• Energy Research

A potential‐pH diagram of the system was constructed based on diagrams of the and systems and discussed in connection with the redox behavior of an ammonia‐alkaline CdTe electrolytic bath with pH 10.7. CdTe has a wide domain of stability throughout the acidic and alkaline regions, and the redox behavior was well explained with the diagram. The diagram indicated that the cathodic electrodeposition of CdTe occurs across a domain of stability of tellurium metal, i.e., at lower potentials than the deposition potential of bulk Te and higher than that of bulk Cd, with respect to the bath with pH < ca. 11.5, while in the higher pH region, CdTe is expected to deposit directly from Te(IV) and Cd(II) ions. The deposition mechanism is considered as follows: (i) deposition of tellurium layer followed by (ii) an immediate underpotential deposition of Cd on it, which prevents the bulk deposition of tellurium. It can be considered that the stoichiometric CdTe is more easily electrodeposited from alkaline baths, since the domain for tellurium metal is narrower in the alkaline region compared to the conventionally employed acidic region with pH 0–2. Therefore, the bulk deposition of elemental tellurium is less apt to occur from an alkaline bath. © 1999 The Electrochemical Society. All rights reserved.

Abstract Electrochemical Ni–Mo alloying of the surface of a nickel substrate was investigated using alternating pulsed electrolysis in an aqueous solution containing only molybdate ions (MoO42−) as a metal ion component. In this electrochemical process, the nickel substrate was slightly dissolved during the anodic pulses, providing nickel ions into the solution in the vicinity of the substrate, while Ni and Mo were both electrodeposited on the substrate surface during the subsequent cathodic pulses. Through the optimization of anodic and cathodic conditions independently based on a set of direct-current electrolysis data, amorphous Ni–Mo alloy layers were found to be formed at the surface of the nickel substrate by the alternating pulsed electrolysis using the MoO42− solution of pH 3.0–5.0. The conditions for Ni–Mo alloy formation were discussed in terms of the dissolving regime of ionic species in the electrolytes determined by an equilibrium calculation.

The induced electrodeposition of Ni-Mo alloy was studied to elucidate the mechanism involved in terms of the chemical species present in plating baths, which affects the behavior of codeposition. To determine the chemical species in acidic Ni(II)-Mo(VI)-citrate aqueous baths with pH 5, factor analysis of visible absorption spectra was employed as were previous results by extended X-ray absorption fine structure (EXAFS) and anomalous X-ray scattering. In citrate-free acidic Ni(II)-Mo(VI) baths (pH 5) from which codeposition of molybdenum metal is impossible, the ions form a large Ni 2+ -MoO 4 2- cluster, NiMo 6 O 24 H 6 4 - . To deposit Ni-Mo alloy, a sufficient amount of citrate must be added to break down the Ni 2+ -MoO 4 2- cluster so that Ni 2+ and citrate ions form complexes, NiCit - and NiCit 2 4- (Cit 3- = C 6 H 5 O 7 3- ). An insufficient addition of citrate, however, restrains the complexing between Ni 2+ and citrate, since citrate is preferentially consumed for complexing with MoO 4 2- , and codeposition does not occur. Profiles of the molar absorption coefficient for aquated species Ni 2+ , NiCit - , and NiCit 2 4- , were obtained by factor analysis.

Anodic dissolution of elemental Mg was examined in an ionic liquid, trimethyl-n-hexylammonium bis[(trifluoromethyl)sulfonyl]amide (TMHA-Tf2N), containing a simple salt, Mg(Tf2N)2, having a common anion. faradaic anodic dissolution was markedly stimulated in the presence of water dissolved within its solubility limit. The dissolution current efficiency for elemental Mg was found to be almost 100% without decreasing the water content, indicating that spontaneous reaction of Mg with water was limited and water molecules play a catalytic role in the overall dissolution mechanism, where a magnesium(II) oxide/hydroxide is involved. The Mg2+/Mg0 redox potentials, or onset potentials for Mg dissolution, vs. Li+/Li0 redox with and without water were also estimated from a set of sampled-current voltammograms obtained by a potential-step method. © 2013 The Electrochemical Society. [DOI: 10.1149/2.057310jes] All rights reserved.

We report a novel, cyanide-free, and low-cost displacement silver (Ag) plating bath, i.e., AgCl-dissolved highly concentrated CaCl2/LiCl aqueous solution. Compared to dilute CaCl2/LiCl solutions, this aqueous solution exhibited much higher AgCl solubility because of the high activity of Cl–; the maximum AgCl solubility was achieved at 44.4 mmol dm–3 (i.e., [Ag(I)] = 8.07 g kg−1 H2O). Smooth Ag deposits with a lusterless gray-colored appearance were successfully obtained by displacement plating on a Cu substrate. The mechanism of smooth Ag plating is discussed in terms of its electrochemical and diffusive properties.

The lamination interface generated by a power outage during the electrorefining of copper using a wax-less permanent-cathode was investigated to elucidate the formation mechanism of the interface. X-ray diffraction, X-ray photoelectron spectroscopic measurements and electrochemical quartz crystal microbalance measurements revealed that the interface is composed mostly of CuCl (s) . Based on the thermodynamics of aqueous solution containing copper ions and chloride anions, it is considered that Cu+ ions are spontaneously generated through the reaction Cu + Cu2+ → 2Cu+ at the surface of the copper cathode, resulting in the deposition of insoluble CuCl (s) . Circulation of electrolyte during the power outage could suppress the accumulation of Cu+ ions in the vicinity of the cathode and minimize the formation of CuCl (s) layer, which makes the lamination interface after recovery from the power outage.

Abstract The galvanic contact deposition of CdTe layers from an ammoniacal basic electrolyte was carried out at a temperature range from 363 K (90 °C) to 423 K (150 °C) using an auto-clave type electrolysis vessel. The current densities at 363 and 393 K were almost the same level as that at 343 K under the dark condition, resulting in the deposition of near-stoichiometric CdTe layers on Au-plated Cu substrates, while the current density at 423 K was larger due to the codeposition of a Cd 3 Au phase. The mean crystallite size of the resulting CdTe layers was increased with the increase in the temperature of the electrolytes. The current density was enhanced by irradiating the cathode surface with visible light during the CdTe deposition and, in this case, the current efficiency was also dramatically increased. The layer obtained under illumination at 393 K consisted of near stoichiometric CdTe and a small amount of elemental Cd, while the layer prepared in the dark had a single phase CdTe. The mean crystallite size of the CdTe layer prepared at 393 K under illumination was about 24 nm.