Electrocatalytic Enhancement of Salicylic Acid Oxidation at Electrochemically Reduced TiO₂ Nanotubes

In this study, TiO 2 nanotubes were treated via electrochemical reduction and tested as a novel catalyst, for the first time, toward the electrochemical oxidation of salicylic acid (SA), where the effects of cathodic current and reduction time were systemically investigated. The fabricated TiO 2 nanotubes were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV), chronoamperometry, chronopotentiometry, ultraviolet–visible light (UV-vis) absorbance spectroscopy, and Mott–Schottky plots were employed to study the enhanced electrochemical activity of the TiO 2 nanotubes. Our experimental results revealed that the optimal electrochemical treatment conditions were −5 mA cm –2 for 10 min. The treated TiO 2 nanotubes possessed a much higher overpotential for oxygen evolution than a Pt electrode, and exhibited a high electrocatalytic activity toward the oxidation of SA. The oxidation of SA at the treated TiO 2 nanotubes was shown to be 6.3 times greater than a Pt electrode. Stability tests indicated that treated TiO 2 nanotubes are very stable over eight cycles of electrochemical oxidation of SA. The high electrocatalytic activity and stability of the treated TiO 2 nanotubes enabled by the facile electrochemical reduction can be attributed to the decrease of Ti(IV), the increase of Ti(II) and Ti(III), and the increase of the oxygen vacancies, as well as significant improvement of the donor density.