JP2013189515A - Aromatic hydrocarbon-based polymer and electrolyte membrane using the same, membrane-electrode assembly, and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer exhibiting high protonic conductivity and very low temperature dependence of the protonic conductivity when used as an electrolyte membrane for a fuel cell.SOLUTION: There is disclosed an aromatic hydrocarbon-based polymer including a structural unit of general formula (1) and a structural unit of general formula (2) in the molecule. In formula (1), Ar1 represents a divalent aromatic group; and M each represents any of hydrogen, alkali metal and alkaline earth metal. In formula (2), Ar2 is a divalent aromatic group identical with or different from Ar1; Z is at least one selected from a group consisting of a heteroatom, a group containing a heteroatom or a direct bond; n, l and p are each an integer of 0 or more, and any of n, l and p is an integer of 1 or more; and M each represents hydrogen, alkali metal or alkaline earth metal.

Description

  The present invention relates to a polymer electrolyte, particularly a polymer suitably used as a proton conductive membrane for a fuel cell.

In recent years, fuel cells have attracted attention as highly efficient and clean energy conversion devices. Above all, a polymer electrolyte fuel cell using a proton conductive polymer membrane as an electrolyte can obtain a high output with a compact structure and can be operated with a simple system. Attention has been paid.
Conventionally, perfluoroalkylsulfonic acid polymers have been widely used in polymer electrolyte fuel cells. In recent years, sulfonated polyetheretherketone (Patent Document 1) and the like have been proposed, but proton conductivity is inferior to perfluoroalkylsulfonic acid polymers. Therefore, a block copolymer having a fluorinated benzenesulfonic acid by introducing fluorine into the aromatic ring corresponding to these main chains (Patent Document 2) or a polymer in which perfluoroalkylsulfonic acid is randomly grafted to an aromatic main chain polymer. (Patent Document 3) has been proposed, but the proton conductivity is still inferior to that of a perfluoroalkylsulfonic acid polymer.

JP 2002-75403 A JP 2008-88420 A JP 2004-220962 A

  The present invention solves the above-mentioned drawbacks of the prior art and has a high degree of proton conductivity when used as an electrolyte membrane for fuel cells. In addition, the humidity dependence of the proton conductivity is remarkably small, particularly under low humidity conditions. An object of the present invention is to provide an aromatic hydrocarbon polymer having good proton conductivity.

The present inventors have completed the present invention as a result of intensive studies to solve the above problems.
An aromatic hydrocarbon polymer characterized by containing a structural unit of the following general formula (1) and a structural unit of the general formula (2) in the molecule.

(Ar1 represents a divalent aromatic group, M represents hydrogen, an alkali metal, or an alkaline earth metal.)

(Ar2 is the same or different divalent aromatic group as Ar1, Z is a heteroatom, n, l, p is an integer of 0 or more, and at least one of n, l, p is an integer of 1 or more, M is hydrogen or Indicates either alkali metal or alkaline earth metal.)

The polymer according to 0005, having a repeating unit represented by the following general formula (3), comprising the structural units represented by the general formula (1) and the general formula (2).

(Ar1, Ar2 are aromatic groups, X, Y, Z are the same or different heteroatoms, n, l, p are integers of 0 or more, at least one of n, l, p and q is an integer of 1 or more, M is Each of hydrogen, alkali metal, and alkaline earth metal is indicated.)

Item 0006. The polymer according to item 0006, which has a hydrophilic segment containing the repeating unit represented by the general formula (3) and a hydrophobic segment having no sulfonic acid group.

The polymer according to any one of claims 0006 to 0007, wherein Z is any one of O, S, or a sulfonyl group -SO2-, and l is 0 or 1.

Ar1 and Ar2 are one or more divalent aromatic groups selected from the group consisting of phenyl group, naphthyl group, biphenyl, phenylsulfonylphenyl, phenylmethylphenyl, phenyldifluorophenyl, and phenylcarbonylphenyl, The polymer which has an aromatic principal chain hydrophilic part in any one of -0008.

The polymer according to any one of 0006 to 0009, wherein X and Y have an aromatic main chain that is at least one selected from the group consisting of O, S, a sulfonyl group, a carbonyl group, or a direct bond.

The polymer according to paragraphs 0006 to 0010, wherein the range of q is 3 to 100.

Electrolyte membrane using polymer according to item 0006-0011

A membrane electrode assembly using the membrane according to item 0012.

A fuel cell using the membrane according to item 0012 or the membrane electrode assembly according to item 0013.

The present invention is a polymer having a sulfonic acid group bonded directly to an aromatic group, or a salt thereof and a sulfonic acid group bonded to the aromatic group via a fluoroalkyl group, or a salt thereof. By arranging these two types of sulfonic acid groups close to each other, they have high heat resistance derived from the aromatic main chain, high IEC by arylsulfonic acid and fluoroalkylsulfonic acid, high proton conductivity, and proton conductivity. Provided is a polymer characterized by extremely low humidity dependency and good proton conductivity even under low humidity, and further provides an electrolyte membrane, a membrane electrode assembly, and a fuel cell using the polymer. .

The present invention is described in detail below.
The polymer of the present invention is an aromatic hydrocarbon polymer characterized by containing in the molecule a structural unit of the following general formula (1) and a structural unit of the general formula (2). The structural unit of the general formula (1) is (a) a sulfonic acid group directly bonded to an aromatic group or a salt thereof, and the structural unit of the general formula (2) is (b) an aromatic group via a fluoroalkyl group. Having a sulfonic acid group bonded thereto, or a salt thereof.

(Ar1 represents a divalent aromatic group, and M represents hydrogen, an alkali metal, or an alkaline earth metal.)

(Ar2 is the same or different divalent aromatic group as Ar1, Z is at least one selected from the group consisting of heteroatoms, groups containing heteroatoms, or direct bonds, and n, l, p, are zero or more. (It is an integer, and at least one of n, l, and p is an integer of 1 or more, and M represents hydrogen, an alkali metal, or an alkaline earth metal.)

The structural units of the above general formula (1) and general formula (2) may be the same type and may be continuous, or may constitute the main chain alternately. In particular, it is preferably a structural unit of the following general formula (3).

(Ar1 and Ar2 are aromatic groups, X, Y and Z are the same or different heteroatoms, groups containing heteroatoms, or at least one selected from the group consisting of direct bonds, and n, l and p are 0 or more. (It is an integer and at least one of n, l, and p and q are integers of 1 or more, and M is hydrogen, an alkali metal, or an alkaline earth metal.)

In the above general formulas (1) to (3), Ar1 and Ar2 serving as the aromatic ring main chain are the same or different and can be various kinds of divalent aromatic groups. For example, monocyclic aromatic rings such as phenyl groups, polycyclic aromatic rings such as naphthyl groups and biphenyl groups, heterocyclic aromatic rings such as pyridine groups, and polycyclic heterocyclic aromatic rings such as benzimidazole groups Etc. Among these, a monocyclic aromatic ring (phenyl group) and a biphenyl group are preferable, and a monocyclic aromatic ring is more preferable.

M bonded to the sulfonic acid group is a cation, for example, an alkali metal ion such as a proton, sodium ion, potassium ion, or rubidium ion. Further, alkaline earth metal ions such as beryllium ions, magnesium ions, and calcium ions can be mentioned. Among these, protons, sodium ions, and potassium ions are preferred, and protons are more preferred when used as membrane electrode assemblies and fuel cells.

Z is at least one selected from the group consisting of a divalent hetero atom or a substituent containing a hetero atom connecting a fluoroalkyl group in the side chain, or a direct bond, and for example, -O for a direct bond or a hetero atom Substituents containing heteroatoms such as — and —S— include —SO 2 —, —CO—, —CH 2 —, —C (CH 3) 2 —, —CF 2 —, —C (CF 3) 2 —, and the like. . Among these, a direct bond or —O— is preferable.

X and Y are at least one or more selected from the group consisting of a divalent heteroatom or a substituent containing a heteroatom that connects aromatic rings or a direct bond, for example, a direct bond, -O- Substituents containing heteroatoms such as, -S-, etc. include -SO2-, -CO-, -CH2-, -C (CH3) 2-, -CF2-, -C (CF3) 2-, and the like. Among these, -O-, -SO2-, -CO- or a direct bond is preferable, and -O- and -SO2- are particularly preferable. X and Y may be the same or different.

-(CF) n- and-(CF) p- represent a fluoroalkyl group, which is an alkyl chain substituted with fluorine, and usually n and p are integers ranging from 0 to 10. Examples thereof include a difluoromethylene group, a tetrafluoroethylene group, a hexafluoropropylene group, and an octafluorobutylene group. Of these, a tetrafluoroethylene group is most preferred. n and p may be the same or different, but either n or p must be 1 or more.

q is an integer representing the number of repeating units, and is usually in the range of 2 to 5000. Among these, 3-100 are preferable. It is also possible to use this repeating unit as a hydrophilic part and to form a block copolymer with a hydrophobic polymer having no sulfonic acid group.
In the present invention, the molecular weight of the aromatic polymer having a super strong acid group in the side chain and a strong acid group in the main chain is usually 5000 to 500,000, preferably 10,000 to 300,000, particularly preferably 15,000 to 100,000, in terms of number average molecular weight. .

The aromatic polymer having a super strong acid group in the side chain and a strong acid group in the main chain as described above includes, for example, an aryl halide having a sulfonic acid group in the main chain as represented by the general formula (4) and the general formula (5). It can synthesize | combine by reaction with the fluoroalkyl halide which has a sulfonic acid group which is such a super strong acid.


(Hal is at least one halogen selected from the group consisting of Cl, Br, I, F, n, l, p are integers of 0 or more, and at least one of n, l, p and q Represents an integer of 1 or more, and M represents either hydrogen, an alkali metal, or an alkaline earth metal.)

The above method is not particularly limited. For example, the halogens represented by Hal may be the same or different, and the compounds of the general formula (4) and the general formula (5) are reacted in the presence of a metal. Examples thereof include a method for forming a direct bond. Examples of the halogen include fluorine, chlorine, bromine and iodine, preferably chlorine, bromine and iodine. Although this reaction can usually be carried out without using a solvent, it is preferably carried out in an appropriate solvent. As the solvent, hydrocarbon solvents, ether solvents, ketone solvents, amide solvents, sulfone solvents, sulfoxide solvents and the like can be used. Tetrahydrofuran, diethyl ether, dimethyl sulfoxide, sulfolane, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, N, N'-dimethylimidazolidinone and the like are preferably used. Examples of the metal include copper, sodium, lithium, potassium, zinc, iron, chromium, nickel, magnesium, and the like, preferably copper, zinc, or sodium. The amount of the metal used is at least 1/2 equivalent of the total of alkyl halide and / or aryl halide. The reaction temperature is preferably −10 ° C. to 250 ° C., more preferably 0 ° C. to 200 ° C.

The polymer represented by the general formula (4) in the present invention, that is, the aromatic polymer having Hal is obtained by, for example, introducing Hal into the aromatic polymer having a sulfonic acid group by a polymer reaction. Can be obtained.
As this method, for example, a method in which bromine is introduced by the action of N-bromosuccinimide, a method in which halogen is introduced by the direct action of chlorine gas, bromine, iodine, etc., a hydroxyl group is converted into a bromine group using phosphorus tribromide Examples thereof include a conversion method and a method of chlorinating a hydroxyl group using thionyl chloride. (McMurry Organic Chemistry (above), pages 291-296, Tokyo Chemical Doujin, 1992)

Here, the aromatic polymer into which Hal is introduced by the polymer reaction is particularly limited as long as it has a sulfonic acid group and the main chain is mainly composed of an aromatic ring as described above. For example, sulfonated polyphenylene ether, sulfonated polynaphthylene, sulfonated polyphenylene, sulfonated polyethersulfone, sulfonated polyphenylene sulfide, sulfonated polyetheretherketone, sulfonated polyetherethersulfone, Examples of the polymer include sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyetherketone, and sulfonated polybenzimidazole. Of these, sulfonated polyphenylene ether, sulfonated polynaphthylene, sulfonated polyphenylene, and polyethersulfone polymers are preferably used. These polymers are composed of any two or more kinds of polymers, such as a block copolymer, a random copolymer, an alternating copolymer, a multi-block copolymer, or a graft copolymer. Also good.
These polymers can be obtained by sulfonating polymers obtained from manufacturers such as Aldrich and Sumitomo Chemical. For example, Sumitomo Chemical Co., Ltd. sulfonates Sumika Excel PES3600P, PES4100P, PES4800P, PES5200P, PES5003P (all of which are registered trademarks of Sumitomo Chemical Co., Ltd., the same shall apply hereinafter) to obtain sulfonated polyether sulfones. It can be obtained.

The polymer electrolyte membrane used in the present invention is composed of the polymer electrolyte as described above, and as its production method, for example, a solvent cast method or the like can be used. Specifically, a polymer electrolyte membrane can be produced by casting a solution of the polymer electrolyte as described above on a substrate and then removing the solvent.
Here, the substrate is not particularly limited as long as it is resistant to a solvent and can be peeled off after film formation. Usually, glass plate, PET (polyethylene terephthalate) film, stainless steel plate, stainless steel belt, silicon wafer Etc. are used. As these substrates, those having a surface subjected to a release treatment, an embossing process, and a matting process may be used as necessary. Although there is no restriction | limiting in particular in the thickness of a polymer electrolyte membrane, 5-300 micrometers is preferable. A thickness of more than 10 μm is preferable to obtain a membrane strength that can withstand practical use, and a thickness of less than 300 μm is preferable in order to reduce membrane resistance, that is, improve power generation performance. The film thickness can be controlled by the solution concentration or the coating thickness on the substrate.

The polymer electrolyte solution is usually prepared using a solvent that can dissolve the polymer electrolyte and can be removed thereafter. Examples of such solvents include aprotic polar solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide, dichloromethane, chloroform, 1,2-dichloroethane, chlorobenzene, Chlorinated solvents such as dichlorobenzene, alcohols such as methanol, ethanol and propanol, alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether are preferably used. It is done. These can be used singly, but two or more solvents can be mixed and used as necessary. Among these, N-methyl-2-pyrrolidone, dimethylformamide, and dimethyl sulfoxide are preferable because of high solubility.
As a method for forming a polymer electrolyte membrane, it is preferable to use a bar coater method, a spin coater method, or a dry film forming machine because a uniform layer can be formed.

Next, the joined body of the electrolyte membrane and the catalyst layer of the present invention will be described.
As the joined body of the electrolyte membrane and the catalyst layer of the present invention, one in which the polymer electrolyte membrane and the catalyst layer are laminated is usually used. The catalyst layer may be laminated on one side or both sides of the polymer electrolyte membrane. However, when the fuel cell is operated, the catalyst layer / polymer electrolyte membrane / catalyst layer 3 in which the catalyst layer is laminated on both sides is used. It preferably consists of layers. Here, the polymer electrolyte membrane is made of a polymer electrolyte. As the electrolyte, for example, —SO 3 H, —COOH, —PO (OH) 2, —POH (OH), — Examples thereof include polymers having a cation exchange group such as SO 2 NHSO 2-, -Ph (OH) (Ph represents a phenyl group). Some or all of the ion exchange groups may form a salt with a counter ion.

Next, the assembly (membrane electrode assembly) of the current collector, the catalyst layer, and the electrolyte membrane of the present invention will be described.
As the joined body of the current collector, the catalyst layer, and the electrolyte membrane, a laminate in which a current collector, a catalyst layer, and a polymer electrolyte membrane are usually used is used. When it is intended to operate as a fuel cell using this, it is preferably a joined body comprising 5 layers in the order of current collector / catalyst layer / polymer electrolyte membrane / catalyst layer / current collector.
As the lamination method, for example, (1) the above-mentioned current collector-catalyst layer assembly and the polymer electrolyte membrane are joined, and (2) the above-mentioned polymer electrolyte membrane-catalyst layer assembly and the current collector are joined. Can be mentioned. The five-layered assembly can be obtained, for example, by sandwiching both surfaces of a polymer electrolyte membrane with a current collector-catalyst layer assembly in which the catalyst layer is on the polymer electrolyte side. It can also be obtained by sandwiching a current collector between both surfaces of a three-layered assembly of catalyst layer / polymer electrolyte membrane / catalyst layer in which catalyst layers are laminated on both surfaces of the electrolyte membrane.
The current collector-catalyst layer-polymer electrolyte membrane assembly thus obtained can be subjected to heat treatment and / or press treatment as necessary.

Next, the fuel cell of the present invention will be described.
It is possible to operate as a fuel cell by flowing oxygen gas on one side of the current collector-catalyst layer-polymer electrolyte membrane assembly obtained above and hydrogen gas on the other side. At this time, it is also possible to supply oxygen gas and / or hydrogen gas with humidification. Although there is no restriction | limiting in particular in the temperature range to operate, 0-150 degreeC is preferable, 30-120 degreeC is more preferable, 50-100 degreeC is especially preferable.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not limited at all by these Examples.
Synthesis Example 5-Iodo-octafluoropentyl-3-oxapentanesulfonyl fluoride 15.01 g, water 5 ml, methylene chloride 5 ml, 2,6-lutidine 4.80 g, tetra n-butylammonium fluoride 1M THF ( Tetrahydrofuran) solution was placed in 0.1 ml and reacted at room temperature for 4 days. After extracting with methylene chloride three times and distilling off the solvent under reduced pressure, 30 ml of THF and 2.82 g of potassium carbonate were added and stirred at room temperature for 10 hours. The solid was filtered off and the filtrate was concentrated to precipitate a white solid. The white solid was recrystallized from a THF / toluene mixed solvent to obtain 12.3 g of a white solid. The obtained white solid was confirmed to be potassium 5-iodo-octafluoro-3-oxapentanesulfonate represented by Formula 6 from the results of 19F-NMR and elemental analysis.

Example 1 Into a flask, 15 g of a separately synthesized block polymer having the structure of Formula 7 and 80 ml of DMF were added and dissolved, and 46.5 g of bromine was added over 10 minutes while maintaining the temperature at 0 ° C. After stirring at 80 ° C. for 4 hours, the reaction solution was added to an aqueous solution in which excess Na 2 SO 3 was dissolved. Thereafter, methylene chloride was distilled off under reduced pressure, filtered and dried to obtain 17.5 g of a polymer. As a result of elemental analysis, 1H NMR, and 13C NMR measurement, a bromo group was introduced into the phenyl ring of the obtained polymer, and it was confirmed that the polymer represented by Formula 8 was obtained. In the polymer, 16.5% by weight of bromo groups were introduced.

A flask substituted with nitrogen was charged with 0.500 g of the polymer represented by formula 8, 0.500 g (7.87 mmol) of copper powder and 10 ml of N, N-dimethylsulfoxide, and the mixture was stirred at 120 ° C. for 2 hours. Next, while maintaining the temperature at 120 ° C., a solution of (b) 1.00 g (2.16 mmol) of N, N-dimethylsulfoxide in 10 ml was added. After reacting at 120 ° C. for 40 hours, the polymer was precipitated by adding to 100 ml of 1N HCl aqueous solution. The precipitated polymer was dried and confirmed to be an aromatic polymer represented by Formula 9 having a super strong acid group in the side chain.

The present invention provides a polymer having high IEC, high proton conductivity, and extremely low humidity dependency of proton conductivity, and particularly good proton conductivity even under low humidity. Electrolyte membrane, membrane electrode assembly Furthermore, it can be suitably used for a fuel cell.

Claims (10)

An aromatic hydrocarbon polymer characterized by containing a structural unit of the following general formula (1) and a structural unit of the general formula (2) in the molecule.

(Ar1 represents a divalent aromatic group, and M represents hydrogen, an alkali metal, or an alkaline earth metal.)

(Ar2 is the same or different divalent aromatic group as Ar1, Z is at least one selected from the group consisting of heteroatoms, groups containing heteroatoms, or direct bonds, and n, l, p, are zero or more. (It is an integer, and at least one of n, l, and p is an integer of 1 or more, and M represents hydrogen, an alkali metal, or an alkaline earth metal.) The aromatic hydrocarbon polymer according to claim 1, which has a hydrophilic segment containing a repeating unit represented by the following general formula (3) containing the structural units represented by the general formula (1) and the general formula (2).

(Ar1, Ar2 are the same or different divalent aromatic groups, X, Y, Z are the same or different, and are at least one selected from the group consisting of heteroatoms, groups containing heteroatoms, or direct bonds, n , l, p are integers of 0 or more, and at least one of n, l, p and q are integers of 1 or more, and M is hydrogen, an alkali metal, or an alkaline earth metal. The aromatic hydrocarbon polymer according to claim 2, comprising a hydrophilic segment containing the repeating unit represented by the general formula (3) and a hydrophobic segment having no sulfonic acid group. The aromatic hydrocarbon polymer according to any one of claims 2 to 3, wherein Z is any one of O, S, and a sulfonyl group, and l is 0 or 1. Ar1 and Ar2 are the same or different and are at least one selected from the group consisting of phenyl group, naphthyl group, biphenyl group, phenylsulfonylphenyl group, phenylmethylphenyl group, phenyldifluorophenyl group, and phenylcarbonylphenyl group. The aromatic hydrocarbon polymer according to any one of claims 2 to 4, which is a divalent aromatic group. The X and Y are the same or different and have an aromatic main chain which is at least one selected from the group consisting of O, S, a sulfonyl group, a carbonyl group, or a direct bond. The aromatic hydrocarbon polymer as described. The range of said q is 3-100, The aromatic hydrocarbon type polymer in any one of Claims 2-6. An electrolyte membrane comprising the polymer according to claim 1. 9. A membrane electrode assembly using the membrane according to claim 8. 10. A fuel cell using the membrane electrode assembly according to claim 9.