Surface modified ruthenium nanoparticles structural investigation and surface analysis of a novel catalyst for oxygen reduction

ABSTRACT Ruthenium catalysts modified by selenium are of interest as a methanol insensitive oxygen reduction catalyst in a Polymer Electrolyte Membrane Fuel Cell for mobile application. To elucidate the structural and chemical features of unsupported and carbon supported ruthenium nano particles prepared by thermolysis of Ru3 CO 12 in an organic solvent with and without the presence of dissolved selenium different bulk and surface sensitive methods such as Transmission Electron Microscopy TEM, X Ray Diffractometry XRD, Thermogravimetry coupled with Mass Spectrometry TG MS, X ray Photo electron Spectroscopy XPS and Extended X ray Absorption Fine Structure EXAFS analysis were performed. It was found that the as grown catalytic particles prepared without selenium and handled under ambient conditions are distinguished by a ruthenium core of 4 nm size, the surface of which is covered by an amorphous ruthenium oxide hydroxide and metal organic residues from the process of synthesis. In presence of selenium Ru Se and Se O bondings has additionally been found at the surface. After heat treatment under vacuum organic residues could be removed. The particles can now be described by a metallic core of lt; 10 nm grown by coalescence due to thermal treatment the surface of which exhibits Ru O, Se O and Ru Se bondings. While a pure ruthenium catalyst totally oxidises within several weeks the selenium containing counterpart becomes stabilised against corrosion for years. Beside the protecting property it is suggested that selenium also leads to a concentration of ruthenium d electrons close to the top of the Fermi level facilitating four electron transfer to reduce oxygen at the cathode side of a fuel cell