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Controllabe Synthesis Of Carbon Nano-onions And Carbon Nanotubes And Their Energy Storage Study

Posted on:2014-09-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:C G ZhangFull Text:PDF
GTID:1261330422468096Subject:Materials science
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Carbon nano-onions (CNOs), carbon nanotubes (CNTs) and graphene are thethree allotropes for graphite at nanoscale. They are0-dimensional particle,1-dimensional wire and2-dimensional film structures, respectively. Due to theirexcellent electrical and thermal conductivity, high specific surface area, as well as thegood mechanical properties, they show great application potentialities in the fields ofelectronics device, composites, energy-storage media, biomaterials, and etc. However,at present there still remains a number of problems in the growth and applications ofcarbon nano-materials, including controllable growth of carbon nano-materials,synthesis of novel-structured carbon nano-materials and applications of carbonnano-materials in energy storage field.This study first reports the synthesis of Fe-Ni alloy catalyst from NaBH4reduction method and the use of Fe-Ni alloy catalyst and MgO substrate for growingcarbon nano-onions by CVD method. The influence of catalyst content, types ofsubstrate, growth temperature and growth time on the structure and morphology ofCNOs has been investigated. The influence of annealing temperatures on the growthof hollow CNOs, the growth mechanism of hollow CNOs and the mechanism of itsuse in electrochemical hydrogen storage have been also investigated. Studies haveshown that well-dispersed and uniform-sized CNOs can be obtained at the optimumconditions: catalyst content of10%, use of MgO substrate, growth temperature of850°C and growth period of0.5h. Due to the presence of Ni atoms which have a lowcarbon solubility, the deactivation of Fe-Ni alloy catalyst can be retarded, allowing forthe growth of hollow CNOs. By annealing at1100°C, large amounts of hollow CNOscan be obtained from the Fe-Ni alloy encapsulated CNOs. Hollow CNOs exhibit asuperior electrochemical hydrogen storage performance to the solid CNOs, with acapacity of1.76%. A comparative study of the influence of three types of catalysts: Ni,Fe-Ni alloy and Fe on the structure and morphology of CNOs was also carried out inthis study. The anti-friction properties of the CNOs as lubricants and their magneticstorage properties have also been investigated. Studies have shown that the CNOsgrown by different catalysts are Ni@CNOs, Fe0.64Ni0.36@CNOs and Fe3C@CNOs,respectively. By growing at a catalyst content of5%, a high purity of CNOs have been obtianed without any other carbon structures. As lubricants, the optimum additionamount in the oil of the CNOs is0.1%. A friction coefficient μ of0.026is achievedunder500N from Fe3C@CNOs. The magnetic propery tests show that the Ni@CNOsexhibit paramagnetic behavior, whereas the Fe0.64Ni0.36@CNOs exhibit a Mr/Ms andcoercive Hc of0.22and228.4Oe, respectively, indicating an application potentialityin high-density magnetic storage media and its encapsulating materials.This study first reports the synthesis of large-diameter SWCNT carpet by CVDmethod from monodispersed AlFe2O4nanoparticles with an average diameter of~4nm. The influence of types and concentrations of catakysts, types and coatingamounts of the substrate, growth pressure and water vapor amounts on the height,growth quality and structures of the SWCNT carpet have been investigated. Thecollapsing behavior and critical diameters of the few-walled CNTs have been studiedusing atomic force microscope, transmission electron microscope and moleculardynamics simulations. Studies show that the AlFe2O4nanoparticle has a highercatalyst activity Fe3O4nanoparticle, as the doping of Al atom is able to prevent thecoalescence of catalyst nanoparticles, thus providing a high-quality and tall SWCNTcarpet. The optimum conditions for growing the best quality SWCNT carpet is:pressure of mixing gas of acetylene, hydrogen and water vapor at4.9Torr, sputteredAl as substrate, concentration of AlFe2O4nanoparticles of25nM. The SWCNT carpethas a bottom IG/IDratio of18.5and a height of100μm. Through the experimentcharacterizations and simulation verifications, the critical diameterDe eqxepforSWCNT and DWCNT collapsing are2.6nm and4.0nm, respectively.This study first reports the splitting of MWCNT carpet by K atom intercalationapproach into graphene nano-ribbon carpet. The structural changing, supercapacitorproperties and charge storage mechanism of the split MWCNT carpet have beeninvestigated. Studies show that the split MWCNTs have a composite structureconsisting of outer graphene nanoribbons-inner few-walled CNTs.The split MWCNTcarpet as supercapacitor electrode materials exhibit a specific capacity of106.2F/g,~4times more than that of the original MWCNT capet. The split MWCNT carpet alsoshows higher power and energy densities than that of the original MWCNTs. Powerdensity of103kW/kg was obtained while maintaining an energy density of5.2Wh/kg.The split MWCNT carpets have increased their effective surface area for storing theions. The good conductivity of the inner few-walled CNTs and the vertical CNTarrays both accout for the efficient ions conducting and transportations.
Keywords/Search Tags:Carbon Nano-Onions, Carbon Nanotube Carpet, Large-diameterSingle-Walled Carbon Nanotubes, Graphene Nanoribbons, Chemical VaporDeposition, Collapsed Carbon Nanotubes, Supercapacitor
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