Chemically Modified Graphene Based Supercapacitor

Supercapacitors have attracted a great deal of attention because of their high power density and long cycling life.Chemically modified graphene?CMG?is regarded as one of the most promising electrode materials for supercapacitors,mainly due to its high theoretical specific surface area,excellent conductivity and electrochemical stability,various assembly nanostructure and scalable chemical synthesis method.This dissertation systematically developed several effective methods for the fabrication of CMG-or its composite-based electrodes,and investigated their applications for constructing supercapacitors for energy storage or alternating current line-filtering.The main contents are listed as follows.Graphene/activated carbon?AC?composite organogels were prepared by one-step solvothermal reduction of homogeneous graphene oxide?GO?/AC dispersion in propylene carbonate.The addition of AC increased the packing density of the integrated electrode,increasing the volumetric capacitances of graphene-based supercapacitors.On the other hand,three-dimensional conductive graphene framework provided AC particles with highly conductive electron transfer pathways,improving the rate capability of AC based-supercapacitors.A dense and high-defective graphene hydrogel film was prepared by hydrothermal reduction of highly oxidized GO?HGO?sheets with optimized sizes of 1²?m,followed by mechanical compression.The corresponding supercapacitors is a promising energy storage device with excellent integrated performance.It exhibited high gravimetric(231 F g^-1)and volumetric(274 F cm^-3)capacitances at 1 A g^-1,ultrahigh rate-capability(80%capacitance retention at 100 A g^-1),and good electrochemical stability.The effects of the structural defects and sizes of GO precursors on electrochemical performance of graphene based supercapacitors has been systematically studied.This work offers a guidance of rational designing graphene materials for their applications in supercapacitors.Three-dimensional porous graphene/polyaniline?PANI?composites with pores vertically oriented on current collectors were prepared by one-step electrochemical co-deposition from the homogeneous mixed solution of aniline monomer and GO.The conductive graphene network provided a scaffold with large specific surface area for the deposition of PANI with high redox capacitance.The resulting graphene/PANI composite electrode showed a high areal specific capacitance with excellent rate capability.This method is simple,environmental-friendly and controllable.The graphene/PANI electrodes have a great potential for ultrafast supercapacitor application.Nitrogen-doped holey graphene?NHG?films were prepared via doctor-bladingofgrapheneoxide?GO?/ferricoxide?Fe₂O₃?nanorods/polyvinylpyrrolidone?PVP?hybrid gel,followed by thermal annealing and acid treatment.During thermal treatment,Fe₂O₃ nanorods catalyzed the etching of carbon atoms to form mesopores/macropores and the decomposition of PVP led to dope N atoms into reduced graphene oxide?rGO?sheets.This fabrication method is industrially compatible and scalable.The NHG-based supercapacitors exhibited high specific capacitances and ultrafast frequency responses,promising to replace aluminum electrolytic capacitors for miniaturizing alternating current line-filters.