Synthesis Of Nickel Hydroxide/Carbon Composite As Supercapacitor Materials

Graphene oxide （GO） and Carbon nanotubes （CNTs） are two types of the mostpotential supercapacitor materials with good electrical, mechanical and optical properties.As an important derivative of graphene, GO is also a typical two-dimensional layerednanomaterial with plenty of functional groups such as-OH,-COOH and-C=O on itssurface, which can significant lead to improving the hydrophilicity, providing richembedded chemical properities, preventing the stack layers effectively. Carbon nanotubes isanother excellent carbon material, which has a unique structure of hollow structure,nanosize and good conductivity, provides the favorable condition to application insurpercapacitors. Compared with another carbon materials, the opened CNTs can be used ofalmost all the effective surface area because of the interconnected holes, and make chargescontinue to accumulate. The crystal structure and morphology of the two obtained sampleswere characterized by SEM, TEM, XRD and IR, while the investigations of theelectrochemical performances were carried out through cyclic voltammetry （CV）,electrochemical impedance spectrum （EIS） and galvanostatic charge/discharge text.We prepared GO using an improved Hummers method followed with sonication, andobtained Ni（OH）₂/GO composite by hydrothermal method which leaded Ni2+swim onto thesheets of GO, and grow on it in the form of Ni（OH）₂. It shows the surfaces of grapheneoxide in the composite of Ni（OH）₂/GO are rough and the layers are multi-stacked, and theinitial discharge capacity is120F·g^-1. The typical XRD pattern of Ni（OH）₂/GO exhibits theobvious oxygen-containing functional groups of GO and a high purity of β-Ni（OH）₂. Thecomposite electrode material shows pseudocapacitance, and stable discharge capacityreaches816F·g^-1, which is much higher than the ordinary graphite. These results suggestethe composite materials have high-performance energy applications.We prepared Ni（OH）₂/CNT composite using hydrothermal method which made nickelhydroxide grow on the wall of CNTs. The tube diameter of CNTs in the as-synthesizedNi（OH）₂/CNT composite is larger than the pure CNTs, and the electrochemical performanceis significant improved. The highest specific capacitance of the optimal operating forpreparing the composite is924.4F·g^-1, which is much higher than the pure CNTs with capacitance of16F·g^-1.We prepared asymmetric supercapacitors using Ni（OH）₂/GO or Ni（OH）₂/CNT aspositive electrode and active carbon as negative and the electrochemical performance wereinvestigated. Ni（OH）₂-CNT//AC achieved very high power and energy densities of2484.5W kg^-1and25.5Wh kg^-1and Ni（OH）₂-GO//AC got long-term cycling behavior.