Study On Preparation Of Carbon/Carbon Composite Materials And Their Electrochemical Properties

The aim of this research is to explore the synthesis of different morphologies carbon materials by simple methods.The major contents can be summarized as follows:(1)In this paper,Tungsten carbide(WC) nanocrystal was prepared via an anhydrous ethanol solvothermal method,Mg was used as a reductant,WO₃ and anhydrous ethanol were used as the raw materials.The influence of the reaction time and synthesis temperature on the WC formation and probable formation mechanism were also discussed.The crystal structure,the morphology,the composition and electrochemical properties of the WC were characterized by X-ray diffraction(XRD), transmission electron microscopy(TEM),energy dispersive spectroscopy(EDS) and electrochemical methods.The XRD spectra indicated that hexagonal WC was successfully prepared when temperature was as low as 500℃.EDS analysis revealed that the content of carbon was more than W and testified the composition of the treated sample was carbon and WC only.TEM results showed that the diameter of WC nanocrystal was ranged from 40 to 70 nm,and WC was dispersed by carbon films.Electrochemical measurements indicated that the hydrogen storage was about 0.7 g mol^-1.The tungsten carbide nanocrystal promoted Pt/C electrocatalyst was very obvious for the oxygen reduction reaction with the onset potential was over 173 mV more positive compared with that of traditional Pt/C electrocatalyst.(2)An in-situ silica template method has been employed to prepare mesoporous carbon(MC) materials.By the method,sulfate/three block copolymer(P123)/ tetraethyl orthosilicate/sucrose were mixed,then,the resultant solution was aged, Precarbonized,carbonized and de-silicified.As-prepared carbon materials have been characterized by transmission electron microscopy,small-angle X-ray diffraction,N₂ adsorption-desorption,Fourier transform infrared spectroscopy and electrochemical techniques.The results reveal that highly ordered mesoporous carbon with high specific surface area(～1628 m² g^-1),narrow pore size distribution,faint graphite microcrystal structure and abundant hydrophilic functional groups was obtained. Electrochemical measurements indicate that HOMC aged in the open vessel exhibits high surface area(1628 m² g^-1) and high specific capacitance(161 F g^-1) at low sweep rate of 5 mV s-1.Although the value is slightly lower,the specific capacitance of HOMC aged in the closed vessel does not decay in the range from 1 to 100 mV s-1, demonstrating its capability of fast ion diffusion within its mesoporous structure.The excellent performance makes HOMCs as potential candidate for electrode materials in EDLCs.(3)The properties of electrode materials play an important role in super capacitors. In order to get perfect electrode materials,mesoporous carbon materials were loaded with oxides(MnO₂,Bi₂O₃ and SnO₂).The morphology,BET specific surface area, pore size and electrochemical properties of oxide/HOMC materials were characterized.Cyclic voltammogram and galvanostatic charge-discharge were performed for the measurements of electrochemical properties of oxide/HOMC materials.The results showed that the oxide/HOMC materials still saved the mesoporous structure of HOMC,the BET specific surface area decreased from 1202 m².g^-1 to 304～827 m².g^-1 while the pore size became much smaller.The specific capacitance increased from 161 F g^-1 to 232 F g^-1 after loading Bi₂O₃,the results showed that oxide produced pseudo-capacitance,which could potentially be the perfect electrode material for supercapacitors.