Abstract:Octahedral-shaped PtNi-alloy nanoparticles
are highly
active oxygen
reduction reaction catalysts for the cathode in proton exchange membrane
fuel cells. However, one major drawback in their application is their
limited long-term morphological and compositional stability. Here,
we present a detailed in situ electron microscopy characterization
of thermal annealing on octahedral-shaped PtNi catalysts as well as
on doped octahedral PtNi(Mo) and PtNi(MoRh) catalysts. The evolution
of their morphology and composi… Show more
“…We have presented earlier a program based on machine learning to analyse individual nanoparticles for their shape and size from HRTEM images. 29,30 Here we extend this approach to an automated classification of nanoparticles with respect to their crystallinity. As the generation of manually labelled training data for this task is not only time-consuming but also highly error-prone, different image simulation approaches were tested to establish a feasible training pipeline.…”
“…We have presented earlier a program based on machine learning to analyse individual nanoparticles for their shape and size from HRTEM images. 29,30 Here we extend this approach to an automated classification of nanoparticles with respect to their crystallinity. As the generation of manually labelled training data for this task is not only time-consuming but also highly error-prone, different image simulation approaches were tested to establish a feasible training pipeline.…”
“…The properties of alloyed nanoparticles can be easily varied by changing their composition. − Thus, they are of considerable interest in heterogeneous catalysis, − imaging, , and sensing. , If the particles are very small, i.e., smaller than about 3 nm, they enter the regime of ultrasmall nanoparticles approaching atom-sharp metal clusters with defined structure and stoichiometry. Such nanoparticles consist of only a few hundred atoms. − As they are so small, they are interesting objects in biomedical studies as they may penetrate biological barriers like nuclear membranes , and the blood–brain barrier .…”
Alloyed ultrasmall silver–platinum nanoparticles
(molar
ratio Ag:Pt = 50:50) were prepared and compared to pure silver, platinum,
and gold nanoparticles, all with a metallic core diameter of 2 nm.
They were surface-stabilized by a layer of glutathione (GSH). A comprehensive
characterization by high-resolution transmission electron microscopy
(HRTEM), electron diffraction (ED), X-ray diffraction (XRD), small-angle
X-ray scattering (SAXS), differential centrifugal sedimentation (DCS),
and UV spectroscopy showed their size both in the dry and in the water-dispersed
state (hydrodynamic diameter). Solution NMR spectroscopy (1H, 13C, COSY, HSQC, HMBC, and DOSY) showed the nature
of the glutathione shell including the number of GSH ligands on each
nanoparticle (about 200 with a molecular footprint of 0.063 nm2 each). It furthermore showed that there are at least two
different positions for the GSH ligand on the gold nanoparticle surface.
Platinum strongly reduced the resolution of the NMR spectra compared
to silver and gold, also in the alloyed nanoparticles. X-ray photoelectron
spectroscopy (XPS) showed that silver, platinum, and silver–platinum
particles were at least partially oxidized to Ag(+I) and Pt(+II),
whereas the gold nanoparticles showed no sign of oxidation. Platinum
and gold nanoparticles were well crystalline but twinned (fcc lattice)
despite the small particle size. Silver was crystalline in electron
diffraction but not in X-ray diffraction. Alloyed silver–platinum
nanoparticles were almost fully amorphous by both methods, indicating
a considerable internal disorder.
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