Effect of fluoride-mediated transformations on electrocatalytic performance of thermally treated TiO2 nanotubular layers

Abstract

The peculiarities of morphology, crystalline structure and chemical composition of TiO2 nanotubular layers (TNT) and TiO2 nanoparticulate (NP) layers obtained by fluoride-mediated transformation of TNT have been described in the present paper. The annealing of amorphous TNT in a confined space under limited air access conditions leads to TNT-to-NP transformation accompanied by fluorine doping of the titania matrix as supported by X-ray photoelectron spectroscopy investigations. The collapse of tubular structure as well as the formation of nanoparticles was confirmed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. Electrocatalytic activity of both TNT and NP electrodes toward oxygen reduction reaction (ORR) has been examined by cyclic voltammetry (CV). The positive shift of ORR wave of the NP layers in comparison with TNT makes the NP-based electrodes more suitable for oxygen reduction. The improved activity of the NP electrodes is attributed to the increased concentration of redox active Ti3+ species owing to fluorine doping of TiO2 which plays a crucial role in electoreduction of oxygen molecules.