TiSi₂O_x Coated N‑Doped Carbon Nanotubes as Pt Catalyst Support for the Oxygen Reduction Reaction in PEMFCs

Composite nanostrucutres of TiSi₂O_x coated nitrogen-doped carbon nanotubes (NCNTs) were synthesized by a combination of chemical vapor deposition (CVD) and magnetron sputtering processes. The synthesized nanostructures were used as supports for Pt catalyst for oxygen reduction reaction (ORR) in proton exchange memberane fuel cells (PEMFCs). An amorphous layer of TiSi₂O_x with controlled thicknesses was sputtered on NCNTs and followed by post-treatment at high temperature (1000 °C, <i>An</i>-TiSi₂O_x-NCNTs), inducing TiO₂ nanoparticles of around 5 nm in diameter embedded in the amorphous layer. Further analyses via X-ray absorption spectroscopy of the Ti K edge and Si K edge revealed the Ti atoms were in a TiO₂ rutile environment and the Si atoms were in a SiO₂ environment. Pt nanoparticles with an average diameter of 3 nm were deposited on the composite support, and their electrochemical behaviors toward ORR were studied. It was revealed that, even with lower electrochemical surface area (ECSA), Pt/<i>An</i>-TiSi₂O_x-NCNTs showed better catalytic activity toward ORR than Pt/NCNT catalysts. The origin of enhanced activity of Pt/<i>An</i>-TiSi₂O_x-NCNTs was examined by high resolution transmission electron microscopy (HRTEM) and the X-ray absorption near edge structure spectra (XANES) of the deposited Pt nanoparticles