Electrochemical tuning of titania nanotube morphology in inhibitor electrolytes

Amrita Centre for Nanosciences, Amrita Institute of Medical Science & Research Centre, Amrita Vishwa Vidyapeetham, Elamakkara P O, Cochin 682 041, Kerala, India
Electrochimica Acta 01/2010; 55:3713. DOI: 10.1016/j.electacta.2009.12.096
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    ABSTRACT: Although one-dimensional anodic TiO2 nanotube arrays have shown promise as supercapacitor electrode materials, their poor electronic conductivity embarrasses the practical applications. Here, we develop a simple electrochemical doping method to significantly improve the electronic conductivity and the electrochemical performances of TiO2 nanotube electrodes. These TiO2 nanotube electrodes treated by the electrochemical hydrogenation doping (TiO2-H) exhibit a very high average specific capacitance of 20.08 mF cm−2 at a current density of 0.05 mA cm−2, ∼20 times more than the pristine TiO2 nanotube electrodes. The improved electrochemical performances can be attributed to ultrahigh conductivity of TiO2-H due to the introduction of interstitial hydrogen ions and oxygen vacancies by the doping. The supercapacitor device assembled by the doped electrodes delivers a specific capacitance of 5.42 mF cm−2 and power density of 27.66 mW cm−2, on average, at the current density of 0.05 mA cm−2. The device also shows an outstanding rate capability with 60% specific capacitance retained when the current density increases from 0.05 to 4.00 mA cm−2. More interestingly, the electrochemical performances of the supercapacitor after cycling can be recovered by the same doping process. This strategy boosts the performances of the supercapacitor, especially cycling stability.
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    ABSTRACT: The main objective of this study is to show the effect of TiO2 nanotube length, diameter and intertubular lateral spacings on the performance of back illuminated dye sensitized solar cells (DSSCs). The present study shows that processing short TiO2 nanotubes with good lateral spacings could significantly improve the performance of back illuminated DSSCs. Vertically aligned, uniform sized diameter TiO2 nanotube arrays of different tube lengths have been fabricated on Ti plates by a controlled anodization technique at different times of 24, 36, 48 and 72 h using ethylene glycol and ammonium fluoride as an electrolyte medium. Scanning electron microscopy (SEM) showed formation of nanotube arrays spread uniformly over a large area. X-ray diffraction (XRD) of TiO2 nanotube layer revealed the presence of crystalline anatase phases. By employing the TiO2 nanotube array anodized at 24 h showing a diameter ∼80 nm and length ∼1·5 μm as the photo-anode for back illuminated DSSCs, a full-sun conversion efficiency (η) of 3·5 % was achieved, the highest value reported for this length of nanotubes.
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    ABSTRACT: Here, we report on how the energy band diagram of a nanostructured semiconductor- metal interface aligns in accordance with semiconductor morphology. Electrochemically, titanium metal is anodized to form titanium dioxide nanotubes, which forms a junction with the free Ti substrate and this junction forms a natural Schottky barrier. With reduced dimensionality of the nanotube structures (lower wall thickness), we have observed band edge movements and band gap quantum confinement effects and lowering of the Schottky barrier. These results were corroborated with the help of cyclic voltammetry, ultraviolet-visible spectrometry, and impedance analysis. Current voltage analysis of the Schottky barrier showed a lowering of the barrier (by 25 %) with reducing dimensionality of the nanotube structures. At externally applied voltages higher than the Schottky barrier, charges can travel along the nanotubes and reside at an interface between the nanotubes and a high-κ dielectric. This property was utilized to develop high surface area solid-state capacitors.
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Sep 23, 2014