Ultrathin membrane with robust and superior CO₂ permeance by precision control of multilayer structures

Reducing CO₂ emissions in the atmosphere is an urgent task to resolve serious environmental issues including global warming. Polymer-based ultrathin film composite (UTFC) membranes are an attractive strategy compared with other CO₂ separation technologies due to their lower environmental impacts, higher cost-efficiency, and ease of scale-up. However, improving the gas separation performance with a simplified fabrication process is still needed for practical uses. The key to designing a high-performing gas separation composite membrane is the development of a highly gas-permeable gutter layer and ultrathin high-selective top layer. While the top layers in nanoscale thicknesses have been recently developed, achieving high gas permeance is still challenging due to the existing less controlled gutter layer. Gutter layers afford a uniform and highly permeable base to which an ultrathin selective layer can be coated, minimising the gas permeance loss while maintaining the gas selectivity. Polydimethylsiloxane (PDMS) is a common and widely used material for gutter layers due to its inherent high gas permeability. However, the CO₂ permeance of these films is limited to between 1,500 and 5,000 GPU as the current uncontrollable fabrication methods tend to produce thicker layers. Here we report a new fabrication method with precise thickness control, which results in ultrathin gutter layers showing consistent CO₂ permeance with 13,920 ± 1,770 GPU without any reduction in CO₂/N₂ selectivity. When this gutter layer was coated with a selective layer of PolyActive™ (PA), the resultant PAN/PDMS/PA composite membranes outperformed previously reported UTFC membranes with a CO₂ permeance of 3,555 GPU and CO₂/N₂ selectivity of 40.