Low Temperature Molten Salt Research Articles

Electrodeposition behavior of aluminum from urea-acetamide-lithium halide low-temperature molten salts

Urea-acetamide-lithium halide (LiBr, LiCl, LiF) low-temperature molten salts were used as the electrolytes to study the electrodeposition of aluminum on a tungsten electrode. Al(III) was introduced into the salts by the addition of AlCl3. The reduction potential of Al(III) is dependent on the molar ratio of AlCl3/(urea+acetamide). The nucleation mechanism of aluminum on the tungsten electrode was determined to be three-dimensional instantaneous nucleation with diffusion-controlled growth at 333K. Aluminum coatings were prepared at different cathodic potentials (from −0.10V to −0.25V) and different temperatures (from 313K to 343K) in urea-acetamide-LiBr molten salt. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to characterize the surface of the deposits. The SEM images indicate that the morphologies of the aluminum deposits are dependent on the deposition potential and temperature. The XRD analysis confirms that the obtained deposits are pure aluminum.

Polymer Gel Membranes for Aluminum Deposition and Rechargeable Aluminum Ion Batteries

Aluminum and its many versatile alloys are routinely used as surface coatings for the corrosion protection of many metals, offering both barrier and sacrificial protection. Among various methods for aluminum coating, electrodeposition is the most attractive one because it leads to thin, economical coatings that usually are adherent and do not affect the structural and mechanical properties of the substrate. Unfortunately, neither aluminum nor its alloys can be electrodeposited from aqueous solutions because hydrogen is evolved before aluminum is plated. Thus, it is necessary to employ nonaqueous solvents (both molecular and ionic) for this purpose. Room-temperature ionic liquids (low-temperature molten salts) possess a unique set of physical properties such as nonflammability, negligible vapor pressure, high ionic conductivity, and high thermal, chemical and electrochemical stability. Therefore, they open the door for the electroplating of reactive elements, which is impossible using aqueous or other organic solvents. Thus far, most research about the use of ionic liquids for electrodeposition of aluminum and its alloys has focused on chloroaluminate anions, which were obtained by mixing anhydrous AlCl3 with organic chloride salt such as 1-ethyl-3-methyl imidazolium chloride (EMImCl) and 1-(1-butyl)pyridinium chloride (N-BPCl) etc. Unfortunately, because of the hygroscopic nature of AlCl3 and the chloroaluminate, the electroplating has to be performed in an inert-gas atmosphere. 1 One way to reduce the moisture sensitivity of the chloroaluminate based ionic liquids for practical application is to form polymer gel electrolytes, either by impregnating liquid electrolytes into the preformed membranes or co-cast polymer and liquid electrolytes, or by copolymerization of monomers in the presence of plasticizers. In this paper, polymer gel membranes were synthesized using the latter approach, that is, copolymerization of monomers in the presence of plasticizers. The gel membranes are transparent with good mechanical properties, which can be used for practical applications. Fig. 1 shows the ionic conductivities of the gel membranes containing different amount of eutectic mixture of AlCl3 and 1-ethyl-3-methylimidazolium chloride (EMIm.Cl) in a molar ratio of 1.5:1. At 20oC the ionic conductivities of the gel membranes containing 50, 60, 70 and 80 wt% of AlCl3-EMIm.Cl are 5.3 x 10-5, 2.0 x 10-4, 8.7 x 10-4 and 1.7 x 10-3 S cm-1, respectively. Fig. 2 shows a typical cyclic voltammetry of the membrane containing 60 wt% of AlCl3-EMIC (1.5:1) with copper plate as the working electrode and aluminum plate as the counter electrode. Reversible aluminum deposition and stripping is clearly observed. It is noticed that the current densities increase with increasing the scan cycles, indicating an activation process, probably due to the residual surface oxide on the Al plate. For rechargeable aluminum ion battery application, reversible aluminum deposition/ stripping with high coulombic efficiency is a necessary step to realize stable cycling performance. Therefore, this gel membrane can also be used for rechargeable aluminum ion batteries. 2More details about the gel membrane will be presented at the meeting. Acknowledgements:This work was funded by the Strategic Environmental research and Development Program (SERDP) (WP2316). 1. Liao, Q.; Pitner, W. R.; Stewart, G.; Hussey, C. L.; Stafford, G. R., J. Electrochem. Soc. 1997, 144 (3), 936. 2. Lin, M. C., Gong, M., Lu, B. , Wu, Y., Wang, D. Y. , Guan, M. Angell, M. , Chen, C. , Yang, J. , Hwang, B. J., Dai, H., Nature, 2015, 520, 324–328 Figure 1

Preparation and Electrochemical Properties of LiCuxMn2-xO4 (x ≤ 0.10) Cathode Material by a Low-Temperature Molten-Salt Combustion Method

Preparation and Electrochemical Properties of LiCuxMn2-xO4 (x ≤ 0.10) Cathode Material by a Low-Temperature Molten-Salt Combustion Method

Structural and Dielectric Properties of Strontium Bismuth Samarium Tantalate Layered Perovskites

The polycrystalline Sr(Bi0.9Sm0.1)2Ta2O9 (SBSmT) ceramics were fabricated via the promising low temperature molten salt synthesis route using KCl as flux material. The X-ray powder diffraction patterns of these ceramics confirmed the existence of monophasic perovskite crystal structure. The scanning electron microscopic studies revealed the presence of plate shaped morphological features of the SBSmT ceramics. Interestingly, the dielectric constant of the SBSmT ceramics in the frequency range of 20 Hz - 1MHz could be tuned as a function of sintering duration. It is observed that the SBSmT ceramics sintered at 1050°C for 10h exhibited higher dielectric constant (ϵr = 76) at 100 kHz than those of ceramics sintered at other durations. The magnitude of the electrical conductivity of the order of 10−7 - 10−9 S/cm at 300 K indicates that the conductivity mechanism might be attributed to the migration of oxygen ion vacancies in these ceramics.

Electrochemical study of nickel from urea-acetamide-LiBr low-temperature molten salt

The electrochemical behavior of nickel was studied by cyclic voltammetry and chronoamperometry techniques at 353K using a tungsten electrode in urea-acetamide-LiBr low-temperature molten salt. The cyclic voltammograms indicate that the reduction of Ni(II) to Ni proceeds via a single-step, two-electron transfer process. Chronoamperometric measurements show that the electrodeposition of nickel on the tungsten electrode involves three-dimensional (3D) progressive nucleation under diffusion-controlled growth at 353K. Nickel coatings were prepared at different cathodic potentials (−0.70 to −0.85V) and different temperatures (343–373K) in urea-acetamide-LiBr molten salt. The deposits were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The SEM images reveal that uniform, dense, and compact deposits were obtained at more positive cathodic potentials within the temperature range of 343–363K. The EDS and XRD analyses confirm that the obtained deposits are pure nickel.

Effects of alkyl-imidazolium ionic liquid [Omim]Cl on the functional diversity of soil microbial communities.

As low-temperature molten salts, ionic liquids (ILs) were considered to be "green" solvents and have begun to see large-scale applications in the chemical reactions, in separation processes, in electrochemistry studies, etc. In recent years, the toxicity of ILs has started to draw attention. To evaluate the effects of the ionic liquid [Omim]Cl on indigenous microbial community in soil, Biolog-ECO plate method were used with the addition of four different concentrations of [Omim]Cl after four different incubation periods (7, 14, 21, 28 days). The present results showed that the average well color development (AWCD) was strongly activated when the soil was contaminated with [Omim]Cl in the early stages of the incubation. However, the activation effect disappeared with extended incubation time. Therefore, the toxic effects of the alkyl-imidazolium ionic liquid ([Omim]Cl) on the functional diversity of soil microbial communities may be reversible. In addition, the kinetic characteristics of microorganisms that used different categories of carbon sources indicated that phenolic compounds were the main C source in the sample soil.

Research Progress of Electrochemical and Extractible Characteristics of Actinide Elements in the Molten Salt System

Molten salts are non-aqueous solvents which are divided into high temperature molten salts,low temperature molten salts and room temperature molten salts. Due to their unique physical and chemical properties,they are used as the reaction and electrolytic media to electrodeposit the active metal coatings that can not be obtained in aqueous solution. In recent years,the research hot spot in the field of molten electrochemistry is that it is applicable in non-aqueous reprocessing by substituting caustic molten salts for electro-deposition and separation of actinide metal ions. This article reviews the properties of actinide elements in electrochemistry,thermodynamics and physics in high temperature molten salt. The recent research progress of room temperature ionic liquids and the latest extraction advancement of actinide elements in room temperature ionic liquids are introduced. The future research trend in molten system is also given.

A low temperature molten salt process for aluminothermic reduction of silicon oxides to crystalline Si for Li-ion batteries

A molten salt system is developed for low-temperature metallothermic reduction of various silicates or silica to crystalline Si nanoparticles as high-performance anode materials.

Property reinforcement of acrylonitrile‐butadiene‐styrene by simultaneous incorporation of carbon nanotubes and self‐prepared copper particles

ABSTRACTIn this article, copper (Cu) crystallites were successfully prepared via low temperature molten salt method, and the possible formation mechanisms were proposed. The conductive fillers of multiwalled carbon nanotubes (MWCNTs) and as‐prepared Cu particles were designed and introduced into acrylonitrile‐butadiene‐styrene (ABS) blend to prepare different conductive composites. The dispersion states of conductive fillers and the morphologies of the composites were characterized using a field emission scanning electron microscope. The electrical resistivity of different composites was measured. The results showed that Cu and MWCNTs exhibited a synergistic effect in decreasing the electrical resistivity of the Cu/MWCNTs/ABS composites, because Cu that could locate between MWCNTs chain segments provides a better charge transport in the conductive pathways. Compared with pure ABS, the tensile strength, elastic modulus and thermal stability of the Cu/MWCNTs/ABS composites were significantly improved with the incorporation of Cu and MWCNTs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41738.

Low temperature molten salt preparation of nano-SnO2 as anode for lithium-ion batteries

We conduct the synthesis of nano-sized tin oxides by the one-pot molten salt method at low temperature. A sample of SnO2 is obtained by heating a mixture of tin (II) chloride, lithium hydroxide and lithium nitrate at 180°C. The nano-sized SnO2 powder is characterized using the techniques of X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, scanning and transmission electron microscopy and density analysis. The electrochemical properties are analysed using galvanostatic cycling and cyclic voltammetry. The results show that the SnO2 prepared is a single phase material and shows reversible capacities of 471 and 767mAhg−1 in the voltage ranges 0.005–1.0V and 0.005–3.0V vs. Li respectively, at a current rate of 100mAg−1. Reduction of Sn4+ to Sn at characteristic cathodic peak potentials is observed in the initial and subsequent cycles of cathodic scan. Alloying and de-alloying reactions of Sn are observed at ~0.25 and ~0.5V vs. Li in the voltage range 0.005–1.0V, and the formation of Sn to SnO and SnO2 is observed in the voltage range 0.005–3.0V vs. Li. Lower capacity fading is observed when cycled in the voltage range 0.005–1.0V as compared to 0.005–3.0V.

Application of ionic liquids in hydrometallurgy.

Ionic liquids, low temperature molten salts, have various advantages manifesting themselves as durable and environmentally friendly solvents. Their application is expanding into various fields including hydrometallurgy due to their unique properties such as non-volatility, inflammability, low toxicity, good ionic conductivity, and wide electrochemical potential window. This paper reviews previous literatures and our recent results adopting ionic liquids in extraction, synthesis and processing of metals with an emphasis on the electrolysis of active/light, rare earth, and platinum group metals. Because the research and development of ionic liquids in this area are still emerging, various, more fundamental approaches are expected to popularize ionic liquids in the metal manufacturing industry.

Influence of samarium doping on structural and dielectric properties of strontium bismuth tantalate ceramics derived by molten salt synthesis route

Layered Sr(Bi1−xSmx)2Ta2O9 ceramics with x ranging from 0 to 0.10 (10 mol%) were fabricated by the low temperature molten salt synthesis route. X-ray powder diffraction studies revealed that the single phase orthorhombic layered perovskite structure is retained in all these compositions. Scanning electron microscopic studies on these ceramics confirmed the presence of well packed equiaxed plate shaped grains. The dielectric and electrical conductivity properties were studied in the 100 Hz–1 MHz frequency range at 300 K. Interestingly, the 10 mol% samarium doped SrBi2Ta2O9 ceramics exhibited high dielectric constant (er = 155) and low dielectric loss (0.00298) compared to those of other compositions. The electrical conductivity of undoped and samarium doped ceramics increased linearly with increase in frequency.

Electrodeposition of Mg-Ni-Al Alloy in Low Temperature Molten Salts

Mg-Ni-Al alloys were prepared in urea-acetamide-NaBr low temperature molten salts by electrodeposition method. Effects of electrodeposition parameters such as deposition temperature and time on the composition and microstructure of deposits were investigated. The results show that the content of Mg decreases with the increase of deposition temperature, while it increases first, and then decreases with prolonged deposition time. XRD results indicate that the deposits are composed of Mg-Cu, Mg-Al-Cu metallic compounds and Mg-Ni oxides.

Electrodeposition of Mg-Ni-Al Alloy in Low Temperature Molten Salts

Mg-Al-Ni alloys were prepared in urea-acetamide-NaBr low temperature molten salts by electrodeposition method. The results show that Mg2+ could not be electrochemically reduced in this molten salt independently. However, it could be co-deposits with Ni. Effects of electrodeposition parameters such as temperature and electrodeposition time on the composition and microstructure of coatings were investigated. Also, the kinetic process was investigated using electrochemical methods.

Electrode/Electrolyte Interphase Studies of Ceria Based Electrolytes for IT-SOFCs

Solid oxide fuel cells (SOFCs) have emerged as an efficient and environmental friendly tecnology to convert directly hydrogen and fosil fuels into electric energy. Usually these devices use ytria based electrolytes, requiring operation temperatures around 1000ºC. These high temperatures challenge the long term stability and induce rapid degradation of the cell. Ceria based oxides are interesting alternatives because they present higher conductivities at lower operation temperatures. However, these materials require sinterization temperatures in the 1300-1600ºC range to achieve complete densification, which produces very large grain sizes and poor mechanical properties. The addition of transition metals oxides is effective in improving the densification and thus, lowering the sinterization temperatures. In this work we studied Ce0.8(Gd,Nd)0.2O2 with and without Co doping synthesized by a molten salt route [1], which allows obtaining smaller grain sizes at lower temperatures, improving microstructural properties. The synthesis methodology is fast, simple and cheap and combines a metathesis or displacement reaction and a low-temperature molten salt flux.A (La,Sr)(Co,Fe)O3 nanostructured electrode with high electrochemical performance [2,3] was deposited by spin coating techniques on electrolyte pellets. The assemblies were studied by Electrochemical Impedance Spectroscopy, X-Ray Diffraction and Transmission and Scanning Electron Microscopy. The correlation between the electrochemical behavior within the 300-600ºC range, and the bulk and interfacial characteristics will be discussed.[1] Mendoza-Mendoza E., Padmasree K., Montemayor S. and Fuentes A., J Mater Sci 47 (2012) 6076-6085.[2] Baqué L, Caneiro A, Moreno MS, Serquis A., Electrochem Commun 10 (2008) 1905-1908.[3] Soldati A., Baqué L., Troiani H., Cotaro C., Schreiber A., Caneiro A, Serquis A. Int J Hyd Energy 36 ( 2011) 9180-9188.

Carbonization behavior and mesophase conversion kinetics of coal tar pitch using a low temperature molten salt method

Mesophase pitch can be prepared from coal tar pitch (CTP) with AlCl3–NaCl molten salt mixture at low temperature via the molten salt method. The carbonized and mesophase products were characterized using polarized optical microscope, FTIR, XRD, 13C NMR and TEM. The kinetic parameters of the mesophase conversion were calculated by isothermal kinetics. These experimental results demonstrated that the molten salt catalyzed the mesophase transition and the formation temperature of CTP was lowered to 250°C. An abundance of mesophase spheres formed in the carbonized products when the CTP was treated with molten salt at 280°C for 30min (CTPS-280-30). The optical textures of these carbonized products exhibited mosaic anisotropy and the degree of order was reduced when the heating temperature and holding time were increased. It was found that the building units of CTPS-280-30 mesophase products were parallel molecular layers with a thickness of 0.6–2.5nm, and the building units of CTPS-280-120 were 1–3.5nm in thickness. Naphthene and methylene-bridge structures were found in the mesophase products. The kinetics study showed that the molten salt conversion of CTP to mesophase pitch was first-order kinetic with a low apparent activation energy (40.5kJ/mol).

Carbon Modified Li-rich Cathode Materials Li1.26Fe0.22Mn0.52O2 Synthesized via Molten Salt Method with Excellent Rate Ability for Li-ion Batteries

Li-rich layered oxide cathode Li1.26Fe0.22Mn0.52O2 is synthesized via a low temperature molten salt method, and the carbon modified samples are fabricated through coating sucrose on the precursors with different sucrose ratios. The crystal structure and morphology of the pristine and the carbon modified samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The crystal structure appears as a hexagonal α-NaFeO2 layered structure (space group: R3¯m) and is kept after carbon modified. The carbon element distributes uniformly on the surface of the modified samples verified by Energy Dispersive Spectrometer (EDS). The electrochemical performance of the Li1.26Fe0.22Mn0.52O2 Li-rich cathode materials is greatly improved after carbon modification. The cycling stability of the carbon modified samples is also highly improved compared with the pristine. Particularly the rate performance is enhanced by the appropriate coating content of sucrose (1:6), the discharge capacities are 160mAh/g, 133mAh/g and 78mAh/g at 2C, 3C and 5C rate respectively. They also have 83.4%, 82.5% and 83.4% capacity retention after 50cycles at 2C, 3C and 5C respectively. Electrochemical Impedance Spectroscopy (EIS) results demonstrate that the charge transfer resistance of the carbon modified sample decreases obviously. It is suggested that the carbon modification could minimize the cell polarization and increase the electronic conductivity of the Li-rich cathode materials. Additionally, the annealing process of sucrose coating may offer much higher local temperature to improve the crystallization and volatile the excess Li source to suppress Li2CO3 impurity formation verified by the result of XPS.

MnO2nano/micro hybrids for supercapacitors: “Nano's Envy, Micro's pride”

The present study provides the first reports on a low temperature molten salt route which can generate unique architecture of MnO2nanospikes arrayed in a peculiar fashion to form micron sized ball morphology.

Low temperature molten salt synthesis of anatase TiO2 and its electrochemical properties

Abstract This study investigates the electrochemical properties of TiO 2 nanoparticles that were obtained using molten salt method (MSM) synthesis when applied as anodic material for lithium-ion batteries. TiO 2 nanoparticles were synthesized from 0.62LiNO 3 :0.38LiOH molten salt at 180 °C for 2 h in air followed by reheating at 300 °C for 2 h in air. Another separate sample was prepared in addition to molten salt and urea was added then heated at 180 °C for 2 h. X-ray diffraction studies showed a single anatase phase, with characteristic lattice parameter values of a = 3.81 A and c = 9.46 A. Cyclic voltammetry studies on the TiO 2 nanoparticles show main cathodic and anodic redox peaks at ~ 1.7 and ~ 1.9 V respectively. Further galvanostatic discharge–charge cycling studies were performed on all samples at a current rate of 30 mA/g. TiO 2 nanoparticles synthesized at 180 °C for 2 h and treated with urea delivered a high reversible capacity of ~ 275 mAh/g, whereas TiO 2 reheated at 300 °C displayed a capacity of ~ 215 mAh/g. In both compounds capacity fading was found to be at 9.8 to 15% between 5 and 60 cycles.

Low temperature preparation of tungsten nanoparticles from molten salt

Tungsten (W) nanoparticles were synthesised by using a novel low temperature molten salt technique. Na2WO4 and Al were used as starting materials, and NaCl, KCl, and NaF used to form the reaction media. Among the three salts, NaF showed the best accelerating effect in the W formation. When it was used alone, phase pure W could be produced after 4h at 850°C. On the other hand, when it was combined with the other two salts (forming a NaCl–KCl–NaF eutectic salt), phase pure W nanoparticles could be produced at as low as 650°C. As no water-insoluble by-product phases formed in the final samples, acid leaching which has to be used by many other techniques previously proposed, can be avoided. In addition, the by-product NaAlO2, happening to be the key intermediate product phase in the Bayer process, could be further used to prepare two important industrial materials Al2O3 and Na2CO3, adding more value to the molten salt technique developed with this work.