Characterization of (Y 1-xCa x)BaCo 4-yZn yO 7 as cathodes for intermediate temperature solid oxide fuel cells

Abstract

The effects of Ca and Zn substitution, respectively, for Y and Co in (Y 1-xCa x)BaCo 4-yZn yO 7 (0.25 ≤ x ≤ 0.75 and 1.0 ≤ y ≤ 1.75) on the structure, high-temperature phase stability, thermal expansion coefficient (TEC), and electrochemical performance for intermediate temperature solid oxide fuel cells (IT-SOFC) have been investigated. The (Y 1-xCa x)BaCo 4-yZn yO 7 oxides crystallize in a trigonal P31 c symmetry similar to YBaCo 4O 7. The substitution of Zn for Co improves the long-term phase stability at high temperatures, but at the expense of the electrochemical performance. In contrast, the substitution of Ca for Y is improves electrochemical performances, but deteriorates the long-term phase stability at high temperatures at high Ca contents ( x = 0.75 and 1.0). Among the various chemical compositions investigated in the (Y 1-xCa x)BaCo 4-yZn yO 7 system, the (Y 0.5Ca 0.5)BaCo 2.5Zn 1.5O 7 composition offers a combination of good electrochemical performance and low TEC, while maintaining the phase stability at 600–800 °C for 120 h. The (Y 0.5Ca 0.5)BaCo 2.5Zn 1.5O 7 + GDC (50 : 50 wt. %) composite cathodes exhibit a maximum power density of ∼ 450 mW cm −2 at 700 °C in anode-supported single SOFC.