JP2010257771A - High-durability electrolyte film, electrode, and polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-durability electrolyte film that achieves improvement of hydrogen peroxide resistance, and restraint of performance degradation caused by decrease of impurity ion with Fenton activity as well as elution of precious metal elements and that sustains these effects for a long period of time; and to provide an electrode and a polymer electrolyte fuel cell. <P>SOLUTION: The high-durability electrolyte film includes a solid polymer electrolyte membrane and heteropolyacid salt dispersed in the solid polymer electrolyte membrane, wherein the heteropolyacid salt is one or more selected from pyridinium salt, imidazolium salt, phosphonium salt, guanidinium salt, 1,10 phenanthroline salt, nucleic acid base salt, and pyrazolone compound salt. The electrode includes such heteropolyacid salt, and the polymer electrolyte fuel cell uses such a high-durability electrolyte film or such an electrode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a highly durable electrolyte membrane, an electrode, and a solid polymer fuel cell. More specifically, the present invention relates to a solid polymer fuel cell suitable as an in-vehicle power source, a stationary small power generator, a cogeneration system, The present invention relates to a highly durable electrolyte membrane and an electrode used therefor.

  A solid polymer fuel cell has a membrane electrode assembly (MEA) in which electrodes are bonded to both surfaces of a solid polymer electrolyte membrane as a basic unit. In the polymer electrolyte fuel cell, the electrode generally has a two-layer structure of a diffusion layer and a catalyst layer. The diffusion layer is for supplying reaction gas and electrons to the catalyst layer, and carbon paper, carbon cloth, or the like is used. The catalyst layer is a part that becomes a reaction field for electrode reaction, and generally comprises a composite of carbon carrying an electrode catalyst such as platinum and a solid polymer electrolyte.

The electrolyte membrane or the catalyst layer electrolyte that constitutes such an MEA includes a perfluorinated electrolyte excellent in oxidation resistance (an electrolyte that does not contain a C—H bond in the polymer chain. For example, Nafion (registered trademark, DuPont). ), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), etc.) are generally used.
In addition, perfluorinated electrolytes are excellent in oxidation resistance but are generally very expensive. Therefore, in order to reduce the cost of the solid polymer fuel cell, a hydrocarbon electrolyte (an electrolyte that includes a C—H bond and does not include a C—F bond in a polymer chain) or a partial fluorine electrolyte The use of (electrolytes containing both C—H bonds and C—F bonds in the polymer chain) has also been studied.

  However, in order to put the polymer electrolyte fuel cell into practical use as a vehicle-mounted power source, there remain problems to be solved. For example, the electrolyte membrane constituting the MEA is unstable with respect to hydrogen peroxide generated as a by-product in the catalyst layer or a radical that is a decomposition product thereof, and it is necessary to improve durability. When the electrolyte in the catalyst layer or the electrolyte membrane is a perfluorinated electrolyte, the deterioration in durability is relatively small. On the other hand, in the case of a hydrocarbon-based electrolyte, the stability against hydrogen peroxide and radicals is remarkably inferior to that of a perfluorinated electrolyte, so that it is difficult to stably operate the fuel cell for a long period of time.

  Further, the noble metal element such as Pt used as a catalyst for the air electrode of the fuel cell is eluted from the catalyst layer during the operation of the fuel cell and is deposited inside the membrane or re-precipitated in the catalyst layer. It is known that the catalyst particles in the layer grow. The elution and grain growth of the noble metal element causes a decrease in battery performance. In addition, it is known that some precious metal ions exhibit Fenton activity, and such elution of precious metal ions degrades the electrolyte, and the degradation products poison the electrodes, thereby improving battery performance. It is said to decrease.

In order to solve this problem, various proposals have heretofore been made.
For example, in Patent Document 1, an oxide catalyst such as manganese dioxide, a macrocyclic metal complex catalyst such as iron phthalocyanine, or a transition metal alloy catalyst such as Cu—Ni alloy particles is provided on a hydrocarbon-based solid polymer electrolyte membrane. An added solid polymer electrolyte membrane is disclosed.
This document describes that when an oxide catalyst or the like is added to a hydrocarbon electrolyte, hydrogen peroxide is decomposed into water by a disproportionation reaction, and deterioration of the electrolyte due to hydrogen peroxide can be suppressed.

Patent Document 2 discloses a proton conductive polymer membrane in which a part of protons of a sulfonic acid group of a sulfonated polyphenylene sulfide membrane is substituted with a polyvalent metal such as Mg, Ca, Al, or La.
This document describes that when a part of protons of a sulfonic acid group is replaced with a certain polyvalent metal, resistance to peroxide radicals (oxidation resistance) is improved.

Further, Patent Document 3 does not aim at suppressing electrolyte degradation caused by radicals or suppressing elution of noble metal elements, but a part of a heteropolyacid having a molecular weight of 800 to 10,000 made of noble metal and / or transition metal. A solid heteropolyacid fuel cell catalyst that is a salt is disclosed.
In this document, all platinum in polyacids is present on the surface of the polyacid cluster and all platinum becomes active. Therefore, even though the platinum content in these polyacids is very small, it has high activity. The points to show are described.

Further, Patent Document 4 discloses a solid high membrane in which an ion exchange membrane having a sulfonic acid group is immersed in an aqueous cerium nitrate solution to partially exchange sulfonic acid groups with cerium ions, and then this membrane is immersed in an aqueous phosphoric acid solution. A method for producing an electrolyte membrane for a molecular fuel cell is disclosed.
In this document, it is possible to deposit cerium phosphate in the film by such a method, and by depositing a hardly soluble cerium compound in the film, The point that oxide radical tolerance improves is described.

  Further, although Patent Document 5 does not have any purpose for suppressing electrolyte deterioration due to radicals or suppressing elution of noble metal elements, a methanol fuel electrode for a direct type methanol fuel cell made of heteropolyacid-Pt-C. A material is disclosed.

Patent Document 6 discloses an electrode catalyst layer for a polymer electrolyte fuel cell containing a platinum scavenger such as 2,2-bipyridine.
This document describes that when a platinum scavenger is added to the catalyst layer, elution of platinum ions from the electrode catalyst layer is prevented, and a decrease in catalyst activity is suppressed.

JP 2000-106203 A JP 2004-018573 A International Publication WO 04/045009 JP 2008-98179 A JP 2002-134122 A JP 2006-147345 A

When a certain macrocyclic metal complex or transition metal oxide is added to the perfluorinated electrolyte, or a part of protons of the perfluorinated electrolyte is replaced with a certain metal ion, hydrogen peroxide and Resistance to radicals can be improved. However, there are many cases where sufficient corrosion resistance cannot be obtained even if these techniques are directly applied to hydrocarbon-based electrolytes.
This is because hydrocarbon electrolytes have an unstable basic skeleton compared to perfluorinated electrolytes, so additives that have the ability to decompose hydrogen peroxide decompose not only hydrogen peroxide but also the hydrocarbon skeleton. it is conceivable that.

  Furthermore, many of the conventionally known compounds and ions having hydrogen peroxide resistance are readily soluble in water. For this reason, they may be taken out of the system due to long-term use, and good durability may not be maintained. On the other hand, if the amount of compound or ion added is excessive in order to maintain durability, the performance of the fuel cell may be degraded. In particular, in the case of a hydrocarbon-based electrolyte, when a large amount of a compound or ion is introduced, rigidity, which is a general drawback of hydrocarbon-based electrolytes, is further increased. As a result, the mechanical strength and flexibility are greatly reduced, and cross leaks (perforations and cracks) may occur in the initial operation of the fuel cell.

Conventionally, the Fenton test is generally used for the hydrogen peroxide resistance test of polymer electrolytes. The Fenton test (Fe ²⁺ ion-added hydrogen peroxide solution immersion test) is a method for examining the degree of deterioration under high humidity conditions (saturated humidity).
On the other hand, during fuel cell operation, the MEA is often not in a sufficiently wet state but in a dry state, and the Fenton test alone is insufficient to evaluate the durability of the polymer electrolyte. Therefore, recently, a so-called dry Fenton test in which high-temperature hydrogen peroxide vapor is applied to a device under test in a low humidity (dry environment) is being adopted as an accelerated test that can simulate the deterioration of MEA. However, when the electrolyte membrane treated by the durability improving method described above is evaluated by the dry Fenton test, there are some that show completely different results from the Fenton test.

It is also known that transition metal ions (particularly Fe ions (Fe ²⁺ / Fe ³⁺ )) are present in an electrolyte exceeding a certain threshold value, thereby degrading the hydrogen peroxide resistance of the electrolyte. In addition, although not known so far, there is an interaction between impurities having Fenton activity and various additives and added ions having hydrogen peroxide resistance, and transition metal ions (especially Fe ions). ) Exceeds a certain threshold value, the effects of various additives and added ions may be lost, or the hydrogen peroxide resistance may be worsened.
In addition, the method of adding a nitrogen-containing organic compound such as 2,2-bipyridine in order to suppress the elution of platinum is insufficient in stability of 2,2-bipyridine to hydrogen peroxide and is water-soluble. For this reason, it is difficult to suppress the elution of platinum over a long period of time.

  Furthermore, in order to improve resistance to hydrogen peroxide, reduce impurity ions having Fenton activity, and suppress performance degradation caused by elution of noble metal elements, it has been necessary to take separate measures in the past. There has never been an example in which a method for solving the problem simultaneously has been proposed.

The problem to be solved by the present invention is a highly durable electrolyte membrane capable of simultaneously solving the improvement of hydrogen peroxide resistance, the reduction of impurity ions having Fenton activity, and the suppression of the performance degradation due to the elution of noble metal elements An electrode and a polymer electrolyte fuel cell are provided.
Another problem to be solved by the present invention is to provide a highly durable electrolyte membrane, an electrode, and a solid polymer fuel cell capable of sustaining these effects over a long period of time. is there.

In order to solve the above problems, a highly durable electrolyte membrane according to the present invention is:
A solid polymer electrolyte membrane;
A heteropolyacid salt dispersed in the solid polymer electrolyte membrane,
The gist of the heteropolyacid salt is at least one selected from pyridinium salts, imidazolium salts, phosphonium salts, guanidinium salts, 1,10 phenanthroline salts, nucleobase salts, and pyrazolone compound salts.

The electrode according to the present invention is
An electrocatalyst;
A solid polymer electrolyte covering the electrode catalyst;
A heteropolyacid salt dispersed in the solid polymer electrolyte,
The gist of the heteropolyacid salt is at least one selected from pyridinium salts, imidazolium salts, phosphonium salts, guanidinium salts, 1,10 phenanthroline salts, nucleobase salts, and pyrazolone compound salts.

  Furthermore, the polymer electrolyte fuel cell according to the present invention is summarized in that the highly durable electrolyte membrane according to the present invention or the electrode according to the present invention is used.

When any one or more selected from pyridinium salt, imidazolium salt, phosphonium salt, guanidinium salt, 1,10 phenanthroline salt, nucleobase salt and pyrazolone compound salt of heteropolyacid is added to the electrolyte membrane or electrode, hydrogen peroxide It is possible to simultaneously improve resistance, reduce impurity ions having Fenton activity, and suppress performance degradation due to elution of noble metal elements.
this is,
(1) Since the heteropolyacid salt itself becomes an ion decomposition catalyst for hydrogen peroxide and detoxifies hydrogen peroxide,
(2) The heteropolyacid salt traps impurity transition metal ions (particularly soluble iron ions) having Fenton activity and deactivates Fenton activity; and
(3) To capture and chelate the precious metal ions eluted by the heteropoly acid salt and prevent the precious metal ions from eluting and diffusing off the electrode,
it is conceivable that.
Furthermore, since the salt of a predetermined cation and heteropolyacid is hardly soluble and can remain in an electrolyte membrane or an electrode for a long period of time, these effects can be sustained for a long period of time.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. High durability electrolyte membrane]
A highly durable electrolyte membrane according to the present invention includes a solid polymer electrolyte membrane and a heteropolyacid salt dispersed in the solid polymer electrolyte membrane.

[1.1. Solid polymer electrolyte membrane]
In the present invention, the material of the solid polymer electrolyte membrane is not particularly limited, and various materials can be used.
That is, the material of the solid polymer electrolyte membrane is a hydrocarbon-based electrolyte containing a C—H bond in the polymer chain and not containing a C—F bond, and a fluorine-based material containing a C—F bond in the polymer chain. Any of electrolytes may be used. Further, the fluorine-based electrolyte may be a partial fluorine-based electrolyte containing both C—H bonds and C—F bonds in the polymer chain, or contains C—F bonds in the polymer chain, and A perfluorinated electrolyte containing no C—H bond may be used.
In addition to the fluorocarbon structure (—CF ₂ —, —CFCl—), the fluorine-based electrolyte includes a chlorocarbon structure (—CCl ₂ —) and other structures (eg, —O—, —S—, —C ( ═O) —, —N (R) —, etc. provided that “R” may be an alkyl group). The molecular structure of the polymer constituting the solid polymer electrolyte membrane is not particularly limited, and may be either linear or branched, or may have a cyclic structure.

  Also, the type of acid group provided in the solid polymer electrolyte is not particularly limited. Examples of the acid group include a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, and a sulfonimide group. Only one of these acid groups may be contained in the solid polymer electrolyte, or two or more of them may be contained. Furthermore, these acid groups may be directly bonded to the linear solid polymer compound, or may be bonded to either the main chain or the side chain of the branched solid polymer compound.

Specifically, as the hydrocarbon electrolyte,
(1) Polyamide, polyacetal, polyethylene, polypropylene, acrylic resin, polyester, polysulfone, polyether, etc. in which an acid group such as a sulfonic acid group is introduced into any of the polymer chains, and derivatives thereof (aliphatic hydrocarbons) System electrolyte),
(2) Polystyrene having an acid group such as a sulfonic acid group introduced into any of the polymer chains, polyamide having an aromatic ring, polyamideimide, polyimide, polyester, polysulfone, polyetherimide, polyethersulfone, polycarbonate, and the like, and These derivatives (partial aromatic hydrocarbon electrolytes),
(3) Polyetheretherketone, polyetherketone, polysulfone, polyethersulfone, polyimide, polyetherimide, polyphenylene, polyphenylene ether, polycarbonate, in which an acid group such as a sulfonic acid group is introduced into any of the polymer chains, Polyamide, polyamideimide, polyester, polyphenylene sulfide, etc., and derivatives thereof (fully aromatic hydrocarbon electrolytes),
and so on.

Further, as the partial fluorine-based electrolyte, specifically, polystyrene-graft-ethylenetetrafluoroethylene copolymer, polystyrene-graft-polytetra, in which an acid group such as a sulfonic acid group is introduced into any of the polymer chains. There are fluoroethylene and the like and derivatives thereof.
Further, as the perfluorinated electrolyte, specifically, Nafion (registered trademark) manufactured by DuPont, Aciplex (registered trademark) manufactured by Asahi Kasei Co., Ltd., Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., etc. There are derivatives.

  Further, in the present invention, the solid polymer electrolyte membrane may be composed of only a solid polymer electrolyte, or a composite including a reinforcing material composed of a porous material, a long fiber material, a short fiber material, or the like. There may be.

  In general, fluorine-based electrolytes, particularly all-fluorine-based electrolytes have excellent oxidation resistance because they have a C—F bond in the polymer chain, but when the present invention is applied to fluorine-based electrolytes, Furthermore, the oxidation resistance is improved. In addition, hydrocarbon electrolytes have lower oxidation resistance than fluorine electrolytes. Therefore, when the present invention is applied to a hydrocarbon-based electrolyte, a solid polymer fuel cell that exhibits high oxidation resistance even in the operating environment of the fuel cell (particularly in a dry environment) and is low in cost can be obtained. .

[1.2. Heteropolyacid salt]
“Heteropolyacid salt” refers to a compound in which all or part of the protons contained in the heteropolyacid are replaced with cations.
In the present invention, the heteropolyacid salt particularly means any one or more selected from pyridinium salts, imidazolium salts, phosphonium salts, guanidinium salts, 1,10 phenanthroline salts, nucleobase salts, and pyrazolo compound salts. All of these heteropolyacid salts have the effect of improving the durability of MEA. Further, among these heteropolyacid salts, those having poor solubility in water can remain in the electrolyte membrane for a long period of time.

As will be described later, the heteropolyacid salt is obtained by adding a solution containing a heteropolyacid to a solution containing a cation such as pyridinium ion and reacting them.
Any one of these heteropolyacid salts may be contained in the electrolyte membrane, or two or more thereof may be contained. The heteropolyacid salt may be a complex salt in which two or more kinds of cations and one heteropolyacid anion are bonded, or may be a mixture in which a plurality of heteropolyacid salts bonded to a single cation are mixed.

[1.2.1. Heteropoly acid]
The heteropolyacid is a combination of an oxyacid anion having Mo, W, V as the central element M and an oxyacid anion having P, Si, Ge, Ti, Zr, Sn, Ce, Th, etc. as the central element X. Multi-element polyanion is a generic term for polyoxometalates. These generally generally hydrate a large amount of water, and the molecular weight of the polyanion may be 800 or more.

For example, in a heteropolyacid ion in which 40 oxygen atoms are bonded, when X is a central element and M is an atom constituting a polyacid, M = Mo, X = P ⁵⁺ , As ⁵⁺ , Si ⁴⁺ , Ge ⁴⁺ , Ti ⁴⁺ , Zr ⁴⁺ and Sn ⁴⁺ take [X ^{n +} M ₁₂ O ₄₀ ] ^{−10 + n} as the anion structure.
In X = Ce ⁴⁺ , Th ⁴⁺ and Sn ⁴⁺ , [X ^{n +} M ₁₂ O ₄₀ ] ^{-12 + n} is taken as the anion structure.
X: M = 1: 11, and X = P ⁵⁺ , As ⁵⁺ , Fe ³⁺ , Ce ⁴⁺ takes [X ^{n +} M ₁₁ O ₃₉ ] ^{-12 + n} as the anion structure.
X: M = 1: 10, and X = P ⁵⁺ , As ⁵⁺ , Pt ⁴⁺ takes [X ^{n +} M ₁₀ O _x ] ^{−2x + 60 + n} as the anion structure.
X: M = 1: 9, and X = Mn ⁴⁺ , Co ⁴⁺ , and Ni ⁴⁺ take [X ^{n +} M ₉ O ₃₂ ] ^{−10 + n} as the anion structure.
X: M = 2: 18, and X = P ⁵⁺ and As ⁵⁺ take [X ₂ ^{n +} M ₁₈ O ₅₆ ] ^{-16 + 2n} as the anion structure.
X: M = 2: 17, and X = P ⁵⁺ and As ^{5+ take} [X ₂ ^{n +} M ₁₇ O _x ] ^{−2x + 10 + 2n} as the anion structure.
X: M = 2: 12, and in X = Co ³⁺ , Al ³⁺ , Cr ³⁺ , Fe ³⁺ , Rh ³⁺ , [X ₂ ^{n +} M ₁₂ O ₄₂ ] ^{-12 + 2n} is used as the anion structure. take.
X: M = 1: 6, and X = Ni ²⁺ , Co ²⁺ , Mn ²⁺ , Cu ²⁺ , Se ⁴⁺ , P ³⁺ , As ³⁺ , P ⁵⁺ , [X ^{n +} M ₆ O _x ] ^{-2x + 36 + n} .

Among these, when X: M = 1: 12, a thermally stable so-called Keggin structure ([X ^{n +} M ₁₂ O ₄₀ ] ^{−8 + n} ) is representative. For example, when excluding hydration water, H ₄ SiW ₁₂ O ₄₀ (silicotungstic acid), H ₃ PW ₁₂ O ₄₀ (phosphotungstic acid), H ₄ SiMo ₁₂ O ₄₀ (silicomolybdic acid), H ₃ PMo ₁₂ O ₄₀ (phosphomolybdic acid) may be mentioned.
In addition, composite heteropolyacids (for example, H ₃ PMo _12-x V _x O ₄₀ , H ₃ PW _12-x V _x O _40, etc.) in which some of these W and Mo are substituted with V are also known. .
Furthermore, these acids are known to form a salt by substituting a part of proton, tungsten or molybdenum with a monovalent cation, a divalent cation or a transition metal cation.
Heteropolyanions based on sandwich structure ions such as the Dawson structure ([X ₂ M ₁₂ O ₆₂ ] ⁿ⁻ ), which is a polyanion different from the Keggin structure, and the isopolyanion Mo ₇ O ₂₄ ⁶⁻ of the Anderson structure Co (III) Mo ₆ O ₂₄ H ₆ ³⁻ , Ni (II) Mo ₆ O ₂₄ H ₆ ^{4− and the} like are also known as heteropolyanions containing a relatively stable transition metal element.

The ions located in the central portion of the heteropolyacid structure, which are substituted with protons, are in a different state from the free ions and are coordinated and stabilized.
For example, a porphyrin compound is an organic compound having a structure similar to a heteropolyacid composed of 40 oxygen atoms and having a metal ion coordinated to an N atom from four directions. Porphyrin compounds are easily decomposed by cleavage of the porphyrin ring by the attack of hydrogen peroxide.
On the other hand, it is known that heteropolyacid salts are much more stable and can be used repeatedly for organic synthesis catalysts using hydrogen peroxide. Among them, when a proton is substituted with a specific ion, the solubility becomes small, and it becomes hardly soluble even under strong acidity at a low pH. For example, phosphomolybdic acid includes cesium ions, quaternary alkyl ammonium ions, phosphonium ions, platinum ions, and the like.

[1.2.2. Pyridinium salt]
The “pyridinium salt” refers to a compound in which all or part of the protons of the heteropolyacid are substituted with pyridinium ions.
Specific examples of compounds that form pyridinium ions include pyridine, dipyridine, terpyridine, and salts thereof.

[1.2.3. Imidazolium salt]
The “imidazolium salt” refers to a compound in which all or part of the protons of the heteropolyacid are replaced with imidazolium ions.
Specific examples of the compound that forms an imidazolium ion include imidazole, 1-methylimidazole, 1,3-dimethylimidazole, and salts thereof.

[1.2.4. Phosphonium salt]
“Phosphonium salt” refers to a compound in which all or part of protons of a heteropolyacid are substituted with phosphonium ions.
“Phosphonium ion” refers to a monovalent cation in which four alkyl groups are bonded around a P atom.
A compound that forms a phosphonium ion (phosphonium compound) is a compound [P (R ₁ ) (R ₂ ) (R ₃ ) (R ₄ )] ⁺ in which a phosphonium ion and an anion B paired therewith are ionically bonded. B ^- refers to. R _{1 to} R ₄ represent an alkyl group.

  Specific examples of the cation part of the phosphonium compound include tetraethylphosphonium, triethylbenzylphosphonium, tetrabutylphosphonium, tetraoctylphosphonium, trimethyldecylphosphonium, trimethyldodecylphosphonium, trimethylhexadecylphosphonium, trimethyloctadecylphosphonium, tributylmethylphosphonium, tributyl Dodecylphosphonium, tributyloctadecylphosphonium, trioctylethylphosphonium, tributylhexadecylphosphonium, methyltriphenylphosphonium, ethyltriphenylphosphonium, diphenyldioctylphosphonium, triphenyloctadecylphosphonium, tetraphenylphosphonium, tributylallylphosphonium, tetra Scan (hydroxymethyl), and the like phosphonium.

  Specific examples of the phosphonium compound include tetraethylphosphonium hydroxide, tetra-n-butylphosphonium hydroxide, ethyltriphenylphosphonium acetate, tetrabutylphosphonium acetate, tetrakis (hydroxymethyl) phosphonium sulfate, tetrabutylphosphonium nitrate, Bis (2,4,4-trimethylpentyl) phosphinic acid trihexyl (tetradecyl) phosphonium, tetrabutylphosphonium methanesulfonate, triisobutylmethylphosphonium tosylate, tetrabutylphosphonium tosylate, tetrabutylphosphonium tetraphenylborate, tetraphenylphosphonium Tetraphenylborate, tri-tert-butylphosphonium tetraphenylborate, di-tert-butylmethylphos Nium tetraphenylborate, trihexyl (tetradecyl) phosphonium bis [oxalato (2-)] borate, tetraphenylphosphonium tetra-P-tolylborate, benzylphenylphosphonium tetraphenylborate, P-tolyltriphenylphosphonium tetra-P-tolylborate, Examples include triethylmethylphosphonium dibutyl phosphate, ethyltriphenylphosphonium phosphate, tributylmethylphosphonium dibutyl phosphate, tetrabutylphosphonium benzotriazolate, trihexyl (tetradecyl) phosphonium decanoate, tributylmethylphosphonium methyl carbonate, and the like.

[1.2.5. Guanidium salt]
“Guanidinium salt” refers to a guanidinium ion in which all or part of the protons of the heteropolyacid are substituted.
Specific examples of compounds that form guanidinium ions include aminoguanidine, guanylurea, biguanide, guanidine, guanidine carbonate, guanidine borate, phosphoric acid / monoguanidine, phosphoric acid / diguanidine, guanylurea phosphate, sulfuric acid. Examples include guanidine, guanidine sulfamate, and 1,3 diphenylguanidine.

[1.2.6. 1,10 phenanthroline salt]
The “1,10 phenanthroline salt” refers to a compound in which all or part of the protons of the heteropolyacid are replaced with 1,10 phenanthroline ions.

[1.2.7. Nucleobase salt]
“Nucleobase salt” means a nucleobase ion in which all or part of the protons of the heteropolyacid are replaced.
Specifically, as a nucleobase,
(A) pyrimidine bases such as cytosine, 5-methylcytosine, 5-hydroxylmethylcytosine, thymine, uracil,
(B) Purine derivatives such as purine, adenine, guanine, hypoxanthine, xanthine, theophylline, theobromine, caffeine, isoguanine, uric acid,
and so on.

[1.2.8. Pyrazolone compound salt]
The “pyrazolone compound salt” refers to a compound in which all or part of the protons of the heteropolyacid are replaced with ions of the pyrazolone compound.
Specific examples of the compound that generates a pyrazolone ion include aminopyrine, antipyrine, 3methyl-1-phenyl-5-pyrazolone, and 1 phenyl-3-carboxy-5- which are known to react with silicomolybdic acid. Examples include pyrazolone and 1- (4-tolyl) -3-methyl-5-pyrazolone.

[1.3. Slightly soluble]
In order to retain the heteropolyacid salt in the electrolyte membrane or electrode and maintain the effect for a long period of time, the heteropolyacid salt is preferably insoluble.
Here, “slightly soluble” means that 5 mL of a solution in which a heteropolyacid is dissolved at a concentration of 10 g / L and 1 mL of a solution having a cation concentration of 4 × 10 ⁻³ N are mixed and left at room temperature for 1 day. This means that a precipitate is formed. Since the pH inside the electrolyte is known to be strong acidity of about 0 to 1, the heteropolyacid salt does not completely dissolve at around 80 ° C. (fuel cell operating temperature) under strong acidity, that is, insoluble. Is ideal. However, even if it is not completely insoluble, if it is a heteropoly acid salt that forms a precipitate under predetermined conditions, the durability of MEA can be sufficiently improved without impairing the cell performance even under the operation of the fuel cell. .
Among the above-mentioned heteropolyacid salts, those having particularly high solubility include, for example, tributylmethylphosphonium phosphotungstate, phosphotungstic acid 1,3-diphenyl group whose counter cation is phosphonium ion or guanidinium ion. Anidium salt.

[1.4. Content of heteropolyacid salt]
The optimum content of the heteropolyacid salt is selected according to the purpose. In general, when the content of the heteropolyacid is small, the hydrogen peroxide decomposition activity is lowered and the durability improving effect is reduced. In order to obtain practically sufficient durability, the content of the heteropolyacid salt is preferably 0.05% by weight or more based on the weight of the solid polymer electrolyte membrane.
On the other hand, when the content of the heteropolyacid salt becomes excessive, electrode poisoning due to partially dissolved heteropolyacid ions increases, and the battery performance decreases. In addition, the electrolyte membrane is easily embrittled and the mechanical properties are greatly reduced. Therefore, the content of the heteropolyacid salt is preferably 5% by weight or less based on the weight of the solid polymer electrolyte membrane.

[1.5. Halogen ion content]
Halogen ions (particularly chloride ions) promote electrode poisoning and elution of catalytic metals, and cause battery performance to deteriorate. Therefore, the smaller the halogen ion content in the film, the better. In order to suppress a decrease in battery performance, the halogen ion content is preferably 10 ppm or less per electrolyte weight. This also applies to the electrodes described later.

[2. electrode]
The electrode according to the present invention includes an electrode catalyst, a solid polymer electrolyte covering the electrode catalyst, and a heteropolyacid salt dispersed in the solid polymer electrolyte.

[2.1. Electrode catalyst]
In general, an optimum electrode catalyst is used depending on the purpose of use of MEA, use conditions, and the like. In the case of a polymer electrolyte fuel cell, the electrode catalyst includes platinum, palladium, ruthenium, rhodium, iridium, or an alloy thereof, or an alloy of a noble metal such as Pt and a transition metal element such as cobalt, iron, or nickel. Used. As the amount of the electrode catalyst contained in the electrode, an optimal amount is selected according to the use of MEA, use conditions, and the like.

  The electrode catalyst may be used as it is, or may be used while being supported on the surface of the catalyst carrier. The catalyst carrier is for carrying electrons at the electrodes at the same time as supporting a fine electrode catalyst. Generally, carbon, activated carbon, fullerene, carbon nanophone, carbon nanotube or the like is used as the catalyst carrier. As the amount of the electrode catalyst supported on the surface of the catalyst carrier, an optimum amount is selected according to the materials of the electrode catalyst and the catalyst carrier, the use of the MEA, use conditions, and the like.

[2.2. Electrolyte in catalyst layer]
The solid polymer electrolyte (electrolyte in the catalyst layer) that coats the electrode catalyst is for transferring protons between the solid polymer electrolyte membrane and the electrode. For the electrolyte in the catalyst layer, the same material as that constituting the solid polymer electrolyte membrane is usually used, but a different material may be used. As the amount of the electrolyte in the catalyst layer, an optimal amount is selected according to the use of MEA, use conditions, and the like.
The electrolyte in the catalyst layer may be a fluorine-based electrolyte or a hydrocarbon-based electrolyte. In particular, when the present invention is applied to an electrode whose catalyst layer electrolyte is a hydrocarbon electrolyte, a high effect can be obtained. Since the other points regarding the electrolyte in the catalyst layer are the same as those of the solid polymer electrolyte membrane, description thereof is omitted.

[2.3. Heteropolyacid salt]
The electrode according to the present invention includes a heteropolyacid salt dispersed in the electrolyte in the catalyst layer in addition to the electrode catalyst and the electrolyte in the catalyst layer. This is different from conventional electrodes.
Since the details of the heteropolyacid salt are as described above, the description thereof is omitted.

The optimum content of the heteropolyacid salt is selected according to the purpose. In general, when the content of the heteropolyacid is small, the hydrogen peroxide decomposition activity is lowered and the durability improving effect is reduced. In order to obtain practically sufficient durability, the content of the heteropolyacid salt is preferably 0.05% by weight or more with respect to the weight of the electrode.
On the other hand, when the content of the heteropolyacid salt becomes excessive, electrode poisoning due to partially dissolved heteropolyacid ions increases, and the battery performance decreases. Accordingly, the content of the heteropolyacid salt is preferably 5% by weight or less with respect to the weight of the electrode.
The “electrode weight” means the weight of the electrode catalyst, the solid polymer electrolyte covering the electrode catalyst, and the layer (catalyst layer) containing the heteropolyacid salt dispersed in the solid polymer electrolyte.

[2.4. Diffusion layer]
The electrode constituting the MEA usually has a two-layer structure of a catalyst layer and a diffusion layer, but may be constituted only by the catalyst layer. When the electrode has a two-layer structure of a catalyst layer and a diffusion layer, the electrode is joined to the electrolyte membrane via the catalyst layer.

A catalyst layer is a part used as the reaction field of an electrode reaction. The diffusion layer is for supplying and receiving a reaction gas to the catalyst layer at the same time as transferring electrons to and from the catalyst layer.
Generally, carbon paper, carbon cloth, or the like is used for the diffusion layer. In order to increase water repellency, a surface of carbon paper or the like coated with a mixture of water repellent polymer powder such as polytetrafluoroethylene and carbon powder (water repellent layer) is used as a diffusion layer. Also good.

[3. Solid polymer fuel cell]
A polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) in which electrodes are bonded to both surfaces of a solid polymer electrolyte membrane (electrolyte membrane). In addition, the polymer electrolyte fuel cell is usually formed by sandwiching both sides of such an MEA with a separator having a gas flow path and laminating a plurality of them.
The polymer electrolyte fuel cell according to the present invention uses a highly durable electrolyte membrane containing the above-described heteropoly acid salt as an electrolyte membrane and / or uses an electrode containing the above-mentioned heteropoly acid salt as an electrode. And

  The heteropolyacid salt may be added to either the electrolyte in the catalyst layer or the electrolyte membrane, but since hydrogen peroxide is generated at the electrode, it is added to the electrolyte in the catalyst layer or at the membrane / catalyst layer interface. It is preferable to concentrate and exist in the catalyst layer or electrolyte membrane to prevent hydrogen peroxide from diffusing into the membrane. That is, these compounds are preferably concentrated and added to the membrane surface or the deepest portion of the catalyst layer (junction with the membrane). However, caution is required because excessive concentration reduces the membrane / catalyst layer bondability.

[4. Method for producing heteropolyacid salt]
Next, a method for producing a heteropolyacid salt will be described. Heteropolyacids are very soluble in polar solvents such as water and THF. Its solubility is generally 10 g / L or more at room temperature. In the reagent, SiO ₂ and WO ₃ may be decomposed and mixed as insoluble impurity components. Accordingly, it is preferable to use the solution after filtration or decantation after dissolving the heteropolyacid.

  In the case of using water as a solvent, the heteropolyacid is added to water at a concentration of 1 to 10 g / L and sufficiently stirred, and the impurity components are removed by filtration. A solution in which phosphonium ions, imidazolium ions, pyridinium ions and the like are dissolved at a concentration of 0.01 to 0.1 mol / L is added to the filtrate to form a precipitate. When the precipitated solid is heat-aged, filtered, washed with water and dried, a heteropolyacid salt is obtained.

The amount ratio between the heteropolyacid and these ions may be added close to the stoichiometric ratio. Alternatively, it may be precipitated in the form of a so-called partial acid salt in which the heteropolyacid is excessive. The partial acid salt has a large ability to precipitate impurity ions entering from the outside and deactivate the Fenton activity. For example, an acid salt formed by 1 mol of phosphonium ion (Pho ⁺ ) and 1 mol of phosphotungstic acid can inactivate 1 mol of Fe ²⁺ ions as shown in the formulas (1) and (2).
Pho ⁺ + H ₃ PW ₁₂ O ₄₀ → Pho H ₂ PW ₁₂ O ₄₀ + H ⁺ (1)
PhoH ₂ PW ₁₂ O ₄₀ + Fe ²⁺ → PhoFePW ₁₂ O ₄₀ + 2H ⁺ (2)

  The anion paired with the cation of the reagent used to produce the heteropolyacid salt is preferably a non-halogen ion. In particular, chloride, bromide and iodide are not recommended. When these halogen ions are adsorbed and remain on the heteropolyacid salt, electrode poisoning and elution of the catalyst metal are promoted, resulting in a significant decrease in battery performance.

For example, specific examples of the counter ion of a preferred compound include hydroxide ion, carbonate ion, hydrogen carbonate ion, formate ion, acetate ion, propionate ion, oxalate ion, maleate ion, adipate ion, and salicylate ion. , Tartrate ion, citrate ion, metasulfonate ion, sulfamate ion, tosylate ion, tetraphenylborate ion, borate ion, sulfate ion, hydrogen sulfate ion, nitrate ion, perchlorate ion, phosphate ion, phosphorus Preference is given to oxyhydrogen ions, dibutyl phosphate ions, benzotriazolate ions, decanoic acid ions, methyl carbonate ions and the like.
In particular, formate, carbonate and bicarbonate are suitable as raw materials for producing heteropolyacid salts because the pH is extremely alkaline and does not precipitate coexisting ions and has a low poisoning effect on the catalyst. is there. The hydroxide can be used without any problem because it does not extremely increase the pH if the concentration is low.
For example, in the case of Cs ⁺ , cesium perchlorate, cesium nitrate, cesium sulfate, cesium formate, cesium acetate, cesium oxalate, cesium citrate, cesium hydroxide, cesium carbonate and the like are preferable.

When forming a heteropolyacid salt in which two or more cations are substituted, first, a solution containing a cation that forms a heteropolyacid salt having a relatively high solubility is added to the heteropolyacid solution. Then, it is preferable to add to this heteropolyacid solution a solution containing a cation that forms a heteropolyacid salt having a relatively low solubility. This method has the advantage that the heteropolyacid salt previously precipitated does not interfere with the formation of the multi-component heteropolyacid salt.
Alternatively, a solution in which a cation that forms a heteropoly acid salt having a relatively high solubility and a cation that forms a heteropoly acid salt having a relatively low solubility may be mixed with a solution in which a heteropoly acid is dissolved, and reacted. .

Examples of cations that produce heteropolyacid salts with relatively high solubility include:
(1) Alkali ions such as Li ⁺ , Na ⁺ , K ⁺ ,
(2) transition metal ions such as Ni ⁺ and Ag ⁺ ,
(3) There are rare earth metal ions such as Ce ³⁺ and Ce ⁴⁺ .
Examples of the cation that forms a heteropolyacid salt having a relatively low solubility include cesium ion, quaternary alkyl ammonium ion, pyridinium ion, imidazolium ion, phosphonium ion, guanidinium ion, 1,10 phenanthroline, nucleobase, There are platinum ions, pyrazolone ions, and the like.
It is preferable to use a cation counteranion used for precipitation of these heteropolyacid salts, such as a hydroxide ion or carbonate ion, which has a small poisoning action even if it remains.

For example, when H ₄ SiMo ₁₂ O ₄₀ is used, a solution containing phosphonium ions (Pho ⁺ ) and Ce ³⁺ ions and a solution containing H ₄ SiMo ₁₂ O ₄₀ are mixed and reacted. According to the formula (3), Ce ³⁺ ions and Pho ⁺ ions can be fixed as hardly soluble complex salts.
Ce ³⁺ + Pho ⁺ + H ₄ SiMo ₁₂ O ₄₀ → CePhoSiMo ₁₂ O ₄₀ ↓ + 4H ⁺ (3)

[5. Manufacturing method of highly durable electrolyte membrane and electrode]
The highly durable electrolyte membrane according to the present invention is
(1) A casting method in which a heteropolyacid salt and a solid polymer electrolyte are dispersed or dissolved in a solvent such as alcohol, the solution is cast on a metal container, glass container, PTFE film, PET film, etc., and the solvent is removed by heating. ,
(2) A melt extrusion method in which a heteropoly acid salt and a solid polymer electrolyte are heated and melted and mixed, and a film is formed by an extruder.
Etc. can be manufactured.

The electrode according to the present invention is
(1) A catalyst paste is prepared by mixing an electrolyte in a catalyst layer dissolved in a solvent, a heteropoly acid salt, and an electrode catalyst or an electrode catalyst supported on a conductive carrier, and the catalyst paste is sprayed on the electrolyte membrane (or diffusion layer). Spray method to apply,
(2) A transfer sheet method in which the catalyst paste is applied onto a PTFE film or PET film by a doctor blade method or the like to form a transfer sheet, and the film and the transfer sheet are joined by hot pressing,
Etc. can be manufactured.

In general, if the polymerization catalyst remaining in the polymer electrolyte and its decomposition product, transition metal element and impurity Fe ions are not sufficiently removed from the electrolyte, resistance to hydrogen peroxide and .OH radicals may be insufficient. Are known. For example, as a polymerization catalyst for hydrocarbon-based polymer electrolytes, inorganic salts (such as chlorides) of Ru, Pd, Cu, and Ni and organic complexes thereof are used. , Transition metal elements such as Ni may be contained as impurities in concentrations exceeding 100 ppm. All of these metal ions have Fenton activity, and when these ions are present in the electrolyte (especially hydrocarbon-based electrolyte) at a concentration equal to or higher than a threshold value (both tens of ppm), the electrolyte is in a dry state. Greatly reduces the radical resistance at.
In the present invention, since the heteropolyacid capable of capturing the transition metal ions having the fenton activity is added to the film or the electrode, the fenton activity is deactivated and the radical resistance of the electrolyte can be increased. However, in order to further improve the durability, it is preferable to remove the impurity transition metal ions from the electrolyte as much as possible by subjecting the electrolyte to acid washing or reduction treatment and acid washing before the addition of the heteropolyacid salt.

[6. Operation of high durability polymer electrolyte membrane, electrode and polymer electrolyte fuel cell]
In order to improve the durability of MEA, various compounds and ions are introduced into a membrane or an electrode. However, these conventional additives of this type often require a relatively large amount of addition in order to obtain practically sufficient resistance. Addition of a large amount of this type of additive causes a decrease in the mechanical strength and flexibility of the membrane, or a decrease in the proton conductivity of the electrolyte contained in the membrane or electrode.
Furthermore, when certain additives are added to the hydrocarbon electrolyte, the durability may be reduced. On the other hand, examples of the additive for improving the radical resistance of the hydrocarbon electrolyte include an alkali metal compound capable of non-radical decomposition of hydrogen peroxide and a quaternary ammonium compound which includes hydrogen peroxide and stabilizes it. However, many alkali metal compounds are easily soluble in water, and they are taken out of the MEA system for a long period of use and cannot maintain good durability. Moreover, many quaternary alkyl ammonium compounds are unstable to hydrogen peroxide and radicals at high temperatures, and the durability improvement effect is not sufficient.

In addition, when compounds or ions are added to improve durability, there is an interaction between these additives and impurities having Fenton activity. That is, if transition metal ions (especially iron ions (Fe ²⁺ / Fe ³⁺ )) exist in the electrolyte above a certain threshold, the effect of the additive is lost or conversely the hydrogen peroxide resistance deteriorates. There is a case to let you.

  Furthermore, noble metal elements such as Pt, Pd, Ru, and Ag used as a catalyst for the air electrode of the fuel cell elute from the catalyst layer during operation and precipitate inside the membrane or reprecipitate in the catalyst layer. It is known that catalyst particles grow and battery performance is reduced. In addition, it is said that the Pt—Ru alloy used as a fuel electrode catalyst also deteriorates in battery performance due to elution or grain growth of Pt and Ru. It is known that the deterioration of the noble metal elements of these electrodes is promoted by fluctuations in the operating potential. Furthermore, it is known that some noble metal ions exhibit Fenton activity. Such elution of noble metal ions degrades the electrolyte, and the degradation products poison the electrodes, resulting in a decrease in battery performance. It is said that.

  However, in order to improve the resistance to hydrogen peroxide, reduce the impurity ions having Fenton activity, and suppress the performance degradation caused by the elution of noble metal elements, it is necessary to take separate measures in the past. There has never been an example in which a method for solving the problem simultaneously has been proposed.

On the other hand, when one or more selected from pyridinium salts, imidazolium salts, phosphonium salts, guanidinium salts, 1,10 phenanthroline salts, nucleobase salts, and pyrazolone compound salts of heteropolyacids are added to the electrolyte membrane or electrode. In addition, it is possible to simultaneously improve resistance to hydrogen peroxide, reduce impurity ions having Fenton activity, and suppress performance degradation caused by elution of noble metal elements.
this is,
(1) Since the heteropolyacid salt itself becomes an ion decomposition catalyst for hydrogen peroxide and detoxifies hydrogen peroxide,
(2) The heteropolyacid salt traps impurity transition metal ions (particularly soluble iron ions) having Fenton activity and deactivates Fenton activity; and
(3) To capture and chelate the precious metal ions eluted by the heteropoly acid salt and prevent the precious metal ions from eluting and diffusing off the electrode,
it is conceivable that.
Furthermore, since the salt of a predetermined cation and heteropolyacid is hardly soluble and can remain in an electrolyte membrane or an electrode for a long period of time, these effects can be sustained for a long period of time.

(Examples 1-6, Comparative Examples 1-6)
[1. Test method]
5 mL of a solution in which each heteropolyacid was dissolved at a concentration of 10 g / L and 1 mL of a solution having a concentration of each cation of 4 × 10 ⁻³ N were mixed in a glass container. This was left to stand at room temperature for 1 day, and the presence or absence of precipitation was observed (Examples 1 to 6). The pH of the solution was strong acidity of 1-2.
For comparison, the presence or absence of precipitation was observed in the same manner as in Examples 1 to 6 except that cerium ions (III and IV) were used as cations (Comparative Examples 1 to 6).

[2. result]
Table 1 shows the results. In Table 1, “◎” indicates that a precipitate was immediately formed, “◯” indicates that a precipitate was formed after several hours, and “×” indicates that no precipitate was generated. "-" Represents not implemented.
Either cation caused precipitation with at least one heteropolyacid. On the other hand, no precipitation occurred with cerium ions.

(Example 7, Comparative Examples 7 to 10)
[1. Preparation of sample]
A polymer dispersion solution of perfluorosulfonic acid (water-alcohol mixed solution having a solid content of 22 wt%) was placed in a glass petri dish, and the solvent was removed at 40 ° C. Thereafter, vacuum drying at 80 ° C. × 2 hr was further performed. The membrane was peeled from the petri dish, and one casted fluorine-based electrolyte membrane having a thickness of about 50 μm and a size of 30 mm × 30 mm was prepared (Comparative Example 7).

  In the same manner as in Example 1, precipitation reaction between tributylmethylphosphonium (TBMP) ions and phosphotungstate ions was performed. The precipitate was filtered from this solution, washed with water, and vacuum-dried at 80 ° C. for 2 hours to obtain a sparingly soluble heteropolyacid salt of TBMP ions and phosphotungstate ions. A hardly soluble heteropolyacid salt was added to the same polymer dispersion solution as in Comparative Example 7 so that the solid content concentration was 0.5 wt%. The solution was mixed with an ultrasonic homogenizer and cast to obtain a film of the same size (Example 7).

For comparison,
(1) Commercially available perfluorosulfonic acid polymer membrane (Comparative Example 8),
(2) a cast film (Comparative Example 9) to which 0.5 wt% of cesium phosphotungstic acid salt precipitated from a cesium nitrate solution and a phosphotungstic acid solution, and
(3) A membrane in which 1% of acid groups are ion-exchanged with Cs ⁺ ions using a cesium nitrate solution (Comparative Example 10),
Prepared.

[2. Test method]
These samples were subjected to a hydrogen peroxide vapor exposure test (dry Fenton test) under the conditions of 120 ° C. × 5 hr.
First, the membrane before the test was vacuum dried at 80 ° C. for 2 hours to obtain the membrane weight W ₁ .
Next, 1 wt% aqueous hydrogen peroxide was added dropwise to a PTFE evaporator heated to 120 ° C. at a rate of 0.12 mL / min to vaporize the entire amount. This was diluted by adding 0.3 L / min of N ₂ . Under this condition, the relative humidity at 120 ° C. was calculated to be about 31%. The test membrane was fixed in a PTFE net and placed in a PTFE inner cylinder heated to 120 ° C.
After the exposure test, a vacuum drying process at 80 ° C. × 2 hr was performed to determine the film weight W ₂ . Further, a weight change ΔW (= (W ₁ −W ₂ ) / W ₁ × 100) was calculated from the film weights W ₁ and W ₂ .

The hydrogen peroxide vapor that passed through the sample was recovered by bubbling into 100 mL of ultrapure water in a PE container (cooled around the ice). Its recovery was detected in the water F ^- amount was measured by ion-selective electrode made Orion Corporation, a unit time from the test membrane area and test time, per unit area F ^- elimination rate FRR (μg / cm ² / hr )
The conductivity of the recovered water (about 130 mL) was measured with a simple conductivity meter (manufactured by Horiba, Ltd .; Twin cond B-173). Further, the pH of the recovered water was examined with a pH meter (manufactured by Horiba, Ltd .; F-7, corrected with buffer solution pH 4.0 and pH 2.0).

[3. result]
Table 2 shows the results. Example 7 is a cast film (Comparative Example 7) to which the conductivity of the recovered water is not added, a commercially available perfluorosulfonic acid polymer film (Comparative Example 8), or a cast film to which a Cs heteropolyacid salt is added (Comparative Example). 9) It was smaller than the membrane obtained by introducing cesium ions into a commercially available perfluorosulfonic acid polymer membrane (Comparative Example 10), and the degree of membrane deterioration (discharge of ionic components) was small. Moreover, in Example 7, pH was higher than Comparative Examples 7-10, F discharge rate (FRR) was also small, and the production | generation of hydrofluoric acid was suppressed.

(Examples 8 to 12, Comparative Example 11)
[1. Preparation of sample]
The phosphotungstic acid tributylmethylphosphonium salt produced by the method of Example 1 is equivalent to 0.01 to 20 wt% of the 60 wt% Pt / C catalyst in the amount of electrode, 2.0 g of distilled water, 2.5 g of ethanol, propylene 1.0 g of glycol and 0.9 g of 22 wt% Nafion (registered trademark) solution (manufactured by DuPont) were added in this order. This solution was dispersed with an ultrasonic homogenizer to prepare a catalyst ink. This was coated on a polytetrafluoroethylene sheet and dried to obtain a cathode transfer electrode. The amount of Pt used was fixed in the range of 0.5 to 0.6 mg / cm ² .
As the anode, 30 wt% Pt / C was used, and an electrode obtained by the same production method as described above was used without using the heteropolyacid salt. The amount of Pt used was 0.2 mg / cm ² .
These electrodes were cut into 36 mm squares and thermocompression-bonded (120 ° C., 50 kgf / cm ² (4.9 MPa)) to a perfluoro-based electrolyte membrane NRE212CS (manufactured by DuPont) to prepare an MEA.

[2. Test method]
The durability test was performed under the following conditions.
Anode gas: H ₂ (100 ml / min)
Cathode gas: Air (100 ml / min)
Cell temperature: 80 ° C
Humidifier temperature: 60 ° C (both anode and cathode)
Test time: A cycle test with an open circuit of 1 minute and 0.1 A / cm ² of 1 minute was performed for 150 hours. A voltage value at 0.8 A / cm ² was measured before and after the durability test, and the rate of decrease was calculated.

[3. result]
Table 3 shows the initial voltage and the voltage drop rate after the durability test. In Example 12, the durability test was not performed because the initial voltage was significantly reduced.
From Table 3,
(1) When no phosphotungstate is added (Comparative Example 11), the initial voltage is high, but the voltage drop rate is large.
(2) When phosphotungstate is added, the voltage drop rate decreases as the amount added increases.
(3) When the amount of phosphotungstate added becomes excessive, the initial voltage decreases.
(4) In order to achieve both a high initial voltage and a low voltage drop rate, the amount of phosphotungstate added is preferably 0.05 to 5 wt% with respect to the electrode weight.
I understand that.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

The highly durable electrolyte membrane and electrode according to the present invention are various types such as a polymer electrolyte fuel cell, a water electrolysis device, a hydrohalic acid electrolysis device, a salt electrolysis device, an oxygen and / or hydrogen concentrator, a humidity sensor, and a gas sensor. It can be used for electrolyte membranes and electrodes used in electrochemical devices.
Moreover, the polymer electrolyte fuel cell according to the present invention can be applied to an in-vehicle power source, a stationary small power generator, a cogeneration system, and the like.

Claims (9)

A solid polymer electrolyte membrane;
A heteropolyacid salt dispersed in the solid polymer electrolyte membrane,
The high-durability electrolyte membrane, wherein the heteropolyacid salt is at least one selected from pyridinium salt, imidazolium salt, phosphonium salt, guanidinium salt, 1,10 phenanthroline salt, nucleobase salt, and pyrazolone compound salt.   The highly durable electrolyte membrane according to claim 1, wherein the heteropolyacid salt is hardly soluble.   The highly durable electrolyte membrane according to claim 1 or 2, wherein a content of the heteropolyacid salt is 0.05 to 5 wt% with respect to a weight of the solid polymer electrolyte membrane.   The highly durable electrolyte membrane according to any one of claims 1 to 3, wherein a halogen ion content is 10 ppm or less per weight of the solid polymer electrolyte membrane. An electrocatalyst;
A solid polymer electrolyte covering the electrode catalyst;
A heteropolyacid salt dispersed in the solid polymer electrolyte,
The electrode, wherein the heteropolyacid salt is one or more selected from pyridinium salts, imidazolium salts, phosphonium salts, guanidinium salts, 1,10 phenanthroline salts, nucleobase salts, and pyrazolone compound salts.   The electrode according to claim 5, wherein the heteropolyacid salt is hardly soluble.   The electrode according to claim 5 or 6, wherein the content of the heteropolyacid salt is 0.05 to 5% by weight with respect to the weight of the electrode.   A polymer electrolyte fuel cell using the highly durable electrolyte membrane according to any one of claims 1 to 4.   A polymer electrolyte fuel cell using the electrode according to claim 5.