Preparation And Performance Study Of Porous Double Hydroxides Composites For Supercapacitors

The nickel-cobalt double hydroxides can offer excellent supercapacitors performancedue to its unique spatial structure, and have aroused extensive researcher interests in the fieldof materials science. But the existing synthesis techniques easily cause materials with seriousagglomeration, which reduces its specific surface area and leads to that active ingredients cannot sufficiently contact with the electrolyte so that the number of effective electro-activeingredients was decreased, so supercapacitor performance of materials was remarkablylowered. In this paper, nickel-cobalt double hydroxides composites with3D spatial structuresare built to make these materials offer a larger specific surface, smaller mass transferresistance and superior structural stability, in order to obtain more outstanding supercapacitorperformance.Using SiO2@AlOOH as the hard template and urea as the precipitant, and addingnickel-cobalt precursor into reaction medium composed of ethanol-water（V:V=9:1）.Nickel-cobalt layered double hydroxides microspheres with flower-like patterns structurewere successfully synthesized by hydrothermal synthesis method. The scanning electronmicroscope （SEM）, transmission electron microscope （TEM）, X-ray diffraction （XRD） andIR spectrum and electrochemical workstation were employed for the characterizations of thecomposites. The results indicates that the flower-like microspheres are fabricated with doublehydroxides nanosheets with the thickness of about10nm as in situ formed building units, andpresent a porous structure, the microspheres have a average size of about2.5μm, Itsmaximum specific capacitance was found to be1108.8F·g^-1at current density of1A·g^-1,which is obviously higher than that of common nickel-cobalt layered double hydroxides(710.5A·g^-1). The specific capacitance can remain at700.5F·g^-1when the current densityincreases to7A·g^-1. After galvanostatic charge-discharge1500cycles, the specificcapacitance can keep at more than96.5%.Using ammonia as the precipitant, and adding nickel-cobalt precursor into reactionmedium composed of tert-butanol-water （V:V=95:5）. Nickel-cobalt layered doublehydroxides microspheres with porous structure were successfully synthesized byhydrothermal synthesis method. The scanning electron microscope （SEM）, transmissionelectron microscope （TEM）, X-ray diffraction （XRD） and IR spectrum and electrochemicalworkstation were employed for the characterizations of the composite. The results indicatesthat the as-prepared microspheres were fabricated with double hydroxides nanosheets withthe thickness of about30nm as in situ formed building units and display a porousarchitecture, Its maximum specific capacitance was found to be1698.8F·g^-1at currentdensity of1A·g^-1, which is more than2-fold that of common nickel-cobalt layered double hydroxides (710.5A·g^-1), The specific capacitance can remain at1013.8F·g^-1when thecurrent density increases to11A·g^-1. After galvanostatic charge-discharge3000cycles, thespecific capacitance can keep at more than95.5%.Using ammonia as the precipitant and adding nickel-cobalt precursor into reactionmedium composed of ethanol-water （V: V=99:1）,3D flower-like clusters nickel-cobalt layereddouble hydroxides were successfully synthesized by microwave-assisted hydrothermalsynthesis method. The scanning electron microscope （SEM）, transmission electronmicroscope （TEM）, X-ray diffraction （XRD） and IR spectrum and electrochemicalworkstation were employed for the characterizations of the composites. The results indicatesthat3D flower-like clusters nickel-cobalt layered double hydroxides nanocomposites werefabricated with nanosheets with the thickness of about3nm as in situ formed building units,the overall morphology structure is of singleness and presents a special3D structure formed bythe superb flower clusters, which provides the nanocomposites with the larger specificsurface, the smaller mass transfer resistance and more outstanding structure stability. Atcurrent density of1A·g^-1, its maximum specific capacitance was found to be2163.8F·g^-1,which is more than3-fold that of common nickel-cobalt layered double hydroxides (710.5A·g^-1). The specific capacitance can remain at1800.8F·g^-1when the current density increasesto9A·g^-1. After galvanostatic charge-discharge3000cycles, the specific capacitance cankeep at more than98.5%.