# NO2 Adsorption on Oxygen-Modified Ag at Ambient Conditions

## TL;DR

This study investigates how NO2 interacts with oxygen-modified silver surfaces under normal conditions, using both experiments and theory to clarify conflicting XPS results.

## Contribution

A combined ab initio/experimental approach is introduced to resolve XPS spectral assignments for NO2 adsorption on silver.

## Key findings

- Hydroxyl groups on the surface are thermodynamically favored and explain the observed O 1s binding energy.
- NO2 adsorbs as a dimer (N2O4), explaining the N 1s binding energy at 405.8 eV.
- The N 1s XPS peak at 405.8 eV should be reevaluated as it does not correspond to NO3.

## Abstract

Silver-based materials
are promising for the removal and detection
of NO2 via surface reactions. Under ambient conditions,
NO2 has been reported to adsorb on silver surfaces as NO3. However, theoretical calculations are in conflict with the
N 1s X-ray photoelectron spectroscopy (XPS) assignment of NO3 adsorbed on Ag(111). Here, density functional theory calculations,
ab initio thermodynamics, and core-level shift calculations, in combination
with XPS measurements, are used to investigate the adsorption of H2 and NO2 on oxygen-covered Ag(111). We found that
the presence of hydrogen on the surface as hydroxyl groups is thermodynamically
favored and explains the experimentally observed O 1s binding energy
(BE) signature on Ag(111) at 530.4 eV. Moreover, we determined that
NO2 adsorbed in a dimer form (N2O4) elucidates the N 1s BE signature observed at 405.8 eV, whereas
the N 1s BE signature for NO3 is predicted to be closer
to 407 eV. Overall, our results suggest that the species assignment
for N 1s XPS peak at 405.8 eV on O-covered Ag(111) upon exposure to
NO2 should be reevaluated. This work demonstrates a combined
ab initio/experimental methodology capable of resolving XPS spectra
of a system with chemoresponsive and catalytic applications.