JP2006059551A - Polymetric solid electrolyte membrane having reinforcing material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymetric solid electrolyte membrane having improved durability at a high temperature. <P>SOLUTION: A fluorine-based polymetric solid electrolyte membrane has a porous aromatic series polyamide film that is subjected to at least one type of surface treatment selected from corona discharge treatment, ultraviolet irradiation treatment, and plasma treatment; and heat-treated at 120°C or higher. The fluorine-based polymetric solid electrolyte membrane contains a parfluorocarbonsulfone acid polymer and a basic polymer, and the total content of both of them is 1-50 vol.%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fluorine-based polymer solid electrolyte membrane useful as a fuel cell membrane.

In recent years, fuel cells using solid polymer electrolyte membranes as electrolytes have attracted attention because they can be reduced in size and weight, and high power density can be obtained even at relatively low temperatures, and development for automotive applications in particular has been accelerated. ing.
The polymer solid electrolyte membrane material used for such purposes is required to have excellent proton conductivity, appropriate water retention, gas barrier properties against hydrogen gas, oxygen gas, and the like. As materials satisfying such requirements, various polymers having a sulfonic acid group or a phosphonic acid group at the main chain or at the end of the side chain have been studied. For example, as described in Non-Patent Document 1, sulfonated polystyrene, etc. Many materials have been proposed.

However, under actual fuel cell operating conditions, active oxygen species with high oxidizing power are generated at the electrode, and in order to operate the fuel cell stably over a long period of time, it is necessary to operate under such a harsh oxidizing atmosphere. Durability is required. Many of the hydrocarbon-based materials that have been proposed so far often exhibit excellent characteristics with respect to the initial characteristics of the fuel cell operation, but do not exhibit sufficient resistance for long-term operation.
For this reason, the following general formula (1):

（式中、ｍは０〜３、ｎは１〜５、ｋ、ｌは１以上の整数で、１．５≦ｋ／ｌ≦１４）
で表されるパーフルオロカーボンスルホン酸ポリマーが主に採用されている。

(In the formula, m is 0 to 3, n is 1 to 5, k and l are integers of 1 or more, and 1.5 ≦ k / l ≦ 14)
The perfluorocarbon sulfonic acid polymer represented by the following is mainly employed.

These perfluorocarbon sulfonic acid polymer membranes exhibit extremely high chemical durability due to the fully fluorinated skeleton, and can be used even in harsh operating conditions compared to the hydrocarbon membranes described above. It is.
However, it is well known that these perfluorocarbon sulfonic acid polymers have a glass transition point close to the actual use temperature range. Then, physical strength is insufficient.

Actually, there are Nafion (registered trademark made by DuPont) and Flemion (registered trademark made by Asahi Glass Co., Ltd.) as perfluorocarbon sulfonic acid polymer membranes often used for research, but these membranes are 90 under a sufficiently humidified environment. When trying to operate in the range exceeding ℃, stable power generation could not be performed and long-term durability could not be demonstrated. This durability is because the dimensional change between the polymer solid electrolyte membrane when it is dried and when it contains water is large, and the local strain becomes the starting point for deterioration and breakage of the polymer membrane.
In order to solve this problem, a membrane (for example, Patent Documents 1 and 2) reinforced with a PTFE (polytetrafluoroethylene) porous membrane or the like has also been developed, and exhibits higher mechanical strength than an unreinforced membrane. However, it could not withstand continuous operation at a high temperature of 90 ° C. or higher.

  In addition, aromatic polyamide resin (aramid) is used as a nonwoven fabric for various reinforcing materials as a reinforcing material excellent in heat resistance and chemical resistance. For example, in Patent Document 3, aromatic polyamide porous material coated with a fluororesin is used. Although a solid polymer electrolyte membrane having a sheet is disclosed, the coated fluororesin peels off due to the difference in thermal expansion coefficient between the fluororesin and the aromatic polyamide resin and the low surface free energy of the fluororesin itself. There was a problem such as.

JP-A-8-162132 Japanese Patent Publication No. 63-61337 JP 2001-113141 A O. Savadogo, Journal of New Materials for Electrochemical Systems I, 47-66 (1998)

  The present invention provides a polymer solid electrolyte membrane for a fuel cell with little dimensional change when containing water even at a high temperature of 90 ° C. or higher.

  As a result of intensive studies to solve the above problems, the inventor is a polymer solid electrolyte membrane having a porous aromatic polyamide film having a large number of holes and subjected to surface treatment as a reinforcing material, And only when the said polymer solid electrolyte membrane was heat-processed at 120 degreeC or more, it discovered that it could be used stably also in the high temperature area | region which could not be used stably until now, and came to this invention.

That is, the present invention
(1) Having a porous aromatic polyamide film that has been subjected to at least one surface treatment selected from corona discharge treatment, ultraviolet irradiation treatment, and plasma treatment, and has been subjected to heat treatment at 120 ° C. or higher. Fluoropolymer solid electrolyte membrane characterized by
(2) The fluoropolymer solid electrolyte membrane contains a perfluorocarbon sulfonic acid polymer (a) and a basic polymer (b), and the total content of the (a) and the (b) 1 to 50% by volume in the polymer solid electrolyte membrane, and the content of (a) ([(a) / ((a) + (b))] × 100) is 50.00 to 99.99. 999% by mass, content of (b) ([(b) / ((a) + (b))] × 100) is 0.001 to 50.00% by mass (1) 2. The fluorine-based polymer solid electrolyte membrane according to 1.
(3) A fluoropolymer solid electrolyte membrane laminate comprising two or more fluoropolymer solid electrolyte membranes according to (1) or (2) laminated.
(4) A membrane / electrode assembly in which the anode and the cathode are opposed to each other through the fluoropolymer solid electrolyte membrane or the fluoropolymer solid electrolyte membrane laminate according to any one of (1) to (3) .
(5) A polymer electrolyte fuel cell comprising the membrane / electrode assembly according to (4).

  The fluorine-based polymer solid electrolyte membrane of the present invention maintains a high proton conductivity even before and after a 95 ° C. bath treatment, and does not change in wet and dry dimensions. It became possible.

Hereinafter, the fluoropolymer solid electrolyte membrane of the present invention will be described in more detail.
The aromatic polyamide film used as a reinforcing material for the fluoropolymer solid electrolyte membrane of the present invention will be described.
For the aromatic polyamide film used as a reinforcing material for the fluoropolymer solid electrolyte membrane of the present invention, meta-oriented aromatic polyamide or para-oriented polyamide is used. Particularly preferred is para-oriented aromatic polyamide from the viewpoint of mechanical strength and heat resistance. The para-oriented aromatic polyamide is a homopolymer or copolymer composed of repeating units selected from the three types of repeating units represented by the formula (2). However, in the case of using (c) and (d) in the formula (2), it always becomes a copolymer with other repeating units to form a polyamide structure.

In the present invention, Ar ₁ , Ar ₂ , and Ar ₃ must each be a so-called linear orientation group in order to ensure good heat resistance. Here, the linear orientation means that the bond growing the molecular chain is positioned coaxially or parallel to the opposite direction of the aromatic.
Specific examples of such a divalent aromatic group include paraphenylene, 4,4′-biphenylene, 1,4-naphthylene, 1,5-naphthylene, 2,5-pyridylene and the like. They may be substituted with one or more inactive groups such as halogen, lower alkyl, nitro, methoxy, cyano group.
Moreover, the bivalent group of the form represented by Formula (3) is also mentioned as these bivalent aromatics.

式（２）のＡｒ_１、Ａｒ_２およびＡｒ_３は、いずれも２種以上であってもよく、また相互に同じであってもよい。 Specific examples of X include the following formula (4).

Ar ₁ , Ar ₂ and Ar ₃ in the formula (2) may all be two or more, or may be the same as each other.

The aromatic polyamide used for the reinforcing material of the fluorine-based polymer solid electrolyte of the present invention can be produced from diamine, dicarboxylic acid, and aminocarboxylic acid corresponding to each unit by a conventionally known method.
Specifically, a method is used in which a carboxylic acid group is first derived into an acid halide, acid imidazolide, ester, etc., and then reacted with an amino group. The polymerization method is also a so-called low temperature solution polymerization method, interfacial polymerization method. Alternatively, a melt polymerization method, a solid phase polymerization method, or the like can be used.

In the aromatic polyamide used for the reinforcing material of the fluorine-based polymer solid electrolyte of the present invention, groups other than those described above may be copolymerized or other polymers may be blended. Specific examples of groups used for copolymerization include 3,3′-diaminodiphenyl ether, 3,4-diaminodiphenyl ether, 3,3′-diamino-4,4′dichlorodiphenyl, and the like.
A method for forming an aromatic polyamide film as a reinforcing material used in the present invention is not particularly limited, and generally used methods such as wet film formation and dry film formation are used.
Since the reinforcing material of the fluoropolymer solid electrolyte of the present invention can be used in the form of a porous film, the porous film will be described next. Here, the reinforcing material means that contained in the fluorine-based polymer solid electrolyte membrane of the present invention, and the reinforcing material is preferably embedded in the fluorine-based polymer solid electrolyte membrane.

The porous film used as a reinforcing material for the fluoropolymer solid electrolyte membrane of the present invention is obtained by processing a reinforcing material film made of the above-mentioned aromatic polyamide.
The film thickness is 0.1 μm or more and 20 μm or less, preferably 10 μm or less. The thicker the film thickness, the worse the initial characteristics as a fuel cell.
The pore diameter of the porous film of the present invention is preferably in the range of 0.001 μm to 500 μm, more preferably in the range of 1 μm to 450 μm. If it is less than 0.001 μm, the fluorine-based polymer solid electrolyte is not sufficiently filled in the pores and voids are formed, so that sufficient ion conductivity cannot be achieved, which is not preferable. On the other hand, if it exceeds 500 μm, the reinforcing effect as a reinforcing material cannot be sufficiently exhibited, which is not preferable.

The porosity of the porous film as a reinforcing material that can be used for the fluoropolymer solid electrolyte of the present invention is preferably 30% or more, more preferably 50% or more and 95% or less. If it is less than 30%, the ion conductivity as a fuel cell is hindered, which is not preferable. If it exceeds 95%, the effect of suppressing the dimensional change in the wet and dry state cannot be obtained, which is not preferable.
As the shape of the hole, a perfect circle is usually used. However, when the hole having a major axis to minor axis ratio of 1.1 to 10 is used, the hole area ratio can be improved without reducing the mechanical strength. Therefore, it is preferable because ion conductivity can be secured.
In addition, in the case of a porous film having pores with a ratio of major axis to minor axis of 1.1 to 10, each hole present in the film may or may not have the major axis and minor axis directions oriented. It doesn't matter.

Examples of the method for forming a hole include punching, drilling, carbon dioxide laser, excimer UV laser, and the like, but are not limited thereto.
Specifically, for punching by punching, an NC control punching machine equipped with a die having a large number of hole shapes is preferably used.
Explaining the drill, an NC control drilling machine that is usually used for drilling a printed wiring board is preferably used.
As for the carbon dioxide laser and the excimer UV laser, a laser processing machine used for drilling a build-up printed wiring board that is a high-density printed wiring board is preferably used.

In the above opening method, a single wafer aromatic polyamide film can be processed by performing batch processing. On the other hand, when the aromatic polyamide film has a roll shape, a roll-shaped porous aromatic polyamide film can be obtained by feeding the film to a stage of a drilling machine and performing a drilling process.
Since the porous film used as a reinforcing material for the fluoropolymer solid electrolyte of the present invention is characterized by being surface-treated, the surface treatment used in the present invention will be described next.
Examples of the surface treatment used in the present invention include corona discharge treatment, ultraviolet irradiation treatment, and plasma treatment. Of these, corona discharge treatment is preferable from the viewpoint of productivity.

Corona discharge treatment is a porous aromatic polyamide film that can be used in the present invention, in which a high voltage of alternating current or direct current is applied between an electrode and a film conveying roll to generate corona discharge in the air. In general, the roll is a dielectric roll in which a metal roll is coated with a dielectric such as hyperon rubber, EPT (ethylene propylene terpolymer), silicon rubber, or ceramic. However, in the case of an aromatic polyamide film, it is also possible to use a metal roll directly without using a dielectric.
The power to be applied varies depending on the thickness of the film, the polymer composition, the surface property, etc., and it is necessary to select conditions, but usually 30 to 600 W / m ² / min, preferably 50 to 300 W / m ² / min. A range of densities is used. When the applied power is too low, the adhesion between the aromatic polyamide film and the polymer solid electrolyte becomes insufficient. On the other hand, when the applied power is too high, problems such as deterioration of film characteristics, wrinkles, and surface roughness occur.

Next, the ultraviolet irradiation treatment that can be used in the present invention will be described.
As the gas used in the ultraviolet treatment, oxygen, carbon tetrafluoride gas, hydrogen gas, argon gas, nitrogen gas, ammonia gas, helium gas or the like may be used alone or in combination. Of course, UV treatment in air is also acceptable. The wavelength of the irradiated ultraviolet light is 400 nm or less. If it exceeds 400 nm, the adhesive strength with the body becomes insufficient. As the ultraviolet irradiation lamp to be used, a low-pressure mercury lamp (ultraviolet wavelengths: 185 nm and 254 nm), a xenon excimer lamp (ultraviolet wavelength: 172 nm) and the like are preferably used.
The distance between the ultraviolet rays and the film during irradiation is preferably 10 cm or less, more preferably 5 cm or less, and still more preferably 4 cm or less. If it exceeds 10 cm, the adhesion between the aromatic polyamide film and the polymer solid electrolyte becomes insufficient.

The ultraviolet treatment time is preferably in the range of 0.01 seconds to 30 minutes, more preferably 0.1 seconds to 15 minutes. If less than 0.01 seconds, the modification becomes insufficient. On the other hand, when the time exceeds 30 minutes, the deterioration of the resin surface proceeds.
Next, plasma treatment that can be used in the present invention will be described.
The gas used for the plasma treatment is oxygen gas, carbon tetrafluoride gas, hydrogen gas, argon gas, nitrogen gas, ammonia gas, helium gas, etc., which may be used alone or in combination. .
As the plasma method, a barrel type or a parallel plate type is preferable, and as a processing mode, an RIE mode in which a sample is placed on a HOT electrode, a PE mode in which a sample is placed on a ground electrode, and further, outside the electrode A remote method for installing a sample is preferably used.

In the present invention in which an aromatic polyamide film is used as a reinforcing material, plasma treatment under a pressure in the vicinity of atmospheric pressure, which is easy to treat a roll product (continuous film), is preferably used. Here, the vicinity of atmospheric pressure is preferably in the range of 20 kPa to 200 kPa, more preferably 70 kPa to 130 kPa. Below 20 kPa, if the reaction vessel is not made airtight, air will flow in and the processing will not be possible. On the other hand, if it exceeds 200 kPa, the plasma will tend to become unstable.
The plasma treatment time is preferably 0.01 seconds to 30 minutes, more preferably 0.1 seconds to 15 minutes. If less than 0.01 seconds, the modification becomes insufficient. On the other hand, when the time exceeds 30 minutes, the deterioration of the resin surface proceeds.

As mentioned above, although the surface treatment method of the reinforcing material which can be used for this invention was demonstrated, the above-mentioned surface treatment can also combine 2 or more types of surface treatment methods in order to raise the effect. In addition, surface roughening treatment such as sand blasting or wet blasting may be performed before the surface treatment described above for the purpose of further improving the adhesion between the aromatic polyamide film as a reinforcing material and the polymer solid electrolyte. Good.
As described above, the aromatic polyamide film as a reinforcing material used for the fluoropolymer solid electrolyte membrane of the present invention may be subjected to a surface treatment step after the step of opening a hole, and after the surface treatment is performed. Although a hole may be formed, it is preferable to perform a surface treatment after forming the hole.

Next, the electrolyte component of the fluoropolymer solid electrolyte membrane of the present invention will be described.
The electrolyte component constituting the solid polymer electrolyte membrane used in the present invention is characterized by comprising a perfluorocarbon sulfonic acid polymer and a basic polymer as an additive.
First, the perfluorocarbon sulfonic acid polymer will be described.
The perfluorocarbon sulfonic acid polymer is specifically represented by the following general formula (1).

（式中、ｍは０〜３、ｎは１〜５、ｋ、ｌは１以上の整数で、１．５≦ｋ／ｌ≦１４）
このポリマーは、通常、パーフルオロビニルエーテルモノマーとテトラフルオロエチレン（ＴＦＥ）を共重合して得られる熱可塑性の下記一般式（５）で表されるパーフルオロカーボンスルホニルフルオライドポリマーを加水分解反応を施すことによって得られる。

(In the formula, m is 0 to 3, n is 1 to 5, k and l are integers of 1 or more, and 1.5 ≦ k / l ≦ 14)
This polymer is usually obtained by subjecting a thermoplastic perfluorocarbonsulfonyl fluoride polymer represented by the following general formula (5) obtained by copolymerizing a perfluorovinyl ether monomer and tetrafluoroethylene (TFE) to a hydrolysis reaction. Obtained by.

（式中、ｍは０〜３、ｎは１〜５、ｋ、ｌは１以上の整数で、１．５≦ｋ／ｌ≦１４）

(In the formula, m is 0 to 3, n is 1 to 5, k and l are integers of 1 or more, and 1.5 ≦ k / l ≦ 14)

Next, the basic polymer will be described.
In the fluorine-based polymer solid electrolyte membrane of the present invention, the durability is drastically improved particularly by adding a basic polymer as an additive to the electrolyte component. Although it does not specifically limit as a basic polymer used for the polymer electrolyte membrane of this invention, A nitrogen-containing aliphatic basic polymer and a nitrogen-containing aromatic basic polymer are mentioned.

Examples of nitrogen-containing aliphatic basic polymers include polyethyleneimine. Examples of the nitrogen-containing aromatic basic polymer include polyaniline and heterocyclic compounds such as polybenzimidazole, polypyridine, polypyrimidine, polyvinylpyridine, polyimidazole, polypyrrolidine, and polyvinylimidazole. Among these, polybenzimidazole is particularly preferable because of its high heat resistance.
Examples of polybenzimidazole include compounds represented by chemical formula (6) and chemical formula (7), and poly 2,5-benzimidazole represented by chemical formula (8).

以上のようなポリベンズイミダゾールの中でも、下記式（９）で表されるポリ[２、２’−（ｍ−フェニレン）−５，５’−ビベンゾイミダゾール]が特に好ましい。

Among the polybenzimidazoles as described above, poly [2,2 ′-(m-phenylene) -5,5′-bibenzimidazole] represented by the following formula (9) is particularly preferable.

The polymer solid electrolyte membrane of the present invention contains a perfluorocarbon sulfonic acid polymer (a) as an electrolyte and a basic polymer (b) as an additive in the electrolyte composition, and the (a) and (( b) The total content is 1 to 50% by volume in the fluoropolymer solid electrolyte membrane, and the content of (a) ([(a) / ((a) + (b))] × 100) is 50.00 to 99.999% by mass, and the content of (b) ([(b) / ((a) + (b))] × 100) is 0.001 to 50.00% by mass It is characterized by being.
The content rate of a basic polymer (b) is 0.001-50000 mass% with respect to the total mass of a component (a) and a component (b) as mentioned above, Preferably it is 0.005-20. 0.000% by mass, more preferably 0.010 to 10.000% by mass, still more preferably 0.100 to 5.000% by mass, and most preferably 0.100 to 2.000% by mass. By setting the content of the basic polymer (b) in the above range (0.001 to 50.000 mass%), a polymer solid electrolyte having high durability while maintaining good proton conductivity A membrane can be obtained.

In the present invention, the perfluorocarbon sulfonic acid polymer (a) and the basic polymer (b) may be chemically bonded, and whether or not they are chemically bonded is determined, for example, by a Fourier-transform infrared spectrophotometer (Fourier-Transform Infrared Meter). Spectrome-ter) (hereinafter referred to as “FT-IR”). That is, when the FT-IR measurement of the polymer solid electrolyte membrane composed of the perfluorocarbon sulfonic acid polymer (a) and the basic polymer (b) was performed, the perfluorocarbon sulfonic acid polymer (a) and the basic polymer (b If an absorption peak derived from other than any of the above is observed, it can be determined that chemical bonding has occurred. For example, the perfluorocarbon sulfonic acid polymer represented by the above formula (1) and the poly [(2,2 ′-(m-phenylene) -5,5′-bibenzimidazole) represented by the above formula (9) ( hereinafter, the case of the solid polymer electrolyte membrane of the present invention consisting referred to as) and PBI is, when the FT-IR ^{measurement, 1460cm -1, 1565cm -1,} absorption peaks were observed around 1635 cm ^-1, chemical It can be seen that a bond exists.

  The production method of the polymer solid electrolyte membrane of the present invention is not particularly limited, but the perfluorocarbon sulfonic acid polymer (a) and the basic polymer (b), which are the above electrolyte compositions, are water, alcohols and other proton solvents, , A reinforcing material is immersed in a polar aprotic solvent such as DMF (dimethylformamide), DMAc (dimethylacetamide), DMSO (dimethylsulfoxide), or a mixed solution dissolved or dispersed in the mixed solvent. A method of coating the electrolyte composition or a film of the electrolyte composition of the perfluorocarbon sulfonic acid polymer (a) and the basic polymer (b) is prepared in advance, and the two polymer solid electrolyte films are used as a reinforcing material. And a method of pressure bonding by sandwiching a porous film, heating and pressurizing. In addition, when making it crimp, it is necessary to adjust heating and pressurization temperature so that electrolyte composition may fill the hole of a porous film.

As described above, the solid polymer electrolyte membrane in which the electrolyte composition is coated or thermocompression bonded to the porous film as the reinforcing material is characterized in that it is subsequently heat treated. The porous film and the electrolyte composition are firmly bonded by the heat treatment, and as a result, the mechanical strength is stabilized.
The heat treatment temperature is preferably 120 ° C. or higher and 300 ° C. or lower, more preferably 160 ° C. or higher and 250 ° C. or lower.
If the heat treatment temperature is low, the adhesion between the porous film as the reinforcing material and the electrolyte composition cannot be secured, which is not preferable. On the other hand, if the heat treatment temperature is high, the electrolyte composition may be altered, which is not preferable. Although the heat treatment time depends on the heat treatment temperature, it is preferably 5 minutes or longer and 3 hours or shorter, more preferably 10 minutes or longer and 2 hours or shorter.

In addition, when producing a fluorine-based solid polymer solid electrolyte membrane by heating and pressure-bonding the electrolyte composition film and the reinforcing material porous film, if the heating temperature is set to 120 ° C. or higher, the heating / pressure-bonding and heat treatment are performed. It becomes possible to carry out at the same time.
In the fluorine-based polymer solid electrolyte membrane of the present invention, when the 15 μm × 15 μm region of the cross section in the film thickness direction is observed with a transmission electron microscope (hereinafter referred to as “TEM”), the par It is preferred that the fluorocarbon sulfonic acid polymer and the basic polymer exhibit a sea / island structure. The sea / island structure here refers to a state in which black island particles are dispersed in a gray or white sea (continuous phase) in an electron microscopic image obtained by observation with an electron microscope without performing a staining treatment. The shape of the island particles is not particularly limited, such as a circle, an ellipse, a polygon, and an indeterminate shape. The diameter (or major axis or maximum diameter) of the island particles is in the range of 0.01 to 10 μm. In the sea / island structure, the contrast of the black island particles is mainly attributed to the basic polymer (b), and the white sea (continuous phase) part is mainly attributed to the perfluorocarbon sulfonic acid polymer (a).

In the sea / island structure, the total area of the island particles of the sea / island structure is preferably 0.1 to 70%, more preferably 1 to 70% of the 15 μm′15 μm region of the membrane cross section. More preferably, it is 5 to 50%. Further, the density of island particles having a sea / island structure is preferably 0.1 to 100 per 1 μm ^{2 in the} 15 μm′15 μm region of the film cross section.
Having such a sea / island structure indicates that the portion mainly composed of the basic polymer (b) is uniformly finely dispersed in the portion mainly composed of the perfluorocarbon sulfonic acid polymer (a). And higher durability can be obtained.
The ion exchange capacity of the polymer solid electrolyte membrane of the present invention is not particularly limited, but is preferably 0.50 to 4.00 milliequivalents per gram, more preferably 0.83 to 4.00 milliequivalents, and most preferably 1 0.001 to 1.50 milliequivalents. The use of a polymer solid electrolyte membrane having a larger ion exchange capacity exhibits higher proton conductivity under high temperature and low humidification conditions, and when used in a fuel cell, a higher output can be obtained during operation.

The ion exchange capacity can be measured by the following method. First, the polymer solid electrolyte membrane cut out to about 10 cm ^{2 is} vacuum-dried at 110 ° C. to obtain a dry weight W (g). This membrane is immersed in 50 ml of a saturated NaCl aqueous solution at 25 ° C. to release H ⁺ , and neutralization titration is performed with 0.01 N sodium hydroxide aqueous solution using phenolphthalein as an indicator, and the equivalent amount of NaOH required for neutralization. Obtain M (millimeter equivalent). The value obtained by dividing M thus determined by W is the ion exchange capacity (milli equivalent / g). The value obtained by dividing W by M and multiplying by 1000 is the equivalent mass EW, which is the dry mass in grams per equivalent of ion-exchange groups.
Further, the state of the perfluorocarbon sulfonic acid polymer (a) and the basic polymer (b) in the polymer solid electrolyte membrane of the present invention is not particularly limited as long as the above requirements are satisfied. For example, the component (a) and the component (B) may be in a state of simple physical mixing, or in a state in which at least a part of component (a) and at least a part of component (b) are reacted with each other (for example, ionic bond, acid base A state of forming an ion complex or a state of covalent bonding).

The foregoing has described the fluorine-based solid polymer solid electrolyte membrane of the present invention. Two or more fluoropolymer solid electrolyte membranes of the present invention can be laminated. When laminating, it is preferable to shift the openings of the upper and lower porous films with respect to each other so that dimensional changes and cross leaks can be more effectively suppressed.
When the polymer solid electrolyte membrane of the present invention is used in a polymer electrolyte fuel cell, a membrane / electrode assembly (membrane / electrode assembly) in which the polymer solid electrolyte membrane of the present invention is held tightly between an anode and a cathode ( Hereinafter often referred to as "MEA"). Here, the anode is composed of an anode catalyst layer and has proton conductivity, and the cathode is composed of a cathode catalyst layer and has proton conductivity. Further, a gas diffusion layer (described later) joined to the outer surface of each of the anode catalyst layer and the cathode catalyst layer is also referred to as MEA.

The anode catalyst layer includes a catalyst that easily oxidizes fuel (for example, hydrogen) to easily generate protons, and the cathode catalyst layer reacts protons and electrons with an oxidizing agent (for example, oxygen or air) to generate water. Includes catalyst. For both the anode and the cathode, platinum or a catalyst in which platinum and ruthenium are alloyed is preferably used as the catalyst, and the catalyst particles are preferably 10 to 1000 angstroms or less. Such catalyst particles are preferably supported on conductive particles having a size of about 0.01 to 10 μm such as furnace black, channel black, acetylene black, carbon black, activated carbon, and graphite. The amount of catalyst particles supported relative to the projected area of the catalyst layer is preferably 0.001 mg / cm ^{2 to} 10 mg / cm ² or less.

Furthermore, the anode catalyst layer and the cathode catalyst layer preferably contain a perfluorocarbon sulfonic acid polymer. The supported amount relative to the projected area of the catalyst layer is preferably 0.001 mg / cm ^{2 to} 10 mg / cm ² or less.
As a method for manufacturing the MEA, for example, the following method can be given. First, commercially available platinum-supported carbon (for example, TEC10E40E manufactured by Tanaka Kikinzoku Co., Ltd.) as a catalyst is dispersed in a solution in which a perfluorocarbon sulfonic acid polymer is dissolved in a mixed solution of alcohol and water to form a paste. A certain amount of this is applied to one side of each of the two PTFE sheets and dried to form a catalyst layer. Next, the coated surfaces of the PTFE sheets are faced to each other, the polymer solid electrolyte membrane of the present invention is sandwiched between them, and transferred and bonded by hot pressing at 100 to 200 ° C., and then the PTFE sheet is removed, thereby removing the MEA. Can be obtained. A person skilled in the art knows how to make MEAs. The method for producing MEA is described in, for example, JOURNAL OF APPLIED ELECTROCHEMISTRY, 22 (1992) p. 1-7.

  As the gas diffusion layer, commercially available carbon cloth or carbon paper can be used. Representative examples of the former include carbon cloth E-tek, B-1 manufactured by DE NORA NORTH AMERICA, USA. Representative examples of the latter include CARBEL (registered trademark, Japan Gore-Tex Co., Ltd.), Toray Industries, Inc. ) Manufactured by TGP-H, carbon paper 2050 manufactured by SPCTRACORP, USA, and the like. A structure in which the electrode catalyst layer and the gas diffusion layer are integrated is called a “gas diffusion electrode”. MEA can also be obtained by joining the gas diffusion electrode to the solid polymer electrolyte membrane of the present invention. A typical example of a commercially available gas diffusion electrode is a gas diffusion electrode ELAT (registered trademark) manufactured by DE NORA NORTH AMERICA (using carbon cloth as a gas diffusion layer).

When the anode and cathode of the MEA are coupled to each other via an electron conductive material located outside the polymer solid electrolyte membrane, an operable polymer electrolyte fuel cell can be obtained. A person skilled in the art knows how to make a polymer electrolyte fuel cell. The polymer electrolyte fuel cell is prepared by, for example, FUEL CELL HANDBOOK (VAN NOSTRAND REINHOLD, AJ APPLEBY et.al, ISBN 0-442-31926-6), Chemical One Point, Fuel Cell (Second Edition). ), Masao Taniguchi, Manabu Senoo, Kyoritsu Shuppan (1992).
As the electron conductive material, a current collector such as a composite material of graphite or resin having a groove for flowing a gas such as fuel or oxidant on its surface, or a metal plate is used. When the MEA does not have a gas diffusion layer, the MEA is incorporated into a single cell casing (for example, PEFC single cell manufactured by Electrochem Inc., USA) with the gas diffusion layer positioned on the outer surface of each anode and cathode of the MEA. Thus, a polymer electrolyte fuel cell can be obtained.

In order to extract a high voltage, the fuel cell is operated as a stack cell in which a plurality of single cells as described above are stacked. In order to produce such a fuel cell as a stack cell, a plurality of MEAs are produced and assembled into a stack cell casing (for example, PEFC stack cell manufactured by US Electrochem Corp.). In such a fuel cell as a stack cell, a current collector called a bipolar plate is used which serves to separate the fuel and oxidant of adjacent cells and to serve as an electrical connector between the adjacent cells.
The fuel cell is operated by supplying hydrogen to one electrode and oxygen or air to the other electrode. The higher the operating temperature of the fuel cell, the higher the catalyst activity. Usually, it is often operated at 50 to 80 ° C., where moisture management is easy, but it can also be operated at 80 to 150 ° C.

  Hereinafter, the present invention will be described in detail based on examples.

As Reference Example 1 fluorine-based solid polymer electrolyte solution preparation method fluorine-based solid polymer _{electrolyte, [CF 2 CF 2] 0.812} - [CF 2 -CF (-O- (CF 2) 2 -SO 3 H)] A fluoropolymer solid electrolyte solution (cast solution) having a PFS / PBI = 100/1 (mass ratio) using a perfluorocarbonsulfonic acid polymer represented by _0.188 (hereinafter referred to as “PFS”). D) was prepared as follows.
Poly [2,2 ′-(m-phenylene) -5,5′-bibenzimidazole] having a weight average molecular weight of 27000 (manufactured by Sigma Aldrich Japan Co., Ltd., hereinafter referred to as PBI) is placed in an autoclave together with DMAC. And then heated up to 200 ° C. and held for 5 hours. Thereafter, the autoclave was naturally cooled to obtain a PBI solution having a composition of PBI / DMAC (dimethylacetamide) = 10/90 (mass%). The intrinsic viscosity of this PBI solution was 0.8 (dl / g). Further, this PBI solution was diluted 10-fold with dimethylacetamide to prepare a pre-stage solution A having a composition of PBI / DMAC = 1/99 (mass%).

Next, a perfluorocarbon polymer (MI: 3.0) of tetrafluoroethylene and CF ₂ ═CFO (CF ₂ ) ₂ —SO ₂ F was produced as a PFS precursor polymer. The precursor polymer was subjected to a hydrolysis treatment by bringing it into contact with an aqueous solution in which potassium hydroxide (15% by mass) and dimethyl sulfoxide (30% by mass) were dissolved at 60 ° C. for 4 hours. Then, it was immersed in 60 degreeC water for 4 hours. Next, it was immersed in a 2N aqueous hydrochloric acid solution at 60 ° C. for 3 hours, then washed with ion-exchanged water and dried to obtain PFS having an ion-exchange capacity of 1.41 meq / g.

  This PFS was placed in an autoclave together with an aqueous ethanol solution (water: ethanol = 50.0: 50.0 (mass ratio)), sealed, heated to 180 ° C. and held for 5 hours. Thereafter, the autoclave was naturally cooled to obtain a polymer solution having a composition of PFS: water: ethanol = 5.0: 47.5: 47.5 (mass%). This polymer solution was concentrated under reduced pressure using an evaporator, and then water was added to prepare a PFS / water = 8.5 / 91.5 (mass ratio) solution as the pre-stage solution B.

After adding DMAC to the obtained pre-stage solution B and refluxing at 120 ° C. for 1 hour, the solution was concentrated under reduced pressure with an evaporator to obtain a PFS / DMAC = 1.5 / 98.5 (mass ratio) solution. Manufactured as C.
Next, after adding 6.5 g of the pre-stage solution A to 40.0 g of the pre-stage solution C and mixing, 68.9 g of the pre-stage solution B is added and stirred, and further concentrated under reduced pressure at 80 ° C. and cast. Liquid D was obtained. The concentrations of PFS and PBI in this casting solution were 5.600% by mass and 0.056% by mass, respectively.

[Examples 1 to 9]
A hole was made in a 10 cm × 10 cm sheet of aromatic polyamide film (trade name: Aramika Teijin Advanced Film). Table 1 shows the film thickness, hole shape, arrangement, and hole area ratio. Next, both surfaces of the aromatic polyamide film having the predetermined open area ratio were subjected to surface treatment to obtain a reinforcing material. In Examples 1 to 3 and 9, corona discharge treatment was performed, in Examples 4, 5 and 6, ultraviolet irradiation was performed, and in Examples 7 and 8, plasma treatment was performed on both surfaces of the porous aromatic polyamide film. Each surface treatment condition is shown in Table 1.

In Examples 1 to 3 and 6 to 8, the porous film thus prepared was used as the fluorine-based polymer solid electrolyte solution prepared in Reference Example 1 or a 5% by mass Nafion solution (Nafion ^™ / H ₂ O / isopropanol, manufactured by Solution Technology, Inc., USA, equivalent mass EW (dry mass in grams per equivalent of proton exchange groups = 1100), coated with a fluorine-based polymer solid electrolyte, and dried at room temperature The polymer solid electrolyte membrane was prepared by drying at 100 ° C. using an oven.
On the other hand, in Examples 4 and 5, the above polymer solution was cast in advance on a PTFE sheet, dried at room temperature, and then dried at 100 ° C. for 1 hour using an oven. A porous solid polyamide membrane was sandwiched and molded with a vacuum press at 200 ° C. for 1 hour to prepare a polymer solid electrolyte membrane.

In Example 9, the porous polymer film was immersed in a Nafion solution as in Example 1, then dried at room temperature, and then dried at 100 ° C. using an oven. The laminated body of the polymer solid electrolyte membrane was prepared by shifting the positions of the holes in the conductive film so as to be staggered without overlapping and forming by a vacuum press at 200 ° C. for 1 hour. Table 1 shows the thickness of the polymer solid electrolyte membrane obtained.
The polymer solid electrolyte membrane thus prepared was evaluated by the following method, and all showed good characteristics. The results are shown in Table 1.

(Proton conductivity)
After the polymer solid electrolyte membrane was treated in hot water at 95 ° C., it was cut into a width of 1 cm and a length of 7 cm in a swollen state, and the thickness T was measured. This sample was attached to a two-terminal conductivity measuring cell for measuring conductivity in a swollen state. This cell was immersed in 95 ° C. ion-exchanged water, the resistance value R at a frequency of 10 kHz was measured by the AC impedance method, and the proton conductivity σ was calculated from the following equation.
σ = L / (R × T × W)
σ: Proton conductivity (S / cm)
T: Thickness (cm)
R: Resistance value (Ω)
L: Distance between two terminals (= 5cm)
W: Sample width (= 1 cm)
(Change in wet and dry dimensions)
The polymer solid electrolyte membrane was cut into 5 cm square and immersed in 95 ° C. hot water for 5 minutes. And the length after immersion was divided | segmented by the length before immersion, and the change was calculated | required.

[Comparative Examples 1 and 2]
A polymer solid electrolyte membrane was prepared with the structure shown in Table 1. Comparative Example 1 was prepared by casting the fluoropolymer solid electrolyte solution produced in Reference Example 1 without using an aromatic polyamide film as a reinforcing material. In Comparative Example 2, a solid polymer electrolyte membrane was produced in the same manner as in Example 1 except that the porous aromatic polyamide film as a reinforcing material was not subjected to surface treatment.
In Comparative Example 1, the wet and dry dimensional change was 20%. In Comparative Example 2, peeling occurred between the aromatic polyamide film and the polymer solid electrolyte.

The present invention exhibits an effect of improving high temperature durability and is suitable as a polymer solid electrolyte membrane for a fuel cell.

Claims (5)

  It has a porous aromatic polyamide film that has been subjected to at least one surface treatment selected from corona discharge treatment, ultraviolet irradiation treatment, and plasma treatment, and has been subjected to a heat treatment at 120 ° C. or higher. Fluorine polymer solid electrolyte membrane.   The fluoropolymer solid electrolyte membrane contains a perfluorocarbon sulfonic acid polymer (a) and a basic polymer (b), and the total content of the (a) and the (b) is the fluoropolymer. It is 1 to 50% by volume in the solid electrolyte membrane, and the content of (a) ([(a) / ((a) + (b))] × 100) is 50.00 to 99.999% by mass The content of (b) ([(b) / ((a) + (b))] × 100) is 0.001 to 50.00% by mass. Fluorine polymer solid electrolyte membrane.   A fluorine polymer solid electrolyte membrane laminate comprising two or more fluorine polymer solid electrolyte membranes according to claim 1 or 2 laminated.   A membrane / electrode assembly in which an anode and a cathode are opposed to each other via the fluorine-based polymer solid electrolyte membrane or the fluorine-based polymer solid electrolyte membrane laminate according to any one of claims 1 to 3.   A polymer electrolyte fuel cell comprising the membrane / electrode assembly according to claim 4.