Exploration On Electrode Performance Of Energy Storage Device Based On Graphene Quantum Dots

In recent years,graphene,as the most popular material,has been widely used in the fields of energy storage,field emission,and sensors.Graphene quantum dots?GQDs?,as one of them,not only inherit the characteristics of graphene's stable chemical properties,low electrical conductivity,and multiple preparation methods,but also have the unique characteristics of quantum dots such as quantum size effect,edge effect,and fluorescent effect,so it has shown broad application prospects in the fields of biological imaging,fluorescence detection,and photoelectric conversion.In addition,compared with traditional quantum dots such as cadmium sulfide,graphene quantum dots are rich in oxygen-containing groups and edge defects,which can better absorb metal ions,and also shows great potential in the field of energy storage.Graphite felt?GF?is a three-dimensional porous carbon-based material with low cost,stable properties,and good electrical conductivity.Due to its corrosion resistance and large specific surface area,it is suitable as an electrode material for energy storage devices.Therefore,in view of the great advantages of graphene quantum dots and graphite felt in energy storage,combining graphene quantum dots with graphite felt has great research value and application prospect in the field of electrochemical energy storage.In this dissertation,the graphite felt was first cleaned with an organic solvent and ultrasonic method.Then,a"bottom-up"chemical synthesis method was used to prepare the graphene quantum dots solution.The graphene quantum dots were attached to the surface of the graphite felt by ultrasound,and finally graphene quantum dots modified graphite felt was prepared.In order to prove that graphene quantum dots were successfully attached to the surface of graphite felt.First,the fluorescence spectrophotometer and transmission electron microscope were used to prove that the graphene quantum dots solution was successfully prepared.Then the surface morphology of graphite felt was characterized by field emission scanning electron microscope,Raman spectroscopy and X-ray photoelectron spectroscopy.According to the characterization results,the graphene quantum dots were successfully attached to the surface of the graphite felt.The graphene quantum dot modified graphite felt electrodes prepared with different concentrations and different carbonization times and original graphite felt electrodes were placed in 1 mol.L^-11 KOH aqueous solution,respectively,and subjected to a series of electrochemical tests including cyclic voltammetry test,charge and discharge test,electrochemical impedance spectroscopy,and Tafel curve found that GQDs/GF-1/2 electrode has the best supercapacitor characteristics.The graphene quantum dots can effectively reduce the contact resistance between graphite felt and solution,increase the discharge time of the graphite felt electrode.The GQDs/GF-1/2electrode has an ultra-high specific capacity of 2394 F.g^-11 at a discharge current density of 1 mA.cm^-2.In addition,the graphene quantum dots attached to the surface of the graphite felt can also protect the surface of the graphite felt.After 5000 charge and discharge test,the specific capacity remains basically unchanged,and the capacity retention rate reaches 95%,has very good supercapacitor characteristics.Then a series of cyclic voltammetry?CV?and electrochemical impedance spectroscopy?EIS?tests were performed on graphite felt electrode modified by graphene quantum dots with best electrochemical performance and original graphite felt electrodes in a 3 mol.L^-11 ZnI₂ solution.The results show that the graphene quantum dots modified graphite felt electrode has lower contact resistance and more outstanding performance than the original graphite felt electrode,and it is completely feasible to use it as an electrode of zinc-iodine battery.Therefore,a non-liquid flow zinc iodine battery structure was designed using industrial design software.The graphene quantum dots modified graphite felt electrode and the original graphite felt electrode were used as the negative electrode of the zinc iodine battery to assemble the battery.The blue electricity test system was used to test that the graphene quantum dots modified graphite felt electrode can reduce the ohmic drop of the battery.When the coulomb efficiency is close,the graphene quantum dots modified graphite felt electrode has higher voltage efficiency and energy efficiency.These results indicate that the attachment of graphene quantum dots to the surface of graphite felt can improve the performance of zinc-iodine batteries.After 47 charge and discharge tests,it was found that the discharge capacity of batteries assembled with graphene quantum dots modified graphite felt electrodes remained basically the same,with a capacity retention rate of more than 99%,while the battery assembled with the original graphite felt has a relatively obvious attenuation,which is only 43%.These results undoubtedly show that the use of graphene quantum dots modified graphite felt electrodes for zinc-iodine batteries is very promising.