The KOH Activation Mechanism Of Graphene And Its Application In Supercapacitors

Supercapacitors, storing charge at the interface of electrode and electrolyte via physical adsorption, are able to supply energy at an extremely high power. However, the commercial supercapacitors based on activated carbons suffer from the low energy density, which cannot meet our current requirements for energy storage devices.Graphene, due to its high theoretic specific surface area (SSA), excellent electrical conductivity and physical and chemical stability, has a great potential used for supercapacitors as electrode materials. Unluckily, the graphene obtained through chemical reduction method has limited SSA, partly resulting from the restacking of graphene layers under van der waals force, which cannot provide with enough active sites for charge storage when used as electrode materials of supercapacitors. Using the method of alkali activation, the SSA of graphene can be improved efficiently, but the mechanism of this process is not very clear yet.In this thesis, the process of alkali activation of microwave exfoliated graphite oxide (MEGO) was investigated through activation at a relatively low temperature (450℃-550℃), in order to trap the structure transition during the activation process. In addition, it is founded that nanometer-sized pores are created in the graphene platelets at the activation temperature of around 450℃, leading to a carbon that maintains the platelet-like morphology, yet with a SSA much higher than that of MEGO. Such a porous yet highly conducting carbon shows a largely enhanced electrochemical performance when used as electrodes in supercapacitors. A specific capacitance of 265 F g1 (185 F cm-3) is obtained at a current load of 1 A g-1 in 6 M KOH electrolyte, which remains 223 F g-1 at the current density of 10 A g-1.