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.