“…On the other hand, the broad diffusional-like feature between +0.50 and +0.70 V suggests a slow process. This might be accounted by the existence of intermediate states during the reduction of Hg(I) to Hg(0), as indicated in previous electrochemical studies on polycrystalline Au. − In this paper, we will focus on the structure and kinetics of Hg UPD layers at potentials within this broad wave. 1 Cyclic voltammogram of a Au(111) electrode in 0.10 M sulfuric acid containing 1.0 mM Hg 2+ at a scan rate of 2 mV/s. Inset: voltammetric profile over the range of +1.05 to +0.70 V vs Ag/AgCl (3 M KCl).…”
Section: Resultsmentioning
confidence: 95%
“…The lattice constant of this structure is 28.2% larger than the nearest neighbor distance in bulk Hg (3.01 Å). Considering that this structure might correspond to one of the partially charged states, − the expanded lattice can be readily rationalized by the Coulombic repulsion between partially charged Hg atoms. 3 Schematic of the real space model of Hg UPD phase I. 4 Schematics of two possible commensurate real space structural models of Hg UPD phase II.…”
Section: Resultsmentioning
confidence: 99%
“…Salié and Bartels − found that in perchloric acid solutions containing Hg(I) or Hg(II), the UPD of mercury involves a nonintegral partial charge transfer. Two different processes were detected during the deposition of Hg(I) at polycrystalline Au electrodes in the underpotential range by potentiostatic measurements at a rotating ring-disk electrode 13-15 and by impedance spectroscopy . The first process was proposed to be the adsorption of metal ions onto the gold substrate surface to form an intermediate species with a partial charge of about 0.53e - per Hg atom.…”
We report on an in situ surface X-ray diffraction study of the underpotential deposition (UPD) of mercury on Au(111). We have observed three UPD phases present at potentials prior to bulk mercury deposition. These phases consist of two well-ordered intermediate states and what appears to be either a fully discharged twodimensional liquid Hg layer or a monolayer of an amorphous Hg-Au alloy. Both ordered intermediate phases have hexagonal structures with lattice vectors that are rotated 30°from those of the Au(111) substrate. The first phase (phase I), present at a potential of +0.68 V, was only observed on fresh flame-annealed Au( 111) electrodes and appears to be an open incommensurate structure with a lattice constant of 3.86 ( 0.03 Å. This phase appears to be metastable since it changes to a second ordered phase (phase II) after a certain time at +0.68 V or after the potential is moved to more negative values (+0.63 V). The second phase has a more compact lattice with a ) 3.34 ( 0.01 Å and appears to be a commensurate 2×2 structure with 2 / 3 of the Hg atoms at threefold hollow sites and 1 / 3 on atop sites. Similar to the first one, this phase is also metastable and can be transformed to a final, fully discharged, state of a two-dimensional liquid Hg layer or an amorphous Hg-Au alloy. The entire Hg UPD process, from Hg 2+ to the fully discharged metallic Hg layer, agrees well with a multistep mechanism based on previous electrochemical kinetic studies on polycrystalline Au electrodes. Our results also show that the UPD of Hg on Au(111) electrodes is quite different from that of other metals such as Cu, Ag, Tl, and Pb.
“…On the other hand, the broad diffusional-like feature between +0.50 and +0.70 V suggests a slow process. This might be accounted by the existence of intermediate states during the reduction of Hg(I) to Hg(0), as indicated in previous electrochemical studies on polycrystalline Au. − In this paper, we will focus on the structure and kinetics of Hg UPD layers at potentials within this broad wave. 1 Cyclic voltammogram of a Au(111) electrode in 0.10 M sulfuric acid containing 1.0 mM Hg 2+ at a scan rate of 2 mV/s. Inset: voltammetric profile over the range of +1.05 to +0.70 V vs Ag/AgCl (3 M KCl).…”
Section: Resultsmentioning
confidence: 95%
“…The lattice constant of this structure is 28.2% larger than the nearest neighbor distance in bulk Hg (3.01 Å). Considering that this structure might correspond to one of the partially charged states, − the expanded lattice can be readily rationalized by the Coulombic repulsion between partially charged Hg atoms. 3 Schematic of the real space model of Hg UPD phase I. 4 Schematics of two possible commensurate real space structural models of Hg UPD phase II.…”
Section: Resultsmentioning
confidence: 99%
“…Salié and Bartels − found that in perchloric acid solutions containing Hg(I) or Hg(II), the UPD of mercury involves a nonintegral partial charge transfer. Two different processes were detected during the deposition of Hg(I) at polycrystalline Au electrodes in the underpotential range by potentiostatic measurements at a rotating ring-disk electrode 13-15 and by impedance spectroscopy . The first process was proposed to be the adsorption of metal ions onto the gold substrate surface to form an intermediate species with a partial charge of about 0.53e - per Hg atom.…”
We report on an in situ surface X-ray diffraction study of the underpotential deposition (UPD) of mercury on Au(111). We have observed three UPD phases present at potentials prior to bulk mercury deposition. These phases consist of two well-ordered intermediate states and what appears to be either a fully discharged twodimensional liquid Hg layer or a monolayer of an amorphous Hg-Au alloy. Both ordered intermediate phases have hexagonal structures with lattice vectors that are rotated 30°from those of the Au(111) substrate. The first phase (phase I), present at a potential of +0.68 V, was only observed on fresh flame-annealed Au( 111) electrodes and appears to be an open incommensurate structure with a lattice constant of 3.86 ( 0.03 Å. This phase appears to be metastable since it changes to a second ordered phase (phase II) after a certain time at +0.68 V or after the potential is moved to more negative values (+0.63 V). The second phase has a more compact lattice with a ) 3.34 ( 0.01 Å and appears to be a commensurate 2×2 structure with 2 / 3 of the Hg atoms at threefold hollow sites and 1 / 3 on atop sites. Similar to the first one, this phase is also metastable and can be transformed to a final, fully discharged, state of a two-dimensional liquid Hg layer or an amorphous Hg-Au alloy. The entire Hg UPD process, from Hg 2+ to the fully discharged metallic Hg layer, agrees well with a multistep mechanism based on previous electrochemical kinetic studies on polycrystalline Au electrodes. Our results also show that the UPD of Hg on Au(111) electrodes is quite different from that of other metals such as Cu, Ag, Tl, and Pb.
“…The Hg UPD process is particularly important because of the technical significance of Hg amalgams and Hg surfaces in electrochemical and other processes. Underpotential deposition of Hg has been studied extensively with standard electrochemical techniques [9][10][11][12][13][14][15], but fundamental insight has been elusive because of the lack of microscopic surface structural information. In addition, the sensitivity of this process to different electrolytes is unknown.…”
Section: Department Of Chemistry University Of Illinois 505 S Mathmentioning
The structures of monolayers of Hg atoms underpotentially deposited on Au(l 11) were resolved with the atomic force microscope. In sulfate, nitrate, and perchlorate electrolytes, a hexagonal overlayer with a 0.58 ±0.02-nm spacing was seen. In acetate, a hexagonal lattice exhibiting a 0.74±0.05-nm spacing was observed positive of the underpotential-deposition potential, a rhombic lattice with a 0.43 ± 0.02-nm spacing was seen at intermediate potentials, and another hexagonal lattice with a 0.30±0.03-nm spacing was found just positive of bulk deposition. PACS numbers: 68.55.-a, 82.45.+Z Development of a detailed understanding of the structure of the electrified solid-liquid interface is a central step in understanding electrochemical reactivity. A fundamental example of this reactivity is the deposition of a monolayer of one metal onto another. This phenomenon, known as underpotential deposition (UPD) [1], occurs when metal ions are electrodeposited onto a (different) metal surface at potentials positive from the reversible (Nernst) potential. In this process, only a monolayer or submonolayer of the metal forms on the electrode surface. The structure of these monolayers has attracted considerable attention because of their importance in electrodeposition and electrocatalytic [2] processes. In UHV environments, monolayers of foreign metal adatoms evaporated onto (ill) surfaces exhibit closepacked incommensurate structures [3,4]. These closepacked structures arise from net attractive forces between the adatoms. The demonstration that UPD monolayers of Cu [5,6] and Ag [7] form open adlattice structures in the electrochemical environment has been taken to imply that the force between adatoms has become repulsive, possibly deriving from coadsorption of electrolyte with the metal. Alternatively, other effects could also serve to open the adlattice. In particular, retention of a partial charge on the adatom, complex formation with the electrolyte, or deposition of a non-fcc element onto a (111) surface of an fee material could all lead to open lattices.In this Letter, we report an atomic force microscope (
AFM) [8] structural study of UPD of Hg onto Au(l 11) surfaces in four different electrolytes. The Hg UPD process is particularly important because of the technical significance of Hg amalgams and Hg surfaces in electrochemical and other processes. Underpotential deposition of Hg has been studied extensively with standard electrochemical techniques [9-15], but fundamental insight has been elusive because of the lack of microscopic surface structural information. In addition, the sensitivity of this process to different electrolytes is unknown. This latter point is important because UPD lattices of Cu [5,6] andAg [7] on Au(lll) surfaces exhibit strong electrolyte sensitivity. AFM images were obtained with a Nanoscope II AFM [16] operating in constant force mode. The force, optimized for each image, was nominally 1 x 10"^ N. A cell made from glass held the electrolyte. Au(l 11) electrodes were prepared by evaporation onto ...
“…The electrochemistry of Hg(II) on noble metal electrodes has been studied extensively on polycrystalline Au [1][2][3][4][5][6][7][8], well defined single crystal Au(1 1 1) surface [9][10][11][12][13], and Au nanoparticles on glassy carbon [14]. The progress in underpotential deposition phenomena on Au, Pt, Ag and other single crystal surfaces has been recently reviewed by Abruna and coworkers [15].…”
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
