| Supercapacitors have received extensive attention due to their excellent electrochemical performance,such as good cycle stability,ultra-fast charge and discharge speed,and high power density.The further improvement of the electrochemical performance of supercapacitors is closely related to the development of electrode materials.Graphene with extremely high specific surface area,high chemical stability and excellent electrical conductivity make it an excellent choice for supercapacitor electrode materials.Nitrogen doping can significantly improve the electrical conductivity of graphene and provide pseudo capacitance,thereby improving the electrochemical performance of graphene.Traditional methods for preparing nitrogen-doped graphene,such as solvothermal method,chemical vapor deposition,and nitrogen plasma treatment,have some problems such as low nitrogen doping amount or complicated instrument steps,which limit the further improvement of the performance of nitrogen-doped graphene electrode.Therefore,in order to further increase the nitrogen content of nitrogen-doped graphene and improve the electrochemical performance of graphene,it is necessary to develop a simpler and more effective method to increase the nitrogen doping amount.Based on the synthesis of ultra-high nitrogen content nitrogen-doped graphene by thermal annealing of fluorinated graphene under ammonia atmosphere,a simple and safe method to achieve high concentration nitrogen doping has been developed in this paper.Fluorinated graphene oxide is prepared from fluorinated graphitic polymer,and nitrogen doped graphene is prepared by thermal annealing of fluorinated graphene oxide in the atmosphere of ammonia.By comparing the properties of nitrogen-doped graphene prepared by different annealing temperatures and annealing times,we obtained the following main conclusions:1)Fluorinated graphene oxide has fewer layers and obvious lattice structure defects.The Raman spectrum shows that there is a higher intensity ratio between the D peak and the G peak of fluorinated graphene oxide,which indicates that fluorinated graphene oxide has more defects and can provide a large number of vacancies for high concentration doping of nitrogen atoms.The XRD and XPS characterization results of fluorinated graphene oxide show that the structure and elements of fluorinated graphene oxide have changed,and the fluorine content in the sample is as high as 31.91 at.%.2)With the increase of annealing temperature,the nitrogen content in the prepared nitrogen-doped graphene sample first rises and then decreases.When the annealing temperature is 800 °C and the annealing time is 3 h,the nitrogen-doped graphene The nitrogen content reached a maximum(12.45 at.%).3)The nitrogen-doped graphene CV curves with different annealing temperatures all show good rectangular-like shapes,which proves that nitrogen-doped graphene has the characteristics of electric double layer capacitance.The small redox peaks appearing on the CV curve indicate that the nitrogen atoms and the remaining oxygen-containing groups provide additional tantalum capacitance for the electrode material.With the increase of annealing temperature,the specific capacitance of nitrogen-doped graphene electrode material first rises and then decreases.At 800 °C,3h,the specific capacitance of electrode material reaches 225.2F/g.4)The nitrogen-doped graphene electrode material prepares at 800 ° C for 3 h showed good cycle stability.After 5000 cycles of charge and discharge at a current density of 5 A/g,the specific capacitance of the electrode is attenuated from the original 188.75 F/g to 168.89 F/g,and the capacitor retention rate is 90.1%.The charge transfer resistance of the electrode material is extremely low,and the equivalent series resistance is only 50 mΩ,which proves that the nitrogen-doped graphene has excellent conductivity.The curve in the low frequency region shows a lower ion diffusion resistance of the nitrogen-doped graphene and exhibits good electric double layer characteristics. |
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