Architecting multilayer hollow spheres of high-entropy spinel oxides for enhanced electrochemical performance

The development of cost-effective multifunctional materials for supercapacitors and oxygen evolution reaction (OER) is highly desirable. Herein, high-entropy spinel oxide (Al0.2Mn0.2Fe0.2Ni0.2Zn0.2)Co2O4 with unique hollow spherical multilayer structure (HES-HSM) and enriched oxygen vacancies were designed and prepared by a combination of hydrothermal process and calcination treatment. The developed HES-HSM displayed a high specific capacitance of 748 F/g at 1 A/g, and a capacitance retention of 65% after 5000 cycles. Moreover, the fabricated HES-HSM//AC (active carbon) asymmetric supercapacitor device delivered a high energy density of 42.6 Wh/kg at a power density of 600 W/kg. Furthermore, HES-HSM exhibited the remarkable oxygen evolution reaction (OER) electrocatalytic properties with a low overpotential of 254 mV at 10 mA/cm2, and a small Tafel slope of 56.18 mV/dec, which is better than the commercial IrO2 catalyst. Long-term stability of HES-HSM was achieved by continuous electrolysis in 1 mol/L KOH aqueous solution at 10 mA/cm2 after 50 h. This work provides a strategy to design and prepare high-entropy oxides with hollow spherical multilayer structure, which have promising application in energy storage and conversion.