Preparation Of Nitrogen And Fluorine Co-doped Holey Graphene Hydrogel And Its Application In Supercapacitor

Graphene,a two-dimensional mono-layer of sp²-hybridized carbon atoms,has been considered as an ideal electrode material for supercapacitors due to its intrinsic outstanding electrical conductivity,excellent chemical and thermal stability and large theoretical specific surface area.However,most of graphene-based electrodes for supercapacitors usually deliver low specific capacitances due to the strong?-?interaction,electrochemical inertness and low electrochemical active sites.Therefore,the capacitance performance of the graphene is improved by expanding the specific surface area and introducing the heteroatom doped structure.In this paper,the activation of graphene oxide by H₂O₂ was employed to obtain the holey graphene precursor at first,and then it was underwent a one-step hydrothermal reaction with pyridine hydrofluoride as the doping source of both N and F simultaneously so as to obtain the NF-HGH.We first discussed the effect of reaction temperature on the content of element doping and determined the optimum doping temperature.We also investigated the effects of etching graphene oxide on the content of elements,the bond type and the specific surface area.For the doping of heteroatom,the contents of N and F in NF-HGH are 2.56 and 1.14 at.%respectively.Moreover,NF-HGH mainly formed pyrrolic and pyridine N,semi-ionic C-F bonds and the specific surface area is as high as 735 m² g^-1.Therefore,NF-HGH is pressed into nickel foam directly as the electrode of supercapacitor,which exhibits a high specific capacitance(345.4 F g^-1 at 1 A g^-1),good rate capability(specific capacitance of 198 F g^-1 at 100 A g^-1),and superior cycling stability(capacitance retention of 96%after 10,000 cycles at 2 A g^-1).The fabricated symmetric flexible solid-state supercapacitor shows superb rate capability with the maximum power density of 10.00 kW kg^-1,associated with the maximum energy density of 7.99 Wh kg^-1.It has a wide potential range from 2 to 4.5 V with good discharge characteristics in organic electrolyte,which shows the potential application in the cathode materials of super energy density hybrid supercapacitor.