PtRu Alloy Nanoparticles I. Physicochemical Characterizations of Structures Formed as a Function of the Type of Deposition and Their Evolutions on Annealing

Abstract

We have physicochemically characterized the formation of PtRu nanoparticles, deposited by evaporation onto highly oriented pyrolytic graphite, using in situ X-ray photoelectron spectroscopy, ex situ high-angle annular dark-field/scanning transmission electron microscopy, electron energy loss spectroscopy, and time-of-flight secondary ion mass spectrometry. We used three different orders of metal deposition: Pt evaporated onto Ru, Ru evaporated onto Pt and both metals evaporated simultaneously, and then followed the evolutions of the alloys as a function of annealing temperature. The C 1s, O 1s, Ru 3d, and Pt 4f core level spectra were employed to describe the alloying interactions between the metals. For all deposition methods, Ru diffuses to the NP surface through the Pt, and not the reverse. Each of the preparation methods produces surface and volume structures that differ from those of the others, even after prolonged annealing at temperatures over 700 °C, indicating the source of confusion in the literature concerning the physicochemical characterization of PtRu nanoparticles.

PtRu Alloy Nanoparticles. 2. Chemical and Electrochemical Surface Characterization for Methanol Oxidation

“…As in our previous Ru study on HOPG, the metals do not wet the carbon paper, causing the deposit to retract and form NPs. In addition, TOF-SIMS, high-angle annular dark-field scanning transmission electron microscopy (HAADF/STEM), and electron energy loss spectroscopy (EELS) on PtRu NPs showed that all the samples begin to form alloys on deposition, due to the high heats of condensation of Pt and Ru (∼5 and ∼6 eV, respectively). In both photomicrographs, many NPs are in contact because of their high number density.…”

“…(Whether or not the anodic peak, seen during the reverse scan, is related to the removal of incompletely oxidized carbonaceous species is still debatable. 2,17−22 ) Although the value of the ratio for annealed deposit 2 is higher than that for the unannealed deposit, its peak areas are much smaller (Figure 3a,b and Table 1), and XPS 12 reveals that annealing has resulted in the deposition of surface hydrocarbon. This deposit may block active catalytic sites on the NP surface.…”

“…Core level spectra were obtained for the Ru 3d, Pt 4f, C 1s, and O 1s electron emissions, and valence band (VB) spectra were obtained for the Ru 4d, Ru 5s, Pt 5d, and Pt 6s emissions. The core level spectra were discussed in our previous paper; 12 the VB spectra are discussed here.…”

“…Following our earlier studies , of pure Ru and Pt NPs deposited onto HOPG, we prepared PtRu bimetallic materials on a carbon paper substrate, using the three different orders of deposition of the two metals employed in our investigation of NPs deposited onto HOPG: Pt was evaporated onto previously deposited Ru (deposit 1), the two metals were evaporated simultaneously (deposit 2), and Ru was evaporated on previously deposited Pt (deposit 3). All the evaporations were carried out in the preparation chamber of a VG ESCALab 3 MARK II XPS spectrometer (Thermo VG Scientific), at a pressure of <3 × 10 –8 Torr, using a Quad-EVC evaporator (Mantis Deposition, Ltd.) containing high purity Ru and Pt rod targets (American Elements) and a tungsten filament electron-beam source.…”

Colloidal bimetallic platinum–ruthenium nanoparticles in ordered mesoporous carbon films as highly active electrocatalysts for the hydrogen evolution reaction

“…H 2 /Ar) might induce Pt-nanoclusters to appear on the surface of the PtRu alloy NPs. 60 The electronic structure of the surface Ptatoms is changed by neighbouring Ru-atoms, which weakens the hydrogen adsorption energy. 19,61,62 Density functional (DFT) calculations of metal surfaces show synergistic effects (strain and ligand effects) when adjacent M-atoms are present alongside Pt-atoms.…”