JPH11339824A - Manufacture of electrode-membrane joining body for solid polymer electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid polymer electrolyte fuel cell capable of operating at high temperature and obtaining high output. SOLUTION: An ion exchange membrane is made of a perfluorocarbon polymer having a phosphonic acid group, and an adhesive is a solution prepared by dissolving ion exchange resin comprising 0.1-30 wt.% perfluorocarbon polymer in a hydrocarbon alcohol solvent, a fluorine-containing hydrocarbon solvent, or a mixed solvent of them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Hydrogen-oxygen fuel cells have attracted attention as a power generation system which has only a small reaction product in principle and has little influence on the environment. Above all, a solid polymer electrolyte type hydrogen-oxygen fuel cell has been able to obtain a high output due to the rapid progress of recent research, and its practical application is greatly expected.

In a solid polymer electrolyte type hydrogen-oxygen fuel cell, gas diffusion electrode layers are formed on both surfaces of an ion exchange membrane, and hydrogen as a fuel is supplied to one electrode layer and the other is supplied to the other electrode layer. Electric power is generated by supplying oxygen or air serving as an oxidant to the electrode layer.

As an ion exchange membrane serving as an electrolyte, an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group or a carboxylic acid group has been conventionally used. A fuel cell using the ion exchange membrane needs to be operated while keeping the ion exchange membrane at a relatively high water content by humidification or the like, and is usually operated at a normal pressure of less than 100 ° C.
This is because the ion exchange membrane is extremely dried under the temperature condition of 100 ° C. or more, and the membrane resistance sharply increases. For the same reason, a fuel cell using a hydrocarbon-based membrane which has been eagerly developed in recent years for the purpose of low cost is also operated at a normal pressure of less than 100 ° C.

However, at a temperature lower than 100 ° C., a part of the water produced by the reaction or the water added for humidifying the ion exchange membrane remains in the electrode layer or the gas diffusion layer as a liquid. There is a problem in that the pores of the layer are blocked, the supply of fuel gas is hindered, and the output of the battery is reduced.

Conventionally, as a method for producing an ion exchange membrane having gas diffusion electrodes on both surfaces (hereinafter referred to as an electrode-membrane assembly), mainly, a sheet-shaped gas diffusion electrode containing a catalyst is ion-exchanged. A hot press method of joining by applying heat and pressure to an exchange membrane is used.

In the hot press method, the glass transition point of the polymer forming the ion-exchange membrane is set to one hundred and several tens of degrees so that the electrode-membrane assembly has sufficient bonding strength and low electric resistance. Press with In this case, there is a problem that the gas diffusion performance is reduced because the pores of the gas diffusion electrode are deformed or closed.

As a method for solving the above problems, the present inventors have provided a method for producing an electrode-membrane assembly at normal temperature and under slight pressure (Japanese Patent Application Laid-Open Nos. 7-220741 and 7-254420). ). However, even in the fuel cell using the electrode-membrane assembly obtained by this method, the problem that the pores of the electrode layer are blocked by the water produced by the reaction or the water added for humidification described above is still improved. There was room for

[0009]

SUMMARY OF THE INVENTION The present invention provides an electrode for a solid polymer electrolyte type fuel cell which can operate at a high temperature, has a small concentration overvoltage, and can stably provide a high cell output.
An object of the present invention is to provide a method for manufacturing a membrane assembly.

[0010]

The present invention relates to a method for producing an electrode-membrane assembly for a fuel cell of a solid polymer electrolyte type in which a gas diffusion electrode and an ion exchange membrane are joined using an adhesive, The ion exchange membrane is made of a perfluorocarbon polymer having a phosphonic acid group, and the adhesive is made of a hydrocarbon alcohol solvent, a fluorinated hydrocarbon solvent, or 0.1 to 30% by weight of a perfluorocarbon polymer in a mixed solvent thereof. The present invention provides a method for producing an electrode-membrane assembly for a fuel cell of a solid polymer electrolyte type, which is a solution in which an ion exchange resin is dissolved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a perfluorocarbon polymer having a phosphonic acid group is used as an ion exchange membrane. Since the polymer has an essentially high water content, it can maintain a relatively high water content even at a high temperature of 100 ° C. or higher. Therefore, when an ion exchange membrane made of the above polymer is used as an electrolyte, an increase in membrane resistance at a high temperature can be suppressed, and the fuel cell can be operated under a high temperature condition of 100 ° C. or higher. As a result, since the reaction product water and the water added for humidifying the ion exchange membrane are easily removed as water vapor, the pores of the gas diffusion electrode are not blocked, and a stable high battery output can be obtained.

As the perfluorocarbon polymer having a phosphonic acid group, CF ₂ ＣＦCF— (OCF ₂ CFX)
_{m -O p - (CF 2)} n -A ( wherein, m is 0-8 integer, n represents 0 to 12 integer, p is 0 or 1, X is fluorine atom or a trifluoromethyl group, A is A copolymer obtained by copolymerizing a fluorovinyl compound represented by a phosphonic acid group (—PO ₃ H ₂ ) or a precursor functional group thereof) with tetrafluoroethylene is preferable.

Preferred examples of the above fluorovinyl compound include the following compounds. R and R 'represent an alkyl group, and R and R' may be the same alkyl group or different alkyl groups. The alkyl group preferably has 1 to 3 carbon atoms. Also, q and r are integers of 1 to 8, s is an integer of 0 to 8, t
Is an integer of 1 to 5.

[0014]

## STR1 ## _{CF 2 = CFO (CF 2)} q -PO 3 RR ', CF 2 = CFOCF 2 CF (CF 3) O (CF 2) r -
_{PO 3 RR ', CF 2 =} CF (CF 2) s -PO 3 RR', CF 2 = CF (OCF 2 CF (CF 3)) t - (CF
_{2) 2} -PO ₃ RR '.

The perfluorocarbon copolymer having a phosphonic acid group includes a polymerized unit based on a perfluoroolefin such as hexafluoropropylene and chlorotrifluoroethylene and a polymerized unit based on perfluoro (alkyl vinyl ether) as a third component. May be included.

The gas diffusion electrode according to the present invention can be manufactured according to a commonly known method. For example, it can be obtained by a method in which a catalyst for imparting activity as a hydrogen electrode or an air electrode is held by a hydrophobic resin binder such as polytetrafluoroethylene (PTFE) to form a porous sheet.
Further, it can also be obtained by a method such as spraying and applying a dispersion mixture containing a material constituting the gas diffusion electrode.

When using a catalyst coated with an ion exchange resin as the catalyst contained in the gas diffusion electrode,
Since a relatively high water content can be maintained even under a high temperature condition of 100 ° C. or more, it is preferable to use an ion exchange resin made of a perfluorocarbon polymer having a phosphonic acid group as the ion exchange resin.

The adhesive used in the present invention is a hydrocarbon alcohol solvent, a fluorinated hydrocarbon solvent, or a solution obtained by dissolving an ion exchange resin composed of a perfluorocarbon polymer in a mixed solvent thereof.

The above solutions are often in the form of a gel. In the production method of the present invention, this gel-like solution is interposed between the gas diffusion electrode and the ion exchange membrane, and the gel-like solution is infiltrated into the pores of the gas diffusion electrode by pressing the whole, Next, the gas diffusion electrode and the ion exchange membrane are joined by removing the solvent in the solution and solidifying the ion exchange resin. According to this bonding, the gas diffusion electrode and the ion exchange membrane can be bonded at normal pressure or slight pressure, so that the pores of the gas diffusion electrode are not closed, and many large pores having a pore diameter of several microns remain. . Therefore, the obtained electrode-membrane assembly has excellent gas diffusion performance.

The perfluorocarbon polymer used as the ion exchange resin constituting the adhesive is preferably CF ₂ ＣＦCF— (OCF ₂ CFX) _i —O _k — (C
F _{2) j} -B (wherein, i is 0-8 integer, j is 0 to 12 integer, k is 0 or 1, X is fluorine atom or trifluoromethyl group, B is a phosphonic acid group (-PO ₃ H ₂ ) or its precursor functional group, sulfonic acid group (—SO ₃ H) or its precursor functional group, carboxylic acid group (—COOH) or its precursor functional group. And those obtained from copolymers obtained by copolymerization with tetrafluoroethylene are preferred.

Among them, in the above formula, the perfluorocarbon polymer in which B is a phosphonic acid group or a precursor functional group thereof has a relatively high water content, so that it is relatively high even under a high temperature condition of 100 ° C. or more. The electrode can maintain the water content,
An increase in electric resistance of the membrane assembly can be suppressed.

As the solvent constituting the adhesive, a hydrocarbon alcohol solvent, a fluorinated hydrocarbon solvent, or a mixed solvent thereof is used. The boiling point of the hydrocarbon alcohol solvent and the fluorinated hydrocarbon solvent is preferably from 10 to 140C, particularly preferably from 25 to 80C.

As the hydrocarbon alcohol solvent, specifically, methanol, ethanol, n-propanol, isopropyl alcohol, tert-butyl alcohol and the like are preferable. The number of carbon atoms in the main chain of the hydrocarbon alcohol solvent is 1
3 are preferable.

The following are specific examples of the fluorinated hydrocarbon solvent.

1,1,1,2,3,3-hexafluoropropane (HFC-236ea), 1,1,2,2,
3,3,4,4-octafluorobutane (HFC-33
8 pcc), 1,1,1,2,3,4,4,5,5,5
-Decafluoropentane (HFC-43-10me
e), 1,1,1,2,3,4,5,5,5-nonafluoro-2-trifluoromethylpentane (HFC-53
-12 myee), 1,1,1,2,3,3,4,4
5,6,6,6-dodecafluorohexane (HFC-5
3-12-mec)), 1,1,1,2,3,4
4,5,5,5-decafluoro-2-trifluoromethylpentane (HFC-52-13-mcey), 1,
2,3,3,4,4-hexafluoro-1,2-bis (trifluoromethyl) cyclobutane (FC-C-51
-12 mym), fluorocarbons such as perfluorooctane, perfluoroheptane and perfluorohexane, and 1,1-dichloro-1-fluoroethane (HCFC
-141b), 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123), 1,1-dichloro-2,2,3,3,3-pentafluoropropane (HC
FC-225ca), 1,3-dichloro-1,1,2,2
2,3-pentafluoropropane (HCFC-225c
b) hydrochlorofluorocarbons such as;
1,1,1-trifluoroethyl = 1 ′, 1 ′, 2 ′,
2'-tetrafluoroethyl = ether (HFE-34
7), hydrofluoroethers such as methyl = 1,1,1,2,3,3-hexafluoropropyl ether (HFE-356mec), 2,2,2-trifluoroethanol, 2,2,3 Fluorinated alcohols such as 3,3 pentafluoropropanol and 2,2,2-trifluoro-1-trifluoromethylethanol.

Also, C ₈ F ₁₆ O, (C ₄ F ₉ ) ₃ N, C
₁₀ H ₅ F ₁₇ or trichloromonofluoromethane (CFC
-11), chlorofluorocarbons such as 1,1,2-trichlorotrifluoroethane (CFC-113) can also be used.

In general, among the fluorinated hydrocarbon solvents, those having a large number of carbon atoms in the main chain or those having a large number of fluorine atoms in the molecule are preferably used because of high solubility of the ion exchange resin. When a solvent having a high solubility of the ion exchange resin is used as the adhesive, the bonding between the gas diffusion electrode and the ion exchange membrane becomes easy.

For the same reason, a mixed solvent of a hydrocarbon alcohol solvent and a fluorine-containing hydrocarbon solvent is preferably used. The mixing ratio (hydrocarbon alcohol solvent / fluorinated hydrocarbon solvent) of the above mixed solvent is 1/9 to 9 by weight.
/ 1, particularly preferably 3/7 to 7/3. Thus, the amount of the ion exchange resin dissolved in the solvent can be controlled by changing the type of the solvent and the mixing ratio of the mixed solvent.

Further, in order to make the gas diffusion electrode and the ion exchange membrane more intimate, it is important to control the amount of the adhesive impregnated inside the gas diffusion electrode. When the amount of the adhesive is large, the pores of the gas diffusion electrode are blocked by the ion exchange resin in the adhesive, and when the amount is small, the adhesive strength may be reduced. Therefore, the solution viscosity of the adhesive is 1
It is preferably 000 to 50,000 cP. When the solution viscosity of the adhesive is within the above range, an appropriate amount of the adhesive is easily impregnated into the gas diffusion electrode (the solution viscosity in this specification is a value measured by the S method of JIS K7117, and Is a value measured at a rotation speed of 10 min ^-1 .)

The content of the ion exchange resin in the adhesive in the present invention is 0.1 to 30% by weight, and particularly preferably 0.1 to 10% by weight. When the content of the ion exchange resin is within the above range, an adhesive having a preferable solution viscosity is obtained.

Further, as the gas diffusion electrode, the one having a higher porosity allows the ion exchange resin in the adhesive to easily penetrate into the pores of the gas diffusion electrode, so that an electrode-membrane assembly having a higher bonding strength can be obtained. However, even with a gas diffusion electrode having a porosity as small as about 50%, an equal weight mixed solution of ethanol and HCFC-225 containing about 5% by weight of an ion exchange resin as an adhesive (solution viscosity: 10,000 to 20,000 c.
By using an adhesive having a high viscosity and a high solubility of the ion exchange resin as in P), an electrode-membrane assembly having sufficient strength can be obtained. It is important to select the concentration of the ion exchange resin used for the adhesive, the type of the solvent, and the mixing ratio of the mixed solvent according to the gas diffusion electrode.

The preferred amount of the adhesive to be applied cannot be unequivocally limited because it varies depending on the solution viscosity of the adhesive. For example, ethanol containing 5% by weight of a perfluorocarbon ion exchange resin having a sulfonic acid group and HCFC-225 are used.
(Mixing ratio is ethanol / HCFC by weight ratio)
When (−225 = 1/1) is used, the coating amount is preferably about 20 mg / cm ² per apparent surface area of the gas diffusion electrode.

The adhesive may be applied to at least one of the gas diffusion electrode and the ion exchange membrane. That is, the adhesive may be applied only to the ion exchange membrane side, only to the electrode side, or to both the ion exchange membrane side and the electrode side. However, when the adhesive is applied to the ion exchange membrane, the ion exchange membrane swells and bonds. In some cases, it is preferable to apply the coating only on the electrode side.

The method for producing the electrode-membrane assembly in the present invention is not particularly limited. For example, two sheets of a sheet-like gas diffusion electrode having one surface coated with an adhesive are prepared, and this gas diffusion electrode is prepared. It is obtained by, for example, a method in which the surfaces on which the adhesive is applied are opposed to each other, an ion exchange membrane is inserted between the surfaces, the whole is pressed, and the solvent of the adhesive is dried.

It is not necessary to apply a particularly large pressure to the gas diffusion electrode and the ion exchange membrane after the application of the adhesive. For example, the bonding can be sufficiently performed even at a pressure of 1 kg / cm ² or less.
At this time, it is preferable to obtain good adhesion by performing an operation of expelling bubbles between the electrode and the membrane. Specifically, the adhesive between the electrode and the membrane is passed between rolls that are so close that excessive pressure is not applied. For example, a method of applying a roller to an adhesive placed on a flat plate or the like is preferable. In order to increase the bonding strength of the electrode-membrane assembly, a treatment such as roughening the ion exchange membrane may be performed before the bonding.

The time for maintaining the pressurized state at the time of joining the gas diffusion electrode and the ion exchange membrane varies depending on the adhesive. For example, the adhesive contains 5% by weight of the above-mentioned perfluorocarbon ion exchange resin having a sulfonic acid group. When a mixed solution of ethanol and HCFC-225 is used, a few seconds are sufficient.

Further, according to the method of the present invention, the temperature for bonding the ion exchange membrane and the gas diffusion electrode is not particularly limited, and the bonding can be preferably performed at 5 to 35 ° C. The temperature at which the adhesive is dried is preferably less than 100 ° C., particularly preferably 70 ° C. or less, in order to prevent drying of the ion exchange membrane.

[0038]

According to the present invention, a bonded body of the ion exchange membrane and the gas diffusion electrode can be obtained by normal pressure or slight pressure, so that the pores of the gas diffusion electrode are not deformed or clogged. And good gas diffusion performance can be obtained. In addition, since the ion exchange membrane is a perfluorocarbon membrane having a phosphonic acid group having a high water content, a relatively high water content can be maintained even under conditions where the ion exchange membrane is easily dried at a high temperature. The rise in resistance can be suppressed.

[0039]

EXAMPLES Example 1 Tetrafluoroethylene and CF ₂ =
CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ PO ₃ (C
An ion exchange capacity of 2.2 meq / g of a copolymer with H ₃ ) ₂ was formed by copolymerization of a dry resin by a melt casting method to obtain a film having a thickness of 50 μm. This film is
Hydrolysis was performed in a mixed aqueous solution of an aqueous solution of N hydrochloric acid and an aqueous solution of 1N acetic acid, washed with water, and then immersed in an aqueous solution of 1N hydrochloric acid. Next, it was washed with water and dried at 60 ° C. for 1 hour to obtain an ion exchange membrane. The water content of the obtained ion exchange membrane in pure water at 90 ° C. was 78% by weight.

As the gas diffusion electrode, a gas diffusion electrode composed of 60 parts by weight of carbon black carrying a platinum catalyst and 40 parts by weight of PTFE and having a thickness of about 100 μm and an apparent surface area of 10 cm ² (the amount of Pt carried per apparent surface area of the electrode: 0.5 mg / cm ² ). As an adhesive, the solvent was 50 parts by weight of ethanol, 1,3-dichloro-1,1,2,2,3-pentafluoropropane (HC
FC-225cb) A 5 wt% solution (solution viscosity: 18000 cP) was prepared by dissolving granules of an ion exchange resin having the same composition as the ion exchange membrane in a mixed solvent with 50 parts by weight of FC. Next, 0.05 g of the adhesive is uniformly applied to one surface of each of the two gas diffusion electrodes, and the two gas diffusion electrodes are arranged so that the surfaces on which the adhesive is applied face each other,
In the meantime, insert the ion-exchange membrane, press the whole with a hand-rolled roller at room temperature, and dry it sufficiently at room temperature.
A membrane assembly was obtained.

The electrode-membrane assembly was immersed in water for 30 minutes, but did not peel off. When the electrode-membrane assembly was forcibly peeled off from the end of the electrode, a part of the electrode layer remained on the membrane side.

Example 2 (Comparative Example) An ion exchange membrane and a gas diffusion electrode were hot-pressed (with a temperature of 15) without using an adhesive.
An electrode-membrane assembly was obtained in the same manner as in Example 1 except that the bonding was performed at 0 ° C. and a pressure of 10 kg / cm ² for 10 seconds.

Example 3 (Comparative Example) As an ion exchange membrane,
Perfluorocarbon ion exchange membrane having a sulfonic acid group having a thickness of 50 μm (ion exchange capacity: 1.0 meq / g)
An electrode-membrane assembly was obtained in the same manner as in Example 1 except that the dried resin) was used. The electrode-membrane assembly was placed in water for 30 minutes.
After immersion for a minute, there was no peeling, and when the film was forcibly peeled off from the end of the electrode, a part of the electrode layer remained on the film side.

Example 4 (Comparative Example) An electrode-membrane assembly was obtained in the same manner as in Example 2 except that the ion exchange membrane used in Example 3 was used as the ion exchange membrane.

[Evaluation] Each of the electrode-membrane assemblies prepared in Examples 1 to 4 was incorporated into a cell for measuring battery performance. At a cell temperature of 105 ° C., humidified hydrogen was supplied to the anode, and humidified air was supplied to the cathode to perform a power generation test. The terminal voltage of the cell at a current density of 1.0 A / cm ² (unit:
V) and IR loss (unit: Ω · cm ² ).
Table 1 shows the results.

[0046]

[Table 1]

[0047]

According to the electrode-membrane assembly obtained by the present invention, since the pores of the gas diffusion electrode are hardly crushed and maintain a fine structure having pores having a pore diameter of several μm, Excellent gas diffusion performance. Further, the fuel cell having the above-mentioned electrode-membrane assembly can operate at a high temperature of 100 ° C. or higher, and the pores of the gas diffusion electrode are not easily blocked by the reaction water, so that the concentration overvoltage is small and the concentration is stable. The output is obtained.

When the perfluorocarbon polymer in the adhesive is a polymer having a phosphonic acid group, the concentration overvoltage is further reduced in the fuel cell, and a more stable high output is obtained.

Claims (4)

[Claims] An electrode for a fuel cell of a solid polymer electrolyte type in which a gas diffusion electrode and an ion exchange membrane are joined using an adhesive.
A method for producing a membrane assembly, wherein the ion-exchange membrane is made of a perfluorocarbon polymer having a phosphonic acid group, and the adhesive is used in a hydrocarbon alcohol solvent, a fluorinated hydrocarbon solvent, or a mixed solvent thereof. A method for producing a solid polymer electrolyte type electrode-membrane assembly for a fuel cell, wherein the solution is a solution in which an ion exchange resin composed of a perfluorocarbon polymer is dissolved in an amount of 30 to 30% by weight. 2. The method for producing an electrode-membrane assembly for a solid polymer electrolyte fuel cell according to claim 1, wherein the perfluorocarbon polymer in the adhesive is a perfluorocarbon polymer having a phosphonic acid group. 3. A gas diffusion electrode and an ion exchange membrane at 5 to 35 ° C.
The method for producing an electrode-membrane assembly for a fuel cell of a solid polymer electrolyte type according to claim 1 or 2, wherein the bonding is performed. 4. The solvent of the adhesive is a mixed solvent of a hydrocarbon alcohol solvent and a fluorinated hydrocarbon solvent, and the mixing ratio of the mixed solvent (hydrocarbon alcohol solvent / fluorinated hydrocarbon solvent) is 1/9 to 9 The method for producing an electrode-membrane assembly for a fuel cell of a solid polymer electrolyte type according to claim 1, 2 or 3.