Preparation Of Phenanthrenequinone-modified Carbon-based Materials And Their Performance In Supercapacitors

Nowadays,with the depletion of fossil fuels and the increasing of environmental pressure,the development of sustainable and environmentally friendly new energy is particularly important.While the renewable sources such as solar energy and wind energy have the drawback of incontinuous.The developement of an efficient energy storage device is disired for the usage of such renewable resources.As a new type of energy storage equipment,supercapacitor has attracted the scientific researching interest for its advantages of high power density and good cycling stability.The development of electrode materials with good electrochemical properties is the key to improve the performance of supercapacitors.Carbon nanotubes and graphene are the most studied carbon materials in recent years due to the large specific surface area,good electrical conductivity and good physical and chemical properties.On the other side,phenanthoquinone（PQ）with electrochemically active functional groups is expected to have high theoretical specific capacitance.While the low electrical conductivity of the PQ molecules limits its directing usage as electrod materials for supercapacitor.In this thesis hybrid materials PQ-PCNTS and PQ-r GO have been prepared by modifying porous carbon nanotubes（PCNTs）and reduced graphene（r GO）with PQ molecules via non-covalent interaction using chemical reflux method as well as solvothermal reaction method.The non-covalent adhesion of PQ molecules on the surfaces of the basal carbon materials is expected to give hybrid materials with high specific capacitance.Moreover,good electrochemical performance of the hybrid materials are expected as the adhesion of PQ molecules would avoid the restacking of the graphene.（1）The carbon nanotubes were produced from the reaction with pyrrole as precursor.After carbonization and activation of the obtained CNTs,PCNTs with large specific surface area(2172 m²g^-1)and good electrochemical performance(262 F g^-1specific capacitance at 1 A g^-1)were obtained.Then PQ was modified to the surface of PCNTs using simple chemical reflux method to produce PQ-R-PCNTs.The obtained PQ-R-PCNTs was measured to have a high specific capacitance(772 F g^-1 at1 A g^-1)and excellent rate performance in a three electrod system.PQ-R-PCNTs were assembled into a symmetrical capacitor with an energy density of 26.2 Wh kg^-1 at a power density of 0.8 k W kg^-1.The PQ-S-PCNTs composites were also prepared by solvothermal reaction using the PCNTs obtained above as the substrate material.The composites have excellent electrochemical properties,i.e.,the specific capacitance is400 F g^-1 at 1 A g^-1,and the specific capacitance of 92.9%of the initial value remains after 10 000 cycles.The electrode material was assembled into a symmetric capacitor,which showed good electrochemical energy storage performance,i.e.,the power density was 0.8 k W kg^-1,and the energy density was up to 21.5 Wh kg^-1.The adsorption direction of small organic molecules PQ on the surface of carbon nanotubes is explored through first-principles calculations.（2）Graphene oxide has been prepared by he improved Hummers method.The obtained GO was reduced by sodium ascorbate using chemical refluxing method.The produced R-r GO with a specific area of 229.0 m² g^-1 gives a specific capacitance of146 g^-1 at 1 A g^-1.Moreover,the PQ modified reduced graphene oxide（PQ-R-r GO）was prepared by the smae method with some amount of PQ adding into the mixurte.The obtained hybrid materials displayed excellent electrochemical performance(specific capacitance reached 356 F g^-1 at 1 A g^-1)and excellent electrochemical stability（91.3%of the initial value after 10 000 cycles）.The symmetrical capacitor assembled with same amount of PQ-R-RGO as positive and negative electrodes possese an energy density of 17.0 Wh kg^-1 at the power density of 0.8 k W kg^-1.PQ functionalized reduced graphene oxide（PQ-S-r GO）was prepared by one-step solvothermal reaction with PQ as the modified molecules and sodium ascorbate as the reducing agent.The obtained PQ-S-r GO material has good electrochemical performance(up to 265 F g^-1 at 1 A g^-1),excellent rate performance(76.2%of the initial value at 20 A g^-1)and excellent electrochemical stability（97.7%of the initial value after 10 000 cycles）.After the symmetrical capacitor was assembled with the PQ-S-r GO as positive and negative electrodes,the device has an energy density of12.3 Wh kg^-1 and a power density of 0.8 k W kg^-1.The adsorption direction of small organic molecules PQ on the graphene surface is explored through first-principles calculations.