NO₂ Adsorption on Oxygen-Modified Ag at Ambient Conditions

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.