An Experimental Insight into the Structural and Electronic Characteristics of Strontium-Doped Titanium Dioxide Nanotube Arrays

The possibility of in situ doping during electrochemical anodization of titania nanotube arrays is demonstrated and the mechanism and variations in structural and electronic characteristics of the nanotube arrays as after doping is systematically explored. In the presence of strontium as the dopant, bulk analysis shows strontium mainly incorporated into the lattice of TiO2. Surface analysis, however, reveals phase segregation of SrO in the TiO2 matrix at high Sr doping levels. The near edge X‐ray absorption fine structure (NEXAFS) spectroscopy analysis reveals that Sr2+ doping only alters the Ti and O ions interaction in the TiO2 lattice on the surface with no effect on their individual charge states. An in‐depth understanding of the dopant incorporation mechanism and distribution into TiO2 nanotube arrays is achieved using high resolution transmission electron microscopy (HRTEM) and the high angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) coupled with the electron energy loss spectroscopy (EELS) measurements on the surface and bulk of the nanotubes. Upon their use to photoelectrochemically split water, the Sr‐doped TiO2 nanotube film shows incident photon conversion efficiencies (IPCE) as high as 65%. The enhanced light activity in conjunction with the ordered one‐dimensional morphology makes the fabricated films promising candidates for water photoelectrolysis. Doping mechanism and the induced structural changes/defects in the bulk and surface of in situ synthesized strontium‐doped titania (Sr‐doped TiO2) nanotube arrays are systematically studied. Here, surface and bulk characterization of the doped nanotubes, which enables reliable identification of success or failure, uniformity, and the mechanism of divalent doping along the nanotube axisandin the radial direction, is reported.