Electrochemical deposition of zinc from zinc oxide in 2:1 urea/choline chloride ionic liquid

Zinc Electrode Cycling in Deep Eutectic Solvent Electrolytes: An Electrochemical Study

Among post-lithium ion battery technologies, rechargeable chemistries with Zn anodes bear notable technological promise owing to their high theoretical energy density, lower manufacturing cost, availability of raw materials and inherent safety. However, Zn anodes, when employed in aqueous electrolytes, suffer from hydrogen evolution, passivation, and shape changes. Alternative electrolytes can help tackle these issues, preserving the green and safe characteristics of aqueous-based ones. Deep eutectic solvents (DESs) are promising green and low-cost non-aqueous solvents for battery electrolytes. Specifically, the cycling of Zn anodes in DESs is expected to be reversible, chiefly owing to their dendrite-suppression capability. Nevertheless, apart from a few studies on Zn plating, insight into the cathodic-anodic electrochemistry of Zn in DESs is still very limited. In view of developing DES-based battery electrolytes, it is crucial to consider that a potential drawback might be their low ionic conductivity. Water molecules can be added to the eutectic mixtures by up to 40% to increase the diffusion coefficient of the electroactive species and lower the electrolyte viscosity without destroying the eutectic nature. In this study, we address the electrochemistry of Zn in two different hydrated DESs (ChU and ChEG with ~30% H₂O). Fundamental electrokinetic and electrocrystallization studies based on cyclic voltammetry and chronoamperometry at different cathodic substrates are completed with a galvanostatic cycling test of Zn|Zn symmetric CR2032 coin cells, SEM imaging of electrodes and in situ SERS spectroscopy. This investigation concludes with the proposal of a specific DES/H₂O/ZnSO₄-based electrolyte that exhibits optimal functional performance, rationalized on the basis of fundamental electrochemical data, morphology evaluation and modeling of the cycling response.

Ionometallurgical Step-Electrodeposition of Zinc and Lead and its Application in a Cycling-Stable High-Voltage Zinc-Graphite Battery

Ionometallurgy is a new development aiming at the sustainable low-temperature conversion of naturally occurring metal ores and minerals to their metals or valuable chemicals in ionic liquids (ILs) or deep eutectic solvents. The IL betainium bis((trifluoromethyl)sulfonyl)imide, [Hbet][NTf₂ ], is especially suited for this process due to its redox-stability and specific-functionalization. The potentiostatic electrodeposition of zinc and lead starting directly from ZnO and PbO, which dissolve in [Hbet][NTf₂ ] in high concentrations is reported. The initial reduction potentials of zinc(II) and lead(II) are about -1.5 and -1.0 V, respectively. The ionic conductivity of the solution of ZnO in [Hbet][NTf₂ ] is measured and the effect of various temperatures and potentials on the morphology of the deposited material is explored. The IL proves to be stable under the chosen conditions. From IL-solutions, where ZnO, PbO, and MgO have been dissolved, metallic Zn and Pb are deposited under potentiostatic control either consecutively by step-electrodeposition or together in a co-electrodeposition. Using the method, Zn is also deposited on 3D copper foam and assembles into high-voltage zinc-graphite battery. It exhibits a working-voltage up to 2.7 V, an output midpoint discharge-voltage of up to 2.16 V, up to 98.6% capacity-retention after 150 cycles, and good rate performance.

Treatment of copper converter slag with deep eutectic solvent as green chemical

Industrial copper slag is among the most important wastes to be evaluated in terms of containing valuable metals and the amount of waste approaching 30 million tons per year. Therefore, in this study, it was aimed to propose a feasible route for copper and zinc recovery from copper converter slag (CCS) by using choline chloride (ChCl) based deep eutectic solvent which is applied on this type of slag for the first time. During the leaching experiments with the pure ChCl-2urea mixture, temperature (25-95 °C), leaching duration (2-72 h), and pulp density (1/10-1/40 g/mL) were selected as the parameters to be investigated for Cu and Zn extraction. After the experimental results, the optimized conditions for the ChCl-2urea leaching process, which gave 89.9% Cu and 65.3% Zn extraction was found at 48 h, 95 °C, 1/20 g/mL pulp density with 600 rpm stirring speed. It is noted that the iron dissolution ratio is very low (max. 4.7%) under the selected conditions. At the end of the iron cementation stage, the total recovery efficiency as a pure metallic copper was 63%. The calculated activation energy for the dissolution of the copper and zinc from CCS is 8.86 kJ mol^-1 and 14.48 kJ mol^-1, respectively.

A Zn-Ce Redox Flow Battery with Ethaline Deep Eutectic Solvent

Compared with conventional aqueous and ionic liquid electrolytes, deep eutectic solvent (DES) are considered as electrolyte for redox flow batteries because they have a wider electrochemical window and relatively low price. In this study, Ce^IV /Ce^III and Zn^II /Zn redox couples are used as the positive and negative active materials, respectively, in an electrolyte consisting of choline chloride ethylene glycol (ethaline). The structure of Ce^III in the positive electrolyte is inferred through spectrum detection. Ce^IV /Ce^III and Zn^II /Zn redox couples show a stable potential difference of 2.2 V (vs. Ag) through cyclic voltammetry. The charge and discharge performance of battery was tested at different current densities. In addition, battery performance was evaluated at different temperatures and concentrations of cerium in the electrolyte. Consequently, at a current density of 0.5 mA cm^-2 at room temperature and using 1.0 m Ce^III , the battery performance reaches the best coulombic efficiency of 84 %.

Speciation of Copper(II)-Betaine Complexes as Starting Point for Electrochemical Copper Deposition from Ionic Liquids

The application of ionic liquids for the dissolution of metal oxides is a promising field for the development of more energy- and resource-efficient metallurgical processes. Using such solutions for the production of valuable chemicals or electrochemical metal deposition requires a detailed understanding of the chemical system and the factors influencing it. In the present work, several compounds are reported that crystallize after the dissolution of copper(II) oxide in the ionic liquid [Hbet][NTf2 ]. Dependent on the initial amount of chloride, the reaction temperature and the purity of the reagent, copper crystallizes in complexes with varying coordination geometries and ligands. Subsequently, the influence of these different complex species on electrochemical properties is shown. For the first time, copper is deposited from the ionic liquid [Hbet][NTf2 ], giving promising opportunities for more resource-efficient copper plating. The copper coatings were analyzed by SEM and EDX measurements. Furthermore, a mechanism for the decomposition of [Hbet][NTf2 ] in the presence of chloride is suggested and supported by experimental evidence.

Electrochemical Behavior and Electrodeposition of Sn Coating from Choline Chloride–Urea Deep Eutectic Solvents

The electrochemical behavior and electrodeposition of Sn were investigated in choline chloride (ChCl)–urea deep eutectic solvents (DESs) containing SnCl2 by cyclic voltammetry (CV) and chronoamperometry techniques. The electrodeposition of Sn(II) was a quasi-reversible, single-step two-electron-transfer process. The average transfer coefficient and diffusion coefficient of 0.2 M Sn(II) in ChCl–urea at 323 K were 0.29 and 1.35 × 10−9 cm2∙s−1. The nucleation overpotential decreased with the increase in temperature and SnCl2 concentration. The results of the chronoamperometry indicated that the Sn deposition on tungsten electrode occurred by three-dimensional instantaneous nucleation and diffusion controlled growth using the Scharifker–Hills model. Scanning electron microscopy (SEM) showed that the morphology of the deposits is uniform, as a dense and compact film prepared by potentiostatic electrolysis on Cu substrate. X-ray diffraction (XRD) analysis revealed that the deposits were pure metallic Sn.

Electrodeposition of ZnNi Alloys from Choline Chloride/Ethylene Glycol Deep Eutectic Solvent and Pure Ethylene Glycol for Corrosion Protection

The present work follows the trend to develop non-aqueous electrolytes for the deposition of corrosion resistant ZnNi alloys. It investigates the use of the choline chloride/ethylene glycol (1:2 molar ratio) eutectic mixture and of pure ethylene glycol as solvents for ZnNi electroplating. The electrochemical behavior of Zn and Ni is investigated via cyclic voltammetry, and potentiostatic ZnNi deposition is performed. Ni content is found to be precisely tunable in the 10–20% wt range, which presents the highest industrial interest for corrosion protection. ZnNi coatings obtained are characterized from the morphological and phase composition point of view. Evidence of the formation of a metastable γ ZnNi phase is observed for both choline chloride/ethylene glycol and pure ethylene glycol. Finally, potentiodynamic corrosion tests are performed to assess their corrosion properties.

Progress in Electrodeposition of Zinc and Zinc Nickel Alloys Using Ionic Liquids

Zinc (Zn) and zinc–nickel (Zn–Ni) electrodeposition has been widely used in many industries, such as automotive and aerospace, for corrosion protection of steel components owing to their excellent corrosion resistance. Conventional zinc and zinc–nickel electrodeposition is performed in different types of aqueous baths (acid and alkaline). Such electrolytes suffer from certain drawbacks such as hydrogen gas evolution, low coulombic efficiencies, and environmental toxicity. Electrodeposition of Zn and Zn–Ni alloys from ionic liquids has gained significant attention in aerospace and automotive sectors owing to the different environments they provide for electrodeposition. This paper reviews the progress in deposition of zinc and zinc-nickel alloys in non-aqueous systems, especially ionic liquids. In addition, the challenges and technological developments associated with the Zn and Zn–Ni deposition on different substrates and the factors that need to be considered while electroplating at an industrial scale are discussed.

Synthesis and Dissolution of Metal Oxides in Ionic liquids and Deep Eutectic Solvents

Ionic liquids (ILs) and deep eutectic solvents (DESs) have proven to be suitable solvents and reactants for low-temperature reactions. To date, several attempts were made to apply this promising class of materials to metal oxide chemistry, which, conventionally, is performed at high temperatures. This review gives an overview about the scientific approaches of the synthesis as well as the dissolution of metal oxides in ILs and DESs. A wide range of metal oxides along with numerous ILs and DESs are covered by this research. With ILs and DESs being involved, many metal oxide phases as well as different particle morphologies were obtained by means of relatively simple reactions paths. By the development of acidic task-specific ILs and DESs, even difficultly soluble metal oxides were dissolved and, hence, made accessible for downstream chemistry. Especially the role of ILs in these reactions is in the focus of discussion.

Deposition of Zinc⁻Cerium Coatings from Deep Eutectic Ionic Liquids

This work studies the electrodeposition of zinc and cerium species on carbon steel substrates from choline chloride-based ionic liquid bath in order to develop a protective coating with anti-corrosion, sacrificial, and self-repairing properties. Hull cell tests were used to study the influence of the current density on composition of the coatings and their morphology. Surface morphology, chemical composition and oxidation state of the obtained coatings were examined by scanning electron microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS), respectively. Furthermore, electrochemical characterization and corrosion tests were performed in order to evaluate the corrosion properties of the electrodeposited Zn–Ce coatings. The cathodic deposition of Zn–Ce was achieved for the first time using the deep eutectic solvent choline chloride-urea as an electrolyte. Cerium was incorporated in the coating as oxide or mixed oxide within the Zn metal matrix. The composition and morphology of the electrodeposited coating were dependent on the applied current density. Electrochemical corrosion tests showed similar corrosion rates for all the coatings. Nevertheless on scratched tests with a ratio area of 15:1, for Zn–Ce coatings cerium oxide somehow migrates from the coating to the high pH cathodic areas developed on the surface of the bare steel substrate. Further study is still necessary to improve the corrosion protection of the Zn–Ce coating for carbon steel.

Electrochemical mechanism of tin membrane electrodeposition under ultrasonic waves

Tin was electrodeposited from chloride solutions using a membrane cell under ultrasonic waves. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CHR), and chronopotentiometry were applied to investigate the electrochemical mechanism of tin electrodeposition under ultrasonic field. Chronoamperometry curves showed that the initial process of tin electrodeposition followed the diffusion controlled three-dimensional nucleation and grain growth mechanism. The analysis of the cyclic voltammetry and linear sweep voltammetry diagrams showed that the application of ultrasound can change the tin membrane electro-deposition reaction from diffusion to electrochemical control, and the optimum parameters for tin electrodeposition were H⁺ concentration 3.5 mol·L^-1, temperature 35 °C and ultrasonic power 100 W. The coupling ultrasonic field played a role in refining the grain in this process. The growth of tin crystals showed no orientation preferential, and the tin deposition showed a tendency to form a regular network structure after ultrasonic coupling. While in the absence of ultrasonic coupling, the growth of tin crystals has a high preferential orientation, and the tin deposition showed a tendency to form tin whiskers. Ultrasonic coupling was more favorable for obtaining a more compact and smoother cathode tin layer.

Zinc Electrodeposition in the Presence of an Aqueous Electrolyte Containing 1-Ethylpyridinium Bromide: Unexpected Oddities

The reversible electrodeposition of zinc was investigated in an aqueous electrolyte containing zinc bromide (50 mM) and 1-ethylpyridinium bromide ([C2Py]Br, 50 mM) by cyclic voltammetry, chronoamperometry, and scanning electron microscopy. Unusual voltammetric behaviour for the Zn/ZnII redox couple was observed in the presence of [C2Py]Br. Passivation of the redox couple was observed after a single deposition–stripping cycle at switching potentials more negative than −1.25 V versus Ag/AgCl. This unusual behaviour was attributed to the reduction of 1-ethylpyridinium cations to pyridyl radicals and their follow-up reactions, which influenced the zinc electrochemistry. This behaviour was further seen to modify the nucleation process of electrodeposition, which altered the morphology of zinc electrodeposits.

Electrodeposition in Ionic Liquids

Due to their attractive physico-chemical properties, ionic liquids (ILs) are increasingly used as deposition electrolytes. This review summarizes recent advances in electrodeposition in ILs and focuses on its similarities and differences with that in aqueous solutions. The electrodeposition in ILs is divided into direct and template-assisted deposition. We detail the direct deposition of metals, alloys and semiconductors in five types of ILs, including halometallate ILs, air- and water-stable ILs, deep eutectic solvents (DESs), ILs with metal-containing cations, and protic ILs. Template-assisted deposition of nanostructures and macroporous structures in ILs is also presented. The effects of modulating factors such as deposition conditions (current density, current density mode, deposition time, temperature) and electrolyte components (cation, anion, metal salts, additives, water content) on the morphology, compositions, microstructures and properties of the prepared materials are highlighted.

Electrochemical fabrication of nanoporous copper films in choline chloride–urea deep eutectic solvent

Schematic illustration of the in situ electrochemical alloying/dealloying process for fabrication of nanoporous copper (NPC) film in choline chloride–urea deep eutectic solvent.