Temperature-mediated phase control in high entropy transition metal oxides for hybrid supercapacitors

Abstract

High-entropy oxides (HEOs) are getting significant interest due to their unique crystal structure and diverse functional properties. This study has investigated a temperature-driven hydrothermal approach to achieve unique morphological architecture and phase-induced HEOs, attributed to accepted energy storage performances. The synthesis of HEOs has been carried out at three different temperatures of 110 degrees C, 140 degrees C, and 170 degrees C, named HEO-110, HEO-140, and HEO-170, respectively. This low-temperature variation synthesis depicts a change in structural information of the as-prepared materials from an amorphous phase to a single crystalline phase. In view of their application, the electrochemical results showed pseudocapacitive behavior and single-phase HEO-140 exhibited a capacitance value of 216.2 F g-1, amongst the two other temperature-varied modified electrode materials. The improved performance is due to its stable single-phase structure and large specific surface area (138.38 m2 g-1) that provides effective sites and channels for electrochemical reactions. Moreover, a hybrid supercapacitor device has been fabricated by considering HEO-140 and activated carbon (AC) as the cathode and anode electrode materials. The maximum specific capacitance of 62 F g-1 at 1 A g-1, with a maximum energy density of 25.17 W h kg-1 at a power density of 1006.8 W kg-1, and a high power density of 5038.5 W kg-1 at an energy density of 13.67 W h kg-1 was observed. The device showed 86.7% capacity retention and 95.3% coulombic efficiency after 5000 cycles, demonstrating excellent stability and reversibility. Based on these above findings we presumed that precious metal-free high entropy oxides could be a replaceable electrode material for advanced electrochemical storage.