Highly efficient H₂ separation and purification performance of C₇N₆ membranes with strain modulation: DFT calculations and MD simulations

Abstract The ever-increasing demand for high-quality hydrogen drives a strong emphasis on developing high-efficiency membranes for hydrogen purification and separation. By adopting a combined approach of density functional theory and molecular dynamics simulations, the structural stabilities, and H 2 purification and separation properties of strain modulated C 7 N 6 monolayer membranes were performed. Our results show that when the applied biaxial tensile strains (BT-strains) are ⩽12%, the C 7 N 6 monolayer is still stable enough for applications. The H 2 permeability of the C 7 N 6 membrane under 5%–7% BT-strains separating from the gas mixture (H 2 , O 2 , CO 2 , CO, N 2 and H 2 O) can reach 2.51 × 10 7 –5.83 × 10 7 GPU at 300 K, much higher than most of the known membranes. H 2 , O 2 , CO 2 , CO, N 2 and H 2 O molecules overcoming an energy barrier of 0.145, 0.502, 0.574, 0.725, 0.798 and 0.587 eV, respectively, can pass through the 7%-strained C 7 N 6 . The selectivity of H 2 /O 2 , H 2 /H 2 O, H 2 /CO 2 , H 2 /CO and H 2 /N 2 at 300 K under 5% strain is 1.38 × 10 8 , 2.65 × 10 10 , 2.25 × 10 10 , 1.17 × 10 13 and 3.54 × 10 14 , respectively. This is 1–2 orders of magnitude higher than that of the pure C 7 N 6 membrane at 500 K, and even under 7% strain, the corresponding selectivity reduces to 1.03 × 10 6 , 2.71 × 10 8 , 1.65 × 10 7 , 5.53 × 10 9 and 9.39 × 10 10 , respectively. The 5%–7% strained C 7 N 6 membranes were revealed to possess highly efficient H 2 separation performance at room temperature. Our findings provide favorable guidance for practical hydrogen separation and purification via strain-modulated C 7 N 6 membranes.