Study On Modified Binary Metal Oxides And Supercapacitor

With the development of our society,the deformable and flexible devices are increasing the attention of researchers.Thus,the flexible device（supercapacitor）is regarded as our reaseach direction.The carbon cloth with intrinsic flexibility,favorable chemical stability and high conductivity is the idea collector.Due to metal oxide’s special capacitive properties of higher capacitance than most of conductive polymers,considerable research efforts have been focused on developing metal oxide materials.Metal oxide materials can be divided into three categories:（a）single metal oxides NiO,Co3O4,MnO2,RuO2,etc.（b）binary metal oxides,such as NiCo3O4,NiMoO₄,CoMoO4,etc.（c）hybrid nanostructure,such as Co3O4@NiMoO₄,NiCo3O4@MnO2,MnO2/KCu7S4,etc.Binary metal oxides,which have the property of synergistic effect between the two metal atoms and crystal structure can contribute to enhancing the capacitance of our device.The metal oxides offer high energy and better cycling stability but suffer from poor conductivity.So the improment of conductivity on metal oxides has been an important element in our work.Above all,the collector of carbon cloth and the hybrid materials are the starting point of our research.In this thesis,the NiMoO₄ nanowires arrays grown on carbon cloth,hybrid C/Na2Ti3 O and hybrid K@K₂Ti₆O₁₃ are regard as our study.The study can be divided into modification,characterization,electrochemical test and application respectively.The main research contents and results are as follow:（1）β-NiMoO₄ 3D nanostructure grown on carbon cloth for solid asymmetry supercapacitorThe approach of β-NiMO4 NWs synthesis on carbon cloth is a facile hydrothermal method.The handled carbon cloth by KMnO4 solution,Ni（NO3）2·6H2Oand Na2MoO4·2H2O are the reagents.The crystal structure,element,morphology and size of β-NiMO4 NWs are characterized by XRD、FESEM、EDS and TEM.The NiMO4 are the β crystal phase and the micro-structure.The binary metal oxides are fabricated to the asymmetry supercapacitor and the devices are bind free.Furthermore,the carbon rod and the carbon cloth are also cheap.The cyclic voltammetry（CV）,galvanic charge-discharge（GCD）measurement and electrochemical impedance spectroscopy（EIS）were conducted using a chemical workstation（CHI760D）.The electrode has a highest energy density of 36.86 W h/kg,a maximum power density of 1100 W /kg,and a large capacitance of 414.7 F/g at a current density of 0.25 A/g,all of which demonstrate excellent behavior.And the capacitance of the supercapacitor reached 65.96% of the initial capacitance over 6000 cycles.Hybrid device could light a light-emitting diode（LED）for 260 seconds.All of these results indicated that the β-NiMoO₄ NW arrays grown on carbon cloth could be a promising candidate for high performance supercapacitors.（2）Carbon-Modified Na₂Ti₃O₇·2H₂O Nanobelts as Redox Active Materials for High-Performance SupercapacitorThe Na₂Ti₃O₇·2H₂O Nanobelts are synthesized by titanium dioxide（Ti O2,99.8% pure）and sodium hydroxide（99.99 %,pure）at the temperature of 180o.And the sample are dried in the furnace and white materials the Na₂Ti₃O₇·2H₂O Nanobelts.The Na₂Ti₃O₇·2H₂O show a highly electron-insulating character but have a good chemical stability and a good ionic conductivity.So the conductivity of Na-TNBs can be improved with carbon（C）particles modified.Na-TNBs are characterized by XRD、EDX and TGA.The Na-TNBs are the layered crystallographic structure.From the characterization of FESEM、TEM、EDX-Mapping,we can further prove that the hybrid materials are average diameters about 150 nm and the length up to 25 μm,respectively and the C particles can distribute homogeneously among the Na-TNBs.The hybrid C/Na-TNBs are deposited on the carbon cloth by the titration method and are fabricated to the solid capacitor encapsulated by PDMS.The cyclic voltammetry（CV）,galvanic charge-discharge（GCD）measurement and electrochemical impedance spectroscopy（EIS）were conducted using a chemical workstation（CHI760D）.The capacitance of the device can attain 459.71 F·g-1 at scan rate of 25 mV/S and energy density of 33.2 Wh·kg-1 at power density 478 W·kg-1 and power density of 2.13 kW·kg-1 at energy density 25.36 Wh·kg-1.The retention of specific capacitance remains 74.3 % after 6000 cycles at high current value of 35 mA.Three supercapacitors in series can light 100 green color commercial light emitting diodes（LEDs）for about 10 minutes.All these results indicate that the C/Na-TNBs nanomaterial could provide the potential application in high performance supercapacitor.（3）Based on the stable tunnel structure of C@K₂Ti₆O₁₃ hybrid compositions for supercapacitorThe synthesis of K₂Ti₆O₁₃ is as same as the Na₂Ti₃O₇·2H₂O at 220℃ by hydrothermal process.K-TNBs crystallize in a monoclinic crystalline structure with continuous tunnel channels along c axis that can offer a space for accommodation of alkali metals.The tunnel structure is ensured by the XRD and the crystal structure.The anisotropic framework came into being the beams uniformly with a length of 500-600 nm and a diameter of 50-80 nm by the FESEM、TEM.The capacitance of the device can attain 301 F·g-1 at current of 3 m A and energy density of 26.8 Wh·kg-1 at power density 400 W·kg-1 and power density of 1.47 kW·kg-1 at energy density 16.3 Wh·kg-1.The retention of specific capacitance remains 82.7% after 10000 cycles at high current value of 21 mA.Three supercapacitors in series can light 100 green color commercial light emitting diodes（LEDs）for about 16 minutes.All these results indicate that the C@K-TNBs nanomaterial could provide the potential application in high performance supercapacitor.