Preparation And Electro-chemical Properties Of Nano Nickel Oxides, Cobalt Oxides And Nickel-based Graphene Composites

Electrochemical supercapacitors(ESs), also called supercapacitor, are regarded as promising candidates for energy storage due to short charging time, long cycle life,and high power density and so on. Making the electrodes materials with enhanced electrochemical properties may be considered as a breakthrough in the field of energy technology. Nano metal oxides possess ideal pseudocapacitance properties and also can achieve an enchanced electrochemical performance when combining with carbon-based materials. Hence, we, herein, prepared nano NiO, Co3O4 and Ni-based graphene electrode materials and application in supercapacitor.A simple and efficient method has been designed and developed to synthesize NiO nanostructures without using of any templates and surfactants. By adjusting the volume ratio of water to ethanol, the NiO microstructure can be facilely controlled,and different nanostructures such as sheets-structure, cluster-structure,microflowers-structure and sphere-structure are obtained. The electrochemical properties are examined by cyclic voltammetry, electrochemical impedance spectroscopy and life-cycle tests. The cluster–like NiO nanoparticles show the highest specific capacity of 470 F/g at 5 m V/s in the range of 0.0–0.6 V(vs.Ag/AgCl) and have a good life-cycle performance with nearly no decrease after 500 cycles at 50 mV/s.The self-assembled Co3O4 nanorods are obtained by a facile calcinations of the Co-composites, which is synthesized with the precursors of CoCl2, 1,3,5-Benzenetri carboxylic acid(H3BTC) and phenanthroline(PHEN). The Co-composites nonorods are about 1 um long and 50 nm wide and are composed of nanoparticles in 20-40 nm.After calcinations, the Co3O4 nanorods with numerous mesopores possess a surface area of 23 m2/g due to the release of the organic molecules. The electrochemical properties are examined by cyclic voltammetry, electrochemical impedance spectroscopy and cyclic charge-discharge tests. The results show that the rod-like Co3O4 nanoparticles have the highest specific capacity of 262 F/g at 5 mV/s in the range of 0.2–0.7 V(vs. Ag/AgCl) and have a good cycle life with nearly no decreaseafter 500 cycles at 50 mV/s. The asymmetrical Co3O4//AC button cell is also tested by two-electrode system with a large potential testing window of 1.5 V and the biggest specific capacity achieves to 194 F/g. The highest energy density diasplay a high value of 60.6 Wh/kg at the discharge current of 0.1 A/g.Ni-based/graphene as electrode materials for supercapacitor are prepared by a simple hydrothermal synthesis method using the GO( GO is prepared by a solvothermal method at 70 °C, using natural graphite treated with potassium permanganate and concentrated sulfuric acid) as the precursor. The effect of the graphene support, Ni loading, the testing potential window and the Ni species of the Ni-based/graphene for supercapacitor are investigated in details. As a result, nickel hydroxide materials could be a kind of efficient active electrode under the assistance of graphene. The 15%-Ni(OH)2/graphene has the biggest specific capacity of 2077F/g at 5 mV/s in the potential window ranging from 0.0–0.7 V(vs. Ag/AgCl) and has a stable cycle life.