Preparation And Superelectric Properties Of Nickel Foam In Situ Grown Metal Oxide/sulfide Materials

Advanced electrodes with high power density are urgently needed for high-performance energy storage devices,such as supercapacitors,to fulfil the requirements of future electrochemical power sources for applications.Transition metal oxides/sulfides with unique physical and chemical properties are currently studied as promising electrode materials.The specific capacitance of transition metal oxides/sulfides are typically multiple times higher than that of carbon-based materials.Furthermore,they have many fascinating properties such as excellent redox reversibility,great electrical conductivity and abundant active reaction sites.However,the applications of these electrodes in energy-consuming devices are hindered by their inferior rate performance and cycling stability.Hence,this paper briefly describes the energy storage mechanism of supercapacitors,the research status of various electrode materials and the application of metal oxides/sulfides electrode materials in supercapacitors.Supercapacitor electrode materials with high specific capacity and good cycling performance were successfully obtained via modification strategies such as morphology control,surface modification and heteroatom doping.The effects of microstructure,phase composition and electronic conductivity on electrochemical performance were summarized.The main research contents and achievements are as follows:(1)A facile hydrothermal-thermal decomposition method was used to grow Co₃O₄ material on the nickel foam.By changing the types of surfactants,Co₃O₄ materials with different morphologies were obtained.Compared with nanorods and honeycomb structures,the 3D flower-like Co₃O₄ material synthesized with sodium lauryl sulfate(SDS)can provide the larger specific surface area and the faster ion transfer rate.Based on the analysis of the structure and element composition,it is found that the flower-like Co₃O₄ electrode prepared at 400°C possesses excellent structural stability,which is conducive to the improvement of cycle life.The results show that the prepared Co₃O₄-400 electrode has a good specific capacitance of 1150F g^-1 at 1 A g^-1.After 5000 cycles,the capacitance of Co₃O₄-400 electrode remained 74%of the initial level.In addition,the Co₃O₄//AC flexible device provides an energy density of 30 W h kg^-1 at a power density of 813 W kg^-1.(2)The highly porous Co₃S₄@Ni₃S₄ heterogeneous nanoflower arrays supported on Ni foam were synthesized by the facile two-step hydrothermal reaction.A special structure was prepared by controlling both anion exchange and Ostwald ripening reactions during the sulfurization process,in which Ni₃S₄ nanoparticles were uniformly dispersed on the skeleton of Co₃S₄ nanoflowers.Owing to the significant synergistic effect in heterogeneous components,the Co₃S₄@Ni₃S₄-2h electrode exhibited excellent conductivity and capacitance.The heterogeneous electrode not only can show a good specific capacitance of 2817 F g^-1 at 1 A g^-1,but also present excellent rate performance.Moreover,the Co₃S₄@Ni₃S₄-2h//AC flexible supercapacitor delivers a high energy density of 54.2 W h kg^-1 at a power density of 799.7 W kg^-1,which is superior to those of the hybrid supercapacitors assembled by other sulfides and oxides.(3)The phosphorous-doped Co₃S₄@Ni₃S₄-175 electrode was prepared by the two-step strategy.The Co₃S₄@Ni₃S₄ nanostructure is grown on the nickel foams by hydrothermal treatment and subsequently phosphatization in a tube furnace.As expected,the P-Co₃S₄@Ni₃S₄-175 electrode has efficient ion/electron transfer channels and excellent redox activity.In the 2 M KOH alkaline electrolyte,the electrode exhibits an ultrahigh specific capacity of 3614 F g^-1 at 1 A g^-1.Furthermore,the fabricated hybrid P-Co₃S₄@Ni₃S₄-175//AC supercapacitor shows an outstanding energy density of 72 W h kg^-1 at a power density of 800W kg^-1.These results reveal that the phosphorous-doped P-Co₃S₄@Ni₃S₄-175 is a promising energy storage electrode.