The Role of Substrate Surface Geometry in the Photo-Electrochemical Behaviour of Supported TiO2 Nanotube Arrays: A Study Using Electrochemical Impedance Spectroscopy (EIS)

Highly ordered TiO2 nanotube (NT) arrays grown on Ti mesh and Ti foil were successfully prepared by a controlled anodic oxidation process and tested for water photo-electrolysis. Electrochemical impedance spectroscopy (EIS), combined with other electrochemical techniques (cyclic voltammetry and chronoamperometry) in tests performed in the dark and under illumination conditions, was used to correlate the photoactivity to the specific charge transfer resistances associated with a 3D (mesh) or 2D (foil) geometry of the support. The peculiar structure of the nanotubes in the mesh (with better light absorption and faster electron transport along the nanotubes) strongly impacts the catalytic performances under illumination. H-2 production and current density in water photo-electrolysis were over three times higher with the TiO2NTs/Ti mesh, compared to the foil in the same conditions. The results obtained by the EIS technique, used here for the first time to directly compare TiO2 nanotubes on two different supports (Ti foil and Ti mesh), led to a better understanding of the electronic properties of TiO2 nanotubes and the effect of a specific support on its photocatalytic properties.