Study Of Properties Of Supercapacitor Based On Carbon Nano Tube Composited Materials

As a type of carbon material,carbon nano tube(CNT)has been drawing tremendous interest from scientific research and industrial filed,for its desirable electrical conductivity,stability and extraordinary mechanical properties.For supercapacitors,the electrode material of pure CNT has limited capacitive ability,and nitrogen doping,composite with cobalt metal can significantly increase the capacitive performance of it.This dissertation starts with synthesis of Zn O nano wires(NWs)as the templates,for the subsequent preparation of CNT with tunable diameter and controllable thickness of the wall.Characterization of morphology and energy capacity of the CNT is also employed.Nitrogen doping procedure is added to elevate the wettability,electrical conductivity,electrochemical active sites,and therefore the capacitance.Capsulation of cobalt particles inside CNT is synthesized,and the investigation of the capacitive performances is added.The innovation of this dissertation is achieved and addressed as below:1.Catalytic property on the surface of Zn O is utilized to decompose Ethonal as carbon resource,and the resulted carbonaceous is uniformly deposited on the Zn O NWs templates.Parameters,such as deposition duration and temperature are controlled to result in tunable thickness(3-6 nm)of the wall with meso-pore structure.The Zn O NWs templates will be reduced by an evaporation process.As a result,when the thickness is 3 nm,the specific area of the CNT is 1124 m~2/g,and the pores are in the size range of 10-30 nm,from BET test.From the Raman spectroscopy,the intensity ratio of defect peak to graphitic peak(I_D/I_G)is 0.996,indicating low defect and high graphitization of the synthesized CNT.Assembled as electrode,the CNT with 3 nm thickness possesses specific capacitance of 193 F/g,compared to 90 F/g of that of 6nm-thick CNT.The porous structure and 3 nm thickness of the wall is more suitable for electrolyte ions diffusion and double layer capacitance generation.2.The as prepared CNT material is nitrogen doped by floating ammonia gas,and properties of N doped CNT under different conditions are compared.Finally,CNT doped at 700?for 5h possesses the best capacitive performance,with 317 F/g of specific capacitance at 5 A/g,compared with 147 F/g of pure CNT.The 700C-5h sample has great rate capability with 64.6%of the capacitance maintained when the current density increases from 5 to 200 A/g,and superior cyclic stability after 20000cycles of charge-discharge,95%of capacitance is still retained.From the intensity of different element peaks of XPS spectra,6.7at%of doped nitrogen atoms can be extracted.The intensity ratio of I_D/I_G in Raman spectra increases from 0.996 to 1.024after nitrogen doping,suggesting the introduced defects from doping boost the capacitance of CNT.3.Cobalt precursor is attached on the surface of Zn O NWs,followed by the ethanol decomposition and Zn O reduction procedures,and Co@CNT composite will be achieved.The prepared Co@CNT material is fabricated as electrodes for further capacitive performance investigation.According to the cyclic voltammetry curves,highly reversible redox reaction can be indicated from the intense redox peaks,and tremendous pseudo capacitance is introduced.From the galvanostactic charge discharge curves,3750 F/g can be calculated at a current density of 1 A/g,almost 10times higher than that of pure CNT materials.As the current density increases to 200A/g,the specific capacitance is still as high as 1750 F/g,and after 1500 times of charge-discharge cycling at 15 A/g,87.5%of the capacitance retention can be obtained.