Excellent membranes for hydrogen purification: Dumbbell-shaped porous γ-graphynes

Abstract

Two dumbbell-shaped porous γ-graphynes were designed by substituting one-third acetylenic linkages with heteroatoms nitrogen and hydrogen named γ-GYN and γ-GYH, respectively. The calculated cohesive energies and phonon dispersion spectra indicate the possibility to realize the new membranes in experiments. The separation performance of the designed monolayers for H2 from H2O, CO2, N2, CO, and CH4 was investigated using both first-principle density functional theory (DFT) and molecular dynamic (MD) simulations. The DFT calculations suggest the designed membranes are excellent in H2 separation because of the super high selectivities of H2 over other gases H2O, CO2, N2, CO, and CH4 (>1010, 1013, 1021, 1018, and 1046, respectively, at room temperature) together with the high/extremely low permeances for H2/other gases, e.g., reaching the industrial standard at 400 K (γ-GYN) and 425 K (γ-GYH)/lower than the industrial limit by 3–22 orders even at 600 K. The MD simulations indicates that only H2 in the gas mixture containing H2, H2O, CO2, N2, CO, and CH4 can penetrate across the membranes even at the temperature of 600 K and γ-GYN is more favorable for H2 penetration. All these results indicate both the designed membranes, especially γ-GYN, are excellent candidates for H2 purification from gas mixtures.