Surface oxidation via water plasma for increased H2 permselectivity of Allylhydridopolycarbosilane (AHPCS)-derived SiC membranes

The objective of this research was to enhance the H₂ permselectivity of Allylhydridopolycarbosilane (AHPCS)-derived membranes through water plasma (WP) modification and subsequent pyrolysis. The WP modification, applied for 10 s, significantly improved the surface properties of the membranes to form ≡ Si–H, leading to enhanced H₂ permselectivity. Pyrolysis at 500−700 °C further transformed the membranes into a dense ceramic structure while maintaining high permeability for He and H₂ (0.3–1 × 10⁻⁶ mol/(m² s Pa)), achieved a significant increase in the permeance ratios of conventional SiC membrane from approximately 20 to 300 for H₂/N₂ and from 80 to 500 for He/N₂. Structural evolution analyses via Water contact angle (WCA) and X-Ray photoelectron spectroscopy (XPS) confirmed significant surface oxidation of ≡ Si–H groups to silanol ones via WP and condensation via pyrolysis. These modifications resulted in a structure ≡ of Si–O–Si ≡ on the surface, but SiC in bulk had markedly higher selectivity and permeance than AHPCS membranes pristine and modified with other methods. This design offers excellent thermal and chemical resistance, particularly for small to mid-sized molecules like He and H₂.