Co-deposition of Al-Cr-Ni alloys using constant potential and potential pulse techniques in AlCl3-NaCl-KCl molten salt

To improve the oxidation resistance of TiAl intermetallic compound under high temperature condition, cathodic co-deposition of Al-Cr and Al-Ni alloy was carried out by constant potential control or potential pulse control in AlCl₃-NaCl-KCl molten salt containing CrCl₂ and/or NiCl₂ at 423 K. Cathodic reduction of Ni and Cr starts at potential of 0.8 and 0.15 V versus Al/Al³⁺ in the molten salt, respectively. The co-deposition of Al, Cr, and Ni occurred at potentials more negative than −0.1 V to form a mixture of intermetallic compounds of Cr₂Al, Ni₃Al, and Al₃Ni. Concentration of Cr in the deposit was enhanced to 43 at% at −0.1 V; however, concentration of Ni in the deposit was 6 at% at the same potential. The concentration of Ni further decreased with more negative potential to 1 at% at −0.4 V. The potential pulse technique enhanced the Ni concentration in the deposit to about 30 at%, due to anodic dissolution of Al content from the deposit at the higher side of potential on the potential pulse electrolysis.     

Electrochemical formation of Sm-Co alloys by codeposition of Sm and Co in a molten LiCl-KCl-SmCl3-CoCl2 system

Electrocodeposition of Sm and Co on a Cu substrate was investigated in a molten LiCl-KCl-SmCl₃ (0.5 mol.%)-CoCl₂ (0.1 mol.%) system at 723 K. Phase of the deposited Sm-Co alloys could be controlled by electrolysis potential. SmCo₃ was formed on a Cu substrate by potentiostatic electrolysis in the potential range of 0.20-0.90 V (vs. Li⁺/Li). Sm₂Co₁₇ was obtained in the potential range of 0.90-1.50 V.     

Composition-dependent characterization and optimal control of electrodeposited Bi2Te3 films for thermoelectric application

A method to control composition of Bi₂Te₃ films by mass transfer manipulation has been developed. The film composition can be varied by a diffusion-controlled method, which is related to the change of Bi³⁺/HTeO₂⁺ ratios in a controlled diffusion layer. A homogeneous and dense film with precise chemical composition could thus be obtained under constant electrode polarization. Meanwhile, the solo dependence of film properties on composition change of both Te-rich and Bi-rich films were investigated. Firstly, the studies of XRD and FE-SEM showed that different Te contents in deposit would lead to different dimensions of unit cell and grain sizes. The Seebeck coefficient increased apparently when the Te content was over 60 at.% Te. Te-rich films had higher carrier concentration but slower mobility than Bi-rich films. Inverse relations were observed between carrier concentration and carrier mobility and between Seebeck coefficient and conductivity. Therefore, an optimal power factor of 7 × 10⁻⁴ W/m K² was realized near the stoichiometric Bi₂Te₃.     

Orientation-controlled synthesis and characterization of Bi2Te3 nanofilms, and nanowires via electrochemical co-deposition

An electrochemical deposition technique based on co-deposition was used to deposit preferentially oriented Bi₂Te₃ nanostructures (nanofilm, and nanowire). The shared underpotential deposition (UPD) potentials for both Bi and Te co-deposition were determined by cyclic voltammetric measurements. The scanning probe microscopy (scanning tunneling microscopy (STM) and atomic force microscopy (AFM)) and the X-ray diffraction (XRD) data indicated that the electrodeposition of Bi₂Te₃ results in nanofilm-structured deposits with a preferential orientation at (0 1 5) and nanowired-structured deposits with a preferential orientation at (1 1 0) in acidic and basic (in the presence of ethylenediaminetetraacetic acid (EDTA)) medium, respectively. The results show that the nucleation and growth mechanism follows 3D mode in acidic solutions and 2D mode in basic solution containing EDTA additive. The optical characterization performed by reflection absorption Fourier transform infrared (RA-FTIR) spectroscopy showed that the band gap energy of Bi₂Te₃ nanostructures depends on the thickness, size, and shape of the nanostructures and the band gap increases as the deposition time decreases. Moreover, the quantum confinement is strengthened in the wire-like deposits relative to the film-like deposits. Energy dispersive X-ray spectroscopy (EDS) analysis demonstrated that Bi₂Te₃ nanostructures were always in 2:3 stoichiometry, and they were made up of only pure Bi and Te.     

FT-IR studies on interactions of AlCl3 with PEO-NaSCN polymer electrolytes

Solid polymer electrolytes are potentially useful electrolytes to be applied in high-energy batteries. In the present work, a novel polymer electrolyte, polyethylene oxide (PEO)-NaSCN-AlCl₃, was prepared and investigated by FT-IR spectroscopic techniques. Based on the FT-IR data, the bands in the CN stretching envelope have been assigned and the effect of AlCl₃ on ion-ion and ion-polymer interactions in the polymer electrolyte has been examined. It is shown that the Lewis acid-base interaction of AlCl₃ with SCN¹⁻ leads to the formation of the complex anions AlCl₃SCN⁻ and Al₂Cl₆SCN⁻, depending on the content of AlCl₃ and/or NaSCN in PEO; the preferential interactions of AlCl₃ with crystal complex P(EO)₃NaSCN occur in PEO-NaSCN-AlCl₃ electrolytes; the AlCl₃-NaSCN complex anions can play a plasticization role in PEO-NaSCN-AlCl₃ electrolyte, and are expected to be a important factor to improve the conductivity and to enhance the cation transference number. In addition, the interactions between AlCl₃ and ether oxygen of PEO were analyzed, and their effect on ionic association was also discussed.     

Electrodeposition and characterization of Bi2Se3 thin films by electrochemical atomic layer epitaxy (ECALE)

Bismuth selenide thin films were grown on Pt substrate via the route of electrochemical atomic layer epitaxy (ECALE) in this work for the first time. The electrochemical behaviors of Bi and Se on bare Pt, Se on Bi-covered Pt, and Bi on Se-covered Pt were studied by cyclic voltammetry and coulometry. A steady deposition of Bi₂Se₃ could be attained after negatively stepped adjusting of underpotential deposition (UPD) potentials of Bi and Se on Pt in the first 40 deposition cycles. X-ray diffraction (XRD) analysis indicated that the films were single phase Bi₂Se₃ compound with orthorhombic structure, and the 2:3 stoichiometric ratio of Bi to Se was verified by EDX quantitative analysis. The optical band gap of the as-deposited Bi₂Se₃ film was determined as 0.35 eV by Fourier transform infrared spectroscopy (FTIR), which is consistent with that of bulk Bi₂Se₃ compound.     

Electrodeposition of tungsten from ZnCl2-NaCl-KCl-KF-WO3 melt and investigation on tungsten species in the melt

The electrodeposition of tungsten in ZnCl₂-NaCl-KCl-KF-WO₃ melt at 250 °C was further studied to obtain a thicker deposit. In the ordinary electrolysis at 0.08 V vs. Zn(II)/Zn, the current density decreased from 1.2 mA cm⁻² to 0.3 mA cm⁻² in 6 h. A thickness of the obtained tungsten layer was 2.1 μm and the estimated current efficiency was 93%. A supernatant salt and a bottom salt were sampled after 6 h from the melting and were analyzed by ICP-AES and XRD. It was found that the soluble tungsten species slowly changes to insoluble ones in the melt. The soluble species was suggested to be WO₃F⁻ anion. One of the insoluble species was confirmed to be ZnWO₄ and the other one was suggested to be K₂WO₂F₄. Electrodeposition was carried out under the same condition as above except for the intermittent addition of WO₃ every 2 h. The current density was kept at the initial value and the thickness was 4.2 μm. The intermittent addition of WO₃ was confirmed to be effective to obtain a thicker tungsten film.     

Preparation and characterization of Bi2Se3 nanowires by electrodeposition

The electrodeposition of Bi₂Se₃ nanowires on an anodic aluminum oxide template was investigated by cyclic voltammetry in a tartaric acid aqueous solution. The electrochemical behavior of the Bi₂Se₃ nanowires in the electrolytic solution was also investigated using cyclic voltammetry, and the underpotential deposition mechanism of the Bi₂Se₃ nanowires was determined. According to the cyclic voltammetric curves, −0.20 V vs. SCE (saturated calomel electrode) was chosen as the deposition potential of the Bi₂Se₃ nanowires. The ratio of Bi to Se is nearly 2:3, verified by energy-dispersive X-ray spectroscopy and with the addition of surfactant. X-ray diffraction, scanning electron microscopy, selected-area electron diffraction and high-resolution transmission electron microscopy indicate that annealing can improve the crystallinity and chemical composition of Bi₂Se₃ nanowires. Surfactant can also improve the surface morphology and composition of the Bi₂Se₃ nanowires.     

Electrodeposition and electrochemical characterisation of thick and thin coatings of Sb and Sb/Sb2O3 particles for Li-ion battery anodes

The possibilities to electrodeposit thick coatings composed of nanoparticles of Sb and Sb₂O₃ for use as high-capacity anode materials in Li-ion batteries have been investigated. It is demonstrated that the stability of the coatings depends on their Sb₂O₃ concentrations as well as microstructure. The electrodeposition reactions in electrolytes with different pH and buffer capacities were studied using chronopotentiometry and electrochemical quartz crystal microbalance measurements. The obtained deposits, which were characterised with XRD and SEM, were also tested as anode materials in Li-ion batteries. The influence of the pH and buffer capacity of the deposition solution on the composition and particle size of the deposits were studied and it is concluded that depositions from a poorly buffered solution of antimony-tartrate give rise to good anode materials due to the inclusion of precipitated Sb₂O₃ nanoparticles in the Sb coatings. Depositions under conditions yielding pure Sb coatings give rise to deposits composed of large crystalline particles with poor anode stabilities. The presence of a plateau at about 0.8 V versus Li⁺/Li due to SEI forming reactions and the origin of another plateau at about 0.4 V versus Li⁺/Li seen during the lithiation of thin Sb coatings are also discussed. It is demonstrated that the 0.4 V plateau is present for Sb coatings for which the (0 1 2) peak is the main peak in the XRD diffractogram.     

Synthesis of NiWO4 nano-particles in low-temperature molten salt medium

Nickel tungstate (NiWO₄) nano-particles were successfully synthesized at low temperatures by a molten salt method, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet visible spectra techniques (UV–vis), respectively. The effects of calcining temperature and salt quantity on the crystallization and development of NiWO₄ crystallites were studied. Experimental results showed that the well-crystallized NiWO₄ nano-particles with about 30 nm in diameter could be prepared at 270 °C with 6:1 mass ratio of the salt to NiWO₄ precursor. XRD analysis confirmed that the product was a pure monoclinic phase of NiWO₄ with wolframite structure. UV–vis spectrum revealed that NiWO₄ nano-particles had good light absorption properties in both ultraviolet and visible light region.     

Electrodeposition behavior of nickel and nickel-zinc alloys from the zinc chloride-1-ethyl-3-methylimidazolium chloride low temperature molten salt

The electrodeposition of nickel and nickel-zinc alloys was investigated at polycrystalline tungsten electrode in the zinc chloride-1-ethyl-3-methylimidazolium chloride molten salt. Although nickel(II) chloride dissolved easily into the pure chloride-rich 1-ethyl-3-methylimidazolium chloride ionic melt, metallic nickel could not be obtained by electrochemical reduction of this solution. The addition of zinc chloride to this solution shifted the reduction of nickel(II) to more positive potential making the electrodeposition of nickel possible. The electrodeposition of nickel, however, requires an overpotential driven nucleation process. Dense and compact nickel deposits with good adherence could be prepared by controlling the deposition potential. X-ray powder diffraction measurements indicated the presence of crystalline nickel deposits. Non-anomalous electrodeposition of nickel-zinc alloys was achieved through the underpotential deposition of zinc on the deposited nickel at a potential more negative than that of the deposition of nickel. X-ray powder diffraction and energy-dispersive spectrometry measurements of the electrodeposits indicated that the composition and the phase types of the nickel-zinc alloys are dependent on the deposition potential. For the Ni-Zn alloy deposits prepared by underpotential deposition of Zn on Ni, the Zn content in the Ni-Zn was always less than 50 atom%.     

Investigations on the electrodeposition behaviors of Bi0.5Sb1.5Te3 thin film from nitric acid baths

The electrochemical reduction process of Bi³⁺, HTeO₂⁺, Sb^III and their mixtures in nitric acid medium was investigated by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The reduction products electrodeposited at various potentials were examined using X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The results show that cathodic process in the nitric acid solution containing Bi³⁺, HTeO₂⁺ and Sb^III involves the following reduction reactions in different polarizing potential ranges: In low polarizing potential ranges, Te⁰ is formed firstly on the electrode surface through the electrochemical reduction of HTeO₂⁺; with the negative shift of the cathodic polarizing potential, the reduction reaction of Bi³⁺ with Te⁰ to form Bi₂Te₃ takes place; when the cathodic polarizing potential is negative enough, Bi³⁺ and Sb^III react with Te⁰ to form Bi_0.5Sb_1.5Te₃. The results indicate that Bi_0.5Sb_1.5Te₃ films can be fabricated by controlling the electrodepositing potential in a proper high potential ranges.     

Electrolytic reduction behavior of U3O8 in a molten LiCl-Li2O salt

An electrolytic reduction of U₃O₈ in a molten LiCl-Li₂O salt was investigated using the electrochemical techniques of cyclic voltammetry (CV) and chronopotentiommetry (CP). The electrolytic reduction of U₃O₈ powder exhibited a different behavior when the initial current density was higher than for 10 g U₃O₈/batch run. Two kinds of reduction mechanisms, an electro-metallothermic reduction (EMR) and a direct electrochemical reduction (DER) were adopted to explain the resultant behavior. Current efficiencies and reduction products were obtained by a series of constant current runs. Current efficiencies, evaluated for a reduction side, were estimated to be more than 75% throughout a series of constant current runs and lithium uranium oxides (lithium uranates) were detected during the U₃O₈ reduction to metallic uranium.     

Effect of salt species on characterization of Bi3NbTiO9 powders prepared by molten salt method

The carbonates, chloride and sulphate salts were chosen as fluxes to synthesize Bi₃NbTiO₉ (BNTO) powders at low temperature by the molten salt synthesis (MSS) method and the influence of salt species on the formation and powder characteristics of BNTO was investigated in this paper. The results showed that for the sulphate flux the formed particle size was the largest among all the used salts, but the fastest particle growth rate was found in the carbonates flux. Investigations on morphology characteristics of powders showed the plate-like powders with smaller particle size were synthesized in the chloride flux, but the powders obtained in the sulphate flux were shown to be irregular blocks in shape. Further studies indicated the salt content had a strong influence on crystallization of BNTO from the chloride flux.     

Nucleation and surface morphology of aluminum-lanthanum alloy electrodepsited in a LaCl3-saturated AlCl3-EtMeImCl room temperature molten salt

The cathodic polarization curve on a tungsten disk electrode was measured in a LaCl₃-saturated AlCl₃-EtMeImCl [1-ethyl-3-methylimidazolium chloride] melt (N=0.667: N is molar fraction of AlCl₃) at 298 K. The deposition overpotential of aluminum increases compared with the curve obtained before adding LaCl₃. It was found that the nucleation/growth process is instantaneous nucleation from chronoamperometric data. When galvanostatic electrolysis was performed in the LaCl₃-saturated melt, the strong orientation of (200) for the electrodeposits is observed at low current densities (≤7.5 mA cm⁻²). On the other hand, the normalized integrated intensity of XRD for (200) and (220) reflections has similar strength at high current densities (≥10.0 mA cm⁻²). The electodeposits become denser than those obtained in the original melt. In particular, very smooth surface is obtained in the case of 15.0 mA cm⁻² with stirring the bath.     

Synthesis of Bi0.5(Na0.7K0.2Li0.1)0.5TiO3 powders through the molten salt method

The Bi_0.5(Na_0.7K_0.2Li_0.1)_0.5TiO₃ powder synthesis through molten salt method was investigated in the temperature range of 650–700 °C for 2–4 h. The XRD results indicated that the optimal synthesizing temperature for molten salt method was 700 °C, significantly lower than that for conventional processing route of solid state reaction method, where a calcining temperature of 850 °C was needed. The SEM results revealed better crystallization of the powders obtained through molten salt method, compared with those through the conventional processing route of solid state reaction method.     

A facile molten salt route to K2Nb8O21 nanoribbons

Single-crystalline K₂Nb₈O₂₁ nanoribbons with width of 100–500 nm and thickness of ca. 30 nm, and length up to tens of micron, have been successfully synthesized by simply calcining Nb₂O₅ powders in molten KCl, and characterized with XRD, SEM, SEM, HRTEM and selected-area electron diffraction technique. The growth direction of the obtained K₂Nb₈O₂₁ nanoribbons was determined to be the 〈1 0 0〉 crystallography direction.     

Molten salt synthesis of α-Al2O3 platelets using NaAlO2 as raw material

α-Al₂O₃ platelets were prepared by a molten salt synthesis method when NaAlO₂ was used as raw material. The effects of the stirring rate during the gel preparation, heating temperature, type and addition amount of molten salts, addition of plate-like α-Al₂O₃ seeds, additives such as TiOSO₄ and Na₃PO₄·12H₂O on the morphology of α-Al₂O₃ were studied. High stirring rate during the gel preparation and high heating temperature not only help to restrain the overlapping of α-Al₂O₃ platelets, but also improve the size distribution. When the heating temperature increases to 1200 °C, most of α-Al₂O₃ platelets are hexagonal in its morphology, and the size of platelets becomes relatively uniform. When Na₂SO₄-K₂SO₄ flux is used instead of NaCl-KCl flux, it is easy to obtain α-Al₂O₃ platelets with a big size. When the molar ratio of salt to final Al₂O₃ powders increases to 4:1, most of α-Al₂O₃ platelets are hexagonal, and the overlapping of powders is inhibited. The addition of a small amount of plate-like seeds has a significant effect on the size of α-Al₂O₃ platelets. With the increase of seed amount, the diameter of α-Al₂O₃ platelets tends to decrease. The addition of 5.45 wt.% TiOSO₄ results in the formation of hexagonal α-Al₂O₃ platelets with an average diameter of 5.1 μm and an average thickness of 1.4 μm. Thin α-Al₂O₃ platelets with a discal shape are obtained owing to the co-addition of 0.51 wt.% Na₃PO₄·12H₂O and 3 wt.% TiOSO₄.     

Electrochemical aspects of depositing Sb2Te3 compound on Au substrate by ECALE

Deposition of Sb₂Te₃ thin films on polycrystalline Au substrates by electrochemical atomic layer epitaxy (ECALE) is described in this paper. Electrochemical aspects were characterized by means of cyclic voltammetry, anodic potentiodynamic scanning and coulometry. A steady ECALE deposition for Sb₂Te₃ compound could be attained after negatively adjusting the underpotential deposition (UPD) potentials of Sb and Te on Au in steps over the initial 40 cycles, and the potentials could be kept constant for the following deposition. A 400 cycle deposit, which was grown with the steady deposition potentials, was proved to be a single phase Sb₂Te₃ compound by X-ray diffraction analysis and SEM observation shows the deposit consisted of nanoscale particles with average size about 100 nm. The 2:3 stoichiometric ratio of the deposit was further verified by energy dispersive X-ray (EDX) quantitative analysis.     

Electrodeposition of bismuth telluride films from a nonaqueous solvent

The author examines Bi₂Te₃ deposition from a DMSO solution containing TeCl₄ and Bi(NO₃)₃ × 5H₂O by means of cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). Accumulated charges and related mass changes for Bi₂Te₃ deposition on working electrodes are measured in situ. The deposit composition is more dependent on Te⁴⁺ concentrations in DMSO solution than on the potential. In a DMSO solution containing 0.01 M Te⁴⁺ and 0.0075 M Bi³⁺, Bi₂Te₃ deposits were obtained in the potential range between −0.2 and −0.8 V vs. Ag/AgCl. In a DMSO solution containing 0.05 M Te⁴⁺ and 0.0375 M Bi³⁺, Te-rich deposits were formed from −0.2 to −0.8 V vs. Ag/AgCl.