Facile Preparation of Carbon Membranes Derived from a Fluorenyl‐Containing Polyimine for Selective Hydrogen Separation

ABSTRACT Efficient hydrogen purification requires membrane materials that combine high perm‐selectivity, high permeance, and scalable fabrication. Here, we report carbon membranes (CMs) derived from a fluorenyl‐containing polyimine, synthesized through a simple, catalyst‐free condensation of inexpensive, commercially available monomers. The linear precursor exhibits thermal robustness (T d5% = 470°C; char residue ∼43% at 800°C) and an intrinsically kinked molecular architecture that promotes free volume and, upon pyrolysis, enables the formation of defect‐free carbon layers with enhanced gas permeance. Carbon membranes were fabricated on porous alumina supports and carbonized at 500, 700, or 900°C under varied heating rates to investigate the influence of pyrolysis conditions on gas transport behavior and performance. Structural characterization (Raman, XPS, SEM, TEM) revealed formation of carbon frameworks, with transport governed by selective adsorption/surface diffusion or molecular sieving depending on the carbonization profile. Membranes carbonized at 700°C showed the best overall performance, achieving H 2 permeances up to 5.8 × 10 −7 mol m −2 s −1 Pa −1 and ideal perm‐selectivities exceeding the 2008 Robeson Upper Bound for H 2 /N 2 , H 2 /CH 4 , and H 2 /CO 2 separations. The facile synthesis, reproducibility, and tunability of this platform highlight fluorenyl‐containing polyimines as a promising route to scalable, high‐performance CMs for hydrogen purification.