Anodic underpotential deposition and cathodic stripping of iodine at polycrystalline and single-crystal gold: studies by LEED, AES, XPS, and electrochemistry

Abstract

The oxidative chemisorption and cathodic stripping reductive desorption of iodine have been compared at smooth polycrystalline and well-defined Au( 1 1 1) singlacrystal electrodes. Experimental measurements were based upon cyclic voltammetry, thin-layer coulometry, X-ray photoelectron spectroscopy, Auger electron spectroscopy, and low-energy electron diffraction. The results indicate that iodide is oxidatively adsorbed as zerovalent atomic iodine at potentials between -0.4 V and +0.4 V (Ag/AgCl reference); at lower potentials, surface iodine is reductively desorbed as aqueous iodide, while at considerably more positive potentials, it is oxidized to aqueous iodate. Studies with the Au( 11 1) electrode in dilute aqueous CsI solutions showed ordered adlayer structures at the selected potentials investigated. Below -0.4 V, the potential at which oxidative deposition of iodine starts to occur, a distinct (4x4) quarter-coverage CsI layer (0, = rCr/rAu = O1 rl/rAU -0.25) was formed. At -0.4 V < E < -0.2 V, increased to 0.33; this increase was coupled with the loss of adsorbed Cs, and the structure of this adlattice was Au( 11 1)(v'3Xt/3)R30°-I. At E > -0.2 V, the I coverage reached 0.4, a value made possible by a compression of the original (d3Xt/3)R30° structure in one dimension to form a nearly hexagonal iodine adlattice with a ( 5 x 4 3 ) unit cell. The amount of adsorbed iodine continues to increase as the potential is made still more positive until the surface is saturated with a monolayer of close-packed I atoms of coverage limited by van der Waals interactions; additional iodine forced into the already space-limited interfacial layer only leads to the formation of molecular iodine, which is evolved into the solution as I,(aq). The oxidative chemisorption process may be thought of as the oxidative underpotential deposition of I atoms, while the reductive desorption reaction may be viewed as the cathodic stripping of iodide ions.

Three-Dimensional Atom Probe Tomography of Oxide, Anion, and Alkanethiolate Coatings on Gold

“…Under a high positive electric field, these fragments can lose one or more hydrogen atoms and form lighter ions. Notably, clear evidence in the low-mass region can be found for molecular fragments associated with C 1 H x (14-15), C 2 H x (27-29), C 3 H x (36)(37)(38), and C 4 H x (55-56). There is also evidence for sulfur-containing species, such as S (32) and SCH x (44-46).…”

“…With an approximated detector efficiency of 50%, this number is comparable to the ion density values determined for iodide-covered gold surfaces from STM or LEED. 35,38 Notably, iodide surface densities of 4.6 and 4 ions nm -2 for the Au (111) and Au (100) surfaces are expected based upon a surface coverage of ∼0.3 monolayers, which is typical for adsorption from aqueous solutions. These results demonstrate the ability to detect a single monolayer of adsorbed ions on the surface of this gold specimen using the 3DAPT.…”

Observation of ‘inverted peak’ during molecular oxygen reduction at Au electrode in alkaline media

“…The broad response in the wide potential range of ca. −0.5 to −0.9 V is due to the reversible adsorption/deposition of I − [38]. The current in the potential zone of 0-0.2 V is diminished owing to the inhibition of chemisorption of OH − by I-adlayer [37].…”

“…In the presence of 0.1 mM KI ( Fig. 1(b)), the amplitude and broadness of the redox peak at −0.32 V corresponding to the UPD of Pb at the Au(1 1 1) domain increase due to the overlapping with the adsorption/deposition of I − [38], while the redox peak at −0.17 V is inhibited by the adsorbed I − [39]. The broad response in the wide potential range of ca.…”

Photocurrent enhancement in hybrid cadmium sulfide/conjugated polyaniline nanofiber composites by introducing iodine

“…3d. The I3d 5/2 for I 2 @PANI-CdS appears as one strong peak at 618.6, which can be attributed to triiodide (I 3 -) [36][37][38]. To study the photoresponse of the as-prepared electrode, the photocurrent generation is observed in the presence of CdS, PANI-CdS and I 2 @PANI-CdS ITO electrodes with Na 2 SO 3 solution (1 M, pH 12) as a sacrificial donor under visible-light ( = 420 nm) irradiation.…”