Spray deposition followed by sintering of nickel oxide (NiO (x) ) nanoparticles (average diameter: 40 nm) has been chosen as method of deposition of mesoporous NiO (x) coatings onto indium tin oxide (ITO) substrates. This procedure allows the scalable preparation of NiO (x) samples with large surface area (similar to 10(3) times the geometrical area) and its potential for applications such as electrocatalysis or electrochemical solar energy conversion, which require high electroactivity in confined systems. The potential of these NiO (x) films as semiconducting cathodes for dye-sensitized solar cell (DSC) purposes has been evaluated for 0.3-3-mu m-thick films of NiO (x) sensitized with erythrosine B (ERY). The electrochemical processes involving the NiO (x) coatings in the pristine and sensitized states were examined and indicated surface confinement as demonstrated by the linear dependence of the current densities with the scan rate of the cyclic voltammetry. Cathodic polarization of NiO (x) on ITO can also lead to the irreversible reduction of the underlying ITO substrate because of the mesoporous nature of the sintered NiO (x) film that allows the shunting of ITO to the electrolyte. ITO-based reduction processes alter irreversibly the properties of charge transfer through the ITO/NiOx interface and limit the range of potential to NiO (x) coatings sintered for DSC purposes.