| Owing to its unique advantages,such as:highly ordered tubular structure,easily controlled morphology,large specific surface area,excellent chemical stability and environmental friendliness,the one-dimensional TiO2 nanotube arrays(TNTs)prepared by anodization have become one of the most concerned electrode materials in supercapacitors field.However,the poor conductivity of semiconductor TiO2 results in TNTs electrode only having a very small specific capacity,which severely limits its further application in supercapacitors field.To solve this problem,the TNTs electrodes were respectively modified by carbon coating,oxygen vacancy introduction,and metal oxide modification in this paper.The morphology,microstructure,and surface element valence of the electrodes before and after modification were analyzed with the characterization of scanning electron microscope(SEM),X-ray diffraction(XRD),Raman spectroscopy(Raman),the transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS),what's more,cyclic voltammetry(CV),galvanostatic charge-discharge(GCD)and electrochemical impedance spectroscopy(EIS)were used to analyze the changes of the supercapacitor performance before and after modification.The main contents and conclusions are as follows:(1)Amorphous carbon-coated mixed-crystal TiO2 nanotube arrays(C@TNTs)were prepared by a combination of anodic oxidation,hydrothermal carbonization and annealing,and the effects of different annealing temperature on the morphology and electrochemical properties of C@TNTs were discussed.Compared with TNTs,the electrochemical performance of C@TNTs had been significantly improved,and the sample(C@TNTs-650)obtained after annealing in Ar atmosphere at 650°C that showed a better comprehensive electrochemical performance.The thickness of the amorphous carbon layer on the TiO2 nanotube arrays in C@TNTs-650 was about 3.3 nm and carbon coating had no obvious effect on the microstructure and crystal structure of the TiO2 nanotube arrays.When the current density was 60?A·cm-2,the discharge specific capacity of the C@TNTs-650 electrode reached 6.52 m F·cm-2,which was 52 times higher than TNTs.In addition,C@TNTs-650 electrode still had a better specific discharge capacity of 5.78 m F·cm-2at a current density of 0.8 m A·cm-2,and the discharge specific capacity retention rate reached 94.6%after 1000 cycles of charge and discharge under this current density,which showed that C@TNTs-650 electrode had a better rate performance and cycle performance.(2)Combined with electrochemical hydrogenation,H-TNTs and H-C@TNTs were successfully prepared after introducing oxygen vacancy defects(Vo)into TNTs and C@TNTs,respectively.While the oxygen vacancy defects were introduced into the TiO2lattice by electrochemical hydrogenation,it also changed the valence state of Ti in the lattice,then effectively increased the carrier concentration in the TiO2 nanotubes array,resulting in the improvement of electrochemical performance of the electrodes.When the current density was 0.1m A·cm-2,H-TNTs and H-C@TNTs respectively had specific discharge capacities of 3.05 m F·cm-2 and 9.17 m F·cm-2,which were improved 29 times and 1.4 times compared with TNTs and C@TNTs,respectively.(3)Through the redox reaction between potassium permanganate and amorphous carbon during the low-temperature hydrothermal process,the C@TNTs electrode was covered with amorphous MnO2 in situ to obtain a MnO2-C@TNTs electrode,and the electrode showed typical characteristics of the faraday capacitor electrode material.What's more,the area specific capacity of the MnO2-C@TNTs electrode increased significantly.The discharge specific capacity of the MnO2-C@TNTs electrode at a current density of 0.1 m A·cm-2 was151.9 m F·cm-2,which was higher than that of the electrode before modification.In addition,the energy density and power density of MnO2-C@TNTs composite electrode at a current density of 0.8 m A·cm-2 were about 13.98 m Wh·cm-2 and0.28 W·cm-2,respectively. |
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