Abstract
Advances in catalysis rely on the synthesis and characterisation of nanoparticles that have tailored structures and compositions. Although energy-dispersive X-ray (EDX) spectroscopy can be used to study local variations in the compositions of individual supported nanoparticles on the atomic-scale in the scanning transmission electron microscope, electron beam induced damage and contamination can preclude the use of long exposure times and tomographic approaches. Here, we perform simulations of EDX maps of seven different octahedral PtNi nanoparticles for a selection of crystallographic orientations and tilts, to evaluate which of them can be distinguished from elemental mapping performed in only one orientation.
Highlights
Pt-based bimetallic nanoparticles have demonstrated great promise as catalysts for the oxygen reduction reaction (ORR) in hydrogen fuel cells [1]
It was shown that anisotropic growth is responsible for such inhomogeneous compositional distributions [12], with rapid growth of Pt-rich hexapods/concave octahedra along ⟨100⟩ directions preceding the deposition of a Ni-rich phase in the concave {111} regions
When the sample composition and thickness are both unknown, as is the case with the PtNi octahedra that we describe below, the annular dark-field (ADF) scanning transmission electron microscope (STEM) signal alone provides insufficient information to characterise the particles fully
Summary
Pt-based bimetallic nanoparticles have demonstrated great promise as catalysts for the oxygen reduction reaction (ORR) in hydrogen fuel cells [1]. In light of the exceptionally high ORR activity demonstrated by Pt3Ni (111) surfaces, large efforts have been dedicated to the synthesis and characterisation of uniform-Pt-skin octahedral Pt-Ni nanoparticles [6,7,8,9,10]. Cui et al [11] described inhomogeneous compositional distributions in shaped Pt alloy nanoparticles, in the form of Pt-rich frames and Nirich facets. They showed that the selective etching of Nirich {111} facets during electrochemical cycling results in the formation of concave octahedra, thereby exposing less active facets and leading to a significant reduction in activity. They reported the formation of Ni octahedra encased by octahedral Pt frameworks, with three intersecting perpendicular Pt
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