Preparation Of Porous Carbon And Graphene Nanospheres And Their Performance For Supercapacitors

Supercapacitor is a new type of energy storage device,which has been widely concerned and studied because of its advantages of high power density,long cycle life,safety and environmental protection.The performance of supercapacitors mainly depends on electrode materials.The electrochemical performance of supercapacitors mainly depends on electrode materials.porous carbon materials as electrodes of super capacitors have the advantages of long service life,low price and high power density.however,the slow kinetic process due to improper pore size,poor geometry and conductivity limits its application as a major power source.therefore,the development of carbon materials with good structural properties and safety and stability has become the key to current research.Biomass derived carbon and graphene are two important directions in the development of carbon materials.Cheap and renewable waste biomass is beneficial to obtain carbon-based porous materials with various components and structures because of its advantages of biodiversity source,unique structure and natural heteroatoms.Graphene is widely used in energy storage because of its high mechanical strength,high conductivity,large surface area and high electrochemical stability.Biomass derived hierarchical porous carbon materials and porous graphene nanospheres were successfully prepared,and their surface structure,graphitization degree and supercapacitor properties were studied.The main research contents are as follows:1.Using waste biomass material(Bulrush leaf)as carbon source,KOH as activator and Fe(NO₃)₃as graphitic catalyst,a bulrush carbon was prepared by simple chemical activation and high temperature carbonization.Theierarchical porous interconnected network structure and large specific surface area of the prepared carbon materials(S_BET=1517.2887 m²g^-1).due to the synergistic effect of multilayer hierarchical pores,the prepared materials exhibit excellent electrochemical properties.6 M KOH aqueous solution as electrolyte in three-electrode system,the materials show excellent electrochemical performance.the high specific capacitance of 308 F g^-1at a current density of 0.5 A g^-1and The specific capacitance of 215 F g^-1is maintained at 50 A g^-1high current density.In addition,a symmetrical two-electrode system was assembled with 1 M Na₂SO₄as the electrolyte.the symmetric cell exhibits high specifific energy density of 15.5 Wh kg^-1at a power density of 500 k W kg^-1,This is far better than traditional activated carbon.The bulrush carbon material has the advantages of simple synthesis method,low cost and abundant raw materials.It is a promising electrode material for commercial application.2.Using glucose as carbon source and polystyrene spheres(PS)as hollow structure templates,a novel hollow graphene nanospheres material(GNSs)was synthesized by template separation and microwave heating technology;the morphology and structure of graphene nanospheres can be controlled by changing the PS/glucose ratio,microwave heating time and Fe content.The typical GNS have high surface area(2794 m²g^-1),large pore volume(1.48 cm³g^-1)and high packing density(0.74 g cm^-3).hence,the GNS also shows excellent gravimetric specific capacitance and volume specific capacitance at high current density.the electrochemical measurements were carried out in 6 M KOH solution.in the three-electrode system,the gravimetric and volume specific capacitance was 529 F g^-1and 392 F cm^-3at 1 A g^-1with a capacitance retention of 62.5%at 100 A g^-1.Under the two-electrode system,the energy density is 18.6 Wh kg^-1(13.8 Wh L^-1)at a power density of 504 W kg^-1.which is higher than all reported pure carbon materials in gravimetric energy density and higher than all reported heteroatom-doped carbon materials in volumetric energy density.