Optimization of Ba_xSr_1-xCo_0.9Nb_0.1O_3-δ perovskite as oxygen semi-permeable membranes by compositional tailoring

Mixed conducting SrCo_0.9Nb_0.1O_3-δ perovskite is a newly developed promising ceramic membrane material for air separation. In this work, SrCo_0.9Nb_0.1O_3-δ was further optimized by the introduction of Ba to partially replace Sr in the A-site of the perovskite structure. The phase structure, phase stability, carbonate formation rate under carbon dioxide atmosphere, electrical conductivity, oxygen desorption properties, and oxygen permeation properties of Ba_xSr_1-xCo_0.9Nb_0.1O_3-δ (BSCNx) with varying Ba²⁺ doping level were systematically investigated. Pure phase cubic perovskite was formed at x = 0.0-0.8. BSCNx (x = 0.0-0.8) can be stably operated in atmospheres with oxygen partial pressure varying from at least 1 atm to as low as 10^-5 atm (Ar atmosphere). The barium doping concentration had a significant effect on electrical conductivity and oxygen permeability of the membranes. BSCN0.6 had the highest oxygen permeation flux of 2.67 × 10^-6 mol cm^-2 s^-1 for 0.87 mm thickness at 900 °C and the highest oxygen ionic conductivity of 1.38 S cm^-1 at 900 °C.