Research On Preparation And Electrochemical Properties Of Nickel Cobalt Sulfide

The growing energy demand has forced human beings to use clean and abundant renewable resources to meet future energy needs.Because traditional fossil energy resources are limited and can cause serious pollution to the environment,the task of developing sustainable energy storage and conversion devices is an urgent task.Supercapacitors,hydrogen evolution reactions?HER?and oxygen evolution reactions?OER?are recent research hotspots in the field of energy storage and conversion.Because supercapacitors are excellent green energy storage devices,they have the advantages of high power density,good rate performance and stable cycle life.They are strong competitors of traditional batteries and common capacitors.The hydrogen evolution reaction?HER?and the oxygen evolution reaction?OER?are important reactions involved in the process of green hydrogen production?electrolyzed water?.However,the mainstream electrodes used for supercapacitors,HER,and OER are all precious metals,they are expensive and scarce,which limit their wide industrial application.Therefore,the development of inexpensive and electrochemically superior electrode materials to replace precious metals has great economic value for supercapacitors,HER and OER process.It is well known that cobalt sulfide nickel is used as an electrode material in the above mentioned filed.The details of the thesis are as follows:1.In order to study the influence of the composition ratio of the electrode materials of supercapacitors and hydrogen evolution reaction and oxygen evolution reaction on its electrochemical performance,the molar ratio of Ni and Co in the reactants in the solvothermal reaction were varied.And,nickel cobalt sulfide with different Ni/Co ratios was deposited on the carbon fiber cloth?CFC?in order study its electrochemical properties as a supercapacitor electrode material and as a HER electrocatalyst.The electro-chemical measurements showed that the nickel cobalt sulfide with a theoretical molar ratio of Ni/Co to be 1.5:1.5 demonstrates the superior pseudocapacitive performance with a high specific capac-itance(6.47 F cm^-2 at 10 mA cm^-2)and a favorable Coulombic efficiency??99%?.Whereas,when applied as the catalyst for hydrogen evolution reaction in 1 M KOH aqueous electrolyte,the nickel cobalt sulfide with a theoretical molar ratio of Ni/Co is 1:2 displays better catalytic activity,and it requires a relatively lower overpotential of 282 mV to deliver the current density of 10mA cm^-2.2.Nano-rods and nano-networks of NiCo₂S₄ with two different morphologies were fabricated on carbon fiber paper?CFP?by using the same raw materials and changing the reaction time in a solvothermal reaction.Subsequently,the effects of the morphology of NiCo₂S₄ upon its electrochemical properties was investigated,including supercapacitors and oxygen evolution reactions.Among them,NiCo₂S₄ nano-network composite electrode material showed better electrochemical activity.3.The heterostructure composite has excellent electrochemical properties..Three-dimensional flower-like Ni-Co-LDH/NiCo₂S₄ was prepared on carbon fiber paper by a two-step reaction method..The unique morphology not only improves the structural stability of Ni-Co-LDH/NiCo₂S₄,but also accelerates electron transfer and electrolyte transport during electrochemical processes.Ni-Co-LDH/NiCo₂S₄/CFP electrodes have high specific capacitance and good cycle ability for supercapacitors.In addition,the assembled Ni-Co-LDH/NiCo₂S₄/CFP symmetrical supercapacitor device has very good cycle stability and retain a specific capacitance of 115.4%after 5000 cycles.Moreover,the Ni-Co-LDH/NiCo₂S₄/CFP electrode also performed well in the oxygen evolution reaction and hydrogen evolution reaction.