Preparation Of Novel Graphene Hydrogel Functionalized With Organic Small Molecule And Its Application In Supercapacitors

Supercapacitor as a new type of energy storage has been widespread concerned,due to the features of high power density,long cycle life and high level safety.However,the energy density is relatively low,which limits the development of supercapacitors in various fields.Therefore,it is important to improve the energy density without sacrificing high power density.It is an ultimate goal to improve the energy density of supercapacitors in our works.We prepared several kinds of high-performance composites in which the holey graphene hydrogel used as the carbon substrate,and the various organic molecules used as the modified material.The psuedocapacitance adds the double-layer capacitance on basis of changing the surface property and porous structure,and then improves the specific capacitance obviously.Otherwise,we also explore the effect of electrochemistry performance by changing the carbon material into special structure.The main contents are as follows:（1）A lamellar holey oxygen-enriched graphene hydrogel（LGH）,which is consisted of graphene sheets with a large amount in-plane pores and oxygen functional groups,was prepared.Comparing with the traditional graphene hydrogel,both the lamellar morphology and hierarchically porous structure of LGH are quite different.The in-plane pores on the graphene sheets link up the out-of-plane interval between the graphene sheets to form a linking-up network porous structure.The present of in-plane pores on graphene sheets is result in more micropores and oxygen functional groups.The LGH electrode material exhibits an ultrahigh capacitance（337.8 F g-1 at 1 A g-1）and excellent rate capability.The LGH was used as positive electrode material and the graphene hydrogel modified by anthraquinone（GH-AQ）was used as negative electrode material respectively to assemble asymmetric supercapacitor（ASC）.The device exhibits great performance of energy storage,energy density reaches 31.5 Wh kg-1 along with power density of 0.9 k W kg-1.（2）The graphene nanomesh（GNM）with amount of in-plane pores was prepared with H₂O₂ using as oxide etching agent.After mixing with the caffeic acid（CAF）,the graphene nanomesh non-covalently modified with the CAF（GNM-CAF）was prepared.In three-electrode system,the specific capacitance of GNM-CAF is 466.3 F g-1 with the current density of 1 A g-1.The ASC is assembled with the GNM-CAF using as positive material and the GH-AQ as negative materials.The ASC shows superior energy performance that energy density is 23.25 Wh kg-1 along with the power density of 0.8 k W kg-1.（3）The holey graphene hydrogel-phenanthrenequinone composite（HGH-PQ）is prepared through a sample one-step hydrothermal method with the PQ as modified molecule,and H₂O₂ as activator.There is amount of in-plane pores on the graphene sheets after oxide etching by the H₂O₂.And the holey graphene sheets further restack into the 3D graphene hydrogel during the hydrothermal process.HGH-PQ has an excellent electrochemistry performance,the specific capacitance is 382.9 F g-1,and after 8000 cycles charge-discharge still retain 92.2% relative to the initial value.To match with the HGH-PQ positive material,the GH-AQ is used as negative electrode to assemble the ASC.The energy density of GH-AQ//HGH-PQ ASC is 21.05 Wh kg-1 along with the power density of 0.90 k W kg-1.（4）The cellulose acetate（CA）was used as carbon sources and the nano-Zn O flowers as the templates to prepare the carbon nano-flowers（CNF）via a high-temperature carbonization process.To characterize the electrochemical performance,the CNF electrode was tested in the three electrode system.As a result,the specific capacitance of is up to 229.7 F g-1 with current density of 1 A g-1,and retains 78.4% at 100 A g-1,which shows an excellent rate capability.The CNF also exhibits ultrahigh cycle stability with no capacitance decay after 6000 cycles.