Platinum nanoparticles supported on nitrogen-doped carbon for ammonia electro-oxidation

Pt nanoparticles supported on carbon (Pt/C) and nitrogen-doped carbon (Pt/NC) were prepared by an alcohol-reduction process and used for ammonia electro-oxidation in alkaline media. Nitrogen-doped carbons were prepared by thermal treatment of urea and Carbon Vulcan XC72 at 800 °C under argon atmosphere. The obtained materials showed the presence of face centered cubic structure of Pt and mean particle sizes in the range of 3-3.7 nm. X-ray photoelectron spectroscopy results revealed that Pt/NC 5 (carbon prepared with 5% of urea) presents more Pt on the surface than Pt/C, and the nanoparticles are predominantly in the metallic state. The electrocatalytic activity was investigated by cyclic voltammetry and chronoamperometry experiments. Pt/NC materials showed a higher electrocatalytic activity for ammonia electro-oxidation than Pt/C, whereby the material Pt/NC 5 showed the peak current density 161% higher than Pt/C. The increase of activity might be related to the high electrochemically accessible area of Pt/NC and the improvement on the interaction with water due to the nitrogen onto the support which could contribute to the oxidation of intermediate products from ammonia electro-oxidation.