Theoretical investigation on two-dimensional conjugated aromatic polymer membranes for high-efficiency hydrogen separation : The effects of pore size and interaction

Based on two-dimensional conjugated aromatic polymer (2D-CAP), CAP-1S/CAP-1P monolayers were designed by substituting N with S/P atoms for H₂ purification. By using MD and DFT approaches, the H₂ purification performance and separation mechanisms of CAP-1S/CAP-1P membranes were investigated. Results showed that ultrahigh H₂ permeances of 3.546 × 10⁻⁵ and 2.593 × 10⁻⁴ mol m⁻² s⁻¹ Pa⁻¹ were obtained in CAP-1S/CAP-1P, which were almost 10⁴–10⁵ times larger than the industrially acceptable standard. The selectivities of H₂ over CO₂/CO/CH₄/N₂ ranged from 5.719 × 10¹⁸ to 3.683 × 10³⁹ in CAP-1S and 4.554 × 10¹³ to 2.153 × 10³³ in CAP-1P. From a statistic viewpoint, the CAP-1S/CAP-1P membranes exhibited complete selectivities of H₂ over CO₂/CO/CH₄/N₂. The cohesive energies confirmed the high stabilities of CAP-1S/CAP-1P membranes. The minimum energy pathways, energy profiles, electron density, and charge density difference were analyzed to illustrate the significant impact of precise pore size on the H₂ separation performance. From a statistic mechanics view, the interaction between gases and CAP-1S/CAP-1P membranes indicated that the long-range Coulomb interactions dominated the gas diffusion processes. Results of this work highlighted CAP-1P as a promising H₂ separation membrane and elucidated the promotion mechanism by fine-tunning pore size and interaction between gases and membranes to balance the H₂ permeance and selectivity jointly.