Oxygen transport model for layered MIEC composite membranes

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 La0.5Sr0.5Fe0.8Ga0.2O3-delta/SrCo0.8Fe0.2O3-delta membrane achieved an oxygen outwards flux of 0.45 mL/min*cm(2) at 1000 degrees C from an air/helium gradient. This was a similar to 50% increase over that obtained using an uncoated LSFG tube. (c) 2006 Elsevier B.V. All rights reserved.