The semiconductor properties of titanium dioxide (TiO₂) offer an interesting alternative to convert sunlight into electrical energy by water splitting. This is because of its band gap, a high photogenerated charges mobility and the possibility to be doped both n-type and p-type. However, it has been found that charge recombination and low visible radiation sensitivity are the bottlenecks in the efficient solar energy conversion. Although in the last decade important advances in the synthesis of nanostructured morphologies with high interaction area like nanotubes have been achieved, the conversion efficiency growth has decreased. This is a logical result because there are intrinsic limitations imposed by the electronic properties of TiO₂.

One of the alternatives to modifying the TiO₂’s band gap and improving its photoactivity under visible light irradiation is to dope the nanotubes with transition metals. This option requires fabricating efficient nanostructured photoelectrodes with controlled morphology and specific properties able to offer a suitable surface area for metallic doping. Also, transition-metal oxides and hydroxides are frequently applied as low-cost water-splitting catalysts because they reduce the needed activation energy to overcome the kinetic barrier and increase the electrochemical reaction rate. There are thus important challenges and opportunities from the material science point of view that require a substantial effort for developing new knowledge and advancing in the controlled synthesis of this type of nanostructures. This research focuses on the synthesis and characterization of Ni doped titanium dioxide nanotubes (TNTs) for improving its photocatalytic activity in solar energy conversion applications. Initially, TNTs with controlled morphology were synthesized by two-step potentiostatic anodization of titanium foil. The anodization was carried out at room temperature in an electrolyte composed of ammonium fluoride, deionized water and ethylene glycol. Consequent thermal annealing of as-prepared TNTs was conducted in the air between 450 °C - 550 °C. Afterwards, the nanotubes were superficially modified by nickel deposition.

Studies of the morphology and crystalline phase of the samples, before and after nickel deposition, were carried out by SEM, EDS and XRD analysis. Determining the photoelectrochemical performance of photoelectrodes is based on typical electrochemical characterization techniques (OCP, EIS, LSV). Also, the morphological characterization associated electrochemical behavior analysis were discussed to establish the effect of nickel nanoparticles modification on the TNTs. The methodology proposed in this research allows using other transition metal for nanotube surface modification and studying new routes for improving the performance of low cost water-splitting catalysts.