Abstract
Herein, highly ordered TiO2 nanotube (NT) arrays on a Ti substrate is synthesized in a fluoride‐containing electrolyte, using the electrochemical anodization method, which yields amorphous oxide tubes. The effects of different thermal annealing profiles for the crystallization of the amorphous TiO2 NTs are studied. It is found that the temperature ramping rate has a significant impact on the magnitude of the resulting photocurrents (incident photon‐to‐current conversion efficiency [IPCE]) from the tubes. No appreciable changes are observed in the crystal structure and morphology of the TiO2 NTs for different annealing profiles (to a constant temperature of 450 °C). The electrochemical properties of the annealed TiO2 NTs are investigated using intensity‐modulated photocurrent spectroscopy (IMPS), open‐circuit potential decay, and Mott–Schottky analysis. The results clearly show that the annealing ramping rate of 1 °C s−1 leads to the highest IPCE performance. This beneficial effect can be ascribed to a most effective charge separation and electron transport (indicating the least amount of trapping states in the tubes). Therefore, the results suggest that controlling the annealing ramping rate is not only a key factor affecting the defect structure but also a powerful tool to tailor the physical properties, and photocurrent activity of TiO2 NTs.
Highlights
The results clearly show that the annealing ramping rate of 1 C sÀ1 leads to the applications in gas sensors, lithium-ion batteries, dye-sensitized solar cells, environmental purpose, hydrogen production, organic light-emitting diodes, and photovoltaic energy production.[3,4,5,6,7,8,9,10] 1D structures, especially nanotubes (NTs), have highest IPCE performance
The anodized TiO2 NTs were annealed at 450 C for 1 h in air at different ramping/heating rates.[39]
The IPCE data were further plotted for the evaluation of the bandgap (Eg) of TiO2 NTs annealed at 450 C for 1 h in air for different ramping/heating rates
Summary
The obtained titanium foil was cut into 1.5 Â 1.5 cm pieces and cleaned with acetone, ethanol, and DI water using sonication for 30 min followed by drying in a nitrogen (N2) stream. The highly ordered TiO2 NTs were synthesized using a two-electrode potentiostatic electrochemical cell configuration with a platinum electrode as a cathode and titanium foil (1.5 Â 1.5 cm2) as an anode, which was mounted at the bottom of the cell. After completion of the anodization experiment, the samples were washed with ethanol and DI water followed by drying in an N2 stream. To see the effect of annealing temperature and time, we annealed all samples at different ramping/heating rates. The samples were annealed at 50, 10, 1, and 0.1 C ramping rates with different heating times such as 9, 43, 430, and 4300 s, respectively, and named as T-50, T-10, T-1, and T-0.1, respectively
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