Monday, July 25, 2016, 10:00 am — Room 300, Chemistry Bldg. 555 - 3rd Floor
The synchrotron-based X-ray absorption spectroscopy (XAS) is a non-destructive technique that measures the changes in the x-ray absorption coefficient of a material as the function of energy. The X-rays are highly penetrating and allow studies of gases, solids or liquid at concentrations of as low as a few ppm. As an element-specific technique, XAS can resolve the oxidation state of the element, as well as its coordination environment and subtle changes within. Its unique power is found in application to metal clusters, particularly in nanomaterials. It can resolve the inner structure of a nanoparticle composed of two or more elements, i.e. solid solution, aggregate mixtures, or core-shell particles in which one metal is present mostly in the center of the particle (core), and the other forms a shell around it. The latter nanoparticle systems are of a special interest for electrocatalysts composed of expensive noble metals because minimizing the noble metal content is the goal of the present technology development. The lecture focuses on in-situ characterization of electrochemical systems composed of two or more metal atoms for fuel cell technology. Selected examples show the changes in the inner structure of the catalyst during the oxidation of fuels on anode systems, or oxygen reduction on cathodes, including size, shape and partial oxidation state, and correlate them to the catalyst's activity and stability.
Hosted by: Miomir Vukmirovic
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