JP2001345111A - Electrolyte membrane for solid polymer fuel cell and method of manufacturing it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid polymer fuel cell having a cation exchange membrane with low resistance and high strength as an electrolyte membrane and high stability in the initial performance and long-term performance. SOLUTION: The cation exchange membrane reinforced with a reinforcing material made from a fibril-like fluorocarbon polymer in which the fibrils having a fibril fiber diameter of 1 μm or less occupy 70% or more of the number of total fibrils, and having a thickness of 3-70 μm made from a perfluorocarbon polymer having a sulfonic group is used as the electrolyte membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrolyte membrane for a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art A hydrogen / oxygen fuel cell has attracted attention as a power generation system whose reaction product is only water in principle and has almost no adverse effect on the global environment. Solid polymer fuel cells were once mounted on spacecraft in the Gemini and Biosatellite programs, but the power density at that time was low. Since then, higher performance alkaline fuel cells have been developed, and up to the present space shuttle, alkaline fuel cells have been adopted for space applications.

However, in recent years, polymer electrolyte fuel cells have attracted attention again due to technological advances. The reasons are as follows. (1) A highly conductive film was developed as a solid polymer electrolyte. (2) By supporting a catalyst used for the gas diffusion electrode layer on carbon and coating the same with an ion exchange resin, high activity can be obtained.

In order to further improve the performance, it is conceivable to reduce the electric resistance by increasing the sulfonic acid group concentration and reducing the thickness of the solid polymer electrolyte membrane. However, a remarkable increase in the sulfonic acid group concentration decreases the mechanical strength and tear strength of the electrolyte membrane, causes dimensional changes during handling, and reduces the durability because the electrolyte membrane is easily creeped during long-term operation. And the like. On the other hand, a reduction in thickness causes problems such as a decrease in mechanical strength and tear strength of the electrolyte membrane, and a decrease in workability and handleability when the membrane is bonded to a gas diffusion electrode.

[0005]

As a method for solving the above problem, polytetrafluoroethylene (hereinafter, referred to as PT) is used.
It is called FE. ) A method of impregnating a porous membrane with a fluorinated ion exchange polymer having a sulfonic acid group has been proposed (Japanese Patent Publication No. 5-75835). However, although the thickness can be reduced, the electrical resistance of the porous PTFE membrane is sufficient. There was a problem that did not decrease.

As a method for solving this problem, there has been proposed a cation exchange membrane in which the cation exchange membrane is reinforced with a fibril-like, woven-like or non-woven-like perfluorocarbon polymer (JP-A-6-231779). This membrane has low resistance, and the power generation characteristics of a fuel cell produced using this membrane were relatively good, but the thickness was at most 100 to 200 μm.
However, since the thickness was not sufficiently thin and the thickness was uneven, the power generation characteristics and mass productivity were insufficient.

Accordingly, an object of the present invention is to provide a thin and uniform reinforcing membrane, to provide an electrolyte membrane for a polymer electrolyte fuel cell which has excellent power generation characteristics and can be mass-produced.

[0008]

SUMMARY OF THE INVENTION The present invention provides a cation exchange membrane comprising a perfluorocarbon polymer having a sulfonic acid group and reinforced with a reinforcing material comprising a fibril-like fluorocarbon polymer and having a thickness of 3%. And a reinforcing material having a fibril fiber diameter of 1 μm or less occupying 70% or more of the total number of fibrils.

Further, the present invention provides a method of forming a mixture of a perfluorocarbon polymer having a sulfonic acid group or a precursor group thereof and a fluorocarbon polymer capable of fibrillation into a film, and stretching the film on at least one surface of the obtained film. A method for producing an electrolyte membrane for a polymer electrolyte fuel cell, comprising laminating an auxiliary film and then biaxially stretching the film under heating.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a precursor group of a sulfonic acid group refers to a group which can be converted to a sulfonic acid group by performing hydrolysis, acid-forming treatment and the like. Specifically,-
An SO ₂ F group and a —SO ₂ Cl group are exemplified.

In the present invention, a reinforcing material comprising a fibril-like fluorocarbon polymer (hereinafter referred to as a fibril-like reinforcing material) increases tear strength and reduces dimensional change even if the amount contained in a cation exchange membrane is small. And a reinforcing effect such as reduction of Further, since the increase in the resistance of the membrane due to the inclusion of the fibril-like reinforcing material can be reduced, it is an effective reinforcing material.

In the present invention, the thickness of the membrane reinforced with the fibril-like reinforcing material is 3 to 70 μm. If the thickness is less than 3 μm, defects are likely to be generated when joining the electrodes.
If the thickness is larger than μm, the film resistance increases. Especially the thickness is 10-3
When the thickness is 0 μm, the film resistance is low, no defects are generated, and the power generation characteristics are favorable and stable when incorporated in a fuel cell and evaluated.

In the fibril-like reinforcing material of the present invention, fibrils having a fiber diameter of 1 μm or less have a total fibril number of 70.
%, Preferably 95% or more. The fiber diameter of the fibrils of the fibril-like reinforcing material is finally obtained because it is refined by applying a stress at the time of processing and forming the reinforcing film.
It is necessary to evaluate with the membrane incorporated in the fuel cell.

The fiber diameter of the fibrils of the fibril-like reinforcing material can be determined by immersing the membrane in a polar solvent such as ethanol at a high temperature to obtain a perfluorocarbon polymer having a sulfonic acid group (hereinafter referred to as a sulfonic acid type perfluorocarbon polymer). Can be dissolved and only the fibril-like reinforcing material can be taken out and evaluated. However, a method of observing the cross section of the membrane with a scanning electron microscope and evaluating the fiber diameter and the number of fibers is preferable because it can be easily evaluated. The fibril of the fibril-shaped reinforcing material has a small reinforcing effect when the fibril having a fiber diameter of 1 μm or less is less than 70% of the total number of fibrils.

The content of the fluorocarbon polymer serving as the fibril reinforcing material used in the present invention is preferably 0.5 to 15% based on the total mass of the ion exchange membrane. 0.5
%, The reinforcing effect is not sufficiently exhibited, and when it is more than 15%, the film resistance tends to increase. In the case of 2 to 8%, the membrane resistance does not increase and the reinforcing effect is sufficiently exhibited,
It is particularly preferable because the moldability is good.

In the present invention, the fibril-like reinforcing material is P
It is preferable that a copolymer containing 95 mol% or more of a polymerized unit based on TFE or tetrafluoroethylene is contained in an amount of 80% or more based on the total mass of the reinforcing material. When the content of the copolymer containing 95 mol% or more of the polymer units based on PTFE or tetrafluoroethylene is less than 80%, fine fibrils are hardly formed, and the reinforcing effect may be insufficient.

Examples of copolymers containing 95 mol% or more of polymerized units based on tetrafluoroethylene include tetrafluoroethylene-hexafluoropropylene copolymer,
Tetrafluoroethylene-chlorotrifluoroethylene copolymer, tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer, tetrafluoroethylene-perfluoro (2,2-dimethyl-1,3-dioxole) copolymer, tetra Fluoroethylene-perfluoro (butenyl vinyl ether) copolymer and the like can be mentioned. If the content of the polymerized units based on tetrafluoroethylene in these copolymers is less than 95% by mole, it is difficult to fibrillate, and the reinforcing effect is undesirably reduced.

As the sulfonic acid type perfluorocarbon polymer in the present invention, conventionally known polymers are widely used. Preferred polymers include those of the general formula CF ₂ =
_{CF (OCF 2 CFX) m -O} p - (CF 2) n SO 3 H ( wherein X is a fluorine atom or a trifluoromethyl group,
m is an integer of 0 to 3, n is an integer of 0 to 12,
p is 0 or 1, and when n = 0, p = 0. )) And a copolymer of a perfluorovinyl compound represented by the formula (1) with a perfluoroolefin or a perfluoroalkylvinyl ether. Specific examples of the perfluorovinyl compound include a compound represented by the following formula. Here, in the following formula, q is an integer of 1 to 9, and r is 1
S is an integer of 0 to 8, and z is 2 or 3.

[0019]

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The polymer containing a polymerized unit based on a perfluorovinyl compound having a sulfonic acid group is usually -SO ₂
It is polymerized using a perfluorovinyl compound having an F group. The perfluorovinyl compound having a —SO ₂ F group can be homopolymerized, but has low radical polymerization reactivity. Therefore, it is usually used together with a comonomer such as perfluoroolefin or perfluoro (alkyl vinyl ether) as described above. Used after polymerization. Examples of the perfluoroolefin to be a comonomer include tetrafluoroethylene, hexafluoropropylene, and the like, but usually tetrafluoroethylene is preferably employed.

The perfluoro (alkyl vinyl ether) serving as a comonomer includes CF ₂ ＣＦCF— (OCF ₂ C
FY) a compound represented by _t -O-R ^f are preferred. However, in the formula, Y is a fluorine atom or a trifluoromethyl group, t is an integer from 0 to 3, perfluoroalkyl group and R ^f represented by C _u F _{2u + 1} linear or branched (1 ≦
u ≦ 12).

CF ₂ ＣＦCF— (OCF ₂ CFY) _t —O—
Preferred examples of the compound represented by R ^f include the following compounds. However, in the following formula, v is an integer of 1 to 8, w is an integer of 1 to 8, and x is an integer of 1 to 3.

[0023]

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In addition to perfluoroolefins and perfluoro (alkyl vinyl ethers), fluorine-containing monomers such as perfluoro (3-oxahepta-1,6-diene) are also perfluorovinyl compounds having a —SO ₂ F group as a comonomer. May be copolymerized.

In the present invention, the concentration of the sulfonic acid group in the sulfonic acid type perfluorocarbon polymer constituting the electrolyte membrane, that is, the ion exchange capacity is 0.5 to 0.5.
It is preferably 2.0 meq / g dry resin, especially 0.7 to 1.6 meq / g dry resin. When the ion exchange capacity is lower than this range, the resistance of the obtained electrolyte membrane increases, while when the ion exchange capacity is high, the mechanical strength of the electrolyte membrane becomes insufficient.

The electrolyte membrane of the present invention preferably has a tear strength of 2 N / mm or more in any direction. The ratio of the tear strength in the direction with the highest tear strength to the tear strength in the lowest direction is preferably 1: 1 to 10: 1. For example, when the electrolyte membrane is formed into a film by single-screw extrusion, the direction through a single-screw extruder (hereinafter referred to as MD) is usually determined by the orientation of the fibrils.
It is called direction. ) Has the lowest tear strength, and the direction perpendicular to the MD direction (hereinafter referred to as the TD direction) has the highest tear strength.

In the present invention, the tear strength is measured by a method according to JIS-K7128 as follows. After immersing the film in 90 ° C. pure water for 16 hours, a strip sample having a width of 5 cm and a length of 15 cm is cut out, and the direction in which the tear strength is to be measured is defined as the length direction. Each sample has a length of 15c from the center of the short side so as to be bisected along the length direction.
Make a cut to 7.5 cm, half of m. Next, one of the cut ends is attached to the upper chuck of the tensile tester and the other is attached to the lower chuck so as to be torn from the cut portion, and the distance between the chucks is increased at a speed of 200 mm / min at 25 ° C., and the tear load is measured. The tear strength is calculated as a value (N / mm) obtained by dividing the tear load by the thickness of the sample. About 5 to 10 samples are measured in each direction, and the average value is defined as the tear strength.

In the present invention, the electrolyte membrane reinforced by the fibril-like reinforcing material is formed into a film by mixing a mixture of a perfluorocarbon polymer having a sulfonic acid group or a precursor group thereof and a fluorocarbon polymer capable of fibrillation, It is obtained by laminating a stretching auxiliary film on at least one side of the obtained film and then stretching the film under heating. When a film serving as an electrolyte membrane is stretched, if the film alone is stretched, it is easily broken and it is difficult to make the film uniform. However, if a stretching auxiliary film is laminated and stretched, the film serving as an electrolyte membrane can be made uniform and thin. That is, the stretching auxiliary film in the present invention is a film that is laminated to assist the stretching of the film serving as the electrolyte membrane. The stretching at this time is preferably performed biaxially.

More specifically, it is preferable to manufacture it by the following procedure. (1) Mixing of a fibrillable fluorocarbon polymer and a perfluorocarbon polymer having a sulfonic acid group precursor group (hereinafter referred to as a sulfonic acid group precursor type perfluorocarbon polymer). (2) Kneading and pelletizing the mixture obtained in (1) by twin-screw extrusion. (3) Using the pellets obtained in (2), forming a film and smoothing the film by uniaxial extrusion. (4) Hydrolysis, acid-form treatment, washing and drying. (5) Biaxial stretching after laminating the stretching auxiliary film.

The steps (1) to (5) will be described more specifically. Since the fibril-like reinforcing material is obtained by applying a shearing force to the fibrillable fluorocarbon polymer powder, first, only the fibril-like reinforcing material is prepared using the above fluorocarbon polymer, and the sulfonic acid group precursor type perfluorocarbon is prepared. A fibril-like reinforcing material may be mixed with a polymer or dispersed in a solution of a sulfonic acid precursor-type perfluorocarbon polymer, and cast to form a reinforced membrane.

However, in order to uniformly disperse the fibril-like reinforcing material in the film, the above-mentioned fluorocarbon polymer powder and sulfonic acid group precursor type perfluorocarbon polymer powder are mixed (step (1)), and then kneaded. Then, the method of fibrillating the fluorocarbon polymer powder (step (2)) is preferable. Further, after mixing and dispersing the fluorocarbon polymer powder in the polymerization solution obtained by polymerizing the sulfonic acid group precursor type perfluorocarbon polymer,
Aggregation, washing and drying may be performed before kneading.

At this time, the mixture of the sulfonic acid group precursor type perfluorocarbon polymer and the above fluorocarbon polymer powder is kneaded by twin-screw extrusion molding and pelletizing. Alternatively, the mixture may be kneaded first and then subjected to twin-screw extrusion.

Next, the obtained pellets are uniaxially extruded and formed into a film in step (3), preferably under heating. Also, without going through the pelletizing step (2),
The mixture may be directly uniaxially extruded and formed into a film in the uniaxial extrusion molding step, and the fluorocarbon polymer may be fibrillated at the same time. In the case of uniaxial extrusion molding under heating, the temperature of the film is 200 to 270 ° C.
It is preferable to mold to such an extent. If the film temperature is less than 200 ° C., the discharge pressure becomes too high,
Productivity may be reduced. Film temperature is 270
When the temperature exceeds ℃, the surface of the obtained film becomes rough and the thickness of the film becomes uneven, which is not preferable. The thickness of the film obtained after completing the step (3) in this manner is 80 to 500 μm.
About.

The surface of the film obtained in the above-mentioned process decreases as the amount of the fibril-like reinforcing material increases, and if necessary, the film is smoothed by a hot press. In the steps (1) to (3), since the molding is performed mainly under heating, it is preferable to use a sulfonic acid group precursor type perfluorocarbon polymer.

When a sulfonic acid group precursor type perfluorocarbon polymer is used, hydrolysis, acidification treatment, washing and drying are then performed (step (4)) to convert the sulfonic acid group precursor group to sulfonic acid. To the base. This step (4) may be performed after the step (5) described later.
When performing biaxial stretching a plurality of times in the step (5), the biaxial stretching may be performed in the middle of the step (5).

Next, a thin film is obtained by laminating the stretching auxiliary film on the above-mentioned film by using a roll press heated to, for example, about 70 to 100 ° C., biaxially stretching under heating, and peeling the stretching auxiliary film. (Step (5)). The stretching ratio in one stretching operation varies depending on the type of the sulfonic acid type perfluorocarbon polymer used, but is preferably 30% or less in area ratio. The biaxial stretching may be repeated several times, and a thin film having a thickness of less than 1 μm can be obtained by repeating the biaxial stretching.

When the thickness of the film obtained after the step (3) exceeds 200 μm, even if the sulfonic acid group precursor type perfluorocarbon polymer is used, the film before the step (4) is used. First, it is preferable to adjust the thickness of the film to 200 μm or less by the step (5).
That is, a stretching auxiliary film is laminated on at least one side of the film, and biaxial stretching is performed once or more as necessary. When the amount of the fibril-like reinforcing material increases, defects are likely to be generated by biaxial stretching. Therefore, it is preferable that the film is heat-treated at about 160 to 200 ° C. by a hot press after the biaxial stretching.

The stretching auxiliary film used in the step (5) is not particularly limited as long as it can be stretched. For example, a polyethylene terephthalate film, a polybutylene terephthalate film, a polyethylene film, an ethylene-α-olefin copolymer Film, ethylene-vinyl alcohol copolymer film, ethylene-vinyl acetate copolymer film, ethylene-vinyl acetate-vinyl chloride copolymer film, ethylene-vinyl chloride copolymer film, polypropylene film, polyvinyl chloride film, polyamide And a polyvinyl alcohol film. Among them, a polyethylene terephthalate film or a polypropylene film is preferable.

In particular, an amorphous polyethylene terephthalate film and a cast polypropylene film are preferred because they can be stretched at a relatively low temperature and have good stretchability. The temperature at the time of stretching varies depending on the type of the stretching auxiliary film, but a temperature range of 40 to 150 ° C is preferable from the viewpoint of stretchability.

The polymer electrolyte fuel cell of the present invention can be obtained according to a usual method, for example, as follows. First,
A solution of a conductive carbon black powder carrying platinum catalyst fine particles and a solution of a sulfonic acid type perfluorocarbon polymer are mixed to obtain a uniform dispersion, and a gas diffusion electrode is formed by any of the following methods to form a membrane electrode junction. Get the body. As the membrane, a cation exchange membrane made of a sulfonic acid type perfluorocarbon polymer reinforced with a fibril-like reinforcing material is used.

The first method is a method in which the uniform dispersion is applied to both sides of the cation exchange membrane and dried, and then both sides are brought into close contact with two sheets of carbon cloth or carbon paper.
In the second method, the uniform dispersion is applied to two carbon cloths or carbon papers and dried, and then the cation exchange membrane is applied so that the surface coated with the uniform dispersion adheres to the cation exchange membrane. It is a method of sandwiching from both sides.

The obtained membrane / electrode assembly is provided with a groove serving as a passage for a fuel gas or an oxidizing gas, sandwiched between separators made of a conductive carbon plate, and incorporated in a cell to be assembled into a polymer electrolyte fuel cell. Is obtained.

In the polymer electrolyte fuel cell obtained as described above, hydrogen gas is supplied to the anode side, and oxygen or air is supplied to the cathode side. At the anode, a reaction of H ₂ → 2H ⁺ + 2e ⁻ occurs, and at the cathode, a reaction of 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O occurs, whereby chemical energy is converted into electric energy.

[0044]

EXAMPLES Example 1 (Example) Tetrafluoroethylene
Polymerized unit based on CF and CF_Two= CF-OCF_TwoCF (C
F _Three) O (CF_Two)_TwoSO_TwoConsisting of polymerized units based on F
Copolymer powder (ion exchange capacity 1.1 meq / g)
9730 g of dry resin and PTFE powder (trade name: Fluo)
270 g) and mixed with two screws.
9500 g of pellets were obtained by extrusion molding. The obtained pe
The film is made into a film by a single screw extruder and has a thickness of 250 mm.
A μm film was obtained. Once the obtained film is
After heating roll press at the temperature of ℃ and smoothing the surface,
Amorphous with a thickness of 200μm as a stretching aid film
Sandwiched between two polyethylene terephthalate films
, And hot roll press at 80 ° C.
A film laminated on both sides was obtained.

The laminated film is biaxially stretched at 85 ° C. in a biaxial direction 1.4 times each of the axial directions (the direction (MD direction) through a single-screw extruder and the direction perpendicular to the MD direction (TD direction)). This was carried out (area stretching ratio 2 times) to obtain a laminated film in which a stretched film having a thickness of 120 µm was sandwiched between two stretching auxiliary films. The obtained stretched film was heat-treated with a hot roll press at 180 ° C. in a state where the stretching auxiliary film was kept laminated. Then, after peeling off the stretching auxiliary film, it is hydrolyzed using an aqueous solution containing dimethyl sulfoxide and potassium hydroxide,
The film was acidified with hydrochloric acid, washed, and dried to obtain a film having a thickness of 120 μm.

This film was again sandwiched from both sides with an amorphous polyethylene terephthalate film having a thickness of 200 μm as a stretching auxiliary film and heated and laminated in the same manner as described above.
The biaxial stretching was performed twice in each axial direction at a temperature of 4 ° C. (area stretching ratio was 4 times), and the stretching auxiliary film was peeled off to obtain a fibril reinforcing film having a thickness of 30 μm. The thickness of the obtained film was measured at 10 points at intervals of 5 cm, and the thickness variation was in a range of ± 3 μm.

[Scanning Electron Microscope Observation of Cross Section of Reinforcement Film] The cross section of the fibril reinforcement film was observed using a scanning electron microscope. Observe at 5 or more places at 10000x magnification,
When the number of fibrils with a fiber diameter of 1 μm or less was counted in a region of 5 μm square on one side, it was 98% of the total number of fibrils.

[Measurement of Tear Strength of Fibril Reinforcement Membrane] The fibril reinforcement film was immersed in pure water at 90 ° C. for 16 hours, and then a strip sample having a width of 5 cm and a length of 15 cm was cut out. As for this sample, a sample whose length direction coincides with the MD direction and a sample whose length direction coincides with the TD direction were each 5 samples. Each sample was cut from the center of the short side to 7.5 cm, which is half the length of 15 cm, so as to be bisected along the length direction. Attach one of the cut pieces to the upper chuck of the tensile tester and the other to the lower chuck so that the cut piece is torn from the cut part.
The distance between the chucks was widened at a speed of 200 mm / min at a temperature of ° C, and the tear load was measured. The tear strength was calculated by dividing the tear load by the thickness of the sample, and the average value of five samples was taken. The tear strength of the obtained fibril reinforcing membrane was 2.5 N in the MD direction,
The TD direction was 15N.

[Measurement of Resistance of Fibril Reinforcement Membrane] A strip-shaped film sample having a width of 5 mm was prepared from the fibril reinforcement film, and a platinum wire (diameter: 0.2 mm) was formed on the surface thereof at intervals of 5 mm so as to be parallel to the width direction. 5 pcs, 80 ℃,
The sample was held in a thermo-hygrostat at a relative humidity of 95%, and the AC impedance between the platinum wires at an AC of 10 kHz was measured to determine the AC specific resistance. 5mm
Since five platinum wires are pressed against the interval, the interelectrode distance can be changed to 5, 10, 15, and 20 mm. Therefore, the AC resistance at each interelectrode distance is measured, and the interelectrode distance and the gradient of the resistance are measured. The influence of the contact resistance between the platinum wire and the film was excluded by calculating the specific resistance of the film from. A good linear relationship was obtained between the distance between the electrodes and the measured resistance, and the specific resistance was calculated from the gradient and the thickness by the following equation. Specific resistance R (Ω · cm) = sample width (cm) × sample thickness (cm) × resistance electrode gradient (Ω / cm) The specific resistance of the obtained fibril reinforcing film was 5 Ω · cm.

[Fabrication and evaluation of fuel cell] The fuel cell was assembled as follows. Polymerized units based on tetrafluoroethylene and CF ₂ ＣＦCF—OCF ₂ CF (CF
₃ ) Ethanol containing a copolymer consisting of polymerized units based on O (CF ₂ ) ₂ SO ₃ H (ion exchange capacity 1.1 meq / g dry resin) and platinum-supported carbon in a mass ratio of 1: 3 Was applied on a carbon cloth by a die coating method, and dried to form a gas diffusion electrode layer having a thickness of 10 μm and a platinum carrying amount of 0.5 mg / cm ² .

The two carbon cloths were opposed to each other so that the respective gas diffusion electrode layers faced inward, the fibril reinforcing film was interposed therebetween, and pressed using a flat plate press to produce a membrane electrode assembly. . A fuel cell having an effective membrane area of 25 cm ² was assembled by disposing a separator made of a carbon plate in which narrow grooves for gas passages were cut in a zigzag shape on both outer sides of the membrane electrode assembly and a heater on the outside thereof.

While maintaining the temperature of the fuel cell at 80 ° C., air was supplied to the cathode and hydrogen was supplied to the anode at 1.5 atm. When the terminal voltage at a current density of 1 A / cm ² was measured, the terminal voltage was 0.62 V. Further, the above fuel cell was continuously operated at 80 ° C. and a current density of 1 A / cm ² . The terminal voltage after 1000 hours was 0.62 V, and there was no change.

Example 2 (Example) Tetrafluoroethylene
And polymerized units based on CF_Two= CF-OCF_TwoCF (CF
_Three) O (CF_Two)_TwoSO_TwoAnd a polymer unit based on F
The polymer powder was changed to 9600 g, and the PTFE powder was changed to 40 g.
Pellets were obtained in the same manner as in Example 1 except that the amount was changed to 0 g.
The film was later formed into a film having a thickness of 250 μm.
This film was stretched in the same manner as in Example 1 to obtain a film having a thickness of 3
A 0 μm fibril reinforcing membrane was obtained. Of the resulting film thickness
When the variation was measured in the same manner as in Example 1, the variation was within ± 3 μm.
It was an enclosure.

When the obtained fibril reinforcing membrane was evaluated in the same manner as in Example 1, the number of fibrils having a fiber diameter of 1 μm or less was 96% of the total number of fibrils. Further, the tear strength of the fibril reinforcing film was 5.5 N / mm in the MD direction and TD.
The direction was 18 N / mm, and the AC specific resistance was 6 Ω · cm.

Using the fibril reinforcing film, a fuel cell was assembled in the same manner as in Example 1, and the power generation characteristics were evaluated in the same manner as in Example 1. When the terminal voltage at a current density of 1 A / cm ² was measured, the terminal voltage was 0.61 V.
The terminal voltage after 1000 hours is 0.61 V,
There was no change.

Example 3 (Example) Using the film having a thickness of 250 μm obtained during the preparation of the fibril reinforcing film in Example 1, smoothing it with a hot roll press, and then applying a 200 μm thick film as a stretching aid film on both surfaces. A film in which an amorphous polyethylene terephthalate film was laminated in the same manner as in Example 1 was obtained. This laminated film is subjected to MD and TD at 85 ° C.
Biaxial stretching of 3 times in the direction was performed (area stretching ratio 9
Times), a laminated film in which a stretched film having a thickness of 30 μm is sandwiched between two stretching auxiliary films. This stretched film was heat-treated in the same manner as in Example 1, and after the stretching auxiliary film was peeled off, it was hydrolyzed, acidified, washed and dried to obtain a fibril reinforced film having a thickness of 30 μm. When the thickness variation of the obtained film was measured in the same manner as in Example 1, it was in the range of ± 3 μm.

When the obtained fibril reinforcing membrane was evaluated in the same manner as in Example 1, the number of fibrils having a fiber diameter of 1 μm or less was 97% of the total number of fibrils. Further, the tear strength of the fibril reinforcing film was 2.2 N / mm in the MD direction, 14 N / mm in the TD direction, and the AC specific resistance was 5 Ω · cm.

A fuel cell was assembled in the same manner as in Example 1 using the above fibril reinforcing film, and the power generation characteristics were evaluated in the same manner as in Example 1. When the terminal voltage at a current density of 1 A / cm ² was measured, the terminal voltage was 0.60 V.
The terminal voltage after 1000 hours is 0.60 V,
There was no change.

Example 4 (Comparative Example) The film having a thickness of 250 μm obtained during the production of the fibril reinforcing film in Example 1 was roll-rolled at a temperature of 180 ° C. using a heated roll press. Reduce the thickness of the membrane,
A 100 μm thick fibril reinforcing film was obtained. This film was hydrolyzed, acidified, washed and dried in the same manner as in Example 1 to a thickness of 10
A 0 μm fibril reinforcing membrane was obtained. When the variation in the thickness of the obtained film was measured in the same manner as in Example 1, there was a variation of ± 15 μm.

When the obtained fibril reinforcing membrane was evaluated in the same manner as in Example 1, the number of fibrils having a fiber diameter of 1 μm or less was 90% of the total number of fibrils. Further, the tear strength of the fibril reinforcing film was 1.6 N / mm in the MD direction, 10 N / mm in the TD direction, and the AC specific resistance was 5 Ω · cm.

A fuel cell was assembled in the same manner as in Example 1 using the above fibril reinforcing membrane, and the power generation characteristics were evaluated in the same manner as in Example 1. When the terminal voltage at a current density of 1 A / cm ² was measured, the terminal voltage was 0.54 V.
The terminal voltage after 1000 hours was 0.52V.

Example 5 (Comparative Example) In the production of the film in Example 4, an attempt was made to produce a film having a thickness of 70 μm or less by a heated roll press. When a film having a thickness of 70 μm was obtained and the thickness variation of the obtained film was measured in the same manner as in Example 1, the thickness variation was ± 25 μm, and a film having a uniform thickness was not obtained.

Example 6 (Example) In Example 1, the stretching ratio after the hydrolysis and the acid type treatment was increased by 1.1 times (area ratio: 1.2).
A fibril reinforcing film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the thickness was changed to (fold). When the thickness variation of the obtained film was measured in the same manner as in Example 1, it was in the range of ± 5 μm. When the obtained fibril reinforcing membrane was evaluated in the same manner as in Example 1, the number of fibrils having a fiber diameter of 1 μm or less was 95% of the total number of fibrils. The tear strength of the fibril reinforcing film was 2.0 N / mm in the MD direction and 16 N / mm in the TD direction.
mm, and the AC specific resistance was 6 Ω · cm.

Using the fibril reinforcing film, a fuel cell was assembled in the same manner as in Example 1, and the power generation characteristics were evaluated in the same manner as in Example 1. When the terminal voltage was measured at a current density of 1 A / cm ² , the terminal voltage was 0.53 V, but after 1000 hours, the terminal voltage was 0.53 V and remained unchanged.

Example 7 (Example) In Example 1, a mixture of the copolymer powder and PTFE was kneaded at 230 ° C. by using two rolls instead of pelletizing by twin-screw extrusion. After the obtained kneaded material was crushed by a crusher, it was uniaxially extruded and formed into a film in the same manner as in Example 1 to obtain a film having a thickness of 250.
A μm film was obtained. This film was uniaxially extruded and formed into a film in the same manner as in Example 1 to obtain a fibril reinforcing film having a thickness of 30 μm. When the thickness variation of the obtained film was measured in the same manner as in Example 1, it was in the range of ± 3 μm.

When the obtained fibril reinforcing membrane was evaluated in the same manner as in Example 1, the number of fibrils having a fiber diameter of 1 μm or less was 55% of the total number of fibrils. Further, the tear strength of the fibril reinforcing film was 0.8 N / mm in the MD direction, 1.8 N / mm in the TD direction, and the AC specific resistance was 6 Ω · cm.

Using the fibril reinforcing film, a fuel cell was assembled in the same manner as in Example 1, and the power generation characteristics were evaluated in the same manner as in Example 1. When the terminal voltage at a current density of 1 A / cm ² was measured, the terminal voltage was 0.57 V.
The terminal voltage after 000 hours was 0.51V.

Example 8 (Comparative Example) Tetrafluoroethylene
And polymerized units based on CF_Two= CF-OCF_TwoCF (CF
_Three) O (CF_Two)_TwoSO_TwoAnd a polymer unit based on F
Using only the polymer, a film was formed in the same manner as in Example 1,
50 μm membrane without fibril-like reinforcement
Made. This membrane was hydrolyzed, acidified, washed as in Example 1.
It was purified and dried to form a film having a thickness of 50 μm. The thickness of the obtained film
When the variation in thickness was measured in the same manner as in Example 1, ± 5 μm
Was in the range.

When the obtained film was evaluated in the same manner as in Example 1, the tear strength was 0.4 N in the MD direction and 0.4 in the TD direction.
6N, and the AC specific resistance was 5 Ω · cm. A fuel cell was assembled using the above membrane in the same manner as in Example 1, and the power generation characteristics were evaluated in the same manner as in Example 1. Current density 1A / c
When the terminal voltage at m ² was measured, the terminal voltage was 0.53 V. The terminal voltage after 1000 hours was 0.50V.

[0070]

According to the present invention, a reinforced cation exchange membrane having low electric resistance, high mechanical strength and uniform thickness, which is not available in conventional membranes, is used as a solid polymer electrolyte. A solid polymer electrolyte fuel cell having excellent performance and long-term stability is obtained.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryo Motomura 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term in Asahi Glass Co., Ltd. CX02 CX05 EE19 HH03 HH05 HH08

Claims (9)

[Claims] 1. A cation exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group reinforced with a reinforcing material made of a fibril-like fluorocarbon polymer, having a thickness of 3 to 70 μm, An electrolyte membrane for a polymer electrolyte fuel cell, wherein the number of fibrils having a fibril fiber diameter of 1 μm or less accounts for 70% or more of the total number of fibrils. 2. The method according to claim 1, wherein the reinforcing material comprises 0.5% of the total weight of the electrolyte membrane.
2. The electrolyte membrane for a polymer electrolyte fuel cell according to claim 1, wherein the content of the electrolyte membrane is about 15%. 3. The reinforcing material comprises polytetrafluoroethylene or 95 polymerized units based on tetrafluoroethylene.
3. The electrolyte membrane for a polymer electrolyte fuel cell according to claim 1, wherein the copolymer containing at least 80 mol% of the total mass of the reinforcing material is at least 80%. 4. A perfluorocarbon polymer having a sulfonic acid group, CF ₂ = polymerized units based on CF ₂ and CF ₂ =
_{CF (OCF 2 CFX) m -O} p - a (CF _{2) n} SO ₃ X polymerized units (here based on H fluorine atom or a trifluoromethyl group, m is an integer of 0 to 3, n is 0-1
Is an integer of 2, p is 0 or 1, and when n = 0, p = 0. 4. The electrolyte membrane for a polymer electrolyte fuel cell according to claim 1, which is a copolymer comprising: 5. A mixture of a perfluorocarbon polymer having a sulfonic acid group or a precursor group thereof and a fibrillable fluorocarbon polymer is formed into a film, and a stretching auxiliary film is laminated on at least one surface of the obtained film. And then stretching the film under heating to produce an electrolyte membrane for a polymer electrolyte fuel cell. 6. The film is stretched under heating so that the film has a thickness of 3 to 70 μm and the fibrils of the fluorocarbon polymer are fibrillated so that the number of fibrils having a fibril fiber diameter of 1 μm or less is the total number of fibrils. The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to claim 5, wherein the content is 70% or more. 7. A mixture of a perfluorocarbon polymer having a precursor group of a sulfonic acid group and the fluorocarbon polymer is formed into a film, and the precursor group of the sulfonic acid group is subjected to hydrolysis and acidification. 7. The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to claim 5, wherein the film is axially stretched after heating. 8. The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to claim 5, wherein the stretching auxiliary film is made of a polyethylene terephthalate film or a polypropylene film, and the stretching is performed at a temperature of 40 to 150 ° C. Method. 9. A polymer electrolyte fuel cell, wherein gas diffusion electrodes are arranged on both sides of the electrolyte membrane according to claim 1, 2, 3 or 4.