Synthesis, oxygen permeability, and structural stability of BaCo0.7Fe0.3-xZrxO3-δ ceramic membranes

A series of mixed ionic-electronic conducting materials, BaCo0.7Fe0-3-xZrxO3-delta (x=0-0.12) were successfully synthesized and evaluated as potential ceramic membrane materials for oxygen separation applications. Effects of zirconium content on the crystal structure, internal and surface morphologies, electrical conductivity, structural stability and oxygen permeability of these membranes were systematically studied. A basic perovskite structure was for x=0.04-0.12, and the grain size of the samples gradually decreases with increasing zirconium content. The structural stabilities of the membranes in different atmospheres (H-2, O-2 and CO2) are significantly improved by substituting an appropriate amount of iron by zirconium. However, increase of the zirconium content also leads to a decrease in the electrical conductivity, which is confirmed by the first principles calculations. With increasing the zirconium content, oxygen permeation flux of the membranes increases and reaches a peak at x=0.06, and then decreases. The highest oxygen permeation flux of 2.7 ml min(-1) cm(-2) at 925 degrees C is achieved by the 1 mm thick BaCo0.7Fe0.24Zr0.06O3-delta membrane. With the same zirconium content, samples with larger grain membrane. With the same zirconium content, samples with larger grain sizes have remarkably higher oxygen permeation flux. Both theoretical and experimental works indicate that the oxygen permeability depends on the combined effect of the oxygen vacancy concentration, grain size and electrical conductivity. (C) 2016 Elsevier B.V. All rights reserved.