Capturing Catalyst Strain Dynamics during Operando CO Oxidation.

Understanding the strain dynamic behavior of catalysts is crucial for the development of cost-effective, efficient, stable, and long-lasting catalysts. Using time-resolved Bragg coherent diffraction imaging at the fourth generation Extremely Brilliant Source of the European Synchrotron (ESRF-EBS), we achieved subsecond time resolution during operando chemical reactions. Upon investigation of Pt nanoparticles during CO oxidation, the three-dimensional strain profile highlights significant changes in the surface and subsurface regions, where localized strain is probed along the [111] direction. Notably, a rapid increase in tensile strain was observed at the top and bottom Pt {111} facets during CO adsorption. Moreover, we detected oscillatory strain changes (6.4 s period) linked to CO adsorption during oxidation, where a time resolution of 0.25 s was achieved. This approach allows for the study of adsorption dynamics of catalytic nanomaterials at the single-particle level under operando conditions, which provides insight into nanoscale catalytic mechanisms.

Unveiling Core-Shell Structure Formation in a Ni3Fe Nanoparticle with In Situ Multi-Bragg Coherent Diffraction Imaging.

Solid-state reactions play a key role in materials science. The evolution of the structure of a single 350 nm Ni3Fe nanoparticle, i.e., its morphology (facets) as well as its deformation field, has been followed by applying multireflection Bragg coherent diffraction imaging. Through this approach, we unveiled a demixing process that occurs at high temperatures (600 °C) under an Ar atmosphere. This process leads to the gradual emergence of a highly strained core-shell structure, distinguished by two distinct lattice parameters with a difference of 0.4%. Concurrently, this transformation causes the facets to vanish, ultimately yielding a rounded core-shell nanoparticle. This final structure comprises a Ni3Fe core surrounded by a 40 nm Ni-rich outer shell due to preferential iron oxidation. Providing in situ 3D imaging of the lattice parameters at the nanometer scale while varying the temperature, this study─with the support of atomistic simulations─not only showcases the power of in situ multireflection BCDI but also provides valuable insights into the mechanisms at work during a solid-state reaction characterized by a core-shell transition.

Unraveling the synergistic effects of Cu-Ag tandem catalysts during electrochemical CO2 reduction using nanofocused X-ray probes.

Controlling the selectivity of the electrocatalytic reduction of carbon dioxide into value-added chemicals continues to be a major challenge. Bulk and surface lattice strain in nanostructured electrocatalysts affect catalytic activity and selectivity. Here, we unravel the complex dynamics of synergistic lattice strain and stability effects of Cu-Ag tandem catalysts through a previously unexplored combination of in situ nanofocused X-ray absorption spectroscopy and Bragg coherent diffraction imaging. Three-dimensional strain maps reveal the lattice dynamics inside individual nanoparticles as a function of applied potential and product yields. Dynamic relations between strain, redox state, catalytic activity and selectivity are derived. Moderate Ag contents effectively reduce the competing evolution of H2 and, concomitantly, lead to an enhanced corrosion stability. Findings from this study evidence the power of advanced nanofocused spectroscopy techniques to provide new insights into the chemistry and structure of nanostructured catalysts.

Imaging the strain evolution of a platinum nanoparticle under electrochemical control.

Surface strain is widely employed in gas phase catalysis and electrocatalysis to control the binding energies of adsorbates on active sites. However, in situ or operando strain measurements are experimentally challenging, especially on nanomaterials. Here we exploit coherent diffraction at the new fourth-generation Extremely Brilliant Source of the European Synchrotron Radiation Facility to map and quantify strain within individual Pt catalyst nanoparticles under electrochemical control. Three-dimensional nanoresolution strain microscopy, together with density functional theory and atomistic simulations, show evidence of heterogeneous and potential-dependent strain distribution between highly coordinated ({100} and {111} facets) and undercoordinated atoms (edges and corners), as well as evidence of strain propagation from the surface to the bulk of the nanoparticle. These dynamic structural relationships directly inform the design of strain-engineered nanocatalysts for energy storage and conversion applications.

Gwaihir: Jupyter Notebook graphical user interface for Bragg coherent diffraction imaging.

Bragg coherent X-ray diffraction is a nondestructive method for probing material structure in three dimensions at the nanoscale, with unprecedented resolution in displacement and strain fields. This work presents Gwaihir, a user-friendly and open-source tool to process and analyze Bragg coherent X-ray diffraction data. It integrates the functionalities of the existing packages bcdi and PyNX in the same toolbox, creating a natural workflow and promoting data reproducibility. Its graphical interface, based on Jupyter Notebook widgets, combines an interactive approach for data analysis with a powerful environment designed to link large-scale facilities and scientists.