N-methylpyrrolidinium Bis Research Articles

Electrochemical behavior of hexafluoroniobate, heptafluorotungstate, and oxotetrafluorovanadate anions in N-butyl- N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide room temperature ionic liquid

Electrochemical behavior of hexafluoroniobate (Nb(V)F 6 −), heptafluorotungstate (W(VI)F 7 −), and oxotetrafluorovanadate (V(V)OF 4 −) anions has been investigated in N-butyl- N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPyrTFSA) ionic liquid at 298 K by means of cyclic voltammetry and chronoamperometry. Cyclic voltammograms at a Pt electrode showed that Nb(V)F 6 − anion is reduced to Nb(IV)F 6 2− by a one-electron reversible reaction. Electrochemical reductions of W(VI)F 7 − and V(V)OF 4 − anions at a Pt electrode are quasi-reversible and irreversible reactions, respectively, according to cyclic voltammetry. The diffusion coefficients of Nb(V)F 6 −, W(VI)F 7 − and V(V)OF 4 − determined by chronoamperometry are 1.34 × 10 −7, 7.45 × 10 −8 and 2.49 × 10 −7 cm 2 s −1, respectively. The Stokes radii of Nb(V)F 6 −, W(VI)F 7 −, and V(V)OF 4 − in BMPyrTFSA have been calculated to be 0.23, 0.38, and 0.12 nm, from the diffusion coefficients and viscosities obtained.

Mixtures of ionic liquid and organic carbonate as electrolyte with improved safety and performance for rechargeable lithium batteries

In this paper we report the results of physical–chemical and electrochemical investigations performed on ternary mixtures of the room temperature ionic liquid (IL) N-butyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 14TFSI), propylene carbonate (PC), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as electrolyte for lithium-ion batteries. The thermal stability, ionic conductivity, viscosity and electrochemical stability windows of all considered mixtures were investigated and compared with those of electrolytes based on the pure PYR 14TFSI and PC. The mixtures were also used as electrolyte in combination with LiFePO 4-based electrodes. The specific capacity and cycling stability of these systems were investigated at different C-rates, both at room temperature and 60 °C.

Density, viscosity, and electrical conductivity of N-methoxymethyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide

The densities, viscosities, and electrical conductivities of the ionic liquid N-methoxymethyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide, [Pyr 1,1O1][Tf 2N] have been measured with expanded uncertainties of ±0.05 kg m −3, ±2%, and ±2% over a wide temperature range between 273.15 and 363.15 K at atmospheric pressure. The temperature dependence of the viscosity and conductivity was analyzed by the Litovitz and Vogel–Fulcher–Tammann equations. The effect of the methoxymethyl group instead of the propyl one on such physicochemical properties is discussed in comparison with the similar analogue, N-methyl- N-propylpyrrolidinium bis(trifluoromethanesulfonyl)amide, [Pyr 1,3][Tf 2N].

Electrochemical study of Pt and Fe and electrodeposition of PtFe alloys from air- and water-stable room temperature ionic liquids

The voltammetric behavior of Pt(II), Fe(II), and mixtures of Pt(II) and Fe(II) was studied in N-butyl- N-methylpyrrolidinium dicyanamide ionic liquid (BMP-DCA IL), N-butyl- N-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide ionic liquid (BMP-TFSI IL), and a mixture of BMP-DCA and BMP-TFSI, respectively. Electrodeposition of PtFe coatings was achieved by controlled-potential electrolysis on tungsten from the aforementioned ILs containing Pt(II) and Fe(II). The Pt(II) species required to prepare these PtFe coatings was introduced into the ILs by addition of PtCl 2. In BMP-TFSI, an additional two equivalents of N-butyl- N-methylpyrrolidinium chloride (BMP-Cl) were essential to assist one equivalent of PtCl 2 to dissolve. The Fe(II) species was introduced into the ILs by addition of FeCl 2 or by anodizing an iron spiral electrode. In BMP-TFSI, additional BMP-Cl had to be added to assist FeCl 2 dissolution (FeCl 2:BMP-Cl = 1:2 (mol:mol)). The PtFe coatings with various atomic ratios of Pt/Fe were studied for their voltammetric behavior towards the oxygen reduction reaction (ORR) in acidic solutions. This study shows that the PtFe alloy coatings with atomic ratios of ∼0.5/0.5 had the highest reductive current density for ORR, better than regular Pt or Pt-electrodeposited electrodes.

The electrode potentials of the Group I alkali metals in the ionic liquid N-butyl- N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide

The redox couples M/M + of the Group I alkali metals Lithium, Sodium, Potassium, Rubidium and Caesium have been extensively investigated in a room temperature ionic liquid (IL) and compared for the first time. Cyclic voltammetric experiments in the IL N-butyl- N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C 4mpyrr][NTf 2]) and subsequent simulation of the data has allowed the determination of the formal potential ( E f 0 vs. ferrocene/ferrocenium), standard electrochemical rate constant ( k 0) and transfer coefficient ( α) for each couple in the group. The trend in E f 0 in [C 4mpyrr][NTf 2] is remarkably similar to the established trend in the common battery electrolyte, propylene carbonate.

Uranyl Complexes of Carboxyl-Functionalized Ionic Liquids

Uranium(VI) oxide has been dissolved in three different ionic liquids functionalized with a carboxyl group: betainium bis[(trifluoromethyl)sulfonyl]imide, 1-(carboxymethyl)-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, and N-(carboxymethyl)-N-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide. The dissolution process results in the formation of uranyl complexes with zwitterionic carboxylate ligands and bis[(trifluoromethyl)sulfonyl]imide (bistriflimide) counterions. An X-ray diffraction study on single crystals of the uranyl complexes revealed that the crystal structure strongly depends on the cationic core appended to the carboxylate groups. The betainium ionic liquid gives a dimeric uranyl complex, the imidazolium ionic liquid a monomeric complex, and the pyrrolidinium ionic liquid a one-dimensional polymeric uranyl complex. Extended X-ray absorption fine structure measurements have been performed on the betainium uranyl complex. The absorption and luminescence spectra of the uranyl betainium complex have been studied in the solid state and dissolved in water, in acetonitrile, and in the ionic liquid betainium bistriflimide. The carboxylate groups remain coordinated to uranyl in acetonitrile and in betainium bistriflimide but not in water.

Lithium ion conducting PVdF-HFP composite gel electrolytes based on N-methoxyethyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)-imide ionic liquid

Blends of PVdF-HFP and ionic liquids (ILs) are interesting for application as electrolytes in plastic Li batteries. They combine the advantages of the gel polymer electrolytes (GPEs) swollen by conventional organic liquid electrolytes with the nonflammability, and high thermal and electrochemical stability of ILs. In this work we prepared and characterized PVdF-HFP composite membranes swollen with a solution of LiTFSI in ether-functionalized pyrrolidinium-imide ionic liquid (PYRA 12O1TFSI). The membranes were filled in with two different types of silica: (i) mesoporous SiO 2 (SBA-15) and (ii) a commercial nano-size one (HiSil™ T700). The ionic conductivity and the electrochemical properties of the gel electrolytes were studied in terms of the nature of the filler. The thermal and the transport properties of the composite membranes are similar. In particular, room temperature ionic conductivities higher than 0.25 mS cm −1 are easily obtained at defined filler contents. However, the mesoporous filler guarantees higher lithium transference numbers, a more stable electrochemical interface and better cycling performances. Contrary to the HiSil™-based membrane, the Li/LiFePO 4 cells with PVdF-HFP/PYRA 12O1TFSI–LiTFSI films containing 10 wt% of SBA-15 show good charge/discharge capacity, columbic efficiency close to unity, and low capacity losses at medium C-rates during 180 cycles.

Electrochemical codeposition of copper and manganese from room-temperature N-butyl- N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid

The voltammetric behavior of N-butyl- N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid (BMP-TFSI) containing Cu(I), Mn(II), or mixtures of Cu(I) and Mn(II) as well as the electrodeposition of copper–manganese alloy coatings (Cu–Mn alloy coatings) was studied at 323 K. The Cu(I) and Mn(II) species required to prepare these coatings were introduced into the BMP-TFSI by anodic dissolution of the relevant metallic electrodes. Electrodeposits of Cu, Mn, and Cu–Mn with various contents of Mn can be obtained by controlled-potential electrolysis. It was found that the compositions and surface morphology of the electrodeposited Cu–Mn alloy coatings depend on the deposition potentials and the concentration ratio of [Cu(I)]/[Mn(II)] in BMP-TFSI. The Cu–Mn alloy coatings obtained in this study were compact and adherent. They did not show any significant X-ray diffraction signal that could be assigned to the crystalline structures of Cu, Mn, or Cu–Mn alloys. In the aqueous solution containing 0.1 M NaCl, the Cu–Mn alloy coatings demonstrated passive behavior—no continuous oxidation was observed. However, a significant oxidation current was observed at the electrodes deposited with Cu or Mn.

Electrochemical formation of polycarbazole films in air- and water-stable room-temperature ionic liquids

Carbazole was electropolymerized on indium tinoxide (ITO) electrodes in two air- and water-stable room-temperature ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF 6) and N-butyl- N-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide (BMP-TFSI), respectively, using three potentiostatic methods ( i.e., cyclic voltammetry, potentiostatic electrolysis, and potentiostatic pulse electrolysis). The polymer films obtained in both ionic liquids (ILs) adhered on the electrode surface well; however, the polycarbazole (PCz) films obtained in the more viscous BMI-PF 6 exhibited a denser structure. The PCz films showed electrochromic behavior; deep green was observed in the oxidative state and pale green in the reductive state. Anions or viscosities of the ILs seem to influence the depth of color change. PCz films were also prepared under a normal atmosphere.

Extracting Cu(II) from aqueous solutions with hydrophobic room-temperature ionic liquid in the presence of a pyridine-based ionophore to attempt Cu recovery: A laboratory study

Extraction of Cu(II) from neutral aqueous solutions with the hydrophobic room-temperature ionic liquid (IL) N-butyl- N-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide (BMP-TFSI) in the presence of the pyridine-based ionophore N 1, N 1, N 4, N 4-tetrakis(2-(pyridin-2-yl)ethyl)butane-1,4-diamine (C 4N 2Py 4) is demonstrated in this study. Although the distribution coefficients, D M, of Cu(II) extraction depend on the concentration of Cu(II) in aqueous solutions, all values were higher than 200, indicating extremely high extraction efficiency. Based on spectrophotometric, electrochemical, and X-ray crystallography studies, the coordination number of the C 4N 2Py 4-coordinated Cu(II) ions was determined as 2. The voltammetric behavior of Cu(I), Cu(II), and their C 4N 2Py 4 complex ions were also studied. The recovery of Cu from the IL was conducted by washing the IL phase containing the extracted Cu(II) complex with an acidic aqueous phase or by controlled-potential electrolysis. The IL containing C 4N 2Py 4 was employed for two complete rounds and a decrease in extraction efficiency was only observed when higher concentration of Cu(II) was used.

Effect of the alkyl group on the synthesis and the electrochemical properties of N-alkyl- N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquids

The effect of the alkyl side group on the synthesis and the electrochemical properties of N-alkyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 1ATFSI) ionic liquids (ILs) is reported. The investigation was focused on the PYR 1ATFSI ionic liquid family because of the interesting electrochemical properties of the members with propyl and butyl side chains. Side alkyl groups (A = C n H 2 n+1 with n ranging from 1 to 10) of different length and structure were used for the synthesis of PYR 1ATFSI materials. NMR and DSC have shown that the ionic liquids were correctly synthesized with the exception of the compounds with tertiary side chains. Most of the materials exhibited a conductivity higher than 10 −3 S cm −1 already at 12 °C. In the molten state a moderate conductivity decrease was observed with increasing the length and the branching of the side chain (C 2H 2 n+1 ) group according with the change of viscosity of the ionic liquids. Most of the PYR 1ATFSI samples exhibited an electrochemical stability window exceeding 5 V.

Production of nanoparticles composed of ionic liquid [C 4mpyrr][NTf 2] and their chemical identification by diameter analysis and X-ray photoelectron spectroscopy

Production of nanoparticles composed of ionic liquid [C 4mpyrr][NTf 2], N-butyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, was demonstrated by a gas aggregation technique under low pressure. The diameter spectra were measured by a differential mobility analyzer (DMA) and were dependent on the heating temperature. Photoelectron spectra for the nanoparticles diameter-selected at 10 nm were also measured by X-ray photoelectron spectroscopy (XPS), and their chemical composition and structure were identified by comparison with photoelectron spectra for neat ionic liquid. The form and surface structure of the nanoparticles deposited onto an Au-coated Si substrate were also determined.

Liquid structure of N-butyl- N-methylpyrrolidinium bis-(trifluoromethanesulfonyl) amide ionic liquid studied by large angle X-ray scattering and molecular dynamics simulations

Large angle X-ray scattering of the N-butyl- N-methylpyrrolidinium bis-(trifluoromethanesulfony) amide (P 14 +TFSA −) ionic liquid was measured at 298 K. The total interference function i LAXS( s) and the total pair correlation function G LAXS( r) were successfully obtained. The i LAXS( s) was analyzed in terms of the intra-molecular geometries of the conformational isomers of the P 14 + and TFSA − ions based on the crystal structures, the inter-molecular correlation function G inter LAXS( r) and the inter-molecular radial distribution function as the form D inter LAXS( r) − 4 πr 2 ρ 0 were evaluated. With D inter LAXS( r) − 4 πr 2 ρ 0, the inter-molecular correlation peaks at 3.5, 4.5 and 5–6 Å evidently appeared as the short range interaction, while considerable long range interactions were found as the broad peaks at 10 and 15 Å. Molecular dynamics simulations of the ionic liquid based on the effective pairwise potentials were carried out. The X-ray total interference function derived from the MD simulations i MD( s) was in agreement with the experimental one. According to the inter-molecular partial atom–atom correlation functions from MD simulations, the observed peaks at 3.5, 4.5 and 5–6 Å can be predominantly ascribed to the closest atom–atom correlations between the P 14 + and TFSA – ions such as C···O and C···F. In the inter-molecular partial atom–atom correlation function between terminal methyl carbons of the butyl chain in the P 14 + ion, a peak at 4.0 Å was found as the inter-molecular correlation, suggesting that the ionic liquid shows an alkyl chain aggregation, which is similar to that observed for 1-alkyl-3-methylmidazolium ionic liquids.

The influence of air and its components on the cathodic stability of N-butyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide

Although water- and air-stable ionic liquids have been in use for some years, experiments found in the literature are still performed in inert gas with ppm levels of oxygen and water. In this study, the influence of different environments (vacuum, argon, nitrogen, air and oxygen and water) on the cathodic electrochemical window of the ionic liquid N-butyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 14TFSI) is reported and compared with investigations and processes found in the literature. The investigation indicates that this ionic liquid is highly stable in a vacuum and under argon flow. However, its cathodic stability is reduced in nitrogen and dry air. The simultaneous presence of water and air strongly affected the useful electrochemical window, as seen previously for imidazolium-based ionic liquids.

Solvent-free, PYR 1ATFSI ionic liquid-based ternary polymer electrolyte systems : I. Electrochemical characterization

The electrical properties of solvent-free, PEO–LiTFSI solid polymer electrolytes (SPEs), incorporating different N-alkyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, PYR 1ATFSI, ionic liquids (ILs), are reported. For this purpose, PYR 1ATFSI materials containing side alkyl groups with different chain-length and branching, i.e., n-propyl, sec-propyl, n-butyl, iso-butyl, sec-butyl and n-pentyl, were properly synthesized and homogeneously incorporated into the SPE samples without phase separation. The addition of ILs to PEO–LiTFSI electrolytes results in a large increase of the conductivity and in a decrease of the interfacial resistance with the lithium metal anode. Most of the PEO–LiTFSI–PYR 1ATFSI samples showed similar ionic conductivities (>10 −4 S cm −1 at 20 °C) and stable interfacial resistance values (400 Ω cm 2 at 40 °C and 3000 Ω cm 2 at 20 °C) upon several months of storage. Preliminary battery tests have shown that Li/P(EO) 10LiTFSI + 0.96 PYR 1ATFSI/LiFePO 4 solid-state cells are capable to deliver a capacity of 125 mAh g −1 and 100 mAh g −1 at 30 °C and 25 °C, respectively.

Electrode materials for ionic liquid-based supercapacitors

The use of ionic liquid (IL) electrolytes is a promising strategy to enhance the performance of supercapacitors above room temperature. In this paper we present the results of a study on optimization of electrode materials for IL-based supercapacitors featuring a hybrid configuration with carbon negative electrode and poly(3-methylthiophene) (pMeT) as positive operating at 60 °C with the ILs N-butyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 14TFSI) and 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI). As it concerns the carbon electrode two routes have been pursued: (i) surface modification of commercial activated carbon and (ii) synthesis of mesoporous cryo- and xerogel carbons. Pore size distribution and electrochemical characterization data are related and suggest that the second route should be the most promising for carbons of high specific capacitance and low time constant in IL. For the polymer electrode the nature of the galvanostatic polymerization bath plays a crucial role to provide pMeT of high specific capacitance and the best results may be obtained when pMeT is electropolymerized in the same IL used for the capacitance tests. The strategy of using the acid additive trifluoromethanesulfonimide in IL-based polymerization baths is also described in some detail. This strategy that provides pMeT featuring more than 200 F g −1 in IL is a clean procedure which prevents consumption of the ionic liquid with great advantage in terms of costs.

Strategies for high-performance supercapacitors for HEV

Our paper highlights the role of supercapacitors in hybrid electric vehicles (HEVs), the current response to the worldwide demand for a clean and low fuel-consuming transport. The main strategies for increasing the specific energy of supercapacitors, which are electrochemical energy storage/conversion systems of high-specific power, are discussed, with the focus on electrode material, electrolyte and electrode/electrolyte interface properties. Particular emphasis is given to the use of ionic liquids (IL), which are attracting much attention as green and solvent-free electrolytes, and to the development of high-voltage, IL-based hybrid supercapacitor with high surface area carbon negative electrode and poly(3-methylthiophene) positive. Based on the results of laboratory cells featuring N-butyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide and 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonylimide) ILs, the specific energies of hybrid supercapacitor modules are evaluated and compared to those expected for double-layer carbon supercapacitors displaying the same ILs.

Capacitance response of carbons in solvent-free ionic liquid electrolytes

Ionic liquids (IL) are very promising “solvent-free” electrolytes for high-voltage double-layer supercapacitors (EDLCs) and to this purpose they are generally selected on the basis of their bulk properties, such as electrochemical stability and ion conductivity, without taking into account those of the electrified electrode-IL interface. This interface, which has yet to be well characterized, has features that notably affect electrode capacitance, and our paper for the first time highlights the importance of the molecular chemistry and structure of the ions for the double-layer capacitive response of carbonaceous electrodes in IL. The double-layer capacitive responses of negatively charged electrodes based on activated carbons and aero/cryo/xerogel carbons in two ILs featuring the same anion and different cations of almost the same size, i.e. the N-butyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 14TFSI) and 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI) are reported. The porosity, structure and surface chemistry of the carbons are compared to their capacitive response to evince the role played by these carbon properties and by the chemistry and structure of the IL ions in the electric double-layer.

High temperature carbon–carbon supercapacitor using ionic liquid as electrolyte

This paper presents results about the electrochemical and cycling characterizations of a supercapacitor cell using a microporous activated carbon as the active material and N-butyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 14TFSI) ionic liquid as the electrolyte. The microporous activated carbon exhibited a specific capacitance of 60 F g −1 measured from the three-electrode cyclic voltammetry experiments at 20 mV s −1 scan rate, with a maximum operating potential range of 4.5 V at 60 °C. A coin cell assembled with this microporous activated carbon and PYR 14TFSI as the electrolyte was cycled for 40,000 cycles without any change of cell resistance (9 Ω cm 2), at a voltage up to 3.5 V at 60 °C, demonstrating a high cycling stability as well as a high stable specific capacitance in this ionic liquid electrolyte. These high performances make now this type of supercapacitor suitable for high temperature applications (≥60 °C).

Cycling stability of a hybrid activated carbon//poly(3-methylthiophene) supercapacitor with N-butyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid as electrolyte

A long cycle-life, high-voltage supercapacitor featuring an activated carbon//poly(3-methylthiophene) hybrid configuration with N-butyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid, a solvent-free green electrolyte, was developed. The cyclability of a laboratory scale cell with electrode mass loading sized for practical uses was tested at 60 °C over 16,000 galvanostatic charge–discharge cycles at 10 mA cm −2 in the 1.5 and 3.6 V voltage range. The reported average and maximum specific energy and power, specific capacitance and capacity, equivalent series resistance and coulombic efficiency over cycling demonstrate the long-term viability of this ionic liquid as green electrolyte for high-voltage hybrid supercapacitors.