Preparation and characterization of Nb-doped TiO2 nanoparticles used as a conductive support for bifunctional CuCo2O4 electrocatalyst

Nb-doped TiO2 powders with various Nb contents (0%, 5% and 10%) were prepared using a sol-gel process and annealed at 450, 650 and 1050 degrees C with the aim to be used as a conductive support for bifunctional electrocatalysts in rechargeable metal-air batteries, substituting the more conventional carbon particles which slowly corrode at high potentials during cell recharge. X-ray diffraction analyses revealed that niobium hinders the anatase-rutile transformation and prevents the grain growth, which is important to achieve a conductive support with high specific surface area. X-ray photoelectron spectroscopy measurements have shown that the powders possess surface Ti(4+)and Nb(4+)species, and that the Nb0.05Ti0.95O2 (1050 degrees C) sample also contains Ti3+ and Nb5+ ions. Composite film electrodes containing CuCo2O4 particles (60 w/w%), Nb0.05Ti0.95O2 or Vulcan XC72R or Ebonex powder (25%), and poly(vinylidene fluoride-co-hexafluoropropylene) (15%) were formed on the glassy carbon disk surface of a rotating ring-disk electrode and studied for both the O-2 evolution and O-2 reduction reactions in 1 M KOH solution and O-2-saturated 1 M KOH solution, respectively. Rutile Nb0.05Ti0.95O2 (1050 degrees C) powder was chosen owing to its larger overpotential for H-2 evolution (detrimental to the performance of bifunctional electrodes) and its low and stable anodic activity, whereas anatase Nb0.05Ti0.95O2 (450 degrees C) powder was mainly selected due to its higher specific surface area. The results have shown that the Nb0.05Ti0.95O2 powders are more suitable than Vulcan XC72R for use as a conductive support material, based oil the higher electrode intrinsic current densities recorded for O-2 evolution and reduction reactions. Crown Copyright (C) 2007 Published by Elsevier B.V. All rights reserved.