Formation Mechanism of Epitaxial Palladium–Platinum Core–Shell Nanocatalysts in a One‐Step Supercritical Synthesis

Abstract

The scarcity of platinum group metals provides a strong incentive to optimize the catalytic activity and stability e.g. through nanoalloys or core-shell nanoparticles. Here, time-resolved X-ray total scattering and transmission electron microscopy characterization are used to study the formation of platinum-palladium core-shell nanoparticles under solvothermal conditions. It is shown that Pd rapidly forms small (5-10 nm), disordered primary particles, which agglomerate and crystallize when reaching 20-25 nm. The primary Pd particles provide nucleation sites for Pt, and with extended reaction time the Pd cores become fully covered with Pt shells. The observed core-shell material is surprising when considering the Pt-Pd phase diagram and relative surface energies, but it can be rationalized through the kinetics of precursor conversion. To bridge the gap between

Autocatalytic Formation of High‐Entropy Alloy Nanoparticles

“…The large particles consist of agglomerated crystallites, and the particles increase in size and density with increasing reaction time (see S3 and S8). It is likely that small primary particles are formed, and extended reaction times are required for these to agglomerate and merge, as recently observed in the formation of epitaxial Pd‐Pt core–shell particles from metal acetylacetonates [22] …”

There's no place like real-space: elucidating size-dependent atomic structure of nanomaterials using pair distribution function analysis

“…[203][204][205][206] In situ PDF studies, on the other hand, allow for identication and characterization of disordered or amorphous intermediate structures and species in solution, which are important in nanomaterials. For example, in studies of nanomaterial synthesis, in situ PDF analysis gives the possibility for studying the atomic structure of the species present before, during and aer crystallization of nanoparticles, 183,[207][208][209][210][211][212][213][214][215][216][217][218][219] which is essential for gaining a deeper understanding of material nucleation processes, where atomic scale mechanistic information generally is scarce. Knowledge of the relation between chemical synthesis and the resulting atomic structure of the material is crucial in the advancement of nanoscience.…”

Autocatalytic Formation of High‐Entropy Alloy Nanoparticles

“…It is likely that small primary particles are formed, and extended reaction times are required for these to agglomerate and merge, as recently observed in the formation of epitaxial Pd-Pt core-shell particles from metal acetylacetonates. [22] The in situ X-ray scattering data show that the alloy adopts a face centered cubic (fcc) structure with a unit cell length of 3.84 , see Figure 2. Sequential Rietveld refinements (see details in the SI) show that the formation of crystalline material is slow and the 77 min.…”