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 °C, 140 °C, and 170 °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.