Cation Effect on the Electrochemical Formation of Very High Aspect Ratio TiO2 Nanotube Arrays in Formamide−Water Mixtures

Abstract

Highly ordered TiO2 nanotube arrays are of considerable interest for their use as gas sensors, materials for water photoelectrolysis, and as photoanodes in dye sensitized solar cells. For example, under UV illumination highly ordered TiO2 nanotube arrays ≈35 μm in length achieve a light-to-chemical energy photoconversion efficiency of 16.25% [M. Paulose et al., J. Phys. Chem. B 2005, 110, 16179−16184]. It is now well-established that the properties of the nanotube arrays are dependent upon their specific architecture, including nanotube array length, wall thickness, pore diameter, and tube-to-tube spacing. In this work we investigate the effect of five different cationic species on the formation of TiO2 nanotube arrays by potentiostatic anodization of titanium in formamide−water mixtures containing fluoride ions. We find the cation choice to be a key parameter influencing both the nanotube growth rate and resulting nanotube length. The length and aspect ratio of the nanotubes increases with increasing cat...