Fabrication Of TiO₂ Nanotubes And Its Electrochemical Applications

Titania nanotubes (TNT), which is a typical one dimension nanomaterial, possess unique combinations of physicochemical properties and relatively low synthesis costs than other nanomaterials. Several recent studies have indicated that titania nanotubes have improved properties compared to any other form of titania for application in photocatalysis, sensing, photoelectrolysis, and photovoltaics due to their high surface-to-volume ratios and sizedependent properties. In this paper,we fabricated highly-ordered tinatia nanotube arrays by anodization,investigated the changes of its morphology and crystallized structure at different annealing conditions,studied the electrochemical properties of TiO₂ nanotubes and its application in medium enzyme electrode and lithium battery electrode. We abstract the main content of this dissertation as following:1)Fabricate the TiO₂ nanotubes arrays by anodization in different electrolyte and investigate the electrochemical conditions. In HF-based electrolyte, uniform titania nanotube arrays of various pore sizes (40¹00nm), lengths (100⁵00 nm) are grown by controlling the anodization potential between 10V²2V and the concentration of F—between 0.05 0.3mol/L. Based in KF and ethylene glycol + NH4F electrolytes respectively, the nanotube pore size is from 40nm to 110nm, the length is from 1μm to 60μm. The as-prepared TiO₂ nanotubes are amorphous, EDX and XPS spectra presented that the TiO₂ nanotubes consisted by O and Ti, also existing F & C traces.2)Fabricate the TiO₂ nanotubes film on FTO substrate. The TiO₂ nanotubes film was fabricated by anodization Ti film and annealed in air. The XRD analysis showed that anatase phase of TiO₂ nanotubes were formed and the film was transparent after annealing, Uv-vis spectra of the transparent TiO₂ nanotubes film presented an adsorption peak on 400nm wavelength.3)Investigate the electrochemical properties of TiO₂ nanotubes arrays by cyclic voltammetric and AC impedance spectra. For amorphous TiO₂ nanotubes, the electrode reaction shows an irreversible response. For TiO₂ nanotubes annealed in air, the peak current is linear to scan rate, showing a irreversible response with absorption. While for the TiO₂ nanotubes annealed in nitrogen, the CV results showed a quasi-reversible response with a potential separationΔEp 0.18V, the electron transformation constant is k 0 = 1 .87×10?3cm/s. The electrochemical impedance spectra showed that the electron transformation resistance Rct of TiO₂ nanotubes annealed in nitrogen was less 70% ⁸0% than the Rct of TiO₂ nanotubes annealed in air, this presented that the electrical conductivity of TiO₂ nanotubes annealed in nitrogen was much improved than TiO₂ nanotubes annealed in air.4)Coadsorbed of horseradish peroxidase (HRP) with thionine (Th) on TiO₂ nanotubes and fabricated the medium enzyme biosensor. The addition of H2O2 leads to the biocatalytic oxidation of the reduced thionine in the presence of HRP. The investigation of TiO₂ nanotubes biosensor for H2O2 presented that the sensitivity of TiO₂ nanotubes electrode annealed in nitrogen was 4-7 times higher than the sensitivity of as-grown TNT electrodes. This allows us to develop a novel H2O2 sensor with a detection range from 0.5×10-5M to 3.6×10-3M and the sensitivity 89μA/mM.5)Investigate the lithium ions intercalation for TiO₂ nanotubes annealed in nitrogen at different temperatures. The electrochemical measurement showed that 300°C annealed arrays exhibited the best performance with a high discharge capacity of 240 mAh/g in the first cycle at a high current density of 640 mA/g. Good cycling stability was also observed in 400°C annealed arrays: beginning with a discharge capacity of 163mAh/g, after 50 cycles, the capacity still remained at145 mAh/g. This great enhancement of discharge capacity and stability at high current density could be attributed to the large active surface area of the nanotube arrays, a short facile diffusion path for Li-ions and improved electrode charge transfer conductivity brought about by N2 annealing. MnO2 film was deposited by electrochemical method, the measurement of lithium ions intercalation was performed by CV and CP, the results were compared with the properties of TiO₂ nanotubes.