Hydrogen fuel-cells are a ‘zero emission’ technology because they only release H2O, making them a very attractive source of clean electric power. Unfortunately, fuel-cells such as the polymer exchange membrane (PEM) fuel-cell are heavily reliant on a platinum catalyst at both the anode and cathode in order for the reaction to proceed at the low operating temperatures. It is largely the cost of this platinum metal which limits their more wide-scale manufacture and use.
In light of this, the search is on for more active catalysts with lower platinum content. A great deal of success has been seen in the research of bimetallic alloy catalysts where the expensive platinum metal is combined with a much less expensive metal such as nickel or cobalt. Such catalysts not only provide a reduction in the amount of platinum used but also an increase in the activity, which may be due to the compressive strain that the alloying element introduces.
In order to develop these catalysts further and make them a viable alternative to platinum, we need to understand what is happening at the nanometre and even sub-nanometre scales. For this we need to be able to characterise our catalysts at high resolution, understanding both the composition and structure. A new method for quantitative energy dispersive x-ray (EDX)  analysis in the scanning transmission electron microscope (STEM) has been developed with this in mind.
In the same way that the scattering cross section, σ, can be calculated from ADF image intensity and for ionisation edges in EELS, it is possible to calculate an EDX partial cross section using an approach that demonstrates similarities with the ζ-factor method. Rather than the ratio approach provided by the traditional k-factor method, this is a direct measurement which yields the number of atoms of each element after quantification, as such thickness can easily be extracted as well. This quantification method was applied to PtCo alloy nanoparticles that have been acid-leached to provide platinum enrichment (or rather cobalt depletion) at the particle surface . It is possible to quantify the levels of cobalt depletion in the first few atomic layers of the particle, showing that the leaching produces a localised surface depletion that can only be determined by this high resolution EDX quantification.
 K. E. MacArthur, T. J. A. Slater et al. Microsc. & Microanal. 22 (1) (2016) 71-81
 K. E. MacArthur, T. J. A. Slater et al. Mater. Sci. Technol. In press
To cite this abstract:Katherine MacArthur, Thomas Slater, Sarah Haigh, Dogan Ozkaya, Marc Heggen, Peter Nellist, Sergio Lozano-Perez; Quantitative compositional characterisation of fuel-cell catalysts using EDX ionisation cross sections.. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/quantitative-compositional-characterisation-of-fuel-cell-catalysts-using-edx-ionisation-cross-sections/. Accessed: January 21, 2022
EMC Abstracts - https://emc-proceedings.com/abstract/quantitative-compositional-characterisation-of-fuel-cell-catalysts-using-edx-ionisation-cross-sections/