Preparation And Supercapacitive Performance Of Transition-metal Oxide And Its Composites

Supercapacitors are a new type of energy storage devices, which combine theadvantages of both conventional capacitors that can deliver high power density withina very small period and conventional rechargeable batteries that have high energydensity. Supercapacitors have a wide range of applications and have already becomeone of the research interests relative to new chemical energy sources. Electrodes areessential components of supercapacitors, and furthermore, electrode is composed ofthe electrode materials. Therefore, the main researches about supercapacitors focus onthe design and synthesis of electrode materials. The research and preparation ofelectrode materials with good electrochemical performances are very important fordeveloping supercapacitors. This dissertation is associated with the preparations andthe capacitive performances of electrode materials.In the present work, we have simply reviewed the type, application and recentdevelopment of supercapacitors and its electrode materials. We have successfullysynthesized different electrode materials for supercapacitors such as cobalt-bismuthoxidecomposite?NiMoO4·xH2O nanoflowers?NiWO4nanosheets by using variousmethods. The composition, morphology, and microstructure of the as-obtainedsamples were systematically characterized by X-ray diffraction(XRD), FT-IR,thermogravimetric(TG) analysis, field emission scanning electron microscopy(FE-SEM) and transmission electron microscopy (TEM). Moreover, theirelectrochemical properties were investigated using cyclic voltammetry andgalvanostatic charge/discharge techniques. The main contents are as follows:1.A cobalt-bismuth oxidecomposite was firstly synthesized by thermally treatingthe cobalt-bismuth hydroxide mixture precursor, which was obtained throughsimultaneous solvothermal hydrolyzation of cobalt and bismuth salt in N,N-dimethylformamide (DMF) at180°C. After analysis, the optical ratio of the oxide compositeis Bi1.6Co0.2O2.6. Electrochemical measurements showed that the oxide compositeachieved a specific capacitance of838F g-1within the potential window of1.6V at aspecific current of1A g-1. Therefore, the cobalt-bismuth oxidecomposite displayedthe exciting commercial potential aselectrode materials for supercapacitors.2.The NiMoO4·xH2O nanoflowers with high performance were synthesized through mild reflux process following thermal treatments.The results showed that theprimitive structure of the sample was nanorods, which were transformed intonanoflowers by self-assembling. During the heat treatment process, the water contentof NiMoO4·xH2O reduced as the heat treatment temperature increased, but subsequentheat treatment did not change the crystal structureof the initial product.Theexperimental results indicated that the NiMoO4·xH2O obtained at250°C achieved thespecific capacitance of798F g-1at a specific current of1A g-1in the three-electrodesystem. Meanwhile, at the current density of7A g-1, there was71.8%retention in thecapacitance relative to1A g-1. In addition, the electrode material had excellent cyclestability that the capacitance retention rate was80.1%after2000cycles.3.A electrode material made of NiWO4nanosheets were successfully synthesizedby a mild reflux method following thermal treatments. The composite achieved thespecific capacitance of502F g-1at a specific current of1A g-1. Meanwhile, at thecurrent density of10A g-1, there was68.9%retention in the capacitance relative to1A g-1. In addition, good capacitance retention ration of81%was achieved by thecomposite electrode after4000charge-discharge cycles. The resultant compositesdisplayed the exciting commercial potential for high performance, environmentallyfriendly and low-cost electrical energy storage devices.