Electrochemical Preparation Of Graphene And Short Carbon Nanotubes And Research Of Their Electrochemical Properties

Electrochemical exfoliation method has attracted attention due to its easy, fast, and environmentally friendly nature to produce high-quality graphene. Compared to oxidation-reduction method, it has an imponderable advantages in the preparation of graphene with low content oxygen-containing groups. But the obtained product has a low concent of single or few layers graphene, due to the graphite particle premature falling from the electrode during the exfoliation process. In view of this, this paper plans to introduce spatial confinement method into the process of electrochemical exfoliation to prevent the graphite particle premature falling from the electrode, and obtain high quality graphene. In addition, a considerable amount of oxygen-containing functional groups cannot be avoided due to the overoxidation of graphite in acid electrolyte, which would affect its electrical conductivity. So, the graphene has been electrochemical prepared in alkaline solution. The obtained graphene was further fabricated into transparent conductive films, and the conductivity and light transmittance were tested. Then, the graphene was composited with graphite oxide, and the capacitive performance of the composite was tested. On this basis, we adopts the electrochemical method into cutting carbon nanotubes. By scanning electron microscope(SEM),transmission electron microscope(TEM), Fourier transform infrared spectrometer(FTIR) and confocal microscopic laser Raman spectrometer, the truncated carbon nanotubes were characterized. Then the carbon nanotubes and graphite oxide were mixed together, and the capacitor performance was charactered.The main research content is as follows:1.Electrochemical preparation of graphene by spatial confinement methodThe graphite flake was packaged with solid paraffin and kept the bottom exposing to the electrolyte to be exfoliated. The influence of different voltages, electrolyte concentrations on the quality of the preparaed graphene was studied in NaOH electrolyte. The prepared graphene were characterized by SEM, TEM and AFM, and the results showed that the product iwas of porous structure, large area and thin layer. The results of Raman and FTIR illustrated the graphene contained less oxygen containing functional groups.2.Preparation of graphene/graphite oxide composite material and transparent conductive graphene thin films and the electrical properties research.The high oxidation degree graphite oxide(GO)(1:6) solution and the as-prepared graphene was mixed at the ratio of 10:1 and 10:3 respectively by ultrasound. The SEM images showed they did not well composited each other because the prepared graphene is serious agglomeration. The capacitance of the composite is lower than the GO through the constant-current charge and discharge test. On the other hand,Graphene transparent conductive thin films were prepared by self-assembled monolayers and vacuum filtering. The transparent conductive graphene thin film by self-assembly is discontinuous with a high resistance. It is easy to prepare of graphene films with different thickness through suction filter.Considering the hydrophobicity of graphene, the membrane was transferred to a quartz substrate which has been hydrophilic treatment, and was good continuity according to the results of SEM. The resistance of the film after annealing treatment at 500 ? is about 3.7 k?/? and the light transmittance is of 67.2 %.3.Preparation of truncated carbon nanotubes by electrochemical method and the electrochemistry performance researchTruncated carbon nanotubes were prepared by electrochemical method. The carbon nanotube was cut by electrochemical method at the above optimal conditions. SEM, TEM, Raman, FTIR and thermogravimetric analysis were used to characterize the properties of the product and the results indicated that MWCNT was shortened, Meanwhile, the results of Raman and FTIR analysis showed the shortened product had less oxygen functional groups. According to the analysis of SEM and TEM, we can see that the MWCNT can be truncated in this way, but the uniformity of needs to be improved.The graphite oxide was mixed with MWCNT at the mass ratio of 10:1 and 10:2 by ultrasonic treatment. The compounds were characterized by SEM and indicated that the MWCNT was well dispersed in the interlayers of graphite oxide; the capacitance of the compound was also improved. So, graphite oxide(1:6) and the truncated MWCNT were composited in the mass ratio of 10:0.2, 10:0.5 and 10:0.8. SEM images showed that the truncated MWCNT evenly dispersed in the interlayer of graphite oxide. XRD pattern indicates that electrical conductivity of the composites was improved. N2 adsorption and desorption isotherms and pore diameter distribution showed that with the additive amount of truncated MWCNT increased, the number of mesoporous of the composites had been increased, and a number of macropore appeared, This will effectively improve the capacitive performance of composite in high-ratio. But the specific surface area of the composites was significantly decreased when the mass ratio of the compositewas 10:0.8, this is bad for the improvement of capacitance. So the capacitance of composite showed a trend of decrease after the first increase. The capacitance of the composite was highest when the mass ratio of the compound was 10:0.5. The electrode had a high specific capacity of 115.7 F/g at a current density of 80 A/g which was almost twice as the capacitance of GO at the same current density.