Microwave-Assisted Solvothermal Synthesis of Cupric\nOxide Nanostructures for High-Performance Supercapacitor

Abstract

Enhancing\nthe performance and stability of the low-cost materials\nfor electrochemical energy storage device is an important aspect.\nHerein, we report microwave-assisted solvothermal synthesis of three-dimensional\n(3D) spherical CuO structures composed of either one-dimensional (rod-like)\nor two-dimensional (2D) flake-like building blocks by varying the\nreaction medium, i.e., water and ethylene glycol (EG). A higher EG\nin the reaction medium facilitates formation of the flake-like structures.\nA specific surface area of 168.47 m² g^–1 is achieved with the 3D flower-like CuO, synthesized using copper\nacetate precursor in 1:3 water/EG solvent ratio. The same sample delivers\na specific capacitance of 612 F g^–1 at an applied\ncurrent density of 1 A g^–1 and shows high stability\nwith capacity retention of 98% after 4000 galvanostatic charge–discharge\ncycles. The high specific capacitance of flower-shaped CuO architecture\nis attributed to large surface area and availability of sufficient\npores for ions diffusion. Furthermore, two-electrode asymmetric supercapacitor\ndevice is fabricated using the 3D flower-shaped CuO as positive electrode\nand activated carbon as negative electrode, which shows an energy\ndensity of 27.27 Wh kg^–1 at a power density of 800\nW kg^–1. This underlines the potential of inexpensive\nCuO architecture as an active material for energy storage devices.