Studying Strain Evolution of Platinum Nanograins using Nanopipette Electrochemical Cell Combined with X-ray Bragg Coherent Diffraction Imaging*

Understanding the structure of materials under electrochemical polarization is key to developing design principles for electrocatalysts. Probing structural rearrangements in catalytic materials during electrocatalysis is challenging experimentally and further complicated by structural heterogeneities including crystalline defects, strain inhomogeneities, and variations in chemical composition. Nonetheless, in operando measurements are often the most direct ways to improve our understanding of catalytic reactions. To address this challenge, we demonstrate a new approach that combines a nanopipette electrochemical cell with three-dimensional X-ray Bragg Coherent Diffractive Imaging (BCDI) to study how strain in a single Pt grain evolves in response to applied potential. During electrochemical polarization, in-situ BCDI measurements have revealed marked changes in surface strain arising from the Coulombic attraction between the electrode surface and the electrolyte ions in electrochemical double layers, while the strain in the bulk of the crystal remained unchanged. The concurrent surface redox reactions have a strong influence on the magnitude and nature of the strain dynamics under polarization.