H₂O‑Dissociative Adsorption on Mg(0001) SurfaceCorrosion Process under Atmospheric Conditions

Area of Science:

• Materials Science
• Surface Chemistry
• Corrosion Science

Background:

• Metallic magnesium, the lightest structural metal, has significant application potential but suffers from high corrosion susceptibility.
• The precise mechanism of magnesium corrosion, particularly under atmospheric conditions, remains incompletely understood.

Purpose of the Study:

• To investigate the reactions of water (H₂O) on the magnesium (Mg(0001)) surface under atmospheric conditions.
• To explore the influence of oxygen on the interaction between water and the Mg(0001) surface.
• To provide an atomic-level understanding of adsorption and reaction mechanisms.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model the interactions.
• Electronic structure analyses, including Partial Density of States (PDOS), Crystal Orbital Hamilton Population (COHP), and Bader charge analysis, were performed.

Main Results:

• Molecular H₂O adsorption on pure Mg(0001) is weak; dissociative adsorption is favored both kinetically and thermodynamically.
• Formed hydrogen (H*) and hydroxyl (OH*) species preferentially occupy surface sites.
• Oxygen (O*) species migrate to subsurface sites, facilitating deep oxidation, especially at higher coverages.
• Surface oxygen significantly enhances water dissociation.
• Oxidized surface layers, rich in hydroxyls, can form protective barriers against further reactions.

Conclusions:

• Dissociative adsorption of water is the primary initial reaction pathway on Mg(0001).
• Oxygen plays a crucial role in promoting deeper oxidation by facilitating water dissociation and migrating into subsurface sites.
• The formation of hydroxyl-rich oxidized layers can impart a degree of protection to the magnesium surface under specific conditions.