Comparison of Photoelectrochemical and Electrochemical Properties of TiO2 Nanotube Arrays Crystallized by Hydrothermal and Annealing Methods

Abstract

Well aligned TiO2 nanotube arrays (NTAs) were prepared by anodic oxidation on Ti sheet and were crystallized by hydrothermal and annealing methods. The differences of structures and morphologies between TiO2 NTAs crystallized by the two methods were examined by X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Comparison of photoelectrochemical and electrochemical properties of TiO2 NTAs crystallized by the two methods was performed by measuring the photocurrents and cyclic voltammograms. Both methods can achieve the crystallization of TiO2 nanotubes. However, the structures, photoelectrochemical and electrochemical properties of samples crystallized by the two methods were much different. Compared with thermal annealing method, hydrothermal method can achieve finer anatase crystals, but has a destructive effect on the structure of ordered nanotube array to some extent, which results in the increase of electrochemical activity and the decrease of photoelectrochemical properties. Reasons for the sharp decrease of photocurrent are discussed by comparing the optical absorption properties and nanotubes structures between TiO2 NTAs crystallized by the two methods. The mesoporous structures and the existence of noncrystalline TiO2 are believed to be responsible to the sharp decrease of photoelectrochemical properties of hydrothermally crystallized TiO2 nanotubes.