Medium entropy design of the cobalt-free perovskite La0.25Ba0.25Sr0.25Ca0.25FeO3-δ as a cathode for IT-SOFCs

The development of highly active cobalt-free cathodes is crucial for the commercialisation of intermediate temperature solid oxide fuel cells (IT-SOFCs). Here, the A-site medium entropy perovskite oxide La 0.25 Ba 0.25 Sr 0.25 Ca 0.25 FeO 3-δ (LBSCF) is developed as a cathode material for IT-SOFCs. Its phase structure, chemical state, thermal stability, thermal expansion coefficient (TEC), electrical conductivity and electrochemical performance are systematically characterised. LBSCF exhibits a Pm-3m cubic perovskite structure with excellent phase stability and high CO 2 tolerance at elevated temperatures. It exhibits high electrical conductivity (58–131 S cm ⁻ 1 ) over 600–800 °C and an average TEC of 22.9 × 10 ⁻ 6 K ⁻ 1 in air between 30–1000 °C, although slightly higher than conventional SOFC electrolytes. As a cathode on Gd 0.1 Ce 0.9 O 1.95 (GDC) electrolyte, LBSCF achieves superior electrochemical performance with an ultra-low area specific resistance (ASR) of 0.015 Ω cm 2 at 800 °C just 4.3 % of the ASR of La 0.25 Ca 0.75 FeO 3–δ under identical conditions. A single cell with a 300-μm thick GDC electrolyte delivers a maximum peak power density of 595 mW cm ⁻2 at 800 °C. The results indicate that a rational medium-entropy design approach may lead to improvements in cathode material performance, thus enhancing SOFC performance. • A-site medium entropy La 0.25 Ba 0.25 Sr 0.25 Ca 0.25 FeO 3-δ synthesized via solid-state reaction. • Medium entropy LBSCF shows excellent structural stability and CO 2 tolerance. • LBSCF exhibits higher ORR activity than conventional materials. • Fe-based medium entropy perovskites serve as potential IT-SOFC cathodes.