Research On Carbon Dot Modified Electrode Used In Supercapacitor

Supercapacitor is a new type of energy storage device between traditional chemical electrolytic capacitors and batteries.It has the advantages of short charge and discharge time,long cycle life,and high power density.It can be used in industrial energy storage,electric vehicles,and consumer electronics etc.As a new type of carbon material with a size of less than100 nm,nano-carbon materials have attracted wide attention and have a wide range of applications in the fields of sewage treatment,biological detection,sensors,field emission,and energy storage.Carbon dots（CDs）,as one of them,have attracted wide attention in the field of new energy storage due to their high specific surface area,excellent electrical conductivity,rich surface functional groups and defects.Carbon cloth and carbon felt are a common low-cost three-dimensional self-supporting carbon structure material.They have stable chemical properties,good flexibility,rich pore structure and high conductivity,and can be used as electrodes for energy storage devices.Materials and current collectors.However,the original carbon cloth,carbon felt directly applied to supercapacitor electrodes have poor capacitance capacity due to their poor hydrophilicity,single capacitance formation,and small specific area.So try to use heat treatment to modify and activate it,and on this basis,carbon dots,manganese dioxide and the composite of the two（CD/Mn O₂）are synthesized on the carbon cloth and carbon felt electrode to improve the electrochemical performance of the electrode.First,the original carbon cloth,carbon felt（OCC,OCF）was annealed at 400℃.The results show that the carbon cloth,carbon felt（CC,CF）after heat treatment activation have better performance than the original electrode without heat treatment.Compared with OCC,the area specific capacity of CC is increased by 1250%,and the specific capacity of CF is also increased by 82%compared to OCF.Then,a bottom-up method was used to pyrolyze and synthesize a kind of carbon dots with fluorescence characteristics.Through HRTEM observation,it was found that it was spherical,uniformly distributed,stable in nature,and had a graphene lattice structure with a particle size of 2.1 nm,it is in line with the characteristics of graphene/carbon quantum dots.Fluorescence test was performed on it with a fluorometer,and it was found that the resulting product emitted 435 nm blue light under 365 nm ultraviolet light,which was consistent with the fluorescence spectrum characteristics of carbon quantum dots,indicating that the synthesized product was carbon dots.The synthesized fluorescent carbon dots of different concentrations are compounded on the improved carbon cloth and carbon felt by the hydrothermal method.The synthesized carbon dot carbon cloth and carbon dot carbon felt composite electrodes（CD/CC,CD/CF）are subjected to electrochemical tests of cyclic voltammetry characteristics,AC impedance spectroscopy,constant current charge and discharge,and Tafel curve.The results show that the carbon cloth modified by carbon dots has improved capacitance performance compared with the carbon cloth without carbon dots modification.At the same time,the test of carbon dots and carbon cloth composite electrodes with different concentrations indicate that the capacity of carbon dot modified carbon cloth composite electrode is 242%higher than that of carbon cloth without carbon dots,reaching 65.2 m F/cm²in 1m A/cm².Compared with CC,the contact impedance of the composite electrode has a certain decrease,which is reduced by 1.95Ω.The composite electrode has a capacity retention rate of 92.3%after 10,000 cycles of testing.The same experiment is performed on the carbon felt,and it is found that the performance retention rate of the carbon felt carbon dot composite electrode was 89.1%after 10000 cycles.These reflect the stability of the combination of carbon dots and carbon cloth carbon felt.The introduction of transition metal oxides on the carbon cloth as the active material of the electrode improves the capacitance performance of the electrode.Theδ-Mn O₂ with a layered structure is synthesized by hydrothermal method.This pseudocapacitance electrode material greatly increases the specific capacity of carbon cloth to 1322 m F/cm².However,the compositeδ-Mn O₂ increases the impedance of the carbon cloth,and the phenomenon of shedding occurs after multiple cycles,resulting in unstable electrochemical performance.Improve the electrochemical performance of manganese dioxide by introducing carbon dots.The synthesized carbon dot manganese dioxide carbon cloth composite electrode with different concentrations is tested.The carbon dot manganese dioxide composite electrode has better electrochemical properties.It grows very uniformly on the carbon cloth without obvious agglomeration.After CV and The CP test find that the specific capacity is 1884.9 m F/cm² at a sweep rate of 1 m V/s,and the electrode capacitance reduce by 13%after 5000 cycles,showing good cycle stability.The composite electrode is used as the working electrode,and the gel made of PVA and carbon dot solution is used as the electrolyte to make a flexible and bendable supercapacitor.The performance of the capacitor is basically unchanged after being bent at 90°and 180°,showing good bending resistance.