Atomistic insights into the nucleation and growth of platinum on palladium nanocrystals

Abstract

Despite the large number of reports on colloidal nanocrystals, very little is known about the mechanistic details in terms of nucleation and growth at the atomistic level. Taking bimetallic core-shell nanocrystals as an example, here we integrate in situ liquid-cell transmission electron microscopy with first-principles calculations to shed light on the atomistic details involved in the nucleation and growth of Pt on Pd cubic seeds. We elucidate the roles played by key synthesis parameters, including capping agent and precursor concentration, in controlling the nucleation site, diffusion path, and growth pattern of the Pt atoms. When the faces of a cubic seed are capped by Br−, Pt atoms preferentially nucleate from corners and then diffuse to edges and faces for the creation of a uniform shell. The diffusion does not occur until the Pt deposited at the corner has reached a threshold thickness. At a high concentration of the precursor, self-nucleation takes place and the Pt clusters then randomly attach to the surface of a seed for the formation of a non-uniform shell. These atomistic insights offer a general guideline for the rational synthesis of nanocrystals with diverse compositions, structures, shapes, and related properties.

Probing the atomically diffuse interfaces in core-shell nanoparticles in three dimensions

“…Although TEM/STEM has been employed to explore the growth mechanism of CS structures in 2D 10,18,[40][41][42] , it was speculated that the intermixing of core and shell atoms could happen before a perfect shell was formed 43 . Our experimental study of 3D interfaces in CS-NPs reveals several observations at the single-atom level.…”

Hydroquinone-Based Synthesis of Pd Nanostructures and the Interplay of Surface Capping, Reduction Kinetics, Attachment, Diffusion, and Fusion

“…This concept was recently validated by an in situ TEM study on the growth trajectories of Pd@Pt core−shell nanocubes. 31 Taken together, we propose a nonclassical growth mechanism to account for the generation of the various types of nanostructures at different temperatures, as illustrated in Figure 7. At the beginning of the synthesis, the Pd(II) precursor was reduced by hydroquinone to Pd atoms, which were supersaturated for the generation of Pd primary particles through homogeneous nucleation, whereas the initial reduction rate varied significantly with reaction temperature.…”

“…The transformation from concave to flat surfaces could be achieved if the deposition is relatively slow while the temperature is high enough to transport atoms to other sites through adequate surface diffusion rather than gathering at the corners. This concept was recently validated by an in situ TEM study on the growth trajectories of Pd@Pt core–shell nanocubes …”

A Symmetry‐Based Kinematic Theory for Nanocrystal Morphology Design

“…The further growth of cubes has been recently researched by in situ experiments, which supports the suitability of SBKT to describe and predict NP growth at PGDs (Figure S17). [32] Notably, while this phenomenon has been previously termed the deposition-diffusion growth mode or thermodynamically-kinetically controlled growth, [1] SBKTbased analysis provides a more advanced and straightforward approach. In the deposition-diffusion growth mode, the location of atom deposition, the driving force for atom diffusion, and the sites where it diffuses to, all need to be carefully investigated under the given conditions.…”