JP2001319521A - Method of reforming electrolyte and reformed electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of reforming a polymer electrolyte for granting high heat resistance and durability thereto while maintaining conductivity, and the reformed electrolyte. SOLUTION: The method of reforming the electrolyte comprises putting an amine compound in contact with a perfluoro-polymer electrolyte or its precursor to give amine treatment thereto. Preferably, after amine treatment, either heat treatment of heating the perfluoro-polymer electrolyte or its precursor or base treatment of putting a base in contact with the perfluoro-polymer electrolyte or its precursor is performed. Further preferably, after amine treatment, base treatment is followed by heat treatment. The suitable used amine compound is ammonia. The reformed electrolyte in this way can be improved in heat resistance and durability while maintaining conductivity. Softening or deformation at a high temperature is inhibited and creeping in long-time use is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for reforming an electrolyte and a reforming electrolyte, and more particularly, to a fuel cell, water electrolysis, hydrohalic acid electrolysis, salt electrolysis, oxygen concentrator, humidity sensor, gas sensor and the like. The present invention relates to a method for modifying a polymer electrolyte for modifying a polymer electrolyte used in the present invention and a modified electrolyte.

[0002]

2. Description of the Related Art Conventionally, a solid polymer electrolyte has been known as a polymer electrolyte. This solid polymer electrolyte is a solid polymer material having an electrolyte group such as a sulfonic acid group or a carboxylic acid group in a polymer chain, and firmly binds to a specific ion or selectively forms a cation or an anion. Since it has the property of penetrating into water, it is formed into particles, fibers, or membranes, and is used in various applications such as electrodialysis, diffusion dialysis, and battery diaphragms.

Under these circumstances, for example, a solid polymer electrolyte membrane formed by forming a solid polymer electrolyte into a film shape is used for a polymer electrolyte fuel cell, a water electrolysis cell and the like. A polymer electrolyte fuel cell is provided with a pair of electrodes on both sides of an electrolyte membrane, supplies a fuel gas containing hydrogen such as a reformed gas to one electrode (a fuel electrode), and an oxidant gas containing oxygen such as air. Is supplied to the other electrode (air electrode), and the chemical energy generated when the fuel is oxidized is directly extracted as electric energy.

Water electrolysis is an electrolysis method for producing hydrogen and oxygen by electrolyzing water, and an SPE electrolysis method and the like are known. What is SPE? Solid Polymer
Electrolyte (Solid Polymer Electrolyte)
As the electrolyte, a solid polymer electrolyte membrane having proton conductivity is used instead of the conventional alkaline aqueous solution.

[0005] As a solid polymer electrolyte membrane used in such applications, for example, a perfluorocarbon sulfonic acid membrane represented by Nafion (registered trademark, manufactured by DuPont) is known. The shape of the perfluorocarbon sulfonic acid membrane is maintained by the perfluoroalkylene chain, but since it is not cross-linked, the electrolyte groups in the side chains have a relatively high degree of freedom of molecular motion, and are inherently hydrophobic when ionized. A strong main chain portion and a hydrophilic electrolyte group coexist, and the electrolyte groups associate in a fluorocarbon matrix to form an ion cluster.

The perfluoropolymer electrolyte membrane having such a structure has been recognized as an electrolyte membrane used under severe conditions because of its extremely high chemical stability and excellent durability. It is.

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

[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 natural gas or methanol reformed gas, as a fuel gas, in order to avoid carbon monoxide poisoning, a temperature of 100 ° C. or more is required. It is desired to operate under high temperature conditions.

[0010] In water electrolysis, electric energy is consumed to produce hydrogen and oxygen, and thus it is desired to use electric energy effectively. It is known that the minimum voltage required for electrolysis of water, that is, the theoretical decomposition voltage, decreases as the temperature increases, and therefore, if electrolysis is performed at a high temperature, the power required for electrolysis is reduced, and efficiency is reduced. Is advantageous.

However, a perfluoropolymer electrolyte membrane typified by Nafion has a low heat resistance because it is non-crosslinked, and the molecular motion in the membrane becomes easy at a temperature of 120 ° C. or higher, which is near the glass transition temperature. However, there is a problem in use as an electrolyte membrane at a high temperature and for a long period of time, such as a change in temperature and creep of the membrane.

For this reason, when a perfluoropolymer electrolyte is used in a fuel cell or an SPE electrolyzer, the operating temperature must be 100 ° C. or less, which prevents the poisoning of the electrode catalyst by carbon monoxide and the efficiency. There is a problem that it cannot be used at a high temperature which is advantageous in this respect. In addition, since the perfluoropolymer electrolyte is non-crosslinked, if the amount of the introduced electrolyte group is excessively increased to improve the conductivity, the perfluoropolymer electrolyte swells remarkably in water or is solubilized, and the degree of freedom in designing the membrane is also increased. Was very limited.

On the other hand, if the perfluoropolymer electrolyte can be crosslinked, the flow of the polymer chains at high temperatures is suppressed, so that it is considered effective for the high-temperature creep resistance of the perfluoropolymer electrolyte. Furthermore, even if the introduction amount of the electrolyte group of the membrane is increased by the crosslinking, the membrane is not solubilized, and the degree of design freedom such as improvement in conductivity is improved. However, since the bond between carbon and fluorine in the perfluoropolymer electrolyte is chemically very stable and inert, crosslinking is not easy. Also, when cross-linked via the electrolyte group,
The number of electrolyte groups decreases, and the conductivity decreases.

Further, the crosslinked hydrocarbon polymer electrolyte disclosed in US Pat. No. 5,741,408 has a high resistance to oxidation at high temperatures because its main part, including the crosslinking agent, has a hydrocarbon structure. It cannot be used at high temperature as it is.

As described above, the polymer electrolyte is often exposed to high-temperature oxidation conditions for a long period of time, and long-term durability and heat resistance are required. For example, in a polymer electrolyte fuel cell, when the film is thinned to reduce the film resistance, if the durability and heat resistance are low, the film will creep and a locally and microscopically very thin portion will be formed. As a result, there is a problem that the circuit voltage is extremely lowered or an electric short circuit is caused, and long-term reliability is impaired.

The problem to be solved by the present invention is to provide a method for modifying a polymer electrolyte and a modified electrolyte in order to impart high heat resistance and durability with excellent conductivity and high temperature creep resistance. Is to provide.

[0017]

SUMMARY OF THE INVENTION In order to solve this problem, a method for modifying an electrolyte according to the present invention is characterized in that it comprises an amine treatment step of bringing an amine compound into contact with a perfluoropolymer electrolyte or a precursor thereof. Is what you do.

The method for modifying an electrolyte according to the present invention has an amine treatment step of bringing an amine compound into contact with a perfluoropolymer electrolyte or a precursor thereof. The electrolyte has excellent conductivity, and since the flow of molecules at high temperatures is suppressed, the high-temperature creep resistance is greatly improved, and the electrolyte has excellent durability and heat resistance.

[0019]

Embodiments of the present invention will be described below in detail. The method for modifying an electrolyte according to the present invention includes an amine treatment step.

Here, the amine treatment refers to bringing an amine compound into contact with a perfluoropolymer electrolyte or a precursor thereof. As a contacting method, the amine compound may be directly contacted, may be dissolved in an appropriate solvent and contacted, or may be exposed to the vapor of the amine compound. The solvent used in the case of dissolving and contacting with an appropriate solvent is not particularly limited as long as it dissolves the amine compound, but is preferably one in which the amine compound is dissolved in an amount of 10 mg / L or more, and from the viewpoint of solubility. The solvent used is preferably fluorine-based R113 or AK225.

The temperature at the time of the amine treatment is -30.
The range of from 200C to 200C is preferred. When the temperature is −30 ° C. or lower, the processing speed is significantly reduced due to a decrease in molecular mobility in the perfluoropolymer electrolyte, and when the temperature is 200 ° C. or higher, decomposition of the perfluoropolymer electrolyte occurs. Because. Further, the contact time, the amount of the amine compound added, and the like vary depending on the type of the amine compound, but may be appropriately adjusted within a range in which the creep resistance is improved and the electric conductivity is not significantly reduced, and is particularly limited. Not something.

Further, in the method for modifying an electrolyte according to the present invention, it is preferable that any one of a heat treatment step and a base treatment step is provided after the amine treatment step.

Here, the heat treatment means heating the perfluoropolymer electrolyte or its precursor. At this time, the heating temperature is preferably in the range of 40 ° C to 200 ° C. More preferably, from the viewpoint of the reaction rate, it is preferable to heat near the softening temperature of the perfluoropolymer electrolyte or its precursor (in the case of Nafion, in the range of 100 to 150 ° C.). If the temperature is lower than 40 ° C., the reaction rate is extremely slow. If the temperature is higher than 200 ° C., decomposition of the perfluoropolymer electrolyte occurs, which is not preferable. In addition, the heating time varies depending on the amine treatment time for contacting the amine compound, the amount and type of the amine compound added, etc., but if the creep resistance is improved and the electric conductivity is appropriately adjusted within a range that does not significantly decrease. Well, it is not particularly limited.

Here, the base treatment means that the base is brought into contact with the perfluoropolymer electrolyte or its precursor. As a method for contacting, the base may be directly contacted, or may be dissolved in an appropriate solvent and contacted, or may be exposed to a base vapor. The solvent used in the case of dissolving in a suitable solvent and contacting it is not particularly limited as long as the solvent dissolves the base.
g / L or more are preferable. From the viewpoint of solubility, the solvent used is preferably fluorine-based R113 or AK225. The base treatment time varies depending on the amount and type of base used, the temperature at the time of base treatment, etc., but the creep resistance can be improved, and the electric conductivity can be appropriately adjusted within a range that does not significantly decrease. However, there is no particular limitation.

It is more preferable that both the heat treatment step and the base treatment step are provided after the amine treatment step. In this case, after the amine treatment step, there is a heat treatment step, and after the heat treatment step,
It may have a base treatment step, or may have a base treatment step after the amine treatment step, and after the base treatment step,
A heat treatment step may be provided. Particularly preferably, from the viewpoint that the reaction between the perfluoropolymer electrolyte or the precursor thereof and the amine compound or the base is further promoted by the heat treatment, the base treatment step is provided after the amine treatment step. Is preferably followed by a heat treatment step.

Here, the above-mentioned perfluoropolymer electrolyte does not contain a C—H bond and is a fluorocarbon (—C
F ₂ -, - CFCl-), chlorocarbons (-CCl ₂
-), Other (-O-, -S-, -C (= O)-, -N
A perfluoropolymer having (R)-) as a main chain and a side chain, and having a structure in which this is substituted with an electrolyte group or a functional group capable of becoming an electrolyte by derivatization by a chemical reaction. Here, particularly, those substituted with a functional group that can become an electrolyte by derivatization by a chemical reaction are called perfluoropolymer electrolyte precursors.

[0027] Such perfluoropolymers include:
For example, polytetrafluoroethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer Specific examples include a polymer and polychlorotrifluoroethylene.

In addition, for derivatization by an electrolyte group or a chemical reaction,
As a functional group that can be more electrolyte (marked with *)
Is, for example, -SO₃H, -SO₂F^*, -SO₂Cl
^*, -SO₂Br^*, -SO₃Na, -SO₃K, -S
O₃Li, -SO₃Mg, -SO₃Ca, -CO₂H,
-COF^*, -COCl^*, -COBr^*, -CON
a, -COK, -COLi, -COMg, -COCa,
-PO₃H₂, = PO₂H, -OP (O₂H) O-,-
OPO₃H₂, -OPOCl₂ ^*, -OPOF₂ ^*, −
OPOBr₂ ^*, -POCl₂ ^*, -POF₂ ^*, -P
OBr₂ ^*, -OP (OCl) O-^*, -OP (OF)
O-^*, -OP (OLi) O-, carboxylic acid ester
Le^*, Sulfonic acid ester^*, Phosphate ester^*, Cal
Boric anhydride^*, Sulfonic anhydride^*, Phosphoric anhydride
object^*And mixed anhydride of carboxylic acid, sulfonic acid and phosphoric acid
object^*And the like are specific examples.

More specifically, as the electrolyte group,
—SO ₃ H (sulfonic acid group), and a perfluoropolymer electrolyte having —SO ₂ F (sulfonyl fluoride group) in its chemical structure as a functional group that can become an electrolyte by derivatization by a chemical reaction are preferable. Among them, a sulfonyl fluoride group is particularly preferable, as described later, because the amine treatment can easily improve the creep resistance and the like.

The structure of the perfluoropolymer electrolyte or its precursor used here is not particularly limited, and the polymer chain may have any of a linear or branched structure. Is also good. Above all, a perfluoropolymer electrolyte having a functional group which can be an electrolyte by derivatization by an electrolytic group or a chemical reaction in a side chain or a precursor thereof can be suitably used.

The amine compound used in the amine treatment step means that the hydrogen atom of ammonia is 0 to 3 depending on the substituent.
Refers to a monosubstituted amine compound.

Examples of the substituent in this case include various substituents, for example, an alkyl group, an aryl group, an allyl group, an alkene group, an alkyne group, an alkoxy group, a hydroxy group, a hydroxyl group, a hydroxylate group, Thiocarboxy, dithiocarboxy, sulfo, sulfino, sulfeno, oxycarbonyl, haloformyl, carbamoyl, hydrazinocarbonyl, amidino, cyano, isocyanate, cyanato, isocyanato, thiocyanato, Consists of components including isothiocyanato group, formyl group, oxo group, thioformyl group, thioxo group, mercapto group, amino group, imino group, hydrazino group, allyloxy group, sulfide group, halogen group, nitro group, silyl group, etc. Substituents are mentioned as specific examples.

The substituent is a metal such as Li, Na,
It may be substituted with K, Rb, Cs, Fr, Be, Mg, Ca, Ba or the like. In addition, such an amine compound is called a metal amide.

Among them, it is preferable to use, as the amine compound, a primary amine compound which is an amine compound in which one hydrogen atom of ammonia is substituted by the above substituent.
Specifically, for example, 1-hexylamine, ethylamine, propylamine, butylamine, pentylamine,
Heptylamine, nonylamine, decylamine, perfluoromethylamine, perfluoroethylamine, perfluorobutylamine, perfluoropentylamine,
Perfluoroheptylamine and the like.

It is more preferable to use ammonia as it is as the amine compound.

As the base used in the base treatment step, triethylamine, pyridine, DBU (1,8
-Diazabicyclo [5.4.0] -7-un
decene), triethylamine, DBN (1,5-
Amine compounds such as diazabicyclo [4.3.0] nonene-5), sodium hydroxide, lithium hydroxide, calcium hydroxide, aluminum hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, sodium alkoxide And metal bases such as sodium hydride, potassium hydride, calcium hydride, lithium aluminum hydride, sodium boron hydride, and organic metal compounds such as butyllithium, sodium cyclopentadienide, and phenyllithium. .

The modified electrolyte obtained by the above-described method for modifying an electrolyte according to the present invention is based on the total number of electrolyte groups in the perfluoropolymer electrolyte and the total number of functional groups which can be converted into electrolytes by derivatization by chemical reaction. Containing nitrogen derived from an amine compound in a mole fraction of 0.1 to 85% (hereinafter referred to as an electrolyte due to an electrolyte group in a perfluoropolymer electrolyte or derivatization by a chemical reaction). The molar amount of the nitrogen derived from the amine compound with respect to the total number of
(%)).

When the nitrogen mole fraction N (%) is 0.1% or less, the effect of durability and heat resistance is small because the amount of crosslinking generated between polymer chains is too small. In the above case, the amount of the electrolyte group is significantly reduced,
The use as an electrolyte is difficult, which is not preferable.

In the case of a perfluoropolymer electrolyte membrane in which the obtained modified electrolyte is formed into a membrane, a nitrogen mole fraction N (%) per unit volume in the membrane cross section (hereinafter, nitrogen density n (%) Is preferable that the maximum value n _max of the nitrogen density n (%) is in the range of 0.1% or more and 50% or less, and the distribution of the nitrogen density n (%) is It is preferable to distribute the density n (%) so that the level is substantially constant and uniform. If the distribution is non-uniform, that is, if there is a local peak in the distribution of the nitrogen density n (%), a portion where the amount of the electrolyte group is significantly reduced exists in the film, and the electric conductivity is reduced. It is not preferable because problems such as lowering the degree arise.

The distribution of the nitrogen density n (%) varies depending on various conditions such as the amount and type of the amine compound used in the amine treatment step, and the amine compound used is a perfluoropolymer electrolyte or a perfluoropolymer electrolyte. It is preferable to use a perfluoropolymer electrolyte or a material having a higher diffusion rate than the perfluoropolymer electrolyte or its precursor. If the rate at which the amine compound diffuses into the perfluoropolymer electrolyte or its precursor is slower than the rate of reaction with the perfluoropolymer electrolyte or its precursor, the amine compound will Before permeation, a reaction occurs on the surface of the perfluoropolymer electrolyte or its precursor, and as a result, the distribution of the nitrogen density n (%) tends to be non-uniform, and a portion where the electrical conductivity locally decreases occurs. Is not preferred.

The distribution of the nitrogen density n (%) can be evaluated by the distribution of the nitrogen element derived from the amine compound and the distribution of the physical properties of the obtained modified electrolyte. The characteristics and the electric conductivity may be evaluated so as to obtain an optimal distribution as appropriate.

The maximum value n of the distribution of the nitrogen density n (%) in the cross section of the perfluoropolymer electrolyte membrane
_{When max} is in the range of 0.1% or more and 50% or less, and the conductivity in the direction perpendicular to the film is 10 ⁻³ S / cm or more, the film has sufficient electric conductivity; In addition, an electrolyte membrane having excellent heat resistance and durability can be obtained.

As described above, the method for modifying an electrolyte according to the present invention has an amine treatment step of bringing an amine compound into contact with a perfluoropolymer electrolyte or a precursor thereof. The molecular electrolyte is
While maintaining electrical conductivity, the flow of molecules at high temperatures is suppressed, and deformation due to softening at high temperatures and creep during long-term use can be prevented, greatly improving heat resistance and high-temperature creep resistance. Will be able to do it. Further, since the polymer chain is formed of a perfluoropolymer, there is no problem in oxidation resistance at high temperatures.

Although the reason why the heat resistance and the durability can be improved while maintaining the electrical conductivity as described above is not clear, it is not clear by the derivatization due to the electrolyte group in the perfluoropolymer electrolyte or the chemical reaction. In the part of the functional group that can be an electrolyte, covalent bond by amine compound or cross-link by ionic bond has occurred,
It is considered that heat resistance and high temperature creep resistance are improved, and at the cross-linking point, electrons contributing to the bonding of hydrogen atoms are attracted to fluorinated carbon having electron-withdrawing properties and move, and hydrogen atoms are removed. It is considered that the electric conductivity is maintained because it is easily released as protons.

When a base treatment step is provided after the amine treatment step of bringing the amine compound into contact with the perfluoropolymer electrolyte or a precursor thereof, it is considered that the base promotes the crosslinking reaction and causes efficient crosslinking. Can be

When a heat treatment step is provided after the amine treatment step in which the amine compound is brought into contact with the perfluoropolymer electrolyte or its precursor, the crosslinking reaction is promoted by heating, and crosslinking occurs efficiently. It is considered something.

In particular, when a base treatment step is provided after an amine treatment step of bringing an amine compound into contact with a perfluoropolymer electrolyte or a precursor thereof, and a heat treatment step is provided after the base treatment step. It is considered that the combination of the effects described above makes it possible to significantly improve the heat resistance and the high-temperature creep resistance while maintaining the electric conductivity more efficiently.

Therefore, when the modified electrolyte obtained by the method for modifying an electrolyte according to the present invention is used in, for example, a polymer electrolyte fuel cell, it operates stably even at a high temperature of 120 ° C. or more. In addition, the efficiency can be dramatically improved, and the voltage drop caused by the poisoning of the electrode catalyst by carbon monoxide, which is a problem in the methanol reforming fuel cell, is reduced by such a high temperature operation. It is possible to greatly reduce.

[0049]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for reforming an electrolyte and a modified electrolyte according to the present invention will be described below in detail.

(Example 1) First, according to the following procedure,
An amine treatment was performed in which an amine compound was brought into contact with the perfluoropolymer electrolyte. That is, in a glove box, a film thickness of 50 μm was added to 80 ml of a fluorocarbon solvent (R113).
5 cm of Nafion membrane (F112) measuring 1 cm x 8 cm
Soak for minutes. Next, 5 ml of a 1.0 M (mol / L) THF solution of lithium bis (trimethylsilyl) amide (hereinafter referred to as LBTMSA) as an amine compound was added with stirring, and the resultant was immersed for 15 minutes.
Washed with 13 and THF solution. Subsequent operations are in the air,
Performed at room temperature. The obtained film was refluxed for 2 hours in a 25% aqueous sodium hydroxide solution, washed with water, and then washed with 6M hydrochloric acid for 5 hours.
Hydrolysis by immersion for a time converted the remaining sulfonyl fluoride groups to sodium sulfonate groups. further,
Refluxed in 1 M sulfuric acid for 1 hour to convert to proton form. Thereafter, the mixture was refluxed in pure water for 10 minutes, washed with water, and the obtained film was stored in pure water. This electrolyte membrane is referred to as Example 1.

Next, the electric conductivity of the thus obtained electrolyte membrane of Example 1 was measured by the following procedure. That is, the obtained electrolyte membrane having a width of 1 cm is mounted on a two-terminal electric conductivity measuring cell, and platinum foil plated with platinum black is used for the current and voltage terminals of the cell to improve the contact with the membrane. did. Each of these cells is immersed in pure water, and the LCR meter (YHP 4262A LC
R METER) and the membrane resistance of the electrolyte membrane was measured by an alternating current method (10 kHz). Then, the electrical conductivity (σ) was determined by the following equation (1). In addition, the value measured with the micrometer after the electric conductivity measurement was used for each film thickness.

[0052]

Σ = L / R · A = L / R · w · t where σ: electric conductivity (S / cm) R: resistance (Ω) L: distance between voltage terminals (= 1 cm) A: Cross-sectional area of film (cm ² ) t: film thickness (cm) w: film width (cm)

Next, a creep resistance test at 160 ° C. of the electrolyte membrane of Example 1 was performed according to the following procedure. That is, a weight was hung on the film so that the load became 0.8 MPa, the film was exposed to an atmosphere at 160 ° C., and the ratio of the elongation of the film after one minute to the initial length (creep elongation) was measured.

Examples 2 to 4 LB as an amine compound
Each film was treated according to the same procedure as in Example 1 except that the immersion time in TMSA was 30 minutes, 1 hour, and 2 hours. These electrolyte membranes were used in Example 2, Example 3,
Example 4 is assumed. Further, the measurement of electric conductivity and the evaluation of creep resistance were performed in the same manner as in Example 1.

Example 5 LBTM was used as an amine compound.
5 ml of a 1.0 M (mol / L) THF solution of SA was added under stirring and immersed for 15 minutes.
13 and a THF solution, and subsequently the membrane was treated in the same procedure as in Example 1 except that the membrane was subjected to a heat treatment at 120 ° C. for 12 hours under reduced pressure of a rotary pump. This electrolyte membrane is referred to as Example 5. Further, the measurement of electric conductivity and the evaluation of creep resistance were performed in the same manner as in Example 1.

(Examples 6 and 7) LB which is an amine compound
Except that the immersion time in TMSA was 1 hour and 2 hours,
Each film was treated according to the same procedure as in Example 5. These electrolyte membranes are referred to as Example 6 and Example 7, respectively. Further, the measurement of electric conductivity and the evaluation of creep resistance were performed in the same manner as in Example 1.

(Comparative Example 1) As a comparison, Nafion membrane which is a perfluoropolymer electrolyte was not subjected to any of amine treatment, base treatment, and heat treatment. It was stored in water. This electrolyte membrane is referred to as Comparative Example 1. Further, the electrical conductivity was measured in the same manner as in Example 1, and the creep resistance was evaluated by measuring the creep elongation for 8 minutes.

Table 1 shows the test conditions and the measurement results of the characteristics of the electrolyte membranes of Examples 1 to 7 and Comparative Example 1 produced as described above.
Shown in

[0059]

[Table 1]

First, Examples 1 to 4 in which the amount of the amine compound (LBTMSA) was fixed and the amine treatment was performed by changing the amine treatment time will be described. Example 1
According to No. 4, as the amine treatment time increased, the creep elongation for one minute sharply decreased, and the behavior became almost constant after one hour. Further, the creep elongation of Examples 2 to 4 was about 1/2 that of the creep elongation of Comparative Example 1.
This is significantly smaller than the following, and it can be seen that the creep resistance is improved.

On the other hand, the electrical conductivity did not decrease so much in Examples 1 and 2 as compared with Comparative Example 1, but in Examples 3 and 4 where the amine treatment time was longer than 1 hour, the decrease was not so large. The percentage has increased. From these results, when the amine treatment time is too short, the effect of improving the creep resistance is small. Conversely, when the amine treatment time is too long, the creep resistance is improved but the electric conductivity is reduced. You can see that. That is, it can be seen that it is necessary to select the amine treatment time within a range that does not significantly reduce the electrical conductivity and improves the creep resistance.

Next, the amount of the amine compound (LBTMSA) was fixed, the amine treatment step was performed by changing the amine treatment time, and then the heat treatment step at 120 ° C. for 12 hours was performed. Will be described. The creep elongation per minute of Example 1 in which the amine treatment time was short and no improvement in the creep resistance was observed was 126%, whereas the amine treatment time was the same as 15 minutes. The creep elongation per minute of Example 5 in which the
It can be seen that the percentage is significantly reduced to%. The other examples 6 and 7 had almost the same creep elongation as the examples 3 and 4. That is, it is understood that by performing the heat treatment after the amine treatment step, the creep elongation can be significantly reduced even if the amine treatment time is relatively short.

In addition, as can be seen from Examples 1 and 5, regarding the electric conductivity, it can be seen that the creep resistance is greatly improved without lowering the electric conductivity by the heat treatment. However, when the amine treatment time is relatively long as in Examples 6 and 7, it can be seen that the electric conductivity is reduced by the heat treatment.

As described above, the reason why the amine treatment in which the amine compound is brought into contact with the perfluoropolymer electrolyte greatly improves the creep resistance is as follows.
Although details are not clear, it is thought that covalent bonds with amine compounds or cross-links due to ionic bonds have occurred in the electrolyte groups in the perfluoropolymer electrolyte and the functional groups that can become electrolytes by derivatization due to chemical reactions. Can be

In the case of only the amine treatment step, as the contact time between the perfluoropolymer electrolyte and the amine compound becomes longer, the crosslinking points of the amine compound are formed in the perfluoropolymer electrolyte. It is considered that the rate of decrease in the electrical conductivity is suppressed to a low level mainly because the crosslinks are formed in an ionic bond state.

Regarding the influence of the presence or absence of the heat treatment step after the amine treatment step on the electric conductivity and the creep resistance, the shorter the amine treatment time, the greater the effect of the subsequent heat treatment.

This is because when the heat treatment is performed, the contact time with the amine compound is short, and even if the number of crosslinking points is small,
It is considered that the cross-linking between the perfluoropolymer electrolyte and the amine compound due to the covalent bond caused by the heating significantly improves the creep resistance. However, when the contact time with the amine compound is long and the number of crosslinking points is increased, it is considered that the heat treatment promotes the reaction at the crosslinking points, and the electrolyte groups are damaged, thereby lowering the electric conductivity.

(Examples 8 to 11) L which is an amine compound
2.5m of 1.0M (mol / L) THF solution of BTMSA
1, 1.25 ml, 0.6 ml and 0.3 ml were added under stirring, and each membrane was treated in the same procedure as in Example 5 except that the immersion time was 30 minutes. These electrolyte membranes are referred to as Example 8, Example 9, Example 10, and Example 11, respectively. Further, the measurement of electric conductivity and the evaluation of creep resistance were performed in the same manner as in Example 1.

(Examples 12 to 15) 2.5 M (mol / L) THF solution of LBTMSA which is an amine compound in 2.5 M
ml, 1.25 ml, 0.6 ml and 0.3 ml were added under stirring, and each membrane was treated according to the same procedure as in Example 5 except that the immersion time was 1 hour. These electrolyte membranes are referred to as Example 12, Example 13, Example 14, and Example 15, respectively. Further, the measurement of electric conductivity and the evaluation of creep resistance were performed in the same manner as in Example 1.

Table 2 shows the test conditions of the electrolyte membranes of Examples 8 to 15 and Comparative Example 1 produced as described above and the results of measurement of each characteristic.

[0071]

[Table 2]

Table 2 shows the results of performing the amine treatment by changing the amine treatment time and the amount of the amine compound added, while keeping the heat treatment conditions after the amine treatment step with the amine compound (LBTMSA) constant. First, Examples 8 to 11 in which the amine treatment time was 30 minutes and the amount of the amine compound added was changed will be described. Examples 8 to 1
1 has a creep elongation of about 1/3 to 1/2 as compared with Comparative Example 1.
, And the creep resistance is greatly improved. Further, the electrical conductivity increased as the amount of the amine compound added decreased, and in Example 11, both the electrical conductivity and the creep resistance were significantly improved as compared with Comparative Example 1. That is, it can be seen that the electrolyte membrane has been modified to have heat resistance and durability without lowering the electric conductivity.

On the other hand, in Examples 12 to 15 in which the amine treatment time was 1 hour and the amount of the amine compound added was changed in the same manner as in Examples 8 to 11, the same tendency as in Examples 8 to 11 was observed. In the case of Example 12 in which the amount of the amine compound added was large, the creep elongation for one minute was significantly smaller than that of Comparative Example 1, but the electrical conductivity was lower than that of Example 8.

From these facts, when the heat treatment conditions after the amine treatment step are constant, the smaller the amount of the amine compound added and the shorter the amine treatment time, the better both the creep resistance and electrical conductivity. It can be seen that the characteristics are improved.

Example 16 1.0 M (mol / L) of 1,4-dioxane solution 5 of ammonia as an amine compound
After immersion for 2 days, the membrane was taken out, and R
The membrane was treated according to the same procedure as in Example 1 except that the membrane was washed with 113 and a THF solution, and then heat-treated at 120 ° C. for 3 days under reduced pressure of a rotary pump. This electrolyte membrane is referred to as Example 16. Example 1
The electrical conductivity was measured in the same manner as described above, and the creep resistance was evaluated by measuring the creep elongation for 8 minutes.

(Examples 17 to 19) Each film was treated according to the same procedure as in Example 16 except that the immersion time in the amine compound, ammonia, was changed to 5, 7 and 10 days. These electrolyte membranes were used in Examples 17 and 1, respectively.
Eighth, and a nineteenth embodiment. The measurement of electric conductivity and the evaluation of creep resistance were performed in the same manner as in Example 16.

Example 20 A film was treated according to the same procedure as in Example 16 except that the heating time was changed to 2 hours. This film is referred to as Example 20. Example 16
In the same manner as in the above, the electric conductivity was measured and the creep resistance was evaluated.

Example 21 A film was processed according to the same procedure as in Example 16 except that the heat treatment was not performed.
This film is referred to as Example 21. The measurement of electric conductivity and the evaluation of creep resistance were performed in the same manner as in Example 16.

Example 22 1.0 M (mol / L) of 1,4-dioxane solution 5 of ammonia as an amine compound
After immersion for 2 days, the membrane was taken out, and R
After washing with a 113 solution and a THF solution, the mixture was heated in a 10% triethylamine R113 solution at 100 ° C. for 5 hours, and subjected to a base treatment. Subsequently, the membrane was heated at 120 ° C. under reduced pressure using a rotary pump for 2 hours. The film was processed according to the same procedure as in Example 1 except that the processing was performed. This electrolyte membrane is referred to as Example 22. The measurement of electric conductivity and the evaluation of creep resistance were performed in the same manner as in Example 16.

Examples 16 to 22 produced as described above,
Table 3 shows test conditions of the electrolyte membrane of Comparative Example 1 and measurement results of each characteristic.

[0081]

[Table 3]

Table 3 shows the results of changing the amine treatment time with the amine compound (ammonia) and the heat treatment conditions performed after the amine treatment, and the results of the amine treatment and the heat treatment after the amine treatment.
The result of having performed base treatment is shown. First, Examples 16 to 19 in which the heat treatment conditions performed after the amine treatment were fixed and the amine treatment time was changed will be described.

From Examples 16 to 19, it can be seen that the creep elongation of each of Examples 1 to 8 for 1 minute and 8 minutes is significantly smaller than that of Comparative Example 1, and the creep resistance is improved. As for the electric conductivity, the shorter the amine treatment time, the less the electric conductivity decreases. Example 16
Showed higher electric conductivity than Comparative Example 1.

That is, similarly, when the amine compound used is ammonia, when the heat treatment performed after the amine treatment step is constant, the shorter the amine treatment time, the better the properties of both creep resistance and electric conductivity. Is good. Further, the optimal time for performing the amine treatment differs depending on the type of the amine compound used, and it is also understood that the amine treatment time needs to be changed depending on the type of the amine compound.

Next, a comparison was made between Example 21 in which the heat treatment was not performed and Example 20 and 16 in which the heat treatment was performed for 2 hours and 3 days with the same amine treatment time. The lower the creep elongation, and the longer the heat treatment time, the better the electrical conductivity and the creep resistance.

From these facts, it is necessary to appropriately adjust the amine treatment time and the heat treatment condition according to the conditions of use of the electrolyte and the application so that the desired electric conductivity and creep resistance can be obtained. It turns out to be good.

Further, after the amine treatment, a heat treatment was carried out at 120 ° C. for 2 hours, and a base treatment was carried out at 100 ° C. for 5 hours using triethylamine as a base. Example 20 in which
A comparison of Comparative Example 1 shows that Example 22 has improved heat resistance and creep resistance without lowering the electrical conductivity. In addition, compared to Example 20,
The 8-minute creep elongation also improved.

As described above, the reason that the electric conductivity did not decrease when the base treatment was performed is that the base at the cross-linking point acts as a proton acceptor, so that the proton at the cross-linking point is more released. It is considered that the electrical conductivity was increased and the heat resistance and the durability were improved.

Example 23 A suspension of 500 mg of sodium amide as an amine compound in 5 ml of a THF solution was added and, after immersion for 2 days, the membrane was taken out, washed with R113 and a THF solution, and then the membrane was rotated with a rotary pump. The film was treated according to the same procedure as in Example 1 except that the heat treatment was performed at 120 ° C. under reduced pressure for 3 days. This electrolyte membrane is referred to as Example 23. Further, the measurement of electric conductivity and the evaluation of creep resistance were performed in the same manner as in Example 1.

(Example 24) After adding 1 ml of 1-hexylamine as an amine compound and immersing for 2 days, the film was taken out, washed with R113 and a THF solution, and then the film was heated to 120 ° C. under reduced pressure of a rotary pump. The film was treated according to the same procedure as in Example 16 except that the heat treatment was performed for 3 days. This electrolyte membrane is referred to as Example 24.
Further, the measurement of electric conductivity and the evaluation of creep resistance were performed in the same manner as in Example 1.

Table 4 shows the test conditions and the results of measurement of the characteristics of the electrolyte membranes of Examples 23 and 24 and Comparative Example 1 manufactured as described above.

[0092]

[Table 4]

In Examples 23 and 24, sodium amide as a metal amide was used as an amine compound, and 1 was used as a primary amine.
-In the case where hexylamine was used, when these were also compared with Comparative Example 1, although the creep elongation was reduced and the creep resistance was improved as in the above-described Examples,
As compared with the case where ammonia was used as the amine compound as in Example 16 shown in Table 3, a decrease in electric conductivity was observed. However, in the case of Example 16 using ammonia as the amine compound, both the electrical conductivity and the creep resistance were improved, indicating that ammonia is preferred as the amine compound.

Next, an elemental analysis was carried out for the purpose of examining the mole fraction of the amount of nitrogen derived from the amine compound with respect to the total number of sulfonic acid groups in the perfluoropolymer electrolyte. As a result, the nitrogen mole fraction N _{sul based} on the total number of sulfonic acid groups in Example 1 was obtained.
(%) Was 1.5%, Example 2 was 4.2%, Example 3 was 9.3%, and Example 4 was 17%. FIG. 1 shows the relationship between the nitrogen mole fraction N _sul (%), the creep elongation for one minute, and the electric conductivity with respect to the total number of sulfonic acid groups.

As can be seen from FIG. 1, the nitrogen mole fraction N
_{As the sul} (%) increased, the creep elongation for one minute rapidly decreased until the nitrogen mole fraction N _sul (%) became about 10%, and thereafter showed a behavior of becoming substantially constant. As for the electric conductivity, the nitrogen mole fraction N _sul
(%) Did not decrease so much until about 5%.
After 0%, the rate of the decrease became large.

From these results, it is found that when the nitrogen mole fraction N (%) is too small, the effect of improving the creep resistance is small, and when the nitrogen mole fraction N (%) is too large, the creep resistance is poor. It can be seen that the electrical conductivity decreases but the electrical conductivity decreases.

Next, the nitrogen density n (%) in the cross section of the film
The result of measuring the distribution of (nitrogen mole fraction per unit volume N (%)) will be described. FIG. 2 shows the nitrogen density distribution over the section of the film of Example 4 using LBTMSA as the amine compound, and FIG. 3 shows the nitrogen density distribution over the section of the film of Example 17 using ammonia as the amine compound.

According to FIG. 2, the film of Example 4 has a non-uniform distribution with a peak of the nitrogen density n (%) locally on the surface side of the film, and its maximum value n _max is 7
It has reached almost 5%. On the other hand, from FIG.
In the film No. 7, the distribution of the nitrogen density n (%) is uniform over the film cross section, and the maximum value n _max is 10% to 20%.
It can be seen that the nitrogen density distributions are completely different from each other.

This is because in Example 4, as the amine compound, the diffusion rate at which the amine compound diffuses into the perfluoropolymer electrolyte membrane is lower than that of the reaction between the amine compound and the perfluoropolymer electrolyte membrane. It is presumed that the reaction locally occurred in the vicinity of the surface of the film before the amine compound was diffused to the center of the film due to the use of.

On the other hand, in Example 17, as the amine compound, ammonia having a diffusion rate at which the amine compound diffuses into the perfluoropolymer electrolyte membrane was faster than the reaction rate between the amine compound and the perfluoropolymer electrolyte membrane was used. It is presumed that the use caused a reaction after the amine compound was sufficiently diffused to the center of the film, resulting in a uniform nitrogen density distribution over the cross section of the film.

When the electric conductivity of the electrolyte membrane of Example 4 was compared with that of the electrolyte membrane of Example 17, Example 4 was 1.7 × 10
⁻² (S / cm), whereas the value of Example 17 was 5.
It showed a relatively high value of 54 × 10 ⁻² S / cm. This is presumably because in the case of Example 4, the electric conductivity was lowered due to the presence of a portion in the membrane where the amount of the electrolyte group exhibiting proton conductivity was significantly reduced.
From this, it became clear that the nitrogen density distribution level was almost constant over the cross section of the film, and it was better to distribute the nitrogen uniformly.

The present invention is not limited to the above-described embodiment at all, and it is needless to say that various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, examples of the perfluoropolymer electrolyte in the amine treatment step of contacting with a Nafion membrane and an amine compound were lithium bis (trimethylsilyl) amide, ammonia, sodium amide, and 1-hexylamine as the amine compound. , Other than that.
Also, the conditions in the amine treatment step with the amine compound and various conditions in the case where the base treatment or the heat treatment is performed thereafter can be adjusted so that the creep resistance and the electrical conductivity are optimized.

[0103]

According to the method for modifying an electrolyte according to the present invention, the perfluoropolymer electrolyte or its precursor, which has been difficult to use at high temperatures, is treated with an amine to soften or deform at high temperatures. Can be suppressed, and
It has become possible to prevent creep during long-term use.
Further, heat resistance and durability can be significantly improved without lowering electric conductivity.

[Brief description of the drawings]

FIG. 1: Nitrogen mole fraction N to total number of sulfonic acid groups
It is the figure which showed the relationship between _sul (%), creep elongation for 1 minute, and electric conductivity.

FIG. 2 is a diagram showing a nitrogen density distribution over a cross section of an electrolyte membrane which has been subjected to an amine treatment using LBTMSA as an amine compound.

FIG. 3 is a diagram showing a nitrogen density distribution over a cross section of an electrolyte membrane which has been subjected to an amine treatment using ammonia as an amine compound.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaya Kawasaku 41-41, Chuchu-Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory, Inc. (72) Inventor Tomo Morimoto, Nagakute-machi, Aichi-gun Aichi-gun 41, Yokomichi, Toyoda Central R & D Co., Ltd. F term (reference) 2G004 ZA00 ZA05 4F070 AA23 AA24 AB01 AB06 AB18 AC11 AC13 AC14 AC19 AC45 AC46 AC47 AC50 AC52 AC66 AC67 AE08 BA02 BA07 BB08 GA06 GA10 GB05 GC02 5G301 CA30 CD01 CE10 5H026 AA06 BB01 BB10 HH00

Claims (5)

[Claims] 1. A method for modifying an electrolyte, comprising an amine treatment step of bringing an amine compound into contact with a perfluoropolymer electrolyte or a precursor thereof. 2. The method according to claim 1, further comprising a heat treatment step of heating the perfluoropolymer electrolyte or a precursor thereof after the amine treatment step. 3. The method according to claim 1, further comprising a base treatment step of bringing a base into contact with the perfluoropolymer electrolyte or a precursor thereof after the amine treatment step. . 4. In the amine treatment, the rate of diffusion of the amine compound into the perfluoropolymer electrolyte or a precursor thereof is higher than the rate of reaction between the amine compound and the perfluoropolymer electrolyte or a precursor thereof. The method for modifying an electrolyte according to any one of claims 1 to 3, wherein the treatment is a treatment of bringing an amine compound into contact with the perfluoropolymer electrolyte or a precursor thereof. 5. A modified electrolyte modified by the method for modifying an electrolyte according to claim 1.