Ta-doped SrCo0.8Fe0.2O3-δ membranes: Phase stability and oxygen permeation in CO2 atmosphere

The chemical and structural stability of perovskite-derived SrCo0.8Fe0.2O3−δ (SCF) and Sr(Co0.8Fe0.2)0.9Ta0.1O3−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.

► Phase transition of SrCo0.8Fe0.2O3−δ in low pO2 is prevented by Ta doping. ► Ta doping greatly increases CO2 resistance of SrCo0.8Fe0.2O3−δ. ► O2 permeation of SrCo0.8Fe0.2O3−δ at 900oC in CO2 is largely retained by Ta doping. ► XPS indicates less electron donating capacity if Ta is added to the system. ► The reaction between CO2 and SrCo0.8Fe0.2O3−δ can be regarded as acid–base reaction.