Synthesis And Pesudocapacitance Behavior Of Nanocomposition Derived From Nickel, Cobalt-Based Metal Complex

Transition metal oxide was the first material of pseudocapacitors which was found and studied initially.Transition metal has various valence states,for instance,Ni and Co,which provide much more possibility for the development of high-performance pseudocapacitors.Electrode material with single category can't meet people's requirements for supercapacitor any more,a growing number of composite electrode materials,such as metal compound-carbon composites,metal compound-polymer composites,and metal oxides-metal sulfides composites,et al.,attract the attention of many researchers.In this work,CoO/C,Ni/NiO/CNTs and Ni/Ni3S2 composite materials have been synthesized by heat treatment,and electrochemical tests of three electrode materials were performed in an alkaline electrolyte.?1?CoO/C composite was synthesized by solid reaction process using cobalt nitrate hexahydrate and melamine as raw materials,and the product was characterized by scanning electron microscopy?SEM?,transmission electron microscope?TEM?,X-ray photoelectron spectroscopy?XPS?and X-ray diffraction spectra?XRD?et al..The results showed a honeycomb composite of CoO/C and the porous structure provide an enlarged area of the composite's surface,which is advantageous to improve the performance of the capacitor.The results of electrochemicial test show that at the current density of 1 A/g,the CoO/C composite exhibits a capacitance of 1071 F/g.At the current density of 10 A/g,the cyclic stability test was carried out and CoO/C shows an excellent retention rate of 94.8%after 1000 cycles.CoO/C//AC asymmetric supercapacitor?ASC?was fabricated using CoO/C electrode as the positive electrode and active carbon?AC?electrode as the negative electrode.The power density of CoO/C//AC ASC achieves up to 51.7 Wh/kg while the energy density is 762 W/kg.?2?Spheres Ni-BTC complex material was synthesized by hydrothermal method using Ni²⁺as the central ion and trimesic acid?H₃BTC?as bridging ligand.Then,Ni/NiO/CNTs composite was synthesis in argon for 8 h with Ni-BTC act as the precursor at 435 ^oC.Trimesic acid contains rich hexatomic carbon rings,which can be converted into carbon nanotubes under the catalysis of nickel ions and grown on the surface of materials.Electrochemical tests showe that when the current density of Ni/NiO/CNTs composite is 4A/g,the specific capacitance is 1472 F/g,which is higher than Ni-BTC's specific capacitance?738 F/g?.When the current density was elevated to 20 A/g,and the specific capacitance of Ni/NiO/CNTs and Ni-BTC reduced to 748 F/g and 508 F/g,respectively.The capacitance retention rate of Ni/Ni O/CNTs is also much higher than that of Ni-BTC electrode materials after 5000 charge-discharge cycles under the current density of 8 A/g.Therefore,Ni/NiO/CNTs composites have outstanding pseudocapacitance.The Ni/NiO/CNTs//AC ASC with Ni/NiO/CNTs as the positive electrode and AC as the negative electrode,demonstrates remarkable power density of 810 W/kg while the energy density is 27.9 Wh/kg.?3?Ni?NO₃?₂·6H₂O and 2-methyl imidazole were dissolved in methanol totally,then the flower-like Ni-ZIF was synthesized at 140 ^oC by solvothermal method.Put Ni-ZIF composite and sulfur sublimed on the opposite sides of the quartz boat,respectively.Then,Ni/Ni3S2composite material was achieved in the tubular furnace with Ni-ZIF acted as precursor and sulfur sublimed acted as sulfur source during the calcine process.We got Ni/NiO composite under the same condition,except sulfur source.The product was characterised by SEM,transmission electron microscope?TEM?,XRD,and XPS.Experimental results show that Ni/Ni3S2 microsheet composite composed of nanoparticles.The specific capacitance of Ni-ZIF,Ni/NiO and Ni/Ni3S2 is 1289,1324 and 2222 F/g,respectively,at the current density of 4 A/g.The stability of these three electrodes was tested at a especially high current density?20 A/g?,and the retention rate of Ni/Ni₃S₂ was 73.4%,higher than Ni-ZIF and Ni/NiO.In the two-electrode system,Ni/Ni₃S₂ composite was used as the positive electrode and AC was used as the negative electrode,Ni/Ni3S2//AC ASC exhibits the power density of 800 W/kg with the energy density is 18.4 Wh/kg.