Synthesis of Platinum Nanoparticles by Plasma Sputtering onto Glycerol: Effect of Argon Pressure on Their Physicochemical Properties

Platinum nanoparticles (Pt NPs) were synthesized in glycerol as a liquid substrate via a magnetron sputtering method at different argon pressures (1.0, 4.0, and 9.0 Pa). Then, Pt NPs were deposited onto a Vulcan XC-72 powder to form carbon-supported Pt NPs catalysts. Molecular dynamics (MD) simulations were carried out using parameters mimicking the deposition conditions of Pt in plasma sputtering experiments to determine key parameters for the growth of Pt NPs and to understand the growth mechanism at the atomic scale. MD simulations showed that Pt NPs growth depended on the kinetic energy of Pt atoms arriving onto the liquid substrate, which is related to the argon (Ar) pressure. The Pt NPs obtained for different Ar pressures and dispersed in glycerol were characterized by small-angle X-ray scattering (SAXS) to investigate the Ar pressure effect on Pt NPs size. Independently on the Ar pressure, SAXS results revealed the presence of two NPs populations. The first population is composed of isolated small NPs with an average diameter increasing from 1.8 to 3.2 nm with the pressure. Transmission electron microscopy (TEM) analysis performed on carbon-supported Pt NPs (Pt NPs/C) displayed the same diameter evolution, but the Pt NPs diameters were found to be slightly larger (from 2.5 to 3.7 nm) than those obtained by SAXS in glycerol. Both SAXS and TEM measurement revealed a second population of larger nano-objects that could correspond to agglomerates of individual small NPs from the first population formed either during the deposition in the liquid bulk or more probably at the liquid surface. The electrochemical behavior of the Pt NPs/C catalysts was studied in a conventional three-electrode electrochemical cell at room temperature in a N2-saturated 0.50 mol L–1 H2SO4 electrolyte. It was shown that the Pt NPs size increased with argon pressure, which further led to a decrease of the Pt electrochemical surface area.