Preparation And Supercapacitive Performance Of Graphene Functionalized By Organic Quinone Molecules

Due to the increasingly severe global energy and environmental problems,it is urgent to develop a high-performance,low-cost and clean energy storage equipment.As a new type of energy storage device,supercapacitor has been widely used in many fields due to its advantages of fast storage/release of electricity,high power density,long cycle life and wide range of operating temperature.In recent years,supercapacitors designed and fabricated from graphene-based carbon materials have been favored by researchers because of their higher cycle life and stability.At present,researchers are paying their attention to a hot topic that small organic molecules are fixed on the surface layers of graphene to form a new functionalized carbon-based materials with higher specific capacitance.Among them,the anthraquinones are one of the most important organic molecules with reversible electrochemical active groups and multiple electron exchange sites which can be expected to provide additional pseudocapacitance.In this paper,the various anthraquinone organic molecules are used to modify reduced graphene oxide substrate to form functionalized carbon-based electrode materials.Furthermore,several supercapacitors are fabricated on the base of the resultant functionalized carbon materials to evaluate their performance in the electrochemical energy storage.The main objective of the research is that the surface functionalization of carbon-based materials is used to realize their capacitance enhancement by superposing pseudocapacitance to electric double layer capacitance.The main research contents are as follows:（1）A layered cross-linked graphene conductive network was prepared by diazotization of 2,6-Diaminoanthraquinone and graphene.2,6-Diaminoanthraquinone as an organic molecule with diamine radicals and rigid structure can cross-link reduced graphite oxide and prevent the accumulation of reduced graphite oxide as a molecular pillar.What’s more,the 2,6-Diaminoanthraquinone contains two reversible electrochemically active functional groups,and these functional groups are responsible for increasing the pseudocapacitance.In a three-electrode system,the electrode material has a high specific capacitance of 522 F g^-11 at 5 mV s^-1 in 1 M H₂SO₄ solution.（2）A new type of graphene hydrogel is prepared by a one-step hydrothermal method,in which indanthrone organic molecules reacts with graphite oxide under the hydrothermal conditions（IT-GH）.The resultant 3D graphene hydrogels have a three-dimensional（3D）porous network,which provides a unobstructed path for the diffusion of electrolyte ions.The results show that in a three-electrode system,the specific capacitance of the IT-GH electrode material can reach 327 F g^-1 at 5 mVs^-1 in 1M H₂SO₄electrolyte.In addition,when the electrode material is assembled into a symmetrical supercapacitor,the specific capacitance of the device is up to 37 F g^-1 at 5 mV s^-1.After5000 cycles,the capacitance retention rate was 82.8%.（3）Anthracene-1,4,9,10-tetraol can be used as a new guest molecules（AT）with high functionalized performances due to their abundant hydroxyl functional group.Graphene with high specific surface area and high conductivity is selected as a conductive substrate to anchor AT molecules and form electrode materials（AT@GH）with high conductivity and high specific capacitance via one-step hydrothermal method.The graphene in the composite,as an electron transport medium,not only provide electrical double layer capacitance,but also form synergistic effect with organic molecules,which provides pseudocapacitance.In a three-electrode system,the AT@GH electrode can achieve specific capacitance of 206 F g^-1 at 5 mV s^-11 in 1 M H₂SO₄ electrolyte.Finally,an asymmetric supercapacitor device was fabricated by using IT-GH as the positive electrode and the AT@GH as the negative electrode,respectively,and then this device is used to test its electrochemical performance.The results show that the specific capacitance of asymmetric supercapacitor is as high as 22 F g^-1 at 5 mV s^-11 in 1 M H₂SO₄electrolyte.