Honeycomb-like Cobalt Nickel Based Nanomaterials:Morphology Modulation,Surface Modification And Its Electrochemical Property

Transition metal cobalt-nickel based compounds have excellent electrochemical properties and can be used as supercapacitor electrode materials and electrolytic water catalysts.In this paper,their different shapes have been obtained successively by double solvothermal method,hydrothermal method,room temperature sulfuration process and chemical vapor deposition method etc.The formation mechanism of some special structures has been deeply studied.The electrochemical performance has also been measured.There are the main conclusions as follows:?1?Based on double solvents of ethylene glycol,NiCo₂S₄ with different shapes is obtained.The electrochemical experiments showed that the morphology of the matter have a great influence on its redox reaction.Especially,the specific capacitance value of honeycomb-like sample reaches 1464 F/g at 1 A/g,and its capacitance retention rate can still reach 87%at 5 A/g.The formation of honeycomb-like structure is mainly related to the hollow sphere rupture caused by water pressure.Based on glycerol-based double solvents,different crystalline NiCo₂S₄ can be obtained by regulating the synthesis time.As electrode materials,one sample?NiCo₂S₄-GE-3?has a specific capacitance of 1816 F/g at 1 A/g.?2?Based on Ethylene glycol-Isopropanol double solvents,graphene coated honeycomb-like NiCo₂S₄ composite were obtained.Under a three-electrode system,its specific capacitance is tested as 1244 F/g at 1 A/g and especially,at high current density of 20 A/g,the capacitance can still reach 960 F/g.At 5 A/g,the capacitance retention rate of 1000 cycles was 91%.In the composite,graphene not only enhances the conductivity but also affectes the morphology with a big specific surface area,which has a positive effect on the capacitive performance.?3?A series of cobalt-nickel base compounds with various shapes are prepared by hydrothermal method,and then the honeycomb shape of NiCo₂S₄ is obtained again by room temperature sulfuration process.As electrode,the honeycomb NiCo₂S₄ also shows an excellent electrochemical performance.Its specific capacitance can reach1020 F/g at 30 A/g;the specific capacitance of 3000 cycles can still remain at 82.5%at10 A/g.The energy density can reach 68 Wh/kg at 807 W/kg.Even if the power density rises to 7999 W/kg,the energy density can still reach 28 Wh/kg.Moreover,the lit LED?1.5V?lasts for about 60s,demonstrating its practical value as electrode materials.?4?Without other carbon source,a carbon layer coated cobalt/nickel phosphate composite can be easily and effectively prepared by CVD.Meanwhile,the morphology of the product can also be effectively regulated by adjusting the element composition.The sample,named as Co₂P₂O₇/Ni?PO₃?₂@C,has excellent catalytic activity as oxygen evolution catalyst.The Tafel slope of Co₂P₂O₇/Ni?PO₃?₂@C can be 102 mV/dec.When the current density is 10 mA/cm²,the corresponding overpotential is merely 279 mV,and 96.1%of its electrocatalytic activity can be maintained after 12 hours,indicating excellent electrochemical activity and stability.There are 32 figures,9 tables and 119 references in this paper.