JP2013191500A - Manufacturing method of membrane electrode assembly for solid polymer electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane electrode assembly for a fuel cell which suppress a crack in an electrode, coagulation of a fibrous conductive material, a crack in a solid polymer electrolyte membrane, etc., from occurring in a manufacturing process where using the fibrous conductive material like CNT as a conductive material for supporting a catalyst.SOLUTION: A manufacturing method of a membrane electrode assembly for a solid polymer electrolyte fuel cell comprises the steps of: forming a membrane electrode assembly precursor where an electrolyte precursor membrane and an electrode precursor including a fibrous conductive material supporting a catalyst, aligned substantially vertical to the electrolyte precursor membrane, are laminated with each other; forming the membrane electrode assembly where at least an electrolyte membrane and an electrode including the fibrous conductive material supporting the catalyst and an electrolyte are laminated with each other, by carrying out an alkaline hydrolysis process using an alkaline aqueous solution and an acid treatment using an acid aqueous solution to the electrolyte precursor; and drying the membrane electrode assembly. The manufacturing method of the membrane electrode assembly for the solid polymer electrolyte fuel cell includes at least one of the steps of: compressing the membrane electrode assembly precursor in the lamination direction, and compressing the membrane electrode assembly in the lamination direction, after the step forming the membrane electrode assembly precursor and before the drying step.

Description

  The present invention relates to a method for producing a membrane electrode assembly for a solid polymer electrolyte fuel cell.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle, and thus exhibit high energy conversion efficiency. A fuel cell is usually configured by laminating a plurality of single cells having a basic structure of a membrane electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes.

  An electrode of a solid polymer electrolyte fuel cell using a solid polymer electrolyte membrane as an electrolyte membrane is generally an electrode (catalyst layer) including a catalyst supported on a conductive material and a solid polymer electrolyte (electrolyte resin). Is provided. In such an electrode, since the electrode reaction proceeds at a so-called three-phase interface where the conductive material, the solid polymer electrolyte, and the reactive gas are in contact, it is important to efficiently form the three-phase interface.

  A membrane electrode assembly constituting a solid polymer electrolyte fuel cell is manufactured by forming an electrode containing a conductive material carrying a catalyst and a solid polymer electrolyte on the surface of the solid polymer electrolyte membrane. Can do. Specific production methods include, for example, (A) a method of applying and drying a solution containing a solid polymer electrolyte, and (B) an alkali hydrolysis treatment and an acid treatment. Examples of a method for producing an electrode include a method in which a solid polymer electrolyte precursor that expresses proton conductivity is melt-molded into a film and then subjected to alkali hydrolysis treatment and acid treatment. C) a method of applying and drying a catalyst ink containing a solid polymer electrolyte and a conductive material carrying a catalyst, and (D) a solid polymer electrolyte precursor that exhibits proton conductivity by alkali hydrolysis treatment and acid treatment; Examples include a method in which a catalyst ink containing a conductive material carrying a catalyst is applied and dried, followed by alkali hydrolysis treatment and acid treatment of the solid polymer electrolyte precursor.

As a method using a solid polymer electrolyte precursor as in the above (B) and (D), for example, the method described in Patent Document 1 can be mentioned.
Specifically, in Patent Document 1, (1) a polymer electrolyte precursor is formed into a polymer electrolyte precursor film, and (2) a catalyst is added to the solvent dispersion of the polymer electrolyte precursor. (3) The catalyst ink is applied to the polymer electrolyte membrane to produce a membrane electrode assembly (MEA). (4) The membrane electrode assembly is subjected to alkali hydrolysis and acid treatment. A method for producing a membrane electrode assembly for a polymer electrolyte fuel cell is described.

  On the other hand, since improvement effects such as gas diffusibility and electron conductivity in the electrode can be expected, it has been proposed to use carbon nanotubes (CNT) as a conductive material for supporting a catalyst (for example, Patent Document 2). A membrane electrode assembly for a fuel cell using CNT as a conductive material, for example, after supporting a catalyst and a solid polymer electrolyte on CNT grown on a support substrate, the CNT on the support substrate is converted to a solid polymer By transferring it to the electrolyte membrane, CNTs can be bonded and oriented on the solid polymer electrolyte membrane.

  Patent Document 2 discloses a conductive nanocolumnar body (for example, CNT) that is oriented with an inclination of 60 ° or less with respect to the surface direction of the electrolyte membrane, a catalyst supported on the conductive nanocolumnar body, A fuel cell having an electrolyte resin that coats conductive nano-columns is disclosed. Further, in Patent Document 2, as a method of manufacturing the fuel cell as described above, a process of growing conductive nano-columns substantially perpendicularly aligned with a surface direction of the substrate on the substrate, A step of supporting the catalyst on the columnar body, a step of applying perfluorocarbon sulfonic acid resin (solid polymer electrolyte) to the conductive nanocolumnar body supporting the catalyst, and the perfluorocarbon under specific conditions on the conductive nanocolumnar body. And a step of thermally transferring to a sulfonic acid resin membrane (solid polymer electrolyte membrane).

JP 2009-289463 A JP 2007-257886 A

  As in Patent Document 1, a fuel that performs alkali hydrolysis treatment and acid treatment on a membrane electrode assembly precursor obtained by joining an electrode precursor containing a solid polymer electrolyte precursor and a solid polymer electrolyte precursor membrane The method for producing a membrane electrode assembly for a battery can be expected to have effects such as simplification of the process and improvement of battery performance.

However, as a result of intensive investigations by the present inventors, a membrane electrode assembly for a fuel cell using a fibrous conductive material such as CNT as a conductive material for supporting a catalyst is used as a precursor for a membrane electrode assembly as described above. A membrane electrode assembly precursor in which a fibrous conductive material carrying a catalyst and a solid polymer electrolyte precursor is oriented substantially vertically on the solid polymer electrolyte precursor film to be produced by a production method using a body. It was found that the following problems occur when the membrane electrode assembly precursor is prepared and subjected to alkali hydrolysis treatment, acid treatment, or the like.
That is, the fibrous conductive material constituting the electrode aggregates, cracks occur in the surface direction of the electrode, and further, cracks in the solid polymer electrolyte membrane occur at locations corresponding to the cracked parts of the electrode Was found.

This is because, when a membrane electrode assembly obtained by subjecting a membrane electrode assembly precursor to alkaline hydrolysis treatment and acid treatment is dried, the shrinkage stress generated in the electrode as the solid polymer electrolyte membrane shrinks. This is considered to be because it is larger than the crack propagation stress in the surface direction of the electrode.
When a particulate conductive material such as carbon black is used as the catalyst-carrying conductive material as in Patent Document 1, as shown in FIG. 6 (6B), particles carrying the catalyst 2 in the electrode 5 ′ A solid polymer electrolyte 3 ′ covering the conductive material 8 is bound three-dimensionally. Therefore, when the membrane electrode assembly 6 ′ is dried after the alkali hydrolysis treatment and the acid treatment, even when the solid polymer electrolyte membrane 4 ′ contracts from the swollen state, the fibrous conductive material is used. In contrast, the aggregation of the particulate conductive material 8, the cracks in the electrodes, the cracks in the solid polymer electrolyte membrane 4 ', and the like do not occur.
On the other hand, when a fibrous conductive material such as CNT is used as the catalyst-carrying conductive material and is oriented substantially vertically on the solid polymer electrolyte precursor film, as shown in FIG. 6 (6A). In addition, in the electrode 5 ′, the CNTs (fibrous conductive material) 1 carrying the catalyst 2 are independently oriented on the solid polymer electrolyte membrane 4 ′, and the solid CNTs 1 that cover the adjacent CNTs 1 are coated. The molecular electrolytes 3 ′ are not bound to each other. Therefore, it is considered that when the membrane / electrode assembly 6 ′ is subjected to a drying treatment, the above-described aggregation or cracking occurs due to the shrinkage of the solid polymer electrolyte membrane 4 ′.

The above problems that occur when using a fibrous conductive material are peculiar to the method of manufacturing a membrane electrode assembly for a fuel cell in which alkaline hydrolysis treatment and acid treatment are performed on the membrane electrode assembly precursor. It has been newly found by the present inventors.
Aggregation of fibrous conductive material and cracks in the electrode cause a decrease in catalyst utilization, mass transfer inhibition (reduced gas diffusivity, reduced water mobility, etc.), etc., resulting in decreased power generation performance of the membrane electrode assembly Let Furthermore, since the strength of the membrane electrode assembly is also reduced, the durability of the membrane electrode assembly is also reduced. Therefore, the above problem is a problem to be solved in order to improve the power generation performance and durability of the fuel cell.

  In addition, the manufacturing method of the fuel cell described in Patent Document 2 is not a method using a solid polymer electrolyte precursor membrane or a solid polymer electrolyte precursor. Therefore, the manufacturing method of the fuel cell described in Patent Document 2 does not include a step of subjecting the solid polymer electrolyte precursor membrane or the solid polymer electrolyte precursor to an alkali hydrolysis treatment and an acid treatment. The drying process required later is also unnecessary. Therefore, the manufacturing method of the fuel cell described in Patent Document 2 does not have the above-described problem found by the present inventors, and Patent Document 2 describes nothing about the above problem and its solution. Not.

  The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to produce a solid polymer electrolyte precursor membrane and a membrane electrode assembly for a fuel cell using the solid polymer electrolyte precursor. In this case, when a fibrous conductive material such as CNT is used as a catalyst-carrying conductive material, cracks in the electrode, aggregation of the fibrous conductive material, cracks in the solid polymer electrolyte membrane, etc. that occur during the manufacturing process An object of the present invention is to provide a fuel cell membrane electrode assembly that is suppressed and excellent in power generation performance and durability.

A method for producing a membrane electrode assembly for a solid polymer electrolyte fuel cell according to the present invention includes a solid electrode having a catalyst and a fibrous conductive material carrying a solid polymer electrolyte, and a solid polymer electrolyte membrane. A method for producing a membrane electrode assembly for a polymer electrolyte fuel cell, comprising:
A solid polymer electrolyte precursor membrane including a first solid polymer electrolyte precursor that exhibits proton conductivity by alkali hydrolysis treatment and acid treatment, and a catalyst, and proton conductivity by alkali hydrolysis treatment and acid treatment A membrane / electrode assembly comprising at least a laminate of an electrode precursor supporting a second solid polymer electrolyte precursor and including a fibrous conductive material oriented substantially perpendicular to the solid polymer electrolyte precursor film Producing a precursor; and
The first and second solid polymer electrolyte precursors of the membrane electrode assembly precursor are subjected to an alkali hydrolysis treatment with an aqueous alkali solution and an acid treatment with an aqueous acid solution, and the first solid polymer electrolyte is contained. Producing a membrane electrode assembly in which at least a solid polymer electrolyte membrane and an electrode containing the fibrous conductive material carrying the catalyst and the second solid polymer electrolyte are laminated;
After the membrane electrode assembly manufacturing step, the step of drying the membrane electrode assembly,
Pressing the membrane electrode assembly precursor in the stacking direction of the solid polymer electrolyte precursor film and the electrode precursor after the membrane electrode assembly precursor preparation step and before the drying step; and It has at least one of the process which pressurizes a membrane electrode assembly to the lamination direction of the said solid polymer electrolyte membrane and the said electrode, It is characterized by the above-mentioned.

  According to the method for producing a membrane electrode assembly for a polymer electrolyte fuel cell of the present invention (hereinafter sometimes referred to as a membrane electrode assembly for a fuel cell or a membrane electrode assembly), a conductive material for supporting a catalyst Even if a fibrous conductive material is used as the fibrous conductive material, the fibrous conductive material resulting from the alkali hydrolysis treatment and acid treatment for converting the solid polymer electrolyte precursor into a solid polymer electrolyte and the drying treatment accompanying these treatments. It is possible to suppress the occurrence of aggregation of the conductive material, cracking of the electrode, cracking of the solid polymer electrolyte membrane, and the like. Therefore, according to the present invention, it is possible to manufacture a membrane electrode assembly for a fuel cell that is excellent in power generation performance and durability.

  It is preferable that the manufacturing method of the membrane electrode assembly of this invention has the said pressurization process before the said membrane electrode assembly preparation process. A solid polymer supported on an adjacent fibrous conductive material by performing the pressurizing step on the membrane electrode assembly precursor before the conversion of the solid polymer electrolyte precursor to the solid polymer electrolyte This is because the electrolyte precursors can be bound together more efficiently, and aggregation of the fibrous conductive material, cracking of the electrodes, and the like can be more effectively suppressed.

As a specific aspect of the method for producing a membrane electrode assembly for a fuel cell of the present invention, the membrane electrode assembly precursor preparation step carries the catalyst and the second solid polymer electrolyte precursor, and supports a support substrate. The aspect which has the process of transcribe | transferring the said fibrous conductive material orientated substantially perpendicularly on the said solid polymer electrolyte precursor film | membrane, and the process of peeling the said support substrate is mentioned.
Thus, by performing a pressurizing process after peeling off the support substrate, it is possible to bind the second solid polymer electrolyte precursors supported on the fibrous conductive material more reliably.

In the pressurizing step, when the object to be pressurized is the membrane electrode assembly precursor, the applied pressure is 1 to 10 MPa, the temperature is 0 ° C. or higher, and is equal to or lower than the glass transition temperature of the second solid polymer electrolyte precursor. In the case where the object to be pressurized is the membrane electrode assembly, it is preferable that the applied pressure is 1 to 10 MPa, the temperature is 0 ° C. or higher, and is not higher than the glass transition temperature of the second solid polymer electrolyte.
At this time, in the pressurization step, when the pressurization target is the membrane electrode assembly precursor, the temperature is lower than the glass transition temperature of the first solid polymer electrolyte precursor, and the pressurization target is the membrane. In the case of an electrode assembly, the temperature is preferably lower than the glass transition temperature of the first solid polymer electrolyte.

  Examples of the fibrous conductive material include carbon nanotubes.

  According to the present invention, in a method for producing a membrane electrode assembly for a fuel cell using a solid polymer electrolyte precursor membrane and a solid polymer electrolyte precursor, a fibrous conductive material is used as a conductive material for catalyst support. It is possible to suppress cracking of the electrode, aggregation of the fibrous conductive material, cracking of the solid polymer electrolyte membrane, and the like, which are generated when the contact is made. Therefore, according to this invention, it is providing the membrane electrode assembly for fuel cells excellent in electric power generation performance and durability.

It is a figure explaining an example of the mechanism of the conversion to the solid polymer electrolyte (H type) by the alkali hydrolysis process and acid treatment of a solid polymer electrolyte precursor (F type). It is a flowchart which shows an example of embodiment of the manufacturing method of the membrane electrode assembly for fuel cells of this invention. It is a schematic diagram explaining the effect of the pressurization process in this invention. 2 is an SEM photograph of an electrode of a fuel cell membrane electrode assembly in Example 1. FIG. 4 is an SEM photograph of an electrode of a fuel cell membrane electrode assembly in Comparative Example 1. It is a cross-sectional schematic diagram which shows the structure of the membrane electrode assembly in the manufacturing method of the conventional membrane electrode assembly for fuel cells.

A method for producing a membrane electrode assembly for a solid polymer electrolyte fuel cell according to the present invention comprises an electrode including a catalyst and a fibrous conductive material carrying a solid polymer electrolyte, and a solid polymer electrolyte membrane. A method for producing a membrane electrode assembly for a molecular electrolyte fuel cell, comprising:
A solid polymer electrolyte precursor membrane including a first solid polymer electrolyte precursor that exhibits proton conductivity by alkali hydrolysis treatment and acid treatment, and a catalyst, and proton conductivity by alkali hydrolysis treatment and acid treatment A membrane / electrode assembly comprising at least a laminate of an electrode precursor supporting a second solid polymer electrolyte precursor and including a fibrous conductive material oriented substantially perpendicular to the solid polymer electrolyte precursor film Producing a precursor; and
The first and second solid polymer electrolyte precursors of the membrane electrode assembly precursor are subjected to an alkali hydrolysis treatment with an aqueous alkali solution and an acid treatment with an aqueous acid solution, and the first solid polymer electrolyte is contained. Producing a membrane electrode assembly in which at least a solid polymer electrolyte membrane and an electrode containing the fibrous conductive material carrying the catalyst and the second solid polymer electrolyte are laminated;
After the membrane electrode assembly manufacturing step, the step of drying the membrane electrode assembly,
Pressing the membrane electrode assembly precursor in the stacking direction of the solid polymer electrolyte precursor film and the electrode precursor after the membrane electrode assembly precursor preparation step and before the drying step; and It has at least one of the process which pressurizes a membrane electrode assembly to the lamination direction of the said solid polymer electrolyte membrane and the said electrode, It is characterized by the above-mentioned.

The method for producing a membrane electrode assembly for a fuel cell according to the present invention uses a solid polymer electrolyte precursor that exhibits proton conductivity by alkali hydrolysis treatment and acid treatment. Specifically, alkaline hydrolysis is performed on a membrane electrode assembly precursor in which a solid polymer electrolyte precursor membrane containing a solid polymer electrolyte precursor and an electrode precursor containing a solid polymer electrolyte precursor are laminated. By performing the treatment and the acid treatment, a membrane electrode assembly in which the solid polymer electrolyte membrane and the electrode containing the solid polymer electrolyte are laminated is obtained.
When using a membrane electrode assembly precursor including the solid polymer electrolyte precursor as described above, the solid polymer electrolyte precursor is superior in thermal stability compared to the solid polymer electrolyte, The film has a merit that the film can be melt-molded and the interfacial adhesion between the electrode and the electrolyte film can be improved by thermocompression bonding of the solid polymer electrolyte precursor film and the electrode precursor. In addition, since the pressure during the thermocompression bonding can be reduced, the manufacturing apparatus can be simplified. Furthermore, since the alkali hydrolysis treatment and the acid treatment of the solid polymer electrolyte precursor film and the electrode precursor can be performed at the same time, the manufacturing process can be simplified.

Here, the solid polymer electrolyte precursor that exhibits proton conductivity by alkali hydrolysis treatment and acid treatment will be described.
The solid polymer electrolyte has a proton exchange group such as a sulfonic acid group, and has proton conductivity without treatment such as modification.
On the other hand, a solid polymer electrolyte precursor that expresses proton conductivity by alkali hydrolysis treatment and acid treatment is a precursor group that is converted into a proton exchange group such as a sulfonic acid group by alkali hydrolysis treatment and acid treatment (for example, , those having a _-SO 3 F, _-SO 3 Cl, etc.).
FIG. 1 shows a typical example of conversion of a solid polymer electrolyte precursor into a solid polymer electrolyte by alkali hydrolysis treatment and acid treatment. As shown in FIG. 1, the solid polymer electrolyte precursor (F type) having —SO ₃ F as a precursor group converts —SO ₃ F into —SO ₃ Na or the like by alkaline hydrolysis, and by converting the acid treatment -SO 3 _H, express proton conductivity.

  The present inventors have used CNT as a catalyst-supporting conductive material by a method of manufacturing a membrane electrode assembly using a membrane electrode assembly precursor in which a solid polymer electrolyte precursor membrane and an electrode precursor as described above are laminated. As shown in FIG. 3 (3A), the CNT 1 carrying the catalyst 2 and the solid polymer electrolyte precursor 3 is made substantially perpendicular to the solid polymer electrolyte precursor film 4 to produce a membrane electrode assembly using A membrane electrode assembly precursor 6 oriented in the same manner as above was prepared, and the membrane electrode assembly precursor 6 was subjected to alkali hydrolysis treatment, acid treatment, and the like. When applied, in the drying step subsequent to the alkali hydrolysis treatment and the acid treatment, as shown in FIG. 3 (3D), aggregation of CNT1, crack of the electrode 5 ′, and further crack of the solid polymer electrolyte membrane 4 ′ occur. The problem was found.

  The drying step removes moisture from the membrane electrode assembly obtained after an alkaline hydrolysis treatment in which the membrane electrode assembly precursor is immersed in an alkaline aqueous solution and an acid treatment in which the membrane electrode assembly precursor is immersed in an aqueous acid solution. In addition, drying the swollen solid polymer electrolyte membrane and the electrode is an essential process for ensuring the dimensional stability and handling properties of the membrane electrode assembly during assembly of the fuel cell. That is, it is an essential step in the method for producing a membrane / electrode assembly using a solid polymer electrolyte precursor that exhibits proton conductivity by alkali hydrolysis treatment and acid treatment.

  As described above, in the conventional method of manufacturing a membrane electrode assembly using a particulate conductive material, the solid polymer electrolyte covering the particulate conductive material is three-dimensionally connected in the electrode. The crack growth stress in the surface direction of the electrode is large. Therefore, in the drying process, even if the solid polymer electrolyte membrane shrinks greatly due to drying, even if shrinkage stress occurs in the electrode, the electrode cracks, the aggregate of the particulate conductive material constituting the electrode, the solid polymer There is no cracking of the electrolyte membrane.

  On the other hand, when a fibrous conductive material such as CNT is oriented substantially vertically on the solid polymer electrolyte precursor film as in the present invention, solid polymer electrolyte precursors covering adjacent CNTs Is supported on the CNT surface so as not to be connected (see (3A) in FIG. 3). Therefore, the strength in the surface direction of the electrode is small, and the crack propagation stress is small. Therefore, in the drying process, when the solid polymer electrolyte membrane is largely shrunk by drying, the electrode strength cannot tolerate the stress generated from the difference between the swelling shrinkage amount of the solid polymer electrolyte membrane and the swelling shrinkage amount of the electrode. As shown in (3D), cracking of the electrode and aggregation of CNTs occur, and further, the load applied to the portion of the solid polymer electrolyte membrane corresponding to the crack of the electrode is increased, cracking of the solid polymer electrolyte membrane, etc. Will occur. Since the catalyst supported on the agglomerated CNT does not contribute to power generation, the power generation performance of the membrane electrode assembly decreases. In addition, when cracks or agglomeration occurs in the electrode, concentration overvoltage increases due to inhibition of mass transfer in the electrode (reduced reaction gas diffusibility, decreased water mobility, etc.), and power generation performance deteriorates. Moreover, since the strength of the membrane electrode assembly decreases due to cracks in the electrodes and cracks in the solid polymer electrolyte, cross leakage and an increase in short circuit current occur, and the durability of the membrane electrode assembly deteriorates.

  The cracks of the electrode and the solid polymer electrolyte membrane as described above, and the aggregation of the fibrous conductive material are substantially the same as the fibrous conductive material carrying the solid polymer electrolyte precursor on the surface of the solid polymer electrolyte precursor membrane. Specific to a method comprising a step of drying a membrane electrode assembly after subjecting the membrane electrode assembly precursor having a vertically oriented structure to alkali hydrolysis treatment and acid treatment of the solid polymer electrolyte precursor. The present invention is a problem newly found by the present inventors.

Therefore, in the present invention, by improving the strength of the electrode, particularly the strength in the plane direction, it is possible to suppress the occurrence of cracks in the electrode, aggregation of the fibrous conductive material, and cracks in the solid polymer electrolyte membrane as described above. Made possible.
FIG. 2 is a flowchart showing a specific embodiment example of the method for producing a membrane electrode assembly of the present invention.
In FIG. 2, first, a solid polymer electrolyte precursor (first solid polymer electrolyte precursor) is formed to produce a solid polymer electrolyte precursor film, while the CNTs supporting the catalyst are on the support substrate. An electrode precursor is prepared by impregnating and drying a dispersion of a solid polymer electrolyte precursor (second solid polymer electrolyte precursor) on a CNT substrate that is substantially vertically oriented.
Next, a membrane electrode assembly (MEA) precursor is produced by transferring the electrode precursor to the solid polymer electrolyte precursor membrane. The support substrate of the CNT substrate is peeled off. At this time, as shown in FIG. 3 (3A), the membrane / electrode assembly precursor 6 comprises a solid polymer electrolyte precursor film 4, a catalyst 2 and a solid polymer electrolyte precursor (second solid polymer electrolyte). It has a structure in which a precursor) 3 and an electrode precursor 5 containing CNTs 1 that are substantially vertically oriented on the surface of the solid polymer electrolyte precursor film 4 are laminated.
Subsequently, pressure is applied using a press or the like in the stacking direction of the solid polymer electrolyte precursor film of the membrane electrode assembly precursor and the electrode precursor. As shown in (3B) of FIG. 3, in the membrane electrode assembly precursor 6 to which pressure is applied by the press machine 7, the CNT1 carrying the solid polymer electrolyte precursor 3 is pushed down and covers the adjacent CNT1. The solid polymer electrolyte precursors 3 to be bonded are bound to each other (a region indicated by a broken line frame in (3B) of FIG. 3).
Then, the solid polymer electrolyte in the electrode precursor is immersed in an aqueous alkaline solution by immersing the membrane electrode assembly precursor 6 in a state where the solid polymer electrolyte precursors 3 are connected to each other as shown in FIG. 3 (3B). The precursor and the solid polymer electrolyte precursor film are subjected to alkali hydrolysis treatment, and further immersed in an acid aqueous solution to perform acid treatment of the solid polymer electrolyte precursor and the solid polymer electrolyte precursor film. As shown in FIG. 2, you may provide the process of wash | cleaning a membrane electrode assembly precursor with pure water after alkali aqueous solution immersion, and the process of wash | cleaning a membrane electrode assembly with pure water after acid aqueous solution immersion.
Finally, after the alkali hydrolysis treatment and the acid treatment, the obtained membrane electrode assembly is dried. At this time, as shown in (3C) of FIG. 3, since the solid polymer electrolyte 3 ′ covering the adjacent CNT1 is connected to the electrode 5 ′ of the membrane electrode assembly 6 ′, the solid polymer electrolyte membrane 4 is connected. Even if “shrinks greatly”, aggregation of CNT1 and cracks in the surface direction of the electrode 5 ′ do not occur.

  The present invention has been accomplished in order to solve the problems newly found by the present inventors as described above, and the electrode cracks and fibrous conductive materials associated with the drying treatment as described above have been achieved. It is possible to produce a membrane electrode assembly excellent in power generation performance and durability by suppressing aggregation and cracking of the solid polymer electrolyte membrane.

  Hereinafter, each process of the manufacturing method of the membrane electrode assembly for fuel cells of this invention is demonstrated.

[Membrane / electrode assembly precursor preparation process]
The membrane electrode assembly precursor preparation step includes a solid polymer electrolyte precursor film including a first solid polymer electrolyte precursor that exhibits proton conductivity by alkali hydrolysis treatment and acid treatment, a catalyst, and alkali hydrolysis treatment. And an electrode precursor comprising a fibrous conductive material carrying a second solid polymer electrolyte precursor that expresses proton conductivity by acid treatment and oriented substantially perpendicular to the solid polymer electrolyte precursor film, Is a step of producing a membrane / electrode assembly precursor that is at least laminated.

First, the solid polymer electrolyte precursor film will be described.
The solid polymer electrolyte precursor film includes a first solid polymer electrolyte precursor that expresses proton conductivity by alkali hydrolysis treatment and acid treatment, and is formed by forming the first solid polymer electrolyte precursor. Can be produced. Specifically, a method in which a dispersion in which the first solid polymer electrolyte precursor is dispersed or a solution in which the first solid polymer electrolyte precursor is dissolved is cast and dried, or the first solid polymer electrolyte A solid polymer electrolyte precursor film can be produced by a method in which a molecular electrolyte precursor is melted and formed into a film.

The first solid polymer electrolyte precursor may be any material that exhibits proton conductivity by alkali hydrolysis treatment and acid treatment. For example, the monomers shown in the following (1) to (6) are listed as monomers that are polymerized to form a solid polymer electrolyte precursor.
_{(1) CF 2 = CF (} SO 2 X 1) ( wherein, ^{X 1} is is -F or -Cl halogen group. Hereinafter the _{same.), CH 2 = CF (} SO 2 X 1), and CF _{2 = CF (OCH 2 (CF 2} ) m SO 2 X 1) ( wherein, m is the same. 1 to 4. below) a monomer having one or more sulfonyl halide groups selected from the group consisting of.
(2) CF ₂ = CF (SO ₃ R ¹ ) (wherein R ¹ is an alkyl group and is —CH ₃ , —C ₂ H ₅ or —C (CH ₃ ) _{3. The} same shall apply hereinafter), CH _2. A monomer having one or more sulfonic acid ester groups selected from the group consisting of ═CF (SO ₃ R ¹ ) and CF ₂ ═CF (OCH ₂ (CF ₂ ) _m SO ₃ R ¹ ).
(3) CF ₂ = CF (O (CH ₂ ) _m X ² ) (wherein is an X ² halogen group and is —Br or —Cl. The same shall apply hereinafter), and CF ₂ = CF (OCH ₂ (CF ₂ ) One or more monomers selected from the group consisting of _m X ² ).
(4) CF ₂ = CR ² (COOR ³ ) (wherein R ² is —CH ₃ or —F, and R ³ is —H, —CH ₃ , —C ₂ H ₅ or —C (CH ₃ )). _{3. The} same shall apply hereinafter), and one or more acrylic monomers selected from the group consisting of CH ₂ = CR ² (COOR ³ ).
(5) One or more styrenic monomers selected from the group consisting of styrene, 2,4-dimethylstyrene, vinyltoluene, and 4-tertbutylstyrene.
(6) Acetylnaphthylene, vinyl ketone CH ₂ ═CH (COR ⁴ ) (wherein R ⁴ is —CH ₃ , —C ₂ H ₅ or a phenyl group (—C ₆ H ₅ )), and vinyl ether CH. ₂ = CH (OR ⁵ ) (wherein R ⁵ is —C _n H _{2n + 1} (n = 1 to 5), —CH (CH ₃ ) ₂ , —C (CH ₃ ) ₃ , or a phenyl group). One or more monomers selected from the group consisting of:

  Preferred solid polymer electrolyte precursors include those having the following structure.

As described above, since the solid polymer electrolyte precursor has high thermal stability, it is excellent in thermal workability, and can be formed into a stretched thin film by heating and kneading and melting. . Film forming conditions by such a melting method are not particularly limited, and can be set as appropriate.
A solid polymer electrolyte precursor film is formed by casting a dispersion in which the first solid polymer electrolyte precursor is dispersed or a solution in which the first solid polymer electrolyte precursor is dissolved. In this case, the solvent for dispersing or dissolving the first solid polymer electrolyte precursor is not particularly limited. For example, fluorine ether (for example, hydrofluoroether (for example, 3M NOVEC)), carbon fluoride, alcohol, ether and the like can be mentioned. Among these, those having a fluoroalkyl group are preferable.

  The solid polymer electrolyte precursor film may include a reinforcing film having a porous structure. For example, a solid polymer electrolyte precursor film including a reinforcing film is produced by impregnating the porous structure of the reinforcing film with the dispersion, solution, or molten first solid polymer electrolyte precursor. can do. More specifically, the reinforcing membrane is sandwiched between two membrane-shaped solid polymer electrolyte precursors, and the solid polymer electrolyte precursor is melted and impregnated in the pores of the reinforcing membrane by heating and pressing. Can do. Examples of the material for the reinforcing film include polytetrafluoroethylene (PTFE).

Next, the electrode precursor will be described.
The electrode precursor is a fiber that carries a catalyst and a second solid polymer electrolyte precursor that exhibits proton conductivity by alkali hydrolysis treatment and acid treatment, and is oriented substantially perpendicular to the solid polymer electrolyte precursor membrane. A conductive material.

The fibrous conductive material is not particularly limited as long as it has a fibrous shape and has conductivity. Specific examples of the material include fibrous conductive carbon materials such as CNT, carbon nanofiber, and carbon nanohorn. Here, the fiber shape means that the aspect ratio [length in the long direction (fiber length) / diameter (fiber diameter)] is 10 or more. As a fibrous conductive material, it is relatively easy to make a substantially vertical orientation to the solid polymer electrolyte precursor film, and it is effective for improving power generation performance such as gas diffusivity and electron conductivity in the membrane electrode assembly. Therefore, CNT is preferable.
The fiber length of the fibrous conductive material is preferably 5 μm to 500 μm, for example, from the viewpoint of securing the number of catalyst particle supporting sites.

Here, a method of generating CNT will be described.
CNT is synthesized using an arc discharge method, a laser vapor deposition method, a catalytic metal for generating CNT (hereinafter referred to as a CNT-forming catalytic metal), and a hydrocarbon gas or a hydrogen-based gas is supplied thereto. Or a HiPco method in which carbon monoxide is disproportionated (CO + CO → C + CO ₂ ) under high temperature and high pressure conditions.
Hereinafter, an example of a method for producing carbon nanotubes will be described, taking as an example the case of synthesizing single-walled carbon nanotubes using a catalytic metal.
In vacuum, a raw material gas (carbonized) is applied to a catalyst-carrying substrate that supports a CNT-forming catalytic metal at a desired thickness (for example, 4 nm) and is heated to a predetermined temperature or higher (for example, 400 ° C. or higher, preferably 500 to 1000 ° C.) CNT can be generated by supplying a hydrogen-based gas, an alcohol-based gas, a hydrogen-based gas, or the like (CNT generation step). In the CNT production process, the catalyst-carrying substrate is placed in a vacuum (for example, 10 ^{−3 to} 10 Pa) and heated to a predetermined temperature suitable for the production of CNTs, and a raw material gas is supplied to the catalyst-carrying substrate. To do.
Examples of the source gas include hydrocarbon gas, alcohol gas (CH gas), hydrogen gas (H gas), and the like. Specifically, at least one selected from a hydrocarbon-based gas and an alcohol-based gas, or at least one selected from a hydrocarbon-based gas and an alcohol-based gas and at least one selected from a hydrogen-based gas. Both can be used (optionally gasified). As a hydrocarbon component of the hydrocarbon-based gas, for example, a hydrocarbon having 1 to 6 carbon atoms (for example, methane, ethane, acetylene, benzene, etc.) is preferably exemplified. As the alcohol-based gas, for example, methanol Preferred examples include ethanol and the like. Moreover, as said hydrogen type gas, hydrogen gas, ammonia gas, etc. are mentioned suitably, for example.
The catalyst-carrying substrate is configured by carrying a CNT-generating catalyst metal on the surface of the substrate. Examples of the CNT-forming catalytic metal include Fe, Pd, Co, Ni, W, Mo, Mn, and alloys thereof. Examples of the substrate include Al, Ni, stainless steel, Si, SiC, zeolite, activated carbon and the like.

In the membrane electrode assembly precursor, the fibrous conductive material carries the catalyst and the second solid polymer electrolyte precursor on its surface and is oriented substantially perpendicular to the solid polymer electrolyte precursor membrane. Yes.
Here, the fibrous conductive material is oriented substantially perpendicularly to the solid polymer electrolyte precursor film when the surface direction of the solid polymer electrolyte precursor film and the longitudinal direction of the fibrous conductive material (fibrous conductive material). It means that the angle formed with the fiber length direction of the functional material is in the range of 90 ° ± 30 °. If it is in the range of 90 ° ± 30 °, the same effect as in the case of being oriented vertically (90 °) can be obtained. The fibrous conductive material includes a straight line and a non-linear fiber. In the case of a non-linear fibrous conductive material, the direction of the straight line connecting the centers of both end faces in the fiber length direction. Is the fiber length direction.

  The method for orienting the fibrous conductive material substantially perpendicular to the solid polymer electrolyte precursor film is not particularly limited.

As a preferred method for orienting the fibrous conductive material substantially perpendicularly to the solid polymer electrolyte precursor film, for example, a fibrous conductive material oriented substantially perpendicularly on the support substrate is used as the solid polymer electrolyte precursor. There is a method of transferring to a film. Specifically, there is a method in which CNTs are grown substantially vertically on the catalyst-carrying substrate used in the above-described CNT production method, and the CNTs on the catalyst-carrying substrate are transferred to the solid polymer electrolyte precursor film. At this time, a catalyst carrying substrate can be used as the support substrate.
Typically, a catalyst and a second solid polymer electrolyte precursor are first supported on a fibrous conductive material oriented substantially vertically on a support substrate, and then the catalyst and the second solid polymer are supported. The fibrous conductive material carrying the electrolyte precursor and oriented substantially vertically on the support substrate is transferred to the solid polymer electrolyte precursor film.
The conditions for transferring the fibrous conductive material oriented substantially vertically on the support substrate to the solid polymer electrolyte precursor film are appropriately set according to the type, performance, etc. of the film, fibrous conductive material, and electrolyte precursor. For example, it may be 1 to 15 MPa, 30 to 200 ° C., and 1 to 60 minutes.

  Although the timing which peels the said support substrate is not specifically limited, It is preferable to carry out before a pressurization process. When the support substrate is peeled off after the pressurizing step, the fibrous conductive material pushed down in the pressurizing step is pulled by the support substrate when the support substrate is peeled off, and may rise up substantially again. As a result, the connection between the second solid polymer electrolyte precursors supported on the adjacent fibrous conductive material is broken, and the effect of the pressurizing step may not be sufficiently obtained. When peeling a support substrate before a pressurization process, it is preferable to peel a support substrate in a membrane electrode assembly precursor preparation process. This is because in the subsequent alkali hydrolysis treatment step, acid treatment step, etc., the contact between the membrane electrode assembly precursor and the aqueous alkali solution or aqueous acid solution is improved, and the treatment can be performed efficiently.

  Catalysts supported on fibrous conductive materials include platinum, palladium, ruthenium, iridium, rhodium, osmium, and other platinum elements, as well as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, and gallium. And metals such as aluminum, or alloys, oxides, composites, and the like thereof. In general, the catalyst is preferably in the form of particles having a particle size of 0.5 to 20 nm, particularly preferably 1 to 5 nm. When the particle size is 0.5 nm or more, the stability of the catalyst particles is obtained, and when the particle size is 20 nm or less, good catalytic activity is obtained.

  The method for supporting the catalyst on the surface of the fibrous conductive material is not particularly limited. For example, the platinum element and its precursor (platinum halide, nitrate, carbonate, acetylacetonate, tetraammine salt, alkoxide, etc. ), And other metals and precursors thereof (metal halides, nitrates, carbonates, acetylacetonates, tetraammine salts, alkoxides, etc.), so-called impregnation method, precipitation method, kneading Methods such as the ion exchange method and the like can be employed. The catalyst supporting treatment can be usually performed before supporting the second solid polymer electrolyte precursor on the fibrous conductive material oriented substantially vertically on the support substrate.

  The second solid polymer electrolyte precursor supported on the fibrous conductive material exhibits proton conductivity by alkali hydrolysis treatment and acid treatment. Specific examples of the second solid polymer electrolyte precursor include those similar to the first solid polymer electrolyte precursor, and thus the description thereof is omitted here. The first solid polymer electrolyte precursor and the second solid polymer electrolyte precursor may be the same or different from each other.

Examples of the method for supporting the second solid polymer electrolyte precursor on the fibrous conductive material include, for example, a precursor dispersion in which the second solid polymer electrolyte precursor is dispersed in a fibrous shape supporting the catalyst. Examples thereof include a method of applying or dropping onto a conductive material (catalyst-carrying conductive material) and then drying, a method of immersing the catalyst-carrying conductive material in the precursor dispersion, and then drying. Application, dripping, dipping, etc. of the precursor dispersion liquid may be repeated until a desired amount of the second solid polymer electrolyte precursor is supported on the surface of the catalyst-carrying conductive material. The method for drying the precursor dispersion is not particularly limited. The solid polymer electrolyte precursor supporting treatment is usually preferably performed on a catalyst-supporting fibrous conductive material that is oriented substantially vertically on a support substrate.
The solvent in which the second solid polymer electrolyte precursor is dispersed is not particularly limited, and examples thereof include fluorine ether (for example, hydrofluoroether (for example, 3M NOVEC)), carbon fluoride, alcohol, ether, and the like. Is mentioned. Among these, those having a fluoroalkyl group are preferable.
The precursor dispersion liquid is preferably prepared by, for example, dispersing the precursor dispersion so as to be less than 5% by weight with respect to the solvent. At this time, it is preferable to heat (for example, 200 degreeC or more) as needed. Moreover, it is preferable that the precursor dispersion liquid decomposes or removes the aggregate of the second solid polymer electrolyte precursor in advance by ultrasonic treatment, filtration, or the like.

[Membrane electrode assembly manufacturing process]
In the membrane electrode assembly preparation step, the first and second solid polymer electrolyte precursors of the membrane electrode assembly precursor are subjected to an alkali hydrolysis treatment with an alkaline aqueous solution and an acid treatment with an acid aqueous solution. This is a process for producing a membrane electrode assembly in which a solid polymer electrolyte membrane containing a solid polymer electrolyte and an electrode containing a fibrous conductive material carrying a catalyst and a second solid polymer electrolyte are at least laminated.

  The method of performing an alkali hydrolysis treatment with an aqueous alkali solution on the first and second solid polymer electrolyte precursors of the membrane electrode assembly precursor is not particularly limited. For example, the membrane electrode assembly precursor is treated with an alkali. By contacting with the aqueous solution, it is possible to simultaneously perform the alkali hydrolysis treatment of the first solid polymer electrolyte precursor and the second solid polymer electrolyte precursor. Specifically, for example, a method of immersing a membrane electrode assembly precursor in an alkaline aqueous solution at 25 to 90 ° C., a method of spraying, applying, dropping, etc. the alkaline aqueous solution on the membrane electrode assembly precursor. Can be mentioned. By simultaneously performing the alkali treatment on the first and second solid polymer electrolyte precursors, the manufacturing process of the membrane electrode assembly can be shortened and simplified.

The aqueous alkali solution is not particularly limited, and an aqueous solution in which NaOH, KOH or the like is dissolved can be mentioned.
You may add organic solvents, such as dimethyl sulfoxide (DMSO) and alcohol (for example, ethanol, methanol, etc.), to aqueous alkali solution. By adding such an organic solvent, hydrolysis can be promoted.

In the alkaline hydrolysis treatment step, typically, if all of the precursor groups of the first and second solid polymer electrolyte precursors can be alkali hydrolyzed, the concentration of the aqueous alkali solution, the treatment temperature, the treatment time, Etc. are not particularly limited.
Specific examples of the alkali hydrolysis treatment include an alkaline aqueous solution in which a 1 mol / L sodium hydroxide aqueous solution is mixed at a ratio of 60% by volume and DMSO at a rate of 40% by volume, and an aqueous sodium hydroxide solution at 25 to 90 ° C. The method of heating and immersing an electrode precursor for 1 to 60 minutes is mentioned.

  The membrane electrode assembly precursor subjected to the alkali hydrolysis treatment may be subjected to the acid treatment step as it is, but the electrode precursor is washed with pure water before the acid treatment step as shown in FIG. It is preferable. This is because, by performing pure water cleaning, excess alkali can be removed, and the first and second solid polymer electrolyte precursors can be efficiently converted to a solid polymer electrolyte with an acid aqueous solution. The method of pure water cleaning is not particularly limited.

  The method of performing the acid treatment with the acid aqueous solution on the first and second solid polymer electrolyte precursors of the membrane electrode assembly precursor is not particularly limited. For example, the membrane electrode assembly precursor brought into contact with an alkaline aqueous solution The first and second solid polymer electrolyte precursors constituting the membrane electrode assembly precursor can be acid-treated by further contacting the body with an acid aqueous solution. By performing the acid treatment, the first solid polymer electrolyte precursor and the second solid polymer electrolyte precursor are converted into proton conductive first solid polymer electrolyte and second solid polymer electrolyte, respectively. Thus, the membrane electrode assembly precursor functions as a membrane electrode assembly.

Specifically, the acid treatment of the first and second solid polymer electrolyte precursors is, for example, a method of immersing the membrane electrode assembly precursor in an acid aqueous solution at 25 to 90 ° C., Examples of the membrane electrode assembly precursor include a method of spraying, coating, and dropping. By simultaneously performing the acid treatment of the first and second solid polymer electrolyte precursors, the manufacturing process of the membrane electrode assembly can be shortened and simplified.
It does not specifically limit as aqueous acid solution, A sulfuric acid aqueous solution, nitric acid aqueous solution, hydrochloric acid, acetic acid aqueous solution etc. are mentioned.

In the acid treatment step, typically, if all of the precursor groups of the first and second solid polymer electrolyte precursors can be converted into proton exchange groups, the concentration of the aqueous acid solution, the treatment temperature, the treatment time, Etc. are not particularly limited.
Specific acid treatment includes, for example, a method in which a 0.5 to 8 mol / L nitric acid aqueous solution is heated to 25 to 90 ° C. and the membrane / electrode assembly precursor is immersed for 1 to 60 minutes.

  The membrane electrode assembly subjected to the acid treatment is preferably washed with pure water as shown in FIG. This is because by performing pure water cleaning, excess acid can be removed and handling can be simplified. The method of pure water cleaning is not particularly limited.

  The alkali hydrolysis treatment and the acid treatment may be repeated a plurality of times until the precursor group contained in the membrane electrode assembly precursor is converted into a proton exchange group.

[Drying process]
The drying step is a step of drying the membrane electrode assembly obtained by converting the solid polymer electrolyte precursor into a solid polymer electrolyte by performing alkali hydrolysis treatment and acid treatment in the membrane electrode assembly preparation step. .

  The method for drying the membrane / electrode assembly is not particularly limited as long as moisture in the solid polymer electrolyte membrane and the electrode can be removed. Examples thereof include warm air drying, heat drying by placing on a hot plate, and natural drying.

[Pressure process]
The pressurizing step is a step that is performed after the membrane electrode assembly precursor preparation step and before the drying step. (1) The membrane electrode assembly precursor is converted into a solid polymer electrolyte precursor. Pressurization in the stacking direction of the membrane and the electrode precursor, and / or (2) pressurizing the membrane-electrode assembly in the stacking direction of the solid polymer electrolyte membrane and the electrode. That is, said (1) is a case where a pressurization process is implemented before the said acid treatment, and said (2) is a case where a pressurization process is implemented after the said acid treatment. The pressurization step may be performed only once or multiple times.
As already described, before the drying step, at least one of the membrane electrode assembly precursor and the membrane electrode assembly is pressurized in the laminating direction, and the second solid carried on the adjacent fibrous conductive material. By binding and connecting the polymer electrolyte precursors and / or the second solid polymer electrolyte, in the drying process, cracks in the electrodes, aggregation of the fibrous conductive material, cracks in the solid polymer electrolyte membrane, etc. Generation | occurrence | production can be suppressed.

The implementation time of the pressurizing step is not particularly limited as long as it is after the production step of the membrane electrode assembly precursor and before the drying step, since the occurrence of the above problem in the drying step can be suppressed. It is preferable to carry out the pressurizing step before the assembly production step, that is, the membrane electrode assembly precursor.
Since the solid polymer electrolyte precursor is more flexible than the solid polymer electrolyte obtained by converting the precursor, it is supported on the adjacent fibrous conductive material by pressurizing the membrane electrode assembly precursor. This is because the solid polymer electrolyte precursors can be reliably bonded with each other at a low pressure. Application of pressure by low pressure prevents crushing or excessively pushing down the substantially vertically oriented fibrous conductive material, and makes it possible to maintain high gas diffusibility and electron conductivity of the electrode.
Moreover, by performing the pressurizing step before the membrane / electrode assembly manufacturing step, the occurrence of the above problem in the drying step can be more reliably suppressed. This is because when the solid polymer electrolyte precursor is converted into a solid polymer electrolyte by hydrolysis treatment and acid treatment in the membrane electrode assembly preparation step, the membrane electrode assembly is in a water-containing state, and the solid polymer electrolyte membrane Therefore, as the solid polymer electrolyte membrane swells, swelling stress is also generated in the electrode in the surface direction, and there is a possibility that cracks of the electrode may occur. Therefore, before the membrane electrode assembly manufacturing step, the fibrous conductive material is connected by the second solid polymer electrolyte precursor, and the strength in the surface direction of the electrode precursor is improved, as described above. It is possible to suppress the generation of cracks in the electrode due to the swelling of the film due to a simple hydrolysis treatment and acid treatment.

The pressurizing conditions of the membrane electrode assembly precursor and the membrane electrode assembly in the pressurizing step are not particularly limited, and the second solid polymer electrolyte precursors covering the fibrous conductive material or the second solid polymer What is necessary is just to be able to connect electrolytes. Typically, the fibrous conductive material oriented substantially perpendicularly (90 ° ± 30 °) with respect to the solid polymer electrolyte precursor membrane or the solid polymer electrolyte membrane by the pressure application in the pressurizing step is The angle between the surface direction of the film and the fibrous conductive material is less than the angle before applying pressure (acute angle).
Specific pressurizing conditions include the first and second solid polymer electrolyte precursors or the first and second solid polymer electrolyte types (glass transition temperature, etc.), the fibrous conductive material type (material, It is preferable to set appropriately according to the shape and the like.

For example, when the object to be pressurized is a membrane electrode assembly precursor, it is preferable that the applied pressure is 1 to 10 MPa, the temperature is 0 ° C. or higher, and is equal to or lower than the glass transition temperature of the second solid polymer electrolyte precursor. In particular, it is preferable that the applied pressure is 1 to 5 MPa, the temperature is 25 ° C. or more, and the glass transition temperature is not more than the second solid polymer electrolyte precursor. By pressurizing the membrane electrode assembly precursor under the above conditions, the second solid polymer electrolyte precursor is more reliably connected to each other, and the void in the electrode is secured while improving the strength in the surface direction of the electrode. This is because the gas diffusibility can be maintained.
In addition, in the heating step, the temperature during pressurization is the first solid polymer electrolyte precursor in order to prevent the solid polymer electrolyte precursor film from being excessively softened and thinned, or generating holes or the like. It is preferable that it is less than the glass transition temperature.

When the object to be pressurized is a membrane electrode assembly, the applied pressure is preferably 1 to 10 MPa, the temperature is preferably 0 ° C. or higher, and is not higher than the glass transition temperature of the second solid polymer electrolyte. Is preferably 1 to 5 MPa, the temperature is 25 ° C. or higher, and is not higher than the glass transition temperature of the second solid polymer electrolyte. By pressurizing the membrane electrode assembly under the above conditions, the second solid polymer electrolytes are more reliably connected to each other, and the strength in the surface direction of the electrodes is improved, while ensuring voids in the electrodes, and gas diffusion It is because it can keep sex.
Further, in the heating step, the temperature during pressurization is the glass transition temperature of the first solid polymer electrolyte in order to prevent the solid polymer electrolyte membrane from being excessively softened and thinned, or generating holes or the like. It is preferable that it is less than.

  The pressurization time in the pressurization step may be set as appropriate, but in the case of the applied pressure and temperature conditions as described above, for example, it is preferably 1 to 60 minutes, preferably 5 to 30 minutes.

[Other processes]
In addition to the membrane electrode assembly precursor preparation step, the membrane electrode assembly preparation step, the drying step, and the pressurization step, the manufacturing method of the fuel cell membrane electrode assembly of the present invention includes other steps. You may have.

For example, you may have the process of making the electrode precursor contact the low surface tension solvent whose surface tension is smaller than pure water before alkali hydrolysis treatment. Before the alkali hydrolysis treatment, the low surface tension solvent and the electrode precursor are brought into contact with each other, thereby improving the permeability of the alkaline aqueous solution into the electrode precursor, and further improving the permeability of the acid aqueous solution. The alkaline hydrolysis treatment and acid treatment of the second solid polymer electrolyte precursor can be performed efficiently and uniformly.
Since the low surface tension solvent is an organic solvent having a surface tension smaller than that of pure water, it is possible to improve the permeability of the aqueous liquid such as an alkaline aqueous solution and pure water to the electrode precursor, as described above. It is not limited. The low surface tension solvent can be selected by actually measuring its surface tension using a known method and comparing it with pure water, or by utilizing the numerical value of the surface tension described in known literature etc. You can also choose.
The method for measuring the surface tension is not particularly limited, and examples thereof include Wilhelmy (plate method), hanging drop method (pendant drop method), and maximum bubble pressure method.
Since the surface tension varies depending on the temperature, the low surface tension solvent is preferably selected based on the value of the surface tension under the same temperature condition.

Specific examples of the low surface tension solvent include alcohols such as ethanol and methanol, acetone, propylene glycol, hexane, n-pentane, and benzene. Among these, alcohols, acetone, and propylene glycol are preferable.
In addition, a low surface tension solvent may be used individually by 1 type, and may be used in combination of multiple types.

The method of bringing the electrode precursor (a fibrous conductive material carrying the catalyst and the second solid polymer electrolyte precursor) into contact with the low surface tension solvent is not particularly limited. For example, the membrane electrode assembly precursor is Examples thereof include a method of immersing in a low surface tension solvent and a method of spraying, coating, dropping, etc., the low surface tension solvent on the membrane electrode assembly precursor.
Moreover, although the temperature of a low surface tension solvent is not specifically limited, For example, it is preferable to set it as 30-90 degreeC.

  The membrane electrode assembly precursor contacted with the low surface tension solvent is typically contacted with an aqueous alkaline solution before the low surface tension solvent attached to the surface of the electrode precursor is evaporated, By replacing the solvent with the alkaline aqueous solution, the permeability of the alkaline aqueous solution and further the permeability of the acid aqueous solution can be improved. When the low surface tension solvent has reactivity with an alkaline aqueous solution, it is preferable to wash the membrane / electrode assembly precursor with pure water and then treat with the alkaline aqueous solution.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples.

[Preparation of membrane electrode assembly for fuel cells]
Example 1
2 except that the MEA precursor was immersed in a low surface tension solvent between the pressure application of the membrane electrode assembly (MEA) precursor for a fuel cell and the immersion in an alkaline aqueous solution. Based on the flow, a fuel cell membrane electrode assembly (MEA) of Example 1 was produced as follows.

A CNT (CNT substrate) oriented substantially vertically on a support substrate was prepared. The CNT substrate was immersed in a Pt salt solution, dried, fired and reduced, and Pt was supported on the CNT surface.
Next, a plurality of CNTs carrying Pt on the support substrate are immersed and dried in a dispersion of the second solid polymer electrolyte precursor (F type, perfluorocarbon sulfonyl fluoride, Tg = 300 ° C.). Repeatedly, the second solid polymer electrolyte precursor was supported on the surface of the CNT. The dispersion liquid of the second solid polymer electrolyte precursor removes aggregates of the second solid polymer electrolyte precursor by ultrasonic treatment and filtration, and also removes the second solid polymer electrolyte precursor. The concentration was adjusted to less than 5% by weight.

  On the other hand, a solid polymer electrolyte precursor film in which a first solid polymer electrolyte precursor (F type, perfluorocarbon sulfonyl fluoride, Tg = 300 ° C.) was formed into a film shape was prepared.

  Subsequently, the solid polymer electrolyte precursor film is superimposed on the CNT substrate so as to face the CNT alignment surface of the CNT substrate, and thermocompression-bonded at 140 ° C. and 10 MPa for 30 minutes, whereby Pt and second CNTs are applied to the CNT surface. The CNT electrode precursor supporting the solid polymer electrolyte precursor was transferred to the surface of the solid polymer electrolyte precursor film. Similarly, the CNT electrode precursor was transferred to the other surface of the solid polymer electrolyte precursor to produce an MEA precursor. The support substrate of the CNT substrate was peeled off.

  Subsequently, the MEA precursor was pressurized at 100 ° C. and 1 MPa for 5 minutes in the stacking direction of the solid polymer electrolyte precursor film and the CNT electrode precursor.

  Next, the MEA precursor was immersed in ethanol (first low surface tension solvent). Then, after washing with pure water, it was immersed in an 80 ° C. NaOH aqueous solution (alkali aqueous solution for alkali hydrolysis treatment).

  Further, the MEA precursor was washed with pure water, and then immersed in an aqueous nitric acid solution (acid aqueous solution for acid treatment) at 80 ° C. for neutralization.

  Thereafter, the MEA was washed with pure water and then left in the air for 3 hours to naturally dry the MEA.

(Comparative Example 1)
In Example 1, an MEA was produced in the same manner except that the step of pressurizing the MEA precursor was not performed.

[Evaluation of MEA]
For the MEAs of Example 1 and Comparative Example 1 produced above, the surface of the CNT electrode was observed with a scanning electron microscope (SEM). The results are shown in FIG. 4 (Example 1) and FIG. 5 (Comparative Example 1).
As can be seen from FIG. 5, it was confirmed that in the MEA of Comparative Example 1 in which the step of pressurizing the MEA precursor was not performed, cracking of the CNT electrode and aggregation of the CNT occurred. This is because in the MEA precursor or MEA, the second solid polymer electrolyte precursors covering adjacent CNTs or the second solid polymer electrolytes are not bound to each other. The strength in the surface direction is low, and the area where CNT aggregates and the area between adjacent CNTs are greatly separated due to the swelling and shrinkage of the solid polymer electrolyte membrane precursor and the solid polymer electrolyte membrane, resulting in the formation of CNT rough areas. Conceivable. Thus, it can be easily predicted that an MEA having a CNT electrode in which CNT aggregation or cracking has occurred has poor power generation performance and durability.
On the other hand, as shown in FIG. 4, Example 1 in which the second solid polymer electrolyte precursors covering the adjacent CNTs and the second solid polymer electrolytes were connected by pressurizing the MEA precursor. The MEA was confirmed to have a uniform and uniform structure with no cracks or CNT aggregation observed at the CNT electrode. It can be easily predicted that the MEA of Example 1 including the CNT electrode having such a uniform structure is superior in power generation performance and durability as compared with the MEA of Comparative Example 1.

1 ... CNT
DESCRIPTION OF SYMBOLS 2 ... Catalyst 3 ... 1st solid polymer electrolyte precursor 3 '... 1st solid polymer electrolyte 4 ... Solid polymer electrolyte precursor film | membrane 4' ... Solid polymer electrolyte membrane 5 ... Electrode precursor 5 '... Electrode 6 ... Membrane electrode assembly precursor 6 '... Membrane electrode assembly 7 ... Press 8 ... Particulate conductive material

Claims (6)

A method for producing a membrane electrode assembly for a solid polymer electrolyte fuel cell, comprising: an electrode including a fibrous conductive material carrying a catalyst and a solid polymer electrolyte; and a solid polymer electrolyte membrane,
A solid polymer electrolyte precursor membrane including a first solid polymer electrolyte precursor that exhibits proton conductivity by alkali hydrolysis treatment and acid treatment, and a catalyst, and proton conductivity by alkali hydrolysis treatment and acid treatment A membrane / electrode assembly comprising at least a laminate of an electrode precursor supporting a second solid polymer electrolyte precursor and including a fibrous conductive material oriented substantially perpendicular to the solid polymer electrolyte precursor film Producing a precursor; and
The first and second solid polymer electrolyte precursors of the membrane electrode assembly precursor are subjected to an alkali hydrolysis treatment with an aqueous alkali solution and an acid treatment with an aqueous acid solution, and the first solid polymer electrolyte is contained. Producing a membrane electrode assembly in which at least a solid polymer electrolyte membrane and an electrode containing the fibrous conductive material carrying the catalyst and the second solid polymer electrolyte are laminated;
After the membrane electrode assembly manufacturing step, the step of drying the membrane electrode assembly,
Pressing the membrane electrode assembly precursor in the stacking direction of the solid polymer electrolyte precursor film and the electrode precursor after the membrane electrode assembly precursor preparation step and before the drying step; and A method for producing a membrane electrode assembly for a solid polymer electrolyte fuel cell, comprising at least one step of pressurizing the membrane electrode assembly in the stacking direction of the solid polymer electrolyte membrane and the electrode.   The method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell according to claim 1, comprising the pressurizing step before the membrane / electrode assembly preparation step. The membrane electrode assembly precursor preparation step includes
Transferring the fibrous conductive material carrying the catalyst and the second solid polymer electrolyte precursor and oriented substantially vertically on a support substrate to the solid polymer electrolyte precursor film;
The method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell according to claim 1, comprising a step of peeling the support substrate.   In the pressurizing step, when the object to be pressurized is the membrane electrode assembly precursor, the applied pressure is 1 to 10 MPa, the temperature is 0 ° C. or higher, and is equal to or lower than the glass transition temperature of the second solid polymer electrolyte precursor. When the object to be pressurized is the membrane electrode assembly, the applied pressure is 1 to 10 MPa, the temperature is 0 ° C. or higher, and is not higher than the glass transition temperature of the second solid polymer electrolyte. 4. A method for producing a membrane / electrode assembly for a solid polymer electrolyte fuel cell according to any one of 3 above.   In the pressurization step, when the pressurization target is the membrane electrode assembly precursor, the temperature is lower than the glass transition temperature of the first solid polymer electrolyte precursor, and the pressurization target is the membrane electrode assembly. 5. The method for producing a membrane electrode assembly for a solid polymer electrolyte fuel cell according to claim 4, wherein the temperature is lower than the glass transition temperature of the first solid polymer electrolyte.   The method for producing a membrane electrode assembly for a solid polymer electrolyte fuel cell according to any one of claims 1 to 5, wherein the fibrous conductive material is a carbon nanotube.