Synthesis and characterization of Ba_0.6Sr_0.4Ce _0.8-xZr_xY_0.2O_{3- δ} proton-conducting oxides for use as fuel cell electrolyte

Ba_0.6Sr_0.4Ce_0.8-xZr _xY_0.2O_3-δ (x = 0-0.8) proton-conducting oxides are prepared using a sol-gel complexing process. The effects of the Ce/Zr ratio on various material properties are systematically investigated. The sintered samples show a perovskite crystal structure without impurity phases and have a rather compact interior, making them suitable for use as a fuel cell electrolyte. Increasing the Zr content in the oxides causes lattice constriction and suppresses grain growth during sintering at 1600 C. The ionic conductivity of the oxides increases with increasing Ce/Zr ratio. At 800 C, Ba_0.6Sr_0.4Ce_0.8Y_0.2O _3-δ has a conductivity of as high as 0.14 S/cm. However, X-ray diffraction and Raman spectroscopy evaluations show that this oxide cannot withstand a CO₂ atmosphere. A suitable substitution of Ce with Zr in the structure significantly improves the chemical stability of the oxide without significantly degrading conductivity.