Preparation And Electrochemical Properties Of Fe/Co-Based Metal Oxides

Due to the diminishing supply of fossil fuels with the rapid development of energy electric vehicles and portable electronic devices,various efficient green energy storage technologies have been explored.Supercapacitors have attracted much attention due to their high energy density,long cycle life,fast charging-discharging,and environmental friendliness.Among the reported electrode materials for supercapacitors,Fe/Co-based metal oxides have received much attention because of their high theoretical specific capacitances.However,Fe/Co-based metal oxides have a fast drop in capacitance due to their relatively low electrical conductivity and tend to detach from the current collector during the electrochemical reaction.The above problems can be improved by compounding iron-group oxides with graphene or producing the active material directly on the current collector.In this paper,Fe3O4/RGO,Co3O4/RGO composites and CoO in-situ grown on foamed nickel were prepared by different methods.The morphology and structure of these samples were performed by TEM,FE-SEM,XRD and XPS techniques.Moreover,the electrochemical performance was tested by galvanostatic charge-discharge(GCD),cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS).The main contents are as follows.(1)Fe3O4/RGO composites were prepared by a co-precipitation method at 80?.A unique dual-scale coupling structure was formed by Fe3O4 nanoparticles with size of 8-10 nm and graphene.Fe3O4 nanoclusters,which were formed by dozens of Fe3O4 nanoparticles,were attached to the surface of the graphene.A certain gap is formed because these Fe3O4 nanoparticels were close to each other,which woule help improve its electrochemical performance.Compared with Fe3O4 nanoparticles,the Fe3O4/RGO composites exhibited better electrochemical performance.The specific capacitance of the Fe3O4/RGO composites electrode reached to 553 F·g-1 at the scan rate of 5 mV·s-1.Furthermore,the specific capacitance of Fe3O4/RGO composites electrode only attenuated approximately 5.87%after 1000 charge-discharge cycles.(2)The porous Co3O4 nanosheets were successfully synthesized via hydrothermal-heat treatment process.GO was dissolved in methanol as reaction solvent,and the unique structure of graphene-coated porous Co3O4 nanosheets was prepared under the same conditions with the content of graphene was about 24.17%.In electrochemical tests,the Co3O4/RGO composites exhibited a large specific capacitance of 980 F·g-1 at a current density of 0.5 A·g-1,and the specific capacitance retained 91.16%after 2000 cycles at a current density of 5A·g-1.(3)CoO precursors with three-dimensional ordered nano-array structure were synthesized directly on the Ni foam substrate by a simple hydrothermal method.By increasing the reaction temperature,the thickness of nanosheets and nanosheet arrays of CoO precursors also increases.After thermal treatment at 350 ? in vacuum,the CoO precursor is converted to CoO with quantities of nanopores.Investigations on the supercapacitor performance of CoO/Ni-foams indicated that CoO precursors synthesized at 120 ? exhibited superior specific capacitance and capacity retention after thermal treatment.