Benzimidazole‐and‐amide‐linked thin polymer membranes for <scp> H ₂ </scp> / <scp> CO ₂ </scp> separation under pressures up to 30 bar

Abstract The separation of H 2 /CO 2 imposes stringent demands on membrane performance, cost‐effectiveness, and scalable preparation. This study presents an innovative three‐layer composite membrane structure designed to enable pressure‐resistant membrane fabrication on an organic substrate. Specifically, a polyethyleneimine layer (first layer) was employed to coat the substrate, onto which a novel benzimidazole‐and‐amide‐linked polymer separation layer (second layer) was formed via interfacial polymerization with a new monomer combination. The resulting dual‐layer membranes demonstrated exceptional separation performance under 30 bar (423 K), achieving an H 2 /CO 2 selectivity of 16.5 (H 2 permeance of 53.7 GPU) and maintained stability during 200‐h pressure cycling tests (5–30 bar). A third layer was subsequently introduced via polydimethylsiloxane coating for defect repair, and the membrane area was scaled up from 17.9 cm 2 to 56.6 cm 2 (effective test area increasing from 1.33 cm 2 to 19.6 cm 2 for each). The final membranes retained H 2 /CO 2 selectivity &gt;10.0 (20 bar), significantly enhancing the industrial application potential.