Polyethylene oxide-intercalated nanoporous graphene membranes for ultrafast H2/CO2 separation: Role of graphene confinement effect on gas molecule binding

Abstract

H2/CO2 separation is essential for various industrial applications, such as hydrocarbon steam reforming for H2 production. Herein, a layered composite membrane composed of nanoporous graphene (NG) and polyethylene oxide (PEO) is developed. The membrane demonstrates an ultrafast H2 permeability of ca. 32 240 barrer with a moderate H2/CO2 selectivity of 25, which far surpasses the upper bound of the separation performance demonstrated by existing membrane materials. The regularly layered structure is fabricated by facilitating the intercalation of PEO via an aqueous graphene-oxide liquid crystal (GOLC) scaffold. After preparing the layered GO/PEO membrane, hot pressing is conducted to activate dense nanopores on the basal plane of graphene, resulting in an NG/PEO membrane. The permeation of gas molecules is significantly enhanced owing to the presence of nanopores and expansion of the interlayer spacing by PEO. In contrast, CO2 permeation is lower than that of H2 owing to its strong binding interaction with PEO, and molecular simulations demonstrate that this CO2–PEO interaction is significantly enhanced owing to the confinement of PEO in the graphene interlayer spacing, particularly at d-spacing of approximately 7–8 Å.