Metal Particle Size and Structure of the Metal−Support Interface of Carbon-Supported Platinum Catalysts as Determined with EXAFS Spectroscopy

Abstract

The metal particle size and structure of the metal−support interface of platinum supported on Vulcan XC-72 (a commercial catalyst used in platinum fuel-cell electrodes) and on carbon nanofibers (CNF) have been determined with extended X-ray absorption fine structure spectroscopy (EXAFS). The CNF-supported Pt catalysts were synthesized using a homogeneous deposition precipitation (HDP) method. The amount of acidic oxygen groups on the CNF surface was modified by treatment in an inert atmosphere at different temperatures. The average first shell Pt−Pt coordination number (∼5.5) detected in Pt/CNF is much smaller than for Pt/Vulcan XC-72 (∼8.2). The presence of oxygen-containing groups in the CNF support most probably leads to the stabilization of small Pt particles on the CNF support. A prominent interaction between the metal particles and the support atoms was detected on both kinds of catalysts, which confirms that the metal is in direct contact with the carbon support atoms. After reduction, a long metal...