Synthesis And Application Of Graphene-based Composites In Supercapacitors

Supercapacitor is new green energy storge device between the traditional capacitors and chemical batteries,which due to high power density,fast charge and discharge,long cycle life and environmental-friendly.The specific capacitance of the supercapacitor depends mainly on the electrode material.Graphene is a novel nanomaterial with atomic-sized thickness,owning to promising mechanical,thermal,and electrical properties has become one of the most promising candidate materials for supercapacitor.Polyaniline has specially electrical,optical and electrochemical properties,which can be used to synthsice functional electrode materials by doping.In this work,the performance of supercapacitor was enhanced by preparation of graphene-based composites and the modification of electrolyte,The main research contents are as follows:Firstly,graphene oxide(GO)were prepared by the Hummers' method,then the as-prepared GO was reduced to graphene hydrogel(GHG)by hydrazine hydrate.The results show that graphene has a three-dimensional mesoporous structure,the specific capacitance of the graphene hydrogel can reache 200 F g"1.The graphene hydrogel were employed as electrodes and assembled into supercapacitors.Then their electrochemical performances were tested in a solvent of 1 M H2SO4,and a mixed solvent of 0.4 M CuSO4 and 1 M H2SO4,respectively.When the current density was 0.65 A g-1,the specific capacitance test in CuSO4 was 120 F g'1,and the specific capacitance test in H2SO4 was 58 F g-1.which shows the three-dimensional mesoporous structure of graphene hydrogel can facilitates the diffusion of the electrolyte and the transport of ions,thereby providing a larger electric double layer capacitor;CuSO4 as an electrolyte can provide a greater pseudocapacitance.Then,The polyaniline/grapheme hydrogel(PANI/GHG)composite materials were successfully prepared by electrochemical polymerization.The electrochemical polymerization of PANI/GHG was carried out under the condition of different segments of cyclic voltammetry.At a current density of 0.65 A g-1,the specific capacitance was 470 F g-1.The as-prepared PANI/GHG were utilized to assemble supercapacitors.To make a comparison with that of graphene,the electrochemical performances of PANI/GHG were also tested in a solvent of 1M H2SO4,and a mixed solvent of 0.4 M CuSO4 and 1 M H2SO4,respectively.The results show that the specific capacitance was 280 F g-1 when the current density was 1.3 A g-1 test in CuSO4.When the self-discharge time is 5000 s,the voltage remains can remain at 0.35 V.it was concluded that polyaniline and CuSO4 can provide pseudocapacitance;The reaction of Cu2+ to reduce Cu can inhibit the diffusion resistance of ions in the solution and the occurrence of additional redox reactions,which can extended self-discharge time.In this paper,the addition of metal oxide into graphene composites were prepared by electrospinning.Then the as-prepared composites were characterized by SEM,TEM,the result show that the nanofibers with uniform diameter were observed.The specific capacitance of the nanofibers with hollow structure is 1667 F g-1 at 10 mv s-1,and the specific capacitance of nanofibers with the solid structure is 1116 F g-1.