Oxygen permeation rates through ion-conducting perovskite membranes

An explicit oxygen permeation model has been developed for ion-conducting membranes with a high ratio of electronic to ionic conductivity, which makes it possible to correlate the permeation flux to directly measurable variables. Surface exchange kinetics at each side of the membrane is emphasized and their resistance to oxygen permeation has been quantitatively distinguished from the bulk diffusion resistance. A series of experimental measurements of oxygen fluxes for La0.6Sr0.4Co0.2Fe0.8O3-delta over a wide range of temperature and oxygen partial pressures were used for model regression purposes and for mechanism analysis. It is concluded that oxygen permeation at low temperatures (750 degrees C) is limited by the rate of oxygen-ion recombination but is dominantly controlled by bulk diffusion at high temperatures (950 degrees C). This is consistent with activation energies for oxygen vacancy diffusion and for the surface exchange rates, which are estimated at 74 kJ/mol and 227, 241 kJ/mol, respectively. (C) 1999 Elsevier Science Ltd. All rights reserved.