Electrochemical Performance Of Ni-based Materials And Their Composites With Graphene

With the rapid development of the global economy, the problem of fast depletion of fossil fuels and environmental pollution becomes increasingly serious. It is very urgent to find efficient, clean and sustainable sources of energy, as well as new technologies associated with energy storage. As a new member of chemical power source family, electrochemical capacitor, also named supercapacitor, combining the advantages of both dielectric capacitors that can deliver high power and rechargeable batteries that can store high energy, have shown large amounts of features, such as long cycle life, good rate capability,excellent temperature characteristics, fast charge,and non-pollution, which could guarantee its extensive application prospect in many fields.According to previous reports, the excellent electrochemical performance of supercapacitor electrode is contributed to the active materials, which should possess highly reversible redox reaction, high specific surface, and good electrical conductivity. As one of the most promising candidates, nickel-based materials,such as nickel oxide/hydroxide and nickel sulfide, have been considered as promising effective alternatives, because of their high theoretical capacitance, good thermal stability, resources-abundance and environmental friendly features. Besides,combining nickel-based active materials with graphene is an effective approach to achieve supercapacitor electrode with high capacitance, rate capability and excellent cycling stability. In this study, we try to prepare nanostructured nickel oxides, nickel sulfide and the composite of nickel sulfide with graphene. Details are shown as follows:?1? The Ni₃S₂ dendritic nanostructure is fabricated by one-step hydrothermal rout with TAA and nickel foam used as sulfide and nickel resource, respectively. The impacts of experimental temperature and time are also studied. The electrochemical performance of the obtained binder-free electrodes is also conducted, and the Ni₃S₂ electrode anchored by dendritic nanostructure prepared under 120? for 6 h shows the best electrochemical properties, which exhibit the specific capacitance of 710 F/g at a current density of 2A/g, as well as no obvious capacitance decay after 2000 cycle charge-discharge tests.?2? Via a facile hydrothermal process, coupled with TAA and nickel foam used as sulfide and nickel resource, respectively, the graphene oxide can be reduced andsimultaneously Ni₃S₂ particles are synthesized, resulting in the composite of Ni₃S₂ and graphene. Compare to the poor Ni₃S₂, the obtained Ni₃S₂/graphene binder-free electrode shows improved specific capacitance?1420 F/g at the current density of 2 A/g? and excellent stability.?3? A novel electrode material of NiMoO₄@CoMoO₄ hierarchical nanospheres constructed by thin nanosheets has been synthesized via a facile one-step hydrothermal strategy. Besides, the effect of Ni/Co molar ratios of raw materials on morphological, structural and electrochemical behaviors is also investigated. The resulting NiMoO₄@CoMoO₄ hierarchical nanospheres with a Ni/Co ratio of 8:2exhibit greatly enhanced specific capacitive of 1601.6 F/g at the current density of 2A/g, as well as good rate capability and excellent cycling stability. Moreover, a symmetric supercapacitor is constructed by using NiMoO₄@CoMoO₄ as positive and negative electrodes, which shows good specific capacitance and cycling life.