Characterization of GdBa[sub 1−x]Sr[sub x]Co[sub 2]O[sub 5+δ] (0≤x≤1.0) Double Perovskites as Cathodes for Solid Oxide Fuel Cells

Abstract

The effect of Sr2+Sr2+ substitution for Ba2+Ba2+ on the crystal chemistry, oxygen content, thermal expansion, electrical conductivity, and catalytic activity for oxygen reduction reaction (ORR) of the double perovskite oxides GdBa1−xSrxCo2O5+δGdBa1−xSrxCo2O5+δ has been investigated for 0⩽x⩽1.00⩽x⩽1.0 . The GdBa1−xSrxCo2O5+δGdBa1−xSrxCo2O5+δ system exhibits a structural change from orthorhombic (x=0)(x=0) to tetragonal (0.2⩽x⩽0.6)(0.2⩽x⩽0.6) to orthorhombic (x=1)(x=1) with increasing Sr content. The difference in ionic radii between (Ba1−xSrx)2+(Ba1−xSrx)2+ and Gd3+Gd3+ plays a dominant role in determining the oxygen-content value in GdBa1−xSrxCo2O5+δGdBa1−xSrxCo2O5+δ , and the oxygen content and the oxidation state of cobalt increase with increasing Sr content. The electrical conductivity of the GdBa1−xSrxCo2O5+δGdBa1−xSrxCo2O5+δ system increases with Sr content due to an increasing oxygen content and a straightening of the O–Co–O bonds as evidenced by the structural change from orthorhombic to tetragonal. Sr substitution also improves the chemical stability of the GdBa1−xSrxCo2O5+δGdBa1−xSrxCo2O5+δ cathodes in contact with the Ce0.9Gd0.1O1.95Ce0.9Gd0.1O1.95 and La0.8Sr0.2Ga0.8Mg0.2O2.8La0.8Sr0.2Ga0.8Mg0.2O2.8 electrolytes at 1100°C1100°C . The x=0.2x=0.2 and 0.6 samples with a tetragonal structure exhibit higher catalytic activity for ORR in single-cell solid oxide fuel cell than the x=0x=0 and 1.0 samples with an orthorhombic structure.