JP2011034739A - Solid polymer fuel cell, and manufacturing method thereof - Google Patents

Abstract

To provide a polymer electrolyte fuel cell having high radical resistance without greatly reducing battery performance and a method for producing the same.
A membrane electrode assembly is provided in which electrodes are bonded to both surfaces of an electrolyte membrane. The membrane electrode assembly has an amount of soluble iron ions of 10 ppm or less per electrolyte weight and has an effect of improving hydrogen peroxide resistance. A polymer electrolyte fuel cell in which the amount of ions other than protons is 0.1 to 20% in terms of the acid group ratio of the electrolyte. A reduction / pickling step in which the membrane electrode assembly or its constituent elements are subjected to reduction treatment and pickling treatment in this order or simultaneously so that the soluble iron ions contained in the membrane electrode assembly are 10 ppm or less per weight of the electrolyte; An ion introduction step for introducing ions other than protons so that the amount of ions other than protons contained in the membrane electrode assembly is 0.1 to 5% in terms of the acid group ratio of the electrolyte. A method for producing a molecular fuel cell.
[Selection] Figure 1

Description

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

  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.

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.

Patent Document 3 discloses a method in which a polystyrene graft ETFE membrane is immersed in a 1N hydrochloric acid aqueous solution or a 1N sulfuric acid aqueous solution and held at room temperature to 90 ° C. for 1.5 to 2 hours.
This document describes that the Fe element in the polymer electrolyte can be reduced to 0.01% by mass (100 ppm) or less by such a method.

Patent Document 4 does not intend to suppress degradation of the electrolyte membrane caused by radicals, but immerses the carbon fiber / carbon paper composite carrying platinum in a hydrazine aqueous solution or a sodium borohydride aqueous solution. And the manufacturing method of the electrode for solid polymer fuel cells which carries out a reduction process for 30 minutes at room temperature is disclosed.
This document describes that the preliminary operation time can be shortened because the oxide layer on the catalyst surface is removed by such a method.

Patent Document 5 does not intend to suppress the deterioration of the electrolyte membrane caused by radicals, but the carbon fiber / carbon paper composite carrying platinum is immersed in a 1 mol / L sulfuric acid aqueous solution. , A method for producing an electrode for a polymer electrolyte fuel cell is disclosed in which redox treatment is performed 10 times at a scanning speed of 50 mV / sec in the range of −0.3 to 0.5 V.
This document describes that the catalyst surface is cleaned by such a method, so that the preliminary operation time can be shortened.

Further, Patent Document 6 does not intend to suppress the deterioration of the electrolyte membrane caused by radicals, but the proton type S-PES electrolyte membrane is immersed in a 1 mol / L NaOH aqueous solution to form Na type S-PES. A manufacturing method of a membrane electrode assembly is disclosed in which an electrolyte membrane is formed and this is overlaid with a catalyst layer and hot pressed.
In this document, when the electrolyte membrane is made into a salt type, the melting temperature is lowered, and the electrolyte membrane and the catalyst layer can be joined at a low temperature, so that chemical and mechanical damage to the electrolyte membrane can be suppressed. Is described.

JP 2000-106203 A JP 2004-018573 A JP 2005-235523 A JP 2007-227088 A JP 2007-227083 A JP 2007-299705 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 tolerance cannot be obtained even if these techniques are directly applied to hydrocarbon 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.

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.

Furthermore, it is known that transition metal ions (particularly, Fe ions (Fe ²⁺ / Fe ³⁺ )) exist in the electrolyte exceeding a certain threshold value, deteriorate 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.
On the other hand, as disclosed in Patent Document 3, a method of treating an electrolyte with an acid and washing away transition metal ions is effective as a method for removing impurity transition metal ions having Fenton activity. However, sufficient pickling resistance cannot be obtained by simple pickling.

The problem to be solved by the present invention is to provide a polymer electrolyte fuel cell having high radical resistance and a method for producing the same without greatly degrading battery performance.
Another problem to be solved by the present invention is a polymer electrolyte fuel cell that exhibits high oxidation resistance even in the operating environment of the fuel cell (especially in a dry environment), regardless of the type of electrolyte, and its It is to provide a manufacturing method.

In order to solve the above problems, a polymer electrolyte fuel cell according to the present invention is
Provided with a membrane electrode assembly in which electrodes are bonded on both sides of the electrolyte membrane,
The membrane electrode assembly is
(A) The amount of soluble iron ions is 10 ppm or less per electrolyte weight, and
(B) The gist of the invention is that the amount of ions other than protons having an effect of improving hydrogen peroxide resistance is 0.5 to 5% in terms of the acid group ratio of the electrolyte.
In addition, a method for producing a polymer electrolyte fuel cell according to the present invention includes:
A reduction / pickling step in which reduction treatment and pickling treatment of the membrane electrode assembly or its constituent elements are performed in this order or simultaneously so that the amount of soluble iron ions contained in the membrane electrode assembly is 10 ppm or less; ,
The membrane / electrode assembly so that the amount of ions other than protons having an effect of improving hydrogen peroxide resistance contained in the membrane / electrode assembly is 0.5 to 5% in terms of the acid group ratio of the electrolyte. Or an ion introduction step of introducing ions other than protons into the constituent elements;
The main point is that

Slightly soluble Fe compounds do not exhibit Fenton activity, but rather have the effect of non-radical decomposition of hydrogen peroxide. On the other hand, soluble Fe ions exhibit high Fenton activity. Therefore, when an electrolyte having a soluble Fe ion amount of 10 ppm or less is used, the durability of the fuel cell is improved. Moreover, when a predetermined amount of ions having an action of improving hydrogen peroxide resistance is introduced into an electrolyte having a soluble iron ion amount of 10 ppm or less, the interaction with soluble iron ions is suppressed, and the oxidation resistance is improved.
A fuel cell equipped with such an electrolyte performs the reduction treatment and pickling treatment of MEA or its components in this order or at the same time, and then introduces ions having an effect of improving hydrogen peroxide resistance. can get.

A perfluoro-based electrolyte membrane and a hydrocarbon-based electrolyte membrane are immersed in an aqueous solution of iron sulfate (Fe ²⁺ ) at various concentrations at 80 ° C. for 8 hours, and Fe ²⁺ is ion-exchanged, followed by hydrogen peroxide vapor exposure test (3 wt% H ₂ O ₂ , 120 ° C. × 5 hr).

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Solid polymer fuel cell]
The polymer electrolyte fuel cell according to the present invention is
Provided with a membrane electrode assembly in which electrodes are bonded on both sides of the electrolyte membrane,
The membrane electrode assembly is
(A) The amount of soluble iron ions is 10 ppm or less per electrolyte weight,
(B) The amount of ions other than protons having an effect of improving hydrogen peroxide resistance is 0.5 to 5% in terms of the acid group ratio of the electrolyte.

[1.1. Membrane electrode assembly]
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.

[1.1.1. 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. .

[1.1.2. 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.

[1.2. Soluble Fe ion]
“Soluble iron ion” refers to the amount of Fe ions eluted in a solution when immersed in 0.3 L of 1 + 10 hydrochloric acid (hydrochloric acid 1: water 10 solution) per gram of electrolyte for 1 day at room temperature. “Soluble” means that during actual operation of the fuel cell, the iron element is present as ions inside the electrolyte, and can easily move inside the electrolyte.
In the present invention, the membrane / electrode assembly needs to have an amount of soluble iron ions of 10 ppm or less per electrolyte weight. “Per electrolyte weight” refers to the amount of soluble iron ions relative to the weight of all electrolytes contained in the electrolyte membrane and the electrolyte in the catalyst layer.

[1.3. Ions other than protons]
[1.3.1. Definition]
The membrane electrode assembly contains ions other than protons in addition to 10 ppm or less of soluble iron ions.
“Ions other than protons” refer to ions having an action of improving resistance to hydrogen peroxide. “Including ions other than protons”
(1) The presence of a poorly soluble compound capable of gradually releasing ions other than protons in the electrolyte membrane or the catalyst layer, or
(2) It means that protons of acid groups contained in the electrolyte membrane or the electrolyte in the catalyst layer are ion-exchanged with ions other than protons.

[1.3.2. Content of ions other than protons]
If the content of ions other than protons is too small, the effect of improving hydrogen peroxide resistance cannot be obtained. Therefore, the content of ions other than protons needs to be 0.5% or more in terms of the acid group ratio of the electrolyte contained in MEA.
On the other hand, when the content of ions other than protons is excessive, the battery performance is greatly lowered. Therefore, the content of ions other than protons needs to be 5% or less in terms of the acid group ratio of the electrolyte contained in MEA.
“0.5 to 5% in terms of the acid group ratio of the electrolyte” means that 0.5 to 5% of the acid group of the electrolyte contained in the MEA is ion exchanged in an amount other than protons or such ions. Contains ionic compounds.

  In general, the acid group ratio of 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. In general, the number of acid groups in the electrolyte membrane is large. Therefore, for example, when an MEA is prepared by adding a compound containing ions other than protons only to the electrolyte in the catalyst layer or only to the electrolyte membrane, a part of the ions of the compound added during operation is inside the MEA. Diffusion and transfer to the electrolyte membrane or catalyst layer to homogenize. Therefore, when ions are introduced only into either the electrolyte membrane or the electrolyte in the catalyst layer, it may be introduced in excess of 5%.

  When adding a compound containing these ions, the compound may be added to either the electrolyte in the catalyst layer or the electrolyte membrane. However, since hydrogen peroxide is generated at the electrode, it is added to the electrolyte in the catalyst layer, or it is present in the catalyst layer or electrolyte membrane so as to be concentrated at the membrane / catalyst layer interface. It is preferable to prevent diffusion into the surface. That is, these compounds are preferably added after being concentrated at the surface of the membrane or the deepest portion of the catalyst layer (the junction with the membrane). However, it should be noted that excessive concentration reduces the membrane / catalyst layer bondability.

[1.3.3. Concrete example]
Examples of ions or compounds having the effect of improving hydrogen peroxide resistance include the following. In particular, it is preferable that these compounds are so-called poorly soluble compounds having low solubility in water because they can remain in the MEA for a long time.

(1) Alkali metal ions:
Examples of the alkali metal ion include Li ⁺ , Na ⁺ , K ⁺ , and Cs ⁺ .
The “alkali metal compound” refers to a compound of an alkali metal ion and an anion that is paired with the alkali metal ion. Examples of poorly soluble compounds include MgKHPO ₄ , CsAl (SO ₄ ) ₂ .12H ₂ O, Cs ₂ PtCl ₆ , Cs ₃ P ₁₂ WO ₄₀ , MgNa (UO ₂ ) ₃ (CH ₃ COO) ₉ · 6H ₂ O And complex salts or double salts.

(2) Phosphonium ion:
“Phosphonium ion” refers to a monovalent cation in which four alkyl groups are bonded around a P atom.
“Phosphonium compound” refers to a compound [P (R ₁ ) (R ₂ ) (R ₃ ) (R ₄ )] ⁺ B ⁻ with a phosphonium ion and an anion B paired therewith.

  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, tetraphenyl Phosphonium tetraphenylborate, tri-tert-butylphosphonium tetraphenylborate, di-tert-butylmethylphosphate Fonium tetraphenylborate, trihexyl (tetradecyl) phosphonium bis [oxalato (2-)] borate, tetraphenylphosphonium tetra-P-tolylborate, benzylphenylphosphonium tetraphenylborate, P-tolyltriphenylphosphonium tetra-P-tolylborate And triethylmethylphosphonium dibutyl phosphate, ethyl triphenylphosphonium phosphate, tributylmethylphosphonium dibutyl phosphate, tetrabutylphosphonium benzotriazolate, trihexyl (tetradecyl) phosphonium decanoate, tributylmethylphosphonium methyl carbonate, and the like.

(3) Nitrogen-containing cation:
“Nitrogen-containing cation” includes N in its structure and forms a cation regardless of whether it is aliphatic or aromatic, or heterocyclic or acyclic. And those capable of ionic bonding.
The “nitrogen-containing basic compound” refers to a compound of a nitrogen-containing cation and an anion paired therewith.

As a nitrogen-containing cation, specifically,
(A) ammonium ion, amine, pyridine, dipyridine, imidazole, quinoline, pyrimidine, imine, triazine, aminotriazine, guanidine, aminocarboxylic acid, nucleobase, pyrazolone, or derivatives thereof,
(B) cations of these salts,
and so on.

Among the basic compounds containing a nitrogen-containing cation, a quaternary ammonium salt represented by the formula (1) is preferable.
_{^{+ N (R 1) (R}} 2) (R 3) (R 4) Z - ··· (1)
R ₁ , R ₂ , R ₃ and R ₄ are alkyl groups, and Z ⁻ is an anion. The alkyl group may be substituted with a halogen other than Cl and Br (for example, I, F).
As a quaternary ammonium ion, specifically,
(A) NH ₄ ⁺ (ammonium ion),
(B) alkyl ammonium ions such as N (CH ₃ ) ₄ ⁺ (tetramethylammonium ion), N (C ₂ H ₅ ) ₄ ⁺ (tetraethylammonium ion), tetrapropylammonium ion, tetrabutylammonium ion,
and so on.

The amine may be any of primary amine (R ₁ NH ₂ ), secondary amine (R ₁ R ₂ NH), and tertiary amine (R ₁ R ₂ R ₃ N). Under acidic conditions (inside the electrolyte), these amines become proton acceptors as shown in the formulas (2a) to (2c), become nitrogen-containing cations A ⁺ , and form ionic bonds with the acid group anion B ^−. can do.
R ₁ NH ₂ + H ⁺ → R ₁ NH ₃ ⁺ (2a)
R ₁ R ₂ NH + H ⁺ → R ₁ R ₂ NH ₂ ⁺ (2b)
R ₁ R ₂ R ₃ NH + H ⁺ → R ₁ R ₂ R ₃ NH ⁺ (2c)

Specific examples of the primary amine include methylamine, ethylamine, propylamine, butylamine, and pentylamine.
Specific examples of the secondary amine include dimethylamine and diethylamine.
Specific examples of the tertiary amine include trimethylamine and trimethylamine.
Specific examples of the cyclic amine include hexamethylenetetramine, cyclohexylamine, cyclohexyldiamine, piperazine, and morpholine.
Specific examples of hindered amines include 2,2,6,6, -tetramethyl-4-piperidone, 1,2,2,6,6-pentamethyl-4-piperidone, 2,2,6,6-6. -Tetramethylpiperidine and the like.
Specific examples of the polyamine include ethylenediamine and dicyclohexyldiamine. Salts of these amine carbonates, phosphates, sulfates and the like can also be used.

  Specific examples of imines include ethyleneimine.

  Specific examples of the aminotriazine include formoguanamine, guanylmelamine, cyanomelamine, arylguanamine, melamine, ammelin, ammelide, melam, melem, and melon.

  Specific examples of the aminocarboxylic acid include histidine, nitrilotriacetic acid, ethylenediaminetetraacetic acid, and diethylenetriaminopentaacetic acid.

  Specific examples of guanidine-based nitrogen compounds include aminoguanidine, guanylurea, biguanide, guanidine, guanidine carbonate, guanidine borate, phosphoric acid / monoguanidine, phosphoric acid / diguanidine, guanylurea phosphate, guanidine hydrochloride, guanidine sulfate. Guanidine sulfamate, 1,3-diphenylguanidine, and the like.

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.

  Specific examples of the compound that generates pyrazolo ions include aminopyrine and antipyrine that are known to react with silicomolybdic acid.

(4) Alkaline earth metal ions:
Examples of alkaline earth metal ions include Mg ²⁺ , Ca ²⁺ , Sr ²⁺ and Ba ²⁺ .
“Alkaline earth metal compound” refers to a compound of an alkaline earth metal ion and an anion paired therewith. Taking Ca ²⁺ as an example, Ca ₃ (PO ₄ ) ₂ (calcium phosphate), CaF ₂ (calcium fluoride), CaWO ₄ (calcium tungstate), CaC ₂ O ₄ (calcium oxalate), and these Hydrates are mentioned.

(5) Typical element ions:
“Typical element ions” are Zr ²⁺ in group 12, Al ³⁺ , Ga ³⁺ , In ³⁺ in group 13, Ga ⁴⁺ in group 14, Si ⁴⁺ , Sn ⁴⁺ , Sb ^{3 in} group 15 ⁺ , Bi ³⁺ cations, etc. Among typical element ions, the effect of improving the durability by Zn ²⁺ ions is particularly large.
“Typical element compound” refers to a compound of a typical element ion and a pair of anions. Taking Zn ²⁺ as an example, Zn ₃ (PO ₄ ) ₂ (zinc phosphate), ZnF ₂ (zinc fluoride), ZnWO ₄ (zinc tungstate), ZnC ₂ O ₄ (zinc oxalate), and These hydrates are mentioned.

(6) Iron ion transition metal ions:
Examples of transition metal ions other than iron ions include Sc ³⁺ , Cr ³⁺ , manganese ions (Mn ²⁺ , Mn ⁴⁺ ), cobalt ions (Co ²⁺ , Co ³⁺ ), Ni ²⁺ , Cu ²⁺ , Y ³⁺ , Zr ⁴⁺ , Mo ³⁺ , Ru ³⁺ , Rh ²⁺ , Pd ²⁺ , Ag ⁺ , Hf ⁴⁺ , Ta ³⁺ , W ³⁺ , Pt ²⁺ , Pt ⁴⁺ and the like.
The “transition metal compound” refers to a compound of a transition metal ion other than iron ions and an anion paired therewith.

(7) Rare earth metal ions:
Examples of rare earth metal ions include La ³⁺ , Ce ³⁺ , Ce ⁴⁺ , Pr ³⁺ , Pr ⁴⁺ , Nd ³⁺ , Sm ³⁺ , Eu ³⁺ , Gd ³⁺ , Tb ³⁺ , Dy ³⁺ , Er ³⁺ , Yb ³⁺ , Lu ³⁺ and the like.
“Rare earth metal compound” refers to a compound of a rare earth metal ion and an anion paired therewith. Taking Ce ³⁺ as an example, CePO ₄ (cerium (III) phosphate), Ce ₃ (PO ₄ ) ₄ (cerium (IV) phosphate), CeF ₃ (cerium fluoride), Ce ₂ (WO ₄ ) ₃ (cerium tungstate), Ce ₂ (C ₂ O ₄ ) ₃ (cerium oxalate), and hydrates thereof.

For the ions other than the various protons described above, the optimum ions are selected according to the type of electrolyte contained in the MEA. In this case, the MEA may include any one of the above-described ions, or may include two or more.
For example, when at least one of the electrolyte membrane and the electrolyte in the catalyst layer is a hydrocarbon electrolyte, ions other than protons are alkali metal ions, phosphonium ions, nitrogen-containing cations, alkaline earth metal ions, and typical element ions. Any one or more selected is preferable.
For example, when at least one of the electrolyte membrane and the electrolyte in the catalyst layer is a fluorine-based electrolyte, ions other than protons are selected from phosphonium ions, nitrogen-containing cations, transition metal ions other than iron ions, and rare earth metal ions. Any one or more of these is preferable.

[1.4. Halogen content]
MEA has a soluble iron ion content of 10 ppm or less per electrolyte weight, and contains 0.5 to 5% of ions other than protons in terms of acid group ratio, and the content of halogen ions excluding F Is preferably 10 ppm or less per electrolyte weight.
If the halogen ion content excluding F exceeds 10 ppm, electrode poisoning increases and the voltage decreases, which is inappropriate. The halogen ion may be quantified by anion analysis (ion-selective electrode, ion chromatography analysis) of the extracted water after bringing the catalyst layer, the electrolyte membrane or MEA into contact with high-temperature pure water.

In order to bring the halogen ions excluding F to a predetermined amount or less, it is preferable to use a compound containing no halogen element as a counter ion when introducing ions other than protons into the MEA.
Specific examples of counter ions for introducing ions other than protons include hydroxide ions, carbonate ions, formate ions, acetate ions, propionate ions, oxalate ions, maleate ions, adipate ions, 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 Hydrogen phosphate ion, dibutyl phosphate ion, benzotriazolate ion, decanoic acid ion, methyl carbonate ion and the like are preferable.

Conversely, inappropriate ions are chloride ion (Cl ⁻ ), bromide ion (Br ⁻ ), and iodide ion (I ⁻ ). In particular, care must be taken because chloride ions tend to remain as contamination ions in MEA.
These halogen ions have strong adsorptive power with metals, and catalyst poisoning and Pt of catalyst are eluted from the catalyst layer as halogen complex ions (for example, PtCl ₄ ²⁻ , PtCl ₆ ^2−, etc.), thus greatly improving battery performance. Since it lowers, it is not preferable. Therefore, when these halogen ion-containing compounds are added or ion exchanged, dehalide removal treatment (washing with warm water and anion exchange resin) or specific cations (Ag ⁺ , Cs ⁺ , BiO ⁺⁾ , YbO ^+, etc.) to fix the halogen ions as hardly soluble halides.

On the other hand, when the counter anion of ions other than protons is an ion other than halogen ions other than F, the corrosiveness is weak and there is no possibility of eluting the catalyst metal.
Note that complex ions in which fluoride ions and fluorine atoms are complexed with other cations (for example, AlF ₄ ⁻ , GaF ₄ ⁻ , AlF ₆ ^−, etc.) are also relatively weak in adsorption power compared to other halogen ions. Ions other than protons may be introduced using compounds having these as counter ions.

[2. Method for producing polymer electrolyte fuel cell]
The method for producing a polymer electrolyte fuel cell according to the present invention includes a reduction / pickling step and an ion introduction step.

[2.1. Reduction / pickling process]
In the reduction / pickling step, reduction treatment and pickling treatment of the membrane electrode assembly or its constituent elements are performed in this order so that the amount of soluble iron ions contained in the membrane electrode assembly is 10 ppm or less per electrolyte weight. Or a step performed simultaneously.
“Reducing treatment” refers to treating MEA or its components in a reducing atmosphere. In addition, the “reducing atmosphere” refers to an atmosphere that is reducing (the oxygen partial pressure is small or the equilibrium potential is lower) than in the air or in a solution in equilibrium with the air. The reduction treatment is divided into treatment in the gas phase and treatment in the liquid phase.

It is known that the state of Fe in the iron compound takes +2 and +3. In some cases, it is also known that these mixed valence compounds and intermediate valence compounds exist. Among them, the Fe ³⁺ ion compound is less soluble than the Fe ²⁺ ion compound and is difficult to remove by acid cleaning. The reduction treatment is performed to reduce hardly soluble Fe ³⁺ ions to soluble Fe ²⁺ ions and facilitate removal by acid washing.

[2.1.1. Processing object]
The MEA is generally manufactured by transferring a catalyst layer containing an electrode catalyst to an electrolyte membrane and pressing a diffusion layer on the outside of the catalyst layer as necessary. You may perform a reduction process and a pickling process in the state of MEA. Alternatively, the MEA components such as electrolyte membranes and electrodes may be subjected to reduction treatment and pickling treatment, and the MEA may be manufactured using the treated components. Since it is sufficient that the amount of soluble iron ions finally contained in the MEA is equal to or less than a predetermined amount, the processing target can be appropriately selected according to the type and purity of the starting material.

[2.1.2. Concrete example]
[2.1.2.1. First Specific Example]
The first specific example of the reduction / pickling process is:
A reduction step of reducing the membrane electrode assembly or a component thereof in the gas phase;
A pickling step for pickling the membrane electrode assembly or its constituent elements.

[A. Reduction process]
The reduction treatment in the gas phase refers to a heat treatment at an oxygen partial pressure or less in the atmosphere. Unlike the reduction treatment in the liquid phase, the reduction treatment in the gas phase has an advantage that there is no need for waste liquid treatment or liquid management.
Specifically, as the reduction treatment in the gas phase,
(1) heat treatment in vacuum,
(2) heat treatment in an inert gas such as Ar or N ₂ ;
(3) heat treatment in a reducing gas such as H ₂ , NH ₃ , CO, CH ₄ ,
and so on.
Among these, heat treatment in an H ₂ atmosphere is particularly suitable as a reduction method because it is easy to reduce Fe ³⁺ → Fe ²⁺ .

The reduction is performed under conditions such that the concentration of soluble iron ions is 10 ppm or less.
When the reduction treatment is performed on the electrolyte membrane, the catalyst layer, or the MEA, the reduction reaction rate can be increased as the reduction treatment temperature increases.
However, if the reduction treatment temperature is too high,
(A) MEA is deformed beyond the glass transition temperature of the polymer,
(B) Desulfonation occurs from the polymer electrolyte, and the battery performance decreases.
There is a problem.
Accordingly, when the reduction treatment is performed on the electrolyte membrane, the catalyst layer, or the MEA, the reduction treatment temperature is preferably 120 ° C. or less.

In addition, at least one ion selected from the group consisting of Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ , NH ₄ ⁺ , tetrabutylammonium ion, Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , and Ba ²⁺ A reduction treatment may be performed after ion exchange of 50% or more of the acid groups of the electrolyte, and then the electrolyte may be returned to the H form by pickling. In this case, even if the reduction treatment temperature exceeds 120 ° C., the reduction treatment may be possible for a short time. However, in this case, the cation introduced to stabilize the acid group is discarded, which is not preferable because the cost increases.
Moreover, about the electrode catalyst and diffusion layer which do not contain electrolyte, you may reduce-react at the temperature exceeding 120 degreeC.

The reduction treatment time may be a time during which Fe ³⁺ ions are sufficiently reduced to Fe ²⁺ ions. The reduction treatment time is preferably 30 minutes or longer, more preferably 1 hour or longer.
After the reduction treatment at a high temperature, before being cooled to room temperature, the air is released from the reducing atmosphere at once. The iron compound reduced to Fe ²⁺ is easily re-oxidized by oxygen in the air and becomes a compound of Fe ³⁺ again. . In addition, when reduction is performed using hydrogen gas, there is a risk of explosion due to residual hydrogen gas. Therefore, after the reduction treatment, it is preferable to sufficiently replace with an inert gas such as N ₂ or Ar as necessary, and perform pickling immediately after cooling.

[B. Pickling process]
After the reduction treatment, pickling is performed with an aqueous acid solution. The acid aqueous solution for pickling may be an aqueous solution containing an acid capable of dissolving the Fe compound solubilized by the reduction treatment or detoxifying Fe ions.
As an acid used for pickling, specifically,
(1) Inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid, perchloric acid, sulfuric acid,
(2) organic acids such as formic acid, hydroxycarboxylic acid, ascorbic acid,
(3) heteropolyacid,
and so on. Any one of these may be used, or two or more may be used in combination.

[B. 1. Inorganic acid]
Hydrochloric acid or nitric acid can dissolve the Fe compound. However, it is not preferable to use these acids for electrolytic reduction, which will be described later, because chlorine gas and NO _x gas are generated at the counter electrode, and the working environment tends to deteriorate.
Sulfuric acid and perchloric acid can dissolve the solubilized Fe compound, and no harmful gas is generated even when electrolytic reduction is performed. However, since all of these acids are high-boiling compounds, there is a problem that they tend to remain in MEA. Therefore, these acids need attention from the viewpoint of corrosion and catalyst poisoning, and it is necessary to perform subsequent washing with water sufficiently.

[B. 2. Organic acid]
Formic acid is a strong acid and has a reducing power among organic acids, and a salt formed with a transition metal such as iron has a high solubility. Therefore, pH can be lowered and Fe ions can be effectively removed with a small amount of use. Even if it remains in the MEA, its catalytic poisoning action is small as compared with inorganic acids such as sulfuric acid, hydrochloric acid, phosphoric acid and nitric acid. Moreover, since the oxidation-reduction potential is base, it is easily decomposed and removed even if it remains on the electrode, and the voltage drop is relatively small. In addition, formic acid reacts with hydrogen peroxide to eventually become harmless CO ₂ and H ₂ O, which acts as a sacrificial agent that protects the electrolyte. Therefore, formic acid is suitable as an acid used for pickling.
However, formic acid is slightly inferior in chelating ability and reducing power with transition metals. Therefore, when formic acid is used to remove soluble iron ions, reduction treatment is performed in advance, or various reducing agents (for example, reducing agents having a chelating action such as hydroxycarboxylic acid and heteropolyacid, ascorbic acid, as described later) It is preferable to use in combination with a reducing agent having a large reducing action such as a reducing agent that generates hydrogen such as sodium borohydride or dimethylamine borane.

Hydroxycarboxylic acids (eg, glycolic acid, gluconic acid, citric acid, malic acid, tartaric acid, etc.) and ascorbic acid not only dissolve Fe compounds but also transition metal ions (eg, Fe ²⁺ ions) and complex ions. Easy to form. Therefore, iron ions that are readily soluble in water under acidic conditions can be effectively removed. Further, it is possible to dissolve hardly soluble compounds such as iron oxides. Furthermore, ascorbic acid has an action of reducing Fe ³⁺ to Fe ²⁺ .
Hydroxycarboxylic acid and ascorbic acid are less corrosive than inorganic acids even if they remain. They also react with hydrogen peroxide to eventually become harmless CO ₂ and H ₂ O, which act as sacrificial agents that protect the electrolyte. Furthermore, they are much less susceptible to electrode poisoning than hydrochloric acid or sulfuric acid.
Since hydroxycarboxylic acid and ascorbic acid have a relatively low degree of dissociation as an acid, it may be difficult to return the electrolyte to an H ⁺ form alone. In that case, it is preferable to use in combination with an acid having a high degree of dissociation as an acid. In particular, when hydroxycarboxylic acid or ascorbic acid is used in combination with formic acid, both hydroxycarboxylic acid and ascorbic acid act as reducing agents rather than acids. Therefore, Fe ions can be removed efficiently.

[B. 3. Heteropoly acid]
The heteropolyacid is an oxyacid anion having Mo, W, or V as a central element M, an oxyacid anion having P, Si, Ge, Ti, Zr, Sn, Ce, or Th as a central element X, and Is a multi-element polyanion in which is bonded, and is collectively called polyoxometalate. 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.

In these heteropolyacids, various cations and protons are exchanged (coordinated), and the cations are stabilized unlike the free state. For example, transition metal ions such as Fe ²⁺ , Cu ²⁺ , and Pd ²⁺ having Fenton activity deactivate Fenton activity in the presence of a heteropolyanion. Accordingly, even an electrolyte contaminated with a transition metal (for example, an electrolyte having a transition metal polymerization catalyst residue) can increase the hydrogen peroxide resistance of the electrolyte.
When the electrolyte is washed with these heteropolyacids, the heteropolyacid anion forms a sparingly soluble salt with the transition metal ion, or remains in the electrolyte as a heteropolyacid and contributes to the improvement of hydrogen peroxide resistance. .

[B. 4). Pickling conditions]
The pickling is performed under conditions such that the concentration of soluble iron ions is 10 ppm or less.
For example, when the acid is formic acid, hydroxycarboxylic acid, or ascorbic acid, the acid concentration is preferably 0.05 to 1 M / L. If the acid concentration is too low, the pH will be high and it will be difficult to remove impurity ions such as iron ions. On the other hand, if the acid concentration is too high, the cost of the chemical solution increases and the amount of pure water required for rinsing increases, which is not economical.

For example, when the acid is a mixed acid of formic acid and hydroxycarboxylic acid or ascorbic acid, the molar concentration ratio of formic acid and hydroxycarboxylic acid or ascorbic acid is preferably 1: 0.1 to 1: 2, 1: 1 is preferred. When the concentration of hydroxycarboxylic acid or ascorbic acid is too low, the chelating action of Fe ²⁺ ions is not observed. On the other hand, if the concentration of hydroxycarboxylic acid or ascorbic acid is too high, the pH becomes high and the ability to remove Fe ²⁺ ions decreases.

  For example, when the acid is a heteropolyacid, the acid concentration is preferably 0.01 to 10 g / L. If the acid concentration is too low, the pH will be high and it will be difficult to remove impurity ions such as iron ions. On the other hand, if the acid concentration is too high, the cost of the chemical solution increases and the amount of pure water required for rinsing increases, which is not economical. In addition, since the heteropolyacid has a slight oxidation catalytic action, the remaining heteropolyacid that cannot be removed by rinsing may oxidize and degrade the electrolyte (particularly, the hydrocarbon electrolyte). Therefore, cleaning at a high concentration is not recommended.

  The pickling temperature is preferably 40 ° C. or higher, and the time is preferably 30 minutes or longer. If necessary, ultrasonic waves may be irradiated to allow the acid to penetrate into the membrane. It is preferable to rinse with warm pure water after pickling to remove water-soluble ionic components.

[C. Degreasing process]
Prior to the reduction treatment, MEA and its constituent elements may be degreased in order to remove organic contaminants. As a degreasing method,
(1) A method of immersing MEA and its components in an aqueous alkali solution (for example, sodium carbonate, sodium hydrogen carbonate, sodium hydroxide, sodium silicate, etc.).
(2) A method of spraying an alkaline aqueous solution onto MEA and its constituent elements,
(3) A method of electrolytically degreasing MEA and its components in an aqueous alkaline solution,
and so on.

[2.1.2.2. Second specific example]
In the second specific example of the reduction / pickling step, MEA or a component having electron conductivity such as a catalyst layer or a diffusion layer is immersed in an acid aqueous solution, and the MEA or the component is lower than the hydrogen generation potential. This is a method (electrolytic reduction treatment method) in which electricity is supplied while maintaining a potential and generating hydrogen. By this method, pickling can be performed simultaneously with the reduction.

[A. Electrolytic reduction treatment]
[A. 1. Electrolytic reduction solution]
The acid aqueous solution (electrolytic reduction treatment solution) used for the electrolytic reduction treatment may be an aqueous solution containing an acid capable of dissolving the Fe compound solubilized by the electrolytic reduction treatment or detoxifying Fe ions.
Specifically, as the acid contained in the electrolytic reduction treatment solution,
(1) Inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid, perchloric acid, sulfuric acid,
(2) organic acids such as formic acid, hydroxycarboxylic acid, ascorbic acid,
(3) heteropolyacid,
and so on. Any one of these may be used, or two or more may be used in combination.

Among these, as an acid contained in the electrolytic reduction treatment solution,
(1) formic acid, hydroxycarboxylic acid, ascorbic acid, heteropolyacid,
(2) a mixture of formic acid and hydroxycarboxylic acid, a mixture of formic acid and ascorbic acid,
Etc. are suitable.
Since the other points regarding the acid are the same as in the first specific example, description thereof is omitted.

[A. 2. Electrolysis conditions]
Electrolysis is performed under conditions such that the concentration of soluble iron ions is 10 ppm or less.
The bath temperature during electrolytic reduction is preferably 60 ° C. or higher. The current density is preferably 0.01 A / cm ² or more so that generation of hydrogen gas can be sufficiently confirmed visually.
The object to be processed (working electrode, cathode) is preferably sandwiched between insoluble meshes made of Pt or Ti and leads are taken. For the counter electrode (anode), Pt, Au, C, ferrite, or the like as an insoluble anode may be used, or an object to be processed may be used.
The electrolytic reduction treatment may be performed using the object to be treated as the cathode at all times, or so-called PR electrolytic treatment in which the polarity is appropriately reversed. In particular, when PR electrolysis is performed using an object to be processed as a counter electrode, there is an advantage that two objects to be processed can be reduced and pickled at a time.

[B. Degreasing process]
Before performing the electrolytic reduction treatment, the MEA or a component thereof may be degreased. The details of the degreasing step are the same as those of the first specific example, and thus the description thereof is omitted.

[2.1.2.3. Third specific example]
A third specific example of the reduction / pickling process is:
A reduction step of reducing the membrane electrode assembly or a component thereof in a liquid phase;
Pickling step of pickling the membrane electrode assembly or its components;
It has.

[A. Reduction process]
[A. 1. Reducing agent solution]
Reduction in the liquid phase is performed using a reducing agent solution. Specific examples of the reducing agent solution include the following.
A first specific example of the reducing agent solution is a hydrogen gas saturated aqueous solution in which hydrogen gas is saturated with water. Hydrogen gas saturated aqueous solution is, for example,
(1) A method of bubbling hydrogen gas into pure water,
(2) A method of using cathode water saturated with hydrogen generated from the cathode side by electrolyzing pure water;
Etc. can be manufactured.

A second specific example of the reducing agent solution is a reducing aqueous solution in which a reducing agent that generates hydrogen is dissolved. As a reducing agent for generating hydrogen, there is a borohydride compound. Boron hydride compounds dissolve in water and decompose to generate hydrogen gas.
The borohydride compound may be an inorganic borohydride compound such as lithium borohydride, sodium borohydride, or potassium borohydride, or an organic borohydride compound such as dimethylamine borane or cyanomethylamine borane. But it ’s okay. Among these, sodium borohydride and dimethylamine borane are both particularly preferable as a reducing agent because they are both relatively stable in the air and have a mild reaction with water.
The borohydride compound can be kept in a lower state of reduction potential than the saturated aqueous solution of hydrogen gas due to the presence of hydride ions (BH ₄ ⁻ ). Therefore, the reduction of Fe ³⁺ contained in MEA or its constituent elements to Fe ²⁺ can be performed more smoothly than when H ₂ gas is simply contacted.

[A. 2. Reduction conditions]
The reduction is performed under conditions such that the concentration of soluble iron ions is 10 ppm or less.
The contact between the reducing agent solution and the MEA or a component thereof can be performed by a method such as dipping, spraying or spin coating. This method is effective for removing Fe ions contained in components that cannot be energized (for example, electrolyte membrane).
When the reducing agent solution is a hydrogen gas saturated aqueous solution, the treatment temperature and treatment time may be any temperature and time at which Fe ³⁺ ions are sufficiently reduced to Fe ²⁺ ions.

When the catalyst layer or MEA is treated using a reducing aqueous solution in which a borohydride compound is dissolved, the borohydride compound is decomposed by an electrode catalyst having a large specific surface area, and heat generation and H ₂ gas generation are remarkable. Therefore, it is dangerous to treat with a concentrated solution of borohydride compound.
The concentration of the borohydride compound is preferably 0.1 mol / L or less, more preferably 0.01 to 0.5 mol / L. In addition to boron hydride compound, NaOH, KOH, adding an alkali such as NH _3, when the pH is adjusted to 10 or higher, the reducing power of the treatment solution is increased, it is possible to shorten the processing time.

  It is sufficient that the immersion time in the reducing aqueous solution in which the borohydride compound is dissolved is 5 to 30 minutes and the temperature is room temperature to 90 ° C. At room temperature, the reduction reaction rate is slow and requires a long time. Although the reduction reaction rate increases at a high temperature exceeding 90 ° C., the amount of evaporation of the treatment solution increases, and it is difficult to control the process, which tends to increase the cost. Standard processing conditions are, for example, 1 hr at 80 ° C.

[B. Pickling process]
After the reduction treatment, pickling treatment of MEA or its constituents is performed. The details of the pickling process are the same as those in the first specific example, and thus the description thereof is omitted.
In addition, when pickling after performing reduction processing of MEA or its component using a borohydride compound, the cation introduced into the electrolyte by the borohydride compound is replaced with 100% protons during pickling. It is not necessary. This is because the remaining cations such as ammonium, sodium and potassium act as a decomposition catalyst for hydrogen peroxide and can stabilize the acid group. Also, it is possible to use a large amount of ions such as ammonium, Na ⁺ , K ^+, etc., but there is no problem. However, when an expensive but particularly effective ion (for example, Cs ⁺ , phosphonium ion) is introduced. It is economical to remove a small amount of ions such as Cs ⁺ after removing ions such as ammonium by pickling.

[C. Degreasing process]
You may degrease MEA or its component before the reduction process by a reducing agent solution. The details of the degreasing step are the same as those of the first specific example, and thus the description thereof is omitted.
In addition, when reducing using an alkaline reducing agent solution (for example, an aqueous solution of a borohydride compound), degreasing and reduction are performed at the same time. Therefore, it is not always necessary to degrease in advance.

[2.1.2.4. Fourth Specific Example]
The fourth specific example of the reduction / pickling step is a method of pickling simultaneously with the reduction of the membrane electrode assembly or its constituent elements using an acidic reducing agent solution.

[A. Reduction pickling process]
[A. 1 Reducing agent solution]
As an acidic reducing agent solution used for the reduction treatment,
(1) an acidic hydrogen gas saturated aqueous solution in which hydrogen gas is bubbled into an acid aqueous solution,
(2) Hydrogen-saturated electrolytic cathodic water obtained by electrolyzing an acidic solution such as formic acid in a two-chamber or three-chamber electrolytic cell;
(3) A mixture of a strong acid (eg, formic acid) having a relatively high degree of dissociation and a weak acid (eg, hydroxycarboxylic acid, ascorbic acid, heteropolyacid, etc.) having a chelating action and a relatively low degree of dissociation,
and so on.
The other points regarding the acid are the same as in the first specific example, and thus the description thereof is omitted.

[A. 2 Reducing pickling conditions]
The reduction pickling is performed under conditions such that the concentration of soluble iron ions is 10 ppm or less.
The contact between the reducing agent solution and the MEA or a component thereof can be performed by a method such as dipping, spraying or spin coating. This method is effective for removing Fe ions contained in components that cannot be energized (for example, electrolyte membrane).
When the reducing agent solution is an acidic hydrogen gas saturated aqueous solution, the treatment temperature and treatment time are:
^Any temperature and time may be sufficient as long as the Fe ³⁺ ions are sufficiently reduced to Fe ²⁺ ions.

For example, when the acid contained in the reducing agent solution is a mixed acid of formic acid and hydroxycarboxylic acid or ascorbic acid, the molar concentration ratio of formic acid and hydroxycarboxylic acid or ascorbic acid is 1: 0.1 to 1: 2 is preferable, and 1: 1 is particularly preferable. When the concentration of hydroxycarboxylic acid or ascorbic acid is too low, the chelating action of Fe ²⁺ ions is not observed. On the other hand, if the concentration of hydroxycarboxylic acid or ascorbic acid is too high, the pH will be high,
The ability to remove Fe ²⁺ ions decreases.

  For example, when the reducing agent solution contains a heteropolyacid, the concentration of the heteropolyacid is preferably 0.01 to 10 g / L. If the concentration of the heteropolyacid is too low, a sufficient chelating effect cannot be obtained. On the other hand, if the concentration of the heteropolyacid is too high, the cost of the chemical solution increases and the amount of pure water required for rinsing increases, which is not economical. In addition, since the heteropolyacid has a slight oxidation catalytic action, the remaining heteropolyacid that cannot be removed by rinsing may oxidize and degrade the electrolyte (particularly, the hydrocarbon electrolyte). Therefore, cleaning at a high concentration is not recommended.

  The temperature of the reduction treatment is preferably 40 ° C. or higher and the time is preferably 30 minutes or longer. If necessary, ultrasonic waves may be irradiated to allow the reducing agent solution to penetrate into the membrane. It is preferable that the water-soluble ionic component is removed by sufficiently rinsing with warm pure water after the reduction treatment.

[B. Degreasing process]
You may degrease MEA or its component before the reduction process by a reducing agent solution. The details of the degreasing step are the same as those of the first specific example, and thus the description thereof is omitted.

[2.2. Ion introduction process]
The ion introduction step is performed so that the amount of ions other than protons having an effect of improving hydrogen peroxide resistance contained in the membrane electrode assembly is 0.5 to 5% in terms of the acid group ratio of the electrolyte. In this step, ions other than protons are introduced into the electrode assembly or its constituent elements.

[2.2.1. Introduction method]
Since the amount of ions finally contained in the MEA only needs to be a predetermined amount, the ion introduction method can be appropriately selected according to the processing target. Specific examples of methods for introducing ions into MEA subjected to reductive pickling or components thereof include the following methods.
(1) The electrolyte that has been subjected to the reductive pickling is dissolved in a solvent such as alcohol, and a compound containing ions other than protons is further dissolved or dispersed in this solution, and this solution is dissolved in a suitable substrate (for example, a metal container, A casting method in which a solvent is removed by casting on a glass container, PTFE film, PET film or the like.
(2) A melt-extrusion method in which a compound containing ions other than protons is added to an electrolyte that has been subjected to reductive pickling, and this is heated and melted and mixed, and film-molded with an extruder.
(3) The electrolyte that has been subjected to the reductive pickling is dissolved in a solvent such as alcohol, and a conductive carrier carrying a catalyst and a compound containing ions other than protons are further added to the solution to form a catalyst paste. A spray method in which the surface of the electrolyte membrane is sprayed.
(4) A transfer sheet method in which a transfer sheet is formed on a PTFE film or PET film by the doctor blade method or the like using the catalyst paste, and the electrolyte membrane and the transfer sheet are joined by hot pressing.
(5) An ion exchange method in which MEA subjected to reductive pickling or a component thereof is immersed in a solution in which a compound containing ions other than protons is dissolved, and ion exchange is performed.

Some phosphonium compounds and compounds containing nitrogen-containing cations become insoluble in water as the molecular weight increases, and the solubility in alcohols and other organic solvents also decreases. In such a case, it is preferable to use a method of mechanically and uniformly mixing these compounds having a large molecular weight and the electrolyte subjected to the reduction pickling.
On the other hand, when compounds containing ions other than protons are soluble in a solvent, these compounds are once dissolved in a solvent such as water or alcohol, and then the electrolyte is dissolved in the solution or the compound is dissolved in the solution. It is preferable to perform ion exchange by immersing the electrolyte membrane, the catalyst layer, or the MEA. In these methods, compared to a method in which a compound containing ions other than protons is merely mechanically mixed, the ions are strongly bonded to each other by interacting with an acid group of the electrolyte. Therefore, since it is difficult to take out of the MEA by generated water or humidified water, long-term durability can be ensured even in a small amount as compared with the mechanical mixing method.

[2.2.2. Ion exchange method]
The ion exchange method will be described in detail.
The ion exchange can be performed by bringing a solution containing ions other than protons into contact with an electrolyte using a method such as immersion or spray coating. The solvent should just be what can melt | dissolve these compounds. The solvent is particularly preferably a polar solvent such as water, ethanol or isopropanol.
Prior to ion exchange, it is preferable to perform ion exchange after the electrolyte is immersed in a nonaqueous solvent such as alcohol or a mixed solvent of water and a nonaqueous solvent to swell the electrolyte. If the electrolyte is swollen before the ion exchange, the inside of the electrolyte can be easily ion exchanged.
Moreover, it is preferable that the compound hardly soluble in water is once dissolved in a non-aqueous solvent such as ethanol or propanol and then dissolved in water. By such a method, a homogeneous treatment solution can be prepared even for a compound that is sparingly soluble in water.

What is necessary is just to melt | dissolve the compound of an amount required in order to carry out partial ion exchange of the acid group of electrolyte in a solution.
The concentration of these compounds in the solution is preferably a dilute solution of 1 mM / L to 0.01 M / L. When ion exchange is performed at a high concentration exceeding 0.01 M / L, protons of nearly 100% are ion-exchanged, and the proton conductivity of the electrolyte may be lost.

The pH of the solution is preferably 2 or more. In ion exchange in an acidic solution having a pH of less than 2, since the number of protons is too large, the acid body of the electrolyte becomes stable. As a result, it becomes difficult to introduce desired ions.
The time required for the ion exchange process varies depending on the temperature. For example, at room temperature, it takes 8 hours or more for the acid group of the electrolyte to be exchanged with these ions by nearly 100%. On the other hand, when heating is performed at a temperature of 40 ° C. or higher, ion exchange proceeds in about 1 to 4 hours. Therefore, it is preferable to perform ion exchange by heating.

When a small amount of ions are ion-exchanged with the acid group of the electrolyte, the amount of counter anion contained in the treatment liquid is small, so that the battery performance is not hindered and washing with water is not particularly required.
However, when ion exchange of 1% or more of the protons in the electrolyte is performed, electrode poisoning due to counter anions cannot be ignored, ion conductivity of condensed water increases, and piping 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.

In addition, when impurity metal ions such as Fe ²⁺ , Fe ³⁺ , Cu ²⁺ , Ru ³⁺ , and Pd ²⁺ are mixed in the treatment solution, the desired ions are converted into a polymer electrolyte (particularly, carbonized). When introduced into the hydrogen-based electrolyte), these impurity metal ions are also ion-exchanged at the same time, which may greatly deteriorate the resistance of the electrolyte to hydrogen peroxide. Therefore, it is necessary to pay sufficient attention to the impurity concentration in the reagent used for ion exchange and the dissolution of metal ions from the processing vessel. The allowable concentration of these metal ions in the treatment solution is 0.1 ppm or less, preferably 0.001 ppm (10 ppb) or less.
On the other hand, alkali metal ions and alkaline earth metal ions such as ammonium ion, sodium ion, magnesium ion, and calcium ion are about several ppm (impurity acid group of the electrolyte) as impurity ions in the treatment liquid in order to improve hydrogen peroxide resistance. Up to 5%).

[2.2.3. Ion introduction amount]
In any case where ions other than protons are added as a compound or introduced by ion exchange, the amount of ion introduction is preferably 0.5 to 5% in terms of the acid group ratio of the electrolyte contained in MEA. Since the ion introduction amount is as described above, a detailed description is omitted.

[3. Operation of polymer electrolyte fuel cell and method for producing the same]
The total Fe content refers to the total amount of iron ions extracted by boiling the MEA or its constituents or those incinerated in aqua regia. The problem in terms of durability is not the total Fe content but the concentration of soluble iron ions. That is, even if the total Fe content exceeds 10 ppm, Fe is a poorly soluble iron compound (for example, iron oxide, iron tungstate, iron oxide (including complex oxides such as Fe—Ni—Cr—O)). ) Etc.), these iron compounds do not exhibit Fenton activity that radically decomposes hydrogen peroxide, and conversely, hydrogen peroxide is converted to 2H ₂ O ₂ → 2H on the surface of the iron compound. ₂ O + O ₂ and non-radical decomposition (ionic decomposition, catalytic decomposition). That is, since hydrogen peroxide is rendered harmless, the deterioration of the polymer is suppressed. Therefore, there may be no correlation between the total Fe content and the durability of MEA.

On the other hand, soluble Fe ions exhibit high Fenton activity. Therefore, if the amount of soluble Fe ions in the electrolyte can be reduced to 10 ppm or less, the durability of the fuel cell can be improved. However, it is known that the state of Fe in the iron compound takes +2 and +3. Further, among iron compounds, Fe ³⁺ ion compounds are hardly soluble and are difficult to remove only by acid cleaning.
In contrast, when the reduction treatment is performed before or simultaneously with the acid cleaning, the hardly soluble Fe ³⁺ ions become soluble Fe ²⁺ ions. Therefore, it can be easily removed by acid cleaning, and the amount of soluble iron ions can be easily reduced to 10 ppm or less.

Fig. 1 shows hydrogen peroxide vapor exposure test after perfluoro-type electrolyte membrane and hydrocarbon-type electrolyte membrane are immersed in aqueous iron sulfate (Fe ²⁺ ) solution at various concentrations at 80 ° C for 8 hours, and ion exchange of Fe ²⁺ is performed. The change in film weight when (3 wt% H ₂ O ₂ , 120 ° C. × 5 hr) is performed is shown. As can be seen from FIG. 1, the hydrogen peroxide vapor resistance of the hydrocarbon-based electrolyte membrane is highly dependent on the Fe concentration, and further, the deterioration suppressing action due to the excess iron ions found in the perfluoro-based electrolyte membrane is not observed. This is compared to the perfluorinated electrolyte membrane, the hydrocarbon-based electrolyte membrane, because the basic skeleton is fragile, · OH radicals OH by Fe ²⁺ ions ^- before being reduced to ions, produced by Fenton reaction -It shows that the film is deteriorated by OH radicals.
That is, in the hydrocarbon electrolyte membrane, it is necessary to limit the amount of soluble iron ions more than the perfluoro electrolyte membrane. Therefore, thorough removal of soluble iron ions by a combination of reduction treatment and acid cleaning is particularly effective for hydrocarbon electrolytes.

Furthermore, in addition to making soluble iron ions 10 ppm or less, if ions other than certain protons are introduced, the oxidation resistance is further improved. This is presumably because ions other than protons (for example, alkali metal ions and zinc ions) present in the electrolyte decompose H ₂ O ₂ ionic (non-radical) and render it harmless.

(Examples 1-2, Comparative Examples 1-2)
[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 a 0.05 M / L NaBH ₄ aqueous solution in a PP (polypropylene) container and stirred at 80 ° C. for 2 hours. . Thereafter, it was sufficiently washed with water.
Next, the membrane was immersed in 120 mL of a 0.1 M / L formic acid aqueous solution placed in a PP container, treated at 80 ° C. for 8 hours, and the membrane was returned to H form. After the formic acid treatment, 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 formic acid.
Next, a solution obtained by dissolving Ce (NO ₃ ) ₃ .6H ₂ O at a concentration of 0.9 mM / L in 120 mL of ultrapure water is placed in a PP container, the film is immersed in the solution, and an acid group of 2.5 % Was ion exchanged with Ce ³⁺ ions. Thereafter, 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 nitrate ions (Example 1).

Separately, one membrane having the same size as above was treated at 80 ° C. for 8 hours with 120 mL of an aqueous solution in which 0.1 M / L formic acid and 0.1 M / L ascorbic acid were dissolved. Ions were removed by acid washing while reducing.
Thereafter, 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 formate ions and ascorbate ions.
Next, in the same manner as in Example 1, 2.5% of the acid groups of the membrane were ion-exchanged with Ce ³⁺ ions, and rinsing with ultrapure water at 80 ° C. × 2 hr was repeated four times, and excess nitrate ions were removed. Excluded (Example 2).

For comparison, a membrane (comparative example 1) as obtained and a membrane (comparative example 2) in which only ion exchange with Ce ³⁺ was performed without performing reduction treatment and pickling treatment were prepared.

[2. Test method]
[2.1. Dry Fenton test]
These films were subjected to a hydrogen peroxide vapor exposure 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 placed in a PE (polyethylene) container (cooled around with 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 120 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).

[2.2. Soluble iron ion content and total iron content]
The membrane after the reduction and pickling treatment was immersed in a 1 + 10 HCl solution to extract soluble iron ions.

[3. result]
Table 1 shows the results. In Examples 1 and 2, the conductivity of the recovered water is smaller than that of the untreated membrane (Comparative Example 1) or the membrane of only ion exchange without performing the reduction treatment and the acid treatment (Comparative Example 2). The degree (discharge of ionic components) is small. In Examples 1 to 2, pH is higher than Comparative Example, and F ^- elimination rate (FRR) is also smaller than that of the comparative example, the generation of hydrofluoric acid was suppressed.

(Examples 3-4, Comparative Examples 3-5)
[1. Preparation of sample]
One hydrocarbon electrolyte membrane having a size of 60 mm × 60 mm and a thickness of 10 μm was immersed in 120 mL of a 0.05 M dimethylamine borane (DMAB) aqueous solution placed in a PP container, and stirred at 80 ° C. for 1 hr. Thereafter, it was sufficiently washed with water.
Next, the membrane was immersed in 120 mL of 0.1 M formic acid aqueous solution placed in a PP container, treated at 80 ° C. for 8 hours, and the membrane was returned to H form. After the formic acid treatment, rinsing at 80 ° C. × 2 hr was repeated 4 times to remove excess formic acid.
Next, 120 mL of ultrapure water containing Zn (NO ₃ ) ₂ · 6H ₂ O or tributylmethyl carbonate is placed in a PP container, the film is immersed in the solution, and 1% of the acid groups of the film are made up of Zn ²⁺ ions or Ion exchange with phosphonium ions. Thereafter, rinsing at 80 ° C. × 2 hr was repeated 4 times to remove excess ions (Examples 3 and 4).

For comparison, a membrane as obtained (Comparative Example 3), a membrane in which 1% of the acid groups of the membrane were ion-exchanged with Zn ²⁺ ions or phosphonium ions without performing reduction treatment and pickling (Comparative Examples 4 and 5). Prepared.

[2. Test method]
Under the same conditions as in Examples 1 and 2, the dry Fenton test and the amount of soluble iron ions were measured. Further, the film shape after the dry Fenton test was visually evaluated. The case where the film shape was good and no crack was generated was indicated by “◯”, and the case where the crack was generated was indicated by “X”.

[3. result]
Table 2 shows the results. The untreated film (Comparative Example 3) was cracked when vacuum-dried after the dry Fenton test. On the other hand, none of the membranes of only ion exchange (Comparative Examples 4 and 5) and the membranes subjected to reduction treatment + pickling treatment + ion exchange (Examples 3 to 4) were cracked. Further, in Examples 3 to 4, the amount of soluble iron ions was 10 ppm or less.

  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 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.
In addition, the use of a solid polymer electrolyte with a small amount of soluble iron ions is not limited to the electrolyte membrane or electrolyte in a catalyst layer of a solid polymer fuel cell, but a water electrolysis device, a hydrohalic acid electrolysis device, a salt solution It can also be used as electrolyte membranes, electrode materials, etc. used in various electrochemical devices such as electrolyzers, oxygen and / or hydrogen concentrators, humidity sensors, gas sensors and the like.

Claims (13)

Provided with a membrane electrode assembly in which electrodes are bonded on both sides of the electrolyte membrane,
The membrane electrode assembly is
(A) The amount of soluble iron ions is 10 ppm or less per electrolyte weight, and
(B) A polymer electrolyte fuel cell in which the amount of ions other than protons having an effect of improving hydrogen peroxide resistance is 0.5 to 5% in terms of the acid group ratio of the electrolyte. At least one of the electrolyte in the catalyst layer contained in the electrolyte membrane and the electrode is a hydrocarbon electrolyte,
2. The polymer electrolyte fuel cell according to claim 1, wherein the ions other than protons are any one or more selected from alkali metal ions, phosphonium ions, nitrogen-containing cations, alkaline earth metal ions, and typical element ions. . At least one of the electrolyte in the catalyst layer included in the electrolyte membrane and the electrode is a fluorine-based electrolyte,
2. The polymer electrolyte fuel cell according to claim 1, wherein the ions other than protons are any one or more selected from phosphonium ions, nitrogen-containing cations, transition metal ions other than iron ions, and rare earth metal ions.   4. The polymer electrolyte fuel cell according to claim 1, wherein the membrane electrode assembly has a halogen ion content excluding F of 10 ppm or less per electrolyte weight. 5. Reduction / acid treatment in which reduction treatment and pickling treatment of the membrane electrode assembly or its components are performed in this order or simultaneously so that the amount of soluble iron ions contained in the membrane electrode assembly is 10 ppm or less per weight of the electrolyte. A washing process;
The membrane / electrode assembly so that the amount of ions other than protons having an effect of improving hydrogen peroxide resistance contained in the membrane / electrode assembly is 0.5 to 5% in terms of the acid group ratio of the electrolyte. Or an ion introduction step of introducing ions other than protons into the constituent elements;
A method for producing a polymer electrolyte fuel cell comprising: The reduction / pickling step includes
A reduction step of reducing the membrane electrode assembly or a component thereof in a gas phase;
The method for producing a polymer electrolyte fuel cell according to claim 5, further comprising a pickling step for pickling the membrane electrode assembly or a component thereof.   The method for producing a polymer electrolyte fuel cell according to claim 6, wherein the reduction step includes heat-treating the membrane electrode assembly or a component thereof in a hydrogen gas atmosphere at a temperature of 120 ° C. or lower. The reduction / pickling step includes
A component of the membrane electrode assembly or the membrane electrode assembly having electronic conductivity is immersed in an acid aqueous solution, and the membrane electrode assembly or the component is maintained at a potential lower than a hydrogen generation potential, and hydrogen is removed. 6. The method for producing a polymer electrolyte fuel cell according to claim 5, wherein the energization is performed while generating the polymer electrolyte fuel cell. The reduction / pickling step includes
A reduction step of reducing the membrane electrode assembly or a component thereof in a liquid phase;
Pickling step of pickling the membrane electrode assembly or its components; and
The manufacturing method of the polymer electrolyte fuel cell of Claim 5 provided with these. The reduction step is to reduce the membrane electrode assembly or a component thereof using a reducing solution containing a borohydride compound,
10. The polymer electrolyte fuel cell according to claim 9, wherein the pickling step is a step of pickling the membrane electrode assembly or a component thereof using an acid aqueous solution containing sulfuric acid, formic acid, or heteropolyacid. Method. 6. The production of a polymer electrolyte fuel cell according to claim 5, wherein the reduction / pickling step performs pickling simultaneously with the reduction of the membrane electrode assembly or its constituent elements using an acidic reducing agent solution. Method. The method for producing a polymer electrolyte fuel cell according to claim 11, wherein the reducing agent solution includes a mixture of formic acid and hydroxycarboxylic acid, a mixture of formic acid and ascorbic acid, or a mixture of formic acid and heteropolyacid.   13. The ion exchange of the electrolyte according to claim 5, wherein the ion-introducing step performs ion exchange of the electrolyte using a compound composed of an ion other than the proton and a counter ion not containing a halogen element (excluding F). A method for producing a polymer electrolyte fuel cell according to claim 1.

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