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

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 2013-09, Vol.704, p.57-66
• Main Authors: Tsypkin, Mikhail, de la Fuente, José Luis Goméz, García Rodríguez, Sergio, Yu, Yingda, Ochal, Piotr, Seland, Frode, Safonova, Olga, Muthuswamy, Navaneethan, Rønning, Magnus, Chen, De, Sunde, Svein
• Format: Article
• Language: English
• Subjects: Bifunctional; carbon; catalysts; CO electrooxidation; Electrocatalyst; fuel cells; heat treatment; Ligand; methanol; Methanol electrooxidation; nanoparticles; oxidation; ruthenium; temperature; transmission electron microscopy; X-ray diffraction
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/j.jelechem.2013.06.007

•Heat-treatment of Ru@Pt core–shell particles to 300 and 500°C compressed Pt–Pt bond lengths.•For heat-treatment at 500°C the extent of alloying also increased.•The rate of CO oxidation increased uniformly in the whole temperature range.•The activity for methanol oxidation increased only for catalysts heat-treated at 500°C. 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 5nm 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.