Monitoring Galvanic Replacement Through Three-Dimensional Morphological and Chemical Mapping

Abstract

Galvanic replacement reactions on metal nanoparticles are often used for the preparation of hollow nanostructures with tunable porosity and chemical composition, leading to tailored optical and catalytic properties. However, the precise interplay between the three-dimensional (3D) morphology and chemical composition of nanostructures during galvanic replacement is not always well understood as the 3D chemical imaging of nanoscale materials is still challenging. It is especially far from straightforward to obtain detailed information from the inside of hollow nanostructures using electron microscopy techniques such as SEM or TEM. We demonstrate here that a combination of state-of-the-art EDX mapping with electron tomography results in the unambiguous determination of both morphology transformation and elemental composition of nanostructures in 3D, during galvanic replacement of Ag nanocubes. This work provides direct and unambiguous experimental evidence toward understanding the galvanic replacement reaction. In addition, the powerful approach presented here can be applied to a wide range of nanoscale transformation processes, which will undoubtedly guide the development of novel nanostructures.

Self‐Templated Synthesis of Ultrathin Nanosheets Constructed TiO2 Hollow Spheres with High Electrochemical Properties

“…Generally, two main strategies, e.g., template‐based (hard‐ and soft‐templates) and template‐free (Kirkendall effect, galvanic replacement, and Ostwald ripening), are used to obtain well‐defined hollow spheres with different compositions and shapes 5, 10, 11, 12, 13, 14, 15, 16, 17. Recent researches have demonstrated that hollow spheres constructed with 1D nanorods/nanoneedles18 and 2D nanosheets19, 20, 21, 22 even exhibit faster surface reaction rates and better physicochemical stability because they occupy much larger specific surface areas than the most hollow spheres composed of 0D nanoparticles,23 and simultaneously inherit the characteristics of the constituent units.…”

Controllable Cobalt Oxide/Au Hierarchically Nanostructured Electrode for Nonenzymatic Glucose Sensing

“…The template being oxidized, possessing the lower reduction potential and higher rate of diffusion, loses electrons and the metal being reduced gains electrons. Oxidation is initiated on the crystal lattice plane of the sacrificial template exhibiting the highest surface energy [84,[100][101][102]. Small pinholes, or Kirkendall voids, are formed as a result of this oxidation [103,104].…”

“…Recently Goris et al used high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) tomography to investigate pinhole formation during a galvanic replacement reaction between Ag nanocubes and chloroauric acid (HAuCl 4 ) [102]. As gold salt was added to the Ag nanocubes, circular holes appeared on the highest energy [111] plane.…”

“…2 [84]. However, Gori's work was the first experimental evidence that pinholes are initiated on only one facet of the crystal lattice and that the reduced metal in a galvanic replacement reaction is deposited first around these pinholes [102].…”

Quantitative Aspects of 3D Chemical Tomography in the Scanning Transmission Electron Microscope

“…In ET, the 3-D structure of a specimen is mathematically calculated from a series of 2-D projections acquired over a range of specimen orientations. Recent advances in specimen preparation, automation of data collection, and improved reconstruction methods have also made it feasible to couple tomographic data acquisition with X-ray energy dispersive and electron energy-loss spectroscopies (XEDS and EELS, respectively) in order to carry out 3-D elemental and chemical analysis at similar length scales [1][2][3][4][5][6][7].…”