Effect of heat treatment on the electrocatalytic properties of nano-structured Ru cores with Pt shells

Ru@Pt core shell particles are relevant for application as electrocatalysts in fuel cells. The Ru core is expected to influence the activity of the Pt in the shell through a compression of bond lengths and electronic interaction with the core. In this work Ru@Pt core shell (Ru core and Pt shell) and pure Ru nanoparticles of diameter below less than 5 nm were synthesized and supported on carbon black (Vulcan XC-72). The supported catalysts were heat-treated at temperatures up to 500 degrees C. Analysis of the catalysts by TEM, EXAFS, XRD, and CO-stripping indicates a strongly segregated architecture with Ru in the core of the particles. Upon heat-treatment we observed moderate particle growth, increased extent of alloying, and a decrease of the Pt Pt bond lengths. The Pt Pt bond lengths decreased uniformly with heat-treatment temperature in the entire range. The extent of alloying and particle growth were significant (i.e. beyond measurement uncertainties) only at a heat-treatment temperature of 500 degrees C. The electrocatalytic activity for oxidation of adsorbed CO (CO-stripping) increased in the entire temperature interval. The activity for methanol oxidation only increased when catalysts were heated to 500 degrees C. The results indicate that the surface concentration of ruthenium in the pristine Ru@Pt catalysts is small. (C) 2013 Elsevier B.V. All rights reserved.