Electrical conductivity and oxygen permeation properties of SrCoFeO x membranes

Abstract

The total conductivity and oxygen permeation properties of dense SrCoFeO x membranes synthesized from the solid state method were studied in the temperature range of 700–900 °C. The SrCoFeO x membranes consist of an intergrowth (Sr 4Fe 6 − x Co x O 13 ± δ ), perovskite (SrFe 1 − x Co x O 3 − δ ), and spinel (Co 3 − x Fe x O 4) phase. SrCoFeO x 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 SrCoFeO x and SrFeCo 0.5O x membranes were measured with either an inert or carbon monoxide sweep gas. The oxygen permeation fluxes were higher through SrCoFeO x membranes than SrFeCo 0.5O x 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.