Investigation of Strain in Pt and Pd nanoparticles under electrochemical conditions and through Bragg Coherent Diffraction Imaging

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 and production reactions, while Pd possesses a unique property of absorbing hydrogen into its volume, leading to a phase transition. This makes it a valuable model for hydrogen storage. In this study, Bragg Coherent Diffraction X-ray Imaging (BCDI) is employed to probe in situ individual nanoparticles (ca. 200 nm in size). This lens-less technique enables determining the morphology, mapping displacement, strain and d-spacing fields of these nanoparticles. However, the broad concepts of strain, and particularly the strain provided by BCDI, require clarification and precision to accurately interpret the electrochemical behaviour of Pt and Pd nanoparticles in action. An in-depth analysis of the strain reveals the surface adsorption mechanisms of a Pt nanoparticle and the insertion of hydrogen into the volume of Pd nanoparticles, which reversibly transitions between hydrogen-rich and hydrogen-poor phases.