Electrochemistry of TiF4 in 1-butyl-2,3-dimethylimidazolium tetrafluoroborate

Electrochemical behaviour of Ti(IV) species in the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BMMImBF₄) was studied by means of chronopotentiometry (CP) and cyclic voltammetry (CV) in melts with different concentrations of TiF₄ (2-35 mol%) within a temperature range of 65-180 °C. The electrochemical reduction of Ti(IV) was suggested to proceed via the sequence of one-electron steps with the formation of poorly soluble low valence intermediates (LVI). LVIs undergo further solid-state electrochemical reduction to Ti metal. Thin Ti coatings on a Pt substrate were thus obtained and characterized by ESEM method. FTIR spectroscopy was used for identification of the electrochemical active species of Ti(IV). The reaction 2BF₄⁻ + TiF₄ ⇔ TiF₆²⁻ + 2BF₃↑ takes place in the concentrated solutions of TiF₄ at elevated temperatures.     

Direct electrochemical reduction of titanium dioxide in Lewis basic AlCl3–1-butyl-3-methylimidizolium ionic liquid

The direct electrochemical reduction of titanium dioxide (TiO₂) to metallic titanium at room temperature is firstly studied in Lewis basic AlCl₃–1-butyl-3-methylimidizolium (AlCl₃–BMIC) ionic liquid. In this study, cyclic voltammetry, potentiodynamic polarization, sampled current voltammetry and X-ray photoelectron spectroscopy (XPS) techniques were utilized. Analysis of the cyclic voltammetry suggested that TiO₂ film can be reduced to metallic Ti. The sampled current voltammetry was applied to elaborate the reduction mechanism and the results showed that this reduction process may include two steps. When the output potential difference of 2.8 V was applied, a TiO₂ cylindrical pellet was partly reduced to metallic Ti. However, due to the very slow reaction rate, there was only about 12 wt% of TiO₂ was reduced during the electrolysis time of 48 h. It was predicted that the process for the direct reduction of solid TiO₂ would be explained as follows: given enough cathode potential, the reduction happened at the cathode/ionic liquids interface, where the oxygen was ionized, then dissolved in the ionic liquid and discharged at the anode, with the metallic Ti left at the cathode.     

Electrochemical production of Ti-Al alloys using TiCl4-AlCl3-1-butyl-3-methyl imidazolium chloride (BmimCl) electrolytes

Electrochemical production of Ti-Al alloys was investigated using TiCl₄-AlCl₃-1-butyl-3-methyl imidazolium chloride (BmimCl) electrolytes (molar ratio 0.019:2:1). The experiments were conducted at different temperatures between 70 and 125 ± 3 °C and at various cell voltages between 1.5 and 3.0 V. Morphology and composition of deposited Ti-Al alloys were characterized using scanning electron microscope (SEM), along with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The Ti-Al alloys containing about 15-27 at% Ti were produced with a current efficiency of about 25-38%. TiCl₃ passivation on electrodes hinders the deposition kinetics and hence very low cathodic current density and cathodic current efficiency was obtained. This study also focused to determine the effect of process variables such as applied voltage, electrolyte composition and temperature on cathode current density, current efficiency, composition and morphology of Ti-Al alloys. The optimized condition for producing finer particle size and high Ti content in Ti-Al alloys was obtained between the applied voltages of 1.5-2.0 V and temperature ranges from 70 to 100 °C.     

Cathodic behaviour of samarium(III) in LiF–CaF2 media on molybdenum and nickel electrodes

The electrochemical behaviour of SmF₃ is examined in molten LiF–CaF₂ medium on molybdenum and nickel electrodes. A previous thermodynamic analysis suggests that the reduction of SmF₃ into Sm proceeds according to a two-step mechanism:

Sm^III + e⁻ = Sm^II

Sm^II + 2e⁻ = Sm

The second step occurs at a potential lower than the reduction potential of Li⁺ ions.

Cyclic voltammetry, chronopotentiometry and square-wave voltammetry were used to confirm this mechanism and the results show that it was not possible to produce samarium metal in molten fluorides on an inert cathode (molybdenum) without discharging the solvent. The electrochemical reduction of SmF₃ is limited by the diffusion of SmF₃ in the solution. The diffusion coefficient was calculated at different temperatures and the values obtained obey Arrhenius’ law.

For the extraction of the samarium from fluoride media, the use of a reactive cathode made of nickel leading to samarium–nickel alloys is shown to be a pertinent route. Cyclic voltammetry and open-circuit chronopotentiometry were used to identify and to characterise the formation of three alloys: liquid Sm₃Ni and a compact layer made of SmNi₃ and SmNi₂.     

Electrodeposition of Ti from TiCl4 in the ionic liquid l-methyl-3-butyl-imidazolium bis (trifluoro methyl sulfone) imide at room temperature: study on phase formation by in situ electrochemical scanning tunneling microscopy

Titanium was electrodeposited from a nominal 0.24 M TiCl₄ in l-methyl-3-butyl-imidazolium bis (trifluoro methyl sulfone) imide ([BMIm]BTA) at room temperature on a Au(1 1 1) substrate. The process of electrodeposition was studied by cyclic voltammetry, chrono amperometry and in situ scanning tunneling microscopy (STM). In a first step TiCl₄ is reacted to TiCl₂, which is subsequently reduced to metallic Ti. Two dimensional (2D) clusters form preferentially on the terraces in the under potential deposition range. 2D clusters presumably of TiCl₃ precipitates grow and coalesce to cover the whole substrate with a 2D film at a substrate potential below −1.1 V versus ferricenium/ferrocene ([Fc]⁺/[Fc]) redox couple. At a potential of −1.8 V a dense layer of three dimensional (3D) clusters of titanium of 1-2 nm thickness is formed. The features of the I-U tunneling spectra and the relative reduction of the effective tunneling barrier by 0.8 eV with respect to gold clearly indicate the metallic character of Ti deposits. Observation of circular holes on the Au(1 1 1) substrate after dissolution of the deposited Ti indicates the formation of Au-Ti surface alloying.     

Spectroscopic study of the electrochemical behaviour of tantalum(V) chloride and oxochloride species in 1-butyl-1-methylpyrrolidinium chloride

FTIR spectroscopy was used to identify the oxochloride species of tantalum(V) in ionic liquids and to confirm the correlations between their presence in electrolytes and the changes in the route of electrochemical reduction of tantalum(V). Electrochemical behaviour of the mixtures (x)1-butyl-1-methyl-pyrrolidinium chloride-(1 − x)TaCl₅ at x = 0.80, 0.65, and 0.40 was investigated over the temperature range 90-160 °C with respect to the electrochemical deposition of tantalum and was discussed in terms of spectroscopic data. The mechanism of electrochemical reduction of tantalum(V) in the basic and acidic electrolytes depends strongly on the structure and composition of the electro active species of tantalum(V) defined by the molar composition of ionic liquids and on the competition between tantalum(V) chloride and oxochloride species. In the basic mixture at x = 0.80, with octahedral [TaCl₆]⁻ ions as the electrochemically active species only the first reduction step Ta⁵⁺ → Ta⁴⁺ at −0.31 V was observed. The competitive reduction of tantalum(V) oxochloride species occurs at more anodic potential (−0.01 V) than the reduction of the chloride complexes and can restrict the further reduction of tantalum(IV). In the basic ionic liquid at x = 0.65, the cyclic voltammograms exhibit reduction peaks at −0.31 V and −0.51 V attributed to the diffusion controlled process as [TaCl₆]⁻ + e⁻ → [TaCl₆]²⁻ and [TaCl₆]²⁻ + e⁻ → [TaCl₆]³⁻. The further irreversible reduction of tantalum(III) to metallic state may occur at −2.1 V. In the acidic ionic liquids, at x = 0.40 the electrochemical reduction of two species occurs, TaCl₆⁻ and Ta₂Cl₁₁⁻ and it is limited by two electron transfer for both of them at −0.3 V and −1.5 V, respectively.     

离子液体及其在电化学中的应用

离子液体即在室温或接近室温下呈液态的完全由离子构成的物质,作为环境友好和“可设计性”溶剂正在引起越来越多的重视。它具有熔点低、蒸汽压小、酸性可调及良好的溶解度、粘度和密度等特点。综述了离子液体的组成、分类、性质、制备和纯化,就离子液体在电池技术、电合成、电沉积、电容器等电化学方面的应用和研究进展加以阐述,并对该领域的研究前景作了展望。     

Study of a gold electrode modified by trans-[Ru(NH3)4(Ist)SO4] to produce an electrochemical sensor for nitric oxide

The modification of a gold electrode surface by electropolymerization of trans-[Ru(NH₃)₄(Ist)SO₄]⁺ to produce an electrochemical sensor for nitric oxide was investigated. The influence of dopamine, serotonin and nitrite as interferents for NO detection was also examined using square-wave voltammetry (SWV). The characterization of the modified electrode was carried out by cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM) and SERS techniques. The gold electrode was successfully modified by the trans-[Ru(NH₃)₄(Ist)SO₄]⁺ complex ion using cyclic voltammetry. The experiments show that a monolayer of the film is achieved after ten voltammetric cycles, that NO in solution can coordinate to the metal present in the layer, that dopamine, serotonin and nitrite are interferents for the detection of NO, and that the response for the nitrite is much less significant than the responses for dopamine and serotonin. The proposed modified electrode has the potential to be applied as a sensor for NO.     

Understanding specific effects on the standard potential shifts of electrogenerated species in 1-butyl-3-methylimidazolium ionic liquids

It has been established that the dependence of the E° values in function of the electrochemical media selected for a large amount of reversible redox probes in reduction and also in oxidation. For such a purpose several electroactive substances either in reduction (4-nitrotoluene, 1,3-dinitrobenzene, tetrakis(dimethylamino)ethylene, 1,3,5-trinitrobenzene, and 2,4,6-trinitroanisole) or oxidation (ferrocene, tetrathiofulvalene, tris-4-bromophenylamine, tris-4-tolylamine, and N,N,N′,N′-tetramethyl-para-phenylenediamine) have been studied in aprotic RTILs based on unsymmetrical organic cations (quaternary ammonium cations, such as 1-butyl-3-methyl imidazolium) and a weakly coordinating inorganic anion (anions with low Lewis basicities, e.g., BF₄, PF₆). Ion-pairing effects between imidazolium ions and anions and dianions for the electrochemically generated species, the solvation differences between BF₄⁻/PF₆⁻ cations and dications as well as some different reaction mechanism pathways followed by these electrogenerated species in function of the solvent have also been carefully examined.     

Data acquisition in thermodynamic and electrochemical reduction in a Gd(III)/Gd system in LiF-CaF2 media

The electrochemical reduction of GdF₃ was studied in the LiF-CaF₂ eutectic (77/23 mol%) on a tantalum electrode for various GdF₃ concentrations in the 800-900 °C temperature range. A previous thermodynamic study showed that gadolinium trifluoride is reduced into metal in a one-step process:

Gd(III)+3e⁻=Gd     

[As8W48O184], a new crown-shaped heteropolyanion: Electrochemistry and electrocatalytic properties towards reduction of nitrite

The electrochemical behavior of the new crown-shaped heteropolyanion [As₈W₄₈O₁₈₄]⁴⁰⁻ was investigated. Compared to the analogous complex [P₈W₄₈O₁₈₄]⁴⁰⁻, [As₈W₄₈O₁₈₄]⁴⁰⁻ displayed a close similar behavior. As previously reported for [P₈W₄₈O₁₈₄]⁴⁰⁻, [As₈W₄₈O₁₈₄]⁴⁰⁻ is found to be stable in a large range of pH, roughly from 0 to 8 and found to be slightly more soluble than [P₈W₄₈O₁₈₄]⁴⁰⁻. Comparison between the cyclic voltammetry curves of the two complexes reveals that the potentials of the redox waves of [As₈W₄₈O₁₈₄]⁴⁰⁻ are slightly shifted towards the positive values. Contrary to the high dependence of [P₈W₄₈O₁₈₄]⁴⁰⁻ to buffer capacity of the supporting electrolyte, interestingly, [As₈W₄₈O₁₈₄]⁴⁰⁻ displays less sensitivity. The numerous possibilities for chemical applications opened up by the electrochemistry of this new complex are exemplified here by the good linear relationship between the peak potentials of the redox waves as a function of pH and, by the electrocatalytic reduction of nitrite.     

Studies of structure and cycleability of LiMn2O4 and LiNd0.01Mn1.99O4 as cathode for Li-ion batteries

Lithium manganese oxides LiMn₂O₄ and rare earth elements doped LiNd_0.01Mn_1.99O₄ were synthesized by microwave method. The structure and the electrochemical performances of the samples were characterized. XRD data shows both samples exhibit the same pure spinel phase. But due to the introduction of Nd³⁺ ion into the unit cell, the lattice parameter of the Nd-doped spinel was larger than that of the undoped one. The two samples had a similar morphology including small particle size and homogeneous particle distribution as tested by SEM. The cyclic voltammmetry and constant-current charge-discharge tested that Nd-doped spinel displayed a better reversibility and cycleability.     

TiCl4-AlCl3催化1-己烯齐聚的研究

用TiCl4-AlCl3催化1-己烯齐聚,合成聚α-烯烃油。探讨了反应温度、Al与Ti摩尔比、反应时间、TiCl4的浓度对1-己烯齐聚反应的影响。用气相色谱对齐聚物的组成进行分析。结果表明,齐聚的最佳工艺条件为:聚合温度60℃,Al与Ti摩尔比25,催化剂中TiCl4的物质的量浓度7 mmol/L,齐聚时间1 h。齐聚物收率最高达到96%,主要组成是三聚体、四聚体和五聚体。     

Electrochemical behavior of LiCoO2 in a saturated aqueous Li2SO4 solution

The electrochemical behavior of a commercial LiCoO₂ with spherical shape in a saturated Li₂SO₄ aqueous solution was investigated with cyclic voltammetry and electrochemical impedance spectroscopy. Three redox couples at E_SCE = 0.87/0.71, 0.95/0.90 and 1.06/1.01 V corresponding to those found at ELi/Li⁺=4.08/3.83, 4.13/4.03 and 4.21/4.14 V in organic electrolyte solutions were observed. The diffusion coefficient of lithium ions is 1.649 × 10⁻¹⁰ cm² s⁻¹, close to the value in organic electrolyte solutions. The results indicate that the intercalation and deintercalation behavior of lithium ions in the Li₂SO₄ solution is similar to that in the organic electrolyte solutions. However, due to the higher ionic conductivity of the aqueous solution, current response and reversibility of redox behavior in the aqueous solution are better than in the organic electrolyte solutions, suggesting that the aqueous solution is favorable for high rate capability. The charge transfer resistance, the exchange current and the capacitance of the double layer vary with the charge voltage during the deintercalation process. At the peak of the oxidation (0.87 V), the charge transfer resistance is the lowest. These fundamental results provide a good base for exploring new safe power sources for large scale energy storage.     

Dependence of the reliability of electrochemical quartz-crystal nanobalance mass responses on the calibration constant, Cf : analysis of three procedures for its determination

The acquisition of accurate results in use of the electrochemical quartz-crystal nanobalance (EQCN) for surface-electrochemical studies depends on reliability of the value of the calibration constant relating changes of the crystal oscillator frequency to the specific surface mass change resulting from some chemisorption or electrosorption process. Three electrochemical methods are employed comparatively to determine the calibration constant for use of an EQCN. In the present paper, study of electrodeposition/electrodissolution of silver on Pt(poly) electrode surfaces provides a means of determining values of the calibration constant for the EQCN response using cyclic voltammetry, chronopotentiometry and chronoamperometry. The experimentally determined value of the calibration constant (C_f) is found to depend on the electrochemical methodology and technique used for its measurement as well as the thickness of the Ag deposit. Use of these three complementary procedures applied under well-defined conditions provides a basis for adoption of a preferred and reliable procedure for determination of the calibration constant; the resulting mean value is precise and very reproducible.     

Hydrogen bioelectrooxidation in ionic liquids: From cytochrome c3 redox behavior to hydrogenase activity

Electrochemistry of polyheme bacterial cytochrome c₃ and catalytic oxidation of hydrogen by two different bacterial [NiFe] hydrogenases were investigated for the first time in pure room-temperature ionic liquids (RTILs) as electrolyte. Direct electrochemical response of Desulfovibrio vulgaris Hildenborough cytochrome c₃ (DvH cytc₃) adsorbed at a pyrolytic graphite (PG) electrode was observed in the RTILs used in this work: 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4), 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EmimNTf2). The electrochemical signal differed however from that obtained in aqueous buffer, and depended on the type of RTIL. UV–vis measurements as well as transfer experiments from aqueous buffer to RTILs or RTILs to aqueous buffer strongly suggested that the protein was not denatured in the presence of RTILs. EmimNTf2, as a hydrophobic non-water-miscible RTIL, was demonstrated to stabilize the native form of DvH cytc₃. Moreover it allowed an amount of electroactive DvH cytc₃ 30-fold higher than observed in aqueous buffer. Catalytic oxidation of H₂ via Desulfovibrio fructosovorans [NiFe] hydrogenase (Df Hase) mediated by DvH cytc₃ failed however. Further investigation suggested that Df Hase could be inhibited in the presence of RTILs. Reasons for such an inhibition were explored, including the blocking up of the substrate channels. By using hyperthermophilic [NiFe] membrane-bound hydrogenase from Aquifex aeolicus (Aa Hase) an efficient direct catalytic oxidation process was obtained in mixed aqueous buffer/RTILs electrolytes, although direct H₂ oxidation was not observed in pure RTIL. Chronoamperometric experiments showed that Aa Hase could afford 80% RTILs in aqueous buffer, thus giving the opportunity of future electrolytes with uncommon and variable properties for biofuel cell design.     

Electrochemical storage of polypyrrole-Fe2O3 nanocomposites in ionic liquids

Electroactive polypyrrole-Fe₂O₃ nanocomposite materials were prepared by chemical polymerization of pyrrole in aqueous Fe₂O₃ colloidal solution, using FeCl₃ as oxidant and tosylate anions (TS) as doping agent. The nanocomposite material named (PPyTSNC) was studied by X-ray diffraction analysis, Fourier Transform Infra-Red spectroscopy and thermogravimetric analysis. Their electrochemical storage properties were investigated on composite electrodes using 80% in weight of active materials in different immidazolium and pyrrolidinium based room temperature ionic liquids (RTILs) as electrolytes. Cyclic voltammetry and constant current charge discharge cycling showed high charge storage properties of the nanocomposite based electrodes in 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide (EMITFSI) and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₄TFSI) (respectively 72 mAh/g and 62 mAh/g at 1 mA/cm² discharge current) which are more than twice higher than the values obtained with pure PPy. These improvements in capacities have been attributed to the PPyTSNC morphology modification which ensures a large incorporation of the electrolyte inside the nanostructure. The specific capacitances of the nanocomposite electrodes reached 210 F/g and 190 F/g in EMITFSI and PYR₁₄TFSI and their cyclability has shown only 3-5% capacitance loss after one thousand cycles for both ionic liquids.     

离子液体在电化学中的应用

离子液体作为新型绿色环保溶剂,在电化学中的应用正在引起越来越多的关注。就离子液体在电池技术、电合成、电沉积、电容器等方面的应用和研究进展加以阐述,并对该领域的研究前景作了展望。     

Investigations on electroreduction of TiCl4 in dimethylsulfoxide

The process of electroreduction of TiCl₄ in DMSO has been investigated by cyclic voltammetry and rde methods. It has been found that the first step of the cathodic reaction is reduction of Ti(IV) to Ti(III) with α = 0.38 and k_f = 6.5210^?4 cms^?1. It has also been found that a secondary chemical reaction follows the TiCl₄ reduction in DMSO. Products of these reactions may behave as inhibitors of cathodic processes and in consequence the rate of the latter decreases. The mechanism of electroreduction of TiCl₄ to Ti(III), Ti(II) and Ti(0) has been suggested.The purpose of the investigation was to determine the effect of solvent type on the kinetics and the mechanism of the electroreduction process of TiCl₄. The results obtained with the use of acetonitrile (AN) and dimethylformamide (DMF) solutions have been discussed previously (Electrochim. Acta25, 1209 (1980) and Elektrokhimya (1981), in press).     

Synthesis and electrochemical characterizations of nano-scaled Zn doped LiMn2O4 cathode materials for rechargeable lithium batteries

The LiZn_xMn_2−xO₄ (x = 0.00-0.15) cathode materials for rechargeable lithium-ion batteries were synthesized by simple sol-gel technique using aqueous solutions of metal nitrates and succinic acid as the chelating agent. The gel precursors of metal succinates were dried in vacuum oven for 10 h at 120 °C. After drying, the gel precursors were ground and heated at 900 °C. The structural characterization was carried out by X-ray powder diffraction and X-ray photoelectron spectroscopy to identify the valance state of Mn in the synthesized materials. The sample exhibited a well-defined spinel structure and the lattice parameter was linearly increased with increasing the Zn contents in LiZn_xMn_2−xO₄. Surface morphology and particle size of the synthesized materials were determined by scanning electron microscopy and transmission electron microscopy, respectively. Electrochemical properties were characterized for the assembled Li/LiZn_xMn_2−xO₄ coin type cells using galvanostatic charge/discharge studies at 0.5 C rate and cyclic voltammetry technique in the potential range between 2.75 and 4.5 V at a scan rate of 0.1 mV s⁻¹. Among them Zn doped spinel LiZn_0.10Mn_1.90O₄ has improved the structural stability, high reversible capacity and excellent electrochemical performance of rechargeable lithium batteries.