PNNL

Abstract

Grain boundaries (GBs) are frequently implicated as key defect structures facilitating metal hydride formation, yet their specific role remains poorly understood due to their structural complexity. Here, we investigate hydrogen inser-tion in Pd nanostructures enriched with well-defined S3(111) GBs (PdGB) synthesized via electrolysis-driven nanoparticle assembly. In situ synchrotron X-ray diffraction reveals that PdGB exhibits dramatically accelerated hydriding and dehydrid-ing kinetics compared to ligand-free and ligand-capped Pd nanoparticles with similar crystallite sizes. Strain mapping using environmental transmission electron microscopy shows that strain is highly localized at GBs and intensifies upon hydrogen exposure, indicating preferential hydrogen insertion along GB sites. Density functional theory calculations support these findings, showing that hydrogen insertion near S3(111) GBs is energetically more favorable and that tensile strain lowers insertion barriers. These results provide atomic-level insights into the role of GBs in hydride formation and suggest new design strategies for GB-engineered Pd-based functional materials.