JP4810868B2 - ELECTROLYTE MEMBRANE FOR SOLID POLYMER FUEL CELL, METHOD FOR PRODUCING THE SAME, MEMBRANE ELECTRODE ASSEMBLY FOR SOLID POLYMER TYPE FUEL CELL, AND METHOD FOR OPERATING THE SAME - Google Patents

Description

  The present invention relates to an electrolyte membrane for a polymer electrolyte fuel cell that can be operated at a high temperature, has a high initial output voltage, and can obtain a high output voltage over a long period of time.

  A fuel cell is a cell that directly converts the reaction energy of a gas that is a raw material into electric energy. In a hydrogen / oxygen fuel cell, the reaction product is only water in principle and has little influence on the global environment. In particular, solid polymer fuel cells that use solid polymer membranes as electrolytes have been developed with high ionic conductivity polymer electrolyte membranes that can operate at room temperature and have high output density. With increasing social demand for environmental problems, there is great expectation as a power source for mobile vehicles for electric vehicles and small cogeneration systems.

Conventionally, as an electrolyte membrane of a polymer electrolyte fuel cell, a sulfonic acid group composed of a repeating unit based on CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₃ H and a repeating unit based on tetrafluoroethylene has been used. Copolymer (hereinafter referred to as sulfonic acid type copolymer A) is used.

  Since the sulfonic acid type copolymer A has a softening temperature of around 70 to 80 ° C, the operating temperature of a fuel cell using this copolymer is usually 80 ° C or lower. However, when hydrogen obtained by reforming methanol, natural gas, gasoline, etc. is used as the fuel gas for a fuel cell, the electrode catalyst is poisoned and the output of the fuel cell decreases if even a small amount of carbon monoxide is contained. It becomes easy to do. Therefore, it is desired to increase the operating temperature to prevent this. Further, in order to reduce the size of the fuel cell cooling device, it is desired to increase the operating temperature, and a membrane that can be operated at 120 ° C. or higher is desired. However, since the conventional sulfonic acid type copolymer A has a low softening temperature, it cannot meet these demands.

Therefore, a copolymer having a high softening temperature as described below has been developed. For example, a copolymer containing a repeating unit based on tetrafluoroethylene and a repeating unit based on CF ₂ = CFOCF ₂ CF ₂ SO ₃ H (see Patent Document 1), a repeating unit based on tetrafluoroethylene and CF ₂ = CFCF ₂ A copolymer containing a repeating unit based on OCF ₂ CF ₂ SO ₃ H (see Patent Document 2), a repeating unit based on a monomer that gives a polymer having a repeating unit containing an aliphatic ring structure in the main chain, and CF ₂ = CFOCF _It is a copolymer having a repeating unit based on ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₃ H (see Patent Document 3). A fuel cell using these copolymers as an electrolyte membrane can be operated even at a high temperature of 80 ° C. or higher.

On the other hand, since the oxygen reduction reaction at the cathode of the polymer electrolyte fuel cell proceeds via hydrogen peroxide (H ₂ O ₂ ), hydrogen peroxide or peroxide radicals generated in the catalyst layer Therefore, there is a concern that the electrolyte membrane may be deteriorated. Moreover, since oxygen molecules permeate through the membrane from the cathode to the anode, there is a concern that hydrogen peroxide or peroxide radicals may be similarly generated. In particular, when a hydrocarbon-based membrane is used as a solid polymer electrolyte membrane, the stability against radicals is poor, which has been a serious problem in long-term operation.

  Even in a fuel cell using an ion exchange membrane made of a sulfonic acid type copolymer A, which is a perfluorocarbon polymer, is very stable when operated under high humidification, but operating conditions under low or no humidification. Is reported to have a large voltage drop (see Non-Patent Document 1). That is, under operating conditions with low or no humidification, it is considered that deterioration of the electrolyte membrane proceeds due to hydrogen peroxide or peroxide radicals even in an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group. .

JP 63-297406 A (page 8, Example 1) JP 2002-231268 A (Claim 1) JP 2002-260705 A (page 18, synthesis example 8) Summary of the 2000 Annual Report on Solid Polymer Fuel Cell Research and Development Results Sponsored by New Energy and Industrial Technology Development Organization, p. 56, lines 16-24

  In view of this, the present invention is able to generate power with sufficiently high energy efficiency even at high operating temperatures in the practical application of polymer electrolyte fuel cells for in-vehicle and residential markets. In both low and non-humidity operation where the dew point is lower than the cell temperature and high humidification operation that humidifies at a temperature close to the cell temperature, it has high power generation performance and stable power generation over a long period of time. An object of the present invention is to provide a membrane for a solid polymer fuel cell.

  In the fuel cell using an ion exchange membrane made of a fluorine-containing polymer having an acidic group, the present inventors can withstand use under a high operating temperature and degrade the membrane under operating conditions with low or no humidification. As a result, the inventors of the present invention have intensively studied for the purpose of preventing the above-described problems, and found that the deterioration of the electrolyte membrane can be remarkably suppressed by containing a cerium atom or a manganese atom in the polymer film having a high softening temperature.

The present invention includes softening temperature is an ion exchange membrane made of a fluoropolymer having and sulfonic acid groups at 90 ° C. or higher, at least one member selected from the group consisting of cerium atoms and manganese atoms as ions, cerium ions Is contained in an amount of 0.3 to 20 mol% of —SO ₃ ^— group contained in the ion exchange membrane .
Further, the present invention comprises an ion exchange membrane comprising a fluorine-containing polymer having a softening temperature of 90 ° C. or higher and having a sulfonic acid group, and includes one or more selected from the group consisting of cerium atoms and manganese atoms as ions, Provided is an electrolyte membrane for a polymer electrolyte fuel cell comprising manganese ions in an amount of 0.5 to 30 mol% of —SO ₃ ^— groups contained in the ion exchange membrane .

Further, the present invention provides a method of obtaining an electrolyte membrane described above, the dispersion of the fluoropolymer having sulfonic acid groups, from the group consisting of cerium following compounds soluble in the dispersion and manganese compounds Provided is a method for producing an electrolyte membrane for a polymer electrolyte fuel cell, wherein one or more selected types are mixed, and then the obtained liquid is cast to form an electrolyte membrane.
(Cerium compound)
Cerium carbonate (Ce ₂ (CO ₃ ) ₃ · 8H ₂ O), cerium acetate (Ce (CH ₃ COO) ₃ · H ₂ O), cerium chloride (CeCl ₃ · 6H ₂ O), cerium nitrate (Ce (NO ₃₎ ) ₃ · _6H 2 O), cerium sulfate _{(Ce 2 (SO 4) 3} · 8H 2 O), cerium sulfate _{(Ce (SO 4) 2 ·} 4H 2 O), diammonium cerium nitrate (Ce _{(NH 4) 2} (NO ₃ ) ₆ ), tetraammonium cerium sulfate (Ce (NH ₄ ) ₄ (SO ₄ ) ₄ ) · 4H ₂ O), and cerium acetylacetonate (Ce (CH ₃ COCHCOCH ₃ ) ₃ · 3H ₂ O).
(Manganese compounds)
Manganese carbonate, manganese acetate (Mn (CH ₃ COO) ₂ .4H ₂ O), manganese chloride (MnCl ₂ .4H ₂ O), manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O), manganese sulfate (MnSO ₄ · _5H 2 O), manganese acetate _{(Mn (CH 3 COO) 3} · 2H 2 O), and manganese acetylacetonate _{(Mn (CH 3 COCHCOCH 3)} 2).

  Further, the present invention is a membrane electrode assembly for a polymer electrolyte fuel cell comprising an anode and a cathode having a catalyst layer containing a catalyst, and an electrolyte membrane disposed between the anode and the cathode, Provided is a membrane / electrode assembly for a polymer electrolyte fuel cell, wherein the electrolyte membrane comprises the above-described electrolyte membrane.

  The present invention is also a method for operating a polymer electrolyte fuel cell comprising the membrane electrode assembly described above, wherein hydrogen gas is supplied to the anode side, oxygen or air is supplied to the cathode side, and power is generated at 90 ° C. or higher. A method for operating a polymer electrolyte fuel cell is provided.

  Since the electrolyte membrane of the present invention has a high softening temperature and excellent resistance to hydrogen peroxide or peroxide radicals, a polymer electrolyte fuel cell comprising a membrane electrode assembly having the electrolyte membrane of the present invention is It can be operated at high temperatures, has excellent durability, and can stably generate power over a long period of time.

  The electrolyte membrane of the present invention is composed of an ion exchange membrane made of a fluorine-containing polymer having a softening temperature of 90 ° C. or higher and having an acidic group. In the present specification, the softening temperature is the maximum loss elastic modulus in dynamic viscoelasticity measurement at a temperature rising rate of 2 ° C./min and a frequency of 1 Hz in a temperature region where the polymer softens and the storage elastic modulus rapidly decreases. It is defined as the temperature that indicates the value. The softening temperature is preferably 95 ° C. or higher, and more preferably 100 ° C. or higher.

  In order to improve the durability performance of the electrolyte membrane, it is necessary to be a fluorine-containing polymer, and in particular, the structure other than the acidic group is a perfluorocarbon (which may contain an etheric oxygen atom). Is preferred.

  The acidic group of the fluorine-containing polymer is not particularly limited as long as it has a function of dissociating to generate protons, and a strongly acidic group is preferable. Specifically, there are a sulfonic acid group, a sulfonimide group, a phosphonic acid group, a carboxylic acid group, a ketoimide group, and the like, and a sulfonic acid group that has particularly strong acidity and high chemical stability is preferable.

As the perfluorocarbon polymer having a sulfonic acid group, the following copolymers [1] to [5] are preferable.
[1] and repeating units based on _{tetrafluoroethylene, CF 2 = CF (CF 2} ) a SO 3 H ( wherein, a is an integer of 0-6.) A copolymer comprising the repeating units based on. In view of the convenience of synthesis, a is preferably 2 or 4.

[2] and repeating units based on _{tetrafluoroethylene, CF 2 = CFO (CF 2} ) b SO 3 H ( wherein, b is an integer of 1-6.) A copolymer comprising the repeating units based on. The shorter the length of the side chain having a sulfonic acid group (the number of carbon atoms in b), the higher the softening temperature of the copolymer. In consideration of the simplicity of synthesis, b is preferably 2.

[3] and repeating units based on _{tetrafluoroethylene, CF 2 = CFCF 2 O (} CF 2) ( wherein, c is an integer of 1-6.) C _SO 3 H copolymerization containing a repeating unit based on Coalescence. In consideration of easiness of synthesis, c is preferably 2.

[4] A repeating unit based on tetrafluoroethylene and a monomer represented by the formula (1) (wherein R ^{1 to} R ³ may each independently contain an ether-bonded oxygen atom and have 1 to 6 carbon atoms) It is a perfluoroalkyl group or a fluorine atom, and R ⁴ is a C1-C6 perfluoroalkylene group which may contain an etheric oxygen atom.

The etheric oxygen atom in the perfluoroalkyl group that may contain an etheric oxygen atom or the perfluoroalkylene group that may contain an etheric oxygen atom is introduced between carbon-carbon atom bonds. May be inserted at the carbon atom bond terminal. The monomer represented by the formula (1) is represented by the formula (2) in which R ^{1 to} R ³ are fluorine atoms and R ⁴ is —CF ₂ OCF ₂ CF ₂ — for ease of synthesis. Monomers are preferred.

[5] A repeating unit based on tetrafluoroethylene and CF ₂ ═CF (OCF ₂ CFX) _d O (CF ₂ ) _e SO ₃ H (wherein d is 0 or 1, X is a fluorine atom or a trifluoromethyl group) Wherein e is an integer of 1 to 5), a monomer represented by the formula (3) and a monomer represented by the formula (4) (wherein R ⁵ is an ether-bonded oxygen atom) A C 1-5 perfluoroalkyl group or fluorine atom, R ⁶ and R ⁷ may be each independently a C 1-5 perfluoroalkyl group or fluorine atom, or R ⁶ and R ⁷ jointly forms a perfluoroalkylene group having 3 to 5 carbon atoms, R ^{8 to} R ¹¹ are each independently a perfluoroalkyl group or fluorine atom having 1 to 5 carbon atoms, or R ^{8 to} R 11 ¹ Copolymer two comprising the repeating units based on at least one selected from the group consisting of jointly form a perfluoroalkylene group having 3 to 5 carbon atoms.) Of.

  By having as a third component a repeating unit based on at least one selected from the group consisting of the monomer represented by formula (3) and the monomer represented by formula (4), the softening temperature of the copolymer is high. Especially, the monomer represented by the formula (5) is preferable. The ratio of the repeating unit based on at least one selected from the group consisting of the monomer represented by the formula (3) and the monomer represented by the formula (4) to the entire repeating unit of the polymer is 0.1 to 50 mol%. It is preferable.

The perfluorocarbon polymer having a sulfonic acid group can be obtained by copolymerizing a monomer having a corresponding fluorosulfonyl group (—SO ₂ F group) and then performing hydrolysis and acidification treatment.

The perfluorocarbon polymer having a sulfonimide group (—SO ₂ NHSO ₂ R ^f group) is a monomer obtained by converting a —SO ₂ F group of a monomer having a corresponding fluorosulfonyl group (—SO ₂ F group) into a sulfonimide group. the copolymerized, or corresponding to synthesize a polymer having -SO 2 _F groups, it is obtained by converting the -SO 2 _F groups of the polymer. The —SO ₂ F group is converted into a salt-type sulfonimide group (—SO ₂ NMSO ₂ R by reaction with R ^f SO ₂ NHM (R ^f is a perfluoroalkyl group, M is an alkali metal or a quaternary ammonium group). ^f group) and can be converted into an acid form by treatment with an acid such as sulfuric acid, nitric acid or hydrochloric acid.

As the perfluorocarbon polymer having a phosphonic acid group, the following copolymers are preferred. A copolymer comprising a repeating unit based on tetrafluoroethylene and a repeating unit based on CF ₂ ═CFO (CF ₂ ) ₃ PO (OH) ₂ .

  The ion exchange capacity of the fluorine-containing polymer having an acidic group is preferably 0.7 to 2.5 meq / g dry resin, particularly 1.0 to 2.0 meq / g dry resin. Is preferred. If the ion exchange capacity is less than 0.7, the ionic conductivity of the fluoropolymer will be insufficient. On the other hand, when the ion exchange capacity exceeds 2.5, the water content becomes too high, and the film strength becomes insufficient when a film is formed using this fluoropolymer. In particular, as will be described later, when cerium ions or manganese ions are present in the electrolyte membrane, the ion conductivity of the ion exchange membrane tends to be ion exchanged and proton conductivity tends to decrease. 1.2-2.0 meq / g dry resin is preferred.

  When a perfluorocarbon polymer having a sulfonic acid group is used, it may be treated with a fluorine gas in order to stabilize the unstable site at the end of the polymer. When the terminal of the polymer is fluorinated, the durability against hydrogen peroxide and peroxide radicals is further improved, so that the durability is improved. In the fluorination reaction, the fluorine gas is preferably a fluorine gas diluted with an inert gas.

  The electrolyte membrane of the present invention is excellent in durability due to the presence of one or more selected from the group consisting of cerium atoms and manganese atoms in the membrane. Although the form of the cerium atom or manganese atom in the film is not particularly limited, for example, there are forms such as cerium ion, manganese ion, cerium compound, manganese compound, and the form of cerium ion or manganese ion is particularly preferable. In addition, since the form of a single metal and an alloy may cause a short circuit of an electrolyte membrane, it is not preferable.

  For example, in the case of cerium ion or manganese ion (hereinafter referred to as cerium ion or the like), it may be present in any state in the electrolyte membrane as long as it exists as an ion, but one of the acidic groups in the ion exchange membrane may be present. A state in which the part is ion-exchanged with cerium ions or the like can be mentioned. Moreover, it is not necessary to contain cerium ion etc. uniformly. It is an ion exchange membrane (laminated membrane) consisting of two or more layers, and at least one of the layers is ion-exchanged with cerium ions or the like, that is, it contains cerium ions and the like nonuniformly in the thickness direction. You may go out. Therefore, when it is necessary to increase the durability against hydrogen peroxide or peroxide radicals particularly on the anode side, only the layer closest to the anode can be a layer made of an ion exchange membrane containing cerium ions or the like.

The method for obtaining the electrolyte membrane of the present invention by containing cerium ions or the like in the fluorine-containing polymer having an acidic group is not particularly limited, and examples thereof include the following methods.
(1) In a dispersion of a fluorine-containing polymer having an acidic group, one or more selected from the group consisting of a cerium compound or a manganese compound that can be dissolved in the dispersion is mixed, and then the obtained liquid is used. A method for producing an electrolyte membrane by casting a film.
(2) A method of immersing a film made of a fluoropolymer having an acidic group in a solution containing cerium ions and the like.
(3) A method of bringing a cerium or manganese organometallic complex salt into contact with an ion exchange membrane made of a fluorine-containing polymer having an acidic group to contain cerium ions or the like.

Considering mass productivity, the method (1) is preferable because the process is the simplest.
In the electrolyte membrane obtained by the above method, it is considered that a part of acidic groups is ion-exchanged with cerium ions or the like.

Here, the cerium ions may be +3 or +4, and a cerium compound that can be dissolved in a liquid medium (for example, water, alcohol, etc.) is used to obtain a solution containing cerium ions. Specific examples of salts containing + trivalent cerium ions include, for example, cerium carbonate (Ce ₂ (CO ₃ ) ₃ · 8H ₂ O), cerium acetate (Ce (CH ₃ COO) ₃ · H ₂ O), and chloride. Examples thereof include cerium (CeCl ₃ .6H ₂ O), cerium nitrate (Ce (NO ₃ ) ₃ .6H ₂ O), cerium sulfate (Ce ₂ (SO ₄ ) ₃ .8H ₂ O), and the like. Examples of the salt containing +4 valent cerium ions include cerium sulfate (Ce (SO ₄ ) ₂ .4H ₂ O), diammonium cerium nitrate (Ce (NH ₄ ) ₂ (NO ₃ ) ₆ ), and tetraammonium cerium sulfate. (Ce (NH ₄ ) ₄ (SO ₄ ) ₄ ) · 4H ₂ O) and the like. Examples of the organometallic complex salt of cerium include cerium acetylacetonate (Ce (CH ₃ COCHCOCH ₃ ) ₃ .3H ₂ O).

In the case of manganese ions, the valence may be +2 or +3, and a manganese compound that can be dissolved in a liquid medium is used to obtain a solution containing manganese ions. Specific examples of the salt containing +2 valent manganese ions include manganese acetate (Mn (CH ₃ COO) ₂ .4H ₂ O), manganese chloride (MnCl ₂ .4H ₂ O), manganese nitrate (Mn (NO _{3) 2 · 6H 2 O)} , and the like manganese sulfate _{(MnSO 4 · 5H 2 O)} . Examples of the salt containing + trivalent manganese ions include manganese acetate (Mn (CH ₃ COO) ₃ .2H ₂ O). Examples of the organometallic complex salt of manganese include manganese acetylacetonate (Mn (CH ₃ COCHCOCH ₃ ) ₂ ).

  Among the above compounds, when preparing an electrolyte membrane by the production method of (1) above, as one or more selected from the group consisting of a cerium compound or a manganese compound that can be dissolved in a dispersion of a fluoropolymer, Cerium carbonate or manganese carbonate is preferred. Cerium carbonate and the like are dissolved in the dispersion of the fluoropolymer to produce cerium ions and the like, and at the same time, carbonic acid can be removed as a gas, which is preferable. Moreover, when producing an electrolyte membrane by the manufacturing method of said (2), it is easy to handle and it is preferable to use an aqueous solution of cerium nitrate, cerium sulfate, manganese nitrate or manganese sulfate. Nitric acid or sulfuric acid produced when ion-exchange of a fluorine-containing polymer having an acidic group in these aqueous solutions can be easily dissolved and removed in the aqueous solution.

For example, when the cerium ion is trivalent and the acidic group is a sulfonic acid group, when the sulfonic acid group is ion-exchanged with the cerium ion, Ce ³⁺ bonds to _three —SO ₃ ^— as shown below. .

When the acidic group of the fluoropolymer is a sulfonic acid group, the number of cerium ions contained in the electrolyte membrane is preferably 0.3 to 20 mol% of the —SO ₃ ^— group in the membrane (hereinafter referred to as “the sulfonic acid group”). This ratio is referred to as “cerium ion content”). When the cerium ion has the above-described structure, the sulfonic acid group ion-exchanged with the cerium ion is 0.9% of the total amount of the sulfonic acid group and the sulfonic acid group ion-exchanged with the cerium ion. It is synonymous with being ~ 60 mol%. The content of cerium ions is more preferably 0.7 to 16 mol%, still more preferably 1 to 13 mol%.

  If the cerium ion content is lower than the above range, sufficient stability against hydrogen peroxide or peroxide radicals may not be ensured. On the other hand, if the content of cerium ions is larger than the above range, sufficient conductivity of hydrogen ions cannot be ensured, resulting in an increase in membrane resistance and a decrease in power generation characteristics.

Further, when the manganese ion is +2 valent, when the sulfonic acid group is ion-exchanged by the manganese ion, two protons and manganese ions are replaced, and Mn ²⁺ is bonded to two —SO ₃ ^—. .

When the acidic group of the fluoropolymer is a sulfonic acid group, the number of manganese ions contained in the electrolyte membrane is preferably 0.5 to 30 mol% of the —SO ₃ ^— group in the membrane (hereinafter referred to as “the sulfonic acid group”). This ratio is referred to as “manganese ion content”). In the case where the manganese ion is completely bonded to two —SO ₃ ^— groups, the sulfonic acid group ion-exchanged with the manganese ion is converted into a sulfonic acid group ion-exchanged with the manganese ion. It is synonymous with 1 to 60 mol% of the total amount. The content of manganese ions is more preferably 1 to 25 mol%, still more preferably 1.5 to 20 mol%.

  If the content of manganese ions is smaller than this range, sufficient stability against hydrogen peroxide or peroxide radicals may not be ensured. On the other hand, when the content of manganese ions is larger than the above range, sufficient conductivity of hydrogen ions cannot be ensured, resulting in an increase in membrane resistance and a decrease in power generation characteristics.

When the electrolyte membrane of the present invention is a laminated membrane, the ratio of cerium ions to the —SO ₃ ^— group in the entire electrolyte membrane should be in the above range, and the cerium of the layer itself containing cerium ions etc. The content of ions or the like may be higher than the above range. In addition, as a method for producing a laminated film, for example, a cation exchange membrane containing cerium ions or the like is produced by any one of the methods (1) to (3) described above, and an ion exchange membrane containing no cerium ions or the like Although it is preferable to produce through the process of laminating, it is not particularly limited.

  The durability of the electrolyte membrane can also be improved by including a cerium compound or a manganese compound (hereinafter referred to as “cerium compound etc.”) in the electrolyte membrane. When the cerium compound or the like is water-soluble, it is considered that it exists as an ion in the film as described above. However, even if the cerium compound or the like is poorly soluble in water, the electrolyte membrane of the present invention is not limited to hydrogen peroxide or peroxide. Excellent resistance to radicals and excellent durability. The reason is not clear, but one of the following mechanisms is considered. For example, cerium ions and the like are generated by dissociation or partial dissolution of a hardly soluble cerium compound or the like, and a part of the acidic group is ion-exchanged with cerium ions or the like, and the ions are converted into an electrolyte. It is considered that the hydrogen peroxide or peroxide radical resistance of the film is effectively improved. Another is considered that the cerium element in the hardly soluble cerium compound has a function of effectively decomposing hydrogen peroxide diffused from the catalyst layer into the film.

  Specific poorly soluble cerium compounds include: cerium phosphate, cerium phosphate, cerium oxide, cerium hydroxide, cerium hydroxide, cerium fluoride, cerium oxalate, cerium tungstate, heteropoly The cerium salt of an acid is mentioned. Examples of the hardly soluble manganese compound include manganese (II) oxide, trimanganese tetroxide, manganese (III) oxide, manganese (IV) oxide, manganese oxide (VII) and the like.

The method for obtaining the electrolyte membrane of the present invention by incorporating a sparingly soluble cerium compound or the like into the fluorine-containing polymer having an acidic group is not particularly limited, and examples thereof include the following methods.
(1) A method in which a hardly soluble cerium compound or the like is added to a dispersion of a fluorine-containing polymer having an acidic group and is contained in the dispersion, and then the resulting solution is used to form a film by a casting method or the like. At this time, the hardly soluble cerium compound or the like may be mixed in advance with a solvent (dispersion medium) capable of highly dispersing the compound and then mixed with a solution or dispersion of a fluoropolymer having an acidic group.

  (2) After immersing a film made of a fluorine-containing polymer having an acidic group in a solution containing cerium ions and the like to contain ions in the film, phosphoric acid, oxalic acid, NaF, sodium hydroxide, etc. A method of immersing in a solution containing a substance that reacts with cerium ions or the like to form a hardly soluble cerium compound or the like, and deposits the hardly soluble cerium compound or the like in the film.

  (3) A cerium compound or the like that can be dissolved in the dispersion is added to the dispersion of the fluoropolymer having acidic groups, and the acidic groups are ion-exchanged with cerium ions or the like. A substance that reacts with cerium ions or the like, such as acid, NaF or sodium hydroxide, to form a hardly soluble cerium compound or the like or a solution containing the same is added to form a hardly soluble cerium compound or the like in the dispersion; A method of forming a film by a casting method or the like using the obtained liquid. Examples of the cerium compound that can be dissolved in the dispersion of the fluoropolymer include cerium acetate, cerium chloride, cerium nitrate, cerium sulfate, manganese acetate, manganese chloride, manganese nitrate, manganese sulfate, and the like. It is done.

(4) Adding a sparingly soluble cerium compound or the like to the precursor of a fluorine-containing polymer having an acidic group, kneading by biaxial extrusion molding, pelletization, film formation by uniaxial extrusion molding, hydrolysis, acidification treatment A method of forming a film is conceivable. Here, the precursor of the fluoropolymer is a polymer having a functional group that can be converted into an acidic group that functions as an ion exchange group. For example, when the acidic group is a sulfonic acid group, a —SO ₂ F group The polymer which has this.

  Among the above methods, the method (2) is particularly preferable. This is because the amount of substitution of cerium ions and the like can be controlled, and the thickness of the film can be adjusted during film formation, so that a film having a uniform thickness can be easily obtained.

  In the present invention, a preferred ratio of the hardly soluble cerium compound or the like contained in the electrolyte membrane is preferably 0.3 to 80% (mass ratio) of the total mass of the electrolyte membrane, more preferably 0.4 to 70. %, More preferably 0.5 to 50%. If the content of the hardly soluble cerium compound or the like in the film is less than this range, sufficient stability against hydrogen peroxide or peroxide radicals may not be ensured. On the other hand, if the content is larger than this range, current shielding occurs, so that the membrane resistance increases and the power generation characteristics may be deteriorated.

The polymer electrolyte fuel cell having the electrolyte membrane of the present invention has the following configuration, for example. That is, a membrane / electrode assembly in which an anode and a cathode having a catalyst layer containing a catalyst and an ion exchange resin are arranged on both surfaces of the electrolyte membrane of the present invention is provided. The anode and cathode of the membrane electrode assembly are preferably provided with a gas diffusion layer made of carbon cloth, carbon paper or the like outside the catalyst layer (opposite the membrane). Grooves serving as fuel gas or oxidant gas passages are formed on both surfaces of the membrane electrode assembly to form a stack in which a plurality of membrane electrode assemblies are stacked via the separator. Hydrogen gas is supplied, and oxygen or air is supplied to the cathode side. A reaction of H ₂ → 2H ⁺ + 2e ⁻ occurs at the anode, and a reaction of 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O occurs at the cathode, and chemical energy is converted into electric energy.
The electrolyte membrane of the present invention can also be used in a direct methanol fuel cell in which methanol is supplied to the anode side instead of fuel gas.

  The catalyst layer described above is obtained in the following manner, for example, according to a normal method. First, a conductive carbon black powder carrying platinum catalyst or platinum alloy catalyst fine particles and a solution of a fluorine-containing polymer having an acidic group are mixed to obtain a uniform dispersion. For example, gas can be obtained by any of the following methods: A diffusion electrode is formed to obtain a membrane electrode assembly.

  The first method is a method in which the dispersion liquid is applied to both surfaces of the electrolyte membrane, dried, and then both surfaces are adhered to each other with two carbon cloths or carbon paper. The second method is a method in which the dispersion liquid is applied onto two carbon cloths or carbon papers and then sandwiched from both surfaces of the electrolyte membrane so that the surface on which the dispersion liquid is applied is in close contact with the electrolyte membrane. It is. Here, the carbon cloth or the carbon paper has a function as a gas diffusion layer and a function as a current collector for diffusing the gas uniformly by the layer containing the catalyst. In addition, a method can be used in which a catalyst layer is prepared by applying the dispersion to a separately prepared substrate, bonded to the electrolyte membrane by a method such as transfer, and then peeled off and sandwiched between the gas diffusion layers. .

  Although the fluorine-containing polymer having an acidic group contained in the catalyst layer is not particularly limited, like the resin constituting the electrolyte membrane of the present invention, the fluorine-containing copolymer having an acidic group having a softening temperature of 90 ° C. or higher. It is preferable that Similarly to the electrolyte membrane of the present invention, the catalyst layer may contain one or more selected from the group consisting of cerium atoms and manganese atoms. The catalyst layer containing one or more selected from the group consisting of cerium atoms and manganese atoms can be applied to both the anode and the cathode, and the decomposition of the resin is effectively suppressed, so that the polymer electrolyte fuel cell is more durable. Sex is imparted.

  The electrolyte membrane of the present invention may be a membrane consisting only of a fluorine-containing copolymer having an acidic group, including one or more selected from the group consisting of cerium atoms and manganese atoms, but other components It may be a film reinforced with fibers such as other resins such as polytetrafluoroethylene and perfluoroalkyl ether, woven fabrics, nonwoven fabrics, porous bodies and the like.

  A polymer electrolyte fuel cell including the membrane electrode assembly of the semi-invention can be operated at 90 ° C. or higher to generate electric power. When hydrogen obtained by reforming methanol, natural gas, gasoline, or the like is used as the fuel gas, if a small amount of carbon monoxide is contained, the electrode catalyst is poisoned and the output of the fuel cell is likely to decrease. When the operating temperature is 90 ° C. or higher, poisoning can be suppressed. The operating temperature is more preferably 120 ° C. or higher, and the effect of suppressing poisoning is higher.

EXAMPLES Hereinafter, the present invention will be specifically described using Examples (Examples 1 to 6) and Comparative Examples (Examples 7 to 12), but the present invention is not limited to these [Example 1].
CF ₂ = CFCF ₂ CF ₂ SO ₂ F was synthesized by the same method as that described in JP-T-2002-528433 (page 25, Example 1). (CF ₃ ) ₃ C—O—O—C (CF ₃ ) ₃ (5.6 mg), CF ₂ = CFCF ₂ CF ₂ SO ₂ F (63.75 g) was charged into a stainless steel autoclave having an internal volume of 100 mL, The liquid was sufficiently deaerated under cooling with liquid nitrogen. Thereafter, the temperature was raised to 100 ° C., tetrafluoroethylene was introduced into the system, and the pressure was maintained at 0.59 MPaG. Nitrogen gas was added thereto to obtain 1.05 MPaG. Thereafter, the temperature was raised to 130 ° C. to 1.3 MPaG. After stirring at 130 ° C. for 17 hours, the gas in the system was purged, and the autoclave was cooled to complete the reaction.

After diluting the product with CClF ₂ CF ₂ CHClF, CH ₃ CCl ₂ F was added and the polymer was flocculated and filtered. The polymer was then stirred in CClF ₂ CF ₂ CHClF, re-agglomerated with CH ₃ CCl ₂ F, and dried in vacuo at 80 ° C. overnight. The amount produced was 2.5 g.

About the obtained polymer, the fluorine gas diluted to 20% with nitrogen gas was introduce | transduced to 0.3 MPaG, and it hold | maintained at 180 degreeC for 4 hours. Thereafter, a film having a thickness of about 50 μm was obtained by hot pressing. Hydrolysis is first immersed in a solution of KOH water and dimethyl sulfoxide as a solvent (KOH / water / dimethyl sulfoxide = 15/55/30 mass ratio), then immersed in hydrochloric acid to convert to acid form, Washed with water.
When the ion exchange capacity of the obtained ion exchange membrane was measured by titration, it was 1.13 meq / g dry resin.

  The softening temperature was measured for this film. Using a dynamic viscoelasticity measuring device DVA200 (manufactured by IT Measurement Co., Ltd.), dynamic viscoelasticity was measured at a sample width of 0.5 cm, a length between grips of 2 cm, a frequency of 1 Hz, and a heating rate of 2 ° C./min. . The softening temperature obtained from the maximum value of the loss modulus was 130 ° C.

As containing the resulting film of cerium corresponding to 10% of the amount of the sulfonic acid group amount ions (+3), the cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) 12.0mg of 500mL of distilled water Then, 0.8 g of the ion exchange membrane is immersed in the solution, and stirred with a stirrer at room temperature for 40 hours to contain cerium ions in the ion exchange membrane. The cerium nitrate solution before and after the immersion was analyzed by ion chromatography, and the content of cerium ions in the ion exchange membrane (the ratio of cerium ions to the number of —SO ₃ ^— groups in the membrane) was calculated to be 10%.

CF ₂ = CF ₂ / CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₃ H copolymer (ion exchange capacity 1.2 meq / g dry resin) made of Hastelloy C alloy on the inner surface The obtained pressure-resistant autoclave is dispersed in ethanol to obtain an ethanol dispersion having a solid content of 10% by mass ratio. This is designated as electrolyte solution A. 126 g of water was added to 20 g of a catalyst in which 50% by mass of platinum was supported on carbon black powder, and ultrasonic waves were uniformly dispersed over 10 minutes. Electrolyte solution A80g is added to this, 54g of ethanol is further added, solid content concentration is made into 10%, and this is made into the coating solution for cathode catalyst layer preparation. This coating solution is applied and dried on a sheet (trade name: Aflex 100N, manufactured by Asahi Glass Co., Ltd., hereinafter simply referred to as ETFE sheet) made of an ethylene / tetrafluoroethylene copolymer, and the platinum amount is 0.5 mg / cm. ² cathode catalyst layers are prepared.

In addition, 124 g of water was added to 20 g of a catalyst in which an alloy of platinum and ruthenium was supported by 53% (platinum / ruthenium ratio = 30/23) on a carbon black powder, and ultrasonic waves were uniformly dispersed over 10 minutes. The electrolyte solution A (75 g) was added to the mixture, and 56 g of ethanol was further added to adjust the solid content concentration to 10% (mass ratio). This was used as the anode catalyst layer preparation coating solution. This coating solution is applied onto an ETFE substrate film and dried to produce an anode catalyst layer having a platinum amount of 0.35 mg / cm ² .

The electrolyte membrane is sandwiched between the cathode catalyst layer and the anode catalyst layer and pressed with a hot press (press conditions: 120 ° C., 2 minutes, 3 MPa) to bond both catalyst layers to the membrane, and the base film is peeled off to remove an electrode area of 25 cm. ² membrane catalyst layer assembly is obtained.

The membrane electrode assembly is obtained by sandwiching the membrane catalyst layer assembly between two carbon paper gas diffusion layers. The carbon paper used here has a layer made of carbon and polytetrafluoroethylene on the surface of one side, and is arranged so that the layer is in contact with the catalyst layer of the membrane-catalyst layer assembly. This membrane electrode assembly is incorporated into a power generation cell, and hydrogen (utilization rate 50%) and air (utilization rate 50%) are supplied into the cell as a humidified gas having a pressure of 0.2 MPa and a dew point of 100 ° C. The cell voltage is recorded at a cell temperature of 120 ° C. and a current density fixed at 0.2 A / cm ² . Examine the initial voltage and time to drop to 0.5V. The results are shown in Table 2. In Table 2, the case where the time until the voltage drops to 0.5 V is 2000 hours or more is indicated by ◎, the case where the time is 900 hours or more and less than 2000 hours is indicated by ◯, and the case where the time is less than 900 hours is indicated by ×.

[Example 2]
Based on a repeating unit based on tetrafluoroethylene and CF ₂ ═CFO (CF ₂ ) ₂ SO ₃ H by a method similar to the method described in JP-A-63-297406 (page 8, Example 1) When an ion exchange membrane made of a polymer having a repeating unit is formed and the ion exchange capacity and softening temperature are measured, the results shown in Table 1 are obtained. Furthermore, when an electrolyte membrane containing cerium ions in an ion exchange membrane is obtained and the content of cerium ions is measured by the same method as in Example 1, the results shown in Table 1 are obtained. Moreover, when the membrane electrode assembly was obtained by the same method as in Example 1 and the cell voltage was examined, the results shown in Table 2 were obtained.

[Example 3]
In a manner similar to that described in US 2004/0121210 (page 2, paragraph 0028), repeating units based on tetrafluoroethylene and CF ₂ ═CFO (CF ₂ ) ₄ SO ₃ H When an ion exchange membrane made of a polymer having a repeating unit based thereon is formed and the ion exchange capacity and softening temperature are measured, the results shown in Table 1 are obtained. Furthermore, when an electrolyte membrane containing cerium ions in an ion exchange membrane is obtained and the content of cerium ions is measured by the same method as in Example 1, the results shown in Table 1 are obtained. Moreover, when the membrane electrode assembly was obtained by the same method as in Example 1 and the cell voltage was examined, the results shown in Table 2 were obtained.

[Example 4]
According to a method similar to the method described in JP-A-2002-231268 (page 6, Example 1), a repeating unit based on tetrafluoroethylene and CF ₂ = CFCF ₂ O (CF ₂ ) ₂ SO ₃ H When an ion exchange membrane made of a polymer having a repeating unit based thereon is formed and the ion exchange capacity and softening temperature are measured, the results shown in Table 1 are obtained. Furthermore, when an electrolyte membrane containing cerium ions in an ion exchange membrane is obtained and the content of cerium ions is measured by the same method as in Example 1, the results shown in Table 1 are obtained. Moreover, when the membrane electrode assembly was obtained by the same method as in Example 1 and the cell voltage was examined, the results shown in Table 2 were obtained.

[Example 5]
Ion comprising a polymer having a repeating unit based on tetrafluoroethylene and a repeating unit based on the following monomer (2) by a method similar to the method described in WO 2004/97851 pamphlet (page 33, Example 7) When the exchange membrane is formed and the ion exchange capacity and the softening temperature are measured, the results shown in Table 1 are obtained. Furthermore, when an electrolyte membrane containing cerium ions in an ion exchange membrane is obtained and the content of cerium ions is measured by the same method as in Example 1, the results shown in Table 1 are obtained. Moreover, when the membrane electrode assembly was obtained by the same method as in Example 1 and the cell voltage was examined, the results shown in Table 2 were obtained.

[Example 6]
According to a method similar to that described in JP-A-2002-260705 (page 18, Synthesis Example 8), a repeating unit based on tetrafluoroethylene, a repeating unit based on the following compound (5), and CF ₂ ═CFOCF A polymer having ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₃ H based repeating units is synthesized. The repeating unit based on the following compound (5) is 42 mol%.

The obtained polymer was immersed in a solution containing KOH water and dimethyl sulfoxide (KOH / water / dimethyl sulfoxide = 15/55/30 mass ratio) as a solvent, and then immersed in hydrochloric acid to be converted into an acid form. Washed with water. The polymer converted into the acid form was dispersed in a mixed solvent of ethanol and water (70/30 mass ratio) to obtain a dispersion having a solid content of 9% by mass ratio. To 100 g of the dispersion, 0.29 g of cerium carbonate hydrate (Ce ₂ (CO ₃ ) ₃ · 8H ₂ O) is added to obtain a dispersion containing cerium ions. Next, this dispersion is coated on a 100 μm ETFE sheet with a die coater to form a film. This is dried at 80 ° C. for 30 minutes, and further annealed at 150 ° C. for 30 minutes to form an ion exchange membrane having a thickness of 50 μm. When the ion exchange capacity and softening temperature of the ion exchange membrane are measured, the results shown in Table 1 are obtained.

  Furthermore, when an electrolyte membrane containing cerium ions in an ion exchange membrane is obtained and the content of cerium ions is measured by the same method as in Example 1, the results shown in Table 1 are obtained. Moreover, when the membrane electrode assembly was obtained by the same method as in Example 1 and the cell voltage was examined, the results shown in Table 2 were obtained.

[Examples 7 to 11]
An electrolyte membrane is formed in the same manner as in Examples 2 to 6 except that cerium ions are not contained, and a membrane electrode assembly is obtained. When the cell voltage is examined, the result shown in Table 2 is obtained.

[Example 12]
An ion exchange membrane comprising a repeating unit based on tetrafluoroethylene and a polymer having a repeating unit based on CF ₂ ═CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₃ H is formed, and the ion exchange capacity and softening temperature When measured, the results shown in Table 1 are obtained. When a membrane electrode assembly was obtained in the same manner as in Example 1 and the cell voltage was examined, the results shown in Table 2 were obtained.

The electrolyte membrane of the present invention has a high softening temperature and extremely excellent durability against hydrogen peroxide or peroxide radicals generated by power generation of a fuel cell. Therefore, the polymer electrolyte fuel cell including the membrane electrode assembly having the electrolyte membrane of the present invention has long-term durability in both high-humidity low-humidity power generation and high-humidity power generation.

Claims (14)

Softening temperature is an ion exchange membrane made of a fluoropolymer having and sulfonic acid groups at 90 ° C. or higher, at least one member selected from the group consisting of cerium atoms and manganese atoms include as an ion,
An electrolyte membrane for a polymer electrolyte fuel cell comprising cerium ions in an amount of 0.3 to 20 mol% of —SO ₃ ^— groups contained in the ion exchange membrane. It consists of an ion exchange membrane consisting of a fluorine-containing polymer having a softening temperature of 90 ° C. or higher and having a sulfonic acid group, and contains one or more selected from the group consisting of cerium atoms and manganese atoms as ions,
Manganese ions are contained in the ion exchange membrane -SO ₃ ⁻ An electrolyte membrane for a polymer electrolyte fuel cell, comprising 0.5 to 30 mol% of the group. The fluoropolymer having sulfonic acid groups is a polymer electrolyte according to claim 1 or a perfluorocarbon polymer having sulfonic acid groups (which may contain ether bond oxygen atom.) Fuel cell electrolyte membrane. The perfluorocarbon polymer having a sulfonic acid group is based on a repeating unit based on tetrafluoroethylene and CF ₂ = CF (CF ₂ ) _a SO ₃ H (wherein, a is an integer of 0 to 6). The electrolyte membrane for a polymer electrolyte fuel cell according to claim 3 , which is a copolymer containing a repeating unit. The perfluorocarbon polymer having a sulfonic acid group is based on a repeating unit based on tetrafluoroethylene and CF ₂ = CFO (CF ₂ ) _b SO ₃ H (wherein b is an integer of 1 to 6). The electrolyte membrane for a polymer electrolyte fuel cell according to claim 3 , which is a copolymer containing a repeating unit. The perfluorocarbon polymer having a sulfonic acid group includes a repeating unit based on tetrafluoroethylene and CF ₂ = CFCF ₂ O (CF ₂ ) _c SO ₃ H (wherein c is an integer of 1 to 6). The electrolyte membrane for a polymer electrolyte fuel cell according to claim 3 , which is a copolymer containing a repeating unit based on. The perfluorocarbon polymer having a sulfonic acid group includes a repeating unit based on tetrafluoroethylene and a monomer represented by the formula (1) (wherein R ^{1 to} R ³ each independently contain an etheric oxygen atom. R ⁴ is a perfluoroalkyl group having 1 to 6 carbon atoms or a fluorine atom, and R ⁴ is a perfluoroalkylene group having 1 to 6 carbon atoms which may contain an etheric oxygen atom. solid polymer electrolyte membrane according to claim 3 which is a copolymer comprising and.

The monomer represented by formula (1) are solid polymer electrolyte membrane according to claim 7 of the formula (2).

The perfluorocarbon polymer having a sulfonic acid group includes a repeating unit based on tetrafluoroethylene, CF ₂ ═CF (OCF ₂ CFX) _d O (CF ₂ ) _e SO ₃ H (wherein d is 0 or 1, X is a fluorine atom or a trifluoromethyl group, and e is an integer of 1 to 5.), a monomer represented by formula (3) and a monomer represented by formula (4) (provided that , R ⁵ may contain an etheric oxygen atom, a C 1-5 perfluoroalkyl group or fluorine atom, and R ⁶ and R ⁷ are each independently a C 1-5 perfluoroalkyl group or fluorine. is an atom, or, ^{R 6} and ^{R 7} jointly form a perfluoroalkylene group having 3 to 5 carbon atoms ^.R 8 ^{to R 11} Pafuruoroa of 1 to 5 carbon atoms are each independently A kill group or a fluorine atom, or two repeats based on at least one selected from the group consisting of forming a perfluoroalkylene group having 3 to 5 carbon atoms.) Jointly of R ⁸ to R ¹¹ solid polymer electrolyte membrane according to claim 3 which is a copolymer containing a unit.

The solid polymer type according to claim 9 , wherein at least one selected from the group consisting of the monomer represented by the formula (3) and the monomer represented by the formula (4) is represented by the formula (5). Fuel cell electrolyte membrane.

A process for producing an electrolyte membrane according to any one of claims 1 to 10, the dispersion of the fluoropolymer having sulfonic acid groups, cerium following compounds soluble in the dispersion and manganese after mixing one or more selected from the group consisting of compounds obtained liquid was cast film using a method for producing a polymer electrolyte fuel cell electrolyte membrane, characterized in that to produce the electrolyte membrane .
(Cerium compound)
Cerium carbonate (Ce ₂ (CO ₃ ) ₃ · 8H ₂ O), cerium acetate (Ce (CH ₃ COO) ₃ · H ₂ O), cerium chloride (CeCl ₃ · 6H ₂ O), cerium nitrate (Ce (NO ₃₎ ) ₃ · _6H 2 O), cerium sulfate _{(Ce 2 (SO 4) 3} · 8H 2 O), cerium sulfate _{(Ce (SO 4) 2 ·} 4H 2 O), diammonium cerium nitrate (Ce _{(NH 4) 2} (NO ₃ ) ₆ ), tetraammonium cerium sulfate (Ce (NH ₄ ) ₄ (SO ₄ ) ₄ ) · 4H ₂ O), and cerium acetylacetonate (Ce (CH ₃ COCHCOCH ₃ ) ₃ · 3H ₂ O).
(Manganese compounds)
Manganese carbonate, manganese acetate (Mn (CH ₃ COO) ₂ .4H ₂ O), manganese chloride (MnCl ₂ .4H ₂ O), manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O), manganese sulfate (MnSO ₄ · _5H 2 O), manganese acetate _{(Mn (CH 3 COO) 3} · 2H 2 O), and manganese acetylacetonate _{(Mn (CH 3 COCHCOCH 3)} 2). The soluble cerium compound and one or more selected from the group consisting of manganese compounds, method for producing a polymer electrolyte fuel cell electrolyte membrane according to claim 11 which is a carbonate of cerium or manganese carbonate. A membrane electrode assembly for a polymer electrolyte fuel cell, comprising: an anode and a cathode having a catalyst layer containing a catalyst; and an electrolyte membrane disposed between the anode and the cathode, wherein the electrolyte membrane is claimed. A membrane electrode assembly for a polymer electrolyte fuel cell, comprising the electrolyte membrane according to any one of 1 to 10 . 14. A method for operating a polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 13 , wherein hydrogen gas is supplied to the anode side, oxygen or air is supplied to the cathode side, and power is generated at 90 ° C. or higher. A method for operating a polymer electrolyte fuel cell.