Studies On TiO₂-based Supercapacitor

Supercapacitors are energy storage devices possessing botih high power density and a much higher energy density than that of dielectric capacitors.According to the different principles of energy storage,they can be divided into double layer supercapacitors and tantalum capacitor supercapacitors.Tantalum capacitors generally rely on chemisorption-desorption or redox reactions of electrode materials including polymer materials and metal oxides to store charge and energy.Titanium dioxide(TiO2)has three kinds of crystal structures such as plate titanium,anatase and rutile in nature.The plate-titanium crystal is unstable and has little industrial utility.Anatase and rutile(Rutile))has a stable crystalline phase.The ideal TiO2 is a semiconductor with a band gap of about 3.2 eV,which absorbs ultraviolet light and produces a photo-electric effect,generating electron-hole pairs.In addition,the Ti element of the transition metal element in TiO2 has a variety of valences and can store charge and energy through redox reactions,so TiO2 can be used as a tantalum-capacitor type supercapacitor electode material.The research content and main results of this paper are as follows:First,we prepared titania nanotubes by anodic oxidation.The electrolyte used contains 0.3%NH4F and 5%H2O.Different morphologies of TiO2 nanotubes can be obtained by controlling the oxidation time and oxidation voltage.Under the condition of constant oxidation voltage of 60 V,the diameter and length of TiO2 nanotubes increase with the increase of anodizing time.After 13 h,the growth of TiO2 nanotubes decreases significantly,and the diameter of the TiO2 nanotubes is basically maintained.Invariable,the specific capacitance reached its maximum at 13 h,about 20 mF/cm2.Under the oxidizing time of 13 h,when the anodic oxidation voltage is lower than 60 V,the tube length of TiO2 nanotubes increases as the voltage increases,and when the voltage exceeds 60 V,it becomes shorter as the voltage increases;In the test voltage range,the pipe diameter increases with voltage,and the specific capacitance also increases with voltage.Secondly,titania nanoparticles were prepared by hydrothermal synthesis method with titanium sulfate as the titanium source.The structure and morphology of the nanoparticles were characterized by XRD and SEM,and the effect of hydrothermal temperature on the size of TiO2 nanoparticles was analyzed.Studies have shown that hydrothermally synthesized TiO2 nanoparticles are anatase structures with a diameter of 30-50 nm.After the electric cycle treatment,the conductivity of TiO2 increased significantly,and the specific capacitance also drastically increased from 10 mF/cm2 to 103 mF/cm2 and remained stable.A clear redox peak was observed in the TiO2 CV curve,demonstrating that its capacitive properties mainly come from the redox reaction of titanium dioxide.