The O permeation fluxes across the perovskite ceramic membranes, La1-xSrxCoO3 and SrCo0.8Fe0.2O3, were measured – using gas chromatography - as a function of O chemical potential gradient, temperature, thickness and surface catalytic activity. Power-law exponents of 0.5 to 0 were deduced for uncatalyzed La1-xSrxCoO3, and of 1 to 0.5 for SrCo0.8Fe0.2O3, when the permeation flux was plotted against the partial-pressure differential. The results clearly revealed an overall permeation process, which was controlled by surface O exchange and bulk O diffusion, for uncatalyzed La1-xSrxCoO3 and SrCo0.8Fe0.2O3. The application of a thin layer of catalytically active SrCo0.8Fe0.2O3, on the input surface of La0.5Sr0.5CoO3, using a fixed partial pressure of 0.21atm and a variable partial pressure, not only markedly increased the overall O flux but also changed the process from mixed control to bulk-diffusion control. This permitted the evaluation of the bulk transport properties of the mixed conductors. The results clearly revealed that there was a higher activation energy for surface exchange kinetics, than for ambipolar transport, in the mixed conductors.

Oxygen Permeation through Cobalt-Containing Perovskites - Surface Oxygen Exchange versus Lattice Oxygen Diffusion. K.Huang, J.B.Goodenough: Journal of the Electrochemical Society, 2001, 148[5], E203-14