Molecular-Level Engineering of Interlayer Channels in Vertically-Aligned LDH Arrays for Efficient Hydrogen Purification

2D layered double hydroxide (LDH) composite membrane in gas separation was limited by insufficient orientation control accuracy and interface incompatibility with the organic substrate. In this study, we proposed a molecular-level channel engineering strategy to construct an LDH composite membrane by synergistically integrating vertical orientation, interlayer ion intercalation, and surface chemisorption sites. Specifically, LDH was induced hydrothermally to grow vertically along the (003) crystal plane on hydrophilic HPAN substrate, forming straight-through transfer channels with low tortuosity. Furthermore, the interlayer spacing was precisely adjusted to 0.306 nm by Cl^- intercalation instead of CO₃ ^2- to sieve H₂ and CO₂. Concurrently, polyethyleneimine (PEI) was covalently grafted on LDH surface to further enhance H₂/CO₂ selectivity by CO₂ chemosorption. This multiple synergistic mechanism achieves simultaneous improvements of H₂ permeance and H₂/CO₂ selectivity. The prepared LDH(Cl^-)/PEI-HPAN membranes exhibited a H₂ permeance of 707 GPU and a H₂/CO₂ selectivity of 78.5, representing increasements of 244% and 185%, compared with the pristine LDH-HPAN membrane, exceeding the 2008 Robeson upper bound. This membrane integrates the anti-swelling stability of Cl^- (weak hydration) and the mechanical robustness of PEI hydrophobic chains, providing a new paradigm for 2D material membranes with high separation performances and ease of scalable preparation for industrial hydrogen purification.