Highly-Ordered Magnéli Ti4O7 Nanotube Arrays as Effective Anodic Material for Electro-oxidation

Pure Magnéli Ti4O7 nanotube arrays (NTA) were successfully fabricated by reducing TiO2 NTA with hydrogen at 850 °C for 30 minutes. The microstructure, composition and electrochemical behavior of the prepared Ti4O7 NTA were characterized by means of X-ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy, Cyclic Voltammetry and Electrochemical Impedance Spectroscopy. The as-prepared Ti4O7 NTA had a highly-ordered tubular structure with high crystallinity, large electrochemical window of water electrolysis (2.4 V vs. Ag/AgCl, pH = 6.0) and low interfacial charge transfer resistance when they were employed as anode for electro-oxidation. Phenol was electro-oxidized on Ti4O7 particles and Ti4O7 NTA with the latter giving 20% more Chemical Oxygen Demand (COD) removal. Pure Ti4O7 NTA also displayed larger degradation coefficient as well as higher COD removal and current efficiency than Boron-doped Diamond and other types of Magnéli NTAs. Cathodic polarization was found to be an effective way of restoring the electrochemical performance of oxidized Ti4O7 NTA as an anode.