Preparation And Electrochemical Properties Of Three Dimensional Graphene Based Electrode Materials

Graphene has potential application prospect in supercapacitors due to its high theoretical specific surface area,high conductivity and good heat resistance.However,the two-dimensional structure of graphene usually has a serious restacking phenomenon,leading to lower specific capacity than its theoretical value(550 F g-1).Constructing of three-dimensional graphene material can effectively reduce the stacking phenomenon of graphene sheet and simultaneously form meso/macro-porous structure,which is beneficial for the transfer of electrolyte ion and electron.Moreover,the three-dimensional graphene can be directly used as binder-free electrode material of supercapacitor to improve the specific capacitance of graphene based electrode materials.Therefore,it has become a hot research topic to develop a new type of three-dimensional graphene based electrode material and further improve its specific capacity.In this paper,two typical three-dimensional graphene based electrode materials have been prepared by one step hydrothermal method.The facile methods and analysis conclusion are shown as follows:(1)Preparation and electrochemical properties of nitrogen doped three-dimensional graphene(3DNG): 3DNG materials with high nitrogen content and density(1.31 g cm-3)were prepared by one-step hydrothermal method with graphite oxide and ammonia as raw materials.In 6 M KOH electrolyte,the material exhibited the maximum volumetric capacitance of 437.5 F cm-3at 0.5 A g-1and the capacitance still maintained 93% after working 20000 cycles at high current density of 10 A g-1.Further analyses indicate that N-configurations are of great significance to the improvement of electrochemical behavior as well as the N-content.Pyridinic N and quaternary N can enhance the conductivity of the 3DNG materials and the quaternary N plays a major role for the conductivity improving,meanwhile,the pyrrolic N and Pyridinic N acted as pseudocapacitance group also play a crucial role in enhancing the energy storage performance.(2)Preparation and electrochemical properties of three dimensional graphene/carbon dots:With graphite oxide and carbon dots as raw materials,three-dimensional graphene decorated with homo-dispersed carbon dots have been synthesized through a facile one-step hydrothermal method.When the material is used as binder-free electrode for supercapacitors,the specific capacitance could reach at 308 F g-1at 0.5 A g-1,and it still maintained at 92% of its initial capacitance after working 20 000 cycles at 10 A g-1.The decorating of CDs act as intercalator to effectively reduce the aggregation and/or re-stack of graphene sheets and enable the electrolyte ion to easily penetrate through the 3D r GO framework and allow sufficient contact with the electrolyte.The relatively rich oxygen-containing functional groups of r GO/CDs are expected to afford much more redox active sites to provide higher pseudocapacitance.