Sythesis And Supercapacitor Properties Of Graphene/Nickel Hydroxide Composite Electrode

Chemical capacitor, which is also called supercapacitor, is known as a new kind ofenergy storage device. It has the advantages of high power density and fast rechargecapability, broad application prospects, environment frendly, etc. According to the chargestorage mechanism, supercapacitor can be divided into two kinds: electical double layercapacitors and pesudocapacitors. The electrode materials of the supercapacitors usually arecarbon materials, conductive polymers, metals oxides, and their composite materials. As anexcellent representative of carbon material, graphene is a one atom thick and twodimensional material with sp2bound. Graphene can provide very high specific surface area,and superior conductivity; it is widely utilized as electrode materials for EDLCs with goodcycle stability. Nickel oxide and hydroxide have low prices and good pesudocapacitorperformance, but poor conductivity. Therefore graphene and nickel oxide compositematerial are expected to produce a composite electrode with good capacitive performanceand high conductivity.In this paper, graphene were produced by an improved Hummer method. Expandedgraphite was used as raw material to produce graphene oxide; graphene oxide was treatedby ultrasound to form one or several layers of graphene oxide sheets with many oxygencontaining groups. Nickel hydroxide was prepared by one step hydrothermal method.Nickel hydroxide materials with different morphologies and properties were produced bychanging the reaction temperature, reaction time, and reactant ratio. The optimum processconditions of hydrothermal reaction are as follows: the molar ratio of NaOH:NiCl2is1:1,the reaction is carried out at140℃for24hours; the specific capacitance of the electrode isup to670Fg-1at the scan rate of2mv/s. The composite materials were prepared by mixingnickel hydroxide and graphene oxide using ultrasonic; sodium bisulfate was used to reducegraphene oxide to graphene. Self-assembly capture happened during the reduction processand the composite of nickel hydroxide and graphene was produced. The effects of the ratioof graphene and nickel hydroxide on the structure and performance were studied. Theresults of electrochemical tests indicated that the specific capacitance of nickelhydroxide/composite was higher than that of nickel hydroxide or graphene; the specificcapacitances of the composite, nickel hydroxide, and graphene were264,120and32Fg-1respectively at the scan rate of4A/g; the specific capacitances of the composite is as high as921Fg-1at the scan rate of4A/g.