Study On The Electrochemical Performance Of Graphene Based Hydrogels As Supercapacitor Electrode Materials

Supercapacitors supposed to be a promising candiate for alternative energy storage devices as a result of their high rate capability, long cycle life, simple principles, and low maintenance cost have been under an ever increasing demand as a result of the needs of modern society and emerging ecological concerns. Graphene hydrogel with less-agglomerated,self-supported, binder-free, and cross-linked 3D porous is a kind of novel materials used for supercapacitor electrodes. The recent researches demonstrated that graphene hydrogel shows excellent electrochemical performance including long cycle life and high rate capability besides high specific capacitance. Hence, this work concentrates on the synthesis of graphene based composite hydrogel and enhancing the specific capacitance and energy density.Graphene/CNTs composite hydrogel has been prepared by a facile one-step hydrothermal method. The graphene hydrogel has a large specific surface area because of the existence of the 3D porous which is accessible of the electrolyte. Meanwhile, CNTs not only can enhance the electrical conductivity and specific capacitance but can also reduce the agglomeration of the graphene by being incorporated into the graphene layers. Consequently, the specific capacitance of the graphene/CNTs composite hydrogel is measured to be 350.1 F/g at the current density of 5 mA/cm2. Furthermore, the capacitor has an energy density of 175.1 Wh/kg and a high rate capability. It also shows a long cycle life along with 90% retention after 1000 cycle tests, which has practical value.A one-step hydrothermal procedure has been used to synthesize the graphene/VO2 composite hydrogel. Besides a large specific surface area the existence of the 3D porous can also enhance the electrical conductivity of the composite. Simultaneously, VO2 can enhance the specific capacitance and reduce the agglomeration of the graphene by being incorporated into the grapheme layers. Under the combined effect of the two components, the specific capacitance of the graphene/VO2 composite hydrogel is measured to be 281.5 F/g at the current density of 5 mA/cm2. Furthermore, the capacitor has a long cycle life along with 95%retention after 1000 cycle tests and an energy density of 140.1 Wh/kg which has an obvious advantage compared wth the conventional batteries. Consequently, this hydrogel is suitable for supercapacitor eletrodes.Graphene/NiOOH composite hydrogel has been prepared by a facile CBD method using graphene hydrogel which is prepared via hydrothermal reduction of graphene oxide. The existence of the 3D porous which is accessible of the electrolyte not only can enhance the electrical conductivity of the composite but can also reduce the agglomeration of the graphene.Meanwhile,compared with pristine graphene,the graphene hydrogel has a larger specific surface area and can provide more active sites. Although NiOOH has a high theoretical capacity, the specific capacitance of the composite hydrogel increases barely from 61.7 F/g to 91.3 F/g because of too little NiOOH modified on the graphene. However,it shows a long cycle life along with 91.5% retention after 1000 cycle tests, which has practical value.