Directing Ultramicropore Architecture in Carbon Molecular Sieve Membranes with Lanthanum for High‐Fidelity Gas Separation

A crucial performance ceiling has long limited carbon molecular sieve (CMS) membranes in demanding gas separations, a limitation stemming directly from the inability to precisely dictate their ultramicroporous architecture. Herein, we demonstrate a novel lanthanum (La)-doping strategy to precisely control the structural evolution of polyimide-based carbon CMS membranes. Lanthanum incorporation fundamentally alters pyrolysis dynamics by significantly increasing aromatic strand mobility and enabling La complexes to serve as nanoscale Langmuir templates. This entropic-driven templating effect guides the alignment of carbon strands and optimizes their narrow arrangement, resulting in a markedly narrow pore size distribution for precise gas separation. La-doped CMS membranes exhibit exceptional molecular sieving capabilities, notably, achieving 100-fold increase in H₂/CH₄ selectivity while maintaining high H₂ permeability. Even under realistic operating conditions involving variations in pressure, feed composition, and temperature, the La-doped CMS membranes retained their high H₂ permeability and selectivity, showing minimal sensitivity to feed composition and pressure and excellent resistance to physical aging. This straightforward, versatile, and scalable metal-doping approach presents a significant advancement for developing high-performance CMS membranes, opening new opportunities for challenging industrial gas separations that require precise differentiation of molecules with similar kinetic diameters.