in efficiency and energy consumption. This modular design offers a sustainable, scalable solution for industrial hydrogen purification and gas separation.