Tunable Hydrogen Separation in Porous Graphene Membrane: First-Principle and Molecular Dynamic Simulation

First-principle density functional theory (DFT) calculation and molecular dynamic (MD) simulation are employed to investigate the hydrogen purification performance of two-dimensional porous graphene material (PG-ESX). First, the pore size of PG-ES1 (3.2775 angstrom) is expected to show high selectivity of H-2 by DFT calculation. Then MD simulations demonstrate the hydrogen purification process of the PG-ESX membrane. The results indicate that the selectivity of H-2 over several other gas molecules that often accompany H-2 in industrial steam methane reforming or dehydrogenation of alkanes (such as N-2, CO, and CH4) is sensitive to the pore size of the membrane. PG-ES and PG-ES 1 membranes both exhibit high selectivity for H-2 over other gases, but the permeability of the PG-ES membrane is much lower than the PG-ES 1 membrane because of the smaller pore size. The PG-ES2 membrane with bigger pores demonstrates low selectivity for H-2 over other gases. Energy barrier and electron density have been used to explain the difference of selectivity and permeability of PG-ESX membranes by DFT calculations. The energy barrier for gas molecules passing through the membrane generally increase with the decreasing of pore sizes or increasing of molecule kinetic diameter, due to the different electron overlap between gas and a membrane. The PG-ES1 membrane is far superior to other carbon membranes and has great potential applications in hydrogen purification, energy clean combustion, and making new concept membrane for gas separation.