In Situ Kinetic and Thermodynamic Growth Control of Au–Pd Core–Shell Nanoparticles

Abstract

One-pot wet-chemical synthesis is a simple way to obtain nanoparticles (NPs) with a well-defined shape and composition. However, achieving good control over NP synthesis would require a comprehensive understanding of the mechanisms of NP formation, something that is challenging to obtain experimentally. Here, we study the formation of gold (Au) core-palladium (Pd) shell NPs under kinetically and thermodynamically controlled reaction conditions using in situ liquid cell transmission electron microscopy (TEM). By controlling the reaction temperature, we demonstrate that it is possible to tune the shape of Au nanorods to Au-Pd arrow-headed structures or to cuboidal core-shell NPs. Our in situ studies show that the reaction temperature can switch the Pd shell growth between the kinetically and thermodynamically dominant regimes. The mechanistic insights reported here reveal how the reaction temperature affects the packing of the capping agents and how the facet selection of depositing shell atoms drives the shell formation under different kinetic conditions, which is useful for synthesizing NPs with greater design flexibility in shape and elemental composition for various technological applications.

Well‐Defined Metal Nanoparticles@Covalent Organic Framework Yolk–Shell Nanocages by ZIF‐8 Template as Catalytic Nanoreactors

“…The dispersibility and accessibility of the MNPs are paramount for their catalytic performance . However, MNPs without surface capping agents easily aggregate due to their high surface energy, leading to an unexpected decrease of their catalytic activity over time . Thus, fully exploiting the intrinsic catalytic properties of MNPs while protecting them from aggregation is highly desirable.…”

Liquid phase transmission electron microscopy with flow and temperature control

“…This enables the user to initiate a reaction, or change the liquid in the cell. 20 Preventing depletion of the precursor can be especially important, as this can limit a reaction process, 21 or alter reaction kinetics. 22 Flow cells exist in two flavors: monolithic and dual-chip configuration.…”

“…37,38 More recently, one of the two micro-electro mechanical system (MEMS) chips was equipped with a microheater. This enables the imaging of thermally induced shrinking of coreshell microgels 39 ,thermally induced polymerization 40 , galvanic replacement in silver nanocubes with gold 41 the growth of gold-palladium core-shell nanoparticles 21 , and metal-organic nanotubes 42 were visualized.…”

Liquid phase transmission electron microscopy for imaging of nanoscale processes in solution

“…9,30 SiN x liquid cells can have multiple capabilities, such as multiline-flow, specimen heating, and electrochemical biasing (Figure 1b). 10,17 These capabilities allow probing chemical reactions triggered by the mixing of multiple reactants, 24,[31][32][33] explore nanoparticle growth 32,[34][35][36][37] at elevated temperatures, and the nanoscale details of electrochemical processes related to batteries. 26,38 Other types of membranes, for example, graphene or other 2D materials, have been used for liquid cell fabrication, where small pockets of solutions are encapsulated between two 2D films.…”