Preparation And Electrochemical Performance Of Graphene Quantum Dots/Polyaniline Composites

With the reduction in the supply of fossil fuels and the intensification of environmental pollution,the demand for high-efficiency energy storage equipment has also gradually increased.New energy storage systems have been developed for a variety of applications.Supercapacitors（SCs）have been one of the most promising types of energy storage devices due to their unique features of light weight,flexibility,portability,long-term cycle life,operational safety,high power density,and fast charging.Graphene quantum dots（GQDs）since it has the advantages of small size,unique quantum confinement with edge effects,excellent optical performance,and good solubility,make graphene quantum dots can solve the application limitation of the graphene due to their large size,poor solubility and easy agglomeration.This paper mainly carried out the following content:（1）GQDs were prepared by hydrothermal method using citric acid as carbon source and urea as nitrogen source.The effects of GQDs addition on the structure and electrochemical performance of GQDs/PANI were studied.By FT-IR,Raman analysis can be seen that the surface of the prepared GQDs contains a large number of oxygen-containing functional groups,has surface structure defects,this kind of defect structure is conducive to the transmission and passage of electrons.TEM results show that the prepared GQDs have uniform size distribution,are concentrated in the range of 3 to 5 nm,and the crystal plane spacing is 0.35 nm,which is the（002）crystal plane spacing of graphite and is consistent with the XRD test results.By XPS test,the carbon,nitrogen,oxygen and hydrogen elements were found in the GQDs.The ratio of C/O and C/N was 6.48 and 7.95.（2）One-step synthesis of graphene quantum dots/polyaniline（GQDs/PANI）composites by in-situ polymerization.The effects of GQDs addition on the morphology and electrochemical performance of GQDs/PANI composites were studied.The results show that because the GQDs has defect structure,when supplying the PANI with GQDs,the GQDs/PANI composites also show some defect structure,along with the increase of the content of GQDs this defect level also gradually strengthen;through SEM analysis,it was found that the prepared PANI was nanofiber structure,this structure has a large aspect ratio and specific surface area,there are many gaps between the fibers,is conducive to the diffusion and migration of ions;TEM test results show that:GQDs doping in polyaniline fibers,the successful preparation of GQDs/PANI composites was demonstrated.Electrochemical tests showed that with the increase of GQDs content,the specific capacitance of GQDs/PANI composites gradually increased and the electrochemical performance was improved.When the GQDs content is 40%,its specific capacitance is the best under the same test conditions,and after 1000 times of charge/discharge,the capacitance retention rate is still80%.（3）Agraphenequantumdot/polyaniline-encapsulatedgraphenequantum dot/polyaniline/manganese dioxide（GQDs/PANI/MnO₂）ternary composite material was synthesized by in-situ polymerization using manganese dioxide as a template.The effects of MnO₂ content on the structure and electrochemical performance of GQDs/PANI/MnO₂ were studied.The study found that:when the mass ratio of An-MnO₂ is 1:1,the electrochemical performance of GQDs/PANI/MnO₂ is best.