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

Abstract

Deciphering the three-dimensional atomic structure of solid-solid interfaces in core-shell nanomaterials is the key to understand their remarkable catalytical, optical and electronic properties. Here, we probe the three-dimensional atomic structures of palladium-platinum core-shell nanoparticles at the single-atom level using atomic resolution electron tomography. We successfully quantify the rich structural variety of core-shell nanoparticles including bond length, coordination number, local bond orientation order, grain boundary, and five-fold symmetry, all in 3D at atomic resolution. Instead of forming an atomically-sharp boundary, the core-shell interface is atomically diffuse with an average thickness of 4.2 Å, irrespective of the particle’s size, morphology, or crystallographic texture. The high concentration of Pd in the interface is highly related to the electric double layers of the Pd seeds. These results advance our understanding of core-shell structures at the fundamental level, providing potential strategies into nanomaterial manipulation and chemical property regulation.

Revealing the interface-driven atomic local chemical heterogeneity in bimetallic catalysts in three dimensions

“…2a-d) show the Pt shells grow epitaxially in all Pd@PtnL CS-NPs, resulting in a cuboctahedron morphology with the exposure crystal facets being {100} and {111} facets. The AID is observed in the interfaces, which is consistent with our previous work 32 . We calculated the Pd concentrations in each layer and obtained the curves of diffusive Pd concentrations for Pd@PtnL CS-NPs (Fig.…”

“…In all Pd@PtnL CS-NPs, bond lengths gradually decrease from cores to surfaces (Supplementary Fig. 11), which is attributed to the low coordination and lattice relaxation 32,38 , leading to a decrease in the surface bond lengths. However, it is notable that Pd@Pt<1L (2.82 Å), Pd@Pt2L (2.82 Å) and Pd@Pt5L (2.81 Å) have negligible difference in the averaged bond lengths, while the bond length slightly decreases in Pd@Pt8L (2.79 Å) (Supplementary Table 4).…”

“…Pd@Pt CS-NPs with different cutoffs of AID were synthesized using a two-step wet chemistry method ("Methods", Supplementary Table 1) 32,33 . Four types of Pd@PtnL (n = <1, 2, 5, 8) CS-NPs were obtained by precisely controlling the amount of Pt deposition on Pdcube NPs.…”

“…Some surface Pt atoms are misclassified into Pd 27 . This problem is alleviated by incorporating some prior information such EDS mapping measurements 32 . In this work, all the Pt shells grow in a completely epitaxial manner, their Pd diffusion curves of inner-layer atoms (surface excluded) are in good agreements with that of Pd@Pt8L (Fig.…”

“…Miao et al show a combination of the atomic structures of NiPt determined by AET with machine learning to probe possible active sites 31 . Recently, we employed AET to study the 3D atomically diffuse interface in Pd@Pt core-shell nanoparticles (CS-NPs) where the core Pd atoms diffuse into the Pt shell asymmetrically 32 . We hypothesize that, by tuning the atomically interfacial diffusion (AID) between Pd and Pt atoms, as schematically shown in Fig 1a, we can obtain local chemically heterogeneous structures on the subsurface which could modulate the electronic structures of surface atoms and boost the performance of catalysts at atomic level.…”