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

Abstract 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 (Zw) 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.