Alkali metal salts with designable aryltrifluoroborate anions

Article abstract of DOI:10.1021/acs.jpcb.6b06990

Aryltrifluoroborate ([ArBF₃]^-) has a designable basic anion structure. Various [ArBF₃]^--based anions were synthesized to create novel alkali metal salts using a simple and safe process. Nearly 40 novel alkali metal salts were successfully obtained, and their physicochemical characteristics, particularly their thermal properties, were elucidated. These salts have lower melting points than those of simple inorganic alkali halide salts, such as KCl and LiCl, because of the weaker interactions between the alkali metal cations and the [ArBF₃]^- anions and the anions' larger entropy. Moreover, interestingly, potassium cations were electrochemically reduced in the potassium (meta-ethoxyphenyl)trifluoroborate (K[m-OEtC₆H₄BF₃]) molten salt at 433 K. These findings contribute substantially to furthering molten salt chemistry, ionic liquid chemistry, and electrochemistry.

Full text of DOI:10.1021/acs.jpcb.6b06990

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Article
Alkali Metal Salts with Designable Aryltrifluoroborate Anions
Kazuki Iwasaki, Kazuki Yoshii, Seiji Tsuzuki, Hajime Matsumoto, Tetsuya Tsuda, and Susumu Kuwabata
J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.6b06990 • Publication Date (Web): 11 Aug 2016
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Alkali Metal Salts with Designable Aryltrifluoroborate Anions
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Kazuki Iwasaki,† Kazuki Yoshii,† Seiji Tsuzuki,‡ Hajime Matsumoto,†,§ Tetsuya Tsuda,*,†
and Susumu Kuwabata*,†,§
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†Department of Applied Chemistry, Graduate School of Engineering, Osaka University,
2ꢀ1 Yamadaꢀoka, Suita, Osaka 565ꢀ0871, Japan
‡Research Center for Computational Design of Advanced Functional Materials,
National Institute of Advanced Industrial Science and Technology (AIST),
1ꢀ1ꢀ1 Umezono, Tsukuba, Ibaraki 305ꢀ8568, Japan
§Department of Energy and Environment, Research Institute of Electrochemical Energy,
National Institute of Advanced Industrial Science and Technology (AIST),
1ꢀ8ꢀ31 Midorigaoka, Ikeda, Osaka 563ꢀ8577, Japan
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ABSTRACT: Aryltrifluoroborate ([ArBF3]−) has a designable basic anion structure. Various
[ArBF3]−ꢀbased anions were synthesized to create novel alkali metal salts using a simple and safe
preparation process. Nearly forty novel alkali metal salts were successfully obtained, and their
physicochemical characteristics, particularly their thermal properties, were elucidated. These salts
have lower melting points than simple inorganic alkali halide salts, such as KCl or LiCl, due to the
weaker interactions between the alkali metal cations and the [ArBF3]− anions and the anions’ larger
entropy. Moreover, interestingly, potassium cations were electrochemically reduced in the potassium
(metaꢀethoxyphenyl)trifluoroborate (K[mꢀOEtC6H4BF3]) molten salt at 433 K. These findings
contribute substantially to furthering molten salt chemistry, ionic liquid (IL) chemistry, and
electrochemistry.
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INTRODUCTION
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Anhydrous liquid alkali metal salts are known as molten salts and have unique features, such as
negligible vapor pressure, incombustibility, a wide electrochemical window, and relatively high ionic
conductivity.1 Molten salts are very important nonꢀaqueous solvents and have been employed in
various fields, e.g., smelting, fuel cells, and chemical production.2–5 However, most molten salt
systems must be handled under highꢀtemperature conditions to remain in the liquid state, unlike other
common solvents. This requirement is often considered a disadvantage. Thus, by applying several
approaches to decrease the handling temperature, a number of lowꢀtemperature molten salt systems
have been reported in the last decade.6–11 Typical approaches are adding other salt(s) to the original
salt, resulting in, for example, LiCl–KCl binary systems6,8–12 and NaCl–KCl–CsCl ternary
systems,7,13–17and designing ionic species with lower surface charge densities, delocalized charges,
and various molecular motions, thereby decreasing the lattice energy by increasing the interionic
distance and entropy.18 The latter approach is commonly used to obtain ionic liquids (ILs). One
wellꢀknown example is 1ꢀbutylꢀ3ꢀmethylimidazolium bis(trifluoromethanesulfonyl)amide
([C4mim][Tf2N]), which is synthesized using 1ꢀbutylꢀ3ꢀmethylimidazolium chloride ([C4mim]Cl)
(melting point: 342 K)19 and potassium bis(trifluoromethanesulfonyl)amide (K[Tf2N]) (melting
point: 472 K).6 However, few articles on the design and synthesis of alkali metal cationꢀbased
lowꢀtemperature molten salt systems with polyatomic anions are available6–11 because introducing
target substituent(s) to a polyatomic anion is typically difficult because of the simple basic structure.
In this study, to design and synthesize novel polyatomic anions, we focused on
aryltrifluoroborate anions ([ArBF3]−), which can be easily and safely prepared on a large scale using
commercially available reagents.20 The basic chemical structure is depicted in Figure 1. These anions
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−
are elaborated by replacing one fluorine of tetrafluoroborate (BF4 ) with an aromatic group. The
trifluoroborate group substantially decreases the negative charge on the aromatic ring. Because of the
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characteristics of the anion structure, these salts are expected to be molten salts with relatively low
melting temperatures. Nearly forty alkali metal salts with different [ArBF3]− anionic species were
successfully produced. The aim of this study was to elucidate the thermal and electrochemical
properties, such as the electrochemical window, of the resulting salts.
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EXPERIMENTAL SECTION
Aryltrifluoroborate alkali metal salts (M[ArBF3] (M: K or Cs)) were synthesized using appropriate
arylboronic acids (ArB(OH)2) (Wako Pure Chemical Co. (Japan), Tokyo Chemical Co. (Japan), and
others), alkali metal fluorides (MF (M: K or Cs)) (Wako Pure Chemical Co.), and Lꢀtartaric acid
(Wako Pure Chemical Co.), according to the following protocol (Scheme 1).20 An alkali metal
fluoride aqueous solution (4 equiv., 2 mL) containing the target cationic species was added to a
solution of arylboronic acid (5 mmol) in acetonitrile (20 mL), and the mixture was stirred for 5 min
at ambient temperature. LꢀTartaric acid (2.05 equiv.) dissolved in tetrahydrofuran (THF) (10 mL) was
slowly added to the mixture, and then, a white byꢀproduct precipitated immediately. The reaction
mixture was agitated for 1 hour at ambient temperature and filtered to remove the precipitate. The
resultant filtrate was concentrated in vacuo, and the crude alkali metal salt was obtained as a solid.
The crude product was purified by recrystallization to give a pure aryltrifluoroborate alkali metal salt.
The obtained salt was dried at 353 K under vacuum for 4 hours. The final product was confirmed by
nuclear magnetic resonance (NMR), mass spectrometry, and elemental analysis.
Differential scanning calorimetry (DSC) was conducted using a Bruker DSC3100SA. The
sample was sealed in an aluminum pan with an aluminum top. The sealed pan was heated and cooled
at a rate of 5 K min−1. The glassꢀtransition temperature and melting point were obtained from the
DSC curve of the second heating process. These values were estimated by the tangential intersection
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method near the temperature at which a phase transformation occurred. Thermogravimetric (TG)
analysis was performed using a Bruker TGꢀDTA2000SA. The sample was placed on an aluminum
pan, and the pan was heated from room temperature to 773 K at a rate of 5 K min−1 under flowing
dry nitrogen gas. The thermal degradation temperature was determined as the 5 wt% loss point of the
TG curve. These two instruments were controlled with a Bruker MTC1000SA workstation utilizing
the Bruker WS003 software. All specimens for these measurements were prepared in an argon
gasꢀfilled glove box (Vacuum Atmospheres Co., OmniꢀLab, O2 and H2O < 1 ppm).
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Electrochemical measurements were conducted using an IVIUM Technologies CompactStat
portable electrochemical analyzer. All electrochemical experiments were performed in a
threeꢀelectrode cell. The working electrode was a platinum disk (ϕ 1.6 mm), which was polished with
an alumina suspension (ϕ 0.06 ꢁm) before use. Platinum wire (diameters of 0.5 mm) was used as the
counter electrode. Platinum and silver wires (diameters of 1.0 mm) were employed for the
quasiꢀreference electrode. The measurement was conducted at 433 K or 453 K in an argon gasꢀfilled
glove box to prevent any contamination. When a potassium electrodeposition experiment was
performed, a tin plate (5 mm × 5 mm) was used as the working electrode. The electrodeposition was
conducted at 433 K in an argon gasꢀfilled glove box. The electrodeposits were observed by a Hitachi
Sꢀ3400N scanning electron microscope (SEM) system. The composition was determined by an
EDAX Octane Prime energyꢀdispersive Xꢀray spectroscopy (EDX) instrument mounted on the SEM
system. The crystal structure of the electrodeposit was identified by a Rigaku Ultima IV Xꢀray
diffractometer (XRD) with Cu Kα radiation. This measurement was performed in the 2θ/θ scan mode
with a scan rate of 1 degree min−1.
The Gaussian 09 program21 was used for the ab initio molecular orbital calculations. The basis
sets implemented in the Gaussian program were used. Electron correlation was accounted for by the
secondꢀorder MølloerꢀPlesset perturbation (MP2) method.22,23 The geometries of complexes were
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fully optimized at the HF/6ꢀ311G(d,p) level. The intermolecular interaction energies (Eint) were
calculated at the MP2/6ꢀ311G(d,p) level by supermolecule method. Our previous calculations of the
[C2mim][BF4] and Li[Tf2N] complexes24,25 show that the basis set effects on the calculated
interaction energies of the complexes are very small, if basis sets including polarization functions are
used, and that the effects of electron correlation beyond MP2 are negligible. Therefore, we calculated
the interaction energies of the complexes at the MP2/6ꢀ311G(d,p) level in this work. The basis set
superposition error (BSSE)26 was corrected for all the interaction energy calculations using the
counterpoise method.27 The stabilization energy by the formation of complex from isolated ions
(Eform) was calculated as the sum of the Eint and the deformation energy (Edef), which is the increase
of energy of aryltrifluoroborate anion by deformation of the geometry associated with the complex
formation.24,28 The Edef was calculated at the MP2/6ꢀ311G(d,p) level.
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RESULTS AND DISCUSSION
Thermal Behavior of Aryltrifluoroborate Alkali Metal Salts. A large number of
aryltrifluoroborate alkali metal salts were prepared according to Scheme 1, and their thermal
properties were examined by DSC and TG analyses. The melting point (Tm) and thermal degradation
temperature (Td) of M[ArBF3] (M: K or Cs) with different substituents are given in Tables 1ꢀ4.
Nonꢀsubstitutive potassium phenyltrifluoroborate (K[PhBF3]), which is the simplest
aryltrifluoroborate potassium salt, had a melting point of 568 K (Table 1). The aromatic potassium
salts with substituents, R, at the meta position of the phenyl group, K[mꢀRC6H4BF3], showed lower
melting points than the nonꢀsubstitutive K[PhBF3], except for the tertꢀbutyl group, bromomethyl
group, and carbamoyl group. Specifically, potassium (metaꢀethoxyphenyl)trifluoroborate
(K[mꢀOEtC6H4BF3]) with an ethoxy group at the meta position on the aromatic ring melted at 390 K;
thus, introducing the ethoxy group substantially decreased the melting point. As shown in Table 5,
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this value was considerably lower than those of other common potassium salts,6, 29–32likely because
of the obtained salts’ increased interionic distances and entropies. From these data, we can also
discuss the effects of the substituents in a little more detail. For example, there is an obvious
difference between the melting points of K[mꢀOMeC6H4BF3] and K[mꢀOCF3C6H4BF3]. The OCF3
group works as a strong electron withdrawing group because of the electronegativity of the three
fluorine atoms. The charge density of the anion consequently decreases by the OCF3 group compared
to OMe group without the fluorine atom. The resulting weak ionic interaction between the K+ and the
[mꢀOCF3C6H4BF3]− would cause the lower melting point. As described later, quantum chemical
calculations support this idea.
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A similar approach was also applied to Cs salt preparation. The thermal properties of the Cs salts
are summarized in Table 2. Cesium phenyltrifluoroborate (Cs[PhBF3]) exhibited a melting point of
445 K, lower than that of its potassium counterpart. The same was true for other Cs salts with the
following substituents at the meta position: CF3, F, OCF3, and OnPr. The larger ionic radius of the
cesium ion compared to that of the potassium ion is commonly believed to decrease the Cs salt’s
lattice energy.6,8,10,11 In contrast, the Tm of Cs salts with a methylthio or ethoxy group clearly
increased compared to those of potassium salts with the same anions. These Cs salts should have a
favorable ion packing structure. A similar exception regarding the melting temperatures derived from
the differences in the cation and anion radii in inorganic alkali metal halides has been reported.33,34
The thermal properties of the orthoꢀsubstituted potassium aryltrifluoroborate (K[oꢀRC6H4BF3]) are
summarized in Table 3. Most salts showed only a thermal degradation temperature without a melting
point. Furthermore, for those salts, it was much higher than those of the metaꢀsubstituted ones. To
determine the underlying reason, we carried out quantum chemical calculations for evaluating the
interactions of K+ with substituted phenyltrifuluoroborate anions. The optimized structures of the ion
pairs of K+ and metaꢀ and orthoꢀsubstituted phenyltrifuluoroborate anions are depicted in Fig. 2.
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Whereas the K+ has contact with three fluorine atoms of –BF3 in all the ion pairs of metaꢀsubstituted
phenyltrifuluoroborates, in all the ion pairs of orthoꢀsubstituted ones, the K+ has contact with two
fluorine atoms of –BF3 and one negatively charged atom in the substituent. The stabilization energies
by the formation of the complexes from isolated species (Eform) calculated for the ion pairs and the
difference between the Eform for the ion pair of metaꢀsubstituted phenyltrifuluoroborate and that for
the ion pair of orthoꢀsubstituted phenyltrifuluoroborate (∆E) are given in Fig. 2. For example, the
Eform calculated for the optimized structure of K[mꢀOMeC6H4BF3] (−456.7 kJꢂmol−1) was 34.4
kJꢂmol−1 smaller (less negative) than that for the K[oꢀOMeC6H4BF3] (−491.1 kJꢂmol−1). The Eform
calculated for the ion pair of metaꢀsubstituted phenyltrifuluoroborates is always smaller than that for
the ion pair of corresponding orthoꢀsubstituted phenyltrifuluoroborates. These calculations show that
the dissociation of the ion pair of metaꢀsubstituted phenyltrifuluoroborate can occur more easily than
the dissociation of the ion pair of corresponding orthoꢀsubstituted phenyltrifuluoroborates.35,36 The
computational results suggest that the K+ salts with metaꢀsubstituted phenyltrifuluoroborates have
lower melting temperatures compared with the salts of corresponding orthoꢀsubstituted
phenyltrifuluoroborates owing to weaker attraction between the cation and anion. In addition to the
aforementioned salts, the K+ salts with three disubstituted phenyltrifluoroborate anions and two other
aryltrifuluoroborate anions were also synthesized (Table 4). These salts had no melting point except
for a potassium 1ꢀnaphthyltrifluoroborate (K[1ꢀNaphBF3]). The thermal degradation temperatures of
alkali salts with aryltrifluoroborate anions prepared in this study scatter over wide temperature ranges
from 404 to 611 K. Different thermal stability of the substituents in aryltrifluoroborate anions would
be the major source of the difference of the thermal degradation temperatures.
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Electrochemical Analyses. As shown in Tables 1ꢀ4, K[mꢀOEtC6H4BF3] had the lowest melting point,
i.e., 390 K, among the studied salts. Cyclic voltammograms recorded using a Pt disk electrode in the
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K[mꢀOEtC6H4BF3] molten salt are shown in Fig. 3. The electrochemical window was determined
based on the anodic and cathodic limiting potentials at which the current densities reached the
current density of ±0.3 mA cm−2 in a forward scan. The current increment initiated at ca. 1.36 V (vs.
quasiꢀPt wire reference electrode) and ca. 0.71 V (vs. quasiꢀAg wire reference electrode) in the
anodic region (blue line) was attributable to the decomposition of the [mꢀOEtC6H4BF3]− anion. In the
cathodic region (red line), the negative limiting potential was ca. −2.48 V (vs. Pt wire) and ca. −3.13
V (vs. Ag wire) Hence, the electrochemical window was 3.84 V at 453 K. This range is comparable
to those of typical alkali metal molten salt systems, such as LiClꢀKCl (3.8 V).37–39 Therefore, this
K[mꢀOEtC6H4BF3] molten salt has great promise as a lowꢀtemperature molten salt. Further
electrochemical analyses were conducted to elucidate the unknown electrochemical redox reactions
observed at the negative limiting potential. As shown in Fig. 3, a small oxidation peak appeared at
−2.3 V (vs. Pt wire) in the reverse scan of the cathodic region. We speculated that the oxidation wave
was related to the dissolution of metal potassium deposited in the potential range of −2.4 ~ −2.5 V
(vs. Pt wire). However, the coulombic efficiency of the redox reaction estimated based on the cyclic
voltammogram was only 4 %. Given metallic potassium’s low melting point (337 K), it is highly
likely that the metal potassium electrodeposited on the electrode floats or precipitated in the
K[mꢀOEtC6H4BF3] molten salt at 453 K soon after deposition. These processes would lead to the
observed significantly low coulombic efficiency. In fact, we could not identify any deposits on the Pt
electrode after electrolysis at the limiting potential. We collected more accurate information on the
relevant electrochemical reaction via two approaches: doubleꢀstep chronoamperometry using short
potential step times and alloying with a tin electrode that can readily form a KꢀSn binary alloy.40
Figure 4 shows the doubleꢀstep chronoamperograms recorded using a Pt disk electrode in the
K[mꢀOEtC6H4BF3] molten salt at 433 K. Based on these chronoamperograms, we can discuss the
kinetic complications involved in the electrode reaction. When a certain type of ionic species is
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oxidized or reduced ideally on the electrode surface during doubleꢀstep chronoamperometry, the
kinetic complications are determined by the following equation:41
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ꢇ
ꢀꢁ
ꢀꢂ
ꢄ
= 1 − ꢃ1 − ꢆꢈ
ꢅꢁ
(1)
−
where if is the forward current in the first potential step, ir is the reversal current in the second
potential step, tr is the time at any current in the second potential step, and τ is the retention time of
the first potential step. Figure 5a depicts an ideal current response in doubleꢀstep chronoamperometry
when the first step is the cathodic reaction. The data shown in Fig. 4 were converted into –ir/if and tr/τ
by eq. 1 and are presented graphically in Fig. 5b. The solid line in the figure represents an ideal line
calculated using this equation. At a longer step time, i.e., 0.05 s, a large deviation from the ideal line
occurred. Conversely, the plots were very similar to the ideal line when a shorter time step of 0.01 s
was used. Therefore, the electrode reaction proceeded reversibly at only very short reduction
potential step times. Direct evidence of potassium electrodeposition was obtained by constant
potential electrolysis at −2.6 V (vs. Pt wire) for 3600 s on a Pt electrode. No deposits were identified.
However, when a tin plate with metallic luster was used as the working electrode (Fig. 6a), the
surface became covered with a dark gray deposit under the same electrolysis conditions (Fig. 6b).
SEM images of the electrode surface before and after electrolysis are shown in Fig. 6c and d,
respectively. The original tin electrode had a smooth surface, but after electrolysis, the surface
exhibited a dramatic change, becoming rough with many cracks.42–44 The tin electrode was
characterized by XRD, and the results obtained before and after electrolysis are shown in Fig. 7. The
specimen after electrolysis had a unique XRD pattern. In addition to that of metallic tin, the pattern
for the K4Sn23 binary alloy was also evident; thus, KꢀSn binary alloy was formed on the Sn electrode
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surface. The KꢀSn alloy probably formed immediately after K(I) reduction on the Sn electrode. EDX
analysis of the specimen indicated that the major components were potassium and tin. Based on these
results, the redox reaction observed at the negative limiting potential in the K[mꢀOEtC6H4BF3]
molten salt was identified as the electrode reaction for K(I), which is in agreement with the results of
the few papers available that address metal potassium deposition in ILs and organic solvents.45–47
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CONCLUDING REMARKS
Nearly forty aryltrifluoroborate alkali metal salts with various substituents were designed and
successfully obtained via a simple and safe preparation process. We revealed that the choice of
substituents and their positions strongly affected the thermal properties of the resulting salts. The
alkali metal salts clearly had lower melting points than common inorganic alkali halides, e.g., LiCl,
KCl, and KF. We prepared a structureꢀdesigned potassium aryltrifluoroborate, K[mꢀOEtC6H4BF3],
i.e., a lowꢀtemperature molten salt, for the electrodeposition of metal potassium. Our results and the
preparation process for the M[ArBF3] (M: K or Cs) salts reported in this article will be useful for
scientists and engineers in the fields of molten salts, ILs, and electrochemical technology.
ASSOCIATED CONTENT
Supporting Information
Additional experimental data. This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
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Corresponding authors.
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*Eꢀmail: ttsuda@chem.eng.osakaꢀu.ac.jp (T.T.); kuwabata@chem.eng.osakaꢀu.ac.jp (S.K.). Tel.:
8
9
+81ꢀ6ꢀ6879ꢀ7374; Fax: +81ꢀ6ꢀ6879ꢀ7373.
Notes
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Part of this research was supported by a GrantꢀinꢀAid for Scientific Research (Grant Numbers
15H03591, 15K13287, 15H03874, and 15H2202) from the Japanese Ministry of Education, Culture,
Sports, Science and Technology (MEXT) and by the Advanced Low Carbon Technology Research
and Development Program (ALCA) for Specially Promoted Research for Innovative Next
Generation Batteries (SPRING), Japan Science and Technology Agency (JST).
REFERENCES
(1)
(2)
(3)
(4)
Ito, Y.; Nohira, T. NonꢀConventional Electrolytes for Electrochemical Applications.
Electrochim. Acta 2000, 45, 2611–2622.
Lovering, D. G. Molten Salt Technology; Lovering, D. G., Ed.; Springer US: Boston, MA,
1982.
Nohira, T.; Yasuda, K.; Ito, Y. Pinpoint and Bulk Electrochemical Reduction of Insulating
Silicon Dioxide to Silicon. Nat. Mater. 2003, 2, 397–401.
Yasuda, K.; Nohira, T.; Kobayashi, K.; Kani, N.; Tsuda, T.; Hagiwara, R. Improving Purity
and Process Volume During Direct Electrolytic Reduction of Solid SiO2 in Molten CaCl2 for
the Production of SolarꢀGrade Silicon. Energy Technol. 2013, 1, 245–252.
12
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Page 13 of 33
The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
(5)
(6)
(7)
(8)
Murakami, T.; Nishikiori, T.; Nohira, T.; Ito, Y. Electrolytic Synthesis of Ammonia in Molten
Salts under Atmospheric Pressure. J. Am. Chem. Soc. 2003, 125, 334–335.
Hagiwara, R.; Tamaki, K.; Kubota, K.; Goto, T.; Nohira, T. Thermal Properties of Mixed
Alkali Bis(trifluoromethylsulfonyl)amides. J. Chem. Eng. Data 2008, 53, 355–358.
Kubota, K.; Nohira, T.; Goto, T.; Hagiwara, R. Ternary Phase Diagrams of Alkali
Bis(trifluoromethylsulfonyl)amides. J. Chem. Eng. Data 2008, 53, 2144–2147.
Kubota, K.; Nohira, T.; Goto, T.; Hagiwara, R. Novel Inorganic Ionic Liquids Possessing Low
Melting Temperatures and Wide Electrochemical Windows: Binary Mixtures of Alkali
Bis(fluorosulfonyl)amides. Electrochem. Commun. 2008, 10, 1886–1888.
Kubota, K.; Tamaki, K.; Nohira, T.; Goto, T.; Hagiwara, R. Electrochemical Properties of
Alkali Bis(trifluoromethylsulfonyl)amides and Their Eutectic Mixtures. Electrochim. Acta
2010, 55, 1113–1119.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(9)
(10) Kubota, K.; Nohira, T.; Hagiwara, R. Thermal Properties of Alkali
Bis(pentafluoroethylsulfonyl)amides and Their Binary Mixtures. J. Chem. Eng. Data 2010, 55,
2546–2549.
(11) Kubota, K.; Nohira, T.; Hagiwara, R. Thermal Properties of Alkali Bis(fluorosulfonyl)amides
and Their Binary Mixtures. J. Chem. Eng. Data 2010, 55, 3142–3146.
(12) Van Artsdalen, E. R.; Yaffe, I. S. Electrical Conductance and Density of Molten Salt Systems:
KCl–LiCl, KCl–NaCl and KCl–KI. J. Phys. Chem. 1955, 59, 118–127.
(13) Boyarchuk, T. P.; Khailova, E. G.; Cherginets, V. L. Potentiometric Measurements in Molten
Chlorides. Solubilities of Metal Oxides in the Molten Eutectic Mixture CsCl–KCl–NaCl at
600°C. Electrochim. Acta 1993, 38, 1481–1485.
(14) Masset, P.; Schoeffert, S.; Poinso, J.ꢀY.; Poignet, J.ꢀC. LiF–LiCl–LiI vs. LiF–LiBr–KBr as
Molten Salt Electrolyte in Thermal Batteries. J. Electrochem. Soc. 2005, 152, A405–A410.
13
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The Journal of Physical Chemistry
Page 14 of 33
1
2
3
4
5
6
7
8
9
(15) Watarai, A.; Kubota, K.; Yamagata, M.; Goto, T.; Nohira, T.; Hagiwara, R.; Ui, K.; Kumagai,
N. A Rechargeable Lithium Metal Battery Operating at Intermediate Temperatures Using
Molten Alkali Bis(trifluoromethylsulfonyl)amide Mixture as an Electrolyte. J. Power Sources
2008, 183, 724–729.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(16) Tu, X.; Chu, Y.; Ma, C. New Ternary Molten Salt Electrolyte Based on Alkali Metal Triflates.
Ionics 2010, 16, 81–84.
(17) Li, G.; Lu, X.; Coyle, C. A.; Kim, J. Y.; Lemmon, J. P.; Sprenkle, V. L.; Yang, Z. Novel
Ternary Molten Salt Electrolytes for IntermediateꢀTemperature Sodium/nickel Chloride
Batteries. J. Power Sources 2012, 220, 193–198.
(18) Wilkes, J. S.; Zaworotko, M. J. Air and Water Stable 1ꢀEthylꢀ3ꢀMethylimidazolium Based
Ionic Liquids. J. Chem. Soc. Chem. Commun. 1992, 965–697.
(19) Endo, T.; Kato, T.; Nishikawa, K. Effects of Methylation at the 2 Position of the Cation Ring
on Phase Behaviors and Conformational Structures of ImidazoliumꢀBased Ionic Liquids. J.
Phys. Chem. B 2010, 114, 9201–9208.
(20) Lennox, A. J. J.; LloydꢀJones, G. C. Preparation of Organotrifluoroborate Salts:
PrecipitationꢀDriven Equilibrium under NonꢀEtching Conditions. Angew. Chem. Int. Ed. 2012,
51, 9385–9388.
(21) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.;
Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A., et al. Gaussian 09, Revision A.02;
Gaussian, Inc.: Wallingford, CT, 2009.
(22) Møller, C.; Plesset, M. S. Note on an Approximation Treatment for ManyꢀElectron Systems.
Phys. Rev. 1934, 46, 618–622.
(23) HeadꢀGordon, M.; Pople, J. A.; Frisch, M. J. MP2 Energy Evaluation by Direct Methods.
Chem. Phys. Lett. 1988, 153, 503–506.
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The Journal of Physical Chemistry
1
2
3
4
5
6
7
8
9
(24) Tsuzuki, S.; Tokuda, H.; Hayamizu, K.; Watanabe, M. Magnitude and Directionality of
Interaction in Ion Pairs of Ionic Liquids: Relationship with Ionic Conductivity. J. Phys. Chem.
B 2005, 109, 16474–16481.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(25) Tsuzuki, S.; Hayamizu, K.; Seki, S.; Ohno, Y.; Kobayashi, Y.; Miyashiro, H. Quaternary
Ammonium RoomꢀTemperature Ionic Liquid Including an Oxygen Atom in Side
Chain/Lithium Salt Binary Electrolytes: Ab Initio Molecular Orbital Calculations of
Interactions between Ions. J. Phys. Chem. B 2008, 112, 9914–9920.
(26) Ransil, B. J. Studies in Molecular Structure. IV. Potential Curve for the Interaction of Two
Helium Atoms in SingleꢀConfiguration LCAO MO SCF Approximation. J. Chem. Phys. 1961,
34, 2109–2118.
(27) Boys, S. F.; Bernardi, F. The Calculation of Small Molecular Interactions by the Differences
of Separate Total Energies. Some Procedures with Reduced Errors. Mol. Phys. 1970, 19, 553–
566.
(28) Tsuzuki, S.; Kubota, K.; Matsumoto, H. Cation and Anion Dependence of Stable Geometries
and Stabilization Energies of Alkali Metal Cation Complexes with FSA−, FTA−, and TFSA−
Anions: Relationship with Physicochemical Properties of Molten Salts. J. Phys. Chem. B 2013,
117, 16212–16218.
(29) Finze, M.; Bernhardt, E.; Willner, H.; Lehmann, C. W. Cyanoꢀ and
Isocyanotris(trifluoromethyl)borates: Syntheses, Spectroscopic Properties, and Solid State
Structures of K[(CF3)3BCN] and K[(CF3)3BNC]. J. Am. Chem. Soc. 2005, 127, 10712–10722.
(30) Bredig, M. A.; Bronstein, H. R.; Smith, W. T. Miscibility of Liquid Metals with Salts. II. The
PotassiumꢀPotassium Fluoride and CesiumꢀCesium Halide Systems. J. Am. Chem. Soc. 1955,
77, 1454–1458.
(31) Ginnings, D. C.; Phipps, T. E. TemperatureꢀConductance Curves of Solid Salts. III. Halides of
15
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Page 16 of 33
1
2
3
4
Lithium. J. Am. Chem. Soc. 1930, 52, 1340–1345.
5
6
7
8
9
(32) Gramstad, T.; Haszeldine, R. N. Perfluoroalkyl Derivatives of Sulphur. Part IV.
Perfluoroalkanesulphonic Acids. J. Chem. Soc. 1956, 173.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(33) Amini, M.; Fincham, D.; Hockney, R. W. A Molecular Dynamics Study of the Melting of
Alkali Halide Crystals. J. Phys. C Solid State Phys. 1979, 12, 4707–4720.
(34) Furukawa, K. Structure of Molten Salts near the Melting Point. Discuss. Faraday Soc. 1961,
32, 53–62.
(35) Tsuzuki, S.; Umecky, T.; Matsumoto, H.; Shinoda, W.; Mikami, M. Interactions of
Perfluoroalkyltrifluoroborate Anions with Li Ion and Imidazolium Cation: Effects of
Perfluoroalkyl Chain on Motion of Ions in Ionic Liquids. J. Phys. Chem. B 2010, 114, 11390–
11396.
(36) Bernard, U. L.; Izgorodina, E. I.; MacFarlane, D. R. New Insights into the Relationship
between IonꢀPair Binding Energy and Thermodynamic and Transport Properties of Ionic
Liquids. J. Phys. Chem. C 2010, 114, 20472–20478.
(37) Serp, J.; Konings, R. J.; Malmbeck, R.; Rebizant, J.; Scheppler, C.; Glatz, J.ꢀP.
Electrochemical Behaviour of Plutonium Ion in LiCl–KCl Eutectic Melts. J. Electroanal.
Chem. 2004, 561, 143–148.
(38) Masset, P.; Konings, R. J. M.; Malmbeck, R.; Serp, J.; Glatz, J.ꢀP. Thermochemical Properties
of Lanthanides (Ln = La, Nd) and Actinides (An = U, Np, Pu, Am) in the Molten LiCl–KCl
Eutectic. J. Nucl. Mater. 2005, 344, 173–179.
(39) Bermejo, M. R.; Gómez, J.; Martínez, A. M.; Barrado, E.; Castrillejo, Y. Electrochemistry of
Terbium in the Eutectic LiCl–KCl. Electrochim. Acta 2008, 53, 5106–5112.
(40) Sangster, J.; Bale, C. The KꢀSn (PotassiumꢀTin) System. J. Phase Equilibria 1998, 19, 67–69.
(41) Bard, A. J.; Faulkner, L. R. Electrochemical Methods: Fundamentals and Applications, 2nd
16
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2
3
4
Edition; John Wiley & Sons, Inc.: New York, 2000.
5
6
7
8
9
(42) Konishi, H.; Nohira, T.; Ito, Y. Formation of Dy–Fe Alloy Films by Molten Salt
Electrochemical Process. Electrochim. Acta 2002, 47, 3533–3539.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
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33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(43) Eliaz, N.; Sridhar, T. M.; Gileadi, E. Synthesis and Characterization of Nickel Tungsten
Alloys by Electrodeposition. Electrochim. Acta 2005, 50, 2893–2904.
(44) Xu, L.; Guan, H.; Li, D.; Wang, L. Tribological Properties of Electroplated Crack NiꢀW Alloy
Coatings. Proc. Inst. Mech. Eng. Part J J. Eng. Tribol. 2015, 229, 1372–1378.
(45) Wibowo, R.; Aldous, L.; Jacobs, R. M. J.; Manan, N. S. A.; Compton, R. G. Monitoring
Potassium Metal Electrodeposition from an Ionic Liquid Using in Situ ElectrochemicalꢀXꢀRay
Photoelectron Spectroscopy. Chem. Phys. Lett. 2011, 509, 72–76.
(46) Jorné, J.; Tobias, C. W. Electrodeposition of the Alkali Metals from Propylene Carbonate. J.
Appl. Electrochem. 1975, 5, 279–290.
(47) Lu, W.; Baranski, A. S. Electrodeposition of Alkali Metals on Solid and Liquid Mercury
Electrodes. J. Electroanal. Chem. 1992, 335, 105–122.
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Table 1. Thermal properties of the synthesized K[ArBF3] salts with a substituent at the meta
6
7
8
position
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Tm a / K
568
Td b / K
590
(Abbreviations for substituents)
(ꢀMe)
(ꢀtBu)
518
561
c
—
574
501
467
405
409
568
538
539
507
(ꢀOCF3)
(ꢀSMe)
(ꢀSO2Me)
(ꢀCH2Br)
514
600
c
—
410
594
566
465
525
(ꢀCO2Et)
516
576
445
c
(ꢀCONH2)
—
(ꢀOMe)
(ꢀOEt)
430
390
592
521
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9
(ꢀOnPr)
(ꢀOiPr)
(ꢀOnBu)
425
437
439
568
539
548
549
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(ꢀO(CH2)9CH3)
(ꢀO(CH2)2OCH3)
388
419
571
aMelting point. bThermal degradation temperature at 5 wt% loss. cDecomposition before melting.
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Table 2. Thermal properties of the synthesized Cs[ArBF3] salts with a substituent at the meta
8
9
position
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Tm a / K
445
Td b / K
566
(Abbreviations for substituents)
403
549
409
611
(ꢀOCF3)
(ꢀSMe)
(ꢀOEt)
398
534
413
565
433
572
(ꢀOnPr)
409
567
aMelting point. bThermal degradation temperature at 5 wt% loss.
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Table 3. Thermal properties of the synthesized K[ArBF3] salts with a substituent at the ortho
8
9
position
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
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58
59
60
BF3
R
K
Tm a / K
Td b / K
587
(Abbreviations for substituents)
c
—
c
(ꢀOCF3)
(ꢀSMe)
(ꢀOMe)
(ꢀOEt)
—
555
549
554
564
579
c
—
565
c
—
492
c
(ꢀCOCH3)
—
482
aMelting point. bThermal degradation temperature at 5 wt% loss. cDecomposition before melting.
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Table 4. Thermal properties of other K[ArBF3] salts
8
9
Potassium salts (Abbreviations for anions)
Tm a / K
Td b / K
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
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58
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60
c
(2ꢀFꢀ5ꢀOMeC6H3BF3)
—
481
c
(2ꢀClꢀ5ꢀCF3C6H3BF3)
—
404
495
c
(3ꢀCO2Meꢀ5ꢀNO2C6H3BF3)
—
c
(3ꢀC4H3SBF3)
(1ꢀNaphBF3)
—
550
534
461
aMelting point. bThermal degradation temperature at 5 wt% loss. cDecomposition before melting.
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Table 5. Melting points of common potassium salts
6
7
8
9
Salts
KF
Tma / K
1131
1043
1006
952
Ref.
30
10
11
12
13
14
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22
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60
KCl
31
KBr
KI
31
31
KBF4
KTfO
KTf2N
803
29
503
32
472
6
K[mꢀOEtC6H4BF3]
390
This work
aMelting point.
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Scheme and Figure Captions
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Scheme 1. Synthesis of aryltrifluoroborate alkali metal salts.
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Figure 1. Chemical structure of the aryltrifluoroborate anion ([ArBF3]−).
Figure 2. Optimized structures of ion pairs consisting of K+ and metaꢀ and orthoꢀsubstituted
phenytrifluoroborate anions and their stabilization energies by the formation of ion pairs (Eform). ∆E
(= Eform(meta) – Eform(ortho)) is the difference between the Eform for the ion pair of metaꢀsubstituted
phenytrifluoroborate anion (Eform(meta)) and the Eform for the ion pair of orthoꢀsubstituted
phenytrifluoroborate anion (Eform(ortho)).
Figure 3. Cyclic voltammograms recorded at a Pt disk electrode in (―) the cathodic region and (―)
the anodic region in the K[mꢀOEtC6H4BF3] lowꢀtemperature molten salt at 453 K. The scan rate was
10 mV s−1.
Figure 4. Doubleꢀstep chronoamperograms recorded at a Pt disk electrode in the K[mꢀOEtC6H4BF3]
lowꢀtemperature molten salt at 433 K with a potential step of −2.6 V (vs. Pt wire) followed by 0 V
(vs. Pt wire). The potential step times were (―) 0.01 s and (―) 0.05 s.
Figure 5. (a) Ideal current response in typical doubleꢀstep chronoamperometry. if is the forward
current in the first potential step, ir is the reversal current in the second potential step, tf is the time at
any current in the first potential step, and τ is the potential step time for the first potential step. (b) –
ir/if vs. tr/τ plot derived from the chronoamperograms shown in Fig. 4. The potential step times were
(○
) 0.05 s and (
●) 0.01 s. The solid line in the figure represents the ideal line calculated using eq. 1.
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Figure 6. Optical microscope and SEM images of the tin electrode (a and c) before and (b and d)
after electrolysis at −2.6 V (vs. Pt wire) in the K[mꢀOEtC6H4BF3] lowꢀtemperature molten salt at 433
K. The SEM images are shown in (c) and (d).
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Figure 7. XRD patterns (CuꢀKα) of the tin electrode before and after electrolysis at −2.6 V (vs. Pt
wire) in the K[mꢀOEtC6H4BF3] lowꢀtemperature molten salt at 433 K. As references, the diffraction
patterns of βꢀSn (JCPDSꢀICDD, file 00ꢀ004ꢀ0673) and K4Sn23 (JCPDSꢀICDD, file 03ꢀ065ꢀ3351) are
also shown.
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Scheme 1. Synthesis of aryltrifluoroborate alkali metal salts.
Figure 1. Chemical structure of the aryltrifluoroborate anion ([ArBF3]−).
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Figure 2. Optimized structures of ion pairs consisting of K+ and meta- and ortho-substituted
phenytrifluoroborate anions and their stabilization energies by the formation of ion pairs (Eform). ∆E (=
Eform(meta) – Eform(ortho)) is the difference between the Eform for the ion pair of meta-substituted
phenytrifluoroborate anion (Eform(meta)) and the Eform for the ion pair of ortho-substituted
phenytrifluoroborate anion (Eform(ortho)).
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3.0
2.0
1.0
0.0
-1.0
-2.0
-3.0
-3.0
-2.0
-1.0
0.0
1.0
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Potential / V vs. Pt wire
Figure 3. Cyclic voltammograms recorded at a Pt disk electrode in (―) the cathodic region and (―)
the anodic region in the K[m-OEtC6H4BF3] low-temperature molten salt at 453 K. The scan rate was
10 mV s−1.
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