Formation of a More Noble Underpotentially Deposited Silver Layer on Gold by the Adsorption of Chloride

Abstract

The repetitive electrochemical underpotential deposition (upd) and stripping of Ag on Au(111) in sulfuric acid in the presence of small amounts of chloride produce a substantially more noble Ag upd adlayer than that formed during initial depositions. The evidence for this increase in nobility is a gradual and direct replacement of the primary upd and stripping peaks in initial cyclic voltammograms by peaks at anodic potentials higher by roughly 80 mV. The transformation is quantitative and reversible and occurs with a smoothing of the gold substrates, as observed by scanning probe microscopies. The amount of transferred charge increases by about 20% from the initial depositions (92 ± 2 μC/cm2) to the more noble state (110 ± 2 μC/cm2), indicating a change in the Ag adlattice from its initial 3 × 3 structure to a more densely packed structure. X-ray photoelectron spectroscopy (XPS) shows that the more noble Ag adlayer includes a stoichiometric amount of chloride and that its amount varies directly with the amount of silver that deposits at the higher oxidation potential. The combined results from electrochemistry and XPS reveal that chloride adsorbs onto the surface during the underpotential deposition of Ag, produces a weakly adsorbed chloride layer on gold when the silver layer is removed, and is responsible for producing a more noble Ag upd layer on gold.

Electrochemical silver deposition on adsorbate modified Au(111) electrode

“…The deviations between our experiments and the findings discussed in [18] might be due to differences in the emersion potentials. It should be noticed that both silver species, the reduced and the oxidized form, interact with chloride ions at positive potentials.…”

“…Admittedly Michalitsch and co-workers [18] interpret on the basis of XPS data even this peak pair as the surface formation of AgCl caused by small impurities of chloride ions present in suprapure perchloric acid yet.…”

“…A surface coverage of AgCl was calculated giving not more than 0.25 ML with respect to the gold underground after 25 potential cycles. Also Michalitsch et al [18] discussed differences of about 200 meV in d-band energies between the neutral Ag monolayer and Ag species interacting with chloride ions at the surface.…”

Electrochemical Sensing of Thiocyanate Using Gold Electrodes Modified with an Underpotentially Deposited Silver Monolayer

“…We observed the formation of new peaks at ca. 610 mV vs. Ag þ/0 that could be ascribed to silver adatoms coordinated to chloride [16,17]. For conditions that generated higher coverages of adsorbed chloride, the peak at ca.…”

The influence of counter anions on the underpotential deposition of mercury(II) on Au(111): temperature-dependent studies

“…These workers observed the formation and reconstruction of ordered CuX bilayers (X ¼ Br À , Cl À ) prior to the onset of Cu upd. Laibinis and co-workers [12] investigated the upd of Ag onto Au(1 1 1) surfaces from sulfuric acid electrolyte in the presence of trace levels of chloride. Repetitive deposition and stripping cycles resulted in a shift of the upd potential to more negative values.…”