Single‐atom and subnanocluster catalysts (SSCs) represent a highly promising class of low‐cost materials with high catalytic activity and high atom‐utilization efficiency. However, SSCs are susceptible to undergo restructuring during the reactions. Exploring the active sites of catalysts through in situ characterization techniques plays a critical role in studying reaction mechanism and guiding the design of optimum catalysts. In situ X‐ray absorption spectroscopy/small‐angle X‐ray scattering (XAS/SAXS) is promising and widely used for monitoring electronic structure, atomic configuration, and size changes of SSCs during real‐time working conditions. Unfortunately, there is no detailed summary of XAS/SAXS characterization results of SSCs. The recent advances in applying in situ XAS/SAXS to SSCs are thoroughly summarized in this review, including the atomic structure and oxidation state variations under open circuit and realistic reaction conditions. Furthermore, the reversible transformation of single‐atom catalysts (SACs) to subnanoclusters/nanoparticles and the application of in situ XAS/SAXS in subnanoclusters are discussed. Finally, the outlooks in modulating the SSCs and developing operando XAS/SAXS for SSCs are highlighted.
Nanostructured materials with high surface area and low coordinated atoms present distinct intrinsic properties from their bulk counterparts. However, nanomaterials’ nucleation/growth mechanism during the synthesis process and the changes of the nanomaterials in the working state are still not thoroughly studied. As two indispensable methods, X‐ray absorption spectroscopy (XAS) provides nanomaterials’ electronic structure and coordination environment, while small‐angle X‐ray scattering (SAXS) offers structural properties and morphology information. A combination of in situ/operando XAS and SAXS provides high temporal and spatial resolution to monitor the evolution of nanomaterials. This review gives a brief introduction to in situ/operando SAXS/XAS cells. In addition, the application of in situ/operando XAS and SAXS in preparing nanomaterials and studying changes of working nanomaterials are summarized.more » « less
- Award ID(s):
- NSF-PAR ID:
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
null (Ed.)An operando characterization of electrode materials under electrochemical reaction conditions is important for their further development. X-ray absorption spectroscopy (XAS) presents a unique opportunity in this regard as the absence of a vacuum chamber in this technique makes it possible to collect spectroscopy data using user-designed operando cells. In the current study, the design and performance of an operando XAS cell are evaluated for characterizing solid oxide electrolysis cell working electrodes under a reaction environment that mimics high-temperature ammonia production conditions from H 2 O and N 2 . Sr 2 FeMoO 6−x N x (SFMON)-type double perovskite oxides were used as the cathode materials in these experiments. The operando cell contained a sample stage with a turnable head so that XAS data can be collected at different angles between the electrode and the X-ray beam with an accuracy of 0.5°. The mechanism to adjust the angle of incidence of the beam on the sample allows control over the depth of penetration of the X-ray photons into the electrode. At low angles, it becomes possible to collect surface sensitive data, which is of great importance as the electrochemical processes are believed to take place on the surface of the electrodes. Sr K-edge and Fe K-edge XAS collected at 2° and 45° angles showed that these the oxidation state changes occurring in these elements are different in the near-surface region compared to the bulk of the electrode. Such an ability to distinguish between the surface and bulk properties of the electrode during real reaction environment will help to understand the underlying phenomena better, which will enable electrode design targeted towards the reactions of interest.more » « less
The dynamic information of lithium‐ion battery active materials obtained from coin cell‐based in‐situ characterizations might not represent the properties of the active material itself because many other factors in the cell could have impacts on the cell performance. To address this problem, a single particle cell was developed to perform the in‐situ characterization without the interference of inactive materials in the battery electrode as well as the X‐ray‐induced damage. In this study, the dynamic morphological and phase changes of selenium‐doped germanium (Ge0.9Se0.1) at the single particle level were investigated via synchrotron‐based in‐situ transmission X‐ray microscopy. The results demonstrate the good reversibility of Ge0.9Se0.1at high cycling rate that helps understand its good cycling performance and rate capability. This in‐situ and operando technique based on a single particle battery cell provides an approach to understanding the dynamic electrochemical processes of battery materials during charging and discharging at the particle level.
Here, we report the high pressure phase and morphology behavior of ordered anatase titanium dioxide (TiO2) nanocrystal arrays. One-dimensional TiO2 nanorods and nanorices were synthesized and self-assembled into ordered mesostructures. Their phase and morphological transitions at both atomic scale and mesoscale under pressure were studied using in situ synchrotron wide- and small-angle x-ray scattering (WAXS and SAXS) techniques. At the atomic scale, synchrotron WAXS reveals a pressure-induced irreversible amorphization up to 35 GPa in both samples but with different onset pressures. On the mesoscale, no clear phase transformations were observed up to 20 GPa by synchrotron SAXS. Intriguingly, sintering of TiO2 nanorods at mesoscale into nano-squares or nano-rectangles, as well as nanorices into nanowires, were observed for the first time by transmission electron microscopy. Such pressure-induced nanoparticle phase-amorphization and morphological changes provide valuable insights for design and engineering structurally stable nanomaterials.more » « less
Electroactive polymer thin films undergo repeated reversible structural change during operation in electrochemical applications. While synchrotron X‐ray scattering is powerful for the characterization of stand‐alone and ex situ organic thin films, in situ/operando structural characterization has been underutilized—in large part due to complications arising from supporting electrolyte scattering. This has greatly hampered the development of application relevant structure property relationships. Therefore, a new methodology for in situ/operando X‐ray characterization that separates the incident and scattered X‐ray beam path from the electrolyte is developed. As a proof of concept, the operando structural characterization of weakly‐scattering, organic mixed conducting thin films in an aqueous electrolyte environment is demonstrated, accessing previously unexplored changes in the π‐π peak and diffuse scatter, while capturing the solvent swollen thin film structure which is inaccessible in previous ex situ studies. These in situ/operando measurements improve the sensitivity to structural changes, capturing minute changes not possible ex situ, and have multimodal potential such as combined Raman measurements that also serve to validate the true in situ/operando conditions of the cell. Finally, new directions enabled by this in situ/operando cell design are examined and state of the art measurements are compared.