DFT Studies on the Nature of Coadsorbates on SO₄ ²⁻/Au(111)

Density Functional Theory (DFT) studies were performed on the adsorption of sulfate on Au(111). Focusing on the well-known (√3 × √7)R19.1° structure reported by various surface sensitive techniques, the coadsorption of H 3 O + and/or H 2 O has been considered in different combinations. The calculated binding energies show that the coadsorption of a single H 3 O + per sulfate is the most stable configuration, which is in agreement with experimental observations. Further, we find that in the case of coadsorption of both H 3 O + and H 2 O along with sulfate, one of the protons of hydronium moves to sulfate, finally leading to bisulfate with two coadsorbed water molecules. Besides the morphology and energetics of the different configurations, we also discuss the nature of the surface bonds by analyzing the charge density distribution.