Facile Preparation and High Activity of TiO2 Nanotube Arrays toward Oxygen Reduction in Alkaline Media

Four TiO2 electrodes have been investigated for the oxygen reduction reaction (ORR) in 2 M NaOH. Anodic oxidation of Ti-foil was used as the final or the first step in the preparation of four electrodes based on TiO2: amorphous (Ti/AM-TiO2), two anatase forms (Ti/A400-TiO2 and Ti/A550-TiO2), and, finally, lithium-anatase form (Ti/A-Li0.25TiO2), all of them obtained as TiO2 nanotube arrays. The electrodes' structure was examined by Raman spectroscopy. Cyclic voltammetry and chronoamperometry were employed for the study of kinetics of ORR. Ti/A-Li0.25TiO2 and Ti/A400-TiO2 electrodes showed the highest catalytic activity for ORR with the highest cathodic peak current density and the lowest Tafel slope values. Number of electrons exchanged during ORR at TiO2 electrodes was in the range from 2.3 to 2.8. Additionally, TiO2 electrodes showed good stability as well as acceptable selectivity in the presence of borohydride, methanol or ethanol as typical fuels for fuel cells. Thus this study introduces a simple, low-cost preparation route of TiO2-based electrodes with high efficiency for ORR for energy conversion and storage applications. (C) The Author(s) 2018. Published by ECS.