Silver electrochemical reduction

Fig. 13. A speck of developing sdvei on the surface of a sdvei hahde crystal. The silver acts as an electrode for the electrochemical reduction of silver ions.

Although one of the most common storage batteries is called the nickel/cadmium system ( NiCad ), correctly written (-)Cd/KOH/NiO(OH)(+), cadmium is not usually applied as a metal to form a battery anode. The same can be said with regard to the silver/cadmium [(-) Cd / KOH / AgO (+)] and the MerCad battery [(-)Cd/KOH/HgO(+)]. The metallic negative in these cases may be formed starting with cadmium hydroxide, incorporated in the pore system of a sintered nickel plate or pressed upon a nickel-plated steel current collector (pocket plates), which is subsequently converted to cadmium metal by electrochemical reduction inside the cell (type AB2C2). This operation is done by the customers when they start the application of these (storage)... 

Porous aluminum oxide can be used as a template for the production of nanowires and nanotubes. For example, metals can be deposited on the pore walls by the following procedures deposition from the gas phase, precipitation from solution by electrochemical reduction or with chemical reducing agents, or by pyrolysis of substances that have previously been introduced into the pores. Wires are obtained when the pore diameters are 25 nm, and tubes from larger pores the walls of the tubes can be as thin as 3 nm. For example, nanowires and nanotubes of nickel, cobalt, copper or silver can be made by electrochemical deposition. Finally, the aluminum oxide template can be removed by dissolution with a base. 

The stereochemistry of electrochemical reduction of acetylenes is highly dependent upon the experimental conditions under which the electrolysis is carried out. Campbell and Young found many years ago that reduction of acetylenes in alcoholic sulfuric acid at a spongy nickel cathode produces cis-olefins in good yields 126>. It is very likely that this reduction involves a mechanism akin to catalytic hydrogenation, since the reduction does not take place at all at cathode substances, such as mercury, which are known to be poor hydrogenation catalysts. The reduction also probably involves the adsorbed acetylene as an intermediate, since olefins are not reduced at all under these conditions and since hydrogen evolution does not occur at the cathode until reduction of the acetylene is complete. Acetylenes may also be reduced to cis olefins in acidic media at a silver-palladium alloy cathode, 27>. 

Hasse et al. [366] have used in situ AFM for the detection of silver nucleation at the three-phase junction of the type metal-silver halide-electrolyte solution. At this phase boundary, electrochemical reduction of submicrometer size silver halide crystals immobilized on the surface of gold and platinum electrodes took place. Following nucleation, the reaction advanced until the entire surface of the silver hahde crystals was covered with 20 atomic layers of silver. Then, reduction was terminated. The obtained silver layer could be oxidized and the next layer of silver halide crystals became accessible for further reduction. 

The electrodeposition of silver from chloroaluminate ionic liquids has been studied by several authors [45-47], Katayama et al. [48] reported that the room-temperature ionic liquid l-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4) is applicable as an alternative electroplating bath for silver. The ionic liquid [EMIM]BF4 is superior to the chloroaluminate systems since the electrodeposition of silver can be performed without contamination of aluminum. Electrodeposition of silver in the ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) and l-butyl-3-methylimidazoliumhexafluorophosphate was also reported [49], Recently we showed that isolated silver nanoparticles can be deposited on the surface of the ionic liquid Tbutyl-3-methylimidazolium trifluoromethylsulfonate ([BMIMJTfO) by electrochemical reduction with free electrons from low-temperature plasma [50] (see Chapter 10). This unusual reaction represents a novel electrochemical process, leading to the reproducible growth of nanoscale materials. In our experience silver is quite easy to deposit in many air- and water-stable ionic liquids. 

Georgolios, N., Kyriacou, G. and Ritzoulis, G. (2001) Electrochemical reduction of dichlorodiflu-oromethane on silver and lead electrodes. J. Appl. Electrochem. 31, 207-212. 

Guerrini, M., Mussini, P.R., Rondinini, S., Torri, G. and Vismara, E. (1998) Electrochemical reduction of halogenosugars on silver A new approach to C-disaccharides. Chem. Commun. 15, 1575-1575. 

Isse, A.A., De Giusti, A., Gennaro, A., Falciola, L. and Mussini, P.R. (2006d) Electrochemical reduction of benzyl halides at a silver electrode. Electrochim. Acta 51,4956 4964. 

Electrowinning of metals in aqueous solutions is applicable to those metals that possess high electrochemical reduction potentials, such as silver, copper, cadmium, and zinc. Magnesium, aluminum, and sodium, like other reactive metals, are electro-produced from molten salt baths, such as NaCl/CaCh mixture at ca. 600 °C for sodium and MgCl2/NaCl/CaCl2 eutectic mixture at ca. 750 °C for magnesium. 

Disulfides — A disulfide bond (R-S-S-R) is a strong covalent bond formed by the oxidation of two sulfhydryl groups (R-S-H). An amino acid that commonly forms S-S bonds in proteins is cysteine. When two cysteines are bonded by an S-S bond, the resulting molecule between the two protein chains is called cystine. The presence of disulfide bonds helps to maintain the tertiary structure of the protein. Industrial production of L-cysteine is based on the electrochemical - reduction of L-cystine in acidic - electrolytes using lead or silver -> cathodes. 

A simple method for the preparation of 5-nitrobenzimidazolone-2, based on chemical [407, 408] or electrochemical reduction of 2,4-dinitrophenylurea [414], has been proposed. The electrochemical reaction occurs in a cell with an interelectrode space in aqueous solution of mineral acid at 85-95°C in the range of potentials from 0 to -200 mV relative to the silver electrode. 

It has been shown that electroactive polymer films on electrodes can mediate electron transfer for metal deposition (9-11). Haushalter and Krause (5) have described the treatment of PMDA-ODA films with highly reactive Zintl complexes (e.g., Sn9 4, SnTe4 4) to yield an intercalated material able to reduce ions of platinum, palladium and silver at the film surface. Mazur et al., (12) reported the deposition of conductive Ag, Cu, and Au metal interlayers within a PMDA-ODA film by electrochemical reduction. 

Silver(II) complexes are not technically difficult to make, but they are unstable in aqueous solutions unless stabilized by ligands (typically nitrogenbased). Anumberof different oxidants including SaOg, PbOa, and ozone can be used to oxidize sUver(I) to sUver(II). Electrochemical methods also can oxidize sUver(I) compounds to higher oxidation states. Silver(III) species also can be accessed chemically or electrochemi-cally, but are often unstable in the presence of water or many organic molecules and show irreversible electrochemical reductions (12,13). 

In the classical theory of Ostwald, Abegg, and Schaum [96] the homogeneous reduction of silver ion is assumed to be rapid and is followed by the physical deposition of silver on a latent image nucleus from a supersaturated solution of silver. The term physical development arises from this description and developers used at this time often deliberately contained soluble silver ion. It is now considered that physical and chemical development are both chemical, or electrochemical, processes in which silver ion reduction occurs at the latent image surface. 

The electrochemical reduction of CO in fhe COj-methanol solution was carried out under high COj pressure. The high pressure apparatus was assembled from a SUS-316 sfainless steel tube. A glass inner tube was used to avoid contact of the electrolyte with the metal apparatus. Various metal electrodes were used in this study. The details have been described previously [9]. A Ft counter electrode and a silver quasi-reference electrode were used. Reagent grade methanol was used as the solvent. Tetrabutyl or tetraethyl ammonium salts were used as supporting electrolytes. 

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