A short review on electrochemically self-doped TiO2 nanotube arrays: Synthesis and applications

Electrochemically self-doped TiO 2 nanotube arrays (known as reduced TiO 2 nanotube arrays, r -TiO 2 NTAs) are currently drawing great attention as emerging and promising materials for energy and environmental applications as they exhibit highly enhanced electrochemical properties, such as good capacitive properties and electro- and photocatalytic activity when compared to pristine TiO 2 NTAs. Such enhanced properties are attributed to the introduction of trivalent titanium (Ti (III) ) as a self-dopant in the lattice of pristine TiO 2 NTAs through simple electrochemical reduction. However, in spite of the great interest in, and potential of this material, there is no comprehensive review on the synthesis and applications of r -TiO 2 NTAs. Therefore, in this review, we critically and briefly review r -TiO 2 NTAs in terms of the electrochemical self-doping mechanism, their functional features, and various applications including photolysis, dye-sensitized solar cells (DSSCs), biomedical coatings and drug delivery. In addition, to better understanding r -TiO 2 NTAs, pristine TiO 2 NTAs are briefly introduced. Furthermore, this review proposes future research directions with major challenges to be overcome for the successful development of r -TiO 2 NTAs, such as to standardize matrices for performance evaluation, to confirm the organic degradation performance as anode, and to improve mechanical stability.