Preparation Of Graphene Polypyrrole Composites And Its Application

Supercapacitor,as a green energy storage device with ultra-high power density and cycle life,has begun to receive widespread attention.The electrochemical performance of supercapacitor is greatly affected by the performance of electrode materials.Common electrode materials mainly include carbon materials,metal oxides and conductive polymers.Graphene,as a new two-dimensional nano carbon material,has the advantages of large specific surface area and high electrical conductivity,and has become the focus of attention in recent years,but its characteristics limit the improvement of specific capacitance.Conductive polymers have the advantages of low production cost,environmental friendliness and high specific capacitance,but have poor cycle stability.The combination of them is expected to become a supercapacitor electrode material with good electrochemical performance.How to more effectively prepare composites with different morphologies and structures is the focus of research in recent years.Therefore,in this thesis,the graphene polypyrrole composites with different morphologies and structures were prepared by Pickering emulsion polymerization and hydrothermal in-situ polymerization.The electrochemical properties of the composites as supercapacitor electrodes were also studied.(1)Pickering emulsion polymerization is a very effective method for constructing hollow sphere structure composites.In the preparation of graphene polypyrrole hollow sphere structure composites,the effects of oxidant content,reaction time and compounding ratio on the morphology and chemical structure of the composites were investigated by single factor method.The process.conditions:FeCl3.6H2O:pyrrole=1:2(molar ratio),reaction time is 4 h,and graphene oxide:pyrrole=1:10(mass ratio),the electrochemical properties of the resulting composite are optimal.At a current density of 1 A/g,the specific capacitance can reach 238.0 F/g.After 1500 cycles,the specific capacitance can still maintain 90.7%of the initial capacitance,superior than 62.2%of polypyrrole.It has been found that graphene oxide is reduced during the polymerization of pyrrole.(2)In the process of hydrothermal in-situ polymerization to prepare graphene polypyrrole composites,graphene oxide acts as an oxidant for pyrrole polymerization,which initiates polymerization of pyrrole on its surface.The morphologies and electrochemical properties of composites in different ratio with/without SDS were investigated.The test results show that there is an optimum ratio of graphene oxide-induced pyrrole polymerization.In the graphene polypyrrole composites without SDS,the polypyrrole is in the form of nanoparticles,and when graphene oxide:pyrrole=1:5(mass ratio),the composite exhibits better rate performance and cycle stability.At a current density of 1 A/g,the specific capacitance is 219.2 F/g.After 2000 cycles,the capacitance retention can reach 94.3%;In the graphene-polypyrrole composite with SDS,the polypyrrole is fibrous.When graphene oxide:pyrrole=1:5,the composite has a specific capacitance of 184.1 F/g at a current density of 1 A/g,and after 2000 cycles,the capacitance retention can reach 90.1%.It indicates that the morphology of polypyrrole has a great influence on the electrochemical performance of graphene polypyrrole composites.(3)Graphene polypyrrole composites with different structures and morphologies will affect the electrochemical properties of the composites.Compared with traditional two-dimensional graphene polypyrrole composites,the three-dimensional hollow sphere graphene polypyrrole composite can provide more contact area and ion diffusion channels,thus having better capacitance properties.The addition of SDS changes the morphology of the polypyrrole and also increases the internal resistance of the composite,which adversely affects the electrochemical properties of the graphene polypyrrole composite.