Preparation Of Reduced Graphene Oxide And Its Electrochemical Performances

Graphene has shown great potential applications in many fields,such as electronic devices,energy storage,catalysis and composite materials because of its unique structure and excellent properties.However,large-scale production of high-quality graphene with low cost is an important prerequisite for its wide application.In the existing preparation methods,chemical reduction of graphene oxide is widely regarded as one of the most promising routes for large-scale production of graphene due to its extremely high yield,suitability for large-scale production,relatively low cost and easily assembly.Sodium borohydride?Na BH₄?is a mild and inexpensive strong reductant,and widely studied in the reduction of graphene oxide?GO?by many researchers.However,it is reported that the reduction process typically takes place in a hot solution for a long time,and many oxygen-containing functional group residues can be found on the obtained reduced graphene oxide?r GO?since Na BH₄ hardly reduces carboxylic acids.In this dissertation,we try to introduce sodium molybdate?Na₂Mo O₄?to improve the reducing ability of Na BH4.In addition,hydrochloric acid?HCl?and Na₂Mo O₄ was attempted to assistNa BH4 to rapidly reduce GO at room temperature.This novel,energy-saving,high-efficient and low-cost method shows promising application in large-scale production of graphene materials.The main research contents and results are as follows:?1?GO was reduced using Na BH4,and the effect of Na₂Mo O₄ on reducing ability of Na BH4 was studied.The as prepared r GO was characterized by X-ray diffraction?XRD?,ultraviolet-visible absorption spectroscopy?UV-vis?,Raman spectroscopy,Fourier transform infrared spectroscopy?FTIR?and X-ray photoelectron spectroscopy?XPS?.The results show that there are GO residues in r GO prepared by Na BH4 alone with a carbon-to-oxygen atomic ratio?C/O?of 4.58.However,r GO reduced by Na BH4 and Na₂Mo O₄ exhibits fewer oxygen-containing functional groups and more conjugate structure with a C/O of 5.34,which indicates that Na₂Mo O₄ can effectively improve the reducing ability of Na BH4.In addition,cyclic voltammetry?CV?and galvanostatic charge-discharge?GCD?characterization reveal that the r GO electrode exhibits good electrochemical performance with specific capacitance of 134.3F/g at a current density of 1 A/g.?2?Using HCl and Na₂Mo O₄ to assist the reduction of GO by Na BH₄ at room temperature,the reduction only takes 2 min.The morphology,chemical structure,atomic composition and electrochemical performance of r GO prepared by this method were characterized,and the reduction mechanism was explored.The results show that r GO exhibits a wrinkled,folded and rough appearance.The thickness of the r GO sheet is about 1.53 nm.Most of the oxygen-containing functional groups were removed,and the conjugated structure was restored.Compared with r GO prepared by Na₂Mo O₄ and Na BH₄ at high-temperature,r GO prepared at room temperature shows higher C/O?6.51?and less carboxyl and carbonyl,indicating that the reducing ability of Na₂Mo O₄,HCl and Na BH₄ to carboxyl group and carbonyl group is better than that of Na₂Mo O₄ and Na BH₄ at high temperature.Moreover,the r GO electrode also exhibits good electrochemical performance with specific capacitance of 139.8 F/g at a current density of 1 A/g.The probable mechanism for the reduction of GO by sodium borohydride,sodium molybdate and hydrochloric acid is as:HCl can react with Na BH₄ and generate borane in suit,and molybdate can coordinate with oxygen atoms of oxygen-containing groups on GO to increase the positive charge on carbon atom,thus the reduction of GO can rapidly complete at room temperature.