Self-assembled, high-performing cobalt-free Ba0.5A0.5Fe0.8Zr0.2O3-δ (A=Sr2+/Sm3+) composite cathode for intermediate-temperature solid oxide fuel cells

Abstract

In this study, cost-effective cathode materials with high catalysis activity for oxygen reduction reaction (ORR) are proposed for use in intermediate-temperature solid oxide fuel cells. Cobalt-free Ba0.5A0.5Fe0.8Zr0.2O3-δ (A=Sr2+/Sm3+, BSrFZ/BSmFZ) composites were synthesised using a smart self-assembled method that primarily utilised doped-BaZrO3 and doped-BaFeO3 cubic perovskites. The BSrFZ composite possesses a higher doped-BaFeO3 (75 wt%) content, which facilitates the formation of oxygen vacancies and ORR catalysis. The BSmFZ composite exhibits a relatively higher content of doped-BaZrO3 (31 wt%) than that of the BSrFZ composite, which is more suited to the electrolyte and improves the thermal expansion coefficient (16.0 × 10−6 K−1). Both composite cathodes exhibit nano- and micro-particles with extensive heterointerfaces and excellent cathode|electrolyte interfaces, which can assist the surface catalysis and oxygen species transport. The cell with a BSrFZ composite cathode achieved a higher maximum power density of 1.64 W cm−2 at 750 °C compared to that of the cell with a BSmFZ composite cathode that had a maximum power density of 0.99 W cm−2. The electrochemical analysis revealed that the BSrFZ composite cathode demonstrated enhanced oxygen adsorption dissociation and oxygen species reduction processes, which benefit from its enriched oxygen vacancies and high surface and heterointerface activities.