| In the face of energy crisis and environmental problems,it is particularly urgent to develop environmentally friendly and highly efficient new energy and energy storage/conversion devices.The supercapacitor,a high-efficient energy storage and conversion device,is equipped with advantages of fast charge/discharge,large capacity,long cycle stability,large temperature range,free pollution and so on,but the low energy density impedes its widespread application.The electrode material is one of the most significantly influential elements in supercapacitor.Therefore,it is a vital strategy to research and exploit electrode materials with exceptional performance,and then reasonably assembling them to improve the electrochemical performance of supercapacitor.Cobalt-based bimetal oxides,as battery-type materials,have advantages of high specific capacity,easy to adjust chemical states and numerous active sites,but their poor conductivity,small specific surface area and unstable structure limits their application in supercapacitor.Researches reveal that composite materials can combine advantages of different materials and show positive synergistic effects of them,resulting better electrochemical properties than that of a sigle component.Thus,in this dissertation,Cobalt-based bimetal oxides,the core materials,combine with metal sulfides or graphene constructs composite nanoarrays with unique structure as electrode materials,to realize the improvement of capacitance performance of Cobalt-based bimetal oxide composites,by rejusting and optimizing the construction,components and synergistic effects of composite nanoarrays.The relevant studies are as follows:?1?Ni Co O2 nanoflakes had been firstly grown on the nickel form?NF?by hydrothermal method and annealing progress,and then ultrathin interconnected Ni3S2 nanosheets covering on the scaffold of as-prepared Ni Co O2 nanoflakes were prepared by electrochemical deposition.Therefore,the hierarchical Ni Co O2@Ni3S2 core/shell nanoflakes arrays electrode was prepared.Compared to the single material electrode,it appears a porous interconnect structure providing more specific surface area and active sites,which makes for the synergistic effect between components and nanoarrays.The results illustrate that Ni Co O2@Ni3S2 core/shell nanoflakes arrays greatly releasing potential of the Ni Co O2 and Ni3S2 materials,exhibit excellent charge storage capability for supercapacitor.The mass and areal specific capacity of Ni Co O2@Ni3S2/NF are respectively up to 1599.5 C g-1 and 4.06 C cm-2at 1A g-1,overtaking the capacity of the two separate samples Ni Co O2/NF(640.0 C g-1)and Ni3S2/NF(695.3 C g-1),and even higher than the sum of their specific charge stroge performance(1335.3 C g-1).Furthermore,a hybrid supercapacitor device fabricated using Ni Co O2@Ni3S2/NF?positive electrode?and graphene/NF?negative electrode?possesses a high energy density of 73.97 Wh kg-1 at the power density of 800 W kg-1,and maintains 22.01 Wh kg-1 when the power density up to 12.8 k W kg-1.?2?Hierarchical Ni3S2/Ni Co2O4 arrays were designed and prepared on Ni foam framework with core-shell flakes structure as charge-storage materials using hydrothermal treatment and electro-deposition process.Those nanoflakes supported with each other can form a three-dimensional porous and interconnected relatively solid structure,which could afford larger specific area,more active sites and ion/eletron transfer channels for accelerating redox reactions.The results demonstrate that Ni3S2/Ni Co2O4 nanoarrays as supercapacitor materials show excellent charge-storage properties in electrochemical energy storage,including high specific capacity of 1201 C g-1(3.46 C cm-2)at 1 m A cm-2,which is far larger than those of pure Ni Co2O4(572C g-1,0.86 C cm-2)and Ni3S2(612 C g-1,0.98 C cm-2).Meanwhile,Ni3S2/Ni Co2O4 arrays keep a capability of 742 C g-1 at 60 m A cm-2,indicating a great rate performance.?3?Firstly,the best electrodeposition condition was selected out via testing the electrochemical performance of the Ni3S2/Ni S compolex?Ni?electrodeposited on the bare Ni form in different solution concentrations.The results reveal that Ni S?with best performance was prepared by adding 2.5 m M Ni salt in electrodeposited electrolyte.After that,electrodeposition of ultra-nanoslice Ni S?onto the Mn Co-oxide?Mn Co?nanowire arrays which was prepared through conventional hydrothermal and heating approaches formed a two-tiered core-shell NiConanoarrays compound.As supercapacitor electrode materials,the specific capacity of NiCois up to 1358 C g-1(4.84 C cm-2)at the current density of 1 A g-1.In addition,the specific capacity of NiCocan maintain at 985 C g-1(3.52 C cm-2)as the current density increases to 10 A g-1,which obviously implies this kind of material is equipped with outstanding rate property.The charge storage capability of NiCohas a remarkable increase,compared with that of pure Mn Co(661 C g-1,1.35 C cm-2).Ultimately,a hybrid device NiCoGO/NF was made.Its voltage window can extend to 1.6 V,and its energy density can up to as high as 64.61 Wh kg-1.?4?The composite nanoarrays of Ni Co oxides?Ni Co2O4-Ni Co O2?and graphene on Ni foam was synthesized by one step hydrothermal progress?noted as Ni Co2O4-Ni Co O2/r GO?.The crystal structure of Ni Co2O4-Ni Co O2 is a serrated nanoflakes composed of both spinel structure?Ni Co2O4?and Na Cl-type crystal structure?Ni Co O2?.The highly conductive graphene embedded into or coated on the Ni Co2O4-Ni Co O2 arrays forming the Ni Co2O4-Ni Co O2/r GO nano-arrays changes the morphology dramatically.This special structure provides larger specific surface area,more electroactive sites and ions transfer channels for redox reactions.The results demonstrate that the Ni Co2O4-Ni Co O2/r GO nanoarrays can reach its maximum specific capacity of1439 C g-1/3.22 C cm-2 at a low current density of 1 m A cm-2,and a high gravimetric capacity of 1172 C g-1?capacity retention:81.4%?can mentain at a high current density of 60 m A cm-2,indicating an excellent rate capability. |
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