Papers - Serizawa, Nobuyuki

The Local Changes in the Physicochemical Properties during Electrode Reactions in a Chlorocuprate Ionic Liquid

Serizawa N., Kuwahara S., Li X., Katayama Y.

Journal of the Electrochemical Society 172 ( 4 )  2025.04

ISSN  00134651

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The physicochemical and electrochemical properties of an ionic liquid consisting of the dichlorocuprate anion, [CuCl2]-, were investigated. The equimolar mixture of CuCl and 1-butyl-1-methylpyrrolidinium chloride (BMPCl) was found to yield an ionic liquid at 298 K composed predominantly of BMP+ and [CuCl2]-. Fine deposits of metallic Cu were obtained on a glassy carbon electrode by potentiostatic and galvanostatic reduction of [CuCl2]- in CuCl-BMPCl (50.0-50.0 mol%). The overpotential for Cu nucleation was larger on a glassy carbon electrode than on a Pt electrode. The electrochemical deposition and dissolution of Cu were analyzed using an electrochemical quartz crystal microbalance. The local viscosity and density of the electrolyte near the electrode/electrolyte interface increased during both deposition and dissolution of Cu, probably reflecting the shift in the electrolyte composition to the local basic and acidic conditions, respectively.

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Evaluation of the Solid-Electrolyte Interphase Formed in the Carbonate-Based Electrolytes with Different Lithium Salts Using the Redox Probe Method

Katayama Y., Okazaki S., Serizawa N.

Electrochemistry 93 ( 6 )  2025

ISSN  13443542

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The formation of solid-electrolyte interphase (SEI) on a Pt electrode was investigated in ethylene carbonate (EC) and diethyl carbonate (DEC) containing LiPF<inf>6</inf> and lithium bis(trifluoromethylsulfonyl)amide (LiTFSA) using the redox probe method. The formation and properties of the SEI were examined in the electrolytes containing ferrocene as a redox probe. Inhomogeneous and rigid SEI was found to form in 1 M (= mol dm⁻³) LiPF<inf>6</inf>/EC+DEC, probably due to the conversion of decomposition products to LiF by the reaction with HF derived from LiPF<inf>6</inf>. On the other hand, the formation of homogeneous and soluble (or dispersible) SEI was suggested in 1 M LiTFSA/EC+DEC.

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Electrode Reactions of Copper Species in a Bis(fluorosulfonyl)amide Ionic Liquid

Nobuyuki Serizawa, Takumi Hisada, Yasushi Katayama

Electrochemistry ((公社)電気化学会)  92 ( 4 ) 043009 2024.04

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted,  ISSN  13443542

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The electrode reactions of copper species were investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl) amide (BMPFSA). The anodic current assignable to the dissolution of Cu to form monovalent Cu(I) complex was observed at −0.42 V vs. Ag|Ag(I). A pair of anodic and cathodic current peaks attributable to Cu(II)/Cu(I) was observed at 0.5 V, suggesting that a 4 V class redox flow battery combined with a Li metal anode is expected using the redox reaction of Cu(II)/Cu(I) in BMPFSA as the cathode reaction. The electrodeposition of Cu and the quasi-reversible redox reaction of Cu(II)/Cu(I) were affected by the electrode materials.

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Formation and Breakdown of the Solid-electrolyte Interphase in a Bis(fluorosulfonyl)amide-based Ionic Liquid in the Presence of Lithium Ion

Sho Okazaki, Nobuyuki Serizawa, Yasushi Katayama

Electrochemistry ((公社)電気化学会)  92 ( 4 ) 043006 2024.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  13443542

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The formation and breakdown of the solid electrolyte interphase (SEI) on a Pt electrode were investigated in 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) containing a high concentration of LiFSA using a ferrocene/ferrocenium couple as a redox probe. The formation of the SEI was confirmed at the potential more negative than −1.1 V vs. Ag|Ag(I). However, the SEI was found to disappear at the open circuit potential. The SEI was suggested to form by the dissolution and/or dispersion of the decomposition products in the electrolyte.

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Formation and Aging of the Solid Electrolyte Interphase on Lithium in Bis(fluorosulfonyl)amide-Type Ionic Liquids

Serizawa N., Yamashita R., Katayama Y.

Journal of Physical Chemistry C (Journal of Physical Chemistry C)  127 ( 22 ) 10434 - 10444 2023.04

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted,  ISSN  19327447

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The formation and aging of the solid electrolyte interphase (SEI) formed on a Li and Cu electrode in two bis(fluorosulfonyl)amide (FSA-)-type ionic liquids (ILs), 1-methyl-1-butylpyrrolidinium bis(fluorosulfonyl)amide and 1-methyl-1-methoxyethylpyrrolidinium bis(fluorosulfonyl)amide, containing a high concentration of LiFSA were investigated using electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy. The intensity of peaks corresponding to the decomposition of the electrolyte in XPS spectra changed with time. The thicknesses of the SEI formed on a Cu electrode in both ILs were estimated to be 20-100 nm by TEM observation. The resistance of SEI increased with the lapse of time although the change in the thickness of the SEI was small, suggesting the aging of the SEI in the ILs was considered to depend on the composition of the SEI rather than the thickness of the SEI. The Li deposits shrank during dissolution. The Li anode became sparse and porous after deposition and dissolution cycles, probably due to the inhomogeneous reaction through the aged SEI. The SEI formation on the surface of the porous deposits was considered to lead to an increase in the polarization and the isolation of the deposits, i.e., the formation of “dead lithium”.

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Redox Reactions of Ag(I)/Ag and Ferrocenium/Ferrocene in 1-Butyl-1-methylpyrrolidinium Bis(fluorosulfonyl)amide Ionic Liquid

Kato S., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society)  170 ( 4 )  2023.04

ISSN  00134651

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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 those in TFSA--type ionic liquids, reflecting the higher charge density of FSA-. The standard rate constant (k 0) of Fc+/Fc was estimated to be (5.4 ± 1.1) × 10-3 cm s-1. The apparent activation energy for k 0 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.

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Solid-Electrolyte Interphase Formation in Amide-Type Ionic Liquids in the Presence of Different Metal Cations

Kato S., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society)  170 ( 5 )  2023

ISSN  00134651

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The formation of solid-electrolyte interphase (SEI) on a glassy carbon (GC) electrode in 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing Li+, Na+, K+, and Ni2+ was investigated using the redox reaction of ferrocene (Fc). The anodic peak potential (E pa) for the oxidation of Fc changed after holding the electrode at -1.4 to -1.5 V vs Ag|Ag(I) in BMPFSA in the presence of the alkali metal ions. The decomposition of FSA- was confirmed by X-ray photoelectron spectroscopy (XPS) on a GC electrode held at -1.5 V vs Ag|Ag(I) for 6 h in BMPFSA containing the alkali metal ions. The change in E pa may also suggest the formation of homogeneous SEI in the FSA--type ionic liquid. Moreover, E pa changed after holding the electrode at the potential more negative than -0.9 V vs Ag|Ag(I) in 50 mM Ni(TFSA)2/BMPTFSA while the decomposition of TFSA- was not confirmed by XPS on the electrode held at -1.1 V vs Ag|Ag(I) for 6 h, suggesting the bonds except C-F (e.g., S-C) were dissociated to form the SEI. Since the deposition potential of Ni in BMPTFSA was more negative than the SEI formation potential, the deposition of Ni may be inhibited by the SEI.

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Electrochemical Behavior of Silver Halogenocomplexes in an Amide-Type Ionic Liquid

Nobuyuki Serizawa, Suguru Kuwahara, Yasushi Katayama

Journal of The Electrochemical Society 169   092502 2022.09

Research paper (scientific journal), Joint Work, Lead author, Accepted

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Communication - Determination of the Formation Potential of Solid-Electrolyte Interphase in Amide-Type Ionic Liquids Containing Lithium Salts

Kato S., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society)  169 ( 7 )  2022.07

ISSN  00134651

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The formation potentials of solid-electrolyte interphase (SEI) were investigated in 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing LiFSA and LiTFSA, respectively, by monitoring the redox reaction of ferrocene with high sensitivity. The SEI was found to affect the electrode kinetics of the outersphere electron transfer reaction. The SEIs with the thickness of less than a few nm formed in LiFSA/BMPFSA and LiTFSA/BMPTFSA at 2.4 and 2.5 V vs Li|Li(I), respectively. The cathodic decomposition of FSA- and TFSA- was considered to be promoted by the interaction with Li+ based on the ab-initio calculation.

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Potential Dependence of the Impedance of Solid Electrolyte Interphase in Some Electrolytes

Furuya R., Serizawa N., Katayama Y.

Electrochemistry (Electrochemistry)  90 ( 5 )  2022

ISSN  13443542

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The dependence of the impedances of lithium phosphorous oxynitride (LiPON) thin film and solid electrolyte interphase (SEI) formed by decomposition of some electrolytes on the electrode potential was investigated by electrochemical impedance spectroscopy. A LiPON thin film was prepared on a Ni electrode by radio frequency magnetron sputtering of Li3PO4 under nitrogen atmosphere. The resistance of the LiPON thin film decreased with lowering the electrode potential in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide (BMPTFSA) containing 1M LiTFSA. The similar potential dependence of the impedance of the SEI formed in 1M LiTFSA/BMPTFSA was observed, suggesting that the Li+ carrier density in the LiPON thin film and SEI increased with lowering the electrode potential probably due to the doping of Li+ from the electrolyte into the thin Li+ conductors in order to compensate the negative charge on the electrode. On the other hand, the potential dependence of the SEI formed in LiTFSA-tetraglyme (G4) solvate ionic liquid was insignificant because of the high concentration of Li+ in the SEI and electrolyte. The resistance of the SEI formed in 1M LiClO4/EC (ethylene carbonate) + DMC (dimethyl carbonate) (1 : 1 vol%) did not depend on the electrode potential, suggesting the thin and highly Li+ conductive SEI is formed in the organic electrolyte.

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Electrodeposition of Nickel From an Amide-Type Ionic Liquid Under a Magnetic Field

Katayama Y., Manabe Y., Serizawa N.

ECS Transactions (ECS Transactions)  109 ( 14 ) 235 - 238 2022

ISSN  19386737

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Electrodeposition of nickel was investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide (BMPTFSA) containing Ni(TFSA)2 under a external magnetic field. The onset potential of cathodic reduction of Ni(II) with a magnetic field was more positive than that without the magnet field. Ni nanowires were deposited by potentiostatic cathodic reduction with the magnetic field, indicating the magnetic field influence not only the electrode kinetics of the magnetic species but also the morphology of the ferromagnetic metal.

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Determination of the Formation Potential of Solid-Electrolyte Interphase in Some Amide-Type Ionic Liquids Containing Metal Salts

Kato S., Serizawa N., Katayama Y.

ECS Transactions (ECS Transactions)  109 ( 14 ) 215 - 223 2022

ISSN  19386737

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The formation potentials of the solid-electrolyte interphase (SEI) on a platinum and glassy carbon electrode in two amide-type ionic liquids, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), containing some metal salts were investigated by cyclic voltammetry in the presence of ferrocene (Fc). It is considered that the SEI with the thickness of less than a few nm can be observed by monitoring the shift in the peak potential of Fc+/Fc. The SEIs began to form at ∼2.4 V vs. Li|Li(I) in the presence of lithium salts because of a lowering of the lowest unoccupied molecular orbital level of the anion by the interaction with lithium ion. In the case of BMPTFSA containing Ni(TFSA)2, the SEI began to form at -0.7 V vs. Ag|Ag(I), suggesting that the deposition of Ni may be hindered by the SEI formation.

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Deposition and Dissolution of Lithium in 1-Methyl-1-methoxyethylpyrrolidinium Bis(fluorosulfonyl)amide Ionic Liquid Electrolyte with Different Compositions

Furuya R., Hara T., Fukunaga T., Kawakami K., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society)  168 ( 10 )  2021.10

ISSN  00134651

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The solid electrolyte interphase (SEI) between Li and ionic liquid electrolytes was investigated in 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)amide (MPPFSA) and 1-methyl-1-methoxyethylpyrrolidinium bis(fluorosulfonyl)amide (MOEMPFSA) with different LiFSA concentrations. The physicochemical properties and the coordination states of Li+ with FSA- with increasing the LiFSA concentration were similar between xLiFSA-MPPFSA and MOEMPFSA. On the other hand, the SEI resistance obtained by electrochemical impedance spectroscopy using a Li|Li symmetrical cell increased with the lapse of time in xLiFSA-MPPFSA more significantly than in xLiFSA-MOEMPFSA, suggesting that the SEI formed in xLiFSA-MOEMPFSA was more conductive than that in xLiFSA-MPPFSA. The SEI formed on Li was considered to be composed mainly of the ions in the electrolytes and their decomposed products by X-ray photoelectron spectroscopy. The cyclability of deposition and dissolution of Li was improved with increasing the LiFSA concentration in both xLiFSA-MPPFSA and MOEMPFSA. An increase in the conductivity of the SEI with increasing the LiFSA concentration may lead to the promotion of homogeneous growth of Li rather than dendritic growth of Li.

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Electrochemical Recovery of Cobalt from Cobalt Oxide in an Amide-Type Ionic Liquid with Low-Temperature Carbochlorination

Yeh H.W., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society)  168 ( 8 )  2021.08

ISSN  00134651

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Electrochemical recovery of metallic Co was attempted from CoO in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing 0.5 M BMPCl. CoO was dissolved in 0.5 M BMPCl/BMPTFSA with a carbochlorination reagent, C2Cl6, to form [CoCl4]2- at 150 °C. After the removal of electroactive C2Cl6 and byproducts, the electrochemical reduction of [CoCl4]2- was found to be possible on a glassy carbon electrode in the ionic liquid. Co nanowires were deposited by electrochemical reduction of [CoCl4]2- in 0.5 M BMPCl/BMPTFSA under an external magnetic field, which promoted the cathodic reduction and affected the morphology of the deposits. The deposited Co nanowires were found to be composed of crystalline Co nanoparticles by transmission electron microscopy.

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Electrodeposition of Co in an Amide-Type Ionic Liquid under an External Magnetic Field

Manjum M., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society)  168 ( 4 )  2021.04

ISSN  00134651

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Electrodeposition of Co was investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), under an external magnetic field. Neodymium magnets were used as a source of the magnetic field, which was parallel to the ionic current during the electrodeposition of Co on a glassy carbon electrode. Potentiostatic cathodic reduction applying -1.6 and -2.0 V vs Ag|Ag(I) under the magnetic field in BMPTFSA containing Co(TFSA)2 at 25 C gave nanowire-shaped deposits on the electrode surface. The deposits were found to be composed of Co, which was confirmed by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. However, no diffraction peak was observed in the deposits by X-ray diffraction. The nanowires were further examined by transmission electron microscopy. The lattice fringe corresponding to (111) plane of Co was found in the deposits, indicating the nanowires were composed of metallic Co nanoparticles. Therefore, crystalline Co nanoparticles were considered to be formed in the presence of the magnetic field.

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Electropolishing of Tin in an Amide-Type Ionic Liquid

Yuza N., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society)  168 ( 3 )  2021.03

ISSN  00134651

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Anodic dissolution and electropolishing of Sn were investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide. The rate of anodic dissolution was considered to be determined by the diffusion of anodically dissolved Sn(II) species. A large increase in the local viscosity during dissolution was observed in-situ by the impedance-type electrochemical quartz crystal microbalance, reflecting an increase in the local concentration of Sn(II) near the electrode. A shiny and smooth surface was obtained after anodic dissolution at 0.1 V vs Ag|Ag(I) with agitation. A decrease in the surface roughness estimated by confocal laser scanning microscopy suggested electropolishing of Sn was possible in the ionic liquid within the electrochemical potential window probably due to the formation of the viscous layer near the electrode.

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Redox Reaction of 2,2,6,6,-Tetramethylpiperidine-1-oxyl in Lithium Bis(trifluoromethylsulfonyl)amide-tetraglyme Solvate Ionic Liquid

Serizawa N., Wada K., Tachikawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society)  167 ( 4 )  2020.03

ISSN  00134651

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© 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited. The electrode reaction of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was investigated in a solvate ionic liquid composed of lithium bis(trifluoromethylsulfonyl)amide (LiTFSA) and tetraglyme (G4), [Li(G4)]TFSA. A quasi-reversible redox reaction of the oxoammonium (TEMPO+) and TEMPO was observed with a formal potential of 0.19 V vs ferrocene|ferrocenium. The diffusion coefficient of TEMPO+ (2.1 × 10-8 cm2 s-1) was smaller than that of neutral TEMPO (1.3 × 10-7 cm2 s-1), reflecting the coulombic interaction between monovalent TEMPO+ and TFSA- in the solvate ionic liquid. The standard rate constant for TEMPO+/TEMPO redox reaction was estimated to be 1.9 × 10-4 cm s-1 at 25 C by electrochemical impedance spectroscopy. The solubility of TEMPO in [Li(G4)]TFSA was found to be 4.4 M at 25 C.

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Electrochemical Preparation of Cobalt-Samarium Nanoparticles in an Aprotic Ionic Liquid

Manjum M., Serizawa N., Ispas A., Bund A., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society)  167 ( 4 )  2020.03

ISSN  00134651

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© 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. Electrochemical preparation of Co-Sm nanoparticles was conducted in an aprotic room temperature ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing Co(TFSA)2 and Sm(TFSA)3. The cyclic voltammetry on a glassy carbon (GC) electrode indicated the electrochemically generated Sm(II) reacted with Co(II) at 25 C. Potentiostatic cathodic reduction on a GC electrode in BMPTFSA containing 30 mM Co(TFSA)2 and 5 mM Sm(TFSA)3 at 25 C gave the deposits, which were found to be composed of Co and Sm by energy dispersive X-ray spectroscopy (EDX). The deposits were found to be the aggregates of SmCo7 nanoparticles by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The formation of SmCo7 nanoparticles dispersed in the ionic liquid was also confirmed by TEM. SmCo7 nanoparticles were considered to form by the disproportionation reaction of Sm(II) in the presence of elementary Co, which was formed by the reduction of Co(II) by Sm(II).

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Characterization of the Solid-Electrolyte Interphase between a Cu Electrode and LiN(CF<inf>3</inf>SO<inf>2</inf>)<inf>2</inf>-triglyme Solvate Ionic Liquid

Serizawa N., Kitta K., Tachikawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society)  167 ( 11 )  2020.01

ISSN  00134651

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© 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. The formation of the solid electrolyte interphase (SEI) on a Cu electrode was investigated in 50.0-50.0 mol% lithium bis(trifluoromethylsulfonyl)amide (LiTFSA)-triglyme (G3, CH3(OCH2CH2)3OCH3) solvate ionic liquid, [Li(G3)]TFSA, using electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). The Li+ conductive SEI was formed on a Cu electrode by keeping the potential at 0 V vs Li|Li(I). The resistance and capacitance attributable to the SEI changed over a period of 24 h in EIS spectra, suggesting the sluggish SEI formation on the Cu electrode in [Li(G3)]TFSA. XPS and FT-IR spectra indicated the existence of G3, TFSA-, [Li(G3)]+, and/or their decomposition products in the SEI. In contrast, LiF was not found in the SEI, suggesting LiF was not formed by the cathodic decomposition of [Li(G3)]TFSA on the Cu electrode at 0 V. The whisker-like growth of Li on a Cu electrode was suppressed after the SEI formation at 0 V probably due to the formation of homogeneous and low-conductive SEI layer. The coulombic efficiency for deposition and dissolution of Li was improved with the SEI formation at 0 V prior to the measurements, suggesting the SEI on a Cu electrode affected the reversibility of the Li anode.

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Electrochemical Behavior of a Ni Chlorocomplex in a Lewis Basic Ionic Liquid Containing Chloride Ion

Ando K., Tachikawa N., Serizawa N., Katayama Y.

Journal of the Electrochemical Society (Journal of the Electrochemical Society)  167 ( 6 )  2020.01

ISSN  00134651

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© 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. The electrochemical behavior of a chlorocomplex of nickel (Ni) was investigated in a Lewis basic and hydrophobic ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing Cl-. NiCl2 dissolved in BMPTFSA with addition of 0.5 M BMPCl. The dissolved species of Ni(II) in BMPTFSA was identified as [NiCl4]2- by UV-visible spectrometry and magnetic susceptibility balance. The cathodic and anodic currents assignable to deposition and dissolution of Ni, respectively, were observed in cyclic voltammetry. The granular deposits of Ni were obtained on a glassy carbon electrode at 25 and 100 °C. Ni nanoparticles were dispersed in the electrolyte by galvanostatic cathodic reduction. The initial stage of Ni deposition was found to be regarded as instantaneous. The diffusion coefficient of [NiCl4]2- was calculated to be 6.6 × 10-8 cm2 s-1

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