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

The effect of substitution for on the crystal chemistry, oxygen content, thermal expansion, electrical conductivity, and catalytic activity for oxygen reduction reaction (ORR) of the double perovskite oxides has been investigated for . The system exhibits a structural change from orthorhombic to tetragonal to orthorhombic with increasing Sr content. The difference in ionic radii between and plays a dominant role in determining the oxygen-content value in , and the oxygen content and the oxidation state of cobalt increase with increasing Sr content. The electrical conductivity of the 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 cathodes in contact with the and electrolytes at . The and 0.6 samples with a tetragonal structure exhibit higher catalytic activity for ORR in single-cell solid oxide fuel cell than the and 1.0 samples with an orthorhombic structure.