Facilely Cross-Linking Polybenzimidazole with Polycarboxylic Acids to Improve H₂/CO₂ Separation Performance

Polybenzimidazole (PBI) with a strong size-sieving ability exhibits attractive H₂/CO₂ separation properties for blue H₂ production and CO₂ capture. Herein, we report that PBI can be facilely cross-linked with polycarboxylic acids, oxalic acid (OA), and trans-aconitic acid (TaA) to improve its separation performance. The acids react with the amines on the PBI chains, decreasing free volume and increasing size-sieving ability. The acid doping increases H₂/CO₂ selectivity from 12 to as high as 45 at 35 °C. The acid-doped samples demonstrate stable H₂/CO₂ separation performance when challenged with simulated syngas containing water vapor at 150 °C, which surpasses state-of-the-art polymers and Robeson's upper bound for H₂/CO₂ separation.