Abstract
In this study, we investigate the electrochemical properties of graphene-based capacitors using cyclic voltammetry (CV), constant charge/discharge cycling, and electrochemical impedance spectroscopy combined with an equivalent circuit. An easy route incorporated with modified Hummers' method and microwave-assisted reduction is capable of preparing graphene nanosheets (GNs). Two types of capacitors fabricated with GN and graphene oxide (GO) powders are examined in 1 M H2SO4 within a potential of 0 and 0.8 V vs Ag/AgCl. The GO-based capacitor not only presents a better stable capacitance (ca. 211.7 F/g after 1000 cycles), but also a lower equivalent series resistance (ca. 7.6 Ω after 1000 cycles), when compared with the GN-based capacitor. The presence of surface oxides, attached to the edges or defects of the basal planes, imparts hydrophilic coverage for the formation of a double layer (double-layer capacitance) and active sites for reversible redox reaction (pseudocapacitance). When incorporated with structural (nanosheets) and chemical (surface oxides) factors, the GO powder serves as a promising electrode material for electrochemical capacitors or other energy-storage devices.