Synthesis And Properties Of Graphene/Organic Compound Composite Electrode Materials For Supercapacitors

Nowadays,the problems of rapid consumption of fossil fuels,global warming,environmental pollution and energy shortages are becoming increasingly serious.To address these issues,the development of sustainable and efficient clean energy sources and new technologies related to energy conversion and storage become especially important.Supercapacitors,as a new type of energy storage device with advantages of high power density,fast charge and discharge rate,and high cycle stability,have been considered to be the most promising next generation of energy storage devices.At present,carbon based electric double-layer capacitors and transition metal oxide/conducting polymer based pseudocapacitors are two common types of supercapacitors with their own advantages and disadvantages.Carbon materials have good cycling stability,but their specific capacitance is low,and the pseudocapacitive materials have larger specific capacitance,but they are susceptible to structural damage during cycling and are less stable.So how to build a supercapacitor with large specific capacitance and excellent cycle stability is a hot and difficult point.In this thesis,the following studies have been carried out:1.Graphene oxide（GO）was first prepared by the Hummers’method,and then covalently grafted with 1,1’-ferrocenyldicarboxylic acid（Fc（COOH）₂）through p-phenylene diisocyanate（PPDI）.After reduction,the reduced graphene oxide/ferrocenyl binary composite（r GO-P-Fc）was obtained.By introducing small organic compounds with pseudocapacitive properties on the GO nanosheets,not only can prevent GO from restacking in the reduction process,retaining more surfaces contact to the electrolyte solution and providing more reactive sites,but also can realize the synergistic enhancement between electric double layer capacitance and pseudocapacitance.The final product was tested by cyclic voltammetry（CV）,galvanostatic charge/discharge（GCD）,electrochemical impedance spectroscopy（EIS）and the results showed that it has a high specific capacitance(481.3 F g^-1 at 0.5 A g^-1)and good rate performance(the specific capacitance at 10 A g^-1 keeps 77%of 0.5 A g^-1),which is a kind of electrode material for supercapacitors with good performance.2.Based on the above research results,polyaniline was in situ grown on the surface of r GO-P-Fc by chemical oxidation to prepare r GO-P-Fc/PANI ternary composites.In order to investigate the optimal ratio of polyaniline and r GO-P-Fc,r GO-P-Fc/PANI composites with ratios of r GO-P-Fc and aniline of 2:1,1:1,1:2,1:3 and 1:4 were prepared.The related electrochemical test results revealed that the prepared r GO-P-Fc/PANI（1:2）has the most excellent electrochemical performance,with a high specific capacitance of 715.8 F g^-1 at the current density of 0.5 A g^-1.It also has a high specific capacitance of 602 F g^-1 at a high current density of 10 A g^-1.And at the current density of 10 A g^-1,the retention rate of specific capacitance is 88.1%after 500 cycles,which indicated it has good cycle stability.This is because the introduction of polyaniline further enhances the conductivity of the material,and the specific capacitance of the ternary composite is further enhanced by polyaniline’s pseudocapacitance contribution,and the large-plane structure of r GO-P-Fc provides good skeleton support for polyaniline which ensures structural stability of polyaniline during the charge and discharge cycle.These test results showed that the prepared r GO-P-Fc/PANI composites have a good application prospect in electrode materials of supercapacitors.3.The application of free-radical compounds in supercapacitor electrode materials was discussed.First,GO was prepared by the Hummers’method.Then through the epoxy of GO reacted with the amino of 4-Amino-2,2,6,6-tetramethylpiperidinooxy（4-NH₂-TEMPO）introduced 4-NH₂-TEMPO on GO.Last,reduced graphene oxide/4-NH₂-TEMPO（r GO-T）composite was obtained after reduced.The final product was subjected to cyclic voltammetry,galvanostatic charge/discharge and electrochemical impedance spectroscopy test and the test results showed that the r GO-T has a better specific capacitance(～360 F g^-1)than graphene and good cycle stability,indicated that the free radical-based compounds also have promising applications in supercapacitor electrode materials.