Thesis presented December 12, 2023

Abstract:
Pt and Pd nanoparticles are model systems used as electrocatalysts to accelerate reactions of interest in meeting societal energy challenges. Pt is involved in energy storage or production reactions. Pd, on the other hand, has a distinct property of absorbing hydrogen into its volume, leading to a phase transition, making it a model for hydrogen storage. Coherent Bragg X-ray diffraction is a synchrotron-based technique employed to investigate the three-dimensional structural characteristics of individual particles in action. Its application to Pt and Pd particles under electrochemical conditions allows observing how their strain changes as they operate. An in-depth analysis of the strain reveals the surface adsorption mechanisms of Pt particles and the insertion of hydrogen into the volume of Pd particles, which reversibly transitions between hydrogen-rich and hydrogen-poor phases..

Keywords:
Strain, Bragg coherent X-ray diffraction imaging, electrocatalysis, in situ reactions, Pt, Pd, nanostructure