Copper Adlayer Research Articles

Influence of Sulfonates on the Interfacial Ion Transfer Kinetics of Cu at Au(111) Surfaces

Corrosion reactions profoundly impact the operational stability of various electrochemical components, such as electrocatalysts, conductive supports, and semiconducting light absorbers. Understanding the kinetics of ion transfer at electrode/electrolyte interfaces is crucial for deciphering the durability of copper-containing electrochemical devices. This study investigates the corrosion and deposition behavior of copper adlayers on gold(111) surfaces in sulfate and sulfonate electrolytes, with a focus on adsorption kinetics influenced by anion structure and Lewis acidity. At low scan rates, the adsorption and desorption capacitance of the broad adsorption region previously assigned to random adsorption of Cu on Au(111) surface in sulfuric acid, were nearly symmetric in E and invariant with ν, indicating reversible kinetics across all four electrolytes. At faster scan rates, the experiments reveal distinct adsorption/desorption responses for different anions, shedding light on the interplay between ion transfer kinetics, corrosion rates, and the microenvironment of electrocatalysts. The results provide valuable insights into the fundamental processes governing interfacial ion transfer and offer implications for the design and optimization of electrochemical systems. Figure 1

Pushing Cu uphill of the volcano curve: Impact of a WC support on the catalytic activity of copper toward the hydrogen evolution reaction

The adsorption of atomic H and H2 on copper mono- and submonolayers supported on hexagonal WC(0001) surfaces has been investigated using density functional theory with the Perdew–Burke–Ernzerhof exchange correlation functional and D2 van der Waals corrections. Results evidence the impact of the termination of the carbide substrate on fundamental properties of Cu adatoms, and, hence, on the stability of molecular and atomic hydrogen, defining copper's catalytic activity for hydrogen evolution reaction. Using H adsorption energy as a descriptor, catalytic activity of Cu adlayers for hydrogen evolution reaction was estimated using traditional volcano curves and a curve, obtained at low hydrogen coverage. Obtained results evidence that copper adlayers supported on the WC may present a viable low-cost alternative to noble metal-based catalysts, with improved catalytic activity compared to that of copper. This, potentially, can be a useful basis for designing and developing novel functional materials with predetermined catalytic properties.

Electrochemical nucleation and growth of Cu onto Au nanoparticles supported on a Si (111) wafer electrode

This work showed that chemically-synthesized gold nanoparticles, AuNPs, supported onto a Si (111) wafer electrode, can be selectively modified with a copper adlayer through underpotential deposition (upd) conditions, using both: potentiodynamic or potentiostatic electrochemical means. From analysis of experimental potentiostatic current density transients, it is shown that Cu upd onto the AuNPs occurs by a mechanism involving the simultaneous presence of a Langmuir-type adsorption-desorption and an instantaneous two-dimensional, 2D, nucleation process. The influence of the applied potential on the Cu upd kinetics and on the extent of Cu atoms coverage over the AuNPs was also reported. Furthermore, it is shown that the Cu overpotential deposition, opd, onto these AuNPs, starting from a potential in the upd region where the AuNPs surface is free from Cu atoms, occurs through a 2D-3D mechanism, where the 3D nucleation is mass-transfer controlled. Notwithstanding, when Cu opd started at the equilibrium potential the mechanism solely involved 3D nucleation.

Calcite epitaxy on Au and Ag (1 1 1)

Crystallization control is an intensely studied field. This study concerns synthesis of epitaxial calcite on Au and Ag substrate without the use of any template. The crystals were analyzed in situ by micro-Raman spectroscopy and ex situ by Scanning Electron Microscopy (SEM) and Electron Backscattering Diffraction (EBSD). Undersaturated solution containing only calcium and hydrogen carbonate is used. Electrochemically induced dissolved oxygen reduction on the metal electrode was used to increase the pH of the solution in the vicinity of the metallic surface, leading to calcium carbonate formation. The calcite crystals so obtained were uniform in size and orientation and presented a (0 0 1) face parallel to the Au or Ag (1 1 1) surface. In order to verify the selectivity of those surfaces, calcium carbonate was also crystallized on copper (1 1 1) adlayers electrodeposited on gold (1 1 1) film. The epitaxial calcite appeared only on Au or Ag substrate when various rhombohedra could be evidenced on the copper modified surface. From these results, an epitaxial relationship has been suggested where hexagonal symmetry of the (0 0 1) calcite plane was in a R30° √3×√3 arrangement on the Au (1 1 1) surface. This led to a mismatch for lattice parameters below 0.5%. Moreover the cathodic shift of potential needed to form epitaxial calcite on silver was an indirect proof that the first plane in contact with gold was a calcium one.

A comparative electrochemical study of electrosorbed 2- and 4-mercaptopyridines and their application as corrosion inhibitors at C60 steel

The electrochemistry of self-assembled monolayers (SAMs) prepared from 2-mercaptopyridine (2 Mpy) and 4-mercaptopyridine (4 Mpy) dissolved in either water or an aqueous solution of 0·1 M H2SO4 on a polycrystalline gold electrode has been investigated in an aqueous electrolyte solution (0·5 M H2SO4) using cyclic voltammetry. Results suggest that 2 Mpy is adsorbed more strongly than 4 Mpy due to the formation of a S-Au-N chelate. The under- and over-potential deposition of copper from an aqueous solution of 0·1 M sulphuric acid is inhibited in the presence of these SAMs suggesting strong interactions between these adsorbates and the gold surface. A copper adlayer was partially displaced by adsorbing 2 Mpy and 4 Mpy. The inhibition effect of these SAMs on the corrosion of C60 steel has been investigated using electrochemical impedance measurements (EIM) in an aqueous 3·5 wt% NaCl solution. The polarization resistance and the inhibition efficiency were calculated. 2 Mpy has higher inhibition efficiency than 4 Mpy.

Preparation of catalytic films of platinum on Au substrates modified by self-assembled PAMAM dendrimer monolayers

In this work we demonstrate the preparation of highly catalytically active Pt formed by the galvanic replacement of the copper adlayer on Au substrates, modified by the self-assembly of fourth generation amine terminated PAMAM dendrimer (G4NH2). The copper adlayer was formed on the dendrimer-modified gold substrate by chemical preconcentration of copper ions followed by electrochemical reduction. The Pt overlayer was characterized by SEM, XPS and by cyclic voltammetry. The catalytic efficiency of the modified film thus prepared through soft route was evaluated by the electro catalytic oxidation of methanol using cyclic voltammetry, chronoamperometry and AC impedance techniques. This work also demonstrates that the copper adlayer formed on the dendrimer-modified electrode can undergo galvanic replacement by nobler metals like Au and Ag, besides Pt. An elegant soft route involving a new three-step protocol to build the concentration of active Pt on the Au surface has been developed. Concentration of the same metal (Pt) or two different metals (Pt–Au) can be built at the interface in a stepwise manner at ambient temperature.

Initial stages of copper electrocrystallization on polycrystalline platinum and glassy carbon in the presence of acetonitrile

The kinetics of formation of copper adlayer, three-dimensional nucleation, and the deposit growth on polycrystalline platinum and glassy carbon in the 0.5 M H2SO4 + 10 mM CuSO4 + (0–2) M acetonitrile (AcN) solutions at the cathodic overvoltages is studied using the methods of cyclic voltammetry and potentiostatic current transients on a ring-disc electrode. At [AcN] = 2 M, the process of formation of copper adatoms on platinum is significantly retarded. In the solutions with high contents of AcN, the processes of Cu+ ion production, the formation of their complexes with acetonitrile, hydrogen evolution, copper nucleation, and the deposit growth proceed in parallel. The contribution of any process to the overall current depends on the amount of adsorbed AcN at the surface of substrate and copper deposit and on the electrode potential. At [AcN] = 2 M, an increase in the cathodic overvoltage to 0.32 V leads to an abnormal increase in the current of Cu+ ion production on platinum, which is caused by insufficiently rapid formation of copper atoms in the reduction of Cu+(AcN)x complexes.

Structures of Self-Assembled Monolayers of n-Alkanoic Acids on Gold Surfaces Modified by Underpotential Deposition of Silver and Copper: Odd−Even Effect

The structures of n-alkanoic acid monolayers (CH3(CH2)mCO2H, m = 5, 6, 11, 13−22) self-assembled on gold premodified by electrodeposition of a silver or copper adlayer are studied by contact angle measurements, IRAS (infrared reflectance−absorption spectroscopy), and XPS (X-ray photoelectron spectroscopy). Prior to immersion into the fatty acid-containing solutions, the substrates are prepared by underpotential deposition (upd), resulting in a sub-monolayer or full monolayer of silver or copper on gold. The adlayer promotes anchoring of carboxylate headgroup and assembly of n-alkanoic acids, which would otherwise exhibit no chemisorption on bare gold. The results show that the monolayers exhibit low wettability, all-trans methylene conformation, and a bidentate binding scheme of the carboxylate headgroups onto the upd-modified substrate. The odd−even effect of alternating peak intensity of the methyl-stretching modes is significant for monolayers on silver upd surface and, to a less extent, yet notably, f...

Initial Stages of Copper Electrocrystallization on a Glassy-Carbon Ring–Disk Electrode from Sulfate Electrolytes of Various Acidity: A Cyclic Voltammetry Study

Initial stages of copper electrocrystallization on glassy carbon from sulfuric acid electrolytes of pH 0.3 and 3.7 are studied by the cyclic voltammetry method on rotating and stationary ring–disk electrode. The rate of nucleation and growth of a metallic phase of copper in a 0.5 M Na2SO4 + 0.01 М CuSO4 (pH 3.7) solution is marginally higher than in a 0.5 M H2SO4 + 0.01 M CuSO4 acid electrolyte (pH 0.3). Regularities governing the multistage discharge of copper ions, the formation of the new phase nuclei, and the deposit dissolution are analyzed. No copper adlayers form on glassy carbon at potentials more positive than the equilibrium potential of a reversible copper electrode, the copper nucleation occurs via the Volmer–Weber mechanism. The oxygen-containing surface groups of glassy carbon (quinone–hydroquinone, carbonyl, etc.) are probably active centers for the discharge of copper ions and the nucleation of the new phase. The results of the study are compared with the data on the kinetics of copper electrocrystallization on a platinum electrode.

Influence of thiourea on the nucleation of copper on polycrystalline platinum

The influence of thiourea on the nucleation of copper from a 0.30 M CuSO4-1 M H2SO4 solution on polycrystalline platinum electrodes covered by a copper adlayer was investigated. In the case of diffusion controlled nucleation and growth the conditioning potential, that is, the potential of the electrode prior to the application of a large negative potential step, has a strong influence on the nucleation transients. This can result in either a promotion or an inhibition of the nucleation (which is characterized by a change in the nucleation rate constant and/or the site density) depending on the applied potential and the concentration of thiourea. In the region of mixed kinetics and for a fixed value of the conditioning potential (0.175 V vs Cu2+|Cu, that is, in the region of strongest inhibition), a new and rather unexpected effect was observed. Thus, after an induction period, which is proportional to the concentration of thiourea, the current increases sharply to a much higher value, but after reaching a maximum drops again to its original value. At present there is no ready explanation for this phenomenon, which has been called 'nucleation outbursts', but it deserves more investigation because the linearity between the induction time and the concentration of thiourea might have practical applications.

Kinetic study of CO oxidation on copper modified Pt(111)

The kinetics of CO oxidation on Pt(111) modified with submonolayer copper adlayers were studied using mass spectrometry (MS) and photoemission electron microscopy (PEEM). The submonolayer 2D copper adlayers were formed on approximately half of the Pt(111) crystal, by evaporating copper through a mask. More precisely, the article deals with the modifications of the hysteresis in the reaction rate compared to the hysteresis occurring under certain reaction conditions on pure Pt(111) when the CO pressure is cyclically varied. When copper was evaporated onto the Pt crystal, the kinetic phase transition between the high and low rate regimes shifted to higher CO pressures and the reaction rate increased. In addition, the CO pressure range in which bistability was observed became wider. Upon increasing the copper coverage, the shift showed a maximum at a coverage of 0.3 ML until at 0.7 ML no clear first-order transition in the reaction rate could be observed any more. The results suggest that the active site responsible for the increased activity lies at the copper–platinum bimetallic border sites.

Study of copper underpotential deposition on Au(111) surfaces

First-principles total energy calculations are carried out to study the structure of copper underpotential deposition on Au(111) surfaces in sulfuric acid solutions. The norm-conserving method is used to construct the pseudopotentials of all the elements involved. The copper adlayer structure under various copper coverage is investigated. The results show that the proposed honeycomb structure with 2/3 monolayer copper coverage is unstable without the co-adsorption of sulfate. The co-adsorbed sulfate is found to bind to copper. The calculated structural parameters are in general agreement with those obtained from a recent X-ray experiment. In addition, the sulfate adsorption on clean Au(111) surface is studied. The results show that sulfate molecule binds much more weakly with clean Au(111) surfaces. Total energy calculations for bisulfate adsorption suggest that even though it is the dominant species in acidic electrolyte, the adsorbed bisulfate may dissociate thus leave sulfate adsorbed on the surface.

Underpotential Deposition of Copper on Iodine-Modified Pt(111): In Situ STM and ex Situ LEED Studies

The dynamic process of underpotential deposition (UPD) of copper on iodine-modified Pt(111) electrode in sulfuric acid solution was investigated by in situ scanning tunneling microscopy and ex situ low-energy electron diffraction. Prior to the copper deposition, iodine adlayer structures were characterized by both techniques. It was found that well-ordered iodine adlayers with the structures of (3 × 3) and ( × )R19.1° could be prepared by immersion of the electrode in a solution containing iodide ions under potential control. It was also found that the interconversion of the two structures was very slow. After the UPD of copper on the iodine-modified Pt electrode, the iodine atoms formed a c(p × R-30°) structure with a p value of ca. 2.6 on the (1 × 1) copper adlayer on Pt(111). After the copper was stripped, the electrode exhibited a mixture of (3 × 3) and ( × )R19.1° structures of iodine on Pt(111).

A structural analysis of the Co(0001) surface and the early stages of the epitaxial growth of Cu on it

The epitaxial growth of copper on Co(0001) was investigated by combined quantitative LEED and STM, including the clean surfaces Cu(111) and Co(0001). The mode of growth is a modified Stranski–Krastanov type, i.e. pseudomorphic and approximately layer-like up to four monolayers of copper; later on, three dimensional islands develop. The stacking of the copper adlayers is exclusively fcc from the very beginning, whereby the ABAB stacking on a given terrace of the substrate is continued as ABABca. Since there are also terraces with an ABA stacking, fcc-twins (e.g. ABAcb) develop in the Cu films. Whilst in the submonolayer coverage regime of copper the cobalt substrate remains hcp stacked, films with more than about two copper layers are found to have induced a stacking fault in the substrate corresponding to a registry shift of the uppermost cobalt layer. As indicated by the analysis of a film slightly above one monolayer coverage, the registry shift seems to be triggered when the terraces of the substrate are fully covered by copper whereby the rearrangement of atoms probably starts at the step edges.

The influence of copper adlayer structure on the electroreduction of nitrobenzene at ordered au( 111) as studied by cyclic voltammetry combined with solution flushing tactics

The influence of copper adlayer structure on the electroreduction of nitrobenzene at ordered au( 111) as studied by cyclic voltammetry combined with solution flushing tactics

Anion effects and the mechanism of Cu UPD on Pt(111): X-ray and electrochemical studies

We propose a mechanism for the underpotential deposition of Cu on Pt(111) in 0.1M H 2SO 4 in the presence and absence of halides. The mechanism is based on recent results from electrochemical and in situ surface EXAFS and X-ray standing wave (XSW) studies of Cu UPD on Pt on 0.1M H 2SO 4 and in the presence and absence of halides with emphasis on Cl −, Br − and I −. EXAFS data were obtained in the presence and absence of Cl − at a potential of +0.1 V corresponding to a coverage of approximately 0.75 ML. In the absence of chloride, the data were consistent with the presence of an incompletely discharged copper adlayer. The copper—copper bond distance was found to be 2.85Å. In the presence of chloride the X-ray data suggest the presence of a fully discharged copper layer and the Cu Cu bond distance, 2.59Å, approached the bulk copper value (2.56Å). In the presence of chloride, no oxygen is present as a backscatterer in the plane of the Cu Cu adlayer. However, oxygen (from either bisulfate or water) is present as a backscatterer in the absence of chloride giving rise to a copper—oxygen bond distance of 2.16Å. It appears that the chloride acts as a protective overlayer precluding oxygen (from either solvent or electrolyte) adsorption. Qualitatively similar results were obtained for Cu UPD on an iodine treated Pt surface. In addition, XSW data for this last system suggest the presence of electrochemically inactive (solvated) copper ions in the vicinity of but not in contact with the platinum surface which we describe as representing a “pre-adsorbed” state. From electrochemical studies at low (10 μM) copper concentrations, we find that the underpotential deposition of submonolayer amounts of copper induces an enhanced adsorption of chloride and bromide on Pt(111) that is reflected in exceedingly sharp voltammetric peaks that are transient in nature. The adsorbed anions are believed to be in contact with the platinum surface and in the vicinity of the electrodeposited copper. We ascribe this enhanced adsorption to the formation of a CuX adlayer on the surface of the electrode. These exceedingly sharp peaks increase in amplitude for copper coverages of up to half a monolayer and subsequently decrease so that upon completion of the copper monolayer they are absent. Based on these findings and on previous investigations, we propose a mechanism for the underpotential deposition of copper on Pt(111) which involves a “pre-adsorbed” state, the transient formation of a CuAn (An −x =anion) adlayer which in turn gives rise to a copper monolayer which itself is covered by an anion-adlayer.

Structure of metal-electrolyte interfaces: Copper on gold(111), water on silver(111)

Two examples are presented of the application of in situ structure and composition sensitive techniques to elucidating the nature of the electrode-electrolyte interface. One case is the underpotentially deposited submonolayer of Cu on Au(111). Despite extensive electrochemical, LEED, RHEED, STM, AFM, and EXAFS investigations, the structure of the copper adlayer is still controversial. In situ surface EXAFS, surface X-ray scattering, and quartz crystal microbalance (QCM) data lead to the conclusion that the adlayer adopts a (√3 × √3)R30 ° hexagonal honeycomb arrangement of Cu atoms in which the Cu coverage is 2 3 and the sulfate coverage 1 3 . The other case is the structure of water at the Ag(111)-aqueous sodium fluoride interface. Analysis of X-ray scattering shows that the interfacial water molecules exhibit potential dependent layering and reorientation and a markedly increased density (twice bulk water) in the inner layer.

ChemInform Abstract: Total Inhibition of the Oxygen Reduction Reaction at Au(111) by Copper Adlayers in Sulfuric Acid Solution.

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Total Inhibition of the Oxygen Reduction Reaction at Au(111) by Copper Adlayers in Sulfuric Acid Solution

Abstract The influence of an underpotentially deposited adlayer of copper on the oxygen reduction reaction (ORR) at Au(111) has been studied in a 0.05 M H2SO4 solution using hanging meniscus rotating disk voltammetry. The total inhibition of the ORR was found after the formation of the first Cu adlayer. Two possible structures for the Cu adlayer on Au(111) take into account inhibition of the ORR. The total inhibition observed in the present study can be explained by a honeycomb (√3 × √3)R30° structure, rather than a simple (√3 × √3)R30° Cu adlayer. A bridging two-site process (disproportionation reaction) is not expected to occur on the honeycomb Cu adlayer.

In-situ x-ray studies of the underpotential deposition of copper on platinum(111)

Abstract : In-situ x-ray flourescence detected surface EXAFS spectroscopy has been employed to elucidate the in-plane structure of copper underpotentially deposited on a clean and well ordered platinum (111) single crystal electrode. XANES and EXAFS analyses were made as function of applied potential (+0.2V, +0.1V, and 0.0V) corresponding to coverages of approximately 0.5ML, 0.75ML and 1ML, respectively. The charge derived from electrochemical measurements indicate that at the three potentials studied the electrodeposited copper was not completely discharged. The XANES analysis revealed similarities between the electrodeposited copper and the Cu2O reference lending support to earlier findings of a partially discharged copper ad-layer. EXAFS results suggest two cluster phases at the most positive potential (+0.2V) studied and an epitaxial arrangement at the most negative potential (0.0V).