Design And Synthesis Of "Sandwich" Cuco₂O₄/rGo Composites And Their Supercapacitive Behaviors

Supercapacitor is a new type of energy storage devices due to its high powercharacteristics and good cycle life; it is also one of the hotspots in new type ofchemical energy sources. In this thesis, we have simply reviewed the type, applicationand recent development of the electrode materials. The relevant electrode materialsare prepared by using appropriate synthetic methods. Especially, layer by layerself-assembly was used to solve the problem of constructing metallic oxide/reducedgraphene oxide （rGO） composites with ordered structures. Furthermore, theelectrochemical performances of the as-prepared materials were evaluated by cyclicvoltammogram and galvanostatic charge-discharge. The exfoliations about Cu-Colayers double hydroxides without any intercalated organic anionic ion in water werealso explored. The main contents are as follows:1. The Cu-doping cobalt oxide nanoparticles were successfully prepared byheating Cu-Co layered double hydroxides for4h at200℃, which were obtained by achemical co-precipitation method using Co（NO3）2·6H2O and Cu（NO3）2·3H2O as theraw materials and polyethylene glycol6000as the structure-directing agent. Thestructure and morphology of the as-prepared samples were characterized by X-raydiffraction （XRD） and field emission scanning electron microscopy （FESEM）,respectively. The electrochemical performances were investigated by severalelectrochemical techniques such as cyclic voltammetry, galvanostaticcharge-discharge and electrochemical impedance spectroscopy. It was found that themolar ratio of Co²⁺to Cu2+has a significant influence on electrochemical capacitivebehaviors of the resultants. The Cu-doping cobalt oxides with optimal molar ratio upto2.67:0.33(Co²⁺to Cu²⁺) exhibited excellent specific capacitance （492F/g） at acurrent density of1A/g. In addition, the cycling test results showed thatCu0.33Co2.67O4exhibited good cycling performance with no decay in the availablecapacity over2000cycles at a current density of3A/g. 2. Binary composite consisting of CuCo₂O₄nanocrystals and reduced grapheneoxide （rGO） for supercapacitors is synthesized via a self-assembly approachcombined with subsequent annealing. Cu-Co layered double hydroxides （Cu-CoLDHs） and graphite oxide （GO） are exfoliated to form the charged monomolecularlayer nanosheets in formamide and water, respectively. Controlled assembly betweenpositively charged Cu-Co LDHs nanosheets and negatively charged graphene oxideaffords formation of the precursor with ordered structures. After subsequent annealing,Cu-Co LDHs in the precursors are transformed into CuCo₂O₄nanoparticles, whilegraphene oxide are thermally and chemically reduced into rGO, resulting in sandwichstructures in which layers of rGO （or its stacks） and crystallized CuCo₂O₄nanoparticles alternate. Furthermore, the channel architecture formed betweenCuCo2O4nanoparticles and alternating rGO nanosheets provides a fast diffusion pathfor reaction species. The resultant CuCo₂O₄/rGO composite exhibits an initial specificcapacitance of291F/g within a potential range from0.05to0.55V at a specificcurrent of1A/g. Surprisingly, the specific capacitance of the composite, becominghigher as the cycling numbers increased, reaches389F/g at1200cycles and thenremains no decay until5600cycles.3. Cu-Co layers double hydroxides without any intercalated organic anionic ionwere synthesized by conventional precipitation using NaOH （pH～9）. Faint yellowaqueous colloidal suspension of Cu-Co hydroxides nanosheets was obtained whenwashing the precipitate untill the pH was equal to7by followed the ultrasoundexfoliation. Zeta potential, XRD, Fourier transform infrared spectrometer （FT-IR）,transmission electron microscopy （TEM） and Atomic force microscopy （AFM） wereused to characterize physical property of Cu-Co nanosheets.