Preparation,Modification And Electrochemical Performance Research Of TiO₂ Nanotube Arrays Composite Electrode

Faraday pseudocapacitors have higher theoretical specific capacitance and energy density than electrical double-layer capacitors,and are the most likely to achieve higher performance supercapacitors.However,energy density,rate performance and cycle stability still need to be further improved to meet the practical application requirements.At present,the performance of pseudocapacitors is mainly enhanced by improving the specific surface area and conductivity of electrode materials.In this study,high specific surface area TiO₂nanotube arrays prepared by anodization were used as the support materials.Using the electrochemical reduction method to improve the conductivity of the nanotubes,and the pseudo-capacitance material with high specific capacitance is deposited in the nanotube.The synthesized nanocomposite electrode not only has a high specific surface area but also has excellent conductivity.The main research content is as follows:Firstly,TiO₂ nanotube arrays with different array lengths were prepared by anodized titanium foil with different time,and their electrochemical properties were studied,respectively.The formation and growth mechanism of TiO₂nanotube array was explored by the current density-time evolution curve during anodization.The experimental results show that the TiO₂ electrode exhibits a poor current response,and the specific capacitance of the TiO₂ nanotube array is only 1.55 mF?cm^-2 at a current density of 0.1 mA?cm^-2.Second,the TiO₂ nanotube array is modified by a novel and efficient electrochemical reduction process.The experimental results show that the morphology of the nanotubes at before and after the reduction is not change significantly,but the color of the nanotube array?H-TiO₂?changes from the initial light gray to blue.The length of the nanotube array has little effect on the electrochemical performance of the H-TiO₂ electrode,while the doping voltage,time and electrolyte temperature significantly affect the electrochemical performance of the H-TiO₂ electrode.The self-doping voltage 5 V for 30seconds was applied on 0.5 M Na₂SO₄ solution at 25?,exhibiting an outstanding specific capacitance of 22.17 mF?cm^-2,which is 14.3 times that of the pristine TiO₂ nanotube electrodes.Electrochemical reduction significantly improved the conductivity and capacitive properties of TiO₂ nanotubes.At the same time,the morphology and crystal structure of TiO₂ nanotubes are not damaged or changed during the electrochemical self-doping process.Finally,Ni?OH?₂@TiO₂?Co?OH?₂@TiO₂ and NiCo_x?OH?_y@TiO₂ nanotube composite electrodes were successfully prepared by constant current electrodeposition on the substrate material of H-TiO₂ nanotube arrays.Experimental results show that the specific capacitance is 320 mF?cm^-2?Ni?OH?₂@TiO₂?and 347 mF?cm^-2?Co?OH?₂@TiO₂?when the current density is0.5 mA?cm^-2,which shows excellent pseudo capacitance performance.The nickel-cobalt codeposition NiCo_x?OH?_y@TiO₂ has a higher specific capacity of376.8 mF?cm^-2 compared to M?OH?₂@TiO₂ nanotube composite electrode,and the retention rate of the initial capacitor after a 1000-cycle cycle is still 79.8%.It is indicating that ternary metal compound NiCo_x?OH?_y@TiO₂ has a higher redox activity and electrochemical stability,which can be used as a promising electrode material.