JP5447791B2 - Method for producing polymer electrolyte fuel cell - Google Patents

Description

  The present invention relates to a method for producing a polymer electrolyte fuel cell, and more particularly to a method for producing a polymer electrolyte fuel cell suitable as an in-vehicle power source, a stationary small generator, a cogeneration system, and the like.

  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, Patent Document 5 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 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. Particularly in the case of hydrocarbon electrolytes, when a large amount of a compound or ion is introduced, rigidity, which is a general drawback of hydrocarbon 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.
Furthermore, if the compound having hydrogen peroxide resistance is insolubilized in order to suppress the removal outside the system, uniform dispersion in the electrolyte becomes difficult.

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 solid polymer fuel 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 It is in providing the manufacturing method of a battery.
Another object of the present invention is to provide a method for producing a polymer electrolyte fuel cell capable of sustaining these effects over a long period of time.

In order to solve the above problems, a method for producing a polymer electrolyte fuel cell according to the present invention includes:
A cation contact step in which a cation that becomes a heteropolyacid salt by binding to a heteropolyacid ion is brought into contact with an electrolyte;
A heteropolyacid ion contact step for bringing the electrolyte into contact with the heteropolyacid ion,
The gist of the heteropolyacid salt is sparingly soluble.
The second method for producing a polymer electrolyte fuel cell according to the present invention is as follows.
A heteropolyacid ion contacting step of bringing the electrolyte into contact with the heteropolyacid ion ;
After the heteropolyacid ion contacting step, a cation which is a heteropolyacid salt by binding to pre-Symbol heteropoly acid ion, and a cation-contact step of contacting the electrolyte,
The main point is that

When a predetermined cation and an electrolyte are brought into contact, and then a heteropolyacid ion and the electrolyte are brought into contact, a heteropolyacid salt having a predetermined composition can be uniformly formed inside the electrolyte. Similarly, when a heteropolyacid ion is brought into contact with an electrolyte, and then a predetermined cation is brought into contact with an electrolyte, a heteropolyacid salt having a predetermined composition can be uniformly formed inside the electrolyte. When a heteropolyacid salt having a predetermined composition is dispersed inside the electrolyte, it is possible to simultaneously improve resistance to hydrogen peroxide, 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. 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. In the present invention, the polymer electrolyte fuel cell includes a heteropolyacid salt obtained by a method described later in the electrolyte contained in the MEA. This is different from conventional polymer electrolyte fuel cells.

[1.1. 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.

  Furthermore, in the present invention, the solid polymer electrolyte membrane constituting the MEA may be composed only of a solid polymer electrolyte, or a reinforcing material composed of a porous material, a long fiber material, a short fiber material, or the like. It may be a complex containing.

  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. Electrode]
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.

  The catalyst layer is a part serving as a reaction field for the electrode reaction, and includes an electrode catalyst or a carrier carrying the electrode catalyst, and an electrolyte in the catalyst layer covering the periphery thereof. 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 catalyst layer, an optimal amount is selected according to the use of MEA, use conditions, and the like.

  The catalyst carrier is for carrying a fine electrode catalyst and simultaneously transferring electrons in the catalyst layer. 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 material of the electrode catalyst and the catalyst carrier, the use of the MEA, the use conditions, and the like.

The electrolyte in the catalyst layer is for exchanging 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.

  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.

[1.3. 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, as described later,
(1) A method in which a cation and an electrolyte are contacted, and then a heteropolyacid ion and an electrolyte are contacted, or
(2) A method of bringing a heteropolyacid ion into contact with an electrolyte, and then bringing a cation into contact with an electrolyte,
Can be formed in the electrolyte.
Any one of these heteropolyacid salts may be contained in the electrolyte, 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.

[1.3.1. 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 present in these heteropolyacid structures are in a different state from 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 ion, quaternary alkyl ammonium ion, pyridinium ion, imidazolium ion, phosphonium ion, guanidinium ion, nucleobase, platinum ion, pyrazolone ion and the like. Therefore, it is considered that these poorly soluble heteropolyacid salts can exist stably inside the strongly acidic proton conductive polymer electrolyte.

[1.3.2. Cation]
Specific examples of cations that bind to heteropolyacid ions and compounds that can form such cations include the following.

[1.3.2.1. Alkali metal ion]
Examples of the alkali metal ions forming the heteropoly acid salt include lithium ions, sodium ions, potassium ions, and cesium ions. Among these, a cesium ion is suitable as a cation because it forms a hardly soluble salt with a heteropolyacid ion.
Since salts of lithium ions, sodium ions, and potassium ions have relatively high solubility, they are easily taken out of the system, and the durability improving action is smaller than that of cesium ions. Therefore, these ions are preferably co-precipitated with other ions that are likely to precipitate.

[1.3.2.2. Alkaline earth metal ions]
Examples of alkaline earth metal ions that form heteropolyacid salts include Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , and Ba ²⁺ .
Since all of these ions form a salt having a relatively high solubility, the durability improving action is smaller than when cesium ions are used. Therefore, these ions are preferably used together with other ions that are likely to precipitate.

[1.3.2.3. Quaternary ammonium ion]
The “quaternary ammonium ion” refers to an ion represented by ⁺ N (R ₁ ) (R ₂ ) (R ₃ ) (R ₄ ). R ₁ , R ₂ , R ₃ , and R ₄ each represent an alkyl group, H, or a halogen other than Cl and Br (for example, I and F).
The “quaternary ammonium salt” that forms a quaternary ammonium ion refers to a salt represented by ⁺ N (R ₁ ) (R ₂ ) (R ₃ ) (R ₄ ) Z ⁻ . Z ⁻ represents an anion.

Specific examples of the quaternary ammonium ion include NH ₄ ⁺ (ammonium ion), N (CH ₃ ) ₄ ⁺ (tetramethylammonium ion), N (C ₂ H ₅ ) ₄ ⁺ (tetraethylammonium ion), tetra Examples include propylammonium ion and tetrabutylammonium ion.
NH ₄ ⁺ tends to form a salt having a relatively high solubility with the heteropolyacid anion. Therefore, the quaternary ammonium ion is preferably an alkyl-substituted quaternary ammonium ion having a large molecular weight (quaternary alkyl ammonium ion). Quaternary alkyl ammonium ions have the advantage of easily forming salts with low solubility.

  Non-chloride and preferred quaternary ammonium salts include, for example, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetra-n-butylammonium hydroxide, benzyltrimethylammonium hydroxide, benzyltriethylammonium Hydroxide, hexadecyltrimethylammonium hydroxide, phenyltrimethylammonium hydroxide, tris (2-hydroxyethyl) methylammonium hydroxide, choline bitartrate, betaine anhydride, L-carnitine, methyltri-n-octylammonium hydrogensulfate, tetra Butyl ammonium hydrogen sulfate, tetrabutyl ammonium hydrogen sulfate, tetrabutyl ammonium phosphate, There is such as La -n- butyl ammonium salicylate.

[1.3.2.4. Pyridinium ion]
Specific examples of compounds that form pyridinium ions include pyridine, dipyridine, terpyridine, and salts thereof.

[1.3.2.5. Imidazolium ion]
Specific examples of the compound that forms an imidazolium ion include imidazole, 1-methylimidazole, 1,3-dimethylimidazole, and salts thereof.

[1.3.2.6. Nitrogen-containing heterocyclic compound ion]
Specific examples of compounds that form nitrogen-containing heterocyclic compound ions include 1,10 phenanthroline.

[1.3.2.7. Phosphonium ion]
“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.

[1.3.2.8. Guazinium ion]
Specific 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.

[1.3.2.9. Nucleobase]
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.

[1.3.2.10. Platinum ion]
The platinum ion may have any valence of Pt (II) or Pt (IV).
As the compound that forms platinum ions, it is preferable to use a salt of Pt (II) from the viewpoint of easily generating a Pt salt. Specifically, chlorides such as tetraammine dichloride platinum Pt (NH ₃ ) ₄ Cl ₂ , hexaammine dichloride platinum Pt (NH ₃ ) ₆ Cl ₂ can be used as the compound that forms platinum ions. However, these chlorides cause the remaining chloride ions to poison the electrode and promote the complex ionization of PtCl ₄ ²⁻ or PtCl ₆ ²⁻ , thereby causing deterioration in battery performance. Therefore, when these compounds are used as starting materials, they are ion-exchanged using the method described later and then subjected to dechloride ion treatment (washing with warm water and anion exchange resin) It is preferable to fix chloride ions as hardly soluble chlorides by washing with an aqueous solution containing cations (Ag ⁺ , Cs ⁺ , BiO ⁺ , YbO ⁺ ).

Preferable platinum compounds than chlorides are those in which Cl of dichloride is an anion other than Cl. For example, tetraammineplatinum phosphate aqueous solution, tetraammineplatinum bicarbonate, tetraammineplatinum hydroxide solution, tetraammineplatinum hydrate, tetraammineplatinum nitrate, diammineplatinum ammonia aqueous solution, hexaammineplatinum hydroxide Pt (NH ₃ ) ₆ (OH) ₄ , hexaammineplatinum nitrate Pt (NH ₃ ) ₆ (NO ₃ ) ₄ , hexaammineplatinum sulfate Pt (NH ₃ ) ₆ (SO ₄ ) ₂ and the like.
Even when these are used, if excess Pt ion ligands (ammonia, amine, nitrate ion, sulfate ion, etc.) remain, Pt elution is promoted. It is preferable.

[1.3.2.11. Pyrazolone ions]
Specific examples of compounds that generate pyrazolone ions include aminopyrine, antipyrine, and 3-methyl-1-phenyl-5-pyrazolone that are known to react with silicomolybdic acid.

[1.3.3. 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 cations that bind to the heteropolyacid ions mentioned above, in particular, cesium ions, quaternary alkyl ammonium ions, pyridinium ions, imidazolium ions, nitrogen-containing heterocyclic compound ions, phosphonium ions, guanidinium ions, nucleobases, platinum ions Any one or more selected from pyrazolone ions is preferred. All of these heteropolyacid salts have an effect of improving the durability of MEA, and many of them have high insolubility in water, so that they can remain in the electrolyte membrane for a long time.

[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 0.1% or more in terms of the amount of cation per acid group of the electrolyte. The content of the heteropolyacid salt is more preferably 0.5% or more in terms of the cation amount per acid group of the electrolyte.
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 20% or less in terms of the amount of cation per acid group of the electrolyte. The content of the heteropolyacid salt is more preferably 5% or less in terms of the amount of cation per acid group of the electrolyte.

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

[2. Method for producing polymer electrolyte fuel cell (1)]
The method for producing a polymer electrolyte fuel cell according to the first embodiment of the present invention includes a cation contact step and a heteropolyacid ion contact step.

[2.1. Cationic contact process]
The cation contact step is a step in which a cation that becomes a heteropolyacid salt by binding to a heteropolyacid ion is brought into contact with the electrolyte.

[2.1.1. Cation]
The cation is not particularly limited, and various cations described above can be used. The cation is particularly selected from cesium ion, quaternary alkyl ammonium ion, pyridinium ion, imidazolium ion, nitrogen-containing heterocyclic compound ion, phosphonium ion, guanidinium ion, nucleobase, platinum ion and pyrazolone ion. Any one or more of these is preferable.

When introducing the cation, it is preferable that the amount of halogen ions (particularly chloride ions) remaining in the electrolyte be 10 ppm or less per electrolyte weight. For that purpose, it is preferable to use a reagent whose counter anion is a non-halogen ion as a reagent used for cation introduction. In particular, chlorides, bromides and iodides are not recommended.
Specific examples of the counter ion for introducing a cation include a hydroxide ion, a carbonate ion, a formate ion, an acetate ion, a propionate ion, an oxalate ion, a maleate ion, an adipate ion, a 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, phosphate Hydrogen ion, dibutyl phosphate ion, benzotriazolate ion, decanoic acid ion, methyl carbonate ion and the like are preferable.
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.

  In particular, formate, carbonate, and hydrogen carbonate are suitable as a cation-introducing raw material because the pH is extremely alkalinized so that no mixed ions are precipitated and the poisoning action on the catalyst is small. In addition, if the hydroxide is also at a low concentration, the pH will not be increased extremely, so that it can be used without any problem.

[2.1.2. Contact with electrolyte]
“Contacting a cation with an electrolyte” includes MEA or a component of MEA (for example, an electrolyte membrane, a catalyst layer, a transfer catalyst sheet, a catalyst paste in which an electrolyte and a catalyst are dispersed in a solvent) and a cation. It means that the solution is brought into contact with each other to ion-exchange protons and cations of the acid group of the electrolyte.

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 interface of the membrane / catalyst layer. 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). In order to concentrate the heteropolyacid salt at the membrane surface or the deepest part of the catalyst layer, the treatment target is preferably an electrolyte membrane, a catalyst layer, or a transfer catalyst sheet.
However, caution is required because excessive concentration reduces the membrane / catalyst layer bondability.

The contact method is not particularly limited, and various methods such as spray coating and immersion can be used. For example, when immersing the electrolyte membrane, it is preferable to heat at 40 ° C. or higher and to stir the treatment solution. The time for ion exchange can be shortened by heating and stirring. After immersion, unnecessary ionic components are washed with water.
Moreover, once the electrolyte membrane is immersed and swollen in a nonaqueous solvent such as alcohol or a mixed solvent of water and these nonaqueous solvents and then ion exchanged in an aqueous solution, the ion exchange can be performed up to the inside of the electrolyte membrane. it can.

Any solvent may be used as long as it can dissolve a compound that forms a cation. Specifically, polar solvents such as water, ethanol and isopropanol are preferred as the solvent.
Some phosphonium compounds and compounds containing quaternary ammonium ions become insoluble in water as the molecular weight increases, and the solubility in alcohols and other organic solvents also decreases. Therefore, when ion-exchanging these compounds having a large molecular weight, it is preferable that these compounds are once dissolved in an organic solvent such as alcohol and then added to water. When MEA, a catalyst layer, or a membrane is immersed in such a solution, these ions can be easily introduced into the electrolyte.

  The concentration of the compound capable of forming a cation in the solution is preferably a dilute solution of 0.01 mM / L to 1 mM / L, and the compound corresponding to the amount to partially ion-exchange the acid group of the electrolyte can be dissolved. It ’s fine. When ion exchange is performed at a high concentration exceeding 1 mM / L, it is necessary to note that nearly 100% of protons are ion-exchanged and the proton conductivity of the electrolyte may be lost.

The pH of the solution is preferably 2 or more. In the ion exchange in an acidic solution having a pH of less than 2, the number of protons is so large that the acid body of the electrolyte becomes stable, making it difficult to introduce desired ions.
The time required for ion exchange is 8 hours or more in order to exchange nearly 100% of the acid groups of the electrolyte with these ions at room temperature. On the other hand, when heating at a temperature of 40 ° C. or higher, ion exchange proceeds in about 1 to 4 hours.

When a small amount of ions are ion-exchanged with the acid group of the electrolyte, the battery performance is not hindered because the counter anion contained in the treatment liquid is small. Therefore, no particular water washing is required.
On the other hand, when 1% or more of electrolyte protons are ion-exchanged, electrode poisoning due to counter anions cannot be ignored. In addition, the ionic conductivity of the condensed water increases, and the piping and the like may be corroded. When such high-concentration ion exchange is performed, it is preferable to remove excess anions by sufficiently washing with water (heating with water) after contact with the treatment liquid.

[2.1.3. Cation introduction amount]
If the amount of cation introduced is too small, the effect of improving durability is small. Therefore, the cation introduction amount is preferably 0.1% or more in terms of the acid group ratio of the electrolyte. More preferably, the cation introduction amount is 0.5% or more in terms of the acid group ratio of the electrolyte.
On the other hand, when the amount of cation introduced is excessive, the battery performance is significantly lowered. Therefore, the cation introduction amount is preferably 20% or less in terms of the acid group ratio of the electrolyte. More preferably, the cation introduction amount is 5% or less in terms of the acid group ratio of the electrolyte.
Here, “the amount of cation introduced is x% in terms of the acid group ratio of the electrolyte” means that cations are introduced at a ratio of x / n (n is the valence of the cation) with respect to the acid group 100. It means being. For example, divalent cations are introduced at the same acid group ratio with an introduction amount of ½ mole compared to monovalent cations.

In general, the ratio of acid groups in the electrolyte in the catalyst layer and the electrolyte membrane is about 1:20 to 1: 2, although it depends on the weight (film thickness) and ion exchange capacity per unit area, compared with the catalyst layer. The number of acid groups in the electrolyte membrane is large. Therefore, for example, when an MEA containing a heteropoly acid salt is produced by ion-exchange only one of the electrolyte in the catalyst layer or the electrolyte, ions of the compound added during operation diffuse inside the MEA, and the electrolyte membrane Or it may move to a catalyst layer and homogenize. Therefore, when added to only one of them, the cation may be added in excess of 20% in terms of the acid group ratio of the electrolyte.
The addition amount of the heteropoly acid may be 0.1 to 20% in terms of the cation amount per acid group of the entire electrolyte contained in the MEA. A more preferable addition ratio is 0.5 to 5% in terms of the cation amount per acid group of the entire electrolyte contained in the MEA.

[2.2. Heteropolyacid ion contact process]
The heteropolyacid ion contacting step is a step of bringing the electrolyte ion-exchanged with a cation into contact with the heteropolyacid ion.
“Contacting a heteropolyacid ion with an electrolyte” means MEA or MEA components (for example, an electrolyte membrane, a catalyst layer, a transfer catalyst sheet, a catalyst paste in which an electrolyte and a catalyst are dispersed in a solvent) and heteropoly Contacting a solution containing acid ions.
When an electrolyte ion-exchanged with a cation is brought into contact with a solution containing a heteropolyacid ion, a heteropolyacid salt is formed. When the heteropolyacid salt is hardly soluble, the heteropolyacid salt is precipitated and fixed. Since the acid group of the electrolyte becomes H form again by this treatment, proton conductivity is restored. If necessary, further washing with water is performed to remove unnecessary ion components.

  As the solution containing the heteropolyacid ion, a solution obtained by dissolving a heteropolyacid or a soluble salt thereof in water can be used. Examples of the heteropolyacid include silicotungstic acid, phosphotungstic acid, and phosphomolybdic acid. Soluble salts include these ammonium salts and Na salts.

The concentration of the heteropolyacid ion in the solution containing the heteropolyacid ion is not particularly limited, and an optimal concentration is selected according to the type of heteropolyacid ion and the treatment target so that the heteropolyacid ion can be easily introduced. It is preferable to do this.
The total amount of heteropolyacid ions in the solution is preferably an amount capable of fixing all cations as a heteropolyacid salt, but there may be some excess or deficiency.
The contact method is not particularly limited, and various methods such as spray coating and immersion can be used.

In addition, when adding the solution containing a cation to a catalyst paste, it is good also as a transfer electrode after cation introduction | transduction, or good also as a transfer electrode after heteropoly acid ion introduction | transduction.
Further, transition metal ions having a Fenton activity such as Fe existing in the electrolyte before cation introduction may be removed by performing a reduction treatment before acid cleaning or acid cleaning, or by performing acid cleaning in a reduced state. If the transition metal ions are removed in advance, the function of the heteropolyacid salt is ensured and the hydrogen peroxide resistance is strengthened.

[2.3. Concrete example]
The case where ion exchange is performed with Cs ^{+ and} H ₃ PW ₁₂ O ₄₀ is used as the heteropolyacid will be specifically described. In the case where the acid group of the electrolyte is a sulfonic acid group, this reaction is expressed by the following formulas (1) and (2), assuming that all protons of the heteropolyacid are substituted with Cs ⁺ . The formula (1) represents ion exchange between electrolyte protons and cations. Formula (2) represents H-body regeneration and heteropolyacid salt fixation.
R-SO ₃ H + Cs ⁺ → R-SO ₃ Cs + H ⁺ (1)
3R-SO ₃ Cs + H ₃ PW ₁₂ O ₄₀ → 3R-SO ₃ H + Cs ₃ PW ₁₂ O ₄₀ ↓ (2)

It is also possible to form heteropoly acid salts such as alkali ions such as Li ⁺ , Na ⁺ and K ⁺ , transition metal ions such as Ni ⁺ and Ag ⁺ , and rare earth metal ions such as Ce ³⁺ and Ce ^4+. Some have relatively high solubility (easily soluble ions). In that case, the counter anion of the cation used when introducing the cation part of the heteropoly acid into the electrolyte acid group is a cation counter anion having a small poisoning action even if it remains like a hydroxide ion or carbonate ion. After reacting with, avoid excessive washing.

In addition, when it is desired to fix the readily soluble ion as a hardly soluble salt, in addition to the above ions, cesium ions, quaternary alkyl ammonium ions, pyridinium ions, imidazolium ions, phosphonium ions, guanidinium ions that are easily precipitated. Substitution together with ions, nucleobases, platinum ions, pyrazolone ions, etc., may be carried out.
For example, in the case of using H ₄ SiMo ₁₂ O ₄₀ , phosphonium ions (Pho ⁺ ) and cerium ions are ion-exchanged in advance in the electrolyte and contacted with H ₄ SiMo ₁₂ O ₄₀ , so High cerium polyacid cerium salt can be fixed as a poorly soluble complex salt. Equation (3) shows the reaction formula.
Ce ³⁺ + Pho ⁺ + H ₄ SiMo ₁₂ O ₄₀ → CePhoSiMo ₁₂ O ₄₀ ↓ + 4H ⁺ (3)

[3. Method for producing polymer electrolyte fuel cell (2)]
The method for producing a polymer electrolyte fuel cell according to the second embodiment of the present invention includes a heteropoly acid ion contact step and a cation contact step.

[3.1. Heteropolyacid ion contact process]
The heteropolyacid ion contacting step is a step of bringing the electrolyte into contact with the heteropolyacid ion. That is, in this embodiment, heteropoly acid ions are introduced before the introduction of cations. This is different from the first embodiment.
“Contacting a heteropolyacid ion with an electrolyte” means MEA or MEA components (for example, an electrolyte membrane, a catalyst layer, a transfer catalyst sheet, a catalyst paste in which an electrolyte and a catalyst are dispersed in a solvent) and heteropoly Contacting a solution containing acid ions.
When the electrolyte membrane is brought into contact with a solution containing heteropolyacid ions, the heteropolyacid ions are adsorbed inside the electrolyte. Further, in order to concentrate the heteropolyacid salt on the membrane surface or the deepest part of the catalyst layer, the treatment target is preferably an electrolyte membrane, a catalyst layer, or a transfer catalyst sheet.

When the electrolyte is a cation exchange resin (anions such as sulfonic acid and carboxylic acid), the heteropolyacid ions are difficult to permeate into the electrolyte due to the repulsion of charges, and are easily concentrated on the surface. Therefore, it is possible to adsorb heteropoly acid ions and not immediately contact with a solution containing cations, but to rinse the surface once with pure water and react to prevent excessive surface concentration.
Since the other points regarding the heteropolyacid ion contact step are the same as the heteropolyacid ion contact step according to the first embodiment, the description thereof is omitted.

[3.2. Cationic contact process]
The cation contact step is a step of bringing a cation that becomes a heteropolyacid salt by binding with a heteropolyacid ion and an electrolyte into which the heteropolyacid ion is introduced.

When a heteropolyacid ion is introduced into the electrolyte and then brought into contact with a solution containing a predetermined cation C ⁺ , the proton H ⁺ and the cation C ^{+ of the} heteropolyacid ion undergo ion exchange, and the heteropolyacid containing the cation C ⁺ inside the electrolyte Salt is formed. In addition, when the type of cation C ⁺ is optimized, a poorly soluble heteropolyacid salt is generated inside the electrolyte.
Since the other points regarding the cation contact step are the same as those of the cation contact step of the first embodiment, description thereof is omitted.

[4. Operation of production method of 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 deteriorates the electrolyte, and the deterioration products poison the electrodes, and the battery performance is reduced. It is said to decline.

  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 a predetermined cation is brought into contact with the electrolyte, and then the heteropoly acid ion is brought into contact with the electrolyte, a heteropoly acid salt having a predetermined composition can be uniformly formed inside the electrolyte. Similarly, when a heteropolyacid ion is brought into contact with an electrolyte, and then a predetermined cation is brought into contact with an electrolyte, a heteropolyacid salt having a predetermined composition can be uniformly formed inside the electrolyte. When a heteropolyacid salt having a predetermined composition is dispersed inside the electrolyte, it is possible to simultaneously improve resistance to hydrogen peroxide, 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.

  Further, the method of introducing ions into the electrolyte and generating the heteropolyacid salt inside the electrolyte can achieve a high effect in a small amount as compared with the case where the solid heteropolyacid salt powder and the electrolyte are mechanically mixed. This is presumably because fine heteropolyacid salts are uniformly dispersed inside the electrolyte by using such a method.

(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.

[2. result]
Tables 1 and 2 show the results. In Tables 1 and 2, “◎” indicates that a precipitate was immediately generated, “◯” indicates that a precipitate was formed after several hours, and “×” indicates that no precipitate was generated. "-" Represents not implemented.
Among the cations, cesium ion, quaternary alkyl ammonium ion, pyridinium ion, imidazolium ion, nitrogen-containing heterocyclic compound ion, phosphonium ion, guanidinium ion, nucleobase, platinum ion, and pyrazolone ion are at least A precipitation with one heteropolyacid occurred.
On the other hand, precipitation did not occur in any of the rare earth / transition metal ions except alkali metal ions other than Cs, alkaline earth metal ions, and platinum ions. Therefore, it is preferable to use these ions in a state where they are co-precipitated with the former ions capable of being precipitated.

(Examples 7-9, Comparative Examples 1-5)
[1. Preparation of sample]
One fluorine-based electrolyte membrane having a size of 60 mm × 60 mm and a thickness of 50 μm was immersed in 120 mL of an aqueous solution of tributylmethylphosphonium (TBMP ⁺ ) carbonate in a PP container at 80 ° C. for 8 hours, and 1% of the membrane acid group was absorbed. Ion exchange was performed. Next, the membrane was immersed in 120 mL of ultrapure water placed in a PP container, and rinsing at 80 ° C. × 2 hr was repeated four times to remove excess ions.
Next, a solution in which H ₃ PW ₁₂ O ₄₀ was dissolved in 120 mL of ultrapure water at a concentration of 1 g / L was placed in a PP container, and the membrane was immersed in the solution to form a hardly soluble heteropolyacid salt on the membrane. . Thereafter, the membrane was immersed in 120 mL of ultrapure water placed in a PP container, and rinsing at 80 ° C. × 2 hr was repeated 4 times to remove excess ions (Example 7).

Separately, one membrane having the same size as above was treated with 120 mL of an aqueous solution of ammonium hydrogenphosphate platinum complex (Pt ²⁺ ) instead of tributylmethylphosphonium carbonate at 80 ° C. for 8 hours to obtain 1 of the membrane acid group. % ^Was ion exchanged with Pt ²⁺ . Next, the membrane was reacted with an aqueous H ₃ PW ₁₂ O ₄₀ solution to form a heteropolyacid platinum salt on the membrane. Furthermore, the membrane was immersed in 120 mL of ultrapure water placed in a PP container, and rinsed at 80 ° C. × 2 hr four times to remove excess ions (Example 8).

Further, 1% of membrane acid groups were ion-exchanged with Cs ⁺ ions in a cesium nitrate solution. Next, the film was reacted with an aqueous H ₃ PW ₁₂ O ₄₀ solution to form cesium heteropolyacid in the film. Furthermore, the membrane was immersed in 120 mL of ultrapure water placed in a PP container, and rinsed at 80 ° C. × 2 hr four times to remove excess ions (Example 9).

For comparison,
(1) As-received membrane (Comparative Example 1),
(2) Membranes subjected only to ion exchange with TBMP ⁺ , Cs ⁺ or Ce ³⁺ (Comparative Examples 2 to 4),
(3) After replacing 1% of membrane acid groups with Ce ³⁺ (using cerium nitrate Ce (NO ₃ ) ₃ .6H ₂ O), treated with 80 mL of 0.1M phosphoric acid in water at 80 ° C. for 8 hours, A film in which ceric phosphate was formed in the film and rinsed with ultrapure water (Comparative Example 5),
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 3 shows the results. In all of Examples 7 to 9, the conductivity of the recovered water was an untreated membrane (Comparative Example 1), a membrane in which only TBMP ⁺ ions were introduced (Comparative Example 2), and only Cs ⁺ and Ce ³⁺ were ion-exchanged. It was smaller than the film (Comparative Examples 3 and 4), and the degree of film deterioration (discharge of ion components) was small. Moreover, in Examples 7-9, pH was higher than Comparative Examples 1-4, F discharge rate (FRR) was also small, and the production | generation of hydrofluoric acid was suppressed.
The comparative example 5 which formed the 1st cerium phosphate in the film | membrane did not have the inhibitory effect like Examples 7-9.

(Example 10, Comparative Examples 6-7)
[1. Preparation of sample]
One hydrocarbon electrolyte membrane of size 60 mm x 60 mm and thickness 10 μm is immersed in 120 mL of cesium nitrate solution (Cs ⁺ concentration: 0.04 mmol / L) that can replace 1% of acid groups in a PP container. And treated at 80 ° C. for 8 hours. Then, after sufficiently washing with water, the membrane was immersed in 120 mL of a 10 g / L phosphotungstic acid aqueous solution in a PP container, treated at 80 ° C. for 8 hours, and the membrane was returned to H form. Next, the membrane was immersed in 120 mL of ultrapure water placed in a PP container and rinsed at 80 ° C. × 2 hr four times to remove excess ionic components (Example 10).

For comparison,
(1) Cs ₃ PW ₁₂ O ₄₀ precipitated in Example 9 was added to a solution obtained by dissolving a hydrocarbon-based electrolyte in a solvent, subjected to ultrasonic treatment and cast-molded (addition amount is 1 of the membrane acid group). % Equivalent to that exchanged with Cs ⁺ ions, Comparative Example 6),
(2) as-received membrane (Comparative Example 7),
Prepared.

[2. Test method]
The dry Fenton test was performed in the same manner as in Examples 7 to 9, and the weight change ΔW of the membrane, the conductivity of the recovered water, and the pH of the recovered water were measured. Further, the degree of coloration of the film was visually evaluated after the dry Fenton test.

[3. result]
Table 4 shows the results. In Example 10, the conductivity of the recovered water was smaller than the film (Comparative Example 6) or the untreated film (Comparative Example 7) in which the poorly soluble heteropolyacid cesium salt was mechanically mixed, and the degree of film deterioration was small. Moreover, in Example 10, pH was higher than the comparative examples 6 and 7, and the production | generation of the acid component was suppressed.
Furthermore, in Example 10, the degree of coloration of the film was smaller than in Comparative Examples 6 and 7. This shows that it is difficult to form adducts of carbonyl compounds and peroxides due to attacks on .OH and .OOH radicals.

(Examples 11 to 28, Comparative Examples 8 to 13)
[1. Preparation of sample]
One hydrocarbon electrolyte membrane of size 60mm x 60mm and thickness 10μm is put in a PP container and immersed in 120mL (cation concentration: 0.02mmol / L) of various ion solutions that can replace 1% of acid groups. And treated at 80 ° C. for 8 hours. Thereafter, rinsing with ultrapure water at 80 ° C. × 2 hr was repeated four times to remove excess ion components.
After thoroughly washing with water, the membrane is immersed in 120 mL of each 1 g / L heteropolyacid aqueous solution in a PP container, treated at 80 ° C. for 8 hours to fix the heteropolyacid salt in the membrane, and the membrane is in H form. Returned to. Furthermore, the membrane was immersed in 120 mL of ultrapure water placed in a PP container and rinsed at 80 ° C. × 2 hr four times to remove excess ionic components (Examples 11 to 24).

  Further, the above membrane was immersed in 120 mL of each heteropolyacid aqueous solution having a concentration of 1 g / L at 80 ° C. for 8 hours. Subsequently, it was immersed in 80 mL of an aqueous solution containing tributylmethylphosphonium ions corresponding to 1% of membrane acid groups at 80 ° C. for 8 hours. Furthermore, the ultrapure water rinse of 80 degreeC x 2 hr was repeated 4 times, and the excess ion component was removed (Examples 25-28).

As a comparison,
(1) Membranes (Comparative Examples 8 to 10) which were immersed in each aqueous heteropolyacid solution (concentration: 10 g / L) and rinsed with ultrapure water.
(2) A membrane (Comparative Example 11) in which only 1% of membrane acid groups are substituted with a tributylmethylphosphonium carbonate solution,
(3) A membrane in which 1% of membrane acid groups are replaced with Pt ²⁺ in a platinum hydrogen phosphate solution (Comparative Example 12),
(4) A film (Comparative Example 13) in which 1% of the film acid groups are replaced with Cu ²⁺ in a copper nitrate hydrogen solution.
Prepared.

[2. Test method]
The dry Fenton test was performed in the same manner as in Examples 7 to 9, and the weight change ΔW of the membrane, the conductivity of the recovered water, and the pH of the recovered water were measured. Further, the degree of coloration of the film was visually evaluated after the dry Fenton test.

[3. result]
Table 5 shows the results. In each of Examples 11 to 28, compared to Comparative Example 7 and Comparative Examples 8 to 13 in Table 4, since the amount of acidic components due to membrane decomposition is small, the conductivity of the waste water is greatly reduced, and the pH is lowered. Was also suppressed.
In Examples 11 to 28, the degree of coloration of the film was small, and the change in weight was small. This indicates that the formation of carbonyl compounds and hydrogen peroxide by attacking the film against .OH and .OOH radicals is greatly suppressed.

(Examples 29 to 33, Comparative Example 14)
[1. Preparation of sample]
0.5 g of 60 wt% Pt / C catalyst, 2.0 g of distilled water, 2.5 g of ethanol, 1.0 g of propylene 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 anode transfer electrode obtained by the same production method as described above was used. The amount of Pt used was 0.2 mg / cm ² .
These electrodes were cut into 36 mm squares.

The cathode transfer electrode was immersed in 120 mL of an aqueous solution to which 1,10 phenanthroline corresponding to 0.05 to 100% of the number of moles of acid groups of the electrolyte in the catalyst layer of the cathode electrode was added. Thereafter, rinsing was performed at 120 ° C. × 2 hours × 4 times with 120 mL of ultrapure water.
Next, the cathode transfer electrode was immersed in 120 mL of an aqueous phosphotungstic acid (H ₃ PW ₁₂ O ₄₀ ) solution having a concentration of 1 g / L at 80 ° C. for 8 hours. Thereafter, rinsing was performed at 120 ° C. × 2 hours × 4 times with 120 mL of ultrapure water. Further, vacuum drying at 80 ° C. × 2 hr was performed.

The treated cathode transfer electrode and anode transfer electrode were thermocompression-bonded (120 ° C., 50 kgf / cm ² (4.9 MPa)) on both sides of the electrolyte membrane NRE212CS (manufactured by DuPont) to produce an MEA (Examples 29 to 29). 33).
As a comparison, MEA (Comparative Example 14) using an untreated electrode was prepared.

[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 6 shows the initial voltage and the voltage drop rate after the durability test. In Example 33, since the initial voltage was remarkably lowered, the durability test was not performed.
From Table 6,
(1) In the case of MEA using untreated electrodes (Comparative Example 14), the initial voltage is high, but the voltage drop rate is large.
(2) When the salt of 1,10 phenanthroline and heteropolyacid is formed on the electrode, the voltage drop rate decreases as the 1,10 phenanthroline substitution amount increases.
(3) When the salt of 1,10 phenanthroline and heteropolyacid is formed on the electrode, if the 1,10 phenanthroline substitution amount becomes excessive, the initial voltage decreases.
(4) In order to achieve both a high initial voltage and a low voltage drop rate, the substitution amount of 1,10 phenanthroline is preferably 0.1 to 20% per acid group of the electrolyte, more preferably 0 per acid group of the electrolyte. .5-5%,
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 polymer electrolyte fuel cell obtained by the method 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.
The electrolyte obtained by the method according to the present invention includes various types of electrochemical 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 devices.

Claims (9)

A cation contact step in which a cation that becomes a heteropolyacid salt by binding to a heteropolyacid ion is brought into contact with an electrolyte;
E Bei and said electrolyte and said heteropoly acid ion contacting step of contacting a heteropoly acid ion,
The method for producing a polymer electrolyte fuel cell , wherein the heteropolyacid salt is hardly soluble .
However, “poorly 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. It means that a precipitate is formed. The cationic contacting step, the manufacturing method of the solid polymer electrolyte fuel cell according to Der Ru claim 1 which is contacted the with the cationic 0.1% to 20% per acid group of the electrolyte and the electrolyte. The cation is any one selected from a cesium ion, a quaternary alkylammonium ion, a pyridinium ion, an imidazolium ion, a nitrogen-containing heterocyclic compound ion, a phosphonium ion, a guanidinium ion, a nucleobase, a platinum ion, and a pyrazolone ion. polymer electrolyte fuel cell manufacturing method according to one or more der Ru claim 1 or 2 or. The cationic contacting step such that said amount of halogen ions contained in the electrolyte is less than 10ppm by weight of the electrolyte, any one of claims 1 to 3 in which contacting the said electrolyte cation A method for producing a polymer electrolyte fuel cell as described in 1). A heteropolyacid ion contacting step of bringing the electrolyte into contact with the heteropolyacid ion ;
After the heteropolyacid ion contacting step, a cation which is a heteropolyacid salt by binding to pre-Symbol heteropoly acid ion, and a cation-contact step of contacting the electrolyte,
A method for producing a polymer electrolyte fuel cell comprising: The method for producing a polymer electrolyte fuel cell according to claim 5 , wherein the heteropolyacid salt is hardly soluble. The method for producing a polymer electrolyte fuel cell according to claim 5 or 6, wherein the cation contacting step comprises contacting the electrolyte with 0.1 to 20% of the cation per acid group of the electrolyte. The cation is any one selected from a cesium ion, a quaternary alkylammonium ion, a pyridinium ion, an imidazolium ion, a nitrogen-containing heterocyclic compound ion, a phosphonium ion, a guanidinium ion, a nucleobase, a platinum ion, and a pyrazolone ion. The method for producing a polymer electrolyte fuel cell according to any one of claims 5 to 7, which is 1 or more. The cationic contacting step such that said amount of halogen ions contained in the electrolyte is less than 10ppm by weight of the electrolyte, any of the electrolyte from claim 5 wherein in which contacting the cation to 8 A method for producing a polymer electrolyte fuel cell as described in 1).