Expansion of interatomic distances in platinum catalyst nanoparticles

We study the atomistic structure of Pt catalyst nanoparticles using HRTEM (high-resolution transmission electron microscopy). The particles exhibit a faceted, cubo-octahedral shape, extended planar defects, and mono-atomic surface steps. HRTEM imaging with negative spherical aberration yielded atomic-resolution images with a minimum of artifacts. Combining digital image processing, quantitative image analysis, and HRTEM image simulations to determine local variations of the spacing between neighboring Pt atom columns, we have found an expansion of the lattice parameter in the particle core and even larger, locally varying expansion of Pt-Pt next-neighbor distances at the particle surface. The latter likely originates from an amorphous oxide on the nanoparticle surface and/or dissolution of oxygen on subsurface sites. These structural features may significantly impact the catalytic activity of Pt nanoparticles. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.