Electrodeposition chloride

A physical model and a theory have been proposed [72], which might be helpful in comparative studies on electrocompres-sive behavior of electrodeposited chloride, bromide, and iodide monolayers on the Au(lll) electrode. The theoretical results were in good agreement with the experimental data, which evidence that the adatom-adatom interactions (especially repulsive ones) and electrosorption valency of halide anions determine the compressibility within halide adlayers. Also, Lipkowski et al. have discussed various aspects of adsorption of halide anions on Au(lll) in a review paper [36]. From this paper, we have taken quantitative data concerning adsorption of halide anions on Au(lll) (cf Fig. 3). 

The development of scanning probe microscopies and x-ray reflectivity (see Chapter VIII) has allowed molecular-level characterization of the structure of the electrode surface after electrochemical reactions [145]. In particular, the important role of adsorbates in determining the state of an electrode surface is illustrated by scanning tunneling microscopic (STM) images of gold (III) surfaces in the presence and absence of chloride ions [153]. Electrodeposition of one metal on another can also be measured via x-ray diffraction [154]. 

Markovic N M, Gasteiger H A and Ross P N 1995 Copper electrodeposition on Pt(111) in the presence of chloride and (bi)sulphate Rotating ring-Pt(111) disk electrode studies Langmuir 11 4098-108... 

Conducting polymer composites have also been formed by co-electrodeposition of matrix polymer during electrochemical polymerization. Because both components of the composite are deposited simultaneously, a homogenous film is obtained. This technique has been utilized for both neutral thermoplastics such as poly(vinyl chloride) (159), as well as for a large variety of polyelectrolytes (64—68, 159—165). When the matrix polymer is a polyelectrolyte, it serves as the dopant species for the conducting polymer, so there is an intimate mixing of the polymer chains and the system can be appropriately termed a molecular composite. 

It was quite recently reported that La can be electrodeposited from chloroaluminate ionic liquids [25]. Whereas only AlLa alloys can be obtained from the pure liquid, the addition of excess LiCl and small quantities of thionyl chloride (SOCI2) to a LaCl3-sat-urated melt allows the deposition of elemental La, but the electrodissolution seems to be somewhat Idnetically hindered. This result could perhaps be interesting for coating purposes, as elemental La can normally only be deposited in high-temperature molten salts, which require much more difficult experimental or technical conditions. Furthermore, La and Ce electrodeposition would be important, as their oxides have interesting catalytic activity as, for instance, oxidation catalysts. A controlled deposition of thin metal layers followed by selective oxidation could perhaps produce cat-alytically active thin layers interesting for fuel cells or waste gas treatment. 

The anionic composition of the cathodic product is not the only parameter that can be controlled through electrolysis conditions. Grinevitch et al. [559] reported on the investigation of the co-deposition of tantalum and niobium during the electrolysis of fluoride - chloride melts. Appropriate electrodeposition conditions were found that enable to obtain either pure niobium or alloys. 

Recently, a eutectic mixture of choline chloride and urea (commercially known as Reline) was used as a medium from which CdS, as well as CdSe and ZnS, thin films were electrodeposited for the first time [53]. Reline is a conductive room-temperature ionic liquid (RTIL) with a wide electrochemical window. The voltammetric behavior of the Reline-Cd(II)-sulfur system was investigated, while CdS thin films were deposited at constant potential and characterized by photocurrent and electrolyte electroabsorbance spectroscopies. 

The potentiostatic electrodeposition of iron selenide thin films has been reported recently in aqueous baths of ferric chloride (FeCb) and Se02 onto stainless steel and fluorine-doped TO-glass substrates [193], The films were characterized as polycrystalline and rich in iron, containing in particular a monoclinic FesSea phase. Optical absorption studies showed the presence of direct transition with band gap energy of 1.23 eV. 

The UPD and anodic oxidation of Pb monolayers on tellurium was investigated also in acidic aqueous solutions of Pb(II) cations and various concentrations of halides (iodide, bromide, and chloride) [103]. The Te substrate was a 0.5 xm film electrodeposited in a previous step on polycrystalline Au from an acidic Te02 solution. Particular information on the time-frequency-potential variance of the electrochemical process was obtained by potentiodynamic electrochemical impedance spectroscopy (PDEIS), as it was difficult to apply stationary techniques for accurate characterization, due to a tendency to chemical interaction between the Pb adatoms and the substrate on a time scale of minutes. The impedance... 

As well as the adsorption of halogen atoms or molecules, the adsorption of halide anions to gold surfaces has been extensively studied and a comprehensive review of the area has been published by Magnussen [168]. The degree of specific adsorption to gold surfaces increases in the order F < Cl < Br < 1 with only weakly specifically adsorbed. The presence of halide anions can also affect the electrodeposition of organic molecules such as pyridine on Au surfaces with chloride and bromide solutions suppressing the formation of ordered N-bonded pyridine layers [169]. 

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

Kim and Jorne [37] have used a rotating zinc hemisphere to study the kinetics of zinc dissolution and deposition reactions in concentrated zinc chloride solutions. The electrodeposition reaction of cadmium on mercury was used by Mortko and Cover [43] in their investigation of a rotating dropping mercury electrode their data behaved according to Eqs. (74)-(76). 

Relatively little attention has been devoted to the direct electrodeposition of transition metal-aluminum alloys in spite of the fact that isothermal electrodeposition leads to coatings with very uniform composition and structure and that the deposition current gives a direct measure of the deposition rate. Unfortunately, neither aluminum nor its alloys can be electrodeposited from aqueous solutions because hydrogen is evolved before aluminum is plated. Thus, it is necessary to employ nonaqueous solvents (both molecular and ionic) for this purpose. Among the solvents that have been used successfully to electrodeposit aluminum and its transition metal alloys are the chloroaluminate molten salts, which consist of inorganic or organic chloride salts combined with anhydrous aluminum chloride. An introduction to the chemical, electrochemical, and physical properties of the most commonly used chloroaluminate melts is given below. 

In many ways, chloroaluminate molten salts are ideal solvents for the electrodeposition of transition metal-aluminum alloys because they constitute a reservoir of reducible aluminum-containing species, they are excellent solvents for many transition metal ions, and they exhibit good intrinsic ionic conductivity. In fact, the first organic salt-based chloroaluminate melt, a mixture of aluminum chloride and 1-ethylpyridinium bromide (EtPyBr), was formulated as a solvent for electroplating aluminum [55, 56] and subsequently used as a bath to electroform aluminum waveguides [57], Since these early articles, numerous reports have been published that describe the electrodeposition of aluminum from this and related chloroaluminate systems for examples, see Liao et al. [58] and articles cited therein. 

Mitchell, J. A., The Electrodeposition of Cobalt, Iron, Antimony and Their Alloys from Acidic Aluminum Chloride 1 -methyl-3-ethylimidazolium Chloride Room-Temperature Molten Salts, Ph.D. Dissertation, 1997, University of Mississippi University, MS. 

Determination of trace metals in seawater represents one of the most challenging tasks in chemical analysis because the parts per billion (ppb) or sub-ppb levels of analyte are very susceptible to matrix interference from alkali or alkaline-earth metals and their associated counterions. For instance, the alkali metals tend to affect the atomisation and the ionisation equilibrium process in atomic spectroscopy, and the associated counterions such as the chloride ions might be preferentially adsorbed onto the electrode surface to give some undesirable electrochemical side reactions in voltammetric analysis. Thus, most current methods for seawater analysis employ some kind of analyte preconcentration along with matrix rejection techniques. These preconcentration techniques include coprecipitation, solvent extraction, column adsorption, electrodeposition, and Donnan dialysis. 

In general, metal nanoparticles are obtained via reduction of metal complexes, such as metal chlorides, by chemical agents (chemical reduction), or by electrons (electrodeposition). Hybrids of metal oxides are obtained by oxidation, network formation or precipitation of precursors such as metal nitrates and acetates [144]. 

Electrodeposition on Other Electrodes Trejo et al. [224] have investigated the influence of the zinc chloride concentration on the zinc nucleation process on GC electrode in KCl solutions under conditions close to those employed in commercial acid deposition baths for zinc. The results show that the nucleation process and the density number of sites are dependent on ZnCh concentration. The deposits are homogeneous and compact, although a change in morphology is observed as a function of ZnCl2 concentration. 

Trejo etal. [225, 226] have also investigated the influence of several ethoxylated additives (ethyleneglycol and PEG polymers of different molecular weights) on the nucleation, growth mechanism, and morphology of zinc electrodeposited on GG from an acidic chloride bath. Results have shown that the presence of additives modifies the nucleation process and determines the properties of the deposits. 

The same mechanism of zinc electrodeposition on the GC electrode was observed in sulfate, chloride, and acetate ion solutions [227]. The anions mainly affected the nucleation densities during zinc deposition, which resulted in a different surface morphology. The nucleation rate constant was the same in the chloride and sulfate solutions and was equal to 1.22 x 10 s h In the presence of acetate and chloride ions, the deposited zinc film tends to grow in a multilayered pattern, while in sulfate solution, the zinc deposition forms irregular grains. A new approach to the estimation of zinc electrocrystallization parameters on the GC electrode from acetate solutions was described by Yu et al. [228]. 

Also, the influence of benzylideneace-tone on the mechanism of zinc electrodeposition on Pt electrode in a chloride acidic bath was studied [234]. 

Rodriguez-Torres etal. [235] have used ammonia-containing baths for Zn-Ni alloy electrodeposition on Pt. Zinc and nickel species exist in the form of [Zn(NH3)4] + and [Ni(NH3)6] " complexes in such solutions. The deposition at pH 10 was investigated and compared with deposition from ammonium chloride baths at pH 5. The Ni content in the alloys was found to be 40-60% higher from the ammonia-containing bath than from the acidic baths. The deposition mechanism was found to be affected by complexation of the metal cations by ammonia. 

Mechanism of zinc electrodeposition on steel in acidic solution of zinc chloride was investigated [408] as a function of pH, grain-refining additives, and current density. 

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