Controllable Synthesis Of Porous Carbon Materials And Their Electrochemical Performance

Supercapacitors,also called electrochemical capacitors,have attracted worldwide attention due to their high power density,excellent rate capability,fast charging/discharging performance,long cyclic stability and low cost.Currently,carbon materials have been widely used in the electrode of supercapacitors because of their high surface area and good electric conductivity.It is generally known that the specific surface area,porous structure and surface chemistry of porous carbon materials have great influence on the electrochemical performances.In this dissertation,we prepared porous carbon materials with different morphologies and microstructures by template method.The microstructures and surface chemistry of the materials were characterized by X-ray diffraction,scanning and transition electron microscopy,Raman spectra and X-ray photoelectron spectroscopy.Cyclic voltammetry,galvanostatic charge-discharge method and electrochemical impedance method were further employed to investigate the electrochemical performance.Mesoporous SiO₂ was firstly used as template to prepare the two-dimensional mesoporous carbon sheet-like framework?MCSF?.The results suggest that the MCSF possesses a high surface area of 582 m2·g-1.The electrode achieves a high specific capacitance of 264 F·g-1 at a scan rate of 5 mV·s-1.When the scan rate is increased to 1000 mV·s-1,74%of its initial capacitance can be retained,suggesting an excellent rate capability.Only 9%capacitance loss can be found after 5000 cycles,revealing a good cyclic stability.The assembled symmetric supercapacitor delivers an energy density of 9.6 Wh·kg-1 with an ultrahigh maximum power density of 119.4 kW·kg-1.In order to prepare a material possessing not only high surface area but also excellent rate capability,the CNT-HCS composite was prepared using CNTs/MnO₂ as template and C₂H₂ as carbon precursor by chemical vapor deposition.CNT-HCS possesses a surface area of 500.6 m2·g-1.The electrode exhibits a specific capacitance of 201.5 F·g-1 at 0.5 A·g-1 with an excellent rate capability of 69%retention at 20 A·g-1.Flower-like hierarchical porous carbon?FHPC?material has been prepared using ZnO as template,pitch as carbon precursor and KOH as the active agent under high temperature.The FHPC electrode possesses a high specific capacitance of 294 F·g-1 at 2 mV·s-1 with an excellent rate capability.In addition,the assembled symmetric supercapacitor achieves a high energy density of 15.9 Wh·kg-1.The superior electrochemical performance of FHPC is mainly attributed to its hierarchical porous structure.In order to meet the need of compact and portable energy storage devices,oxygen-containing functionalized graphene has been prepared using Mg?OH?₂ as template.We have also studied the influence of thermal treatment temperature on the electrochemical performance.The results suggest that the material treated at 300??FGN-300?shows the highest capacitance.It possesses an ultrahigh volumetric capacitance of 470 F·cm-3 at 2 mV·s-1.Additionally,the assembled symmetric supercapacitor achieves an energy density of 27.2 Wh·L-1.The outstanding performance of FGN-300 is attributed to its high surface area,low pore volume and stable oxygen-containing functionalities.Therefore,FGN-300 could meet the need of compact and portable energy storage devices in practical applications.Finally,graphene/mesoporous polyaniline?G-mPANI?hybrid was synthesized via in-situ polymerization using graphene/mesoporous SiO₂ as template.It possesses sheet-like and mesoporous structure and shows a high surface specific capacitance of 749 F·g-1 at 0.5 A·g-1 with excellent rate capability and cyclic stability.The inspiring electrochemical performance is attributed to its unique structure.N-doped porous graphene?NPCG?was prepared by carbonizing of graphene/polyaniline at high temperature.The influence of carbonization temperature on the microstructure,surface chemistry and electrochemical performance of NPCG was investigated in detail.The NPCG carbonized at 700??NPCG-700?possesses a high surface area and interconnected porous structure with high nitrogen content.Thus,it displays a high specific capacitance of 305 F·g-1 at 2 mV·s-1 with high volumetric capacitance of 287 F·cm-3.These results suggest that nitrogen-doping is an effective method to improve the capacitance properties of the electrodes.