Abstract

Platinum-based catalysts for hydrogen fuel-cell applications have progressed greatly with the addition of a second element in either a mixed-alloy or core-shell structure. Not only does this result in a reduction in mass of expensive platinum metal used, but such particles seem to demonstrate significantly higher catalytic activity. Further improvement of these systems can only be made by careful investigations on their atomic-scale structure and composition.

In the same way that the scattering cross section, σ, can be calculated from annular dark-field (ADF) scanning transmission electron microscopy (STEM) image intensity and for ionization edges in electron energy loss spectroscopy (EELS), it is possible to calculate an energy dispersive x-ray (EDX) partial ionization cross section. The approach which is very similar to the ζ-factor method proposed by Watanabe is beneficial especially because of the simplicity of its implementation. I will discuss the advantages of such an approach and its application to the study of bimetallic catalyst nanoparticles. Once we have a method for quantification of EDX using cross sections we can then begin to exploit the ability to combine such cross sections with those determined using STEM or EELS . The additional image provided on a column by column basis may yield the solutions to extracting 3-dimensional information about bimetallic nanoparticles which has otherwise been difficult.