PNNL

The Science

The formation of metal hydrides is important to a wide range of energy technologies, from hydrogen storage to fusion materials. Researchers used palladium (Pd) nanoparticles, which have a high hydrogen affinity and can be precisely synthesized, as a model system for studying the insertion of hydrogen into a metal. They synthesized Pd nanoparticles, interconnected into assemblies with a high density of Σ3(111) grain boundaries (GBs), to probe the role of GBs in hydridation. They found that the assemblies of Pd particles with the GBs had significantly faster hydrogen insertion than isolated nanoparticles. These assemblies also feature localized strain along the GBs that increased with hydrogen exposure. Computations showed that strain lowers the barriers to hydrogen insertion, making it more favorable along the GB.

The Impact

Metal hydrides play key roles in energy technologies and chemical phenomena, ranging from electrochemical energy storage to plasma processing for microelectronics. Understanding how the presence of GBs in the nanoparticles influences the overall material properties is important for developing materials with targeted properties. The atomic-level insights from this work provide mechanistic information on the role of GBs in hydride formation that can help enable the development of new design strategies for GB-directed synthesis of functional materials.

Summary

GBs are frequently implicated as key defects that facilitate metal hydride formation. However, the structural complexity of GBs makes understanding their specific role challenging. Researchers investigated hydrogen insertion in Pd nanostructures enriched with well-defined Σ3(111) GBs (Pd_GB) synthesized via electrolysis-driven nanoparticle assembly. In situ synchrotron X-ray diffraction reveals that Pd_GB exhibits dramatically accelerated hydriding and dehydriding kinetics compared with similarly sized ligand-free and ligand-capped Pd nanoparticles. Mapping using environmental transmission electron microscopy shows that the strain is highly localized at GBs and intensifies upon hydrogen exposure, indicating preferential hydrogen insertion along GB sites. Density functional theory calculations provide mechanistic insight that supports these findings, showing that hydrogen insertion near Σ3(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-directed synthesis of functional materials.

Contact

Peter Sushko, Pacific Northwest National Laboratory, peter.sushko@pnnl.gov

Funding

This research was supported by the Department of Energy, Office of Science, Basic Energy Sciences program, Materials Sciences and Engineering Division, Synthesis and Processing Science program, FWP 78705. L.L. also gratefully acknowledges support from the University of Utah and the Alfred P. Sloan Foundation (Grant # FH-2023-20829) for the lab setup. Parts of this work were conducted in the Environmental Molecular Sciences Laboratory (EMSL), the Advanced Photon Source, and the beamline 4-ID at the National Synchrotron Light Source II. This work also made use of Nanofab Electron Microscopy and Surface Analysis Lab (EMSAL) shared facilities of the Micron Technology Foundation Inc. Microscopy Suite sponsored by the John and Marcia Price College of Engineering, Health Sciences Center, Office of the Vice President for Research. This research used resources of the National Energy Research Scientific Computing Center, a Department of Energy Office of Science user facility.