Electrocristallization of platinum nanoparticles supported on carbon analyzed with standard and anomalous X-ray diffraction

X-ray powder diffraction using synchrotron radiation in classical and anomalous dispersion mode is used to determine the amount of platinum and the mean diameter of catalyst platinum nanoparticles, round 2-3 nm diameters, supported on carbon. We study the early stages of the electrochemical formation of platinum nanoparticles from PtCl42- species pre-adsorbed on carbon and embedded inside a carbon-Nafion layer, which represents a fuel cell electrode. XRD results demonstrate that, with not too high superficial concentrations, new particles appear for each current pulse. Hydrogen evolution becomes the main electrochemical reaction as the platinum particle size increases, limiting the particle growth. (C) 2004 Published by Elsevier B. V.