Anodic TiO_2 nanotube supercapacitors enhanced by a facile in situ doping method

摘要

In this work, the capacitive properties of anodic TiO_2 nanotubes were enhanced by a facile in situ doping method. The tuning of TiO_2 anodization was realized by adding Fe(NO_3)_3 into the aqueous HF solution as the dopant. The morphology, structure, chemical composition and capacitive properties of the as-prepared TiO_2 nanotubes were characterized by various methods. It is found that N, F, and Fe elements can be doped into TiO_2 nanotubes during the anodization process. The effect of doping concentration on the capacitive properties of TiO_2 nanotubes was also investigated. With the optimum doping concentration of ～ 0.02 M, the doped TiO_2 nanotubes exhibited a capacitance of 1.11 mF cm~(-2) at the scan rate of 100 mV s~(-1), much higher than that of the undoped TiO_2 nanotubes. The X-ray photoelectron spectroscopy (XPS) results indicated the presence of N, F, and Fe in the TiO_2 lattice and absorbed F on the TiO_2 surface, both of which are believed to be the cause for the capacitance enhancement of the doped TiO_2 nanotubes.