Oxygen-induced structural hierarchy in 10-nm-thick carbon membranes for high-performance hydrogen separation

Carbon membranes yielding high selectivity as well as high permeance are attractive to advance the membrane-based gas separation. Herein, we report novel ultrathin carbon membranes (UCMs) which deliver exceptional gas separation performance through oxygen-modulated pyrolysis of poly(4-vinylpyridine) precursor. We show that O2 in pyrolysis environment, transforms the otherwise uniform carbon network featuring ~3.9 Å pore structure into disrupted UCMs (d-UCMs) resulting in hierarchical pore structure comprising ~3.4 Å, 3.9 Å, and 5.5 Å pores. This structural hierarchy enables a record combination of H2 permeance exceeding 10,000 gas permeation units (GPUs) and H2/N2 selectivity surpassing 200. Meanwhile, d-UCM exhibits outstanding physical and thermal stability, showing no aging over 7 days of elevated temperature permeance testing, which overcomes the common issue of rapid aging in carbon membranes. Mechanistic investigations reveal that O2 pyrolysis environment selectively removes relatively weakly-bound carbon species, altering pyrolysis intermediates, resulting in a nitrogen-rich framework with disordered nanodomains and hierarchical porosity. This work advances the material chemistry of ultrathin high-performance carbon membranes, attractive for ultrafast and high-precision molecular-sieving for molecular separation.