U.S. patent application number 10/561519 was filed with the patent office on 2007-05-10 for acid-base mixture and ion conductor comprising the same.
This patent application is currently assigned to UBE INDUSTRIES, LTD.. Invention is credited to Tetsuji Hirano, Nobuharu Hisano, Masayuki Kinouchi.
Application Number | 20070102674 10/561519 |
Document ID | / |
Family ID | 34067335 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070102674 |
Kind Code |
A1 |
Hirano; Tetsuji ; et
al. |
May 10, 2007 |
Acid-base mixture and ion conductor comprising the same
Abstract
Disclosed is an acid-base mixture composed of a base component
and an acid component, wherein at least one of the base component
and the acid component contains at least two compounds, and the
base component contains at least one compound of formula (1):
##STR1## wherein R.sup.1, R.sup.2, and R.sup.3 each represent a
hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms,
provided that at least one of them is a hydrocarbon group. Also
disclosed is an ion conductor comprising an acid-base mixture
composed of an acid component and a base component including at
least one compound of formula (2): ##STR2## wherein R.sup.1,
R.sup.2, and R.sup.3 each represent a hydrogen atom or a
hydrocarbon group having 1 to 20 carbon atoms, provided that
R.sup.1 and R.sup.3 are different.
Inventors: |
Hirano; Tetsuji; (Yamaguchi,
JP) ; Hisano; Nobuharu; (Yamaguchi, JP) ;
Kinouchi; Masayuki; (Yamaguchi, JP) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET
2ND FLOOR
ARLINGTON
VA
22202
US
|
Assignee: |
UBE INDUSTRIES, LTD.
1978-96, OAZA KOGUSHI, YAMAGUCHI
UBE-SHI
JP
755-8633
|
Family ID: |
34067335 |
Appl. No.: |
10/561519 |
Filed: |
July 9, 2004 |
PCT Filed: |
July 9, 2004 |
PCT NO: |
PCT/JP04/09801 |
371 Date: |
December 20, 2005 |
Current U.S.
Class: |
252/500 |
Current CPC
Class: |
H01G 9/035 20130101;
H01M 8/1016 20130101; H01M 2300/0045 20130101; H01M 10/0565
20130101; H01G 9/025 20130101; H01M 10/0564 20130101; H01G 11/58
20130101; H01G 11/56 20130101; Y02E 60/50 20130101; Y02E 60/10
20130101; H01B 1/122 20130101; H01M 2300/0025 20130101; Y02E 60/13
20130101; H01M 10/0566 20130101 |
Class at
Publication: |
252/500 |
International
Class: |
H01B 1/12 20060101
H01B001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 11, 2003 |
JP |
2003-195428 |
Jul 11, 2003 |
JP |
2003-195429 |
Claims
1. An acid-base mixture comprising a base component and an acid
component, at least one of the base component and the acid
component comprising at least two compounds, and the base component
comprising at least one compound represented by chemical formula
(1): ##STR8## wherein R.sup.1, R.sup.2, and R.sup.3 each represent
a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms,
provided that at least one of them is a hydrocarbon group.
2. The acid-base mixture according to claim 1, wherein the base
component comprises at least one compound represented by chemical
formula (2): ##STR9## wherein R.sup.1, R.sup.2, and R.sup.3 each
represent a hydrogen atom or a hydrocarbon group having 1 to 20
carbon atoms, provided that R.sup.1 and R.sup.3 are different.
3. The acid-base mixture according to claim 1, having a melting
point of 120.degree. C. or lower or substantially no melting
point.
4. The acid-base mixture according to claim 1, being an equimolar
mixture of the base component and the acid component.
5. The acid-base mixture according to claim 1, being liquid at room
temperature.
6. The acid-base mixture according to claim 1, wherein at least one
of the base components comprises 2-ethyl-4-methylimidazole.
7. The acid-base mixture according to claim 1, wherein at least one
of the base components comprises 4-methylimidazole.
8. The acid-base mixture according to claim 1, wherein at least one
of the base components comprises 2-ethylimidazole.
9. The acid-base mixture according to claim 1, wherein at least one
of the acid components comprises an acid structurally free from a
fluorine atom.
10. The acid-base mixture according to claim 1, wherein at least
one of the acid components comprises an inorganic acid.
11. The acid-base mixture according to claim 10, wherein at least
one of the acid components comprises sulfuric acid or phosphoric
acid.
12. The acid-base mixture according to claim 1, being ion
conductive.
13. The acid-base mixture according to claim 1, being proton
conductive.
14. An ion conductor comprising an acid-base mixture comprising a
base component and an acid component, the base component comprising
a base represented by chemical formula (2): ##STR10## wherein
R.sup.1, R.sup.2, and R.sup.3 each represent a hydrogen atom or a
hydrocarbon group having 1 to 20 carbon atoms, provided that
R.sup.1 and R.sup.3 are different.
15. The ion conductor according to claim 14, wherein R.sup.1 in
chemical formula (2) is a hydrocarbon group having 1 to 20 carbon
atoms.
16. The ion conductor according to claim 15, wherein R.sup.1 in
chemical formula (2) is a methyl group.
17. The ion conductor according to claim 15, wherein R.sup.2 in
chemical formula (2) is a hydrocarbon group having 1 to 20 carbon
atoms.
18. The ion conductor according to claim 17, wherein R.sup.2 in
chemical formula (2) is an ethyl group.
19. The ion conductor according to claim 14, wherein R.sup.3 in
chemical formula (2) is a hydrogen atom.
20. The ion conductor according to claim 14, wherein the base
component is 4-methylimidazole.
21. The ion conductor according to claim 14, wherein the base
component is 2-ethyl-4-methylimidazole.
22. The ion conductor according to claim 14, wherein the acid
component is an acid structurally free from a fluorine atom.
23. The ion conductor according to claim 14, wherein the acid
component is an inorganic acid.
24. The ion conductor according to claim 23, wherein the inorganic
acid is sulfuric acid.
25. The ion conductor according to claim 14, being a proton
conductor.
Description
TECHNICAL FIELD
[0001] The present invention relates to a mixture of a base
component and an acid component and an ion conductor comprising the
same. The ion conductor of the present invention is useful in fuel
cells, secondary batteries, electric double layer capacitors,
electrolytic capacitors, etc.
BACKGROUND ART
[0002] Imidazolium salts are well known to be useful as an epoxy
resin curing agent. While most of imidazolium salts are solid,
JP-A-57-190018 (Patent Document 1) discloses a 2-ethylhexanoate or
an acetate of an imidazole compound as an epoxy resin cure
accelerator that is liquid at room temperature. Journal of Japan
Society of Colour Material, 50 (1), 2-7 (1977) (Non-Patent Document
1) teaches that an imidazole compound salt with an alkylcarboxylic
acid or a phosphoric acid is liquid at room temperature and reports
epoxy resin curing by the use of the salt. JP-A-48-5900 (Patent
Document 2) discloses an epoxy resin composition containing a
sulfonate of an imidazole compound as a curing agent or a cure
accelerator. U.S. Pat. No. 3,356,645 (Patent Document 3) discloses
a carboxylate, a lactate, and a phosphate of an imidazole compound.
All the references cited above neither describe nor suggest ion
conductivity of these salts.
[0003] Some of ammonium salts such as imidazolium salts and
pyridium salts are known to become a liquid molten salt at or below
100.degree. C., particularly around room temperature and to exhibit
high ion conductivity at relatively low temperatures of 200.degree.
C. or lower without using water or an organic solvent. Such molten
salts have been studied for applicability as an electrolyte of
batteries and the like for their characteristic nonvolatility.
Known ionic liquids include a number of imidazole salts or pyridine
salts having a substituent introduced to their N-position(s) (see
Hiroyuki Ohno (ed.), Ionsei Ekitai--Kaihatsu no Saizensen to
Mirai-, CMC Publishing Co., Ltd., 28-31 (2003): Non-Patent Document
2).
[0004] Watanabe, et al. report protic, room-temperature molten
salts in J. Phys. Chem. B., 107 (17), 4024-4030 (2003) (Non-Patent
Document 3), Chem. Commun., 938-939 (2003) (Non-Patent Document 4),
Proceedings of The 43rd Battery Symposium in Japan, 102-103 (2002)
(Non-Patent Document 5), and ibid., 604-605 (2002) (Non-Patent
Document 6). The reported protic, room-temperature molten salts are
prepared basically using an amine compound with the positions other
than the N-position unsubstituted.
[0005] Kreuer, et al. report a proton conductor composed of
unsubstituted imidazole and sulfuric acid in Electrochimica Acta,
Vol. 43, No. 10-11, 1281-1288 (1998) (Non-Patent Document 7).
JP-T-2000-517462 (Patent Document 4) discloses a proton conductor
containing an acid and a nonaqueous amphoteric material. The
imidazole compounds having a substituent at a position other than
the 1,3-positions which are disclosed therein are given as a
general formula having one substituent at such a position. The
description is absent on limitation of the position of the
substituent. The imidazole compound actually used in the
description is an unsubstituted compound.
[0006] Armand et al. (JP-T-2000-508114: Patent Document 5)
discloses a proton conductor in liquid form comprising a mixture of
an acid addition salt of a nitrogen base and a nitrogen base,
wherein the acid of the acid addition salt is a fluorine-based
acid. The fluorine-based acid involves cost and environmental
concerns in the production. Use of the basic component (nitrogen
base) in excess lowers the melting point but reduces heat
resistance. [0007] Patent Document 1: JP-A-57-190018 [0008] Patent
Document 2: JP-A-48-5900 [0009] Patent Document 3: U.S. Pat. No.
3,356,645 [0010] Patent Document 4: JP-T-2000-517462 [0011] Patent
Document 5: JP-T-2000-508114 [0012] Non-Patent Document 1: Journal
of Japan Society of Colour Material, 50 (1), 2-7 (1977) [0013]
Non-Patent Document 2: Ionsei Ekitai--Kaihatsu no Saizensen to
Mirai-, CMC Publishing Co., Ltd., 28-31 (2003) [0014] Non-Patent
Document 3: J. Phys. Chem. B., 107 (17), 4024-4030 (2003) [0015]
Non-Patent Document 4: Chem. Commun., 938-939 (2003) [0016]
Non-Patent Document 5: Proceedings of The 43rd Battery Symposium in
Japan, 102-103 (2002) [0017] Non-Patent Document 6: Proceedings of
The 43rd Battery Symposium in Japan, 604-605 (2002) [0018]
Non-Patent Document 7: Electrochimica Acta, Vol. 43, No. 10-11,
1281-1288 (1998)
DISCLOSURE OF THE INVENTION
[0019] An object of the present invention is to provide an ion
conductive acid-base mixture having a relatively low melting point
and an ion or proton conductor containing the mixture.
[0020] The present invention accomplishes the above object by
providing an acid-base mixture composed of a base component and an
acid component and an ion or proton conductor containing the
mixture. At least one of the base component and the acid component
includes at least two compounds. The base component contains at
least one compound represented by chemical formula (1) shown below
(The acid-base mixture will hereinafter be referred to as "the
acid-base mixture of the first aspect). ##STR3## wherein R.sup.1,
R.sup.2, and R.sup.3 each represent a hydrogen atom or a
hydrocarbon group having 1 to 20 carbon atoms, provided that at
least one of them is a hydrocarbon group.
[0021] The present invention also accomplishes the above object by
providing an ion conductor comprising an acid-base mixture composed
of a base component containing a base represented by chemical
formula (2) shown below and an acid component (The ion conductor
will hereinafter be referred to as the ion conductor of the second
aspect). ##STR4## wherein R.sup.1, R.sup.2, and R.sup.3 each
represent a hydrogen atom or a hydrocarbon group having 1 to 20
carbon atoms, provided that R.sup.1 and R.sup.3 are different.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a graph showing the temperature dependence of the
ion conductivity of the acid-base mixtures prepared in Examples 1,
2, 6, 7, and 8 and Comparative Example 1.
[0023] FIG. 2 is a graph showing the results of thermogravimetric
analysis on the acid-base mixtures of Examples 1, 7, and 8.
[0024] FIG. 3 is a graph showing the results of thermogravimetric
analysis on the acid-base mixtures of Examples 2 and 3 and
Comparative Example 1.
[0025] FIG. 4 is a graph showing the temperature dependence of the
ion conductivity of the acid-base mixtures of Examples 6, 15, and
16 and Comparative Example 1.
[0026] FIG. 5 is a graph showing the temperature dependence of the
ion conductivity of the acid-base mixtures of Examples 7 and 8 and
Comparative Example 1.
[0027] FIG. 6 is a graph showing the results of thermogravimetric
analysis on the acid-base mixtures of Examples 6, 21, 22, and 24,
2E4MZ, and methanesulfonic acid.
[0028] FIG. 7 is a graph showing the results of thermogravimetric
analysis on the acid-base mixtures of Examples 7, 10, and 11.
[0029] FIG. 8 is a graph showing the results of thermogravimetric
analysis on the acid-base mixtures of Examples 7 and 8 and
Comparative Example 1.
BEST MODE FOR CARRYING OUT THE INVENTION
[0030] The acid-base mixture of the first aspect will be described
first.
[0031] The acid-base mixture of the first aspect is composed of a
base component and an acid component. At least one of the base
component and the acid component includes at least two compounds.
The base component contains at least one base represented by
chemical formula (1) shown below, preferably a base represented by
chemical formula (2) shown below. ##STR5## wherein R.sup.1,
R.sup.2, and R.sup.3 each represent a hydrogen atom or a
hydrocarbon group having 1 to 20 carbon atoms, provided that at
least one of them is a hydrocarbon group. ##STR6## wherein R.sup.1,
R.sup.2, and R.sup.3 each represent a hydrogen atom or a
hydrocarbon group having 1 to 20 carbon atoms, provided that
R.sup.1 and R.sup.3 are different.
[0032] Preferred examples of the hydrocarbon group having 1 to 20
carbon atoms include straight-chain or branched alkyl groups and
aromatic groups. Specific examples are methyl, ethyl, n-propyl,
isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, hexyl, phenyl,
and benzyl, with methyl and ethyl being particularly preferred.
[0033] The bases represented by chemical formulae (1) or (2)
include imidazoles having an alkyl group at a position other than
the N-positions of the ring, such as monoalkylimidazoles, e.g.,
2-alkylimidazoles and 4-alkylimidazoles, and
2,4-dialkylimidazoles.
[0034] Specific examples of the above-described bases include
2-alkylimidazoles, such as 2-methylimidazole and 2-ethylimidazole;
4-alkylimidazoles, such as 4-methylimidazole and 4-ethylimidazole;
2,4-dialkylimidazoles, such as 2-ethyl-4-methylimidazole,
2-octyl-4-hexylimidazole, 2-cyclohexyl-4-methylimidazole, and
2-butyl-4-allylimidazole; 2-phenylimidazole, 4-phenylimidazole, and
2-ethyl-4-phenylimidazole.
[0035] Preferred of them are 2-ethyl-4-methylimidazole,
4-methylimidazole, and 2-ethylimidazole.
[0036] Where the acid component is a single compound, the base
component is a mixture of two or more of the above-described bases.
Where the acid component is a mixture of two or more compounds, the
base component may be either a single compound or a mixture of two
or more compounds selected from the above-described bases. Where
the base component is a mixture of two or more compounds, one of
them may be unsubstituted imidazole. In this case, the proportion
of unsubstituted imidazole in the base component is preferably 90%
by weight or less, still preferably 60% by weight or less.
[0037] Suitable combinations of two or more bases include a mixture
of 2-ethyl-4-methylimidazole and 4-methylimidazole, a mixture of
2-ethyl-4-methylimidazole and 2-ethylimidazole, a mixture of
2-ethyl-4-methylimidazole and imidazole, and a mixture of
2-ethylimidazole and 4-methylimidazole.
[0038] The acid component that can be used in the first aspect of
the invention includes sulfonic acids, sulfonic acid compounds,
carboxylic acids, and inorganic acids. It is preferred that at
least one compound making up the acid component be an inorganic
acid. Examples of the acid component include organic aliphatic or
aromatic sulfonic acids, such as p-toluenesulfonic acid,
methanesulfonic acid, and trifluoromethanesulfonic acid; and
aromatic or aliphatic carboxylic acids. Preferred inorganic acids
include inorganic mineral acids, such as sulfuric acid, phosphoric
acid, and perchloric acid. The acid component is preferably an acid
containing no fluorine atom in its structure. Sulfuric acid,
phosphoric acid, etc. are advantageous from the standpoint of cost.
Methanesulfonic acid, etc. are advantageous from the standpoint of
ease of handling.
[0039] Where the base component is a mixture of two or more bases,
the acid component may be either one or a mixture of two or more
selected from the above-recited acids. Where the base component is
a single compound, the acid component should be a mixture of two or
more of the above-described acids.
[0040] Suitable combinations of the acid component and the base
component include: a combination of
2-ethyl-4-methylimidazole/4-methylimidazole and sulfuric acid
(2E4MZ/4MI.H.sub.2SO.sub.4), a combination of
2-ethyl-4-methylimidazole/2-ethylimidazole and sulfuric acid
(2E4MZ/2EI.H.sub.2SO.sub.4), a combination of
2-ethyl-4-methylimidazole/imidazole and sulfuric acid
(2E4MZ/Im.H.sub.2SO.sub.4), and a combination of
2-ethylimidazole/4-methylimidazole and sulfuric acid
(2EI/4MI.H.sub.2SO.sub.4).
[0041] The mixing ratio of the base component to the acid component
preferably ranges from 99:1 to 1:99, still preferably from 95:1 to
1:95, by mole. It is not preffered that the ratio of the base
component or the acid component exceeds the recited range because
the heat resistance reduces. A particularly preferred mixing ratio
of the base component and the acid component is 1:1 (an equimolar
mixture).
[0042] The acid-base mixture of the first aspect is preferably an
acid-base mixture having a melting point of 120.degree. C. or lower
or a liquid acid-base mixture showing no melting point.
[0043] It is particularly preferred that the acid-base mixture of
the first aspect be an acid-base mixture that is liquid at room
temperature or an acid-base mixture having a glass transition
temperature of 25.degree. C. or lower.
[0044] The acid-base mixture of the first aspect is preferably an
ion conductor having an ion conductivity of, for example, 10.sup.-4
Scm.sup.-1 or higher at 100.degree. C. The acid-base mixture of the
first aspect is superior in ion conductivity in a low temperature
region of room temperature or lower.
[0045] The ion conductor according to the second aspect of the
invention will then be described.
[0046] The ion conductor of the second aspect comprises an
acid-base mixture composed of a base component containing a base
represented by chemical formula (2) shown below and an acid
component. ##STR7## wherein R.sup.1, R.sup.2, and R.sup.3 each
represent a hydrogen atom or a hydrocarbon group having 1 to 20
carbon atoms, provided that R.sup.1 and R.sup.3 are different.
[0047] Preferred examples of the hydrocarbon group having 1 to 20
carbon atoms include straight-chain or branched alkyl groups and
aromatic groups. Specific examples are methyl, ethyl, n-propyl,
isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, hexyl, phenyl,
and benzyl, with methyl and ethyl being particularly preferred.
[0048] The base represented by chemical formula (2) used in the
second aspect is an asymmetric imidazole compound in which the
substituents R.sup.1 and R.sup.3 are not the same.
[0049] Such asymmetric imidazole compounds include
monoalkylimidazoles having one alkyl group at a position other than
the N-positions of the ring, such as 4-alkylimidazoles.
[0050] Specific examples include 4-alkylimidazoles such as
4-methylimidazole and 4-ethylimidazole, and 4-phenylimidazole.
[0051] The asymmetric imidazole compounds further include those
having an alkyl group at two or more positions other than the
N-positions of the ring, such as 2,4-dialkylimidazoles.
[0052] Specific examples include 2,4-dialkylimidazoles such as
2-ethyl-4-methylimidazole, 2-octyl-4-hexylimidazole,
2-cyclohexyl-4-methylimidazole, and 2-butyl-4-allylimidazole, and
2-ethyl-4-phenylimidazole.
[0053] Of the asymmetric imidazole compounds described above,
preferred are 4-methylimidazole and 2-ethyl-4-methylimidazole.
[0054] The base component used in the second aspect may be either
one of the above-described bases or a mixture of two or more of
them. Where a mixture of two or more bases is used, one of them may
be unsubstituted imidazole or a symmetric imidazole compound such
as a 2-alkylimidazole or 2-phenylimidazole. Examples of the
2-alkylimidazole are 2-methylimidazole and 2-ethylimidazole. In
this case, the proportion of the unsubstituted imidazole or the
symmetric imidazole compound in the base component is preferably
90% by weight or less, still preferably 60% by weight or less.
[0055] Suitable combinations of the two or more bases include a
mixture of 2-ethyl-4-methylimidazole and 4-methylimidazole, a
mixture of 2-ethyl-4-methylimidazole and 2-ethylimidazole, a
mixture of 2-ethyl-4-methylimidazole and imidazole, and a mixture
of 4-methylimidazole and 2-ethylimidazole.
[0056] The acid component that can be used in the second aspect
includes the acids described for use in the first aspect of the
invention, which can be used either individually or as a mixture of
two or more thereof.
[0057] Suitable combinations of the acid component and the base
component include: a combination of 2-ethyl-4-methylimidazole and
sulfuric acid (2E4MZ.H.sub.2SO.sub.4), a combination of
2-ethyl-4-methylimidazole and trifluoromethanesulfonic acid
(2E4MZ.HTf), a combination of 4-methylimidazole and sulfuric acid
(4MI.H.sub.2SO.sub.4), a combination of
2-ethyl-4-methylimidazole/4-methylimidazole and sulfuric acid
(2E4MZ/4MI.H.sub.2SO.sub.4), a combination of
2-ethyl-4-methylimidazole/2-ethylimidazole and sulfuric acid
(2E4MZ/2EI.H.sub.2SO.sub.4), a combination of
2-ethyl-4-methylimidazole/imidazole and sulfuric acid
(2E4MZ/Im.H.sub.2SO.sub.4), a combination
4-methylimidazole/2-ethylimidazole and sulfuric acid
(4MI/2EI.H.sub.2SO.sub.4), and a combination of
2-ethyl-4-methylimidazole and methanesulfonic acid
(2E4MZ.CH.sub.3SO.sub.3H).
[0058] The mixing ratio of the base component to the acid component
preferably ranges from 99:1 to 1:99, still preferably from 95:1 to
1:95, by mole. If the ratio of the base component or the acid
component exceeds the recited range, the heat resistance reduces. A
particularly preferred mixing ratio of the base component and the
acid component is 1:1 (an equimolar mixture).
[0059] The ion conductor of the second aspect contains the
acid-base mixture composed of the base component and the acid
component and exhibits an ion conductivity of, for example,
10.sup.-4 Scm.sup.-1 or higher at 100.degree. C. The ion conductor
of the second aspect is superior in ion conductivity in a low
temperature region of room temperature or lower.
[0060] The ion conductor of the second aspect is preferably one
having a melting point of 120.degree. C. or lower or a liquid one
with no melting point.
[0061] It is particularly preferred for the ion conductor of the
second aspect to have a glass transition temperature of 25.degree.
C. or lower.
EXAMPLES
[0062] The present invention will now be illustrated in greater
detail with reference to Examples and Comparative Examples.
Measurements in Examples and Comparative Examples were made in
accordance with the following methods.
(1) Measurement of Ion Conductivity
[0063] A dried sample was put in a sample bottle. Platinum plates
measuring 1.5 cm wide and 2 cm long were immersed in the sample in
parallel with each other at a 1 cm distance. The sample bottle was
closed to make a cell for conductivity measurement. The ionic
conductivity was obtained by complex impedance measurement with FRD
1025 and Potentiostat/Galvanostat 283, supplied by Princeton
Applied Research, in a thermostat set at a prescribed
temperature.
(2) Melting Point
[0064] Measured with DSC-7 from Perkin-Elmer Inc. or DSC-50 from
Shimadzu Corp. at a rate of temperature rise of 10.degree. C./min
in a helium stream.
(3) Thermogravimetry
[0065] Carried out with TGA-50 from Shimadzu Corp. in air at a rate
of temperature rise of 10.degree. C./min.
Example 1
Mixture of 2-ethyl-4-methylimidazole/4-methylimidazole and sulfuric
acid (2E4MZ/4MI.H.sub.2SO.sub.4; molar ratio=1:1:2)
[0066] In 12.7 g of 2E4MZ (from Shikoku Chemicals Corp.) was added
dropwise 6 ml of 98% sulfuric acid in a nitrogen atmosphere while
stirring. After 2 hour stirring, 20.5 g of 4MI.H.sub.2SO.sub.4
prepared in Example 8 given later was added thereto, followed by
stirring overnight at room temperature. The mixture was dried under
reduced pressure at 110.degree. C. for 6 hours to remove water to
give 2E4MZ/4MI.H.sub.2SO.sub.4 (molar ratio=1:1:2). The acid-base
mixture maintained the liquid state for more than 4 months. The
results of DSC showed no melting point and a Tg of -54.degree. C.
The temperature dependence of the ion conductivity of the acid-base
mixture is shown in FIG. 1.
Example 2
Mixture of 2-ethyl-4-methylimidazole/2-ethylimidazole and sulfuric
acid (2E4MZ/2EI.H.sub.2SO.sub.4; molar ratio=1:1:2)
[0067] In a flask were put 15.7 g of 2E4MZ and 13.7 g of 2EI (from
Aldrich), and the 2EI was melted at 100.degree. C. to make a
uniform mixture. Into the mixture was added dropwise 15 ml of 98%
sulfuric acid in a nitrogen atmosphere while stirring. The mixture
was stirred at room temperature overnight, followed by drying under
reduced pressure at 110.degree. C. for 6 hours to remove water
thereby to give 2E4MZ/2EI.H.sub.2SO.sub.4 (molar ratio=1:1:2). The
resulting acid-base mixture maintained the liquid state for more
than 5 months. The DSC results revealed no melting point and a Tg
of -61.degree. C. The temperature dependence of the ion
conductivity of the acid-base mixture is shown in FIG. 1. Owing to
the mixed base system, the acid-base mixture of Example 2 exhibited
improvement in ion conductivity in a low temperature region over
the acid-base mixture of Comparative Example 1 hereinafter
given.
Example 3
Mixture of 2-ethyl-4-methylimidazole/imidazole and sulfuric acid
(2E4MZ/Im.H.sub.2SO.sub.4; molar ratio=1:1:2)
[0068] In 30 ml of ethanol were dissolved 5.17 g of 2E4MZ and 3.20
g of imidazole (from Sigma). The solution was cooled in an ice
bath, and 5 ml of 98% sulfuric acid was added thereto dropwise in a
nitrogen atmosphere while stirring. The stirring was continued at
room temperature overnight, followed by drying under reduced
pressure at 60.degree. C. for 1 hour and then at 110.degree. C. for
6 hours to remove ethanol and water to give
2E4MZ/Im.H.sub.2SO.sub.4 at a molar ratio of 1:1:2. The resulting
acid-base mixture was solid at room temperature. In DSC, a sample
was maintained at 100.degree. C. to once melt, cooled to
-150.degree. C., and again heated from -150.degree. C. up to
100.degree. C. The sample showed only a Tg with no peak of
crystallization or melting in both the cooling and the heating
thermograms. The Tg was -56.degree. C.
Example 4
Mixture of 2-ethylimidazole/4-methylimidazole and sulfuric acid
(2EI/4MI.H.sub.2SO.sub.4; molar ratio=1:1:2)
[0069] A mixture of 4.51 g of 2EI and 3.85 g of 4MI (from Aldrich)
was melted at 100.degree. C., and 5 ml of 98% sulfuric acid was
added thereto dropwise in a nitrogen atmosphere while stirring.
After the mixture was stirred at room temperature overnight, water
was removed by drying under reduced pressure at 110.degree. C. for
6 hours to give 2EI/4MI.H.sub.2SO.sub.4 (molar ratio=1:1:2). The
acid-base mixture maintained the liquid state for more than 3
months.
Example 5
Mixture of 2-ethyl-4-methylimidazole/4-methylimidazole and sulfuric
acid (2E4MZ/4MI.H.sub.2SO.sub.4; molar ratio=1:1:1)
[0070] In a flask were put 10.5 g of 2E4MZ and 7.70 g of 4MI, and
the 4MI was melted at 70.degree. C. to make a uniform mixture. To
the mixture was added dropwise 5 ml of 98% sulfuric acid in a
nitrogen atmosphere while stirring. After a while, the viscosity
increased to make stirring difficult. From the next day on, the
resulting mixture 2E4MZ/4MI.H.sub.2SO.sub.4 having a molar ratio of
1:1:1 gradually solidified. It completely solidified in three
months.
Example 6
Mixture of 2-ethyl-4-methylimidazole and trifluoromethanesulfonic
acid (2E4MZ.HTf)
[0071] In 50 ml of ethanol was dissolved 62.3 g of 2E4MZ. The
solution was cooled in an ice bath, and 84.9 g of HTf was added
thereto in a nitrogen atmosphere while stirring. The stirring was
continued at room temperature overnight. The mixture was dried at
60.degree. C. for 1 hour and then at 110.degree. C. for 6 hours
under reduced pressure to remove ethanol and water. The resulting
2E4MZ.HTf was in a liquid state for a while but solidified in a few
days. As a result of DSC, the melting point and the Tg were found
to be 6.degree. C. and -91.degree. C., respectively. The
temperature dependence of the ion conductivity of the 2E4MZ.HTf is
displayed in FIGS. 1 and 4.
Example 7
Mixture of 2-ethyl-4-methylimidazole and sulfuric acid
(2E4MZ.H.sub.2SO.sub.4)
[0072] In 10.3 g of 2E4MZ was added dropwise 5 ml of 98% sulfuric
acid in a nitrogen atmosphere while stirring. After the stirring
was continued at room temperature overnight, the mixture was dried
at 110.degree. C. for 6 hours under reduced pressure to remove
water. The resulting 2E4MZ.H.sub.2SO.sub.4 was in a liquid state
for a while but gradually solidified. In DSC, a sample was
maintained at 100.degree. C. to once melt, cooled to -150.degree.
C., and again heated from -150.degree. C. up to 100.degree. C. The
sample showed only a Tg with no peak of crystallization or melting
in both the cooling and the heating thermogram. The Tg was
-58.degree. C. The temperature dependence of the ion conductivity
of the 2E4MZ.H.sub.2SO.sub.4 is displayed in FIGS. 1 and 5.
Example 8
Mixture of 4-methylimidazole and sulfuric acid
(4MI.H.sub.2SO.sub.4)
[0073] At 100.degree. C. was melted 23.1 g of 4MI (from Aldrich),
and 15 ml of 98% sulfuric acid was added thereto dropwise in a
nitrogen atmosphere while stirring. The stirring was continued at
room temperature overnight. The mixture was dried at 110.degree. C.
for 6 hours under reduced pressure to remove water. The resulting
4MI.H.sub.2SO.sub.4 was in a liquid state for at least one week. As
a result of DSC, the melting point and the Tg were found to be
29.degree. C. and -62.degree. C., respectively. The temperature
dependence of the ion conductivity of the 4MI.H.sub.2SO.sub.4 is
shown in FIGS. 1 and 5.
Example 9
Mixture of 2-ethyl-4-methylimidazole and sulfuric acid
(2E4MZ.H.sub.2SO.sub.4; molar ratio=9:1)
[0074] To 2.16 g of 2E4MZ was added 0.521 g of the
2E4MZ.H.sub.2SO.sub.4 obtained in Example 7 to give
2E4MZ.H.sub.2SO.sub.4 having a molar ratio of 9:1, which maintained
a liquid state for more than six months.
Example 10
Mixture of 2-ethyl-4-methylimidazole and sulfuric acid
(2E4MZ.H.sub.2SO.sub.4; molar ratio=3:1)
[0075] To 1.19 g of 2E4MZ was added 1.15 g of the
2E4MZ.H.sub.2SO.sub.4 obtained in Example 7 to give
2E4MZ.H.sub.2SO.sub.4 having a molar ratio of 3:1, which maintained
a liquid state for more than six months.
Example 11
Mixture of 2-ethyl-4-methylimidazole and sulfiric acid
(2E4MZ.H.sub.2SO.sub.4; molar ratio=3:2)
[0076] To 0.512 g of 2E4MZ was added 1.91 g of the
2E4MZ.H.sub.2SO.sub.4 obtained in Example 7 to give
2E4MZ.H.sub.2SO.sub.4 having a molar ratio of 3:2, which maintained
a liquid state for more than six months.
Example 12
Mixture of 2-ethyl-4-methylimidazole and sulfuric acid
(2E4MZ.H.sub.2SO.sub.4; molar ratio=2:3)
[0077] To 2.01 g of the 2E4MZ.H.sub.2SO.sub.4 obtained in Example 7
was added 0.484 g of 98% sulfuric acid to give
2E4MZ.H.sub.2SO.sub.4 having a molar ratio of 2:3, which maintained
a liquid state for more than six months.
Example 13
Mixture of 2-ethyl-4-methylimidazole and sulfuric acid
(2E4MZ.H.sub.2SO.sub.4; molar ratio=1:3)
[0078] To 1.23 g of the 2E4MZ.H.sub.2SO.sub.4 obtained in Example 7
was added 1.16 g of 98% sulfuric acid to give 2E4MZ.H.sub.2SO.sub.4
having a molar ratio of 1:3, which maintained a liquid state for
more than six months.
Example 14
Mixture of 2-ethyl-4-methylimidazole and sulfuric acid
(2E4MZ.H.sub.2SO.sub.4; molar ratio=1:9)
[0079] To 0.510 g of the 2E4MZ.H.sub.2SO.sub.4 obtained in Example
7 was added 1.93 g of 98% sulfuric acid to give
2E4MZ.H.sub.2SO.sub.4 having a molar ratio of 1:9, which maintained
a liquid state for more than six months.
Example 15
Mixture of 2-ethyl-4-methylimidazole and trifluoromethanesulfonic
acid (2E4MZ.HTf; molar ratio=9:1)
[0080] To 30.1 g of 2E4MZ was added 7.92 g of the 2E4MZ.HTf
obtained in Example 6 to give 2E4MZ.HTf having a molar ratio of
9:1, which maintained a liquid state for more than seven months.
The temperature dependence of the ion conductivity of the resulting
2E4MZ.HTf is shown in FIG. 4.
Example 16
Mixture of 2-ethyl-4-methylimidazole and trifluoromethanesulfonic
acid (2E4MZ.HTf; molar ratio=7:3)
[0081] In 40 ml of ethanol was dissolved 43.0 g of 2E4MZ. The
solution was cooled in an ice bath, and 25 g of
trifluoromethanesulfonic acid was added thereto dropwise in a
nitrogen atmosphere while stirring. After the stirring was
continued at room temperature overnight, the mixture was dried at
60.degree. C. for 1 hour and then at 110.degree. C. for 6 hours
under reduced pressure to remove ethanol and water to give
2E4MZ.HTf having a molar ratio of 7:3. The temperature dependence
of the ion conductivity of the resulting 2E4MZ.HTf is shown in FIG.
4.
Example 17
Mixture of 2-ethyl-4-methylimidazole and trifluoromethanesulfonic
acid (2E4MZ.HTf; molar ratio=7:3)
[0082] To 1.71 g of 2E4MZ was added 3.01 g of the 2E4MZ.HTf
obtained in Example 6 to give 2E4MZ.HTf having a molar ratio of
7:3, which maintained a liquid state for more than seven
months.
Example 18
Mixture of 2-ethyl-4-methylimidazole and trifluoromethanesulfonic
acid (2E4MZ.HTf; molar ratio=4:6)
[0083] To 4.01 g of the 2E4MZ.HTf obtained in Example 6 was added
1.17 g of trifluoromethanesulfonic acid to give 2E4MZ.HTf having a
molar ratio of 4:6, which maintained a liquid state for more than
six months.
Example 19
Mixture of 2-ethyl-4-methylimidazole and trifluoromethanesulfonic
acid (2E4MZ.HTf; molar ratio=3:7)
[0084] To 3.05 g of the 2E4MZ.HTf obtained in Example 6 was added
2.35 g of trifluoromethanesulfonic acid to give 2E4MZ.HTf having a
molar ratio of 3:7, which maintained a liquid state for more than
six months.
Example 20
Mixture of 2-ethyl-4-methylimidazole and trifluoromethanesulfonic
acid (2E4MZ.HTf; molar ratio=2:8)
[0085] To 2.02 g of the 2E4MZ.HTf obtained in Example 6 was added
3.54 g of trifluoromethanesulfonic acid to give 2E4MZ.HTf having a
molar ratio of 2:8, which maintained a liquid state for more than
six months.
Example 21
Mixture of 2-ethyl-4-methylimidazole and methanesulfonic acid
(2E4MZ.CH.sub.3SO.sub.3H)
[0086] In an ice bath was cooled 6.62 g of 2E4MZ, and 5.78 g of
methanesulfonic acid (from Aldrich) was added thereto dropwise in a
nitrogen atmosphere while stirring. Stirring was continued at room
temperature overnight. As a result of DSC, the resulting
2E4MZ.CH.sub.3SO.sub.3H was found to have a melting point of
56.degree. C. and a Tg of -63.degree. C.
Example 22
Mixture of 2-ethyl-4-methylimidazole and methanesulfonic acid
(2E4MZ.CH.sub.3SO.sub.3H; molar ratio=7:3)
[0087] To 2.02 g of the 2E4MZ.CH.sub.3SO.sub.3H obtained in Example
21 was added 1.44 g of 2E4MZ to give 2E4MZ.CH.sub.3SO.sub.3H having
a molar ratio of 7:3, which maintained a liquid state for more than
seven months.
Example 23
Mixture of 2-ethyl-4-methylimidazole and methanesulfonic acid
(2E4MZ.CH.sub.3SO.sub.3H; molar ratio=4:6)
[0088] To 1.03 g of the 2E4MZ.CH.sub.3SO.sub.3H obtained in Example
21 was added 0.244 g of methanesulfonic acid to give
2E4MZ.CH.sub.3SO.sub.3H having a molar ratio of 4:6, which
maintained a liquid state for more than seven months.
Example 24
Mixture of 2-ethyl-4-methylimidazole and methanesulfonic acid
(2E4MZ.CH.sub.3SO.sub.3H; molar ratio=3:7)
[0089] To 2.00 g of the 2E4MZ.CH.sub.3SO.sub.3H obtained in Example
21 was added 1.25 g of methanesulfonic acid to give
2E4MZ.CH.sub.3SO.sub.3H having a molar ratio of 3:7, which
maintained a liquid state for more than seven months.
Example 25
Mixture of 2-ethyl-4-methylimidazole and methanesulfonic acid
(2E4MZ.CH.sub.3SO.sub.3H; molar ratio=2:8)
[0090] To 1.09 g of the 2E4MZ.CH.sub.3SO.sub.3H obtained in Example
21 was added 1.53 g of methanesulfonic acid to give
2E4MZ.CH.sub.3SO.sub.3H having a molar ratio of 2:8, which
maintained a liquid state for more than seven months.
Comparative Example 1
Mixture of 2-ethylimidazole and sulfuric acid
(2EI.H.sub.2SO.sub.4)
[0091] 2EI (Aldrich) (27.1 g) was melted at 100.degree. C., and 15
ml of 98% sulfuric acid was added thereto dropwise in a nitrogen
atmosphere while stirring. The mixture was stirred at room
temperature overnight, followed by drying under reduced pressure at
110.degree. C. for 6 hours to remove water. The resulting
2EI.H.sub.2SO.sub.4 was in a liquid state for a while but
solidified in a few days. As a result of DSC, the melting point and
the Tg were found to be 50.degree. C. and -64.degree. C.,
respectively. The temperature dependence of the ion conductivity of
the 2EI.H.sub.2SO.sub.4 is shown in FIGS. 1, 4, and 5. The
2EI.H.sub.2SO.sub.4 largely reduced the ion conductivity in a
temperature region at and below the melting point.
Reference Example 1
Mixture of imidazole and sulfuric acid/phosphoric acid
(Im.H.sub.2SO.sub.4/H.sub.3PO.sub.4; molar ratio=2:1:1)
[0092] To 12.7 g of Im (from Sigma) was added dropwise 10.85 g of a
85% phosphoric acid aqueous solution and mixed. To the mixture was
added dropwise 5 ml of 98% sulfuric acid, followed by stirring
overnight. The mixture was dried under reduced pressure at
80.degree. C. for 1 hour and then at 110.degree. C. for 6 hours to
remove water to give Im.H.sub.2SO.sub.4/H.sub.3PO.sub.4 having a
molar ratio of 2:1:1. When allowed to stand overnight, the
Im.H.sub.2SO.sub.4/H.sub.3PO.sub.4 solidified.
Reference Example 2
Thermogravimetric Analysis:
[0093] The results of thermogravimetric analysis on the acid-base
mixtures of Examples 1, 7, and 8 are shown in FIG. 2.
Reference Example 3
Thermogravimetric Analysis:
[0094] The results of thermogravimetric analysis on the acid-base
mixtures of Examples 2 and 3 and Comparative Example 1 are shown in
FIG. 3.
Reference Example 4
Thermogravimetric Analysis:
[0095] The results of thermogravimetric analysis on the acid-base
mixtures of Examples 6, 21, 22, and 24, 2E4MZ, and methanesulfonic
acid are shown in FIG. 6.
Reference Example 5
Thermogravimetric Analysis:
[0096] The results of thermogravimetric analysis on the acid-base
mixtures of Examples 7, 10, and 11 are shown in FIG. 7.
Reference Example 6
Thermogravimetric Analysis:
[0097] The results of thermogravimetric analysis on the acid-base
mixtures of Examples 7 and 8 and Comparative Example 1 are shown in
FIG. 8.
INDUSTRIAL APPLICABILITY
[0098] The acid-base mixture according to the present invention is
excellent in heat resistance and exhibits high ion conductivity
without water or a solvent and is therefore useful as an ion
conductor or a proton conductor in fuel cells, secondary batteries,
electric double layer capacitors, and electrolytic capacitors.
[0099] The acid-base mixture of the present invention can be
utilized in the above-described applications as a polymer composite
membrane obtained by solution casting wherein the acid-base mixture
and polymers are used or a polymer electrolyte membrane obtained by
infiltrating the acid-base mixture into a porous polymer
membrane.
* * * * *