Nanostructured TiO2 materials for energy and environmental applications

In the field of functional metal oxide nanostructures a particular interest is devoted to TiO2. Its unique chemical and physical properties, biocompatibility, availability and relatively low cost have justified the extensive use of this semiconductor. Combined with the recent progress in design, fabrication, and modification of nanostructured semiconductor materials, the ability to control the structure of TiO2 on the nanometer scale has opened new vistas and perspectives of technological applications in fields concerning the development of advanced materials for energy and solar fuel applications, either to produce hydrogen, or to power solar cells. [1,2] The anodic oxidation of titanium foils represents an attractive route to achieving, at low cost, TiO2 well-defined 1D and 2D structures, controllable on the nanometer scale. Ordered arrays of vertically aligned titania nanotubes are promising substrates as electrodes or components for the fabrication of electrochemical devices for a sustainable production of energy. For example, nanostructured TiO2 was successfully applied, by our research group, as water-splitting photocatalyst for hydrogen production in photoelectrochemical (PEC) reactors [2,3], as photo-anode in dye-sensitized solar cells, as gas sensing material in fuel-cell technology [4] and for safety and control purposes in fermentation processes [5]. Here we present the methodologies for the preparation, under anodic condition [6,7], of two types of thin film: supported on Ti and self-standing (see figure 1), both of them constituted by ordered arrays of vertically aligned TiO2 nanotubes. The characteristics of the obtained materials will be described together with their behavior as photoanodes or components for photoactive membranes used in photoelectrocatalytic (artificial leaf-type) devices to produce solar fuels (Hydrogen from water and alcohols from CO2).