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 °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 °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 °C. The results indicate that the surface concentration of ruthenium in the pristine Ru@Pt catalysts is small.