Carbon Molecular Sieve Membranes Derived From Dual-Cross-linked Polybenzimidazole for Enhanced H₂/CO₂ Separation

The need for efficient CO₂ separation during hydrogen production from fossil fuels drives the development of advanced, energy-efficient solutions. Membrane technology offers a promising approach for separating CO₂ from H₂, which, however, faces the challenge of low H₂/CO₂ selectivity. To address this challenge, a novel strategy to cross-link polybenzimidazole (PBI) using potassium persulfate (K₂S₂O₈) is proposed, followed by pyrolysis to fabricate highly selective carbon molecular sieve (CMS) membranes. The cross-linked PBI-derived CMS membranes exhibit significantly enhanced permeability and H₂/CO₂ selectivity compared to neat PBI-CMS membranes. For instance, the CMS membrane prepared from PBI cross-linked for 24 h and pyrolyzed at 900 °C (denoted as KPBI₂₄ CMS@900) demonstrates outstanding molecular sieving capability. This membrane achieves an H₂ permeability of 55 Barrer with an H₂/CO₂ selectivity of 48 tested at 100 °C, significantly surpassing its non-cross-linked counterparts and the 2008 Robeson upper bound. The design principles of this study provide a robust technical foundation for persulfate-cross-linked PBI and offer an innovative approach for preparing high-performance CMS membranes.