Impedance studies of copper electro-reduction on a disc-shaped ultramicroelectrode in industrial electrolytes

The electrodeposition of copper from industrial sulphate electrolytes has been studied using electrochemical impedance spectroscopy on the gold disc ultramicroelectrode. The influence of dc potential E _dc , temperature, cupric ions and animal glue concentration on electrochemical impedances has been investigated. The mechanism of the copper electro-reduction process in industrial electrolytes has been proposed and experimental impedance data have been analyzed by proper equivalent circuits. According to our knowledge the faradaic and non-faradaic impedance parameters of the process on ultramicroelectrode’s have been estimated for the first time in complex matrix copper industrial electrolytes. The role of animal glue in copper industrial electrolytes has been discussed in the present paper.     

Impedance spectroscopy studies of the dissolution of ferrous- and zinc-based materials in aqueous timber preservatives

The relative degradation rates of metallic materials in aqueous, copper-based timber preservatives have been investigated using electrochemical impedance spectroscopy. The metals examined were AS/NZS 1595:1998, grade CA1 mild steel, AISI 316 stainless steel (UNS S31600) and AS 1397, grade Z275 hot-dipped galvanised coil-coated sheet. The electrolytes consisted of commercially sourced copper–chrome–arsenate, copper azole and alkaline copper quaternary electrolytes diluted to a concentration of 0.1 mol dm⁻³ copper. The electrochemical impedance response of each system has been modelled and the resulting relative rates of corrosion have been shown to broadly correspond to general trends taken from previous weight loss and direct current studies incorporating similar electrolytes. The hot-dipped galvanised steel corroded in an active manner at rates that were two to four orders of magnitude greater than that of the ferrous-based materials; the latter appeared to passivate in all instances.     

Influence of variables in nickel-manganese-zinc alloy plating from a sulphate bath

An Ni-Mn-Zn alloy has been satisfactorily electrodeposited from a sulphate bath containing nickel sulphate (20–23 g dm⁻³), manganese sulphate (76–88 g dm⁻³), zinc sulphate (18–24 g dm⁻³), ammonium sulphate (30 g dm⁻³), thiourea (18g dm⁻³) and ascorbic acid (0.8 g dm⁻³) under various plating conditions, namely, current density 1.0–3.0 A dm⁻²; temperature 30–45° C; pH 2.7–4.2 and duration of electrolysis 15–30 min. Semibright, blackish-grey, thin films were generally deposited with the proportion of nickel and manganese in the deposits increasing with increasing current density, temperature and duration of electrolysis. However, the amount of zinc increased as the pH of the solution was raised. The cathode efficiency for alloy deposition increased linearly as the temperature or the pH of the solution was decreased, whereas at any particular pH and temperature it continuously rose with increasing current density or the time of deposition. The cathode polarization shifted to more negative values on increasing the current density and to less negative values at higher pH values and temperatures which consequently lowered the throwing power under the latter conditions.     

SERS and EQCM studies on the effect of allyl thiourea on copper dissolution and deposition in aqueous sulfuric acid

We investigated the effect of allyl thiourea (ATU) on both the electrodeposition and electrodissolution of copper in aqueous sulfuric acid by combining cyclic voltammetry (CV) with electrochemical quartz crystal microbalance (EQCM) studies and surface enhanced Raman spectroscopy (SERS). The results demonstrated that the two-electron transfer reaction is the predominant process for the copper dissolution–deposition process in 1.0 M H₂SO₄ solution not containing ATU in the potential range −0.65 to 0.05 V versus SCE. In comparison, the copper dissolution–deposition process in 1.0 M H₂SO₄ solution containing ATU corresponds to a one-electron transfer reaction. The spectral features observed from the SERS studies showed at molecular level that ATU can be adsorbed tilted to the copper electrode surface and that coordination occurs via the sulfur atom. The secondary amino group is nearer to the surface than the primary amino group. SO₄²⁻ and HSO₄⁻ can be coadsorbed on the protonated −NH (CH₂CHCH₂) groups.     

Role of Mo<Superscript>6+</Superscript> during nickel electrodeposition from sulfate solutions

The effect of Mo⁶⁺ on the current efficiency, deposit quality, surface morphology, crystallographic orientations and polarisation behaviour of the cathode during electrodeposition of nickel from sulfate solutions was investigated. Mo⁶⁺ did not have a significant effect on current efficiency over the concentration range 2–100 mg dm⁻³. However; a decrease in current efficiency by a magnitude of more than 20% was seen at 500 mg dm⁻³. The quality of the nickel deposit with reference to the visual appearance and contamination level varied with varying concentration of Mo⁶⁺; this was also reflected in the morphology and crystallographic orientations of the deposits. Addition of Mo⁶⁺ to the electrolyte introduced two new crystal planes i.e., (220) and (311). Depolarisation of the cathode was noted at lower concentrations of Mo⁶⁺ (2–40 mg dm⁻³) whereas polarisation of the cathode was observed at Mo⁶⁺ concentration >40 mg dm⁻³ .The effect of Mo⁶⁺ on parameters such as Tafel slope (b), transfer coefficient (α) and exchange current density (i ₀) were also determined.     

Redox and transport behaviors of Cu(I) ions in TMHA-Tf<Subscript>2</Subscript>N ionic liquid solution

The redox and transport behavior of monovalent copper species in an ammonium imide-type ionic liquid, trimethyl-n-hexylammonium bis((trifluoromethyl)sulfonyl)amide (TMHA-Tf₂N) were examined with a micro-disc electrode to clarify its applicability to, for example, electroplating. It was found that the diffusion coefficient of Cu(I) ions in TMHA-Tf₂N containing 12 mmol dm⁻³ Cu(I) ions was 1.2 × 10⁻⁶ cm² s⁻¹ and the redox potential of Cu(I)/Cu was in the potential range 0.1–0.2 V vs. I ⁻/I ₃⁻ at 50 °C. The diffusion coefficient was one order smaller than that of Cu(II) ions in aqueous solution due to the high viscosity of the ionic liquid. The diffusion coefficient of Cu(I) ion increased with rising temperature and was 1.0 × 10⁻⁵ cm² s⁻¹ at 112 °C, which was comparable to that of Cu(II) ions in aqueous CuSO₄ solutions at ambient temperature. This is accounted for by the drastic decrease in the viscosity of the ionic liquid solution with increasing temperature. The activation energy of diffusion was estimated to be 39 kJ mol⁻¹ in the ionic liquid solution.     

A New PVC Membrane Ion Selective Electrode for Determination of Cationic Surfactant in Mouthwash

A new membrane electrode was prepared, using cetylpyridinium chloride based Sn(IV) phosphate (CPC-SnP) as the electroactive material. The electrode exhibits a linear response for the surfactant cetylpyridinium chloride (CPC) in the concentration range 5.0 × 10⁻³–5.0 × 10⁻⁶ mol dm⁻³ with a slope as a 29.1 mV/decade change in the concentration. The working pH range and the response time for the electrode are 2–6 and 30 s respectively. Selectivity coefficients for several cations were determined. The determination of CPC in mouth wash gave results that compare favorably with those obtained by the two phase titration method. This electrode has been utilized as an indicator electrode in the potentiometric titration of cationic surfactant CPC as well as in direct determination of CPC.     

Electrochemical membrane reactor for the reduction of carbondioxide to formate

An electrochemical reactor with anode and cathode chambers separated by a composite perfluoro polymer cation exchange membrane was designed, fabricated and used for the reduction of dissolved carbon dioxide under ambient conditions to formate. The flow reactor enhanced the mass transfer of carbon dioxide compared to the batch reactor and maximum current efficiency of 93% for formate formation was obtained. A formate concentration of 1.5 × 10⁻² mol dm⁻³ was obtained. Experiments were conducted using two different perfluoro polymer membranes – Nafion 961 and Nafion 430. Optimum values of flow rate and current density were evaluated for the energy efficient formation of formate in aqueous phosphate buffer solutions.     

Development of a bath for codeposition of copper and platinum

To improve the mechanical properties of electrodeposited copper, a new bath was developed for the codeposition of copper and platinum. A pyrophosphate bath employing chloroplatinic acid as a source of platinum was investigated at current densities ranging from 1 to 4 A dm⁻² and temperatures from 20 to 60 °C. Bright, shiny and crack-free deposits were obtained at low current densities (i.e., 1–2 A dm⁻²). The amount of platinum observed in the deposits was found to increase with the current density and bath temperature. The Knoop hardness was found to increase with platinum content in the deposits. Corrosion rates measured in solutions of NaCl were found to decrease with platinum content. Deposits containing up to 3.9 wt % of platinum can be obtained by electrodeposition. As compared to electrodeposited copper from the acid bath, the Cu—Pt deposits exhibited a 17% increase in Knoop hardness and a 21% increase in corrosion resistance.     

Sewage treatment for chromium(VI) disposal by combined reduction with sodium sulfite in the presence of solid adsorbents

To improve the existing procedure for the purification of low concentration (50–150 mg/l) sewage from Cr(VI) using sodium sulfite, it was suggested that sewage should be passed through an adsorbent layer. An alternative method is to pass sewage through the adsorbent layer placed in the interelectrode space of an electrochemical cell. Both methods increase the degree of purification for sewage with pH ≥ 6 and allow pH of purified water to be maintained at 6.5–8.0 in accordance with sanitary requirements. It was shown that combined adsorption-reagent and electrochemical reduction can be used by reducing Cr(VI) with sodium sulfite on adsorbents such as Fe₂O₃, kaolin, and activated coal (AC) and passing electric current through an AC adsorbent layer. The degree of purification varied from 80 to 94% for combined processes. The theoretical rate constants were calculated for adsorbent-reagent reduction (4.0–4.7 min⁻¹), and the transfer coefficients were calculated for electrochemical reduction (1–4 mm/s⁻¹).     

Influence of thiourea and thiourea ageing on the electrodeposition of copper from acid sulfate solutions studied by the ring-disc technique

The influence of the additive thiourea in freshly made and aged solutions on copper deposition from acid sulfate solutions was studied using a Pt/Pt rotating ring-disc electrode. In fresh thiourea solutions copper deposition is retarded, but the most distinct effect of thiourea is seen during dissolution of the deposits. The intermediate in copper dissolution, Cu⁺, is partly complexed with adsorbed thiourea. Thus Cu⁺ is adsorbed at the electrode surface and the current peak at the ring due to dissolving Cu⁺ becomes very small. The small peak indicates that active additive is present in the deposit. Thiourea containing solutions aged for only a few days have a distinct effect on the electrode reactions. At low concentrations of thiourea (1 mg dm^–3 ) a correlation between ageing and growth of the Cu⁺ peak at the ring is clearly seen. At high thiourea concentrations (100 mg dm^–3) a small growth of the Cu⁺ peak is seen during the first few days but upon further ageing of the thiourea solution copper deposition becomes strongly inhibited. The ring current can be used as a qualitative diagnostic criterion for the concentration and state of thiourea in copper sulfate solutions.     

Influence of some aromatic amino acids on the swelling behavior of acrylamide/maleic acid hydrogel

Summary Influence of some aromatic amino acids (histidine, phenylalanine and tryptophan) on the swelling behavior of acrylamide/maleic acid hydrogel (AAm/MA) prepared by γ-radiation was investigated. Swelling tests of AAm/MA hydrogel were made in buffer solutions and amino acid solutions at various pH at 37°C. The pH values are ionization of α-carboxyl groups (pK'₁), α-amino groups (pK'₂) and, isoelectric points (pI) of amino acids. The swelling of AAm/MA hydrogel increased when pH values of solutions were increased. The value of equilibrium swelling of AAm/MA hydrogel was 1035% at pH 10 buffer, while it was 880% at pH 2 buffer. The values of equilibrium swelling of AAm/MA hydrogel in phenylalanine, tryptophan and histidine solutions varied among 1130–1245% at pH 10, while they were among 790–975% at pH 2. The rate constant of swelling, diffusional exponent, network parameter and, diffusion and intrinsic diffusion coefficient were calculated by swelling kinetics. Diffusion of the penetrants into the hydrogel was found to be non-Fickian character. The diffusion coefficients of the hydrogel varied between 3.33×10⁻⁶– 7.71×10⁻⁶ cm ²s⁻¹, while the intrinsic diffusion coefficients waried between 4.03×10⁻⁶– 8.48×10⁻⁶ cm ²s⁻¹. Received: 22 December 1997/Revised version: 3 March 1998/Accepted: 5 March 1998     

Response surface modeling and optimization to study the influence of deposition parameters on the electrodeposition of Cu–Zn alloys in citrate medium

Copper–zinc alloy coatings were deposited on mild steel substrates using sodium citrate electrolytes at room temperature and under direct current. For the bath composition studied, factorial design was used to verify the influence of deposition parameters, such as current density and mechanical stirring, on the cathodic efficiency, the contents of copper and zinc, and the amount of hydrogen evolution. Moreover, the four responses were simultaneously studied by using an optimization methodology. The results suggest that the optimum point for reaching good quality copper–zinc alloy deposits from the proposed citrate electrolytes are 29 A m⁻² and 247 rpm for bath 3 and 13 A m⁻² and 67 rpm for bath 4. Applying these conditions, a yellow-reddish coating was obtained from bath 3, while a bright red deposit was produced from bath 4.     

Electrochemical polymerisation of phenol in aqueous solution on a Ta/PbO<Subscript>2</Subscript> anode

This paper deals with the treatment of aqueous phenol solutions using an electrochemical technique. Phenol can be partly eliminated from aqueous solution by electrochemically initiated polymerisation. Galvanostatic electrolyses of phenol solutions at concentration up to 0.1 mol dm⁻³ were carried out on a Ta/PbO₂ anode. The polymers formed are insoluble in acidic medium but soluble in alkaline. These polymers were filtered and then dissolved in aqueous solution of sodium hydroxide (1 mol dm⁻³). The polymers formed were quantified by total organic carbon (TOC) measurement. It was found that the conversion of phenol into polymers increases as a function of initial concentration, anodic current density, temperature, and solution pH. The percentage of phenol polymerised can reach 15%.     

Electro-Catalytic Oxidation of Methanol on a Ni–Cu Alloy in Alkaline Medium

The electro-catalytic oxidation of methanol on a Ni–Cu alloy (NCA) with atomic ratio of 60/40 having previously undergone 50 potential sweep cycles in the range 0–600 mV vs. (Ag/AgCl) in 1 m NaOH was studied by cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS). The electro-oxidation was observed as large anodic peaks both in the anodic and early stages of the cathodic direction of potential sweep around 420 mV vs. (Ag/AgCl). The electro-catalytic surface was at least an order of magnitude superior to a pure nickel electrode for methanol oxidation. The diffusion coefficient and apparent rate constant of methanol oxidation were found to be 2.16 × 10⁻⁴ cm² s⁻¹ and 1979.01 cm³ mol⁻¹ s⁻¹, respectively. EIS studies were employed to unveil the charge transfer rate as well as the electrical characteristics of the catalytic surface. For the electrochemical oxidation of methanol at 5.0 m concentration, charge transfer resistance of nearly 111 Ω was obtained while the resistance of the electro-catalyst layer was ca. 329 Ω.     

Cathodic reaction kinetics and its implication on flow-assisted corrosion of aluminum alloy in aqueous ethylene glycol solution

The cathodic reaction kinetics and anodic behavior of Al alloy 3003 in aerated ethylene glycol–water solution, under well-controlled hydrodynamic conditions, were investigated by various measurements using a rotating disk electrode (RDE). The transport and electrochemical parameters for cathodic oxygen reduction were fitted and determined. The results demonstrate that the cathodic reaction is a purely diffusion-controlled process within a certain potential region. The experimentally fitted value of diffusion coefficient of oxygen is 3.0 × 10⁻⁸ cm² s⁻¹. The dependence of cathodic current on rotation speed was in quantitative agreement with Levich equation. At potentials more positive than the diffusion controlled region, the cathodic process was controlled by both diffusion and electrochemical kinetics. The electrochemical reaction rate constant, k ₀, was determined to be 1.1 × 10⁻⁹ cm s⁻¹. There is little effect of electrode rotation on anodic behavior of Al alloy during stable pitting. However, fluid hydrodynamics play a significant role in formation of the oxide film and the Al alloy passivity. An enhanced electrode rotation would increase the mass-transfer rate of solution, and thus the oxygen diffusion towards the electrode surface for reduction reaction. The generated hydroxide ions are favorable to the formation of Al oxide film on electrode surface.     

Electrochemical study of the codeposition of Mg–Li–Al alloys from LiCl–KCl–MgCl<Subscript>2</Subscript>–AlCl<Subscript>3</Subscript> melts

This work presents a novel electrochemical study on the codeposition of Mg, Li and Al on a molybdenum electrode in LiCl–KCl–MgCl₂–AlCl₃ melts at 943 K to form Mg–Li–Al alloys. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of magnesium on pre-deposited aluminum leads to the formation of a liquid Mg–Al solution, and the succeeding underpotential deposition of lithium on pre-deposited Mg–Al leads to the formation of a liquid Mg–Li–Al solution. Chronopotentiometric measurements indicated that the codeposition of Mg, Li and Al occurs at current densities lower than −0.47 A cm⁻² in LiCl–KCl–MgCl₂ (0.525 mol kg⁻¹) melts containing 0.075 mol kg⁻¹ AlCl₃. Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li and Al is −2.100 V, and the codeposition of Mg, Li and Al is formed when the applied potentials are more negative than −2.100 V. The diffusion coefficient of aluminum ions in the melts was determined by different electrochemical techniques. X-ray diffraction and inductively coupled plasma analysis indicated that α, α + β and β Mg–Li–Al alloys with different lithium and aluminum contents were obtained via potentiostatic and galvanostatic electrolysis.     

Effects of substituents of imidazolium cations on the performance of dye-sensitized TiO2 solar cells

Imidazolium iodides (Im⁺I⁻s) were synthesized with different substituents of the cation and used as electrolytes in dye-sensitized solar cells (DSSCs), and the effects of such substituents were investigated in terms of the photovoltaic performance of the cells. Synthesized iodides were verified by ¹H-NMR. Among the iodides, 1,3-diethylimidazolium iodide enabled a solar energy conversion efficiency of 4.8% for its DSSC, while 1-(4-acetophenyl)-3-ethylimidazolium iodide rendered an efficiency of 3.1% for its cell. In all cases the short-circuit photocurrent (J _sc) was found to increase with decrease in size of the substituent, which was also verified to be valid in the case of a quasi-solid state DSSC. Results are explained by the electrostatic interactions between solvated Im⁺ and negatively charged species based on the correlation between diffusion coefficients of I⁻ and I₃⁻ and J _sc values. These explanations are supported by steady-state voltammetry and electrochemical impedance spectroscopy (EIS).     

Impact of electrolyte additives (alkali metal salts) on the capacitive behavior of NiO-based capacitors

To improve the specific capacitance and energy density of electrochemical capacitor, nanostructured NiO was prepared by high temperature solid-state method as electrode material. The crystal structure and morphology of as-parepared NiO samples were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Cyclic voltammetry (CV) measurement was applied to investigate the specific capacitance of the NiO electrode. Furthermore, a novel mixed electrolyte consisting of NaOH, KOH, LiOH and Li₂CO₃ was prepared for the NiO capacitor, and the component and concentration of the four different electrolytes was examined by orthogonal test. The results showed that the NiO sample has cubic structure with nano-size particles, and the optimal composition of the electrolyte was: NaOH 2 mol L⁻¹, KOH 3 mol L⁻¹, LiOH 0.05 mol L⁻¹, and Li₂CO₃ 0.05 mol L⁻¹. At a scan rate of 10 mV s⁻¹, the fabricated capacitor exhibits excellent electrochemical capacitive performance, while the specific capacitance and the energy density were 239 F g⁻¹ and 85 Wh kg⁻¹, which was higher than one-component electrolyte.     

<Emphasis Type="Italic">Meso</Emphasis>-Tetra-(3,5-Dibromo-4-Hydroxydroxyphenyl) Porphyrin Copper (II) Self-Assembled Modified Gold Electrode Through <Emphasis Type="SmallCaps">l</Emphasis>-Cysteine: The Preparation,Electrochemical Behavior and its Application

In this study, a sensor for the sensitive determination of ascorbic acid (AA) has been fabricated based on meso-tetra-(3,5-dibromo-4-hydroxydroxyphenyl) porphyrin copper (II) (T(DBHP)P-Cu) modified Au electrode through l-cysteine (l-cys). Firstly, l-cys modified Au electrode was prepared through self-assembled technology. Then T(DBHP)P-Cu was adsorbed on l-cys/Au through covalent binding. The fabrication process and electrochemical behavior of T(DBHP)P-Cu/l-cys/Au were studied by cyclic voltammetry and differential pulse voltammetry. The results showed that AA exhibited good electrochemical activity at T(DBHP)P-Cu/l-cys/Au. The oxidation peak current increased linearly with AA concentration in the range of 1.00 × 10⁻³–1.02 × 10⁻⁵ mol L⁻¹ with a detection limit of 5.41 × 10⁻⁷ mol L⁻¹. Additionally, the modified electrode could be applied to the detect AA in practical samples.