| The Carbon nanosheet（CNS） is a new kind of carbon nanomaterials with uniquetwo-dimensional structure. The Graphene is typical material of it, which has attracted moreattentions because of its high specific surface and excellent electrochemistry properties in thearea of electrochemistry energy storage and catalysis. We use three methods to prepare CNS,that is nature graphite milling method, graphite oxide reduction method and template method.And formulate the material appearance by using scanning electron microscope（SEM）, X raydiffraction（XRD） and thermogravimetric analysis （TGA）. And research the internal relationbetween the microscopic structure of GNS and electrochemistry properties by the way ofelectrochemistry analysis, such as cyclic voltammetry, Constant current charging-dischargingand alternatingcurrent impedance techniques.We intermingle raw material with spherical carbon black（CB） and carbon nanotube（CNT）to improve the quality of the graphite nanoplateles for it is easy for them to stack andagglomerate. The specific capacitance of composite GNS/CB/CNT reaches107.8F·g-1whileGNS, GNS/CB and GNS/CNT reach82.6F·g-1,87.7F·g-1and77.6F·g-1. when the voltagesweep speed is2mV·s-1through electrochemistry performance test. The values of those fourkinds of material are45%,41%,49%,34%when the speed is100mV·s-1. We can find thatthe electrochemical performance of GNS/CB/CNT is the best one from the test result, that isbecause it is easy for the spherical carbon black to enter the edge of the graphite sheets andmill it into the graphite nanosheet under the force of mechanical milling, while the carbonblack distributes in the graphite nanosheet equably to prevent agglomeration. In this way, thespecific surface area is increased and carbon nanotube connects adjacent graphite nanosheetwith its tube to enlarge the conductive network and improve the electrochemical performance.The composite of GNS/CB/CNT is a kind of ideal electrode material through electrochemicalanalysis of these four samples.We use improved Hummers method to make graphite oxide, which firstly get oxydicgraphene solution by ultrasonic dispersion in water and then is reduced to graphene byhydrazine hydrate. The specific capacitance of the graphene electrodes is124.9F·g-1while themilled graphite nanosheet just reaches82.6F·g-1when the voltage sweep speed is2mV·s-1,the specific capacitance of the reduced graphene electrodes is84.6F·g-1when the speed is100 mV·s-1and its specific capacitance conservation rate is68%. We can get the result that theelectrochemical performance of the reduced grapheme is better than the milled graphitenanosheet, this is because the milled one is so thick and big that decrease its specific surface.However, as for the graphite oxide, the oxygen-containing functional groups introducedduring the preparation can prevent graphite oxide to agglomerate, so it will be dispersed intopieces by ultrasonic and be reduced in alkaline condition, which can prevent the grapheneoxide to stack and agglomerate during reduction process. In the result, the graphite made bythis method is thinner and smaller than that by milling method, it can increase the specificsurface area efficiently and make electrolyte ions transport and transfer fast. So the chemicalproperties of graphene is much better.Carbon nanosheet with prismatical and porous shape is prepared through the method oftemplate by using the bitumen as the carbon source, porous MgO as the template, whosespecific surface reaches up to883m2/g. The specific capacity of electrode made of it is289.2F·g-1when the scanning rate is2mV·s-1and up to180.2F·g-1when1000mV·s-1. Its specificcapacity conservation rate reaches up to62.3%. The reason for that is the appearance of thegraphene prepared from the template of porous MgO is columnar and porous, which ownsinterconnected open pass surface. The area between the layer of graphene distributes graphenecolumn that can increase the distance of layer and each graphene flake distributes alveolatemesoporous with same size that can enlarge the specific surface area. All of these makeelectrolyte ions transport and spread not only in the hole of Carbon nano-surface but also inthree-dimensional space through porous carbon column, which can improve electrochemicalperformance of the active material greatly. This electrochemical performance is connectedwith its microstructure, the microstructure of porous carbon nanosheet prepared from thetemplate of flake Mg（OH）2nanosheet is stacking together by layers, but there have clearancebetween each layer, so the electrolyte ions transport and spread between the layers. And theporous carbon nanosheet prepared from the template of MgO nanoparticle have bowl-shapedhole distributing evenly on the sheet, however, the sheet is too thick for the electrolyte ions tospread, so they mainly spread through the hole of the sheet, and the spreading speed in asingle sheet is slower than the speed between sheets. So the electrochemical performance ofporous carbon nanosheet prepared from the template of flake Mg（OH）2nanosheet is betterthan the one from MgO nanoparticle. All in all, the3D cylindrical porous carbon nanosheet prepared from the template of porous MgO is a kind of ideal electrode material. |
PDF Full Text Request