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

Abstract

• Deep eutectic solvent (DES)-mediated ionothermal process is applied for the synthesis of porous ZnCo 2 O 4 nanoflakes. • The ZnCo 2 O 4 features a large surface area of 115.18 m 2 g −1 with a high pore volume of 0.411 cm 3 g −1 . • It exhibits a high specific capacity of 311.26 mA h g −1 at a current density of 1.0 A g −1 . • The ZnCo 2 O 4 //AC ASC exhibits a high energy density of 21.2 Wh kg −1 at a power density of 800 W kg −1 . • The ZnCo 2 O 4 //AC ASC shows no capacitance loss up to 10,000 cycles. In this study, highly porous 2D ZnCo 2 O 4 nanoflakes of cubic crystalline structure are synthesized for the first time via an ionothermal method using a deep eutectic solvent (DES). The synthesized ZnCo 2 O 4 features a large surface area of 115.18 m 2 g −1 with a high pore volume of 0.411 cm 3 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 ZnCo 2 O 4 electrode through its porous structure. The ZnCo 2 O 4 //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.