A novel synthesis of 2D porous ZnCo₂O₄ nanoflakes using deep eutectic solvent for high-performance asymmetric supercapacitors

In this study, highly porous 2D ZnCo₂O₄ nanoflakes of cubic crystalline structure are synthesized for the first time via an ionothermal method using a deep eutectic solvent (DES). The synthesized ZnCo₂O₄ features a large surface area of 115.18 m² g⁻¹ with a high pore volume of 0.411 cm³ g⁻¹. As a result, it exhibits a high specific capacity of 311.26 mAh g⁻¹ at a current density of 1.0 A g⁻¹, along with an excellent rate capability (60.4% retention at 15 A g⁻¹). Electrochemical impedance spectroscopy (EIS) study indicates a low Warburg diffusion (Z_w) value of only 0.93 Ω, which suggests the fast movement of OH⁻ ions into the ZnCo₂O₄ electrode through its porous structure. The ZnCo₂O₄//AC asymmetric supercapacitor (ASC) exhibits a high energy density of 21.2 Wh kg⁻¹ at a power density of 800 W kg⁻¹, an ultrahigh power density of 12 kW kg⁻¹ for an energy density of 8 Wh kg⁻¹, and long cyclic stability, with almost 100% capacity retention after 10,000 cycles.