AlCl3 Ionic Liquid Research Articles

Anodic Dissolution of Al–Fe and Al-Fe-Si Alloys in Emimcl–AlCl3 Electrolyte

To produce over 99.9% of high-purity Al from Al–Fe alloy containing Al6Fe and Al–Fe–Si alloy containing β-AlFeSi by electrorefining, their anodic dissolution and cathodic electrodeposition characteristics were investigated in an EmImCl–AlCl3 ionic liquid electrolyte at 323 K. Constant potential electrolysis showed that Fe dissolved from Al–Fe anode at 0.7 V vs Al/Al(III) and from Al–Fe–Si anode at 1.4 V, and was co-deposited with Al on the cathode. Notably, anodic dissolution potential of Fe was changed by forming β-AlFeSi, and Si did not dissolve from β-AlFeSi at either potential. A combination of controlled anodic dissolution potential and the use of the Al alloy containing β-AlFeSi further suppressed the dissolution and cathodic co-deposition of Fe, affording high-purity Al on the cathode.

Anodic Dissolution Behavior of Al Alloys Containing Al6Fe or β-AlFeSi in EmImCl–AlCl3 Electrolyte During Electrorefining

To produce over 99.9% of high-purity Al from Al alloys containing Al6Fe or β-AlFeSi through electrorefining, their anodic dissolution and cathodic electrodeposition characteristics should be clarified. In this study, the anodic dissolution and cathodic electrodeposition behavior of Al–Fe binary and Al–Fe–Si ternary alloys were investigated in an EmImCl–AlCl3 ionic liquid electrolyte at 323 K. Anodic polarization measurements, constant potential electrolysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), field-emission SEM (FE-SEM), and energy dispersive spectroscopy (EDS) were used to study the anode and electrodeposits on the cathode. Constant potential electrolysis showed that Fe dissolved from Al6Fe in the Al–Fe anode at 0.7 V vs Al/Al(III) and from β-AlFeSi in the Al–Fe–Si anode at 1.4 V and was co-deposited with Al on the cathode. Notably, Si did not dissolve from β-AlFeSi at either potential. A combination of controlled anodic dissolution potential and the use of the Al alloy containing β-AlFeSi further suppressed the dissolution and cathodic co-deposition of Fe, affording high-purity Al on the cathode. This suggests that Al alloys with intermetallic compounds that are less likely to dissolve Fe at the anode are optimal for obtaining over 99.9% of high-purity Al from Al alloys containing Fe in the electrorefining method.

Hindered Aluminum Plating and Stripping in Urea/NMA/Al(OTF)3 as a Cl-Free Electrolyte for Aluminum Batteries

Conventional electrolytes for aluminum metal batteries are highly corrosive because they must remove the Al2O3 layer to enable plating and stripping. However, such corrosiveness impacts the stability of all cell parts, thus hampering the real application of aluminum-metal batteries. The urea/NMA/Al(OTF)3 electrolyte is a non-corrosive alternative to the conventional [EMImCl]: AlCl3 ionic liquid electrolyte (ILE). Unfortunately, this electrolyte demonstrates poor Al plating/stripping, probably because (being not corrosive) it cannot remove the Al2O3 passivation layer. This work proves that no plating/stripping occurs on the Al electrode despite modifying the Al surface. We highlight how urea/NMA/Al(OTF)3 electrolyte and the state of the Al electrode surface impact the interphase layer formation and, consequently, the likelihood and reversibility of Al plating/stripping. We point up the requirement for carefully drying electrolyte mixture and components, as water results in hydrogen evolution reaction and creation of an insulating interphase layer containing Al(OH)3, AlF3, and re-passivated Al oxide, which finally blocks the path for the possible Al plating/stripping.

Synthesis of Novel Polycyclic Alkylated Tetralin Base Oils Catalyzed by Ionic Liquids and Its Lubricating Properties

AbstractA novel polycyclic alkylated tetralin (PAT) similar to the naphthenic oil was successfully synthesized through Friedel‐Crafts alkylation. This was accomplished by reacting coal‐based chemical tetralin with 1,7‐octadiene, using Et3NHCl−AlCl3 ionic liquid as a catalyst. To enhance the selectivity towards dialkylated products (C28−2THN), the reaction conditions were systematically studied. Interestingly, the reaction could proceed well even at a low temperature of 0 °C and the selectivity for C28−2THN products could reach 54.0 %. The primary physicochemical properties of PAT were investigated in detail, it was found that the existence of polycyclic structures contributes to high viscosity, better thermal‐oxidative stability and good polarity. Compared with octyltetralins‐ and commercial alkylnaphthalene‐based oil (AN30), the PAT exhibited superior friction‐reducing and anti‐wear properties under the load of 100 N at 50 °C due to its rigid cycle structures and flexible chain.

Toward Tungsten Electrodeposition at Moderate Temperatures Below 100 °C Using Chloroaluminate Ionic Liquids

The electrodeposition of tungsten at moderate temperatures (<100 °C) has been of significant interest for the fabrication of thin films and microelectromechanical system components to decrease energy consumption and increase process safety. In this study, we investigated the electrochemical reduction of WCl4 and WCl5 in 1-ethyl-3-methylimidazolium chloride (EMIC) and EMIC–AlCl3 ionic liquids at 80 °C–120 °C. W-rich films with a thickness of approximately 1 μm were obtained from the Lewis acidic EMIC–AlCl3–WCl5 bath, whereas the other baths did not yield any deposits. The films obtained from the EMIC–AlCl3–WCl5 bath at 80 °C had higher W contents of 54 at.% than those obtained at 120 °C. X-ray absorption near-edge structure spectra of the W-rich films indicated that W existed in an oxidized state. The findings of this study can be used as a guide to explore optimal electrolytes and electrolytic conditions for the electrodeposition of metallic W at moderate temperatures.

Revealing the effect of electrolyte coordination structures on the intercalation chemistry of batteries

In-depth understanding of the electrolyte-dependent intercalation chemistry in batteries through direct operando/in situ characterizations is crucial for the development of the high-performance batteries. Herein, taking the Al/graphite battery as a model system, the effect of electrolyte coordination structure on the intercalation processes has been investigated over the batteries with either 1-hexyl-3-methylimidazolium chloride (HMICl)-AlCl3 or 1-ethyl-3-methylimidazolium chloride (EMICl)-AlCl3 ionic liquid electrolyte using operando X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. With a weaker anion-cation interaction in HMI-based electrolyte, the XPS-derived atomic ratio between co-intercalated N and intercalated Al is 0.9, which is lower than 1.6 for EMI-based electrolyte. Attributed to the additional de-solvation process, the batteries with the HMI-based electrolyte show a lower ionic diffusion rate, capacity, and cycling performance, which agree with the operando characterization results. Our findings highlight the critical role of the electrolyte coordination structure on the (co–)intercalation chemistry.

Aluminum Electrodeposition on the Surface of Boron Carbide Ceramics by Use EMIC–AlCl3 Ions Liquid

Coating technology is decisively important for metallization of ceramic materials and ceramic metal sealing technology. Previous studies have shown that the network-like structure after penetration of molten aluminum can significantly improve the strength of joint components. However, the direct aluminum coating method is limited by the shape of the substrate. To obtain a dense aluminum film on the surface of B4C, in this study, aluminum was deposited by pulse electroplating in EMIC–AlCl3 ionic liquid. The deposited metals were observed and analyzed by SEM–EDS and XRD. A Vickers hardness tester was adopted as an auxiliary equipment to clarify the film quality. The results show that frequency and duty cycle have significant effects on crystal orientation. The content of oxides in the contact gap reduces the bonding strength of the deposited metal, which provides experimental basis for metal electrodeposition on B4C.

Characteristics of Anodic Dissolution for Al-Cu Alloys in EmImCl-AlCl3 Ionic Liquid

To produce high-purity Al from Al–Cu alloys, the dissolution behaviors of various Al–Cu binary alloy anodes in EmImCl–AlCl3 ionic liquid have been investigated at 323 K. In the constant potential electrolysis of the Al–5.0Cu casting alloy and cold-rolled plate at 0.3 V, Al atoms in the matrix phase were preferentially dissolved followed by the formation of Al2Cu surface species. The dissolution of both Al2Cu and Al in the alloy matrix occurred during electrolysis at 0.8 and 1.2 V. Moreover, a Cu-rich layer derived from Al2Cu was formed on the cold-rolled plate surface at a potential of 0.8 V and high electric charge densities. From the results, potential dependence of the anodic dissolution of the Al−Cu alloys in the ionic liquid was clarified.

Anodic Dissolution Behavior in the Electrorefining of Al–Cu Alloys Using an EmImCl–AlCl3 Ionic Liquid

To produce high-purity Al from Al–Cu alloys, the dissolution behaviors of various Al–Cu binary alloy anodes in EmImCl–AlCl3 ionic liquid have been investigated at 323 K. In the anodic polarization measurements, anodic current density peaks were observed at potentials of approximately 0.3 and 0.8 V vs Al/Al(III) for the Al–5.0%Cu casting alloy. In the constant potential electrolysis of the Al–5.0%Cu casting alloy and cold-rolled plate at 0.3 V, Al atoms in the matrix phase were preferentially dissolved followed by the formation of Al2Cu surface species. The dissolution of both Al2Cu and Al in the alloy matrix occurred during electrolysis at 0.8 and 1.2 V. Moreover, a Cu-rich layer derived from Al2Cu was formed on the cold-rolled plate surface at a potential of 0.8 V. Additionally, Cu was co-deposited on the cathode at the potentials at which Al2Cu dissolved. The dependence of the anodic dissolution behavior of the Al−Cu alloys on the potential in the EmImCl–AlCl3 ionic liquid was analyzed. By controlling the anodic dissolution potential, the dissolution of Cu in Al2Cu into the electrolyte can be suppressed, thus considerably increasing the purity of electrorefined Al.

Aluminum Electrodeposition in Dry Air Atmosphere: Comparative Study of an Acetamide–AlCl3 Deep Eutectic Solvent and a 1-Ethyl-3-Methylimidazolium Chloride–AlCl3 Ionic Liquid

Aluminum electrodeposition using ionic liquids or deep eutectic solvents has attracted significant interest for coating applications. Although Al electrodeposition is usually carried out in a nitrogen- or argon-filled glove box, there may be a potential for process cost reduction if the Al electrodeposition process could be carried out in a dry atmosphere. In this study, we examined two commonly used baths, namely a 1-ethyl-3-methylimidazolium chloride (EMImCl)–AlCl3 ionic liquid and an acetamide (AcAm)–AlCl3 deep eutectic solvent, to determine their respective feasibilities for the electrodeposition of a uniform Al film in dry air. Electrodeposition in dry air using the AcAm–AlCl3 bath produced uniform Al films even after the bath had been used for more than 10 weeks, whereas electrodeposition in dry air using the EMImCl–AlCl3 bath failed to produce an Al film covering the entire substrate. The current efficiency was almost 100% in the AcAm–AlCl3 bath, whereas the value decreased to 50% in EMImCl–AlCl3 bath in dry air. The findings of this study therefore reveal that AcAm–AlCl3 is a suitable bath for Al electrodeposition in dry air.

Dissolution Behavior of Hydrated Tungsten Chlorides in Chloroaluminate Ionic Liquids and It's Application in Aluminum–Tungsten Alloy Electrodeposition

Introduction The demand for aluminum (Al) alloys as coating materials have increased owing to their high corrosion and oxidation resistance. In addition, electrodeposition technique has attracted attention for obtaining Al alloy coatings, and various non-aqueous electrolytic baths for Al alloy electrodeposition, including ionic liquids, have been developed. Alloying Al with refractory metals, such as tungsten (W) and molybdenum (Mo), significantly improves the pitting-corrosion resistance of Al. However, the salts of these metals have relatively low solubility in Al electrodeposition baths, and thus, it is difficult to obtain Al alloys with a high content of these metals.In our previous study, we reported that a W(II) salt, namely W6Cl12, which is dissolved in 1-ethyl-3-methylimidazolium (EMIC)–AlCl3 ionic liquids at a higher concentration than other salts such as WCl4, enables the electrodeposition of Al–W alloy films with a high W content[1]. However, the W6Cl12 used previously turned out to contain water due to the synthesis process, which may have increased the solubility of W6Cl12.In this study, we investigated the effect of water content on the solubility of W precursors in ionic liquids. Herein, three W precursors with different water contents were employed, namely anhydrous W6Cl12 and hydrated complexes W6Cl12·2H2O and (H3O)2[W6Cl14]·7H2O (Figure 1). Al–W alloy was electrodeposited using baths containing different W precursors. In addition, the chemical speciation of the hydrated complexes in the ionic liquids was conducted using, Raman, and Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis) spectroscopy. Experimental Herein, three electrolytic baths were prepared by adding anhydrous salt W6Cl12, hydrated complex W6Cl12·2H2O, and (H3O)2[W6Cl14]·7H2O to an EMIC–AlCl3 ionic liquid with EMIC:AlCl3 molar ratio of 1:2. The saturation concentrations of W precursors were determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Potentiostatic electrodeposition was performed on copper substrates at a bath temperature of 80 °C under an Ar atmosphere in a glove box. The W content, current efficiency, and impurity content derived from the hydration water in the electrodeposited material were evaluated by energy dispersive X-ray spectroscopy (EDX), ICP-AES, and X-ray photoelectron spectroscopy (XPS), respectively. The dissolved species in the baths were analyzed by Raman, FT-IR, and UV-Vis spectroscopy. Results and Discussion The saturation concentration of each W ion source in the EMIC–AlCl3 ionic liquid was less than 1 mM for anhydrous W6Cl12; however, it increased to ~80 and 120 mM for W6Cl12·2H2O and (H3O)2[W6Cl14]·7H2O, respectively. Potentiostatic electrodeposition at potentials lower than 0 V (vs. Al/Al(III)) produced films consisting of Al and W. The W content increased to ~1 and 15 at.% from the anhydrous salt bath and hydrated complex bath, respectively. The current efficiency for electrodeposition was close to 100%, even in baths with hydrated precursors. EDX and XPS measurements of Al–15 at.% W alloy film obtained from the hydrated complex bath showed that Al and W existed in metallic states in the film.The Raman spectra of each bath showed that the Al2Cl7 − concentration decreased and AlCl4 − concentration increased in the hydrated complex bath compared to the anhydrous salt bath. This suggests that the hydrated W complex reacted with AlCl3 to form other Al species, thereby decreasing the apparent AlCl3/EMIC ratio in the bath. The FT-IR spectra of baths with the addition of hydrated complex or liquid water showed that both the hydrated water and liquid water reacted with Al anions to produce Al–OH–Cl species[2]. The UV-Vis spectra of the anhydrous salt bath and hydrated complex baths showed two prominent peaks: one at 240 nm (λ1) and the other at ~270–300 nm (λ2). λ1 was almost constant for all the W precursors, whereas λ2 shifted to a lower wavelength for the hydrated complex baths. The dissolved W species estimated from these spectroscopic data and their relationship with solubility are discussed at the meeting.

Conductivity of 1-Ethyl-3-Methylimidazolium Chloride (EMIC) and Aluminum Chloride (AlCl3) Ionic Liquids at Different Temperatures and AlCl3 Mole Fractions

In this work, the conductivity (k) of Lewis acidic ionic liquid (IL) comprising a melt of organic chloride and aluminum chloride (AlCl3) with different molar ratios of organic chlorides with AlCl3 in the temperature range of 70-110 °C are reported. The ILs prepared with three imidazolium-based organic chlorides such as EMIC, BMIC, and HMIC are studied. The molar ratios of 1:1.5, 1:1.8, and 1:2.0 are selected for the study to maintain the acidity of the ILs for possible metal electrodeposition applications. The electrochemical behavior of anion species in the three ILs is studied using electrochemical impedance spectroscopy (EIS) technique and obtained the precise and fast measurement of conductivity values. The measured k values of all the ILs followed the Arrhenius law. The activation energies of conduction determined by fitting the experimental conductivity data are in good agreement with the literature. The conductivity of ILs with lower alkyl group organic chlorides decreased with the higher mole fraction of AlCl3. In contrast, the conductivity of IL having a higher alkyl group organic chloride (HMIC) increased with the increasing mole fraction of AlCl3. Based on the thermodynamic calculations, the differences in conductivities are attributed to the anion concentration, the molecular structure, cation-anion interactions, and hydrogen bonds in the ILs.

Conductivity of 1-Ethyl-3-Methylimidazolium Chloride (EMIC) and Aluminum Chloride (AlCl3) Ionic Liquids at Different Temperatures and AlCl3 Mole Fractions

The conductivity (k) of ionic liquid (IL) comprising a melt of 1-ethyl-3-methylimidazolium chloride (EMIC) and aluminum chloride (AlCl3) with different AlCl3 mole fractions (XAl) and temperatures (343-383 K) are reported. XAl values of 0.6, 0.643, and 0.667 in EMIC-AlCl3 IL are selected to maintain the desired Lewis acidity. Precise and fast conductivity measurements and the behavior of anion species in IL are studied using electrochemical impedance spectroscopy (EIS). The measured k data followed the Arrhenius law using which the activation energies (E a) of conduction are determined. The conductivity of EMIC-AlCl3 IL decreased with the higher XAl. EMIC-AlCl3 with XAl=0.6 exhibited higher k (5.58 S m–1) at 383 K and lowest E a (4.25 KJ mol–1) among studied parameters. Based on the thermodynamic calculations, the differences in conductivities are attributed to the interplay of anion concentration, the molecular structure, cation-anion interactions, and hydrogen bonds in the IL.

Electroanalytical Study of Active Species to Deposit Ti Alloy from 1-Butyl-3-Methylimidazolium Chloride-Aluminum Chloride Ionic Liquid

The electrochemical behavior of titanium-chloroaluminate anion species in Lewis acidic 1-butyl-3-methylimidazolium chloride (BMIC)-aluminum chloride (AlCl3) ionic liquid (IL) electrolyte with 0.667 AlCl3 mole fraction is investigated at 383K by cyclic voltammetry (CV), chronoamperometry (CA), and chronopotentiometry (CP). The effect of scan rate on peak potential and peak current, constant current density, constant applied potential, and the electrolyte temperature are discussed. The redox reaction of the Ti2+/Ti0 deposition from titanium hepta-chloroaluminate ([Ti(Al2Cl7)4]2−) anions is a reversible process with a 2-electron transfer while that of Al3+/Al0 deposition from hepta-chloroaluminate ([Al2Cl7]−) anions is quasi-reversible with 3-electron transfer. The cyclic voltammograms indicated that the reduction of [Al2Cl7]− and [Ti(Al2Cl7)4]2− species to corresponding Al and Ti forms is a diffusion-controlled phenomenon. The diffusion coefficients (D) of the anion-species in BMIC-AlCl3 IL determined at 383 K using CV and CP methods are 9.74 × 10−10 m2 s−1 and 6.36 × 10−10 m2 s−1, respectively.

Deep compositional understanding of TBA: AlCl3 ionic liquid for its applications

Chloroaluminate ionic liquids (ILs) have been immensely used as homogeneous catalyst in Friedel-Crafts reaction. We have recently synthesized chloroaluminate ILs by reacting aluminium chloride with a hydrophobic neutral ligand i.e. tributylamine (TBA:AlCl3). The current study elaborates on the investigations of the composition of the ionic liquids at various stages of their formation. The ionic liquids were synthesized using various mole ratios of tributyl amine and aluminium chloride in range of 1:1 to 1:2.3, in presence of an aromatic solvent in a one pot reaction. Various characterization techniques like Mass spectrometry, 27Al Nuclear Magnetic Resonance, 31P Nuclear Magnetic Resonance and Fourier Transform Infrared spectroscopy were used to elucidate the formation of various moieties of the TBA:AlCl3 Ionic Liquid. This study also elaborates on the investigations of the cationic and anionic moieties and their structure-property relationship for various applications. Various Friedel-Crafts reaction of industrial importance were performed using the ionic liquid having (Al2Cl7)−moiety to assess its performance and compared with conventional processes. The synthesized products were characterised by sophisticated analytical techniques like 1H NMR, 13C NMR, FTIR, GC–MS, GC-FID, to name a few. This class of ionic liquids also have importance in various electrochemical applications like aluminium deposition and aluminium batteries.

Simultaneous Electrodeposition of Silver and Tungsten from [EMIm]Cl:AlCl3 Ionic Liquids outside the Glove Box

Ag–W two-phase system was prepared by electrodeposition using anhydrous 1-ethyl-3-methylimidazolium chloride [EMIm]Cl ionic-liquid (IL) solution with AlCl3 in different ratios. The deposition took place outside the glove box with a continuous Ar stream over the electrolyte at 120 °C and a pulsed-like current regime. Resultant layers show areas of Ag and W with an overall W content with a mass fraction of w W = 50% (mole fraction x W = 36.9%). The phase composition of Ag–W layers was observed by X-ray diffraction, and the chemical composition was characterized by scanning electron microscopy and inductively coupled plasma optical emission spectroscopy.

A Novel Moisture‐Insensitive and Low‐Corrosivity Ionic Liquid Electrolyte for Rechargeable Aluminum Batteries

AbstractRechargeable aluminum batteries (RABs) are extensively developed due to their cost‐effectiveness, eco‐friendliness, and low flammability and the earth abundance of their electrode materials. However, the commonly used RAB ionic liquid (IL) electrolyte is highly moisture‐sensitive and corrosive. To address these problems, a 4‐ethylpyridine/AlCl3 IL is proposed. The effects of the AlCl3 to 4‐ethylpyridine molar ratio on the electrode charge–discharge properties are systematically examined. A maximum graphite capacity of 95 mAh g−1 is obtained at 25 mA g−1. After 1000 charge–discharge cycles, ≈85% of the initial capacity can be retained. In situ synchrotron X‐ray diffraction is employed to examine the electrode reaction mechanism. In addition, low corrosion rates of Al, Cu, Ni, and carbon‐fiber paper electrodes are confirmed in the 4‐ethylpyridine/AlCl3 IL. When opened to the ambient atmosphere, the measured capacity of the graphite cathode is only slightly lower than that found in a N2‐filled glove box; moreover, the capacity retention upon 100 cycles is as high as 75%. The results clearly indicate the great potential of this electrolyte for practical RAB applications.

Electrodeposition of Al–W Alloy Films Using W(II) Salts Synthesized Using Different Methods

Introduction Electrodeposition of Al and its alloys in molten salts, ionic liquids, and organic solvents has been extensively studied to obtain oxidation and corrosion-resistant coatings. Among Al-based binary alloys, Al–W alloys with a W content of ~10 at.% are known to show the highest resistance to chloride-induced pitting corrosion1 – 2. Several studies have been conducted on the electrodeposition of Al–W alloys using chloroaluminate baths containing WCl4 and K3W2Cl9 2–4. We reported on the electrodeposition of dense Al–W alloy films with a high W content exceeding ~12 at.% using 1-ethyl-3-methylimidazolium chloride (EMIC)–AlCl3 ionic liquid containing a W(II) salt, W6Cl12 (WCl2)5 – 7. The W6Cl12 used in our studies was more soluble in EMIC–AlCl3 baths than the other W salts used in the previous studies. The W6Cl12 that we used in our previous studies was obtained from (H3O)2[W6Cl14]·7H2O by annealing. The resulting salt had a Cl/W atomic ratio of 2, and its X-ray diffraction pattern agreed with that of poorly crystallized W6Cl12 reported in the literature. 8 Accordingly, we determined that this W salt was W6Cl12. However, it was recently found that well-crystallized W6Cl12 obtained by annealing this W salt at a higher temperature had a much smaller solubility in the EMIC–AlCl3 bath. Because the W salt was obtained from (H3O)2[W6Cl14]·7H2O, it could contain water as a impurity, which could affect the solubility and electrochemical behavior of this salt. W6Cl12 can also be synthesized by disproportionation of WCl4 in a vacuum. This synthesis method is considered to yield much purer W6Cl12 than that from (H3O)2[W6Cl14]·7H2O. In this study, we investigated the solubility and electrochemical behavior of W6Cl12 synthesized using these two different methods. Experimental An electrolytic bath was prepared by mixing EMIC, anhydrous AlCl3, and W6Cl12. The molar ratio of EMIC and AlCl3 was 1:2. W6Cl12 was prepared using two different methods. One was annealing of (H3O)2[W6Cl14]·7H2O, which was produced by recrystallization of W(II) chloride produced by the reduction of WCl6 with Bi. Annealing of (H3O)2[W6Cl14]·7H2O was conducted at 325–450°C. The other method involved the disproportionation of WCl4 to W6Cl12 and WCl5, which was performed by heating WCl4 at 350–500°C in a vacuum. The electrochemical behavior of W­6Cl12 treated under different conditions was investigated by cyclic voltammetry and potentiostatic/galvanostatic electrolysis in the EMIC–AlCl3 baths at 80°C. All electrochemical experiments were conducted in an argon-filled glove box. The electrodeposited films were analyzed by scanning electron microscopy, energy dispersive X-ray, and X-ray diffraction. Current efficiency for the electrodeposition was determined by inductively coupled plasma atomic emission spectroscopy. Results and discussion W6Cl12 obtained by annealing of (H3O)2[W6Cl14]·7H2O at 325°C dissolved in EMIC–AlCl3 baths up to 49 mM, but the solubility decreased with increasing annealing temperature. W6Cl12 obtained by the disproportionation of WCl4 hardly dissolved in an EMIC–AlCl3 bath, irrespective of the disproportionation temperature. Potentiostatic electrodeposition in a bath containing W6Cl12 produced by the disproportionation of WCl4 yielded Al film with a trace W content of <0.1 at.%. These results indicate the W6Cl12 obtained by annealing of (H3O)2[W6Cl14]·7H2O at a relatively low temperature was more suitable as a W precursor for Al–W alloy electrodeposition than that obtained by the disproportionation of WCl4. References B. A. Shaw, T. L. Fritz, G. D. Davis, and W. C. Moshier, J. Electrochem. Soc., 137, 1317 (1990).T. Tsuda, Y. Ikeda, T. Arimura, M. Hirogaki, A. Imanishi, S. Kuwabata, G. R. Stafford, and C. L. Hussey, J. Electrochem. Soc., 161, D405 (2014).T. Tsuda, Y. Ikeda, T. Arimura, A. Imanishi, S. Kuwabata, C. L. Hussey, and G. R. Stafford, ECS Trans., 50, 239 (2013).K. Sato, H. Matsushima, and M. Ueda, ECS Trans., 75, 305 (2016).S. Higashino, M. Miyake, H. Fujii, A. Takahashi, and T. Hirato, J. Electrochem. Soc., 164, D120 (2017).S. Higashino, M. Miyake, A. Takahashi, Y. Matamura, H. Fujii, R. Kasada, and T. Hirato, Surf. Coat. Technol., 325, 346 (2017) S. Higashino, M. Miyake, H. Fujii, A. Takahashi, R. Kasada, and T. Hirato, Mater. Trans., 59, 944 (2018).S. Kamiguchi and T. Chihara, Catal. Lett., 85, 97 (2003).

Segregation in Aluminum-Zirconium Alloys, Electrodeposited from Ionic Liquids, and Its Modification By Pulse Plating

It is quite typical for aluminum-zirconium alloys, obtained by electrodeposition in chloroaluminate ionic liquids, to have two or more distinct phases with different Zr concentrations. The Zr content in one phase can be several times higher than in the other. In the present work we have studied this segregation in [EMIM]Cl*AlCl3 ionic liquid. Factors like temperature, current density, agitation, and concentrations of both zirconium and aluminum in the electrolyte were investigated. A proposed mechanism for this phenomenon is based on a possibility of two different pathways of zirconium reduction. One pathway is a 4-electron process, taking Zr4+ directly to metal. Another way is a 2-electron reaction via intermediate Zr2+ ions formed in the solution. The difference between these pathways includes variations in chloride ions concentration in the vicinity of the electrode surface, as well as variations in charge and structure of the double layer. The above variations exist only near the cathode surface, and have a limited life time. One approach to eliminating the segregation in the alloy is to utilize pulsed electrodeposition methods, allowing re-mixing and equilibration of the electrolyte during the off periods. As expected, shorter pulses and longer off times lead to more compositionally uniform deposits. Figure 1. Backscatter SEM image of a cross section of Al-Zr deposit. Light areas are zirconium-rich. Figure 1

Enhancement of Al-Ti Alloy Electrodeposition from AlCl3-EMIC Ionic Liquid Based Bath by Mg Additive

Al-Ti was electrodeposited from 1-ethyl-3-methyl-imidazolium chloride (EMIC)-AlCl3 ionic liquid containing TiCl4 on a copper working electrode using a potentiostatic or potential-pulse polarization. Deposits of Al-Ti alloy was obtained beneath the loose precipitate composed of mainly insoluble titanium chloride. Potential-pulse polarization that switched the potential between the two cathodic reduction potential of the multistep reduction of Ti ions improved the efficiency of electrodeposition of Al-Ti alloy. The ratio of Al-Ti alloy against the loose precipitate was increased by adding the Mg powder to the ionic liquid bath. It was supposed that Ti[IV] was reduced to Ti[II] by the substitutional dissolution of Mg and the resultant Ti[II] species such as TiCl42– contributed the electrodeposition of Ti. Simultaneous deposition of Al protected as-deposited Ti from re-oxidation (chlorination) by encapsulation them in the Al-Ti alloy. Although the deposition efficiency increased using Mg additive, the atomic content of Ti in Al-Ti deposits was reduced from ca. 21% for the bath absent of Mg powder to ca. 10% for the bath containing Mg. The decrease in the Ti content in the deposits was probably due to the insufficient supply rate of Ti[II] ions compared to the deposition rate of Al.