Enhanced photoelectrochemical properties of Ta-TiO2 nanotube arrays prepared by magnetron sputtering

In this paper, Ta-TiO2 nanotubes were prepared and characterized its photoelectrochemical performance. TiO2 nanotube arrays were prepared by anodic oxidation of Ti and then Ta was introduced on the surface by direct current magnetron sputtering, followed by an annealing process. The chemical composition, morphology and crystal structure of the Ta-TiO2 nanotubes were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), field-emission scanning electron microscopy (FESEM), X-ray photoemission spectroscopy (XPS), UV-vis diffuse-reflection spectra (DRS), photoelectrochemical measurements and electrochemical impedance spectroscopy (EIS). Highly-uniform nanotube arrays with anatase phase were confirmed by SEM images and XRD patterns, respectively. The light absorption is extended to larger wavelength with the presence of Ta according to UV-vis DRS. Samples with different Ta content were prepared by adjusting the sputtering time and an optimum Ta content in TiO2 was achieved with an improvement of photoconversion efficiency from 0.28% to 0.63%. The enhancement can be attributed to a decreased band gap, lower charge transfer resistance and higher charge carriers density, which was confirmed by EIS and Mott-Schottky measurements. This facile and environmentally-friendly technique can also be applicable for fabricating other metal-modified TiO2 nanotubes for potential use in water splitting.