A Novel Strategy for Rapid Synthesis of Nanostructured High-Entropy Metal Oxides through Thermal Plasma for Supercapacitor Applications

High-entropy oxides (HEOs) are an emerging candidate of materials that has sparked increased attention in the field of sustainable energy because of their unique structure, tailorable chemical composition, and tunable physical, chemical, and functional properties. In this work, phase-pure HEO (Mn, Fe, Co, Ni, Cu)3O4 nanoparticles were synthesized using thermal plasma under optimum processing conditions at 11 kW input power with argon and carbon dioxide as the plasma-forming gases. As-synthesized powders were annealed at different temperatures (200 to 500 °C) and subjected to structural characterization. The electrochemical energy storage performance of HEO nanoparticles was investigated via a conventional three-electrode setup in 1 M KOH electrolyte solution. For 0.5 A g–1 current density, the HEO electrode displayed a specific capacitance of 431 F g–1. Capacitance retention and Coulombic efficiency were found to be 79.5 and 91.8% after 10,000 cycles of 3 A g–1 current density, respectively. This study provides a novel insight on the rapid production of phase-pure HEO nanoparticles through thermal plasma, with a propitious production rate of around 1.5 g/min.