Electrochemistry in the Light of In Situ Bragg Coherent Diffraction Imaging
Résumé
The advent of the new 4th generation x-ray light sources represents an unprecedented opportunity to conduct in situ and operando studies on the structure of nanoparticles in reactive liquid environments. Here, we will illustrate how Bragg coherent x-ray imaging [1] allows to image in three dimensions (3D) and at the nanoscale the strain and defect dynamics inside nanoparticles during an electrochemical reaction. First, we successfully imaged the lattice displacement and the strain inside a single Pt nanoparticle in electrochemical environment. The new Extremely Brilliant Source at the European synchrotron, with unmatched brilliance and coherence, allowed monitoring the changes in structure and morphology of nanocatalysts during in situ conditions. Our results reveal that the strain is heterogeneously distributed between highly- and weakly-coordinated surface atoms, and propagates from the surface to the bulk of the Pt nanoparticle under polarisation [2]. Secondly, we will show how in situ and operando Bragg coherent x-ray imaging allows to study the structural evolution of single Pd nanocrystals at various electrode potentials typical of H adsorption, H absorption, and H2 evolution. Open questions remain regarding the maximal quantity of H that can be inserted into a Pd nanocrystallite, the mechanism and kinetics of hydride (PdHx) nucleation (preferential sites for nucleation or homogeneous nucleation at the whole particle surface) and growth (α/β sharp transition or two-phase coexistence).
[1] I. Robinson and R. Harder, Coherent X-Ray Diffraction Imaging of Strain at the Nanoscale, Nat. Mater. 8, 291 (2009).
[2] C. Atlan et al., Imaging the strain evolution of a platinum nanoparticle under electrochemical control, Nat. Mater. accepted (2023).