Results on the oxygen permeability and stability of perovskite-type La{sub}0.6Sr{sub}0.4Co{sub}0.8Fe{sub}0.2O{sub}3 (LSCF) coated with (Sm{sub}2O{sub}3){sub}0.1(CeO{sub}2){sub}0.9 (SDC) are presented. Bilayer structures were formed by depositing a thin layer of SDC by pulsed laser deposition (PLD) on the reducing side of the membrane. Oxygen permeation fluxes measured with air on the feed side and He-CH{sub}4 mixtures on the sweep or reducing side are compared with non-coated results. With the introduction of CH{sub}4 into the Re sweep, LSCF samples exhibit very high oxygen flux values but degrade rapidly as the membrane decomposes to less conductive phases. In contrast, LSCF/SDC bilayer membranes under similar conditions show superior stability and increased oxygen flux over a period of greater than 50 h. During reaction runs with CH{sub}4, a cyclic redox reaction with respect to ceria was observed and is believed to be due to oscillations in the P{sub}(O{sub}2) at the SDC-gas interface.
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