Influence of Anodic and Thermal Barrier Layers on Physicochemical Behavior of Anodic TiO2 Nanotubes

Abstract

Electrochemical and photo-electrochemical behavior of self-organized TiO2 nanotubes formed in organic solvents have been studied by taking into account the formation of new barrier layers beneath nanotubes either due to the anodic polarization in aqueous solutions or air exposure during high temperature annealing. It has been shown that before annealing, electrochemical and photoelectrochemical answers are dominantly controlled by the physicochemical properties of the anodic barrier layer. Annealing in air at sufficiently high temperatures changes the initial amorphous structure of as-prepared nanotubes and forms a new oxide layer below them due to thermal oxidation of underneath titanium. Affixing tube bottoms to the substrate during annealing, which forms a better electrical contact, can play an important role in collecting a higher photoresponse from annealed nanotubes. In order to improve TiO2 nanotubes performance the role of the new anodic or thermal layers, bridging nanotubes and metal substrate, has to be considered.