Hydrogen Separation in Flexible Nanoporous Graphene under Steady-State Permeation: A Molecular Dynamics Study

Efficient separation of hydrogen from mixed gas feeds remains a key challenge in hydrogen production. Here, nanoporous graphene (NPG) is investigated as a hydrogen-selective membrane using nonequilibrium molecular dynamics simulations that enforce steady-state flux via a constant axial driving force while allowing spontaneous membrane deformation. This approach captures realistic operating conditions often overlooked in idealized fixed-membrane studies. Binary mixtures of H2 with CO2, CO, CH4, O2, H2O, N2, and NH3 were examined across three nanopore geometries. The results demonstrate that membrane flexibility significantly influences separation performance: while dynamic pore expansion (parallel deflection) enhances permeance, it reduces selectivity relative to rigid models. We demonstrate that the hydraulic diameter governs the energy barrier for permeance: increasing pore area while disproportionately enlarging the perimeter reduces the hydraulic diameter, thereby increasing steric hindrance. Under these realistic conditions, NPG exhibits much higher permeance than polymer membranes. These findings highlight the importance of accounting for the dynamic coupling between permeation flux and membrane deformation for accurate performance prediction and suggest that mechanical strain is a potential strategy to balance the permeance–selectivity trade-off.