(726d) Few-Nanometer Organosilica Membranes for High-Temperature H2/CO2 Separation

Traditional silica membranes exhibit excellent H₂/CO₂ separation properties for H₂ purification and CO₂ capture, but they are brittle and faced with challenges for low-cost and large-scale production. Herein, we demonstrate the fabrication of ultrathin silica layer on polymeric membranes via plasma treatment to achieve superior H₂/CO₂ separation properties and excellent scalability of membrane production. Specifically, silica membranes were produced by applying oxygen plasma on polydimethylsiloxane (PDMS) thin films supported by microporous polymer substrates. The plasma treatment successfully converted the PDMS surface layer to a silica ultrathin film, indicated by the formation of SiO₂ as thin as 10 nm. We thoroughly investigated the silica formation mechanism and the effect of the plasma treatment conditions on physical properties and H₂/CO₂ separation properties of the silica membranes. With a plasma exposure time of 120 seconds, the membrane comprising 1.0 µm PDMS exhibits H₂ permeance of 370 GPU (1 GPU = 10^-6 cm³(STP)/cm³ s cmHg) and H₂/CO₂ selectivity of 51 at 200 ºC, which surpasses the Robeson’s upper bound. The membrane shows stable mixed-gas separation performance in the presence of water vapor at 200 °C for 47 h. When the PDMS layer thickness was decreased to 200 nm, the 120-second plasma treatment increases the H₂ permeance to 930 GPU and H₂/CO₂ selectivity decreases to 32, which is still above the upper bound. The robust H₂/CO₂ separation properties coupled with the facile fabrication demonstrate the potential of these organosilica membranes for practical H₂ purification and CO₂ capture.