3D nanoporous titania formed by anodization as a promising photoelectrode material

Nanoscale control of the growth of inorganic metal oxides determines their structures and properties, and leads to development of novel nanostructured materials with fundamental and practical importance from a point of view their further applications. After anodic aluminum oxide, the next nanoporous material which has attracted tremendous interest of researchers around the world, is nanoporous anodic titanium oxide (ATO) formed by anodization. The main objective of this work was to investigate the ability of formation of anodic titanium oxide structures, particularly in the form of TiO2 nanopore arrays on 3D titanium substrates (Ti mesh) in viscous electrolyte containing fluoride ions. Three-dimensional (3D) TiO2 nanopore arrays grown on Ti mesh were prepared via two-step electrochemical anodization process, and the effect of anodizing potential and duration of the process on the formation of ATO layers on titanium mesh were investigated. The 3D TiO2 nanopore arrays on Ti mesh were characterized by using field emission scanning electron microscopy and X-ray diffraction (XRD) technique. The results showed that the optimized anodization conditions for preparation of titanium dioxide nanopore arrays are 40 and 50 V of the applied potential, and 10 min of time processing. The effect of annealing temperature of ATO layers on their morphology and phase composition was also investigated in detail. The amorphous ATO layers on titanium mesh transform to anatase phase at 400 degrees C and further to rutile phase at 600 degrees C. However, photoelectrochemical tests demonstrated that the best photoelectrochemical performance of fabricated 3D photoanodes was observed for the samples anodized at 40 V or 50 V for 10 min, and annealed at 400 degrees C. The photoelectrochemical properties of the mesh-based and typical plate TiO2/Ti electrodes were compared. It was found that the higher photoconversion efficiency was observed for the 3D TiO2/Ti mesh electrode than for a typical plate TiO2/Ti electrode. It is expected that anodizing of three dimensional (3D) Ti substrates will offer an opportunity to enhance various properties of anodic titanium oxide, especially its photoactivity.