Platinum–ruthenium bimetallic clusters on graphite: a comparison of vapor deposition and electroless deposition methods

Abstract

Bimetallic Pt-Ru clusters have been grown on highly ordered pyrolytic graphite (HOPG) surfaces by vapor deposition and by electroless deposition. These studies help to bridge the material gap between well-characterized vapor deposited clusters and electrolessly deposited clusters, which are better suited for industrial catalyst preparation. In the vapor deposition experiments, bimetallic clusters were formed by the sequential deposition of Pt on Ru or Ru on Pt. Seed clusters of the first metal were grown on HOPG surfaces that were sputtered with Ar(+) to introduce defects, which act as nucleation sites for Pt or Ru. On the unmodified HOPG surface, both Pt and Ru clusters preferentially nucleated at the step edges, whereas on the sputtered surface, clusters with relatively uniform sizes and spatial distributions were formed. Low energy ion scattering experiments showed that the surface compositions of the bimetallic clusters are Pt-rich, regardless of the order of deposition, indicating that the interdiffusion of metals within the clusters is facile at room temperature. Bimetallic clusters on sputtered HOPG were prepared by the electroless deposition of Pt on Ru seed clusters from a Pt(+2) solution using dimethylamine borane as the reducing agent at pH 11 and 40 °C. After exposure to the electroless deposition bath, Pt was selectively deposited on Ru, as demonstrated by the detection of Pt on the surface by XPS, and the increase in the average cluster height without an increase in the number of clusters, indicating that Pt atoms are incorporated into the Ru seed clusters. Electroless deposition of Ru on Pt seed clusters was also achieved, but it should be noted that this deposition method is extremely sensitive to the presence of other metal ions in solution that have a higher reduction potential than the metal ion targeted for deposition.

Deposition of copper from Cu(i) and Cu(ii) precursors onto HOPG surface: Role of surface defects and choice of a precursor

“…For Cu(hfac) 2 , although the particle height distribution has a similar range, more of the particles have the size over 4 nm compared to the experiments with the other precursor. The difference in nanoparticle size distribution may imply a difference in the reactivity of the Cu(hfac)VTMS and Cu(hfac) 2 precursors adsorbed on the surface, 14 which will be discussed in detail later. It should be pointed out that the average height can be affected by the slight difference in surface preparation for the two types of experiments; however, it seems unlikely since similar differences in nanoparticle size distributions were observed for at least 3 samples examined for each precursor molecule.…”

“…13 Despite the fact that the deposition processes on HOPG have in general received substantial attention recently, the majority of work targeted physical deposition methods that could deliver controlled amounts of metal to the surface. 7,14,15 In contrast to these methods, chemical vapor deposition (CVD) or atomic layer deposition (ALD) approaches can provide a more direct view of chemical reactivity of the HOPG defect sites and perhaps shed some light onto the chemical reactivity of the basal plane of this material with respect to deposition precursors. Among all the available metals used for practical supported catalysts, copper has a very prominent place, especially for a number of oxidation reactions.…”

“…The general approach of introducing defects on a graphite surface by sputtering to control metal deposition by evaporation 14,28 or by ozone for atomic layer deposition 29 has been tested previously. The work presented here will also take advantage of controlled sputtering/oxidation processes on HOPG to introduce specific defects.…”

Spontaneous selective deposition of iron oxide nanoparticles on graphite as model catalysts

“…[46][47][48] Metal seed sites could be used as a way to selectively deposit material using activated areas to plant nucleation sites for further growth assemblies of nanoparticles. Many groups have utilized physical vapor deposition via metal evaporation 47,[49][50][51][52][53][54][55][56] or electrodeposition to deposit metal nanoparticles on carbon supports. [57][58][59] Soluble metallic precursors have been used previously to deposit and reduce metal nanoparticles onto graphitic materials such as graphite, graphene and carbon nanotubes.…”

In situ thermolysis of Pt-carbonyl complex to form supported clean Pt nanoclusters with enhanced catalytic performance

“…Nanoclusters with a high volume/surface ratio and quantum effect have been proven to be efficient catalysts in various useful reactions. To date, several synthetic approaches have been developed to fabricate these small nanoparticles, including solution-phase reduction, gas-phase synthesis, and the ligand-assisted approach [25][26][27][28][29]. However, the fabrication of small nanoparticles is still challenging because of their severe aggregation, wide size distribution, low output, and low activity.…”