Preparation and supercapacitive performance of high-quality graphene material

High quality graphene material was prepared from flake graphite by chemical oxidation-reduction process. Its microstructure, morphology, surface properties and supercapacitive performance were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brumauer-Emmett-Teller (BET) analysis, galvanostatic charge/discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). XRD results show that the crystal structure of the graphene is amorphous. SEM and TEM images show that the graphene plays flake-like shapes with wrinkles and ripples. Moreover, the graphene has porous structure with a BET specific surface area of 14.2 m²·g^-1, total pore volume of 0.06 cm³·g^-1, and average pore diameter of 17.3 nm. EIS results show that the graphene electrode has a smaller impedance, the equivalent series resistance is 0.16 Ω, and the charge transfer resistance is 0.55 Ω. Galvanostatic charge/discharge test and CV analysis indicate that the graphene exhibits enhanced capacitance, high current charge/discharge characteristics, and stable cycle life as a supercapacitor electrode. It delivers the discharge specific capacities of 123, 113, 101 and 89 F·g^-1 at the scan rates of 2, 5, 10, and 20 mV·s^-1, respectively. Even though the scan rate is 50 mV·s^-1, the discharge specific capacity retains 69 F·g^-1.