Oxygen transport model for layered MIEC composite membranes

Abstract

Surface exchange resistance can reduce the oxygen transport through dense mixed ionic-electronic conducting (MIEC) membranes. Addition of an MIEC surface layer to a base substrate can reduce the surface exchange resistance. Existing oxygen transport relations that consider bulk diffusion and surface exchange resistance are extended to treat coated membranes formed by depositing a highly conductive, thin layer of MIEC on the surface of a dissimilar MIEC substrate and accounting for the solid/solid interfacial resistance. The oxygen flux through the coated membrane may exceed that through the bare membrane only if: 1) the surface exchange coefficient of the added layer is larger than the surface exchange coefficient of the bare membrane; and 2) the solid/solid interfacial resistance is sufficiently small. In general, deposition of the surface layer on the membrane tube surface exposed to lean gas leads to a larger oxygen flux than deposition of the layer on the oxygen rich side. A La 0.5Sr 0.5Fe 0.8Ga 0.2O 3- δ /SrCo 0.8Fe 0.2O 3- δ membrane achieved an oxygen outwards flux of 0.45 mL/min ⁎cm 2 at 1000 °C from an air/helium gradient. This was a ∼ 50% increase over that obtained using an uncoated LSFG tube.