Metal-solution Interface Research Articles

Interaction of halogens with Hg, Ag and Pt surfaces: a density functional study

The interaction of F, Cl, Br and I with three common electrode surfaces (mercury, silver, and platinum) is studied by ab initio density functional methods. The adsorption strength increases in the order I<Br<Cl<F, with silver as the metal having the highest affinity for the halogens, and platinum the lowest. We ascribe the low affinity of halogens for platinum to the high work function of platinum. The importance of considering halogen binding energies instead of halide binding energies is illustrated, and it is shown how the study of the interaction of halides with small metal clusters may lead to results having only limited relevance to uncharged extended metal surfaces. Because of the importance of the electrostatic interaction, the absence of water in our (and previous) calculations makes it difficult to apply these results directly to the metal–solution interface. A simple tight-binding scheme that accounts for the different interactions with metal sp- and d-bands is suggested to reproduce some of the main trends of the ab initio calculations. This model may be of future applicability in the modeling of electrochemical interfaces.

Chemisorption and Chemical Reaction Effects on the Resistivity of Ultrathin Gold Films at the Liquid−Solid Interface

Ultrathin gold films, with thicknesses between the onset of conductivity (d ∼ 5 nm) and the electron mean free path (d ∼ 80 nm), display surface-sensitive resistivities, which have been exploited to follow the adsorption and desorption of molecular monolayers at the metal-solution interface with high precision. For nominal Au film thicknesses (d ∼ 40 nm), strongly chemisorbed thiolate monolayers increase the resistivity of the thin Au films by ∼4%, but weakly adsorbed species, such as pyridine or phenolate at open circuit, induce no observable change in the Au film resistance. Resistivity measurements implemented with a high-stability current source and high-precision digital voltmeter sampling at 1 Hz resulted in 3σ uncertainties in alkanethiolate coverage of 1.4 × 10(-)(4) monolayer. Surface plasmon resonance measurements, performed simultaneously with resistivity measurements, indicate that changes in resistivity vary monotonically with coverage with three distinct regions: a low-coverage region of heightened adsorbate mobility, an intermediate-coverage region with generally linear behavior, and a chain length-dependent saturation region at high coverages. Resistivity measurements were also capable of reproducibly following the chemical state of the Au surface through a complex set of redox manipulations, demonstrating the versatility of this simple measurement.

The influence of the potential sweep rate on the shape of polarization curves

The influence of the potential sweep rate on the shape of polarization curves and the computation of R pa has been examined by accounting for the adsorption-desorption phenomena at the electrode surface and simulating the behaviour of the metal-solution interface with a suitable linear network. Mathematical developments for determining the network response when a triangular wave is applied to its terminals are based on the use of the mesh method and Laplace transform. Short considerations concerning the network proposed by Macdonald are also given. Calculations with reference to a two-mesh network were performed using specific Quickbasic programs and single precision. Examination of the trend of several i (Δ E) functions over the [−10,10] mV Δ E interval showed that their distortion was usually negligible for a 0⩽10 mVs −1 and C⩽10 −3 F cm −2. Significant distortion was only observed for a 0⩾100 mVs −1. The influence of adsorption-desorption phenomena affects the shape of i (Δ E) inside the cathodic zone over an interval having Δ E i as left bound, the position of its right bound depending on a 0. For all the cases examined and a 0<10 mVs −1 the values of the three determinations of R pa are practically coincident with the values of R p when C⩽10 −3 Fcm −2, a difference being observed when a 0>10 mVs −1 and Csime;10 −3 Fcm −2. At last, examination of the response of the network proposed by Macdonald provided a further confirmation of the previous results.

New method for measuring the differential capacity in electrochemistry

Electrical behavior of the ideally polarizable metal–solution interface is similar to a RC series circuit. The dc polarization, E, of the interface is potentiostatically controlled and differential capacity, C, measurements are carried out with a linear variation of E versus time. A precise measurement method of C is described in the case where the time constant of the circuit is rather high (≈10−2 s). The principle of this method is to impose on the interface an ac current perturbation, Iω, and to measure the ac potential response, Eω. A system composed of a low bandwidth potentiostat (&amp;lt;1 Hz) and a galvanostat controls the dc potential, E, and produces the ac current, Iω. In- and out-of-phase components of the ac potential response, Eω, are analyzed by means of a lock-in amplifier. An ohmic drop compensation technique with suppression of the residual common mode is used to improve the determination of the Eω(90°). Using a dummy cell, comparison between the new method and the classic potentiostatic technique is carried out. Results show that it is possible to measure C with a relative error less than 1% in a frequency range up to 2 kHz whereas with the classic potentiostatic technique the frequency range is limited to around 100 Hz.

Corrosion behavior of mechanically alloyed TiSi samples

The corrosion behavior in HCl solutions, of mechanically alloyed TiSi samples in amorphous-crystalline and crystalline state was investigated. The partial and the total corrosion rates have been estimated by means of a weight-loss technique, tracing the quantities of the dissolved elements spectrophotometrically. The polarization resistance at metal-solution interface was established both by weight-loss analysis and in electrochemical way. The experimental data clearly indicate that the amorphous-crystalline TiSi samples possess better corrosion resistance in the investigated HCl solutions than their crystalline counterparts. Such a behavior can be connected with the effects of the amorphous state on the corrosion process.

Electrochemical interactions of biofilms with metal surfaces

Two mechanisms of microbially influenced corrosion (MIC) are discussed and compared: corrosion modified by the presence of (1) sulfate-reducing bacteria (SRB) and (2) manganese-oxidizing bacteria (MOB). It is demonstrated that the nature of MIC in both cases depends on the nature of inorganic materials precipitated at the metal surface, iron sulfides and manganese oxides. Those materials are electrochemically active and, therefore, modify the electrochemical processes naturally occurring at the metal-solution interface. Some of these modifications may lead to accelerated corrosion.

Phenothiazine as inhibitor of the corrosion of cadmium in acidic solutions

The corrosion of cadmium in 0.5m HClO4, CH3COOH or 0.25m H2SO4 in the absence and presence of small amounts of phenothiazine (10−6–10−4 m) as an inhibitor has been studied using both electrochemical impedance spectroscopy (EIS) and Tafel-plot techniques. Measurements were carried out at cathodic, open circuit and anodic potentials at different temperatures. In HClO4 and H2SO4 solutions the inhibition efficiency increases as both the concentration of phenothiazine and the temperature are increased. The effect of temperature in CH3COOH solution gives an opposite effect, that is, a decrease in the inhibition efficiency with increasing temperature. This behaviour is attributed to competitive adsorption between the inhibitor molecules and the acetate ions at the metal–solution interface. Phenothiazine can be considered as an inhibitor of mixed type with more pronounced effects in the anodic direction. The thermodynamic parameters in HClO4 containing the inhibitor were evaluated using the Bockris–Swinkels adsorption isotherm with n=4 as the configurational function. These parameters reveal that phenothiazine is adsorbed on the cadmium surface in molecular form with a strong interaction between the metal and the inhibitor.

Analysis of modern phenomenological approaches toward describing the structure and properties of the electrical double layer dense part on the metal solution interface

In this paper the following issues are discussed: the components of the potential drop at the metal/solution interface and the corresponding components of the differential capacitance; the model interpretation of the metal/solution boundary without and with regard of the metal and solvent separate contributions; the Amokrane-Badiali model and its improvement when taking into account the chemisorptive interaction of solvent molecules with metals; and, finally, the development of views on the Volta's problem solution.

Laser-Enhanced Palladium Electroless Plating

SummaryLaser-enhanced palladium electroless plating was found to be possible in the presence of a small quantity of Tl+ or Pb2+. The thermal conductivity of the substrate is an important factor. In order to induce electroless plating, a localized increase in temperature at the metal-solution interface by laser irradiation is necessary. Although the laser-enhanced palladium plating did not occur on copper and brass, which are good heat-conductive materials, it became possible with 5 μm of poorly heat-conductive nickel plating on these metals. The effects of the velocity of flow of the plating solution and the laser power, on the shape of the palladium deposit were evaluated. Line drawing was attempted, and the best results were obtained at 7–7.5 μm/s of laser sweep rate, with which the line width was about 20 μm.

Electrochemical interactions of biofilms with metal surfaces

Two mechanisms of microbially influenced corrosion (MIC) are discussed and compared: corrosion modified by the presence of (1) sulfate-reducing bacteria (SRB) and (2) manganese-oxidizing bacteria (MOB). It is demonstrated that the nature of MIC in both cases depends on the nature of inorganic materials precipitated at the metal surface, iron sulfides and manganese oxides. Those materials are electrochemically active and, therefore, modify the electrochemical processes naturally occurring at the metal-solution interface. Some of these modifications may lead to accelerated corrosion.

Ultrafast photothermal and photoacoustic measurement of solid/liquid interfaces

Ultrafast photothermal (PT) and photoacoustic (PA) investigation of a metal–solution interface was performed by using subpicosecond time-resolved transient reflectivity (TR) measurement. A polycrystalline platinum film (thickness 30 nm) vapor-deposited on a glass substrate and a polycrystalline platinum disk were investigated in air and in a variety of solutions with and without electrochemical potential control. Transient reflectivity change during and after pulsed laser illumination was measured with a high-precision (&amp;lt;10−6) and high temporal resolution of the pulse width limit (pulse duration 240 fs FWHM). It was found that, in a picosecond time scale, the TR response showed electrolyte dependence as well as electrochemical potential dependence [A. Harata, T. Edo, and T. Sawada, Chem. Phys. Lett. 249, 112–116 (1996)]. These results suggest that interface structure in a molecular scale affects the ultrafast PT/PA phenomena occurring just at the interface. Also observed were ultrahigh-frequency longitudinal acoustic waves ringing in the ultrathin platinum films sandwiched between the glass and the solution. The frequency observed was up to 300 GHz for the sample in air and a strong acoustic damping in the solution was observed.

Modified platinum electrodes: electrochemical characteristics and behaviour in activated sludge

Polished platinum electrodes were coated with platinum black and/or with organic polymers (Nafion, polyurethane) to accelerate the electron transfer rate to the metal-solution interface and/or to constitute a protection barrier for the metal against neutral or anionic contaminants present in wastewater. The modified electrodes were electrochemically characterized (surface roughness and exchange current density) and their behaviour in activated sludge was studied. A platinum black deposit increases the roughness and the exchange current density. However, the response of these electrodes in an anoxic environment is very slow, which results in a low variation amplitude of the potential when they are placed in activated sludge alternately submitted to sequences of aeration and anoxia. A Nafion film provides partial protection against contaminants thus increasing electrode response reproducibility. A polyurethane film has no apparent protective effect.

Modified platinum electrodes: Electrochemical characteristics and behaviour in activated sludge

Polished platinum electrodes were coated with platinum black and/or with organic polymers (Nafion, polyurethane) to accelerate the electron tranfer rate to the metal-solution interface and/or to constitute a protection barrier for the metal against neutral or anionic contaminants present in wastewater. The modified electrodes were electrochemically characterized (surface roughness and exchange current density) and their behaviour in activated sludge was studied. A platinum black deposit increases the roughness and the exchange current density. However, the response of these electrodes in an anoxic environment is very slow, which results in a low variation amplitude of the potential when they are placed in activated sludge alternately submitted to sequences of aeration and anoxia. A Nafion film provides partial protection against contaminants thus increasing electrode response reproducibility. A polyurethane film has no apparent protective effect.

Adsorption of insoluble surfactants at the Au(111)/solution interface

The adsorption of surfactants, which form insoluble monolayers on an aqueous substrate, onto a single crystal gold electrode have been described. Adsorption of this class of surfactants have been characterized using a combination of electrochemistry and Langmuir-Blodgett techniques. We have developed a technique to simultaneously measure the film pressure at the gas-solution (GS) interface and the film pressure of the surfactants that spread to the metal-solution (MS) interface. We have shown that surfactants such as octadecanol and stearic acid, which interact weakly with the metal surface, adsorb at an uncharged MS interface (at the potential of zero charge) and progressively desorb when the electrode surface is charged negatively. The electrode potential (charge density at the metal surface) influences the transfer of the surfactant from the GS interface to the MS interface. The transfer ratio is 1:1 at an uncharged MS interface, and is progressively reduced to zero when the MS interface is charged. We have employed 12-(9-anthroloxy) stearic acid, a surfactant dye molecule, to study the mechanism of potential induced desorption and adsorption of the film of insoluble molecules. With the help of electroreflectance spectroscopy and light scattering measurements, we have shown that if desorbed, the surfactant molecules form micelles (flakes or vesicles) that are trapped under the electrode surface. The micelles spontaneously spread back onto the electrode surface when the charge density at the metal approaches zero. The repeatable desorption and readsorption involve micellisation of the film at negative potentials and spontaneous spreading of the micelles to reform the monolayer at potentials close to pzc.

Structure of Electrified Interfaces

The objective of this book is to provide a state-of-the-art description of the structure of electrified interfaces with particular emphasis on the structure of the metal-solution interface. During the past decade, a molecular picture of the interface has emerged, superseding the notions of metal and solution as electronic and dielectric continua respectively. This book discusses the newest developments, including the progress in surface science, where the structure of the metal surface at the metal-gas interface has become resolved down to the picometer scale.

Sulfate adsorption on well-defined Pt(100) electrodes

Abstract The metal—solution interface of a single-crystal Pt(100) electrode in the presence of specifically adsorbed sulfate ions is investigated by means of in situ FTIR spectroscopy. Sulfate adsorption starts at about 0.2 V vs. Pd/H2 and goes through a maximum at ca. 0.5 V. Sulfate ions are adsorbed through two oxygen atoms presenting a C2v symmetry. The two strong bands observed at around 1100 and 1200 cm−1 are assigned to the symmetric SO stretches of the resulting SO2 groups (coordinated and non-coordinated (respectively).

The partitioning of surfactants from the gas-solution interface onto an electrified metal-solution interface

The spreading of long-chained aliphatic molecules from the gas-solution interface to an electrified gold-solution interface was studied. Three low index planes of gold were used as the electrodes and the film pressure at the metal-solution interface was determined by electrochemical means under equilibrium conditions. The spreading of the molecules from the gas-solution interface to the metal-solution interface was measured and a strong dependence on electrode potential and electrode surface morphology was found. Stressed (compressed) and unstressed (not compressed) monolayers were studied and compared. The stressed monolayer study suggested that the equilibrium for the spreading of molecules between the gas-solution interface and metal-solution interface may be local in character.

Semi-empirical calculations of the vibrational frequency of carbon monoxide adsorbed on noble metal single-crystal surfaces

In this work we perform a theoretical analysis of the shift of the observed IR reflection—absorption spectroscopy (IRRAS) band of CO adsorbed on Pt(111), Rh(111) and Pt(100) single crystals as a function of both the degree of CO surface coverage and the electric potential applied at either the metal—vacuum or the metal—solution interface. The wavefunctions obtained using a modified extended Hückel molecular orbital (EHMO) method are used to predict the vibrational frequency data. The Pt(110), Rh(111) and Pt(111) single crystals are modelled by bilayer clusters of 25 and 22 atoms respectively. A theoretical description of the observed IRRAS shift is analysed by means of a population analysis of CO molecular orbitals, which confirms the donation—back-donation model.

Second harmonic generation and the microscopic structure of the metal-electrolyte interface

A model for second harmonic generation at the metal-solution interface is presented and treated by electron density functional calculations. The coefficient a, characterizing the non-linear optical response perpendicular to the surface, is calculated both for bare metal electrodes and for metals covered with an overlayer of a different metal. The analysis for bare metals is performed with a lattice of pseudopotentials, thus introducing crystal structure into the model.

Thermodynamics of Adsorption of Brighteners on Polarized Nickel from Watts Bath Solution

The adsorption of coumarin, nitrocoumarin, and p‐toluene sulfonamide on nickel from Watts bath solution has been studied using a polarization technique. The exchange current densities with and without additives were evaluated using a Tafel relation. The addition agents inhibited the deposition process. Surface coverages calculated from the values were fit into the Langmuir adsorption isotherm. Thermodynamic parameters (, , and ) for the adsorption of the addition agents have been evaluated using the Bockris‐Swinkles adsorption isotherm. The values of are negative indicating the strong interaction and reactive inhibition of the deposition process by these additives. The electrodeposition interaction is discussed from the viewpoint of the adsorption of the additive molecules on the metal solution interface.