Potential Step Technique Research Articles

Zinc Electrodeposition from a Deep Eutectic System Containing Choline Chloride and Ethylene Glycol

Deep eutectic electrolytes have recently been considered as alternatives to classical room-temperature ionic liquids. This work is an initial study of the zinc deposition process from a basic choline chloride/ethylene glycol deep eutectic solvent containing at . The system was examined by cyclic voltammetry at static and rotating glassy carbon disk electrodes and by potential step techniques. There was little deposition initially on sweeping or stepping the potential to −0.5 to −0.8 V vs Zn/Zn(II), but more rapid deposition was observed when the potential was subsequently raised to −0.4 to −0.2 V. The role of choline chloride was also studied by comparing with a choline-free electrolyte, which exhibited a more conventional voltammetric response. The formation of a dissolved, intermediate species on the cathodic sweep was proposed to account for the observed deposition behavior in the deep eutectic. Furthermore, an observation of the electrodeposition behavior with the addition of sodium ethoxide supports the suggestion that is a complex of and deprotonated components of the solvent.

A Study of Zinc Electrodeposition From Zinc Chloride: Choline Chloride: Ethylene Glycol

This work is an initial study of the zinc deposition process from a Lewis-basic choline chloride/ ethylene glycol deep eutectic solvent containing ZnCl2 at 30{degree sign}C. The system was examined by cyclic voltammetry at static and rotating glassy carbon disc electrodes and by potential step techniques. Although there was little deposition initially on sweeping or stepping the potential to -0.5 to -0.8 V vs. Zn/Zn(II) more rapid deposition was observed when the potential was raised to -0.4 to -0.2 V. The role of choline chloride was also examined by comparison with a choline-free electrolyte, which exhibited a more conventional voltammetric response. A tentative suggestion has been proposed to account for the observed deposition behaviour.

Copper electrocrystallization on titanium electrodes: Controlled growth of copper nuclei using a potential step technique

Copper nanoparticles were synthesized using a pulsed sonoelectrochemical (20 kHz, 78 Wcm−2) method. Two electrolytes used were a copper salt dissolved in Na2SO4 (pH=3.80) or H2SO4 (pH=0.6). For both electrolytes and in the absence of any surfactant, monodispersed spherical copper nanoparticles were strongly aggregated in three-dimensional clusters of about 200nm. The particle size is controlled by varying reaction parameters such as duration of the experiment, current density, temperature and ultrasound power. A potential step technique is proposed to synthesize copper nanoparticules. Under potentiostatic conditions the aim is to control and decrease the nanoparticle size and reduce production costs by avoiding gas evolution and other adverse reactions.

Cobalt electrodeposition onto highly oriented pyrolytic graphite (HOPG) electrode from ammonium sulfate solutions

-2 M of CoSO 4 + 1M (NH 4 ) 2 SO 4 at pH 4.5 (natural pH). All solutions were prepared by using analytic grade reagents with ultra pure water (Millipore-Q system) and were deoxygenated by bubbling N 2 for 15 min before each experiment. Once the solution was deoxygenated a nitrogen atmosphere was maintained over the solutions. During the experiment the bubbling was stopped to avoid the presence of additional diffusional variables caused by the nitrogen bubbles on the electrode surface. The working electrodes were freshly cleaved HOPG surfaces. A graphite bar with an exposed area greater than the working electrode was used as counter electrode. A saturated silver electrode (Ag/AgCl) was used as the reference electrode, and all measured potentials are referred to this scale. The electrochemical experiments were carried out in a BAS potentiostat connected to a personal computer running the BAS100W software to allow the control of experiments and data acquisition. In order to verify the electrochemical behavior of the electrode in the electrodeposition bath, cyclic voltammetry was performed in the 0.600 to -1.300 V potential range. The kinetic mechanism of Co deposit onto HOPG was studied under potentiostatic conditions by the analysis of the experimental potentiostatic current density transients obtained with the potential step technique. In all cases, the perturbation of the potential electrode always started at 0.600 V because this is the null current zone in where the Co deposition had not still begun. Thus, the application of this potential guarantees that the electrochemical signals recorded during the cathodic polarization are caused by the cobalt electroreduction on the electrode. 20

Anodic Pt dissolution in concentrated trifluoromethanesulfonic acid

We investigated the anodic Pt dissolution in concentrated trifluoromethanesulfonic acid (TFMSA). The dependence of the Pt dissolution rate on the TFMSA concentration was first measured from the weight difference of a Pt-flag electrode before and after successive potential cycles. From this measurement, the Pt dissolution rate in 10 mol dm −3 TFMSA is found to be over 40 times greater than those in 1 and 4 mol dm −3 TFMSA. Next, the anodic Pt dissolution was assessed in 10 mol dm −3 TFMSA by a potential step technique using a Pt dual microelectrode having generator and collector electrodes. The obtained result shows that the anodic Pt dissolution in 10 mol dm −3 TFMSA occurs when the Pt generator electrode potential is stepped from 0.25 to 1.0–2.0 V vs. Ag/Ag 2SO 4. Furthermore, the absolute steady-state current-based coulomb charges obtained at the generator (| Q G|) and collector (| Q C|) reflect the anodic Pt dissolution and the reduction of the dissolved Pt, respectively. The magnitude of | Q G| and | Q C| linearly increase when the generator potential shifts from 1.0 to 2.0 V vs. Ag/Ag 2SO 4. The absolute ratio, | Q C/ Q G|, also gradually increases according to the shift in the generator electrode potential. These results demonstrate that the anodic Pt dissolution in 10 mol dm −3 TFMSA occurs at ≥1.0 V vs. Ag/Ag 2SO 4 and that the ratio of the anodic Pt dissolution per total reaction charges increases according to the positive shift of the Pt electrode potential.

Kinetics of dissociative adsorption of formic acid on electrodes of tetrahexahedral platinum nanocrystals

In the present paper we study the kinetics of dissociative adsorption of formic acid on the electrode of tetrahexahedral platinum nanocrystals (THH Pt NCs). In situ FTIR spectroscopic results demonstrate that HCOOH can be oxidized to CO2 at a low potential (−0.2 V(SCE)) on the THH Pt NCs electrode, and the chemical bonds inside formic acid molecule are broken to form adsorbed COL species. The kinetics of the dissociative adsorption of HCOOH was quantitatively investigated by employing programmed potential step technique. It has been determined that, in 5 × 10−3 mol·L−1 HCOOH + 0.1 mol·L−1 H2SO4 solution, the maximal value of the average rate (υ a max ) of dissociative adsorption of HCOOH on a commercial Pt/C catalyst electrode is 8.58 × 10−10 mol·cm−2·s−1, while on the THH Pt NCs the υ a max is 1.5 times larger than the υ a max measured on Pt/C and reaches 13.19 × 10−10 mol·cm−2·s−1. The results have revealed that the reactivity of the THH Pt NCs is much higher than that of the Pt/C catalysts.

Application of Tetrathiafulvalene‐Modified Carbon Nanotubes to Preparation of Integrated Mediating System for Bioelectrocatalytic Oxidation of Glucose

AbstractMultiwalled carbon nanotubes (CNTs), that are modified with ultrathin layers of tetrathiafulvalene (TTF), were demonstrated to form a stable colloidal suspension. Such dispersion was exploited to fabricate an integrated mediating system (utilizing both highly conductive carbon nanostructures, CNTs, and a redox mediator, TTF) capable of facilitating electron transfers between the active sites of the enzyme (glucose oxidase) and the electrode surface. The resulting bioelectrocatalytic system produced sizeable glucose oxidation currents in phosphate buffer solution (pH 7.0). For comparison, the system utilizing TTF‐free (bare) CNTs and the glucose oxidase enzyme showed relatively much lower activity towards the glucose oxidation. Formation, electrocatalytic reactivity, durability, and morphology of proposed bioelectrocatalytic systems were examined using cyclic voltammetry, potential step techniques, rotating disk voltammetry and transmission electron microscopy. The whole concept of the preparation of CNT‐supported redox mediating systems is of potential utility to bioelectroanalytical chemistry.

Adsorption of 2-thiobarbituric acid at the electrochemical interface: Contrasted behaviours on mercury and gold

The adsorption of 2-thiobarbituric acid (TBA) from acid solutions (pH ~1) has been investigated at the Au(111) single crystal electrode and at the dropping mercury electrode. In contrast to the gold electrode where the adsorption is driven by the strong interaction between Au and the S atom, the TBA adsorption at the mercury electrode is more contrasted and distinct features such as capacitance pits are observed in the capacitance–potential curves. The kinetics of phase transformation were investigated by the potential step technique. The formation of films B and C prevailing in two distinct capacity pit regions is controlled by a nucleation and growth mechanism. Ordering of film A observed at the positive end of the potential region is also evidenced on the basis of the charge transients associated with its formation from film B or C. The two successive sigmoidal parts in the charge transient obtained at small overpotentials for the transformation of C to A is explained by the presence of an intermediate metastable film.

Surface dynamics at well-defined single crystal microfacetted Pt(111) electrodes: in situ optical studies

The assembly and electrochemical oxidation of well-defined CO adlayers on Pt(111) microfacets in aqueous CO-saturated 0.1 M H2SO4 were examined by a combination of in situ, simultaneous, time-resolved, reflectance spectroscopy (RS) and second harmonic generation (SHG), and potential step and linear scan techniques. Optical transients were collected following potential steps from a value high enough for a full monolayer of bisulfate (theta = 0.2) to adsorb on the Pt(111) facet, E(ox), to potentials E(ads), at which either the c(2 x 2)-3CO or square root of 19 x square root of 19R23.4 degrees-13CO phase is expected to form once surface saturation is achieved. Similar experiments involving subsequent steps from E(ads) to E(ox) provided unambiguous evidence that the rates of oxidation of c(2 x 2)-3CO on such quasi-perfect Pt(111) facet at constant overpotential are much slower than those of square root of 19 x square root of 19R23.4 degrees -13CO, an effect attributed to the presence of intrinsic vacant sites within the latter, more dilute phase, which are required for oxidation of adsorbed CO to ensue. Furthermore, continuous CO adsorption-oxidation cycles were found to increase the rate of oxidation of the c(2 x 2)-3CO phase. This phenomenon was tentatively ascribed to the progressive emergence of defects along the edge of the facet (and/or within the facet itself) which serve as nucleation sites for the oxidation of adsorbed CO.

Effect of Specific Adsorption of Anions and Surface Structure of Pt(111) Electrode on Kinetics of Dissociative Adsorption of Ethylene Glycol

The effect of specific adsorption of anions and the surface structure of a Pt (111) electrode on the kinetics of dissociative adsorption of ethylene glycol (EG) was studied using cyclic voltammetry and a programmed potential step technique. Quantitative results demonstrated that the specific adsorption of anions remarkably influenced the dissociative adsorption of EG. Both the initial reaction rate (vsubscript i)) of the EG dissociative adsorption and the saturated coverage of dissociative adsorbates, measured in perchloric acid media (without specific adsorption), are significantly larger than the corresponding values acquired in sulfuric acid media (with specific adsorption of SO(superscript 2- subscript 4)/HSO(superscript - subscript 4). We illustrate that the variation of the average reaction rate (average)v of EG dissociative adsorption on Pt(111) in perchloric acid media with an electrode potential yields a volcano-like distribution with a maximum value near 0.22 V (vs SCE). Furthermore, different surface structures of the Pt(111) electrode that were obtained by different treatments also significantly affect this surface process.

The electrochemical behaviour of an exfoliated graphite electrode in simulated seawater containing oil

An exfoliated graphite (EG) electrode was prepared and the electrochemical response to oil in simulated seawater was studied by means of the potential step technique and electrochemical impedance spectroscopy (EIS). The capacitance and other electrochemical characteristics of the electrode were affected by the presence of oil. The effects of temperature and salinity on the electrochemical behaviour of the EG electrode in NaCl solution containing oil were investigated by EIS. The results showed that the higher the temperature or the salinity, the higher the double layer capacitance of the electrode.

A Potentiostatic and Atomic Force Microscopy Study of the Nucleation and Growth Mechanisms of Certain Metallic Cyanometalates

Nucleation and growth mechanisms (NGMs) of nickel(II) hexacyanoferrate, nickel(II) octacyanomolibdate, and copper(II) octacyanomolibdate were performed by means of the potential step technique by oxidizing the respective metal electrode in 0.02 M sulfuric acid containing the potassium salt of either hexacyanoferrate or octacyanomolibdate compounds. The obtained current−time transients (I/t) were analyzed using the theory of electrocrystallization of the metallic phase. As evidenced through these experiments, we can state that for the nickel cyanometalate compounds, electroformation takes place through a three-dimensional progressive NGM, and for the copper(II) octacyanomolibdate compound, electroformation occurs by means of a three-dimensional instantaneous NGM. The electrochemical results were verified through the use of atomic force microscopy (AFM). From these results, we can conclude that AFM is a good complementary technique to determine the nature of the NGMs through which electroformation of a soli...

Electrodeposition Under Forced Convection Conditions

The copper electrodeposition process was studied under the influence of forced convection conditions, varying the electrode angular speed (ω) with the aid of a rotating disc electrode, using the potential step technique. From the analyses of the experimental current transients it was found that both: the nucleation rate constant (A) and the number density of active sites (N0) for ω > 200 rpm depending on the hydrodynamic conditions imposed. However, the current transient recorded in the 0 < ω < 200 rpm could not be analyzed with any of the theoretical formalisms proposed so far.

Computational electrochemistry: Lattice Boltzmann simulations of voltammetry at microelectrodes

This paper describes the development of a two-dimensional lattice Boltzmann method for the simulation of mass transport at a range of microelectrode geometries using potential step and linear sweep voltammetric techniques. The simulations of the current response for microband and micro hemicylinder geometries were compared with previously published analytical solutions. Excellent agreement between the numerical models and the analytical solutions was observed for a series of experimental parameters. To illustrate the flexibility of the lattice Boltzmann method the simulation of the current response for a range of electrode geometries, distorted from microband electrode geometry to micro hemicylinder electrode, is also described.

Electrochemical Nucleation of Zinc onto Glassy Carbon

Metal electrodeposition onto diverse substrates continues to be a subject of significant interest for improved corrosion properties (coatings) and the production of integrated circuits. Among the metallic coatings used to protect steel surface, electrodeposited zinc and zinc alloys are important in both decorative and industrial applications. Unfortunately, in the common electrolytic baths (sulfates, acetates, chlorides), Zn electrodeposition is accompanied by the hydrogen evolution reaction (HER), which cause a competition between both processes. Therefore, in such circumstances, a quantitative evaluation of the kinetic parameters of the zinc electrocrystallization process is almost impossible. In this work, Zn electrodeposition was analyzed using a non- conventional support electrolyte as alternative method to separate the involved processes. Zn electrodeposition onto glassy carbon (GCE) was investigated using cyclic voltammetry (CV) and potential step technique in an aqueous solution 10-2 M ZnCl2, in 1M NH4Cl. The experimental current density transients showed that the mechanism of zinc electrodeposition in 1M NH4Cl occurs by multiple, progressive three-dimensional nucleation with controlled by mass transfer.

Corrosion properties of HVOF-coated steel in simulated concrete pore electrolyte and concentrated chloride environments

The corrosion susceptibility of steel and HVOF-coated steel in solutions simulating the alkaline concrete pore environment and with the addition of chloride was investigated using potentiodynamic polarization and potential step techniques. The surface characterization was performed using SEM and the surface elemental analysis was determined by EDS. The concentration of chloride was 2.8 M to simulate the concentration of chloride spread in many local regions of Saudi Arabia and called Sabkha. It was found that, in the case of the simulated concrete pore electrolytes, the HVOF coating resulted in an anodic shift of the corrosion potential with marginal effect on the corrosion current. However, upon addition of 2.8 M chloride solution, the corrosion rate of the HVOF-coated steel was found to increase by a factor of two. SEM showed a network of pores within the coating which provides a path for the electrolyte. This would result in preferential corrosion around splat boundaries and confirmed by EDS which showed that the corroded splats have higher oxide contents. Potential step experiments at 400 mV above open circuit potential showed a suppressed current of the HVOF-coated steel compared to the steel substrate alone. The corrosion potential versus time experiments resulted in a more anodic Ecorr which decreased with time and became equal to the Ecorr of the bare steel after 34 h. After that, the corrosion potential of the HVOF-coated steel decreased due to the increase in galvanic coupling between the steel and the HVOF coating.

Three-phase-boundary dynamics at Pt/YSZ microelectrodes

Strong electrode activation, inductive hysteresis and non-linearity are well-known phenomena on model Pt-YSZ cathodes, and recently also a regular current fluctuation pattern have been reported. The oxygen electrode reaction with YSZ as electrolyte is studied at Pt microelectrodes prepared by electrochemical etching of platinum wire. The result is a well-defined contact area of ∼ 25 μm in diameter. Due to the small size and a favourable ratio between the three-phase-boundary (TPB) length and the contact area, microelectrodes should have an increased sensitivity to local events at the TPB compared to larger point electrodes normally applied. The electrode processes are studied by potential sweep, step and impedance techniques. Investigation of the YSZ and Pt surfaces afterwards reveals the growth of dendrite-like Pt structures from the TPB. The formation of these structures can explain the observed regular current fluctuation pattern and contributes to the explanation of the activation phenomena of the model Pt-YSZ and SOFC cathodes.

Nanocrystalline structure and nanopore formation in modified thermal TiO 2 films

The anodic TiO 2 films on Ti 0 substrates were synthesized using different electrochemical techniques including potential step, potentiodynamic, and galvanostatic technique, from a 1 M Na 2 SO 4 + 10 mM NaF solution. The AFM imaging of film surfaces revealed that thin films ( h < 20 nm ) are composed of small spherical-shaped nanocrystals, up to 20 nm in size. In thicker TiO 2 films ( h > 20 nm ) , cylindrical nanopores with diameter of ca. 30 nm, are formed. In contrast to the nanocrystalline nature of anodic TiO 2 films, thermally grown TiO 2 films at 850 °C are composed of oriented large pyramidal crystallites (200–500 nm in size), which are transformed into even larger moulds (2– 3 μ m in size) at 1050 °C. Thermal films of this type have been known to show inferior surface properties leading to large reflectance losses and the presence of surface states, which promote the electron–hole recombination. In this paper, we propose a new way to remedy these disadvantages of thermal films by special low temperature electrochemical anodic treatment. We have found that by the anodic treatment of thermally grown TiO 2 films, it is possible to control the surface properties, such as the nanocrystalline structure and nanopore formation. These features are desirable for solar energy conversion devices and solar hydrogen production, where the enhancement of electrocatalytic activity by increasing real surface area, reduction of reflectance losses, and removal of surface states created by thermal growth, are of primary importance. The tested electrochemical treatment included program waveforms inducing nanocrystallinity and nanopore formation. The pulse-voltammetric procedures are proposed to control surface non-stoichiometry of TiO 2 films and surface-states density of the photoelectrodes.

In Situ, Time-Resolved Reflectance Spectroscopy in the Microsecond Domain: Oxidation of Adsorbed Carbon Monoxide on Polycrystalline Pt Microelectrodes in Aqueous Solutions

The dynamics of the electrooxidation of adsorbed CO, COads, on polycrystalline Pt microelectrodes has been examined in CO-saturated 0.5 M H2SO4 and 0.5 M HClO4 aqueous solutions, using in situ, time-resolved, normalized differential reflectance spectroscopy lambda = 633 nm). Attention was focused on the unique dependence of COads oxidation on the potential at which the adsorbed full CO monolayer is assembled (i.e., hydrogen adsorption/desorption vs the double-layer region) using both fast linear scan voltammetry and potential step techniques. As evidenced from the data collected, COads oxidation at a fixed potential proceeds at slower rates when the monolayer is formed in the double- layer region compared to when it is formed in the hydrogen adsorption/desorption region. Possible explanations for this effect are discussed.

Electrochemical Behavior of Tennantite in Chloride Solutions

Electrochemical oxidation of tennantite was investigated in this study. Cyclic voltammetry, potential sweep, and potential step techniques were employed for the study. Based on the experimental results, a reaction mechanism of internal diffusion of through a sulfur film was proposed to describe the effect of , , , and temperature. The relatively small value of charge-transfer coefficient of the reaction, which was obtained from the Tafel slope, and the irreversibility of the reaction could also be explained by this mechanism. Different sulfur allotropes with various porosities and thicknesses contribute to an unusual temperature effect on tennantite oxidation in conditions of below and a potential range of .