Compositing And Modification Of Cobalt Hydroxide Electrode And The Architecture Of Novel Supercapacitor

Due to the excessive use of traditional fossil fuels,the development of clean energy devices is extremely urgent.Supercapacitors are listed among those important families of energy devices with high power density,long service life,security and stability,which are attracting considerable attention.Whereas,the low energy density of supercapacitors seriously limits their practical application.The main contents of this thesis are as follows:1.Four substrates are selected as the current collector to support Co（OH）₂,and the effects of these four different current collectors on the electrochemical properties of cobalt hydroxide are investigated.NiO at the surface of Ni foam shows a high redox activity,together with the performance of Co（OH）₂ which can contribute to overall specific capacitance Co（OH）₂,however it shows a poor stability.The stability of Co（OH）₂ on porous Ti and CNF with Co（OH）₂ is far better.The chemical bonds between carbon fiber and cobalt hydroxide provide a chemical grasp force to enhance both capacity and stability of the electrode.In terms of the capacity,the best occurs for the Ni foam,while an equivalent level was performed for the porous Ti and CNF.The worst case is the one with Cu foam.2.It is found that a lot of CH₂ functional groups exist at the surface of reduced graphene oxides after reduction.These functional groups can react in the Co（OH）₂ compositing process,forging C-O-Co bonds and facilitate electron transport.In boron oxide incorporating reduced graphene oxides,the CH₂ functional group is destroyed,forming C-BxOy-Co（OH）₂ chemical bonds,which decelerates the electron transfer.Therefore,the specific capacity of rGO/Co（OH）₂ is significantly higher than that of BG/Co（OH）₂.Therefore,the chemical bond between graphene and cobalt hydroxide has an important effect on electron transport and capacitance properties.3.In situ X-ray photoelectron spectroscopy proved that the Co-Ni double hydroxide and carbon fiber surface can form a large number of C-O-Co（Ni）chemical bonds,and these chemical bonds are changing druing the charge and discharge process.When the electrode is fully charged these chemical bonds exhibit covalent behavior.While the electrode is fully discharged these bonds show an ionic character,revealing that the chemical bond can also store charge.4.Both K₃Fe（CN）₆ and K₄Fe（CN）₆ can boost the capacitance in the electrolyte for Co（OH）₂ electrode,but the improvement of the contrast capacity of K₄Fe（CN）₆ is smaller than that of K₃Fe（CN）₆.Compared with that without K₃Fe（CN）₆ or K₄Fe（CN）₆,the specific capacity of the cobalt hydroxide electrode（765 F/g）is improved.As we can see that the specific capacitance and coulombic efficiency are in direct proportion to the addition amount of K₃Fe（CN）₆.5.In this thesis,three kinds of asymmetric supercapacitors are assembled respectively,including Co（OH）₂-active carbon（AC）asymmetric supercapacitor（26.4 Wh/kg）,Co（OH）₂/K₃Fe（CN）₆-K₄Fe（CN）₆/AC asymmetric supercapacitor（38 Wh/kg）and Co（OH）₂/K₃Fe（CN）₆-p-phenylenediamine（PPD）/AC asymmetric supercapacitor（136 Wh/kg）.To sum up,the preparation of highly electrochemical active Co（OH）₂ composite electrode and the method of the independent contribution in capacitance from both electrode and electrolyte are of significant merits for the development of energy storage devices with high energy density.