JP7471794B2 - Polyelectrolytes - Google Patents

Description

The present invention relates to a polymer electrolyte, an electrode catalyst ink containing the polymer electrolyte, an electrode catalyst layer containing the polymer electrolyte, a membrane electrode assembly including the electrode catalyst layer, and a fuel cell including the membrane electrode assembly.

In recent years, polymer electrolyte fuel cells have been installed in home fuel cell systems and fuel cell vehicles and are commercially available, and their use is expected to continue to grow from the perspective of preventing global warming.
This solid polymer electrolyte fuel cell is provided with a membrane electrode assembly (MEA) in which an electrolyte membrane such as perfluorocarbon sulfonic acid is attached to both sides of the electrolyte membrane, and electrode catalyst layers made of platinum-loaded carbon and a binder resin (ionomer) are bonded to both sides of the electrolyte membrane.
When humidified hydrogen gas flows through one electrode catalyst layer of this MEA, and humidified oxygen gas flows through the other electrode catalyst layer, protons are generated on the electrode catalyst on the hydrogen gas side (hereafter, anode) and move through the electrolyte membrane to the oxygen gas side (hereafter, cathode). Conversely, oxygen is reduced on the electrode catalyst of the cathode, and water is generated by reacting with electrons flowing from a separate circuit and protons flowing from the anode.

In a polymer electrolyte fuel cell, a particular issue is how to efficiently cause the oxygen reduction reaction on the electrode catalyst of the cathode.
Meanwhile, in order to ensure further market growth for polymer electrolyte fuel cell systems in the future, it is necessary to reduce the costs of the various components that make up the systems, and in particular, it is necessary to reduce the amount of platinum catalyst used, which has a high cost ratio.
In conventional solid polymer fuel cell systems, performance was ensured by using a large amount of platinum catalyst in the cathode, but reducing the amount of platinum catalyst used results in a problem of reduced power generation performance due to a decrease in the catalyst surface area that contributes to power generation.
Therefore, in order to supply more oxygen to a small catalyst surface, attempts have been made to improve the oxygen permeability of the ionomer and distribute oxygen throughout the electrode.

Patent Documents 1 and 2 describe a copolymer containing repeating units based on a fluorine-containing monomer that gives a polymer having an aliphatic ring structure in the main chain by radical polymerization and repeating units based on a fluorine-based sulfonic acid-containing monomer, as a polymer electrolyte with high oxygen permeability and suitable as a polymer electrolyte for a cathode-side catalyst layer, and a gas diffusion electrode containing the copolymer.

Patent Document 3 describes a copolymer of perfluoro(1,3-dioxole) having a perfluoro ring structure at the 2-position and perfluorovinyl ether having sulfonic acid as a polymer electrolyte that has a bulky ring structure, thereby reducing density and promoting oxygen permeability.

Patent Document 4 describes an electrolyte having a perfluoroaliphatic and sulfonimide in the main chain or side chain as a polymer electrolyte that has both proton conductivity and oxygen permeability.

JP 2003-36859 A JP 2002-260705 A JP 2018-39937 A JP 2012-38515 A

However, the polymer electrolytes disclosed in Patent Documents 1 to 4 above have a bulky ring structure, and although increasing the amount of the polymer electrolyte increases the oxygen permeability, when an electrode catalyst layer is formed, cracks appear on the surface, reducing the power generation performance and the durability of the battery.

In view of the above-mentioned current situation, the present invention aims to provide a polymer electrolyte that suppresses cracking of the electrode catalyst layer and has good power generation performance and durability in a battery.

As a result of intensive research to solve the above problems, the inventors discovered that a polymer electrolyte containing a benzodioxole derivative skeleton improves the power generation performance and durability of a battery without causing cracks on the surface of the electrode catalyst layer, and thus completed the present invention.

（式（１）中、Ｒ_１、Ｒ_２は、それぞれ独立に水素原子、フッ素原子、又は有機基を表し、Ｘは、それぞれ独立にエーテル結合又はスルホンアミド結合を含む構造を表し、Ｙは、それぞれ独立に水素原子、フッ素原子、又は有機基を表し、ａ及びｂは整数を表し、ａ＋ｂ＝４、ａ≧１である。）
［２］
上記式（１）中、Ｘが、下記式（２）又は下記式（３）で表される構造を含む、［１］に記載の高分子電解質。

（式（２）、（３）中、Ｒ_３、Ｒ_４、Ｒ_５は、それぞれ独立に水素原子、フッ素原子、又は有機基を表し、ｌは、１から１０のいずれかの整数を表し、＊は結合手を表す。）
［３］
［１］または［２］に記載の高分子電解質と、触媒とを含むことを特徴とする、電極触媒インク。
［４］
［１］または［２］に記載の高分子電解質と、触媒とを含むことを特徴とする、電極触媒層。
［５］
［４］に記載の電極触媒層と電解質膜とを備えることを特徴とする、膜電極接合体。
［６］
［５］に記載の膜電極接合体を備えることを特徴とする、燃料電池。 That is, the present invention is as follows.
[1]
The compound includes a benzodioxole structural unit having a benzodioxole derivative skeleton in a side chain, the skeleton including the structure represented by the following formula (1):
The ratio of the benzodioxole structural unit in 100 mol % of the polymer electrolyte is 12 to 100 mol %,
The oxygen solubility measured by the Pt thick film method under the condition of 80°C and 30% RH is 7.0 mol/m3 or ^more ,
A polymer electrolyte having an equivalent weight EW of 100 to 2000 g/eq.

(In formula (1), R ₁ and R ₂ each independently represent a hydrogen atom, a fluorine atom, or an organic group; X each independently represent a structure containing an ether bond or a sulfonamide bond; Y each independently represent a hydrogen atom, a fluorine atom, or an organic group; a and b each independently represent an integer, a+b=4, a≧1.)
[2]
The polymer electrolyte according to [1], wherein in the above formula (1), X includes a structure represented by the following formula (2) or the following formula (3):

(In formulas (2) and (3), R ₃ , R ₄ , and R ₅ each independently represent a hydrogen atom, a fluorine atom, or an organic group, l represents an integer of 1 to 10, and * represents a bond.)
[3]
An electrode catalyst ink comprising the polymer electrolyte according to [1] or [2] and a catalyst.
[4]
An electrode catalyst layer comprising the polymer electrolyte according to [1] or [2] and a catalyst .
[5]
A membrane electrode assembly comprising the electrode catalyst layer according to [4] and an electrolyte membrane.
[6]
A fuel cell comprising the membrane electrode assembly according to [5].

The polymer electrolyte of the present invention can suppress cracking of the electrode catalyst layer and provide a polymer electrolyte with good power generation performance and durability.

The present invention will be specifically described below.
[Polymer electrolyte]
The polymer electrolyte of the present embodiment contains a benzodioxole derivative skeleton, and therefore not only exhibits high oxygen permeability, but also has no cracks on the surface of the electrode catalyst layer containing the polymer electrolyte, and exhibits high performance and high chemical durability during operation of the fuel cell.

式（１）において、Ｒ₁、Ｒ₂は、それぞれ独立に水素原子、フッ素原子、又は有機基を表す。上記有機基としては、例えば、部分的又は完全にフッ素化されていてもよい炭素数１～１０の炭化水素基、エーテル結合、芳香族環等が挙げられる。上記Ｒ₁、Ｒ₂としては、合成の容易性から、水素原子、フッ素原子、メチル基が好ましい。
式（１）において、Ｘは、それぞれ独立にエーテル結合を含む構造又はスルホンアミド結合を含む構造を表し、Ｙは、それぞれ独立に水素原子、フッ素原子、又は有機基を表し、ａ及びｂは整数を表し、ａ＋ｂ＝４、ａ≧１である。上記有機基としては、例えば、部分的又は完全にフッ素化されていてもよい炭素数１～１０の炭化水素基等が挙げられる。Ｘは他の構造との連結基であってよく、Ｙはベンゼン環の末端置換基であってよい。 The benzodioxole derivative skeleton includes a skeleton containing a structure represented by the following formula (1), and the skeleton having a structure represented by the following formula (1) is preferable.

In formula (1), R ₁ and R ₂ each independently represent a hydrogen atom, a fluorine atom, or an organic group. Examples of the organic group include a hydrocarbon group having 1 to 10 carbon atoms which may be partially or completely fluorinated, an ether bond, an aromatic ring, and the like. From the viewpoint of ease of synthesis, R ₁ and R ₂ are preferably a hydrogen atom, a fluorine atom, or a methyl group.
In formula (1), X's each independently represent a structure containing an ether bond or a structure containing a sulfonamide bond, Y's each independently represent a hydrogen atom, a fluorine atom, or an organic group, a and b represent integers, a+b=4, a≧1. Examples of the organic group include hydrocarbon groups having 1 to 10 carbon atoms which may be partially or completely fluorinated. X may be a linking group to another structure, and Y may be a terminal substituent of a benzene ring.

ここで、式（２）（３）中、Ｒ₃、Ｒ₄、Ｒ₅は、それぞれ独立に水素原子、フッ素原子、又は有機基を表し、lは、１から１０のいずれかの整数を表し、＊は結合手を表す。上記有機基としては、例えば、部分的又は完全にフッ素化されていてもよい炭素数１～１０の炭化水素基等が挙げられる。上記Ｒ₃、Ｒ₄、Ｒ₅としては、合成の容易性から、水素原子、フッ素原子、メチル基が好ましい。 From the viewpoints of further suppressing cracking of the electrode catalyst layer and further improving oxygen permeability, the above-mentioned X preferably includes a structure represented by the following formula (2) or (3), and more preferably is a structure represented by the following formula (2) or (3).

In formulas (2) and (3), R ₃ , R ₄ and R ₅ each independently represent a hydrogen atom, a fluorine atom or an organic group, l represents an integer of 1 to 10, and * represents a bond. Examples of the organic group include hydrocarbon groups having 1 to 10 carbon atoms which may be partially or completely fluorinated. From the viewpoint of ease of synthesis, R ₃ , R ₄ and R ₅ are preferably a hydrogen atom, a fluorine atom or a methyl group.

Here, the benzodioxole derivative refers to a structure in which at least one hydrogen atom of the benzodioxole skeleton is substituted with a substituent such as a hydroxyl group, a thiol group, an amino group, a carboxyl group, a hydrocarbon group having 1 to 10 carbon atoms which may be substituted, a structure containing an ether bond or a sulfonamide bond, or an aromatic ring. The benzodioxole derivative may be, for example, a structure in which two hydrogen atoms of the dioxole ring of the 1,3-benzodioxole skeleton represented by the above formula (1) and one or more of the four hydrogen atoms of the benzene ring are substituted with the above substituents. Note that when the structure represented by the above formula ( ₁ ) is a structure in which a number of Xs, b number of Ys, R ₁ and R ₂ are bonded to the benzodioxole derivative, in formula (1), R 1 , R ₂ , a number of Xs, and b number of Ys may not be present except for one X, and for example, a+b, etc. may be appropriately changed.

The polymer electrolyte is preferably a homopolymer or copolymer containing at least a structural unit (repeating unit) containing a benzodioxole derivative skeleton (sometimes referred to as a "benzodioxole structural unit" in this specification). The benzodioxole structural unit contained in the polymer electrolyte may be of one type or of multiple types, but is preferably of one type from the viewpoint of productivity.
The polymer electrolyte may have other structural units in addition to the benzodioxole structural unit. The other structural units may be of one type or of multiple types.

(Benzodioxole structural unit)
Examples of the benzodioxole structural unit include a structural unit having the benzodioxole derivative skeleton in its main chain (sometimes referred to as "structural unit A" in this specification), a structural unit having the benzodioxole derivative skeleton in its side chain (sometimes referred to as "structural unit B" in this specification), a structural unit having the benzodioxole derivative skeleton in its main chain and side chain, and the like.

--Structural unit A--
The structural unit A may have one or more benzodioxole derivative skeletons in the main chain.

式（４）
上記式（４）中、側鎖Ｒ₆、Ｒ₇、Ｒ₈、Ｒ₉としては、それぞれ独立に水素原子、フッ素原子、プロトン伝導性基を末端に有する側鎖、部分的又は完全にフッ素化されていてもよい炭素数１～１０個の炭化水素基、エーテル結合、これらの組み合わせ、等が挙げられる。上記炭化水素基は構造中にエーテル性酸素原子を含んでも良い。プロトン伝導性基としては、スルホン酸基、カルボン酸基、リン酸基、スルホンアミド基等が挙げられ、後述の式（３７）～（４０）で表される構造等が挙げられる。 Examples of the structural unit A include a structure represented by the following formula (4).

Equation (4)
In the above formula (4), the side chains R ₆ , R ₇ , R ₈ , and R ₉ each independently represent a hydrogen atom, a fluorine atom, a side chain having a proton-conducting group at its end, a hydrocarbon group having 1 to 10 carbon atoms which may be partially or completely fluorinated, an ether bond, or a combination thereof. The above-mentioned hydrocarbon group may contain an ether oxygen atom in the structure. Examples of the proton-conducting group include a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, and a sulfonamide group, and examples of the structures represented by the formulas (37) to (40) described below are given.

--Structural unit B--
The structural unit B may have a benzodioxole derivative skeleton between the main chain and the side chain terminal, or may have a benzodioxole derivative skeleton at the side chain terminal. Among them, from the viewpoint of ease of synthesis, it is preferable that the benzodioxole derivative skeleton is at the side chain terminal, and it is more preferable that the dioxole ring is located on the side chain terminal side.

In the structural unit B, the main chain and the benzodioxole derivative skeleton at the end of the side chain may be bonded via an ether bond, the structure represented by the above formula (3), a sulfonyl group, a thioether group, a ketone group, an ester group, an imide group, an aromatic ring, a hydrocarbon group having 1 to 10 carbon atoms which may be partially or completely fluorinated, or a combination thereof.

式（２１）
（式（２１）中、ｎは構造単位の繰り返し数を表す。Ｘ₁～Ｘ₃は、それぞれ独立に、水素原子、フッ素原子、塩素原子を表す。Ａはベンゾジオキソール誘導体骨格を有する側鎖を表す。）；下記式（２３）で表される主鎖

式（２３）
（式（２３）中、ｎは構造単位の繰り返し数を表す。Ａｒは、ベンゼン、ナフタレン、アントラセン、フルオレン、ヘリセン、ピレン等の芳香環を表す。Ａは、ベンゾジオキソール誘導体骨格を有する側鎖を表す。Ｒ_xは、水素原子、フッ素原子、塩素原子、部分的又は完全にフッ素化されていてもよい炭素数１～１０の炭化水素基、プロトン伝導性基などが挙げられる。上記炭化水素基は構造中にエーテル性酸素原子を含んでも良い。プロトン伝導性基としては、例えば、－（ＣＦ₂）₂Ｏ（ＣＦ₂）₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦＨ－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦＨ－ＯＣＦ₂ＣＦ（ＣＦ₃）－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦＨ－ＯＣＦ₂ＣＦ（ＣＦ₂ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ）－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ等が挙げられる。）；下記式（２４）で表される主鎖

式（２４）
（式（２４）中、ｎは構造単位の繰り返し数を表す。Ａｒは、ベンゼン、ナフタレン、アントラセン、フルオレン、ヘリセン、ピレン等の芳香環を表す。Ａは、ベンゾジオキソール誘導体骨格を有する側鎖を表す。Ｒ_xは、水素原子、フッ素原子、塩素原子、部分的又は完全にフッ素化されていてもよい炭素数１～１０の炭化水素基、プロトン伝導性基などが挙げられる。上記炭化水素基は構造中にエーテル性酸素原子を含んでも良い。プロトン伝導性基としては、例えば、－（ＣＦ₂）₂Ｏ（ＣＦ₂）₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦＨ－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦＨ－ＯＣＦ₂ＣＦ（ＣＦ₃）－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦＨ－ＯＣＦ₂ＣＦ（ＣＦ₂ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ）－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ等）が挙げられる。）；等が挙げられる。 The main chain of the structural unit B is not particularly limited, but may be, for example, a main chain having a structure represented by the following formula (21):

Formula (21)
(In formula (21), n represents the number of repeating structural units. X ₁ to X ₃ each independently represent a hydrogen atom, a fluorine atom or a chlorine atom. A represents a side chain having a benzodioxole derivative skeleton.) A main chain represented by the following formula (23):

Equation (23)
In formula (23), n represents the number of repeating structural units. Ar represents an aromatic ring such as benzene, naphthalene, anthracene, fluorene, helicene, or pyrene. A represents a side chain having a benzodioxole derivative skeleton. _Rx represents a hydrogen atom, a fluorine atom, a chlorine atom, a hydrocarbon group having 1 to 10 carbon atoms which may be partially or completely fluorinated, a proton conductive group, or the like. The hydrocarbon group may contain an etheric oxygen atom in the structure. Examples of the proton conductive group include -( _CF2 ) _2O ( _CF2 ) _{2SO3H , -OCF2CF2SO3H , -OCF2CFH - OCF2CF2SO3H , -OCF2CFH -} OCF2CF _{( CF3 ) -OCF2CF2SO3H , -OCF2} CFH-OCF ₂ CF(CF ₂ OCF ₂ CF ₂ SO ₃ H)-OCF ₂ CF ₂ SO ₃ H, etc.; a main chain represented by the following formula (24):

Equation (24)
In formula (24), n represents the number of repetitions of the structural unit. Ar represents an aromatic ring such as benzene, naphthalene, anthracene, fluorene, helicene, or pyrene. A represents a side chain having a benzodioxole derivative skeleton. _Rx represents a hydrogen atom, a fluorine atom, a chlorine atom, a hydrocarbon group having 1 to 10 carbon atoms which may be partially or completely fluorinated, a proton conductive group, or the like. The hydrocarbon group may contain an etheric oxygen atom in the structure. Examples of the proton conductive group include -( _CF2 ) _2O ( _CF2 ) _{2SO3H , -OCF2CF2SO3H , -OCF2CFH - OCF2CF2SO3H , -OCF2CFH - OCF2CF} ( _{CF3 ) -OCF2CF2SO3H , -OCF2} CFH-OCF ₂ CF(CF ₂ OCF ₂ CF ₂ SO ₃ H)-OCF ₂ CF ₂ SO ₃ H, etc.

Preferred examples of the main chain include ethylene-based main chains such as -( _CF2 -CFA)- and -( _CH2 -CHA)-; main chains having an ether bond in the main chain, such as polyether ketone (PEK), polyether ether ketone (PEEK), polyether sulfone (PES), and polyphenylene ether (PPE); and main chains represented by formula (23) or (24).

式（２５）、（２６）において、Ｒ₁、Ｒ₂は、それぞれ独立に水素原子、フッ素原子、又は有機基を表し、Ａｒは、ベンゼン、ナフタレン、アントラセン、フルオレン、ヘリセン、ピレン等の芳香環を表す。Ｒ₆は、エーテル結合及びプロトン交換基を含む炭素数１以上のフッ素化炭化水素基を表し、フッ素化炭化水素基の炭素数が２以上である場合は炭素－炭素原子間にエーテル結合が挿入されていてもよい。上記Ｒ₆としては、例えば、－（ＣＦ₂）₂Ｏ（ＣＦ₂）₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦＨ－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ等が挙げられる。上記有機基としては、例えば、部分的又は完全にフッ素化されていてもよい炭素数１～１０の炭化水素基、エーテル結合、芳香族環等が挙げられる。上記Ｒ₁、Ｒ₂としては、合成の容易性から、水素原子、フッ素原子、メチル基が好ましい。

式（２７）
式（２７）において、Ｒ₇は、下記式（３１）の構造を表し、Ｒ₈は、それぞれ独立に水素原子、フッ素原子、又は有機基を表す。上記有機基としては、例えば、部分的又は完全にフッ素化されていてもよい炭素数１～１０の炭化水素基等が挙げられる。Ｒ₉は、エーテル結合及びプロトン交換基を含む炭素数１以上のフッ素化炭化水素基を表し、フッ素化炭化水素基の炭素数が２以上である場合は炭素－炭素原子間にエーテル結合が挿入されていてもよい。上記Ｒ₉としては、例えば、－（ＣＦ₂）₂Ｏ（ＣＦ₂）₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦＨ－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦＨ－ＯＣＦ₂ＣＦ（ＣＦ₃）－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ、－ＯＣＦ₂ＣＦＨ－ＯＣＦ₂ＣＦ（ＣＦ₂ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ）－ＯＣＦ₂ＣＦ₂ＳＯ₃Ｈ等が挙げられる。
ｃ～ｇは整数を表し、ｃ＋ｄ＝５、ｃ＋ｅ≧１、ｅ＋ｆ＋ｇ＝５、ｇ≧１である。

式（２９）

式（３０）
式（２９）、（３０）において、Ｒ₁、Ｒ₂はそれぞれ独立に水素原子、フッ素原子、又は有機基を表す。Ｒ₃、Ｒ₄、Ｒ₅は、それぞれ独立に水素原子、フッ素原子、又は有機基を表す。上記有機基としては、例えば、部分的又は完全にフッ素化されていてもよい炭素数１～１０の炭化水素基、エーテル結合、芳香族環等が挙げられる。ｌは、１から１０のいずれかの整数を表す。ｑは０～２の整数であり、ｒは０～１２の整数である。ただし、ｑ及びｒは同時に０にならない。Ｒ₁₀、Ｒ₁₁はそれぞれ独立にフッ素原子、又は下記式（３１）の構造を表す。

式（３１）
式（３１）において、Ｒ₁、Ｒ₂は、それぞれ独立に水素原子、フッ素原子、又は有機基を表す。上記有機基としては、例えば、部分的又は完全にフッ素化されていてもよい炭素数１～１０の炭化水素基、エーテル結合、芳香族環等が挙げられる。 As the structural unit B, from the viewpoints of ease of synthesis, further suppression of cracking of the electrode catalyst layer, and further improvement of oxygen permeability, structures represented by the following formulae (25) to (30) are preferred.

In formulae (25) and (26), R ₁ and R ₂ each independently represent a hydrogen atom, a fluorine atom, or an organic group, and Ar represents an aromatic ring such as benzene, naphthalene, anthracene, fluorene, helicene, or pyrene. _{R 6} represents a fluorinated hydrocarbon group having one or more carbon atoms and containing an ether bond and a proton exchange group, and when the fluorinated hydrocarbon group has two or more carbon atoms, an ether bond may be inserted between the carbon and carbon atoms. Examples of R ₆ include -(CF ₂ ) ₂ O(CF ₂ ) ₂ SO ₃ H, -OCF ₂ CF ₂ SO ₃ H, and -OCF ₂ CFH-OCF ₂ CF ₂ SO ₃ H. Examples of the organic group include a hydrocarbon group having one to ten carbon atoms, which may be partially or completely fluorinated, an ether bond, or an aromatic ring. From the viewpoint of ease of synthesis, R ₁ and R ₂ are preferably a hydrogen atom, a fluorine atom or a methyl group.

Equation (27)
In formula (27), R ₇ represents a structure of formula (31) below, and R ₈ each independently represents a hydrogen atom, a fluorine atom, or an organic group. Examples of the organic group include a hydrocarbon group having 1 to 10 carbon atoms which may be partially or completely fluorinated. R ₉ represents a fluorinated hydrocarbon group having 1 or more carbon atoms which contains an ether bond and a proton exchange group, and when the fluorinated hydrocarbon group has 2 or more carbon atoms, an ether bond may be inserted between the carbon atoms. Examples of _R9 include -( _CF2 ) _2O ( _CF2 ) _{2SO3H , -OCF2CF2SO3H , -OCF2CFH - OCF2CF2SO3H , -OCF2CFH - OCF2CF} ( _CF3 ) _{-OCF2CF2SO3H , -OCF2CFH - OCF2CF ( CF2OCF2CF2SO3H} ) _{-OCF2CF2SO3H , and the like} .
c to g represent integers, where c+d=5, c+e≧1, e+f+g=5, and g≧1.

Equation (29)

Equation (30)
In formulae (29) and (30), R ₁ and R ₂ each independently represent a hydrogen atom, a fluorine atom, or an organic group. R ₃ , R ₄ , and R ₅ each independently represent a hydrogen atom, a fluorine atom, or an organic group. Examples of the organic group include a hydrocarbon group having 1 to 10 carbon atoms, which may be partially or completely fluorinated, an ether bond, and an aromatic ring. l represents an integer from 1 to 10. q is an integer from 0 to 2, and r is an integer from 0 to 12. However, q and r are not 0 at the same time. R ₁₀ and R ₁₁ each independently represent a fluorine atom, or a structure of the following formula (31).

Formula (31)
In formula (31), R ₁ and R ₂ each independently represent a hydrogen atom, a fluorine atom, or an organic group, such as a hydrocarbon group having 1 to 10 carbon atoms which may be partially or completely fluorinated, an ether bond, or an aromatic ring.

(Other structural units)
The other structural unit may be a structural unit having the same main chain as the benzodioxole structural unit and not having a benzodioxole derivative skeleton in the side chain. The other structural unit may be, for example, a structural unit having the same main chain as the benzodioxole structural unit and not having a side chain, or a structural unit having the same main chain as the benzodioxole structural unit and having a side chain that promotes proton conductivity.
For example, the other structural units may include a structural unit (--CF ₂ -CF ₂ -) derived from tetrafluoroethylene.

式（３７）
（式（３７）中、Ｘは、Ｆ、Ｃｌ、又は置換されていてもよい炭素数１～３のフッ素化炭化水素基を表す。ｋは０～２の整数、ｎは０～８の整数を表す。ｎ個のＸは、同一でも異なっていてもよい。Ｙは、Ｆ又はＣｌを表す。ｍは１～６の整数を表す。ｍ個のＹは、同一でも異なっていてもよい。Ｚは、Ｈ、アルカリ金属、又はアルカリ土類金属表す。）
上記式（３７）において、特に、ｋが０又は２、ｎが０、ｍが２、ＹがＦ、ＺがＨであることが好ましい。

式（３８）
（式（３８）中、Ｘは、Ｆ、Ｃｌ、又は置換されていてもよい炭素数１～３のフッ素化炭化水素基を表す。ｋは０～２の整数、ｎは０～８の整数を表す。ｎ個のＸは、同一でも異なっていてもよい。Ｙは、Ｆ又はＣｌを表す。ｍは１～６の整数を表す。ｍ個のＹは、同一でも異なっていてもよい。Ｚは、ＮＲ¹Ｒ²を表す。Ｒ¹及びＲ²は、それぞれ独立に、置換されていてもよい炭素数１～１０のアルキル基、水素原子、－ＳＯ₂－Ｒ³を表す。ここでＲ³は、炭素数１～１０の炭化水素基を表す。Ｒ¹、Ｒ²の一方が置換されても良いアルキル基又は水素であるとき、Ｒ²は、－ＳＯ₂－Ｒ³である。）
上記式（３８）において、特に、ｋが０又は２、ｎが０、ｍが２であることが好ましい。

式（３９）
（式（３９）中、Ｒｆは、それぞれ独立にエーテル結合性酸素原子を含む炭素数１～１０のフッ素化炭化水素基、単結合を表す。Ｘは、Ｈ、アルカリ金属、又はアルカリ土類金属を表す。）

式（４０）
（式（４０）中、Ｒｆは、それぞれ独立にエーテル結合性酸素原子を含む炭素数１～１０のフッ素化炭化水素基、単結合を表す。Ｘは、ＮＲ¹Ｒ²を表す。Ｒ¹及びＲ²は、それぞれ独立に、置換されていてもよい炭素数１～１０のアルキル基又は水素原子、－ＳＯ₂－Ｒ³を表す。ここでＲ³は、炭素数１～１０の炭化水素基を表す。Ｒ¹、Ｒ²の一方が置換されても良いアルキル基又は水素原子であるとき、Ｒ²は、－ＳＯ₂－Ｒ³である。） The polymer electrolyte may have side chains that promote proton conductivity.
The side chain that promotes proton conductivity is preferably one having a structure represented by the following formula (37) to formula (40).

Equation (37)
(In formula (37), X represents F, Cl, or a fluorinated hydrocarbon group having 1 to 3 carbon atoms which may be substituted. k represents an integer of 0 to 2, and n represents an integer of 0 to 8. The n number of Xs may be the same or different. Y represents F or Cl. m represents an integer of 1 to 6. The m number of Ys may be the same or different. Z represents H, an alkali metal, or an alkaline earth metal.)
In the above formula (37), it is particularly preferable that k is 0 or 2, n is 0, m is 2, Y is F, and Z is H.

Equation (38)
(In formula (38), X represents F, Cl, or an optionally substituted fluorinated hydrocarbon group having 1 to 3 carbon atoms. k represents an integer of 0 to 2, and n represents an integer of 0 to 8. The n Xs may be the same or different. Y represents F or Cl. m represents an integer of 1 to 6. The m Ys may be the same or different. Z represents NR ¹ R ^2. R ¹ and R ² each independently represent an optionally substituted alkyl group having 1 to 10 carbon atoms, a hydrogen atom, or -SO ₂ -R ^3. Here, R ³ represents a hydrocarbon group having 1 to 10 carbon atoms. When one of R ¹ and R ² is an optionally substituted alkyl group or hydrogen, R ² is -SO ₂ -R ^3. )
In the above formula (38), it is particularly preferable that k is 0 or 2, n is 0, and m is 2.

Equation (39)
(In formula (39), Rf's each independently represent a fluorinated hydrocarbon group having 1 to 10 carbon atoms containing an ether-bonded oxygen atom or a single bond. X represents H, an alkali metal, or an alkaline earth metal.)

Formula (40)
(In formula (40), Rf's each independently represent a fluorinated hydrocarbon group having 1 to 10 carbon atoms containing an ether-bonding oxygen atom or a single bond. X represents NR ¹ R ^2. R ¹ and R ² each independently represent an alkyl group having 1 to 10 carbon atoms which may be substituted, a hydrogen atom, or -SO ₂ -R ^3. Here, R ³ represents a hydrocarbon group having 1 to 10 carbon atoms. When one of R ¹ and R ² is an alkyl group which may be substituted or a hydrogen atom, R ² is -SO ₂ -R ^3. )

式（４１）
（式（４１）中、Ｒｆは、炭素数１～１０のフッ素化炭化水素基を表す。上記フッ素化炭化水素基は構造中にエーテル性酸素原子を含んでも良い。）
上記側鎖（Ｄ）としては、－Ｏ－ＣＦ₃、－Ｏ－Ｃ₂Ｆ₅、－Ｏ－Ｃ₃Ｆ₇、－Ｏ－Ｃ₂Ｆ₄－Ｏ－Ｃ₂Ｆ₅、－Ｏ－（ＣＦ₂ＣＦ（ＣＦ₃））－Ｏ－Ｃ₃Ｆ₇、が挙げられる。 The other structural unit may include a structural unit having a side chain (D) having a structure represented by the following formula (41), and may be a structural unit in which the side chain (D) is directly bonded to A in -( _CF2 -CFA)-. By introducing the structural unit having the side chain (D), it becomes easier to adjust the solubility in a solvent when preparing a polymer electrolyte solution.

Formula (41)
(In formula (41), Rf represents a fluorinated hydrocarbon group having 1 to 10 carbon atoms. The fluorinated hydrocarbon group may contain an etheric oxygen atom in the structure.)
Examples of the side chain (D) include -O _{-CF3, -O-C2F5, -O-C3F7 , -O - C2F4 - O - C2F5} , _and -O-( _CF2CF ( _CF3 ))-O- _C3F7 .

The main chain in the other structural units may be the same as the main chain in structural unit B described above.

The polymer electrolyte preferably contains a proton-conducting group. Examples of the proton-conducting group include a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, and a sulfonamide group. From the viewpoint of proton conductivity, a sulfonic acid group, which is a strong acid, is preferable.
The polymer electrolyte preferably contains a structural unit having the proton-conducting group. The structural unit having the proton-conducting group may be the benzodioxole structural unit or another structural unit.

From the viewpoints of chemical durability and hydrophobicity, the above polymer electrolyte is preferably a fluorine-containing polymer electrolyte.

式（７）
；下記式（８）で表される化合物

式（８）
（式（７）、（８）中、Ｒ₁、Ｒ₂はそれぞれ独立に水素原子、フッ素原子、又は有機基を表す。Ｒ₃、Ｒ₄、Ｒ₅はそれぞれ独立に水素原子、フッ素原子、又は有機基を表す。上記有機基としては、例えば、部分的又は完全にフッ素化されていてもよい炭素数１～１０の炭化水素基、エーテル結合、芳香族環等が挙げられる。ｌは、１から１０のいずれかの整数を表す。ｑは０～２の整数であり、ｒは０～１２の整数である。ただし、ｑ及びｒは同時に０にならない。Ｒ₁₀、Ｒ₁₁はそれぞれ独立にフッ素原子、又は上記式（３１）の構造を表す。）；が好ましい。 As the polymer electrolyte, from the viewpoint of further suppressing cracking of the electrode catalyst layer and obtaining a battery having better power generation performance and durability, a polymer comprising at least one structural unit selected from the group consisting of the above formula (25), the above formula (26), and the above formula (27); a compound represented by the following formula (7):

Equation (7)
A compound represented by the following formula (8):

Equation (8)
(In formulas (7) and (8), R ₁ and R ₂ each independently represent a hydrogen atom, a fluorine atom, or an organic group. R ₃ , R ₄ and R ₅ each independently represent a hydrogen atom, a fluorine atom, or an organic group. Examples of the organic group include a hydrocarbon group having 1 to 10 carbon atoms which may be partially or completely fluorinated, an ether bond, an aromatic ring, and the like. l represents an integer of 1 to 10. q is an integer of 0 to 2, and r is an integer of 0 to 12, with the proviso that q and r are not 0 at the same time. R ₁₀ and R ₁₁ each independently represent a fluorine atom, or a structure of the above formula (31).) is preferable.

(Ratio of structural units)
The total proportion of the benzodioxole structural units in 100 mol % of the polymer electrolyte is preferably 5 to 600 mol %, more preferably 10 to 500 mol %, from the viewpoint of further suppressing cracking of the electrode catalyst layer and obtaining a battery with better power generation performance and durability.
The total proportion of the structural unit A in 100 mol % of the polymer electrolyte is preferably 1 to 100 mol %, and more preferably 5 to 90 mol %, from the viewpoint of further suppressing cracking of the electrode catalyst layer and obtaining a battery having better power generation performance and durability.
The total proportion of the structural unit B in 100 mol % of the polymer electrolyte is preferably 1 to 100 mol %, and more preferably 5 to 90 mol %, from the viewpoint of further suppressing cracking of the electrode catalyst layer and obtaining a battery having better power generation performance and durability.
The molar ratio of the structural units in the polymer electrolyte can be measured by the method described in the Examples below.

(Characteristic)
The polymer electrolyte preferably has an equivalent weight EW (the number of grams of dry mass of the polymer electrolyte per equivalent of proton exchange group) of 100 to 2000 g/eq. That is, it is preferable to control the copolymerization ratio and the proton conductive group introduction rate so as to be within the above EW range. The upper limit of the EW is preferably 1000 g/eq, more preferably 900 g/eq. The lower limit of the EW is preferably 300 g/eq, more preferably 500 g/eq. By having the EW within the above range, the processability is further excellent, the conductivity of the electrode catalyst layer is not too low, and the solubility in hot water is also small. The EW can be calculated by the method described in the Examples below.

The polymer electrolyte preferably has a number average molecular weight of 10,000 to 2,000,000, and more preferably 30,000 to 1,000,000, in order to provide even better processability, electrical conductivity, and mechanical strength. When the number average molecular weight is relatively low and the mechanical strength is poor, the polymer may be mixed with a polymer having a relatively low MI, i.e., a high molecular weight polymer, as described in Reference Example 1 of Japanese Patent Application No. 2016-171717.
The number average molecular weight is a value measured by GPC (gel permeation chromatography). For example, the number average molecular weight can be calculated using standard polystyrene as the standard by the method described below.
The column is a Tosoh HLC-8020, and three polystyrene gel MIX columns (Tosoh GMH series, 30 cm size) are used, and the temperature is 40° C., NMP (containing 5 mmol/L LiBr) is used as the solvent, and the flow rate is 0.7 mL/min. The sample concentration is 0.1 wt %, and the injection amount is 500 μL. The number average molecular weight is more preferably about 100,000 to 800,000, more preferably about 130,000 to 700,000, and particularly preferably about 160,000 to 600,000, in terms of polystyrene.

For polymers whose molecular weight cannot be measured by GPC, it may be measured by melt flow rate (MFR).
The MFR of the polymer electrolyte is preferably 0.1 to 1000 g/10 min, more preferably 0.5 g/10 min or more, and even more preferably 1.0 g/10 min or more, more preferably 200 g/10 min or less, and even more preferably 100 g/10 min or less.
The MFR can be measured according to ASTM standard D1238 under conditions of 270° C. and a load of 2.16 kg using a MELT INDEXER TYPE C-5059D (product name, manufactured by Toyo Seiki Seisakusho Co., Ltd.).

(Production method)
The polymer electrolyte may be obtained by polymerizing a monomer capable of forming a predetermined structural unit, or by introducing a predetermined side chain into a polymer after polymerization.
The polymer electrolyte can be synthesized by a conventional method such as polycondensation, radical polymerization, or anionic polymerization, and among these, polycondensation or radical polymerization is preferably used.
The polymer electrolyte is obtained in the form of an emulsion in which the polymer electrolyte particles are dispersed or dissolved in water.

The radical polymerization may be carried out in the presence of a surfactant. The surfactant is preferably a known fluorine-containing anionic surfactant.

The radical polymerization is preferably carried out by adding a polymerization initiator. The polymerization initiator is not particularly limited as long as it can generate radicals at the polymerization temperature, and a known oil-soluble and/or water-soluble polymerization initiator can be used. A redox initiator may also be used. The concentration of the polymerization initiator is appropriately determined depending on the molecular weight and reaction rate of the target polymer.
Examples of the polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate, and organic peroxides such as disuccinic acid peroxide, diglutaric acid peroxide, and tert-butyl hydroperoxide. Examples of the redox initiator include a combination of a persulfate or an organic peroxide with a reducing agent such as a sulfite such as sodium sulfite, a bisulfite such as sodium hydrogensulfite, a bromate, a diimine, or oxalic acid.

Radical polymerization can be carried out under a pressure of 0.05 to 5.0 MPa. The preferred pressure range is 0.1 to 1.5 MPa. Radical polymerization can be carried out at a temperature of 5 to 100°C. The preferred temperature range is 10 to 90°C. In radical polymerization, known stabilizers, chain transfer agents, etc. may also be added depending on the purpose.

The method for synthesizing the polymer electrolyte of the above formula (25) is not particularly limited, but for example, it can be synthesized by polycondensing octafluorocyclopentene with a monomer having two or more hydroxyl groups, and then reacting it with a benzodioxole derivative having a hydroxyl group (e.g., sesamol, etc.) to substitute the fluorine atom at the allylic position.

式（１０）において、Ｒ₁、Ｒ₂は、それぞれ独立に水素原子、フッ素原子、又は有機基を表す。 The synthesis method of the polymer electrolyte of the above formula (26) is not particularly limited, but for example, first, octafluorocyclopentene is reacted with a benzodioxole derivative having a hydroxyl group (e.g., sesamol, etc.) to synthesize a monomer such as that of formula (10). Then, this monomer is polycondensed with a monomer having two or more hydroxyl groups to synthesize the polymer electrolyte. The introduction method of the sulfonic acid group is not particularly limited, but for example, it can be introduced by dehalogenation coupling, etc.

In formula (10), R ₁ and R ₂ each independently represent a hydrogen atom, a fluorine atom, or an organic group.

The method for synthesizing the polymer electrolyte of the above formula (27) is not particularly limited. For example, after radical polymerization of a pentafluorostyrene monomer, a benzodioxole derivative having a hydroxyl group (e.g., sesamol, etc.) can be introduced by an aromatic nucleophilic substitution reaction. The method for introducing sulfonic acid groups is not particularly limited, but for example, the obtained polymer can be treated with potassium hydroxide or sodium hydroxide to introduce hydroxyl groups into the aromatic rings, and then a sulfonic acid derivative having a double bond (for example, CF ₂ ═CF-OCF ₂ CF ₂ SO ₃ X, CF ₂ ═CF-OCF ₂ CF(CF ₃ )-OCF ₂ CF ₂ SO ₃ X, CF ₂ ═CF-OCF ₂ CF(CF ₂ OCF ₂ CF ₂ SO ₃ X)-OCF ₂ CF ₂ SO ₃ X, where X is hydrogen, an alkali metal, an alkaline earth metal, or a quaternary ammonium salt) can be added to introduce the sulfonic acid groups.

式（１１）において、ｑは０～２の整数であり、ｒは０～１２の整数である。ただし、ｑ及びｒは同時に０にならない。 The method for synthesizing the polymer electrolytes of the above formulae (29) and (30) is not particularly limited, but for example, they can be synthesized by radical polymerization or by reacting a polymer of formula (11) with a benzodioxole derivative having an amino group (e.g., piperonylamine, etc.) and then subjecting it to hydrolysis.

In formula (11), q is an integer of 0 to 2, and r is an integer of 0 to 12, provided that q and r are not 0 at the same time.

From the viewpoint of cell performance, it is preferable that the above-mentioned polymer electrolyte has an oxygen solubility of 7.0 mol/ ^m3 or more measured by the Pt thick film method under conditions of 80°C and 30% RH. The thin film of the polymer electrolyte covering the catalyst surface is about several nm thick, and the oxygen permeability therein differs from the behavior in the bulk. That is, oxygen diffusivity is the rate-limiting factor in the bulk, but oxygen solubility is the rate-limiting factor in the thin film. The above-mentioned oxygen solubility can be calculated by the method described in the Examples below.

(Polyelectrolyte solution)
The polymer electrolyte solution of the present embodiment preferably contains the above-mentioned polymer electrolyte and water and/or an organic solvent. The above-mentioned polymer electrolyte solution can be suitably used as a raw material for forming an electrode catalyst layer of a fuel cell (e.g., an electrode catalyst layer for a cathode). The above-mentioned polymer electrolyte solution is preferably a polymer electrolyte solution for forming an electrode catalyst layer of a fuel cell.

The mass proportion of the polymer electrolyte in the polymer electrolyte solution is preferably 2 to 50% by mass, more preferably 5% by mass or more, even more preferably 10% by mass or more, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 25% by mass or less.

Examples of the organic solvent include protic organic solvents such as methanol, ethanol, n-propanol, isopropyl alcohol, butanol, and glycerin; aprotic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, acetonitrile, and ethyl acetate; and fluorine-based solvents such as trifluoroethanol, Vertrel XF, Novec 7100, and Novec 7300. These can be used alone or in combination of two or more.

The polymer electrolyte solution may contain an organic additive. The polymer electrolyte solution may also contain an inorganic additive.

Examples of the organic additives include compounds whose atoms are easily extracted by radicals, such as compounds having hydrogen bonded to a tertiary carbon or a carbon-halogen bond in the structure. Specific examples include aromatic compounds partially substituted with functional groups, such as polyaniline, and unsaturated heterocyclic compounds, such as polybenzimidazole, polybenzoxazole, polybenzothiazole, polybenzoxadiazole, phenylated polyquinoxaline, and phenylated polyquinoline.
In addition, thioether compounds may also be used, for example, dialkyl thioethers such as dimethyl thioether, diethyl thioether, dipropyl thioether, methyl ethyl thioether, and methyl butyl thioether, cyclic thioethers such as tetrahydrothiophene and tetrahydroapyran, and aromatic thioethers such as methyl phenyl sulfide, ethyl phenyl sulfide, diphenyl sulfide, and dibenzyl sulfide.

The mass ratio of the organic additive in the polymer electrolyte solution is preferably 0.1 mass% or more, more preferably 1 mass% or more, and even more preferably 3 mass% or more. By containing 0.1 mass% or more of the organic additive, it is possible to improve chemical durability during fuel cell operation.

Examples of the inorganic additives include metal oxides, metal carbonates, metal nitrates, etc. The inorganic additives may be used alone or in combination of two or more.
Examples of the metal oxide include zirconia ( _ZrO2 ), titania ( _TiO2 ), silica ( _SiO2 ), alumina ( _Al2O3 ) _, iron oxide ( _Fe2O3 , FeO, _Fe3O4 ), copper oxide (CuO, _Cu2O ), zinc oxide ( _{ZnO), yttrium oxide (Y2O3 ) ,} niobium oxide ( _Nb2O5 ), molybdenum oxide ( _MoO3 ), indium oxide ( _In2O3 , _In2O ), tin oxide ( _SnO2 ) _, tantalum oxide ( _Ta2O5 ), tungsten oxide _{( WO3 , W2O5} ), lead oxide (PbO, _PbO2 ), bismuth oxide ( _Bi2O3 ), cerium oxide ( _{CeO2 , Ce2O3 ) .} ), _{antimony oxide (Sb2O3 , Sb2O5 )} , germanium oxide ( _GeO2 , GeO), lanthanum oxide ( _{La2O3 )} , ruthenium oxide ( _RuO2 ), manganese oxide (MnO), etc. These metal oxides may be used alone or in combination, and examples of the metal oxides include composite oxides such as tin-doped indium oxide (ITO), antimony-doped tin oxide (ATO), aluminum zinc oxide ( _ZnO.Al2O3 ), _etc.
Examples of the metal carbonates include zirconium carbonate (Zr( _CO3 ) ₂ ), titanium carbonate (Ti( _CO3 ) ₂ ), iron carbonate ( _FeCO3 ), copper carbonate ( _Cu2CO3 ), zinc carbonate ( _ZnCO3 ), molybdenum carbonate, cerium carbonate ( _CeCO3 ), nickel carbonate ( _NiCO3 ), cobalt _{carbonate (CoCO3 )} , manganese carbonate ( _MnCO3 ), and the like.
Examples of the metal nitrates include zirconium nitrate (Zr( _NO3 ) ₄ ), iron nitrate (Fe( _NO3 ) ₃ ), copper nitrate (Cu( _NO3 ) ₂ ), titanium nitrate (Ti( _NO3 ) ₄ ), cerium nitrate (Ce( _NO3 ) ₃ ), nickel nitrate (Ni( _NO3 ) ₂ ), cobalt nitrate (Co( _NO3 ) ₂ ), manganese nitrate (Mn( _NO3 ) ₂ ), and the like.
Among these, silica ( _SiO2 ) is preferred from the viewpoint of improving hydrophilicity, and cerium oxide ( _CeO2 , _Ce2O3 ), manganese oxide ( _MnO ), cerium carbonate (CeCO3), manganese carbonate ( _MnCO3 ), cerium nitrate (Ce( _NO3 ) ₃ ), manganese nitrate (Mn( _NO3 ) ₂ ), and titanium nitrate (Ti( _NO3 ) ₄ ) are preferred from _the viewpoint of improving chemical durability.

The inorganic additive may be in the form of particles or fibers, but it is particularly desirable that the additive be amorphous. In this case, "amorphous" means that no particulate or fibrous metal oxide is observed when observed with an optical microscope or electron microscope. In particular, no particulate or fibrous metal oxide is observed when the electrode catalyst layer is magnified to several hundred thousand times using a scanning electron microscope (SEM). Furthermore, no particulate or fibrous metal oxide can be clearly observed when the electrode catalyst layer is magnified to several hundred thousand times to several million times using a transmission electron microscope (TEM). In this way, it means that the particulate or fibrous metal oxide cannot be confirmed within the scope of current microscopy technology.

The mass ratio of the inorganic additive in the polymer electrolyte solution is preferably 0.01 to 100 mass%, more preferably 0.01 to 45 mass%, even more preferably 0.01 to 25 mass%, and particularly preferably 0.5 to 6.0 mass%. By including 0.01 mass% or more of the inorganic additive, it is possible to improve chemical durability during fuel cell operation.

The polymer electrolyte solution can be concentrated to a desired solids concentration. There are no particular limitations on the concentration method. For example, there is a method of heating to evaporate the solvent, or a method of concentrating under reduced pressure. The solids content of the resulting polymer electrolyte solution is preferably 0.5 to 50% by mass, taking into account ease of handling and productivity.

It is more preferable that the polymer electrolyte solution is filtered from the viewpoint of removing coarse particle components. The filtration method is not particularly limited, and a conventional method can be applied. For example, a method of pressure filtration using a filter processed from a filter material having a commonly used rated filtration accuracy is exemplified. It is preferable to use a filter material whose 90% collection particle size is 10 to 100 times the average particle size of the particles. This filter material may be filter paper or a filter material such as a sintered metal filter. In particular, in the case of filter paper, it is preferable that the 90% collection particle size is 10 to 50 times the average particle size of the particles. In the case of a sintered metal filter, it is preferable that the 90% collection particle size is 50 to 100 times the average particle size of the particles. Setting the 90% collection particle size to 10 times or more the average particle size can prevent the pressure required for liquid delivery from becoming too high or the filter from clogging in a short period of time. On the other hand, setting it to 100 times or less the average particle size is preferable from the viewpoint of effectively removing particle aggregates and undissolved resin that may cause foreign matter in the film.

式（１２）
（式（１２）中、Ｙ³¹は、Ｆ、Ｃｌ、又は炭素数１～３のパーフルオロアルキル基を表す。ｋは０～２の整数、ｎは０～８の整数を表し、ｎ個のＹ³¹は、同一でも異なっていてもよい。Ｙ³²は、Ｆ又はＣｌを表す。ｍは２～６の整数を表す。ｍ個のＹ³²は、同一でも異なっていてもよい。Ｚ³¹は、Ｈ、アルカリ金属、アルカリ土類金属、又はＮＲ₄を表す。Ｒは、それぞれ独立に、アルキル基又はＨを表わす。）

式（１３）
（式（１３）中、Ｙ³³は、Ｆ、Ｃｌ、又は炭素数１～３のパーフルオロアルキル基を表す。ｏは０～１の整数を表す。Ｑ³¹は、エーテル結合を有していてもよい炭素数１～６のパーフルオロアルキレン基であり、Ｑ³²は、単結合又はエーテル結合を有していてもよい炭素数１～６のパーフルオロアルキレン基である。Ｒ³¹は、エーテル結合を有していてもよいパーフルオロアルキル基である。Ｘは、Ｏ、Ｎ、又はＣであって、ＸがＯの場合はａは０であり、ＸがＮの場合はａは１であり、ＸがＣの場合はａは２である。Ｚ³²は、Ｈ、アルカリ金属、アルカリ土類金属、又はＮＲ³² ₄を表す。Ｒ³²は、それぞれ独立に、アルキル基又はＨを表わす。）
上記繰り返し単位（１２）について、Ｙ³¹はＦ又はＣＦ₃であることが好ましい。ｋは０であることが好ましい。ｎは０又は１であることが好ましい。Ｙ³²はＦであることが好ましい。ｍは２であることが好ましい。Ｚ³¹はＨ、Ｎａ、Ｋ、又はＮＨ₄であることが好ましい。
上記繰り返し単位（１２）は、上述したものの中でも特に、－ＣＦ₂－ＣＦ（－Ｏ－ＣＦ₂－ＣＦ₂－ＳＯ₃Ｈ）－、又は－ＣＦ₂－ＣＦ（－Ｏ－ＣＦ₂－ＣＦ（ＣＦ₃）－Ｏ－ＣＦ₂－ＣＦ₂－ＳＯ₃Ｈ）－が好ましい。
上記繰り返し単位（１３）について、Ｙ³³はＦであることが好ましい。ｏは０であることが好ましい。Ｑ³¹は、－ＣＦ₂－ＣＦ₂－又は－ＣＦ₂－Ｏ－ＣＦ₂－ＣＦ₂－であることが好ましい。Ｑ³²は、－Ｏ－ＣＦ₂－ＣＦ₂－であることが好ましい。Ｒ³¹は、－ＣＦ₃又は－ＣＦ₂－ＣＦ₃であることが好ましい。ＸはＯであることが好ましい。Ｚ³²は、Ｈ、Ｎａ、Ｋ、又はＮＨ₄であることが好ましい。
上記繰り返し単位（１３）は、上述したものの中でも特に、－ＣＦ₂－ＣＦ（－Ｏ－ＣＦ₂－ＣＦ（－ＣＦ₂－Ｏ－ＣＦ₂－ＣＦ₂－ＳＯ₃Ｈ）（－Ｏ－ＣＦ₂－ＣＦ₂－ＳＯ₃Ｈ）－が好ましい。 The polymer electrolyte solution may contain, in addition to one or more types of polymer electrolytes containing a benzodioxole derivative skeleton, other polymer electrolytes not having a benzodioxole derivative skeleton.
The other polymer electrolyte not having a benzodioxole derivative skeleton is not particularly limited, and any known polymer electrolyte can be used, for example, a polymer having a repeating unit represented by the following formula (12) or (13).

Equation (12)
(In formula (12), Y ³¹ represents F, Cl, or a perfluoroalkyl group having 1 to 3 carbon atoms. k represents an integer of 0 to 2, n represents an integer of 0 to 8, and the n Y ^31s may be the same or different. Y ³² represents F or Cl. m represents an integer of 2 to 6. The m Y ^32s may be the same or different. Z ³¹ represents H, an alkali metal, an alkaline earth metal, or NR _4. Each R independently represents an alkyl group or H.)

Equation (13)
(In formula (13), Y ³³ represents F, Cl, or a perfluoroalkyl group having 1 to 3 carbon atoms. o represents an integer of 0 to 1. Q ³¹ represents a perfluoroalkylene group having 1 to 6 carbon atoms which may have an ether bond, and Q ³² represents a perfluoroalkylene group having 1 to 6 carbon atoms which may have a single bond or an ether bond. R ³¹ represents a perfluoroalkyl group which may have an ether bond. X represents O, N, or C, and when X is O, a is 0, when X is N, a is 1, and when X is C, a is 2. Z ³² represents H, an alkali metal, an alkaline earth metal, or NR ³² _4. Each of R ³² independently represents an alkyl group or H.)
In the above repeating unit (12), ^Y31 is preferably F or _CF3 . k is preferably 0. n is preferably 0 or 1. ^Y32 is preferably F. m is preferably 2. ^Z31 is preferably H, Na, K, or _NH4 .
Of the repeating units mentioned above, the repeating unit (12) is preferably --CF ₂ --CF(--O--CF ₂ --CF ₂ --SO ₃ H)-- or --CF ₂ --CF(--O--CF ₂ --CF(CF ₃ )--O--CF ₂ --CF ₂ --SO ₃ H)--.
In the above repeating unit (13), Y ³³ is preferably F. o is preferably 0. Q ³¹ is preferably _-CF2 - _CF2- or _-CF2 -O- _CF2 - _CF2- . Q ³² is preferably -O- _CF2 - _CF2- . R ³¹ is preferably _-CF3 or _-CF2 - _CF3 . X is preferably O. Z ³² is preferably H, Na, K, or _NH4 .
Of the repeating units mentioned above, the repeating unit (13) is preferably --CF ₂ --CF(--O--CF ₂ --CF(--CF ₂ --O--CF ₂ --CF ₂ --SO ₃ H)(--O--CF ₂ --CF ₂ --SO ₃ H)--.

(Electrocatalytic ink)
The polymer electrolyte can be suitably used as a raw material for forming an electrode catalyst ink. The electrode catalyst ink preferably contains the polymer electrolyte and a catalyst, and may further contain water and/or an organic solvent. The electrode catalyst ink can be suitably used as a raw material for forming an electrode catalyst layer (e.g., an electrode catalyst layer for a cathode) of a fuel cell. The electrode catalyst ink is preferably an electrode catalyst ink for forming an electrode catalyst layer of a fuel cell.

The catalyst is not particularly limited as long as it can have activity in the electrode catalyst layer, and is appropriately selected depending on the intended use of the fuel cell in which the electrode catalyst layer is used. The catalyst is preferably a catalytic metal.
The catalyst is preferably a metal that promotes the oxidation reaction of hydrogen and the reduction reaction of oxygen, and more preferably at least one metal selected from the group consisting of platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese, vanadium, and alloys thereof. Of these, platinum is preferred.

The particle size of the catalyst metal is not limited, but is preferably 10 to 1000 angstroms, more preferably 10 to 500 angstroms, and most preferably 15 to 100 angstroms.

The content of the polymer electrolyte in the electrode catalyst ink is preferably 5 to 30% by mass, more preferably 8% by mass or more, even more preferably 10% by mass or more, more preferably 20% by mass or less, and even more preferably 15% by mass or less, relative to the electrode catalyst ink.
The content of the catalyst in the electrode catalyst ink is preferably 50 to 200% by mass, more preferably 80% by mass or more, and even more preferably 100% by mass or more, more preferably 150% by mass or less, and even more preferably 130% by mass or less, relative to the polymer electrolyte.

It is preferable that the electrode catalyst ink further contains a conductive agent. In one preferred embodiment, the catalyst and the conductive agent are composite particles (e.g., Pt-supported carbon, etc.) made of a conductive agent carrying particles of the catalyst. In this case, the polymer electrolyte also functions as a binder.

The conductive agent is not limited as long as it is a particle having electrical conductivity (conductive particle), but it is preferable that it is at least one type of conductive particle selected from the group consisting of carbon black such as furnace black, channel black, and acetylene black, activated carbon, graphite, and various metals (excluding catalytic metals). The particle diameter of these conductive agents is preferably 10 angstroms to 10 μm, more preferably 50 angstroms to 1 μm, and most preferably 100 to 5000 angstroms.

The composite particles preferably have a catalyst particle content relative to the conductive particles of 1 to 99% by mass, more preferably 10 to 90% by mass, and most preferably 30 to 70% by mass. Specific examples of suitable catalyst particles include Pt catalyst-supported carbon such as TEC10E40E, TEC10E50E, and TEC10E50HT manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.

The content of the composite particles is preferably 1.0 to 3.0% by mass, more preferably 1.4 to 2.9% by mass, even more preferably 1.7 to 2.9% by mass, and particularly preferably 1.7 to 2.3% by mass, relative to the polymer electrolyte.

The electrode catalyst ink may further contain a water repellent agent.
The electrode catalyst ink may further contain polytetrafluoroethylene (hereinafter, PTFE) or a copolymer of tetrafluoroethylene and perfluoro(2,2-dimethyl-1,3-dioxole) to improve water repellency. In this case, the shape of the water repellent is not particularly limited as long as it has a fixed shape, and is preferably particulate or fibrous, and these may be used alone or in combination.

The content of the water repellent agent is preferably 0.01 to 30.0% by mass, more preferably 1.0 to 25.0% by mass, even more preferably 2.0 to 20.0% by mass, and particularly preferably 5.0 to 10.0% by mass, relative to the polymer electrolyte.

(Electrode catalyst layer)
The electrode catalyst layer of this embodiment is preferably an electrode catalyst layer containing the above polymer electrolyte. The electrode catalyst layer preferably contains the above electrode catalyst ink, and more preferably is made of the above electrode catalyst ink. The electrode catalyst layer can be produced at low cost and has high oxygen permeability. The electrode catalyst layer can be used as a cathode electrode catalyst layer, and is suitable for use in fuel cells.

The electrode catalyst layer preferably comprises the polymer electrolyte and the catalyst, and the amount of the polymer electrolyte supported in the electrode catalyst layer relative to the electrode area is preferably 0.001 to 10 mg/cm ² , more preferably 0.01 to 5 mg/cm ² , and even more preferably 0.1 to 1 mg/cm ² .

The electrode catalyst layer is preferably made of a polymer electrolyte, a catalyst, and a conductive agent. In one preferred embodiment, the electrode catalyst layer is made of a polymer electrolyte and composite particles (e.g., Pt-supported carbon, etc.) made of catalyst particles and a conductive agent supporting the catalyst. In this case, the polymer electrolyte also functions as a binder.

The conductive agent may be any of those mentioned above, and is preferably the same as those mentioned above.
In the composite particles, the catalyst particles are preferably 1 to 99% by mass, more preferably 10 to 90% by mass, and most preferably 30 to 70% by mass relative to the conductive particles. Specifically, a suitable example is Pt catalyst-supported carbon such as TEC10E40E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.

The content of the composite particles is preferably 20 to 95 mass%, more preferably 40 to 90 mass%, even more preferably 50 to 85 mass%, and particularly preferably 60 to 80 mass%, relative to the total mass of the electrode catalyst layer. When the electrode catalyst layer is used as an electrode catalyst layer for a fuel cell, the amount of catalyst metal supported relative to the electrode area is preferably 0.001 to 10 mg/ ^cm2 , more preferably 0.01 to 5 mg/ ^cm2 , even more preferably 0.1 to 1 mg/ ^cm2 , and even more preferably 0.2 to 0.5 mg/ ^cm2 , after the electrode catalyst layer is formed.

The thickness of the electrode catalyst layer is preferably 0.01 to 200 μm, more preferably 0.1 to 100 μm, and most preferably 1 to 50 μm.

The electrode catalyst layer may contain a water repellent agent as necessary.
The water repellent agent may be any of those mentioned above, and is preferably the same as those mentioned above.
When the electrode catalyst layer contains a water repellent, the content of PTFE and a copolymer of tetrafluoroethylene and perfluoro(2,2-dimethyl-1,3-dioxole) is preferably 0.001 to 20 mass%, more preferably 0.01 to 10 mass%, and most preferably 0.1 to 5 mass%, relative to the total mass of the electrode catalyst layer.

The electrode catalyst layer may contain an inorganic additive in order to improve hydrophilicity and chemical durability.
Examples of the inorganic additives include those mentioned above, and the same ones as those mentioned above are preferable.
The content of the inorganic additive is preferably 0.001 to 20 mass %, more preferably 0.01 to 10 mass %, and most preferably 0.1 to 5 mass %, relative to the total mass of the electrode catalyst layer.

The porosity of the electrode catalyst layer is not particularly limited, but is preferably 10 to 90% by volume, more preferably 20 to 80% by volume, and most preferably 30 to 60% by volume.

The method for producing the electrode catalyst layer includes the steps of dispersing the catalyst in the obtained polymer electrolyte solution to prepare the electrode catalyst ink, applying the electrode catalyst ink to a substrate, and drying the electrode catalyst ink applied to the substrate to obtain an electrode catalyst layer.

The step of preparing an electrode catalyst ink by dispersing the catalyst in the obtained polymer electrolyte solution preferably involves preparing an electrode catalyst ink by dispersing composite particles of catalyst particles and a conductive agent carrying the catalyst in the obtained emulsion or polymer electrolyte solution.

The electrode catalyst ink can be applied using a variety of commonly known methods, such as screen printing and spraying.

(Membrane Electrode Assembly)
The membrane/electrode assembly (hereinafter also referred to as "MEA") of this embodiment preferably includes the above-mentioned electrode catalyst layer. Since the membrane/electrode assembly of this embodiment includes the above-mentioned electrode catalyst layer, it has excellent battery characteristics, mechanical strength, and stability. The membrane/electrode assembly can be suitably used for fuel cells.

A unit in which two types of electrode catalyst layers, an anode and a cathode, are bonded to both sides of an electrolyte membrane is called a membrane electrode assembly (hereinafter also referred to as "MEA"). An assembly in which a pair of gas diffusion layers are bonded to the outer sides of the electrode catalyst layers so that they face each other may also be called an MEA. The electrode catalyst layers are required to have proton conductivity.

The electrode catalyst layer serving as the anode contains a catalyst that easily produces protons by oxidizing fuel (e.g., hydrogen), and the electrode catalyst layer serving as the cathode contains a catalyst that reacts protons and electrons with an oxidant (e.g., oxygen or air) to produce water. For both the anode and the cathode, the above-mentioned catalytic metals can be suitably used as the catalyst.

The gas diffusion layer may be made of commercially available carbon cloth, carbon paper, carbon felt, etc. These gas diffusion layers are preferably treated with polytetrafluoroethylene or the like to make them water repellent.
Specific examples include carbon fiber Torayca (manufactured by Toray Industries, Inc.), Pyrofil (manufactured by Mitsubishi Chemical Corporation), and SIGRACET GDL (manufactured by MFC Technologies, Inc.).

The MEA can be produced, for example, by sandwiching an electrolyte membrane between electrode catalyst layers and bonding them by heat pressing. More specifically, the polymer electrolyte is dispersed or dissolved in a mixed solution of alcohol and water, and a commercially available platinum-supported carbon (for example, TEC10E40E manufactured by Tanaka Kikinzoku Co., Ltd.) is dispersed as a catalyst in the resulting mixture to form a paste. A certain amount of this is applied to one side of each of two PTFE sheets and dried to form an electrode catalyst layer. Next, the coated surfaces of the PTFE sheets are placed face to face, an electrolyte membrane is sandwiched between them, and the sheets are transferred and bonded by heat pressing at 100 to 200°C, and then the PTFE sheets are removed to obtain an MEA. The method of producing an MEA is well known to those skilled in the art. The method of producing an MEA is described in detail, for example, in JOURNAL OF APPLIED ELECTROCHEMISTRY, 22 (1992), pp. 1-7.

The above-mentioned MEA (including an MEA with a pair of gas diffusion electrodes facing each other) is further combined with components used in general fuel cells, such as bipolar plates and backing plates, to form a fuel cell.

(Fuel cell)
The fuel cell of this embodiment preferably includes the membrane electrode assembly. The fuel cell is preferably a polymer electrolyte fuel cell. The fuel cell is not particularly limited as long as it includes the membrane electrode assembly, and may generally include components such as gas that constitute a fuel cell. Since the fuel cell includes the membrane electrode assembly having the electrode catalyst layer, it has excellent cell characteristics and mechanical strength, and is excellent in stability.

A bipolar plate is a composite material of graphite and resin, or a metal plate, with grooves on its surface for the flow of gases such as fuel and oxidant. In addition to transmitting electrons to an external load circuit, bipolar plates also function as flow paths that supply fuel and oxidant to the vicinity of the electrode catalyst. A fuel cell is manufactured by stacking multiple bipolar plates by inserting an MEA between them.

The present invention will now be described with reference to examples, but the present invention is not limited to these examples.

(Ion exchange capacity)
A polymer electrolyte membrane with a size of approximately 2 to 20 cm2 in which the counter ions of the ion exchange groups are in the state of protons was immersed in ³⁰ ml of a saturated NaCl aqueous solution at 25°C and left for 30 minutes while stirring. Next, the protons in the saturated NaCl aqueous solution were neutralized by titration with a 0.01N aqueous sodium hydroxide solution using phenolphthalein as an indicator. The polymer electrolyte membrane obtained after neutralization in which the counter ions of the ion exchange groups are in the state of sodium ions was rinsed with pure water, further vacuum dried, and weighed. The amount of sodium hydroxide required for neutralization was M (mmol), and the weight of the polymer electrolyte membrane in which the counter ions of the ion exchange groups are sodium ions was W (mg), and the equivalent weight EW (g/eq) was calculated by the following formula.
EW = (W/M) - 22

(Oxygen Solubility)
The oxygen solubility of the polymer electrolyte membrane was measured using the chronoamperometry method. A glass-encapsulated platinum microelectrode with a diameter of 100 μm was pressed against a sample with a thickness of about 200 μm to adjust the temperature and humidity. After the potential was held at 1100 mV (vs. SHE) under a nitrogen or oxygen atmosphere, the potential was stepped to 400 mV to measure the current value. The difference in the current values observed under the nitrogen and oxygen atmospheres was plotted against the power of −1/2 of the applied time, and the oxygen solubility was calculated using the following formula within the range where linearity was obtained.
I = 4πFrDc [1 + r/(πDt) ^1/2 + 0.2732 exp {-0.3911r/(Dt) ^1/2 }]
In the above, I is the current value (A), F is the Faraday constant (96,500 C/mol), r is the electrode radius (cm), D is the oxygen diffusion coefficient (cm ² /s), c is the oxygen solubility (mol/m ³ ), and t is time (s).
In this study, the oxygen solubility was evaluated at a temperature of 80° C. and a humidity of 30%.

(SEM Observation)
The surface of the catalyst layer prepared by the die coater was observed using a scanning electron microscope (product name: VE8800, manufactured by Keyence Corporation) at a magnification of 50 times and an acceleration voltage of 1 kV. As a result of the observation, the catalyst layer surface was marked with "A" (good) when no cracks were observed, and marked with "B" (poor) when cracks were observed.

(Fuel cell evaluation)
In order to evaluate the performance of the MEA under high temperature and low humidity conditions, a power generation test was carried out according to the following procedure.
(1) Preparation of electrode catalyst ink A polymer electrolyte solution with a solid content concentration of 15% by mass and an electrode catalyst (TEC10E40E, manufactured by Tanaka Kikinzoku Kogyo K.K., platinum loading 36.7 wt%) were mixed so that the platinum/perfluorosulfonic acid polymer was 1/1.15 (by mass), and then ethanol was added so that the solid content (sum of the electrode catalyst and perfluorosulfonic acid polymer) was 11 wt%, and the mixture was stirred with a homogenizer (manufactured by AS ONE CORPORATION) at a rotation speed of 3000 rpm for 10 minutes to obtain an electrode catalyst ink.
(2) Preparation of electrode catalyst layer Using a die coater (product name: Rika Die, manufactured by Itochu Fine Techno Co., Ltd.), the above electrode catalyst ink was applied to a Teflon (registered trademark) substrate (product name: Naflon Tape, manufactured by Nichias Corporation) with a thickness of 100 μm so that the amount of platinum was 0.2 mg/ ^cm2 , and the coating was dried and solidified under conditions of 160° C. and 5 minutes to obtain an electrode catalyst layer.
(3) Preparation of MEA Using a press (product name: SFA-37, manufactured by Shinto Metal Industries Co., Ltd.), an electrode catalyst layer using NafionDE2020CS as a polymer electrolyte on the anode side and an electrode catalyst layer using the polymer electrolyte of this embodiment on the cathode side were hot-pressed on both sides of an electrolyte membrane (product name: NafionHP, manufactured by Chemours) at a temperature of 160° C. and a pressure of 13 MPa to obtain an MEA.
(4) Preparation of a Single Fuel Cell A gas diffusion layer (product name: GDL35BC, manufactured by MFC Technologies) was laminated on both electrodes of the MEA, and then a gasket, a bipolar plate, and a backing plate were laminated to obtain a single fuel cell.
(5) Power Generation Test The above single fuel cell was set in an evaluation device (Fuel Cell Evaluation System 890CL manufactured by Toyo Corporation) and a power generation test was carried out.
The power generation test conditions were as follows: high humidity condition: cell temperature 65° C., anode and cathode humidification bottles 60° C., low humidity condition: cell temperature 90° C., anode and cathode humidification bottles 61° C., hydrogen gas was supplied to the anode side and air gas was supplied to the cathode side at 900 ml/min. Both the anode side and the cathode side were unpressurized (atmospheric pressure).
Under the above-mentioned high humidity conditions, if the voltage value was 0.830 V or more at a current density of 0.2 A/ ^cm2 , it was indicated as "A" (excellent), if it was more than 0.820 V and less than 0.830 V, it was indicated as "B" (average), if it was 0.820 V or less, it was indicated as "C" (poor), if the voltage value was 0.685 V or more at a current density of 0.8 A/ ^cm2, it was indicated as "A" (excellent), if it was more than 0.675 V and less than 0.685 V, it was indicated as "B" (average), and if it was 0.675 V or less, it was indicated as "C" (poor).
In addition, under the above-mentioned low humidification conditions, if the voltage value was 0.750 V or more at a current density of 0.2 A/ ^cm2 , it was indicated as "A" (excellent), if it was more than 0.720 V and less than 0.750 V, it was indicated as "B" (average), if it was 0.720 V or less, it was indicated as "C" (poor), if the voltage value was 0.550 V or more at a current density of 0.8 A/ ^cm2 , it was indicated as "A" (excellent), if it was more than 0.440 V and less than 0.550 V, it was indicated as "B" (average), and if it was 0.440 V or less, it was indicated as "C" (poor).

(Chemical durability)
The above single fuel cell was set in an evaluation device (Toyo Technica Fuel Cell Evaluation System 890CL) and an OCV test was performed under the following conditions: cell temperature 90°C, humidification bottle 61°C (relative humidity 30% RH), hydrogen gas on the anode side, and air gas on the cathode side, each at 300 cc/min.
To determine the end point of the OCV test, a micro gas chromatograph (product name: CP-4900, manufactured by GL Sciences) was connected to the cathode side, and the concentration of _H2 gas permeating from the anode side was measured. The end point was determined to be the time when the concentration of _H2 gas exceeded 1000 ppm. The end point was indicated as "A" (good) for 200 hours or more, and "B" (bad) for less than 200 hours.

(Proportion of structural units)
The introduction rate of the benzodioxole structural unit was calculated by subjecting the polymer electrolyte to H-NMR and F-NMR analysis, and combining the results with the amount of proton-conductive groups introduced by EW measurement.

得られたポリマーＡ３をエタノールとともに５Ｌオートクレーブ中に入れて密閉し、窒素置換した後、翼で攪拌しながら１６０℃まで昇温して３時間保持した。その後、オートクレーブを自然冷却して、固形分濃度１０質量％の均一なポリマー溶液を作製した。
得られた固形分濃度１０質量％のポリマー溶液を８０℃にて減圧濃縮して、固形分濃度１５質量％のポリマー溶液ＡＳ１（高分子電解質溶液）を作製した。
上記ＡＳ１を用いて上述の方法によりキャスト製膜して、厚み２００μｍの膜ＡＭ１を作製した。ＡＭ１のＥＷ及び酸素溶解度を表１に示す。またＡＳ１を含む電極触媒層のひび割れ有無、電池性能及び化学耐久性の結果を表２に示す。
ＡＭ１は高い酸素溶解度を示す。またＡＳ１を含む電極触媒層にはひび割れがなく、電池性能及び化学耐久性が比較例の材料よりも高いことが分かる。 Example 1
In a 300 ml three-neck flask, 4.2 g (22 mmol) of 5-bromoresorcinol, 50 ml of dehydrated N,N-dimethylacetamide, and 4.9 g (49 mmol) of triethylamine were placed, replaced with nitrogen, and then capped, followed by stirring and mixing at room temperature. 4.7 g (22 mmol) of octafluorocyclopentene was placed, and the mixture was stirred at room temperature for 30 minutes, then stirred at 50°C for 30 minutes, then stirred at 80°C for 30 minutes, and then stirred and mixed at 100°C for 24 hours. After the reaction was completed, the mixture was allowed to cool, and the reaction solution was poured into 500 mL of ion-exchanged water, filtered under reduced pressure with a glass filter, thoroughly washed with ion-exchanged water, and dried under reduced pressure at 60°C for 12 hours. The obtained polymer A1 was a light brown solid, and the yield was 6.0 g (yield 77%). In ¹⁹ F-NMR (d-DMSO), broad peaks with an integral ratio of 4 were observed at -113 to -121 ppm, and broad peaks with an integral ratio of 2 were observed at -133 to -137 ppm.
Next, the introduction reaction of a benzodioxole derivative was carried out as follows.
In a 300 ml three-neck flask, 5.0 g of the above A1, 50 ml of dehydrated N,N-dimethylacetamide, 5.7 g (42 mmol), and 5.7 g (42 mmol) of potassium carbonate were placed, substituted with nitrogen, and capped. Then, the mixture was stirred and mixed at 100° C. for 24 hours. After the reaction was completed, the mixture was allowed to cool, and the reaction solution was poured into 500 mL of ion-exchanged water, filtered under reduced pressure with a glass filter, thoroughly washed with ion-exchanged water, and dried under reduced pressure at 60° C. for 12 hours. The obtained polymer A2 was a light brown solid, and the yield was 5.0 g (yield 61%). In ¹⁹ F-NMR (d-DMSO), broad peaks with an integral ratio of 2 were observed at -113 to -121 ppm and at -133 to -137 ppm.
Next, a reaction for introducing a sulfonic acid group was carried out as follows.
In a 300 mL three-neck flask, 4.0 g of the above A2, 3.0 g of copper powder having a diameter of 100 nm, and 20 mL of dimethyl sulfoxide were placed, replaced with nitrogen, and then capped, and mixed by stirring at 120 ° C. for 2 hours. Next, referring to Macromolecules, 2009, Vol. 42, p. 9302-9306, 6.0 g (13 mmol) of potassium 1,1,2,2-tetrafluoro-2-(1,1,2,2-tetrafluoro-2-iodoethoxy)ethanesulfonate obtained by hydrolysis of 1,1,2,2-tetrafluoro-2-(1,1,2,2-tetrafluoro-2-iodoethoxy)ethanesulfonyl fluoride was dissolved in 20 ml of dimethyl sulfoxide, dropped into the reaction solution, and mixed by stirring at 120 ° C. for 6 hours. After the reaction was completed, the flask was cooled, and the reaction solution was filtered through Celite to remove the copper powder. The filtrate was then dropped into 500 mL of 5N hydrochloric acid, centrifuged, and filtered under reduced pressure to recover the precipitate. This was repeated three more times. The supernatant was then washed with ion-exchanged water until the pH of the supernatant became neutral. The solid obtained was dried under reduced pressure at 50° C. for 12 hours. The polymer A3 obtained was a black solid, with a yield of 2.8 g (52% yield) (formula (14)). The molar ratio of the benzodioxole structural unit in polymer A3 was 100 mol%.

The obtained polymer A3 was placed in a 5 L autoclave together with ethanol, sealed, and purged with nitrogen, and then heated to 160° C. with stirring by a blade and maintained for 3 hours. Thereafter, the autoclave was naturally cooled to prepare a homogeneous polymer solution with a solid content concentration of 10 mass %.
The obtained polymer solution having a solid content concentration of 10% by mass was concentrated under reduced pressure at 80° C. to prepare a polymer solution AS1 (polymer electrolyte solution) having a solid content concentration of 15% by mass.
The AS1 was used to produce a 200 μm-thick membrane AM1 by the above-mentioned method. The EW and oxygen solubility of AM1 are shown in Table 1. Table 2 also shows the results of the presence or absence of cracks in the electrode catalyst layer containing AS1, as well as the cell performance and chemical durability.
AM1 exhibits high oxygen solubility, and the electrode catalyst layer containing AS1 is crack-free and has higher cell performance and chemical durability than the comparative materials.

実施例１と同様な方法で溶液化し、固形分濃度１５質量％のポリマー溶液ＢＳ１（高分子電解質溶液）を得た。上記ＢＳ１を用いて上述の方法によりキャスト製膜して、厚み２００μｍの膜（ＢＭ１）を作製した。ＢＭ１のＥＷ及び酸素溶解度を表１に示す。またＢＳ１を含む電極触媒層のひび割れ有無、電池性能及び化学耐久試験の結果を表２に示す。
ＢＭ１は高い酸素溶解度を示す。またＢＳ１を含む電極触媒層にはひび割れがなく、電池性能及び化学耐久性が比較例の材料よりも高いことが分かる。 Example 2
In a 300 ml three-neck flask, 13 g (94 mmol) of sesamol, 50 ml of dehydrated N,N-dimethylacetamide, and 11 g (105 mmol) of triethylamine were placed, replaced with nitrogen, and then capped, followed by stirring and mixing at room temperature. 10 g (47 mmol) of octafluorocyclopentene was placed, stirred at room temperature for 2 hours, and then stirred and mixed at 80°C for 6 hours. After the reaction was completed, the reaction solution was allowed to cool, and 200 mL of ion-exchanged water and 200 mL of ethyl acetate were added to the reaction solution. The organic layer was dried with sodium sulfate, filtered under reduced pressure with a glass filter, and the solvent was removed with an evaporator. The mixture was then purified by column chromatography to obtain Compound B1, in which R ₁ and R ₂ in formula (10) are hydrogen atoms, as a light brown solid in a yield of 16 g (78%). In ¹⁹ F-NMR (CDCl ₃ ), peaks with an integral ratio of 4 at -116 ppm and an integral ratio of 2 at -132 ppm were observed, respectively.
Next, 9.9 g (22 mmol) of the above B1, 4.2 g (22 mmol) of 5-bromoresorcinol, 50 ml of dehydrated N,N-dimethylacetamide, and 4.9 g (49 mmol) of triethylamine were placed in a 300 ml three-neck flask, substituted with nitrogen, and capped. Then, the flask was stirred and mixed at 100° C. for 24 hours. After the reaction was completed, the flask was cooled, and the reaction solution was poured into 500 mL of ion-exchanged water, filtered under reduced pressure with a glass filter, thoroughly washed with ion-exchanged water, and dried under reduced pressure at 60° C. for 12 hours. The obtained polymer B2 was a light brown solid, and the yield was 8.8 g (yield 67%). In ¹⁹ F-NMR (d-DMSO), broad peaks with an integral ratio of 2 were observed at -113 to -121 ppm and at -133 to -137 ppm.
The introduction reaction of sulfonic acid groups was carried out in the same manner as in Example 1, except that polymer B2 (6.0 g) was used, to obtain polymer B3 (formula (15)). The molar proportion of benzodioxole structural units in polymer B3 was 100 mol %.

The polymer solution BS1 (polymer electrolyte solution) having a solid content of 15% by mass was obtained by dissolving the polymer solution in the same manner as in Example 1. The BS1 was used to form a membrane by casting in the manner described above to produce a membrane (BM1) having a thickness of 200 μm. The EW and oxygen solubility of BM1 are shown in Table 1. Table 2 also shows the presence or absence of cracks in the electrode catalyst layer containing BS1, and the results of the cell performance and chemical durability test.
BM1 exhibits high oxygen solubility, and the electrode catalyst layer containing BS1 is crack-free and has higher cell performance and chemical durability than the comparative materials.

実施例１と同様な方法で溶液化し、固形分濃度１５質量％のポリマー溶液ＣＳ１（高分子電解質溶液）を得た。上記ＣＳ１を用いて上述の方法によりキャスト製膜して、厚み２００μｍの膜（ＣＭ１）を作製した。ＣＭ１のＥＷ及び酸素溶解度を表１に示す。またＣＳ１を含む電極触媒層のひび割れ有無、電池性能及び化学耐久試験の結果を表２に示す。
ＣＭ１は高い酸素溶解度を示す。またＣＳ１を含む電極触媒層にはひび割れがなく、電池性能及び化学耐久性が比較例の材料よりも高いことが分かる。 Example 3
A 100 ml three-neck flask was charged with 0.795 g (4.8 mmol) of azobisisobutyronitrile, 10 g (52 mmol) of 2,3,4,5,6-pentafluorostyrene, and 20 g of toluene, and the flask was replaced with nitrogen, capped, and mixed with stirring at 60° C. for 8 hours. After the reaction was completed, the flask was allowed to cool, and the reaction liquid was dropped into 200 ml of methanol, filtered under reduced pressure, and dried to obtain 4.9 g (49% yield) of polypentafluorostyrene C1 as a white solid. In ¹⁹ F-NMR (CDCl ₃ ), broad peaks with an integral ratio of 2 were observed at -140 to -147 ppm, an integral ratio of 1 at -153 to -157 ppm, and an integral ratio of 2 at -159 to -164 ppm.
Next, 4 g of the above polymer C1, 40 g of dehydrated N,N-dimethylacetamide, 1.6 g (12 mmol) of sesamol, and 1.6 g (12 mmol) of potassium carbonate were placed in a 200 ml three-neck flask, and the flask was capped after nitrogen replacement. The flask was then stirred and mixed at 90° C. for 6 hours. After the reaction was completed, the flask was cooled, and the reaction liquid was dropped into 200 ml of methanol, filtered under reduced pressure, and dried to obtain 3.0 g (yield 58%) of polymer C2, in which sesamol was introduced at the para position of polypentafluorostyrene, as a white solid. In ¹⁹ F-NMR (CDCl ₃ ), broad peaks with an integral ratio of 2 were observed at -140 to -147 ppm, an integral ratio of 0.5 at -153 to -157 ppm, and an integral ratio of 2 at -159 to -164 ppm. From NMR, the amount of benzodioxole structural units introduced was 50 mol%.
Next, 2.6 g of the above polymer C2, 8.2 g (31 mmol) of 18-crown 6-ether, 2 g (111 mmol) of water, 1.7 g (31 mmol) of potassium hydroxide, and 40 g of diethylene glycol dimethyl ether were placed in a 200 ml three-neck flask, and after replacing with nitrogen and capping, the flask was stirred and mixed at 90 ° C. for 6 hours. After cooling the reaction solution in air, the supernatant was removed, and 3.8 g of concentrated hydrochloric acid (37 parts by mass) and 40 g of ethanol were added, and the mixture was stirred and mixed at 60 ° C. for 1 hour. After the reaction was completed, the reaction solution was allowed to cool, dropped into 200 ml of water, filtered under reduced pressure, washed with water, and dried to obtain 2.3 g (yield 89%) of polymer C3 in which a hydroxyl group was introduced at the para position of polypentafluorostyrene as a light brown solid. In ¹⁹ F-NMR (CDCl ₃ ), broad peaks with an integral ratio of 2 were observed at -140 to -149 ppm and at -163 to -167 ppm, respectively, but it was confirmed that there was no peak at -153 to -157 ppm corresponding to the para position.
Further, 2 g of the above polymer C3, 0.48 g (65%, 13 mmol) of sodium hydride, and 40 g of 1,2-dimethoxyethane were added to a 200 ml three-neck flask, and the flask was replaced with nitrogen, capped, and then stirred and mixed at 50° C. for 1 hour. The reaction liquid was air-cooled, and then 3.7 g (12 mmol) of CF ₂ ═CF-OCF ₂ CF ₂ SO ₃ Na was added, and the mixture was stirred and mixed at 90° C. for 6 hours. After the reaction was completed, the solvent was removed by vacuum drying, and the remaining solid was washed five times with 60 ml of diethyl ether, and 60 ml of a 0.5 M solution of hydrogen chloride in methanol was added, and the mixture was stirred and mixed for 1 hour, followed by filtration, washing with water, and vacuum drying to obtain 1.8 g (yield 58%) of polymer C4 of formula (16) into which a sulfonic acid group had been introduced. In the solid-state ^19F -NMR, broad peaks with integral ratios of 4 at -70 to -100 ppm, 2 at -110 to -120 ppm, and 9 at -130 to -170 ppm were observed. From NMR and EW, the amount of sulfonic acid groups introduced was 50 mol%. The molar ratio of benzodioxole structural units in polymer C4 was 50 mol%.

The polymer solution CS1 (polymer electrolyte solution) having a solid content of 15% by mass was obtained by dissolving the polymer solution in the same manner as in Example 1. The CS1 was used to form a film by casting using the above-mentioned method to produce a film (CM1) having a thickness of 200 μm. The EW and oxygen solubility of CM1 are shown in Table 1. Table 2 also shows the presence or absence of cracks in the electrode catalyst layer containing CS1, and the results of the cell performance and chemical durability test.
CM1 exhibits high oxygen solubility, and the electrode catalyst layer containing CS1 is crack-free and has higher cell performance and chemical durability than the comparative materials.

実施例１と同様な方法で溶液化し、固形分濃度１５質量％のポリマー溶液ＤＳ１（高分子電解質溶液）を得た。上記ＤＳ１を用いて上述の方法によりキャスト製膜して、厚み２００μｍの膜（ＤＭ１）を作製した。ＤＭ１のＥＷ及び酸素溶解度を表１に示す。またＤＳ１を含む電極触媒層のひび割れ有無、電池性能及び化学耐久試験の結果を表２に示す。
ＤＭ１は高い酸素溶解度を示す。またＤＳ１を含む電極触媒層にはひび割れがなく、電池性能及び化学耐久性が比較例の材料よりも高いことが分かる。 Example 4
Into a glass cylinder for a 100 mL autoclave, a copolymer (3.5 g) of tetrafluoroethylene and CF ₂ ═CFOCF ₂ CF ₂ SO ₂ F obtained by radical polymerization and Novec ^™ 7300 (70 g) manufactured by 3M were charged and dissolved by stirring under nitrogen at 160° C. for 2 hours. After cooling, the solution was taken out and the solid content weight was measured at 200° C. for 1 hour, which was 5.0 wt % of the solution (D1). Into another glass cylinder for a 100 mL autoclave, N,N-diisopropylethylamine (2.8 g, 21 mmol) and piperonylamine (2.6 g, 17 mmol) were added and mixed uniformly. Further, the above solution D1 (40 g) and Novec ^™ 7300 (40 g) were added to the same glass cylinder and reacted by stirring under nitrogen at 130° C. for 6 hours. After cooling, the reaction solution was slowly poured into 400 cc of ethanol, and the precipitate was collected by filtration and washed with ethanol until the deep yellow coloring component was removed. The obtained deep yellow solid was dried to obtain polymer precursor D2. The above polymer precursor D2 was contacted with an aqueous solution of potassium hydroxide (15 mass%) dissolved therein at 70° C. for 10 hours, immersed in 70° C. water for 5 hours, and then immersed in 2N hydrochloric acid aqueous solution at 70° C. for 1 hour, and the process was repeated four times, followed by washing with ion-exchanged water and drying to obtain polymer D3 (2.0 g) (formula (17)). The molar ratio of the benzodioxole structural unit of polymer D3 was 12 mol%.

The polymer solution was dissolved in the same manner as in Example 1 to obtain a polymer solution DS1 (polymer electrolyte solution) having a solid content of 15% by mass. The DS1 was cast into a membrane by the above-mentioned method to produce a membrane (DM1) having a thickness of 200 μm. The EW and oxygen solubility of DM1 are shown in Table 1. Table 2 also shows the presence or absence of cracks in the electrode catalyst layer containing DS1, and the results of the cell performance and chemical durability test.
DM1 exhibits high oxygen solubility, and the electrode catalyst layer containing DS1 is crack-free and has higher cell performance and chemical durability than the comparative materials.

(Comparative Example 1)
A cast membrane having a thickness of 200 μm was formed using a commercially available Nafion solution (Nafion DE2020CS, manufactured by SIGMA-ALDRICH) in the same manner as in Example 1, and the EW and oxygen solubility were measured. The results are shown in Table 1.
Furthermore, an electrode catalyst layer was prepared using the above Nafion solution in the same manner as in Example 1, and tests were carried out to check for cracks, as well as cell performance and chemical durability. The results are shown in Table 2.
Nafion DE2020CS has low oxygen solubility and cracks in the electrode catalyst layer, which reduces the cell performance and chemical durability.

(Comparative Example 2)
A copolymer (69.8 mol%/30.2 mol%) of perfluoro(2,2-dimethyl-1,3-dioxole) and _CF2 = _CFOCF2CF ( _CF3 ) _OCF2CF2SO2F obtained by radical polymerization was used as a polymer precursor, and a polymer electrolyte consisting of perfluoro( _2,2 -dimethyl-1,3-dioxole)/ _CF2 = _CFOCF2CF ( _CF3 ) _OCF2CF2SO3H was obtained by hydrolysis treatment in the same manner as in Example 4. _{Perfluorosulfonic} acid resin solution-1 and a cast membrane having a thickness of 200 μm were prepared in the same manner as in Example 1. The _EW and _oxygen solubility of the cast membrane are shown in Table 1.
Moreover, an electrode catalyst layer was prepared using the above perfluorosulfonic acid resin solution-1 in the same manner as in Example 1, and tests were carried out to check for the presence or absence of cracks, as well as the cell performance and chemical durability. The results are shown in Table 2.
The cast membrane using the perfluorosulfonic acid resin solution-1 has a high oxygen solubility, but cracks occur in the electrode catalyst layer, resulting in poor cell performance and chemical durability.

Claims (6)

The compound includes a benzodioxole structural unit having a benzodioxole derivative skeleton in a side chain, the skeleton including the structure represented by the following formula (1):
The ratio of the benzodioxole structural unit in 100 mol % of the polymer electrolyte is 12 to 100 mol %,
The oxygen solubility measured by the Pt thick film method under the condition of 80°C and 30% RH is 7.0 mol/m3 or ^more ,
A polymer electrolyte having an equivalent weight EW of 100 to 2000 g/eq.

(In formula (1), R ₁ and R ₂ each independently represent a hydrogen atom, a fluorine atom, or an organic group; X each independently represent a structure containing an ether bond or a sulfonamide bond; Y each independently represent a hydrogen atom, a fluorine atom, or an organic group; a and b each independently represent an integer, a+b=4, a≧1.) The polymer electrolyte according to claim 1 , wherein in the formula (1), X includes a structure represented by the following formula (2) or the following formula (3):

(In formulas (2) and (3), R ₃ , R ₄ , and R ₅ each independently represent a hydrogen atom, a fluorine atom, or an organic group, l represents an integer of 1 to 10, and * represents a bond.) An electrode catalyst ink comprising the polymer electrolyte according to claim 1 or 2 and a catalyst. An electrode catalyst layer comprising the polymer electrolyte according to claim 1 or 2 and a catalyst . A membrane electrode assembly comprising the electrode catalyst layer according to claim 4 and an electrolyte membrane. A fuel cell comprising the membrane electrode assembly according to claim 5.