JP5482415B2 - Ionomer for electrode catalyst of fuel cell and method for producing electrode catalyst using the ionomer - Google Patents

Description

  TECHNICAL FIELD The present invention relates to an ionomer for an electrode catalyst of a fuel cell and a method for producing an electrode catalyst using the ionomer, and more specifically, an aromatic polyether ionomer having a phosphonic acid group in the side chain and an electrode using the ionomer. The present invention relates to a method for producing a catalyst.

  Conventionally, for example, Patent Document 1 discloses an electrode catalyst in which a polyethylene-based polymer having a phosphonic acid group in a side chain is applied to an ionomer. In this polyethylene-based polymer, the phosphonic acid group is bonded to the carbon atom of the main chain directly or indirectly via an alkylene group, an alkyleneoxy group or the like. And the fuel cell which used this polyethylene-type polymer for the electrode catalyst has shown the stable ion conductivity in the temperature range of 80 to 160 degreeC.

Special table 2007-504333 gazette

By the way, in a polymer electrolyte fuel cell, a reaction other than a normal electrochemical reaction that consumes hydrogen and oxygen to generate water may occur. One of the reactions is hydrogen peroxide (H ₂ O ₂ ) generation reaction. Hydrogen peroxide is generated, for example, when protons react with oxygen molecules in the electrode catalyst layer of the fuel cell. The generated hydrogen peroxide generates radicals with strong oxidizing power such as hydroxy radicals and peroxide radicals. For this reason, if these radicals move from the electrode catalyst layer to the electrolyte membrane, the polymer main chain constituting the electrolyte membrane may be decomposed. As a result, the deterioration of the electrolyte membrane may progress.

  Therefore, the fuel cell electrode catalyst is required to have radical resistance in addition to various characteristics. Of course, when a polymer having a phosphonic acid group in the side chain is also used as an ionomer, it is desirable to have radical resistance. However, the above-mentioned Patent Document 1 does not mention radicals, and therefore the characteristics of polymer radicals are unknown. Therefore, radical resistance may be insufficient.

  This invention was made in order to solve the above-mentioned subject, and it aims at providing the manufacturing method of the ionomer provided with radical tolerance, and this ionomer using this ionomer.

（式（１）中、Ｒ^ｆは炭素数１〜３のパーフルオロアルキレン基を表し、Ｘは水素原子又は炭素数１〜３のパーフルオロアルキレンホスホン酸基を表し、Ｙは−Ｏ−又は水素原子を表す。） In order to achieve the above object, a first invention is an ionomer for an electrode catalyst of a fuel cell,
An aromatic polyether having at least one structure represented by the following formula (1) in the repeating unit is used.

(In Formula (1), ^Rf represents a C1-C3 perfluoroalkylene group, X represents a hydrogen atom or a C1-C3 perfluoroalkylenephosphonic acid group, Y represents -O- or hydrogen. Represents an atom.)

The second invention is the first invention, wherein
The aromatic polyether has a repeating unit represented by the following formula (2).

The third invention is the first invention, wherein
The aromatic polyether has a repeating unit represented by the following formula (3).

（式（４）中、Ｒ_１及びＲ_２は、炭素数１〜２０の直鎖状又は分岐状のアルキル基、炭素数１〜２０の直鎖状又は分岐状のアルキレン基、炭素数３〜２０の脂環式有機基あるいは炭素数６〜２０のアリール基を表す。） The fourth invention is a method for producing an electrode catalyst in order to achieve the above object,
A first step of preparing a catalyst ink by mixing an aromatic polyether having at least one structure represented by the following formula (4) in a repeating unit, a catalyst-supporting carbon, and a solvent;
A second step of removing the solvent of the catalyst ink obtained in the first step;
After the second step, a third step of hydrolyzing the phosphonic acid ester in the side chain of the aromatic polyether;
It is characterized by providing.

(In the formula (4), _{R 1} and _{R 2} are linear or branched alkyl group having 1 to 20 carbon atoms, straight-chain or branched alkylene group having 1 to 20 carbon atoms, 3 carbon 20 represents an alicyclic organic group or an aryl group having 6 to 20 carbon atoms.)

（式（５）中、Ｒ_１及びＲ_２は、炭素数１〜２０の直鎖状又は分岐状のアルキル基、炭素数１〜２０の直鎖状又は分岐状のアルキレン基、炭素数３〜２０の脂環式有機基あるいは炭素数６〜２０のアリール基を表す。） The fifth invention is the fourth invention, wherein
The aromatic polyether is an aromatic polyether ether sulfone represented by the following formula (5).

(In formula (5), _{R 1} and _{R 2} are linear or branched alkyl group having 1 to 20 carbon atoms, straight-chain or branched alkylene group having 1 to 20 carbon atoms, 3 carbon 20 represents an alicyclic organic group or an aryl group having 6 to 20 carbon atoms.)

（式（６）中、Ｒ_１及びＲ_２は、炭素数１〜２０の直鎖状又は分岐状のアルキル基、炭素数１〜２０の直鎖状又は分岐状のアルキレン基、炭素数３〜２０の脂環式有機基あるいは炭素数６〜２０のアリール基を表す。） The sixth invention is the fourth invention, wherein
The aromatic polyether is an aromatic polyether ether ketone represented by the following formula (6).

(In the formula (6), _{R 1} and _{R 2} are linear or branched alkyl group having 1 to 20 carbon atoms, straight-chain or branched alkylene group having 1 to 20 carbon atoms, 3 carbon 20 represents an alicyclic organic group or an aryl group having 6 to 20 carbon atoms.)

  According to the 1st-3rd invention, the ionomer provided with radical tolerance can be provided. Moreover, according to the 4th-6th invention, the manufacturing method of the electrode catalyst using the ionomer provided with radical tolerance can be provided.

Embodiment.
<Ionomer for Electrocatalyst>
First, the ionomer for an electrode catalyst of the present invention (in the following description, “ionomer for an electrode catalyst” is also simply referred to as “ionomer”) will be described while disclosing a production method thereof. The ionomer of the present invention uses an aromatic polyether, specifically, an aromatic polyether ether sulfone represented by the following formula (7) or an aromatic polyether ether ketone represented by (8) as a starting material.

(Iodobenzoyl group introduction process)
2-iodobenzoic acid is reacted with the above starting material, and an iodobenzoyl group is introduced into the aromatic ring constituting the main chain of the aromatic polyether of the above formulas (7) and (8). According to this step, since a reaction with high regioselectivity can be caused, an iodobenzoyl group can be introduced at a specific position of the aromatic ring.

  The introduced iodobenzoyl group functions as a spacer for introducing the perfluoroalkylene phosphonate onto the aromatic ring. In addition, the substitution position of iodobenzoic acid is not limited to this position, and the number of iodo substitutions may be 1 or more. Examples of such other iodobenzoic acid include 4-iodobenzoic acid, 2,4-diiodobenzoic acid, 2,6-diiodobenzoic acid, and 2,4,6-triiodobenzoic acid.

  The addition amount of 2-iodobenzoic acid can be prepared according to the number of iodobenzoyl groups introduced into the repeating unit. Specifically, the aromatic polyether of the above formula (7) is prepared so that the substance amount ratio is 1: 1 to 1: 2 for the purpose of introducing one iodobenzoyl group per repeating unit. It is preferable. Similarly, in the aromatic polyether of the above formula (8), the purpose is to introduce four iodobenzoyl groups per repeating unit, so that the substance amount ratio should be 1: 4 to 1: 6. Is preferred.

  This step is performed by dissolving the starting material in trifluoromethanesulfonic acid and then adding iodobenzoic acid. The dissolution is not limited to trifluoromethanesulfonic acid, and for example, an acid such as phosphorus pentoxide-methanesulfonic acid mixed solution (PPMA), acetic acid, methanesulfonic acid, trifluoroacetic acid, sulfuric acid, chlorosulfuric acid, and fluorosulfuric acid is used. May be.

  This step is performed by adding 2-iodobenzoic acid and reacting at room temperature for 3 hours. The reaction time can be adjusted from 1 to 48 hours, but if it is 2 hours or longer, a desired polymer intermediate can be obtained. Moreover, reaction temperature can be prepared at 10 to 120 degreeC.

（式（９）中、Ｒ^ｆは炭素数１〜３のパーフルオロアルキレン基を表し、Ｒ_１及びＲ_２はホスホン酸を構成する水酸基に対する保護基を表す。） (Ester group substitution step)
Subsequently, the polymer intermediate obtained by the iodobenzoyl group introduction step is reacted with a monobromoperfluoroalkylenephosphonic acid ester represented by the following formula (9). According to this step, the iodo group on the benzene ring of the introduced iodobenzoyl group can be substituted with a perfluoroalkylenephosphonic acid ester group.

(In the formula (9), ^{R f} represents a perfluoroalkylene group having 1 to 3 carbon atoms, _{R 1} and _{R 2} represents a protecting group for the hydroxyl group constituting the phosphonic acid.)

As the protecting group for the phosphonic acid represented by R ₁ and R ₂ , both ethyl groups are used, but the reactivity as the phosphonic acid ester is not lowered, and the physical properties of the polymer intermediate after substitution with the phosphonic acid ester are reduced. Other protecting groups can be used as long as they are not changed. Examples of such other protecting groups include linear or branched alkyl groups having 1 to 20 carbon atoms, linear or branched alkylene groups having 1 to 20 carbon atoms, and alicyclic rings having 3 to 20 carbon atoms. And an organic group and an aryl group having 6 to 20 carbon atoms.

  Examples of the linear or branched alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a t-butyl group, and an n-pentyl group. , N-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group and the like.

  Examples of the linear or branched alkylene group having 1 to 20 carbon atoms include a vinyl group, 1-methylethenyl group, allyl group, 3-butenyl group, 1-methylallyl group, 2-methylallyl group, 4- A pentenyl group, 5-hexenyl group, etc. can be mentioned.

  Examples of the alicyclic organic group having 3 to 20 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a bornyl group, a norbornyl group, an adamantyl group, a pinanyl group, a tuyoyl group, and a camphanyl group. Can be mentioned.

  Examples of the aryl group having 6 to 20 carbon atoms include a phenyl group, o-tolyl group, m-tolyl group, p-tolyl group, p-hydroxyphenyl group, 1-naphthyl group, 1-anthracenyl group, and benzyl. Groups and the like.

  Moreover, the hydrogen atom on these alkyl groups, alkenyl groups, alicyclic organic groups, and aryl groups may be substituted with a functional group containing an oxygen atom. Examples of the functional group containing an oxygen atom include a hydroxyl group, a hydroxycarbonyl group, and an alkoxy group.

  The addition amount of the phosphonic acid ester of the above formula (7) can be prepared according to the number of iodobenzoyl groups introduced into the repeating unit. Specifically, in the polymer intermediate derived from the aromatic polyether of the above formula (7), since the purpose is to introduce one iodobenzoyl group per repeating unit, the substance amount ratio is 1: 1 to 1: 3. It is preferable to prepare such that Similarly, in the polymer intermediate derived from the aromatic polyether of the above formula (8), since the purpose is to introduce four iodobenzoyl groups per repeating unit, the substance amount ratio is 1: 6 to 1:10. It is preferable to prepare such that

  This step is performed by a cross coupling reaction with a copper catalyst interposed. First, a reaction solution used for the coupling reaction is prepared. This reaction solution is prepared by two-step stirring. First, zinc powder is added to the solvent, and then the phosphonic acid ester represented by the above formula (9) is added and stirred (stirring in the first stage). Here, N, N-dimethylformamide (DMF) is used as the solvent, but any solvent may be used as long as it does not cause decomposition or the like under the cross-coupling reaction conditions. For example, chloroform, dichloromethane, A solvent such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran (THF), methanol, acetone or the like may be used. The first stage of stirring is performed at room temperature for 2 hours, but can be prepared at 10 to 120 ° C. for 1 to 4 hours.

  Subsequently, a copper catalyst is added to the reaction solution and further stirred for about 1 hour (second stage stirring). Here, copper bromide (I) is used as the copper catalyst, but a copper catalyst usually used in a cross-coupling reaction for carbon-carbon generation may be used. Examples of such other copper catalysts include copper (II) bromide, copper (I) chloride, copper (II) chloride, copper (I) iodide, copper (II) iodide, and the like.

  The polymer intermediate obtained in the iodobenzoyl group introduction step is added to the reaction solution thus prepared and reacted. In addition, it is preferable from a soluble viewpoint that a polymer intermediate is added after melt | dissolving in the same solvent as the solvent used when preparing the reaction solution. This reaction is carried out at room temperature for 24 hours, but can be prepared at 10 to 120 ° C. for 12 to 48 hours.

(Deprotection process)
Subsequently, hydrolysis is performed on the polymer intermediate having the perfluoroalkylenephosphonic acid ester group introduced therein. According to this step, the phosphonic acid protecting group can be eliminated to impart ion conductivity to the polymer.

  In this step, specifically, the polymer intermediate is dissolved in a solvent, and then an acid or alkali solution is added. This hydrolyzes the phosphonate to remove the protecting group. Here, a known acid or alkali solution can be used for the hydrolysis. However, in general, a solid polymer electrolyte fuel cell is operated under acidic conditions, and therefore, when an alkaline solution is used, a separate treatment such as neutralization is required. Therefore, from the viewpoint of simplifying the hydrolysis treatment, it is preferable to use an acid solution for the hydrolysis. As such an acid, inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, perchloric acid, hydrofluoric acid and phosphoric acid can be preferably used.

  The polymer obtained through the above steps has good ion conductivity and radical resistance, as will be apparent from Examples described later, and exhibits characteristics equivalent to an expensive ionomer such as Nafion (registered trademark). Therefore, when this polymer is applied to an ionomer, the deterioration of the electrolyte membrane due to radicals can be suppressed, so that a fuel cell having a long-term stable power generation characteristic can be provided at a low cost.

<Method for producing electrode catalyst>
Next, the manufacturing method of the electrode catalyst which used the said polymer for ionomer is demonstrated.
As described above, the polymer is excellent in ionic conductivity and radical resistance. However, there is a problem that the above polymer is soluble only in a solvent having a high boiling point. If the solvent molecules having a high boiling point enter the carbon structure having a high surface area, they may not be completely removed even if the temperature is increased. For this reason, the residual solvent may deteriorate the fuel cell characteristics, which is not preferable. On the other hand, a solvent having a low boiling point (for example, a boiling point of less than 100 ° C.) is easier to remove than a solvent having a high boiling point. And it turned out that the intermediate body of the said polymer is soluble also in a low boiling-point solvent. Therefore, in this production method, the catalyst ink is prepared after dissolving the polymer intermediate in a low boiling point solvent.

  Moreover, since the said polymer has multiple phosphonic acid groups in a side chain, it is easy to hydrate and the handling at the time of coating is difficult. On the other hand, it was found that the intermediate of the above polymer is easy to handle because the phosphonic acid group is protected. Therefore, in this production method, the phosphonic acid protecting group is removed after the electrode catalyst layer is formed in the state of the polymer intermediate.

(Catalyst ink preparation process)
This step is a step of mixing the polymer intermediate, carbon supporting the catalyst particles, and a solvent. According to this step, a catalyst ink in which the polymer intermediate and carbon are uniformly dispersed in a solvent can be prepared.

  The catalyst-supported carbon used in this step can be prepared by dispersing carbon in a solution of a compound containing a catalyst, performing an impregnation method, a coprecipitation method, or an ion exchange method, and then drying and firing the solvent. . Here, carbon black is most commonly used as carbon, but graphite, carbon fiber, activated carbon and the like, pulverized products thereof, carbon compounds such as carbon nanofiber and carbon nanotube, and the like can also be used. Examples of the catalyst include platinum, ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and the like, or alloys thereof. It is done. Preferable are platinum and an alloy made of platinum and another metal such as ruthenium. Moreover, alcohol, such as water and ethanol, can be used as a solvent.

  For example, when platinum is used for the catalyst, a tetraamine platinum salt solution, a dinitrodiammine platinum solution, a platinum nitrate solution, a chloroplatinic acid solution, or the like can be used as the solution of the compound containing platinum. For example, in the case of the impregnation method, after carbon is dispersed in the platinum salt solution, the solvent is evaporated and dried, followed by reduction treatment. Thereby, platinum particles can be supported on the carbon surface.

  The solvent used in this step is not particularly limited as long as it has the above-described low boiling point and can disperse the polymer intermediate and the catalyst-supported carbon. Examples of such a solvent include chlorine solvents such as chloroform and dichloromethane, alcohol solvents such as methanol, ethanol, and isopropanol, dimethylformamide, tetrahydrofuran, acetone, methyl ethyl ketone, ethyl acetate, and diethyl ether. These solvents may be used alone or in combination of two or more.

(Coating / drying process)
This step is a step of drying the solvent in the catalyst ink after coating the catalyst ink prepared in the above step on a substrate such as polyethylene, polyethylene terephthalate, or polytetrafluoroethylene. Thereby, the electrode catalyst containing a polymer intermediate can be formed on a substrate. In this step, the method for applying the catalyst ink is not particularly limited. Examples thereof include a spray method, a screen printing method, a doctor blade method, a gravure printing method, and a die coating method. Further, the method for drying the solvent is not particularly limited, and heating drying, vacuum drying, and the like can be appropriately selected.

(Deprotection process)
This step is a step of hydrolyzing the polymer intermediate in the electrode catalyst. Specifically, the electrode catalyst on the substrate obtained through the coating / drying process is separated from the substrate or the membrane / electrode assembly in which the electrode catalyst is bonded to the electrolyte membrane, or is peeled off from the substrate and gas diffusion. It is immersed in an acid or alkali solution while being bonded to the layer. This hydrolyzes the phosphonic acid ester in the side chain of the polymer intermediate. About the preferable acid and alkali used for this process, since it is the content already demonstrated, it abbreviate | omits.

As described above, according to the production method of the present invention, since the catalyst ink can be prepared after dissolving the polymer intermediate in a low boiling point solvent, the solvent can be easily removed from the carbon structure by drying, and power generation such as ion conductivity can be achieved. A fuel cell having good characteristics can be obtained. Moreover, since a low boiling-point solvent can be used, the cooling time of an electrode catalyst can also be shortened.
Moreover, in this manufacturing method, the protective group of phosphonic acid can be removed after forming an electrode catalyst layer in the state of a polymer intermediate. Therefore, compared to the case where the electrode catalyst layer is formed in a polymer state, the membrane electrode assembly and the like can be efficiently produced.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited to these Examples.

<Preparation of sample>
First, polymers (D) and (I) having a phosphonic acid in the side chain and polymer intermediates (C) and (H) thereof were prepared by the synthesis steps shown below.
Add 2 g of 4,4′-dichlorodiphenylsulfone (molecular weight 287.17, purchased from WAKO), solorcinol (molecular weight 110.11, purchased from WAKO), potassium carbonate, N-methylpyrrolidinone and toluene, 150 ° C., 3 hours Refluxed. After refluxing, toluene was removed and the mixture was stirred at 180 ° C. for 12 hours. After stirring, it was precipitated with water and vacuum dried to obtain the following polymer (A).

ポリマー（Ａ）（０．９７ｇ，３．０ｍｍｏｌ）をトリフルオロメタンスルホン酸（４．５ｍｌ）に溶解させ、そこに２−ヨード安息香酸（０．８２ｇ，３．３ｍｍｏｌ）を加え、室温で３時間反応させた。反応終了後、水に再沈殿させ、繊維状のポリマーを得た。３重量％重曹水、熱水及び熱メタノールで洗浄後、８０℃で減圧乾燥させることでポリマー（Ｂ）１．６３ｇ（収率９８％）を得た。

Polymer (A) (0.97 g, 3.0 mmol) was dissolved in trifluoromethanesulfonic acid (4.5 ml), 2-iodobenzoic acid (0.82 g, 3.3 mmol) was added thereto, and the mixture was stirred at room temperature for 3 hours. Reacted. After completion of the reaction, reprecipitation in water was performed to obtain a fibrous polymer. After washing with 3% by weight sodium bicarbonate water, hot water and hot methanol, it was dried under reduced pressure at 80 ° C. to obtain 1.63 g of polymer (B) (yield 98%).

窒素雰囲気下、Ｎ,Ｎ−ジメチルホルムアミド（ＤＭＦ）（３．５ｍｌ）に亜鉛粉末（０．３３ｇ，５．０ｍｍｏｌ）を加え、そこにジエチル（ブロモジフルオロメチル）ホスホネート（１．３４ｇ，５．０ｍｍｏｌ）をゆっくりと滴下した。室温で２時間撹拌後、臭化銅（Ｉ）（０．７２ｇ，５．０ｍｍｏｌ）を加え、さらに３０分間撹拌した。この反応溶液にポリマー（Ｂ）（１．３９ｇ，２．５ｍｍｏｌ）のＤＭＦ（１０ｍｌ）溶液を加え、室温で２４時間反応後、希塩酸水に再沈殿させた。得られたポリマーをＤＭＦに溶解させ、不溶部分をろ過により除去後、メタノールに再沈殿させた。メタノールで洗浄後、８０℃で減圧乾燥させることで目的とするポリマー（Ｃ）１．５４ｇ（収率１００％）を得た。

Under a nitrogen atmosphere, zinc powder (0.33 g, 5.0 mmol) was added to N, N-dimethylformamide (DMF) (3.5 ml), and diethyl (bromodifluoromethyl) phosphonate (1.34 g, 5.0 mmol) was added thereto. ) Was slowly added dropwise. After stirring at room temperature for 2 hours, copper (I) bromide (0.72 g, 5.0 mmol) was added, and the mixture was further stirred for 30 minutes. To this reaction solution, a DMF (10 ml) solution of polymer (B) (1.39 g, 2.5 mmol) was added, reacted at room temperature for 24 hours, and then reprecipitated in dilute hydrochloric acid. The obtained polymer was dissolved in DMF, the insoluble part was removed by filtration, and then reprecipitated in methanol. After washing with methanol and drying under reduced pressure at 80 ° C., 1.54 g (yield 100%) of the intended polymer (C) was obtained.

ポリマー（Ｃ）（１．２３ｇ，２．０ｍｍｏｌ）をクロロホルム（３０ｍｌ）に溶解させ、そこにトリメチルシリルブロマイド（０．９２ｇ，６．０ｍｍｏｌ）を５℃で滴下して加えた。反応溶液を４０℃に加熱し、２４時間反応させた後、メタノールに再沈殿させた。メタノールで洗浄後、８０℃で減圧乾燥させることで目的とするポリマー（Ｄ）１．０４ｇ（収率９３％）を得た。

Polymer (C) (1.23 g, 2.0 mmol) was dissolved in chloroform (30 ml), and trimethylsilyl bromide (0.92 g, 6.0 mmol) was added dropwise thereto at 5 ° C. The reaction solution was heated to 40 ° C., reacted for 24 hours, and then reprecipitated in methanol. After washing with methanol, drying at 80 ° C. under reduced pressure gave 1.04 g (yield 93%) of the target polymer (D).

４，４’−ジフルオロベンゾフェノン（０．６５ｇ，３．０ｍｍｏｌ）、化合物（Ｅ）及び炭酸カリウム（１．２４ｇ，９．０ｍｍｏｌ）にシクロヘキサン（４ｍｌ）及びＮ，Ｎ−ジメチルアセトアミド（６ｍｌ）を加え、窒素雰囲気下１００℃に加熱した。ディーンスターク装置を用いて水を除去後、シクロヘキサンを留去し、１６０℃で一晩撹拌した。反応終了後、水に再沈殿させ、繊維状のポリマーを得た。熱水及び熱メタノールで洗浄後、８０℃で減圧乾燥させることでポリマー（Ｆ）１．７１ｇ（収率９７％）を得た。

Add cyclohexane (4 ml) and N, N-dimethylacetamide (6 ml) to 4,4′-difluorobenzophenone (0.65 g, 3.0 mmol), compound (E) and potassium carbonate (1.24 g, 9.0 mmol). And heated to 100 ° C. in a nitrogen atmosphere. After removing water using a Dean-Stark apparatus, cyclohexane was distilled off and stirred at 160 ° C. overnight. After completion of the reaction, reprecipitation in water was performed to obtain a fibrous polymer. After washing with hot water and hot methanol, it was dried under reduced pressure at 80 ° C. to obtain 1.71 g of polymer (F) (yield 97%).

ポリマー（Ｆ）（０．８４ｇ，１．０ｍｍｏｌ）をトリフルオロメタンスルホン酸（８ｍｌ）に溶解させ、そこに２−ヨード安息香酸（１．１９ｇ，４．８ｍｍｏｌ）を加え、室温で３時間反応させた。反応終了後、水に再沈殿させ、繊維状のポリマーを得た。３重量％重曹水、熱水及び熱メタノールで洗浄後、８０℃で減圧乾燥させることでポリマー（Ｇ）１．７１ｇ（収率９７％）を得た。

Polymer (F) (0.84 g, 1.0 mmol) is dissolved in trifluoromethanesulfonic acid (8 ml), 2-iodobenzoic acid (1.19 g, 4.8 mmol) is added thereto, and the mixture is reacted at room temperature for 3 hours. It was. After completion of the reaction, reprecipitation in water was performed to obtain a fibrous polymer. After washing with 3% by weight sodium bicarbonate water, hot water and hot methanol, 1.71 g (yield 97%) of polymer (G) was obtained by drying under reduced pressure at 80 ° C.

窒素雰囲気下、ＤＭＦ（４．８ｍｌ）に亜鉛粉末（０．２１ｇ，３．２ｍｍｏｌ）を加え、そこにジエチル（ブロモジフルオロメチル）ホスホネート（０．８５ｇ，３．２ｍｍｏｌ）をゆっくり滴下した。室温で２時間撹拌後、臭化銅（Ｉ）（０．４６ｇ，３．２ｍｍｏｌ）を加え、さらに３０分間撹拌した。この反応溶液にポリマー（Ｇ）（０．７０ｇ，０．４ｍｍｏｌ）のＤＭＦ（５．３ｍｌ）溶液を加え、室温で２４時間反応後、希塩酸水に再沈殿させた。得られたポリマーをＤＭＦに溶解させ、不溶部分をろ過により除去後、メタノールに再沈殿させた。メタノールで洗浄後、８０℃で減圧乾燥させることで、目的とするポリマー（Ｈ）０．７４ｇ（収率９５％）を得た。

Under a nitrogen atmosphere, zinc powder (0.21 g, 3.2 mmol) was added to DMF (4.8 ml), and diethyl (bromodifluoromethyl) phosphonate (0.85 g, 3.2 mmol) was slowly added dropwise thereto. After stirring at room temperature for 2 hours, copper (I) bromide (0.46 g, 3.2 mmol) was added, and the mixture was further stirred for 30 minutes. To this reaction solution, a DMF (5.3 ml) solution of polymer (G) (0.70 g, 0.4 mmol) was added, reacted at room temperature for 24 hours, and then reprecipitated in dilute hydrochloric acid water. The obtained polymer was dissolved in DMF, the insoluble part was removed by filtration, and then reprecipitated in methanol. After washing with methanol and drying under reduced pressure at 80 ° C., 0.74 g (yield 95%) of the target polymer (H) was obtained.

ポリマー（Ｈ）（１．２３ｇ，２．０ｍｍｏｌ）をクロロホルム（３０ｍｌ）に溶解させ、そこにトリメチルシリルブロマイド（０．９２ｇ，６．０ｍｍｏｌ）を５℃で滴下して加えた。反応溶液を４０℃に加熱し、２４時間反応させた後、メタノールに再沈殿させた。メタノールで洗浄後、８０℃で減圧乾燥させることで、目的とするポリマー（Ｉ）１．０４ｇを得た。

Polymer (H) (1.23 g, 2.0 mmol) was dissolved in chloroform (30 ml), and trimethylsilyl bromide (0.92 g, 6.0 mmol) was added dropwise thereto at 5 ° C. The reaction solution was heated to 40 ° C., reacted for 24 hours, and then reprecipitated in methanol. After washing with methanol, drying at 80 ° C. under reduced pressure gave 1.04 g of the target polymer (I).

<Evaluation of sample>
1. Evaluation of inhibition of oxygen reduction reaction First, an electrode catalyst was prepared using the polymers (D) and (I). And about these electrode catalysts, oxygen reduction reaction inhibition property was evaluated by the rotating electrode method.
Specifically, first, a cylindrical working electrode made of polyetheretherketone resin is prepared, and catalyst-supporting carbon is arranged on the end face, and then the catalyst-supporting carbon is coated with the polymers (D) and (I). And dried.

  Then, the working electrode, a counter electrode made of platinum, and a standard hydrogen electrode as a reference electrode were disposed in an aqueous sodium hydroxide solution, and the working electrode was rotated at a rotational speed of 1600 rpm. Then, a voltage is applied between the working electrode and the counter electrode, and the potential is swept at a potential sweep speed of 50 mV, and the relationship between the potential of the working electrode with respect to the potential of the reference electrode and the oxygen reduction current flowing through the working electrode is measured. did. The results are shown in Table 1 below. In addition, oxygen reduction reaction activity is so high that an oxygen reduction electric current value is large.

  For comparison, a polyacrylic acid polymer having a phosphonic acid group in the side chain (trade name: Phosmer, manufactured by Unichemical Co., Ltd.) and a perfluoroalkylene polymer having a sulfonic acid group in the side chain (trade names: Nafion, Aldrich) The working electrode was prepared by the same method using the same method and evaluated by the rotating electrode method. The results are shown in Table 1 below.

  As can be seen from Table 1, the polymers (D) and (I) performed much better than the polymer of Comparative Example 1 and showed the same performance as the polymer of Comparative Example 2.

2. Oxidation resistance test Next, electrolyte membranes were prepared for the polymers (D) and (I). And about these electrolyte membranes, the radical tolerance was evaluated by the Fenton test.
Specifically, the polymers (C) and (H) were dissolved in N-methylpyrrolidinone to prepare 10 wt%, and an electrolyte membrane was prepared using an applicator so that the film thickness was 30 μm. After the preparation, vacuum drying was performed at 50 ° C. for 24 hours, and the weight was measured.
Next, 30 ml of a 3 wt% aqueous hydrogen peroxide solution and 10 ml of a 4 ppm Fe ²⁺ aqueous solution were placed in a sealed container, and the prepared electrolyte membranes were immersed at 80 ° C. for 2 hours. After the immersion, the electrolyte membrane in the sealed container was taken out with tweezers, placed in a sample bag, and vacuum dried at 50 ° C. for 24 hours. After vacuum drying, the weight was measured.

  From the weight before and after the Fenton test of each electrolyte membrane, the weight residual ratio of the electrolyte membrane after the Fenton test was calculated. The results are shown in Table 2 below. In addition, it shows that radical tolerance is so high that a weight residual ratio is high.

  In addition, as a comparison between the polymers (D) and (I), an electrolyte membrane was similarly prepared for the polymer before the phosphonic acid was introduced, that is, the polymers (A) and (F), immersed in the Fenton reagent, and tested. The weight residual ratio was calculated from the weight before and after. Furthermore, the weight residual ratio was similarly calculated for the polymer (trade name Nafion) and Teflon (registered trademark) used in Comparative Example 2. These results are shown in Table 2 below.

As can be seen from Table 2, the polymers of Comparative Examples 5 and 6 have high radical resistance. Here, the main chain of the polymer of Comparative Example _{5 - (CF 2 -CF 2)} m - (CF-CF 2) n - is composed of, the backbone of the polymer of Comparative Example 6 - _{(CF 2} -CF 2 ) _M- . Therefore, the main chain structures of the polymers of Comparative Examples 5 and 6 are similar. Therefore, it can be presumed that the structure of the polymer main chain contributes to high radical resistance.
Moreover, as can be seen from Table 2, the polymers (D) and (I) of Examples 3 and 4 are all highly resistant to radicals and exhibit the same performance as the polymers of Comparative Examples 5 and 6. However, the polymers (A) and (F) of Comparative Examples 3 and 4 have low radical resistance. From these results, it was found that for these polymers, the radical resistance changes depending on the structure of the side chain, regardless of the radical resistance of the main chain structure. The possibility that radical generation can be suppressed by introducing a side chain structure having a phosphonic acid group such as the polymers (D) and (I) was shown.

3. Solubility test Next, the solubility with respect to various solvent was evaluated about the said polymer (C), (D), (H), (I).
Specifically, 1 g of the above polymers (C), (D), (H), and (I) was dissolved in a solvent so as to be 10 wt%, and the presence or absence of dissolution after stirring for 24 hours at 50 ° C. was visually observed. Examined. As a result of visual observation, when there was dissolution, it was evaluated as dissolution, and when there was no dissolution, it was evaluated as insoluble. The results are shown in Table 3 below.

  As can be seen from Table 3, the polymers (C) and (H) are also dissolved in a solvent having a low boiling point. On the other hand, the polymers (D) and (I) could only be dissolved in a solvent having a high boiling point. From these facts, it was found that the selectivity of the solvent is expanded by protecting the phosphonic acid group in the side chain as in the polymers (C) and (H).

Claims (6)

An ionomer for an electrode catalyst of a fuel cell, wherein an aromatic polyether having at least one structure represented by the following formula (1) in a repeating unit is used.

(In Formula (1), ^Rf represents a C1-C3 perfluoroalkylene group, X represents a hydrogen atom or a C1-C3 perfluoroalkylenephosphonic acid group, Y represents -O- or hydrogen. Represents an atom.) The ionomer for a fuel cell electrode catalyst according to claim 1, wherein the aromatic polyether has a repeating unit represented by the following formula (2).

The ionomer for a fuel cell electrode catalyst according to claim 1, wherein the aromatic polyether has a repeating unit represented by the following formula (3).

A first step of preparing a catalyst ink by mixing an aromatic polyether having at least one structure represented by the following formula (4) in a repeating unit, a catalyst-supporting carbon, and a solvent;
A second step of removing the solvent of the catalyst ink obtained in the first step;
After the second step, a third step of hydrolyzing the phosphonic acid ester in the side chain of the aromatic polyether;
A method for producing an electrode catalyst, comprising:

(In the formula (4), _{R 1} and _{R 2} are linear or branched alkyl group having 1 to 20 carbon atoms, straight-chain or branched alkylene group having 1 to 20 carbon atoms, 3 carbon 20 represents an alicyclic organic group or an aryl group having 6 to 20 carbon atoms.) The method for producing an electrode catalyst according to claim 4, wherein the aromatic polyether is an aromatic polyether ether sulfone represented by the following formula (5).

(In formula (5), _{R 1} and _{R 2} are linear or branched alkyl group having 1 to 20 carbon atoms, straight-chain or branched alkylene group having 1 to 20 carbon atoms, 3 carbon 20 represents an alicyclic organic group or an aryl group having 6 to 20 carbon atoms.) The method for producing an electrode catalyst according to claim 4, wherein the aromatic polyether is an aromatic polyetheretherketone represented by the following formula (6).

(In the formula (6), _{R 1} and _{R 2} are linear or branched alkyl group having 1 to 20 carbon atoms, straight-chain or branched alkylene group having 1 to 20 carbon atoms, 3 carbon 20 represents an alicyclic organic group or an aryl group having 6 to 20 carbon atoms.)