Phase Stability, Oxygen-Storage Capability, and Electrocatalytic Activity in Solid Oxide Fuel Cells of (Y, In, Ca)BaCo_4–yGa_yO_7+δ

With an aim of enhancing their high-temperature phase stability, oxygen-storage capability, and electrocatalytic activity in intermediate-temperature solid oxide fuel cells (IT-SOFCs), RBaCo4O 7+δ -based samples have been investigated with a co-substitution at the R site with Y, In, and Ca and Ga substitution at the Co site. YBaCo 4– y Ga y O 7+δ, Y 1– x In x BaCo 3.3 Ga 0.7 O 7+δ, Y 1– x Ca x BaCo 3.3 Ga 0.7 O 7+δ, In 1– x Ca x BaCo 3.3 Ga 0.7 O 7+δ, and Y 0.5 In 0.5 BaCo 4– y Ga y O 7+δ series of materials have been synthesized by a solid-state reaction, and the phase stabilities have been assessed by long-term testing at 600–800 °C for 120 h. The substitution of In for Y mitigates the phase decomposition but decreases the oxygen-storage capacity and electrochemical performance in IT-SOFCs. With In and Y co-dopants, Y 0.5 In 0.5 BaCo 3.5 Ga 0.5 O 7+δ remains stable even with a smaller amount of Ga. In contrast, Ca doping reduces the phase stability regardless of its content. Via optimization of the compositions, Y 0.9 In 0.1 BaCo 3.3 Ga 0.7 O 7+δ is found to exhibit the best electrochemical performance without decomposition in the long-term test at 600–800 °C. The anode-supported single cell with the Y 0.9 In 0.1 BaCo 3.3 Ga 0.7 O 7+δ + GDC composite cathode reaches a maximum power density of 0.91 W cm –2 at 700 °C, which is the highest reported for this class of materials. Moreover, the ideal matching of the relatively low thermal expansion coefficient of Y 0.9 In 0.1 BaCo 3.3 Ga 0.7 O 7+δ (7.5–9.2 × 10 –6 K –1 ) with those of common electrolytes alleviates the thermal stress during long-term operation in IT-SOFCs. The combination of long-term phase stability, high oxygen-storage capability, and electrocatalytic properties makes the Y 0.9 In 0.1 BaCo 3.3 Ga 0.7 O 7+δ + GDC composite cathode appealing for practical application in IT-SOFCs.