Hydrogen (H2) is a vital clean-energy alternative to fossil fuels, with zero-emission potential. H2 obtained from different sources is usually impure, and its effective separation is required for practical application. Microporous cobalt-silica membranes have shown potential for high-temperature H2 separation. The common method of producing these membranes is dip-coating, evaporation drying, and calcination. During evaporation drying, surface tension causes cohesion-adhesion imbalances, which result in uneven solvent evaporation, stress accumulation, and capillary forces that produce cracks and pinholes. Such defects allow non-selective gas permeation, which is a major limitation to membrane separation efficiency. In this work, an innovative supercritical-drying method is proposed to reduce the stress-related defects in silica membrane by preventing surface tension during the drying process. For this purpose, six layers of cobalt-silica membranes were applied on α-alumina substrate and dried using supercritical and traditional evaporation drying methods. Structural and morphological analyses have shown that supercritical drying led to a condensed and amorphous silica structure, a reduction in silanol groups, and an increase in the ratio of completely condensed siloxane bonds. Supercritical drying stabilizes more mesopores by preventing the collapse of pores, producing a structure that is both chemically denser
and physically more open. Smooth surface morphology and the absence of defects in the supercritical-dried membrane led to high separation efficiency. The supercritical-dried membrane exhibited 3 and 2-fold higher selectivity to H2/N2 and H2/CO2, respectively, than the evaporation-dried membrane, achieving ≥90% H2 purity in the permeate to demonstrate its ability to be used in the high-temperature H2 separation process