Clarifying the role of Ru in methanol oxidation at Ru_core@Pt_shellnanoparticles

Abstract

The catalytic activity of Rucore@Ptshell nanoparticles (NPs) towards CO oxidation, a strongly adsorbed intermediate that compromises the performance of direct methanol fuel cells, is known to be significantly better than at Pt alone. However, a systematic study aimed at understanding the beneficial effect of Ru on Pt during the methanol oxidation reaction (MOR) has not been carried out as yet. Here, Rucore@Ptshell NPs, having a controlled Ptshell coverage of zero to two monolayers and two different Rucore sizes (2 and 3 nm), were synthesized using the simple polyol method to determine the precise role and impact of Ru on the MOR in 0.5 M H2SO4 + 1 M methanol at RT and 60 °C. Because the structure of our Rucore@Ptshell NPs is known with such certainty, we were able to show here that the rate of methanol adsorption/dehydrogenation can be accelerated either by compression of the Ptshell (by making the Rucore larger) when it is less than one monolayer in thickness, or by decreasing the electronic effect of the Rucore on the Ptshell (achieved by adding a second Pt layer to the Ptshell). At low overpotentials, decreasing the Ptshell thickness also helps in increasing the rate of the MOR by enhancing the rate of oxidation of adsorbed CO. Finally, it is shown that the bi-functional effect of Ru on the Ptshell plays only a minor role in the catalysis of the MOR, especially at large particles where CO surface diffusion is facilitated.

Noble Metal Based Electrocatalysts for Alcohol Oxidation Reactions in Alkaline Media

“…Therefore, a simplified alternative for rapidly evaluating and screening the AOR electrocatalyst typically relies on the half-cell test carried out in a three-electrode system, with Pt as the counter electrode, Hg/HgO (alkaline media), Hg/Hg 2 Cl 2 (acidic media) or Ag/AgCl (acidic media) as the reference electrode, respectively. The Luggin capillary is highly recommended to separate the counter and reference electrodes in the different compartments to avoid contamination [37] (e.g., chloride anions). The electrocatalysts are typically dispersed in a proper solvent (e.g., ethanol, i-propanol+H 2 O) and drop-cast onto the glassy carbon electrode (GCE) or carbon paper to form the working Figure 1.…”

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

“…Thus, although Pt is known to be the most effective electrocatalyst, as both the anode and the cathode of hydrogen, and of direct methanol fuel cells, an alternate electrocatalyst is needed to reduce both cost and Pt poisoning, while maintaining similar efficiency. PtRu alloys are considered to be among the most promising catalysts in such fuel cells, due to their lower cost, high electrocatalytic activity, high tolerance for CO, superior performance in decomposing methanol, and high activity in oxidizing CO to form CO 2 . − …”

Understanding the Role of Ir during Methanol Oxidation at PtxIryAlloy Nanoparticles

“…60,61 In comparison, for Ru core @Pt shell NPs, 62 we reported an increase of 15-30 times in the MOR activity by moving from 25 to 60…”

“…In this prior work, Ru core @Pt shell NPs, with 2 nm dia Ru cores coated with sub-monolayer Pt shell coverage, showed the highest increase in activity with increasing temperature. 62 Fig . 7b shows that the MOR activity at 60…”