JP5207582B2 - Manufacturing method of electrolyte membrane with little dimensional change - Google Patents

Description

  The present invention relates to an electrolyte membrane having a small dimensional change used for a polymer electrolyte fuel cell.

A fuel cell is one that converts the chemical energy of fuel directly into electrical energy by electrochemically oxidizing hydrogen, methanol, etc. in the battery, and is attracting attention as a clean electrical energy supply source. ing. In particular, polymer electrolyte fuel cells are expected to be used as alternative power sources for automobiles, home cogeneration systems, portable generators, and the like because they operate at a lower temperature than others.
Such a polymer electrolyte fuel cell includes at least a membrane electrode assembly in which a gas diffusion electrode in which an electrode catalyst layer and a gas diffusion layer are laminated is bonded to both surfaces of an ion exchange membrane. The ion exchange membrane here is also called an electrolyte membrane, and is a material having a strong acid group such as a sulfonic acid group and a carboxylic acid group in the polymer chain and a property of selectively permeating ions. As such an ion exchange membrane, a perfluoro ion exchange membrane represented by Nafion (registered trademark, manufactured by DuPont) having high chemical stability is preferably used.

  During operation of the fuel cell, fuel (for example, hydrogen) is supplied to the gas diffusion electrode on the anode side, and an oxidant (for example, oxygen or air) is supplied to the gas diffusion electrode on the cathode side. Operates by connecting. Specifically, when hydrogen is used as a fuel, hydrogen is oxidized on the anode catalyst to generate protons, and after the protons pass through the proton conductive polymer in the anode catalyst layer, they move through the ion exchange membrane, It reaches the cathode catalyst through the proton conducting polymer in the cathode catalyst layer. On the other hand, electrons generated simultaneously with protons by oxidation of hydrogen reach the cathode side gas diffusion electrode through an external circuit, and react with the protons and oxygen in the oxidant on the cathode catalyst to generate water, At this time, electric energy can be taken out.

It has been reported that an ion exchange membrane doped with a strong acid such as phosphoric acid in polybenzimidazole having high heat resistance (hereinafter referred to as a strong acid doped membrane) can be operated at a high temperature of 100 ° C. or higher ( Patent Document 1). However, since there is water in the fuel cell operation at less than 100 ° C., strong acid is eluted from the membrane to the water and the output is reduced. Therefore, the fuel cell operation under the high temperature and low humidity condition maintains a high voltage for a long time. I can't.
Furthermore, the membrane used as an electrolyte membrane for a current polymer electrolyte fuel cell exhibits high battery performance due to its high proton conductivity and low electrical resistance. On the other hand, when the battery is used, the area of the membrane when it contains water There is a problem that the dimensional change in the (vertical × horizontal) direction occurs and the battery life is shortened.

Specifically, since the membrane swells or dries due to water generated in the cells of the polymer electrolyte fuel cell or water vapor supplied together with the fuel gas, the membrane is wrinkled, torn, deformed, folded. This can cause pinholes and shorten the battery life.
Therefore, an electrolyte membrane for a polymer electrolyte fuel cell is desired to have a low electrical resistance and a small dimensional change in the area direction accompanying a change in moisture content or a change in temperature.
When producing a membrane electrode assembly in which an electrolyte membrane for a polymer electrolyte fuel cell is sandwiched and bonded between a pair of gas diffusion electrode layers, it is usually performed under heating. It is also desired that the thickness unevenness is small.

As a method for solving the above-mentioned problem, a method is disclosed in which an electrolyte membrane for a polymer electrolyte fuel cell is biaxially stretched in the temperature range from the glass transition temperature to the melting point to improve the strength of the membrane simultaneously with thinning. (Patent Document 2). However, although this method is effective for improving the strength properties, it is difficult to suppress a change in moisture content and a dimensional change due to a temperature change (heat shrinkage) even if the film is stretched in the above stretching temperature range.
In addition, an electrolyte membrane for a polymer electrolyte fuel cell is disclosed in which the membrane area is increased by 5 to 200% by stretching, and the dimensional change rate when containing water is -5 to + 5% (Patent Document 3). It is difficult to suppress the dimensional change and thickness unevenness during the production of the membrane / electrode assembly by the stretching ratio and the dimensional change at the time of water content by the above method.

Furthermore, in Patent Document 4, a film having a sulfonic acid group and a SO ₂ F group that is a precursor of the sulfonic acid group is stretched at the end of the perfluorocarbon polymer, and after the stretching orientation, a constraining heat treatment is performed at an α dispersion temperature or higher. Although the method etc. are described, the dimensional stability at the time of practical use is inadequate.
Japanese National Patent Publication No. 11-503262 JP 11-354140 A JP 2002-343380 A International Publication WO02-062879 Pamphlet

  The present invention provides a method for producing an electrolyte membrane for a polymer electrolyte fuel cell with little substantial dimensional change (relative to the area direction) in the heated and water-containing state during production and use of the polymer electrolyte fuel cell. The purpose is to do.

  In order to solve the above-mentioned problems, the present inventors diligently studied performance required for an electrolyte membrane for a polymer electrolyte fuel cell used in a fuel cell, particularly dimensional stability. Then, although the dimensional stability is improved to some extent when the conventional stretching process and heat treatment process are performed, bowing distortion occurs and the dimensional stability in the plane (MD direction and TD direction) is not uniform. I confirmed that there was. In addition to finding out that suppressing this bowing strain is a point that can solve the problems of the present invention, the solution is to swell the electrolyte membrane in a wet atmosphere mainly composed of water, It was found that it is important that the substrate is closely adhered to a support having the above-mentioned, and restrained and dried while maintaining the state, and the present invention has been completed.

That is, the present invention is as follows.
1. The electrolyte membrane is swollen in a wet atmosphere containing water as a main component, subsequently, the electrolyte membrane is adhered to a support roll or drum-shaped, 80 ° C. wet for causing constrained dried while it is held to that state The manufacturing method of the electrolyte membrane whose dimensional change rate is -10-30% .
2. 1. The electrolyte membrane is a fluorine-based electrolyte membrane. Electrolyte membrane producing method of electrodeposition described.
3. 1. The membrane area ratio after restraint drying with respect to the electrolyte membrane before swelling is 1.01 to 2.50. Or 2. Electrolyte membrane producing method of electrodeposition described.
4). 1. The membrane area ratio after confined drying with respect to the electrolyte membrane before swelling is 1.1 to 2.0. ~ 3. Method for producing electrolyte membrane electrodeposition according to any one of.
5. 1. The electrolyte membrane contains a perfluorosulfonic acid polymer and a basic polymer. ~ 4. Method for producing electrolyte membrane electrodeposition according to any one of.
6). 1. A roll or drum-shaped support is a rotating body. ~ 5. Method for producing electrolyte membrane electrodeposition according to any one of.

According to the present invention, an electrolyte membrane for a polymer electrolyte fuel cell can be obtained that has a small dimensional change rate with respect to the area direction during hydration and heating. Therefore, when the polymer electrolyte fuel cell is manufactured and in practical use, it is difficult to generate wrinkles, tears, deformations, pinholes, etc. of the membrane, and a solid polymer fuel cell capable of obtaining a long-life and stable cell performance is obtained. be able to.
The electrolyte membrane for a polymer electrolyte fuel cell produced according to the present invention can be a membrane that suppresses the generation of wrinkles even in the portion immediately inside the gasket of a fuel cell that is particularly prone to generation of wrinkles when the battery is used. .

The present invention will be described in detail below.
As the perfluorocarbon polymer having a sulfonic acid group suitably used in the present invention, a known polymer is widely used. For example, a copolymer of a fluorinated olefin compound and an ion exchange group-containing vinyl fluoride compound is used. Etc.
Examples of the fluorinated olefin compound include tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, and the like.

The ion exchange group-containing fluorinated vinyl _{compounds, CF 2 = CF- (OCF 2} CFX) m -O p - (CF 2) can be exemplified compounds represented by _n -Y. (In the formula, X is a fluorine atom or a trifluoromethyl group, m is an integer of 0 to 3, n is an integer of 1 to 12, p is 0 or 1, m + n ≧ 1, and n = 0. In this case, p = 0. Y is a known ion exchange group that exchanges with ions, such as a carboxylic acid group, a sulfonic acid group, and a phosphoric acid group.)
In the present invention, the fluoroolefin compound is preferably tetrafluoroethylene, and the ion exchange group-containing vinyl fluoride compound is represented by the following chemical formulas (1) to (4) using a sulfonic acid group as an ion exchange group. Compounds are preferred.
CF ₂ = CFO (CF ₂ ) _q SO ₃ H (1)
_{CF 2 = CFOCF 2 CF (CF} 3) O (CF 2) r SO 3 H (2)
CF ₂ = CF (CF ₂ ) _s SO ₃ H (3)
_{CF 2 = CF (OCF 2 CF} (CF 3)) t O (CF 2) 2 SO 3 H (4)
In the above formula, q is an integer of 1 to 8, r is an integer of 1 to 8, s is an integer of 1 to 8, and t is an integer of 1 to 5.

Next, as an example of the method for producing a perfluorocarbon polymer having an ion exchange group of the present invention, a method for producing a polymer having a sulfonic acid group as an ion exchange group from a fluorovinyl compound having an SO ₂ F group will be described. .
A precursor can be produced by copolymerizing a fluorovinyl compound and a fluorinated olefin compound by a known polymerization method such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization or the like.
In the present invention, the precursor may contain an etheric oxygen molecule or the like.
The composition ratio of the fluorovinyl compound and the fluorinated olefin compound constituting the precursor is determined in accordance with the ion exchange capacity in a state where the precursor is a perfluorocarbon polymer having a sulfonic acid group of the present invention by a method described later, that is, a sulfonic acid group. The concentration of the sulfonic acid group in the perfluorocarbon polymer having (SO ₃ H group) is preferably 0.5 to 2.0 meq / g dry resin, more preferably 0.7 to 1.6 meq / g Set to be dry resin. When the ion exchange capacity is lower than this range, the electrical resistance of the membrane increases, and when it is high, the mechanical strength of the membrane decreases.

In addition to the polymer, the perfluorocarbon polymer having a sulfonic acid group in the present invention may contain a reinforcing material such as a fibril, a woven fabric, a nonwoven fabric, or a porous body. When the reinforcing material is included, the reinforcing material is preferably made of a fluorine-containing polymer, and a homopolymer or a copolymer containing a polymer unit based on tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene or perfluoro (alkyl vinyl ether). Polymers are preferably used.
Specific reinforcing materials include polytetrafluoroethylene (hereinafter referred to as PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (hereinafter referred to as FEP), and tetrafluoroethylene / perfluoro (propyl vinyl ether) copolymer. Polymer (hereinafter referred to as PFA), tetrafluoroethylene / ethylene copolymer (hereinafter referred to as PETFE), polychlorotrifluoroethylene, tetrafluoroethylene / perfluoro (2,2-dimethyl-1,3-dioxole) Examples thereof include a copolymer and polyperfluoro (butenyl vinyl ether). Of these, PTFE, FEP, PFA, and PETFE are particularly preferable in terms of properties such as mechanical strength and chemical stability.

In the present invention, in addition to a vinyl fluoride compound and a fluorinated olefin compound, a copolymer containing a third component such as a perfluoroolefin such as hexafluoropropylene or chlorotrifluoroethylene or a perfluoroalkyl vinyl ether may be used. Good.
The MFR (g / 10 minutes) measured at 270 ° C., load 21.2 N, orifice inner diameter 2.09 mm based on JIS K-7210 of the precursor polymer that can be used in the present invention is not limited. It is preferably 0.001 or more and 1000 or less, more preferably 0.01 or more and 100 or less, and most preferably 0.1 or more and 10 or less.

  Next, the precursor polymer that can be used in the present invention is immersed in a basic reaction liquid and subjected to an alkali hydrolysis treatment. The reaction liquid is not limited, but an aqueous solution of an alkali metal or alkaline earth metal hydroxide such as potassium hydroxide or sodium hydroxide is preferred. The content of the alkali metal or alkaline earth metal hydroxide is not limited, but is preferably 10% by mass or more and 30% by mass or less. The reaction liquid preferably contains a swellable organic compound such as dimethyl sulfoxide or methanol. The content of the swellable organic compound is preferably 1% by mass or more and 30% by mass or less.

After the precursor polymer is subjected to an alkali hydrolysis treatment, and further subjected to an acid treatment with hydrochloric acid or the like as necessary, a perfluorocarbon polymer having an ion exchange group is produced.
On the other hand, the basic polymer used in the present invention is not particularly limited, and examples thereof include polybenzimidazole, polypyridine, polypyrimidine, polyimidazole, polyvinylpyridine, polyvinylimidazole, and polyaniline. Among these, polybenzimidazole is particularly preferable because of its high heat resistance.

The electrolyte membrane for a polymer electrolyte fuel cell in the present invention is mixed with various heat-resistant polymers, engineer plastics, polymers containing nitrogen-containing components, etc. within the range where the characteristics such as ion exchange capacity and MFR do not deviate from the above-mentioned ranges. May be.
The winding direction when producing a long film by performing extrusion film formation or cast film formation (MD direction) refers to the direction perpendicular to the winding direction (so-called TD direction).

The solvent used for the solution for producing the fuel cell of the present invention is not limited, but a mixed solvent of an aprotic solvent and a protic solvent is more preferable.
Here, the protic solvent is a solvent having a functional group capable of emitting protons such as water, alcohol, and acid, and examples thereof include water, alcohols (such as methanol, ethanol, propanol, and isopropanol), and phenols. . These protic solvents may be used singly or in combination of two or more, and it is particularly preferable to use a mixed solvent of water and alcohol, and water / ethanol = 3/1 to 1/3 (volume ratio). It is more preferable to use a mixed solvent of water / isopropanol = 3/1 to 1/3 (volume ratio).

The aprotic solvent is a solvent other than the protic solvent, and examples thereof include NN-dimethylformamide, NN-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, acetone, and methyl ethyl ketone. These aprotic solvents may be used alone or in combination of two or more, and NN-dimethylformamide, NN-dimethylacetamide, N-methylpyrrolidone, and dimethylsulfoxide are particularly preferably used.
By using a mixed solvent of these protic solvents and aprotic solvents, both the perfluorocarbon polymer and the basic polymer dissolve well, and as a result, the ion exchange has a uniform film thickness that is free of appearance. The production of the membrane is facilitated.

  When a mixed solvent of an aprotic solvent and a protic solvent is used as the solution, the mass ratio of the aprotic solvent to the protic solvent (aprotic solvent: protic solvent) is not limited, but is 10:90 to 80: A range of 20 is preferable, and a range of 15:85 to 70:30 is more preferable. By using both solvents in this range, it is possible to prevent the polymer from precipitating out of the solution, and as a result, it is easy to produce a proton exchange membrane that is uniformly compatible and free from external appearance. The change in the wet and dry dimensions of the exchange membrane can also be kept low.

In the present invention, an ion exchange membrane obtained by removing a solvent after casting using a solution for producing a fuel cell containing a perfluorocarbon polymer having an ion exchange group, a basic polymer and a solvent. Can be used.
The production procedure of the cast solution in the present invention can produce a more durable ion exchange membrane by performing the mixing process in two stages as follows.

  That is, a pre-stage solution A in which a basic polymer is dissolved in an aprotic solvent and a pre-stage solution B in which a perfluorocarbon polymer having an ion exchange group is dissolved in an aprotic solvent are mixed by a known stirring method. Then, the solution for fuel cell manufacture of this invention can be obtained by mixing the obtained mixed solution and the pre-stage solution C which melt | dissolved the perfluorocarbon polymer which has an ion exchange group in the protic solvent. The solution produced in this manner has high solution retention because the polymer does not precipitate in the solution, and as a result, the ion exchange membrane obtained by casting also has a uniform appearance and no polymer in the appearance. It becomes an ion exchange membrane.

The pre-stage solution A and the pre-stage solution B need only have an aprotic solvent as a main component of the solvent, and there may be a protic solvent of 20% by mass or less. In addition, the pre-stage solution C only needs to contain a protic solvent as a main component, and 20% by mass or less of an aprotic solvent may be present.
The pre-stage solution C can be produced by a method in which a perfluorocarbon sulfonic acid having a protic solvent and an ion exchange group is placed in an autoclave and heat-treated at 40 to 300 ° C. The content of the perfluorocarbon polymer having an ion exchange group in the pre-stage solution C is not limited, but is preferably 0.01% by mass to 50% by mass, more preferably 0.1% by mass to 40% by mass. Most preferably, it is 0.5 mass% or more and 30 mass% or less.

  The pre-stage solution A can be produced by a method in which a basic polymer and an aprotic solvent are put in an autoclave and heat-treated at 40 to 300 ° C. The content of the basic polymer in the pre-stage solution A is not limited, but is preferably 0.01% by mass to 50% by mass, more preferably 0.05% by mass to 30% by mass, and most preferably 0.00%. It is 1 mass% or more and 10 mass% or less.

  Similarly, the pre-stage solution B can be produced by a method in which perfluorocarbon sulfonic acid having an ion exchange group in an aprotic solvent is put in an autoclave and heat-treated at 40 to 300 ° C. Alternatively, the aprotic solvent can be added to the pre-stage solution C, and then the protic solvent can be removed by a known concentration method such as using an evaporator. The content of the perfluorocarbon polymer having an ion exchange group in the pre-stage solution B is not limited, but is preferably 0.01% by mass to 50% by mass, more preferably 0.1% by mass to 30% by mass. Most preferably, it is 0.5 mass% or more and 10 mass% or less.

  The mixing ratio of the preceding-stage solutions A, B, and C described above is not limited, and can be concentrated as necessary, but the composition of the obtained solution is mixed as described above. The mass ratio of the aprotic solvent to the protic solvent in the obtained solution is preferably in the range of 10:90 to 80:20, more preferably in the range of 15:85 to 70:30, and the ion exchange in the solution The mass ratio of the perfluorocarbon polymer having a group to the basic polymer is preferably in the range of 99.999: 0.001 to 50:50, more preferably 99.995: 0.005 to 80:20, most preferably Is preferably in the range of 99.99: 0.01 to 90:10.

  As a casting method, a known coating method such as a method of casting into a petri dish, a gravure roll coater, a natural roll coater, a reverse roll coater, a knife coater, or a dip coater can be used. Although the base material used for the casting method is not limited, a general polymer film, a metal foil, a substrate such as alumina or silicon, a porous film obtained by stretching a PTFE film, a fibrillated fiber, or the like can be used.

  As a method for removing the solvent, a method such as heat treatment or reduced pressure treatment at room temperature to 200 ° C. can be used. In addition, when heat treatment is performed, the solvent can be removed by raising the temperature stepwise. In the final stage of the heat treatment process, it is necessary to carry out at a temperature higher than the α dispersion temperature of the polymer because of the uniformity and strength characteristics of the electrolyte membrane. The α dispersion temperature of the film of perfluorocarbon polymer having an ion exchange group indicates a temperature at which the main chain of the polymer is considered to start thermal motion, as measured by a dynamic viscoelasticity measuring apparatus. For example, since the α dispersion temperature of polymers such as nylon is generally much higher than room temperature, it is possible to greatly reduce the thermal motion of the main chain by cooling below the α dispersion temperature after the end of stretching, Thereby, the stretched orientation can be stabilized effectively.

  For example, the α-dispersion temperature of the perfluorocarbon polymer when the ion exchange group is a sulfonic acid group is in the vicinity of 110 to 140 ° C. Therefore, if the α dispersion temperature is 140 ° C., the final heat treatment temperature may be set from a temperature range of 150 to 180 ° C. In view of thermal degradation of the perfluorocarbon polymer, the heat treatment temperature is preferably 190 ° C. or lower.

In the ion exchange membrane thus obtained, since the ion exchange group is present as an amine salt or the like, post-treatments in the acid treatment step and the water washing step are performed to obtain an ion exchange membrane.
In the acid treatment step, a dilute mineral acid such as hydrochloric acid, nitric acid or sulfuric acid may be used, and hydrochloric acid or nitric acid is preferable. The treatment temperature is preferably 60 ° C. or lower, and more preferably 40 ° C. or lower.
The treatment temperature in the water washing step is preferably 60 ° C. or lower, more preferably 40 ° C. or lower.

In the present invention, the wet atmosphere containing water as the main component preferably means a liquid containing 51% by mass or more of water (ethanol may be contained by 49% by mass or less).
The swelling treatment in a humid atmosphere of the present invention is a process for increasing the membrane area without applying external force to the membrane through a pre-process for treating the membrane in a humid atmosphere before increasing the membrane area. is there. The swelling treatment is performed in a humid atmosphere containing water as a main component, and the temperature is preferably 60 ° C. or higher, more preferably 80 ° C. or higher.

The swelling treatment in a humid atmosphere may be immersed in a liquid, or the environmental gas may be in a wet state.
Depending on the atmosphere type and temperature of the swelling, the membrane area ratio after constrained drying with respect to that before swelling increases within the range of 1.01 to 2.50, but the preferred membrane area ratio is 1.05 to 2.0, Swelling treatment conditions that increase the electrolyte membrane area ratio in the range of 1.1 to 1.8 are preferred.
The restrained fixation of the electrolyte membrane subjected to the swelling treatment is performed in a state of being attached to a support having a rotating curved surface and fixed so that the electrolyte membrane subjected to the swelling treatment is not relaxed. Specifically, the entire surface of the electrolyte membrane in the MD direction and the TD direction may be in a fixed state, and as an example of a support having a rotating curved surface, restraint drying is performed using a roll or drum-shaped outer periphery. A method can be mentioned. Although it is limited to a curved body, according to the study by the present inventors, on the flat surface, the shrinkage stress when the electrolyte membrane dries increases the fixing force of the electrolyte membrane, and the contraction cannot be performed without constrained drying. It was confirmed. It is presumed that the planar shape has a smaller surface pressure restraining force than the curved surface shape of the roll or drum.

The surface material of the curved body is preferably glass or stainless steel, and from the viewpoint of surface roughness, solid surface or mirror finish is preferable for constrained drying. The inside of the curved body may be water-cooled.
In addition, it is important for continuous treatment, but when a swollen electrolyte membrane is attached to a rotating curved body, an appropriate pressing pressure by a sponge roll is applied so that no wrinkles or edges are peeled off. It was confirmed that it was suitable for proper pasting. Furthermore, it is preferable to use a crown roll, a reverse crown roll, or a flat roll for the transport roll immediately before the sponge roll depending on the slackness and tension of the electrolyte membrane after the swelling treatment.

The constrained drying conditions may be either drying with a heating drum or drying with hot air blowing, but hot air blowing drying is preferable for continuous processing. Although drying temperature has a correlation with a dimensional change rate, 20-100 degreeC is preferable and 40-80 degreeC is further more preferable. Although the drying time is related to productivity, according to the study by the present inventors, it is preferably 5 minutes or more, more preferably 10 minutes or more.
Regarding the thickness of the electrolyte membrane, generally, when it is thin, the strength of the electrolyte membrane is weak, the handling property is poor, the hydrogen permeability is increased, and the membrane may be broken when a membrane electrode assembly is produced. On the other hand, if it is too thick, the movement of water in the electrolyte membrane is hindered during power generation and power generation characteristics are degraded.

  During power generation, the moisture content differs between the anode side and the cathode side of the membrane, and the moisture content is distributed in the thickness direction. This is one of the causes of deteriorating power generation characteristics, and this phenomenon becomes more prominent as the electrolyte membrane is thicker. That is, it can be said that control of the thickness of the electrolyte membrane for a polymer electrolyte fuel cell is an important factor that affects cell characteristics. Therefore, the thickness range is preferably 5 to 300 μm, more preferably 10 to 200 μm, and still more preferably 15 to 100 μm.

The electrolyte membrane for a polymer electrolyte fuel cell produced by the production method of the present invention has a dimensional change rate when wetted at 80 ° C. within a range of −10 to 30%, preferably within a range of −5 to 20%. More preferably, it is in the range of −2 to 15%. If the rate of dimensional change is within these ranges, it is possible to prevent problems such as wrinkle generation and thickness unevenness during membrane electrode assembly production, and electrolyte membrane slack and thickness unevenness during fuel cell power generation.
The 80 ° C. wet state is the operating temperature range of the fuel cell.

Below, an example of the manufacturing method of a polymer electrolyte fuel cell and its usage method are demonstrated.
The electrolyte membrane for a polymer electrolyte fuel cell is formed into a membrane electrode assembly (MEA) by closely bonding gas diffusion electrodes containing a catalyst to both surfaces of the membrane by a known method.
The gas diffusion electrode and the electrolyte membrane for a polymer electrolyte fuel cell require a step of firmly adhering by a hot press method or the like. Therefore, when the electrolyte membrane for a polymer electrolyte fuel cell obtained by the production method of the present invention is used, since the heat shrinkage rate under heating is small, the variation in film thickness can be reduced, and the gas diffusion electrode having a uniform current density It can be made excellent in adhesiveness.
The gas diffusion electrode usually uses a sheet-like porous body formed by holding conductive carbon black powder carrying platinum catalyst particles or platinum alloy catalyst particles with a hydrophobic resin binder such as PTFE. Can do.

As the porous material, a material containing a perfluorocarbon polymer having a sulfonic acid group can be used. As the polymer, the perfluorocarbon polymer constituting the electrolyte membrane for a polymer electrolyte fuel cell of the present invention is used. The same types of polymers as listed can be used. The carbon black powder may be coated with the perfluorocarbon polymer and the catalyst.
A plurality of the obtained MEAs are stacked as necessary, and a current collector (bipolar plate) is arranged on the outermost side by a known method to form a so-called fuel cell. In the present invention, a fuel cell composed of one MEA is referred to as a single fuel cell.
The current collector is a graphite or metal flange having a gas flow path on the surface or the like, and functions as a flow path for supplying hydrogen and oxygen to the MEA surface in addition to transmitting electrons to an external load circuit. have.

The fuel cell obtained as described above can be further operated as a fuel cell in combination with a fuel cell frame, a gas supply device and the like.
The fuel cell is operated by supplying hydrogen to one electrode and oxygen or air to the other electrode. The higher the operating temperature of the fuel cell is, the higher the catalyst activity in the gas diffusion electrode is. However, the operating temperature is usually 50 to 100 ° C., where moisture management is easy. Further, the higher the supply pressure of oxygen or hydrogen, the higher the output of the fuel cell, which is preferable. However, since the probability of contact between the two due to membrane breakage or the like also increases, it is preferable to adjust the pressure to an appropriate pressure range. Based on the above description, the operating conditions of the fuel cell of the present invention were evaluated as follows, and the fuel cell evaluation of the electrolyte membrane for a polymer electrolyte fuel cell of the present invention was performed.

The physical property values and the fuel cell evaluation method of the present invention will be described below.
(1) MFR measurement (measured according to JIS K-7210)
About 8 g of the sulfonic acid group precursor copolymer composition described above was used in a product name, MELT INDEXER C-50590, manufactured by Toyo Seiki Co., Ltd., at a temperature of 270 ° C. and a load of 2.16 kg for 10 minutes. The amount flowing out is determined in g / 10 minutes.
(2) Ion exchange capacity: measurement of EW Approximately ² to 10 cm ^{2 of} ion exchange membrane was added to 50 ml of a saturated NaCl aqueous solution at 25 ° C. (NaCl was dissolved in ion exchange water until it became supersaturated, and the supernatant was used). Immerse and leave for 10 minutes with stirring. Next, neutralization titration is performed using 0.01N aqueous sodium hydroxide solution using phenolphthalein as an indicator. After neutralization, the obtained Na-type ion exchange membrane is rinsed with pure water, then vacuum dried at 10 kPa or less, 110 ° C., 1 hour, and weighed. The ion exchange capacity is calculated from the sodium hydroxide equivalent required for neutralization and the vacuum dry weight.

(3) Measurement of α dispersion temperature Using a dynamic viscoelasticity measuring apparatus (product name, DVA-225, manufactured by IT Measurement Control Co., Ltd.), a predetermined sample (length 30 mm, width 5 mm) is cut out, The temperature range from room temperature to 250 ° C is measured under conditions of a heating rate of 5 ° C / min, in air, at a frequency of 35 Hz. The temperature is plotted on the horizontal axis, and tan δ is plotted on the vertical axis. Let it be temperature.
(4) Measurement of film thickness After leaving the electrolyte membrane for a polymer electrolyte fuel cell before and after self-swelling in a thermostatic chamber at 23 ° C. and a relative humidity of 50% for 1 hour or more, a film thickness meter (manufactured by Toyo Seiki Seisakusho: Model B -1). Moreover, an average stretch area ratio (longitudinal stretch ratio × lateral stretch ratio) is calculated from the film thickness before and after.

(5) Measurement of bowing strain Two lines parallel to the TD direction of the electrolyte membrane before self-swelling are drawn, and after the self-swelling and constrained drying, the deviation between the end and center of the two lines is measured in the MD direction. The degree of deviation of the central portion in the MD direction is calculated. When the numerical value is +, it is Boeing distortion in which the central portion is delayed with respect to the MD direction, and when the numerical value is-, it is defined as Boeing distortion in which the central portion is advanced with respect to the MD direction.
(6) Measurement of dimensional change when containing water at 80 ° C. After leaving the electrolyte membrane for polymer electrolyte fuel cell (5 cm × 4 cm) in a temperature-controlled room at 23 ° C. and a relative humidity of 50% for 12 hours or more, the vertical direction before containing water And measure the lateral length. Then, it is immersed in 80 degreeC hot water for 30 minutes, and the length of the vertical direction and horizontal direction after water content is measured in water after taking out. The dimensional change rate at the time of water content is calculated from the length before and after water content.

(7) Fuel cell performance evaluation First, an electrode catalyst layer is prepared. A predetermined amount of Pt-supported carbon, persulfonic acid polymer solution and ethanol are weighed and mixed well with a homogenizer to obtain an electrode ink. This electrode ink is applied on the PTFE sheet by screen printing. After coating, it is dried in air at room temperature and 120 ° C. to form an electrode catalyst layer. Two types of electrode catalyst layers are prepared with Pt and a polymer loading, and 0.15 mg / cm ² is used as an anode catalyst layer, and 0.30 mg / cm ² is used as a cathode catalyst layer.
Next, the anode catalyst layer and the cathode catalyst layer face each other, an electrolyte membrane is sandwiched therebetween, and hot pressing is performed at 160 ° C. and a surface pressure of 0.1 MPa to produce a membrane electrode assembly (MEA).
A carbon cloth is set as a gas diffusion layer on both sides of the MEA and incorporated in a battery performance evaluation cell.
The battery performance evaluation conditions were a cell temperature of 80 ° C., hydrogen gas on the anode side, air gas on the cathode side, and pressurization at 0.20 MPa for both the anode and cathode. A water bubbling method is used for gas humidification, and the hydrogen gas is humidified at 90 ° C. and the air gas is humidified at 80 ° C. and supplied to the battery evaluation cell. Power is generated at a current density of 0.2 A / cm ² and the time until the initial cell voltage decreases by 30% is determined.

The present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to these examples.
Example 1
A precursor polymer obtained from tetrafluoroethylene and CF ₂ = CFO (CF ₂ ) ₂ —SO ₂ F was dissolved in an aqueous solution in which potassium hydroxide (15% by mass) and dimethyl sulfoxide (30% by mass) were dissolved. The alkali hydrolysis treatment was performed by contacting at 60 ° C. for 4 hours. Then, it was immersed in 60 degreeC water for 4 hours. Next, after being immersed in a 2N aqueous hydrochloric acid solution at 60 ° C. for 3 hours, washed with ion-exchanged water and dried to obtain a perfluorocarbon sulfonic acid polymer (EW * 710, MFR: 3.FR) having a proton exchange group. 0) was obtained.

The obtained perfluorocarbonsulfonic acid polymer was placed in an autoclave together with an aqueous ethanol solution (water: ethanol = 50: 50 (mass ratio)), sealed, heated to 180 ° C. and held for 5 hours. Thereafter, the autoclave was naturally cooled to obtain a pre-stage solution C1 having a composition of perfluorocarbon sulfonic acid polymer: water: ethanol = 5.0: 47.5: 47.5 (mass ratio).
By adding dimethylacetamide to the obtained pre-stage solution C1, and then removing water and ethanol with an evaporator, the composition before perfluorocarbon sulfonic acid polymer: dimethylacetamide = 1.5: 98.5 (mass ratio) was obtained. Stage solution B was obtained.

On the other hand, after concentrating the pre-stage solution C1 with an evaporator to adjust the polymer concentration to 10% by mass, isopropanol was added and stirred to obtain a perfluorocarbon sulfonic acid polymer: water: isopropanol = 8.5: 76.5: A pre-stage solution C2 having a composition of 15 (mass ratio) was obtained.
On the other hand, polybenzimidazole (manufactured by Sigma-Aldrich Japan Co., Ltd.) having a weight average molecular weight of 27000 was placed in an autoclave together with dimethylacetamide, sealed, heated to 200 ° C. and held for 5 hours. Thereafter, the autoclave was naturally cooled to obtain a polymer solution having a composition of polybenzimidazole: dimethylacetamide = 10: 90 (mass ratio). Further, this polymer solution was diluted 10 times with dimethylacetamide to prepare a pre-stage solution A having a composition of polybenzimidazole: dimethylacetamide = 1: 99 (mass ratio).

Next, 16.25 g of the pre-stage solution A was gradually added to 100.0 g of the pre-stage solution B with stirring to obtain a uniform solution. Next, 172.25 g of the previous stage solution C2 was gradually added and mixed while stirring to obtain a solution containing a perfluorocarbon polymer having an ion exchange group and polybenzimidazole.
This solution was poured into a 30 cm * 40 cm stainless steel petri dish, placed in an oven, heated to 160 ° C., and heat-treated for 3 hours to remove the solvent. Then, it took out from oven, poured ion-exchange water into the cooled stainless steel petri dish, the peeled film was dried with the filter paper, and the electrolyte membrane with a film thickness of 60 micrometers was obtained. The membrane was uniformly yellowish and the perfluorocarbon sulfonic acid polymer and polybenzimidazole were completely compatible. The α dispersion temperature at this time was 151 ° C.

The electrolyte membrane was washed with 2N hydrochloric acid and further washed with pure water. Thereafter, self-swelling treatment was performed by the following procedure to obtain an electrolyte membrane for a polymer electrolyte fuel cell. First, the electrolyte membrane was immersed in a stainless steel pad containing hot water of 80 ° C. for 30 minutes. At this time, the surroundings of the membrane are not particularly restricted, and the self-swelling state is caused by the characteristics of the electrolyte membrane. Then, the electrolyte membrane was taken out from the stainless steel pad and attached to the periphery of a 5 L glass beaker, and the electrolyte membrane was constrained and dried for 20 minutes in a hot air dryer at 40 ° C. The bowing distortion was 0%.
The physical properties were measured as an electrolyte membrane for a polymer electrolyte fuel cell after constrained drying. The thickness of the electrolyte membrane for the polymer electrolyte fuel cell was 50 μm, and the proton conductivity was 0.23 (S / cm). it was high.

In addition, the polymer electrolyte membrane for a polymer electrolyte fuel cell of the present invention obtained through the drum-type constrained drying step has a wet dimensional change rate at 80 ° C. of 4.5%, which is excellent in dimensional stability. It was found to be an electrolyte membrane for fuel cells.
Further, when the fuel cell was evaluated at an operating temperature of 80 ° C., the cell voltage drop was within 30% even in the operation of 168 hr (1 week) in the initial battery power generation test.

(Example 2)
12 L of a solution having the same composition as in Example 1 was prepared, and coating was performed using a pipe doctor type cast film forming machine. There were 4 drying zones, 1 zone 1m, and the temperatures were 20 ° C, 80 ° C, 110 ° C and 120 ° C, respectively. The coating speed was 0.1 m / min, and a 22 m roll coating film was obtained using a PEN film as a base film. The film thickness was 74 μm.
The α dispersion temperature of this roll coating film was measured and found to be 152 ° C. Thereafter, heat treatment was performed in a heat treatment furnace set at 170 ° C. with a furnace passage time of 50 minutes.
The roll coating film was continuously washed twice using a 2N hydrochloric acid bath and a pure water washing bath at a line speed of 0.15 m / min. In addition, there is a drying zone in front of the winding device, and hot air is blown in two stages of 50 ° C. and 25 ° C., and winding is performed after drying.

  Then, it was set as the electrolyte membrane for polymer electrolyte fuel cells using the continuous processing apparatus which consists of a drawing machine, a self-swelling processing tank, a drum-type hot air spray dryer, and a winder. The line speed is 0.1 m / min, pure water is put in the self-swelling tank, the temperature is 80 ° C., the treatment time is 30 minutes, the hot air temperature of the drum dryer is 40 ° C., and the drying time is 15 minutes. Continuous treatment was performed under the conditions. Note that a sponge roll soaked with water was used for attachment to the drum dryer, and the inside of the drum was not cooled.

The physical properties were measured as an electrolyte membrane for a polymer electrolyte fuel cell after constrained drying. The thickness of the electrolyte membrane for the polymer electrolyte fuel cell was 50 μm, and the proton conductivity was 0.23 (S / cm). it was high. The bowing distortion was 0%.
In addition, the polymer electrolyte membrane for a polymer electrolyte fuel cell of the present invention obtained through the drum-type constrained drying step has a wet dimensional change rate at 80 ° C. of 4.5%, which is excellent in dimensional stability. It was found to be an electrolyte membrane for fuel cells.
Further, when the fuel cell was evaluated at an operating temperature of 80 ° C., the cell voltage drop was within 30% even in the operation of 168 hr (1 week) in the initial battery power generation test.

(Comparative Example 1)
Using the electrolyte membrane obtained in Example 1, dry stretching was performed by the following procedure to obtain an electrolyte membrane for a polymer electrolyte fuel cell. The thickness of the electrolyte membrane for a polymer electrolyte fuel cell after simultaneous biaxial dry stretching at a stretching temperature of 160 ° C., a stretching ratio of 1.2 times, and a heat set temperature of 180 ° C. is 50 μm, and the proton conductivity is 0.23. (S / cm) and the same as Example 1. The bowing strain was 0% due to simultaneous biaxial stretching.
However, the wet dimensional change rate at 80 ° C. of the electrolyte membrane for a polymer electrolyte fuel cell of the present invention obtained through the dry stretching process is 15.0%, and it can be said that measures for dimensional stability are taken. It was found to be an electrolyte membrane for a polymer electrolyte fuel cell which is difficult.
In addition, when the fuel cell was evaluated at an operating temperature of 80 ° C., the cell voltage drop was within 30% even in the operation of 168 hours (1 week) in the initial battery power generation test, and the drum type constrained drying electrolyte membrane for polymer electrolyte fuel cells It was the same result.

(Comparative Example 2)
Using the electrolyte membrane obtained in the same manner as in Example 2, biaxial dry stretching was successively performed under the following conditions to obtain an electrolyte membrane for a polymer electrolyte fuel cell. The sequential biaxial dry stretching conditions were MD and TD stretching temperature of 160 ° C., MD and TD stretching ratio of 1.2 times, and heat set temperature of 180 ° C. The thickness of the electrolyte membrane for a polymer electrolyte fuel cell after successive biaxial dry stretching was 50 μm, and the proton conductivity was 0.23 (S / cm), which was the same as in Example 2. The bowing strain was 15% due to sequential biaxial stretching.
Further, the wet dimensional change rate at 80 ° C. of the electrolyte membrane for a polymer electrolyte fuel cell of the present invention obtained through the dry stretching process is 15.0%, and it can be said that a measure for dimensional stability is taken. It was found to be an electrolyte membrane for a polymer electrolyte fuel cell which is difficult.
In addition, when the fuel cell was evaluated at an operating temperature of 80 ° C., the cell voltage drop was within 30% even in the operation of 168 hours (1 week) in the initial battery power generation test, and the drum type constrained drying electrolyte membrane for polymer electrolyte fuel cells It was the same result.

  The electrolyte membrane produced by the present invention with little dimensional change can be suitably used in the field of fuel cells as an electrolyte membrane for a polymer electrolyte fuel cell having excellent dimensional stability.

Claims (6)

The electrolyte membrane is swollen in a wet atmosphere containing water as a main component, subsequently, the electrolyte membrane is adhered to a support roll or drum-shaped, 80 ° C. wet for causing constrained dried while it is held to that state The manufacturing method of the electrolyte membrane whose dimensional change rate is -10-30% . Method for producing electrolyte membrane electrodeposition according to claim 1, wherein the electrolyte membrane is a fluorine-based electrolyte membrane. Method for producing electrolyte membrane electrodeposition according to claim 1 or 2, wherein the membrane area ratio after restraint drying for before swelling of the electrolyte membrane is from 1.01 to 2.50. Method for manufacturing electrolyte membranes according to any one of claims 1 to 3, wherein the membrane area ratio after restraint drying for before swelling of the electrolyte membrane is 1.1 to 2.0. Method for producing electrolyte membrane electrodeposition according to any one of claims 1 to 4, characterized in that the electrolyte membrane contains a perfluorosulfonic acid polymer and a basic polymer. Method for manufacturing electrolyte membranes according to any one of claims 1 to 5, wherein the support of the roll or drum shape is rotating body.