Oxygen permeability and improved stability of a permeable Zr-substituted perovskite membrane for air separation

Zr-substituted Ba0.5Sr0.5Co0.8Fe0.1Zr0.1O3−δ (BSCFZO) powders for oxygen membrane were synthesized by the solid-state reaction (SSR) method. Oxygen permeation fluxes (JO2JO2) across the dense Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCFO) and BSCFZO membrane disks were measured at 973–1123 K, and they increased as BSCFO (synthesized by improved EDTA–citric acid complexing method, ECC) > BSCFO (SSR) > BSCFZO. The reduced oxygen permeability of Zr-substituting BSCFZO material can be attributed primarily to the higher oxidation state of Zr cations than ones of iron cations, thus lead to the decrease in the oxygen vacancy concentration in BSCFO. Oxygen permeation measurements with different oxygen partial pressure gradients and membrane thicknesses demonstrate the bulk oxide ionic diffusion is the rate-limiting step for the BSCFZO membrane in the range of temperatures investigated (973–1123 K). The enhanced stability of BSCFZO demonstrated by the differential thermal analysis (DTA) and high-temperature X-ray diffraction (HT-XRD) characterizations, show that the structural stability can be improved when the Fe ions in the B-sites of BSCFO materials are substituted partially by Zr cations.