Investigation of the permeation behavior and stability of a Ba_0.5Sr_0.5Co_0.8Fe_0.2O(3-δ) oxygen membrane

SrCo_0.8Fe_0.2O(3-δ) (SCFO) and Ba_0.5Sr_0.5Co_0.8Fe_0.2O(3-δ) (BSCFO) oxides were successfully prepared, using a combined citrate-EDTA complexing method. The results of O₂-TPD and XRD showed that the introduction of barium into SCFO could effectively suppress the oxidation of Co³⁺and Fe³⁺ to higher valence states of Co⁴⁺ and Fe⁴⁺ in the lattice, and stabilize the perovskite structure under lower oxygen partial pressures. Oxygen permeation experiment showed that BSCFO membrane also had higher oxygen permeation flux than that of SCFO under air/He oxygen partial pressure gradient. At 950°C, the permeation flux through 1.80mm BSCFO membrane exposed to flowing predried air (P(O(2))'=0.21atm) and helium (P(O(2))''=0.037atm) is ca. 1.4ml/cm²min and the activation energy for oxygen transportation is 40.9kJ/mol within the temperature range of 775-950°C. The permeation flux of BSCFO was less sensitive to minor amounts of CO₂ and water vapor presented in the air than that of SCFO. Long-term oxygen permeation study of more than 1000h at 850°C indicated that the BSCFO membrane could operate stably as an oxygen generator at that temperature. A very slow exponential decay in the measured oxygen permeation flux occurred at temperatures lower than 825°C, which was caused by a phase transition. The phase transition was found to be reversible at higher temperatures, but a long time was needed for the equilibration. Copyright (C) 2000 Elsevier Science B.V.