The Preparation Of Titanium Dioxide Nanotubes/Polypyrrole Composite Materials And Its Electrochemical Performance Study

As a new type of energy storage device,supercapacitors,which combines the advantages of high energy density of chemical battery and high power density of conventional capacitors,at the same time,it has the advantages of long cycle life,environmental protection and wide working temperature range,has become an important member of the new chemical power family.One dimensional highly ordered titanium dioxide?TiO₂?nanotubes is a promising supercapacitor electrode material for its excellent physical and chemical properties,large specific surface area,and a good electronic transmission path.However,the TiO₂ nanotubes have wide band gap,poor conductivity and small capacitance,which limit their application in supercapacitors.Therefore,it is of great significance to improve the conductivity and capacitance of TiO₂ nanotubes by reasonable modification.In this thesis,two step anodization method is employed to fabricate TiO₂ nanotubes and then the TiO₂ nanotubes were modified by electrochemical reduction method.On the basis of this,combination method of electrochemical reduction and electropolymerization is adopted to prepare r-TiO₂ nanotubes/ppy composite electrode.In addition,impregnation/calcination method is used to synthesis the molybdenum doped titania nanotube composite film electrode,which greatly improved the conductivity and specific capacitance of TiO₂ nanotubes.Also,a ternary composite material constituted of Mo doping and ppy loading on TiO₂ nanotubes is synthsised by dip-calcination and electropolymerization way.The details are presented as below:A combination method of electrochemical reduction and electropolymerization is adopted to prepare r-TiO₂ nanotubes/ppy and the influences of morphologies and structures of nanotubes and electrochemical performance are studied.The galvanostatic charge-discharge analysis shows that r-Ti O₂ nanotube/PPy exhibit capacitance of 777.5 F/g at the current destiny of 1.0 A/g,which is much higher than that of TiO₂ nanotube and r-TiO₂ nanotube.Mo/TiO₂ nanotube electrode materials are successfully fabricated via dip-calcination method and the influences of morphologies and structures of nanotubes and electrochemical performance are studied.Compared with TiO₂ nanotube,Mo/TiO₂ nanotubes show higher capacitance,as high as 323.75 F/g,which may be ascribed to the enhanced electronic and ionic conductivity.Due to a large number of Mo6+ replace the position of the lattice Ti4+,which may lead to the generation of more free holes.Thus the increased hole concentration in the valence band can contribute to the electrical conductivity of the doped sample.The ternary composite materials composed of Mo,PPy and TiO₂ nanotube are prepared by a coupling technique of electropolymerization and dip-calcination,and also the influences of morphologies and structures of nanotubes and electrochemical performance are studied.Compared with the traditional binary composite,this ternary composite show excellent electrochemical performance.The ternary composite material exhibit capacitance of 1432 F/g at the current destiny of 1.0 A/g;PPy/Mo/TiO₂ nanotubes also show remarkable long-term cycling stability with only 21 % reduction of the initial capacitance after 1000 charge-discharge cycles.