Effect of Synthesis Conditions on the Physical and Electrocatalytic Properties of Ru@Pt Nanoparticles

Abstract

A first-time comparison of carbon-supported Ru@Pt core@shell nanoparticles (NPs) with varying Pt shell coverages (0−3 monolayers, ML), synthesized by two different methods, was carried out. This includes the polyol method ("Method I"), where a suspension of NPs (plus stabilizer) is exposed to vulcan carbon (VC) powder particles to attach them to the surface, as well as a "stabilizer-free" method ("Method II"), involving the reduction (using ethanol) and direct nucleation of Ru core NPs on the carbon surface, followed by thermal annealing and then Pt shell deposition. It is shown that for both Methods I and II, the Ru/Pt ratios in the NPs could be controlled by the ratio of metal precursors in the synthesis solution. NPs produced using either Method I or Method II exhibited Ru@Pt core@shell structures, with a controllable Pt shell coverage, as confirmed by scanning transmission electron microscopy and electron energy loss spectroscopy analyses. NPs produced by Method I were smaller (3−4 nm), more spherical in shape, contained a residual stabilizer, and were more agglomerated than Method II NPs (4−6 nm). X-ray diffraction analysis showed that Method I NPs were also more amorphous, while the thermal annealing step in Method II was critical to obtaining highly crystalline Ru cores when compared to their nonannealed analogues. By tuning the composition, size, and Pt shell coverage of both types of Ru@Pt NPs, it was shown that Method II NPs with annealed Ru cores were more electrocatalytically active than their nonannealed analogues and Method I NPs.

Microwave-Assisted Scalable Synthesis of Pt/C: Impact of the Microwave Irradiation and Carrier Solution Polarity on Nanoparticle Formation and Aging of the Support Carbon

“…However, for synthesis of Pt/C, such a process has not been explored in detail. The typical polyol process of Pt/C synthesis involves reduction of Pt on carbon using a high boiling point poly alcohol such as ethylene glycol (EG) in basic media at temperatures ranging between 150 and 180 °C. ,,, However, for scalability, mild synthesis conditions including the minimized use of chemicals such as EG, lower reaction temperature, ambient pressure, etc., are important. In our previous studies, MW-assisted Pt/C synthesis using a mixture of water and EG (30 vol % EG) as the reducing agent and the carrier solution was explored.…”

Efficient Oxidation of Ethanol at Ru@Pt Core-Shell Catalysts in a Proton Exchange Membrane Electrolysis Cell

“…alloying with Ru or surface modification) is still required to remove strongly adsorbed CO that causes high anode overpotentials. 8,9 Deposition of a few monolayers of Pt onto a more active metal such as Ru to create core-shell nanoparticles (Ru@Pt) [10][11][12] can decrease the overpotential relative to Pt, 13,14 while improving selectivity for CO 2 formation relative to PtRu alloys. 14 Ligand and lattice strain effects that result from interactions between the Pt shell and Ru core weaken the bonding of CO to the Pt surface.…”

“…15,16 As a result, Ru@Pt catalysts have recently been used for the electrochemical oxidation of organic fuels, including methanol 14,[17][18][19][20][21][22][23][24][25][26][27] and ethanol. 13,14,19,20,[27][28][29] Methanol electrooxidation has been studied more than ethanol because it occurs at lower overpotentials and methanol can be oxidized completely to CO 2 because it does not require cleavage of a C-C bond. However, ethanol is a much less toxic fuel than methanol and can be produced in large quantities from biomass.…”

“…Ru nanoparticle size, 13,18 crystallinity of the Ru core, 13,23,29 and Pt shell thickness 14,17,18 are the main factors that affect the catalytic activity of Ru@Pt catalysts toward the oxidation of alcohols. In nanoparticle syntheses, capping agents such as polyvinyl pyrrolidone (PVP) serve as stabilizers to prevent their overgrowth.…”

“…13,19,29 Hseieh et al 30 have reported atomically ordered Ru@Pt nanoparticles prepared by using ethanol as a reductant in an alkaline medium at a temperature lower than 100 o C. These crystalline core-shell nanoparticles prevented partial alloying at the Ru/Pt interface, which greatly increases the catalytic activity for methanol and ethanol oxidation. 13,29,30 However, large particle sizes, broadening of the size distribution, less spherical shape and non-uniform Pt shells were identified as limitations of this method. 13,29 Hu et al 19 prepared Ru@Pt catalysts by using ethylene glycol as a reducing agent and a fast microwave technique.…”