Mechanistic studies for depositing highly dispersed Pt nanoparticles on carbon by use of trimethyl(methylcyclopentadienyl)platinum(IV) reactions with O₂ and H₂

A fundamental understanding is developed for the chemical reaction mechanism that underlies platinum atomic layer deposition (ALD) on a carbon support, XC72R, for use as a fuel cell catalyst. Specifically, trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPtMe₃) was fed as the 1st reactant for ALD on high surface area particles using a well-instrumented fluidized bed reactor equipped with an in-line mass spectrometer. The precursor’s organic ligands were removed by reaction with the 2nd reactant, either oxygen or hydrogen. These experiments were performed on both unmodified and functionalized XC72R. Carbon modification involved reflux with nitric acid, which oxygenated the XC72R. Platinum weight loading, average particle size, and particle dispersion depended on carbon treatment and on the reactant used for ligand removal (oxygen or hydrogen). Deposited platinum particle sizes ranged from 2.6 to 6.7 nm. Transmission electron microscopy, chemisorption, and diffuse reflectance infrared Fourier transform spectroscopy were used to characterize the Pt deposition and carbon support functionalization. More discrete and non-agglomerated platinum nanoparticles were produced using hydrogen, rather than oxygen, as a reactant and when deposition was conducted on functionalized, rather than unmodified, XC72R carbon. The platinum nanoparticles are stabilized by the underlying oxygen added during substrate functionalization and the avoidance of carbon substrate combustion when using hydrogen, instead of oxygen, as the 2nd reactant to remove residual ligands.