A high-entropy Swedenborgite-type oxide with low thermal expansion coefficient as a cathode for solid oxide fuel cells

Conventional cobalt-based cathodes for solid oxide fuel cells (SOFCs) typically exhibit high thermal expansion coefficients (TEC), posing a significant challenge for TECs matching with electrolytes. Consequently, developing new cathode materials with lower TEC is critical. In this work, two high-entropy Swedenborgite-type oxides, Y 0.2 Pr 0.2 Tb 0.2 Er 0.2 Lu 0.2 BaCo 3 ZnO 7+δ (YPTELBCZ) and (Y 0.2 Pr 0.2 Tb 0.2 Er 0.2 Lu 0.2 ) 0.9 In 0.1 BaCo 3 ZnO 7+δ (YPTELIBCZ), are successfully synthesized via solid-state reaction. Both oxides exhibit excellent chemical compatibility with La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3–δ (LSGM) electrolyte and show TECs that closely match that of LSGM, with average values of 9.0 × 10 −6 K −1 and 10.3 × 10 −6 K −1 between 30 and 1000 °C, respectively. Electrical conductivities reached 18.3 S cm −1 and 17.1 S cm −1 at 800 °C for YPTELBCZ and YPTELIBCZ, respectively. Phase stability assessments confirmed the superior thermal stability of YPTELIBCZ, which remained impurity-free across all tested temperatures. In contrast, YPTELBCZ exhibited minor decomposition into BaCoO 3-δ at 700 °C. Electrochemical performance is excellent: symmetric cell tests yielded area-specific resistances of 0.018 Ω cm 2 and 0.039 Ω cm 2 at 800 °C for YPTELBCZ and YPTELIBCZ, respectively. Corresponding single-cell maximum power densities are 1242 mW cm −2 and 1043 mW cm −2 at 800 °C. Combining outstanding electrochemical performance, high CO 2 tolerance, and excellent TEC compatibility with LSGM, these high-entropy oxides are promising cathode materials for SOFCs. This work demonstrates that high-entropy design of Swedenborgite-type oxides can enhance material stability while maintaining robust electrochemical properties, thereby expanding the design space for SOFC cathode materials. • High-entropy tailoring is first applied to a Swedenborgite-type oxide cathode. • YPTELIBCZ exhibits superior stability and CO 2 tolerance. • YPTELBCZ and YPTELIBCZ possess low thermal expansion coefficient and high catalytic activity.