Preparation Of Graphene And Graphene-based Nanocomposites And Their Electrochemical Supercapacitive Behaviors

Graphene, a novel carbon material with two-dimensional nanostructures, has receivedintensive attention in recent years for its fascinating thermal conductivity, superior mechanicalproperties and extraordinary electron transport properties. Owing to its excellent chemicalstability, large specific surface area and a wide electrochemical window, grapheme hasbecome a new star of super capacitor. This paper mainly studies the preparation andapplications in supercapacitor of graphene and graphene-based/metal oxide composites. Thesupercapacitor is the device utilizing the electrochemical double layer or redox reactionoccurs in the electrode/solution interface to store energy. As the newest energy storage device,the supercapacitor not only has the advantages of conventional capacitor （high power density）and battery （high energy density）, but also exhibits a rapid charge and discharge, good cyclestability and long cycle life. Recently, the researches of supercapacitor main focus on thesynthesis of materials with high electrochemical activity.In this article, according to use ascorbic acid as a reducing agent we successfullyprepared high quality graphenes and investigated their performance as supercapacitorelectrode. Through a series of characterization methods such as XRD, X-ray photoelectronspectroscopy, Raman, TGA, the advantages and disadvantages of the two methods has beencompared. It is found microwave-assisted method could rapid preparation of high-qualitygraphene. Experimental results show that the graphenes prepared by the two methods aremore ideal for an electric double layer electrode with good conductivity and cycle stability.The graphenes prepared by microwave assisted and oil bath delivers a capacity of75F/g,52F/g after500cycles at a current density of20mA/cm2, and the capacity retention is93.6%,85.7%, respectively. The results suggested that the graphene prepared by microwave-assistedhas higher specific capacitance and cycle stability.In order to improve the specific capacity of graphene, we using metal nanoparticles tomodify the surface of graphene. In this paper, a simple one-step solvothermal method wasproposed to prepare composites of Fe₃O₄and graphene for the supercapacitor. The results ofthe galvanostatic charge/discharge are as follows: after500cycles, the specific capacitancevalues of iron oxide and composite are145F/g,274F/g at a current density of50mA/cm2, respectively. It is suggested that the specific capacitance of the composite is either higher thanFe₃O₄or graphene, proving the doping of graphene can improve the electrochemicalperformance of composite.Using ascorbic acid as reducing agent, α-nickel hydroxides successfully grown ongraphene nanosheets surface and the impact of the proportion of α-nickel hydroxide on theelectrochemical properties was also investigated. The results showed that the composite hashigh electrochemical activity and specific capacitance. With the increasing proportion ofα-nickel hydroxide in the composite, the specific capacity of composite increases. All the testresults show that when graphite oxide: α-nickel hydroxide（m:m）=1:3, the compositepossesses a specific capacitance of738.4F/g at the current density of20mA/cm2, and displaysan excellent specific capacitance retention of94.6%after500continuous charge/dischargecycles, the highest specific capacitance and excellent cycle stability, so it is the best ratio.