Rare-Earth-Element-FreeFerrite Cathode for ProtonicSolid Oxide Fuel Cells

Cu doping in ferrite perovskites was reported to enhance the low-temperature performance for the oxygen reduction reaction (ORR) of a protonic solid oxide fuel cell (H-SOFC). Zr⁴⁺ as a donor for doping in rare-earth-element-free BaFe_{0.9–<i>x</i>}Cu_0.1Zr_<i>x</i>O_3−δ (<i>x</i> = 0, 0.05, and 0.1) was studied to achieve a trade-off between the high-performance electrocatalysis and stability of the Cu-containing perovskite. Zr⁴⁺ stabilized the cubic structure of the perovskite and inhibited the formation of hexagonal BaFeO₃ by decreasing the Goldschmidt tolerance factor of the perovskite. Compared with BaFe_0.9Cu_0.1O_3−δ (Zr0), BaFe_0.85Cu_0.1Zr_0.05O_3−δ (Zr5) and BaFe_0.8Cu_0.1Zr_0.1O_3−δ (Zr10) exhibit higher electric conductivity and surface exchange kinetics but a lower thermal expansion coefficient. At 600 °C, the cell with Zr10 exhibits a peak power of 547.73 mW cm^–2, a polarization resistance of 0.03 Ω cm², and a chronoamperometry of 673.13 mA cm^–2 at 0.6 V after 140 h. Therefore, Zr⁴⁺ doping in the ferrite cathode can improve the ORR kinetics and durability of low-temperature H-SOFCs.