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 first-principles calculations and molecular dynamics simulations, the structural stabilities and H2 purification and separation properties of strain modulated C7N6 monolayer membranes were performed. Our results show that when the applied biaxial tensile strains (BT-strains) are ≤12%, the C7N6 monolayer is still stable enough for applications. The H2 permeability of the C7N6 membrane under 5%-7% BT-strains separating from gas mixture (H2, O2, CO2, CO, N2 and H2O) can reach 2.51×107~5.83×107 GPU at 300 K, much higher than most of known membranes. H2, O2, CO2, CO, N2, and H2O molecules overcoming energy barrier of 0.145, 0.502, 0.574, 0.725, 0.798, and 0.587 eV, respectively, can pass through the 7%-strained C7N6. The selectivity of H2/O2, H2/H2O, H2/CO2, H2/CO, and H2/N2 at 300 K under 5% strain is 1.38×108, 2.65×1010, 2.25×1010, 1.17×1013, and 3.54×1014, respectively, which is 1-2 order of magnitude higher than that of the pure C7N6 membrane at 500 K, even under 7% strain, the corresponding selectivity reduces to 1.03×106, 2.71×108, 1.65×107, 5.53×109, and 9.39×1010, respectively. The 5%-7% strained C7N6 membranes were revealed to possess high-efficient H2 separation performance at room temperature. Our findings provide a favorable guidance for practical hydrogen separation and purification via strain-modulated C7N6 membranes.