Preparation Of Polypyrrole/Nitrogen-doped Porous Carbon Composite And Its Performance In Supercapacitors

Supercapacitor is a new type of energy storage device which is environmentally friendly,high power fast charging and high safety.It is above advantages that has attracted the attention which comes from scientific research and industry.The key to the industrial application of supercapacitors is to find electrode materials with high energy storage capacity,fast charge and discharge,high stability,low cost and environmental friendliness.At present,polypyrrole(PPy)conductive polymer has become one of the excellent electrode materials for supercapacitors due to its advantages,such as simple raw materials,good conductivity and easy synthesis.However,the PPy electrode materials suffer significant volume changes during high-rate charge-discharge cycles which leads to adverse consequences,such as reduced cycle life and capacitance attenuation.Therefore,it is urgent to improve the energy storage capacity and stability of PPy electrode materials.In this thesis,the conductive polymer PPy was combined with graphene oxide(GO),nitrogen-doped carbon matrix(rGO-C)and nitrogen-doped porous carbon matrix(N-PCM).On the one hand,the structural characteristics of the different carbon materials are used to support template for PPy.On the other hand,they can fully play a synergistic role,so as to achieve the purpose of gradually improving the electrochemical performance of PPy.This article mainly includes the following:(1)The first chapter summarizes the types and energy storage mechanisms of supercapacitors.It also introduces the structure,preparation methods of graphene and the applications on supercapacitors.The properties and synthetic methods of polypyrrole,and the research status of carbon materials and polypyrrole are briefly introduced.Finally,combining the above analysis,the thesis mainly expound purpose,significance and conception.(2)In the second chapter,the experiment used the modified Hummers method to prepare GO with high specific surface area,its morphology and structure were analyzed.Then,the PPy was polymerized on the surface of GO by chemical oxidation method to obtain PPy/GO nanocomposite and characterize the composite.It was found that the prepared PPy/GO had a flower-like shape.Electrochemical analysis shows that the PPy/GO composite strategy can effectively improve the energy storage capacity and stability of the PPy electrode.In 1 mol L^-1H₂SO₄solution,the capacity retention rate of PPy/GO after 1000 times of charge and discharge was 76.25%,while that of pure PPy was only 60.76%.(3)The PPy/GO prepared in Chapter 2 was subjected to a graded temperature carbonization process to obtain a nitrogen-doped carbon matrix(rGO-C).In the process,PPy in the composite provides nitrogen and introduces nitrogen functional groups to prevent the stacking of GO nanosheets.The PPy/rGO-C composites were obtained by in-situ polymerization method of growing PPy nanospheres on rGO-C.Electrochemical performance analysis found that the improved carbon matrix has more excellent electrochemical characteristics than GO,and the electrochemical performance has also been improved due to PPy/rGO-C obtained by polymerizing polypyrrole on rGO-C.(4)The rGO-C prepared in Chapter 3 was subjected to alkali-activated pore-forming treatment to investigate the effect of the different proportions of activation on properties of the nitrogen-doped porous carbon matrix.It was found that when the mass ratio of KOH and rGO-C is 2:1,the nitrogen-doped porous carbon matrix(N-PCM)obtained has a large specific surface area,a more uniform pore size distribution,and a high specific capacitance.Scanning electron microscopy showed that no obvious agglomeration was observed on the surface of this porous carbon matrix.In summary,N-PCM was proved to be the best choice for PPy substrates.Compounding PPy on N-PCM simultaneously explores the effect of the different pyrrole concentrations on the properties of the final product.Through physical characterization and electrochemical performance tests,it was found that when the pyrrole concentration was 0.06 mol L^-1,the prepared PPy/N-PCM composite had a capacity retention rate of 88.53%after 1000charge/discharge cycles at a current density of 10 A g^-1.It is much larger than PPy,PPy/GO and PPy/rGO-C.At a current density of 1 A g^-1,the specific capacitance of PPy/N-PCM is 237.5 F g^-1.This is because the new structure has a high specific surface area and a diffusion channel for rapid ion transfer.At the same time,electrolyte ions can enter the interior of the material along the surface of the polypyrrole nanospheres,which further improves the utilization rate of the electrode material.