This work is intended to define a new possible methodology for the TiO2 doping through the use of an electrochemical deposition of cobalt directly on the titanium nanotubes obtained by a previous galvanostatic anodization treatment in an ethylene glycol solution. This method does not seem to cause any influence on the nanotube structure, showing final products with news and interesting features with respect to the unmodified sample. Together with an unmodified photoconversion efficiency under UV light, the cobalt doped specimen reports an increase of the electrocatalytic efficiency for the oxygen evolution reaction (OER). 1. Introduction The publication of the fundamental work of Gong et al. [1], in which the authors created the basis for the development of a new synthesis model for the titania nanotubes based on the anodic oxidation of a titanium foil in fluoride based solutions, opened the way to a new methodology able to combine a simplicity of preparation of the material with a complete control of physical characteristics of the nanosystem [2–5]. Besides, its particular geometric shape is particularly appropriate for application as photo-anode in the photo-electrolysis of water [6]. For this reason, many studies have been directed towards this field, obtaining elevated values of UV photoconversion efficiency for these nanosystems [7, 8]. In the meanwhile, a large range of different applications for this material has been discovered. In fact, for example, it is reported that the electrical resistance of the titania nanotubes was highly sensitive to the chemisorbed hydrogen molecules hydrogen sensing [9, 10], creating a new route in the hydrogen sensing research field [11, 12]. But many other similar examples of the wide versatility of the TiO2 nanotube arrays are available in literature, as the dye-sensitized solar cells [13–17], lithium batteries [18], and also in different biological and medical researches, like the osteoblast growth [19–22] or drug elution [23–25]. As regards the application of the TiO2 nanotube arrays as photo-electrodes for water photoelectrolysis, it is important to emphasize that although many important results have been reached in this field, the commercialization of such nanosystem is still far because of the high band gap of titania, which limits the light adsorption only to limited UV region [6]. In addition, also the titania electrocatalytic activity for the OER is very low if compared with that obtained on conventional metallic electrodes (Pt, Ni, etc.). These problems limit the use of this material due to the low
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