Preparation And Electrochemical Properties Of Cobalt-based Bimetallic Compounds

With the rapid consumption of fossil energy and the proliferation of portable electronic devices,more and more research has conducted on new energy storage technologies and energy storage devices.Supercapacitors attracted much attention due to their advantages of fast charge and discharge speed,high power density and long cycle life.And they are widely used in energy storage devices.Due to the special energy storage method,electrode material is a key factor affecting the performance of supercapacitors.In recent years,cobalt-based transition metal compounds attracted more interest of researchers due to their high ideal capacitance and abundant resources.Therefore,in order to prepare electrode materials with high specific capacitance and long cycle life,the following work was carried out:(1)A nickel-cobalt precursor was prepared on a foamed nickel substrate by a one-step hydrothermal method,and then calcined in a muffle furnace to obtain a NiCo2O4 electrode material.NiCo2O4 composites with different morphologies were prepared by controlling the ratio of H2O to methanol in hydrothermal.The effects of different structures on the electrochemical properties of NiCo2O4 electrode materials can be further understood by SEM.TEM,XRD characterization and electrochemical system testing.The NiCo2O4 sample prepared by the all-methanol solvent has a large specific surface area due to its three-dimensional network sheet structure,and the flaky structure can facilitate ion diffusion/electron transport,and obtains good electrochemical performance at a current of 2 mA/cm2.The density has a capacitance of 1.75 F/cm2 and can maintain an initial capacitance of 62%after 8000 cycles of cycling.(2)The needle-shaped nickel-cobalt precursor was prepared by hydrothermal method on nickel foam,and then anion exchange was carried out by microwave-assisted hydrothermal treatment to obtain hollow interdependent NiCo2S4 nanotubes.Through structural characterization and electrochemical testing,it is found that the unique nanotube structure can provide abundant redox reaction sites,provide sufficient channels for ion transport,and form a triangular structure to consolidate the cycle capacity and improve the electrochemical performance of NiCo2S4 electrode.The hollow structure facilitates the diffusion of ions and the transmission of electrons.The triangular system facilitates the improvement of stability,and generally improves the electrochemical performance of the electrode material,and has a high specific capacitance of 8.6 F/cm2 at 10 mA/cm2,and is special.The triangular structure retains full initial capacitance performance after 48,000 cycles,showing excellent cycle stability.(3)The three-dimensional networked nickel-cobalt precursor grown on the foamed nickel was converted into an ultra-thin porous network-like Ni2S2/NiCo2S4 composite electrode by a simple microwave-assisted vulcanization process.Through the analysis of the morphology of the sample and the electrochemical performance test,the results show that the presence of ultra-thin Ni3S2 nanosheets increases the specific surface area of the active material,and the synergy between Ni3S2 and NiCo2S4 ensures a rich redox reaction and high conductivity.It also brings a highly porous but strong structure,which comprehensively improves the electrochemical performance of the Ni3S2/NiCo2S4 composite electrode.The Ni3S2/NiCo2S4 composite electrode obtained by reacting at 150? for 15 min exhibited ultra-high specific capacitance(3299 F/g,13.3 A/g)and remarkable rate performance(maintaining 77.7%capacity at 20 A/g current density)Excellent cycle performance(61%retention after 8000 cycles at a current density of 50 mA/cm2).