Controllable Preparation And Performance Study Of Nitrogen-doped Hollow Mesoporous Carbon Spheres

Supercapacitors which are considered to be a promising energy storage equipment have great market potentials because of higher power energy,longer cycle stability and faster charging and discharging ability.Electrode material is one of the important factors to decide the supercapacitor performance.Ordered mesoporous carbon materials are of current great interest and high degree of attention for scientific researcher on account of their unique features,such as ordered mesostructure,high specific surface area,uniform and tunable pore size,good conductivity and stability.To further enhance their capacitance,it is necessary to provide some functional groups to devoted to modifying the surface and frameworks of carbon materials.In order to prepare the novel porous carbon materials for supercapacitors,we explored a new and simple process to prepare the nitrogen-doped hollow mesoporous carbon spheres and investigated the electrochemical performance in alkaline electrolyte and neutral electrolyte,respectively.In this research,the nitrogen-doped hollow mesoporous carbon spheres were produced based on the use of the starch as carbon precursor and ammonium as nitrogen source by means of these pretreatments using potassium carbonate/potassium bicarbonate solution and calcium chloride solution,the influence factors in the synthesis of hollow carbon microspheres were studied,mainly including the carbonizing temperatures and the concentrations of calcium chloride solution.The microstructure,pore structure and surface functional groups of the carbon materials were characterized by Scanning Eletron Microscope(SEM),Transmission Electron Microscope(TEM),X-ray Diffraction(XRD),X-ray Photoelectron Spectroscopy(XPS)and N2 adsorption/desorption isotherms(BET).The electrochemical performances were measured by cyclic voltammetry,constant current charge and discharge and circulation performance test.The effects of structure properties to thesupercapacitor performances were analysed by combining the electrochemical testing results and the microstructure and surface functional groups of the carbon materials.The results showed that the nitrogen-doped hollow mesoporous carbon spheres can be prepared with a good dispersion and a controllable particle size distribution by one step carbonization and nitrating method.The surface area was 750.6 m2 g-1,the specific capacitance was 240 F g-1 when the scan rate was 5 mv s-1 in 6 M potassium hydroxide solution,when 300 mV s-1 was 163 F g-1,the capacity retention ratio was 67.9%;nevertheless,the specific capacitance was 155 F g-1 when the scan rate was 5 mv s-1 in 1 M neutral sodium sulfate aqueous electrolyte,when 200 mV s-1 was 69.4 F g-1,the capacity retention ratio was 45%,the operation potential window was broaded to 2.0 V,possessing higher energy density.The potassium hydroxide solution is a kind of corrosive liquid,especially at high concentration,this limits its application in commercial supercapacitors.The results showed that this material owned higher specific capacitance and larger energy density in 1 M neutral sodium sulfate aqueous electrolyte,moreover,neutral electrolyte costed lower and was friendly to the environment.