The effectiveness of graphene oxide added in activated carbon for superior supercapacitor performance

Background: Graphene oxide (GO) added to activated carbon electrodes is investigated for the supercapacitor performance. It is well known that GO possesses both low electrical conductivity and surface area but functional groups containing oxygen which assist in attracting cation for improving ion movement.Methods: GO is synthesized via the modified Hummers' method and added to the activated carbon slurry for preparing the electrode of supercapacitors. The supercapacitor is assembled with symmetric carbon electrodes and hydrogel electrolytes for the electrochemical test.Significant Findings: The Raman spectroscopy analyzes the interface between 1 M Na2SO4 solution and the electrodes with various GO content and indicates the ratio of free ion increases with increasing GO content. The conductivities of electrodes by the 4-point probes method decrease with increasing GO content. A compromise between the free ion ratio and conductivity is obtained with 5 wt% GO in electrode (GO5) in accordance with the minimum equivalent series resistance (ESR) from Nyquist plot. The supercapacitor with GO5 possesses the maximum specific capacitance of 117.7 F g-1 in galvanostatic charge/discharge. SC-GO5 shows a large energy density of 15.6 Wh kg-1 at a high power density of 4.1 kW kg-1.