Selective penetration mechanism of hydrogen isotope through graphene membrane

Abstract

High selectivity of protons over deuterons transport through one-atom-thick graphene membrane has been demonstrated experimentally, but its fundamental mechanism has been controversially discussed. Proposed hypotheses involve local hydrogenation, but the detailed penetration process has not been rigorously explained. In the present study, based on electron cloud density, transition path selection and corresponding barrier calculations, perfect graphene is quasi-impermeable to protons, yet lateral ring chemically bonded protons adjacent hydrogenated hexa-cyclohydride shows the lowest barrier for the penetration of proton. The bridge-flip as a link provides the site for the penetration of the proton through the graphene. The chemically bonded protons slip into C–C to forms a C–H–C bridge bonds, and then flip over the graphene membrane to complete the penetration process. • Electron cloud distribution is the main factor driving protons to have different penetration paths and barriers. • Protons exhibit lateral ring penetration under the combined action of spatial effects and interatomic forces. • A slight difference in vibrational zero point energies is sufficient to exhibit a higher separation effect.