Oxygen transport through dense La0.6Sr0.4Fe0.8Co0.2O3-δ perovskite-type permeation membranes

In this study, we examine the parameters that govern the overall oxygen flux through a permeation membrane. The chemical diffusion (D-delta) and the surface exchange (k(delta)) coefficients for oxygen in La0.6Sr0.4Fe0.8Co0.2O3-delta were determined as a function of temperature using a specially designed electrochemical cell combined with impedance spectroscopy. Typically, D-delta = 1.7 10(-5) cm(2)/s and k(delta) = 3.6 10(-4) cm/s in air at 900 degreesC. These values were compared with literature O-18/O-16 isotope exchange data. Oxygen permeation measurements were also performed on the same material in an air/Ar gradient, in the temperature range 800-1000 degreesC. At 900 degreesC, the oxygen flux across a 1.53 mm thick membrane was 8.0 10(-8) mol/(cm(2)s). The measured fluxes were compared with fluxes calculated on the basis of the D-delta and k(delta) values using expressions derived from Fick's law. Comparison showed that the flux is controlled by both bulk diffusion and surface exchange, even for such thick membranes, and that the apparent k(delta) varies significantly from one experiment to another. (C) 2003 Elsevier Ltd. All rights reserved.