WO2023085206A1 - Solid polymer-type water electrolysis membrane-electrode joint body and water electrolysis device - Google Patents

Abstract

Provided are a solid polymer-type water electrolysis membrane-electrode joint body and a water electrolysis device, which can achieve a low electrolytic voltage and can suppress degradation of a fluorine-containing polymer included therein.　A solid polymer-type water electrolysis membrane-electrode joint body according to the present invention: includes a solid polymer electrolysis membrane containing a fluorine-containing polymer having an ion exchange group, a cathode catalyst layer disposed on one surface side of the solid polymer electrolysis membrane and containing a fluorine-containing polymer having an ion exchange group, and an anode catalyst layer disposed on the other surface side of the solid polymer electrolysis membrane; contains cerium ions in a region overlapping the cathode catalyst layer when the surface of the solid polymer-type water electrolysis membrane-electrode joint body is observed in a normal line direction; and satisfies the relation of formula (X). In formula (X), A_Ce represents the substance quantity of cerium ions contained in said region, and A_{IEG_C} represents the substance quantity of the ion exchange groups in the fluorine-containing polymer contained in the cathode catalyst layer. Formula (X): (A_Ce×3)/A_{IEG_C}≤0.90

Description

Solid polymer type membrane electrode assembly for water electrolysis and water electrolysis device

The present invention relates to a polymer electrolyte membrane electrode assembly for water electrolysis and a water electrolysis device.

From the point of view of power-to-gas, that is, surplus electric power is converted into gas for storage and utilization, the use of polymer electrolyte water electrolyzers (PEM water electrolyzers) is being studied.
For example, Patent Document 1 discloses a solid polymer type water electrolysis device having a membrane electrode assembly including an anode and a cathode each having a catalyst layer, and a solid polymer electrolyte membrane disposed between the anode and the cathode. It is

WO2019/088299

In recent years, there has been a demand for further improvement in the performance of water electrolysis devices, and specifically, it is demanded that the electrolysis voltage can be lowered.
When the inventors of the present invention evaluated a water electrolysis apparatus including a membrane electrode assembly as described in Patent Document 1, it was found that although a low electrolysis voltage could be achieved, the decomposition of the fluorine-containing polymer contained in the membrane electrode assembly was observed. I found that it can happen.

The present invention has been made in view of the above problems, and aims to provide a polymer electrolyte membrane electrode assembly for water electrolysis and a water electrolysis apparatus that can achieve a low electrolysis voltage and suppress decomposition of the fluorine-containing polymer contained therein. and

As a result of intensive studies on the above problems, the present inventors have found that a solid polymer type having an anode catalyst layer, a cathode catalyst layer, and a solid polymer electrolyte membrane disposed between the anode catalyst layer and the cathode catalyst layer In the membrane electrode assembly for water electrolysis, when observed from the normal direction of the surface of the solid polymer membrane electrode assembly for water electrolysis, cerium ions are contained in the region overlapping with the cathode catalyst layer, and the above The inventors have found that a desired effect can be obtained if the amount of cerium ions in the region and the amount of ion-exchange groups in the fluorine-containing polymer contained in the cathode catalyst layer satisfy a predetermined relationship, leading to the present invention. .

That is, the inventors have found that the above problems can be solved by the following configuration.
[1] a solid polymer electrolyte membrane containing a fluorine-containing polymer having ion exchange groups;
a cathode catalyst layer containing a fluorine-containing polymer having an ion-exchange group, disposed on one side of the solid polymer electrolyte membrane;
A polymer electrolyte membrane electrode assembly for water electrolysis, comprising an anode catalyst layer disposed on the other side of the solid polymer electrolyte membrane,
When observed from the normal direction of the surface of the polymer electrolyte membrane electrode assembly for water electrolysis, the region overlapping with the cathode catalyst layer contains cerium ions,
A polymer electrolyte membrane electrode assembly for water electrolysis, characterized in that it satisfies the relationship of formula (X).
(A _Ce × 3)/A _{IEG_C} ≤ 0.90 Formula (X)
In formula (X), A _Ce represents the substance amount (mol) of cerium ions contained in the region, and A _{IEG_C} represents the substance amount (mol) of the ion exchange groups in the fluorine-containing polymer contained in the cathode catalyst layer. mol).
[2] The membrane electrode junction for solid polymer type water electrolysis according to [1], wherein the ion exchange capacity of the fluorine-containing polymer contained in the solid polymer electrolyte membrane is 1.10 meq/g dry resin or more. body.
[3] The content of the fluorine-containing polymer contained in the solid polymer electrolyte membrane is 80 to 100% by mass with respect to the total mass of the polymer in the solid polymer electrolyte membrane, [1] or [ 2].
[4] The solid polymer membrane electrode assembly for water electrolysis according to any one of [1] to [3], wherein the cerium ions are contained in the solid polymer electrolyte membrane.
[5] The polymer electrolyte membrane electrode assembly for water electrolysis according to any one of [1] to [4], wherein the cathode catalyst layer contains the cerium ions.
[6] The solid polymer-type water according to any one of [1] to [5], wherein the ion-exchange group possessed by the fluorine-containing polymer contained in the solid polymer electrolyte membrane is a sulfonic acid-type functional group. Membrane electrode assembly for electrolysis.
[7] A group in which the fluorine-containing polymer contained in the solid polymer electrolyte membrane consists of a unit represented by formula (1-3) below and a unit represented by formula (1-4) below. The solid polymer membrane electrode assembly for water electrolysis according to any one of [1] to [6], comprising at least one unit selected from
In formulas (1-3) and (1-4) described below, R ^f1 is a perfluoroalkylene group that may contain an oxygen atom between the carbon atoms and the carbon atoms, and R ^f2 is a single bond or a carbon a perfluoroalkylene group optionally containing an oxygen atom between atoms, R ^f3 is a single bond or a perfluoroalkylene group optionally containing an oxygen atom between carbon atoms, r is is 0 or 1, m is 0 or 1, and M is a hydrogen atom, an alkali metal or a quaternary ammonium cation.
[8] The solid polymer membrane electrode assembly for water electrolysis according to any one of [1] to [7], wherein the solid polymer electrolyte membrane further contains a reinforcing material.
[9] the polymer electrolyte membrane electrode assembly for water electrolysis according to any one of [1] to [8];
a power supply section connected to the cathode catalyst layer side and the anode catalyst layer side of the polymer electrolyte membrane electrode assembly for water electrolysis;
and a water supply unit that supplies water to the anode catalyst layer side.

According to the present invention, it is possible to provide a polymer electrolyte membrane electrode assembly for water electrolysis and a water electrolysis device that can achieve a low electrolysis voltage and suppress decomposition of the fluorine-containing polymer contained therein.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows typically an example of the solid polymer type membrane electrode assembly for water electrolysis of this invention. FIG. 2 is a plan view schematically showing an example of the surface of the polymer electrolyte membrane electrode assembly for water electrolysis of the present invention observed from the normal direction.

The following term definitions apply throughout the specification and claims unless otherwise indicated.
An "ion-exchange group" is a group capable of exchanging at least part of the ions contained in this group with other ions, and examples thereof include the following sulfonic acid-type functional groups and carboxylic acid-type functional groups.
A "sulfonic acid-type functional group" means a sulfonic acid group (--SO ₃ H) or a sulfonic acid group. Here, the form of the sulfonate group includes, for example, (-SO ₃ ^- )Ma ⁺ , (-SO ₃ ^- ) ₂ Mb ²⁺ and (-SO ₃ ^- ) ₃ Mc ³⁺ (with the proviso that Ma ⁺ is an alkali metal ion or a quaternary ammonium cation, Mb ²⁺ is a divalent metal ion and Mc ³⁺ is a trivalent metal ion). When there are two ligands, the number of ion-exchange groups is counted as two, and when there are three ligands, the number of ion-exchange groups is counted as three.
"Carboxylic acid-type functional group" means a carboxylic acid group (--COOH) or a carboxylic acid group. Examples of forms of carboxylic acid groups include (-COO ^- ) Ma ⁺ , (-COO ^- ) ₂ Mb ²⁺ and (-COO ^- ) ₃ Mc ³⁺ (where Ma ⁺ is alkaline are metal ions or quaternary ammonium cations, Mb ²⁺ is a divalent metal ion and Mc ³⁺ is a trivalent metal ion). When there are two ligands, the number of ion-exchange groups is counted as two, and when there are three ligands, the number of ion-exchange groups is counted as three.
A "precursor membrane" is a membrane comprising a polymer having groups that can be converted to ion exchange groups.
The “group convertible to an ion-exchange group” means a group convertible to an ion-exchange group by treatment such as hydrolysis treatment or acidification treatment.
The “group convertible to a sulfonic acid type functional group” means a group convertible to a sulfonic acid type functional group by treatment such as hydrolysis treatment or acidification treatment.
The “group convertible to a carboxylic acid type functional group” means a group convertible to a carboxylic acid type functional group by a known treatment such as hydrolysis treatment or acidification treatment.

A "unit" in a polymer means an atomic group derived from one molecule of a monomer formed by polymerizing the monomer. The unit may be an atomic group directly formed by the polymerization reaction, or may be an atomic group in which a part of the atomic group is converted to another structure by treating the polymer obtained by the polymerization reaction. good.

A numerical range expressed using "~" means a range that includes the numerical values described before and after "~" as lower and upper limits. In the numerical ranges described stepwise in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the upper limit or lower limit of another numerical range described stepwise. Moreover, in the numerical ranges described in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the values shown in the examples.

[Membrane electrode assembly]
The polymer electrolyte membrane electrode assembly for water electrolysis of the present invention (hereinafter also simply referred to as "membrane electrode assembly") is a fluorine-containing polymer having ion exchange groups (hereinafter simply "fluoropolymer (I)"). and a fluoropolymer having ion-exchange groups disposed on one side of the solid polymer electrolyte membrane (hereinafter simply referred to as "fluoropolymer (II)"). and an anode catalyst layer disposed on the other side of the solid polymer electrolyte membrane. In addition, the membrane electrode assembly of the present invention contains cerium ions in the region overlapping with the cathode catalyst layer when observed from the normal direction of the surface of the membrane electrode assembly. Moreover, the membrane electrode assembly of the present invention satisfies the relationship of formula (X) described later.
INDUSTRIAL APPLICABILITY The membrane electrode assembly of the present invention can achieve a low electrolysis voltage and suppress decomposition of the fluoropolymer contained in the membrane electrode assembly when applied to a water electrolysis apparatus. Although the details of this reason have not been clarified, it is presumed to be due to the following reason.

During operation of the water electrolyzer, hydrogen peroxide may be generated in the system. When OH radicals generated from hydrogen peroxide react with the fluorine-containing polymer contained in the solid polymer electrolyte membrane or the cathode catalyst layer, there is a problem that the fluorine-containing polymer is decomposed.
To address this problem, the present inventors have found that the decomposition of the fluoropolymer can be suppressed by using a membrane electrode assembly containing cerium ions. That is, it is presumed that the decomposition of the fluorine-containing polymer was suppressed as a result of quenching of OH radicals by cerium ions.

Here, although the inclusion of cerium ions provides the above advantages, depending on the content of cerium ions, the proton conductivity of the fluorine-containing polymer having ion exchange groups in the solid polymer electrolyte membrane or catalyst layer may decrease. Therefore, the electrolysis voltage may be high. Therefore, there is a trade-off relationship between achieving a low electrolysis voltage and suppressing decomposition of the fluoropolymer.
Regarding this problem, when observed from the normal direction of the surface of the membrane electrode assembly, the amount of cerium ions contained in the region overlapping the cathode catalyst layer and the fluorine-containing content of the cathode catalyst layer If the amount of ion exchange groups in the polymer (fluoropolymer (II)) satisfies the following formula (X), a low electrolysis voltage can be achieved even when the membrane electrode assembly contains cerium ions. The inventors have found that it is possible.

(A _Ce × 3)/A _{IEG_C} ≤ 0.90 Formula (X)
In formula (X), A _Ce represents the amount (mol) of cerium ions contained in the above region, and A _{IEG_C} represents ions in the fluorine-containing polymer (fluorine-containing polymer (II)) contained in the cathode catalyst layer. It represents the amount (mol) of the exchange group.
Note that “3” in “A _Ce ×3” means the valence of cerium ions.

Here, cations constituting ion-exchange groups in the fluoropolymer (fluoropolymer (II)) contained in the cathode catalyst layer (for example, H ⁺ when the ion-exchange groups are —SO ₃ H) are replaced by cerium ions present in the vicinity of the cathode catalyst layer. In a water electrolyzer, water moves from the anode side to the cathode side, so cerium ions contained in the membrane electrode assembly tend to gather on the cathode side. Therefore, in the above formula (X), the relationship between the substance amount (mol) of the ion-exchange groups in the fluorine-containing polymer contained in the cathode catalyst layer and the substance amount (mol) of the cerium ions contained in the region is I am paying attention.
The above formula (X) is an index showing the extent to which the cations constituting the ion-exchange groups of the fluoropolymer (II) are likely to be replaced by cerium ions. For example, when (A _Ce ×3)/A _{IEG_C} is 1 or more, it means that all the cations of the ion exchange groups in the fluoropolymer (II) may be replaced with cerium ions. do.
The present inventors found that even when all the cerium ions contained in the above region are replaced with cations constituting the ion-exchange groups of the fluoropolymer (II), ion exchange It is presumed that the presence of a certain amount of groups left the fluorine-containing polymer (II) with good proton conductivity, thereby achieving a low electrolysis voltage.

In the formula (X), (A _Ce ×3)/A _{IEG_C} is 0.90 or less, and from the viewpoint of further reducing the electrolysis voltage, it is preferably 0.80 or less, more preferably 0.60 or less, and 0.50. More preferred are:
In the formula (X), (A _Ce ×3)/A _{IEG_C} is preferably 0.01 or more, more preferably 0.10 or more, and further preferably 0.30 or more, because the decomposition of the fluoropolymer can be further suppressed. preferable.

A _Ce is preferably 0.02 μmol or more, more preferably 0.20 μmol or more, and even more preferably 0.60 μmol or more, from the viewpoint of further suppressing the decomposition of the fluoropolymer.
A _Ce is preferably 2.00 μmol or less, more preferably 1.90 μmol or less, and even more preferably 1.40 μmol or less, in terms of further reducing the electrolysis voltage.

A _{IEG_C} is preferably 1.00 μmol or more, more preferably 1.50 μmol or more, in terms of further reducing the electrolysis voltage and providing sufficient mechanical strength to the catalyst layer.
A _{IEG_C} is preferably 25.00 μmol or less, more preferably 10.00 μmol or less, and even more preferably 8.00 μmol or less, in terms of further reducing the electrolysis voltage.

A _Ce and A _{IEG_C} are determined by the method described in the Examples section below.

FIG. 1 is a cross-sectional view schematically showing an example of the membrane electrode assembly of the present invention. In the example of FIG. 1, the membrane electrode assembly 20 includes the electrolyte membrane 10, the cathode catalyst layer 26B disposed in contact with one surface of the electrolyte membrane 10, and the cathode catalyst layer 26B opposite the electrolyte membrane 10. The cathode gas diffusion layer 28B arranged on the side surface, the anode catalyst layer 26A arranged in contact with the other surface of the electrolyte membrane 10, and the surface of the anode catalyst layer 26A opposite to the electrolyte membrane 10 and a disposed anode gas diffusion layer 28A.

Although the example of FIG. 1 shows the case where the electrolyte membrane has a single-layer structure, the electrolyte membrane may have a multi-layer structure. A specific aspect of the electrolyte membrane having a multilayer structure is an aspect in which a plurality of electrolyte membranes having different ion exchange capacities are laminated.

<Electrolyte membrane>
The electrolyte membrane contains the fluoropolymer (I).

The thickness of the electrolyte membrane is preferably 30 μm or more.
The thickness of the electrolyte membrane is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 100 μm or less.
When the electrolyte membrane has a multilayer structure, the thickness of the electrolyte membrane means the total thickness of each layer.
The thickness of the electrolyte membrane is measured using a magnified image (for example, objective lens magnification of 50) of the cross section of the electrolyte membrane photographed by a laser microscope (product name “VK-X1000”, manufactured by Keyence Corporation).

(Fluorine-containing polymer (I))
The ion-exchange capacity of the fluoropolymer (I) is preferably 1.10 meq/g dry resin or more, more preferably 1.25 meq/g dry, because the electrolysis voltage can be further reduced when applied to a water electrolysis device. Resin or greater is more preferred, and 1.40 meq/g dry resin or greater is even more preferred.
From the viewpoint of the strength of the membrane electrode assembly, the ion exchange capacity of the fluoropolymer (I) is preferably 1.90 meq/g dry resin or less, more preferably 1.80 meq/g dry resin or less.
The fluorine-containing polymer (I) may be used alone, or two or more may be laminated or mixed to be used.

The electrolyte membrane may contain a polymer other than the fluoropolymer (I), but the polymer in the electrolyte membrane is preferably substantially composed of the fluoropolymer (I) in order to further reduce the electrolysis voltage. . Consisting essentially of the fluoropolymer (I) means that the content of the fluoropolymer (I) is 95% by mass or more with respect to the total mass of the polymer in the electrolyte membrane. The upper limit of the content of the fluoropolymer (I) is 100% by mass relative to the total mass of the polymer in the electrolyte membrane.
Specific examples of polymers other than the fluoropolymer (I) include polymers of heterocyclic compounds containing at least one nitrogen atom in the ring, and at least one nitrogen atom in the ring and an oxygen atom and/or or one or more polyazole compounds selected from the group consisting of polymers of heterocyclic compounds containing sulfur atoms.
Specific examples of polyazole compounds include polyimidazole compounds, polybenzimidazole compounds, polybenzobisimidazole compounds, polybenzoxazole compounds, polyoxazole compounds, polythiazole compounds, and polybenzothiazole compounds.
From the standpoint of oxidation resistance of the electrolyte membrane, other polymers include polyphenylene sulfide resins and polyphenylene ether resins.

The fluoropolymer (I) has ion exchange groups. Specific examples of ion exchange groups include sulfonic acid-type functional groups and carboxylic acid-type functional groups. Functional groups are preferred.
Hereinafter, embodiments of the fluoropolymer having a sulfonic acid-type functional group (hereinafter also referred to as "fluoropolymer (S)") will be mainly described in detail.

The fluorine-containing polymer (S) preferably contains units based on a fluorine-containing olefin and units having a sulfonic acid-type functional group and a fluorine atom.
Examples of fluorine-containing olefins include fluoroolefins having 2 to 3 carbon atoms and having one or more fluorine atoms in the molecule. Specific examples of fluoroolefins include tetrafluoroethylene (hereinafter also referred to as “TFE”), chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride, and hexafluoropropylene. Among these, TFE is preferable from the viewpoint of the production cost of the monomer, the reactivity with other monomers, and the excellent properties of the obtained fluoropolymer (S).
A fluorine-containing olefin may be used individually by 1 type, and may be used in combination of 2 or more type.

A unit represented by the formula (1) is preferable as the unit having a sulfonic acid type functional group and a fluorine atom.
Formula (1) -[CF ₂ -CF(-L-(SO ₃ M) _n )]-

In formula (1), L is an n+1-valent perfluorohydrocarbon group which may contain an etheric oxygen atom.
The etheric oxygen atom may be located terminally or between carbon atoms in the perfluorohydrocarbon group.
The number of carbon atoms in the n+1-valent perfluorohydrocarbon group is preferably 1 or more, particularly preferably 2 or more, preferably 20 or less, and particularly preferably 10 or less.

L is preferably an n+1 valent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, and a divalent perfluoroalkylene group which may contain an etheric oxygen atom, in which n=1. , or a trivalent perfluoroaliphatic hydrocarbon group optionally containing an etheric oxygen atom, in which n=2, is particularly preferred.
The divalent perfluoroalkylene group may be linear or branched.

In formula (1), M is a hydrogen atom, an alkali metal or a quaternary ammonium cation. Also, when there are multiple Ms, the multiple Ms may be different.
In formula (1), n is 1 or 2.

The unit represented by formula (1) includes a unit represented by formula (1-1), a unit represented by formula (1-2), a unit represented by formula (1-3), or a unit represented by formula ( The unit represented by 1-4) is preferable, and the unit represented by formula (1-3) or the unit represented by formula (1-4) can further reduce the electrolysis voltage when applied to a water electrolysis device. units are more preferred.

Formula (1-1) -[CF ₂ -CF(-OR ^f1 -SO ₃ M)]-
Formula (1-2) -[CF ₂ -CF(-R ^f1 -SO ₃ M)]-

In the above formula, R ^f1 is a perfluoroalkylene group optionally containing an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, preferably 20 or less, and particularly preferably 10 or less.

In the above formula, R ^f2 is a single bond or a perfluoroalkylene group optionally containing an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, preferably 20 or less, and particularly preferably 10 or less.

In the above formula, R ^f3 is a single bond or a perfluoroalkylene group optionally containing an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, particularly preferably 2 or more, preferably 20 or less, and particularly preferably 10 or less.

In the above formula, r is 0 or 1.
In the above formula, m is 0 or 1.
M is a hydrogen atom, an alkali metal or a quaternary ammonium cation. Also, when there are multiple Ms, the multiple Ms may be different.

As the unit represented by formula (1-1) and the unit represented by formula (1-2), the unit represented by formula (1-5) is more preferable.
Formula (1-5) -[CF ₂ -CF(-(CF ₂ ) _x -(OCF ₂ CFY) _y -O-(CF ₂ ) _z -SO ₃ M)]-
In formula (1-5), x is 0 or 1, y is an integer from 0 to 2, z is an integer from 1 to 4, and Y is F or _CF3 . M is as described above.

Specific examples of units represented by formula (1-1) include the following units. w in the formula is an integer of 1-8, and x is an integer of 1-5. The definition of M in the formula is as described above.
-[ _CF2 -CF(-O-( _CF2 ) _w - _SO3M )]-
-[ _CF2 -CF(-O- _CF2CF ( _CF3 )-O-( _CF2 ) _{w- SO3M} )]-
-[ _CF2 -CF(-(O- _CF2CF ( _CF3 )) _x - _SO3M )]-

Specific examples of units represented by formula (1-2) include the following units. w in the formula is an integer of 1-8. The definition of M in the formula is as described above.
-[ _CF2 -CF(-( _CF2 ) _w - _SO3M )]-
-[ _CF2 -CF( _-CF2 -O-( _CF2 ) _w - _SO3M )]-

Units represented by formula (1-3) are preferably units represented by formula (1-3-1). The definition of M in the formula is as described above.

In formula (1-3-1), R ^f4 is a linear perfluoroalkylene group having 1 to 6 carbon atoms, and R ^f5 may contain a single bond or an oxygen atom between carbon atoms. It is a linear perfluoroalkylene group having 1 to 6 carbon atoms. The definitions of r and M are as described above.

Specific examples of units represented by formula (1-3-1) include the following.

As the unit represented by formula (1-4), a unit represented by formula (1-4-1) is preferable. The definitions of R ^f1 , R ^f2 and M in the formula are as described above.

Specific examples of units represented by formula (1-4-1) include the following.

Units having a sulfonic acid-type functional group and a fluorine atom may be used singly or in combination of two or more.

The fluorine-containing polymer (I) may contain units based on other monomers other than units based on the fluorine-containing olefin and units having a sulfonic acid type functional group and a fluorine atom.
Specific examples of other monomers include CF ₂ =CFR ^f6 (where R ^f6 is a perfluoroalkyl group having 2 to 10 carbon atoms), CF ₂ =CF-OR ^f7 (where R ^f7 has 1 carbon 1 to 10 perfluoroalkyl groups), CF ₂ =CFO(CF ₂ ) _v CF=CF ₂ (where v is an integer of 1 to 3).
The content of units derived from other monomers is preferably 30% by mass or less with respect to all units in the fluoropolymer (I) from the viewpoint of maintaining ion exchange performance.

The content of the fluoropolymer (I) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, based on the total mass of the electrolyte membrane, from the viewpoint of reducing the electrolysis voltage.

(reinforcing material)
The electrolyte membrane may further contain a reinforcing material. Thereby, the strength of the electrolyte membrane can be improved.
Specific examples of reinforcing materials include porous bodies, fibers, woven fabrics, and non-woven fabrics.
The reinforcing material is polytetrafluoroethylene (hereinafter also referred to as "PTFE"), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (hereinafter also referred to as "PFA"), polyether ether ketone, and polyphenylene sulfide. It is preferably composed of at least one material selected from the group consisting of

When the electrolyte membrane contains a reinforcing material, the content of the reinforcing material is preferably 3% by mass or more, more preferably 5% by mass or more, and preferably 50% by mass or less, with respect to the total mass of the electrolyte membrane. % by mass or less is more preferable, and 30% by mass or less is even more preferable.

(other ingredients)
The electrolyte membrane may further contain components other than those described above. Specific examples of such components include cerium ions. Details of the cerium ion will be described later.
When the electrolyte membrane contains cerium ions, the ratio of the amount of cerium ions to the amount of ion-exchange groups of the fluoropolymer (I) in the electrolyte membrane is preferably 1 mol % or less, more preferably 0.5 mol % or less. , 0.4 mol % or less is more preferable.

(Manufacturing method of electrolyte membrane)
As an example of a method for producing an electrolyte membrane, a polymer of a fluoromonomer having a group convertible to an ion-exchange group (hereinafter also referred to as a fluoromonomer (I′)) (hereinafter referred to as a “fluoropolymer (I′)”) ), and optionally a reinforcing material (hereinafter also referred to as "precursor membrane") is produced, and then groups convertible to ion-exchange groups in the precursor membrane are ion-exchanged. A method of converting to a group is exemplified. An electrolyte membrane is thus obtained.
Further, as a method for producing an electrolyte membrane containing cerium ions, the electrolyte membrane obtained as described above is immersed in a solution containing a water-soluble cerium salt, and then the membrane is dried to obtain an electrolyte membrane containing cerium ions. is obtained. Specific examples of water-soluble cerium salts include cerium acetate, cerium chloride, cerium nitrate, cerium sulfate, and cerium carbonate.

As the fluoropolymer (I'), a polymer of a fluoromonomer having a group convertible to a sulfonic acid type functional group (hereinafter also referred to as "fluoromonomer (S')") (hereinafter referred to as "fluoropolymer ( S′)”) is preferred, and copolymers of a fluorine-containing olefin with a monomer having a group convertible to a sulfonic acid type functional group and a fluorine atom are particularly preferred.
The fluorine-containing polymer (S') will be described in detail below.

Known methods such as solution polymerization, suspension polymerization, and emulsion polymerization can be employed for copolymerizing the fluoropolymer (S').

Examples of the fluorine-containing olefin include those exemplified above, and TFE is preferable from the viewpoint of the production cost of the monomer, reactivity with other monomers, and excellent properties of the obtained fluorine-containing polymer (S).
A fluorine-containing olefin may be used individually by 1 type, and may be used in combination of 2 or more type.

Examples of the fluorine-containing monomer (S') include compounds having one or more fluorine atoms in the molecule, having an ethylenic double bond, and having a group convertible to a sulfonic acid type functional group. .
As the fluorine-containing monomer (S'), a compound represented by formula (2) is preferable from the viewpoints of production cost of the monomer, reactivity with other monomers, and excellent properties of the obtained fluorine-containing polymer (S).
Formula (2) CF ₂ = CF-L-(A) _n
The definitions of L and n in formula (2) are as described above.
A is a group that can be converted to a sulfonic acid type functional group. The group convertible to a sulfonic acid type functional group is preferably a functional group convertible to a sulfonic acid type functional group by hydrolysis. Specific examples of groups convertible to sulfonic acid-type functional groups include -SO ₂ F, -SO ₂ Cl, and -SO ₂ Br.

The compounds represented by formula (2) include compounds represented by formula (2-1), compounds represented by formula (2-2), compounds represented by formula (2-3) and formula ( Compounds represented by 2-4) are preferred.
Formula (2-1) CF ₂ =CF-OR ^f1 -A
Formula (2-2) CF ₂ =CF-R ^f1 -A

The definitions of R ^f1 , R ^f2 , r and A in the formula are as described above.

The definitions of R ^f1 , R ^f2 , R ^f3 , r, m and A in the formula are as described above.

As the compound represented by formula (2-1) and the compound represented by formula (2-1), the compound represented by formula (2-5) is preferable.
Formula (2-5) _CF2 =CF-( _CF2 ) _x- ( _OCF2CFY ) _y -O-( _CF2 ) _z - _SO3M
The definitions of M, x, y, z and Y in the formula are as described above.

Specific examples of the compound represented by formula (2-1) include the following compounds. w in the formula is an integer of 1-8, and x is an integer of 1-5.
_CF2 =CF-O-( _CF2 ) _w - _SO2F
CF2 =CF-O- _CF2CF ( _CF3 )-O-( _CF2 ) _{w- SO2F}
CF ₂ =CF-[O-CF ₂ CF(CF ₃ )] _x -SO ₂ F

Specific examples of the compound represented by formula (2-2) include the following compounds. w in the formula is an integer of 1-8.
CF ₂ =CF-(CF ₂ ) _w -SO ₂ F
_CF2 =CF-CF2 _- O-( _CF2 ) _w - _SO2F

The compound represented by formula (2-3) is preferably a compound represented by formula (2-3-1).

The definitions of R ^f4 , R ^f5 , r and A in the formula are as described above.

Specific examples of the compound represented by formula (2-3-1) include the following.

The compound represented by formula (2-4) is preferably a compound represented by formula (2-4-1).

The definitions of R ^f1 , R ^f2 and A in the formula are as described above.

Specific examples of the compound represented by formula (2-4-1) include the following.

The fluorine-containing monomer (S') may be used alone or in combination of two or more.
In addition to the fluorine-containing olefin and the fluorine-containing monomer (S'), other monomers may be used to produce the fluorine-containing polymer (S'). Other monomers include those exemplified above.

The ion exchange capacity of the fluoropolymer (I') can be adjusted by changing the content of groups convertible to ion exchange groups in the fluoropolymer (I').

A specific example of the method for producing the precursor film is an extrusion method.
A specific example of the manufacturing method when the precursor film contains the reinforcing material is as follows. First, a film (I') containing a fluorine-containing polymer (I') is formed. After that, the film (I'), the reinforcing material, and the film (I') are arranged in this order, and these are laminated using a lamination roll or a vacuum lamination device.

Specific examples of the method for converting the groups convertible into ion-exchange groups in the precursor film to ion-exchange groups include a method of subjecting the precursor film to hydrolysis treatment, acidification treatment, or the like.
Among them, the method of contacting the precursor film and the alkaline aqueous solution is preferable.

Specific examples of the method of contacting the precursor film with the alkaline aqueous solution include a method of immersing the precursor film in the alkaline aqueous solution and a method of spray coating the surface of the precursor film with the alkaline aqueous solution.
The temperature of the alkaline aqueous solution is preferably 30-100°C, particularly preferably 40-100°C. The contact time between the precursor film and the alkaline aqueous solution is preferably 3 to 150 minutes, particularly preferably 5 to 50 minutes.

The alkaline aqueous solution preferably contains an alkali metal hydroxide, a water-soluble organic solvent and water.
Alkali metal hydroxides include sodium hydroxide and potassium hydroxide.
As used herein, the term "water-soluble organic solvent" refers to an organic solvent that readily dissolves in water. 0.5 g or more of organic solvent is particularly preferred. The water-soluble organic solvent preferably contains at least one selected from the group consisting of aprotic organic solvents, alcohols and aminoalcohols, and particularly preferably contains aprotic organic solvents.
One of the water-soluble organic solvents may be used alone, or two or more thereof may be used in combination.

Specific examples of aprotic organic solvents include dimethylsulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and dimethylsulfoxide is preferable.
Specific examples of alcohols include methanol, ethanol, isopropanol, butanol, methoxyethoxyethanol, butoxyethanol, butylcarbitol, hexyloxyethanol, octanol, 1-methoxy-2-propanol, and ethylene glycol.
Specific examples of aminoalcohols include ethanolamine, N-methylethanolamine, N-ethylethanolamine, 1-amino-2-propanol, 1-amino-3-propanol, 2-aminoethoxyethanol, 2-aminothio ethoxyethanol, 2-amino-2-methyl-1-propanol.

The concentration of the alkali metal hydroxide in the alkaline aqueous solution is preferably 1% by mass or more, more preferably 3% by mass or more, and is preferably 60% by mass or less, more preferably 55% by mass or less.
The content of the water-soluble organic solvent is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less, in the alkaline aqueous solution.
The concentration of water is preferably 39-80% by mass in the alkaline aqueous solution.

After the precursor film is brought into contact with the alkaline aqueous solution, a treatment for removing the alkaline aqueous solution may be performed. A method for removing the alkaline aqueous solution includes, for example, a method of washing the precursor film contacted with the alkaline aqueous solution.

After contacting the precursor film with the alkaline aqueous solution, the resulting film may be contacted with an acidic aqueous solution to convert the ion-exchange groups to their acid form.
Specific examples of the method of contacting the precursor film with the acidic aqueous solution include a method of immersing the precursor film in the acidic aqueous solution and a method of spray coating the surface of the precursor film with the acidic aqueous solution.
The acidic aqueous solution preferably contains an acid component and water.
Specific examples of acid components include hydrochloric acid and sulfuric acid.

<Anode catalyst layer>
A specific example of the anode catalyst layer is a layer containing a catalyst and a polymer having ion exchange groups.
Specific examples of the catalyst include supported catalysts in which platinum, platinum alloys, or platinum-containing catalysts having a core-shell structure are supported on carbon supports, iridium oxide catalysts, alloys containing iridium oxide, and iridium oxides having a core-shell structure. catalysts. Examples of carbon supports include carbon black powder.
Polymers having ion-exchange groups include fluorine-containing polymers having ion-exchange groups. Specific examples of the fluoropolymer having ion-exchange groups may be the same as the fluoropolymer (I) contained in the electrolyte membrane described above, including preferred embodiments thereof.

The mass of the catalyst per 1 cm ² of the anode catalyst layer is preferably 0.05 mg/cm ² or more, more preferably 0.10 mg/cm ² or more, still more preferably 0.20 mg/cm ² or more, and 2.00 mg/cm 2 or more. cm ² or less is preferable, 1.50 mg/cm ² or less is more preferable, and 1.00 mg/cm ² or less is even more preferable.
The mass ratio of the catalyst to the polymer having ion-exchange groups in the anode catalyst layer (mass of catalyst/mass of polymer having ion-exchange groups) is preferably 1-4.

The anode catalyst layer may further contain components other than the above. Specific examples of such components include cerium ions. Details of the cerium ion will be described later.

The anode catalyst layer is formed, for example, by a known method using an anode catalyst ink containing a catalyst, a polymer having an ion exchange group, a solvent (water, organic solvent), and optionally a water-soluble cerium salt. can be manufactured.

The film thickness of the anode catalyst layer is preferably 5 μm or more, preferably 100 μm or less, more preferably 50 μm or less, still more preferably 30 μm or less, and particularly preferably 15 μm or less, from the viewpoint that the effect of the present invention is more excellent.
The film thickness of the anode catalyst layer is measured using an image obtained by measuring a section cut in the film thickness direction of the membrane electrode assembly with a laser microscope, and is an arithmetic average value at 20 arbitrary points.

<Cathode catalyst layer>
A specific example of the cathode catalyst layer is a layer containing a catalyst and a fluorine-containing polymer (II).
Specific examples of the catalyst are the same as those contained in the anode catalyst layer, including preferred embodiments.
Specific examples of the fluoropolymer (II) may be the same as the fluoropolymer (I) described above, including preferred embodiments thereof.

The mass of the catalyst per 1 cm ² of the cathode catalyst layer is preferably 0.05 mg/cm ² or more, more preferably 0.10 mg/cm ² or more, and preferably 1.00 mg/cm ² or less, and 0.50 mg/cm 2 or less. ² or less is more preferable, and 0.40 mg/cm ² or less is even more preferable.
The mass ratio of the catalyst to the fluoropolymer (II) in the cathode catalyst layer (mass of the catalyst/mass of the fluoropolymer (II)) is preferably 0.3 or more, preferably 1.0 or less, and 0.3. 7 or less is more preferable, and 0.5 or less is even more preferable.

The cathode catalyst layer may further contain components other than those described above. Specific examples of such components include cerium ions. Details of the cerium ion will be described later.
When the cathode catalyst layer contains cerium ions, the ratio of the amount of cerium ions to the amount of ion-exchange groups of the fluoropolymer (II) in the cathode catalyst layer is preferably 0.1 mol % or more, and preferably 0.3 mol. % or more, preferably 15 mol % or less, and more preferably 10 mol % or less.

The cathode catalyst layer is formed according to a known method using, for example, a cathode catalyst ink containing a catalyst, a fluorine-containing polymer (II), a solvent (water, organic solvent), and optionally a water-soluble cerium salt. can be manufactured.

The film thickness of the cathode catalyst layer is preferably 5 μm or more, preferably 100 μm or less, more preferably 50 μm or less, still more preferably 30 μm or less, and particularly preferably 15 μm or less, from the viewpoint that the effect of the present invention is more excellent.
The method for measuring the film thickness of the cathode is the same as the method for measuring the film thickness of the anode.

<Gas diffusion layer>
The gas diffusion layers (anode gas diffusion layer and cathode gas diffusion layer) have the function of diffusing gas uniformly in the catalyst layer and the function of current collectors. Specific examples of the gas diffusion layer include carbon paper, carbon cloth, carbon felt, titanium oxide fiber sintered bodies, and titanium oxide particle sintered bodies. The titanium oxide sintered body may be plated with platinum or the like, if necessary.
The cathode gas diffusion layer is preferably treated with PTFE or the like to make it water-repellent.
Although the membrane electrode assembly of FIG. 1 includes the anode gas diffusion layer 28A and the cathode gas diffusion layer 28A, the gas diffusion layers (anode gas diffusion layer A and cathode gas diffusion layer B) are optional members, and the membrane electrodes It does not have to be included in the conjugate.

<Cerium ion>
The cerium ions are contained in the region overlapping with the cathode catalyst layer when observed from the normal direction of the surface of the membrane electrode assembly. The cerium ions present in the above region tend to gather in the vicinity of the cathode catalyst layer due to movement of water during operation of the water electrolysis device.
The above area will be described in detail with reference to FIG. FIG. 2 is a plan view schematically showing an example of observing the surface of the membrane electrode assembly of the present invention from the normal direction. Specifically, the membrane electrode assembly 20 is observed from the direction of the arrow in FIG. It is a plan view in the case of.
As shown in FIG. 2, the cathode catalyst layer 26B is formed on part of the surface of the electrolyte membrane 10. As shown in FIG. Therefore, the above region corresponds to a portion of the membrane electrode assembly 20 where the cathode catalyst layer 26B is projected along the thickness direction (normal line) of the membrane electrode assembly 20 .
In the example of FIG. 1, the above regions are the portion of the cathode gas diffusion layer 28B that overlaps the cathode catalyst layer 26B along the thickness direction, the entire cathode catalyst layer 26B, and the electrolyte membrane 10 along the thickness direction. A portion of the cathode catalyst layer 26B that overlaps with the cathode catalyst layer 26B, a portion of the anode catalyst layer 26A that overlaps the cathode catalyst layer 26B along the thickness direction, and a portion of the anode gas diffusion layer 28A that overlaps with the cathode catalyst layer 26B along the thickness direction. It is a duplicate part.

The cerium ions need only be contained in the above region, but are preferably contained in at least one of the solid polymer electrolyte membrane present in the region and the cathode catalyst layer present in the region.
The cerium ions may be contained outside the above region as long as they are contained within the above region.

The cerium ions contained in the region are preferably trivalent cerium ions.
Specific examples of methods for introducing cerium ions into the region include a method using an electrolyte membrane containing cerium ions and a method using a cathode catalyst layer containing cerium ions.

<Method for manufacturing membrane electrode assembly>
As a method for producing a membrane electrode assembly, for example, a laminate having an anode catalyst layer and a release base material (e.g., ETFE sheet), a cathode catalyst layer and a release base material (e.g., ETFE sheet), and using a laminate having, the catalyst layers (anode catalyst layer and cathode catalyst layer) are joined to both surfaces of the electrolyte membrane, and then the releasable substrate is peeled off.
The laminate may have a gas diffusion layer between the catalyst layer and the release substrate. In this case, gas diffusion layers (anode gas diffusion layer and cathode gas diffusion layer) can be formed on the opposite side of the catalyst layer to the electrolyte membrane.
In addition, examples of the method for producing the catalyst layer include a method in which the catalyst layer-forming coating solution is applied to a predetermined position (for example, the surface of the releasable base material) and dried as necessary. The catalyst layer-forming coating liquid is a liquid in which a polymer having an ion-exchange group and a catalyst are dispersed in a dispersion medium.

<Application>
The membrane electrode assembly of the present invention is used in a solid polymer type water electrolysis device.

[Water electrolysis device]
The water electrolysis apparatus of the present invention includes the membrane electrode assembly described above, a water supply section for supplying water to the anode catalyst layer side, and a power supply section electrically connected to the anode catalyst layer side and the cathode catalyst layer side. and have
In the water electrolysis apparatus of the present invention, when a DC voltage is applied by the power supply unit while water is being supplied to the anode catalyst layer side by the water supply unit, water is decomposed on the anode catalyst layer side into oxygen. Protons are generated. Further, on the cathode catalyst layer side, the protons that have migrated to the cathode catalyst layer side via the electrolyte membrane obtain electrons to generate hydrogen.
Since the water electrolysis apparatus of the present invention includes the membrane electrode assembly described above, it is possible to suppress the decomposition of the fluoropolymer contained in the membrane electrode assembly and achieve a low electrolysis voltage.
The water electrolysis device of the present invention has the same configuration as a known water electrolysis device (for example, an oxygen recovery member for recovering the generated oxygen and a hydrogen recovery member for recovering the generated hydrogen) except for having each member described above. can have

The present invention will be described in detail below with examples. Examples 1-1 to 1-10 and Examples 2-1 to 2-3 are examples of film (layer) production, Examples 3-1 to 3-10 are examples, and Examples 4-1 to 4-1 to Example 4-3 is a comparative example. However, the present invention is not limited to these examples.

[Ion Exchange Capacity of Fluoropolymer]
The fluoropolymer was placed in a glove box in which dry nitrogen was flowed for 24 hours, and the dry mass of the fluoropolymer was measured. After that, the fluoropolymer was immersed in a 2 mol/L sodium chloride aqueous solution at 60° C. for 1 hour. After washing the fluoropolymer with ultrapure water, the ion exchange capacity (millimeter equivalents/gram dry resin) was determined.
In the tables below, IEC (meq/g) means ion exchange capacity (meq/g dry resin).

[Thickness of solid polymer electrolyte membrane]
The thickness of the solid polymer electrolyte membrane was measured using a laser microscope (product name “VK-X1000” manufactured by Keyence Corporation) under the conditions of temperature: 23° C. and relative humidity: 50% RH. It was measured using a magnified image of the cross section (objective lens magnification of 50 times).

[Substance amount of ion-exchange groups in fluorine-containing polymer]
The amount (mol) of the ion-exchange group substance contained in the fluoropolymer is obtained by obtaining the milliequivalent of the ion-exchange group from the following formula and dividing the obtained milliequivalent of the ion-exchange group by the ion valence of the ion-exchange group. calculated by For example, when the ion exchange group is a sulfonic acid group, the ion valence is one.
Milliequivalent of ion-exchange group = dry mass of fluoropolymer (g) x ion-exchange capacity (milliequivalent/g dry resin)

Here, the dry mass (g) of the fluorine-containing polymer was determined as follows.
When measuring the dry mass of a fluoropolymer using a membrane (e.g., an electrolyte membrane), the membrane is cut into 7 cm x 7 cm pieces, dried for 72 hours in a glove box in which dry nitrogen is flowed, and then placed in the same glove box. The mass was measured in
When measuring the dry mass of a fluoropolymer using a dispersion containing a fluoropolymer (for example, a dispersion containing a fluoropolymer used for producing a cathode catalyst layer), the solid content concentration (mass %) and the mass of the dispersion, the dry mass of the fluoropolymer in the dispersion was calculated.

"A _{IEG_C} ", which is the amount of ion exchange groups in the fluorine-containing polymer contained in the cathode catalyst layer, is calculated by the above-described method using the dispersion containing the fluorine-containing polymer used for manufacturing the cathode catalyst layer. bottom.

[Substance amount of cerium ion]
A method for measuring the amount of cerium ions using a membrane (for example, an electrolyte membrane) is as follows.
First, a film cut into a size of 4 cm×4 cm was immersed in 10 mL of hydrochloric acid at a temperature of 80° C. for 3 hours to extract cerium ions in the film. The film was taken out and the concentration of cerium ions in the hydrochloric acid was analyzed by ICP emission spectrometry to determine the substance amount (mol) of cerium ions contained in the film.

The amount of cerium ions in a dispersion containing a fluoropolymer (for example, a dispersion containing a fluoropolymer used for producing a cathode catalyst layer) is calculated based on the mass of the cerium salt added during production of the dispersion. bottom.

Note that "A _Ce ", which is the amount of cerium ions contained in the region overlapping the cathode catalyst layer when observed from the normal direction of the surface of the membrane electrode assembly, is the amount of cerium ions from the membrane electrode assembly to the cathode. The amount of cerium ions was measured in the same manner as in the method for measuring the amount of cerium ions using the membrane, except that a sample cut out only from the region overlapping the catalyst layer was used.
Here, the sample was obtained by cutting off the peripheral portion of the membrane electrode assembly (that is, the portion where the cathode catalyst layer was not provided), and had the same size (4 cm×4 cm) as the cathode catalyst layer. The samples include a cathode catalyst layer, an electrolyte membrane and an anode catalyst layer.

[Electrolytic voltage]
The membrane electrode assembly was sandwiched between platinum-plated titanium fiber sintered bodies (manufactured by Bekaert) with a thickness of 0.25 mm and a porosity of 60% ^. The membrane electrode assembly was incorporated into a single cell of the above and evaluated. When sandwiching the membrane electrode assembly, it was fastened so that a pressure of 1.5 MPa was applied to the electrode portion.
Next, 50 mL of pure water having a conductivity of 1.0 μS/cm or less, a temperature of 60° C. and normal pressure was applied to the anode catalyst layer side and the cathode catalyst layer side in order to sufficiently hydrate the solid polymer electrolyte membrane and both electrode ionomers. /min for 8 hours. After that, water supply to the cathode catalyst layer side is stopped, and pure water having a conductivity of 1.0 μS/cm or less and a temperature of 60° C. is supplied to the anode catalyst layer side at a flow rate of 50 mL/min, and the back pressure is applied to the anode catalyst layer. Water electrolysis was carried out as a preconditioning operation for 4 hours while maintaining the pressure at 16 A (current density 1 A/cm ² ) with a large current potentio/galvanostat HCP-803 (manufactured by Biologic) while keeping both the cathode catalyst layers at normal pressure. After that, for the main measurement, the current was increased stepwise by 2 A in the range of 0 to 48 A (current density 0 to 3 A/cm ² ). At each stage, the current was held for 5 minutes, and the electrolysis voltage at a current of 48 A (current density of 3 A/cm ² ) was evaluated according to the following criteria.
◎: less than 1.80 ○: 1.80 V or more and 1.83 V or less ×: greater than 1.83 V

[Fluorine release rate]
The membrane electrode assembly was sandwiched between platinum-plated titanium fiber sintered bodies (manufactured by Bekaert) with a thickness of 0.25 mm and a porosity of 60% ^. The membrane electrode assembly was incorporated into a single cell of the above and evaluated. When sandwiching the membrane electrode assembly, it was fastened so that a pressure of 1.5 MPa was applied to the electrode portion.
Next, 50 mL of pure water having a conductivity of 1.0 μS/cm or less, a temperature of 60° C. and normal pressure was applied to the anode catalyst layer side and the cathode catalyst layer side in order to sufficiently hydrate the solid polymer electrolyte membrane and both electrode ionomers. /min for 8 hours. After that, pure water having a conductivity of 1.0 μS/cm or less and a temperature of 60° C. was supplied to the anode catalyst layer side at a flow rate of 50 mL/min, and the back pressure was increased to normal pressure for both the anode catalyst layer and the cathode catalyst layer. Water electrolysis was carried out as a 4-hour preconditioning operation while maintaining at 16 A (current density 1 A/cm ² ) by current potentio/galvanostat HCP-803 (manufactured by Biologic). After that, the amount of water supplied to the anode catalyst layer was changed to 150 mL/min, the back pressure was changed to 50 kPa for both the anode and the cathode, and the operation was continued at a current density of 1 A/cm ² for 1000 hours.
Waste water discharged from the cathode catalyst layer side was sampled between 500 hours and 1000 hours after the break-in operation. The amount of fluoride ions contained in this waste water was quantified by ion chromatography and averaged to calculate the average amount of fluoride ions per unit electrode area/unit time, and evaluated as the fluorine release rate according to the following criteria. It can be said that the smaller the value of the fluorine release rate, the more suppressed the decomposition of the fluoropolymer.
○: Less than 3.0×10 ⁻⁶ mg/(h·cm ² ) ×: 3.0×10 ⁻⁶ mg/(h·cm ² ) or more

[Abbreviation]
_TFE : Tetrafluoroethylene PSVE _{: CF2} = _CFOCF2CF ( _CF3 ) _OCF2CF2SO2F
P2SVE: a monomer represented by the following formula m32-1

[Preparation of Solid Polymer Electrolyte Membrane]
<Example 1-1>
A polymer (ion exchange capacity: 1.25 meq/g dry resin) obtained by copolymerizing TFE and PSVE and converted into an acid form through hydrolysis and acid treatment was added to a solvent of water/ethanol = 40/60 (mass%). A dispersion liquid (hereinafter also referred to as "dispersion liquid X") was obtained by dispersing at a solid content concentration of 20.0%. The obtained dispersion liquid X was coated on a 100 μm ethylene-tetrafluoroethylene copolymer (ETFE) sheet with a die coater to form a film, which was dried at 80° C. for 15 minutes, and further dried at 160° C. for 30 minutes. A heat treatment was performed for a minute to obtain an electrolyte membrane. The coating amount of the liquid composition was adjusted so that the film thickness of the electrolyte membrane after drying was 100 μm.
Next, ultrapure water (100 g) and an electrolyte membrane having a size of 10 cm×15 cm were placed in a container made of PFA, and the electrolyte membrane was immersed in the ultrapure water. Further, a 9.8 mmol/L cerium (III) nitrate aqueous solution (1.79 g) was added, and the mixture was allowed to stand at room temperature for 16 hours. After 16 hours, the liquid in the container was discarded, and the electrolyte membrane was washed with ultrapure water. After washing, the membrane was taken out, sandwiched between filter papers and air-dried for 3 days to obtain a solid polymer electrolyte membrane M-1.
The ratio of the amount of cerium ions to the amount of ion-exchange groups in the solid polymer electrolyte membrane M-1, which is calculated from the amount of ion-exchange groups (sulfonic acid groups) and cerium ions obtained by the above method. (mol%) is shown in Table 1. In the table, the ratio of the substance amount of cerium ions to the substance amount of ion-exchange groups is abbreviated as "Ce/IEG (mol%) in the electrolyte membrane".

<Example 1-2>
A solid polymer electrolyte membrane M-2 was obtained in the same manner as in Example 1-1, except that the amount of the 9.8 mmol/L cerium (III) nitrate aqueous solution added was changed to 1.15 g. Table 1 shows the ratio (mol %) of the amount of cerium ions to the amount of ion exchange groups.

<Example 1-3>
A solid polymer electrolyte membrane M-3 was obtained in the same manner as in Example 1-1, except that the amount of the 9.8 mmol/L cerium (III) nitrate aqueous solution added was changed to 0.26 g. Table 1 shows the ratio (mol %) of the amount of cerium ions to the amount of ion exchange groups.

<Example 1-4>
As a dispersion liquid for forming a solid polymer electrolyte membrane, a polymer obtained by copolymerizing TFE and PSVE and converted into an acid form through hydrolysis and acid treatment (ion exchange capacity: 1.10 meq/g dry resin) is dispersed in a solvent of water / ethanol = 40/60 (mass%) at a solid content concentration of 26.0% (hereinafter also referred to as "dispersion liquid Y"). A solid polymer electrolyte membrane M-4 was obtained in the same manner as in Example 1-1, except that the amount of the L cerium (III) nitrate aqueous solution was changed to 1.01 g. Table 1 shows the ratio (mol %) of the amount of cerium ions to the amount of ion exchange groups.

<Example 1-5>
In the same procedure as in Example 1-1, TFE and P2SVE were copolymerized as a dispersion liquid when forming a solid polymer electrolyte membrane, and the polymer was converted into an acid form through hydrolysis and acid treatment (ion exchange capacity: 1.95 meq/g dry resin) was dispersed in a solvent of water/propanol = 30/70 (% by mass) at a solid content concentration of 13.0%, and the film thickness was adjusted to 50 µm. By adjusting the coating amount, an electrolyte membrane of 50 μm was obtained. Cerium ions were introduced into this electrolyte membrane in the same manner as in Example 1-1, except that the amount of the 9.8 mmol/L cerium (III) nitrate aqueous solution to be added was changed to 0.99 g. Got 5. Table 1 shows the ratio (mol %) of the amount of cerium ions to the amount of ion exchange groups.

<Example 1-6>
As a dispersion liquid for forming a solid polymer electrolyte membrane, a polymer obtained by copolymerizing TFE and PSVE and converted into an acid form through hydrolysis and acid treatment (ion exchange capacity: 1.38 meq/g dry resin) was dispersed in a solvent of water/ethanol = 40/60 (% by mass) at a solid content concentration of 20.0%, and the amount of 9.8 mmol/L cerium (III) nitrate aqueous solution to be added was 1. A solid polymer electrolyte membrane M-6 was obtained in the same manner as in Example 1-1 except that the weight was changed to 27 g. Table 1 shows the ratio (mol %) of the amount of cerium ions to the amount of ion exchange groups.

<Example 1-7>
As the solid polymer electrolyte membrane, the woven fabric reinforced electrolyte membrane described in Example 1 of WO 2020/162511 is used, and the amount of 9.8 mmol/L cerium (III) nitrate aqueous solution to be added is 1.03 g. A solid polymer electrolyte membrane M-7 was obtained in the same manner as in Example 1-1 except for the change. Table 1 shows the ratio (mol %) of the amount of cerium ions to the amount of ion exchange groups.

<Example 1-8>
A solid polymer electrolyte membrane M-8 containing no cerium ions was obtained in the same manner as in Example 1-1, except that the 9.8 mmol/L cerium (III) nitrate aqueous solution was not added. Table 1 shows the ratio (mol %) of the amount of cerium ions to the amount of ion exchange groups.

<Example 1-9>
A solid polymer electrolyte membrane M-9 was obtained in the same manner as in Example 1-1, except that the amount of the 9.8 mmol/L cerium (III) nitrate aqueous solution added was changed to 6.50 g. Table 1 shows the ratio (mol %) of the amount of cerium ions to the amount of ion exchange groups.

<Example 1-10>
A solid polymer electrolyte membrane M-10 was obtained in the same manner as in Example 1-1, except that the amount of the 9.8 mmol/L cerium (III) nitrate aqueous solution added was changed to 3.19 g. Table 1 shows the ratio (mol %) of the amount of cerium ions to the amount of ion exchange groups.

[Preparation of Cathode Catalyst Layer Decal]
<Example 2-1>
Water (59.4 g) and ethanol (39.6 g) are added to a supported catalyst ("TEC10E50E" manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) (11 g) in which 46% by mass of platinum is supported on carbon powder, and mixed and pulverized using an ultrasonic homogenizer. to obtain a catalyst dispersion.
A mixture (29.2 g) obtained by previously mixing and kneading Dispersion Y (20.1 g), ethanol (11 g), and Zeorola-H (manufactured by Nippon Zeon) (6.3 g) was added to the catalyst dispersion. rice field. Furthermore, water (3.66 g) and ethanol (7.63 g) were added to the obtained dispersion and mixed for 60 minutes using a paint conditioner to adjust the solid content concentration to 10.0% by mass. Obtained.
The cathode catalyst ink was applied to the ETFE sheet with a die coater, dried at 80° C., and heat-treated at 150° C. for 15 minutes to obtain a cathode catalyst layer decal D-1 having a platinum content of 0.4 mg/cm ² . .

<Example 2-2>
Dispersion Y (50 g) and cerium (III) carbonate octahydrate (0.43 g) were mixed for 3 days at room temperature to obtain a dispersion. This dispersion was heated at 160° C. for 3 hours, and the ratio (mol %) of the amount of cerium ions to the amount of ion exchange groups (sulfonic acid groups) of the fluorine-containing polymer obtained by removing the solvent is shown in Table 2. show. In the table, the ratio of the amount of cerium ions to the amount of ion exchange groups is abbreviated as "Ce/IEG (mol %) in the cathode catalyst layer".
A cathode catalyst layer decal D-2 was obtained in the same manner as in Example 2-1, except that 20.1 g of this dispersion was added in place of dispersion Y as the polymer dispersion used in the cathode catalyst ink.

<Example 2-3>
Dispersion Y (50 g) and cerium (III) carbonate octahydrate (0.014 g) were mixed for 3 days at room temperature to obtain a dispersion. This dispersion was heated at 160° C. for 3 hours, and the ratio (mol %) of the amount of cerium ions to the amount of ion exchange groups (sulfonic acid groups) of the fluorine-containing polymer obtained by removing the solvent is shown in Table 2. show. A cathode catalyst layer decal D-3 was obtained in the same manner as in Example 2-1, except that 20.1 g of this dispersion was added in place of dispersion Y as the polymer dispersion used in the cathode catalyst ink.

<Production of anode catalyst layer decal>
Dispersion liquid Y (33.0 g) was added with ethanol (18.06 g) and Zeorola-H (manufactured by Nippon Zeon) (10.58 g), and a rotation and revolution mixer (Thinky's Awatori Mixer) was used at 2200 rpm for 5 minutes. Mixed. Ethanol (46.44 g) and water (75.75 g) were added to the mixed composition (54.06 g), and an iridium oxide catalyst (Tanaka ^Kikinzoku Co.) (40.0 g) was added. The resulting mixture was treated with a planetary bead mill (rotational speed: 300 rpm) for 90 minutes to obtain an anode catalyst ink having a solid content concentration of 22% by mass.
An anode catalyst ink was applied to the ETFE sheet with an applicator so that the iridium content was 1.0 mg/cm ² , dried at 80° C. for 10 minutes, and further subjected to heat treatment at 150° C. for 15 minutes to form an anode catalyst layer decal. Obtained.

[Fabrication of membrane electrode assembly]
<Example 3-1>
The surface where the catalyst layer of the anode catalyst layer decal cut into 4 cm × 4 cm faces one surface of the solid polymer electrolyte membrane M-1 cut out to 7 cm × 7 cm, and the other surface of the solid polymer electrolyte membrane M-1 is cut out. The surface on which the catalyst layer of the cathode catalyst layer decal D-1 cut to 4 cm×4 cm was placed was opposed to one surface, and hot-pressed at a press temperature of 150° C. for 10 minutes and a pressure of 3 MPa. After the temperature was lowered to 70° C., the pressure was released, the assembly was taken out, and the ETFE sheets of the anode catalyst layer decal and the cathode catalyst layer decal were peeled off to obtain a membrane electrode assembly with an electrode area of 16 cm ² . The resulting membrane electrode assembly was subjected to evaluation of electrolytic voltage and fluorine release rate. Table 3 shows the evaluation results.

<Examples 3-2 to 3-7>
Membrane electrode assemblies were obtained in the same manner as in Example 3-1, except that solid polymer electrolyte membranes M-2 to M-7 were used instead of solid polymer electrolyte membrane M-1. Table 3 shows the evaluation results.

<Examples 3-8 to 3-9>
In the same manner as in Example 3-1, except that a solid polymer electrolyte membrane M-8 was used instead of the solid polymer electrolyte membrane M-1, and D-2 or D-3 was used instead of the cathode catalyst layer decal D-1. A membrane electrode assembly was obtained. Table 3 shows the evaluation results.

<Example 3-10>
A membrane electrode assembly was prepared in the same manner as in Example 3-1, except that a solid polymer electrolyte membrane M-3 was used instead of the solid polymer electrolyte membrane M-1, and D-2 was used instead of the cathode catalyst layer decal D-1. got Table 3 shows the evaluation results.

<Examples 4-1 to 4-3>
Membrane electrode assemblies were obtained in the same manner as in Example 3-1 except that solid polymer electrolyte membranes M-9, M-10 and M-8 were used instead of solid polymer electrolyte membrane M-1. Table 3 shows the evaluation results.

All of the membrane electrode assemblies of Examples 3-1 to 3-10 contained cerium ions in the region overlapping the cathode catalyst layer when observed from the normal direction of the surface of the membrane electrode assembly. was

From the results in Table 1, when using the membrane electrode assemblies of Examples 3-1 to 3-10 according to the present invention, a lower electrolytic voltage can be achieved than in Examples 4-1 to 4-3, and , it was confirmed that decomposition of the contained fluoropolymer can be suppressed.

In addition, the entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2021-182813 filed on November 9, 2021 are cited here, and as a disclosure of the specification of the present invention, It is taken in.

REFERENCE SIGNS LIST 10 electrolyte membrane 20 membrane electrode assembly 22 anode 24 cathode 26A anode catalyst layer 26B cathode catalyst layer 28 gas diffusion layer

Claims (9)

1. a solid polymer electrolyte membrane containing a fluorine-containing polymer having ion exchange groups;
   a cathode catalyst layer containing a fluorine-containing polymer having an ion-exchange group, disposed on one side of the solid polymer electrolyte membrane;
   A polymer electrolyte membrane electrode assembly for water electrolysis, comprising: an anode catalyst layer disposed on the other surface side of the solid polymer electrolyte membrane;
   When observed from the normal direction of the surface of the polymer electrolyte membrane electrode assembly for water electrolysis, the region overlapping with the cathode catalyst layer contains cerium ions,
   A polymer electrolyte membrane electrode assembly for water electrolysis, characterized in that it satisfies the relationship of formula (X).
   (A _Ce × 3)/A _{IEG_C} ≤ 0.90 Formula (X)
   In the formula (X), A _Ce represents the substance amount (mol) of cerium ions contained in the region, and A _{IEG_C} represents the substance amount (mol) of the ion exchange groups in the fluorine-containing polymer contained in the cathode catalyst layer. mol).
2. The solid polymer membrane electrode assembly for water electrolysis according to claim 1, wherein the ion exchange capacity of the fluorine-containing polymer contained in the solid polymer electrolyte membrane is 1.10 meq/g dry resin or more.
3. 3. The solid polymer electrolyte membrane according to claim 1, wherein the content of said fluorine-containing polymer contained in said solid polymer electrolyte membrane is 80 to 100% by mass with respect to the total mass of polymers in said solid polymer electrolyte membrane. Solid polymer type membrane electrode assembly for water electrolysis.
4. The solid polymer membrane electrode assembly for water electrolysis according to any one of claims 1 to 3, wherein the cerium ions are contained in the solid polymer electrolyte membrane.
5. The polymer electrolyte membrane electrode assembly for water electrolysis according to any one of claims 1 to 4, wherein the cerium ions are contained in the cathode catalyst layer.
6. The polymer electrolyte membrane for water electrolysis according to any one of claims 1 to 5, wherein the ion exchange group possessed by the fluorine-containing polymer contained in the polymer electrolyte membrane is a sulfonic acid type functional group. electrode junction.
7. The fluorine-containing polymer contained in the solid polymer electrolyte membrane is at least one selected from the group consisting of units represented by formula (1-3) and units represented by formula (1-4). The polymer electrolyte membrane electrode assembly for water electrolysis according to any one of claims 1 to 6, comprising a unit of
   

   

   In formulas (1-3) and (1-4), R ^f1 is a perfluoroalkylene group that may contain an oxygen atom between carbon atoms and carbon atoms, and R ^f2 is a single bond or a carbon atom- a perfluoroalkylene group optionally containing an oxygen atom between carbon atoms, R ^f3 is a single bond or a perfluoroalkylene group optionally containing an oxygen atom between carbon atoms, r is 0 or is 1, m is 0 or 1, and M is a hydrogen atom, an alkali metal or a quaternary ammonium cation.
8. The solid polymer membrane electrode assembly for water electrolysis according to any one of claims 1 to 7, wherein the solid polymer electrolyte membrane further contains a reinforcing material.
9. a solid polymer membrane electrode assembly for water electrolysis according to any one of claims 1 to 8;
   a power supply section connected to the cathode catalyst layer side and the anode catalyst layer side of the polymer electrolyte membrane electrode assembly for water electrolysis;
   and a water supply unit for supplying water to the anode catalyst layer side.

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