Spherical Core-Shell Titanium (Oxy) nitride@Nitrided Carbon Composites as Catalysts for the Oxygen Reduction Reaction: Synthesis and Electrocatalytic Performance

Aiming at the development of highly active and stable platinum-free catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs), we explored the potential of a new composite material, where the core-shell structure should result in a combination of high ORR activity and improved electric conductivity. TiOxNy@CnNm composite nanoparticles were prepared by covering uniform carbon spheres of about 300 nm in size, synthesized through the hydrothermal reaction of glucose, with a homogeneous titania shell made by sol-gel processing. The core-shell particles were then subjected to nitridation in ammonia vapor at different temperatures (550 degrees C-150 degrees C). The influence of the nitridation temperature on the structure and phase composition of the resulting composite particles was evaluated by a variety of techniques, including electron microscopy (SEM, TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), elemental analysis, thermogravimetric (TG) analysis, and N-2 sorption measurements, the electrochemical properties and the ORR performance of the materials were determined by rotating ring disk electrode (RRDE) measurements. Trends in the evolution of the structural/chemical properties and electrochemical/electrocatalytic properties as well as correlations between them are discussed; an optimized mesoporosity of the titanium (oxy) nitride shell was identified as the key criterion for the catalyst's ORR performance.