Synthesis And Supercapacive Properties Of NiCo₂S₄ As Electrode Materials

Recently, with the energy crisis is getting distinct gradually, environmental issues are being concerned seriously by human beings at the same time. For reducing the consumption of fossil fuels and to make use energy more efficiently, supercapacitors, also called pseudocapacitors, have been paid great attention due to the properties of high energy density and long cycling life. By far, supercapacitors are being utilized in our daily life, such as hybrid vehicles, micro-electronic devices and so on. While the NiCo2S4 as a material that shows high specific capacitance and conductivity, which has a bright future using as an electrode materials for supercapacitors. Therefore, it is meaningful to synthesis NiCo2S4 electrode materials with good property. In this thesis different morphologies of MCo2S4 nano materials were acquired by using solvothermal methods, eletrodeposition and hydrothermal methods respectively. The main contents are as follows.1) The foam-like NiCo2S4 electrode material was synthesized by a two-step solvothermal method. Its structure was characterized by several analytical techniques. Its foam-like structure was confirmed by using the transparent electron microscope. The foam was assembled by many stacking bubble clearly, and this material could have high specific surface area, so that it might contact with electrolyte well. As a result, during the charge and discharge process, the specific capacitance of this material is 841 Fg-1 at the current density of 2 Ag-+1. After 1000 cycles of charge and discharge the capacitance retention is 48%.2) NiCo2S4 nano material were successfully deposited and acquired at nickel foam substrates by cycling voltammetry in the solution containing cobalt nitrate, nickel nitrate and thiourea at a certain concentration. Its chemical structure and morphology were characterized by X-ray photoelectron spectroscopy and electronic microscopy. The results show NiCo2S4 3-dementional porous loose structure assembled with nanosheets, which may provide high specific surface area. The electrochemical characterization shows that the integrative electrode reaches a specific capacitance of 586 Fg"1 at the current density of 1 Ag"!. the capacitive performance of the electrode was enhanced after the further eletrodeposition of MnO2 on the surface of MCo2S4 electrode. Its specific capacitance became 844 Fg"1 at the same current density. The capacitance retention of 70% was found after 2000 cycles in the test of charge-discharge test.3) By hydrothermal reaction, MCo2S4 was synthesized on the surface of graphite oxide; simultaneously the graphite oxide was reduced into reduced graphite oxide (RGO) in the glycol-water solution. The loading amount of NiCo2S4 on the surface of RGO could be controlled by the experimental parameters. The TEM images confirmed that NiCo2S4 nanoparticles grew on the surface of RGO. The electrochemical properties of composites with different loading amount(Low, NiCo2S4/RGO-1; high, NiCo2S4/RGO-2) were compared. The specific capacitance of NiCo2S4/RGO-l and NiCo2S4/RGO-2 were 593.3 and 627.5 Fg’1 respectively at 1 Ag-1. After 2000 loops of GCD test, the capacitance retention values of both were 49% and 57% respectively.