JP2007305577A - Method for manufacturing film-electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing film-electrode assembly, using a catalyst ink direct coating method, capable of inhibiting formation of wrinkles which causes problems, such as deterioration in its output capacity, and to provide a solid polymer electrolyte fuel cell that uses it. <P>SOLUTION: (1) In the film-electrode assembly manufacturing method, after applying a low water absorption treatment to a hydrocarbon polymer electrolyte for manufacturing a polymer electrolyte film, a low water absorption film is manufactured by forming a film from the treated object. Then, the catalyst ink, containing at least a catalyst material and solvent, is coated directly, at least on a surface of the obtained low water absorption film and the solvent is volatilized to form a catalyst layer. (2) In the film-electrode assembly manufacturing method, a low water absorption film is manufactured, by applying the low water absorption treatment to a hydrocarbon polymer electrolyte film, obtained by forming a film from the hydrocarbon polymer electrolyte for manufacturing the polymer electrolyte film. Then, the catalyst ink including at least the catalyst material and the solvent is coated directly, at least on a surface of the obtained low water absorption film, and the solvent is volatilized to form a catalyst layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a membrane-electrode assembly, and a membrane-electrode assembly and a polymer electrolyte fuel cell produced thereby.

  In recent years, solid polymer fuel cells are expected to be put to practical use as power generators in applications such as residential use and automobile use. The polymer electrolyte related to the ion conductive membrane (polymer electrolyte membrane) used in the polymer electrolyte fuel cell is replaced with a fluorine-based polymer electrolyte represented by Nafion (registered trademark of DuPont), which has been mainly used conventionally. Attention has been focused on hydrocarbon polymer electrolytes that are inexpensive and have excellent mechanical strength and heat resistance.

  By the way, the polymer electrolyte fuel cell has electrodes called catalyst layers containing a catalyst such as platinum that promotes the oxidation-reduction reaction between hydrogen and air on both sides of the polymer electrolyte membrane, and further on the outside of the catalyst layer. It is used as a form having a gas diffusion layer for efficiently supplying gas to the catalyst layer. Here, what formed the catalyst layer on both surfaces of the polymer electrolyte membrane is usually called a membrane-electrode assembly (hereinafter also referred to as “MEA”).

  As a method for producing such MEA, a method of directly forming a catalyst layer on a polymer electrolyte membrane, a catalyst layer is formed on a base material that becomes a gas diffusion layer such as carbon paper, and this is joined to the polymer electrolyte membrane. And a method of forming a catalyst layer on a flat support substrate, transferring it to a polymer electrolyte membrane, and then peeling the support substrate. In these methods, a dispersion or solution in which a catalyst is dispersed or dissolved (hereinafter referred to as “catalyst ink”) is used to form a catalyst layer. The catalyst ink usually contains a catalyst substance (catalyst powder) in which a platinum group metal is supported on activated carbon or the like, a polymer electrolyte, and, if necessary, a water repellent, a pore former, and a thickener, and these are solvents. It is dispersed or dissolved in.

Among the MEA manufacturing methods, a method of directly applying a catalyst ink to a polymer electrolyte membrane (catalyst ink direct application method) has attracted attention as a method of directly forming a catalyst layer on a polymer electrolyte membrane. When the catalyst layer is formed by this method, the adhesion between the membrane and the catalyst layer becomes strong, and a polymer electrolyte fuel cell having excellent power generation characteristics can be obtained. Here, as a method of applying the catalyst ink, there are usually existing methods such as a die coater, screen printing, spray method, and ink jet.
However, usually, when the catalyst layer is formed by the method of directly applying the catalyst ink to the polymer electrolyte membrane, the polymer electrolyte membrane in contact with the peripheral portion of the catalyst layer is likely to generate large wrinkles that can be visually judged, A fuel cell using such an MEA has a problem that stable output performance cannot be obtained.

  As a method for suppressing the generation of wrinkles as described above in the MEA production method, for example, after fixing a polymer electrolyte membrane to a substrate such as a PET film, the catalyst layer is applied by applying a catalyst ink by screen printing. A method for forming the substrate and then peeling the substrate has been proposed (for example, see Patent Document 1). In this method, the catalyst ink is applied to one side and dried, and then the polymer electrolyte membrane is peeled off from the substrate, fixed to the substrate again with the front and back sides reversed, and the catalyst ink is applied to the other side. By manufacturing a catalyst layer, MEA can be obtained.

In addition, when applying the catalyst ink to the polymer electrolyte membrane by the ink-jet method, when dropping the droplet, the droplet is dropped at a predetermined distance, and then the droplet is dropped between the dropped droplets. There is disclosed a method for suppressing generation of wrinkles due to direct application of catalyst ink by repeating the dropping of droplets a plurality of times in the manner of dripping (see, for example, Patent Document 2).
JP 2001-160405 A (Claims) JP-A-2005-267916 (Claims)

However, the method of Patent Document 1 has a drawback that a very complicated process is required, and the polymer electrolyte membrane is mechanically removed in the process of peeling or bonding the polymer electrolyte membrane from the substrate. Expected to take damage. Further, the method of Patent Document 2 can be applied only to the ink jet method, and further, it takes much time to apply the catalyst ink over a large area, so that productivity is higher than that of other application techniques. There was a disadvantage of being inferior.
The present invention relates to a simple method for producing a membrane-electrode assembly using a catalyst ink direct coating method, which causes problems such as a reduction in output performance, and is capable of suppressing the generation of wrinkles. The purpose is to provide. In addition, a membrane-electrode assembly obtained by the production method and a polymer electrolyte fuel cell using the same are provided.

In order to achieve the above object, the present inventors have intensively studied, and as a result, completed the present invention. That is, this invention provides the manufacturing method shown to following [1] as 1st Embodiment.
[1] A hydrocarbon polymer electrolyte for production of a polymer electrolyte membrane is obtained by subjecting the hydrocarbon polymer electrolyte to a treatment for reducing water absorption as shown below to produce a low water absorption membrane by forming the treatment product. Subsequently, a catalyst ink containing a catalyst substance and a solvent is directly applied to at least one surface of the obtained low water absorption membrane, and the catalyst layer is formed by volatilizing the solvent to form a membrane-electrode assembly. [Low water absorption treatment]
Treatment for reducing the water absorption obtained by the following formula when the salt substitution rate is 1% or less by 10% or more Water absorption (wt%) = 100 × (W1-W2) / W2 Formula 1
(W1 represents the weight (saturated water absorption weight) when the membrane is saturatedly absorbed, and W2 represents the dry weight of the membrane.)

Referring to the definition of the salt substitution ratio, when the ion exchange groups of the polymer electrolyte is an acidic group, among the acidic group, hydrogen ions (H ⁺⁾ of cations other than (e.g., an alkali metal ion, an alkaline earth It means the ratio of a group having a metal ion, a transition metal ion, a quaternary ammonium ion, etc.) as a counter ion to the total number of the acidic groups. On the other hand, when the ion exchange group of the polymer electrolyte is a basic group, an anion other than hydroxide ion (OH ⁻ ) in the basic group (eg, halogen ion, sulfate ion, nitrate ion, acetate ion) Or the like) as a counter ion to the ratio of the total number of the basic groups. Usually, when the salt substitution rate is lowered in the polymer electrolyte membrane, the water absorption rate tends to increase. When the salt substitution rate is 1% or less, the water absorption rate is saturated. Further, the polymer electrolyte membrane having a salt substitution rate of 1% or less as defined in the low water absorption treatment is a polymer electrolyte having a salt substitution rate of 1% or less in the polymer electrolyte that is a precursor of the membrane. A polymer electrolyte membrane formed by forming such a polymer electrolyte.
The “hydrocarbon polymer electrolyte” is a polymer electrolyte having an acidic group or a basic group as an ion exchange group, and when the salt substitution rate is 1% or less, a carbon atom, a hydrogen atom, an oxygen atom It means a polymer electrolyte having a total composition of atoms consisting of nitrogen atoms, sulfur atoms and silicon atoms of 85% by weight or more.

Furthermore, this invention provides the manufacturing method shown to following [2] as 2nd Embodiment.
[2] A polymer electrolyte membrane obtained by forming a hydrocarbon polymer electrolyte for producing a polymer electrolyte membrane was subjected to the following low water absorption treatment to produce a low water absorption membrane, and then obtained. A method for producing a membrane-electrode assembly, wherein a catalyst layer containing a catalyst substance and a solvent is directly applied to at least one surface of the low water absorption membrane, and the solvent is volatilized to form a catalyst layer. processing]
Treatment for reducing the water absorption obtained by the following formula when the salt substitution rate is 1% or less by 10% or more Water absorption (wt%) = 100 × (W1-W2) / W2 Formula 1
(W1 represents the weight (saturated water absorption weight) when the membrane is saturatedly absorbed, and W2 represents the dry weight of the membrane.)
Here, the definitions of “salt substitution rate” and “hydrocarbon polymer electrolyte” are as defined above.

Furthermore, the following [3] is provided as the low water absorption treatment according to the present invention.
[3] The above-mentioned [1] or [2], wherein the lower hydration treatment is a treatment for reducing the water absorption obtained by Formula 1 by 30% or more when a polymer electrolyte membrane having a salt substitution rate of 1% or less is used. ] The manufacturing method of the membrane-electrode assembly as described in

Furthermore, in the hydrocarbon-based polymer electrolyte for producing the polymer electrolyte membrane, the higher the water absorption when the salt substitution rate is 1% or less, the more the ion conductivity of the polymer electrolyte membrane according to the MEA obtained is improved. Preferably, the following [4] is provided.
[4] When the hydrocarbon-based polymer electrolyte is a polymer electrolyte membrane having a salt substitution rate of 1% or less, the water absorption obtained by Formula 1 is 80% by weight or more, [1] to [3] ] The manufacturing method of the membrane-electrode assembly in any one of

Here, the water-absorbing treatment is not particularly limited as long as it is a method capable of reducing the water-absorbing rate obtained by the water-absorbing rate measuring method described later by 10% or more. The obtained low water absorption membrane can dramatically reduce the generation of soot during the formation of the catalyst layer, which is the object of the present invention. However, the water-absorbing treatment may reduce the ionic conductivity of the polymer electrolyte membrane itself, and not only suppresses the generation of soot by improving the water absorption after the formation of the catalyst layer as described later. When MEA having practical ion conductivity is obtained, the following [5] is provided.
[5] The method for producing a membrane-electrode assembly according to any one of [1] to [4], further improving the water absorption rate of the low water absorption membrane after the formation of the catalyst layer.

In the low water absorption treatment, the present inventors pay attention to the relationship between the salt substitution rate of the polymer electrolyte and the water absorption rate as described above, and the treatment for reducing the water absorption rate is simple by increasing the salt substitution rate. In addition, it has been found that once the water absorption is reduced, it is easy to improve the water absorption again, and it has been found that it can be suitably used in the production method of the present invention. That is, the following [6] is preferable.
[6] The method for producing a membrane-electrode assembly according to any one of [1] to [5], wherein the low water absorption membrane is a membrane made of a polymer electrolyte having a salt substitution rate of 50% or more.

Among the methods of directly applying the catalyst ink to the low water absorption film, the spray method is preferable because it is industrially simple and provides the following [7].
[7] The method for producing a membrane-electrode assembly according to any one of [1] to [6], wherein the catalyst ink is directly applied to the low water absorption film using a spray method.

Further, the hydrocarbon polymer electrolyte is preferably an acidic ion group because the ion conductivity (proton conductivity) of the obtained polymer electrolyte membrane is further improved, and the following [8] is provided. [8] The method for producing a membrane-electrode assembly according to any one of [1] to [7], wherein the ion exchange group of the hydrocarbon-based polymer electrolyte is an acidic group.

The above MEA can be suitably used as a fuel cell, and provides the following [9] or [10].
[9] Membrane-electrode assembly [10] obtained by any of the above production methods [10] A polymer electrolyte fuel cell comprising a pair of separators and a membrane-electrode assembly disposed between the pair of separators The membrane-electrode assembly is the membrane-electrode assembly according to [9] above, wherein the polymer electrolyte fuel cell is characterized in that

  ADVANTAGE OF THE INVENTION According to this invention, the simple manufacturing method of MEA which does not have a wrinkle on the polymer electrolyte membrane surface which contact | connects the catalyst layer periphery part concerning said catalyst ink direct coating method can be provided. The MEA obtained by the production method of the present invention is extremely useful industrially because it is less likely to cause a decrease in output due to the occurrence of such soot and can provide an excellent fuel cell.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings as necessary.

  The hydrocarbon-based polymer electrolyte for producing a polymer electrolyte membrane applied to the first embodiment and the second embodiment of the present invention is a polymer having an ion exchange group related to ion conduction, and the ion exchange The group may be either an acidic group (cation exchange group) or a basic group (anion exchange group). A suitable example of the polymer electrolyte or a solution casting method suitable for making the polymer electrolyte into a membrane will be described later. Such a polymer electrolyte exhibits water absorption according to the hydration of its ion exchange group. The MEA manufacturing method provided by the present invention is characterized by using a low water absorption film obtained by reducing the water absorption.

First, the low water absorption film according to the first embodiment will be described.
The low water absorption treatment in this embodiment is obtained by the above formula 1 when the polymer electrolyte applied to the present invention is in the form of a polymer electrolyte membrane composed of a polymer electrolyte having a salt substitution rate of 1% or less. The water absorption rate is an index, and the water absorption rate is reduced by 10% or more.

  The low water absorption treatment is a treatment for reducing the water absorption rate of the hydrocarbon-based polymer electrolyte by 10% or more, preferably a treatment for reducing by 30% or more, and more preferably a treatment for reducing by 40% or more. The treatment is preferably 50% or more, more preferably 60% or more. Thus, since the effect which suppresses generation | occurrence | production of the target flaw becomes high when the water absorption rate reduction effect by the said low water absorption process is large, it is preferable.

Here, the method for measuring the water absorption rate will be described in detail.
About 200 mg of the membrane is cut out at room temperature. The cut out membrane is put into a 250 mL beaker made of polypropylene with a screw cap, and about 150 mL of ion-exchanged water that has been preliminarily kept at 100 ° C. is added thereto, and then the membrane is immersed in ion-exchanged water. After covering with a screw cap, it is placed in a thermostatic bath that has been kept warm at 100 ° C. for 2 hours. In this way, the film is sufficiently absorbed at a storage temperature of 100 ° C. while being slightly pressurized. Thereafter, the membrane was taken out from the above beaker, immersed in ion exchange water at room temperature (about 25 ° C.) for several seconds and cooled, then the membrane was taken out, and the water adhering to the surface was wiped off with a filter paper. Saturated water absorption weight W1 is measured with HR73 type. Thereafter, the heating temperature of the moisture meter is set to 105 ° C., the film is dried until a constant weight is reached, and the dry weight W2 is measured. The water absorption rate can be obtained by substituting W1 and W2 obtained in this way into the above formula 1.
Here, “ion-exchanged water” is water having a resistivity at 25 ° C. of 10 MΩ · cm or more, and these can be easily obtained by using a commercially available pure water production apparatus. Further, in the immersion, the film may be gently stirred as long as the shape of the film can be maintained. In these operations, it is necessary to prevent the membrane from causing contamination that affects the weight measurement. However, the degree of contamination caused by a small amount of dust or the like in the above operation is allowable in the error of the measured values of W1 and W2. .

Here, a method for obtaining a polymer electrolyte membrane having a salt substitution rate of 1% or less will be described. When a polymer electrolyte having an acidic group as an ion exchange group is obtained with a salt substitution rate exceeding 1% after its production, the polymer electrolyte can be easily treated by acid treatment with a large amount of acid. A polymer electrolyte having a salt substitution rate of 1% or less can be obtained. On the other hand, when a polymer electrolyte having a basic group as an ion exchange group is obtained with a salt substitution rate exceeding 1% after its production, the polymer electrolyte can be subjected to an alkali treatment with a large amount of alkali. A polymer electrolyte having a salt substitution rate of 1% or less can be easily obtained. Here, the definition of “large amount” means that it is 10 equivalent times or more with respect to the ion exchange capacity (ion exchange group equivalent per unit weight) of the polymer electrolyte to be used. It means that the above acid is used or 10 equivalent times or more alkali is used for the alkali treatment.
The polymer electrolyte having an acid-treated acidic group or an alkali-treated basic electrolyte is subjected to salt substitution by washing with water if necessary, and then forming a film. A polymer electrolyte membrane having a rate of 1% or less can be obtained. The film forming method is preferably a solution casting method, and details thereof will be described later.

Next, the water absorption reduction process according to the first embodiment will be described.
As described above, it is a treatment for reducing the water absorption rate of the polymer electrolyte membrane by 10% or more, and the low water absorption treatment is particularly limited as long as it can reduce the water absorption rate as described above. Although it is not a thing, it is preferable when a low water absorption film | membrane is obtained by the low water absorption process shown by the following (i).
(i) Converting the salt substitution rate of the hydrocarbon-based polymer electrolyte to 50% or more, and then producing a low water absorption membrane from the polymer electrolyte with the converted salt substitution rate by a film-forming method such as a solution casting method Do

The method shown in (i) is a method in which ions having opposite charges are neutralized with respect to the ion exchange groups in the polymer electrolyte to form a salt form group. As described above, the existence ratio of the number of ion-exchange groups converted into a salt form group to the total number of ion-exchange groups is defined as the salt substitution rate. Here, a compound capable of providing an ion having the opposite charge is referred to as a “salt substitute”.
Specifically, it will be explained that the ion exchange group becomes a group in the form of a salt.
When the polymer electrolyte has an acidic group such as a sulfonic acid group (—SO ₃ H), a carboxyl group (—COOH), or a phosphonic acid group (—PO ₃ H ₂ ) as an ion exchange group, the acidic group This is achieved by ion-exchange of hydrogen ions that ionically bond with cation other than hydrogen ions. Examples of cations other than hydrogen ions include alkali metal ions such as lithium ion, sodium ion and potassium ion, alkaline earth metal ions such as magnesium ion and calcium ion, transition metal ions such as iron ion, nickel ion and copper ion, ammonium Examples thereof include quaternary ammonium ions such as ions, tetramethylammonium ions, tetraethylammonium ions, tetrabutylammonium ions and benzyltrimethylammonium ions. Among these, a cation having a valence of 2 or more or a quaternary ammonium ion is preferable because the effect of suppressing generation of soot is higher.
As a specific method by ion exchange, a polymer electrolyte having an acidic group as an ion exchange group is dissolved or dispersed in water and / or an organic solvent in advance, and a salt substitution agent having a cation exemplified above is added. The acid group can be converted into a salt form group by an ion exchange reaction. The treatment time for the ion exchange reaction is usually 10 minutes to 24 hours, preferably 0.5 to 10 hours, more preferably 1 to 5 hours. The treatment temperature is selected from 0 to 100 ° C., preferably 10 to 50 ° C., but usually about room temperature is sufficient. Here, examples of the salt displacing agent having the cation include a basic compound (for example, a hydroxide of the cation exemplified above) or a salt (for example, the chloride, bromide, etc. of the cation exemplified above). It is done.

  Specific examples of the salt displacing agent having the cation will be given. Examples of the basic compound include sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and benzyltrimethylammonium hydroxide. As salts, sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium bromide, potassium bromide, calcium bromide, magnesium bromide, sodium acetate, calcium acetate, magnesium acetate, tetramethylammonium chloride, benzyltrimethylammonium chloride , Tetraethylammonium bromide, benzyltrimethylammonium bromide, and the like. Among these, a salt displacing agent that supplies a divalent or higher cation or a quaternary ammonium ion, which is a preferred cation, is preferable. Calcium hydroxide, magnesium hydroxide , Calcium chloride, magnesium chloride, tetramethylammonium hydroxide, tetraethylammonium hydroxide, benzyltrimethylammonium hydroxide, tetraethylammonium chloride, benzyl chloride Trimethyl ammonium are preferred.

On the other hand, when the polymer electrolyte has a basic group such as a trimethylammonio group (—N ⁺ (CH ₃ ) ₃ ) or a triethylammonio group (—N ⁺ (C ₂ H ₅ ) ₃ ), the base The basic group is ion-exchanged with an anion other than hydroxide ions, such as chloride ion, bromine ion, iodine ion, acetate ion, nitrate ion, sulfate ion, etc. To a salt form group.
In this method, as in the case of the polymer electrolyte having an acidic group, a polymer electrolyte having a basic group is dissolved or dispersed in water and / or an organic solvent and has an anion other than hydroxide ions. By adding a salt substitution agent, the basic group can be converted into a salt form group by an ion exchange reaction. Examples of the treatment time and treatment temperature related to the ion exchange reaction are the same conditions as those of the polymer electrolyte membrane having an acidic group. Examples of the salt displacing agent for the basic group include acidic compounds (for example, protonic acids of the anions exemplified above) or salts (for example, sodium salts and potassium salts of the anions exemplified above).
As the salt-substituting agent, hydrochloric acid, sulfuric acid, nitric acid and the like, which are usually strongly acidic compounds, are preferable, and hydrochloric acid is particularly preferable. When used as these acidic compounds, an ion exchange reaction can be performed regardless of the type of the basic group in the polymer electrolyte.

  Here, the salt substitution rate of the polymer electrolyte is preferably 50% or more, more preferably 70% or more, still more preferably 80% or more, still more preferably 90% or more, and particularly preferably. Is 95% or more, particularly preferably 99% or more. A higher salt substitution rate is preferred because the water-absorbing effect tends to be higher. A method for controlling the salt substitution rate will be described. First, the ion exchange capacity of the polymer electrolyte to be used is obtained in advance by a known method. It can be easily controlled by adding a salt substitution agent in a desired equivalent ratio with respect to the ion exchange capacity (number of moles of ion exchange groups per unit weight of the polymer electrolyte). When the salt substitution rate is 95% or more, a salt substitution agent may be added to the ion exchange group in excess of the equivalent value calculated from the ion exchange capacity of the polymer electrolyte. In particular, when the salt substitution rate of the ion exchange capacity is 99% or more, the salt substitution agent may be used in an amount of 10 equivalents or more with respect to the number of ion exchange groups determined from the ion exchange capacity.

  In order to form a polymer electrolyte having a salt substitution rate of 50% or more and obtain a low water-absorbing film obtained in this manner, when the polymer electrolyte is soluble in a solvent, a solution casting method, When insoluble, known film forming methods such as an extrusion molding method and an inflation molding method can be applied.

The salt substitution rate of the obtained low water absorption membrane can be determined by a titration method. In the case of a low water absorption membrane obtained from a polymer electrolyte having an acidic group and having a salt substitution rate of 50% or more, by immersing the low water absorption membrane in an aqueous sodium hydroxide solution having a predetermined concentration and volume, After ion exchange of acidic groups that are ion-bonded with proton ions, sodium hydroxide solution is titrated with hydrochloric acid at a predetermined concentration to calculate the amount of residual sodium hydroxide. it can.
On the other hand, in the case of a low water absorption membrane obtained from a polymer electrolyte having a basic group and having a salt substitution rate of 50% or more, by immersing the low water absorption membrane in an aqueous hydrochloric acid solution having a predetermined concentration and volume, After ion exchange of basic groups in the polymer electrolyte, which are ion-bonded with hydroxide ions, to chloride ions, this hydrochloric acid solution is titrated with a sodium hydroxide aqueous solution of a predetermined concentration to determine the amount of residual hydrochloric acid. It can be calculated by obtaining.

  In this way, a low water absorption film comprising a polymer electrolyte having a salt substitution rate of 50% or more is obtained, and then a catalyst layer is formed on the obtained low water absorption film by a catalyst ink direct coating method, To do. Thereafter, the ion-exchange group in the form of a salt in the low water-absorbing membrane is bound to a free acidic group (an acidic group ionically bonded to hydrogen ions) or a free basic group (an ion bond to hydroxide ions). The basic group can be easily restored. This method can be carried out by applying an acid treatment in the case of a low water absorption membrane having an acidic group and an alkali treatment in the case of a low water absorption membrane having a basic group.

Next, the low water absorption film according to the second embodiment will be described.
The low water absorption treatment in such an embodiment means that a hydrocarbon-based polymer electrolyte to be applied to the present invention is formed in advance to obtain a polymer electrolyte membrane, and the water absorption rate of the polymer-electrolyte membrane is determined according to the hydrocarbon-based high electrolyte. When the molecular electrolyte is in the form of a polymer electrolyte membrane having a salt substitution rate of 1% or less, the water absorption obtained by the above formula 1 is reduced to 10% or more.

  Also for this low water absorption treatment, the water absorption rate of the resulting low water absorption membrane is to reduce the water absorption rate by 10% or more, preferably 30% or more, and preferably 40% or more reduction. More preferably, it is a treatment that reduces by 50% or more, and even more preferred is a treatment that reduces by 60% or more. Thus, since the effect which suppresses generation | occurrence | production of the target flaw becomes high when the water absorption rate reduction effect by the said low water absorption process is large, it is preferable.

The low water absorption treatment applied to the second embodiment is preferably the following (ii) or (iii).
(ii) A polymer electrolyte having a salt substitution material of less than 50% is formed in advance by a solution casting method or the like to obtain a polymer electrolyte membrane, and the salt substitution rate of the polymer electrolyte membrane is 50% or more. To produce a low water absorption membrane
(iii) A low water-absorbing film obtained by crosslinking a polymer electrolyte molecule by a treatment selected from a heat treatment, an ionizing radiation irradiation treatment, or a chemical treatment on a polymer electrolyte membrane obtained by forming a polymer electrolyte by a solution casting method or the like Manufacture

First, the process shown in (ii) above will be described.
In this method, first, a polymer electrolyte membrane having a salt substitution rate of less than 50% is formed in advance to obtain a polymer electrolyte membrane, and then the salt substitution rate of the polymer electrolyte membrane is set to 50% or more. Yes, the low water absorption film finally obtained is the same low water absorption film as the above (i). The salt substitution rate before film formation can be within the above range, but it is preferable to use a polymer electrolyte having a salt substitution rate of 1% or less because it can be easily formed by a solution casting method.

Specifically, in the case of a polymer electrolyte having an acidic group with a salt substitution rate of less than 50%, the polymer electrolyte is formed into a polymer electrolyte membrane by a solution casting method, and then this polymer electrolyte is formed. The electrolyte membrane is immersed in water and / or an organic solvent. Into the polymer electrolyte membrane, a salt-substituting agent having a cation other than hydrogen ions is added and immersed for 10 minutes to 24 hours, preferably 0.5 to 10 hours, more preferably 1 to 5 hours. The hydrogen ion ion-bonded to the acidic group is ion-exchanged with the cation of the salt substitution agent. The temperature in the ion exchange is selected from 0 to 100 ° C., preferably 10 to 50 ° C., but about room temperature is usually sufficient.
In such a method, the salt substitute agent may be dissolved in water and / or an organic solvent in advance to prepare a salt substitute solution, and the polymer electrolyte membrane may be immersed therein. Moreover, the method of spraying the said salt-substitution agent solution on a polymer electrolyte membrane may be used.

  On the other hand, in the case of a polymer electrolyte having a basic group with a salt substitution rate of less than 50%, after forming a polymer electrolyte membrane by a solution casting method, salt substitution having an anion other than hydroxide ions Except for using an agent, it is the same as the above-described polymer electrolyte having an acidic group.

  Here, examples of the salt substitution agent having a cation other than the hydrogen ion and the salt substitution agent having an anion other than the hydroxide ion may be the same as those exemplified in the above (i).

Here, when converting the salt substitution rate of the polymer electrolyte membrane, the salt substitution rate is more preferably 70% or more, more preferably 80% or more, still more preferably 90% or more, and even more preferably 95% or more. If it is, it is especially preferable, and it is especially preferable when it is 99% or more.
Thus, the method of controlling the salt substitution rate can be easily carried out by replacing “polymer electrolyte” with “polymer electrolyte membrane” in the above (i). In addition, when the salt substitution rate (referred to as “initial salt substitution rate”) of the polymer electrolyte membrane before the water absorption treatment is more than 1% and less than 50%, the low water absorption membrane after the treatment Thus, the equivalent ratio of the salt-substituting agent to be used can be controlled so that the salt-substitution rate is 50% or more. Moreover, what is necessary is just to use the titration method demonstrated in said (i) as a method of calculating | requiring an initial stage salt substitution rate.

Next, the method shown in (iii) will be described.
The heat treatment in the above (iii) is usually an effective treatment for a polymer electrolyte membrane obtained from a polymer electrolyte having an acidic group such as a carboxyl group or sulfonic acid. When a polymer electrolyte membrane made of such a polymer electrolyte is subjected to a heat treatment, the acid groups are condensed to form an acid anhydride group, thereby reducing the water absorption rate. In addition, the low water absorption membrane obtained by converting the acidic group into the acid anhydride group in this manner is obtained by immersing the MEA after manufacturing the catalyst layer in water and heating (hydrolyzing) it as necessary. Thus, the acid anhydride can be returned to the original acidic group.

As for the conditions for the heat treatment (treatment temperature, treatment time, etc.), it is possible to obtain suitable conditions by confirming the ratio at which the acidic groups are converted into acid anhydrides with an IR spectrum or the like. Usually, the processing temperature is 100 to 400 ° C, preferably 150 to 300 ° C. The treatment time varies depending on the reaction temperature, but is usually 10 seconds to 100 hours, preferably 1 minute to 1 hour. The treatment atmosphere is not particularly limited in air, in an inert gas (nitrogen gas, helium gas, argon gas, etc.), in a vacuum, or the like.
More specifically, it can be performed according to the method described in JP-T-2000-501223.
In addition, the polymer electrolyte constituting the polymer electrolyte membrane includes an ethylenically unsaturated group (vinyl group, allyl group, styryl group, etc.), acetylenically unsaturated group (ethynyl group, propynyl group, etc.), nitrile group, epoxy When there is a group capable of causing a crosslinking reaction by heating (hereinafter collectively referred to as “thermal crosslinking group”), exemplified by a group, oxetanyl group, etc., these thermal crosslinking groups may be crosslinked by heat treatment. .

Next, ionizing radiation processing will be described.
The ionizing radiation irradiation treatment is a treatment for generating a radical in the molecular chain of the polymer electrolyte by the ionizing action and causing a crosslinking reaction by a recombination reaction between the radicals. Examples of the ionizing radiation include γ rays, X rays, vacuum ultraviolet rays, ultraviolet rays, visible rays, near infrared rays, infrared rays, and electron beams. By irradiating the polymer electrolyte membrane with ionizing radiation selected from these examples, a low water absorption membrane in which the polymer electrolyte is crosslinked can be obtained. In addition, when ultraviolet rays or visible rays are selected as the ionizing radiation, groups capable of causing a crosslinking reaction by the action of these ionizing radiations in the polymer electrolyte (hereinafter collectively referred to as “ionizing radiation groups”). Applicable to what you have. Examples of the ionizing radiation group include benzophenone group, α-diketone group, acyloin group, acyloin ether group, benzylalkyl ketal group, acetophenone group, quinone group, thioxanthone group, and acylphosphine group. Furthermore, when it has an ethylenically unsaturated group and an acetylenic unsaturated group which were illustrated to the said thermal crosslinking group with this ionizing radiation group, a crosslinking reaction will arise easily.
The ionizing radiation irradiation is preferably performed in an inert gas such as nitrogen or argon. The temperature at the time of a process can be performed in the range of room temperature to 250 degreeC. Irradiation time can be performed between 1 second and 100 hours, and more specifically, can be performed according to the method described in JP-A No. 2003-217342.
Further, when the main chain or side chain of the polymer electrolyte membrane has a saturated hydrocarbon group, radicals can be generated in the saturated hydrocarbon group by irradiation with X-rays, γ-rays or electron beams. A crosslinking reaction can also be caused by such a radical recombination reaction.

Next, chemical treatment will be described.
Here, the chemical treatment is a cross-linking reaction using a reactive agent (hereinafter referred to as a cross-linking agent) having a reactive group that forms a covalent bond with the polyelectrolyte constituting the polymer electrolyte membrane in a plurality of molecules. Means a process that generates By allowing the crosslinking agent to coexist in the polymer electrolyte, the crosslinking agent becomes a bridging group for the polymer electrolyte and causes a crosslinking reaction. Here, specific examples of the crosslinking agent include methylol crosslinking agents such as dimethylol urea, trimethylol melamine, and dimethylol cresol, epoxy crosslinking agents such as bisglycidyl bisphenol A and bisglycidyl bisphenol F, and isocyanates such as tolylene diisocyanate. Examples thereof include a system cross-linking agent. In addition, as described above with reference to the action of ionizing radiation, a crosslinking agent that can cause a proton radical abstraction reaction in the molecular chain of the polymer electrolyte is also within the category of the above chemical treatment. Examples thereof include peroxides such as oxide and benzoyl peroxide.
These chemical treatments can be carried out after the polymer electrolyte membrane has been produced in advance, or can be formed into a membrane from a mixture of a polymer electrolyte and a crosslinking agent, and simultaneously crosslinked.
Any of these methods can provide a low water-absorbing film in which polymer electrolyte molecules are crosslinked.

  A low water absorption membrane can be obtained by any of the above methods (i), (ii), or (iii). Furthermore, after obtaining the low water absorption film, it is preferable to perform water washing or the like, wash the low water absorption film, and then dry. The drying method is not particularly limited, but it is necessary to perform the drying under conditions where the water absorption rate of the low water absorption film can be maintained, and it is preferable to dry at room temperature.

  Among the methods selected from (i) according to the first embodiment and (ii) and (iii) according to the second embodiment exemplified as a method for obtaining a low water absorption membrane, the low water absorption once reduced in water absorption It is preferable if the water absorption rate of the low water absorption membrane can be improved after the catalyst layer is formed by the method described later. From such a viewpoint, among the above, the low water absorption membrane obtained by (i) of the first embodiment or (ii) of the second embodiment is preferable. The low water absorption membrane obtained in (i) or (ii) is composed of a polymer electrolyte having a salt substitution rate of 50% or more. The ion exchange group once salt-substituted is converted into a free ion exchange group (hydrogen ion). And an anion exchange group ion-bonded to a hydroxide ion). By doing in this way, the water absorption of a low water absorption film | membrane can be improved. Increasing the water absorption rate is preferable because the ion conductivity of the MEA itself finally obtained can be increased, and a fuel cell having such an MEA can be obtained with better power generation performance.

As a method for forming a polymer electrolyte membrane having a salt substitution rate of 1% or less for obtaining the water absorption rate, or a method for forming a low water absorption membrane shown in (i), (ii) or (iii) above, The solution casting method is preferable because the operation is simple. Here, the solution casting method is a method of forming a film by dissolving a polymer electrolyte in an appropriate solvent, casting the solution onto a glass plate, and removing the solvent. The solvent used for film formation is not particularly limited as long as the applied polymer electrolyte can be dissolved and can be removed after film formation. N, N-dimethylformamide (hereinafter referred to as “DMF”) Aprotic polar solvents such as N, N-dimethylacetamide (hereinafter referred to as “DMAc”), N-methyl-2-pyrrolidone (hereinafter referred to as “NMP”), dimethyl sulfoxide (hereinafter referred to as “DMSO”), Or, chlorinated solvents such as dichloromethane, chloroform, 1,2-dichloroethane, chlorobenzene, dichlorobenzene, alcohols such as methanol, ethanol, propanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol mono Echi Alkylene glycol monoalkyl ethers such as ether is preferably used.
These solvents can be used alone, or two or more solvents can be mixed and used as necessary. Among these, DMF, DMAc, NMP, DMSO and the like are preferable because of high solubility of the polymer electrolyte.

The catalyst layer is formed by directly applying the catalyst ink to at least one surface of the low water absorption film obtained as described above.
Here, the catalyst ink includes a catalyst substance and a solvent as essential components. As the catalyst material, those used in conventional fuel cells can be used as they are, and examples thereof include those well known in the art such as noble metals such as platinum and platinum-ruthenium alloys. Further, from the viewpoint that hydrogen ions and electrons can be easily transported in the catalyst layer, it is preferable to use a catalyst material supported on a conductive material. Examples of the conductive material include conductive carbon materials such as carbon black and carbon nanotubes, and ceramic materials such as titanium oxide.

The catalyst ink applied to the present invention preferably contains a polymer electrolyte in addition to the catalyst substance and the solvent. The polymer electrolyte is not particularly limited as long as it has ion conductivity and functions as a binder for binding the catalyst substance, and conventionally known Nafion (trade name) manufactured by DuPont or an aliphatic high polymer. Molecular electrolytes and aromatic polymer electrolytes can be used.
The other components constituting the catalyst ink are optional and are not particularly limited. For the purpose of increasing the water repellency of the catalyst layer, a water repellent material such as PTFE is used, and for the purpose of increasing the gas diffusibility of the catalyst layer, A pore former such as calcium carbonate may contain a stabilizer such as a metal oxide for the purpose of further enhancing the durability of the obtained MEA.

  On the other hand, the solvent related to the catalyst ink is not particularly limited, but components other than the solvent constituting the catalyst ink are dissolved, dispersed uniformly at the molecular level, or from nanometer to micrometer. It is desirable to form aggregates at a level and disperse the aggregates. The solvent may be a single solvent or a mixture of a plurality of solvents. When a fluorine-based polymer electrolyte such as Nafion is used as the polymer electrolyte, a mixed solvent composed of water and a hydrophilic organic solvent is usually used.

  The catalyst ink is obtained by mixing the above-described catalyst material and / or a catalyst-supporting material in which a catalyst material is supported on a conductive material, a solvent, and other components by a known method. Examples of the mixing method include a method using an ultrasonic dispersing device, a homogenizer, a ball mill, a planetary ball mill, a sand mill and the like.

  The method for directly applying the catalyst ink to the surface of the low water absorption film is not particularly limited, and an existing method such as a die coater, screen printing, a spray method, or an ink jet method can be used. Among these, the present inventors have found that a coating method by a spray method is particularly preferable in terms of suppressing the generation of the target wrinkles in addition to simple operation. Although the reason for this is not clear, in the direct application by the spray method, the solvent is vaporized in the atmosphere while the catalyst ink reaches the film from the discharge port, and the solvent taken in when the catalyst ink contacts the low water absorption film. It is presumed that this can be reduced. Moreover, this spray method is preferable also from operation being easy industrially.

As a method for spraying the catalyst ink, for example, an apparatus and a method described in JP-A-2004-89976 can be specifically exemplified, and these can be used.
That is, a low water absorption film is installed on the stage, and the catalyst ink is directly applied to the low water absorption film. In the spray method, catalyst ink scatters in the form of particles from the discharge port and adheres to the low water absorption film. The stage is desirably heated in order to remove the solvent immediately after coating, and the temperature is preferably 50 ° C to 150 ° C. A temperature range of the above range is preferable because the solvent of the catalyst ink is easily removed and the low water absorption film is less likely to be thermally damaged.
As described above, following the application by the spray method, the solvent is removed by heating the stage, and the catalyst layer is manufactured on the low water absorption film.
In order to make the removal of the solvent more reliable, the low water absorption membrane on which the catalyst layer is produced may be put in a heated oven or the like and dried, or may be vacuum dried as necessary.

  Alternatively, the catalyst ink may be sprayed a plurality of times, and a layer by each spray may be applied repeatedly on the low water absorption film to form a multilayer coating. This multi-layer coating can reduce the coating amount of one layer, promotes drying of the catalyst ink after coating, and prevents generation of wrinkles in the low water absorption film after coating even when the removal of the solvent is insufficient. Can be reduced.

  The MEA production method of the present invention can be applied to both a polymer electrolyte membrane having an acidic group and a polymer electrolyte membrane having a basic group as described above, but a polymer electrolyte having an acidic group. The use of a membrane is preferable because a fuel cell with further improved power generation performance can be obtained.

Examples of the polymer electrolyte membrane having an acidic group include a phosphinic acid group (—OPO ₃ H ₂ ) and a sulfonylimide group (—SO ₂ NHSO ₂ —) in addition to the sulfonic acid group, carboxyl group, phosphonic acid group and the like described above. Or having a cation exchange group such as a phenolic hydroxyl group. Among these, as the acidic group, a sulfonic acid group or a phosphonic acid group is more preferable, and a sulfonic acid group is particularly preferable.

  As a typical example of a polymer electrolyte constituting such a polymer electrolyte membrane, for example, (A) a polymer in which a sulfonic acid group and / or a phosphonic acid group are introduced into a hydrocarbon polymer whose main chain is an aliphatic hydrocarbon. (B) a hydrocarbon polymer electrolyte in which a sulfonic acid group and / or a phosphonic acid group is introduced into a polymer having a main chain having an aromatic ring; (C) a main chain consisting of an aliphatic hydrocarbon, a siloxane group, and phosphazene. A hydrocarbon-based polymer electrolyte obtained by introducing a sulfonic acid group and / or a phosphonic acid group into a polymer having an inorganic unit structure such as a group; (D) the sulfonic acid group and / or phosphone of (A) to (C) above; Carbonization in which a sulfonic acid group and / or a phosphonic acid group is introduced into a copolymer composed of any two or more repeating units selected from repeating units constituting the polymer before introduction of the acid group Motokei polyelectrolyte; and the like.

  Examples of the polymer electrolyte (A) include polyvinyl sulfonic acid, polystyrene sulfonic acid, poly (α-methylstyrene) sulfonic acid, and the like.

  The polymer electrolyte (B) may be one in which the main chain is interrupted by a hetero atom such as an oxygen atom. For example, polyether ether ketone, polysulfone, polyether sulfone, poly (arylene ether) ), Polyimide, poly ((4-phenoxybenzoyl) -1,4-phenylene), polyphenylene sulfide, polyphenylquinoxalen, and other homopolymers each having a sulfonic acid group introduced therein, sulfoarylated polybenz Imidazole, sulfoalkylated polybenzimidazole, phosphoalkylated polybenzimidazole (for example, see JP-A-9-110882), phosphonated poly (phenylene ether) (for example, J. Appl. Polym. Sci., 18, 1969). (1974)).

  Examples of the polymer electrolyte (C) include those obtained by introducing a sulfonic acid group into polyphosphazene described in the literature (Polymer Prep., 41, No. 1, 70 (2000)), phosphonic acid It can be easily produced according to the polysiloxane having a group.

  As the polymer electrolyte of the above (D), a sulfonic acid group and / or a phosphonic acid group is introduced into a random copolymer, but a sulfonic acid group and / or a phosphonic acid group is introduced into an alternating copolymer. Those having a sulfonic acid group and / or phosphonic acid group introduced into the block copolymer may be used. Examples of the sulfonic acid group introduced into the random copolymer include sulfonated polyethersulfone polymers described in JP-A-11-116679.

Among the above polymer electrolytes, the polymer electrolytes (C) and (D) are preferable from the viewpoint of achieving both high power generation performance and durability, and among the above (D), the block copolymer is particularly preferable. It preferably has a structure in which a sulfonic acid group is introduced into the polymer, and the polymer main chain has an aromatic ring, and particularly preferably includes a block having a sulfonic acid group and a block having substantially no ion exchange group. Is a block copolymer.
Examples of such a block copolymer include a block copolymer having a sulfonated aromatic polymer block described in JP-A-2001-250567, JP-A-2003-32322, and JP-A-2004-359925. And block copolymers having a main chain structure of polyetherketone and polyethersulfone described in JP-A-2005-232439 and JP-A-2003-113136.

  In addition, said block copolymer has one or more each of the block which has a sulfonic acid group, and the block which does not have an ion exchange group substantially, and either block has two or more. The block may have a sulfonic acid group and may have a plurality of blocks each having substantially no ion exchange group. In addition, the definition of a block having a sulfonic acid group means a block having 0.5 or more when expressed by the average number of sulfonic acid groups per structural unit constituting the block. More preferably. In addition, the definition of a block having substantially no ion exchange group means that it is 0.1 or less in terms of the average number of ion exchange groups per structural unit constituting the block. It is particularly preferred that zero, that is, no ion exchange groups exist in the entire block.

Furthermore, the polymer electrolyte membrane according to the membrane-electrode assembly obtained by the production method of the present invention can be used in addition to the polymer electrolytes exemplified above as long as the proton conductivity is not significantly reduced depending on the desired characteristics. May be included. Examples of such other components include additives such as plasticizers, stabilizers, mold release agents, and water retention agents that are used in ordinary polymers.
In particular, during the operation of the fuel cell, peroxide is generated in the catalyst layer adjacent to the polymer electrolyte membrane, and this peroxide diffuses and changes into radical species, which constitutes the polymer electrolyte membrane. The polymer electrolyte may be deteriorated. In order to avoid such inconvenience, it is preferable to add a stabilizer capable of imparting radical resistance to the polymer electrolyte.

  For the purpose of improving the mechanical strength of the low water absorption membrane, a composite membrane in which a polymer electrolyte and a predetermined support are combined can be used for the MEA of the present invention. In this case, by obtaining a low water absorption membrane from the composite membrane, it is possible to suppress the generation of soot on the composite membrane in contact with the catalyst layer. In addition, as a support body, base materials, such as a fibril shape and a porous membrane shape, are mentioned.

  In any of the polymer electrolyte membranes or composite membranes as described above, according to the present invention, high adhesion between the catalyst layer and the polymer electrolyte membrane or composite membrane can be maintained by directly applying the catalyst ink. It is possible to suppress the generation of wrinkles.

Furthermore, the production method of the present invention is a low water absorption film in a membrane-electrode assembly (low water absorption) obtained by forming a catalyst layer on a low water absorption film according to the first embodiment or the second embodiment. It is preferable to improve the water absorption rate. As described above, by improving the water absorption rate of the low water absorption film once having reduced the water absorption rate, an ion conductivity can be further improved, and an MEA having high power generation performance when the fuel cell is operated can be obtained. In particular, when the method shown in the above (i) or (ii), which is a preferred embodiment, is selected as the production of the low water absorption membrane, the ion exchange group once formed as a salt form once again exhibits ion conductivity. The water absorption can be improved by returning to the free ion exchange group.
When a polymer electrolyte having an acidic group as an ion exchange group as a preferred hydrocarbon polymer electrolyte, the above (low water absorption) membrane-catalyst layer assembly can be easily implemented by performing acid treatment. it can.

The acid treatment can be performed by a simple method of immersing the (low water absorption) membrane-catalyst layer assembly in an acid aqueous solution having a predetermined concentration and temperature for a predetermined time. Although there is no restriction | limiting in particular in the kind of acid, Strong acids, such as hydrochloric acid, a sulfuric acid, nitric acid, are used preferably.
Moreover, in the said acid treatment, you may stir the acid aqueous solution used for immersion in the range which does not impair the form of this low water absorption membrane-catalyst layer assembly.
By doing in this way, MEA which has the target suppression of wrinkles and high ion conductivity can be manufactured.

In addition, after the acid treatment, the acid may remain inside the MEA after the treatment, and therefore, it is preferable to perform water washing following the acid treatment. If it does in this way, the surplus acid component which remains inside can be removed. As a method for washing with water, a method of exposing the membrane-electrode assembly after acid treatment to running water for a predetermined time is effective.
Moreover, after acid-treating and washing with water as necessary, it may be dried.

The MEA obtained by the production method of the present invention has high output performance when used as a fuel cell. In addition, although it described in detail about forming the catalyst layer of at least one side of MEA, it is also possible to form the catalyst layer of both sides of MEA. In this case, the catalyst layer can be formed on both surfaces by forming the catalyst layer on one surface of the low water absorption membrane and performing the same method on the other surface through the method described above.
In addition, a catalyst layer formed by the production method of the present invention is formed on one catalyst layer of MEA, and another catalyst layer is formed on the other surface by a conventionally known method. You can also. Here, as a known method related to the catalyst layer forming method, for example, J. Org. Electrochem. Soc. : Methods described in Electrochemical Science and Technology, 1988, 135 (9), 2209, and the like.

  Next, a fuel cell provided with MEA obtained by the manufacturing method of the present invention will be described.

FIG. 1 is a diagram schematically showing a cross-sectional configuration of a fuel cell according to a preferred embodiment. As shown in FIG. 1, the fuel cell 10 includes catalyst layers 14a and 14b on both sides of a polymer electrolyte membrane 12 (ion conductive membrane) so as to sandwich the membrane, and this is an MEA 20 obtained by the manufacturing method of the present invention. is there. Furthermore, the catalyst layers on both sides are provided with gas diffusion layers 16a and 16b, respectively, and separators 18a and 18b are formed in the gas diffusion layers.
Here, the one provided with the MEA 20 and the gas diffusion layers 16a and 16b is called a membrane-catalyst layer-gas diffusion layer assembly and is usually abbreviated as MEGA.

  Here, the catalyst layers 14a and 14b are layers that function as electrode layers in the fuel cell, and either one of them is an anode electrode layer and the other is a cathode electrode layer.

  The gas diffusion layers 16a and 16b are provided so as to sandwich both sides of the MEA 20, and promote the diffusion of the raw material gas into the catalyst layers 14a and 14b. The gas diffusion layers 16a and 16b are preferably made of a porous material having electron conductivity. For example, a porous carbon non-woven fabric or carbon paper is preferable because the raw material gas can be efficiently transported to the catalyst layers 14a and 14b.

  Separator 18a, 18b is formed with the material which has electronic conductivity, As this material, carbon, resin mold carbon, titanium, stainless steel etc. are mentioned, for example. Although not shown, the separators 18a and 18b are preferably provided with grooves serving as flow paths for fuel gas or the like on the catalyst layers 14a and 14b.

  The fuel cell 10 can be obtained by sandwiching MEGA as described above between a pair of separators 18a and 18b and joining them together.

  The fuel cell of the present invention is not necessarily limited to the above-described configuration, and may have a different configuration as long as it does not depart from the spirit of the fuel cell.

  The fuel cell 10 may be one having the above-described structure sealed with a gas seal body or the like. Furthermore, a plurality of the fuel cells 10 having the above structure can be connected in series to be put to practical use as a fuel cell stack. The fuel cell having such a configuration can be used as a solid polymer fuel cell when the fuel is hydrogen, and as a direct methanol fuel cell when the fuel is an aqueous methanol solution.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.

Production Example 1 [Synthesis of dipotassium 4,4′-difluorodiphenylsulfone-3,3′-disulfonate]
To a reactor equipped with a stirrer, 467 g of 4,4′-difluorodiphenylsulfone and 3500 g of 30% fuming sulfuric acid were added and reacted at 100 ° C. for 5 hours. After cooling the obtained reaction mixture, it was added to a large amount of ice water, and 470 mL of a 50% aqueous potassium hydroxide solution was further added dropwise thereto.
Next, the precipitated solid was collected by filtration, washed with ethanol, and dried. The obtained solid was dissolved in 6.0 L of deionized water, 50% aqueous potassium hydroxide solution was added to adjust the pH to 7.5, and then 460 g of potassium chloride was added. The precipitated solid was collected by filtration, washed with ethanol, and dried.
Thereafter, the obtained solid was dissolved in 2.9 L of DMSO, insoluble inorganic salts were removed by filtration, and the inorganic salts were further washed with 300 mL of DMSO. 6.0 L of a solution of ethyl acetate / ethanol = 24/1 was added dropwise to the obtained filtrate, and the precipitated solid was filtered, washed with methanol, dried at 100 ° C., and 4,4′-difluorodiphenylsulfone. 482 g of a solid of dipotassium-3,3′-disulfonate was obtained.

Production Example 2 [Production of polymer electrolyte]
(Synthesis of polymer compound having sulfonic acid group)
In a flask equipped with an azeotropic distillation apparatus, 9.32 parts by weight of dipotassium 4,4′-difluorodiphenylsulfone-3,3′-disulfonate obtained in Production Example 1 in an argon atmosphere, 2,5-dihydroxybenzene 4.20 parts by weight of potassium sulfonate, 59.6 parts by weight of DMSO, and 9.00 parts by weight of toluene were added, and argon gas was bubbled for 1 hour while stirring these at room temperature.
Thereafter, 2.67 parts by weight of potassium carbonate was added to the obtained mixture, and azeotropic dehydration was performed by heating and stirring at 140 ° C. Thereafter, heating was continued while distilling off toluene, and a DMSO solution of a polymer compound having a sulfonic acid group was obtained. Total heating time was 14 hours. The resulting solution was allowed to cool at room temperature.

(Synthesis of polymer compounds substantially free of ion exchange groups)
A flask equipped with an azeotropic distillation apparatus was charged with 8.32 parts by weight of 4,4′-difluorodiphenylsulfone, 5.36 parts by weight of 2,6-dihydroxynaphthalene, 30.2 parts by weight of DMSO, and 30.2 parts by weight of NMP in an argon atmosphere. And 9.81 parts by weight of toluene were added, and argon gas was bubbled for 1 hour while stirring at room temperature.
Thereafter, 5.09 parts by weight of potassium carbonate was added to the obtained mixture, and azeotropic dehydration was performed by heating and stirring at 140 ° C. Thereafter, heating was continued while toluene was distilled off. Total heating time was 5 hours. The resulting solution was allowed to cool at room temperature to obtain a NMP / DMSO mixed solution of a polymer compound substantially free of ion exchange groups.

(Synthesis of block copolymer)
While stirring the obtained NMP / DMSO mixed solution of the polymer compound having substantially no ion exchange group, the total amount of the DMSO solution of the polymer compound having the sulfonic acid group and 80.4 parts by weight of NMP were added thereto. DMSO (45.3 parts by weight) was added and a block copolymerization reaction was carried out at 150 ° C. for 40 hours.
The obtained reaction solution was dropped into a large amount of 2N hydrochloric acid and immersed for 1 hour. Thereafter, the produced precipitate was filtered off and then immersed again in 2N hydrochloric acid for 1 hour. The obtained precipitate was filtered and washed with water, and then immersed in a large amount of hot water at 95 ° C. for 1 hour. And this solution was dried at 80 degreeC for 12 hours, and the polymer electrolyte which is a block copolymer was obtained. The structure of this polymer electrolyte is shown below.
In addition, description of "block" in a following formula represents having at least one block each having a sulfonic acid group and no block having an ion exchange group.

Production Example 3 [Production of polymer electrolyte membrane]
The polymer electrolyte obtained in Production Example 2 was dissolved in NMP to a concentration of about 30% by weight to prepare a polymer electrolyte solution. Next, this polymer electrolyte solution was dropped on a glass plate. Then, the polymer electrolyte solution was uniformly spread on the glass plate using a wire coater. At this time, the coating thickness was controlled using a 0.2 mm clearance wire coater. After application, the polymer electrolyte solution was dried at 80 ° C. under normal pressure. Then, the obtained membrane was immersed in 1N hydrochloric acid, washed with ion-exchanged water, and further dried at room temperature to obtain a polymer electrolyte membrane (salt substitution rate of 1% or less).

Production Example 4 [Preparation of catalyst ink]
0.83 g of platinum-supported carbon (SA50BK, manufactured by N.E. Chemcat), in which 50% by weight of platinum is supported in 6 mL of a commercially available 5% by weight Nafion solution (solvent: mixture of water and lower alcohol), and ethanol Of 13.2 mL was added. The obtained mixture was subjected to ultrasonic treatment for 1 hour and then stirred for 5 hours with a stirrer to obtain a catalyst ink.

Here, physical property measuring methods according to the following examples are listed.
[Measurement of ion exchange capacity]
The dry weight of the polymer electrolyte membrane to be measured was determined using a halogen moisture meter set at a heating temperature of 105 ° C. Next, this polymer electrolyte membrane was immersed in 5 mL of a 0.1 mol / L sodium hydroxide aqueous solution, and then 50 mL of ion-exchanged water was added and left for 2 hours. Thereafter, titration was performed by gradually adding 0.1 mol / L hydrochloric acid to the solution in which the polymer electrolyte membrane was immersed, and the neutralization point was determined. Then, the ion exchange capacity (unit: meq / g) of the polymer electrolyte membrane was calculated from the dry weight of the polymer electrolyte membrane and the amount of hydrochloric acid required for the neutralization.

[Measurement of water absorption rate]
About 200 mg of a polymer electrolyte membrane made of a polymer electrolyte having a salt substitution rate of 1% or less was cut out at room temperature. The cut-out membrane was put into a 250 mL beaker made of polypropylene with a screw cap, and about 150 mL of ion-exchanged water kept at 100 ° C. in advance was added thereto, and the membrane was immersed in ion-exchanged water. After covering with a screw cap, put it in a constant temperature bath that has been kept at 100 ° C in advance, and hold it for 2 hours, so that the membrane is sufficiently absorbed at a storage temperature of 100 ° C in a slightly pressurized state. It was. Thereafter, the membrane is taken out from the above beaker, immersed in ion exchange water at room temperature for several seconds and cooled, and then the membrane is taken out, wiped off the water adhering to the surface with a filter paper, and saturated water absorption with a moisture meter HR73 manufactured by METTLER TOLEDO The weight W1 was measured. Thereafter, the heating temperature of the moisture meter was set to 105 ° C., and the dry weight W2 as a constant weight was measured. The water absorption rate was determined by substituting W1 and W2 determined in this way into the above formula 1.

Example 1
First, when the ion exchange capacity of the polymer electrolyte membrane obtained in Production Example 3 was measured, it was 1.9 meq / g. On the other hand, 500 mL of 1.0 mol / L calcium chloride aqueous solution was prepared, and this polymer electrolyte membrane (8 cm square) was immersed for 2 hours while stirring. Thereafter, the polymer electrolyte membrane was washed with running water for 2 hours and dried to obtain a low water absorption membrane in which the sulfonic acid group of the polymer electrolyte membrane was converted into a calcium salt form. When the ion exchange capacity of this low water absorption membrane was measured, it was 0.0 meq / g, and almost all of the hydrogen ions of the sulfonic acid groups were substituted with calcium ions (salt substitution rate: about 100%). Further, the water absorption was measured and found to be 59%.

Subsequently, in accordance with the method described in Japanese Patent Application Laid-Open No. 2004-089976, a catalyst ink was applied to a 5.2 cm square region at the center of one side of the low water absorption film. The distance from the discharge port to the film was set to 6 cm, and the stage temperature was set to 75 ° C. After eight times of overcoating, the mixture was left on the stage for 15 minutes to remove the solvent and form a catalyst layer. Similarly, the catalyst ink was applied to the other surface to form a catalyst layer. From the composition of the catalyst layer and the applied weight, a (low water absorption) membrane-catalyst layer assembly in which 0.6 mg / cm ² of platinum was disposed on one side was obtained. In the polymer electrolyte membrane adjacent to the periphery of the catalyst layer of this (low water absorption) membrane-catalyst layer assembly, no wrinkle was observed visually.

Example 2
A membrane-catalyst layer assembly was obtained in the same manner as in Example 1 (low water absorption) except that a 0.1 mol / L potassium chloride aqueous solution was used instead of the 1.0 mol / L calcium chloride aqueous solution. The ion-exchange capacity of the low water absorption film before applying the catalyst ink was 0.0 meq / g (salt substitution rate: about 100%), and the water absorption rate was 79%. The catalyst layer obtained using the catalyst ink had 0.6 mg / cm ² of platinum arranged on one side. In the polymer electrolyte membrane adjacent to the periphery of the catalyst layer of this (low water absorption) membrane-catalyst layer assembly, no wrinkle was observed visually.

Example 3
A membrane-catalyst layer assembly was obtained in the same manner as in Example 1 (low water absorption) except that a 0.1 mol / L benzyltrimethylammonium chloride aqueous solution was used instead of the 1.0 mol / L calcium chloride aqueous solution. The ion-exchange capacity of the low water absorption film before applying the catalyst ink was 0.0 meq / g (salt substitution rate: about 100%), and the water absorption rate was 43%. The catalyst layer obtained using the catalyst ink had 0.6 mg / cm ² of platinum arranged on one side. In the polymer electrolyte membrane adjacent to the periphery of the catalyst layer of this (low water absorption) membrane-catalyst layer assembly, no wrinkle was observed visually.

Example 4
2 g of the polymer electrolyte obtained in Production Example 2 was immersed in 500 mL of a 0.1 mol / L benzyltrimethylammonium chloride aqueous solution and stirred with a stirrer for 2 hours. The mixture after stirring was separated by filtration and dried at 80 ° C. for 12 hours to obtain a polymer electrolyte in which the sulfonic acid group was converted into a salt form with benzyltrimethylammonium ions. The obtained polymer electrolyte was dissolved in NMP to a concentration of about 30% by weight to prepare a polymer electrolyte solution. Next, this polymer electrolyte solution was dropped on a glass plate. Then, using a wire coater, the polymer electrolyte solution was uniformly spread on a glass plate. At this time, the coating thickness was controlled using a 0.2 mm clearance wire coater. After coating, the polymer electrolyte solution was dried at 80 ° C. under normal pressure to obtain a low water absorption film. When the ion exchange capacity of this low water absorption membrane was measured, it was 0.0 meq / g, and almost all of the hydrogen ions of the sulfonic acid group were substituted with benzyltrimethylammonium ions (salt substitution rate: about 100%). Further, the water absorption was measured and found to be 52%.

Subsequently, in accordance with the method described in Japanese Patent Application Laid-Open No. 2004-089976, a catalyst ink was applied to a 5.2 cm square region at the center of one side of the low water absorption film. The distance from the discharge port to the film was set to 6 cm, and the stage temperature was set to 75 ° C. After eight times of overcoating, the mixture was left on the stage for 15 minutes to remove the solvent and form a catalyst layer. Similarly, the catalyst ink was applied to the other surface to form a catalyst layer. From the composition of the catalyst layer and the applied weight, a (low water absorption) membrane-catalyst layer assembly in which 0.6 mg / cm ² of platinum was disposed on one side was obtained. In the polymer electrolyte membrane adjacent to the periphery of the catalyst layer of this (low water absorption) membrane-catalyst layer assembly, no wrinkle was observed visually.

Example 5
A membrane-catalyst layer assembly was obtained in the same manner as in Example 1 (low water absorption) except that a 0.5 mol / L copper (II) chloride aqueous solution was used instead of the 1.0 mol / L calcium chloride aqueous solution. . The ion exchange capacity of the low water absorption membrane before applying the catalyst ink was 1.4 meq / g (salt substitution rate: about 26%), and the water absorption rate was 63%. The catalyst layer obtained using the catalyst ink had 0.6 mg / cm ² of platinum arranged on one side. In the polymer electrolyte membrane adjacent to the periphery of the catalyst layer of this (low water absorption) membrane-catalyst layer assembly, no wrinkle was observed visually.

Example 6
A membrane-catalyst layer assembly was prepared in the same manner as in Example 1 (low water absorption) except that a 6.9 × 10 ⁻⁴ mol / L calcium chloride aqueous solution was used instead of the 1.0 mol / L calcium chloride aqueous solution. Obtained. The ion-exchange capacity of the low water absorption film before the application of the catalyst ink was 0.25 meq / g (salt substitution rate: about 87%), and the water absorption rate was 65%. The catalyst layer obtained using the catalyst ink had 0.6 mg / cm ² of platinum arranged on one side. In the polymer electrolyte membrane adjacent to the periphery of the catalyst layer of this (low water absorption) membrane-catalyst layer assembly, no wrinkle was observed visually.

Production Example 5 [Production of polymer electrolyte membrane]
The polymerization was performed using a 2 mL separable flask fitted with a Dean-Stark tube. In a flask, 13.04 g (56.95 mmol) of potassium hydroquinonesulfonate, 23.50 g (125.39 mmol) of 4,4′-dihydroxybiphenyl, 27.27 g (200.58 mmol) of potassium carbonate, 3,3′-sulfonylbis ( (Potassium 6-fluorobenzenesulfonate) 34.71 g (68.34 mmol) and 4,4′-difluorodiphenylsulfone 29.35 g (114.00 mmol) were taken, and DMSO 395 ml and toluene 70 ml were charged. Thereafter, azeotropic dehydration was carried out in an argon atmosphere at a bath temperature of 170 ° C. (internal temperature 140 ± 5 ° C.) for 3 hours. After 3 hours, toluene was removed from the system, and the reaction was further performed at an internal temperature of 150 ° C. for 3 hours. The reaction was followed by GPC measurement. After completion of the reaction, the reaction solution was allowed to cool to 80 ° C. and added dropwise to 3 L of 2N aqueous hydrochloric acid. The precipitated white polymer was filtered, washed with water until the pH of the washing filtrate was about 7, and then treated with 80 ° C. water for 2 hours twice. It was dried in an oven (80 ° C.) to obtain 81.60 g of a white transparent polymer. Subsequently, a polymer electrolyte membrane was obtained in the same manner as in Production Example 3.

Example 7
The ion exchange capacity of the polymer electrolyte membrane obtained in Production Example 5 was measured and found to be 2.0 meq / g. A membrane-catalyst layer assembly of this polymer electrolyte membrane was obtained in the same manner as in Example 1 (low water absorption). The ion-exchange capacity of the low water absorption membrane before applying the catalyst ink was 0.0 meq / g (salt substitution rate: about 100%), and the water absorption rate was 45%. The catalyst layer obtained using the catalyst ink had 0.6 mg / cm ² of platinum arranged on one side. In the polymer electrolyte membrane adjacent to the periphery of the catalyst layer of this (low water absorption) membrane-catalyst layer assembly, no wrinkle was observed visually.

Comparative Example 1
About the polymer electrolyte membrane obtained in Production Example 3, a membrane-catalyst layer assembly was obtained in the same manner as in Example 1 except that the polymer electrolyte membrane was not immersed in a 1.0 mol / L calcium chloride aqueous solution and then washed with water. It was. The ion exchange capacity of the polymer electrolyte membrane before applying the catalyst ink was 1.9 meq / g (salt substitution rate: 1% or less), and the water absorption rate was 124%. The catalyst layer obtained using the catalyst ink had 0.6 mg / cm ² of platinum arranged on one side. In the polymer electrolyte membrane adjacent to the periphery of the catalyst layer of the membrane-catalyst layer assembly, wrinkles were clearly observed visually.

Comparative Example 2
About the polymer electrolyte membrane obtained in Production Example 5, a membrane-catalyst layer assembly was obtained in the same manner as in Example 1 except that the polymer electrolyte membrane was not immersed in a 1.0 mol / L calcium chloride aqueous solution and then washed with water. It was. The ion exchange capacity of the polymer electrolyte membrane before applying the catalyst ink was 2.0 meq / g (salt substitution rate: 1% or less), and the water absorption rate was 122%. The catalyst layer obtained using the catalyst ink had 0.6 mg / cm ² of platinum arranged on one side. In the polymer electrolyte membrane adjacent to the periphery of the catalyst layer of the membrane-catalyst layer assembly, wrinkles were clearly observed visually.

１） 比較例１（塩置換率１％以下）の吸水率を１としたとき、実施例１〜６の低吸水膜の吸水率を対比して表す。
２） 比較例２（塩置換率１％以下）の吸水率を１としたとき、実施例７の低吸水膜の吸水率を対比して表す。

1) When the water absorption rate of Comparative Example 1 (salt substitution rate of 1% or less) is 1, the water absorption rates of the low water absorption membranes of Examples 1 to 6 are shown in comparison.
2) When the water absorption rate of Comparative Example 2 (salt substitution rate of 1% or less) is 1, the water absorption rate of the low water absorption film of Example 7 is shown in comparison.

Example 8
The (low water absorption) membrane-catalyst layer assembly obtained in Example 1 is immersed in 500 mL of 1N sulfuric acid aqueous solution for 6 hours, washed with ion-exchanged water, and dried at room temperature, thereby being in the polymer electrolyte membrane. When almost all of the sulfonic acid groups were converted to free sulfonic acid groups, no soot was generated around the catalyst layer of the polymer electrolyte membrane. From the membrane-catalyst layer assembly (MEA) thus obtained, a fuel cell was produced using a commercially available JARI standard cell. That is, on both outer sides of the membrane-electrode assembly obtained above, a carbon cloth as a gas diffusion layer and a carbon separator in which a groove for a gas passage is cut are disposed, and further, a current collector and an end are disposed on the outer side. plates were placed in this order, by tightening these with a bolt to assemble the effective membrane area of 25 cm ² fuel cell.

While maintaining the obtained fuel cell at 80 ° C., humidified hydrogen was supplied to the anode and humidified air was supplied to the cathode. At that time, the back pressure at the gas outlet of the cell was set to 0.1 MPaG. Each source gas was humidified by passing the gas through a bubbler. The water temperature of the hydrogen bubbler was 80 ° C., and the water temperature of the air bubbler was 80 ° C. Here, the hydrogen gas flow rate was 529 mL / min, and the air gas flow rate was 1665 mL / min. As a result of the power generation test, the cell voltage at a current density of 2.0 A / cm ² was 0.37 V, and this fuel cell was found to exhibit high power generation performance.

Examples 9-14
When the membrane-catalyst layer assembly obtained in Examples 2 to 7 was immersed in a large excess of 1N sulfuric acid aqueous solution in the same manner as in Example 8, the salt-form group in the low water absorption membrane was obtained. Can be returned to free sulfonic acid groups, and the membrane-electrode assembly (MEA) thus obtained becomes MEA in which no generation of soot is observed in the periphery of the catalyst layer of the polymer electrolyte membrane. . In addition, when a large excess of sulfuric acid aqueous solution is heated to about 80 ° C., it can be returned to the free sulfonic acid group more quickly.
The MEA obtained in this way is excellent in ion (proton) conductivity, and further has no deterioration in output performance due to generation of soot, and therefore can be suitably used for a fuel cell.

It is a figure which shows typically the cross-sectional structure of a fuel cell provided with MEA obtained by the manufacturing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 12 ... Polymer electrolyte membrane, 14a, 14b ... Catalyst layer, 16a, 16b ...
Gas diffusion layer, 18a, 18b ... separator, 20 ... MEA.

Claims (10)

A hydrocarbon polymer electrolyte for production of a polymer electrolyte membrane was obtained by performing the treatment for reducing water absorption shown below, and then producing the low water absorption membrane by forming the treatment product into a film. A method for producing a membrane-electrode assembly, wherein a catalyst ink containing a catalyst substance and a solvent is directly applied to at least one surface of the low water absorption membrane, and the solvent is volatilized to form a catalyst layer.
[Low water absorption treatment]
A treatment that reduces the water absorption obtained by the following formula by 10% or more when the polymer electrolyte membrane has a salt substitution rate of 1% or less.
Water absorption rate (% by weight) = 100 × (W1-W2) / W2 Formula 1
(W1 represents the weight (saturated water absorption weight) when the membrane is saturatedly absorbed, and W2 represents the dry weight of the membrane.) The polymer electrolyte membrane obtained by forming a hydrocarbon polymer electrolyte for producing a polymer electrolyte membrane is subjected to the following low water absorption treatment to produce a low water absorption membrane, and then the obtained low water absorption membrane A method for producing a membrane-electrode assembly, wherein a catalyst ink containing a catalyst substance and a solvent is directly applied to at least one side of the substrate, and the solvent is volatilized to form a catalyst layer.
[Low water absorption treatment]
A treatment that reduces the water absorption obtained by the following formula by 10% or more when the polymer electrolyte membrane has a salt substitution rate of 1% or less.
Water absorption rate (% by weight) = 100 × (W1-W2) / W2 Formula 1
(W1 represents the weight (saturated water absorption weight) when the membrane is saturatedly absorbed, and W2 represents the dry weight of the membrane.)   The low water absorption treatment is a treatment for reducing the water absorption obtained by Formula 1 by 30% or more when a polymer electrolyte membrane having a salt substitution rate of 1% or less is used. The manufacturing method of the membrane-electrode assembly as described in 1 above.   The water-absorbing rate calculated | required by Numerical formula 1 is 80 weight% or more when the said hydrocarbon polymer electrolyte is made into a polymer electrolyte membrane with a salt substitution rate of 1% or less, The claim 1 in any one of Claims 1-3. A method for producing a membrane-electrode assembly.   Furthermore, the water absorption rate of the low water absorption film | membrane after catalyst layer formation is improved, The manufacturing method of the membrane-electrode assembly in any one of Claims 1-4 characterized by the above-mentioned.   6. The method for producing a membrane-electrode assembly according to claim 1, wherein the low water absorption membrane is a membrane made of a polymer electrolyte having a salt substitution rate of 50% or more.   The method for producing a membrane-electrode assembly according to any one of claims 1 to 6, wherein the catalyst ink is directly applied to a low water absorption film using a spray method.   The method for producing a membrane-electrode assembly according to any one of claims 1 to 7, wherein the ion exchange group of the hydrocarbon-based polymer electrolyte is an acidic group.   A membrane-electrode assembly obtained by the production method according to claim 1.   10. A polymer electrolyte fuel cell comprising a pair of separators and a membrane-electrode assembly disposed between the pair of separators, wherein the membrane-electrode assembly is the membrane-electrode assembly according to claim 9. A solid polymer fuel cell.

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