Morphological, electrochemical and photoelectrochemical characterization of nanotubular TiO ₂ synthetized electrochemically from different electrolytes

The electrochemical synthesis of auto-organized TiO ₂ arrays generated by Ti anodization in different non-aqueous electrolytes was analyzed. Propylene carbonate-based electrolytes seem to be good electrolytic media for the controlled growth of titania nanotube structures. Scanning electron microscopy (SEM) analysis indicated that, depending on the media employed in the synthesis of the TiO ₂ nanotubes, different aspect ratios (length/diameter) could be obtained. Impedance analysis using the passive pit model gave the electrical properties of the layers during the different stages of nanotubes formation. Mott-Schottky analysis and the impedance results showed that the TiO ₂ nanotubes layers were n-type semiconductors with highly defective walls on top of a resistive barrier layer. Photoelectrochemical measurements showed that tetra(4-carboxyphenyl)porphyrin (TCPP) adsorbed onto the TiO ₂ nanotube arrays, which could be employed as an efficient photosensitizer for solar-energy conversion by TCPP-sensitized nanotubular TiO ₂ electrodes.