Hard Template Synthesis And Supercapacitor Applications Of Three-Dimentional Porous Carbon Nanosheet

Supercapacitors not only possess ultra-high capacitance,but also have superiorities of high cycle stability,fast charge and discharge rate over traditional chemical power sources,indicating their considerable potentials on energy storage applications.Particularly,carbon materials-based supercapacitors have been commercialized for years.However,To further enhance the energy density and the storage capacity,as well as to further reduce the cost are the main challenges for large-scale applications of supercapacitors.Therefore,high-performance carbon electrode materials with excellent conductivity and large specific surface area have attracted intense attention.Porous carbons are among the most popular carbon electrode materials,and continue to stimulate much research interest as a resul t of their advantages of low cost,high surface area and rich pore structures.To achieve high electrochemical performance of porous carbons,Mg O-based hard template method is considerd to be one of the most appealing synthesis techniques.However,optimization and growth mechmism investigtion of the MgO-based hard template method as well as exploration on properties and supercapacitor applications of the carbon products are still highly desirable.Herein,three-dimensional(3-D)porous carbon nanosheets were produced by a Mg O-based template method and a MgO/Zn O-based dual-template method using urea as precursor.The growth properties,electrochemical properties,and supercapacitor applications of the products were systematically studied.The related mechanisms were discussed accordingly.The main contents of this thesis include:(1)Magnesium was used as a reducing agent to prepare carbon material at high temperatures.MgO atomic-scale structures not only catalyzed the formation of highly graphitized lamellar structures but also acted as hard templates to fill in the channels inside the carbon materials.After removal of the template by using dilute hydrochloric acid,3-D porous carbon nanosheets were obtained.Based on KOH electrolyte,the achieved maximum specific capacitance was up to 169.3 F/g.(2)By employing Zn O as an auxiliary template,Mg O/Zn O-based dual-template method was used to produce 3-D porous carbon nanosheets.The pruducts presented a significanly enhanced specific surface area of 765 m2/g.As a result,the specific capacitance of 320 F/g at 1 A/g and the energy density of 5.4 Wh/kg were achieved by using KOH electrolyte.(3)To further enhance the energy density of the symmetric supercapacitors,1-Ethyl-3-methylimidazolium Tetrafluoroborate was used as the electrolyte.At room temperature,the obtaimned maximum energy density of 33 Wh/kg at a power density of 1500 W/kg is 6 times of the supercapacitor using KOH electrolyte.Particlularly,energy density as high as 87 Wh/kg at a power density at 1500 W/kg was obtained at a working temperature of 180 °C,implying the obtained porous carbon nanosheets and the related supercapacitors have promising application potentials in high-temperature devices.