JP2010212247A - Membrane electrode assembly and solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane electrode assembly for suppressing both of membrane deterioration due to a chemical cause and membrane deterioration due to mechanical cause simultaneously, and a solid polymer fuel cell using this. <P>SOLUTION: The membrane electrode assembly 10 includes a solid polymer electrolyte membrane 12 and electrodes (catalyst layers 14a, 14b) jointed on both surfaces of the solid polymer electrolyte membrane 12. A whole or a part of proton contained in a whole of the solid polymer electrolyte membrane 12, a non-power-generating region or a strip-shaped region undergoes ion exchange by one or more cations selected from a complex cation, a fourth-class alkyl-ammonium cation and a high-valent-side cation, and/or, a whole of the solid polymer electrolyte membrane 12, a non-power-generating region or a strip-shaped region contains in its end edge organo-metaloxan polymers obtained by impregnating organo-metaloxan-monomers containing ammonium cation or a fourth-class ammonium cation and by carrying out hydrolysis/condensation polymerization. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  A solid polymer fuel cell has a membrane electrode assembly (MEA) in which electrodes are bonded to both surfaces of a solid polymer electrolyte membrane as a basic unit. In the polymer electrolyte fuel cell, the electrode generally has a two-layer structure of a diffusion layer and a catalyst layer. The diffusion layer is for supplying reaction gas and electrons to the catalyst layer, and carbon paper, carbon cloth, or the like is used. The catalyst layer is a part that becomes a reaction field for electrode reaction, and generally comprises a composite of carbon carrying an electrode catalyst such as platinum and a solid polymer electrolyte (electrolyte in the catalyst layer).

The electrolyte membrane or the catalyst layer electrolyte that constitutes such an MEA includes a total fluorinated electrolyte excellent in oxidation resistance (an electrolyte that does not contain a C—H bond in the polymer chain. For example, Nafion (registered trademark, DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd., etc.) are generally used.
Further, a total fluorocarbon electrolyte is excellent in oxidation resistance, but is generally very expensive. Therefore, in order to reduce the cost of the polymer electrolyte fuel cell, a hydrocarbon electrolyte (an electrolyte containing a C—H bond and not containing a C—F bond in a polymer chain) or a partial fluorocarbon electrolyte. The use of (electrolytes containing both C—H bonds and C—F bonds in the polymer chain) has also been studied.

However, in order to put the polymer electrolyte fuel cell into practical use as a vehicle-mounted power source, there remain problems to be solved. For example, hydrocarbon-based electrolytes are less expensive than full-fluorocarbon-based electrolytes, but have a problem that they are easily degraded by peroxide radicals.
Further, the outer peripheral portion of the solid polymer electrolyte membrane is usually tightened with a gasket in order to ensure a gas sealing function. However, tightening with a gasket causes a shear stress to act on the solid polymer electrolyte membrane, resulting in damage to the membrane and a decrease in gas sealing function. Furthermore, the solid polymer electrolyte membrane repeatedly expands and contracts due to temperature changes and humidity changes that occur during use. Therefore, there is a problem that stress is likely to be generated particularly in the outer peripheral portion of the electrode.

In order to solve this problem, various proposals have heretofore been made.
For example, Patent Document 1 discloses proton conductivity obtained by immersing a sulfonated polyphenylene sulfide membrane in a solution in which magnesium acetate tetrahydrate, calcium acetate, aluminum triisopropoxide or lanthanum nitrate hydrate is dissolved. A polymer membrane is disclosed. In this document, by performing such a treatment, a part of hydrogen atoms of proton conductive substituents contained in the sulfonated polyphenylene sulfide membrane is replaced with metal ions such as Mg ²⁺ , and It is described that the oxidation resistance of the sulfonated polyphenylene sulfide is improved by substituting a part thereof with a metal ion.

  Further, in Patent Document 2, a fiber at the center of a plain woven fabric woven with polytetrafluoroethylene fibers is cut into chain lines, and a watermark is formed at the center by pulling out the cut fibers. A membrane electrode assembly is disclosed in which a Nafion solution is impregnated into a composite membrane, and electrodes having an area larger than the watermark portion are joined to both sides of the composite membrane. In this document, by reinforcing the outer periphery of the solid polymer electrolyte membrane, the membrane is damaged by tightening with the gasket, or the portion inside the gasket and outside the electrode expands and contracts. It describes that it is possible to suppress the deterioration of the film.

JP 2004-018573 A JP 2000-215903 A

One of the problems of the fuel cell is suppression of deterioration of the electrolyte membrane. The root causes of degradation include degradation of the polymer by chemical species such as radicals (ie, “chemical factors”) and membrane damage due to stress (ie, “mechanical factors”).
As disclosed in Patent Document 1, when a part of the hydrogen atom of the proton conductive substituent is substituted with a certain metal ion, the chemical resistance of the electrolyte membrane is improved. However, practically sufficient chemical resistance may not be obtained depending on the ion species to be ion-exchanged. Moreover, since the method disclosed in Patent Document 1 ion-exchanges the entire membrane, it is necessary to leave some protons in order to maintain power generation performance. Therefore, there is a problem that the effect is halved compared to the case where all protons are ion-exchanged. Furthermore, some ion species specifically disclosed in Patent Document 1 have an effect of improving chemical resistance, but are not very effective in improving mechanical strength.
On the other hand, the method disclosed in Patent Document 2 is said to have an effect of suppressing deterioration of the film due to tightening by a gasket and expansion / contraction of the film. However, this method cannot suppress deterioration of the film due to chemical factors. In addition, since the outer peripheral portion of the membrane is combined with polytetrafluoroethylene or the like, there is a concern about peeling of the membrane and the reinforcing material during use.
Furthermore, the deterioration of the film due to chemical factors occurs from a specific part of the film. It is also important to control the moisture content of the membrane in order to suppress degradation of the membrane due to chemical and mechanical factors. However, there has never been an example in which a method for strengthening an electrolyte membrane in consideration of these points has been proposed.

The problem to be solved by the present invention is a membrane electrode assembly capable of simultaneously suppressing both deterioration of a membrane due to chemical factors and deterioration of a membrane due to mechanical factors, and a solid polymer type using the membrane electrode assembly It is to provide a fuel cell.
Another problem to be solved by the present invention is to suppress deterioration of the film due to chemical factors generated from a specific part of the film.
Furthermore, another problem to be solved by the present invention is to control the moisture content of the membrane, thereby suppressing the degradation of the membrane due to chemical and mechanical factors.

In order to solve the above problems, a membrane electrode assembly according to the present invention comprises a solid polymer electrolyte membrane and electrodes joined to both surfaces of the solid polymer electrolyte membrane, and the solid polymer electrolyte membrane comprises protons. Are ionized by one or more cations selected from a complex cation, a quaternary alkylammonium cation, and a metal ion capable of taking a plurality of valences and having a valence higher than the minimum valence. The solid polymer electrolyte membrane is exchanged and / or impregnated with a solution containing an organometalloxane monomer having an ammonium cation or a quaternary ammonium cation at its end, and is obtained by hydrolyzing / condensing the organometallo The gist is to include xanthin polymer.
The second membrane electrode assembly according to the present invention includes a solid polymer electrolyte membrane, and an electrode including a catalyst layer bonded to both surfaces of the solid polymer electrolyte membrane, the solid polymer electrolyte membrane Are all or part of the protons contained in the non-power generation region at the outer periphery of which the catalyst layer is not formed on at least one surface, and / or are ion-exchanged by one or more cations and / or The solid polymer electrolyte membrane is obtained by impregnating the non-power generation region with a solution containing an organometalloxane monomer having an ammonium cation or a quaternary ammonium cation at the end, and hydrolyzing / condensing the organometallo. The gist is to include xanthin polymer.
The third membrane electrode assembly according to the present invention includes a solid polymer electrolyte membrane, and an electrode including a catalyst layer bonded to both surfaces of the solid polymer electrolyte membrane, the solid polymer electrolyte membrane. Is an intermediate part thereof, and all or part of protons contained in a band-like region including the outer peripheral part of the catalyst layer therein is ion-exchanged by one or more kinds of cations, and / or The solid polymer electrolyte membrane includes an organometalloxane polymer obtained by impregnating the band-like region with an organometalloxane monomer having an ammonium cation or a quaternary ammonium cation at the end thereof, followed by hydrolysis and condensation polymerization. The gist.
Furthermore, the polymer electrolyte fuel cell according to the present invention is provided with the membrane electrode assembly according to the present invention.

When all or part of protons of the solid polymer electrolyte membrane are ion exchanged with cations (particularly complex cations, quaternary alkylammonium cations, and / or high-value cations), the membranes are caused by chemical and mechanical factors. Degradation can be suppressed at the same time. In addition, when the film and the organometalloxane polymer are combined, deterioration of the film due to chemical factors and mechanical factors can be suppressed at the same time.
Further, the deterioration of the membrane due to chemical factors is particularly remarkable in the single-sided catalyst region. Therefore, when the belt-like region or the non-power generation region including the single-sided catalyst region is previously ion-exchanged with a cation or strengthened with an organometalloxane polymer, the deterioration of the film due to chemical and mechanical factors can be suppressed at the same time. Furthermore, when the moisture content in the membrane is optimized, the deterioration of the membrane due to chemical factors can be suppressed.

Fig.1 (a) is a front view of MEA which concerns on the 2nd Embodiment of this invention, FIG.1 (b) is the top view. FIG. 2 (a) is a front view of an MEA according to the third embodiment of the present invention, and FIG. 2 (b) is a plan view thereof.

Hereinafter, an embodiment of the present invention will be described in detail.
The membrane electrode assembly (MEA) according to the first embodiment of the present invention includes a solid polymer electrolyte membrane and electrodes joined to both surfaces of the solid polymer electrolyte membrane.

In the present invention, various materials can be used for the solid polymer electrolyte membrane. That is, the solid polymer electrolyte membrane may be either a hydrocarbon electrolyte or a fluorocarbon electrolyte. Further, the fluorocarbon electrolyte may be a partial fluorocarbon electrolyte or a total fluorocarbon electrolyte.
Here, the “hydrocarbon electrolyte” means a polymer skeleton containing a C—H bond and no C—F bond. “Fluorocarbon-based electrolyte” refers to a polymer skeleton containing a C—F bond. The “partial fluorocarbon electrolyte” means a polymer skeleton containing both C—H bonds and C—F bonds. “Fully fluorinated electrolyte” means a polymer skeleton containing a C—F bond and no C—H bond. In the present invention, the term “fully-fluorinated electrolyte” refers to a C—Cl bond (for example, —CFCl—, —CCl ₂ —, etc.) other than the C—F bond, and other structures ( For example, -O-, -S-, -C (= O)-, -N (R)-, etc., where "R" is an alkyl group.
The kind of cation exchange group contained in the solid polymer electrolyte membrane is not particularly limited. Specific examples of the cation exchange group include a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, a phosphonous acid group, and a phenol group. The polymer described above may be provided with any one of these cation exchange groups, or may be provided with two or more.

Specific examples of the solid polymer electrolyte in which all or part of the polymer skeleton is fluorinated include a perfluorocarbon sulfonic acid polymer, a perfluorocarbon phosphonic acid polymer, a trifluorostyrene sulfonic acid polymer, and ethylene tetrafluoroethylene. -G-styrene sulfonic acid polymer.
Specific examples of the hydrocarbon-based solid polymer electrolyte not containing fluorine include polysulfonesulfonic acid, polyaryletherketonesulfonic acid, polybenzimidazolealkylsulfonic acid, and polybenzimidazolealkylphosphonic acid.
Among these, the total fluorocarbon electrolyte is particularly suitable as a solid polymer electrolyte membrane constituting the MEA because it has high chemical resistance.

The electrode may be composed of only the catalyst layer, or may have a two-layer structure of the catalyst layer and the diffusion layer.
The diffusion layer is a layer for supplying the reaction gas to the catalyst layer and transferring electrons. The material is not particularly limited as long as it is porous and has electron conductivity. In general, a porous carbon cloth, carbon paper or the like is used.
The catalyst layer is a layer serving as a reaction field for electrode reaction, and includes a catalyst and an electrolyte in the catalyst layer having a cation exchange group. The catalyst may be contained alone in the catalyst layer, or may be contained in the catalyst layer while being supported on the catalyst carrier. In addition, the material of the catalyst or the catalyst carrier is not particularly limited, and various materials can be used depending on the application. Usually, Pt or a Pt-based alloy is used as a catalyst, and is used in a state of being supported on the surface of a catalyst carrier such as carbon black.
The electrolyte in the catalyst layer is added to impart ion conductivity to the catalyst layer and to form a three-phase interface in the catalyst layer. The material of the electrolyte in the catalyst layer is not particularly limited, and various materials can be used depending on the application. Usually, an electrolyte having the same component as the solid polymer electrolyte membrane is used, but an electrolyte having a different component may be used.

  In the present embodiment, the entire solid polymer electrolyte membrane is reinforced by a specific method. Here, “the whole film is strengthened” means that the surface layer and / or the inside of the film is strengthened over the entire surface of the film. In order to improve the durability of the MEA, it is preferable that at least the surface layer of the film is reinforced over the entire surface of the film. In order to greatly improve the durability of the MEA, it is preferable that the surface layer and the inside of the membrane are reinforced over the entire surface of the membrane. When the surface layer and the inside of the film are strengthened, the degree of strengthening of both may be the same or different.

Specific methods for strengthening the entire film include the following methods.
The first method is a method in which a part of protons contained in the solid polymer electrolyte membrane is ion-exchanged with cations. The type of cation for exchanging protons is not particularly limited. Specific examples of the cation having relatively high action to improve the chemical resistance and / or mechanical properties of MEA include (1) There are complex cations, (2) quaternary alkylammonium cations, (3) expensive cation cations, and (4) other cations.

The “complex cation” refers to a compound in which a ligand is bound around a metal atom, and the compound as a whole has a positive valence. In the present invention, the type of complex cation is not particularly limited, and various complex cations can be used. Specifically, as the complex cation,
(1) Hexaammine cobalt (III) cation ([Co (NH ₃ ) ₆ ] ³⁺ ), tetraammine platinum (II) cation ([Pt (NH ₃ ) ₄ ] ²⁺ ), hexaammineruthenium (III) cation ([Ru (NH ₃ ) ₆ ] ³⁺ ), ammine complex cations such as hexaammine platinum (IV) cation ([Pt (NH ₃ ) ₆ ] ⁴⁺ ),
(2) pentaamminenitrosylcobalt (II) cation ([Co (NH ₃ ) ₅ (NO)] ²⁺ ), pentaammine chlorocobalt (III) cation ([Co (NH ₃ ) ₅ Cl] ³⁺ ), tetraammine chloronitrosyl Complex cations containing several types of ligands such as ruthenium (III) cations ([RuCl (NH ₃ ) ₄ (NO)] ²⁺ ),
and so on.
Among these, ammine complex cations are particularly suitable as complex cations for exchanging protons because they have the effect of significantly improving the chemical resistance and mechanical properties of the membrane.

The “quaternary alkyl ammonium cation” refers to a cation represented by the general formula: R ₄ N ⁺ (R is an alkyl group). The four alkyl groups R bonded to the N atom may be the same or different from each other. Specific examples of the quaternary alkyl ammonium cation include a tetrapropyl ammonium cation ([(CH ₃ CH ₂ CH ₂ ) ₄ N] ⁺ ) and a tetrabutyl ammonium cation ([(CH ₃ CH ₂ CH ₂ CH ₂ ) 4N. ] ⁺ ), Trimethylbenzylammonium cation ([(CH ₃ ) ₃ C ₆ H ₅ N] ⁺ ) and the like.

The “expensive cation” is a metal ion that can have a plurality of valences and has a valence greater than the minimum valence. For example, cerium takes two oxidation states, trivalent and tetravalent. In this case, the expensive number side cation refers to Ce ⁴⁺ . Specific examples of the other high-value cation include Pr ⁴⁺ , Sm ³⁺ , Eu ³⁺ , Tb ⁴⁺ and Yb ³⁺ .

Other cations that have a relatively high effect of improving the mechanical properties (particularly the initial elastic modulus) of the membrane include cesium ions (Cs ⁺ ), calcium ions (Ca ²⁺ ), strontium ions (Sr ²⁺ ), barium ions (Ba ²⁺ ), zirconyl ions (ZrO ²⁺ ), chromium (III) ions (Cr ³⁺ ), cerium (III) ions (Ce ³⁺ ), and the like.
Other cations that have a relatively high effect on enhancing the chemical resistance of the film include zirconyl ion (ZrO ²⁺ ), aluminum ion (Al ³⁺ ), chromium (III) ion (Cr ³⁺ ), There is cerium (III) ion (Ce ³⁺ ).

A part of protons contained in the solid polymer electrolyte membrane may be substituted with any one of the above-mentioned various cations, or may be substituted with two or more.
Further, the ion exchange rate (= number of cations × cation number × 100 / number of cation exchange groups (%)) by various cations is preferably 0.01% or more. When the ion exchange rate is less than 0.01%, practically sufficient chemical resistance and mechanical properties cannot be obtained. The ion exchange rate is more preferably 0.1% or more, and further preferably 1% or more.
On the other hand, if the ion exchange rate is too high, the electric conductivity of the solid polymer electrolyte membrane is lowered, and the power generation performance cannot be maintained. Therefore, the ion exchange rate is preferably 95% or less, more preferably 50% or less, and still more preferably 30% or less.

The second method for reinforcing the membrane is a method of introducing an organometalloxane polymer into the solid polymer electrolyte membrane.
Here, the “organometalloxane polymer” refers to a polymer obtained by hydrolysis and polycondensation of an organometalloxane monomer (and other metalloxane monomers as required). Further, the “organometalloxane monomer” is a compound having an ammonium cation or a quaternary ammonium cation at its terminal and represented by the following formula (1).
[(RO) ₃ M- (CH ₂ ) _n − (R ′) (R ″) (R ′ ″) N] X (1)
However, M is a tetravalent metal element (for example, Ge, Si, Ti, Zr, etc.).
n is an integer of 0 or more.
RO is an alkoxy group.
R ′, R ″, R ′ ″ are hydrogen or an alkyl group.
X is a halogen element such as Cl and Br.
The three alkoxy groups RO bonded to M may be the same or different from each other. Similarly, R ′, R ″, R ′ ″ bonded to N may be the same or different.

As the organometalloxane monomer, specifically, N-trimethoxysilylpropyl-N, N, N-trimethylammonium chloride ((TMSiTMA) Cl; [(CH ₃ O) ₃ SiCH ₂ CH ₂ CH ₂ (CH ₃ ) ₃ N] Cl), N-trimethoxysilylpropyl-N, N, N-butylammonium bromide ([(CH ₃ O) ₃ Si (CH ₂ ) ₃ (C ₄ H ₉ ) ₃ N] Br), N - trimethoxysilylpropyl -N, N, N-butyl ammonium chloride _{([(CH 3 O) 3} Si (CH 2) 3 (C 4 H 9) 3 N] Cr) organoalkoxysilane, such as, and the like.

The organometalloxane polymer may be obtained by hydrolysis / polycondensation of any one of these organometalloxane monomers, or may be obtained by hydrolysis / polycondensation of two or more. Things can be used. Further, the organometalloxane polymer may be obtained by hydrolyzing and polycondensing one or more types of organometalloxane monomers and one or more types of metalloxane monomers.
Here, the “metalloxane monomer” can form a polymer having a metalloxane bond (M ₁ -O-M _{2, where} M ₁ and M ₂ are metal elements) by hydrolysis and polycondensation. Refers to a compound.
As a metalloxane monomer, specifically,
(1) Tetraethoxysilane (TEOS; Si (OC ₂ H ₅ ) ₄ ), methyltriethoxysilane (CH ₃ Si (OC ₂ H ₅ ) ₃ ), dimethyldiethoxysilane ((CH ₃ ) ₂ Si (OC ₂ ) H _{5) 2),} phenyltriethoxysilane _{(C 6 H 5 Si (OC} 2 H 5) 3), diethoxy diphenyl silane _{((C 6 H 5) 2} Si (OC 2 H 5) 2) silane compounds such as ,
(2) germanium alkoxide such as tetraethoxygermane (Ge (OC ₂ H ₅ ) ₄ ), tetramethoxygermane (Ge (OCH ₃ ) ₄ ),
(3) titanium alkoxides such as titanium ethoxide (Ti (OC ₂ H ₅ ) ₄ ), titanium dichloride diethoxide (TiCl ₂ (OC ₂ H ₅ ) ₂ ),
and so on.
In particular, since a silane compound having a hydrophobic group such as a methyl group or a phenyl group has an effect of reducing the water content of the electrolyte membrane and improving the chemical resistance of MEA, as a monomer used in combination with an organometalloxane monomer, Particularly preferred.
Furthermore, the solid polymer electrolyte membrane may contain any one of these organometalloxane polymers, or may contain two or more.

As described later, the organometalloxane polymer is obtained by impregnating a solid polymer electrolyte membrane with a solution containing an organometalloxane monomer (and a metalloxane monomer as required), and hydrolyzing and polycondensing the inside of the membrane. It is formed.
In this case, the organometalloxane monomer is introduced so that the ion exchange rate by the cation at the terminal is in the above-described range. That is, in order to obtain practically sufficient chemical resistance and mechanical properties, the introduction amount of the organometalloxane polymer is preferably 0.01% or more in terms of the ion exchange rate by the organometalloxane monomer, Preferably, it is 0.1% or more, more preferably 1% or more. In order to maintain practically sufficient power generation performance, the amount of the organometalloxane polymer introduced is preferably 95% or less, more preferably 50% or less, more preferably, in terms of ion exchange rate. 30% or less.
When a metalloxane monomer is further introduced in addition to the organometalloxane monomer, the amount of the metalloxane monomer introduced is not particularly limited and can be arbitrarily selected according to the purpose. This is because the metalloxane monomer does not contain a cation, and therefore there is little risk of reducing the power generation performance even if it is introduced excessively.

  The first method (strengthening method by ion exchange) and the second method (strengthening method by introduction of organometalloxane polymer) may be used alone or in combination. Moreover, when using combining a 1st method and a 2nd method, it is preferable to introduce | transduce these in a film | membrane so that the sum total of the ion exchange rate by various cations and organometalloxane monomer may become the range mentioned above.

  Next, an MEA according to the second embodiment of the present invention will be described. The MEA according to the present embodiment includes a solid polymer electrolyte membrane and an electrode including a catalyst layer bonded to both surfaces of the solid polymer electrolyte membrane. In the present embodiment, at least the non-power generation region of the solid polymer electrolyte membrane is reinforced by a specific method.

Here, “the non-power generation region is strengthened” means that the surface layer and / or the inside of the membrane is strengthened over the entire surface of the non-power generation region. In order to improve the durability of the MEA, it is preferable that at least the surface layer of the film is reinforced over the entire surface of the non-power generation region. Moreover, in order to significantly improve the durability of the MEA, it is preferable that the surface layer and the inside of the membrane are reinforced over the entire surface of the non-power generation region. When the surface layer and the inside of the film are strengthened, the degree of strengthening of both may be the same or different.
Further, the “non-power generation region” refers to a region that is an outer peripheral portion of the solid polymer electrolyte membrane and in which a catalyst layer is not formed on at least one surface.

FIG. 1 shows a schematic configuration diagram of an MEA according to the present embodiment. In FIG. 1, the MEA 10 includes a solid polymer electrolyte membrane 12 and catalyst layers 14a and 14b bonded to both surfaces thereof. The catalyst layers 14a and 14b usually have the same size. In addition, the catalyst layers 14 a and 14 b are usually joined to substantially the center of the solid polymer electrolyte membrane 12 and symmetrically with respect to the solid polymer electrolyte membrane 12.
However, if the size of the catalyst layers 14a and 14b varies due to an error in the manufacturing process or the joining position of the catalyst layers 14a and 14b is shifted, the catalyst layers 14a and 14b are formed on both surfaces of the solid polymer electrolyte membrane 12. A region where the catalyst layers 14a and 14b are formed only on one side of the solid polymer electrolyte membrane 12 (single-sided catalyst region) is formed. The “non-power generation region” is a region obtained by combining such a single-sided catalyst region and a region where the catalyst layers 14a and 14b are not formed at all.

Specific methods for strengthening the non-power generation area include the following methods.
The first method is a method in which all or part of protons included in the non-power generation region are ion-exchanged with cations. The type of cation for exchanging protons is not particularly limited. Specific examples of the cation having relatively high action to improve the chemical resistance and / or mechanical properties of MEA include (1) There are complex cations, (2) quaternary alkylammonium cations, (3) expensive cation cations, and (4) other cations.
In particular, when the cation exchanging protons is at least one selected from a complex cation, a quaternary alkylammonium cation, and an expensive cation, the chemical resistance and mechanical properties of MEA are significantly improved.

In general, the higher the ion exchange rate by these cations, the higher the chemical resistance and mechanical properties, but the lower the electrical conductivity of the solid polymer electrolyte membrane. However, since the non-power generation region is a region that does not contribute to power generation, the higher the ion exchange rate, the better. The protons may all be ion-exchanged with a predetermined cation.
Specifically, the ion exchange rate by various cations is preferably 1% or more, more preferably 50% or more, and still more preferably 90% or more.

The second method for strengthening the non-power generation region is to impregnate the non-power generation region with an organometalloxane monomer (and another metalloxane monomer as required), and then hydrolyze and polycondensate the organometallosiloxane. This is a method of introducing xanthene polymer.
The organometalloxane polymer may be obtained by hydrolysis / polycondensation of any one of the above-mentioned organometalloxane monomers, or may be obtained by hydrolysis / polycondensation of two or more. Things can be used. Further, the organometalloxane polymer may be obtained by hydrolyzing and polycondensing one or more types of organometalloxane monomers and one or more types of metalloxane monomers.
Further, the non-power generation region may contain any one of these organometalloxane polymers, or may contain two or more.

  Since the non-power generation region is a region that does not contribute to power generation, in order to improve the durability of MEA, it is better that the amount of organometalloxane polymer introduced is larger. The amount of the organometalloxane polymer introduced into the non-power generation region is preferably 1% or more, more preferably 50% or more, and still more preferably 90% or more in terms of the ion exchange rate with the organometalloxane monomer. .

  The first method (strengthening method by ion exchange) and the second method (strengthening method by introduction of organometalloxane polymer) may be used alone or in combination. Further, when the first method and the second method are used in combination, it is preferable to introduce them into the non-power generation region so that the total ion exchange rate by various cations and organometalloxane monomers is in the above-described range. .

In the present embodiment, only the non-power generation region may be strengthened by the first method and / or the second method described above. Alternatively, in addition to the non-power generation region, the entire power generation region or a part of the power generation region and adjacent to the non-power generation region may be strengthened. In particular, when the region adjacent to the non-power generation region is strengthened, deterioration can be reliably suppressed even when the single-sided catalyst region is formed due to an error in the manufacturing process.
However, when strengthening the power generation region, the higher the ion exchange rate and / or the larger the area of the region to be strengthened in the power generation region, the higher the chemical resistance and mechanical properties, but the power generation performance. Tend to decline. Therefore, when strengthening the whole power generation region, it is preferable to make the ion exchange rate in the power generation region smaller than that in the non-power generation region. In addition, when an area that is a part of the power generation area and is adjacent to the non-power generation area is strengthened at an ion exchange rate substantially equal to that of the non-power generation area, 50% or less is preferable.
The other points related to various cations, organometalloxane polymers, organometalloxane monomers, and siloxane monomers, and other points related to the solid polymer electrolyte membrane and the electrodes are the same as in the first embodiment. Description is omitted.

  Next, an MEA according to a third embodiment of the present invention will be described. The MEA according to the present embodiment includes a solid polymer electrolyte membrane and an electrode including a catalyst layer bonded to both surfaces of the solid polymer electrolyte membrane. In the present embodiment, at least the belt-like region of the solid polymer electrolyte membrane is reinforced by a specific method.

Here, “the band-shaped region is strengthened” means that the surface layer and / or the inside of the film is strengthened over the entire surface of the band-shaped region. In order to improve the durability of the MEA, it is preferable that at least the surface layer of the film is reinforced over the entire surface of the belt-shaped region. Further, in order to greatly improve the durability of the MEA, it is preferable that the surface layer and the inside of the film are reinforced over the entire surface of the band-shaped region. When the surface layer and the inside of the film are strengthened, the degree of strengthening of both may be the same or different.
Further, the “strip-shaped region” refers to a region that is an intermediate portion of the solid polymer electrolyte membrane and includes the outer peripheral portion of the catalyst layer therein.

FIG. 2 shows a schematic configuration diagram of the MEA according to the present embodiment. In FIG. 2, the MEA 20 includes a solid polymer electrolyte membrane 22 and catalyst layers 24a and 24b bonded to both surfaces thereof. The catalyst layers 24a and 24b usually have the same size. In addition, the catalyst layers 24 a and 24 b are usually joined to substantially the center of the solid polymer electrolyte membrane 22 and symmetrically with respect to the solid polymer electrolyte membrane 22.
However, if the size of the catalyst layers 24a and 24b varies due to an error in the manufacturing process or the joining position of the catalyst layers 24a and 24b is shifted, as described above, the power generation region is formed on the solid polymer electrolyte membrane 22. A single-sided catalyst region is formed. The “band-like region” refers to a frame-like region that includes the outer peripheral portions of the pair of catalyst layers 24a and 24b and has a predetermined width. Further, when the single-sided catalyst region is formed due to an error in the manufacturing process, the “band-like region” refers to a region including the single-sided catalyst region therein.

Even when the single-sided catalyst region is formed due to an error in the manufacturing process, the belt-like region needs to have a width that allows the single-sided catalyst region to be contained therein. For this purpose, at least the width of the belt-shaped region needs to be wider at the outer periphery than the catalyst layers 24a and 24b, and the inner periphery must be narrower than the catalyst layers 24a and 24b. . The optimum width of the belt-like region is determined by an error in the manufacturing process. In general, the wider the width of the band-like region, the more reliable the single-sided catalyst region within the band-like region even when the dimensional accuracy of the catalyst layers 24a, 24b and / or the accuracy of the joining position of the catalyst layers 24a, 24b is low. Can be paid.
On the other hand, the power generation performance of the MEA is substantially proportional to the area of the power generation region. Therefore, if the width of the band-like region becomes wider than necessary, the power generation performance may be reduced depending on the ion exchange rate. Therefore, the area of the region surrounded by the inner periphery of the belt-like region is preferably 0.5 times or more the area of the catalyst layer. In other words, the width of the inner periphery of the belt-like region is preferably 0.7 times or more the width of the outer periphery of the catalyst layer. Further, in order to surely suppress the deterioration of the film, it is preferable that the area of the band-shaped region surrounded by the inner periphery is equal to or less than the area of the power generation region.
The width of the outer periphery of the belt-shaped region is not particularly limited, but when the joining positions of the catalyst layers 24a and 24b having the same dimensions are shifted, the width of the power generation region is reduced and at the same time the width of the reduced power generation region is the same. Are formed on the left and right sides of the power generation region. Therefore, the width of the outer periphery of the belt-like region is preferably at least the width obtained by adding at least the width of the power generation region and the widths of the left and right single-sided catalyst regions.

As a method for strengthening the band-like region, specifically, there are the following methods.
The first method is a method in which all or a part of protons contained in the band-like region are ion-exchanged with cations. The type of cation for exchanging protons is not particularly limited. Specific examples of the cation having relatively high action to improve the chemical resistance and / or mechanical properties of MEA include (1) There are complex cations, (2) quaternary alkylammonium cations, (3) expensive cation cations, and (4) other cations.
In particular, when the cation exchanging protons is at least one selected from a complex cation, a quaternary alkylammonium cation, and an expensive cation, the chemical resistance and mechanical properties of MEA are significantly improved.

In general, the higher the ion exchange rate by these cations, the higher the chemical resistance and mechanical properties, but the lower the electrical conductivity of the solid polymer electrolyte membrane. However, since the band-like region is a region that hardly contributes to power generation, the higher the ion exchange rate, the better. The entire proton may be ion-exchanged with a predetermined cation.
Specifically, the ion exchange rate by various cations is preferably 1% or more, more preferably 50% or more, and still more preferably 90% or more.

The second method for strengthening the band-like region is that an organometalloxane polymer obtained by impregnating the band-like region with an organometalloxane monomer (and other metalloxane monomer if necessary) and subjecting it to hydrolysis and polycondensation. It is a method to introduce.
The organometalloxane polymer may be obtained by hydrolysis / polycondensation of any one of the above-mentioned organometalloxane monomers, or may be obtained by hydrolysis / polycondensation of two or more. Things can be used. Further, the organometalloxane polymer may be obtained by hydrolyzing and polycondensing one or more types of organometalloxane monomers and one or more types of metalloxane monomers.
Furthermore, the belt-like region may contain any one of these organometalloxane polymers, or may contain two or more.

  Since the belt-like region is a region that hardly contributes to power generation, the larger the amount of organometalloxane polymer introduced, the better in order to improve the durability of MEA. The amount of the organometalloxane polymer introduced into the band-like region is preferably 1% or more, more preferably 50% or more, and still more preferably 90% or more in terms of the ion exchange rate by the organometalloxane monomer.

  The first method (strengthening method by ion exchange) and the second method (strengthening method by introduction of organometalloxane polymer) may be used alone or in combination. Moreover, when using it combining a 1st method and a 2nd method, it is preferable to introduce | transduce these to a strip | belt-shaped area | region so that the sum total of the ion exchange rate by various cations and organometalloxane monomers may become the range mentioned above.

In the present embodiment, only the band-like region may be strengthened by the first method and / or the second method described above. Alternatively, in addition to the belt-like region, a power generation region other than the belt-like region may be strengthened. However, in strengthening the power generation region, the higher the ion exchange rate, the higher the chemical resistance and mechanical properties, but the power generation performance tends to decrease.
Therefore, when strengthening the power generation region other than the belt-like region, it is preferable to make the ion exchange rate smaller than that of the belt-like region.
Since other points regarding various cations, organometalloxane polymers, organometalloxane monomers, and siloxane monomers, and other points regarding the solid polymer electrolyte membrane and the electrodes are the same as those in the first embodiment. Description is omitted.

Next, the MEA manufacturing method according to the present invention will be described.
A solid polymer electrolyte membrane in which all or a part of protons are ion-exchanged with a predetermined cation can be produced by the following method.
The first method is a method of immersing the electrolyte membrane in a solution containing a predetermined amount of a predetermined cation (M ^{n +} ) for a predetermined time. When the electrolyte membrane is immersed in the solution, the concentration ratio ([M ^{n +} ] / [H ⁺ ]) of the cation (M ^{n +} ) other than the proton to the proton (H ⁺ ) in the electrolyte membrane is the concentration ratio outside the electrolyte membrane. Cations (M ^{n +} ) tend to enter the membrane until they are approximately equal or larger.
Therefore, by optimizing the concentration ratio and the dipping time of the cations in the solution (M n ^+), it is possible to arbitrarily control the concentration ratio of cations in the electrolyte membrane (M n ^+). Further, when the electrolyte membrane is immersed in a solution containing cations (M ^{n +} ) excessively with respect to protons in the liquid for a long time, most of the cations (M ^{n +} ) in the solution can be replaced with protons in the electrolyte membrane. . Further, when the amount of the cation (M ^{n +} ) in the solution is excessive with respect to the proton in the solution and more than the amount of the cation exchange group in the electrolyte membrane, most of the protons in the electrolyte membrane are converted to the cation ( M ^{n +} ).
Furthermore, when the immersion time in the solution is optimized, only the vicinity of the surface of the membrane can be ion-exchanged, or ion exchange can be performed almost uniformly up to the inside of the membrane.

In the second method, a porous material (eg, filter paper) having a predetermined shape is impregnated with a solution containing a predetermined amount of a predetermined cation (M ^{n +} ), and this porous material is applied to the whole or a specific portion of the electrolyte membrane. This is a method of contacting for a predetermined time. This method can also be used as a method of ion exchange of the entire electrolyte membrane, but as a method of ion exchange of only a part of the electrolyte membrane, or a method of changing the ion exchange rate between the power generation region and the non-power generation region or the belt-like region. Particularly preferred.
Again, by optimizing the concentration ratio and contact time of cations in the solution (M n ^+), it is possible to arbitrarily control the concentration ratio of the cation (M n ⁺⁾ in the electrolyte membrane. Further, by optimizing the contact time with the porous material, only the vicinity of the surface of the membrane can be ion-exchanged, or ion exchange can be performed almost uniformly up to the inside of the membrane.

A solid polymer electrolyte membrane containing an organometalloxane polymer can be produced by the following method.
In the first method, water is contained in the electrolyte membrane in advance, and then the electrolyte membrane is brought into contact with a solution containing an organometalloxane monomer (and, if necessary, a metalloxane monomer), and the electrolyte membrane is further heated. It is a method to do.
The second method is a method in which an organometalloxane monomer (and a metalloxane monomer if necessary) is included in the electrolyte membrane in advance, then the electrolyte membrane is brought into contact with water, and the electrolyte membrane is further heated. is there.
The third method is a method in which the electrolyte membrane is brought into contact with a solution containing water and an organometalloxane monomer (and, if necessary, a metalloxane monomer), and then the electrolyte membrane is heated. The third method is effective when the dehydration polycondensation rate of the organometalloxane monomer (and the metalloxane monomer) is relatively slow.

Regardless of which method is used, the organometalloxane monomer (and the metalloxane monomer) introduced into the membrane is hydrolyzed by contact with water, and the alkoxy group is replaced with a hydroxyl group. Further, when the organometalloxane monomer is introduced into the membrane, the ammonium cation or quaternary alkyl ammonium cation at the end thereof and the proton in the membrane undergo ion exchange. When this film is further heated, the hydroxyl group undergoes dehydration condensation, and a metalloxane bond (M ₁ -O-M ₂ ) is generated.
As a result, an organometalloxane polymer is formed inside the electrolyte membrane. The organometalloxane polymer is ionically bonded to the cation exchange group in the membrane via the terminal ammonium cation or quaternary alkyl ammonium cation.

As a method of bringing the electrolyte membrane into contact with a solution containing water and / or an organometalloxane monomer (and a metalloxane monomer if necessary), specifically,
(1) a first method of immersing the entire membrane in a solution for a predetermined time;
(2) a second method in which a porous material (for example, filter paper) having a predetermined shape is impregnated with a solution, and the porous material is brought into contact with the entire membrane or a specific portion for a predetermined time;
and so on. Any method may be used in the present invention. In particular, the second method is particularly suitable as a method for introducing an organometalloxane polymer into only a part of the electrolyte membrane, or a method for changing the amount of the organometalloxane polymer introduced between the power generation region and the non-power generation region or the strip region. is there.
The amount of the organometalloxane polymer introduced into the film can be arbitrarily controlled by the concentration of the organometalloxane monomer in the solution and the contact time with this solution. Further, by optimizing the contact time with the solution, the organometalloxane polymer can be introduced only near the surface of the film, or the organometalloxane polymer can be introduced almost uniformly into the film.

  The ion exchange and the introduction of the organometalloxane polymer may be performed either alone or both. Moreover, when performing both ion exchange and introduction of an organometalloxane polymer, either may be performed first.

Next, electrodes are bonded to both surfaces of the electrolyte membrane on which ion exchange and / or introduction of the organometalloxane polymer has been performed. As a method of joining the electrodes, specifically,
(1) a first method of applying a paste containing an electrolyte in a catalyst layer and an electrode catalyst (hereinafter referred to as “catalyst paste”) to both surfaces of an electrolyte membrane;
(2) a second method in which a catalyst paste is applied to the surface of an appropriate substrate (for example, a polytetrafluoroethylene sheet), and this is transferred to both surfaces of the electrolyte membrane;
(3) a third method in which a catalyst layer is formed on both surfaces of the electrolyte membrane by the first method or the second method, and then a diffusion layer is further bonded to both surfaces;
(4) a fourth method in which a catalyst paste is applied to the surface of the diffusion layer, and the diffusion layer is bonded to both surfaces of the electrolyte membrane via the catalyst layer;
and so on.
A solid polymer fuel cell according to the present invention can be obtained by sandwiching both surfaces of the MEA thus obtained with a separator having a gas flow path to form a unit cell and laminating a predetermined number thereof.

Next, the operation of the MEA according to the present invention, the manufacturing method thereof, and the polymer electrolyte fuel cell will be described.
[1. Improving elastic modulus by ion exchange]
In the electrolyte membrane, it is said that multiples composed of cation-exchange group anions (for example, sulfonate anions) and cation ion pairs gather to form a region (ion aggregate) composed only of ions. The bond strength of the ion aggregate is determined by the electrostatic attractive force of the cation and the anion, and the electrostatic attractive force is considered to change depending on the radius of the cation and the anion and the ratio of the radii of both. Therefore, it is considered that by changing the kind of the cation, the strength of binding of the ion aggregate, and hence the elastic modulus of the membrane can be changed.

Among the various cations mentioned above,
(1) Complex cations such as hexaamminecobalt (III) ions,
(2) an expensive cation such as Ce ⁴⁺ and
(3) Cesium ion (Cs ⁺ ), calcium ion (Ca ²⁺ ), strontium ion (Sr ²⁺ ), barium ion (Ba ²⁺ ), zirconyl ion (ZrO ²⁺ ), chromium (III) ion (Cr ³⁺ ), cerium ( III) Ions (Ce ³⁺ )
Has a great effect of improving the elastic modulus. In particular, the rate of increase in elastic modulus when ion exchange is performed with a complex cation is outstanding.
Therefore, if a part of protons in the electrolyte membrane is replaced with these cations, the elastic modulus of the electrolyte membrane is improved, and deterioration of the membrane due to mechanical stress can be suppressed. At this time, if the ion exchange rate is optimized, the elastic modulus of the membrane can be improved without greatly reducing the electrical conductivity of the membrane.

[2. Improvement of elastic modulus by introduction of organometalloxane polymer]
When the electrolyte membrane is impregnated with a silicate ester such as tetraethoxysilane, and the hydrolysis and dehydration polycondensation of the silicate ester is performed inside the electrolyte membrane, silica (siloxane polymer) can be introduced into the membrane. When silica is introduced into the membrane, the strength of the membrane increases. However, since silica is considered to be bonded to the cation exchange group in the membrane only by hydrogen bonds at most, the rate of increase in elastic modulus due to the introduction of silica is relatively small.
On the other hand, when an electrolyte membrane is impregnated with an organometalloxane monomer having an ammonium cation or a quaternary alkylammonium cation at its end, and hydrolysis and dehydration polycondensation of the organometalloxane monomer is performed inside the electrolyte membrane, the membrane is simply Not only an organometalloxane polymer is formed inside, but also the cation exchange group in the membrane and the ammonium cation or quaternary alkylammonium cation at the end of the polymer are firmly bonded by ionic bond. Therefore, it is considered that the elastic modulus of the film is remarkably improved as compared with the case where silica is introduced.

[3. Improved chemical resistance]
Although the details of the reason why the chemical resistance of MEA is improved by the method according to the present invention are not clear, the following mechanism is conceivable.
The first mechanism is that the cation or polymer introduced into the membrane acts as a sacrificial agent against attack on the polymer by radicals and the like, and suppresses decomposition of the polymer by its own consumption. When the Fenton test is performed on a film that has been reinforced by a predetermined method, there is almost no weight reduction in the first test, but when the Fenton test is repeated on the same film, the weight loss after the second time increases. There is a case. This is believed to indicate that the cation or polymer introduced into the membrane acts as a sacrificial agent for radicals. As a cation or polymer strongly showing such a phenomenon,
(1) Tetraethylammonium cation or a quaternary alkylammonium cation having a bulkiness higher than that,
(2) an organometalloxane polymer having an ammonium cation or a quaternary ammonium cation at its end;
and so on.

The second mechanism is that the cation introduced into the membrane acts as a catalyst for inactivating hydrogen peroxide or peroxide radicals, and suppresses the decomposition of the polymer. When the Fenton test is performed on a film reinforced by a predetermined method, there is a case where the weight reduction hardly occurs even if the Fenton test is repeated on the same film as well as the first test. this is,
(A) the cation functions as a catalyst that actively decomposes hydrogen peroxide in a manner that does not generate radicals; or
(B) Since the cation functions as a catalyst for scavenging radicals,
it is conceivable that.
As a cation that strongly shows such a phenomenon,
(1) Zirconyl ion, aluminum ion, chromium (III) ion, cerium (III) ion,
(2) Expensive cations such as cerium (IV) ions,
(3) Complex cations such as hexaamminecobalt (III) ions,
and so on.

[4. Improved chemical resistance and mechanical properties due to reduced water content]
Hydration energy is a measure of stability when a cation is surrounded by water, and a large hydration energy means that the cation is likely to bind to water. It is considered that the moisture content of the electrolyte membrane decreases as the hydration energy per cation contained in the electrolyte membrane decreases.
Hydration energy correlates with the electrostatic attraction between the cation and water. The larger the cation size, the smaller the hydration energy, and the larger the cation valence, the greater the hydration energy. Conceivable. However, when the ion exchange rate is the same, when the cation valence is doubled, the number of cations introduced into the electrolyte membrane is halved, and when the cation valence is triple, The number of cations introduced is one third. That is, the influence of the valence on the hydration energy of the entire electrolyte membrane is offset, and the hydration energy of the entire electrolyte membrane is considered to depend mainly on the size of the cation. Therefore, by replacing the proton that is the smallest possible cation with a larger cation, the hydration energy of the entire electrolyte membrane, and hence the water content of the electrolyte membrane, can be reduced.

As a cation or polymer having the effect of significantly reducing the moisture content of the membrane,
(1) quaternary alkylammonium cations such as tetrapropylammonium cation and tetrabutylammonium cation,
(2) Complex cations such as hexaamminecobalt (III) cation,
(3) an organometalloxane polymer having an ammonium cation or a quaternary alkylammonium cation at its end;
(4) An organometalloxane polymer obtained by hydrolyzing and polycondensing an organometalloxane monomer having an ammonium cation or a quaternary alkylammonium cation at its end and a metalloxane monomer having a hydrophobic group,
and so on.

In general, in a humidified atmosphere, the initial elastic modulus of the electrolyte membrane is significantly reduced. This is presumably because, under a humidified atmosphere, water enters between the molecules in the electrolyte membrane, the van der Waals force between the molecules is weakened, and the structure of the ion aggregate is broken. Here, the “initial elastic modulus” refers to an elastic modulus obtained from an inclination of a tangent line passing through the origin of the strain-stress curve.
On the other hand, when the moisture content of the electrolyte membrane is decreased, the decrease in the initial elastic modulus in a humidified atmosphere can be mitigated. This is presumably because the structure in the dry state is easily maintained even in a humidified atmosphere by reducing the water content of the electrolyte membrane.
Furthermore, the chemical resistance of the electrolyte membrane is improved by reducing the water content of the electrolyte membrane. This is presumably because chemical species attacking the polymer are prevented from spreading throughout the electrolyte membrane by reducing the water content.
Therefore, if the content of the cation or polymer having an action of reducing the water content is optimized, the chemical resistance and mechanical properties of the film can be improved without greatly reducing the electric conductivity of the film.

[5. Improved durability by reinforcing non-power generation areas]
The above-described ion exchange with various cations and introduction of an organometalloxane polymer have the effect of improving the chemical resistance and mechanical properties of the membrane. On the other hand, the number of cation exchange groups in the electrolyte membrane is reduced, and the membrane It has the effect of lowering the electrical conductivity.
On the other hand, the deterioration of the electrolyte membrane due to mechanical and chemical factors is more significant in the non-power generation region (particularly the single-sided catalyst region) than in the power generation region. The non-power generation region is a region that hardly contributes to power generation. Therefore, all the protons contained therein are ion-exchanged with a predetermined cation, or an amount of an organometalloxane polymer corresponding to an ion-bonding of all cation exchange groups with an ammonium cation or a quaternary alkyl ammonium cation is formed. Even if installed, it will not have any adverse effect on power generation performance. Rather, durability increases as the ion exchange rate increases.
Therefore, by reinforcing at least the non-power generation region, the durability of the MEA can be significantly improved without sacrificing the power generation performance.

[6. Improving durability by reinforcing band-like areas including single-sided catalyst areas]
The deterioration of the electrolyte membrane constituting the MEA is remarkable at the end of the catalyst layer. Although the mechanism of this deterioration is not completely clarified, it is assumed that the following factors occur in combination.
(1) The end of the catalyst layer is a boundary between a region swollen by generated water during discharge and a region where it does not occur, and mechanical stress is likely to concentrate.
(2) If both electrodes are slightly shifted during the production of MEA, a single-sided catalyst region is formed at the end of the catalyst layer, but the single-sided catalyst region is more susceptible to chemical degradation than other regions (note that The inventors of the present application have found that chemical deterioration is remarkable in the single-sided catalyst region).
Therefore, the band-like region in the central part of the electrolyte membrane and in the vicinity of the end portion of the catalyst layer can be reinforced in advance, and deterioration of the membrane due to mechanical stress generated at the end portion of the catalyst layer can be suppressed.
Further, even when a single-sided catalyst region is generated due to an error in the manufacturing process, the single-sided catalyst region can be reliably accommodated in the band-shaped region by optimizing the width of the band-shaped region. Therefore, chemical deterioration in the single-sided catalyst region can be suppressed.
Furthermore, when the width of the belt-like region is optimized, all the protons in the belt-like region are ion-exchanged with a predetermined cation, or all the cation exchange groups are ion-bonded with an ammonium cation or a quaternary alkyl ammonium cation. Even if a corresponding amount of the organometalloxane polymer is introduced, adverse effects on the power generation performance of the MEA can be minimized. Therefore, the durability of the MEA can be greatly improved while maintaining the power generation performance substantially equal.

(Examples 1-8)
An 8 × 8 cm electrolyte membrane (Nafion (registered trademark) 112, about 0.7 g) was immersed in an aqueous solution containing various cations overnight. Note that the concentration of each solution was 0.2 M or more, and the amount of the solution was 0.2 L in all cases. This corresponds to exchanging protons of all sulfonic acid groups in the membrane with cations using an aqueous solution containing excess cations.
Example 9
An 8 × 8 cm electrolyte membrane (Nafion® 112, approximately 0.7 g) was added to an N-trimethoxysilylpropyl-N, N, N-trimethylammonium chloride ((TMSiTMA) Cl) 0.2 M methanol solution. Soaked in 2 L overnight. The obtained membrane was immersed in distilled water for 10 minutes and then vacuum-dried at 130 ° C. for 2 hours (Sol-Gel + ion exchange method). This process corresponds to an ion exchange rate of 100%.

(Comparative Example 1)
An 8 × 8 cm electrolyte membrane (Nafion (registered trademark) 112, approximately 0.7 g) was immersed in a 67 vol% methanol aqueous solution for 5 hours. Next, this film was immersed in a 40 vol% tetraethoxysilane (TEOS) methanol solution for 10 minutes and then vacuum-dried at 130 ° C. for 2 hours (Sol-Gel method).
(Comparative Example 2)
An 8 × 8 cm electrolyte membrane (Nafion (registered trademark) 112, approximately 0.7 g) immersed in distilled water for one night or longer was used for the test as it was.

About the film | membrane obtained in Examples 1-9 and Comparative Examples 1-2, the initial stage elasticity modulus, the moisture content, and the fluorine ion elution rate were measured. The measuring method is as follows.
(1) Initial elastic modulus in 95 ° C water:
A piece of electrolyte membrane having a width of 5 mm and a length of 20 mm was stretched in a length direction at a rate of 2 mm / s in 95 ° C. water, and a strain-stress curve was measured. The strain-stress curve was fitted with a straight line passing through the origin to determine the initial elastic modulus.
(2) Moisture content:
The electrolyte membrane was cut out and the dry weight was measured. Next, after being immersed in distilled water for 10 hours or more at room temperature, excess water was wiped off and the weight was measured again. The water content was determined by dividing the change in weight by the dry weight.
(3) Fluorine ion elution rate during Fenton test:
After holding the membrane in a 1 wt% aqueous hydrogen peroxide solution at 100 ° C. in which 10 ppm of Fe ²⁺ was dissolved, the concentration of F ^{− in} the solution was measured with an F ⁻ selective electrode. From the obtained F ⁻ concentration, the F ⁻ elution rate per unit area / unit time of the electrolyte membrane was determined.
Table 1 shows the results.

From Table 1,
(1) The initial elastic modulus is improved over Comparative Example 2 treated with water, except when treated with tetrapropylammonium cation (Example 5) and TEOS (Comparative Example 1).
(2) When treated with Ce ⁴⁺ cation (Example 4), the initial elastic modulus is improved as compared with the case of treatment with Ce ³⁺ cation (Example 3).
(3) When treated with hexaamminecobalt (III) cation (Example 1), the initial elastic modulus is remarkably improved.
(4) When treated with (TMSiTMA) Cl (Example 9), the initial elastic modulus is remarkably improved as compared with the case treated with TEOS (Comparative Example 1).
I understand that.
The reason why the initial elastic modulus is remarkably improved by treatment with the expensive cation or complex cation is considered to be because the size of the cation and the radius ratio with the anion are optimized and the strength of the ion aggregate is improved. In addition, it is considered that the initial elastic modulus is remarkably improved by treating with (TMSiTMA) Cl because the quaternary alkylammonium cation at the terminal is ionically bonded to the cation exchange group in the membrane.

From Table 1,
(1) When treated with hexaamminecobalt (III) cation (Example 1) or tetrapropylammonium cation (Example 5), the water content of the membrane is significantly reduced compared to treatment with other cations.
(2) When treated with (TMSiTMA) Cl (Example 9), the moisture content of the membrane is significantly reduced compared to when treated with TEOS (Comparative Example 1).
I understand that.
The reason why the water content is remarkably reduced by the treatment with a specific cation or (TMSiTMA) Cl is considered to be because the hydration energy of the entire membrane is reduced.

Furthermore, from Table 1,
(1) F ^- dissolution rate, Na ⁺ cation (Example 6), ^{Mg 2+} cations (Example 7), and TEOS unless treated with (Comparative Example 1), compared both treated with water Example 2 To improve,
(2) When treated with Ce ⁴⁺ cation (Example 4), the F ^- elution rate is lower than when treated with Ce ³⁺ cation (Example 3).
(3) In particular, when treated with hexaamminecobalt (III) cation (Example 1), Ce ³⁺ cation (Example 3) or Ce ⁴⁺ cation (Example 4), the F ⁻ elution rate is significantly reduced.
(4) When treated with tetrapropylammonium cation (Example 5) or (TMSiTMA) Cl (Example 9), the F ^- elution rate is greatly reduced as compared with Comparative Example 2.
I understand that.
The F ^- elution rate was greatly reduced by treatment with a specific cation or (TMSiTMA) Cl because the specific cation inactivates hydrogen peroxide or its radical, and the specific cation was sacrificed for the radical. This is considered to be because it acts as an agent, or because the penetration of radicals into the film is suppressed due to a decrease in water content.

(Examples 10 and 11)
Implementation was performed except that [Pt (NH ₃ ) ₄ ] Cl ₂ (Example 10) or [Ru (NH ₃ ) ₆ ] Cl ₃ (Example 11) was used as a reagent for ion exchange of protons. The ion exchange process was performed according to the same procedure as Examples 1-8. About the obtained film | membrane, the initial stage elasticity modulus was measured on the same conditions as Examples 1-8. Table 2 shows the results. From Table 1 and Table 2, it can be seen that the complex cation has an effect of significantly improving the initial elastic modulus as compared with other cations.

Example 12
A 6 × 6 cm electrolyte membrane (Nafion (registered trademark) 112) was prepared, and hexaamminecobalt (III) chloride ([Co ( It was immersed in an aqueous solution of NH ₃ ) ₆ ] Cl ₃ ) for 10 hours or more. If all hexaamminecobalt ions in the solution are replaced with protons of the sulfonic acid group, this corresponds to ion exchange of 10% of the protons with hexaamminecobalt ions throughout the electrolyte membrane. Actually, when the amount of protons in the treated electrolyte membrane was measured, the ion exchange rate was 9.9%. Next, a 3 × 3 cm square catalyst layer was hot-pressed on both surfaces of the electrolyte membrane to produce an MEA. The positions of the anode and the cathode were intentionally shifted as shown in FIG. The shifting width was 1 mm in the x direction and 1 mm in the y direction. Moreover, the hot press was performed by hold | maintaining for 6 minutes at a load of 50 kgf / cm < ² > (4.9 MPa) at 120 degreeC.
(Examples 13 and 14)
As a solution for treating the membrane, an aqueous solution of cerium (IV) sulfate (Ce (SO ₄ ) ₂ ) having a concentration capable of ion-exchange of 10% protons in the entire electrolyte membrane (Example 13), or tetra-n-propylammonium- An MEA was produced according to the same procedure as in Example 12, except that an aqueous solution of hydroxide ([CH ₃ CH ₂ CH ₂ ) ₄ N] OH) (Example 14) was used.
(Example 15)
A 6 × 6 cm electrolyte membrane (Nafion (registered trademark) 112) was immersed in a methanol solution (concentration 50 wt%) of (TMSiTMA) Cl having a concentration capable of ion-exchange of 10% protons over the entire electrolyte membrane overnight. Next, after being immersed in distilled water for 10 minutes, it was vacuum-dried at 130 ° C. for 2 hours. Hereafter, MEA was produced according to the same procedure as Example 12.

(Comparative Example 1)
An MEA was produced according to the same procedure as in Example 12 except that distilled water was used as a solution for treating the membrane.
(Reference Examples 1 and 2)
As a solution for treating the membrane, an aqueous magnesium nitrate (Mg (NO ₃ ) ₂ ) solution (Reference Example 1) having a concentration capable of ion-exchange of 10% protons in the entire electrolyte membrane, or cerium (III) sulfate (Ce ₂ (SO _{2 4} ) ₃ ) MEA was produced in accordance with the same procedure as Example 1 except having used aqueous solution (reference example 2).

(Example 16)
A 6 × 6 cm square filter paper was punched with a 3 × 3 cm square hole and covered with a 6 × 6 cm electrolyte membrane (Nafion® 112) from one side. Next, 2 mL of hexaamminecobalt (III) chloride ([Co (NH ₃ ) ₆ ] Cl ₃ ) in 0.1 M aqueous solution is added to the filter paper, and then the weight is applied so that the electrolyte membrane and the filter paper are in close contact with each other. And left for more than 10 hours. Further, the cathode catalyst sheet having a square shape of 3 × 3 cm and the square hole of the filter paper were positioned accurately, and the electrode catalyst was transferred by hot pressing. Hot pressing was performed by holding for 6 minutes at 120 ° C. with a load of 50 kg / cm ² (4.9 MPa).
Next, the reinforcing treatment and the transfer of the anode catalyst layer were performed in the same manner on the other side of the electrolyte membrane.
The positions of the anode and the cathode were intentionally shifted as shown in FIG. The shifting width was 1 mm in the x direction and 1 mm in the y direction. Further, the ion exchange rate in the non-power generation region was 100%.

(Example 17)
A 2.3 × 2.3 cm square hole was formed in a 3.7 × 3.7 cm square filter paper and covered with a 6 × 6 cm electrolyte membrane (Nafion (registered trademark) 112) from one side. Next, 2 mL of hexaamminecobalt (III) chloride ([Co (NH ₃ ) ₆ ] Cl ₃ ) in 0.1 M aqueous solution is added to the filter paper, and then the weight is applied so that the electrolyte membrane and the filter paper are in close contact with each other. And left for more than 10 hours. Moreover, the reinforcement | strengthening process was performed in the same position also on the other side.
Next, a 3 × 3 cm square catalyst layer was hot-pressed so that the single-sided catalyst region was in the vicinity of the center of the band-shaped region subjected to the strengthening treatment (see FIG. 2). Hot pressing was performed by holding at 120 ° C. with a load of 50 kgf / cm ² (4.9 MPa) for 6 minutes.
The positions of the anode and the cathode were intentionally shifted as shown in FIG. The shifting width was 1 mm in the x direction and 1 mm in the y direction. Further, the ion exchange rate in the band-like region was 100%.

Durability tests were performed on the MEAs obtained in Examples 12 to 16, Comparative Example 1 and Reference Examples 1 and 2 according to the following procedure.
First, MEA (electrolyte membrane-catalyst layer assembly) was sandwiched between 3.6 × 3.6 cm diffusion layers so that the outer periphery of the catalyst layer was positioned inside the outer periphery of the diffusion layer. Further, both sides of the MEA including the diffusion layer were sandwiched between current collectors of 3.6 × 3.6 cm, and a load of 820 N was applied to the current collector. Thereafter, the cell temperature was raised to 90 ° C., 20% humidified hydrogen was supplied to the anode side, and 33% humidified oxygen was supplied to the cathode side at a flow rate of 0.1 L / min.
In this state, (1) holding in an open circuit state for 3 minutes and (2) holding for 1 minute in a state where the current value was controlled to 0.1 A / cm were alternately repeated. During the durability test, the hydrogen concentration in the exhaust gas on the cathode side (corresponding to the amount of cross-leakage of gas) was measured, and the test was terminated when it exceeded 500 ppm. Table 3 shows the durability time (time when the hydrogen concentration exceeded 500 ppm).

From Table 3,
(1) The MEAs of Examples 12 to 17 and Reference Examples 1 and 2 all have improved durability as compared with the untreated Comparative Example 1.
(2) The MEAs of Examples 12 to 15 have durability improved to about 1.5 times or more that of Comparative Example 1 even if the ion exchange rate is only 10%.
(3) MEA ion-exchanged with Ce ⁴⁺ (expensive number side cation) (Example 13) has improved durability compared to MEA ion-exchanged with Ce ³⁺ (Reference Example 2).
(4) In particular, the hexaamminecobalt (III) cation (Example 12) has a large effect of improving the durability of MEA.
I understand that.
Even in the MEA ion-exchanged with tetrapropylammonium cation having little effect of improving the elastic modulus (Example 14), the durability is improved because the water content is reduced by ion exchange. This is thought to be because the swelling / shrinkage of the membrane and the invasion of radicals into the membrane during power generation / rest during the durability test were suppressed.
Further, the improvement in durability of MEA ion-exchanged with Mg ²⁺ (Reference Example 1) is slight because the effect of Mg ²⁺ on durability is relatively small, and the ion exchange rate is relatively low. It is thought that it is small.

  In addition, from Table 3, the MEA in which only the non-power generation region (Example 16) or the band-like region (Example 17) was reinforced as compared with the MEA in which the entire membrane was reinforced (Examples 12 to 15), It can be seen that the durability is high. This is because the ion exchange rate in the non-power generation region or the band-like region including the single-sided catalyst region is higher than that in the case where the entire membrane is reinforced. Moreover, this result shows that deterioration in the single-sided catalyst region is particularly remarkable among the MEAs, and that the durability of the MEA is remarkably improved by strengthening the single-sided catalyst region.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.
For example, in each of the above embodiments, the membrane is strengthened before joining the catalyst layer. However, after joining the catalyst layer, the band-like region including the one-side catalyst region or the non-power generation region may be strengthened. .

The membrane electrode assembly according to the present invention includes various electrochemical devices such as a fuel cell, a secondary battery, a water electrolysis apparatus, a hydrohalic acid electrolysis apparatus, a salt electrolysis apparatus, an oxygen and / or hydrogen concentrator, a humidity sensor, and a gas sensor. It can be used as a membrane electrode assembly used in the above.
Moreover, the polymer electrolyte fuel cell according to the present invention can be used for an in-vehicle power source, a stationary small power generator, a cogeneration system, and the like.

DESCRIPTION OF SYMBOLS 10 Membrane electrode assembly 12 Solid polymer electrolyte membrane 14a, 14b Catalyst layer

Claims (20)

A solid polymer electrolyte membrane;
An electrode bonded on both sides of the solid polymer electrolyte membrane,
In the solid polymer electrolyte membrane, a part of protons is a complex cation, a quaternary alkylammonium cation, and a metal ion capable of taking a plurality of valences, and an expensive cation having a valence larger than the minimum valence Ion exchanged with one or more cations selected from: and / or
The solid polymer electrolyte membrane is a membrane / electrode assembly containing an organometalloxane polymer obtained by impregnating a solution containing an organometalloxane monomer having an ammonium cation or a quaternary ammonium cation at its end, and hydrolyzing / condensing the polymer. body.   The membrane electrode assembly according to claim 1, wherein the complex cation is an ammine complex cation. The quaternary alkylammonium cation includes [(CH ₃ CH ₂ CH ₂ ) ₄ N] ⁺ , [(CH ₃ CH ₂ CH ₂ CH ₂ ) ₄ N] ⁺ , or [(CH ₃ ) ₃ C ₆ H _5. The membrane electrode assembly according to claim 1, which is N] ⁺ . 2. The membrane electrode assembly according to claim 1, wherein the expensive number side cation is Ce ⁴⁺ , Pr ⁴⁺ , Sm ³⁺ , Eu ³⁺ , Tb ⁴⁺ , or Yb ³⁺ .   2. The membrane / electrode assembly according to claim 1, wherein an ion exchange rate (= number of the cations × valence of the cations × 100 / number of cation exchange groups (%)) is 0.01% or more and 95% or less. . A solid polymer electrolyte membrane;
An electrode including a catalyst layer bonded to both surfaces of the solid polymer electrolyte membrane,
In the solid polymer electrolyte membrane, all or part of protons contained in a non-power generation region at the outer peripheral portion where the catalyst layer is not formed on at least one surface are ionized by one kind or two or more kinds of cations. Exchanged and / or
The solid polymer electrolyte membrane is obtained by impregnating the non-power generation region with a solution containing an organometalloxane monomer having an ammonium cation or a quaternary ammonium cation at the terminal, and hydrolyzing / condensing the organometalloxane. A membrane electrode assembly containing a polymer.   The cation exchanging protons is a complex cation, a quaternary alkylammonium cation, or a metal ion capable of taking a plurality of valences, and is selected from an expensive cation having a valence greater than the minimum valence 1 It is the above, The membrane electrode assembly of Claim 6.   The membrane electrode assembly according to claim 7, wherein the complex cation is an ammine complex cation. The quaternary alkylammonium cation includes [(CH ₃ CH ₂ CH ₂ ) ₄ N] ⁺ , [(CH ₃ CH ₂ CH ₂ CH ₂ ) ₄ N] ⁺ , or [(CH ₃ ) ₃ C ₆ H _5. The membrane electrode assembly according to claim 7, which is N] ⁺ . The membrane electrode assembly according to claim 7, wherein the expensive cation is Ce ⁴⁺ , Pr ⁴⁺ , Sm ³⁺ , Eu ³⁺ , Tb ⁴⁺ , or Yb ³⁺ .   The membrane electrode assembly according to claim 6, wherein an ion exchange rate (= number of the cations × valence of the cations × 100 / number of cation exchange groups (%)) is 1% or more. A solid polymer electrolyte membrane;
An electrode including a catalyst layer bonded to both surfaces of the solid polymer electrolyte membrane,
The solid polymer electrolyte membrane is an intermediate portion thereof, and all or part of protons contained in a belt-like region including the outer peripheral portion of the catalyst layer therein is ion-exchanged by one or more cations. And / or
The solid polymer electrolyte membrane is a membrane containing an organometalloxane polymer obtained by impregnating the band-like region with an organometalloxane monomer having an ammonium cation or a quaternary ammonium cation at the end thereof, followed by hydrolysis and condensation polymerization Electrode assembly.   13. The membrane electrode assembly according to claim 12, wherein the belt-like region has an outer circumference width wider than the catalyst layer width and an inner circumference width narrower than the catalyst layer width.   The membrane electrode assembly according to claim 12, wherein the area of the band-shaped region surrounded by the inner periphery thereof is 0.5 times or more of the area of the catalyst layer.   The cation exchanging protons is a complex cation, a quaternary alkylammonium cation, or a metal ion capable of taking a plurality of valences, and is selected from an expensive cation having a valence greater than the minimum valence 1 It is the above, The membrane electrode assembly of Claim 12.   The membrane electrode assembly according to claim 15, wherein the complex cation is an ammine complex cation. The quaternary alkylammonium cation includes [(CH ₃ CH ₂ CH ₂ ) ₄ N] ⁺ , [(CH ₃ CH ₂ CH ₂ CH ₂ ) ₄ N] ⁺ , or [(CH ₃ ) ₃ C ₆ H _5. The membrane electrode assembly according to claim 15, which is N] ⁺ . The membrane electrode assembly according to claim 15, wherein the expensive cation is Ce ⁴⁺ , Pr ⁴⁺ , Sm ³⁺ , Eu ³⁺ , Tb ⁴⁺ , or Yb ³⁺ .   The membrane electrode assembly according to claim 12, wherein an ion exchange rate (= number of the cations × valence of the cations × 100 / number of cation exchange groups (%)) is 1% or more.   A polymer electrolyte fuel cell comprising the membrane electrode assembly according to any one of claims 1 to 19.

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