Ta-doped SrCo_0.8Fe_0.2O_3-δ membranes: Phase stability and oxygen permeation in CO₂ atmosphere

The chemical and structural stability of perovskite-derived SrCo_0.8Fe_0.2O_3−δ (SCF) and Sr(Co_0.8Fe_0.2)_0.9Ta_0.1O_3−δ (SCFTa) were investigated by both isothermal gravimetric and X-Ray diffraction. It was shown that the reaction between SCF and CO₂ at elevated temperature is almost negligible when Ta is doped to SCF. XPS analysis shows that the basicity of SCFTa is less than that of SCF, which may contribute to the enhanced stability of SCFTa in CO₂ atmosphere. Ta⁵⁺ also increases the perovskite phase stability of SCF in low oxygen partial pressure (pO₂<10^-2 atm), which was proven by the disappearance of a strong shrinkage signal during dilatometric thermal expansion measurements. In the oxygen permeation measurement, the flux of SCFTa was slightly lower than that of SCF when an air–helium gradient was applied over the membrane, but it remained almost the same when pure CO₂ was introduced as sweeping gas, while, the oxygen permeation flux of SCF dropped drastically at first and decreased to zero after 60 h in CO₂ atmosphere.