Ammoniacal Electrolyte Research Articles

Improving zinc electrodeposition in ammoniacal electrolytes with the saturated dissolved methyltrioctylammonium chloride

The effect of saturated dissolved methyltrioctylammonium chloride (TOAC) in ammoniacal electrolytes on zinc electrodeposition was investigated in a membrane electrolytic cell. Furthermore, cationic surfactant cetyltrimethylammonium bromide (CTAB), nonionic surfactant polyethylene glycol (PEG) and anionic surfactant sodium dodecylsulphate (SDS) are respectively added into the electrolytes with saturated TOAC to explore the combined effect of two organic additives on zinc deposits. The addition of hydrophobic TOAC can not only completely inhibit the formation of mossy zinc but also refine the grain size. The current efficiency (CE) exceeds 96%, indicating that the TOAC does not deteriorate zinc electrodeposition process. The inhibition mechanism of TOAC on mossy zinc deposits was revealed by cyclic voltammetry, cathodic polarization and Tafel tests. When adding CTAB and PEG into the electrolytes with saturated TOAC, a synergistic effect on improving the smoothness of zinc deposits can be observed, whereas the presence of SDS will weaken the inhibition effect of TOAC on mossy zinc. Therefore, the saturated dissolved TOAC in the electrolytes does not need to be removed before electrodeposition. These results are helpful for zinc recovery from the non-traditional resources.

Real-Time X-ray Imaging Reveals Interfacial Growth, Suppression, and Dissolution of Zinc Dendrites Dependent on Anions of Ionic Liquid Additives for Rechargeable Battery Applications.

The dynamic interfacial growth, suppression, and dissolution of zinc dendrites have been studied with the imidazolium ionic liquids (ILs) as additives on the basis of in situ synchrotron radiation X-ray imaging. The phase contrast difference of real-time images indicates that zinc dendrites are preferentially developed on the substrate surface in the ammoniacal electrolytes. After adding imidazolium ILs, both nucleation overpotential and polarization extent increase in the order of additive-free < EMI-Cl < EMI-PF6 < EMI-TFSA < EMI-DCA. The real-time X-ray images show that the EMI-Cl can suppress zinc dendrites, but result in the formation of the loose deposits. The EMI-PF6 and EMI-TFSA additives can smooth the deposit morphology through suppressing the initiation and growth of dendritic zinc. The addition of EMI-DCA increases the number of dendrite initiation sites, whereas it decreases the growth rate of dendrites. Furthermore, the dissolution behaviors of zinc deposits are compared. The zinc dendrites show a slow dissolution process in the additive-free electrolyte, whereas zinc deposits are easily detached from the substrate in the presence of EMI-Cl, EMI-PF6, or EMI-TFSA due to the formation of the loose structure. Hence, the dependence of zinc dendrites on anions of imidazolium IL additives during both electrodeposition and dissolution processes has been elucidated. These results could provide the valuable information in perfecting the performance of zinc-based rechargeable batteries.

Effects of Br− and I− concentrations on Zn electrodeposition from ammoniacal electrolytes

The effects of Br− and I− concentrations on the cell voltage, anodic polarization, current efficiency (CE), and energy consumption (EC) of zinc electrodeposition from ammoniacal ammonium chloride solutions were investigated. The surface morphology of zinc deposits was also examined. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the morphology of zinc deposits and the phase of anodic sediments produced during electrolysis. The results clearly showed that the CE slightly increased from approximately 95.12% in the absence of I− and Br− to 97.08% in the presence of 10 g·L−1 Br−; in contrast, the CE significantly decreased to less than 83% in the presence of 10 g·L−1 I−. The addition of Br− and I− positively affected the EC, which decreased from 2514 kW·h·t−1 to approximately 2300 kW·h·t−1. The results of anodic polarization measurements showed that the voltage drops were 130 and 510 mV when the concentrations of Br− and I− were 10 g·L−1 at a current density of 400 A·m−2, respectively. SEM images showed that the addition of Br− and I− caused different crystal growth mechanisms, which resulted in the production of compact and smooth zinc deposits. The anodic reactions of I− were also studied.

Anodic Dissolution Behaviour of Tungsten Carbide Scraps in Ammoniacal Media

In the present paper, potentiodynamic studies of WC scrap have been carried out as these studies give better idea about the anodic dissolution behaviour of the scrap material to recover the metal values. However, it has been seen that anodic passivation retards the dissolution of the scrap and adversely affects the recovery of metals. To minimize the passivity and to increase the anodic dissolution, some chemicals are often used as additives. Two different electrolytes namely hydrochloric acid and aqueous ammonia at varying concentrations had been employed for the above studies. The additives citric acid and oxalic acid were added to the acidic electrolyte whereas ammonium chloride, ammonium carbonate and ammonium sulphate were added in different concentration to the ammoniacal electrolyte. The studies revealed that 2% citric acid in 1N HCl was the optimum to achieve maximum anodic dissolution (current) of WC scrap. On the other hand, 5% NH4Cl was found suitable to obtain maximum anodic dissolution (current) in the ammoniacal (150 g/L) medium. The potentiodynamic studies were followed by the actual electrodissolution experiments in an electrolytic cell with the help of a rectifier. The W and Co recoveries were encouraging.

Preparation, characterization, and electrochemical studies of sulfur-bearing nickel in an ammoniacal electrolyte: the influence of thiourea

Sulfur-bearing nickel was prepared by a direct electrodeposition in an ammoniacal Ni(II) electrolyte containing thiourea. This sulfur-bearing nickel showed an excellent dissolving activity when used as anodic materials in the traditional Watt bath. The influence of thiourea on the surface microstructure, crystallization texture, and electrocrystallization process of sulfur-bearing nickel were investigated by scanning electron microscopy, X-ray diffraction, and electrochemical techniques. The results show that the S element is uniformly distributed in the electrodeposited nickel. The prepared nickel samples present a blade shape microstructure, and the blade size decreases by the addition of thiourea. Sulfur-bearing nickel exhibits face-centered cubic structure and (111) preferred orientation, and the orientation distribution is strengthened with increased thiourea concentration. The nucleation parameters, such as N0, A, and J0, are obtained from the initial parts of the transients making use of Sharifker–Mostany theoretical model. Both the nucleation rate and the vertical growth rate are increased by the addition of thiourea, leading to finer grains and better dissolving activity.

Morphology and composition of Ni–Co alloy powders electrodeposited from ammoniacal electrolyte

In this paper, the morphology and phase structure of Ni–Co powders electrodeposited from ammoniacal electrolyte are investigated as a function of alloy powder composition. Composition of the electrolyte, i.e. the ratio of Ni2+/Co2+ concentration is found to influence both, the phase structure and the morphology of Ni–Co alloy powders. It is shown that the current density practically does not influence the morphology of Ni–Co alloy powders as well as alloy powder composition. At the highest ratio of the Ni2+/Co2+ ions typical spongy particles were obtained. With the decrease of the Ni2+/Co2+ ions ratio agglomerates of the size of about 100 μm, composed of a large number of fern-like dendrites on their surface were obtained. At the lowest Ni2+/Co2+ concentration ratio, among more dendritic particles, agglomerates typical for pure Co powder deposition were detected. It is also shown that depending on the Ni2+/Co2+ ratio different types of Ni and Co codeposition could be detected: anomalous and irregular. At the Ni2+/Co2+ ions ratio higher than 1 only β-Ni phase was detected, while at concentration ratios Ni2+/Co2+<1 h.c.p. α-Co phase together with β-Ni phase was detected in the alloy powder deposit.

Morphology, internal structure and growth mechanism of electrodeposited Ni and Co powders

In this paper the morphology (SEM analysis), the internal structure (cross-section analysis) and the growth mechanism of Ni and Co powders electrodeposited from ammoniacal electrolyte are investigated. It is shown that morphology and the internal structure of those powders are quite different. For Ni powder, all particles are of the same morphology, cauliflower-like type. In the case of Co powder, generally two types of particles are detected: (1) dendrite particles and (2) different types of agglomerates, compact, spongy-like and ball-like ones. The growth mechanism for all agglomerates is based on the fact that with the time of growth the disperse (dendrite) agglomerate is branching in different directions and at the tip of each branch spherical diffusion takes over the planar one, providing conditions for the growth of compact deposit. After some time, these branches form compact deposit all over the agglomerate surface and the same agglomerate further grows as a compact one, until it falls off from the electrode surface. Characteristic of all agglomerates is the presence of deep cavities on their surface and the fern-like dendrites on the bottom for most of these cavities.

Comparison of Microstructures of CdTe Layers Electrodeposited from Basic Ammoniacal and Acidic Sulfate Electrolytes

The microstructures of CdTe layers electrodeposited from basic ammoniacal electrolytes were investigated by transmission electron microscopy and compared with those from a conventional acidic sulfate electrolyte. As-deposited CdTe layers with a nearly stoichiometric composition from a basic electrolyte with a relatively high Cd(II)/Te(IV) concentration ratio were composed of randomly oriented crystallites with a grain size of ca. 10 nm, while those from an acidic electrolyte consisted of defective columnar grains with a 〈111〉 preferred growth orientation. Deposit containing around 65 atom % Te from a basic electrolyte with a relatively low Cd(II)/Te(IV) concentration ratio was found to be amorphous, which was easily crystallized into a mixture of CdTe, elemental Te, and a trace amount of by electron beam illumination. By annealing at 300°C for 1 h in an Ar atmosphere, CdTe grains from the basic electrolyte grew by about a factor of four, but at the same time, nano-voids were formed at the grain boundaries. In contrast, CdTe grains from the acidic electrolyte did not grow by annealing under the same conditions. © 2004 The Electrochemical Society. All rights reserved.

Polycrystalline gold electrode redox behavior in an ammoniacal electrolyte

Abstract The underpotential deposition (upd) of copper at polycrystalline gold in an ammoniacal electrolyte (0.1 M NH 3 +0.1 M NaClO 4 ) was investigated. The rotating ring disk electrode (RRDE), the electrochemical quartz crystal microbalance (EQCM) and time of flight secondary ion mass spectrometry (TOF-SIMS) were all used in parallel to study this process. RRDE experiments showed that upd of Cu(0) occurred at −0.4 V E

Polycrystalline gold electrode redox behavior in an ammoniacal electrolyte

Abstract The redox behavior of a gold electrode in an ammoniacal electrolyte (0.1 M NH 3 and 0.1 M NaClO 4 ) was investigated using four techniques. These were the rotating ring disk electrode (RRDE), the electrochemical quartz crystal microbalance (EQCM), X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS). Two different gold surface compounds, AuO and AuNH 2 , are formed in relative amounts that depend on the holding time at +0.6 V (versus SCE). XPS and SIMS studies were used to distinguish the surface species AuO and AuNH 2 from AuO and AuOHNH 2 . When the potential is held at +0.6 V for longer times, other oxidized gold surface species may form, e.g. AuO, AuOHNH 2 , [OH(NH 2 )Au] 2 NH, AuNH 2 , Au 2 O 3 ·2NH 3 and Au 2 O 3 ·3NH 3 . During the gold electrode oxidation process, NH 3 is probably oxidized to N 2 . During the surface gold species reduction process, some soluble Au(III) species form that can be reduced to an adsorbed Au(I) species at −0.4 V.

Compositionally modulated cobalt–tungsten alloys deposited from a single ammoniacal electrolyte

Abstract Electrodeposition of Co–W alloys and the possibility for compositional modulation from single ammoniacal electrolytes were studied. The influence of pH, current density, W:Co ratio, tartrate concentration and temperature on the composition of the deposit and the cathode current efficiency were investigated by a Taguchi experimental plan. It was found that the alloy composition is sensitive to solution chemistry, current density and temperature. It has also been shown that it is possible to reduce the tungsten content in the deposit by current modulation and the use of anodic pulses during deposition, i.e. selective etching. With cross-sectional TEM analysis, it has been shown that the selective etching deposition technique can be utilised to grow layered structures with wavelengths in the nanometer range. The microstructure in the electrodeposited Co–W alloys varied as a function of increasing W content, from crystalline Co over Co3W and Co7W6 to nanocrystalline Co, as determined by XRD.

Electrodeposition of Palladium-Silver Alloys from Ammoniacal Electrolytes

A viable technique for the electrodeposition of palladium-silver alloys could find application during the manufacture of electrical contacts. Previously such a process has not been available but some alloys with useful physical properties can now be deposited from an ammoniacal system, while a better understanding of the mechanisms involved has been gained during the work reported here.

Kinetics of electrode reactions in liquid ammonia. Part 3.—The silver electrode in acid solution

The behaviour of the silver electrode in acid solutions of liquid ammonia has been studied by steady and non-steady state electrochemical measurements and electron microscopy. The apparent rate constant and standard potential have been determined. The rate-determining step in silver deposition and dissolution is the charge transfer reaction which is probably coupled with an adatom diffusion mechanism. Oxidised species originating from the solvent are adsorbed on silver except at cathodic values of electrode potential. The anodic behaviour of silver is complicated by the formation of anodic deposits, probably silver nitride, in parallel with the metal dissolution reaction. By making comparisons with silver electro-deposition from simple and cyanide aqueous baths it is concluded that the adsorbed solvent decomposition products are responsible for the poor quality of deposits from ammoniacal electrolytes.

Electrochemical generation of hydridopentamminerhodium(III) and its reaction with molecular oxygen

The electrochemistry of Rh(NH3)5OH2+ has been studied in a buffered ammoniacal solution. The polarographic reduction wave at the dropping mercury electrode had E1/20 equal to −1.10 V (vs. saturated calomel electrode) in a 0.10 M NH3 – 0.10 M NH4ClO4 electrolyte, and gross Hg cathode electrolysis at −1.19 V produced a stable Rh(NH3)5H2+ hydride species. Both reductions were found to take place through a Rh(I) intermediate.The reaction of the Rh(NH3)5H2+ with molecular O2 in the ammoniacal electrolyte was also studied. The product was demonstrated to be a stable Rh(NH3)4(OH)(O2H)+ hydroperoxo species.

Microchemical methods in radiochemical analysis : Determination of chemical yields by micro-coulometry

Methods are described for the micro-coulometric determination of several elements using the Reilley and Porterfield method of generating EDTA by electrolysis of its mercuric chelate. The determination is carried out in a volume of about 1 ml of electrolyte and polarized mercury electrodes are used to detect the end-point. 0.025–0.5 μequiv. of many elements can be determined using an ammoniacal electrolyte at pH 10.5 or an acetate buffer at pH 5.5. The method is designed for determining chemical yields of radiochemical procedures using 100–1000-μg amounts of carriers.

Electrolytic dissolution of copper in ammoniacal electrolytes.

Electrolytic dissolution of copper in ammoniacal electrolytes.