Layered perovskite Y_1-xCa_xBaCo₄O_7+δ as ceramic membranes for oxygen separation

Layer-structured mixed conducting oxides with the composition Y_1-xCa_xBaCo₄O_7+δ (x = 0.0-0.4) were synthesized and their performance as oxygen separating membranes was explored. The crystal structure, phase stability, oxygen absorption/desorption properties, and electrical conductivity of the oxides, as well as oxygen permeation fluxes of the corresponding membranes, were systematically investigated. The properties of YBaCo₄O_7+δ-based oxides were greatly improved by Ca incorporation into the lattice structure at an optimal concentration. In the series Y_1-xCa_xBaCo₄O_7+δ, the Y_0.8Ca_0.2BaCo₄O_7+δ membrane exhibited the highest oxygen permeation flux, reaching a value of 0.75 × 10^-6 mol cm^-2 s^-1 at 900 °C under the conditions of air/helium oxygen gradient and a membrane thickness of 1.0 mm. Studies of the effect of membrane thickness on the oxygen fluxes implied that at membrane thicknesses larger than 0.7 mm, the permeation process was mainly controlled by bulk diffusion, indicating the potential to further improve the oxygen fluxes via thinner membranes of asymmetric structure.