Abstract Reversible solid oxide cells (R‐SOCs) are promising for energy applications but face limitations due to poor durability and slow oxygen‐reduction/evolution reactions at air electrodes. Here, a high‐entropy perovskite‐based (HEP) tri‐phase composite, (La 0.2 Sr 0.2 Pr 0.2 Ba 0.2 Ce 0.2 ) x CoO 3‐δ , comprising an A‐site deficient La 0.2 Sr 0.2 Pr 0.2 Ba 0.2 Ce 0.2 CoO 3‐δ , doped‐CeO 2 , and Co 3 O 4 phases are presented. The HEP phase provides catalytic sites and robust frameworks, the doped‐CeO 2 phase enhances oxygen‐ion transport; and the Co 3 O 4 nanoparticles offer additional active sites. The optimized (La 0.2 Sr 0.2 Pr 0.2 Ba 0.2 Ce 0.2 ) 0.7 CoO 3‐δ electrode exhibits promising electrochemical performance: a low area‐specific resistance of 0.058 Ω cm 2 at 700 °C and enhance stability (a 2‐fold improvement in ambient air, a 6‐fold enhancement in moisture resistance, and a 3‐fold increase in Cr tolerance compare to (La 0.6 Sr 0.4 ) 0.95 Co 0.2 Fe 0.8 O 3‐𝛿 ). When applied as an air electrode for R‐SOCs, it delivers excellent performance at 800 °C: a peak power density of 1.68 W cm −2 in fuel cell (FC); a current density of 1.5 A cm −2 at 1.2 V in electrolysis cell (EC). Significantly, this work represents the first application of a high‐entropy‐oxide‐based material as an air electrode in large‐area R‐SOCs (10×10 cm 2 ). The assembled R‐SOC achieves an output of 61 W in FC and 66 A at 1.18 V in EC at 800 °C, highlighting its potential for practical applications.
Yao et al. (Tue,) studied this question.