Influence of electrodeposition conditions on the properties of CdTe films

The results of the influence of electrodeposition conditions on the structural, compositional, optical, and photoelectrochemical properties of CdTe thin films deposited in one-step electrochemical method are presented. The CdTe films were prepared electrochemically from aqueous acidic solution with low ratios of Cd²⁺ ions to Te(IV) ions concentration. Instead of commonly used TeO₂, water-soluble Na₂TeO₃ was used as a source of tellurium ions. The cathodic deposition of CdTe was performed at different constant potentials from solutions containing different cadmium and tellurium ions concentration. As-deposited CdTe thin films were studied by different analytical techniques. The X-ray photoelectron spectroscopy spectra exhibited CdTe formation on the electrode with some amount of tellurium oxides and cadmium oxides. The best quality CdTe deposits, free of TeO₂, were formed in bath containing excess of Cd²⁺ ions and at the potential of ?0.65 V vs. saturated calomel electrode, slightly more positive than E _eq of Cd/Cd²⁺ system. Structural X-ray diffraction studies revealed polycrystallinity of deposits with the highest content of the (111)-oriented cubic (111) form. Optical band gap energy values were found in the range from 1.36 to 1.6 eV for CdTe films prepared at various synthesis conditions. The preliminary photoelectrochemical studies have shown that the variation of the deposition potential as well as bath composition leads to the formation of p- or n-type CdTe films. As-deposited CdTe films were not stable in polysulfide solution under illumination.     

Cadmium atomic layers on tellurium electrodes

The process of electrodeposition of atomic layers of cadmium Cd_ad 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 Cd_ad 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 Cd_ad/Te to 3D CdTe nanostructures, which are distributed in the tellurium matrix. In contrast with tellurium, the Te/CdTe_nano heterostructure exhibits photoelectrochemical activity, i.e. it generates a cathodic photocurrent.     

Electroreduction of Tellurium(IV) on Solid Electrodes in Neutral Solutions

Electroreduction of Te(IV) on glassy-carbon and nickel in neutral and weakly alkaline solutions is studied by cyclic voltammetry. A wave for the Te(IV) Te(0) process is discovered. At a limiting current of Te(IV) reduction in a potentiodynamic mode in 0.5 M Na₂SO₄, a peak current is observed on Ni at –1.02 V (Ag/AgCl). The relationship between the peak and the tellurium electroreduction to the tellurium ion and the tellurohydrogen formation involving a proton is discussed. Dependence of the peak current on the concentration of Te(IV) ions is used for their analytical assay.     

The electrochemical synthesis of poly(o-phenylenediamine) on stainless steel and its corrosion protection ability in 3.5 % NaCl solution

In this study, electrochemical synthesis of poly(o-phenylenediamine) (PoPDA) on 316L stainless steel and its corrosion inhibition effect were studied. Electropolymerization of o-phenylenediamine (oPDA) was carried out by a potentiodynamic method using 0.5 M H₂SO₄ solution containing 0.05 M oPDA monomer. The corrosion protection ability of the PoPDA in 3.5 % NaCl was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, and change of open circuit potential with immersion time (E_OCP ? t). The results showed that PoPDA acted as a protective layer on stainless steel against corrosion in 3.5 % NaCl solution.     

Reactivation of passive titanium: the enhancement of O2 evolution after potentiodynamic cyclings

Titanium oxide films were grown potentiodynamically at 50 mV s⁻¹ from −1.1 up to 10.0 V, at room temperature (23±1 °C) in H₃PO₄/NaH₂PO₄ aqueous solutions of ionic strength 0.5 mol L⁻¹ and pH 3.0. After the oxide growth, the passive electrode was subjected to different repetitive potentiodynamic cycles at 50 mV s⁻¹ between pre-set cathodic (E_s,c) and anodic (E_s,a) switching potentials. The changes in the electrochemical behaviour of the passive electrode, specially that of the O₂ evolution reaction, were followed as a function of the number of cycles and of the limiting negative potential value used, E_s,c. The enhancement of the oxygen reaction rate occurring with the repetitive potential sweeps might be due to an increase of both the oxide conductivity and the porous-oxide surface area.     

The effect of potential on the gold dissolution in cyanide solutions in the presence of sulfide ions

The effect of potential on the rate of gold dissolution in the cyanide solutions in the presence of sulfide ions is studied. The dependences of current on the time after the electrode surface renewal were measured under the potentiostatic conditions. The majority of experiments were performed in the solution of the following composition, M: 0.1 KCN, 0.1 KOH, 0.01 KAu(CN)₂, (1.5–2) × 10^?5 Na₂S at 23°C. It is shown that, at the potentials more positive than ?0.1 V (NHE), the rate of gold dissolution starts to increase as soon as the surface is renewed, which is associated with high-rate chemisorption of catalytically active sulfide ions. At E < ?0.1 V, the chemisorption proceeds slowly, and a considerable increase in the current takes much time. Therefore, in the potentiodynamic measurements, at E < ?0.1 V, no catalytic effect of sulfide ions is observed. When the ratio between the concentrations of sulfide and cyanide ions is decreased, the potential, which, by convention, bounds the aforementioned ranges, shifts in the positive direction. Plausible explanations for these regularities are proposed.     

Voltammetric determination of dihydroxybenzenes at a mechanically renewed electrode made from a graphite-epoxy composite

Differences of potentials of anodic and cathodic peaks (ΔE _p) are determined in cyclic voltammograms of dihydroxybenzene/p-benzoquinone redox systems at an electrode made of a graphite-epoxy composite in a wide pH range. The data obtained (ΔE _p = 29 ± 1 mV) are close to the thermodynamic values for two-electron reversible reactions. This indicates that the electrode mechanically renewed by cutting a 0.5-μm surface layer directly in a test solution exhibits a high activity in such electrochemical reactions. The potentials of anodic and cathodic peaks are proportional to the pH of the supporting electrolyte solution in the range from 1.0 to 9.0. A change of 58 ± 1 mV in E _p per unit pH for all isomers shows that the first stage of the oxidation of each dihydroxybenzene isomer involves one electron and is accompanied by the detachment of one hydrogen ion, that is, an intermediate oxidation product, semiquinone, is formed. Despite the closeness of the potentials of hydroquinone and pyrocatechol peaks (ΔE = 100 mV), a scheme is proposed for the selective voltammetric determination of dihydroxybenzene isomers in a 0.1 M HCl solution in hydroquinone-pyrocatechol, pyrocatechol-resorcinol, and hydroquinone-resorcinol binary mixtures. The concentrations of hydroquinone and pyrocatechol are found from cathodic peaks and that of resorcinol, from the anodic peak. The results are well reproducible and contain no systematic error.     

Experimental and theoretical studies of acridine orange as corrosion inhibitor for copper protection in acidic media

The corrosion process commonly limits the use of copper in practical applications. The use of corrosion inhibitors is one of the effective methods to reduce the corrosion rate of copper. In this research, the inhibition effect of acridine orange (3,6-bis(dimethylamine)acridine) (AcO) for the protection of copper in 0.5 ?M ?H₂SO₄ solution was studied. For this aim, the change of open circuit potential with exposure time (E_ocp-t), electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), anodic and cathodic potentiodynamic polarization measurements (PP) and chronoamperometry (CA) techniques were used. Some quantum chemical parameters (E_HOMO, E_LUMO and dipole moment) were calculated and discussed. The AcO film formed over the copper surface was examined by SEM, EDX, AFM and contact angle measurements. The electrochemical data showed that AcO is an effective corrosion inhibitor even at low concentrations (ranging between 99.1% and %99.4 ?at concentrations from 0.01 ?mM to 1 ?mM). The corrosion rate of copper decreases in the presence of the inhibitor by reducing both anodic and cathodic rates, which is depended on its concentration. This compound behaves as mixed-type corrosion inhibitors with predominantly cathodic type. Its adsorption on the copper surface obeys Langmuir adsorption isotherm. The value of adsorption equilibrium constant (K_ads) and the standard free energy of adsorption were ΔG_ads 1.298 x 10³ ?M^?1 and -27.71 ?kJ/mol in the case of 0.5 ?M ?H₂SO₄ solution containing 1.0 ?mM AcO, which shows the adsorption is high and spontaneous. The adsorbed inhibitor film over the metal increase contact angle of the surface, which suggests the more hydrophobic properties of the surface are increasing coming from the orientation of hydrophobic sites to the electrolyte. The zero charge potential (E_pzc) studies showed that the surface charge of the metal is positive in the corrosive media containing the inhibitor. Quantum chemical calculations showed that the binding of inhibitor molecules to the metal surface takes place through N atoms of the inhibitor.     

Electrochemical properties of polyaniline film doped by Ce3+ cation

Electrochemical Synthesis (ES)of polyaniline (PAni) is carried out in the presence in electrolyte (1 M H₂SO₄) of cerium (III) sulfate under potentiostatic and potentiodynamic modes. It is shown that Ce³⁺ cations in electrolyte catalyze ES, i.e. accelerate both ES variants. The obtained polymers were characterized using the scanning electron microscopy (SEM) technique and also on the basis of the calculation of electrochemical characteristics. Relaxation in PAni polymers doped by the Ce³⁺ cation occurs several times faster than in proton-doped PAni. The minimum change in ΔE and E is observed in polymers doped by Ce³⁺ cations during the electrochemical cycling of PAni and PAni-Ce at high rates.     

Corrosion inhibition of mild steel by Laurus nobilis leaves extract as green inhibitor

The efficiency of Laurus nobilis leaves?? extract as a corrosion inhibitor for mild steel in acidic medium (1?M H₂SO₄) was investigated by use of the electrochemical techniques potentiodynamic polarization, electrochemical impedance spectroscopy, and polarization resistance measurements. According to the experimental results, L. nobilis extract acts as a good corrosion inhibitor. In the presence of the inhibitor, corrosion potential shifted toward a more negative value than for the blank solution. Inhibitor efficiency increased with increasing inhibitor concentration, as expected. According to the potentiodynamic polarization results the corrosion of mild steel increased with increasing temperature both in the presence and absence of the inhibitor. The activation energy (E _a) of the corrosion process was calculated from the variation of corrosion current density with temperature.     

Investigation of the surface properties of platinum,rhodium and iridium electrodes in hydrofluoric acid solutions

The charging curves, the potentiodynamic curves and the isoelectric potential shifts have been measured on Pt, Rh and Ir electrodes in HF and HF + KF solutions in a Teflon cell. From the obtained data, the Γ_H⁺?? curves and the Δσ?? curves of the first kind have been calculated by means of the thermodynamic theory of the hydrogen electrode. The Γ_H⁺ values in 0.14 M HF and 0.3 M HF + 0.12 M KF are much less than in 0.005 M H₂SO₄ and 0.005 M H₂SO₄ + 0.5 M K₂SO₄ solutions. In the presence of F^? anions, the potentials ?_ε=0 and ?_Q=0 are by 25–55 mV more anodic than in the presence of SO^2?₄ anions. In an acidified fluoride solution the values of σ are higher than in an acidified sulfate solution. The analysis of the results obtained leads to the conclusion that on platinum metals the fluoride anions in the ?_r region investigated (from ?_r = 0 to ?_r = 900 mV) are the most weakly adsorbed anions.     

Electrochemical Properties of Hydroxyphenazine-Coated Electrodes

Glassy carbon and gold electrodes were coated with 1-hydroxyphenazine, and the electrochemical properties of these electrodes were tested using them as a rotating disc electrode to reduce Ru (bipy)₃³⁺, Fe³⁺, quinoxaline, O₂, and to oxidize Eu²⁺. The fixed redox couple can be reversibly reduced and oxidized, and acts as an intermediate medium for the electron transfer. For example the Ru(bipy)₃³⁺ (E_1/2= 1010 mV vs. SCE. (saturated calomel electrode) on a glassy carbon electrode in 1M H₂SO₄) is only reduced at 50 mV, whereas the oxidation of Eu²⁺ (E_1/2= ?460 mV vs. SCE. on a Hg-electrode in 1M HCl) takes place at ? 100 mV. The heterogeneous rate constant depends on the second order reaction between the attached coating and the redox couple in solution. Depending on this rate constant, selectivity of the electrode is observed.     

UV-Vis and Raman Spectral Analysis of Polyaniline/Gold Thin Films as a Function of Applied Potential

Polyaniline and polyaniline/gold films were prepared by potentiodynamic oxidation of aniline in 1 M H₂SO₄ aqueous solution, and their electrochromic properties were investigated by UV-Vis and Raman spectroscopy. Both tetrachloroaurate and gold nanoparticles were used to deposit gold onto or inside the polyaniline film based on the deposition technique used. Polyaniline films showed multiple color changes (blue to green to yellow) depending on the electrochemical reactions in the potential range ?0.2 to 0.8 V vs. Ag/AgCl. The color of polyaniline films changed from transparent green to yellow at the anodic peak around 0.2 V and gradually changed from green to dark blue at potentials higher than 0.5 V. The deterioration of electrochromic properties is caused by hydrolysis of the diimine structure formed by oxidation at 0.8 V. Furthermore, the polyaniline films showed enhanced Raman characteristics (due to SERS) depending on the treatments with gold and the potentials applied to the films to control the oxidation state.     

Electrodeposition of Copper Selenide onto Mo Electrode in Tartaric Acid Solution

Results are presented of a study of the electrochemical behavior of copper(II) and selenium(IV) ions and their joint reduction on a molybdenum electrode by cyclic voltammetry in a tartaric acid electrolyte. The potentiostatic deposition was used to obtain copper selenide deposits on Mo plates. The diffraction and energydispersive analyses demonstrated that a Cu_2?xSe compound is formed with an admixture of the CuSe phase. A suggestion is made that the process of underpotential reduction affects the formation of copper selenide. Copper selenide films were deposited at a potential of ?0.6 V in the course of 30 min with a thickness of 0.43 μm and high adhesion to the substrate. At potentials in this range, an additional amount of the deposit may be formed due to the chemical reaction between Cu⁺ and Se^2? ions. The p-type conduction was determined for films electrodeposited at various potentials.     

The electrochemical determination of oxygen ion diffusion coefficients in La0.50Sr0.50CoO3−y: Experimental results and related properties

Results of an electrochemical method for the determination of oxygen ion diffusion coefficients D_O^2? in porous pellets of La_0.50Sr_0.50CoO_3?y are presented. Log D_O^2? can be expressed as log D_O^2?=?(2.3±0.2) 10³/T?(6.6±0.6) cm² s^?1. The activation energy E_a for the diffusion process equals 44 kJ mol^?1. Further the related electrochemical measurement and the adjustment of the oxygen deficiency y are described. At 75°C the following empirical Nernst relation between the electrode potential E (vs. a Pt/H₂ (1 atm) electrode in the same solution) and Δy is found: E=627–108 ln (Δy + 0.0054) mV. (Δy=y?y₀; y₀=mole fraction of vacancies at the reversible O₂ potential of 1190 mV). The use of La_0.50Sr_0.50CoO_3?y as a solid solution electrode in practical storage cells seems to be excluded for thermodynamic and kinetic reasons.     

Electrochemical properties of sulfur adsorbed on gold electrodes

The electrochemical properties of sulfur adsorbed on gold electrodes were studied in 10^?5M solutions of S^2? in 1 M NaOH. In general, ∵_S is less than a monolayer. At E=0.05 V only, a monolayer will be formed after long times. The sulfur layer is stable in the potential range between ?0.6 and +0.4 V. At lower potentials, sulfur can be desorbed cathodically (charge Q_red), but at higher potentials, where layers of gold oxide are formed, the sulfur is oxidized anodically (charge Q_ox). From the ratio Q_red·6/Q_ox=γ, the electrosorption valency γ=?2 is obtained. This means, that the sulfide ions are almost completely discharged during adsorption. The same layer can be formed by adsorption from polysulfide solutions, which can be explained by a break of the sulfur bond and adsorption of single sulfur atoms. The double layer capacity decreases during adsorption of sulfur indicating the formation of an insulating sulfur layer with a dielectric constant of about 2. The anodic adsorption of sulfide ions is limited by diffusion only. For longer polarisation times, the coverage is independent of time, i.e. place exchange reactions between Au and S can be excluded. The cathodic desorption as well as the anodic oxidation of the adsorbed sulfur are potential dependent charge transfer processes, as can be concluded from potentiodynamic measurements with various sweep rates.     

Organic Phase Cyclopentadienylnickelthiolate Sensor System for Electrochemical Determination of Sulfur Dioxide

A series of cyclopentadienylnickelthiolate complexes, [Ni(PBu₃)(η⁵‐C₅H₅)(SC₆H₄X‐4)] (X=F, Cl, Br, NH₂), were shown to express stable reversible electrochemical properties even after formation of SO₂ adducts in organic phase consisting of argon purged CH₂Cl₂/0.1 M [n‐Bu₄N][BF₄]. The formal potentials (E°′) values of the compounds ranged from 265 to 431 mV/Ag‐AgCl depending on the para substituent of the benzene thiolate ligand. Electrochemical, UV‐vis and ¹H NMR spectroscopic analyses show that the formation of SO₂ adducts causes the perturbation of the electronic density of the nickel metal center, indicated by shifts in the E°′ values of the Ni^II/III redox couple that is dependent on SO₂ concentration. The detection limits of the resulting organic phase electrochemical gas sensor system was as low as 0.56 ppm SO₂ for the fluoro complex, while the linear range was as high as 700–2000 ppm SO₂ for the amino complex.     

On the hydrolysis of the titanium(IV) ion in chloride media

Determinations of the [Ti(IV)]/[Ti(III) ratio in solutions of titanium(IV) chloride equilibrated with H₂(g), at 25°C in 3 M (Na)Cl ionic medium, have indicated the predominance of the Ti(OH)₂²⁺ species in the concentration ranges 0.5 ? [H⁺] ? 2 M and 1.5 x 10^?3 ? [Ti(IV)] ? 0.05 M. From the equilibrium data the reduction potential has been evaluated Ti(OH)₂²⁺ + 2 H⁺ + e ? Ti³⁺ + 2H₂O, E_oH = (7.7 ± 0.6) x 10^?3 V. The acidification reactions of Ti(OH)₂²⁺ were also studied in 12 M(Li)Cl medium at 25°C by measuring the redox potential of the Ti(IV)/Ti(III) couple as a function of [H⁺]. The potentiometric data in the acidity range 0.3 ? [H⁺] ? 12 M have been explained by assuming Ti⁴⁺ + e ? Ti³⁺, E_o = 0.202 ± 0.002 V Ti⁴⁺ + H₂O ? TiOH³⁺ + H⁺, log K_a1 = 0.3 ± 0.01 Ti⁴⁺ + 2H₂O ? Ti(OH)₂²⁺ + 2H⁺, log K_a1K_a2 = 1.38 ± 0.05.     

Electropolymerization of Mefenamic Acid on Copper and Copper Based Alloy as a New Strategy to Control the Release of Copper Ions from Copper Containing Devices

Poly-2-(2,3-dimethylanilino) benzoic acid (PMF) coatings on copper and brass alloy were synthesized by electrochemical oxidation of 2-(2,3-dimethylanilino) benzoic acid in the presence of oxalic acid as the reaction medium. Electrodeposition was carried out using the cyclic voltammetry technique using a silver/silver-chloride standard electrode, with a scan rate of 600 mV min^–1. Smooth and well adhered PMF coatings were electrosynthesized during sequential scanning of the potential in the range–500 mV to 1400 mV on copper and brass alloy. The electrodeposited coatings were characterized by recording the oxidation peaks at 122 mV for Cu and–0.7 mV for brass, in cyclic voltammetry and using scanning electron microscopy (SEM). Corrosion inhibition efficiency of coated copper and brass alloy was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The impedance results showed that the inhibition efficiency of coated copper is 89% and for coated brass 79.4% compared to the uncoated copper and brass in 0.1 M H₂SO₄.

     

The effect of sulfide ion chemisorption on the kinetics of gold dissolution in cyanide solutions

The effect of sodium sulfide additions (from 5 × 10^?6 to 2 × 10^?5 M) on the kinetics of gold dissolution in cyanide solutions of the following composition, M: 0.1 KCN, 0.02 KAu(CN)₂, 0.5 K₂SO₄, pH 10–13 is studied. Hydrosulfide ions are shown to exert a strong catalytic effect on the dissolution kinetics of this metal in a potential range where their adsorption is accompanied by the formation of polysulfides (?0.2 < E < 0.4 V). The reaction acceleration depend on the potential and is 100-fold for E ? 0.1 V. The effect becomes more pronounced as the concentration of hydrosulfide ions increases to 10^?4 M and is almost pH-independent in the pH range from 10 to 13. An attempt to explain the found relationships is undertaken.