In Situ Techniques for Probing Kinetics and Mechanism of Hollowing Nanostructures through Direct Chemical Transformations

Abstract

Chemical transformation of nanostructures into hollow ones becomes important in the synthesis of materials with unique properties for applications ranging from sensing to energy storage, to high‐performance catalysis. The nanoscale Kirkendall effect and galvanic replacement represent two typical mechanisms responsible for hollowing nanostructures. These two mechanisms occur either independently or simultaneously to form hollow nanostructures with appropriate geometries and desirable properties. Precisely distinguishing the hollowing mechanism and kinetics involved in a chemical transformation relies on in situ characterization methods including in situ electron microscopy, in situ optical spectroscopy, and a suite of in situ synchrotron X‐ray techniques (e.g., imaging, scattering, and X‐ray absorption fine structure spectroscopy). Here, the two typical hollowing mechanisms and the in situ characterization extensively explored in recent years are summarized, providing a timely overview of the promise of in situ methods in studying nanoparticle evolution under real reaction conditions.

Anion replacement in silver chlorobromide nanocubes: two distinct hollowing mechanisms

“…Typical mechanisms include nanoscale galvanic replacement reactions 23 and the Kirkendall process. 24 Galvanic replacement reactions involve redox reactions of the sacrificial template nanostructures, which are usually composed of metals 25 or metal oxides with varying oxidation states. 26,27 The nanoscale Kirkendall process is responsible for the formation of hollow nanoshells when the outward diffusion of the template nanostructure species is larger than the inward diffusion of the reactant species across the newly developed interfacial boundaries.…”

In Situ Synchrotron X‐ray Characterization Shining Light on the Nucleation and Growth Kinetics of Colloidal Nanoparticles

“…In contrast, in situ X-ray techniques characterize ensembles of many NPs, providing higher statistics to describe the NPs with better fidelity. [4] For example, morphological evolution of Fe CNPs in the course of oxidation was obtained from in situ synchrotron small-angle X-ray scattering (SAXS) patterns with the use of ab initio three-dimensional (3D) reconstruction, giving a spatial resolution of 5 Å. [5] In general, interpreting the X-ray data into the parameters describing NPs requires meticulous data-processing protocols and solid mathematical models with reasonable assumptions.…”

Lab‐Scale In Situ X‐Ray Diffraction Technique for Different Battery Systems: Designs, Applications, and Perspectives

“…Due to the complexity of phenomena occurring in cycling and the difficulty in detecting samples with low crystallinity, it is important to combine with various characterization techniques on multiple scales to provide more comprehensive information . In situ XRD technique provides information about structure evolutions and phase transitions, while electron microscopy techniques can further support the results with direct evidence of morphology . Meanwhile, optical techniques are helpful to reveal chemical composition of electrodes.…”