Indium cathode

In an aqueous solution, the electrode potentials of CO2 reduction correlate with the heats of fusion (HoF) of the electrode metals low-HoF metals (Hg, Tl, Pb, In, Cd and Zn) yield formate, while high-HoF metals (Pt, Pd, Ni, Au, Cu, Ag, Zn, Sn and Ga) form CO [77,87]. The above classification is far from being perfect, and does not cover for all possible scenarios of CO2 electroreduction. As shown later, in the section on the S5mthesis of organic carbonate, when used in an ionic liquid, indium cathodes are efficient in the preparation of dimethyl carbonate. Also, copper-based bimetallic electrodes may exhibit an improved catalytic activity in reducing CO2 to hydrocarbons. Examples include Cu-Ni, Cu-Sn and Cu-Pb alloys. By contrast, for Cu-Ag and Cu-Cd alloy electrodes, the catalytic activity is diluted [81]. 

Dimethyl carbonate was obtained from CO2 on an indium cathode, in a high-purity ionic liquid, l-butyl-3-methylimidazoliumtetrafluoborate (BMIMBF4, >99.99%). Prior to the electroreduction, the ionic liquid was dried carefully, under vacuum at 110°C, as the presence of moisture would narrow the potential window of BMIMBF4. As demonsfrafed by cyclic voltammetry, the reduction peak occurred at -1.8 V (vs. Ag). The electrolysis experiments were carried out in an undivided cell, magnesium being used as a sacrificial anode. Preceding... 

The conventional electrochemical reduction of carbon dioxide tends to give formic acid as the major product, which can be obtained with a 90% current efficiency using, for example, indium, tin, or mercury cathodes. Being able to convert CO2 initially to formates or formaldehyde is in itself significant. In our direct oxidation liquid feed fuel cell, varied oxygenates such as formaldehyde, formic acid and methyl formate, dimethoxymethane, trimethoxymethane, trioxane, and dimethyl carbonate are all useful fuels. At the same time, they can also be readily reduced further to methyl alcohol by varied chemical or enzymatic processes. 

Indium chemicals and electroplated metal deposits ate replacing mercury (qv) in the manufacture of alkaline batteries (qv). Indium, like mercury, functions to reduce outgassing within the battery and promotes the uniform corrosion of the anode and cathode while the battery is under electrical load. Indium inorganic chemicals also find use as catalysts in various chemical processes. 

Batteries. Many batteries intended for household use contain mercury or mercury compounds. In the form of red mercuric oxide [21908-53-2] mercury is the cathode material in the mercury—cadmium, mercury—indium—bismuth, and mercury—zinc batteries. In all other mercury batteries, the mercury is amalgamated with the zinc [7440-66-6] anode to deter corrosion and inhibit hydrogen build-up that can cause cell mpture and fire. Discarded batteries represent a primary source of mercury for release into the environment. This industry has been under intense pressure to reduce the amounts of mercury in batteries. Although battery sales have increased greatly, the battery industry has aimounced that reduction in mercury content of batteries has been made and further reductions are expected (3). In fact, by 1992, the battery industry had lowered the mercury content of batteries to 0.025 wt % (3). Use of mercury in film pack batteries for instant cameras was reportedly discontinued in 1988 (3). 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

The electrolytic cells shown ia Figures 2—7 represent both monopolar and bipolar types. The Chemetics chlorate cell (Fig. 2) contains bipolar anode/cathode assembhes. The cathodes are Stahrmet, a registered trademark of Chemetics International Co., and the anodes are titanium [7440-32-6] Ti, coated either with mthenium dioxide [12036-10-17, RUO2, or platinum [7440-06-4] Pt—indium [7439-88-5] Ir (see Metal anodes). Anodes and cathodes are joined to carrier plates of explosion-bonded titanium and Stahrmet, respectively. Several individual cells electrically connected in series are associated with one reaction vessel. 

Currem field characteristics measured wiih conjugated polymers sandwiched between an indium-tin oxide (ITO) anode and an aluminum cathode are usually hole dominated and are, consequently, appropriate for testing injection/lransport models for the case of unipolar current How. Data shown in Figure 12-1 refer to injection-limited currents recorded on typically 100 nm thick spin-coated films of derivatives of poly(y d/"fi-phenylenevinylene) (PPV) and a planarized poly(/ /" -pheny-leue) employing a Keilhley source measure unit. The polymers were ... 

Ueno et al. [172] observed that CuInSe2/Ti with a composition close to the stoichiometric ratio (slight excess of metallic components) could be deposited exclusively at a specific potential value (-0.8 V vs. SCE) from a pH 1 bath of uncom-plexed precursors at 50-55 A positive shift in the potential was seen to result in the co-deposition of a Cu3Sc2 phase (umangite), while a negative shift led to contamination by metallic indium. On the basis of measured electrolysis charge, the overall reaction of the optimum cathodic process was considered to involve the transfer of 13 electrons per mole of the product ... 

A typical multilayer thin film OLED is made up of several active layers sandwiched between a cathode (often Mg/Ag) and an indium-doped tin oxide (ITO) glass anode. The cathode is covered by the electron transport layer which may be A1Q3. An emitting layer, doped with a fluorescent dye (which can be A1Q3 itself or some other coordination compound), is added, followed by the hole transport layer which is typically a-napthylphenylbiphenyl amine. An additional layer, copper phthalocyanine is often inserted between the hole transport layer and the ITO electrode to facilitate hole injection. 

The OLED is composed of hard and soft layers so that the conventional cross-sectional TEM sample preparation techniques cannot be applied. Figure 10.3 is a first DB microscopy-prepared TEM image of an OLED in cross-sectional view [37], The glass substrate, ITO, organic layers, and A1 cathode are indicated in the image. The microstructure and interfaces of all these layers can be well studied now. The nanometer-sized spots in organic layers are indium-rich particles. We believe the combination of DB microscopy and TEM will greatly advance the OLED research and development in the near future. 

Figure 3.26. Structure of an OLED. S = substrate (glass), ANO = anode (e.g., ITO — indium tin oxide), HIL = hole injection layer (e.g., Cu phthalocyanine), HTL = hole transport layer, EML = emission layer, ETL = electron transport layer, EIL = electron injection layer (e.g., LiF), KAT = cathode (e.g., Ag Mg, Al). The light that is generated by the recombination of holes and electrons is coupled out via the transparent anode.

A further problem is the tendency for the ITO itself to be reduced. If there is little or no analyte in solution, and the ITO is polarized cathodically in the presence of moisture, then the indium and tin oxides are themselves reduced to metal, according to the following ... 

Cathode (low-working function metat) Electroluminescent polymer Anode (indium tin oxide)... 

In fact, in 1972, Fujishima and Honda (10) demonstrated that O2 evolution on n-type Ti02 occurs as a photocurrent, proportional to the light intensity (Figure 1) of wavelengths less than 415 nm, i.e. for photon energies equal to or greater than the band gap of Ti02 3.0 eV. In this work and that of Ohnishi et al. (11) a platinum black metal cathode was connected in an external circuit to an indium contact on the back side of the photo-anode (see... 

The reactions are carried out in a 200-mL tail-form beaker, with a tightly fitting rubber stopper through which the platinum electrode leads are inserted gas inlet and outlet tubes can be inserted as required. The cathode is a platinum wire carrying a 2 X 2 cm platinum sheet. The anode is a platinum wire onto which a shot of indium is beaten to form a 1 X 1 cm plate. The electrodes are placed 1-2 cm apart in the liquid phase, which is a mixture of organic solvents. 

Electrolysis in the cell Pt/MeC02H H20(trace)/In caused dissolution of the indium anode and formation of fine feathery crystals of the metal on the cathode. This material slowly reacted with the electrolyte to give crystals of In(OAc)2 which could be converted to In(OAc)3 on boiling with glacial acetic acid. It seems likely that the crystal lattice consists of In1 4- In111 + OAc-, but no detailed structure could be obtained.31 This system warrants further investigation in view of work on the analogous thallium system (see below). 

No CdS film can be deposited on a substrate such as an indium tin oxide (ITO) coated glass by simply placing it in this solution. Cathodic polarization of the substrate at an appropriately negative potential brings about proton reduction to raise the local pH matched to the applied potential. 

The electrochemical procedure for the synthesis of the complex was similar to those described by Tuck [559]. The cell was a 100-cm3 tail-form beaker fitted with a rubber bung through which the electrochemical leads enter the cell. The indium anode was suspended from a platinum wire and the cathode was a platinum wire. [(pySe)2] (0.31 g) was dissolved in acetonitrile and a small amount of tetraethylammonium perchlorate was added to the solution as a current carrier. An applied voltage of 10 V produced a current of 15 mA. During the electrolysis nitrogen gas was bubbled through the solution to provide an inert atmosphere and also to stir the solution phase. After 1 hr of reaction 70 mg of metal had been dissolved from the anode (Ey = 1.1). 

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