NO₂ Adsorption on Oxygen-Modified Ag at Ambient Conditions

Area of Science:

• Surface Science
• Materials Chemistry
• Computational Chemistry

Background:

• Silver-based materials show potential for nitrogen dioxide (NO₂) removal and detection through surface interactions.
• Previous studies suggested NO₂ adsorbs as nitrate (NO₃) on silver surfaces, but theoretical calculations conflicted with experimental X-ray photoelectron spectroscopy (XPS) data.

Purpose of the Study:

• To investigate the adsorption of hydrogen (H₂) and NO₂ on oxygen-covered Ag(111) surfaces.
• To resolve discrepancies between theoretical predictions and experimental XPS assignments for adsorbed species.
• To provide a robust methodology for analyzing XPS spectra in chemoresponsive and catalytic systems.

Main Methods:

• Utilized density functional theory (DFT) calculations.
• Employed ab initio thermodynamics and core-level shift calculations.
• Combined theoretical methods with X-ray photoelectron spectroscopy (XPS) measurements.

Main Results:

• Identified hydroxyl groups (from H₂ adsorption) as thermodynamically favored, explaining the observed O 1s binding energy (BE) at 530.4 eV.
• Determined that NO₂ adsorbs as a dimer (N₂O₄), consistent with the N 1s BE signature at 405.8 eV.
• Predicted the N 1s BE for NO₃ to be around 407 eV, suggesting a reevaluation of current species assignments.

Conclusions:

• The adsorption species of NO₂ on oxygen-covered Ag(111) at 405.8 eV N 1s XPS peak is likely N₂O₄, not NO₃.
• The presence of hydrogen forming hydroxyl groups is crucial for understanding the surface chemistry and observed O 1s BE.
• A combined theoretical and experimental approach effectively resolves XPS spectra for complex surface systems.