Highly Oxygen Non-Stoichiometric BaSc_0.25Co_0.75O_3-δ as a High-Performance Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

Lowering the operating temperature of solid oxide fuel cells (SOFCs) is highly desirable to reduce the cost and increase the lifetime, which relies upon the development of a cathode component with high oxygen reduction reaction (ORR) activity at a lower temperature. Herein, we report the characterization of high-performance BaSc_xCo_1-xO_3-δ (x=0, 0.125, 0.25, and 0.375) perovskite SOFC cathodes. Unlike BaCoO_3-δ, which adopts 2H-hexagonal perovskite structure, the replacement of 25 mol % of Co with Sc stabilizes the cubic structure, which also leads to the significant reduction in area specific resistances and their activation energies between 650 and 500 °C (for BaSc_0.25Co_0.75O_3-δ) relative to the non-doped BaCoO_3-δ. In this temperature range, BaSc_0.25Co_0.75O_3-δ displayed a remarkably high ORR activity compared to Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF), the current cathode benchmark. We attribute such superior ORR performance to the higher oxygen non-stoichiometries of BaSc_0.25Co_0.75O_3-δ relative to BSCF, which also translates to the higher oxygen bulk diffusion and surface exchange coefficients for the former compared to the latter. As a result, a single fuel cell based on an anode-supported 20 μm thick samarium-doped ceria electrolyte and BaSc_0.25Co_0.75O_3-δ cathode achieved a very high peak power density of 1723 mW cm⁻² at 650 °C. We also demonstrated the possibility to increase the ORR activity of the BaSc_0.25Co_0.75O_3-δ cathode by impregnation of a low amount of silver.