Rare-Earth-Element-Free Ferrite Cathode for Protonic Solid 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 BaFe0.9–xCu0.1ZrxO3−δ (x = 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 BaFe0.9Cu0.1O3−δ (Zr0), BaFe0.85Cu0.1Zr0.05O3−δ (Zr5) and BaFe0.8Cu0.1Zr0.1O3−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.