In Situ Construction of a High-Entropy Perovskite Based Tri-Phase Composite Electrode toward Efficient Reversible...

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_0.2Sr_0.2Pr_0.2Ba_0.2Ce_0.2)_xCoO_3-δ, comprising an A-site deficient La_0.2Sr_0.2Pr_0.2Ba_0.2Ce_0.2CoO_3-δ, doped-CeO₂, and Co₃O₄ phases are presented. The HEP phase provides catalytic sites and robust frameworks, the doped-CeO₂ phase enhances oxygen-ion transport; and the Co₃O₄ nanoparticles offer additional active sites. The optimized (La_0.2Sr_0.2Pr_0.2Ba_0.2Ce_0.2)_0.7CoO_3-δ electrode exhibits promising electrochemical performance: a low area-specific resistance of 0.058 Ω cm² 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_0.6Sr_0.4)_0.95Co_0.2Fe_0.8O_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 cm²). 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.