Preparation And Performance Of Graphene Hydrogel Materials For Supercapacitor

Supercapacitor,also called Electric Double-Layer Capacitor,is one type of energy storage which has many advantages,such as long cycle life and easy maintenance compared with bateries.Graphene,one unique two-dimensional carbon matrial,has many extraordinary properties:high carrier fluidity,high optical transmittance,high Yang's modulus,excellent flexibility,high specific surface area,etc.These properties fairly match the requirements of electrode materials used in supercapacitors.The graphene hydrogels prepared by hydrothermal method has high electrical conductivity and high mechanical strength,but the electrochemical performance is still worse than battery.In this thesis,through hydrothermal method graphene hydrogels were prepared.The effects of preparation conditions,hybrid atoms and pseudocapacitance on the electrochemical performance are investigetd:1.Different concentrations of graphene hydrogels were successfully prepared by hydrothermal method:(1)Changing the concentration of graphite oxide,the microstructure and pore size distribution of graphene hydrogels were different.The sample with a concentration of 3 mg ml-1 shows the best specific capacitance and largest specific surface area of 2110 m2 g-1.At a current density of 0.5 A g-1,the specific capacitance is 297 F g-1.After 10,000 cycles,the sample still maintains 93.4%of initial capacitance;(2)Increasing the pressure to 10 MPa,the electrochemical performance of sample can be further improved,which shows the largest specific capacitance of 330 F g-1 with 88%of initial capacitance retained after 10000 cycles.2.The graphene hydrogel doped with different elements was successfully prepared by hydrothermal method.Adding different electrolyte(element source)to the precursor,the microstructure and the electrochemical properties of the graphene hrgrogel changed significantly.With the addition of NH4H2PO4 and NH4BF4,the samples doped with N,P and a small amount of B can be obtained,showing the best specific capacitance and specific surface area(885 m2 g-1)in all samples.At a current density of 0.5 A g-1,the specific capacitance can reach 305 F g-1.After 10,000 cycles,the sample can maintain 85.7%of its initial capacitance.In addition,the pseudocapacitance introduced by doping element and the electric double layer capacitance provided by the electric double layer are investigetd.3.The Co3O4@rGO was successfully prepared by hydrothermal method.The microstructure and electrochemical properties of the material changed significantly after heating treatment in N2 atmosphere.After thermal treatment,the crystallinity of Co3O4 got better and the electrochemical activity was significantly enhanced.Composited with graphene hydrogel,the conductivity of Co3O4@rGO got better.After hydrothermal reaction at 180 ? for 12 h and thermal treatment in N2 atmosphere at 300 ? for 3 h,Co3O4@rGO-N2 sample can be obtained.At a current density of 0.5 A g-1,capacitance can reach 1058 F g-1.After 1900 cycles,the sample can maintain 71%of its initial capacitance.