JP2009032503A - Composite electrolyte membrane, manufacturing method of composite electrolyte membrane, and solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize both size stability and ionic conductivity of a polymer electrolyte membrane at the same time, and thereby aim at improvement of power generation properties and durability of a solid polymer fuel cell. <P>SOLUTION: For the composite electrolyte membrane made of a reinforcement polymer film containing a plurality of fibrous polymer electrolytes, the plurality of fibrous polymer electrolytes 1 are penetrated into and oriented toward a thickness direction of a reinforcement polymer membrane 2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a composite electrolyte membrane having excellent anisotropic ion conductivity and excellent strength and dimensional stability, and a method for producing the same. The present invention also relates to a polymer electrolyte fuel cell.

  A solid polymer electrolyte fuel cell has a structure in which a solid polymer electrolyte membrane is used as an electrolyte and catalyst electrodes are bonded to both surfaces of the membrane.

  When used as a fuel cell, the polymer solid electrolyte membrane needs to have a low membrane resistance. For that purpose, it is desirable that the film thickness be as thin as possible. However, if the film thickness is too thin, there are problems that pinholes are easily formed during film formation, the film is broken during electrode forming, and a short circuit between the electrodes is likely to occur. In addition, since solid polymer electrolyte membranes used in fuel cells are always used in a wet state, reliability such as pressure resistance and cross-leakage during differential pressure operation due to swelling, deformation, etc. of the polymer membrane due to wetting is reliable. Problems will arise.

  Therefore, in Patent Document 1 below, an ion exchange membrane that does not break even when a change in the water content of the ion exchange resin repeatedly occurs, and the ion exchange resin and a porous membrane such as a fluororesin are in close contact with each other and pinholes are difficult to form. For the purpose of the above, at least the pores of a porous membrane such as a fluororesin prepared by stretching are impregnated with a polymer dissolved in a solvent and dried to adhere to the porous membrane, and then ion exchange groups are introduced to introduce ions. A method of manufacturing an exchange membrane is disclosed.

  By the way, the method for producing an ion exchange membrane disclosed in the following Patent Document 1 has a problem in that since the polymer is soluble in a solvent, the chemical stability is low and the electrolyte performance is likely to deteriorate. That is, since the ion exchange membrane is produced using a polymer dissolved in a solvent, the above-described problems have occurred. In addition, the membrane easily deteriorates due to the swelling change caused by the water content of the electrolyte membrane, and there is a problem that the durability of the fuel cell or the like is shortened. Furthermore, the electrolyte has water retention, and the electrolyte swells due to the movement of protons in the membrane or the purification of water at the electrode, but the porous body does not swell. There was a problem that conductivity was lowered. Electrolyte with proton conductivity (H-type polymer electrolyte) that has been hydrolyzed in an alcohol solvent can be impregnated and the porous body can have electrolyte performance, but the intermolecular bonds are weak and soluble. Therefore, there is a problem that it is easily affected by radicals generated at the electrode. Moreover, the H-type electrolyte also has a problem that its strength is inferior to that of an F-type electrolyte that is hydrolyzed in a subsequent process and exhibits proton conductivity.

  Therefore, in Patent Document 2 below, a mixture of a perfluorocarbon polymer having a sulfonic acid group or a precursor group thereof and a fibrillated fluorocarbon polymer is formed into a film shape and stretched on at least one side of the obtained film. A method for producing an electrolyte membrane for a polymer electrolyte fuel cell is disclosed in which an auxiliary film is laminated and then stretched under heating. It is also disclosed that a heated roll press is used to stretch the laminate under heating.

  Patent Document 3 below provides a manufacturing apparatus and a manufacturing method capable of continuously and efficiently manufacturing an ion exchange membrane that is chemically stable and hardly causes deterioration in electrolyte performance, and can improve strength. For the purpose of providing an ion exchange membrane production apparatus and production method that can suppress pore collapse of the porous membrane (base material sheet) and improve the stability of bonding with an electrode catalyst, Means for continuously feeding, means for pressurizing and impregnating molten electrolyte polymer in the porous membrane to form an electrolyte membrane, and means for imparting ion exchange to the electrolyte polymer in the electrolyte membrane An ion exchange membrane manufacturing apparatus is disclosed. This ion exchange membrane manufacturing apparatus pressurizes and impregnates a molten electrolyte polymer into a continuously fed porous membrane to form an electrolyte membrane (F-type polymer electrolyte), and then the electrolyte in the electrolyte membrane An ion exchange property is imparted to the polymer (H-type polymer electrolyte), and the electrolyte membrane is formed on the porous membrane by heating and melting the electrolyte membrane and the electrolyte polymer.

  In the method disclosed in Patent Document 1, the polymer is hydrophilic, while the stretched porous membrane is hydrophobic, and it is easy to become familiar with the solvent, but is highly durable. Absent. Therefore, there is a concern that the electrolyte and PTFE are separated during use.

  In addition, the technique disclosed in Patent Document 2 and Patent Document 3 described above for melting and impregnating a reinforcing membrane with an electrolyte is excellent as a method for producing a composite electrolyte membrane, but achieves both dimensional stability and ion conductivity. There is nothing ingenuity about that.

  By the way, in Patent Document 4 below, a cation is used for the purpose of providing an electrolyte membrane having low electrical resistance and excellent durability without distortion or breakage in a state where humidity and physical conditions change. A solid sheet reinforced by impregnating and compounding a polymer resin with ion conductivity into a base sheet that is entangled in a mesh by a wet papermaking method or a dry nonwoven fabric method using conductive fibers and bonded between the fibers. An electrolyte membrane for a molecular fuel cell is disclosed. However, as shown in FIG. 1 of Patent Document 4, short fibers having cation conductivity are intricately entangled and have no orientation.

JP-A-9-194609 JP 2001-345111 A Japanese Patent Laying-Open No. 2005-162784 JP 2005-285549 A

  In the manufacture of electrolyte membranes for fuel cells, various proposals have been made for composite membranes such as gore from the viewpoints of durability and dimensional stability. As a reinforcing material, there is a proposal of a three-dimensional structural porous body by phase separation or the like in addition to a general two-dimensional stretched membrane. In any case, the electrolyte is filled in the porous body by solvent impregnation or melt impregnation, and not only the electrolyte cannot be densely packed, but also the electrolyte to be filled cannot be oriented efficiently. .

  Currently proposed ion conductive electrolyte membranes use biaxially stretched membranes and phase-separated porous membranes due to problems such as swelling due to water absorption and insufficient strength. The biaxially stretched membrane can achieve a porosity of 80% or more, can maintain a relatively high ionic conductivity, and has a small in-plane dimensional change due to moisture absorption. There are problems such as peeling due to cycles. On the other hand, the phase-separated porous membrane also has constraints in the thickness direction, and dimensional stability can be secured, but the porosity cannot be so high as about 60%, and the actual ion conduction path becomes larger with respect to the film thickness. As a result, there is a problem of low ion conductivity. Therefore, in the prior art, it is difficult to simultaneously form a film having high dimensional stability and high ion conductivity.

  In order to fill the electrolyte material in the porous body, in order to obtain fluidity, the solution in which the electrolyte is dissolved in a solvent is impregnated, or it is heated and melted and pressure impregnated. However, in solution impregnation, since the porous body is filled as a solution, it remains as a void after evaporation of the solvent. For this reason, not only the filling of many times is required, but also 100% electrolyte is not filled. In addition, in the melt impregnation, the filling process is performed with pressure from one direction of the porous body, so that the pores are branched in a complicated manner, or there is a region where the molten electrolyte is not filled due to pore size variation, etc. The pores remain in the membrane. That is, the electrolyte filling rate is 90% or less. In addition, the actual ion conduction path reaches up to about three times the film thickness.

  Therefore, the ionic conductivity of the actual composite membrane = (the ionic conductivity of the electrolyte as a bulk) × (the porosity of the porous body) × (the filling rate of the electrolyte) × (1 / the actual ionic conduction path) On the other hand, only about 20% performance may be obtained. For this reason, it is necessary to further reduce the film thickness, and it becomes difficult to achieve durability reliability and handling properties.

  In addition, for any filling method, it is necessary to lower the fluidity in order to fill the pores with the electrolyte, so the electrolyte resin does not extend due to the crushing force during the filling process, and the functional group Since the ion conduction path is not formed by the alignment, the isotropic ion conduction performance is only achieved. In other words, application of a magnetic field or the like is required for orientation in the film thickness direction.

  The present invention was invented in view of the above-mentioned problems of the prior art, and an object thereof is to simultaneously establish the dimensional stability and ionic conductivity of a polymer electrolyte membrane. Another object of the present invention is to improve the power generation and durability of the polymer electrolyte fuel cell.

  The present inventor has found that the above problems can be solved by penetrating and substantially orienting a plurality of fibrous polymer electrolytes in the thickness direction of the reinforcing polymer membrane, and has reached the present invention.

  That is, first, the present invention is an invention of a composite electrolyte membrane comprising a reinforcing polymer membrane containing a plurality of fibrous polymer electrolytes, wherein the plurality of fibrous polymer electrolytes are the reinforcing polymer membranes. It is characterized by penetrating through and substantially oriented in the thickness direction.

  In the composite electrolyte membrane of the present invention, since the plurality of fibrous polymer electrolytes penetrate and are substantially oriented in the thickness direction of the reinforcing polymer membrane, the fibrous polymer electrolyte that is an ion path is linearly at the shortest distance. It is formed and has excellent ion conductivity. In addition, since the fibrous polymer electrolyte is almost completely surrounded by the reinforcing polymer, it is excellent in membrane strength and dimensional stability. As a result, the dimensional stability and ionic conductivity of the polymer electrolyte membrane could be established at the same time.

  The plurality of fibrous polymer electrolytes may be separated and not penetrated in the thickness direction of the reinforcing polymer membrane and may be substantially oriented, but in order to produce a clear ion path, a manufacturing method described later From this surface, a predetermined number of the plurality of fibrous polymer electrolytes are bound to form a polymer electrolyte bundle, and the plurality of polymer electrolyte bundles penetrates in the thickness direction of the reinforcing polymer membrane and is substantially oriented. It is preferable.

  The polymer electrolyte used in the present invention is a hydrolyzed polymer electrolyte precursor (F-type polymer electrolyte) that exhibits proton conductivity by hydrolysis even with an H-type polymer electrolyte that itself has proton conductivity. However, from the viewpoint of the production method described later, a hydrolyzate of a polymer electrolyte precursor (F-type polymer electrolyte) that exhibits proton conductivity by hydrolysis is preferable.

  In the composite electrolyte membrane of the present invention, sufficient strength can be ensured even if the area of the fibrous polymer electrolyte portion relative to the surface area of the composite electrolyte membrane is increased. Specifically, the area of the fibrous polymer electrolyte portion relative to the surface area of the composite electrolyte membrane is preferably 30% or more.

  Secondly, the present invention is an invention of a method for producing a composite electrolyte membrane in which the plurality of fibrous polymer electrolyte bundles penetrates and is substantially oriented in the thickness direction of the reinforcing polymer membrane. A spinning process for obtaining a fibrous polymer electrolyte by melt-drawing and spinning a polymer electrolyte precursor (F-type polymer electrolyte) that exhibits proton conductivity, and binding a plurality of the fibrous polymer electrolytes A bundling step of obtaining a block material by impregnating the bundling material with a reinforcing polymer material, and slicing the block material substantially perpendicular to the orientation direction of the plurality of fibrous polymer electrolytes A film forming step.

  According to the melt stretching process of the present invention, the electrolyte resin is oriented in the longitudinal direction, ion conduction channels in the longitudinal direction are efficiently formed, and ion conduction in the stretching direction is greatly improved. In addition, by forming a solid block around the fibrous electrolyte by filling it with a reinforcing material, it is possible not only to achieve a filling rate of 100%, but depending on the selection of conditions, pre-stress due to heat shrinkage even in the standard state It is possible not only to suppress the swelling of the electrolyte but also to generate a restraining force in the thickness direction by a frictional force. As a result, the hydrogen permeation preventing performance is improved more than before, and the fuel cell performance is improved.

  In the present invention, after the membrane forming step, a hydrolysis step of hydrolyzing a polymer electrolyte precursor (F-type polymer electrolyte) that exhibits proton conductivity by hydrolysis to obtain a polymer electrolyte is included. preferable.

  Here, as the reinforcing polymer material, known materials can be used as the reinforcing material for the composite polymer electrolyte membrane. Among these, at least one selected from polytetrafluoroethylene (PTFE), a tetrafluoroethylene copolymer containing 10 mol% or less of a copolymer component, and polysiloxane is preferably exemplified.

  A conventional method for producing a composite polymer electrolyte membrane, a porous membrane as a reinforcing membrane, and two polymer electrolyte precursor single membranes having proton conductivity by hydrolysis on both sides of the porous membrane, In addition, two peelable protective sheets are sandwiched from both sides, and these peelable protective sheets-polymer electrolyte precursor single membrane-porous membrane-polymer electrolyte precursor single membrane-peelable protective sheet are laminated. Compared with the case where the composite polymer electrolyte membrane is continuously manufactured by feeding, it is possible to manufacture a composite polymer electrolyte membrane with fewer steps and uniform performance.

  Third, the present invention is a polymer electrolyte fuel cell having the above composite electrolyte membrane.

  In the composite electrolyte membrane of the present invention, the ionic conductivity in the thickness direction can be improved up to about 3 times by orienting the fibrous electrolyte in the thickness direction. Thereby, (1) Even if the area ratio of the electrolyte is as low as about 30%, the composite electrolyte membrane can obtain ion conduction performance comparable to that of an isotropic bulk material. Further, (2) since the electrolyte arrangement is parallel to the thickness direction, the ion conduction path is equal to the film thickness, and conduction through the shortest path is possible. (3) Since the electrolyte filling rate is 100%, water does not enter the electrolyte, so there is no swelling due to moisture absorption even in the actual operating state of the fuel cell, and it is extremely dimensionally stable including the thickness direction. It becomes a composite electrolyte membrane with high reliability and durability.

  FIG. 1 shows a schematic perspective view of the composite electrolyte membrane of the present invention. A fibrous polymer portion 1 oriented in the thickness direction by stretch spinning or the like, or a bundle of electrolyte materials (a diameter of 10 μm or less) 1 in which a plurality of fibrous electrolyte materials are bundled is a reinforcing polymer membrane 2 that is a reinforcing material. It is a composite electrolyte membrane suitable for a polymer electrolyte fuel cell that is disposed so as to penetrate both surfaces and has an area of a fibrous polymer electrolyte portion of 30% or more with respect to the surface area of the composite electrolyte membrane.

  FIG. 2 shows a manufacturing process of the composite electrolyte membrane of the present invention. Table 1 below lists each process and its function.

A polymer electrolyte having proton conductivity (hereinafter referred to as “H-type polymer electrolyte”) has a sulfonic acid group and the like, and in particular has proton conductivity even if it is not modified in a subsequent process. The polymer electrolyte precursor that exhibits proton conductivity by hydrolysis used in the present invention (hereinafter simply referred to as polymer electrolyte precursor or F-type polymer electrolyte) is a hydrolysis treatment or acidification in a later step. It has a precursor group, for example, a —SO ₂ F group or a —SO ₂ Cl group, which is modified into a proton conductive group such as a sulfonic acid group by performing the treatment.

Various known polymer electrolyte precursors (F-type polymer electrolytes) can be used. The polymer electrolyte precursor is not only a polymer electrolyte monomer itself having the above ionic functional group but also a monomer having a group that is converted into an ionic functional group by a reaction in a subsequent step. For example, in the present invention, a polymer film or sheet substrate is impregnated with an electrolyte-generating monomer, polymerized, and further, a sulfonyl halide group [—SO ₂ X ¹ ] or a sulfonate group [—SO ₃ ] in the molecular chain. R ¹ ] or a halogen group [—X ₂ ] is produced by making it into a sulfonic acid group [—SO ₃ H]. In addition, phenyl groups, ketones, ether groups and the like present in the electrolyte-generating monomer units present in the polymer film or sheet substrate can be produced by introducing sulfonic acid groups with chlorosulfonic acid.

  In the present invention, the following monomers (1) to (6) are representative examples of the electrolyte-forming monomer that is polymerized to become a polymer electrolyte precursor.

(1) CF ₂ ═CF (SO ₂ X ¹ ), which is a monomer having a sulfonyl halide group (wherein X ¹ is a halogen group —F or —Cl; the same shall apply hereinafter), CH ₂ ═CF ( SO ₂ X ¹ ), and CF ₂ ═CF (OCH ₂ (CF ₂ ) _m SO ₂ X ¹ ) (wherein, m is 1 to 4, the same shall apply hereinafter). Monomer.
(2) CF ₂ ═CF (SO ₃ R ¹ ), which is a monomer having a sulfonate group (wherein R ¹ is an alkyl group, —CH ₃ , —C ₂ H ₅ or —C (CH ₃ ) ₃ The same shall apply hereinafter.), One or more monomers selected from the group consisting of CH ₂ ═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, ^{X 2} is -Br or -Cl halogen group. Hereinafter the same.), 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 ) which is an acrylic monomer (wherein R ² is —CH ₃ or —F, and R ³ is —H, —CH ₃ , —C ₂ H ₅ or — And C (CH ₃ ) _{3. The} same shall apply hereinafter.), And one or more monomers selected from the group consisting of CH ₂ = CR ² (COOR ³ ).
(5) One or more monomers selected from the group consisting of styrene, styrene derivative monomers 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:

  If desired, specific examples of crosslinking agents for the electrolyte-forming monomers used in the present invention include divinylbenzene, triallyl cyanurate, triallyl isocyanurate, 3,5-bis (trifluorovinyl) phenol, and 3,5- Bis (trifluorovinyloxy) phenol is mentioned. One or more kinds of these cross-linking agents are added in an amount of 30 mol% or less based on the total monomer to cause cross-linking polymerization.

  Examples of the present invention will be described below.

[Example 1]
The present invention was implemented according to the process shown in FIG.
As the electrolyte resin, perfluorosulfonyl floyd was used, and melt extrusion was performed from a screw type extruder to form a fibrous material. In the cooling process, stretching was performed at the same time to obtain an electrolyte fiber bundle having orientation. At this time, tape-like cast molding using a resin such as styrene resin, polyimide, or polyamide and a solvent may be performed and stretched in the length direction.

As the reinforcing material, the fluororesin was heated to the melting point or higher and melt impregnation was performed on the portion where the stretched electrolyte material was bound. In the case of perfluorosulfonyl floyd, the terminal —SO ₂ F is replaced with —SO ₃ H by hydrolysis after thinning to form a function as an electrolyte.

  Once the shape-constrained electrolyte is limited in its swelling rate, dimensional stability can be ensured, and at the same time the stress due to water content is limited to the osmotic pressure of water. Relatively small, there is no need to ensure the strength by stretching or the like to the base material as in the prior art, it is also possible to use other thermoplastic resin for the base material, it is not necessary to correspond to the porous body, The range of material selection can be expanded.

  After hydrolyzing the F-type polymer electrolyte to impart proton conductivity, an MEA cell was prepared, and a plurality of cells were stacked and fixed to prepare a fuel cell stack.

The hydrolysis treatment was performed according to the following procedure.
(1) NaOH aqueous solution + DMSO mixed solution, 80 ° C.
(2) Pure water cleaning (3) H ₂ SO ₄ aqueous solution, 80 ° C.
(4) Pure water cleaning (5) Hot water cleaning, 90 ° C

  According to the present invention, the dimensional stability and ionic conductivity of the polymer electrolyte membrane can be simultaneously established. In addition, the power generation and durability of the polymer electrolyte fuel cell can be improved. This contributes to the practical application and popularization of fuel cells.

The typical perspective view of the composite electrolyte membrane of this invention is shown. The manufacturing process of the composite electrolyte membrane of this invention is shown.

Explanation of symbols

1: a bundle of electrolyte materials obtained by binding a fibrous electrolyte portion or a plurality of the fibrous electrolyte materials, 2: a reinforcing polymer membrane

Claims (7)

  A composite electrolyte membrane comprising a reinforcing polymer film containing a plurality of fibrous polymer electrolytes, wherein the plurality of fibrous polymer electrolytes penetrate and substantially align in the thickness direction of the reinforcing polymer membrane. A composite electrolyte membrane characterized by comprising:   A predetermined number of the plurality of fibrous polymer electrolytes are bound to form a polymer electrolyte bundle, and the plurality of polymer electrolyte bundles penetrate and are substantially oriented in the thickness direction of the reinforcing polymer membrane. The composite electrolyte membrane according to claim 1.   The composite electrolyte membrane according to claim 1 or 2, wherein the polymer electrolyte is a hydrolyzate of a polymer electrolyte precursor (F-type polymer electrolyte) that exhibits proton conductivity by hydrolysis.   4. The composite electrolyte membrane according to claim 1, wherein the area of the fibrous polymer electrolyte portion with respect to the surface area of the composite electrolyte membrane is 30% or more. 5.   A spinning step of obtaining a fibrous polymer electrolyte by melt-drawing a polymer electrolyte precursor (F-type polymer electrolyte) that exhibits proton conductivity by hydrolysis, and binding the plurality of fibrous polymer electrolytes together A bundling step of obtaining a bundling material; an impregnation step of impregnating the bundling material with a reinforcing polymer material to obtain a block material; and the block material being substantially perpendicular to the orientation direction of the plurality of fibrous polymer electrolytes. And a membrane forming step of slicing, wherein a plurality of fibrous polymer electrolyte bundles are penetrated and substantially oriented in the thickness direction of the reinforcing polymer membrane.   A hydrolyzing step of hydrolyzing a polymer electrolyte precursor (F-type polymer electrolyte) exhibiting proton conductivity by the hydrolysis to obtain a polymer electrolyte is included after the membrane forming step. Item 6. A method for producing a composite electrolyte membrane according to Item 5.   A polymer electrolyte fuel cell comprising the composite electrolyte membrane according to claim 1.

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