Advanced polymeric membranes for CO₂ separation: fundamentals, materials, and practical challenges

Membrane-based CO₂ separation is emerging as a central technology for achieving carbon neutrality, yet its widespread deployment remains constrained by longstanding trade-offs among permeability, selectivity, long-term stability, and scalability. This review provides the conceptual foundations, materials evolution, and market drivers shaping the next generation of polymeric CO₂ separation membranes. We first revisit the fundamentals of mass transport through dense polymer films and highlight how trade-offs arise from the interplay among solubility, diffusivity, and free-volume architecture. Building on this framework, we examine three major materials platforms that have redefined performance boundaries: thermally rearranged (TR) polymers that generate controlled microporosity through in situ cyclization; polymers of intrinsic microporosity (PIMs) that embody rigid, contorted backbones with permanent ultramicroporosity; and ether-rich CO₂-philic polymers that achieve high solubility selectivity and excellent processability. By integrating molecular-level insights with thin-film engineering considerations, we evaluate each material family's potential and limitations in realistic process environments. At the system level, we analyze global markets, including natural gas sweetening, post-combustion CO₂ capture, blue hydrogen purification, and biogas upgrading, where polymeric membranes are poised for rapid growth. Finally, we identify future research directions centered on stabilizing free volume, suppressing plasticization, enhancing thin-film robustness, and accelerating materials-to-module translation through digital design and advanced fabrication. Together, these strategies delineate a pathway for polymeric membranes to become scalable, energy-efficient tools for industrial CO₂ management in the coming decade.