Graphene Based On Super Capacitor - Hydroxide Composite Material Preparation, Properties And Mechanism Research

Transition metal hydroxide material, due to the unique structure and excellent electrochemical performance, makes itself to be good super capacitor electrode material instead of noble metal oxide. Graphene has become a concern of carbon family new materials in recent years because of its excellent performance. The combination of transition metal hydroxide and graphene may produce synergistic effects, making full use of transition metal hydroxide’s higher electrochemical performance and graphene’s good cyclical performance. There are abundant active oxygen groups on the surface of graphene oxide owing to the depth oxidation of graphite, which will be helpful for composite reaction.In this paper, a composite of graphene and cobalt hydroxide was firstly prepared via a solvothermal method using ethylene glycol as the solvent. The effects of precipitation agent, solvent; load ratio and reaction way on the morphology and texture of as-obtained products were investigated. The results show that, the composite of Co(OH)2/G, which was fabricated at180℃, using ethylene glycol as solvent, ammonia water as precipitating agent, and with graphite oxide and cobalt hydroxide mass ratio of1:10, has a uniform particle size and good dispersivity. On the basis of above, the possible mechanism of the formation of Co(OH)2/G was discussed.Based on the above experience results, Ni(OH)2/G was also successfully fabricated by in situ oxidation method. The effects of different reaction time and mass ratios on the microstructure of products were studied. The results indicate that Ni(OH)2/G composite, prepared in N-methyl pyrrolidone with nickel nitrate as nickel source at180℃for12h, exhibits good crystallinity and dispersiblity. In addition, the possible mechanism of the formation of Ni(OH)2/G was discussed.Furthermore, the electrochemical properties of the obtained composites were studied by cyclic voltammetry (CV) and galvanostatic charge-discharge measurements. The results show that, the Co(OH)2/G (obtained at180℃, using ethylene glycol as solvent, ammonia water as precipitating agent and with graphite oxide and cobalt hydroxide mass ratio of1:10) and Ni(OH)2/G (obtained at180℃for12h) gained the high specific capacitance of518F/g and688F/g respectively. The as-obtained composites have a higher specific-capacitance as well as electrochemical stabilities than their individual components (Co(OH)2, Ni(OH)2, and GO), indicating the obvious synergistic effects.