Oxygen permeation in SrCo 0.8Fe 0.2O 3 − δ membranes with porous electrodes

Abstract

Measurements of oxygen flux, in the temperature range, 770–870 °C on planar membranes of SrCo 0.8Fe 0.2O 3−δ, consisting of a dense discs ~ 0.1 cm thick modified by coating with porous layers on both sides, yielded an enhancement in the oxygen flux, η ≈ 2, compared to the uncoated membrane. When only one side of the disc was coated with the porous layer on the high pressure side of the membrane then η ≈ 1.2, while when the modified side was on the low pressure side then η ≈ 1.4. The observed values of η were explained by a model of diffusion-reaction transport in mixed ionic electronic conductor membranes with porous electrodes, extended to the case of finite thickness of the dense layer. From a fit of the model to the experimental data, values of the surface exchange coefficient, k iO , and ambipolar oxygen ion-electron hole pair diffusion coefficient, D a , were deduced. At 870 °C, k iO = 2.5 × 10 −4 cm/s and D a = 5 × 10 −6 cm 2/s.