Underpotential Shift Research Articles

Unconventional Electrochemical Behaviors of Cu Underpotential Deposition in a Chloride-Based Deep Eutectic Solvent: High Underpotential Shift and Low Coverage.

The (5 × 5) Moiré pattern resulting from coadsorption of Cu atoms and chloride ions on the Au(111) electrode is one of the most classical structures for underpotential deposition (UPD) in electrochemical surface science. Although two models have been proposed to describe the pattern, the details of the structure remain ambiguous and controversial, leading to a question that remains to be answered. In this work, we investigate the UPD behaviors of Cu on the Au(111) electrode in a chloride-based deep eutectic solvent ethaline by in situ scanning tunneling microscopy (STM). Benefiting from the properties of the ultraconcentrated electrolyte, we directly image not only Cu but also Cl adlayers by finely tuning tunneling conditions. The structure is unambiguously determined for both Cu and Cl adlayers, where an incommensurate Cu layer is adsorbed on the Au(111) surface with a Cu coverage of 0.64, while the Cl coverage is 0.32 (only half of the expected value); i.e., the atomic arrangement of the observed (5 × 5) Moiré pattern in ethaline matches neither of the models proposed in the literature. Meanwhile, STM results confirm the origin of the cathodic peak in the cyclic voltammogram, which indicates that the underpotential shift of Cu UPD in ethaline indeed increases by ca. 0.40 V compared to its counterpart in a sulfuric acid solution, resulting in a significant deviation from the linear relation between the underpotential shift and the difference in work functions proposed in the literature. The unconventional electrochemical behaviors of Cu UPD reveal the specialty of both the bulk and the interface in the chloride-based deep eutectic solvent.

Electrochemistry of metal adlayers on metal chalcogenides

Electrodeposition of metal adlayers on semiconductor metal chalcogenides (CdSe, CdS, PbTe, PbSe, PbS, Bi2Te3) is reviewed. Cathodic underpotential deposition of metal adlayer on metal chalcogenide is the electrochemically irreversible surface limited reaction. The irreversibility of the upd increases in the row from tellurides to selenides and further to sulfides. The underpotential shift on chalcogenide nanoparticles increases with particle size. Metal upd on chalcogenides is applied as a means of measurement of electroactive surface area of chalcogenide electrodes. The method is especially advantageous for multicomponent systems with other component not supporting upd, such as CdSe-TiO2, CdSe-ZnO. Differences of voltammetric profiles of Pb upd on Bi2Te3 and Te are applied for detection of Bi2Te3 surface contamination by elemental tellurium. The further tasks in the electrochemistry of metal adlayers are their incorporation as interlayers in layered chalcogenides and electrodeposition of superlattices.

Progress of Research on Underpotential Deposition—— I. Theory of Underpotential Deposition

Underpotential deposition (upd) has been a hotspot in the field of electrochemical research throughout the years owing to its significant theoretical and applied research value. Theoretical research on upd primarily centers around the relations and rules of interaction among deposition substrates, deposition species, and anions (or other organic additives) during upd process. In this paper, the developments in theoretical research in recent years on upd on both the local and international levels are systematically summarized mainly from two viewpoints, namely, thermodynamics and kinetics. With regard to the thermodynamics of upd process, introductory comments and mathematical formulas are summarized from four aspects, i.e., underpotential shift (ΔEupd), electrosorption valency (γ), influence of temperature, and electrochemical adsorption isotherms. The applications and analyses of those related mathematical formulas are also presented in detail. In terms of the kinetics of upd process, nucleation and growth phenomena are mainly presented. We summarize the relevant mathematical models, and additionally introduce research studies on the characteristics of upd kinetics based on these mathematical models. Furthermore, this paper presents an outline of computational chemistry methods and application achievements concerning upd research. Finally, the theoretical research status of upd is presented, giving an overall view of the development trend.

The underpotential deposition that should not be: Cu(1 × 1) on Au(111)

Underpotential deposition of copper on Au(111) is analyzed in the light of first-principles calculations. The existence of a 1×1 Cu monolayer on Au(111) at underpotentials can be only understood taking into account the free energy excess delivered by the adsorption of sulfate anions. While a naked copper pseudomorphic monolayer results thermodynamically less stable than bulk copper, accounting for the interaction with sulfate ions delivers an underpotential shift which is comparable with the experimental value.

Underpotential deposition on free nanoparticles: Its meaning and measurement

The meaning of underpotential shift is discussed for free nanoparticles, where a redox couple is used to set potential control on them. Atomistic Monte Carlo simulations are performed to study their decoration in the submonolayer regime. The resulting configurations are used to simulate their plasmon spectra by means of a state-of-the art quantum mechanical atomistic model.

An in situ scanning tunneling microscopic study of electrodeposition of bismuth on Au(1 1 1) in a 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid: Precursor adsorption and underpotential deposition

In this article, the electrodeposition of Bi on Au(1 1 1) surface in the underpotential region in BMIBF 4 ionic liquid containing BiCl 3 is studied by cyclic voltammetry and in situ scanning tunneling microscopy (STM). The cyclic voltammogram shows several cathodic and anodic peaks associated with underpotential deposition (UPD) of Bi and dissolution of the UPD deposit, respectively, in the potential region between −0.38 and −0.7 V versus Pt quasi-reference electrode. In situ STM results indicate there is a BiCl 3 precursor adsorption stage prior to the Bi UPD. The adsorption of BiCl 3 leads to the formation of unique hexagonal and trigonal supramolecular assembly with a Au(1 1 1)(10 × 10) structure. The initial stage of Bi UPD proceeds with the formation of Au(1 1 1)(7 × 7) R21.8° adlayer structure composed of Bi trigonal clusters at −0.5 V. A structural transformation occurred at −0.6 V resulting in a unique “zipper-like” double-chain pattern composed of well-aligned Bi trigonal clusters which can be denoted by Au(1 1 1)(5 × 25√3/3) structural model. The trigonal clusters composed of six Bi atoms seem to be the main characteristic elemental units of Bi UPD adlayer regardless of underpotential shift. These features are dramatically different from those observed in Bi(III)-containing acidic aqueous solutions as well as in chloroaluminated ionic liquid, but are similar to those of Sb UPD in BMIBF 4 ionic liquid, which reveals profound solvent effects on the electrodeposition of semimetals.

Density Functional Study on the Stability and Reactivity of Pt(100) and Pt(111) Surfaces Modified by Ni Atoms

AbstractDFT study on the the stability and reactivity of Pt(100) and Pt(111) surfaces modified by nickel UPD monolayer deposition have been carried out. We used the binding energy calculation of bimetallic structures versus the cohesion energy of the bulk adsorbate to quantify the underpotential shift (ΔEupd) to determine the stability of the bimetallic systems. The reactivity of the clean and modified surface was analized by energy levels of the highest occupied molecular orbital (HOMO), softness and local softness. We concluded that the stability of Pt(100)25Ni9 and Pt(111)25Ni10 bimetallic structures cannot be explained by excess of the metal- substrate binding energy but the instability can be explained by structural effects. We found that the modified surfaces are more reactive and the active sites are located in the centre of the cluster which favores the formation of islands of atoms onto these surfaces.

In Situ STM Studies on the Underpotential Deposition of Antimony on Au(111) and Au(100) in a BMIBF4 Ionic Liquid

In this article, the underpotential deposition (UPD) of Sb on Au(111) and Au(100) over a wide potential range in a BMIBF4 ionic liquid containing SbCl3 is investigated by cyclic voltammetry and in situ scanning tunneling microscopy (STM). The cyclic voltammograms of the two surfaces show similar features of Sb UPD, which is kinetically sluggish at high underpotential shift but rapid at low underpotential shift with a large and broad reduction peak. The total charge flux associated with the UPD suggests an equivalent of nearly 1 ML quantity of Sb deposit. In situ STM results showed precursor adsorption and several stages of the UPD. The prior UPD reversible adsorption of SbCl3 precursor occurs only on Au(111) with an ordered hexagonal array of six- and seven-membered clusters in (√31 × √31)R8.9° registration with the Au(111) surface. On both Au(111) and Au(100), the initial stage of Sb UPD (from −0.2 to −0.4 V) proceeds with the formation of similar short atomic strips of Sb atoms with a length of 2−2.5 nm...

Preparation of bismuth telluride thin film by electrochemical atomic layer epitaxy (ECALE)

Thin-layer electrochemical studies of the underpotential deposition (UPD) of Bi and Te on cold rolled silver substrate have been performed. The voltammetric analysis of underpotential shift demonstrates that the initial Te UPD on Bi-covered Ag and Bi UPD on Te-covered Ag fitted UPD dynamics mechanism. A thin film of bismuth telluride was formed by alternately depositing Te and Bi via an automated flow deposition system. X-ray diffraction indicated the deposits of Bi2Te3. Energy Dispersive X-ray Detector quantitative analysis gave a 2: 3 stoichiometric ratio of Bi to Te, which was consistent with X-ray Diffraction results. Electron probe microanalysis of the deposits showed a network structure that results from the surface defects of the cold rolled Ag substrate and the lattice mismatch between substrate and deposit.

Cadmium atomic layers on tellurium electrodes

The process of electrodeposition of atomic layers of cadmium Cdad at order of magnitude polycrystalline tellurium electrodes at potentials in excess of equilibrium potential E Cd 2+/Cd (underpotential deposition, UPD) is studied. In acid sulfate solutions (0.1 M H2SO4 + 0.05 M CdSO4), the magnitude of underpotential (underpotential shift) ΔE UPD = 0.41 V. In cyclic voltammograms, the anodic oxidation of Cdad is recorded in the form of two peaks of anodic current that are displaced relative to one another in the potential scale (weakly and strongly bound adatoms). The cadmium UPD process on tellurium is accompanied by the diffusion of cadmium into the bulk of tellurium and a transition from a 2D structure Cdad/Te to 3D CdTe nanostructures, which are distributed in the tellurium matrix. In contrast with tellurium, the Te/CdTenano heterostructure exhibits photoelectrochemical activity, i.e. it generates a cathodic photocurrent.

Optimization of the formation of bismuth telluride thin film by using ECALE

The formative optimization of Bi 2Te 3 VA–VIA group compound thin film by using electrochemical atomic layer epitaxy (ECALE) was reported. Cyclic voltammograms were used to analyze electrochemical aspects of tellurium and bismuth. The voltammetric analysis of underpotential shift demonstrates that the first Te UPD on Bi-covered Au and Bi UPD on Te-covered Au fit UPD dynamics mechanism. Using the integrated Faradaic charges of anodic stripping currents, the UPD region of the first Bi UPD on Te-covered Au and Te UPD on Bi-covered Au were determined. An optimized deposition program was developed to form 200 cycles deposits. X-ray diffraction indicated the deposits were Bi 2Te 3 compound. EDX quantitative analysis gave a 2:3 stoichiometric ratio of Bi to Te, which is consistent with the XRD result. The surface morphology was determined by field emission scanning electron microscope (FESEM). It showed that the deposits consist of 30–100 nm crystallites and are conformal with the Au substrate, which suggested an epitaxial growth mechanism for Bi 2Te 3 thin films.

The underpotential deposition of bismuth and tellurium on cold rolled silver substrate by ECALE

Thin-layer electrochemical studies of the underpotential deposition (UPD) of Bi and Te on cold rolled silver substrate have been performed. Different approaches have been employed to investigate the influence of silver oxide film on Bi UPD. As a result, the precedent deposition of a little bismuth can effectively prevent silver from surface oxidation. The voltammetric analysis of underpotential shift demonstrates that the first Te UPD on Bi-covered Ag and Bi UPD on Te-covered Ag fit UPD dynamics mechanism. Thin film of bismuth telluride was formed using an automated flow deposition system, by alternately depositing Te and Bi. The electrochemical conditions necessary to form Bi 2Te 3 deposits of 50 cycles on cold rolled silver by ECALE are described here. X-ray diffraction indicated the deposits were Bi 2Te 3. EDX quantitative analysis gave the 2:3 stoichiometric ratio of Bi to Te, which is consistent with XRD result. Electron probe microanalysis of the deposits showed a worm-like network structure. The map of Te and Bi element indicated the distribution of both Te and Bi is homogeneous and locates the same sites, which is favorable to Te–Bi binary system. The composition analysis of structural expanded image also showed the approximately constant composition of Te:Bi ≈ 3:2 has taken place.

Underpotential Deposition of Copper on Electrochemically Prepared Conductive Ruthenium Oxide Surface

Copper underpotential deposition (UPD) on a conductive hydrous ruthenium oxide (RuO x H y ) surface was studied by progressive cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). Cu UPD on an electrochemically prepared RuO x H y surface started at 0.15 V in a 2 mM CuSO 4 solution and reached a coverage plateau of ca. 0.9 monolayer (ML) beyond -0.05 V (vs. Ag/AgCl). XPS data confirmed that Cu deposits underpotentially on RuO x H y surface. The anodic polarization potential determines the chemical states and affects the Cu UPD/bulk deposition of RuO x H y electrode. We observed close to a 55% increase of underpotential shift for Cu UPD on RuO x H y (ca. 170 mV) in comparison to Ru surface (ca. 110 mV). The results suggest that interfacial binding of the first ML of Cu on RuO x H y is stronger than Ru by 12 kJ mol - 1 . Possible applications of Cu UPD to Ru-based plateable seedless Cu diffusion barrier are discussed.

Electrochemical adsorption of rhodium on platinum

Electrosorption of rhodium on a polycrystalline platinum surface has been studied. It has been found that a complete Rh-coverage can be obtained by spontaneous adsorption via the ionization of preadsorbed hydrogen. Underpotential deposition of rhodium has been observed both in 0.5 M H 2SO 4 and 0.2 M HCl supporting electrolytes. The value of the underpotential shift was found to be about 100–120 mV.

Clustering and Anisotropy in Monolayer Formation under Potential Control: Sn on Au(111)

We present an in situ scanning tunneling microscopy study on Sn underpotential deposition (UPD) on reconstructed and unreconstructed Au(111) electrodes. Unusual behaviors in the formation of Sn (sub)monolayer at high underpotential shift are observed on both surfaces. On the unreconstructed Au(111) surface, Sn forms size-confined two-dimensional clusters of 1−2 nm. Decreasing potential leads to immersion of the Sn clusters into the substrate surface lattice forming surface alloying. While on reconstructed Au(111) surface, Sn prefers to nucleate in the face-centered cubic regions followed by anisotropic growth along the [112̄] direction of the reconstruction rows. The nuclei expand toward the hexagonal close packed regions to build up deposit domains which develop until a final gap of 3−6 nm is reached between two adjacent domains. Decreasing potential leads to a structural transformation to cordlike structures aligning all in one direction by rotation of 18−21° with respect to the [112̄] direction, involving surface alloying. The results are in contrast to the previously observed UPD adlayer structure and dynamics. The nanoscale properties of the Sn deposit and the influence from the UPD alloying are discussed as the two possible causes for the unusual Sn UPD phenomena.

Fundamentals of Underpotential Deposition : Importance of Underpotential Deposition in Interfacial Electrochemistry

This article covers the fundamentals of underpotential deposition (UPD), focussing on the importance of UPD in interfacial electrochemistry. Firstly, this article described the basic concepts of UPD, including underpotential shift and electrosorption valency. Secondly, the present article explained UPD of hydrogen, followed by hydrogen evolution or hydrogen absorption, giving special attention to the adsorption sites of hydrogen on metal surface and the absorption mechanism into Pd. Finally, this article briefly presented the important factors associated with UPD in various fields of interfacial electrochemistry from practical viewpoints.

Cu underpotential deposition on Au(111) and Au(100). Can this be explained in terms of the energetics of the Cu/Au system?

In this work we undertake a first principles study of the deposition of Copper on Au(111) and Au(100) surfaces from a density functional point of view. The analysis of the different energetic contributions to the so-called underpotential shift indicates that the deposition of Cu on any of these surfaces should occur at overpotentials. We conclude that some other factors must be taken into account to explain the experimental results, such as anion coadsorption. We also analyze the work function and the electronic density in the system.

An embedded atom approach to underpotential deposition phenomena

We have performed embedded atom calculations for a number of systems of electrochemical interest involving a metallic single-crystal substrate and a metallic adsorbate. Different thermodynamic contributions to the so-called underpotential shift are calculated and analyzed comparatively, drawing some general trends. The metal pairs considered involve silver, gold, platinum, palladium and copper. We consider the possibility of underpotential deposition through the excess of binding energy, arriving at two novel conclusions. First, for some systems consisting of metal M 1 and M 2, underpotential deposition should be energetically possible in both cases, that is M 1 on M 2 and M 2 on M 1. Second, anions may play a decisive role in changing the energetics of some systems. In particular cases like copper on Au(111) they may be responsible to a large extent for the existence of an underpotential deposition. Entropic contributions were neglected in the present analysis.

Bromide Adsorption Induced Formation of Thallium Bromide Adlayers with Varying Composition and Structure on the Au(111) Electrode Surface

The underpotential deposition of Tl on Au(111) in 0.1 M HClO4 solution containing 1 mM Tl+ and 1 mM Br- has been investigated by using cyclic voltammetry, in situ X-ray scattering, and rotating disk-ring techniques. Three interesting phenomena for the UPD of metals in the presence of adsorbed anions are reported, viz., (i) an increase of the underpotential shift for deposition of Tl on Au(111) in the presence of Br- in solution, (ii) a formation of two mixed adlayers, surface compounds, with the stoichiometry Tl−Br2 and Tl−Br, and (iii) an exceptionally complex structural behavior of this system with five ordered phases. Bromide and thallium form incommensurate rotated-hexagonal close-packed phases at ca. 0.85 and −0.3 V, respectively. In the intermediate potential region three mixed phases exist, identified as 3TlBr2-(√13 × √13), 2TlBr-(3 × √3), and TlBr-c(p × √3).

Electrodeposition of Zinc from the Lewis Acidic Aluminum Chloride‐1‐Methyl‐3‐ethylimidazolium Chloride Room Temperature Molten Salt

The electrodeposition of zinc on polycrystalline gold, platinum, and tungsten and on glassy carbon was investigated in the 60.0–40.0 mole percent aluminum chloride‐1‐methyl‐3‐ethylimidazolium chloride molten salt containing electrogenerated zinc (II). The electrodeposition of zinc on all of the polycrystalline metal electrodes was preceded by underpotential deposition processes similar to those reported previously during studies carried out in aqueous solutions. The underpotential shift was found to vary linearly with the difference in the work functions of zinc and the metallic substrate. In contrast, the electrodeposition of zinc on glassy carbon required a substantial nucleation overpotential. Dimensionless chronoamperometric current‐time transients for the electrodeposition of zinc on this substrate were in good accord with the theoretical transients for the limiting case of progressive three‐dimensional nucleation with hemispherical diffusion‐controlled growth of the nuclei. Analysis of the nucleation kinetics by using the atomistic theory of nucleation suggested that active sites on the glassy carbon surface played the role of critical nuclei during the initial stages of the deposition process. The formal potential of the Zn(II)/Zn couple at 40°C was found to be vs. the Al(III)/Al couple in pure melt, and the diffusion coefficient of zinc(II) was determined to be .