Structure, ordering, and surfaces of Pt-Fe alloy catalytic nanoparticles from quantitative electron microscopy and X-ray diffraction.

The current challenge in catalyst development is to produce highly active and economical catalysts. This challenge cannot be overcome without an accurate understanding of catalyst structure, surfaces and morphology as the catalytic reactions occur on the surface active sites. Transmission Electron Microscopy (TEM) is an excellent tool for understanding the structures of the nanoparticles down to the atomic level in determining the relationship with the catalyst's performance in fuel cell applications. This paper describes a detailed structural characterization of Pt-Fe nanoparticles using aberration corrected TEM. Detailed analysis regarding the morphology, structural ordering, facets, nature of the surfaces, atomic displacements and compositions was carried out and presented in the context of their electrochemical performances. In addition, the effects of electrochemical cycling in terms of morphology and composition evolution of the nanoparticles were analyzed. Lastly, along with data from X-ray diffractometry, two different crystallographic models of the unknown Pt(3)Fe(2) nanoparticle phase are proposed. The detailed characterization by TEM provides useful insights into the nanoparticle chemistry and structure that contributes to catalyst development for next generation fuel cells.