Noncrystalline Titanium Oxide Catalysts for Electrochemical Oxygen Reduction Reactions.

Titanium oxides crystals are widely used in a variety of fields, but little has been reported on the functionalities of noncrystalline intermediates formed in their structural transformation. We measured the oxygen reduction reaction activity of titanium oxide nanoparticles heat-treated for a different time and found that the activity abruptly increased at a certain time of the treatment. We analyzed their structures by using X-ray pair distribution functions with the help of high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy and ascertained that the abrupt increase in the activity corresponded to a structural transformation from a reduced lepidocrocite-type layered titanate to a disordered structure consisting of domains of brookite-like TiO octahedral linkages.

Zirconium Oxynitride-Catalyzed Oxygen Reduction Reaction at Polymer Electrolyte Fuel Cell Cathodes.

Most nonplatinum group metal (non-PGM) catalysts for polymer electrolyte fuel cell cathodes have so far been limited to iron(cobalt)/nitrogen/carbon [Fe(Co)/N/C] composites owing to their high activity in both half-cell and single-cell cathode processes. Group IV and V metal oxides, another class of non-PGM catalysts, are stable in acidic media; however, their activities have been mostly evaluated for half-cells, with no single-cell performances comparable to those of Fe/N/C composites reported to date. Herein, we report successful syntheses of zirconium oxynitride catalysts on multiwalled carbon nanotubes, which show the highest oxygen reduction reaction activity among oxide-based catalysts.