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Ag(I)/Ag electrode reaction in amide-type room-temperature ionic liquids
Abstract
Ag(I)/Ag electrode reaction was investigated in some amide-type room-temperature ionic liquids composed of different cations. The morphology of silver deposits and the electrochemical behavior were not sensitive to the difference in the cations of ionic liquids. On the other hand, it was suggested that the adsorption of bis(trifluoromethylsulfonyl)amide (TFSA−) is more important for electrodeposition of silver in both ionic liquids and aqueous solutions. The diffusion coefficients of silver cation in the ionic liquids indicated the silver cation is surrounded by TFSA− to form a bulky species. The rate of crystal growth of silver particles in the ionic liquids by electrochemical Ostwald ripening was much slower than that in a nitrate aqueous solution, suggesting the charge transfer in the ionic liquids is slower than that in the aqueous solution.
... A cathodic and anodic current observed around 0 V vs Ag wire were attributed to deposition and dissolution of Ag, respectively. 9 The similar cyclic voltammogram was observed for the electrode reaction of Ag(I)/Ag in BMPTFSA containing AgTFSA. 9 The overpotential for the Ag deposition was about 0.15 V, which is probably attributable to the nucleation overpotential on a Pt electrode, as observed in some TFSA --based ionic liquids. ...
... 9 The similar cyclic voltammogram was observed for the electrode reaction of Ag(I)/Ag in BMPTFSA containing AgTFSA. 9 The overpotential for the Ag deposition was about 0.15 V, which is probably attributable to the nucleation overpotential on a Pt electrode, as observed in some TFSA --based ionic liquids. 9 The open circuit potential of a Ag electrode was measured against Ag|Ag(I) in BMPFSA containing different concentrations of Ag(I) at 25°C, as shown in Fig. 2. The Ag(I) concentration was calculated from the electric charge during the potentiostatic anodic oxidation assuming the current efficiency to be 100%. ...
... 9 The overpotential for the Ag deposition was about 0.15 V, which is probably attributable to the nucleation overpotential on a Pt electrode, as observed in some TFSA --based ionic liquids. 9 The open circuit potential of a Ag electrode was measured against Ag|Ag(I) in BMPFSA containing different concentrations of Ag(I) at 25°C, as shown in Fig. 2. The Ag(I) concentration was calculated from the electric charge during the potentiostatic anodic oxidation assuming the current efficiency to be 100%. The open circuit potential depended linearly on the logarithm of the Ag(I) concentration. ...
The electrode reactions of Ag(I)/Ag and ferrocenium/ferrocene (Fc+/Fc) were investigated in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA). The potential of Ag(I)/Ag depended on the logarithm of the concentration of Ag(I), as predicted by the Nernst equation, indicating the Ag(I)/Ag can be used as a reference electrode reaction in BMPFSA. The reversible electrode reaction of Fc+/Fc was observed in BMPFSA by cyclic voltammetry. The donor number of BMPFSA was estimated to be 13 from the difference in the formal potentials of Ag(I)/Ag and Fc+/Fc, indicating the coordination ability of FSA– was slightly stronger than that of bis(trifluoromethylsulfonyl)amide (TFSA–). The diffusion coefficients (D) of Fc and Fc+ were (5.7 ± 0.7) and (3.3 ± 0.2) × 10–7 cm2 s–1, respectively. The ratio of D of Fc+ against that of Fc was smaller than that in TFSA–-type ionic liquids, reflecting the higher charge density of FSA–. The standard rate constant (k0) of Fc+/Fc was estimated to be (5.4 ± 1.1) × 10–3 cm s–1. The apparent activation energy for k0 was close to the activation energy for D, suggesting the electrode reaction of Fc+/Fc can be regarded as the outer sphere electron transfer reaction with a very small reorganization energy.
... [6] In contrast to copper(I) bisA C H T U N G T R E N N U N G (triflyl)imide, silver(I) bis-A C H T U N G T R E N N U N G (triflyl)imide has been completely characterized with the exception of its crystal structure determination. [2,[7][8][9][10][11] Within the last two decades AgNTf 2 has attracted a lot of interest due to its versatility: AgNTf 2 is used as catalyst for a variety of organic transformations, such as C À C-coupling reactions or hydroamination of siloxy alkynes. [12] In addition, AgNTf 2 has been applied as a transfer reagent for the introduction of the NTf 2 À moiety, for example, for metathesis reactions within the preparation of trialkylsilyl and trialkylstannyl bis-A C H T U N G T R E N N U N G (triflyl)imides [2] and of catalytically active cationic gold(I) bisA C H T U N G T R E N N U N G (triflyl)imides, [12] in electrochemical studies [7,8] and for alkene/alkane separation processes. ...
... [2,[7][8][9][10][11] Within the last two decades AgNTf 2 has attracted a lot of interest due to its versatility: AgNTf 2 is used as catalyst for a variety of organic transformations, such as C À C-coupling reactions or hydroamination of siloxy alkynes. [12] In addition, AgNTf 2 has been applied as a transfer reagent for the introduction of the NTf 2 À moiety, for example, for metathesis reactions within the preparation of trialkylsilyl and trialkylstannyl bis-A C H T U N G T R E N N U N G (triflyl)imides [2] and of catalytically active cationic gold(I) bisA C H T U N G T R E N N U N G (triflyl)imides, [12] in electrochemical studies [7,8] and for alkene/alkane separation processes. [9,13,14] With respect to silvers lighter homologue copper, the existence of [Cu(CO) n -A C H T U N G T R E N N U N G (NTf 2 )] (n = 1-3) was reported, of which the dicarbonyl complex was crystallographically characterized. ...
... [37] In the case of AgNTf 2 (3) manifold preparation methods are described in the literature. [2,[7][8][9][10][11] In addition, compound 3 has been characterized by means of NMR [2,9,11] and IR [2,9] spectroscopies, ESI mass spectrometry, [9] and elemental analysis. [2,8,10] Within the herein presented studies, two different synthetic strategies were applied for the preparation of AgNTf 2 (3). ...
The chemistry of coinage metal bis(triflyl)imides of technological interest, CuNTf(2) and AgNTf(2) , their synthesis and complexes with excess of comparatively weakly coordinating NTf(2) (-) as well as with ether, olefins, and the arene mesitylene are described. The existence of the solvent-free pure phase [CuNTf(2) ](∞) has not been evidenced so far. Contrary to the literature, in which the preparation of [CuNTf(2) ](∞) is supposed to be carried out by reacting mesityl copper, [Cu(Mes)](5) , and HNTf(2) , we found that in fact this reaction leads reproducibly to the interesting copper diarene sandwich complex [Cu(η(3) -MesH)(2) ][Cu(NTf(2) )(2) ] (1) (MesH=1,3,5-trimethylbenzene). The unexpectedly stable molecular etherate [Cu(Et(2) O)(NTf(2) )] (2) turned out to be the best precursor for CuNTf(2) having only an inert and easily exchangeable solvent ligand. The coordination mode of NTf(2) (-) in 1 and 2 as well as in the hitherto unknown crystalline phase of [AgNTf(2) ](∞) (3) is described. The complex formation, which takes place when dissolving 2 or 3 in the room temperature ionic liquid (RTIL) [emim]NTf(2) ([emim](+) =1-ethyl-3-methylimidazolium), has been studied. Furthermore, the reaction of 1-3 towards the diolefins 1,5-cyclooctadiene (COD), 2,5-norbornadiene (NBD) and isoprene (2-methylbuta-1,3-diene) and towards ethylene has been investigated. The products 4-13 of these conversions have been isolated and fully characterized by NMR- and IR spectroscopies, mass spectrometry, and elemental- and XRD analyses. The potential of [Cu(η(3) -MesH)(2) ][Cu(NTf(2) )(2) ] (1), [Cu(Et(2) O)(NTf(2) )] (2) and [AgNTf(2) ](∞) (3) as well as of [emim][M(NTf(2) )(2) ] (M=Cu 4, Ag 5) as chemisorbers for ethylene was studied by NMR spectroscopy.
... The similar reference electrodes have been used in anhydrous ionic liquids. 1 The electrode reaction of Ag(I)/Ag has been investigated in some TFSA --type ionic liquids. [19][20][21][22][23][24] AgTFSA or AgCF 3 SO 3 (AgOTf) can be used as a soluble salt in the TFSA --type ionic liquids for preparation of the inner electrolyte of the reference electrode, whereas these silver salts are less common than silver halides and nitrate. Dissolution of silver halides, AgX (X -= Cl -, Br -, and I -), and electrochemical behavior of [AgX n ] (n-1)have not been investigated in the ionic liquids containing X -, while AgCl was poorly soluble in the TFSA --type ionic liquid in the absence of Cl -. 5 On the other hand, the dissolution of AgCl has been reported in basic chloroaluminate ionic liquids 25 and a deep eutectic solvent (DES) containing Cl -. 26 Electrodeposition of Pd-Ag alloy was reported in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF 4 ) containing EMICl. ...
The electrode reactions of haloargentates were investigated in an aprotic and hydrophobic amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) in the presence of the halide ions. Silver halides, AgX (X – = Cl – , Br – , and I – ) were found to be soluble in BMPTFSA containing 0.5 M BMPX to form halogenocomplex, [AgX 3 ] 2– . The cathodic reduction of [AgX 3 ] 2– to metallic Ag was observed within the electrochemical potential window of the ionic liquid, while the reduction potential was lower than that in the ionic liquid in the absence of X – . The equilibrium potentials of [AgX 3 ] 2– /Ag were in the order of [AgCl 3 ] 2– > [AgBr 3 ] 2– > [AgI 3 ] 2– , probably reflecting the thermodynamic stability of the complexes. The diffusion coefficients of [AgCl 3 ] 2– , [AgBr 3 ] 2– , and [AgI 3 ] 2– were 2.5, 2.0, and 1.6 × 10 –7 cm ² s –1 , respectively. The morphology of deposits strongly depended on the reduction potential. The nucleation and growth mechanism of Ag deposition was considered to be progressive rather than instantaneous. Formation of Ag nanoparticles dispersed in the ionic liquids was confirmed after potentiostatic cathodic reduction at –2.5 V vs. Ag|Ag(I) using a transmission electron microscope.
... The potentials of room temperature ionic liquids for the industrial application have been developed in a diverse range of forms, such as adsorption/capture of carbon dioxide, [1,2] conversion from biomass into biofuels, [3] organic synthesis by the enzyme immobilization, [4] lubricants for space technology, [5] and electrolytes for rechargeable batteries [6,7] and electroplating/electrodeposition. [8][9][10][11][12] The origins of the tremendous attention to the ionic liquids are the unique physicochemical properties of non-flammability, high ionic conductivity, negligible vapor pressure, and wide electrochemical window, which can be tuned by molecular structures of the cations and anions. [13][14][15][16] In terms of electrochemical applications, the wide electrochemical window allows for handling metals that cannot be deposited in aqueous systems. ...
The electrochemical behavior of Zn deposition in room temperature ionic liquids consisting of bis(trifluoromethanesulfonyl)amide (TFSA − ) combined with N ‐propyl‐ N ‐methylpyrrolidinium (Pyr 1,3 + ) or 1‐ethyl‐3‐methylimidazolium (EMI + ) was investigated in terms of their physicochemical properties and dissolved Zn 2+ species. We examined the effect of cation structure not only on the macroscopic morphologies, but also on the microscopic aspects of crystallographic orientation of Zn deposits obtained from [Zn(TFSA) 2 ] 0.1 [ Cation ‐TFSA] 0.9 . Electron back‐scattered diffraction revealed that the crystal grains grown in Pyr 1,3 ‐TFSA at the current density of 0.5 mA cm −2 were much finer, compared with the sizes of those in EMI‐TFSA. This is probably because Pyr 1,3 cations inhibit the surface diffusion of Zn adatoms, thus preventing growth in a specific plane direction. It was found that higher reversibility on Zn stripping needs larger crystal grains rather than polycrystalline with fine grains. The obtained results will contribute greatly to the realization of longer life batteries using Zn without resource constraints.
... 147 On the one hand, the serving life of aqueous ZIBs can be significantly prolonged, as water evaporation is no longer a problem. On the other hand, the aprotic ILs show great potential to eliminate hydrogen evolution 154,155 and induce metal deposit morphology, [156][157][158] thus improving the coulombic efficiency and battery lifespan. ...
High‐safety and low‐cost aqueous zinc‐ion batteries (ZIBs) are an exceptionally compelling technology for grid‐scale energy storage, whereas the corrosion, hydrogen evolution reaction and dendrites growth of Zn anodes plague their...
... Previous reports investigating the redox behaviors of Ag, Cu, Sn, In, and Zn in [BMPyr] [NTf 2 ] or [BMPyr] [Nf 2 ] were referred to for assigning the number of electrons, especially for metals having more than an oxidation state such as Cu and Sn. [25][26][27][28] As the upper limit of dissolution potential for each metal is indicated by arrows in Fig. 2, the arrows are located on initial uphill sections or plateaus of the current density. An assumption made for the calculation in Table 1 is that all anodic currents before the upper limit of dissolution potential generate metal ions in the ionic liquids. ...
An electrochemical series of pyrrolidinium-based ionic liquids is established by designing a redox system where only one kind of anion is present in the electrolyte and metal ions are supplied by anodic dissolution.
... Most electrodepositions of silver are carried out in environmentally-toxic cyanide and thiosulphate baths [16,17]. In previous studies, a large number of IL families were studied as potential replacements for conventional electroplating baths such as imidazolium -based ILs: 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF 4 ]) [11,18], 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF 6 ]) [18,19], 1-butyl-3methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][TFSI]) [20,21], 1-butyl-3-methylimidazolium trifluoromethylsulfonate ([BMIM] [OTf]) [3,22]; piperidinium -based ILs: N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide ([C 3 mpip][N(Tf) 2 ]) [23], 1-ethyl-1octylpiperidinium bis(trifluoromethylsulfonyl)imide ([C 2 C 8 pip][NTf 2 ]) [24], 1-ethyl-1-octyl-piperidinium bis(trifluoromethylsulfonyl)imide ([EOPip][TFSI]) [25] and pyrrolidinium -based ILs: N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([C4mPyr][TFSI]) [8,26,27], N-butyl-N-methyl-pyrrolidinium dicyanamide ([BMP][DCA]) [8,28], N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl) imide, ([BMP][NTf 2 ]) [29]. However, few applications involving the electrodeposition of metals were carried out from pyridinium -based ILs such as 3-butylpyridinium bis(trifluoromethanesulfonyl)imide ( [NTf 2 ]) [30] and 1-butylpyridinium chloride ([C 4 pyr][Cl]) [31]. ...
The electrodeposition of silver was performed on a platinum electrode from a non-fluorinated ionic liquid (IL), butylpyridinium dicyanamide (Pyri4-DCA). The as-studied IL is characterized by a high ionic conductivity (11.03 mS.cm⁻¹) and a low dynamic viscosity (24.4 mPa.s), which are appropriate for the electrodeposition process. The cyclic voltammetry (CV) curves recorded in Ag-DCA/Pyri4-DCA solutions showed the presence of reduction and oxidation peaks, respectively associated with the deposition and stripping of silver from the Pt surface. The diffusion coefficient of Ag(I) calculated from CV curves varied from 5.3 10⁻⁷ to 1.1 10⁻⁷ when Ag⁺ concentration was changed from 1 to 10 mM. The silver was electrodeposited on the Pt surface at different constant potentials. The nuclei size and population density of silver were monitored by varying the electrolyte concentration, the applied potential and the deposition time. From the analysis of the experimental transient curves, it was shown that the electrochemical deposition process of silver follows a 3D nucleation with diffusion-controlled growth. The nuclei population densities and diffusion coefficients were also determined for various chronoamperometric parameters by using the fitting model of Scharifker and Hills for 3D nucleation and growth.
... This result is more visible on the corresponding Volcano plot (I peak = f(j Q j)) presented on Figure 3 showing two characteristic linear slopes. This behaviour has been observed in the bibliography and can be explained by the Ostwald ripening widely known in the field of crystallization and corresponding to the dissolution of smaller particles that will grow in larger ones [29][30][31]. The effective surface area of Au/AgNPs therefore decreases and the electrode tends to behave as a bare electrode. ...
The aim of this work is to highlight the potential of using a modified gold electrode with controlled quantity of silver nanoparticles as a working electrode to detect low concentrations of nitrate in chloride solutions. Optimal charge for silver deposition has been determined to obtain the highest signal for the nitrate reduction as the electrocatalytic properties of the bimetallic electrode were directly influenced by its composition. According to the Volcano plot obtained the charge chosen was −52 μC for a 3 mm diameter electrode, corresponding to 4.6×10¹⁵ Ag atoms cm⁻². It has been shown that dioxygen did not participate to the nitrate reduction mechanism. In order to decrease the limit of quantification, square wave voltammetry was preferred to less sensitive cyclic voltammetry. Nitrate was quantified in chloride solutions in the concentration range found in the open ocean, i. e. 0.39–50 μmol L⁻¹ with a good linear regression (R²=0.9969). The stability of the bimetallic Au−Ag systems has been evaluated and showed almost no difference on the signal recorded over a 26 days period which is suitable to consider an in situ sensor development for marine applications.
... Several non-cyanide plating baths have been developed and used especially in semiconductor industries because the cyanide baths are incompatible with photoresists. 2 We have reported electrodeposition of such noble metals as palladium, 3,4 silver, [5][6][7] and platinum 8 is possible in an aprotic ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA). Since the noble metals can be electrodeposited in aqueous solutions, it is not necessary to use aprotic ionic liquids as the electrolytes for electrodeposition of noble metals. ...
Electrode reactions of monovalent and trivalent bromoaurates, [(AuBr2)-Br-I] and [(AuBr4)-Br-III](-), have been investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide. [(AuBr4)-Br-III] could be reduced to metallic Au via an intermediate species, [(AuBr2)-B-I](-), which was stable in the ionic liquid. [(AuBr2)-B-I](-) could be prepared by a proportionation reaction of [(AuBr4)-B-III](-) and Au in the ionic liquid. Although metallic Au was deposited on a glassy carbon substrate at -1.5 V vs. Ag/Ag(I), Au nano-particles with an average diameter of (2.6 +/- 0.6) nm were formed and dispersed in the ionic liquid by potentiostatic cathodic reduction on a glassy carbon electrode at -2.5 V vs. Ag/Ag(I).
... The contribution of the ηρ value is given by the Kanazawa equation. 33 f ηρ = − f 3/2 0 ηρ πμ q ρ q 1/2 [5] In case of the impedance-type EQCM, it is possible to obtain the ηρ value from the resonance resistance, R res , with the following equation. 34 ...
The electrochemical behavior of lead (Pb) was investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), containing Pb(TFSA)(2). The cathodic and anodic currents corresponding to electrodeposition and stripping of Pb, respectively, were observed by cyclic voltammetry. The formal potential of Pb(II)/Pb couple was found to be -0.68 V vs. Ag/Ag(I), which is more negative by 0.11 V than that of Sn(II)/Sn couple. The diffusion coefficient of Pb(II) at 25 degrees C was 0.8 x 10(-7) cm(2) s(-1), which was close to those of divalent metal species in BMPTFSA. The local change of the viscosity and density of the ionic liquid near the electrode surface during electrodeposition and stripping of Pb was confirmed by electrochemical quartz crystal microbalance. The nucleation process and the morphology of electrodeposited Pb were found to be dependent on the deposition potential, probably due to accumulation of BMP+ at the surface of the negatively polarized electrode.
... However, it has been found that the coulombic interaction of charged species with the ions of ionic liquids plays an important role in both kinetic and thermodynamic properties of the species. [4][5][6][7][8][9][10] We have already reported the dE/dT values of some redox couples in an amide-based ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), using a nonisothermal cell are linearly dependent on the difference in the charge densities between the oxidized and reduced forms of redox couples, as reported in conventional solutions. 11 On the other hand, The dE/dT values can be also measured by an isothermal cell with a calibrating redox couple, of which dE/dT is known separately. ...
The temperature dependence of the potential, dE/dT, of some redox couples was determined using an isothermal cell with ferrocenium / ferrocene couple as a calibration redox couple in different ionic liquids, BMPTFSA, EMITFSA, PP13TFSA, BMP-BETA and EMI[BF4] (BMP+ = 1-butyl-1-methypyrrolidinium, EMI+ = 1-ethyl-3-methylimidazolium, PP13(+) = 1-methyl-1-propylpiperidinium, TFSA(-) = bis(trifluoromethylsulfonyl)amide and BETA(-) = bis(perfluoroethylsulfonyl)amide). The reaction entropies of the redox couples, Delta S-rc degrees, were calculated from the dE/dT values. It is suggested that the coulombic interaction between the redox couples and the ions with the opposite sign of charge to those of the redox couples is a dominant factor determining the Delta S-rc degrees value and that the absolute Delta S-rc degrees value for the redox couple increases with an increase in the charge density of the ions with the opposite charge to the redox couple. However, the Delta S-rc degrees values are considered to be affected not only by the charge density of the ions but also by the polarization and/or steric shape of the ions.
... Even an aqueous electrodeposition from the nitrate containing electrolyte bath results in nanoplate formation. 34 The redissolution from nitrate containing ionic liquid is also indicated by a decreasing current in the chronoamperogram for silver deposition from [HMPyr][NO 3 ] which is not observed in the case of the acetate based ionic liquid (ESI, † Fig. S3 and S4). ...
Electrodeposition of silver and silver sulphide was carried out from two protic ionic liquids. A change of the anion moiety of ionic liquid was found to bring about significant changes in the morphology of the nanocrystalline silver and silver sulphide deposits obtained. Effects of various parameters like deposition overpotential, change of the substrate, deposition time, etc. on the particle size and shape were studied. It was found that a change of anions of the ionic liquid from acetate to nitrate results in a wide difference in the morphology of the deposits obtained. Acetate containing ionic liquids result in globular nanocrystalline deposits whereas nitrate containing ionic liquids result in flat plates or sheets of silver deposits. Similar results were obtained for silver sulphide nanocrystals.
http://pubs.rsc.org/en/content/articlelanding/2014/cp/c3cp54382j#!divAbstract
... where the adsorption of hydrophobic cations is significant. 48 The k 0 value calculated for the reduction of AuCl with TBA + in the electrolyte was (2.2 ± 1) 10 -6 cm s -1 , around one order of magnitude smaller than in its absence. Simulations were performed employing these electrochemical parameters, leading to a good agreement with the experimental profiles (see inset Fig. 3). ...
Organic species are easily adsorbed onto metal electrodes, due to the high surface energy. This principle is widely employed in electrodeposition to obtain grains with a given shape and size. Electrodeposition in organic electrolytes and ionic liquids is expected to produce deposits whose properties will be modified by the nature of the species present in the bath. Here, we analyse the voltammetric profiles for the reduction of two different gold complexes, tetrachloroaurate (III) (AuCl4-) and dicyanoaurate (I) (Au(CN)2-), in dimethylsufoxide (DMSO) and in the ionic liquid tributylmethylammonium bis(trifluoromethylsulfonyl)imide (TBMA+NTf2-). We evaluate how organic cations present in the electrolyte modify not only the voltammetric response but also the morphology of the deposits obtained. The films range from very smooth with a rms roughness of ∼10nm for 500nm film to rough globular or facetted films with a crystalline size of ∼200nm.
Ag nanoparticles exhibit various colors depending on their localized surface plasmon resonance (LSPR). Based on this phenomenon, Ag deposition-based electrochromic devices can represent various optical states in a single device such as the three primary colors (cyan, magenta, and yellow), silver mirror, black and transparent. A control of the morphology of Ag nanoparticles can lead to dramatic changes in color, as their size and shape influence the LSPR band. In this research, we focused on the diffusion rate of Ag+ ions when Ag nanoparticles are electrochemically deposited. Consequently, well-isolated Ag nanoparticles were obtained due to the slow growth rate by using an electrolyte with a low concentration of Ag+ ions, resulting in an improvement in the color quality of cyan and magenta. Additionally, spherical Ag nanoparticles were deposited in the same device by optimizing their voltage application conditions, which represented yellow and green colors. In particular, green coloration is a unique phenomenon because it can appear by the combination of two absorption peaks of LSPR. As a result of investigating the finite-difference time-domain method, it was observed that the LSPR band in the long wavelength region was originated from the effects of the connection between Ag particles.
The potential-dependent interfacial structures of Pt/tetraglyme-lithium bis(trifluoromethylsulfonyl) amide ((Pt)/G4-Li[TFSA]) systems were assessed with and without 3-(1-butyl-1H-imidazol-3-ium-3-yl)propane-1-sulfonate ([Bimps]) zwitterions, to understand the impact of [Bimps] on the enhancement of the electrochemical stability of G4-Li[TFSA] electrolytes at Pt electrode surfaces. The aforementioned interfacial structures were investigated using in-situ infrared-visible sum frequency generation (IV-SFG) spectroscopy. The results of the linear sweep voltammetry (LSV) revealed that the oxidation limit of G4-Li[TFSA] at the Pt electrode shifted to a higher potential when [Bimps] was introduced, thus indicating that the electrochemical window is extended in the G4-Li[TFSA]-[Bimps] system. The SFG spectra of the G4-Li[TFSA] system confirmed that free G4 molecules and Li⁺-G4 complex cations are dominantly adsorbed on the Pt surface at 1 V (vs. Ag/Ag⁺). In contrast, the addition of [Bimps] to the G4-Li[TFSA] system resulted in almost full coverage of [Bimps] at the Pt surface by forming Li⁺-[Bimps] complex cations, even at 1 V (vs. Ag/Ag⁺), and no free G4 molecules were observed. The ab initio calculation indicated that the highest occupied molecular orbital (HOMO) energy level of free G4 was higher than that of the Li⁺-[Bimps] complex cation. This suggests that the Li⁺-[Bimps] complex was more stable for oxidation than the free G4, which accounts for the enhanced electrochemical stability of G4-Li[TFSA] system with [Bimps] additives.
We present a comprehensive study on the initial stages of silver electrodeposition on Pt (111), Au (111), and Au (100) single crystal surfaces in low-viscosity ionic liquids (ILs) containing dicyanamide anions: 1-butyl-1-methylpyrrolidinium dicyanamide [BMP][DCA] and 1-butyl-3-methylimidazolium dicyanamide [BMIm][DCA]. Electrochemical methods in combination with in situ scanning tunneling microscopy (STM) and ex situ atomic force microscopy (AFM) are employed to explore the Ag underpotential (upd) and overpotential (opd) deposition processes as well as the stability of the single crystal electrode surfaces in the absence of Ag⁺ ions. The substrate material is shown to significantly affect the mechanism of Ag deposit nucleation and growth in the ILs. While no Ag upd is detected on Pt (111), the formation of a Ag upd monolayer on a Au (111) electrode in both ILs is clearly visualized by in situ STM. The Ag adlayer formation on the Au electrodes in the underpotential regime facilitates Ag opd, which starts on Au (111) and Au (100) at much less negative potentials than on Pt (111). There is an excellent agreement between the electrochemical (voltammetry and chronoamperometry), AFM and STM data, demonstrating the nucleation and growth of individual Ag crystallites on Pt (111) according to the Volmer–Weber mechanism and the layer–by–layer growth of Ag deposit on Au (111) and Au (100). Only at high overpotentials, the Ag growth on the gold electrodes switches to the Stranski-Krastanov mode involving the appearance of 3D crystallites.
Understanding the behavior of metal ions in room temperature ionic liquids (ILs) is essential for predicting and optimizing performance for technologies like metal electrodeposition; however, many mechanistic details remain enigmatic, including the solvation properties of the ions in ILs and how they are governed by the intrinsic interaction between the ions and the liquid species. Here, we utilize first-principles molecular dynamics simulations to unravel and compare the key structural properties of Ag^{+} and Cu^{+} ions in a common room temperature ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. We find that, when compared to Cu^{+}, the larger Ag^{+} shows a more disordered and flexible solvation structure with more frequent exchange of the IL species between its solvation shells. In addition, our simulations reveal an interesting analog in the solvation behavior of the ions in the ionic liquid and aqueous environments, particularly in the effect of the ion electronic structures on their solvation properties. This work provides fundamental understanding of the intrinsic properties of the metal ions in the IL, while offering mechanistic understanding and strategy for future selection of ILs for metal electrodeposition processes.
There is a steadily increasing interest in room‐temperature ionic liquids (ILs) as media for metal electrodeposition. However, the fundamental understanding of the underlying surface processes at the electrode/IL interface and of the initial stages of electrodeposition is still at the very preliminary stage. In this article, we investigate the underpotential deposition (upd) of Ag on a well‐defined Au(111) single crystal surface from an air‐ and water‐stable IL, 1‐butyl‐1‐methylpyrrolidinium dicyanamide [BMP][DCA]. By employing in situ scanning tunneling microscopy (STM), we could visualize individual stages of the Ag upd process as a function of the applied electrode potential and correlate voltammetric responses to the obtained STM data. The initial Ag upd process results in the formation of an Ag‐(4x4) lattice, which is further transformed into a pseudomorphic Ag‐(1x1) monolayer at the underpotential of ~40 mV. The structural stability of the Au(111) surface in [BMP][DCA] is also examined in the absence of Ag+ ions in both the cathodic and anodic potential regions.
The dynamic interfacial growth, suppression and dissolution of zinc dendrites have been studied with the imidazolium ionic liquids (ILs) as additives on the basis of in situ synchrotron radiation X-ray imaging. The phase contrast difference of real-time images indicates that zinc dendrites are preferentially developed on the substrate surface in the ammoniacal electrolytes. After adding imidazolium ILs, both nucleation overpotential and polarization extent increase in the order of additive-free<EMI-Cl＜EMI-PF6＜EMI-TFSA＜EMI-DCA. The real-time X-ray images show that the EMI-Cl can suppress zinc dendrites, but result in the formation of the loose deposits. The EMI-PF6 and EMI-TFSA additives can smooth deposit morphology through suppressing the initiation and growth of dendritic zinc. The addition of EMI-DCA increases the number of dendrite initiation sites, whereas decreases the growth rate of dendrites. Furthermore, the dissolution behaviors of zinc deposits are compared. The zinc dendrites show a slow dissolution process in the additive-free electrolyte, whereas zinc deposits are easily detached from the substrate in the presence of EMI-Cl, EMI-PF6 or EMI-TFSA due to the formation of the loose structure. Hence, the dependence of zinc dendrites on anions of imidazolium IL additives during both electrodeposition and dissolution processes has been elucidated. These results could provide the valuable information in perfecting the performance of zinc-based rechargeable batteries.
Metal nanoparticles of the iron group (Fe, Co, and Ni) and noble group of noble metals (Ag, Pd, Au, and Pt) metals are able to be prepared by simple electrolysis in some ionic liquids without any stabilizing agent. The nanoparticles are not deposited on the electrode surface but dispersed in the ionic liquids. Formation of the metal nanoparticles is considered to be related to the potential dependence of the electric double-layer structure in the ionic liquids although the detailed mechanism has not been clarified at present. These metal nanoparticles dispersed in the ionic liquids are expected to be utilized as catalysts for various chemical and electrochemical reactions.
Due to their attractive physico-chemical properties, ionic liquids (ILs) are increasingly used as deposition electrolytes. This review summarizes recent advances in electrodeposition in ILs and focuses on its similarities and differences with that in aqueous solutions. The electrodeposition in ILs is divided into direct and template-assisted deposition. We detail the direct deposition of metals, alloys and semiconductors in five types of ILs, including halometallate ILs, air- and water-stable ILs, deep eutectic solvents (DESs), ILs with metal-containing cations, and protic ILs. Template-assisted deposition of nanostructures and macroporous structures in ILs is also presented. The effects of modulating factors such as deposition conditions (current density, current density mode, deposition time, temperature) and electrolyte components (cation, anion, metal salts, additives, water content) on the morphology, compositions, microstructures and properties of the prepared materials are highlighted.
Electrodeposition of Ag was studied in several ionic liquids. When the potential applied more negative than -0.25 V vs. Ag l Ag(I), the cathodic current density reached in the diffusion-controlled region. The surface morphology of Ag deposits, the initial stage of nucleation and crystal growth behavior and the apparent current efficiency changed depending on the applied potential. These results indicate that the applied potential affects the electrodeposition processes of Ag under diffusion-controlled region. Since the electrode reaction rate is controlled by diffusion, the change of the surface morphology may be caused by the change of the double layer structure, which is expected to depend on the applied potential. In addition, Ag nanoparticles were obtained in the ionic liquid after potentiostatic cathodic reduction, suggesting a part of reduced Ag was dispersed in the ionic liquid.
Electrodeposition of Zn was conducted in a new electrolyte system composed of an alkaline solution (9 M KOH + 5 wt% ZnO) modified with a small amount (0.5 wt%) of room temperature ionic liquid 1-ethyl-3-methylimidazolium dicyanamide (EMI-DCA). At a high deposition current density of 80 mA cm−2, a porous, dendrite-free Zn film characterized by clusters of small Zn particles was obtained. The mechanism for the modified Zn morphology in the EMI-DCA containing electrolyte was studied by cyclic voltammetry, chronoamperometry, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy. It was found that the addition of EMI-DCA changed the Zn nucleation process and reduced the potential variation during electrodeposition, which suppressed the uneven growth of Zn deposits and the formation of Zn dendrites. EIS results indicated that there was adsorption of EMI+ cations at the Zn film/electrolyte interface, which may have contributed to suppressed dendritic Zn growth.
Cobalt nano-particles have been prepared by reducing divalent cobalt species in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide at room-temperature. Potentiostatic cathodic reduction of divalent cobalt species was conducted on a platinum mesh electrode at -2.0 V vs. Ag/Ag(I) in the ionic liquid, resulting in the change of color of the ionic liquid from purple to black. The transmission electron microscope observation of the ionic liquid after the potentiostatic cathodic reduction showed formation of cobalt nano-particles with the diameters from 2 to 10 nm.
The formal potentials for Ag(I)/Ag, Pb(II)/Pb, Sn(II)/Sn, Fe(III)/Fe(II) and [Fe(bpy)3]3+/[Fe(bpy)3]2+ (bpy = 2,2’-bipyridine) were investigated in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) ionic liquid at 25°C. The formal potentials and thermodynamic properties of metal redox couples were evaluated on the basis of the potential of ferrocene/ferrocenium couple in various electrolytes including organic solvents and ionic liquids. The formal potentials for Ag(I)/Ag, Pb(II)/Pb and Sn(II)/Sn are more positive in BMPTFSA than in conventional organic solvents, resulting in the positive Gibbs energy of transfer for metal ion from the organic solvents into BMPTFSA. The donor number of BMPTFSA was estimated from the correlation with the formal potentials of metal redox couples. The estimated donor number of BMPTFSA is consistent with the literature values based on other methods, such as the lanthanide redox potentials and the chemical shift of 23Na NMR. The donor ability of TFSA−-type ionic liquids was located between nitromethane and acetonitrile, suggesting that the interaction between metal ion and TFSA− is weak as compared with other media.
Room-temperature ionic liquid (RTIL) that is a liquid salt at or below room temperature is expected to be an innovative functional solvent and a liquid material due to its anomalous physicochemical properties such as negligible vapor pressure, flame resistance, and relatively-high conductivity. With an eye on what RTIL has negligible vapor pressure, we have created the analytical technique combined with RTIL and secondary electron microscope (SEM). In this paper, we report several RTIL-based SEM techniques that will be a useful analytical method in both electrochemistry and life science. The aim of this study is to show the utility of the RTIL-based SEM techniques.
Motivated by the potential of using room temperature ionic liquids (RTILs) as electrolytes to replace traditional aqueous electrolytes for Zn-anode secondary batteries, Zn/Zn(II) redox reactions have been studied in four aprotic RTILs based on pyrrolidinium ([Pyrr]+) and imidazolium ([Im]+) cations, and bis(trifluoromethanesulfonyl)imide ([TFSI]−) and dicyanamide ([DCA]−) anions. Cyclic voltammetry results suggest a smaller overpotential for Zn redox in [Im]+ cation based and [DCA]− anion based RTILs than in [Pyrr]+ and [TFSI]− based RTILs. Potentiodynamic polarization experiments indicate a strong dependence of the electrode reaction mechanism for the Zn species on the RTIL anions. In [TFSI]− based RTILs, Zn2+ ions are the electroactive species, with the electrode reaction being a single-step, two-electron transfer process. In [DCA]− based RTILs, two-step, single-electron reactions account for the electrode mechanism. The exchange current densities derived from Tafel analysis for the Zn species in the four RTILs are greater than 10−3 mA/cm2, with the [Im]+ cation based RTIL possessing the highest value of 9.9 × 10−3 mA/cm2. The results obtained will assist in obtaining a better understanding of the electrochemical behavior of Zn in RTILs, shedding light on the development of RTILs for Zn-anode secondary batteries.
Several hydroxyl- and ether-functionalized binary task specific ionic liquids (ILs) are prepared, ether-functionalized ILs exhibit higher conductivity and lower viscosity than those of hydroxyl-functionalized ILs, whereas hydroxyl-functionalized ILs show wider potential window than those of ether-functionalized ILs. The correlation between ionic conductivity and viscosity is based on the classical Walden rule; a relatively large deviation of the plots from the ideal Walden line is observed for the ILs without considering the ion size, whereas the deviation decreases significantly when the adjusted Walden plot is adopted. The α values of ILs calculated from the slopes of the Walden plots are compared to those calculated from the ratio of activation energies for viscosity and molar conductivity (Ea,Λ/Ea,η). There are very few reports where electrochemically derived activation energy from conductivity and voltammetric characterization are available for comparison, so a key concept of activation energy in electrochemistry could be developed in this paper.
Silver was successfully electrodeposited from the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIm][TfO]) containing silver ions in various concentrations. The electrochemical windows of the electrolytes were determined by cyclic voltammetry. Moreover, the conductivity and the viscosity–density product were studied with electrochemical impedance spectroscopy (EIS) and electrochemical quartz crystal microbalance (EQCM). Potentiodynamic and potentiostatic depositions were performed at different temperatures. The morphology of the deposited Ag layers depends on temperature and concentration. Thus, by choosing the right experimental conditions one can optimize the properties of the deposited layers. The thus obtained layers can be used in different surface finishing processes, such as in decorative plating, catalysis or for electrical contacts.
The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.
The electrodeposition of silver was investigated with l-butyl-3- methylimidazolium bis[(trifluoromethyl)sulfonyl} amide containing Ag-TFSI at 150°C. The influence of current density on the morphology of the silver deposit was studied by cyclic voltammetry and scanning electron microscopy. The size of the silver crystallite became smaller and dendrite-like growth was suppressed with increasing current density.
The electrochemical interface between a polycrystalline Pt electrode and an ionic liquid 1-butyl-3-methylimidazolium trifluoromethane sulfonate ([bmim]OTf) has been studied by in situ sum frequency generation (SFG) spectroscopy. Potential dependent adsorption and desorption processes of OTf anion as well as [bmim] cation have been observed. A double-layer model of the interface structure has been suggested based on the behavior of both the anion and the cation in the electrochemical potential window. Hysteresis effect has been observed during the desorption and the re-adsorption processes of both the anion and the cation on the Pt surface.
Electrodeposition of aluminum was studied in three hydrophobic ionic liquids, trimethylhexylammonium bis(trifluoromethylsulfonyl)imide (TMHA-TFSI), trimethylpropylammonium bis(trifluoromethyl -sulfonyl)imide (TMPA-TFSI), 1-n-butyl-N-methylpyrrolidinium bis (trifluoromethylsulfonyl)imide (BMP-TFSI). Bright deposits were obtained only in the BMP-TFSI melt containing AlCl3 with low current densities, while gray deposits were obtained from the TMPA-TFSI melt. In the BMP-TFSI melts, the deposits became black and less adhesive with an increase in current density. The current efficiency for the aluminum deposition was quite high in the BMP-TFSI melt, and the thick deposits such as 20μm could be obtained. The effects of the aluminum chloride concentration were also examined.
A room-temperature molten salt, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) with adequate purity was obtained simply by the reaction of 1-ethyl-3-methylimidazolium chloride and tetrafluoroboric acid. Silver tetrafluoroborate dissolves up to similar to0.2 mol dm(-3) in EMIBF4 at room temperature. Electrochemical deposition and dissolution of silver on a platinum electrode were found possible in EMIBF4 containing AgBF4. The reduction of monovalent silver species is electrochemically irreversible, the rate constant being estimated to be 1 X 10(-5) cm s(-1). The diffusion coefficient of Ag(I) is calculated to be 6 x 10(-7) cm(2) s(-1), suggesting that Ag(I) exists as a substantially bare cation (Ag+) in EMIBF4.
Macroporous silver films, ordered or fragmented, were fabricated by electrodeposition of silver into the interstitial spaces of templates formed by polystyrene (PS) latex spheres that had been self-assembled onto bare indium tin oxide (ITO) electrodes or onto gold-coated ITO (ITO/Au) electrodes (in which the electrode had been coated by gold sputtering deposition) from two room-temperature ionic liquids (ILs): N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (BMP-TFSI) and N-butyl-N-methylpyrrolidinium dicyanamide (BMP-DCA), respectively, under normal atmospheric conditions. After electrodeposition of silver, the PS spheres were removed by dissolution in tetrahydrofuran (THF) to leave a macroporous silver structure. The higher wettability of ILs onto PS spheres leads to improved penetration of the ILs into the cavities of the PS templates. Electrodeposition is easier if an electrolyte that has a good penetration into the interstitial spaces between the PS spheres. The macroporous silver electrode exhibited much better electrocatalytic performance with respect to nitrate reduction than a regular silver wire electrode. Quantitative determination of nitrate was also examined.
Based on our previous discovery that ionic liquid (IL) can be observed by a scanning electron microscope (SEM) without charging the liquid, we have developed several novel techniques for SEM observation. Coating of insulating sample with IL is useful for providing electronic conductivity to the samples like metal or carbon coating by vacuum vapor deposition. In this case, dilution of the IL with appropriate volatile solvent like alcohol is effective for coating thin layer of IL on the sample. As a biological sample, seaweed including IL was attempted to be observed by SEM. A seaweed leaf swollen by water was put in an IL bath and the bath was put in an outgassed desiccator to replace water in the seaweed leaf with IL. The resulting sample gave a SEM image of the swollen seaweed whose thickness was several times larger than dried one. Furthermore, the introduction of the IL in vacuum chamber allowed us to develop the in situ electrochemical SEM observation system. Using this system, we observed changes in polypyrrole film thickness caused by the redox reaction of the film and the electrochemical deposition of silver and its oxidative dissolution. It was also found that the energy dispersive X-ray fluorescence (EDX) analysis was available even for the electrode polarized in IL.
We report in this paper on the electrodeposition of nanocrystalline silver films and nanowires in the air and water stable ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate [EMIm]TfO containing Ag(TfO) as a source of silver. The study was performed by means of cyclic voltammetry and chronoamperometry, and the electrodeposits were characterized by SEM-EDX and XRD. The cyclic voltammetry behaviour showed typical reduction and oxidation peaks corresponding to the deposition and stripping of silver in the employed electrolyte. XRD patterns of the electrodeposited silver layers revealed the characteristic peaks of crystalline silver with crystallites in the nanosize regime. Silver nanowires with average diameters and lengths of about 200nm and 3μm, respectively, were prepared by potentiostatic deposition within a commercial nuclear track-etched polycarbonate template.
Electrodeposition of metals from non-aqueous solutions is reviewed. Attention is paid mainly to surface morphology of deposits and their adhesion. The major reasons for carrying out electrodeposition in non-aqueous electrolytes (such as conventional organic solvents, ionic liquids and molten salts) are the water and air stability and the wide electrochemical window of these media. The following metals have been electrodeposited and investigated for the last 15 years: aluminum, zinc, silver, palladium, tantalum, zirconium, gadolinium, plutonium, nickel, cobalt, and other alloys.
The Raman spectra for 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [BMI][TFSA] containing alkaline metal salts of TFSA(-), MTFSA (M = Li, Na, K and Cs), were recorded in the frequency range of 200 - 1800 cm(-1), with varying salt concentrations at 298 K. With Li+ and Na+ ions, at the frequency range of 730 - 760 cm-1, new Raman bands ascribable to the anion bound to the ions appeared at higher frequency relative to that found in the neat ionic liquid. On the other hand, with K+ and Cs+ ions, single Raman bands were solely observed. According to the difference Raman spectra for the ionic liquids containing K+ and Cs+, evaluated by subtracting Raman spectra for the neat ionic liquid, it turned out that two-state approximation, i.e., bulk TFSA(-) and TFSA(-) bound to K+ and Cs+ ions, could hold, as Li+ and Na+-ions. By careful analyses of Raman band intensity arising from bulk TFSA(-) as a function of the salt concentration, the solvation numbers for the respective ions were successfully evaluated to be 1.95 for Li+, 2.88 for Na+, 3.2 for K+ and 3.9 for Cs+, respectively. By taking into account that TFSA(-) acts as a bidentate ligand, the atomic coordination numbers are proposed to be 4, 6, 6 and 8 for Li+, Na+, K+ and Cs+, respectively. Raman shifts for the TFSA- bound to the metal ions relative to that of the bulk TFSA(-) were plotted against the ionic radii for the solvated alkaline metal ions estimated via Shannon's ionic radii, to yield a straight line with a slope of almost unity, suggesting that the electrostatic interaction predominantly operates in the ion-ion interaction between the alkaline metal ions and TFSA(-), as expected. Moreover, the Raman spectra in the frequency range of 370 - 450 cm(-1) strongly depend on the alkaline metal ions, indicating that cis TFSA(-) is favored in the first solvation sphere of the Li+ ion of a relatively small ionic radius, and that such a preferred conformational isomerism of TFSA(-) diminishes with an increase of the ionic radii of the central metal ions.
The electrodeposition of cobalt was investigated in an ionic liquid, 1-
-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide. The overpotential for the electrodeposition of Co was reduced
remarkably by elevating the temperature up to
, probably due to the change in the coordination environment of Co species. The addition of acetone led to the decrease in
the overpotential, indicating the selective coordination of Co cation with acetone enhanced the charge transfer rate. It has
been suggested that the charge transfer and crystal growth in the ionic liquid are affected by the coordination environment
of the dissolved metal species and the structure of electric double layer.
The electrodeposition of silver was investigated at polycrystalline platinum, gold, and tungsten, and at glassy carbon in
the
aluminum chloride‐1‐methyl‐3‐ethylimidazolium chloride room temperature molten salt at 40°C. Of the four materials studied,
the silver deposition‐stripping process seemed to be the least complex at platinum. In contrast, the bulk deposition of silver
at gold appears to be preceded by an underpotential deposition process similar to that seen in aqueous solutions. Large nucleation
overpotentials were needed in order to deposit silver on tungsten and glassy carbon. Instantaneous three‐dimensional nucleation
of silver was found on the former electrode whereas progressive three‐dimensional nucleation predominated on the latter.
Diffusion‐controlled growth of the developing silver nuclei was found at both electrodes. The bulk silver deposition‐stripping
process proceeds with virtually 100% efficiency at all four of the electrodes tested. The diffusion coefficient for silver(I)
in the melt was found to be
at a platinum rotating disk electrode.
The electrochemical behavior of samarium (Sm), europium (Eu), and ytterbium (Yb) was investigated in the hydrophobic room-temperature
molten salts based on bis(trifluoromethylsulfonyl)imide
combined with either 1-ethyl-3-methylimidazolium
or 1-
-butyl-1-methylpyrrolidinium
. The redox reactions of
,
, and
were observed at
,
, and
vs
, respectively. In all cases, the electrode reactions were found to be quasi- or irreversible by the cyclic voltammetry. The
diffusion coefficients of these lanthanides were estimated to be
by chronoamperometry and chronopotentiometry, indicating that their mobility is rather low, probably due to the complex formation
or the strong coulombic interaction with
. The redox potentials of these divalent and trivalent lanthanide couples suggested that the donor property of
-based room-temperature molten salts was lower than that of other conventional solvents.
Electrodeposition of silver was investigated using an impedance technique (separately excited, passive technique) electrochemical
quartz crystal microbalance (EQCM) in a room-temperature ionic liquid. The mass changes during silver deposition and dissolution
were observed with the current efficiencies of nearly 100% during potential sweep, constant potential step, and constant current
step experiments. The product of the viscosity and density of the electrolyte near the electrode,
, can be estimated by the resonance resistance, which can be monitored simultaneously with the resonance frequency. The change
in the
value during silver deposition was consistent with the change in the calculated concentration of Ag(I) near the electrode.
During the outer-sphere electron-transfer reaction between ferrocenium and ferrocene, no significant changes in the mass and
the
value were observed.
A new family of molten salts is reported, based on the N-alkyl, N-alkyl pyrrolidinium cation and the bis(trifluoromethane sulfonyl)imide anion. Some of the members of the family are molten at room temperature, while the smaller and more symmetrical members have melting points around 100 °C. Of the room-temperature molten salt examples, the methyl butyl derivative exhibits the highest conductivity; at 2 × 10-3 S/cm this is the highest molten salt conductivity observed to date at room temperature among the ammonium salts. This highly conductive behavior is rationalized in terms of the role of cation planarity. The salts also exhibit multiple crystalline phase behavior below their melting points and exhibit significant conductivity in at least their higher temperature crystal phase. For example, the methyl propyl derivative (mp = 12 °C) shows ion conductivity of 1 × 10-6 S/cm at 0 °C in its higher temperature crystalline phase.
Room-temperature ionic liquids (RTILs) based on 1-butyl-3-methylimidazolium ([bmim]) with a variety of fluorinated anions were prepared, and the thermal behavior, density, viscosity, self-diffusion coefficients of the cations and anions, and ionic conductivity were measured over a wide temperature range. The temperature dependencies of the self-diffusion coefficient, viscosity, ionic conductivity, and molar conductivity have been fitted to the Vogel−Fulcher−Tamman equation, and the best-fit parameters for the self-diffusion coefficient, viscosity, ionic conductivity, and molar conductivity have been estimated, together with the linear fitting parameters for the density. The self-diffusion coefficients determined for the individual ions by pulsed-field-gradient spin−echo NMR method exhibit higher values for the cation compared with the anion over a wide temperature range, even if its radius is larger than that of the anionic radii. The summation of the cationic and anionic diffusion coefficients for the RTILs follows the order [bmim][(CF3SO2)2N] > [bmim][CF3CO2] > [bmim][CF3SO3] > [bmim][BF4] > [bmim][(C2F5SO2)2N] > [bmim][PF6] at 30 °C, and the order of the diffusion coefficients greatly contrasts to the viscosity data. The ionic association is proposed from the results of the ratios of molar conductivity obtained from impedance measurements to that calculated by the ionic diffusivity using the Nernst−Einstein equation. The ratio for the ionic liquids follows the order [bmim][PF6] > [bmim][BF4] > [bmim][(C2F5SO2)2N] > [bmim][(CF3SO2)2N] > [bmim][CF3SO3] > [bmim][CF3CO2] at 30 °C and provides quantitative information on the active ions contributing to ionic conduction in the diffusion components.
Room-temperature ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI), 1-butylpyridinium tetrafluoroborate (BPBF4), and 1-butylpyridinium bis(trifluoromethylsulfonyl)imide (BPTFSI), were prepared and characterized. The thermal property, density, self-diffusion coefficient of the anions and cations, viscosity, and ionic conductivity were measured for these ionic liquids in wide temperature ranges. A pulsed-gradient spin−echo NMR method was used to independently measure self-diffusion coefficients of the anions (19F NMR) and the cations (1H NMR). The results indicate that the cations diffuse almost equally to the anion in EMIBF4 and BPBF4, whereas they diffuse faster than the anion in EMITFSI and BPTFSI. The summation of the cationic and anionic diffusion coefficients for each ionic liquid follows the order EMITFSI > EMIBF4 > BPTFSI > BPBF4, under an isothermal condition. The order of the magnitude of the diffusion coefficient well contrasts with that of the viscosity for each ionic liquid. The temperature dependencies of the self-diffusion coefficient, viscosity, and ionic conductivity obey the Vogel−Tamman−Fulcher (VTF) equation, and the VTF parameters were presented. Relationships among the self-diffusion coefficient, viscosity, and molar conductivity were analyzed in terms of the Stokes−Einstein equation and the Nernst−Einstein equation. The most interesting feature of the relationships is that the ratios of the molar conductivity, determined by complex impedance measurements, to that calculated from the NMR diffusion coefficients, range from 0.6 to 0.8 for EMIBF4 and BPBF4, whereas the ratios range from 0.3 to 0.5 for EMITFSI and BPTFSI. This difference could be understood by taking the ionic association into consideration for EMITFSI and BPTFSI.
Experimental values are reported for the densities and electrical conductivities of several 1,3-dialkylimidazolium chlorides and for the densities, electrical conductivities, and viscosities of representative compositions of binary mixtures of these salts with aluminum chloride. These data were collected over wide temperature and composition ranges. The transport properties are reported as specific and equivalent conductivities and as kinematic and absolute viscosities. These data and the densities are interpreted in terms of a model of the structure of the binary melts. The solid-liquid phase diagram for the 1-methyl-3-ethylimidazolium-aluminum chloride system was determined, including glass transition temperatures.
Based on our previous finding that room temperature ionic liquid (RTIL) can be observed by scanning electron microscopy (SEM) without charging of the liquid, a specifically designed electrochemical cell has been developed to observe electrochemical metal deposition from RTIL in real time by SEM. The cell was fabricated employing a fluorine doped tin oxide transparent glass, whose surface was divided into three electrodes. Then, the effectiveness of the fabricated cell was confirmed by demonstrating silver deposition form RTIL of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI-TFSI) containing Ag-TFSI, which gave growth of granular and dendritic forms of Ag deposit.
The electrochemical interface between a polycrystalline Pt electrode and the ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([bmim][OTf]) has been studied by in-situ IR-visible sum-frequency generation (SFG) spectroscopy. Potential dependent adsorption/desorption processes of OTf anions has been monitored within the electrochemical window. SFG results indicate that the ions form a double layer structure at the interface. Significant adsorption/desorption hysteresis has been observed for the anions on the Pt surface.
The methods of potentiometry, electrochemical impedance spectroscopy, cyclic voltammetry, and gravimetry were used to study
the electrochemical behavior of a silver electrode in low-temperature ionic liquids of BMImBr and BMImBr—AgBr, and also the
process of cathodic reduction of Ag(I) compounds out of a BMImBr—AgBr melt. It is shown that an AgBr film is formed on the
silver surface and its properties are determined by the ionic liquid composition. It is found that the process of silver electrodeposition
from a BMImBr—AgBr binary alloy occurs irreversibly, at a high current efficiency (up to 100%) and a good quality of the deposit
at low current densities. At 70°C, the transfer coefficients of the cathodic process (α = 0.56 and 0.16) and diffusion coefficients
(D
Ag(I) = 0.48 × 10−7 cm2/s and 3.3 × 10−7 cm2/s) of silver-containing ions are determined in ionic liquids with the AgBr concentration of 0.81 and 1.53 mol/kg BMImBr,
accordingly.
Solvation structures of manganese(II), cobalt(II), nickel(II) and zinc(II) ions in 1-ethyl-3-methylimidazolium bis(trifluoro-methanesulfonyl) amide (EMI(+)TFSA(-)) have been studied by UV-Vis, FT-IR and FT-Raman spectra. The ionic liquid involves TFSA(-) conformers with C(1) (cis) and C(2) (trans) symmetries, and both conformers coexist in equilibrium in the liquid state. The results showed that these metal(II) ions are all six-coordinated with three TFSA(-) ions, i.e., TFSA(-) ligates as a bidentate O-donor in the ionic liquid. Although the metal ion strongly prefers the C(1) conformer in crystals, the metal ion coordinates both the C(1) and C(2) conformers in the liquid state, and the conformational equilibrium in the bulk only slightly shifts to the C(1) conformer in the coordination sphere. We concluded that the conformational equilibrium in the coordination sphere is strongly temperature-sensitive.
New, hydrophobic ionic liquids with low melting points (<-30 degrees C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophobic anions. Other imidazolium molten salts with hydrophilic anions and thus water-soluble are also described. The molten salts were characterized by NMR and elemental analysis. Their density, melting point, viscosity, conductivity, refractive index, electrochemical window, thermal stability, and miscibility with water and organic solvents were determined. The influence of the alkyl substituents in 1, 2, 3, and 4(5)-positions on these properties was scrutinized. Viscosities as low as 35 cP (for 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (bis(triflyl)amide) and trifluoroacetate) and conductivities as high as 9.6 mS/cm were obtained. Photophysical probe studies were carried out to establish more precisely the solvent properties of 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide). The hydrophobic molten salts are promising solvents for electrochemical, photovoltaic, and synthetic applications.
The use of room-temperature ionic liquids (RTILs) as media for electrochemical application is very attractive. In this work, the electrochemical deposition of silver was investigated at a glassy carbon electrode in hydrophobic 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) and hydrophilic 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) RTILs and in KNO3 aqueous solution by cyclic voltammetric and potentiostatic transient techniques. The voltammograms showed the presence of reduction and oxidation peaks associated with the deposition and dissolution of silver from AgBF4 in both BMIMPF6 and BMIMBF(4), resembling the redox behavior of AgNO3 in KNO3 aqueous solution. A crossover loop was observed in all the cyclic voltammograms of these electrochemical systems, indicating a nucleation process. From the analysis of the experimental current transients, it was shown that the electrochemical deposition process of silver in these media was characteristic of 3D nucleation with diffusion-controlled hemispherical growth, and the silver nucleation closely followed the response predicted for progressive nucleation in BMIMPF6 and instantaneous nucleation in KNO3 aqueous solution, respectively. Compared with these two cases, the electrochemical deposition of silver in BMIMBF4 deviated from both the instantaneous and progressive nucleation models, which could be controlled by mixed kinetics and diffusion. On the basis of the experimental results, it was shown that parameters such as viscosity and water miscibility of RTILs would affect the electrodeposition behavior of silver. Atom force microscopy was employed to probe the surface morphology of the silver deposit, and it showed that the shining electrodeposit of silver was fairly dense and separate nanoclusters of <100 nm were in evidence, corresponding to an island growth model. The strongly enhanced Raman scattering from the monolayer film of 4-mercaptobenzoic acid demonstrated that as-prepared silver nanoparticular film was surface-enhanced Raman scattering (SERS) active. The enhancement factor was calculated to be up to 9.0 x 10(5) and 1.0 x 10(6) for the silver film obtained in BMIMPF6 and BMIMBF4 RTILs, respectively.
Thermally evaporated silver nanoparticles on conducting substrates spontaneously evolve in size when immersed in pure water. The process was studied using scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and optical absorption spectroscopy. The particles are proposed to reform through an electrochemical Ostwald ripening mechanism driven by the size dependence of the work function and standard electrode potential. We also discuss prior literature experiments where this process appears to occur. Our results show the sensitivity of the electrochemical properties of metallic nanoparticles at relatively large sizes (approximately 50 nm).
In addition to their stability, the advantages of air- and water-stable ionic liquids over chloroaluminate ionic liquids, which were intensively investigated in the past, are that they are easy to dry, purify, and handle. Moreover, some of these ionic liquids have an extremely large electrochemical window of more than 5 V, and hence they give access to the electrodeposition of many metals and semiconductors, such as Ta, Ti, Si, and Ge. The results to date for the electrodeposition of metals and semiconductors in the most popular air- and water-stable ionic liquids are presented.
The present work shows, for the first time, a comparative experimental study on the electrodeposition of aluminium in three different water and air stable ionic liquids, namely 1-butyl-1-methylpyrrolidinium-bis(trifluoromethylsulfonyl)imide ([BMP]Tf2N), 1-ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide ([EMIm] Tf2N), and trihexyl-tetradecyl-phosphoniumbis(trifluoromethylsulfonyl)imide (P(14,6,6,6) Tf2N). The ionic liquids [BMP]Tf2N and [EMIm]Tf2N show biphasic behaviour in the AlCl3 concentration range from 1.6 to 2.5 mol L(-1) and 2.5 to 5 mol L(-1), respectively. The biphasic mixtures become monophasic at temperatures >/=80 degrees C. It was found that nanocrystalline aluminium can be electrodeposited in the ionic liquid [BMP]Tf2N saturated with AlCl3. The deposits obtained are generally uniform, dense, shining, and adherent with very fine crystallites in the nanometer size regime. However, coarse cubic-shaped aluminium particles in the micrometer range are obtained in the ionic liquid [EMIm]Tf2N. In this liquid the particle size significantly increases as the temperature rises. A very thin, mirrorlike aluminium film containing very fine crystallites of about 20 nm is obtained in the ionic liquid [trihexyl-tetradecyl-phosphonium]Tf(2)N at room temperature. At 150 degrees C, the average grain size is found to be 35 nm.
Room-temperature ionic liquids are a new class of liquids with many important uses in electrical and electrochemical devices. The liquids are composed purely of ions in the liquid state with no solvent. They generally have good electrical and ionic conductivity and are electrochemically stable. Since their applications often depend critically on the interface structure of the liquid adjacent to the electrode, a molecular level description is necessary to understanding and improving their performance.