Oxygen selective membranes based on B-site cation-deficient (Ba0.5Sr0.5)(Co0.8Fe0.2)yO3−δ perovskite with improved operational stability

(Ba0.5Sr0.5)(Co0.8Fe0.2)yO3−δ ((BS)(CF)y, 1.00 ≥ y ≥ 0.77) oxides were investigated for oxygen separation application with emphasis on long-term operational stability. Pure phase cubic perovskite was formed at y ≥ 0.83. The oxygen nonstoichiometry increased while electrical conductivity and permeability decreased with the decrease of y. However, the (BS)(CF)0.97 membrane still displayed an attractive oxygen flux as high as 2.4 × 10−6 mol cm−2 s−1 at 900 °C, as compared to 2.5 × 10−6 mol cm−2 s−1 for a cation stoichiometric BSCF membrane. The B-site deficiency greatly restrained the A-site cation diffusion and stabilized the perovskite structure and permeation properties of the membranes. During the long-term operation of the (BS)(CF)0.97 membrane at 850 °C for more than 300 h, a stable permeation flux of (1.8 ± 0.3) × 10−6 mol cm−2 s−1 was achieved. Further investigation demonstrated that the improved importance of oxygen bulk-diffusion regime in the rate-determination of oxygen permeation through the membranes.