Crystallographically Resolved Hydrogen Uptake Response in Palladium Nanopowders Revealed by Modulation–Excitation Synchrotron X-ray Diffraction

Abstract

Hydrogen absorption in palladium is a prototypical system for understanding solid–gas interactions related to hydrogen storage and catalytic hydrogenation. While the thermodynamics of H2 uptake in Pd has been extensively studied, crystallographically resolved dynamic aspects remain insufficiently understood. Here, we employed modulation–excitation synchrotron X-ray diffraction (ME-XRD) combined with phase-sensitive detection (PSD) to extract reflection-resolved apparent response times of hydrogen-induced lattice expansion in Pd nanopowders under periodic alternation of the gas atmosphere (10% H2/He and pure He). By analyzing the phase response of individual Bragg reflections, we distinguished the onset timing of the reversible structural response for multiple reflections. The apparent response times followed the order of (220) → (200) → (111) → (311) → (222). These results demonstrate crystallographically resolved dynamic heterogeneity in hydrogen uptake response in polycrystalline nanopowders and highlight ME-XRD as a powerful approach for unraveling kinetic heterogeneity in H2 storage materials.