Surface steps dominate the water formation on Pd(111) surfaces.

Area of Science:

• Surface chemistry
• Catalysis
• Computational materials science

Background:

• Water formation on palladium (Pd) surfaces is a critical process in various technologies and a model reaction for surface science.
• Existing research has not fully elucidated the specific active sites or the dominant reaction pathways (e.g., OH* + OH* vs. OH* + H*).

Purpose of the Study:

• To investigate the dominant reaction pathways and active sites for water formation on Pd surfaces.
• To determine the influence of temperature and surface defects on the water formation reaction rate.
• To validate computational findings against experimental observations.

Main Methods:

• Employed first-principles density functional theory (DFT) calculations.
• Utilized kinetic Monte Carlo (KMC) simulations to model reaction dynamics.
• Compared simulation results with experimental data across various conditions.

Main Results:

• Surface steps and point defects significantly influence the overall reaction rate.
• The primary reaction pathway for water formation is temperature-dependent: OH* + OH* at low temperatures and OH* + H* at high temperatures.
• Hydroxyl radical (OH*) formation, facilitated by steps, is the rate-limiting step under all studied conditions.
• OH* formation mechanisms vary with temperature, involving O* + H* association or OOH* splitting at low temperatures and exclusively O* + H* association at high temperatures.

Conclusions:

• The study provides a detailed mechanistic understanding of water formation on Pd surfaces.
• The developed first-principles-based kinetic model accurately reproduces experimental observations.
• Findings highlight the importance of surface structure and temperature in catalytic water formation.