IN-SITU ANOMALOUS SMALL-ANGLE X-RAY-SCATTERING AND X-RAY-ABSORPTION NEAR-EDGE STRUCTURE INVESTIGATION OF CATALYST STRUCTURES AND REACTIONS

Synchrotron radiation is applied to the combined anomalous small angle X-ray scattering (ASAXS) and X-ray absorption near-edge structure (XA NES) in situ studies of platinum electrocatalysts, whose metal content is highly dispersed in the form of small crystallites on high surface area porous carbon supports. Combined measurements with X-ray energie s near the Pt-L(3) X-ray absorption edge have been performed in an ele ctrochemical cell to study in situ the anodic oxidation process in cyc lic voltammetry both for the anodic oxidized and reduced state of the platinum. The reduction process was monitored with XANES. From ASAXS, the sizes of the platinum catalyst particles have been found to increa se during the oxidation process at about 1.1 V vs. Ag/AgCl. From this increase one can infer a shell model with a platinum core and an oxide surface layer with a thickness of about 1 nm for the oxidized particl es.