Evidence for the formation of nitrogen-rich platinum and palladium nitride nanoparticles

We report evidence for the formation of nitrogen-rich precious metal nanoparticles (Pt, Pd) prepared by reactive sputtering of the pure metal in a N₂ plasma. The composition of the nanoparticles varies as a function of particle size and growth conditions. For the smallest particles the nitrogen content appears to be as high as 6.7 N atoms for each Pd atom or 5.9 N atoms for each Pt atom whereas bulk films have nominal compositions of Pt_7.3N and Pd_2.5N. The unusually large N content in the nanoparticles is balanced with H. The nanoparticles are metastable in air and moisture, slowly decomposing over several years. The catalytic properties of these N-rich nanoparticles were accessed by rotating disk electrode electrochemical studies, the liquid phase oxidation of benzyl alcohol, and gas phase CO oxidation, and support the experimental evidence for the materials composition.