Electrical conductivity and oxygen permeation properties of SrCoFeOx membranes

The total conductivity and oxygen permeation properties of dense SrCoFeOx membranes synthesized from the solid state method were studied in the temperature range of 700–900 °C. The SrCoFeOx membranes consist of an intergrowth (Sr4Fe6 − xCoxO13 ± δ), perovskite (SrFe1 − xCoxO3 − δ), and spinel (Co3 − xFexO4) phase. SrCoFeOx exhibits n-type and p-type conduction at low and high oxygen partial pressures, respectively, and has a total conductivity of 16.5 S/cm at 900 °C in air. The oxygen permeation fluxes for SrCoFeOx and SrFeCo0.5Ox membranes were measured with either an inert or carbon monoxide sweep gas. The oxygen permeation fluxes were higher through SrCoFeOx membranes than SrFeCo0.5Ox membranes and can be attributed to a difference in the amount and makeup of the perovskite phase present in each composition. The oxygen permeation fluxes with a carbon monoxide sweep gas were approximately two orders of magnitude larger than the fluxes measured with an inert sweep gas for both compositions. The large oxygen permeation fluxes observed with a carbon monoxide sweep are due to a higher driving force for oxygen transport and a reaction on the sweep side of the membrane that maintains a low oxygen partial pressure.