Silver surfaces in sulfuric acid: Ag(100) – sulfate
In this chapter an overview of the sulfate ion adsorption on Ag(100), Ag(111) and Ag(110) surfaces is described.
Frumkin adsorption isotherms of sulfate adsorption were determined by means of radiometry from HClO4 solution on the three low-index planes Ag(100), Ag(111), and Ag(110). It was found that the adsorption strength decreases in the order Ag(111) > Ag(110) > Ag(100) and showed an intermediate behavior on a polycrystalline silver electrode. The stronger interaction with Ag(111) can be explained by the match between the tetrahedral symmetry of the anion and the trigonal symmetry of the substrate [see however Cu(111), Chap. 195[ https://doi.org/10.1007/978-3-662-53908-8_195]].
With STM an incommensurate (1.3 × 3) structure was observed, corresponding to a coverage of 0.25 ML. Since this structure is only stable in acidic solution (pH = 1), it is likely that this structure is stabilized by H3O+ ions (like on Cu(111), Chap. 194[ https://doi.org/10.1007/978-3-662-53908-8_194]). The structure, however, is not stable at potentials slightly above −0.2 V (SCE). The presence of sulfate does not affect the oxidation potential of silver electrodes but facilitates the hydrogen evolution reaction. The sequence of adsorption in a neutral solution is quite different to that in acidic solution and follows the sequence of the potential of zero charge (Epzc): −0.48 V, −0,65 V, and −0.77 V (RHE) for Ag(111), Ag(100), and Ag(110), respectively [1, 2, 3, 4].
scanning tunneling microscopy
saturated calomel electrode
reference hydrogen electrode