Interfacial alloy hydride destabilization in Mg/Pd thin films.

Area of Science:

• Materials Science
• Thin Film Technology
• Hydrogen Storage

Background:

• Recent studies reported increased equilibrium hydrogen pressure in palladium (Pd)-capped magnesium (Mg) thin films.
• This phenomenon was previously attributed to strain effects.
• The exact mechanism behind this pressure increase remained unclear.

Purpose of the Study:

• To investigate the cause of the increased equilibrium hydrogen pressure in Mg/Pd thin films.
• To differentiate between intermixing and strain effects at the Mg-Pd interface.
• To develop a thermodynamic model explaining the observed pressure changes.

Main Methods:

• Transmission electron microscopy (TEM) to visualize interfacial structure.
• Depth profiling X-ray photoemission spectroscopy (DPXPS) to quantify interfacial composition.
• Annealing experiments to study the effect of temperature on intermixing and pressure.
• Thermodynamic modeling to correlate alloying effects with equilibrium pressure.

Main Results:

• Direct evidence of Mg-Pd intermixing at the interface was observed.
• Both intermixing and equilibrium hydrogen pressure increased with annealing temperature.
• The observed pressure increase is consistent with a few nanometers of intermixed layer.
• Measured stress during hydrogenation showed a negligible effect on equilibrium pressure.

Conclusions:

• Intermixing of Mg and Pd, not strain, is the primary cause for the increased equilibrium hydrogen pressure.
• Annealing significantly enhances both Mg-Pd intermixing and hydrogen pressure.
• The findings support a thermodynamic explanation for pressure changes due to alloying in Mg-based hydrogen storage materials.