Oxygen Permeation Properties of Co-Free Perovskite-Type Oxide Membranes Based on BaFe[sub 1−y]Zr[sub y]O[sub 3−δ]

Abstract

Partially Zr-substituted BaFe 1-yZr yO 3-? membranes were developed as a Co-free oxygen permeable membrane. In order to stabilize the cubic perovskite structure, Fe sites in BaFeO 3-? were partially substituted with Zr 4+. In the substitution range of y=0.01-0.1, the cubic perovskite structure was stabilized even at room temperature. Among the membranes prepared, a BaFe 0.975Zr 0.025O3 -? material (y=0.025) showed the highest oxygen permeation flux of 1.30 cm3 (standard temperature pressure) min-1 cm-2 at 930?C under an air/He gradient. The oxygen permeation flux was higher than that of partially Ce-substituted BaFe 1-yCe yO 3-? membranes reported previously. From the results obtained by chemical and scanning electron microscope analyses, it appears that the oxygen permeability for BaFe 1-yZr yO 3-? membranes was well correlated with the amount of oxygen defects in the lattice as well as the grain size. In addition, the oxygen permeation flux of the BaFe 0.975Zr 0.025O3 -? membrane was significantly increased after decreasing the thickness of the membrane from 2.0 to 0.4 mm. For thin membranes (0.4-1.0 mm), the thickness dependence of the oxygen permeability deviated from the Wagner equation, suggesting that the oxygen permeation of BaFe 0.975Zr 0.025O3 -? is controlled by not only bulk diffusion of oxide ions but also their surface reactions. ? 2009 The Electrochemical Society.