Synthesis of (MgCoNiCuZn)O High‐Entropy Oxide via Reverse Coprecipitation–Hydrothermal Method for High‐Performance Supercapacitors

ABSTRACT Owing to their tunable structures and multicomponent synergistic advantages, high‐entropy oxides (HEOs) are widely studied within supercapacitor energy storage. In the current work, the rock‐salt‐type (MgCoNiCuZn)O HEO was prepared via a combined reverse coprecipitation–hydrothermal procedure. The crystallographic phase, morphological features, and electrochemical behavior of the synthesized (MgCoNiCuZn)O were systematically evaluated as a function of hydrothermal temperature. Among all the samples, the one synthesized at 160°C (hydrothermal) and 900°C (calcination) exhibited the optimal crystallinity and best electrochemical performance, delivering a specific capacitance of 562 F g −1 at 1 A g −1 . Upon elevating the operational current density to 5 A g −1 , approximately 86% of this initial value is retained, indicating a high tolerance to increased current loads. Long‐term stability assessments further corroborate its robustness, corresponding to 77.9% capacitance retention over 10, 000 cycles at 5 A g −1 . The assembled (MgCoNiCuZn)O//AC asymmetric supercapacitor delivers an energy density of 57.08 Wh kg −1 at a power density of 750 W kg −1 and retains 77.9% of its initial capacitance after 10, 000 cycles. The above findings confirm that the reverse coprecipitation method combined with hydrothermal treatment serves as a reliable strategy for fabricating rock‐salt‐type HEOs with enhanced supercapacitive performance.