JP4904750B2 - Liquid electrolyte - Google Patents

Description

The present invention relates to an electrolyte which is composed of a base and phosphoric acid and does not solidify even at a low temperature and is liquid in a wide temperature range. Specifically, it is used for a fuel cell, a secondary battery, an electric double layer capacitor, an electrolytic capacitor and the like. It relates to a liquid electrolyte that can be made. The present invention also relates to a fuel cell using the same.

  In general, electrolytes used in electrochemical devices such as lithium ion batteries and electric double layer capacitors are prepared by dissolving a supporting salt such as a lithium salt or an ammonium salt in an organic solvent such as propylene carbonate. These organic solvents are volatile and remain a safety issue.

On the other hand, those having ammonium salts such as imidazolium salts and pyridinium salts become liquid molten salts at 100 ° C. or lower, particularly near room temperature, and are high at relatively low temperatures of 200 ° C. or lower without using water or organic solvents. It is known to exhibit ionic conductivity. These have been studied for application as electrolytes for batteries and the like due to their characteristic nature of non-volatility. Many examples of ionic liquids include imidazole salts and pyridine salts in which a substituent is introduced at the N-position. (Ionic liquids-forefront and future of development-supervised by Hiroyuki Ohno, CM Publishing, 2003 (non-patent document 1)).

  As a typical electrolyte solution of an organic solvent-based electric double layer capacitor, an electrolyte solution in which an ammonium salt such as tetraethylammonium tetrafluoroborate is dissolved in a polar solvent such as propylene carbonate can be cited. As a result of the precipitation, there is a problem that the capacity is deteriorated and the conductivity is lowered, and the improvement of the low temperature characteristics is an important problem to be solved (Non-patent Document 2).

There are examples of using an electrolytic solution consisting only of an ionic liquid for an electric double layer capacitor, but the ionic liquid solidifies at a low temperature below room temperature, or the ionic conductivity greatly decreases as the viscosity increases without solidifying. This is a problem (Non-Patent Document 2).

There is an example in which the low-temperature characteristics of a system in which an ionic liquid is dissolved in an organic solvent is improved compared to a conventional system in which an ammonium salt is dissolved in an organic solvent. However, the use of an organic solvent causes problems with volatility and safety. (Non-Patent Document 2).

  In phosphoric acid fuel cells, concentrated phosphoric acid of 85 wt% or more is usually used as an electrolyte. According to J. Am. Chem. Soc., 47, 2165 (1925) (Non-patent Document 3), phosphoric acid has a melting point of 100 wt% of about 40 ° C, and when it is 91.6 wt% or more, it is completely below 23.5 ° C. To solidify. If it is 91.6wt% or less, it becomes a mixed state of solid and liquid at 20 ℃ or less. Therefore, in an environment where the outside air is 20 ° C. or lower, phosphoric acid is solidified while the phosphoric acid fuel cell is stopped, and the phosphoric acid must be melted by heating in advance when restarting. It is necessary to prevent the solidification of phosphoric acid during transportation to the installation site after manufacture, and it is necessary to keep the phosphoric acid fuel cell warm using another heat retaining device. Further, when phosphoric acid is solidified, volume change occurs and stress is applied to the fuel cell, which may cause deterioration. From the above, prevention of solidification of phosphoric acid is one of the problems of phosphoric acid fuel cells.

  Japanese Patent Application Laid-Open No. 11-238521 (Patent Document 1) discloses a method for providing a fuel cell that does not require a heat retention device or a wet gas device and can prevent complete solidification of an electrolyte when stopped. However, since a part of phosphoric acid is solidified, the electrolyte resistance at the time of restart increases.

  JP-A-6-275297 (Patent Document 2) describes a phosphoric acid form that can be activated even when the battery temperature is reduced to the outside temperature after the operation is stopped by suppressing freezing of phosphoric acid during battery storage. Although a method for operating a fuel cell is disclosed, it remains a problem that a part of phosphoric acid is solidified and that the output of the fuel cell is reduced because the operating temperature needs to be lowered.

  Japanese Patent Application Laid-Open No. 9-293523 (Patent Document 3) is capable of easily and surely avoiding fuel cell performance degradation induced by freezing of phosphoric acid, is excellent in reliability and inexpensive in transportation costs. However, it is necessary to dilute phosphoric acid by supplying and discharging wet gas and re-concentrating phosphoric acid by supplying and discharging dry gas. In addition, even if phosphoric acid is diluted to 75 wt%, it will freeze at -17 ° C, leaving problems for transportation and stoppage in extremely cold regions.

  Abstract of Molten Salt Chemistry Conference, Vol. 35, 81-82 (2003) (Non-patent Document 4) discloses an acid-excess room temperature molten salt composed of butylamine and phosphoric acid. No particular mention is made of or characteristics.

Japanese Patent Laid-Open No. 2005-44550 (Patent Document 4) discloses an ionic liquid of phosphoric acid and a cyclic organic basic substance, but it is indicated whether it is liquid at a temperature lower than 20 ° C. The above problem has not been solved.

Japanese Patent Laid-Open No. 11-238521 JP-A-6-275297 JP-A-9-293523 JP 2005-44550 A Ionic liquids -The forefront and future of development- Supervised by Hiroyuki Ohno, CMC Publishing, 2003, 28-31 Functional creation and application of ionic liquids, NTS Corporation, 2004, 105-123 J. Am. Chem. Soc., 47, 2165 (1925) Abstracts of Molten Salt Chemistry Conference, Vol. 35, 81-82 (2003)

  An object of the present invention is to provide a novel liquid electrolyte which comprises a base and phosphoric acid and does not solidify even at low temperatures.

  The present invention comprises a base A and a phosphoric acid B, wherein the molar ratio A: B of A to B is in the range of 1: 3 to 1:19, and the solidification temperature is less than −30 ° C. Liquid electrolyte.

The present invention also relates to the above liquid electrolyte, characterized in that the ionic conductivity at −30 ° C. is 10 ⁻⁶ Scm ⁻¹ or more.

The present invention also relates to the above liquid electrolyte, characterized in that the ionic conductivity at 150 ° C. is 10 ⁻² Scm ⁻¹ or more.

  The present invention also relates to the above liquid electrolyte, wherein the base is an amine compound.

（１）
また、本発明は、該塩基が化学式（１）
[式中、R¹, R², R³およびR⁴は、各々独立して、炭素数1〜20の炭化水素基、または、水素原子を表す。]
で表されるイミダゾール化合物であることを特徴とする上記の液体電解質に関する。

(1)
In the present invention, the base is represented by the chemical formula (1).
[Wherein, R ¹ , R ² , R ³ and R ⁴ each independently represents a hydrocarbon group having 1 to 20 carbon atoms or a hydrogen atom. ]
It is related with said liquid electrolyte characterized by being an imidazole compound represented by these.

（２）
また、本発明は、該塩基が化学式（２）
[式中、R¹, R²およびR³は、各々独立して、炭素数1〜20の炭化水素基、水酸基を有する炭素数1〜20の炭化水素基、または、水素原子を表し、少なくともひとつは炭化水素基または水酸基を有する炭化水素基である。]
で表されるアミンであることを特徴とする上記の液体電解質に関する。

(2)
In the present invention, the base is represented by the chemical formula (2).
[Wherein R ¹ , R ² and R ³ each independently represent a hydrocarbon group having 1 to 20 carbon atoms, a hydrocarbon group having 1 to 20 carbon atoms having a hydroxyl group, or a hydrogen atom, One is a hydrocarbon group or a hydrocarbon group having a hydroxyl group. ]
It is related with said liquid electrolyte characterized by being an amine represented by these.

（３）
また、本発明は、該塩基が化学式（３）
[式中、R¹は炭素数1〜20の炭化水素基、または、水素原子を表す。]
で表されるピロリジン化合物であることを特徴とする上記の液体電解質に関する。

(3)
In the present invention, the base is represented by the chemical formula (3).
[Wherein, R ¹ represents a hydrocarbon group having 1 to 20 carbon atoms or a hydrogen atom. ]
It is related with said liquid electrolyte characterized by being the pyrrolidine compound represented by these.

The present invention also relates to the above liquid electrolyte, which is a proton conductor.

  According to the present invention, a novel ion-conductive or proton-conductive liquid electrolyte comprising a base and phosphoric acid and existing in a liquid state at −30 ° C. is provided, such as a fuel cell, a secondary battery, an electric double layer capacitor, and an electrolytic capacitor. Can be used.

  The liquid electrolyte of the present invention comprises a base and phosphoric acid, and the solidifying temperature is preferably less than -30 ° C, more preferably less than -40 ° C, and further preferably less than -50 ° C. If the solidification temperature is higher than the above temperature, the electrolyte solution may solidify in an extremely cold region, which is not preferable.

  Solidification in the present invention means that a liquid becomes a solid. Including both crystallization and vitrification. Depending on the conditions, there is a case where the liquid does not substantially flow as a liquid in a mixed state of solid and liquid or a mixed state of crystal and amorphous. The liquid in the present invention may be in a supercooled state.

  The time required for the liquid electrolyte of the present invention to solidify at a low temperature is preferably not solidified for 12 hours or more, which is half a day. More preferably, it does not coagulate for more than 1 day, more preferably for more than 1 week, particularly preferably for more than 1 month. Moreover, it is preferable not to solidify semipermanently. If the time until solidification is shorter than the above time, there is a possibility of solidification while the applied electrochemical device is stopped, which is not preferable.

The molar ratio of the base and phosphoric acid constituting the liquid electrolyte of the present invention is in the range of 1: 3 to 1:50, more preferably in the range of 1: 3 to 1:40, and 1: 3 More preferably, it is in the range of ˜1: 30. Further, it is more preferably in the range of 1: 3 to 1:20, and particularly preferably in the range of 1: 5 to 1:20. When the proportion of phosphoric acid exceeds the above range, the solidification temperature becomes high or the viscosity becomes high, which is not preferable.

The liquid electrolyte of the present invention preferably exhibits an ionic conductivity of 1 × 10 ⁻⁶ Scm ⁻¹ or more even at a low temperature of −30 ° C., and may exhibit an ionic conductivity of 1 × 10 ⁻³ Scm ⁻¹ or more. More preferred. If the ionic conductivity is lower than the above value, it is not practical because it is not practical when placed in a cold region.

The liquid electrolyte of the present invention preferably exhibits an ionic conductivity of 1 × 10 ⁻² Scm ⁻¹ or higher at 150 ° C., more preferably 1 × 10 ⁻¹ Scm ⁻¹ or higher. When the ionic conductivity is lower than the above value, the resistance at the time of high temperature use becomes large, which is not preferable.

The base component of the liquid electrolyte of the present invention is preferably an amine compound. Preferable amine compounds include imidazole compounds, aliphatic amine compounds, aromatic amine compounds, amine compounds substituted with an alkyl group having a hydroxyl group, and pyrrolidine compounds. Examples of heterocyclic amines other than imidazole compounds and pyrrolidine compounds include azoles such as pyrazole compounds, triazole compounds, oxazole compounds, and thiazole compounds, pyridine compounds, pyrazine compounds, pyrrole compounds, and piperidine compounds.
Preferred examples of the solidification temperature include imidazole compounds, aliphatic tertiary amine compounds, amine compounds substituted with an alkyl group having a hydroxyl group, and pyrrolidine compounds.

  As the imidazole compound, an imidazole compound represented by the chemical formula (1) is preferable.

（１）

式中、R¹, R², R³およびR⁴は、各々独立して、炭素数1〜20の炭化水素基、または、水素原子であることが好ましい。
また、R¹, R², R³またはR⁴の少なくともひとつが炭素数1〜20の炭化水素基であることが好ましい。
R¹, R², R³およびR⁴の炭素数1〜20の炭化水素基としては、例えば、メチル基、エチル基、n-プロピル基、n-ブチル基、ヘキシル基、オクチル基などの直鎖基、イソプロピル基、s-ブチル基、t-ブチル基などの分枝基、シクロヘキシル基などの脂環基、フェニル基などの芳香族基が挙げられる。特に、メチル基、エチル基、n-プロピル基、 n-ブチル基が好ましい。

(1)

In the formula, each of R ¹ , R ² , R ³ and R ⁴ is preferably independently a hydrocarbon group having 1 to 20 carbon atoms or a hydrogen atom.
Moreover, it is preferable that at least one of R ¹ , R ² , R ³ or R ⁴ is a hydrocarbon group having 1 to 20 carbon atoms.
Examples of the hydrocarbon group having 1 to 20 carbon atoms of R ¹ , R ² , R ³ and R ⁴ include methyl, ethyl, n-propyl, n-butyl, hexyl and octyl groups. Examples thereof include a branched group such as a chain group, isopropyl group, s-butyl group and t-butyl group, an alicyclic group such as a cyclohexyl group, and an aromatic group such as a phenyl group. In particular, a methyl group, an ethyl group, an n-propyl group, and an n-butyl group are preferable.

Specific imidazole compounds include imidazole, 4-alkylimidazoles such as 4-methylimidazole, 4-ethylimidazole and 4-phenylimidazole, 2-methylimidazole, 2-ethylimidazole and 2-phenylimidazole. -Alkyl imidazoles, 2-ethyl-4-methylimidazole, 2-cyclohexyl-4-methylimidazole, 2-octyl-4-hexylimidazole, 2-ethyl-4-phenylimidazole, 2-butyl-4-allylimidazole, etc. 1,4-dialkylimidazoles, 1-methylimidazole, 1-ethylimidazole, 1-propylimidazole, 1-butylimidazole, 1-hexylimidazole, 1-alkylimidazoles such as 1-octylimidazole, benzimidazole, 1 -Benzimidazoles such as methylbenzimidazole And the like. Among them, asymmetric imidazoles such as 4-alkylimidazoles and 2,4-alkylimidazoles and 1-alkylimidazoles substituted at the N-position are preferable because of their great effects of suppressing coagulation.
Moreover, it is preferable that it is an amine represented by Chemical formula (2) as an amine compound.

（２）

式中、R¹, R²およびR³は、各々独立して、炭素数1〜20の炭化水素基、水酸基を有する炭素数1〜20の炭化水素基、または、水素原子を表し、少なくともひとつは炭化水素基または水酸基を有する炭化水素基であることが好ましい。

(2)

In the formula, R ¹ , R ² and R ³ each independently represent a hydrocarbon group having 1 to 20 carbon atoms, a hydrocarbon group having 1 to 20 carbon atoms having a hydroxyl group, or a hydrogen atom, and at least one of them Is preferably a hydrocarbon group or a hydrocarbon group having a hydroxyl group.

Moreover, it is preferable that all of R ¹ , R ² and R ³ are hydrocarbon groups having 1 to 20 carbon atoms.

When two or more of R ¹ , R ² and R ³ are hydrocarbon groups, it is preferably composed of two or more hydrocarbon groups.
Examples of the hydrocarbon group R ^1, R ² and carbon atoms R ³ 1 to 20, those described above. Examples of the hydrocarbon group having a hydroxyl group include a substituent corresponding to a primary alcohol such as —CH ₂ OH, —CH ₂ OH, —CH ₂ CH ₂ CH ₂ OH, and —CH ₂ CH (OH) CH ₃ . Substituents corresponding to secondary alcohols and substituents corresponding to tertiary alcohols such as —CH ₂ C (OH) (CH ₃ ) ₂ can be mentioned. Among these, —CH ₂ OH and —CH ₂ OH are preferable.

Specific aliphatic amine compounds include primary amines such as methylamine, ethylamine, propylamine, butylamine, s-butylamine, t-butylamine, hexylamine, cyclohexylamine, octylamine, dimethylamine, diethylamine, and N-ethyl. Secondary amines such as methylamine, N-methylpropylamine, N-methylbutylamine, N-methyl-t-butylamine, N-methylcyclohexylamine, trimethylamine, triethylamine, N, N-dimethylethylamine, N, N-diethyl And tertiary amines such as methylamine and N, N-dimethylcyclohexylamine. Among them, tertiary amines having different substituents such as N, N-dimethylethylamine, N, N-diethylmethylamine, N, N-dimethylcyclohexylamine and the like are preferable because the temperature for solidification becomes low.

Aromatic amine compounds include anilines such as aniline and N-methylaniline, phenylenediamines such as 1,2-phenylenediamine, 1,3-phenylenediamine and 1,4-phenylenediamine, N-methyl-1,2 Phenylenediamines such as -phenylenediamine, aminonaphthalenes such as 1-aminonaphthalene and 2-aminonaphthalene, and diaminonaphthalenes such as 1,5-diaminonaphthalene and 1,8-diaminonaphthalene.

An amine compound substituted with an alkyl group having a hydroxyl group is also preferably used.
Specific compounds include monoalcoholamines such as methanolamine and ethanolamine, dialcoholamines such as dimethanolamine and diethanolamine, trimethanolamine, triethanolamine, methyldiethanolamine, n-butyldiethanolamine, and s-butyl. And trialcoholamines such as diethanolamine and t-butyldiethanolamine. Of these, triethanolamine, methyldiethanolamine, and n-butyldiethanolamine can be preferably exemplified.

  As the pyrrolidine compound, a pyrrolidine compound represented by the chemical formula (3) is preferable.

（３）

式中、R¹は炭素数1〜20の炭化水素基、または、水素原子を表す。

(3)

In the formula, R ¹ represents a hydrocarbon group having 1 to 20 carbon atoms or a hydrogen atom.

  Specific examples of the compound include pyrrolidine and 1-alkylpyrrolidines such as 1-methylpyrrolidine and 1-ethylpyrrolidine. Of these, 1-methylpyrrolidine can be preferably mentioned.

Examples of azole compounds other than imidazole include pyrazoles such as pyrazole, 1-methylpyrazole, 3-methylpyrazole, 4-methylpyrazole, triazoles such as triazole, oxazoles such as oxazole, thiazoles such as thiazole, and the like. .

Examples of pyridine compounds include pyridine, alkyl pyridines such as 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 3-butylpyridine, 4-t-butylpyridine, 2,4-lutidine, 2,3 -Dialkylpyridines such as lutidine, 2,6-lutidine, 3,4-lutidine and the like.

Examples of pyrazine compounds include 2-alkylpyrazine such as 2-methylpyrazine and 2-ethylpyrazine in addition to pyrazine.

Examples of the pyrrole compound include pyrrole and 1-alkylpyrroles such as 1-methylpyrrole and 1-ethylpyrrole.

Examples of the piperidine compound include piperidine, 1-alkylpiperidines such as 1-methylpiperidine and 1-ethylpiperidine, and 2-alkylpiperidines such as 2-methylpiperidine and 2-ethylpiperidine.

The base component may be a mixture of two or more. For example, in the case of a mixture of two kinds, 1-ethylimidazole and 4-methylimidazole, 1-ethylimidazole and 2-ethyl-4-methylimidazole, 4-methylimidazole and 2-ethylimidazole, 4-methylimidazole and 2-methylimidazole Ethyl-4-methylimidazole, N, N-diethylmethylamine and 4-methylimidazole, N, N-dimethylcyclohexylamine and 4-methylimidazole, N, N-diethylmethylamine and N, N-dimethylcyclohexylamine, tri Examples include ethanolamine and 4-methylimidazole, triethanolamine and diethylmethylamine, and a combination of triethanolamine and N, N-dimethylcyclohexylamine.

The liquid electrolyte of the present invention may be a proton conductor. Those having proton conductivity can be preferably used for fuel cells.

The phosphoric acid used in the present invention may be orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, or a mixture thereof. Since condensed phosphoric acid has a high viscosity and is difficult to handle, orthophosphoric acid is preferably used.

The liquid electrolyte of the present invention preferably has a heat resistance of 150 ° C. or higher, more preferably 180 ° C. or higher, and further preferably 200 ° C. or higher. If the heat resistance is lower than the above temperature, the performance is lowered when used in an electrolyte of a device operated at a high temperature such as a phosphoric acid fuel cell.

The liquid electrolyte of the present invention may contain water or an organic solvent. Organic solvents include ethylene carbonate, propylene carbonate, butylene carbonate, acetonitrile, N, N-dimethylformamide, N, N-dimethylacetamide, N, N-dimethylimidazolidinone, N-methyl-2-pyrrolidone, γ-valero Examples include polar solvents such as lactone, sulfolane, acetone, methanol, ethanol, 1-propanol, and 2-propanol.

According to the present invention, a liquid electrolyte composed of a base and phosphoric acid is provided, which does not solidify at low temperature and exhibits high ionic conductivity at low and high temperatures without water or solvent. It can be used for multilayer capacitors, electrolytic capacitors, and the like.

  In addition, inorganic compounds and rayons made of metal oxides such as glass, silica, alumina, zirconium oxide and titanium oxide, polyolefins, polyesters, polyamides, fluororesins, polyimides, polyethers, polysulfides, polyarylenes It can be used by impregnating a porous body such as a sintered body, a nonwoven fabric, a woven cloth, or a microporous film made of a polymer compound such as a polybenzazole, a polybenzazole, a polyquinoxaline, or a polystyrene.

The fuel cell of the present invention uses the above-described liquid electrolyte, and other than the liquid electrolyte, those known in conventional phosphoric acid fuel cells or solid polymer fuel cells can be employed. For example, in a state where a liquid electrolyte is impregnated in a porous body made of an inorganic compound or a polymer, a pair of catalysts such as platinum is sandwiched between porous gas diffusion electrodes made of carbon fine particles or fibers attached, and further It has a structure in which separators made of conductive carbon or metal with fuel gas passages formed on both sides are installed. In the fuel cell of the present invention, the normal use temperature can be in the range of 20 ° C to 250 ° C, preferably 30 ° C to 240 ° C, more preferably 40 ° C to 230 ° C. On the other hand, when the temperature exceeds 250 ° C., it is not preferable because decomposition occurs.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In addition, the measured value shown in the Example and the comparative example was measured with the following method.

1) State observation at -30 ° C Approximately 2 g of dried sample is placed in a sample bottle, sealed, kept in a thermostatic bath at 60 ° C for 2 hours, and at 25 ° C overnight, then left at -30 ° C. Then, it was confirmed whether or not the sample was solidified every predetermined time.

2) Measurement of ion conductivity A dried sample was placed in a sample bottle, and a platinum plate measuring 2 cm in length and 1.5 cm in width was immersed in the sample in parallel at intervals of 1 cm, and sealed to obtain a cell for conductivity measurement. Ionic conductivity was determined by complex impedance measurement using a FRD1025 manufactured by Princeton Applied Reseach and Potentiostat / Galvanostat 283 in a thermostatic chamber at a predetermined temperature.

(Example 1) 4-methylimidazole / phosphoric acid system (4MI H ₃ PO ₄ )
In a glove box in a nitrogen atmosphere, liquid phosphoric acid melted with phosphoric acid crystal (Aldrich) and 4-methylimidazole (4MI; Aldrich) were mixed in predetermined amounts to obtain liquid electrolytes with various molar ratios. The mixing molar ratio of 4MI and phosphoric acid is 1: 1, 1: 2, 1: 3, 1: 4, 1: 5, 1: 6, 1: 7, 1: 8, 1: 9, 1:10, 1:11, 1:13, 1:15, 1:19, 1:24, 1:34, 1:49, and 1:99. Those that did not become a uniform liquid were heated in a 50 ° C. hot air thermostat or 120 ° C. oil bath to make a uniform liquid. Table 1 shows the results of state observation at -30 ° C. Those having a molar ratio of 1: 3 to 1:24 remained liquid for at least 70 days even at low temperatures of -30 ° C. The temperature dependence of the ionic conductivity of 4MI H ₃ PO ₄ 1: 1, 1: 2, 1: 3 and 1:19 is shown in FIG. 4MI H ₃ PO ₄ 1: 3 exhibited an ionic conductivity of 4.9 × 10 ⁻⁶ Scm ⁻¹ at −30 ° C. and 2.0 × 10 ⁻¹ Scm ⁻¹ at 150 ° C. 4MI H ₃ PO ₄ 1:19 exhibited an ionic conductivity of 1.3 × 10 ⁻³ Scm ⁻¹ at −30 ° C. and 4.3 × 10 ⁻¹ Scm ⁻¹ at 150 ° C. Compared to the fact that the ionic conductivity of the phosphoric acid of Comparative Example 1 solidified at a low temperature and decreased rapidly, 4MI H ₃ PO ₄ 1:19 maintained high ionic conductivity without solidifying.

(Example 2) N-ethylimidazole / phosphoric acid system (1EI H ₃ PO ₄ )
Liquid electrolytes having various molar ratios were obtained in the same manner as in Example 1 except that N-ethylimidazole (1EI; Tokyo Chemical Industry Co., Ltd.) was used instead of 4MI. Table 1 shows the results of state observation at -30 ° C. Those with molar ratios of 1: 3 to 1:24 and 1:49 remained liquid for at least 44 days, even at low temperatures of -30 ° C.

(Example 3) N, N-dimethylcyclohexylamine / phosphoric acid system (DMCA H ₃ PO ₄ )
Liquid electrolytes with various molar ratios were obtained in the same manner as in Example 1 except that N, N-dimethylcyclohexylamine (DMCA; Wako Pure Chemical Industries, Ltd.) was used instead of 4MI. Table 1 shows the results of solidification observation at -30 ° C. Those having a molar ratio of 1: 3 to 1:34 remained liquid for at least 65 days even at low temperatures of -30 ° C.

(Example 4) Triethanolamine / phosphoric acid system (TEOA H ₃ PO ₄ )
Liquid electrolytes having various molar ratios were obtained in the same manner as in Example 1 except that triethanolamine (TEOA; Sigma-Aldrich Japan Co., Ltd.) was used instead of 4MI. Table 1 shows the results of state observation at -30 ° C. Those with molar ratios of 1: 3 to 1:24 and 1:49 remained liquid for at least 69 days, even at low temperatures of -30 ° C. Figure 2 shows the temperature dependence of the ionic conductivity of TEOA H ₃ PO ₄ 1: 3. TEOA H ₃ PO ₄ 1: 3 exhibited an ionic conductivity of 4.0 × 10 ⁻⁶ Scm ⁻¹ at −30 ° C. and 1.2 × 10 ⁻¹ Scm ⁻¹ at 150 ° C.

(Example 5) Butylamine / phosphoric acid system (BA H ₃ PO ₄ )
Liquid electrolytes with various molar ratios were obtained in the same manner as in Example 1 except that butylamine (BA; Aldrich) was used instead of 4MI. Table 1 shows the results of solidification observation at -30 ° C. Those with molar ratios of 1: 2 to 1:19, 1:34 and 1:49 remained liquid for at least 65 days, even at low temperatures of -30 ° C.

(Example 6) N, N-diethylmethylamine / phosphoric acid system (DEMA H ₃ PO ₄ )
A liquid electrolyte having a molar ratio of 1: 3 was obtained in the same manner as in Example 1 except that N, N-diethylmethylamine (DEMA; Tokyo Chemical Industry Co., Ltd.) was used instead of 4MI. DEMA H ₃ PO ₄ 1: 3 remained liquid at −30 ° C. for at least 117 days. Fig. 3 shows the temperature dependence of the ionic conductivity of DEMA H ₃ PO ₄ 1: 3. DEMA H ₃ PO ₄ 1: 3 exhibited an ionic conductivity of 3.5 × 10 ⁻⁶ Scm ⁻¹ at −30 ° C. and 1.1 × 10 ⁻¹ Scm ⁻¹ at 150 ° C.

(Example 7) N-methyldiethanolamine / phosphoric acid system (MDEOA H ₃ PO ₄ )
A liquid electrolyte having a molar ratio of 1: 3 was obtained in the same manner as in Example 1 except that N-methyldiethanolamine (MDEOA; Aldrich) was used instead of 4MI. MDEOA H ₃ PO ₄ 1: 3 remained liquid at −30 ° C. for at least 125 days.

Example 8 2,2 ′-(Butylimino) diethanolamine / phosphoric acid system (BDEOA H ₃ PO ₄ )
A liquid electrolyte having a molar ratio of 1: 3 was obtained in the same manner as in Example 1 except that 2,2 ′-(butylimino) diethanolamine (BDEOA; Tokyo Chemical Industry Co., Ltd.) was used instead of 4MI. BDEOA H ₃ PO ₄ 1: 3 remained liquid for at least 117 days at −30 ° C.

(Example 9) 2-ethyl-4-methylimidazole / phosphoric acid system (2E4MZ H ₃ PO ₄ )
A liquid electrolyte having a molar ratio of 1: 3 was obtained in the same manner as in Example 1 except that 2-ethyl-4-methylimidazole (2E4MZ; Shikoku Kasei Kogyo Co., Ltd.) was used instead of 4MI. 2E4MZ H ₃ PO ₄ 1: 3 remained liquid at −30 ° C. for at least 112 days.

(Example 10) 1-methylpyrrolidine / phosphate system (1MP H ₃ PO ₄ )
A liquid electrolyte having a molar ratio of 1: 3 was obtained in the same manner as in Example 1 except that 1-methylpyrrolidine (1MPy; Tokyo Chemical Industry Co., Ltd.) was used instead of 4MI. 1MP H ₃ PO ₄ 1: 3 remained liquid for at least 1 week at -30 ° C. Fig. 4 shows the temperature dependence of the ionic conductivity of 1MP H ₃ PO ₄ 1: 3. 1MP H ₃ PO ₄ 1: 3 exhibited an ionic conductivity of 1.3 × 10 ⁻¹ Scm ⁻¹ at 150 ° C.

(Comparative Example 1) Phosphoric acid Phosphoric acid crystal was heated and melted at 60 ° C to liquefy, and then allowed to stand at -10 ° C to solidify in 2 hours. Figure 1 shows the temperature dependence of the ionic conductivity of phosphoric acid. When solidified from -10 ° C to -20 ° C, the ionic conductivity decreased rapidly.

Example 11 Fuel Cell Power Generation Test FIG. 5 shows the results of power generation at a cell temperature of 120 ° C. using the liquid electrolyte 4MI H ₃ PO ₄ 1:19 prepared in Example 1. For power generation, a phosphoric acid power generation cell FC25-02PA and an electrode matrix assembly FC25-PA / EM manufactured by Electrochem Co. were used, and fuel was supplied as non-humidified hydrogen at 150 ml / min and oxygen at 150 ml / min. .

  According to the present invention, a novel ion-conductive or proton-conductive liquid electrolyte comprising a base and phosphoric acid and existing in a liquid state at −30 ° C. is provided, such as a fuel cell, a secondary battery, an electric double layer capacitor, and an electrolytic capacitor. Can be used.

₄ shows the temperature dependence of 4MI H ₃ PO ₄ 1: 1, 1: 2, 1: 3 and 1:19 in Example 1 and phosphoric acid ion conductivity in Comparative Example 1. FIG. 9 shows the temperature dependence of the ionic conductivity of TEOA H ₃ PO ₄ 1: 3 in Example 4. FIG. FIG. 9 shows the temperature dependence of the ionic conductivity of DEMA H ₃ PO ₄ 1: 3 in Example 6. FIG. The temperature dependence of the ionic conductivity of 1MP H ₃ PO ₄ 1: 3 in Example 10 is shown. 10 shows the relationship between current and output voltage in fuel cell power generation using the liquid electrolyte 4MI H ₃ PO ₄ 1:19 in Example 11.

Claims (5)

It consists of any amine compound A represented by the following chemical formulas (1) to (3) and phosphoric acid B, and the molar ratio A: B of A to B is in the range of 1: 3 to 1:50 and solidifies. A liquid electrolyte characterized by having a temperature of less than -30 ° C.

(1)
[Wherein, R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrocarbon group having 1 to 20 carbon atoms or a hydrogen atom. ]

(2)
[Wherein R ¹ , R ² and R ³ each independently represent a hydrocarbon group having 1 to 20 carbon atoms, a hydrocarbon group having 1 to 20 carbon atoms having a hydroxyl group, or a hydrogen atom, One is a hydrocarbon group or a hydrocarbon group having a hydroxyl group. ]

(3)
[Wherein, R ¹ represents a hydrocarbon group having 1 to 20 carbon atoms or a hydrogen atom. ]
2. The liquid electrolyte according to claim 1, wherein the ionic conductivity at −30 ° C. is 10 ⁻⁶ Scm ⁻¹ or more. The liquid electrolyte according to claim 1 or 2 , wherein the ionic conductivity at 150 ° C is 10 ^-2 Scm ^-1 or more. The liquid electrolyte according to claim 1, wherein the liquid electrolyte is a proton conductor. Fuel cell, which comprises using a liquid electrolyte according to any one of claims 1 to 4.

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