JP2009016344A - Compound proton conductor, proton-conductive electrolyte membrane, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: a compound proton conductor having stably high proton conductivity even under the condition of high temperature without humidification; a proton-conductive electrolyte membrane excellent in mechanical strength using this proton conductor; and a low-cost fuel cell excellent in power generating characteristics. <P>SOLUTION: This invention provides a fuel cell comprising: a compound proton conductor including an organic salt composed of an organic cation and oxo acid anion having at least one or more of hydrogen atoms, and a polymer electrolyte with an acid functional group; a proton conductive electrolyte membrane including this proton conductor; and a membrane electrode assembly using the proton-conductive electrolyte membrane. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a composite proton conductor, a proton conductive electrolyte membrane, and a fuel cell.

  In fuel cells that can be applied to electrochemical devices, and that are attracting attention as a next-generation clean energy, in recent years, protons can be generated under no or low humidification that enables operation at a high temperature of 100 ° C. or higher. Conductive electrolyte membranes are being actively developed. Thus, if an electrolyte membrane capable of proton conduction at a high temperature that does not depend on water is provided, the fuel cell system can be simplified, so that it can be widely used as a household cogeneration application or an automobile application. I can expect.

A polymer electrolyte fuel cell (PEFC) is suitable as a household cogeneration application or an automobile application. PEFC is a polymer electrolyte membrane having proton conductivity as a catalyst. And a membrane electrode assembly (MEA) having a structure sandwiched between a fuel electrode and an oxygen electrode composed of a gas diffusion layer and the like, and hydrogen gas for the fuel electrode and air or oxygen for the oxygen electrode Is a mechanism in which an electrochemical reaction of the following formula occurs to obtain an electromotive force.
(Fuel electrode) H ₂ → 2H ⁺ + 2e ⁻
(Oxygen electrode) 2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O

  As for the above-described polymer electrolyte membrane having proton conductivity, Nafion (registered trademark) manufactured by DuPont, USA, sulfonated polyetheretherketone, and the like are conventionally known. The proton conduction of these polymer electrolytes is generally applied to fuel cells in a certain wet state by humidification or the like because water molecules around the sulfonic acid are involved in conduction. Therefore, the operating temperature is generally set to 80 ° C. or less, and this limitation causes problems such as catalyst carbon monoxide poisoning. Therefore, selective carbon monoxide removal is necessary, and the fuel cell system is more complicated and The situation is inevitably high.

  In view of such problems, various proposals have been made regarding PEFCs driven at 100 ° C. or higher. In general, the catalytic activity is improved in power generation at 100 ° C. or higher, which suggests that the degree of poisoning by carbon monoxide may be reduced, and as a result, the fuel cell life is improved. However, since water molecules cannot exist stably in operation in the middle temperature range of about 150 ° C., a fuel cell using an electrolyte system that does not depend on an aqueous medium, centering on polybenzimidazole doped with phosphoric acid, has been proposed. (For example, refer to Patent Document 1). In such a fuel cell, power generation is possible even in an intermediate temperature range of about 150 ° C.

  In addition to the technique described in Patent Document 1, a fuel cell using a room temperature molten salt as a proton transfer medium has been devised. As such a fuel cell, for example, a normal temperature molten salt is a liquid mainly around an invention using a normal temperature molten salt as a proton transfer medium (see, for example, Patent Document 2). As a method for immobilizing a salt, a combination with polyarylene (for example, see Patent Document 3), a combination with polybenzimidazoles or the like (for example, see Patent Document 4), a Zwitterion type molten salt and an acid Combinations (for example, see Patent Document 5 and Patent Document 6) and the like are being studied.

US Pat. No. 5,525,436 International Publication No. 03/083981 Specification JP 2006-32213 A JP 2005-166598 A JP 2005-228588 A JP 2004-38683 A R. Savinell et al. Electrochem. Soc. 141, (1994) L46 J. et al. Sun et al., Electrochema Acta, 46, (2001) 1703-1708. Z. Zhou et al. Am. Chem. Soc. 127, (2005) 10825 M.M. Yoshizawa-Fujita et al., Electrochem. Comm. 9 (2007) 1202-1205 B. S. Lalia et al. Chem. Phys. Lett. , 425 (2006) 294-300

  However, there has been a problem that the polarization characteristics have been extremely low in the confirmation of characteristics relating to power generation using room temperature molten salts devised so far. Here, although Patent Document 2 shows a polarization curve, it does not show data generated continuously, and Patent Document 3 does not show data that is the basis for power generation. Further, Patent Documents 5 and 6 describe the results of continuous energization tests as electrochemical measurement results, but their characteristics are extremely low.

  On the other hand, a technology in which a conventional perfluorosulfonic acid type polymer electrolyte represented by Nafion (registered trademark) is doped with phosphoric acid (see, for example, Non-Patent Document 1), an electrolyte doped with a normal room temperature molten salt (For example, see Non-Patent Document 2), or a strong acid-weak base combination (for example, see Non-Patent Document 3) in which triazole is doped into sulfonated polysulfone (see Non-Patent Document 3, for example). However, the power generation characteristics are not fully mentioned, and the actual situation is that sufficient verification has not been performed in the practical application of the technology to fuel cells.

  That is, as can be seen in Non-Patent Document 1, in the case where an acidic proton medium such as phosphoric acid is used, the protons necessary for power generation are found as in the above-described polybenzimidazole doped with phosphoric acid. Since it can be achieved relatively easily, power generation is also possible. However, doping with an acid causes problems such as corrosion of the metal separator, which may make it difficult to use the metal separator and the like, and there is a limit to cost reduction that is important in the practical use of fuel cells. There's a problem.

  On the other hand, as in Patent Document 2 and Patent Documents 5 and 6, etc., neutralized salts of acid bases are used as room temperature molten salts, but the acid bases are not balanced and are not completely neutralized. That is, even when an ionic liquid having a non-neutral pH is used, similarly, problems such as corrosion of the metal separator are considered to occur.

  In any room temperature molten salt or a combination of a room temperature molten salt and a polymer electrolyte, the apparent conduction characteristics and the polarization characteristics related to power generation are too far apart. Therefore, it must be considered that the conduction of protons used in the electrochemical reaction during power generation is insufficient.

  Accordingly, the present invention has been made in view of such problems, and is a composite proton conductor having high proton conductivity stably even under conditions of high temperature and no humidification, and a mechanical device using this proton conductor. An object of the present invention is to provide a proton conductive electrolyte membrane having excellent strength, and a fuel cell using the above composite proton conductor and inexpensive and excellent in power generation characteristics.

As a result of intensive research in order to solve the above-mentioned problems, the present inventors have found that an oxo acid having a hydrogen molecule (not a general room temperature molten salt as discussed in each of the aforementioned patent documents) It has been found that by using a neutral organic salt having XO _m (OH) _n ⁻ (X = P, S, or N)) as an anion, high proton conductivity is exhibited even at a high temperature. In addition, when the present inventors combined this organic salt with a polymer electrolyte having an acidic functional group such as a perfluorosulfonic acid type polymer, high temperature and no humidification (including the case of low humidification, the same applies hereinafter) It has been found that even under the conditions of (2), the polymer electrolyte is not altered, and the organic salt can exhibit high proton conductivity as a whole by assisting proton conduction of the polymer electrolyte. Furthermore, the present inventors have found that a fuel cell using such a combination of an organic salt and a polymer electrolyte having an acidic functional group has remarkably superior power generation characteristics (particularly polarization characteristics) as compared with conventional fuel cells. I also found out that Based on such knowledge, the present invention has been completed.

  That is, according to one aspect of the present invention, an organic salt comprising an organic compound cation and an oxo acid anion represented by the following formula (1) having at least one hydrogen atom, and a polymer electrolyte having an acidic functional group And a composite proton conductor comprising:

XO _m (OH) _n ⁻ (1)
(In Formula (1), X is P, S or N, and m and n are 1 or more.)

  In the composite proton conductor, the organic compound cation is preferably an imidazolium cation from the viewpoint of high proton conductivity under high temperature and no humidification, and in particular, a 1,3-substituted imidazolium cation, Is, for example, preferably an imidazolium cation represented by the following general formula (2).

（一般式（２）において、Ｒ_１は、炭素数１〜６のアルキル基、Ｒ_２は、炭素数１〜３０のアルキル基である。）

(In General Formula (2), R ₁ is an alkyl group having 1 to 6 carbon atoms, and R ₂ is an alkyl group having 1 to 30 carbon atoms.)

From the same viewpoint, the oxo acid anion is preferably a dihydrogen phosphate anion (H ₂ PO ₄ ⁻ ) or a monohydrogen sulfate anion (HSO ₄ ⁻ ).

  Further, from the same viewpoint, the organic salt may have a melting point not higher than a high operating temperature (for example, about 150 ° C. to 200 ° C.) of a fuel cell including a proton conductive electrolyte membrane containing the composite proton conductor. Preferably, the melting point is 130 ° C. or lower.

  A fluorinated polymer electrolyte can be used as the polymer electrolyte. As such a fluorinated polymer electrolyte, those having a sulfonic acid group as an acidic functional group are preferable. For example, perfluorosulfonic acid type polymer electrolyte (for example, Nafion (registered trademark) manufactured by Dupont) There is).

  According to another aspect of the present invention, there is provided a proton conducting electrolyte membrane including the composite proton conductor described above. The proton conductive electrolyte membrane of the present invention has high proton conductivity at high temperatures and no humidification, and is excellent in mechanical properties without being altered at high temperatures.

  Here, the proton conductive electrolyte membrane may further contain an inorganic solid oxide.

At this time, examples of the inorganic solid oxide include zirconia (ZrO ₂ ), silica (SiO ₂ ), alumina (Al ₂ O ₃ ), titania (TiO ₂ ), beryllia (BeO), magnesia (MgO), and oxidation. zinc _(ZnO 2), barium titanate (BaTiO _3), lead zirconate the use of at least one oxide selected from the group consisting of _{(ZrO 2} · SiO 2) and mullite _{(3Al 2 O 3 · 2SiO 2} ) Can do.

  According to still another aspect of the present invention, there is provided a fuel cell including a membrane electrode assembly using the proton conductive electrolyte membrane described above. The fuel cell of the present invention has remarkably superior power generation characteristics (particularly polarization characteristics) as compared with conventional fuel cells by using an electrolyte membrane having high proton conductivity under high temperature and no humidification.

  According to the present invention, an organic salt having an oxo acid having at least one hydrogen atom as an anion is used in combination with a polymer electrolyte having an acidic functional group. Composite proton conductor having stable and high proton conductivity, proton conductive electrolyte membrane having excellent mechanical strength using the proton conductor, and fuel cell having excellent power generation characteristics using the composite proton conductor Can be provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

[Structure and physical properties of composite proton conductor]
First, the composite proton conductor of the present invention will be described. As described above, the composite proton conductor of the present invention includes an organic salt composed of an organic compound cation and an oxo acid anion represented by the following formula (1), and a polymer electrolyte having an acidic functional group.

XO _m (OH) _n ⁻ (1)

  In the above formula (1), X is P, S or N, and m and n are 1 or more.

  The organic compound cation constituting the organic salt in the present invention is usually a cation of a heterocyclic compound, particularly a cation of a 3-6 membered heterocyclic compound containing 1 to 5 heteroatoms, particularly Includes cations of 3 to 6-membered ring compounds containing 1 to 5 nitrogen atoms as heteroatoms, among which imidazolium cation, pyrrolidinium cation, piperidinium cation, pyridinium cation and the like are preferable. Moreover, a chain | strand-shaped quaternary ammonium cation, a quaternary phosphonium cation, etc. can also be used.

  Among the above cations, an imidazolium cation is preferable, and a 1,3-substituted imidazolium cation is particularly preferable, and an imidazolium cation represented by the following general formula (2) is preferable.

In the general formula (2), R ₁ is an alkyl group having 1 to 6 carbon atoms, and R ₂ is an alkyl group having 1 to 30 carbon atoms. R ₂ is more preferably an alkyl group having 1 to 25 carbon atoms, more preferably 1 to 20 carbon atoms, and most preferably 1 to 16 carbon atoms.

  Examples of the imidazolium cation represented by the general formula (2) include 1,3-dimethylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1-methyl-3-propylimidazolium cation, 1 -Butyl-3-methylimidazolium cation, 1-methyl-3-pentylimidazolium cation, 1-hexyl-3-methylimidazolium cation, 1-heptyl-3-methylimidazolium cation, 1-methyl-3-octyl Examples include imidazolium cation, 1-decyl-3-methylimidazolium cation, 1-dodecyl-3-methylimidazolium cation, 1-ethyl-3-propylimidazolium cation, 1-butyl-3-ethylimidazolium cation, and the like. It is done.

  By using a compound having a structure as represented by the general formula (2) as an imidazolium cation forming an organic salt, an organic salt composed of the organic salt and the oxo acid anion and a polymer electrolyte having an acidic functional group are obtained. The combined composite proton conductor can have high proton conductivity under high temperature and no humidification.

  As the oxoacid anion in the present invention, it is necessary to use a compound represented by the above formula (1) and to have at least one hydrogen atom. By using a neutral organic salt in which an oxo acid anion and an organic compound cation are ion-bonded as described above, the organic salt can be used as an aqueous medium and a proton donor under conditions of high temperature and no humidification. That is, high proton conductivity can be realized by using an oxo acid anion having high mobility at a site where protons can be exchanged.

  Also, a fuel cell is produced using a polymer electrolyte obtained by compatibilizing an organic salt having an oxoacid anion of the present invention with a polymer having an acidic functional group (particularly perfluorosulfonic acid type polymer). This makes it possible to generate power without humidification even at high temperatures. Specifically, as described in Examples below, the output can be increased to a current density about 10 times or more that of a fuel cell using a conventional ionic liquid together with a perfluorosulfonic acid type polymer. .

  In addition, in this way, a polymer electrolyte that can conduct protons stably even without high humidity (anhydrous) without requiring proton conduction through water even at high temperatures can be obtained. There are no problems such as corrosion when using a catalyst. Therefore, according to the present invention, it is possible to provide an inexpensive and stable fuel cell for the purpose of using a metal separator or a transition metal catalyst.

In view of the purpose of use of the oxo acid anion as described above, it is preferable to use a dihydrogen phosphate anion (H ₂ PO ₄ ⁻ ) as the oxo acid anion in the present invention.

  The organic salt in the present invention is solid at normal temperature and melts and becomes liquid when heated to a high temperature (for example, 100 ° C. or higher). For example, the compound of the above general formula (2) is used as an imidazolium cation. When used, the structure is represented by the following general formula (3).

In the general formula (3), R ₁ is an alkyl group having 1 to 6 carbon atoms, R ₂ is an alkyl group having 1 to 30 carbon atoms, X is P, S or N, and m and n are 1 or more. R ₂ is more preferably an alkyl group having 1 to 25 carbon atoms, more preferably 1 to 20 carbon atoms, and most preferably 1 to 16 carbon atoms.

  The organic salt in the present invention preferably has a melting point not higher than a high operating temperature (for example, about 150 ° C. to 200 ° C.) of a fuel cell provided with a proton conducting electrolyte membrane containing the composite proton conductor. It is more preferable to use one having a temperature of 130 ° C. or lower. Examples of such an organic salt include those using 1-methyl-3-hexylimidazolium dihydrogen phosphate (HMIP) as a cation and dihydrogen phosphate anion as an anion.

  By using an organic salt having a melting point of 130 ° C. or lower, the organic salt in the electrolyte in the intermediate temperature range (200 ° C. to 100 ° C.) has a high molecular motion, unlike an organic salt having no melting point. Conceivable. As a result, the high proton conduction in the intermediate temperature range can be exhibited. Further, according to the present invention, if an organic salt having a melting point of 130 ° C. or lower is in a state compatible with the polymer electrolyte, it can be conducted even at an operating temperature that is lower than the melting point of the organic salt compatible with the composite proton conductor. The inflection point of does not appear clearly. That is, in the case of a compatible state, the melting point is shifted to a lower temperature than the melting point of the pure substance, as is generally known from a melting point drop or the like, and in the operating temperature range below the melting point. It is also possible to express high molecular mobility. That is, the function can be sufficiently exhibited even at 100 ° C. which is lower than the melting point.

  Here, the melting point of the organic salt can be measured, for example, by using differential scanning calorimetry (DSC), differential thermal analysis (DTA), or the like.

  In general, it is known that the melting point of an organic salt in an imidazolium cation decreases as the alkyl chain length increases and melts and liquefies. In addition, it is known that when liquefied as the alkyl chain length becomes longer, the viscosity thereof also decreases (see, for example, Journal of Electrochemical Society, 150 (12) D195-D199 (2003)). ).

  Examples of the organic salt in the present invention include 1,3-dimethylimidazolium dihydrogen phosphate (DMIP), 1-butyl-3-methylimidazolium dihydrogen phosphate (BMIP), 1-hexyl- 3-methylimidazolium dihydrogen phosphate (HMIP), 1-methyl-3-octylimidazolium dihydrogen phosphate (MOIP), 1-dodecyl-3-methylimidazolium dihydrogen phosphate (C12MIP), Examples include 1-hexadecyl-3-methylimidazolium dihydrogen phosphate (C16MIP), 1-dodecyl-3-methylimidazolium hydrogen sulfate (C12MIS), and the like.

  As the polymer electrolyte in the present invention, a fluorinated polymer electrolyte can be used. As such a fluorinated polymer electrolyte, those having a sulfonic acid group as an acidic functional group are preferable. For example, perfluorosulfonic acid type polymer electrolyte (for example, Nafion (registered trademark) manufactured by Dupont) There is).

  Here, the conventional polymer electrolyte having a sulfonic acid group has a problem that adsorbed water is desorbed and the sulfonic acid is decomposed at a high temperature. In the present invention, the organic salt described above is strongly coordinated to the sulfonic acid group in the polymer electrolyte, and the organic salt has no vapor pressure. It has the advantage of being stable at high temperatures (no humidification). Thus, since the polymer electrolyte of the present invention is stable at high temperatures, it is possible to maintain high proton conductivity even under conditions of high temperature and no humidification. This will be described more specifically using an FT-IR spectrum in Examples described later.

[Production method of composite proton conductor]
The composite proton conductor of the present invention having the structure and physical properties as described above can be produced by the following method.

  That is, for example, the above-mentioned organic salt (solid at room temperature) is mixed in a polymer electrolyte solution having an acidic functional group such as Nafion (registered trademark) at a predetermined blending ratio, and at a normal temperature for a predetermined time (for example, ) After stirring using a magnetic stirrer or the like, a mixed solution of the composite proton conductor can be prepared by performing vacuum defoaming.

  In the above production method, the compounding ratio of the polymer electrolyte having an acidic functional group and the organic salt is 0.2 [mol eq. ] Or more, preferably 1.0 mol eq. Most preferably. The molar concentration is 0.2 [mol eq. ] By the above, the temperature stability is increased, and the proton conductivity of the composite proton conductor is sufficient even when used in a fuel cell, which is preferable.

  Moreover, in the said manufacturing method, it is preferable that stirring time is 1 to 24 hours. By setting the stirring time within the above range, there is an effect that it is uniform and can prevent gelation.

[Production method of proton conductive electrolyte membrane]
The proton conductive electrolyte membrane of the present invention can be produced by a known method using the composite proton conductor as described above.

  That is, for example, after dropping the mixed solution of the composite proton conductor obtained as described above onto a substrate such as a glass substrate, it is smoothly stretched using a doctor blade or the like with a gap set to a predetermined distance, The solvent is roughly removed by leaving it on a hot plate set at a temperature (for example, about 40 ° C.) for a predetermined time (for example, about 30 minutes). Next, the dried membrane together with the substrate is put into a high-temperature (for example, about 150 ° C.) constant temperature bath for a predetermined time (for example, about 30 seconds) and annealed, whereby the proton conductive electrolyte of the present invention in the form of a film is obtained. A membrane can be obtained.

  In addition, it is considered that the mechanical strength of the proton conductive electrolyte membrane of the proton conductive electrolyte membrane of the present invention decreases at high temperatures as the Nafion (registered trademark) that forms the structure softens. However, the mechanical strength of the proton conductive electrolyte membrane can be improved by kneading the inorganic solid oxide into a mixed solution of the composite proton conductor at 50% by mass or less to form a membrane. In addition, depending on the organic salt used in the present invention, the produced proton conductive electrolyte membrane has a very high hygroscopic property, and it can be condensed in the air on the membrane surface by leaving it in the air after film formation. is there. In order to prevent this, by arranging the inorganic solid oxide in the proton conductive electrolyte membrane, it is possible to stabilize ions in the polymer electrolyte and to prevent moisture condensation.

Examples of such inorganic solid oxides include zirconia (ZrO ₂ ), silica (SiO ₂ ), alumina (Al ₂ O ₃ ), titania (TiO ₂ ), beryllia (BeO), magnesia (MgO), and zinc oxide. _(ZnO 2), barium titanate (BaTiO _3), it is used zircon _{(ZrO 2} · SiO 2) and mullite _{(3Al 2 O 3 · 2SiO 2} ) at least one oxide selected from the group consisting of it can.

[Fuel Cell Manufacturing Method]
The fuel cell of the present invention can be produced by a known method using the proton conductive electrolyte membrane obtained as described above.

  That is, for example, in the case of PEFC, the proton conductive electrolyte membrane obtained as described above is sandwiched between catalyst layers as electrodes, a gas diffusion layer is provided, and these are integrated to produce an MEA. Next, a fuel cell stack can be manufactured by sandwiching both sides of the MEA with a separator such as a metal separator to form a unit cell and arranging a plurality of the unit cells.

[Relationship with technologies described in Non-Patent Documents 4 and 5]
In Non-Patent Document 4 (M. Yoshizawa-Fujita et al., Electrochem. Comm. 9 (2007) 1202-1205), 1-methyl-3-butylimidazolium dihydrogenphos contained in the organic salt of the present invention. We are studying thermal properties and ionic conductivity of fert. However, in the case of using a solid salt alone, it is physically unsuitable for an electrolyte portion that requires a function as a thin diaphragm, and its ionic conductivity is only about 10 ⁻⁵ Scm ^−2. Therefore, it is not practical to use as a proton conductor in a fuel cell. In addition, since the rational for proton conduction is not shown, the possibility as an electrolyte that requires proton transfer is not shown at all.

  In Non-Patent Document 5 (B.S. Lalia et al., Chem. Phys. Lett., 425 (2006) 294-300), a methyl group is located at the 2-position of the imidazolium cation of the general formula (2) in the present invention. An organic salt is synthesized, a complex with PVdF-HFP is prepared, and ion conduction and thermal decomposition temperature are examined. Since the organic phosphate is a neutral salt, the polymer used in this document does not have the ability of the polymer to give protons as in the present invention. A derivative cation and a phosphate anion are presumed to be main components, and the present invention is different from a polymer having an acidic functional group (for example, a perfluorosulfonic acid type polymer). Moreover, the grounds for proton conduction are not described, and no rationale that can be used for fuel cells such as power generation is shown.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Synthesis example of organic salt]

(Synthesis Example 1)
In Synthesis Example 1, 1,3-dimethylimidazolium dihydrogen phosphate (DMIP) was synthesized as follows.

To the autoclave were added 82.1 g (1.0 mol) of 1-methylimidazole, 123.2 ml of dehydrated methanol, and 180.2 g (2.0 mol) of dimethyl carbonate, and the mixture was heated and stirred at 140 ° C. for 15 hours. Thereafter, the reaction solution was cooled to room temperature, and 115.3 g (1.0 mol) of 85% phosphoric acid was added over 1 hour with sufficient stirring. The reaction solution was filtered, and the resulting crystals were dried under reduced pressure to obtain 100.4 g (0.52 mol, yield 51.7%) of 1,3-dimethylimidazolium dihydrogen phosphate. The structure was confirmed by proton NMR ( ¹ H-NMR (nuclear magnetic resonance)) measurement. The chemical shift is as follows.
¹ H-NMR (MeOH-d4, 300 MHz); δ (ppm); 7.55 (s, 2H): 3.93 (s, 6H)

(Synthesis Example 2)
In Synthesis Example 2, 1-butyl-3-methylimidazolium dihydrogen phosphate (BMIP) was synthesized as follows.

  After adding 68.1 g (1.0 mol) of imidazole, 248.8 g (1.8 mol) of potassium carbonate, and 500 ml of acetonitrile to a flask with a reflux tube, the mixture was heated to 75 ° C. and 137.0 g (1.0 mol) of 1-bromobutane. Was added over about 2 hours, and the mixture was stirred with heating for 10 hours. Thereafter, the reaction solution was cooled to room temperature and filtered, and the obtained filtrate was distilled under reduced pressure to obtain 66.3 g of 1-butylimidazole.

To the autoclave, 37.2 g (0.3 mol) of 1-butylimidazole, 55.8 ml of dehydrated methanol and 54.0 g (0.6 mol) of dimethyl carbonate were added, followed by heating and stirring at 140 ° C. for 15 hours. Thereafter, the reaction solution was cooled to room temperature, and 34.6 g (0.3 mol) of 85% phosphoric acid was added over 1 hour with sufficient stirring, and the reaction solution was concentrated under reduced pressure. The crude crystals thus obtained were added with 1,000 ml of N, N-dimethylformamide and sufficiently stirred and suspended. The crystals were filtered, washed with 800 ml of ethyl acetate, dried under reduced pressure, and 1-butyl-3 -53.4 g (0.23 mol, yield 75.4%) of methyl imidazolium dihydrogen phosphate was obtained. The structure was confirmed by proton NMR measurement. The chemical shift is as follows.
¹ H-NMR (MeOH-d4, 300 MHz); δ (ppm); 7.63 (s, 1H); 7.58 (s, 1H); 4.22 (t, 2H); 3.94 (s, 3H); 1.87 (5th, 2H); 1.38 (6th, 2H); 0.98 (t, 3H)

(Synthesis Example 3)
In Synthesis Example 3, 1-hexyl-3-methylimidazolium dihydrogen phosphate (HMIP) was synthesized as follows.

  After adding 68.1 g (1.0 mol) of imidazole, 248.8 g (1.8 mol) of potassium carbonate, and 500 ml of acetonitrile to a flask equipped with a reflux tube, the mixture was heated to 75 ° C. and 165.1 g (1.0 mol of 1-bromohexane). ) Was added over about 2 hours, and the mixture was stirred with heating for 10 hours. Thereafter, the reaction solution was cooled to room temperature and filtered, and the obtained filtrate was distilled under reduced pressure to obtain 75.2 g of 1-hexylimidazole.

After adding 45.7 g (0.3 mol) of 1-hexylimidazole, 55.8 ml of dehydrated methanol and 54.0 g (0.6 mol) of dimethyl carbonate to the autoclave, the mixture was heated and stirred at 140 ° C. for 15 hours. Thereafter, the reaction solution was cooled to room temperature, and 34.6 g (0.3 mol) of 85% phosphoric acid was added over 1 hour with sufficient stirring, and the reaction solution was concentrated under reduced pressure. After adding 500 ml of acetone to the obtained crude crystals and sufficiently stirring and suspending, the crystals were filtered, washed with 500 ml of acetone, dried under reduced pressure, and 1-hexyl-3-methylimidazolium dihydrochloride. 48.8 g (0.18 mol, yield 61.5%) of gen phosphate was obtained. The structure was confirmed by proton NMR measurement. The chemical shift is as follows.
¹ H-NMR (MeOH-d4, 300 MHz); δ (ppm); 7.63 (s, 1H); 7.57 (s, 1H); 4.21 (t, 2H); 3.93 (s, 3H); 1.88 (5th, 2H); 1.35 (m, 6H); 0.91 (t, 3H)

(Synthesis Example 4)
In Synthesis Example 4, 1-methyl-3-octylimidazolium dihydrogen phosphate (MOIP) was synthesized as follows.

  After adding 68.1 g (1.0 mol) of imidazole, 248.8 g (1.8 mol) of potassium carbonate, and 500 ml of acetonitrile to a flask equipped with a reflux tube, the mixture was heated to 75 ° C. and 148.7 g (1.0 mol) of 1-chlorooctane. ) Was added over about 2 hours, and the mixture was stirred with heating for 10 hours. Thereafter, the reaction solution was cooled to room temperature and filtered, and the obtained filtrate was distilled under reduced pressure to obtain 108 g of 1-octylimidazole.

To the autoclave, 57.9 g (0.3 mol) of 1-octylimidazole, 55.8 ml of dehydrated methanol and 54.0 g (0.6 mol) of dimethyl carbonate were added, followed by heating and stirring at 140 ° C. for 15 hours. Thereafter, the reaction solution was cooled to room temperature, and 34.6 g (0.3 mol) of 85% phosphoric acid was added over 1 hour with sufficient stirring, and the reaction solution was concentrated under reduced pressure. After adding 500 ml of ethyl acetate to the obtained crude crystals and sufficiently stirring and suspending the crystals, the crystals were filtered, washed with 200 ml of ethyl acetate, dried under reduced pressure, and 1-methyl-3-octylimidazolium. 78 g (0.267 mol, 89% yield) of dihydrogen phosphate was obtained. The structure was confirmed by proton NMR measurement. The chemical shift is as follows.
¹ H-NMR (DMSO-d6, 300 MHz); δ (ppm); 9.21 (s, 1H); 7.74 (d, 1H); 7.70 (d, 1H); 4.17 (t, 2H); 3.87 (s, 3H); 1.74 (5th, 2H); 1.21 (m, 10H); 0.83 (t, 3H)

(Synthesis Example 5)
In Synthesis Example 5, 1-dodecyl-3-methylimidazolium dihydrogen phosphate (C12MIP) was synthesized as follows.

  After adding 68.1 g (1.0 mol) of imidazole, 248.8 g (1.8 mol) of potassium carbonate, and 500 ml of acetonitrile to a flask equipped with a reflux tube, the mixture was heated to 90 ° C. and 204.8 g (1.0 mol) of 1-chlorododecane. ) Was added over about 2 hours, and the mixture was stirred with heating for 10 hours. Thereafter, the reaction solution was cooled to room temperature and filtered, and the obtained filtrate was distilled under reduced pressure to obtain 178 g of 1-dodecylimidazole.

To the autoclave, 74.8 g (0.3 mol) of 1-dodecylimidazole, 55.8 ml of dehydrated methanol and 54.0 g (0.6 mol) of dimethyl carbonate were added, followed by heating and stirring at 140 ° C. for 15 hours. Thereafter, the reaction solution was cooled to room temperature, and 34.6 g (0.3 mol) of 85% phosphoric acid was added over 1 hour with sufficient stirring, and the reaction solution was concentrated under reduced pressure. After adding 500 ml of ethyl acetate to the obtained crude crystals and sufficiently stirring and suspending the crystals, the crystals were filtered, washed with 200 ml of ethyl acetate, dried under reduced pressure, and 1-dodecyl-3-methylimidazolium. 96.8 g (0.278 mol, yield 93%) of dihydrogen phosphate was obtained. The structure was confirmed by proton NMR measurement. The chemical shift is as follows.
¹ H-NMR (DMSO-d6, 300 MHz); δ (ppm); 9.43 (s, 1H); 7.74 (s, 1H); 7.69 (s, 1H); 4.12 (t, 2H); 3.85 (s, 3H); 1.74 (t, 2H); 1.21 (m, 18H); 0.83 (t, 3H)

(Synthesis Example 6)
In Synthesis Example 6, 1-hexadecyl-3-methylimidazolium dihydrogen phosphate (C16MIP) was synthesized as follows.

  After adding 68.1 g (1.0 mol) of imidazole, 248.8 g (1.8 mol) of potassium carbonate, and 500 ml of acetonitrile to a flask with a reflux tube, the mixture was heated to 75 ° C. and 260.9 g (1.0 mol) of 1-chlorohexadecane. ) Was added over about 2 hours, and the mixture was stirred with heating for 10 hours. Thereafter, the reaction solution was cooled to room temperature and filtered, and the obtained filtrate was distilled under reduced pressure to obtain 234 g of 1-hexadecylimidazole.

After adding 91.6 g (0.3 mol) of 1-hexadecylimidazole, 55.8 ml of dehydrated methanol and 54.0 g (0.6 mol) of dimethyl carbonate to the autoclave, the mixture was heated and stirred at 140 ° C. for 15 hours. Thereafter, the reaction solution is cooled to room temperature, and 34.6 g (0.3 mol) of 85% phosphoric acid is added over 1 hour with sufficient stirring, and 500 ml of methanol is added to the reaction solution and sufficiently stirred and suspended. Then, the crystals were filtered, washed with 100 ml of methanol, and dried under reduced pressure to obtain 39.8 g (0.098 mol, yield 33%) of 1-hexadecyl-3-methylimidazolium dihydrogen phosphate. . The structure was confirmed by proton NMR measurement. The chemical shift is as follows.
¹ H-NMR (DMSO-d6, 300 MHz); δ (ppm); 9.25 (s, 1H); 7.79 (d, 2H); 4.16 (t, 2H); 3.85 (s, 3H); 1.79 (5th, 2H); 1.23 (m, 26H); 0.85 (t, 3H)

(Synthesis Example 7)
In Synthesis Example 7, 1-dodecyl-3-methylimidazolium dihydrogen sulfate (C12MIS) was synthesized as follows.

  After adding 68.1 g (1.0 mol) of imidazole, 248.8 g (1.8 mol) of potassium carbonate, and 500 ml of acetonitrile to a flask equipped with a reflux tube, the mixture was heated to 75 ° C., and 249.2 g (1.0 mol) of 1-bromododecane was added. ) Was added over about 2 hours, and the mixture was stirred with heating for 10 hours. Thereafter, the reaction solution was cooled to room temperature and filtered, and the obtained filtrate was distilled under reduced pressure to obtain 178 g of 1-dodecylimidazole.

To the autoclave, 74.8 g (0.3 mol) of 1-dodecylimidazole, 55.8 ml of dehydrated methanol and 54.0 g (0.6 mol) of dimethyl carbonate were added, followed by heating and stirring at 140 ° C. for 15 hours. Thereafter, the reaction solution was cooled to room temperature, and 42 g (0.3 mol) of 70% sulfuric acid was added over 1 hour with sufficient stirring, and the reaction solution was concentrated under reduced pressure. After adding 500 ml of ethyl acetate to the obtained crude crystals and sufficiently stirring and suspending the crystals, the crystals were filtered, washed with 200 ml of ethyl acetate, dried under reduced pressure, and 1-dodecyl-3-methylimidazolium. 89 g (0.254 mol, 85% yield) of dihydrogen sulfate was obtained. The structure was confirmed by proton NMR measurement. The chemical shift is as follows.
¹ H-NMR (DMSO-d6, 300 MHz); δ (ppm); 9.16 (s, 1H); 7.75 (d, 1H); 7.69 (d, 1H); 4.13 (t, 2H); 3.83 (s, 3H); 1.75 (5th, 2H); 1.22 (m, 18H); 0.84 (t, 3H)

[Production example of proton conductive electrolyte membrane]
Next, an example of a proton conductive electrolyte membrane using the composite proton conductor of the present invention manufactured using the organic salt synthesized as described above will be described.

Example 1
3.18 mmol (0.617 g) of 1,3-dimethylimidazolium against 20.000 g of 20% Nafion® dispersion (Ew1,100) which is a commercial product of Dupont's Nafion® solution Dihydrogen phosphate (DMIP, R ₁ = methyl group, R ₂ = methyl group in general formula (2)) is blended, stirred at room temperature for 24 hours using a magnetic stirrer, and then vacuum degassed A mixed solution was prepared. After about 5 ml of this mixed solution was dropped on a glass substrate in a rod shape, it was stretched smoothly using a doctor blade with a gap set at 650 μm and left on a hot plate set at a surface temperature of 40 ° C. for 30 minutes to leave the solvent alcohol. Was roughly removed. The dried film was put together with the glass substrate in a thermostatic bath at 150 ° C. for 30 seconds, annealed, and then the polymer electrolyte film obtained from the glass substrate was peeled off. The obtained film was colorless and transparent.

(Example 2)
3.20 mmol (0.750 g) of 1-butyl-3-methyl against 200.000 g of 20% Nafion® dispersion (Ew1,100) which is a commercial product of Dupont's Nafion® solution Imidazolium dihydrogen phosphate (BMIP, R ₁ = methyl group, R ₂ = butyl group in the general formula (2)), stirred for 24 hours at room temperature using a magnetic stirrer, then vacuum degassed To prepare a mixed solution. After about 5 ml of this mixed solution was dropped on a glass substrate in a rod shape, it was stretched smoothly using a doctor blade with a gap set at 650 μm and left on a hot plate set at a surface temperature of 40 ° C. for 30 minutes to leave the solvent alcohol. Was roughly removed. The dried film was put together with the glass substrate in a thermostatic bath at 150 ° C. for 30 seconds, annealed, and then the polymer electrolyte film obtained from the glass substrate was peeled off. The obtained film was colorless and transparent.

(Example 3)
3.20 mmol (0.840 g) of 1-hexyl-3-methyl against 200.000 g of 20% Nafion® dispersion (Ew1,100), a commercial product of Dupont's Nafion® solution Imidazolium dihydrogen phosphate (HMIP, R ₁ = methyl group, R ₂ = hexyl group in general formula (2)), stirred at room temperature for 24 hours with a magnetic stirrer, and then vacuum degassed To prepare a mixed solution. After about 5 ml of this mixed solution was dropped on a glass substrate in a rod shape, it was stretched smoothly using a doctor blade with a gap set at 650 μm and left on a hot plate set at a surface temperature of 40 ° C. for 30 minutes to leave the solvent alcohol. Was roughly removed. The dried film was put together with the glass substrate in a thermostatic bath at 150 ° C. for 30 seconds, annealed, and then the polymer electrolyte film obtained from the glass substrate was peeled off. The obtained film was colorless and transparent.

Example 4
3.63 mmol (1.062 g) of 1-methyl-3-octyl relative to 20.000 g of 20% Nafion® dispersion (Ew1,100) which is a commercial product of Dupont's Nafion® solution Imidazolium dihydrogen phosphate (MOIP, R ₁ = methyl group, R ₂ = octyl group in the general formula (2)) is blended, stirred for 24 hours at room temperature using a magnetic stirrer, and then vacuum degassed To prepare a mixed solution. After about 5 ml of this mixed solution was dropped on a glass substrate in a rod shape, it was stretched smoothly using a doctor blade with a gap set at 650 μm and left on a hot plate set at a surface temperature of 40 ° C. for 30 minutes to leave the solvent alcohol. Was roughly removed. The dried film was put together with the glass substrate in a thermostatic bath at 150 ° C. for 30 seconds, annealed, and then the polymer electrolyte film obtained from the glass substrate was peeled off. The obtained film was colorless and transparent.

(Example 5)
3.63 mmol (1.266 g) of 1-dodecyl-3-methyl versus 20.000 g of 20% Nafion® dispersion (Ew1,100), a commercial product of Dupont's Nafion® solution Compound of imidazolium dihydrogen phosphate (C12MIP, R ₁ = methyl group, R ₂ = dodecyl group in general formula (2)), stirred for 24 hours at room temperature using a magnetic stirrer, then vacuum degassed To prepare a mixed solution. After about 5 ml of this mixed solution was dropped on a glass substrate in a rod shape, it was stretched smoothly using a doctor blade with a gap set at 650 μm and left on a hot plate set at a surface temperature of 40 ° C. for 30 minutes to leave the solvent alcohol. Was roughly removed. The dried film was put together with the glass substrate in a thermostatic bath at 150 ° C. for 30 seconds, annealed, and then the polymer electrolyte film obtained from the glass substrate was peeled off. The obtained film was colorless and transparent.

(Example 6)
3.63 mmol (1.471 g) of 1-hexadecyl-3-methyl against 20.000 g of 20% Nafion® dispersion (Ew1,100) which is a commercial product of Dupont's Nafion® solution Imidazolium dihydrogen phosphate (C16MIP, R ₁ = methyl group, R ₂ = hexadecyl group in general formula (2)), stirred at room temperature for 24 hours using a magnetic stirrer, then vacuum degassed To prepare a mixed solution. After about 5 ml of this mixed solution was dropped on a glass substrate in a rod shape, it was stretched smoothly using a doctor blade with a gap set at 650 μm and left on a hot plate set at a surface temperature of 40 ° C. for 30 minutes to leave the solvent alcohol. Was roughly removed. The dried film was put together with the glass substrate in a thermostatic bath at 150 ° C. for 30 seconds, annealed, and then the polymer electrolyte film obtained from the glass substrate was peeled off. The obtained film was colorless and transparent.

(Example 7)
3.63 mmol (1.266 g) of 1-dodecyl-3-methyl versus 20.000 g of 20% Nafion® dispersion (Ew1,100), a commercial product of Dupont's Nafion® solution Imidazolium hydrogen sulfate (C12MIS, general formula (2), R ₁ = methyl group, R ₂ = dodecyl group) is blended, stirred for 24 hours at room temperature using a magnetic stirrer, and then vacuum degassed A mixed solution was prepared. After about 5 ml of this mixed solution was dropped on a glass substrate in a rod shape, it was stretched smoothly using a doctor blade with a gap set at 650 μm and left on a hot plate set at a surface temperature of 40 ° C. for 30 minutes to leave the solvent alcohol. Was roughly removed. The dried film was put together with the glass substrate in a thermostatic bath at 150 ° C. for 30 seconds, annealed, and then the polymer electrolyte film obtained from the glass substrate was peeled off. The obtained film was colorless and transparent.

(Example 8)
3.63 mmol (1.266 g) of 1-dodecyl-3-methyl versus 20.000 g of 20% Nafion® dispersion (Ew1,100), a commercial product of Dupont's Nafion® solution Imidazolium dihydrogen phosphate (C12MIP, R ₁ = methyl group, R ₂ = dodecyl group in the general formula (2)) and zirconia (nano powder, particle size 20-30 micrometers) which is an inorganic solid oxide 1 .000 g was mixed and stirred with a magnetic stirrer at room temperature for 24 hours, followed by vacuum defoaming to prepare a mixed solution. After about 5 ml of this mixed solution was dropped on a glass substrate in a rod shape, it was stretched smoothly using a doctor blade with a gap set at 650 μm and left on a hot plate set at a surface temperature of 40 ° C. for 30 minutes to leave the solvent alcohol. Was roughly removed. The dried film was put together with the glass substrate in a thermostatic bath at 150 ° C. for 30 seconds, annealed, and then the polymer electrolyte film obtained from the glass substrate was peeled off. The resulting film was white.

Example 9
3.63 mmol (1.266 g) of 1-dodecyl-3-methyl versus 20.000 g of 20% Nafion® dispersion (Ew1,100), a commercial product of Dupont's Nafion® solution 1. Imidazolium dihydrogen sulfate (C12MIS, R ₁ = methyl group, R ₂ = dodecyl group in the general formula (2)) and zirconia (nano powder, particle size 20-30 micrometers) which is an inorganic solid oxide After mixing with 000 g and stirring with a magnetic stirrer at room temperature for 24 hours, vacuum defoaming was performed to prepare a mixed solution. After about 5 ml of this mixed solution was dropped on a glass substrate in a rod shape, it was stretched smoothly using a doctor blade with a gap set at 650 μm and left on a hot plate set at a surface temperature of 40 ° C. for 30 minutes to leave the solvent alcohol. Was roughly removed. The dried film was put together with the glass substrate in a thermostatic bath at 150 ° C. for 30 seconds, annealed, and then the polymer electrolyte film obtained from the glass substrate was peeled off. The resulting film was white.

(Example 10)
It is equivalent to the sulfonic acid group of the sulfonated polyether ether ketone (S-PEEK) subjected to 68.9 mol% sulfonation with respect to the repeating unit of the polyether ether ketone, that is, 1.000 g of S- PEEK and HMIP 0.769g are dispersed in NMP 5.5g, dissolved using a magnetic stirrer, stretched smoothly on a glass substrate using a doctor blade, and dried on a hot plate set at a surface temperature of 80 ° C. An electrolyte membrane was obtained. The obtained film was a pale yellow slightly cloudy at room temperature.

(Comparative Example 1)
About 20 ml of Nafion (registered trademark) dispersion (Ew1,100), a product of Dupont's Nafion (registered trademark) solution, was dropped on a glass substrate in an approximately 5 ml rod shape, and then a doctor blade with a gap set at 650 μm was used. It was stretched smoothly and left on a hot plate set at a surface temperature of 40 ° C. for 30 minutes to roughly remove alcohol as a solvent. Apparently, the dried film was put together with the glass substrate in a thermostatic bath at 150 ° C. for 30 seconds, annealed, and then the polymer electrolyte film obtained from the glass substrate was peeled off. Although the obtained film was slightly brownish, it was almost colorless and transparent.

(Comparative Example 2)
200.00 Nafion (registered trademark) dispersion (Ew1,100) 200.000 g which is a commercial product of Dupont's Nafion (registered trademark) solution is also exemplified in Patent Documents WO03 / 083981A1 and JP-A-2006-32213 3.18 mmol (0.630 g) of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF ₄ ) was blended in the same manner as in the present invention described above, and stirred for 24 hours at room temperature using a magnetic stirrer. Thereafter, vacuum degassing was performed to prepare a mixed solution. After about 5 ml of this mixed solution was dropped on a glass substrate in a rod shape, it was stretched smoothly using a doctor blade with a gap set at 650 μm and left on a hot plate set at a surface temperature of 40 ° C. for 30 minutes to leave the solvent alcohol. Was roughly removed. Apparently, the dried film was put together with the glass substrate in a thermostatic bath at 150 ° C. for 30 seconds, annealed, and then the polymer electrolyte film obtained from the glass substrate was peeled off. The obtained film was colorless and transparent.

(Comparative Example 3)
As in Example 4, an S-PEEK film without HMIP was prepared. The preparation method was the same as that except that HMIP was not added.

[Characteristic Evaluation Method of Proton Conducting Electrolyte Membrane and Fuel Cell]
Next, a proton conductive electrolyte membrane obtained as described above and a method for evaluating the characteristics of a fuel cell prepared using this electrolyte membrane will be described. Specifically, the ion conductivity measurement and thermal analysis of the proton conductive electrolyte membrane were performed by the method described below, and tests on the power generation characteristics of the fuel cell prepared using the proton conductive electrolyte membrane were performed.

(Test method for measuring ionic conductivity)
Each electrolyte was punched into a 13 mmφ circle, sandwiched between bipolar platinum blocking electrode cells having a Teflon (registered trademark) housing, fixed in a thermostatic chamber, heated to 150 ° C., allowed to stand overnight, and then cooled from 150 ° C. The resistance was measured. For resistance measurement, SI1287 Electrochemical Interface and SI1260 Impedance / gain phase Analyzer manufactured by Solartron, UK was used. Ionic conductivity was calculated from the obtained bulk resistance and cell constant.

(Test method for thermal analysis)
In order to examine the thermal stability of the salt with an oxo acid having a hydrogen atom used in the present invention, thermogravimetric analysis was performed under an air stream using TG / DTA6200 manufactured by Seiko Denshi. Moreover, since only Example 3 confirmed melting at 150 ° C. or lower, differential scanning calorimetry was performed to determine the melting point. As an apparatus for differential scanning thermal analysis, DSC6200 manufactured by Seiko Electronics Co., Ltd. was used. About 10 mg of a sample was sealed in a gold-plated stainless steel sealing pan, and the scanning speed was 10 ° C./min. Measured at

(Test method for power generation characteristics of fuel cells)
In order to compare the present invention with the prior art, a commercially available gas diffusion electrode obtained by cutting the produced membrane into 2.8 cm square (electrode with catalyst made by Electrochem, USA; electrode with catalyst Pt 1 mg / cm ² attached to carbon paper; EC -20-10-7) to prepare a simple membrane-electrode assembly (MEA). Next, a Teflon (registered trademark) gasket and the MEA were sandwiched between carbon separators having gas flow paths, and current collector plates and end plates were placed on both outer sides and tightened with bolts to form test cells. . While this test cell was purged with nitrogen, the temperature was raised to 150 ° C., and hydrogen and oxygen were directly introduced into the cell (without passing through a humidifier) through a mass flow whose flow rate was controlled. Hokuto Denko's electrochemical measuring device HZ-3000 was used for investigation of power generation polarization characteristics and continuous power generation characteristics.

[Characteristic evaluation results of proton conductive electrolyte membrane and fuel cell]
Hereinafter, the result of the characteristic evaluation performed by the above-described method will be described with reference to the drawings.

(Ionic conductivity of polymer electrolytes of Examples 1 to 3)
First, the evaluation result of the ionic conductivity of the proton conductive electrolyte membranes of Examples 1 to 3 and Comparative Example 2 of the present invention will be described with reference to FIG. 1 is an Arrhenius plot of ion conductivity of Examples 1 to 3 and Comparative Example 2 of the present invention, where the vertical axis represents ion conductivity [Scm ⁻¹ ] and the horizontal axis represents temperature (1000 / T) [ K ⁻¹ ].

  As shown in FIG. 1, the DMIP blended polymer electrolyte of Example 1 is almost the same as the BMIBF4 blended polymer electrolyte of Comparative Example 2, but the polymer electrolytes of Examples 2 and 3 are significantly higher. It was found to show ionic conductivity. As is clear from FIG. 1, the temperature characteristics of ionic conduction are clearly not governed by a series of mechanisms from low temperature to high temperature because no bending or the like is observed, and both salts are in a compatible state. it is conceivable that. Further, as is clear from FIG. 1, it is clear that the characteristics of the polymer electrolyte containing HMIP of Example 3 having a liquid region in the measurement temperature range are remarkably improved. In all electrolytes, there are three ion species that can move (protons derived from the salt cation / anion and sulfonic acid), so the net mobility of protons necessary for electrode reactions is virtually unclear. Therefore, it is considered that the characteristics need to be compared in power generation tests.

  In addition, since the Nafion single membrane of Comparative Example 1 is a water-containing polymer, the resistance increases with the evaporation of water at the temperature holding stage at 150 ° C., so the temperature characteristics of the stable ionic conductivity are It was not obtained.

(Ion conductivity of HMIP)
Next, the temperature characteristics of the ionic conductivity of the HMIP used in Example 3 of the present invention will be described with reference to FIG. FIG. 2 is an Arrhenius plot of HMIP ion conductivity, where the vertical axis represents ion conductivity [Scm ⁻¹ ] and the horizontal axis represents temperature (1000 / T) [K ⁻¹ ].

  As shown in FIG. 2, HMIP expresses high ionic conductivity even when used alone at a melting temperature or higher. This result suggests that the ionic conduction of the molten salt in which the oxoacid anion having a hydrogen atom is arranged is not known and can be used alone as a proton transfer medium.

(Ionic conductivity of polymer electrolytes of Examples 4 to 7)
Next, the evaluation results of the ionic conductivity of the proton conductive electrolyte membranes of Examples 4 to 7 and Comparative Example 2 of the present invention will be described with reference to FIG. FIG. 3 is an Arrhenius plot of ion conductivity of Examples 4 to 7 of the present invention, where the vertical axis represents ion conductivity [Scm ⁻¹ ] and the horizontal axis represents temperature (1000 / T) [K ⁻¹ ]. Is shown.

  As shown in FIG. 3, even in an electrolyte containing C16MIP in which the alkyl chain bonded to the imidazole cation is a hexadecyl group (the electrolyte of Example 6 in the present invention), stable temperature characteristics of ionic conductivity may be exhibited. This suggests that the alkyl side chain functions stably up to 16 carbon atoms. Further, since the anion which is a pair of imidazole cations is hydrogen sulfate, stable temperature characteristics of ionic conductivity are obtained in the electrolyte of Example 7, so that not only dihydrogen phosphate but also hydrogen It is clear that equivalent characteristics can be obtained with other oxoacid anions such as sulfate.

(Ionic conductivity of polymer electrolytes of Examples 8 to 9)
Next, the evaluation results of the ionic conductivity of the proton conductive electrolyte membranes of Examples 8 to 9 and Comparative Example 2 of the present invention will be described with reference to FIG. FIG. 4 is an Arrhenius plot of ion conductivity of Examples 8 to 9 and Comparative Example 2 of the present invention, where the vertical axis represents ion conductivity [Scm ⁻¹ ] and the horizontal axis represents temperature (1000 / T) [ K ⁻¹ ].

  As shown in FIG. 4, in the polymer electrolytes of Examples 8 and 9 in which zirconia, which is an example of an inorganic solid oxide, is arranged in the polymer electrolyte of the present invention, 20 masses of zirconia that itself does not have ionic conduction. It is clear that the ionic conductivity is not significantly impaired even when placed in the% electrolyte. Moreover, it is clear that the polymer electrolytes of Examples 8 and 9 do not have a bending point even in a wide range of temperatures and show stable ionic conduction.

  Next, the results of evaluating the thermal stability of the HMIP used in Example 3 of the present invention will be described with reference to FIG. In addition, FIG. 5 is a figure which shows the crystallization and melting peak at the time of temperature rising in the differential scanning calorimetry (DSC) of HMIP.

  As shown in FIG. 5, it was found that HMIP melts at about 125 ° C., that is, 130 ° C. or less.

  Next, the results of evaluating the thermal stability of the electrolytes used in Examples 4, 7, and 9 of the present invention will be described with reference to FIGS. 6, 7, and 8 are diagrams showing crystallization / melting peaks at the time of temperature increase in differential scanning calorimetry (DSC) of Example 4, Example 7, and Example 9, respectively.

  As shown in FIGS. 6 to 8, it was found that the electrolytes of Examples 4, 7, and 9 of the present invention melt at a high operating temperature (for example, about 150 ° C.) or less in the fuel cell.

(Power generation characteristics of fuel cells using the polymer electrolytes of Examples 1 to 3)
Next, referring to FIG. 9, the evaluation results of the power generation characteristics (polarization characteristics) of the fuel cell test cells produced using the proton conductive electrolyte membranes of Examples 1 to 3 and Comparative Examples 1 and 2 of the present invention are shown. explain. FIG. 9 is a graph showing polarization curves of fuel cell test cells produced using the proton conductive electrolyte membranes of Examples 1 to 3 and Comparative Examples 1 and 2 of the present invention, and the vertical axis represents voltage [V ], The horizontal axis indicates the current density [mAcm ⁻² ].

As shown in FIG. 9, at 150 ° C. (non-humidified condition), the test cell using the Nafion (registered trademark) single electrolyte membrane of Comparative Example 1 is insufficient because water as a medium for transferring protons is insufficient. It can be seen that no polarization characteristics can be obtained. In addition, in the test cell using the BMIBF4 electrolyte membrane of Comparative Example 2, it can be seen well as compared with Nafion (registered trademark) at an extremely low current density, but at 1 mA · cm ⁻² or more, proton transfer is observed. It showed a sharp decline because the diffusion could not catch up at all. On the other hand, the test cell produced using the electrolytes of Examples 1 to 3 using the electrolyte of the present invention is a test using the electrolyte membrane of Comparative Example 2 using a conventionally proposed room temperature molten salt. Compared with the cell, the polarization characteristics are dramatically improved. In particular, the polymer electrolyte to which the molten salt of Example 3 having a melting point of 130 ° C. or lower is added is 7 to 9 compared with Comparative Example 2. It was found that a current density nearly doubled was obtained. This is considered to be because the mobility in the polymer electrolyte is higher than that of other salts by having a melting point in the operating temperature range. In addition, it is clear that the test cells using the electrolytes of Example 1 and Comparative Example 2 that have substantially the same ionic conductivity or the characteristics of Example 2 and Comparative Example 2 that share the same cation are compared. Thus, it can be seen that the polarization characteristics are remarkably improved by using the molten salt of the present invention. That is, it has been clarified that proton exchange in the electrolyte is smoothly performed via an oxo acid anion having a hydrogen atom.

(Power generation characteristics of fuel cells using the polymer electrolytes of Examples 8 to 9)
Next, evaluation results of power generation characteristics (polarization characteristics) of fuel cell test cells manufactured using the proton conductive electrolyte membranes of Examples 8 to 9 of the present invention will be described with reference to FIG. FIG. 10 is a graph showing a polarization curve of a fuel cell test cell produced using the proton conductive electrolyte membranes of Examples 8 to 9 of the present invention, where the vertical axis represents voltage [V] and the horizontal axis represents current. The density [mAcm ⁻² ] is shown.

  As shown in FIG. 10, similarly to the electrolyte of the present invention containing an organic salt having 6 or less carbon atoms, it is clear that an electromotive force can be applied even at 150 ° C. to generate electricity. In addition, the electrolyte of Example 9 having hydrogen sulfate as an anion clearly satisfies the characteristics of the electrolyte related to power generation and clearly shows that proton transport is possible. Further, it is shown that even when zirconia, which is one of the inorganic solid oxides in the present invention, is arranged, proton transport is possible and power generation is possible under high temperature and no humidification.

(Thermal decomposition characteristics of organic salts used in Examples 1 to 3)
Next, the results of evaluating the thermal decomposition characteristics of the organic salts used in Examples 1 to 3 of the present invention will be described with reference to FIG. In addition, FIG. 11 is a graph which shows the thermal decomposition curve of the organic salt used for Examples 1-3 of this invention, a vertical axis | shaft shows thermal decomposition rate [%] and a horizontal axis shows cell temperature [degreeC]. Yes. In this measurement, air was supplied at 200 mL / min. It was done in the flow.

  As shown in FIG. 11, it was found that all organic salts were stable up to 200 ° C. without being thermally decomposed. That is, it was suggested that the organic salt used in the examples of the present invention can be used for a fuel cell used at an operating temperature up to 200 ° C.

(Stability of the fuel cell using the electrolyte of Example 3)
Next, the results of evaluating the stability of a fuel cell test cell using the polymer electrolyte of Example 3 of the present invention will be described with reference to FIG. FIG. 12 is a graph showing the result of continuous operation of the fuel cell test cell using the polymer electrolyte of Example 3 of the present invention, where the vertical axis represents the closed circuit voltage [V] and the horizontal axis represents the operation time [hour]. ] Is shown. In this test, the current density was 1.0 mAcm ⁻² , the cell temperature was 150 ° C., and the flow rate was 100 mL / min. H ₂ , a cathode gas with a flow rate of 100 mL / min. Using the _{O 2,} it broke off test at the time of 10000 seconds.

  As shown in FIG. 12, the fuel cell produced using the polymer electrolyte of the present invention can be stably operated for a long time with a clearly high current density even when compared with a conventional fuel cell. all right. That is, the fuel cell of the present invention suggests that not only instantaneous power generation but also continuous power generation operation is possible in principle.

(Ionic conductivity of polymer electrolyte of Example 10)
Next, the evaluation results of the ionic conductivity of the proton conductive electrolyte membrane of Example 10 of the present invention will be described with reference to FIG. FIG. 13 is an Arrhenius plot of the ionic conductivity of Example 10 of the present invention, in which the vertical axis represents ion conductivity [Scm ⁻¹ ] and the horizontal axis represents temperature (1000 / T) [K ⁻¹ ]. ing.

  As shown in FIG. 13, although S-PEEK is the same water-containing polymer as Nafion (registered trademark), as is generally said, the retention rate of water is lower than that of the perfluoro type, and 100 It easily dries above ℃, and it is difficult to develop ionic conduction in a high temperature region above 100 ℃. Actually, it can be seen that the temperature characteristics of the ionic conductivity of Example 10 are lower in all temperature ranges than in other Examples 1 to 3 and Comparative Example 2. This is considered to be due to the difference in polymer compatibility and the glass transition point of the polymer. Regarding the temperature characteristics of ion conduction in Example 4, it is considered that the temperature characteristics of the HMIP used were reflected. On the other hand, S-PEEK which does not contain HMIP of Comparative Example 3 was not able to stably obtain a natural potential, and resistance measurement could not be performed. Therefore, it is considered that the conductor is made nonconductive due to evaporation of moisture.

(Power generation characteristics of a fuel cell using the polymer electrolyte of Example 10)
Next, evaluation results of power generation characteristics (polarization characteristics) of a fuel cell test cell manufactured using the proton conductive electrolyte membrane of Example 10 of the present invention will be described with reference to FIG. FIG. 14 is a graph showing a polarization curve of a fuel cell test cell produced using the proton conductive electrolyte membrane of Example 10 of the present invention. The vertical axis represents voltage [V], and the horizontal axis represents current density [ mAcm ⁻² ].

  As shown in FIG. 14, a result demonstrating that S-PEEK can be operated as a polymer substrate even in a non-humidified operation was obtained. In Comparative Example 3, unlike Nafion (registered trademark), no reference potential could be obtained and the test was impossible. Compared with the polarization characteristics of Comparative Example 2 proposed in the past, the characteristics are still good even when S-PEEK is used. The composite proton conductor containing the organic salt of Example 10 and S-PEEK is net. This is probably because it functions well as a proton transfer medium. By using the organic salt of the present invention, it was revealed that the net proton transfer was good although the apparent ionic conductivity was low.

(Relationship between salt concentration and ionic conductivity)
Next, the result of investigating the relationship between the salt concentration of the organic salt and the ionic conductivity using the polymer electrolyte of Example 3 of the present invention will be described with reference to FIG. FIG. 15 is a graph showing the relationship between the salt concentration and the ionic conductivity of the organic salt (HMIP) used in Example 3 of the present invention, where the vertical axis represents the ion conductivity [Scm ⁻¹ ] and the horizontal axis. Is a salt concentration, specifically, a molar concentration of perfluorosulfonic acid (PFSA) to sulfonic acid [mol eq. ] Is shown. In this experiment, a composite electrolyte membrane having a predetermined concentration was prepared separately from the example, and the ionic conductivity was measured after storage at 150 ° C. for 2 days.

  As is apparent from FIG. 15, the ionic conductivity is increased by the combination of the organic salt of the present invention and PFSA, and is approximately 1.0 mol eq. It can be seen that the ionic conductivity is maximum.

(Stability of sulfonic acid in polymer electrolyte)
Next, the results of investigating the stability of the sulfonic acid in the polymer electrolyte at high temperatures using Example 3 and Comparative Example 1 of the present invention will be described with reference to FIG. FIG. 16 shows infrared absorption spectra at 30 ° C. and 150 ° C. of the polymer electrolytes of Example 3 and Comparative Example 1 of the present invention.

As shown in FIG. 16, in Comparative Example 1, the peak of the sulfonic acid modified product is clearly confirmed at a (1415 cm ⁻¹ ) and b (901 cm ⁻¹ ) in the figure. However, in Example 3, it is clear that there is no significant change in peak shape at 30 ° C. and 150 ° C. From this result, it was suggested that the stability of sulfonic acid at high temperature was maintained in Example 3.

(Effect of adding inorganic solid oxide)
Next, referring to Table 1, the results of investigating the stability of the film surface in the atmosphere of Examples 1 to 9 of the present invention will be described. Table 1 shows the results of examining the adhesion of moisture on the electrolyte surface when the polymer electrolytes of Examples 1 to 9 of the present invention were allowed to stand at room temperature (about 22 ° C., humidity 45% RH) for 1 hour. As shown in Table 1, the polymer electrolyte of Example 7 using hydrogen sulfate as an anion absorbed moisture in the atmosphere, and water condensed on the membrane surface was observed. However, it is not observed at all in the polymer electrolyte of Example 9 containing zirconia, and from this result, by adding an inorganic solid oxide typified by zirconia, the stability of ions inside the electrolyte membrane is increased, It was suggested that the phenomenon of water condensation on the surface is eliminated by absorbing moisture from the atmosphere.

  That is, this suggested that there is no need for special consideration in the management of moisture in the atmosphere in the electrolyte manufacturing process and the MEA manufacturing process. In addition, regarding Examples 1 to 6 and Example 8 in which dihydrogen phosphate was used as an anion, a phenomenon that water was condensed on the membrane surface was not observed.

  Subsequently, the effect of adding the inorganic solid oxide will be further described with reference to FIGS. 17 and 18. FIGS. 17 and 18 show a rectangular specimen of a polymer electrolyte of Examples 5 and 7 of the present invention and Examples 8 and 9 in which zirconia, which is an example of an inorganic solid oxide, is arranged in an inert gas stream. This is a result of examining the mechanical strength by changing the temperature while pulling from room temperature to 150 ° C. with a stress of 50 mN. In this experiment, in order to investigate the thermomechanical characteristics of the proton conductive electrolyte membrane, the elongation of the membrane under a constant torque tension condition was examined under a stream of argon gas using a TMA / SS6100 manufactured by Seiko Denshi. Specifically, a sample is cut into a strip having a constant width, fixed to a chuck so that the length of the test piece is about 5 mm, fixed by applying a constant load of 50 mN in the pulling direction, and from a room temperature to 150 ° C. with a heating furnace. The temperature was raised at a rate of 5 ° C./min until the change in the elongation of the test piece was observed.

  The electrolytes to be compared (Examples 5 and 8 or Examples 7 and 9) have a difference in the presence or absence of zirconia, and the organic salts to be mixed are the same. Moreover, the vertical axis | shaft of FIG.17 and FIG.18 has shown the change of the length of a test piece, and the horizontal axis has shown the change of the atmospheric temperature near a sample. As apparent from FIG. 17 and FIG. 18, when the temperature is changed while pulling at a constant stress, the sample temperature increases rapidly when the ambient temperature rises, and the vicinity of 100 ° C. increases. This is considered to be a change accompanying the softening of Nafion (registered trademark) that forms the structure of the polymer electrolyte. It can be seen that by arranging zirconia in any sample, the softening temperature shifts to the high temperature side, and at the same time, the elongation of the sample piece also slows down. That is, when comparing the amount of change in the length of the test piece at a certain temperature after softening, any of the electrolytes in which zirconia is arranged (that is, Examples 8 and 9) is an electrolyte in which no zirconia is arranged (that is, Compared with Examples 5 and 7), the elongation is decreased, and it is clear that the test piece provided with zirconia has higher mechanical strength. From these results, it was suggested that the mechanical strength is also clearly improved by further blending the inorganic solid oxide with the solid polymer electrolyte in which the organic salt according to the present invention is compatible.

  As mentioned above, although preferred embodiment of this invention was described, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

It is an Arrhenius plot of the ionic conductivity of Examples 1 to 3 and Comparative Example 2 of the present invention. It is an Arrhenius plot of the ionic conductivity of HMIP used for Example 3 of this invention. It is an Arrhenius plot of the ionic conductivity of Examples 4 to 7 and Comparative Example 2 of the present invention. It is an Arrhenius plot of the ionic conductivity of Examples 8-9 and Comparative Example 2 of the present invention. It is a figure which shows the crystallization and melting peak at the time of temperature rising in the differential scanning calorimetry (DSC) of HMIP used for Example 3 of this invention. It is a figure which shows the crystallization and melting peak at the time of temperature rising in the differential scanning calorimetry (DSC) of the electrolyte of Example 4 of this invention. It is a figure which shows the crystallization and melting peak at the time of temperature rising in the differential scanning calorimetry (DSC) of the electrolyte of Example 7 of this invention. It is a figure which shows the crystallization and melting peak at the time of temperature rising in the differential scanning calorimetry (DSC) of the electrolyte of Example 9 of this invention. It is a graph which shows the polarization curve of the fuel cell test cell produced using the proton conductive electrolyte membrane of Examples 1-3 and Comparative Examples 1 and 2 of this invention. It is a graph which shows the polarization curve of the fuel cell test cell produced using the proton-conductive electrolyte membrane of Examples 8-9 of this invention. It is a graph which shows the thermal decomposition curve of the organic salt used for Examples 1-3 of this invention. It is a graph which shows the continuous operation result of the fuel cell test cell using the polymer electrolyte of Example 3 of this invention. It is an Arrhenius plot of the ionic conductivity of Example 4 of this invention. It is a graph which shows the polarization curve of the fuel cell test cell produced using the proton-conductive electrolyte membrane of Example 4 of this invention. It is a graph which shows the relationship between the salt concentration of the organic salt (HMIP) used for Example 3 of this invention, and ionic conductivity. It is an infrared absorption spectrum at 30 ° C. and 150 ° C. of the polymer electrolytes of Example 3 and Comparative Example 1 of the present invention. It is a graph which shows the result of having investigated the mechanical strength of the polymer electrolyte of Example 5 and Example 8 of this invention. It is a graph which shows the result of having investigated the mechanical strength of the polymer electrolyte of Example 7 and Example 9 of this invention.

Claims (12)

An organic salt comprising an organic compound cation and an oxoacid anion represented by the following formula (1) having at least one hydrogen atom;
A polymer electrolyte having an acidic functional group;
A composite proton conductor comprising:
XO _m (OH) _n ⁻ (1)
In the formula (1), X is P, S or N, and m and n are 1 or more.   The composite proton conductor according to claim 1, wherein the organic compound cation is an imidazolium cation.   3. The complex proton derivative according to claim 2, wherein the imidazolium cation is a 1,3-substituted imidazolium cation. The composite proton conductor according to claim 3, wherein the 1,3-substituted imidazolium cation is an imidazolium cation represented by the following general formula (2).

In the general formula (2), R ₁ is an alkyl group having 1 to 6 carbon atoms, and R ₂ is an alkyl group having 1 to 30 carbon atoms.   The composite proton conductor according to any one of claims 1 to 4, wherein the oxo acid anion is a dihydrogen phosphate anion or a monohydrogen sulfate anion.   The composite proton conductor according to claim 1, wherein the organic salt has a melting point of 130 ° C. or less.   The composite proton conductor according to claim 1, wherein the polymer electrolyte is a fluorinated polymer electrolyte.   The composite proton conductor according to claim 1, wherein the acidic functional group is a sulfonic acid group.   A proton conductive electrolyte membrane comprising the composite proton conductor according to claim 1.   The proton conductive electrolyte membrane according to claim 9, further comprising an inorganic solid oxide. The inorganic solid oxide includes zirconia (ZrO ₂ ), silica (SiO ₂ ), alumina (Al ₂ O ₃ ), titania (TiO ₂ ), beryllia (BeO), magnesia (MgO), zinc oxide (ZnO ₂ ), barium titanate (BaTiO _3), characterized in that it is a zircon least one oxide selected from the group consisting of _{(ZrO 2} · SiO 2) and mullite _{(3Al 2 O 3 · 2SiO 2} ), claim 11. The proton conductive electrolyte membrane according to 10. A fuel cell comprising a membrane electrode assembly using the proton conductive electrolyte membrane according to claim 9.

Images