Influence of support layer resistance on oxygen fluxes through asymmetric membranes based on perovskite-type oxides SrTi1-xFexO3-δ

Asymmetric membranes of mixed ionic-electronic conducting pemvskite-type oxides SrTi1-xFexO3-delta (STF, x = 0.3, 0.5 and 0.7) were prepared by inverse sequential tape-casting. Both porous support (similar to 600 mu m) and functional membrane layer (similar to 20 mu m) for a given membrane assembly were made from the same composition to ensure thermochemical compatibility between the layers. Oxygen fluxes were assessed in the range 650 -1020 degrees C, using either (non-pressurized) ambient air or pure oxygen as feed gas at the support side of the asymmetric membrane and argon as sweep gas. Notably, similar oxygen fluxes (similar to 1.2 x 10(-6) mol cm(-2) s(-1)) are measured through the membranes of different compositions above 950 degrees C when using ambient air as feed gas. This observation is interpreted to reflect the major role of the support layer resistance in rate-limiting the oxygen fluxes through the STF asymmetric membranes, which conclusion is supported by comparison of the oxygen fluxes with those measured previously through asymmetric membranes of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) and La0.6Sr0.4Co0.2-Fe0.8O3-delta (LSCF). A simple diffusion-convection model is used to account for the observed gas phase polarization in the porous support layers limiting the oxygen fluxes.