Facile solid-state synthesis of Er0.4Tm0.4Yb0.4Ho0.4Dy0.4O3 rare-earth high-entropy oxide for high-performance supercapacitors

High-entropy oxides (HEOs) are attractive electrode materials for next-generation supercapacitors owing to their entropy-driven structural stabilization and tunable compositional diversity; however, rare-earth (RE)-containing HEOs are still scarcely investigated. Herein, a single-phase cubic fluorite-type Er 0.4 Tm 0.4 Yb 0.4 Ho 0.4 Dy 0.4 O 3 high-entropy oxide is synthesized via a one-step solid-state reaction at 1500 °C for 5 h. The structural characterizations of prepared (RE)-based HEOs confirm the formation of a cubic fluorite-type structure. As a supercapacitor electrode in alkaline electrolyte, the material delivers a high specific capacitance of 318 F g −1 at 1 A g −1 with 85.7% capacitance retention after 8000 cycles, demonstrating typical pseudocapacitive behavior. Moreover, the assembled Er 0.4 Tm 0.4 Yb 0.4 Ho 0.4 Dy 0.4 O 3 //AC asymmetric supercapacitor achieves an operating voltage of 1.55 V and an energy density of 11.55 Wh kg −1 @ power density 775 W kg −1 with good rate capability. These results indicate that RE-based HEOs are promising pseudocapacitive electrodes for advanced energy storage.