Clarifying the role of Ru in methanol oxidation at Rucore@Ptshell nanoparticles

The catalytic activity of Ru-core@Pt-shell 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, Ru-core@Pt-shell NPs, having a controlled Pt-shell coverage of zero to two monolayers and two different Ru-core 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 degrees C. Because the structure of our Ru-core@Pt-shell 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 Pt-shell (by making the Ru-core larger) when it is less than one monolayer in thickness, or by decreasing the electronic effect of the Ru-core on the Pt-shell (achieved by adding a second Pt layer to the Pt-shell). At low overpotentials, decreasing the Pt-shell 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 Pt-shell plays only a minor role in the catalysis of the MOR, especially at large particles where CO surface diffusion is facilitated.