Electrochemistry of TiCl4 in 1-butyl-2,3-dimethyl imidazolium azide

Electrochemical behaviour of titanium tetrachloride solutions in 1-butyl-2,3-dimethyl imidazolium azide (BMMImN₃) at 65 °C has been examined. Ti(IV) reduction was studied with chronopotentiometry and cyclic voltammetry methods in melts with different concentrations of TiCl₄. According to IR spectra, Ti(IV) exists in form of a hexaazidotitanate complex. The electrochemical reduction of this complex was found to proceed irreversibly to Ti(III) species only. Diffusion coefficients of Ti(IV) in this ionic liquid at temperature 65 °C were calculated based on the chronopotentiometry measurements at different TiCl₄ concentrations (D_Ti(IV) = 1.3 ± 0.6 × 10⁻⁶ cm² s⁻¹).     

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.     

Electrochemical aspects of black chromium electrodeposition from 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid

The electrochemical behaviour of trivalent chromium (Cr³⁺) in 1-butyl-3-methylimidazolium tetrafluoroborate [BMIm][BF₄] ionic liquid solutions was studied by cyclic voltammetry and chronoamperometry. The reduction of Cr³⁺ occurs in two steps, Cr³⁺ to Cr²⁺ and Cr²⁺ to Cr⁰, respectively. The first step is quasi-reversible with a diffusion coefficient of Cr³⁺ in solution of 3.13 × 10⁻⁸ cm² s⁻¹ at 303 K and 25.8 × 10⁻⁸ cm² s⁻¹ at 358 K, estimated from cyclic voltammetry data.Black chromium films were electrodeposited on copper, stainless steel and carbon steel substrates at a constant potential of −1.5 V vs Pt quasi-reference electrode. The films consist of aggregates of nanosized particles. The coatings in the as-deposited condition present an amorphous structure but after annealing for 4 h, a nanocrystalline Cr₂O₃ phase is formed, with an average crystallite size of 17 nm.     

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.     

Diffusion coefficient of ferrocene in 1-butyl-3-methylimidazolium tetrafluoroborate - concentration dependence and solvent purity

The ionic liquid l-butyl-3-methylimidazolium tetrafluoroborate is used as electrolyte in the electrochemical determination of the diffusion coefficient of ferrocene as a function of concentration by cyclic voltammetry and chronoamperometry. An improved synthesis of the room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate is described, which yields a product of high purity suitable for electrochemical purposes. A qualitative color test is discussed which allows the simple detection of silver ion contaminations. The diffusion coefficient of ferrocene appears to be concentration dependent in the solvent chosen.     

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。     

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.     

1-Alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids as highly safe electrolyte for Li/LiFePO4 battery

Several 1-alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids (alkyl-DMimTFSI) were prepared by changing carbon chain lengths and configuration of the alkyl group, and their electrochemical properties and compatibility with Li/LiFePO₄ battery electrodes were investigated in detail. Experiments indicated the type of ionic liquid has a wide electrochemical window (−0.16 to 5.2 V vs. Li⁺/Li) and are theoretically feasible as an electrolyte for batteries with metallic lithium as anode. Addition of vinylene carbonate (VC) improves the compatibility of alkyl-DMimTFSI-based electrolytes towards lithium anode and LiFePO₄ cathode, and enhanced the formation of solid electrolyte interface to protect lithium anodes from corrosion. The electrochemical properties of the ionic liquids obviously depend on carbon chain length and configuration of the alkyl, including ionic conductivity, viscosity, and charge/discharge capacity etc. Among five alkyl-DMimTFSI-LiTFSI-VC electrolytes, Li/LiFePO₄ battery with the electrolyte-based on amyl-DMimTFSI shows best charge/discharge capacity and reversibility due to relatively high conductivity and low viscosity, its initial discharge capacity is about 152.6 mAh g⁻¹, which the value is near to theoretical specific capacity (170 mAh g⁻¹). Although the battery with electrolyte-based isooctyl-DMimTFSI has lowest initial discharge capacity (8.1 mAh g⁻¹) due to relatively poor conductivity and high viscosity, the value will be dramatically added to 129.6 mAh g⁻¹ when 10% propylene carbonate was introduced into the ternary electrolyte as diluent. These results clearly indicates this type of ionic liquids have fine application prospect for lithium batteries as highly safety electrolytes in the future.     

Electrochemical synthesis of poly(p-phenylene) and poly(p-phenylene)/TiO2 nanowires in an ionic liquid

This study shows for the first time that poly(p-phenylene) (PPP) nanowires can be easily obtained by electrochemical synthesis at room temperature. The method involves the template assisted electropolymerization of benzene in the air and water stable ionic liquid 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIm]FAP). Track-etched polycarbonate membranes (PC) with an average pore diameter of 90 nm were used as templates. Dense and highly flexible bundles of PPP nanowires with a high aspect ratio (>160) were easily obtained by this method. In addition, we present here our first results to obtain PPP/TiO₂ nanowires by the combination of a sol–gel technique with electropolymerization. HR-SEM, TEM and EDX were used for the structural characterization of the nanowires.     

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.     

In situ STM studies of Ga electrodeposition from GaCl3 in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide

In the present paper the electrodeposition of Ga on Au(1 1 1) from 0.5 mol L⁻¹ GaCl₃ in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py_1,4]TFSA, has been investigated by in situ scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and cyclic voltammetry (CV). The CV shows two redox processes: the one at −0.3 V vs. Pt is attributed to a Ga deposition on a Ga layer formed during an electroless deposition process at OCP and/or to the formation of a Au–Ga alloy; the other one at −0.9 V is due to the bulk deposition of Ga. The XPS measurement reveals that there is an oxide layer on the top of the gallium electrodeposit due to exposure to air. In situ STM measurements show that the first layer of the Ga deposit consists of islands of 10–30 nm in width and several nanometers in height surprisingly the result of an electroless deposition at the OCP. If the electrode potential is further reduced the bulk deposition of Ga sets in.     

1-丁基-3-甲基咪唑四氟硼酸盐离子液体的合成与表征

以N-甲基咪唑和1-溴代正丁烷为原料,两步合成法制备了离子液体[bmim]BF4。考察了反应时间、反应温度、原料配比对中间体1-丁基-3-甲基咪唑溴盐[bmim]Br收率的影响和离子交换时间和离子交换温度对目标产物[bmim]BF4产率的影响。结果表明:①合成中间体[bmim]Br的最佳条件为:反应温度65℃,反应时间16 h,N-甲基咪唑与1-溴代正丁烷的摩尔比为1∶1.1,产品收率可达94.8%;②合成离子液体的最佳条件为:反应温度65℃,反应时间24 h。     

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.     

Electrodeposition of palladium-indium from 1-ethyl-3-methylimidazolium chloride tetrafluoroborate ionic liquid

Voltammetry at a glassy carbon electrode was used to study the electrochemical co-deposition of Pd-In from a chloride-rich 1-ethyl-3-methylimidazolium chloride/tetrafluoroborate air-stable room temperature ionic liquid at 120 °C. Deposition of Pd alone occurs prior to the overpotential deposition (OPD) of bulk In. However, underpotential deposition (UPD) of In on the deposited Pd was observed at the potential same as the deposition of Pd. The UPD of In on Pd was, however, limited by a slow charge transfer rate. Samples of Pd-In alloy coatings were prepared on nickel substrates and characterized by energy dispersive spectroscope (EDS), scanning electron microscope (SEM) and X-ray powder diffraction (XRD). The electrodeposited alloy composition was relatively independent on the deposition potential within the In UPD range. At more negative potentials where the OPD of Pd-In has reached mass-transport limited region, the alloy composition corresponds to the Pd(II)/In(III) composition in the plating bath. The Pd-In alloy coatings obtained by direct deposition of Pd and UPD of In on the deposited Pd appeared to be superior to the Pd-In alloys that were obtained via the co-deposition of Pd and bulk In at OPD potentials.     

Electrodeposition of tin and antimony in 1-ethyl- 3-methylimidazolium tetrafluoroborate ionic liquid

The electrodepositions of Sn(II) and Sb(III) were studied in the [EMIm]BF₄ ionic liquid at ambient temperature. Linear sweep voltammetry (LSV) results indicated that the reductions of Sn(II) and Sb(III) on Pt electrode are electrochemically irreversible. The diffusion coefficients of Sn(II) and Sb(III) in the ionic liquid electrolyte were determined in terms of the LSV data. Tin and antimony ions form simpler Sn(II) chlorocomplex species and higher Sb(III) chlorocomplexes, respectively present in the ionic liquid electrolyte. Energy dispersive X-ray spectroscopy (EDX) analysis revealed that tin and antimony alloys can be electroplated in the ionic liquid electrolyte.     

In situ STM and EQCM studies of tantalum electrodeposition from TaF5 in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide

The electroreduction of 0.5 M TaF₅ on Au(1 1 1) and on polycrystalline gold substrates was investigated at room temperature in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py_1,4]TFSA, by cyclic voltammetry, in situ scanning tunneling microscopy (STM) and electrochemical quartz crystal microbalance (EQCM). The electrochemical reduction of TaF₅ in the employed ionic liquid occurs in several steps. The first redox process is attributed to the reduction of TaF₅ to TaF₃, which likely occurs in the solution, as EQCM indicates no mass change. The electrodeposition of tantalum occurs only in a very narrow potential window and is preceded by the formation of various non-stoichiometric tantalum subhalides. Attempts to deposit micrometer thick tantalum layers at room temperature fail, presumably because of kinetic reasons.     

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.     

Surface tension and viscosity of 1-butyl-3-methylimidazolium iodide and 1-butyl-3-methylimidazolium tetrafluoroborate, and solubility of lithium bromide+1-butyl-3-methylimidazolium bromide in water

The surface tension and viscosity of 1-butyl-3-methylimidazolium iodide ([bmim][I]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) were measured over a temperature range of 298. 15 to 323.15 K. It was found that both the viscosity and surface tension decrease with increasing temperature and that the surface tension and viscosity values of [bmim][I] were higher than those of [bmim][BF₄]. Additionally, the solubility of lithium bromide (2)+1-butyl-3-methylimidazolium bromide ([bmim][Br]) (3) in water (1) was measured at three different mass ratios (w₂/w₃=4 and 7, w₃=0) by using a visual polythermal method. The solubility of the suggested systems was better than that of lithium bromide in water.     

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。