JP3307891B2 - High heat-resistant polymer electrolyte and electrochemical device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high heat resistant polymer electrolyte and an electrochemical device using the same, and more particularly, to a fuel cell, a water electrolysis apparatus, a hydrohalic acid electrolysis apparatus, a salt electrolysis apparatus, and an oxygen electrolysis apparatus. The present invention relates to a high heat-resistant polymer electrolyte suitable as an electrolyte membrane used for a concentrator, a humidity sensor, a gas sensor, and the like, and an electrochemical device using the same.

[0002]

2. Description of the Related Art A solid polymer electrolyte is a solid polymer material having an electrolyte group such as a sulfonic acid group in a polymer chain.
Since it has the property of firmly binding to specific ions and selectively permeating cations or anions, it is formed into particles, fibers, or films and used for various purposes.

For example, in a polymer electrolyte fuel cell, a pair of electrodes is provided on both sides of an electrolyte membrane, a fuel gas containing hydrogen such as a reformed gas is supplied to one electrode (a fuel electrode), and oxygen such as air is supplied. Is supplied to the other electrode (air electrode),
This is a battery that directly extracts chemical energy generated when fuel is oxidized as electric energy. In a polymer electrolyte fuel cell, a polymer electrolyte membrane having proton conductivity is used as an electrolyte membrane.

The SPE electrolysis method is a method for producing hydrogen and oxygen by electrolyzing water. A solid polymer electrolyte membrane having proton conductivity is used as an electrolyte instead of a conventional alkaline aqueous solution. Have been.

As a solid polymer electrolyte used for such a purpose, for example, a non-crosslinked perfluoro-based electrolyte represented by Nafion (registered trademark, manufactured by DuPont) is known. Perfluoro-based electrolytes have very high chemical stability and have been used as electrolyte membranes used under severe conditions such as fuel cells and SPE electrolysis.

Also, US Pat. No. 5,741,408 discloses that
A crosslinked hydrocarbon obtained by introducing a sulfonyl halide group into an aromatic polyether ketone, reacting the introduced sulfonyl halide group with a UV effect type amine-based crosslinking agent, and then subjecting the amine-based crosslinking agent to a crosslinking reaction. A system electrolyte membrane is disclosed.

Further, the Journal of Fluorin
Chemistry (Journal of FluorineCemistry) Vol. 72 (1995) pp. 203-208, and Journal of Electrochemical Society (Journal of E)
electro-Chemical Society) Vol. 1 (1
(998) p. 107-109, as a new acid group,
Bis (perfluoroalkylsulfonyl) imide groups have been proposed, and various bis (perfluoroalkylsulfonyl) imide polymers and bis (perfluoroalkylsulfonyl) imide compounds exhibiting strong acidity have been reported. Japanese Patent Application Laid-Open No. 9-263637 discloses a polymer containing a sulfonylcarbonylimide anion at a high concentration.

[0008]

By the way, it is known that the power generation efficiency of a polymer electrolyte fuel cell increases as the operating temperature of the cell increases. In addition, the electrodes bonded to both surfaces of the solid polymer electrolyte contain a platinum-based electrode catalyst, but platinum is poisoned even with a trace amount of carbon monoxide, which lowers the output of the fuel cell. This can cause Moreover, it is known that the poisoning of the electrode catalyst by carbon monoxide becomes more significant at lower temperatures.

Therefore, in a polymer electrolyte fuel cell using a gas containing a trace amount of carbon monoxide, such as a methanol reformed gas, as a fuel gas, it is necessary to increase the efficiency and reduce the poisoning of the electrode catalyst by carbon monoxide. It is desired to increase the operating temperature.

In water electrolysis, the total energy required for electrolysis of water does not change much with temperature.
It is known that the minimum voltage required for water electrolysis, that is, the theoretical decomposition voltage, decreases as the temperature increases.
Therefore, if heat energy can be supplied to the system from the outside and the electrolysis reaction can be performed at a high temperature, consumption of expensive electric energy can be reduced, which is advantageous in terms of efficiency.

However, a perfluoro-based electrolyte typified by Nafion has a low heat resistance because it is non-crosslinked, and has a property of creeping at 130 ° C. or higher, which is near the glass transition temperature. Therefore, when a perfluoro-based electrolyte is used in a fuel cell or an SPE electrolyzer, the operating temperature must be 100 ° C. or less, which is advantageous in terms of preventing poisoning of the electrode catalyst by carbon monoxide and improving efficiency. There was a problem that it could not be used at high temperatures. In addition, since the perfluoro-based electrolyte is non-crosslinked, if the introduction amount of the electrolyte group is excessively increased in order to improve the conductivity, the perfluoro-based electrolyte swells or is solubilized remarkably in water, and the design flexibility of the membrane is greatly increased. Was limited to.

On the other hand, if the perfluoro-based electrolyte can be crosslinked, the flow of the polymer chains at a high temperature is suppressed, so that it is considered to be effective for the high-temperature creep resistance of the perfluoro-based electrolyte. Furthermore, even if the introduction amount of the electrolyte group of the membrane is increased by cross-linking, the membrane is not solubilized, and the degree of freedom in design such as improvement in conductivity is improved. However,
Perfluoro-based electrolytes, due to their structural chemical stability,
Crosslinking in the main chain is difficult.

On the other hand, the method disclosed in US Pat. No. 5,741,408 is diverted to provide a highly reactive electrolyte group or an electrolyte group precursor provided in a perfluoro-based electrolyte and an amine-based crosslinking agent. Is allowed to crosslink the perfluoro-based electrolyte. However, this method has a problem that the amount of electrolyte groups contained in the perfluoro-based electrolyte is reduced, and the conductivity is reduced.

Further, the cross-linked hydrocarbon electrolyte disclosed in US Pat. No. 5,741,408 itself has a hydrocarbon structure in a main part including a cross-linking agent.
It has no oxidation resistance at high temperatures and cannot be used at high temperatures as it is.

Further, Journal of Electrochemical Society, Vol. 1 (1998
On pages 107-109, a bis (perfluoroalkylsulfonyl) imide polymer having almost the same proton conductivity as Nafion was obtained by combining a bis (perfluoroalkylsulfonyl) imide group with a Nafion-like perfluoro skeleton. Has been reported to be However, since these compounds are all non-crosslinked compounds, they have a problem in heat resistance, like Nafion. There is no example in which such a functional group is applied to crosslinking of a perfluoro-based electrolyte.

The polymer (H ⁺ type) disclosed in Japanese Patent Application Laid-Open No. 9-263637 is basically soluble in water because it contains a strong acid group at a high concentration, and is basically used for fuel cells. The electrolyte cannot be used as it is before the heat resistance.

An object of the present invention is to provide a high heat-resistant polymer electrolyte having excellent heat resistance and oxidation resistance and high conductivity.

[0018]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a highly heat-resistant polymer electrolyte according to the present invention is characterized in that a perfluoropolymer compound is crosslinked via a strongly acidic crosslinking group. It is assumed that.

Here, the strongly acidic crosslinking group refers to a group in which the structure of the crosslinking point after crosslinking exhibits strong acidity in a state containing water. Examples of the cross-linking group having such properties include those having various structures. Preferred examples of the strongly acidic cross-linking group include bissulfonylimide, sulfonylcarbonylimide, biscarbonylimide, and bissulfonylmethylene. The crosslinking point is not particularly limited as long as it is at any position in the molecular chain of the perfluoropolymer compound.

In the high heat-resistant polymer electrolyte according to the present invention, since the perfluoropolymer compound is cross-linked through the strongly acidic cross-linking group, the flow of molecules at high temperatures is suppressed,
High temperature creep resistance can be greatly improved.

Further, since the crosslinking point itself is strongly acidic, even if the crosslinking density is increased, the conductivity of the electrolyte is not significantly reduced. Further, since the polymer chain is composed of a perfluoro-based, oxidation resistance at high temperatures does not matter.

For this reason, this can be used, for example, in a fuel cell or SPE
When used in an electrolysis apparatus, it can operate stably even under a high temperature condition of 130 ° C. or more, and the efficiency can be dramatically improved. Moreover, the voltage drop caused by the poisoning of the electrode catalyst by carbon monoxide, which is a problem in the methanol reforming fuel cell, can be significantly reduced by such a high-temperature operation.

[0023]

Embodiments of the present invention will be described below in detail. The highly heat-resistant polymer electrolyte according to the present invention includes a strongly acidic crosslinking group and a perfluoropolymer compound crosslinked via the strongly acidic crosslinking group.

Here, as described above, the strongly acidic cross-linking group refers to a group in which the structure of the cross-linking point after cross-linking exhibits strong acidity, and the functional group before cross-linking does not necessarily need to be strongly acidic. As the strong acidic crosslinking group for crosslinking the perfluoropolymer compound, specifically, bissulfonylimide (—SO ₂ —NH—SO ₂ —) is suitable.

The bissulfonylimide exhibits high proton conductivity equivalent to that of Nafion when combined with a perfluoro skeleton. This is because, by cross-linking a perfluoropolymer compound via bissulfonylimide, electrons contributing to the NH bond are pulled by F having a large electronegativity and move to the perfluoro skeleton side. This is because H bonded to a point is easily released as a proton.

Accordingly, the strongly acidic crosslinking group for crosslinking the perfluoropolymer is not limited to bissulfonylimide, and any crosslinking group having a structure that allows electrons to easily move from the crosslinking point can be used. Can also be a “strongly acidic crosslinking group” in the present invention.

Another preferred example of the strongly acidic crosslinking group is:
For example, bissulfonylmethylene (—SO ₂ —CH ₂ —
SO ₂ —), biscarbonylimide (—CO—NH—C
O-), sulfonylcarbonylimide (-CO-NH-
SO _2- ) and the like.

The structure of the perfluoropolymer compound constituting the main part of the high heat-resistant polymer electrolyte according to the present invention is as follows:
Although not particularly limited, a sulfonic acid group, a carboxylic acid group, a bissulfonylimide group, a perfluoro-based electrolyte polymer having a strongly acidic functional group such as a phosphonic acid group in a side chain, or a precursor or derivative thereof. Particularly preferred. Further, the polymer chain may have a linear or branched structure. The crosslinking point may be at any point in the molecular chain of the perfluoropolymer compound. That is, it may be cross-linked by the main chain or cross-linked by the side chain.

In the case of the present invention, a polymer electrolyte having excellent heat resistance can be obtained as the crosslink density increases. However, when the crosslink density is excessive, water content and movement of water molecules are hindered.
On the contrary, it tends to lower the proton conductivity. Therefore, the crosslink density may be selected to an optimum value according to the heat resistance, conductivity, and the like required for the high heat resistant polymer electrolyte.

The highly heat-resistant polymer electrolyte according to the present invention may be such that a perfluoropolymer compound is cross-linked through one kind of strongly acidic crosslinking group, or two or more kinds of strongly acidic crosslinking compounds are used. The perfluoropolymer compound may be crosslinked via a crosslinking group.

Next, a method for producing a high heat-resistant polymer electrolyte according to the present invention will be described. High heat-resistant polymer electrolyte according to the present invention, perfluoro-based polymer chains, directly,
Alternatively, it can be obtained by causing a crosslinking reaction via a crosslinking agent.

Therefore, the perfluoropolymer compound constituting the main part of the high heat-resistant polymer electrolyte includes any one of the molecular chains constituting the perfluoropolymer compound,
It is necessary to have a functional group that can react with a cross-linking agent to become a strongly acidic cross-linking group (hereinafter, this is referred to as “functional group A”).

As the functional group A provided in the perfluoropolymer compound, specifically, a sulfonyl halide group, a carbonyl halide group, a carboxylic acid ester group, etc.
And their derivatives are preferred examples. In particular, even when the sulfonyl halide group is not consumed for cross-linking, it can easily become a strong acid group by hydrolyzing it and impart high conductivity to the electrolyte. is there.

Specific examples of the perfluoropolymer having the functional group A include tetrafluoroethylene and perfluoro (4-methyl-3,6-
Copolymer of dioxaoct-7-ene) sulfonyl fluoride, tetrafluoroethylene and perfluoro (3
-Oxa-penta-4-ene) sulfonyl fluoride, copolymer of tetrafluoroethylene and perfluoro (4-oxahex-5-ene) sulfonyl fluoride, tetrafluoroethylene and perfluoro (4 -Oxa-5 hexenoyl chloride), and derivatives thereof.

The concentration of the functional group A provided in the perfluoropolymer compound is not particularly limited, and may be optimally selected according to the heat resistance, conductivity and the like required for the high heat resistant polymer electrolyte. Compounds having different concentrations may be used. In general, the higher the concentration of the functional group A, the wider the control range of the crosslink density. Therefore, there is an advantage that various polymer electrolytes having different heat resistance and / or conductivity can be obtained. On the other hand, if the concentration of the functional group A is too low, the crosslink density decreases, and the heat resistance becomes insufficient. Specifically, the concentration of the functional group A is 4 × 10 ⁻³ mol / g.
１1 × 10 ⁻⁶ mol / g, preferably 2 × 10 ⁻³ m
ol / g to 1 × 10 ⁻⁵ mol / g.

The perfluoropolymer compound before cross-linking may contain one type of functional group A, or may contain two or more types of functional groups A. Further, a single perfluoropolymer compound having one or more functional groups A may be crosslinked, or
Two or more kinds of perfluoropolymer compounds having the same or different functional groups A may be mixed at an arbitrary ratio and crosslinked.

Next, the crosslinking agent will be described. The cross-linking agent includes two or more functional groups capable of reacting with and cross-linking with the functional group A of the perfluoropolymer compound in one molecule, and at least one of them has a strong acidic property. It is necessary to use a functional group comprising a functional group that can be a cross-linking group (hereinafter, this is referred to as “functional group B”). In particular,
A compound having two or more functional groups B as described above in one molecule is suitable as a crosslinking agent.

As the functional group B provided in the crosslinking agent,
Physically, a sulfonamide group (NH ₂-SO₂−),
Ruphonyl (N-trimethylsilyl) imide sodium salt
((CH₃)₃Si-N (Na) -SO₂−), Amide
Group (NH₂-CO-) and the like, and their derivatives are preferred.
An example is given. However, sulfonyl (N-trime
Tylsilyl) imide sodium salt
Alkali metals, alkaline earth metals, hydrogen
But it is good.

Specific examples of the crosslinking agent having such a functional group B include perfluoro-1,4-disulfonamidobutane, and its N-trimethylsilylated sodium salt and perfluoro-1 , 4-diamidobutane, ammonia, lithium bis (trimethylsilyl) amide, and the like, and derivatives thereof, are mentioned as preferable examples. Of course, when a perfluoroalkylene group is present in the cross-linking agent, the number of carbons n may be any number as long as n ≧ 1, and there may be a branch or the like in the middle. Further, the crosslinking agent may be a polymer compound having a functional group B in a side chain. Note that substantially the same effect can be obtained even when the perfluoropolymer compound has the functional group B described above and the crosslinking agent has the functional group A.

The crosslinking agent may contain one kind of functional group B as described above, or may contain two or more kinds of functional groups B. Also, a single compound having one or more functional groups B may be used as a crosslinking agent, or two or more compounds having the same or different functional groups B may be mixed at an arbitrary ratio. However, this may be used as a crosslinking agent.

The above-mentioned perfluoropolymer compound having a functional group A is used, a suitable crosslinking agent having a functional group B is added thereto, and a crosslinking reaction is carried out using a conventional method. Depending on the combination of the functional group B and the functional group B, a highly heat-resistant polymer electrolyte crosslinked with a strongly acidic crosslinking group having various structures can be obtained. An example of the structure of a strongly acidic crosslinking group obtained by performing a crosslinking reaction between a perfluoropolymer compound having a functional group A and a crosslinking agent having a functional group B is shown in the following chemical formula 1.
The formulas are shown below.

[0042]

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The cross-linking structure represented by the chemical formula 1 is composed of a perfluoro-type cross-linking agent having a sulfonamide group or its trimethylsilylated sodium salt at both ends of a molecule, and a perfluoro-type cross-linking agent having a sulfonyl halide group in any of the molecular chains. It is obtained by a crosslinking reaction with a polymer compound. The two cross-linking points are each a bisulfonylimide (—SO ₂ —NH—SO ₂
-).

[0044]

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The cross-linking structure represented by the chemical formula 2 is composed of a perfluoro-type cross-linking agent having a sulfonylmethylene lithium group at both ends of the molecule and a perfluoro-type polymer compound having a sulfonyl halide group in any of the molecular chains. Are obtained by a cross-linking reaction of Each of the two crosslinking points is a bisulfonylmethylene (—SO ₂ —CH ₂ —SO ₂ —) that is a strongly acidic crosslinking group.

[0046]

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The cross-linking structure represented by the formula (3) is composed of a perfluoro-type cross-linking agent having a carbonylamide group at both ends of the molecule and a perfluoro-type polymer compound having a carbonyl halide group at any one of the molecular chains. Is obtained by a crosslinking reaction of The two cross-linking points are, respectively, bisphenol imide (-CO
-NH-CO-).

[0048]

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Further, the cross-linked structure represented by the chemical formula (4) is composed of a perfluoro-based cross-linking agent having a sulfonamide group or its trimethylsilylated sodium salt at both ends of the molecule, and a perfluoro-cross-linking agent having a carbonyl halide group in any of the molecular chains. It is obtained by performing a crosslinking reaction with a fluoropolymer compound. The two cross-linking points are, respectively, sulfonylcarbonylimide (-CO-
NH-SO ₂ - has become).

Further, an example of the structure of a strongly acidic crosslinking group obtained by performing a crosslinking reaction between a perfluoropolymer compound having a functional group A and a perfluoropolymer compound having a functional group B is shown below. Are shown in the formulas of Chemical Formulas 5 to 8.

[0051]

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The cross-linking structure represented by the formula (5) has a structure in which a perfluoropolymer compound having a sulfonyl halide group in any of the molecular chains and a sulfonamide group or its trimethylsilylated sodium salt in any of the molecular chains. It is obtained by performing a cross-linking reaction with a perfluoropolymer compound. The two polymer compounds are 1
It is cross-linked at two cross-linking points, and the cross-linking point is a strong acid cross-linking group, bissulfonylimide (—SO ₂ —NH—SO ₂
-).

[0053]

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The crosslinked structure represented by the chemical formula (6) has a molecular chain
Having a sulfonyl halide group in any of the above
Oro-based polymer compound and sulfonium
Perfluoropolymer with lmethylene lithium group
Obtained by a crosslinking reaction with the compound
You. Two polymer compounds are crosslinked at one crosslinking point
The cross-linking point is based on bisulfonylmeth
Tylene (-SO₂-CH ₂-SO₂-).

[0055]

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Further, the crosslinked structure represented by the chemical formula (1) has a perfluoropolymer compound having an amide group in one of the molecular chains and a perfluoropolymer compound having a carbonyl halide group in one of the molecular chains. It is obtained by a crosslinking reaction with a molecular compound. The two polymer compounds are cross-linked at one cross-linking point, and the cross-linking point is a strong acid cross-linking group, biscarbonylimide (—CO—NH—C
O-).

[0057]

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Further, the cross-linking structure represented by the chemical formula (1) is composed of a perfluoropolymer compound having a carbonyl halide group at any point in the molecular chain and a sulfonamide group or a sodium trimethylsilyl salt thereof at any point in the molecular chain. It is obtained by performing a crosslinking reaction with a perfluoropolymer compound having a salt. The two polymer compounds are cross-linked at one cross-linking point, and the cross-linking point is a sulfonylcarbonylimide (—CO—
NH-SO ₂ - has become). In this case, depending on the combination of the reactions, the cross-linking group shown in the formulas (7) and (5) may be generated.

The cross-linked structures of the formulas (5), (7) and (8) are formed by combining a perfluoropolymer compound having a carbonyl halide or a sulfonyl halide with ammonia or bis (trimethylsilyl) amide lithium. It may be formed by reacting with a metal salt.

Any of these strongly acidic cross-linking groups can provide an electrolyte having high heat resistance, which is the object of the present invention. Among them, bissulfonylimide groups are particularly excellent in terms of heat stability. .

The molar ratio of the functional group B in the crosslinking agent to the functional group A of the perfluoropolymer compound may be selected according to the heat resistance and conductivity required for the electrolyte. Generally, (moles of functional group B) / (moles of functional group A) is
0.00001 to 1.0, and more preferably,
0.00005 to 0.8, more preferably 0.000
1 to 0.5. Here, if the molar ratio is too small, crosslinking is insufficient and heat resistance cannot be imparted. On the other hand, if the molar ratio is too large, the crosslinking may proceed too much, and the water content may decrease, or the movement of water may be hindered, resulting in a decrease in conductivity.

Next, the operation of the high heat-resistant polymer electrolyte according to the present invention will be described. In the high heat-resistant polymer electrolyte according to the present invention, since the perfluoropolymer compound is cross-linked through the strongly acidic cross-linking group, even when this is used at a high temperature equal to or higher than the glass transition temperature, the high heat resistance is high. The flow of molecular chains is suppressed. Therefore, the high-temperature creep resistance is improved as compared with a non-crosslinked type perfluoropolymer electrolyte.

In the case of a non-crosslinked perfluoro-based electrolyte, if the concentration of the electrolyte group is excessively large, the electrolyte may swell remarkably in water, the electrolyte may gel, and may be further solubilized in water. Since the high heat-resistant polymer electrolyte according to the above has a crosslinked structure, the electrolyte is hardly gelled or solubilized even when the concentration of the electrolyte group is increased. Therefore, there is an advantage that the concentration of the electrolyte group can be increased and an electrolyte having high conductivity can be obtained as compared with a non-crosslinked perfluoro-based electrolyte.

Further, when the functional group A in the perfluoropolymer compound to be subjected to the crosslinking reaction is also an electrolyte group of the perfluoropolymer compound, or a precursor or derivative thereof, the perfluoropolymer compound may be used. 1 in polymer compound
Each time a crosslinked structure is formed, 2
Functional groups A are consumed. Therefore, US Pat.
In the conventional crosslinking method as disclosed in No. 41408, as the crosslinking density increases, the amount of electrolyte groups in the polymer decreases, which causes a decrease in the conductivity of the obtained polymer compound.

However, since the highly heat-resistant polymer electrolyte according to the present invention becomes a strongly acidic cross-linking group in which the cross-linking point exhibits strong acidity, even if the cross-linking density is increased, the electro-conductivity is higher than that of the conventional cross-linking method. There is little decrease in the rate.

In particular, when cross-linking is performed using a cross-linking agent having two or more functional groups B in the molecule, two strongly acidic cross-linking groups can be introduced into the polymer compound by the cross-linking.
The functional group A consumed in the crosslinking reaction can be supplemented with a strongly acidic crosslinking group. Therefore, even if the crosslink density is increased, the conductivity can be maintained at a value equal to or close to that of the non-crosslinkable perfluoropolymer electrolyte.

Moreover, since the main part of the high heat-resistant polymer electrolyte according to the present invention is composed of a perfluoropolymer compound, there is no problem in oxidation resistance at high temperatures.

[0068]

EXAMPLES (Example 1) First, a crosslinking agent was synthesized according to the following procedure. First, as a raw material of a crosslinking agent, perfluoro-1, which has a sulfonyl fluoride group at both terminals,
4-Disulfonyl fluoride butane was used. The chemical formula of perfluoro-1,4-disulfonyl fluoride butane is shown in the following formula (n is 4).

[0069]

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Next, perfluoro-1,
4-Disulfonyl fluoride butane was sulfonamidated at -78 degrees in excess liquid ammonia. Next, after returning to room temperature and removing ammonia, hydrogen chloride gas was allowed to act to synthesize perfluoro-1,4-disulfonamidobutane having a sulfonamide group at both terminals. The chemical formula of the obtained perfluoro-1,4-disulfonamidobutane is shown in the following chemical formula 10.

[0071]

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Next, a sulfonamide compound represented by the formula (10) was dissolved in methanol, and an equivalent amount of sodium methoxide was allowed to act on the solution to synthesize a sulfonamide sodium salt. The chemical formula of the obtained sulfonamide sodium salt is
It is shown in the following formula.

[0073]

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Further, a 1.2-fold amount of hexamethyldisilazane in acetonitrile was allowed to act on sodium sulfonamide represented by the formula (11) at the reflux temperature to synthesize a desired crosslinking agent. The chemical formula of the obtained crosslinking agent is shown in the following chemical formula 12.

[0075]

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Next, a crosslinking reaction was carried out according to the following procedure. A perfluoro-based sulfonyl fluoride film (hereinafter, referred to as a “PFSF film”), which is an electrolyte precursor before hydrolysis, was used as a perfluoro-based polymer compound as a raw material of the high heat-resistant polymer electrolyte. The concentration of sulfonyl fluoride groups in this PFSF membrane (mol / g of polymer)
Number) is 9.07 × 10 ⁻⁴ mol / g, and the film thickness is 50 μm.
It is. The chemical formula of the PFSF film used for the crosslinking reaction is shown in the following formula.

[0077]

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First, 10 mol% based on the sulfonyl fluoride group contained in the PFSF film represented by the formula (13)
(20 mol% based on the functional group in the crosslinking agent) was dissolved in acetonitrile. Next, the PFSF film was immersed in acetonitrile in which a cross-linking agent was dissolved, and heated as it was for 20 hours to form a cross-linked film.

Next, the obtained crosslinked film was hydrolyzed by heating at 90 ° C. with a 25% aqueous sodium hydroxide solution to convert the remaining sulfonyl fluoride groups into sodium sulfonate groups. Further, a 1-hour aqueous sulfuric acid solution is refluxed twice for 1 hour to convert it into a proton type, whereby a polymer electrolyte membrane cross-linked by a strongly acidic cross-linking group (hereinafter, referred to as a polymer electrolyte membrane)
This is referred to as a “strongly acidic crosslinked electrolyte membrane”). The chemical formula of the obtained strongly acidic crosslinked electrolyte membrane is shown in the following chemical formula 14.

[0080]

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Formula 14 schematically shows a state in which p of n side chains polymerized on the main chain of tetrafluoroethylene are consumed for crosslinking. In the chemical formula (14), the parts shown by wavy lines schematically indicate perfluoropolymer chains having the same structure as that of the chemical formula (13).

Example 2 1 mol% of a crosslinking agent (2 mol% based on a functional group) based on a sulfonyl fluoride group
%), And a strongly acidic crosslinked electrolyte membrane was prepared according to the same procedure as in Example 1.

Example 3 20 mol% of a crosslinking agent based on a sulfonyl fluoride group (40 mol% based on a functional group)
1%), but following the same procedure as in Example 1,
A strongly acidic crosslinked electrolyte membrane was prepared.

Example 4 A strongly acidic crosslinked electrolyte membrane was prepared according to the same procedure as in Example 1 except that a PFSF membrane having a sulfonyl fluoride group concentration of 1.25 × 10 ⁻³ mol / g was used. Produced.

Example 5 (CH ₃ ) ₃ was used as a crosslinking agent.
Except for using 10mol% Si-N (Na) -Si a _{(CH 3) 3} with respect to the sulfonyl fluoride group in accordance with the procedure as in Example 3, to prepare a strongly acidic crosslinking electrolyte membrane.

Comparative Example 1 PFSF film (provided that the concentration of sulfonyl fluoride group: 9.07 × 10 ⁻⁴ mol /
g, film thickness: 50 μm) were hydrolyzed by heating at 90 ° C. with a 25% aqueous sodium hydroxide solution without cross-linking to convert the sulfonyl fluoride group to a sodium sulfonate group. In addition, 1N aqueous sulfuric acid
The non-crosslinked electrolyte membrane (hereinafter, referred to as “non-crosslinked electrolyte membrane”) was obtained by repeating the refluxing treatment twice for two hours to convert to proton type.

Comparative Example 2 US Pat. No. 5,741,087
A perfluoro-based crosslinked membrane was prepared using a method similar to the crosslinking method disclosed in the above-mentioned publication. That is, a PFSF film (provided that the concentration of sulfonyl fluoride group: 9.07 × 10
^-4 mol / g, film thickness: 50 μm) was reacted with p-aminocinamic ester (20 mol% based on the sulfonyl fluoride group).

Thereafter, the obtained film is irradiated with UV,
The p-aminocinamic ester was crosslinked to form a crosslinked film. Next, the obtained crosslinked film was hydrolyzed by heating at 90 ° C. with a 25% aqueous sodium hydroxide solution to convert a sulfonyl fluoride group into a sodium sulfonate group. Further, a 1-hour aqueous sulfuric acid solution is refluxed twice for 1 hour to convert it into a proton type polymer, whereby a polymer electrolyte membrane cross-linked with a non-strongly acidic cross-linking group (hereinafter referred to as a “non-strongly acid cross-linked electrolyte membrane”) ).

Comparative Example 3 A non-strongly acidic crosslinked electrolyte membrane was prepared according to the same procedure as in Comparative Example 2, except that 2 mol% of p-aminocinnamic ester was used based on the sulfonyl fluoride group.

Comparative Example 4 A non-strongly acidic crosslinked electrolyte membrane was prepared in the same manner as in Comparative Example 2, except that 40 mol% of p-aminocinnamic ester was used based on the sulfonyl fluoride group.

Comparative Example 5 A non-crosslinked electrolyte membrane was prepared according to the same procedure as in Comparative Example 1, except that a PFSF membrane having a sulfonyl fluoride group concentration of 1.25 × 10 ⁻³ mol / g was used. did.

Comparative Example 6 According to Example 1 in JP-A-9-263637, (-SO ₂ CF ₂ CONLi
-) synthesizing a polymer having a unit, further ion-exchanged with 1M sulfuric _{acid, (- SO 2 CF 2 CONH-} ) type to obtain a polymer, was investigated solubility in water.

The strongly acidic crosslinked electrolyte membranes obtained in Examples 1 to 5, the non-crosslinked electrolyte membranes obtained in Comparative Examples 1 and 5, and the non-strongly acidic crosslinked electrolyte membranes obtained in Comparative Examples 2 to 4 An equivalent weight representing the weight of the polymer per equivalent of acid,
The conductivity of the film and the creep resistance at 200 ° C. were evaluated. Further, with respect to Comparative Example 6, its solubility in water was examined. In addition, the measuring method of equivalent weight and electric conductivity, and the creep test method are as follows.

Measurement of equivalent weight: First, the obtained membrane was
The film was vacuum-dried at 0 ° C. overnight, and the dry weight (W _dry ) of the film was measured. Next, the dried film was immersed in a 1N HCl aqueous solution at 50 ° C. for about 10 minutes, washed with ion-exchanged water, and then immersed in a 2N NaCl aqueous solution at 50 ° C. for about 10 minutes. Further, the amount of hydrogen ions released into the NaCl aqueous solution was subjected to neutralization titration using a 1N NaOH aqueous solution, and the equivalent weight of the membrane was determined by the following equation (1). The neutralization titration was performed using an automatic MTCl titrator GT-05.

[0095]

( _Equivalent weight) = W _dry / f × N × V where W _dry : dry weight of membrane (g) f: factor of NaOH aqueous solution N: normality of NaOH aqueous solution (N) V: neutralization Required volume of NaOH aqueous solution (l)

Measurement of electric conductivity: The obtained film was immersed in pure water as a pretreatment, and was swelled to a width of 1 cm × length of 1.2 c.
m and cut into a two-terminal conductivity measurement cell.
Note that platinum black plated platinum foil was used for the current / voltage terminals of the cell to improve the contact with the film.

Next, this cell was immersed in pure water at 25 ° C., and an LCR meter (4262A LCR M made by YHP) was used.
ETER), AC method (measuring frequency 10kHz)
The film resistance is obtained by the following equation, and the conductivity (σ) is obtained by the following equation (2).
I asked. In addition, the value measured with the micrometer after the conductivity measurement was used for the film thickness.

[0098]

## EQU2 ## where σ: electric conductivity (S / cm) R: resistance (Ω) l: distance between voltage terminals (= 1) A: film Cross section (cm ² ) t: Film thickness (cm) w: Film width (cm)

Creep resistance test at 200 ° C .: A weight was hung on the film so that the load became 100 ton / m ² , and the film was exposed to an atmosphere at 200 ° C., and the film was stretched to a length of 2 tons.
The doubling time was measured.

Measurements were made on the strongly acidic crosslinked electrolyte membrane obtained in Examples 1 to 5, the non-crosslinked electrolyte membrane obtained in Comparative Examples 1 and 5, and the non-strongly acidic crosslinked electrolyte membrane obtained in Comparative Examples 2 to 4. Table 1 shows the obtained equivalent weight and conductivity, and the results of the creep resistance test at 200 ° C.

[0101]

[Table 1]

The non-crosslinked electrolyte membrane of Comparative Example 1 obtained by simply hydrolyzing the PFSF membrane has an equivalent weight of 11
00 (g / eq), the conductivity is 0.078 S
/ Cm. However, since it was not cross-linked, it was inferior in high-temperature creep resistance and creeped easily within 10 minutes.

On the other hand, the non-strongly acidic crosslinked electrolyte membranes obtained in Comparative Examples 2 to 4 were obtained in Comparative Example 1 because the perfluoropolymer chains were crosslinked via the non-strongly acidic crosslinking groups. The high temperature creep resistance was significantly improved as compared with the non-crosslinked electrolyte membrane. In particular, when the amount of the cross-linking group introduced was 20 mol% or more per sulfonyl halide group, the time required for the film length to double at 200 ° C. exceeded 24 hours.

However, since the crosslinking group was not strongly acidic, the equivalent weight increased remarkably with an increase in the amount of the crosslinking group introduced. In addition, the conductivity was also greatly reduced, and when the amount of the cross-linking group introduced exceeded 20 mol% per sulfonyl halide group, the conductivity was less than half that of the non-cross-linked electrolyte membrane obtained in Comparative Example 1.

On the other hand, in the strongly acidic crosslinked electrolyte membranes obtained in Examples 1 to 3, since the crosslinking point was a strongly acidic crosslinking group, the equivalent weight of Comparative Example 1 was maintained even when crosslinking was introduced. There is no change compared to the obtained non-crosslinked electrolyte membrane, and the conductivity is 0.06.
High values of 9-0.077 S / cm were maintained.

Further, since the polymer chains are cross-linked via the strongly acidic cross-linking group, the high-temperature creep resistance was greatly improved as compared with the non-cross-linked electrolyte membrane. In particular, when the amount of the cross-linking group introduced is 20 mol% or more per sulfonyl halide group, the time required for the film length to double at 200 ° C. is 24 hours.
Time exceeded.

Further, (CH ₃ ) ₃ Si—N is used as a crosslinking agent.
In the strongly acidic crosslinked electrolyte membrane of Example 5 using (Na) —Si (CH ₃ ) ₃ , the equivalent weight is lower than that of Example 3 because the polymer chains are crosslinked at one crosslinking point. It increased slightly to reach 1220 (g / eq). However, since the crosslinking point exhibited a strong acidity, the decrease in conductivity was slight, and good high-temperature creep resistance was exhibited.

Further, the non-crosslinked electrolyte membrane of Comparative Example 5 using a PFSF membrane having a sulfonyl fluoride group concentration of 1.25 × 10 ⁻³ mol / g has a small equivalent weight,
Since the solubility in water was remarkably increased, the film swelled violently during the hydrolysis and became a gel. Therefore, the basic strength of the film could not be maintained, and the electrical conductivity and high-temperature creep resistance could not be evaluated. Similarly, the polymer of Comparative Example 6 was dissolved in water and could not be evaluated any more.

On the other hand, a PFSF membrane having a sulfonyl fluoride group concentration of 1.25 × 10 ⁻³ mol / g was used, and 20 mol% per sulfonyl fluoride group was used.
In the strongly acidic crosslinked electrolyte membrane of Example 4 in which the strong acidic crosslinking group was introduced, despite the small equivalent weight, the membrane shape could be maintained by the crosslinking effect, and high conductivity and high temperature creep resistance were high. Sex was maintained.

From the above results, when the perfluoropolymer compound is cross-linked via a strongly acidic cross-linking group such as bissulfonylimide, the heat resistance,
It was found that a polymer electrolyte having excellent oxidation resistance was obtained.

Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. is there.

For example, in the above embodiment, a perfluoropolymer compound is used as the polymer compound constituting the main part of the polymer electrolyte, but a polymer having a hydrocarbon part in a part of the molecular chain is used. A compound such as a graft copolymer having ethylene tetrafluoroethylene as a main chain may be used as a polymer compound, and the polymer may be crosslinked via a strongly acidic crosslinking group.

In the above embodiment, the perfluoropolymer compound is crosslinked using a linear crosslinker having a sulfonamide group at both ends of the molecule and having a perfluoroskeleton at the center. However, a cross-linking agent having a molecular structure exhibiting a strong acidity, such as one or more bissulfonylimides, may be used in the center of the molecule.

Further, in the embodiment of the present invention, even if the concentration of the electrolyte group is extremely increased in order to improve the conductivity, the film shape is not gelled or solubilized in water due to the crosslinked structure. As a result, the degree of freedom in design was greatly improved.

As described above, applications of the high heat-resistant polymer electrolyte according to the present invention are not limited to fuel cells or SPE electrolyzers, but include hydrohalic acid electrolyzers, salt electrolyzers, and oxygen concentrators. It can also be used as an electrolyte used in various electrochemical devices such as a humidity sensor, a gas sensor, etc., whereby the same effect as in the above embodiment can be obtained.

[0116]

According to the high heat-resistant solid polymer electrolyte of the present invention, the perfluoropolymer compound is cross-linked through the strongly acidic cross-linking group, so that the flow of the polymer chain at high temperatures is suppressed, This has the effect of improving high temperature creep resistance.

Further, since the crosslinking point itself is strongly acidic, there is an effect that even if the crosslinking density is increased, the conductivity of the electrolyte is not reduced. In particular, when bissulfonylimide or the like is used as the strongly acidic crosslinking group, there is an effect that an electrolyte having high conductivity and high-temperature creep resistance can be obtained by combining it with a perfluoro skeleton.

Furthermore, since the polymer chain is composed of a perfluoro-based polymer, there is an effect that a high heat-resistant polymer electrolyte having excellent oxidation resistance at high temperatures can be obtained.

As described above, the high heat-resistant polymer electrolyte according to the present invention is excellent in heat resistance, oxidation resistance, and conductivity. Therefore, when the polymer electrolyte is applied to, for example, an in-vehicle fuel cell or an SPE electrolyzer, The present invention contributes to improvement of fuel efficiency and efficiency, and is an invention having an extremely large industrial effect.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-51-64495 (JP, A) JP-A-50-108182 (JP, A) JP-A-7-213848 (JP, A) JP-A 8- 296075 (JP, A) JP-A-10-40737 (JP, A) JP-A-2000-48834 (JP, A) JP-A-8-512358 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ H01B 1/06 H01B 1/12 C25B 13/08 304 G01N 27/58 H01M 8/02

Claims (19)

(57) [Claims] (1) bissulfonylimide, sulfonylcar
Bonylimide, biscarbonylimide, bissulfonyl
A highly heat-resistant polymer electrolyte, wherein a perfluoropolymer compound is crosslinked via at least one crosslinking group selected from methylene . 2. A sulfonyl halide group, a carbonylhala
And carboxylic acid ester groups and their derivatives
Before having at least one functional group A selected from conductors
Sulfonamido for the perfluoropolymer compound
Group, sulfonyl (N-trimethylsilyl) imido alka
Limetal salt, sulfonyl (N-trimethylsilyl) imidoa
Alkaline earth metal salts, sulfonyl (N-trimethylsilyl)
I) imide group, amide group, and derivatives thereof
Crosslinking agent having at least one functional group B selected from
The ratio of (the number of moles of the functional group B) / (the number of moles of the functional group A) is 0.
Introduced so that it becomes 00001 or more and 1.0 or less, By reacting the functional group A with the functional group B
The highly heat-resistant polymer electrolyte according to claim 1, which is obtained. 3. The cross-linking agent is a perfluoroalkylene.
The functional group B is any of the groups (the number of carbons n is n ≧ 1)
3. The high heat-resistant component according to claim 2, which is bonded.
Child electrolyte. 4. A sulfonyl halide group, carbonylhala
And carboxylic acid ester groups and their derivatives
Before having at least one functional group A selected from conductors
A functional group B for the perfluoropolymer compound
A perfluoro-1,4-disulfo
Amidobutane, perfluoro-1,4-disulfone
N-trimethylsilylated sodium of midbutane
Salt, perfluoro-1,4-diamidobutane, ammonium
A and lithium bis (trimethylsilyl) amide
And at least one type of frame selected from these derivatives
When the ratio of the number of moles of the functional group B to the number of moles of the functional group A is
Introduced to be 0.00001 or more and 1.0 or less, By reacting the functional group A with the functional group B
The highly heat-resistant polymer electrolyte according to claim 1, which is obtained. 5. A sulfonamide group, sulfonyl (N-to
Limethylsilyl) imide alkali metal salt, sulfonyl (N
-Trimethylsilyl) imide alkaline earth metal salts, sulf
Honyl (N-trimethylsilyl) imide group and amide
Group and at least one selected from these derivatives
To the perfluoropolymer compound having a functional group A of
On the other hand, sulfonyl halide group, carbonyl halide
Group, and carboxylic acid ester group, and derivatives thereof
Crosslinking agent having at least one functional group B selected from
The ratio of (the number of moles of the functional group B) / (the number of moles of the functional group A) is 0.
Introduced so that it becomes 00001 or more and 1.0 or less, By reacting the functional group A with the functional group B
The highly heat-resistant polymer electrolyte according to claim 1, which is obtained. 6. The (moles of the functional group B) / (the number of the functional groups A)
(Molar number) ratio is 0.00005 or more and 0.8 or less.
6. The high heat-resistant polymer electrolyte according to any one of claims 2 to 5.
Decomposition. 7. The (mol number of functional group B) / (molar number of functional group A)
Mole) ratio is 0.0001 or more and 0.5 or less
Item 6. High heat-resistant polymer electrolyte according to any one of Items 2 to 5
quality. 8. In the perfluoropolymer compound,
The concentration of the functional group A is 1 × 10 ^-6 mol / g or more 4 ×
10 ^-3 8. The method according to claim 2, wherein the amount is not more than mol / g.
Highly heat-resistant polymer electrolyte as described in any of the above. 9. A method according to claim 1, wherein said perfluoropolymer compound is
The concentration of the functional group A is 1 × 10 ^-5 2 x over mol / g
10 ^-3 8. The method according to claim 2, wherein the amount is not more than mol / g.
Highly heat-resistant polymer electrolyte as described in any of the above. 10. The electric conductivity is 0.062 S / cm or less.
10. High heat resistance according to any one of claims 1 to 9 above.
Polymer electrolyte. 11. 100 ton / m at 200 ° C. ²
When the load is applied, the time for doubling the film length is 20
The method according to any one of claims 1 to 10, wherein the time is longer than an hour.
High heat-resistant polymer electrolyte. 12. An electrochemical device using the high heat-resistant polymer electrolyte according to any one of claims 1 to 11 . 13. A fuel cell using the high heat-resistant polymer electrolyte according to any one of claims 1 to 11 . 14. A water electrolysis device using the high heat-resistant polymer electrolyte according to claim 1. 15. A hydrohalic acid electrolysis apparatus using the high heat-resistant polymer electrolyte according to claim 1 . 16. A salt electrolysis apparatus using the high heat-resistant polymer electrolyte according to any one of claims 1 to 11 . 17. An oxygen concentrator using the high heat-resistant polymer electrolyte according to any one of claims 1 to 11 . 18. A humidity sensor using the high heat-resistant polymer electrolyte according to any one of claims 1 to 11 . 19. A gas sensor using the high heat-resistant polymer electrolyte according to any one of claims 1 to 11 .