JP5319061B2 - Membrane electrode assembly, manufacturing method thereof, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane electrode assembly which serves as a high-performance membrane electrode assembly in which adhesion between a polyelectrolyte membrane and an electrode is strong and the superior physical properties of the polyelectrolyte membrane are exerted sufficiently, and show a high power generation characteristic when supplied with a highly concentrated methanol when the membrane electrode assembly applies to direct methanol type fuel battery. <P>SOLUTION: The membrane electrode assembly includes the polyelectrolyte membrane and electrodes disposed on both sides of the polyelectrolyte membrane. In the membrane electrode assembly, the polyelectrolyte membrane is pressure bonded by heat to the electrodes under heating temperatures ranging from a temperature -30&deg;C or less below a lowest softening point to a temperature +10&deg;C or less higher the softening point when the lowest softening point represents the lowest one of the softening points of high molecular compounds contained in the polyelectrolyte membrane. High adhesion is created between the polyelectrolyte membrane and electrodes and the deterioration of the physical properties of the polyelectrolyte membrane is suppressed. Hence the membrane electrode assembly is provided as a high-performance membrane electrode assembly. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a membrane electrode assembly that can be used for a polymer electrolyte fuel cell, a direct liquid fuel cell, a direct methanol fuel cell, and the like, a method for producing the same, and a fuel cell using the membrane electrode assembly.

  Polymer electrolytes containing proton conductive substituents such as sulfonic acid groups are used as raw materials for electrochemical devices such as fuel cells, humidity sensors, gas sensors, and electrochromic display devices. Among these, fuel cells are expected as one of the pillars of new energy technology.

  Solid polymer fuel cells that use polymer electrolytes with proton-conducting substituents can be operated at low temperatures and can be reduced in size, weight, mobile vehicles such as automobiles, household cogeneration systems, and civilian use. Application to small portable devices is under consideration.

  In particular, a direct methanol fuel cell that uses methanol directly as a fuel has a simple structure, ease of fuel supply and maintenance, and features such as high energy density. It is expected to be applied to small portable devices for private use such as laptop computers.

  As a proton conductive polymer electrolyte used in a polymer electrolyte fuel cell, a perfluorocarbon sulfonic acid polymer electrolyte represented by Nafion (registered trademark) (Nafion) has been widely studied. A perfluorocarbon sulfonic acid polymer electrolyte, which is a fluorine-based hydrocarbon polymer electrolyte, has high proton conductivity and excellent chemical stability such as acid resistance and oxidation resistance. However, since the raw materials used are high and the manufacturing process is complicated, there is a disadvantage that it is very expensive. Further, when immersed in a hydrogen-containing liquid such as methanol, the film swells. In particular, when the methanol concentration is high, the film itself dissolves, so that there is a problem that power generation characteristics deteriorate. Therefore, there is a problem as a polymer electrolyte for a direct methanol fuel cell. Further, when the polymer electrolyte is used as a polymer electrolyte membrane, there is a concern that fuel may be lost due to crossover during power generation.

  On the other hand, Patent Document 1 discloses a hydrocarbon-based proton-conducting polymer electrolyte that is a non-fluorine-based hydrocarbon-based polymer electrolyte that has excellent durability to methanol and can suppress crossover. It is disclosed.

  Patent Document 2 discloses a membrane electrode assembly for a polymer electrolyte fuel cell in which the durability of the membrane electrode assembly is improved by reducing fluorine ions by-produced from the fluorine-based hydrocarbon polymer electrolyte membrane. A manufacturing method is disclosed. Specifically, the electrode layer is subjected to a heat treatment in which pressure is maintained in the temperature range from the glass transition temperature to the thermal decomposition temperature of the fluorine-based hydrocarbon polymer electrolyte membrane before hot-pressing the MEA. In addition, elution of fluorine ions is effectively suppressed by adopting a fluorine-based hydrocarbon polymer electrolyte having a large ion exchange capacity.

Furthermore, in Patent Document 3, in order to obtain a polymer electrolyte membrane-gas diffusion electrode having excellent current-voltage characteristics using a fluorine-based hydrocarbon polymer electrolyte membrane, a catalyst in the reaction part of the gas diffusion electrode is used. Increasing the contact area with the polymer electrolyte resin, improving the adhesion between the polymer electrolyte membrane and the reaction part, and forming a polymer electrolyte membrane-reaction part assembly having a reaction part uniformly joined And a reaction formed by applying a catalyst dispersion having a catalyst, a polymer electrolyte, and a dispersion medium to a substrate for the purpose of producing a polymer electrolyte membrane-reaction part having a thin and uniform reaction part. In the method for producing a polymer electrolyte membrane-reaction part assembly in which a part is heated and pressed against at least one side of a fluorine-based hydrocarbon polymer electrolyte membrane, the fluorine-based hydrocarbon polymer electrolyte membrane is in a water-containing state and heated. Pressure welding A method of setting the temperature to 100 ° C. or less is disclosed, and by doing so, a decrease in the adhesion of the reaction part or peeling due to a dimensional change accompanying a change in the water content of the fluorine-based polymer electrolyte membrane is prevented. The temperature of the thermocompression bonding can be controlled to prevent partial separation of the reaction part due to a sudden volume change of water accompanying vaporization.
International Publication WO2006 / 019029 Pamphlet JP-A-2005-209402 Japanese Patent Laid-Open No. 11-025998

  As in the above-mentioned Patent Document 2 and Patent Document 3, in the membrane / electrode assembly using the fluorine-based hydrocarbon polymer electrolyte membrane, the membrane / electrode bonding considering the influence of the eluting fluorine ions and the dimensional change due to swelling. There is a problem that it is difficult to study a membrane electrode assembly based on the physical properties of the polymer electrolyte membrane itself.

  On the other hand, the polymer electrolyte membrane does not contain fluorine, for example, in the membrane electrode assembly using the membrane of Patent Document 1, the physical properties of the polymer electrolyte membrane itself without being affected by fluorine in the membrane, for example, It is considered that an ideal membrane electrode assembly can be studied based on the relationship between the degree of deterioration of the polymer electrolyte membrane and the adhesive strength depending on the production temperature. It goes without saying that the membrane / electrode assembly examined in this way is effective even for a polymer electrolyte membrane containing fluorine if the influence of fluorine-containing material can be avoided by another method.

  The present invention has been made in view of the above problems, and can be suitably used for solid polymer fuel cells, direct liquid fuel cells, and direct methanol fuel cells based on the physical properties of the polymer electrolyte membrane itself. A membrane electrode assembly, a production method thereof, and a fuel cell using the membrane electrode assembly, and a fuel cell exhibiting excellent power generation characteristics even when high-concentration methanol is supplied.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have invented the membrane / electrode assembly of the present invention that can sufficiently exhibit the physical properties of the polymer electrolyte membrane itself.

  That is, the membrane / electrode assembly of the present invention is a membrane / electrode assembly including a polymer electrolyte membrane and electrodes disposed on both sides thereof, and among the softening points of the polymer compound contained in the polymer electrolyte membrane. A membrane electrode assembly in which the polymer electrolyte membrane and the electrode are heated and pressed at a heating temperature of the lowest softening point −30 ° C. or more and the lowest softening point + 10 ° C. or less when the lowest temperature is the lowest softening point. There is a high performance membrane electrode assembly because an excellent adhesive force is generated between the polymer electrolyte membrane and the electrode, and the physical properties of the polymer electrolyte membrane are prevented from deteriorating. It becomes.

Further, the membrane electrode assembly has an open circuit potential of a single cell of a direct methanol fuel cell including the membrane electrode assembly of 0.00 V / mol ⁻¹ or more, 0.02 V / The direct methanol fuel cell provided with this membrane electrode assembly can exhibit high power generation characteristics, particularly when supplying high-concentration methanol, because it decreases in the range of mol ⁻¹ or less and has excellent methanol barrier properties.

Furthermore, the polymer electrolyte membrane is a polymer electrolyte membrane in which a proton conductive group is introduced into a polymer film containing at least a polymer compound having an aromatic unit and a polymer compound having no aromatic unit. Since it is a non-fluorinated hydrocarbon polymer electrolyte, it is excellent in durability of methanol, is inexpensive, and further, by introducing a proton conductive group into the polymer film, A polymer electrolyte containing a proton-conducting group is formed in the membrane to form a proton-conducting polymer electrolyte membrane, so it is simple and highly productive. In particular, in such a proton-conducting electrolyte membrane, aromatic units A proton-conductive group such as a sulfonic acid group is introduced into a polymer compound portion having a structure, and the portion becomes a polymer electrolyte containing a proton-conducting group. The proton conductive group is not introduced into the polymer compound portion having no unit. Therefore, even though such an electrolyte membrane includes a polymer electrolyte into which a hydrophilic proton conductive group such as a sulfonic acid group is introduced throughout, the skeleton portion has a proton conductive group introduced therein. Since the portion is not formed, it is difficult to swell against water or an aqueous methanol solution, resulting in an electrolyte membrane having high methanol barrier properties.

  In particular, the proton conductive electrolyte membrane preferably has a structure in which a polymer compound having an aromatic unit is dispersed in a polymer compound having no aromatic unit, more preferably several μm to several tens of μm. The island of the polymer compound having an aromatic unit has a sea-island structure in which the polymer compound without the aromatic unit is dispersed in the sea, and has a swelling inhibiting effect on the polymer compound without the aromatic unit. The properties of the polymer electrolyte membrane having sufficient conductivity and sufficient methanol barrier properties are not reduced during the production of the membrane electrode assembly, and the same properties are exhibited as the membrane electrode assembly.

  Here, the polymer compound having an aromatic unit is selected from the group consisting of polystyrene, syndiotactic polystyrene, polyphenylene ether, modified polyphenylene ether, polysulfone, polyethersulfone, polyetheretherketone, polyphenylene sulfide, and derivatives thereof. It is preferable to include one or more kinds of polymer compounds selected, and these polymer compounds have chemical stability and thermal stability and are easy to introduce proton conductive substituents. The proton conductive polymer electrolyte obtained is excellent in proton conductivity and methanol blocking properties.

  Here, the polymer compound having no aromatic unit preferably includes one or more polymer compounds selected from polymer compounds having the following general formula 1, and other polymer compound components, particularly those described later. Excellent compatibility and dispersibility with the catalyst layer forming material, excellent processability when producing polymer films by melt extrusion molding, which will be described later, and handling properties of the polymer films thus obtained. The membrane electrode assembly obtained has excellent methanol barrier properties, chemical stability, thermal stability, and the like.

（一般式１中、Ｘ₁〜Ｘ₄は、Ｈ、ＣＨ₃、Ｃｌ、Ｆ、ＯＣＯＣＨ₃、ＣＮ、ＣＯＯＨ、ＣＯＯＣＨ₃、及びＯＣ₄Ｈ₉、からなる群から選択されるいずれかであって、Ｘ₁〜Ｘ₄は互いに独立で同一であっても異なっていてもよい。）
また、ここで、前記芳香族単位が無い高分子化合物が、ポリエチレン、ポリプロピレン、ポリメチルペンテン、及びそれらの誘導体からなる群から選択される１種類以上の高分子化合物を含むことが好ましく、工業的に入手し易く、得られる高分子フィルムは機械的特性やハンドリング性に優れ、得られる電解質膜はプロトン伝導性やメタノール遮断性、化学的安定性などに優れる。

(In General Formula 1, X _{1 to} X ₄ are any selected from the group consisting of H, CH ₃ , Cl, F, OCOCH ₃ , CN, COOH, COOCH ₃ , and OC ₄ H ₉ . X _{1 to} X ₄ may be the same or different from each other.
Here, the polymer compound having no aromatic unit preferably contains one or more polymer compounds selected from the group consisting of polyethylene, polypropylene, polymethylpentene, and derivatives thereof, The obtained polymer film is excellent in mechanical properties and handling properties, and the obtained electrolyte membrane is excellent in proton conductivity, methanol blocking property, chemical stability and the like.

  Furthermore, the proton conductive group preferably contains a sulfonic acid group, is easily introduced into the polymer, and has a high proton conductivity imparted by the introduction.

  In particular, the direct methanol fuel cell including the membrane electrode assembly of the present invention as described above exhibits high power generation characteristics when supplying high-concentration methanol.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have invented a method for producing a membrane / electrode assembly of the present invention that can sufficiently exhibit the physical properties of the polymer electrolyte membrane itself.

  That is, the method for producing a membrane / electrode assembly of the present invention is a method for producing a membrane / electrode assembly including a polymer electrolyte membrane and electrodes disposed on both sides thereof, and the polymer contained in the polymer electrolyte membrane. When the lowest temperature among the softening points of the compound is the lowest softening point, the polymer electrolyte membrane is heated and pressed at a heating temperature of the lowest softening point −30 ° C. or higher and the lowest softening point + 10 ° C. or lower. A method for producing a membrane electrode assembly characterized in that an excellent adhesive force is generated between the polymer electrolyte membrane and the electrode, and deterioration of physical properties of the polymer electrolyte membrane is suppressed. Therefore, a high performance membrane electrode assembly can be manufactured.

  The membrane / electrode assembly of the present invention preferably includes a method for producing the polymer electrolyte membrane by a process including melt molding, and the productivity and the mechanical properties of the resulting polymer film are excellent. In addition, the thickness of the film can be easily controlled, and the method can be applied to various resins and has a low environmental load.

  Such a membrane electrode assembly according to the present invention is suitably used for a fuel cell, and a fuel cell including the membrane electrode assembly has a low proton permeability and a low methanol permeability while having sufficient proton conductivity. Since swelling with respect to a hydrogen-containing liquid or the like is suppressed, excellent power generation characteristics are exhibited.

  In the membrane / electrode assembly of the present invention, an excellent adhesive force is generated between the polymer electrolyte membrane and the electrode, and the physical properties of the polymer electrolyte membrane are suppressed from being deteriorated. In addition, for example, a direct methanol fuel cell including this membrane electrode assembly can exhibit high power generation characteristics particularly when supplying high-concentration methanol.

  Embodiments of the present invention will be described in detail below.

  The membrane electrode assembly as referred to in the present application includes at least a proton conductive polymer electrolyte membrane and electrodes disposed on both sides thereof, and can be used as a main member of a fuel cell. Here, the electrode is a member having conductivity, and preferably serves also as a catalyst layer containing a fuel cell catalyst described later. In this case, it is preferable that the proton conductive polymer membrane and the catalyst layer are in direct contact with each other, but there may be some substance and / or layer between them as long as the characteristics are not deteriorated. The catalyst layer is preferably a layered structure formed by using a catalyst layer forming material including at least a fuel cell catalyst and a polymer electrolyte, which will be described later. Each electrode does not need to be the same in thickness and composition, for example, and can be appropriately changed, but may be the same. Further, as a part of the configuration of the electrode, a diffusion layer may be disposed on the opposite side of the catalyst layer from the proton conductive polymer electrolyte membrane.

  The proton conductive group can be used as long as it dissociates protons in a water-containing state, and examples thereof include a sulfonic acid group, a phosphoric acid group, a carboxylic acid group, and a phenolic hydroxyl group. It can be used in a plurality or a plurality. Among the exemplified proton conductive groups, a sulfonic acid group is preferable because it can be easily introduced into a polymer and the proton conductivity imparted by the introduction is increased.

  Hereinafter, each component will be described.

(Proton conducting polymer electrolyte membrane)
The proton conductive polymer electrolyte membrane referred to in the present application is a membrane containing a polymer electrolyte containing at least a proton conductive group in the membrane, and is a membrane having both excellent proton conductivity and high methanol blocking property. It is more preferable that different materials are combined. By irradiating radiation such as electron beam, γ-ray, ion beam, etc., a cross-linked structure may be introduced into the polymer electrolyte membrane to further improve the methanol barrier property.

(Polymer electrolytes containing proton conductive groups)
Polymer electrolytes containing proton conductive groups are roughly classified into fluorine-based and non-fluorinated hydrocarbon-based polymer electrolytes. Of these, hydrocarbon-based non-fluorinated hydrocarbon-based polymer electrolytes. A polymer electrolyte is excellent in durability of methanol, and is inexpensive and preferable. Such a hydrocarbon-based electrolyte may literally be a hydrocarbon-based electrolyte that is conventionally known to those skilled in the art. For example, a hydrocarbon-based compound in which a proton conductive group is introduced into a polymer compound having an aromatic unit. An electrolyte can be exemplified.

(Polymer compound having an aromatic unit)
Such a polymer compound having an aromatic unit is literally a polymer compound having an aromatic unit conventionally known to those skilled in the art. For example, polyaryl ether sulfone, polyether ether sulfone, polyether ketone , Polyether ketone ketone, polysulfone, polyparaphenylene, polyphenylene sulfide, polyphenylene ether, polyphenylene sulfoxide, polyphenylene sulfide sulfone, polyphenylene sulfone, polybenzimidazole, polybenzoxazole, polybenzothiazole, polystyrene, syndiotactic polystyrene, polyether sulfone , Styrene- (ethylene-butylene) styrene copolymer, styrene- (polyisobutylene) -styrene copolymer, poly 1,4-biphe Rene ether ether sulfone, polyarylene ether sulfone, polyimide, polyether imide, cyanate ester resin, polyether ether ketone, polyethylene-polystyrene graft copolymer, polyethylene-polystyrene block copolymer, polypropylene-polystyrene graft copolymer, (Ethylene-glycidyl methacrylate) -polystyrene graft copolymer, (ethylene-ethyl acrylate) -polystyrene graft copolymer, polypropylene- (acrylonitrile-styrene) graft copolymer, polycarbonate-polystyrene graft copolymer, polycarbonate- (acrylonitrile) -Styrene) graft copolymer, vinyl acetate resin-polystyrene block copolymer, acrylic resin-polystyrene block Click copolymer, Modi Per series (NOF Corporation, registered trademark), etc. Epofriend series (manufactured by Daicel Chemical Co., Ltd.) are exemplified.

In particular, chemical stability and thermal stability, ease of introduction of proton-conductive substituents, proton conductivity of the resulting proton-conductive polymer electrolyte, and methanol of the resulting proton-conductive polymer electrolyte membrane In view of blocking properties, the polymer compound having an aromatic unit is composed of polystyrene, syndiotactic polystyrene, polyphenylene ether, modified polyphenylene ether, polysulfone, polyethersulfone, polyetheretherketone, and polyphenylene sulfide. It is preferably at least one polymer selected from the group of polymers, copolymers comprising these polymers, and one polymer selected from derivatives of these polymers, or a mixture of these polymers.
(Introducing proton conductive group into polymer film)
Furthermore, by introducing a proton conductive group into the polymer film, a polymer electrolyte containing the proton conductive group is formed in the membrane, and a proton conductive polymer electrolyte membrane is obtained. It is preferable because it is high. As the introduction method, a known method can be used, but a method of bringing a polymer film into contact with a proton conductive group introducing agent, in particular, bringing the polymer film into contact with a proton conductive group introducing agent in the presence of an organic solvent. The method is preferable because a polymer electrolyte membrane having both excellent proton conductivity and high methanol barrier properties can be obtained.

(Skeleton part, electrolyte part)
Specifically, a polymer electrolyte containing a proton conductive group by introducing a proton conductive group into a polymer film containing a polymer compound having an aromatic unit and a polymer compound having no aromatic unit Is preferably formed in the membrane to form a proton conductive electrolyte membrane. In such a proton conductive electrolyte membrane, a proton conductive group such as a sulfonic acid group is introduced into a polymer compound portion having an aromatic unit, and the portion becomes a polymer electrolyte containing a proton conductive group. Thus, a proton conductive group is not introduced into a polymer compound portion having no aromatic unit. Therefore, even though such an electrolyte membrane includes a polymer electrolyte into which a hydrophilic proton conductive group such as a sulfonic acid group is introduced throughout, the skeleton portion has a proton conductive group introduced therein. Since the portion is not formed, it is difficult to swell against water or an aqueous methanol solution, resulting in an electrolyte membrane having high methanol barrier properties.

  That is, such a proton conductive electrolyte membrane preferably has a structure in which a polymer compound having an aromatic unit is dispersed in a polymer compound having no aromatic unit, and more preferably a few μm to This is a sea-island structure in which islands of a polymer compound having an aromatic unit of several tens of μm are dispersed in the sea of a polymer compound having no aromatic unit. At this time, if the polymer compound having an aromatic unit is too dispersed or compatible, the swelling suppression effect of the polymer compound having no aromatic unit may be reduced, and conversely, the polymer compound having an aromatic unit. If the dispersion state is extremely bad, when the polymer electrolyte membrane is used, there is a fear that the proton conductivity may be insufficient or the methanol blocking property may be insufficient.

(Polymer compound without aromatic units)
The polymer compound having no aromatic unit literally means a compound having no aromatic unit in the structure, and whether or not the polymer compound contains an aromatic unit is determined by NMR or the like. Therefore, those skilled in the art can easily understand “a polymer compound having no aromatic unit” and “a polymer compound having an aromatic unit”.

  Examples of the polymer compound having no aromatic unit include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 4-methyl-1-pentene, and 5-methyl- Α-olefin homopolymers such as 1-heptene or polyolefin resins containing these copolymers, cyclic polyolefins such as norbornene resins, polyvinyl chloride, vinyl chloride-vinyl acetate copolymers; vinyl chloride-vinylidene chloride Copolymers, vinyl chloride resins including vinyl chloride-olefin copolymers, polyamide resins including nylon 6, nylon 66, and the like, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetra Fluoroethylene-exafluoropropylene copolymer ; Tetrafluoroethylene - ethylene copolymer, polychlorotrifluoroethylene, polyvinylidene fluoride, and fluorine-based resins such as polyvinyl fluoride and the like.

  The polymer compound having no aromatic unit is compatible or dispersible with other polymer compound components, processability when producing a polymer film, handling property of the resulting polymer film, and electrolyte obtained therefrom In view of the methanol barrier property, chemical stability, thermal stability, etc. of the membrane, it is one polymer selected from a polymer compound having a repeating unit of the following general formula (1), or a mixture thereof. It is particularly preferred.

（一般式１中、Ｘ₁〜₄は、Ｈ、ＣＨ₃、Ｃｌ、Ｆ、ＯＣＯＣＨ₃、ＣＮ、ＣＯＯＨ、ＣＯＯＣＨ₃、及びＯＣ₄Ｈ₉、からなる群から選択されるいずれかであって、Ｘ₁〜₄は互いに同一であっても異なっていてもよい。）
さらに、工業的入手の容易さや、得られる高分子フィルムの機械的特性やハンドリング性、得られる電解質膜のプロトン伝導性やメタノール遮断性、化学的安定性などを考慮すると、前記芳香族単位がない高分子化合物は、ポリエチレンおよび／またはポリプロピレンおよび／またはポリメチルペンテンを含むことが好ましい。また高分子フィルムの製造に通常用いられる、各種添加剤、例えば相溶性向上のための相溶化剤、樹脂劣化防止のための酸化防止剤、フィルムとしての成型加工における取り扱いを向上するための帯電防止剤や滑剤などは、電解質膜への加工性や性能に影響を及さない限りにおいて、適宜用いられ得る。特に異なる材料を組み合わせて高分子樹脂フィルムを製造する場合には、互いの相溶性を上げるために相溶化剤を用いることが好ましい。

(In General Formula 1, X ₁ to ₄ are any one selected from the group consisting of H, CH ₃ , Cl, F, OCOCH ₃ , CN, COOH, COOCH ₃ , and OC ₄ H ₉ , X ₁ to ₄ may be the same as or different from each other.)
Furthermore, in view of industrial availability, mechanical properties and handling properties of the resulting polymer film, proton conductivity, methanol blocking property, chemical stability, etc. of the obtained electrolyte membrane, there is no such aromatic unit. The polymer compound preferably contains polyethylene and / or polypropylene and / or polymethylpentene. Various additives commonly used in the production of polymer films, such as compatibilizers for improving compatibility, antioxidants for preventing resin deterioration, and antistatics for improving handling in film processing Agents, lubricants and the like can be appropriately used as long as they do not affect the processability and performance of the electrolyte membrane. In particular, when a polymer resin film is produced by combining different materials, it is preferable to use a compatibilizing agent in order to increase the compatibility.

(Catalyst for fuel cell)
The catalyst contained in the catalyst layer is preferably one that is active in the electrode reaction of the fuel cell. In this case, the necessary functions include the ability to reduce oxidants (such as oxygen and air) on the cathode side, It is the ability to oxidize fuel (methanol, hydrogen, etc.). Specifically, a high surface area conductive material such as carbon black, ketjen black, activated carbon, carbon nanohorn, or carbon nanotube carries a noble metal catalyst such as platinum. Or a noble metal catalyst such as platinum black is used. Further, the cathode side catalyst may be a composite or alloy catalyst made of platinum and iron, tin, rare earth elements, or the like in order to improve the reducing ability, stabilize the catalytic metal, or extend the life. Furthermore, the anode side catalyst is a composite or alloy catalyst made of platinum and ruthenium instead of platinum in order to suppress catalyst poisoning by carbon monoxide, aldehydes, carboxylic acids, etc., which are by-products during fuel oxidation. Alternatively, a multi-component catalyst containing iron, tin, rare earth elements, etc. may be used for stabilization and long life.

(Manufacturing method of polymer film)
As a method for producing the above-described polymer film, known methods can be used as appropriate. For example, inflation method, melt extrusion molding such as T-die method, calendar method, cast method, cutting method, emulsion method, hot press method , Etc. are exemplified. Among these methods, in view of productivity, mechanical properties of the resulting polymer film, ease of film thickness control, applicability to various resins, environmental load, etc., melt extrusion molding is preferable.

  Further, the molecular orientation may be controlled by subjecting the polymer film to a treatment such as stretching, or the crystallinity may be controlled by performing a heat treatment. Further, the mechanical strength may be improved by adding various fillers to the polymer film, or by combining the polymer film and a reinforcing agent such as a glass nonwoven fabric by pressing.

  Specifically, a method in which a polymer film material is put into an extruder in which a T-die is set, and film formation is performed while melt-kneading can be applied. Furthermore, it is possible to apply a method in which pellets and powders of a polymer compound not having an aromatic unit are preliminarily mixed at a predetermined blending ratio and formed into a film while being similarly melt-kneaded. At this time, if the extruder used is a twin screw extruder, a polymer film in which these components are melted and uniformly dispersed can be obtained. Further, the film may be formed using pellets melt-kneaded with a twin-screw extruder so as to have a predetermined blending ratio in advance, or a masterbatch pellet is used to obtain a predetermined blending ratio. Thus, the film may be formed while melt-kneading. Moreover, when there is no problem in the dispersibility of the components to be combined, the film may be formed with a single screw extruder in which a T die is set.

(Thickness of polymer film)
Arbitrary thickness can be selected as thickness of the polymer film manufactured according to a use. For example, in consideration of reducing the internal resistance of the polymer electrolyte membrane obtained from the polymer film, the thinner the polymer film, the better. On the other hand, in consideration of methanol barrier properties and handling properties of the obtained polymer electrolyte membrane, it may be undesirable if the thickness of the polymer film is too thin. Considering these, the thickness of the polymer film is preferably 1.2 μm or more and 350 μm or less. If the thickness of the polymer film is within the above range, it is easy to form a film, and wrinkles are less likely to occur during processing when a proton conductive group is introduced or during drying. In addition, handling is improved such that damage is unlikely to occur. In addition, the proton conductivity of the obtained polymer electrolyte membrane can be expressed within a desired range.

(Proton conductivity)
The ion exchange capacity derived from the inclusion of the proton conductive group of the polymer electrolyte contained in the proton conductive polymer electrolyte membrane is preferably 0.3 meq / g or more, more preferably 0.5 meq. / G or more. When the ion exchange capacity is 0.3 meq / g or more, the polymer electrolyte membrane containing the polymer electrolyte is likely to exhibit preferable proton conductivity.

(Proton conducting group introduction agent)
As the proton conductive group introducing agent used for introducing the proton conductive group, a sulfonating agent can be preferably used. By bringing the polymer film and the proton conductive group introducing agent into contact with each other in the presence of an organic solvent, the proton conductive group introducing agent is brought into direct contact with the polymer film, thereby preventing an excessive reaction from occurring and deteriorating the film. However, it becomes possible to introduce a desired amount of sulfonic acid groups.

  Examples of the sulfonating agent include known sulfonating agents such as chlorosulfonic acid, fuming sulfuric acid, sulfur trioxide, sulfur trioxide-triethyl phosphate, concentrated sulfuric acid, and trimethylsilyl chlorosulfate. In consideration of industrial availability, ease of introduction of sulfonic acid groups, and characteristics of the obtained polymer electrolyte membrane, it is preferable to use chlorosulfonic acid alone or a mixture containing chlorosulfonic acid. That is, when the sulfonating agent is chlorosulfonic acid, a sulfonic acid group that is a proton conductive group is easily introduced, and a polymer electrolyte membrane having high proton conductivity can be easily obtained.

(Organic solvent)
Examples of the organic solvent used when the polymer film is brought into contact with the proton conductive group introducing agent include, for example, a sulfonic acid group to the aromatic unit without decomposing the sulfonating agent that is the proton conductive group introducing agent. Any material may be used as long as it does not inhibit the introduction and does not cause degradation such as decomposition of the thermoplastic polymer or the antioxidant in the polymer film. By using an organic solvent, the polymer film can easily swell, and the proton conductive group introducing agent can be diffused into the film.

  When a sulfonating agent is used as the proton conductive group introducing agent, it is easy to introduce a sulfonic acid group and a polymer electrolyte membrane having good characteristics can be obtained. Therefore, a halogenated hydrocarbon should be used as the organic solvent. For example, dichloromethane, 1,2-dichloroethane, chloroform, 1-chloropropane, 1-chlorobutane, 2-chlorobutane, 1,4-dichlorobutane, 1-chloro-2-methylpropane, 1-chloropentane, 1- Examples include chlorohexane and chlorocyclohexane. In particular, in view of industrial availability, ease of introduction of sulfonic acid groups, and characteristics of the obtained electrolyte membrane, among these halogenated hydrocarbons, from dichloromethane, 1,2-dichloroethane and 1-chlorobutane An organic solvent containing at least one selected from the group consisting of Among them, dichloromethane or 1-chlorobutane is particularly preferable because the proton conductivity and the methanol blocking property of the obtained polymer electrolyte membrane can be compatible.

(Sulfonating agent amount)
The amount of the sulfonating agent used is 0.1 to 100 times (weight ratio), more preferably 0.5 to 50 times (weight ratio) with respect to the polymer film. It is preferable that a polymer electrolyte membrane with good characteristics can be produced. In other words, since sulfonic acid groups can be introduced in a suitable range, it is possible to prevent the polymer film itself from being chemically deteriorated while imparting sufficient proton conductivity and hydrophilicity to the polymer electrolyte membrane. It is possible to produce a polymer electrolyte membrane having practical characteristics that is easy to handle while maintaining mechanical properties while preventing a decrease in mechanical strength.

  Further, the concentration of the sulfonating agent in the organic solvent may be appropriately set in consideration of the target introduction amount of the sulfonic acid group, reaction conditions such as temperature and time. Specifically, it is preferably 0.05% by weight or more and 20% by weight or less because the sulfonating agent is easily brought into contact with the aromatic unit in the polymer film and a desired amount of sulfonic acid group can be introduced. The time required for introduction is shortened, the sulfonic acid group can be introduced uniformly throughout the polymer film, and the mechanical properties of the resulting polymer electrolyte membrane can be ensured. It is 0.2 weight% or more and 10 weight% or less.

(Sulfonation temperature / time)
The reaction temperature for bringing the polymer film into contact with the sulfonating agent is preferably 0 ° C. or higher and 100 ° C. or lower, more preferably 10 ° C. or higher and 30 ° C. or lower. If reaction temperature is 0 degreeC or more, measures, such as cooling on an installation, are unnecessary and it can prevent taking time more than necessary for reaction. Moreover, if it is 100 degrees C or less, reaction can be adjusted appropriately, generation | occurrence | production of a side reaction can be prevented and the problem of reducing the characteristic of a film | membrane can be avoided. Furthermore, the reaction temperature when the polymer film and the sulfonating agent are brought into contact with each other is preferably equal to or lower than the boiling point of the organic solvent to be used because it is not necessary to use a pressure resistant container.

  Moreover, as a reaction time at the time of making a polymer film and a sulfonating agent contact, 0.5 hour or more is preferable as the minimum, 2 hours or more is more preferable, and 100 hours or less is preferable as an upper limit. When the reaction time is 0.5 hours or longer, the sulfonating agent and the aromatic unit in the polymer film are in sufficient contact, so that a desired amount of sulfonic acid groups can be introduced, and the reaction time is 100 By setting the time to less than or equal to the time, a polymer electrolyte membrane with good characteristics can be produced without impairing productivity. Actually, in consideration of the reaction atmosphere of the sulfonating agent and organic solvent to be used, the target production amount, etc., a polymer electrolyte membrane having desired characteristics can be efficiently produced, and the reaction conditions are set. What is necessary is just to set suitably.

(Catalyst layer forming material)
The catalyst layer-forming material described above is a mixture containing at least the polymer electrolyte and the fuel cell catalyst, and a dispersant is added to improve the mutual dispersion state. In order to improve performance, a water repellent may be included. The form is not particularly limited, and may be a solid mixture, a mixed dispersion, or a mixed solution. In particular, a mixed dispersion or mixed solution is preferable because it is easy to handle. The concentration of the polymer electrolyte in the mixed dispersion or mixed solution that is such a catalyst layer forming material is 1 wt% or more and 90 wt% or less because it is easy to handle as the catalyst layer forming material. More preferably, it is 1 wt% or more and 75 wt% or less, and particularly preferably 1 wt% or more and 50 wt% or less. If the amount is less than 1 wt%, the viscosity of the catalyst layer forming material is small, so that it is difficult to form the catalyst layer itself. If the amount is more than 90 wt%, the viscosity of the catalyst layer forming material is large, so that the catalyst layer is uniformly formed. Tend to be difficult to form.

  The solvent used for preparing the mixed dispersion or mixed solution is not particularly limited, but methanol, ethanol, isopropyl alcohol, dimethylformamide, dimethylacetamide, N, N-dimethylformamide, 1-methyl-2-pyrrolidone, tetrahydrofuran, Dimethyl sulfoxide, chloroform, methylene chloride, 1,2-dichloroethane, cyclohexane, hexane, or ether are preferred.

  The ion exchange capacity derived from the aforementioned proton-conducting substituent contained in the polymer electrolyte to be mixed with the catalyst layer forming material is preferably 0.1 meq / g or more, more preferably 0.3 meq / g. That's it. When the ion exchange capacity is lower than 0.1 meq / g, the catalyst layer having a desired proton conductivity tends not to be developed.

  As a form before mixing of the polymer electrolyte to be mixed with such a catalyst layer forming material, a polymer electrolyte solution is prepared by dissolving or dispersing the above-described catalyst layer forming material in a solvent used to form a mixed dispersion or mixed solution. Alternatively, a polymer electrolyte dispersion is preferable because it is easy to handle.

  Examples of the dispersant include C1-6 alcohol, glycerin, ethylene carbonate, propylene carbonate, butyl carbonate, ethylene carbamate, propylene carbamate, butylene carbamate, acetone, acetonitrile, dimethylformamide, 1-methyl-2-pyrrolidone, difluorobenzene, Sulfolane or a surfactant can be used.

  As the water repellent, polytetrafluoroethylene, a copolymer of polyfluoroethylene and polyfluoropropylene, or the like can be used.

  The method for producing the catalyst layer forming material is not particularly limited, but the above-described materials are mixed using a stirrer or the like, mixed using a ball mill or the like, mixed using a rotor, or injected at ultra high pressure. One or more methods can be used, such as a method of mixing by doing this, or a method of mixing using a homogenizer.

(Catalyst layer formation method)
As a method for producing a catalyst layer, the catalyst layer forming material is deposited on a release film such as a polytetrafluoroethylene (PTFE) film or the diffusion layer by a doctor blade, a roll coater, screen printing, spraying, or the like, and dried. A method of removing the solvent and water is used. In order to prevent cracking of the formed catalyst layer, it may be effective to repeat the coating and solvent removal operations several times.

(Diffusion layer)
As such a diffusion layer, carbon paper, carbon felt, carbon cloth or the like, which is a non-woven fabric of conductive carbon fiber, can be used, and its surface is repelled in order to control the diffusibility of fuel or oxidant. A liquid agent is preferably provided, and a particle layer containing carbon and a water repellent is more preferably provided.

(Membrane / electrode assembly manufacturing method)
As a method for producing a membrane / electrode assembly, for example, a release film on which a catalyst layer is formed is disposed on both surfaces of a polymer electrolyte membrane, and then heated and pressed using a press machine such as a hot press machine or a roll press machine. Or removing the release film and disposing a diffusion layer on the catalyst layer, or disposing the diffusion layer on which the catalyst layer is formed on both sides of the proton conductive polymer membrane, such as a hot press machine or a roll press machine. A method of heat-pressing using a press is preferred.

  The temperature at the time of heating and pressing is set according to the type of polymer electrolyte contained in the polymer electrolyte membrane or catalyst layer to be used. That is, as the heating and pressing temperature, when the lowest temperature among the softening points of the polymer compound substantially contained in the polymer electrolyte membrane is the lowest softening point, for example, it has an aromatic unit, and In the case of a polymer electrolyte membrane made of a polymer compound having no aromatic unit, the minimum softening point of each softening point may be −30 ° C. or higher and the lowest softening point + 10 ° C. or lower. preferable. When the heating temperature is lower than the minimum softening point of −30 ° C., sufficient adhesion cannot be obtained between the film and the electrode, for example, the catalyst layer, and the interface resistance may increase. Further, when the heating temperature is higher than the minimum softening point + 10 ° C., the film deteriorates, which is not preferable.

  As the pressure of the heating and pressing, when the maximum pressure is 0.1 MPa or more and 20 MPa or less, the polymer electrolyte membrane and the catalyst layer are sufficiently adhered, and the characteristic deterioration due to particularly large deformation of the material does not occur. ,preferable. If the maximum pressure is higher than this range, the catalyst layer may collapse and may not function effectively. If the maximum pressure is lower than this range, sufficient adhesion may not be obtained, and interface resistance may increase.

(Softening point measurement method)
The softening point of each polymer compound constituting the polymer electrolyte membrane can be measured from a general thermal analysis. For example, the storage elastic modulus of dynamic viscoelasticity and the change in loss elastic modulus can be measured. It can be obtained from the maximum value of the loss tangent of the inflection point or dynamic viscoelasticity.

(Fuel cell)
The membrane electrode assembly thus produced is divided into two members, such as a separator in which a flow path for feeding fuel is formed and a member such as a separator in which a flow path for feeding oxidant is formed. A fuel cell can be formed by inserting between a pair of members. The separator is not particularly limited, and for example, a conductive material such as carbon graphite or stainless steel can be used. In addition, when using metal materials, such as stainless steel, as a separator, it is preferable to perform the corrosion resistance process. Then, the electrode on the side supplied with the fuel functions as an anode side electrode, and as the fuel, for example, liquid methanol or the like can be used, and the electrode on the side supplied with the oxidant functions as a cathode side electrode, As the oxidizing agent, oxygen or air can be used. The oxidant supplied to the cathode may be humidified with water, but it is preferable to use a non-humidified oxidant because the flooding phenomenon of the cathode can be suppressed.

The amount of liquid fuel such as methanol to be supplied is not particularly limited, but is preferably an amount necessary for the electrode reaction during steady operation. For example, when a current density of 0.5 A / cm ² is passed, it is preferable to supply a methanol amount of 2.5 × 10 ⁻⁴ mol / min per unit electrode area. Furthermore, for example, when increasing the current density to 1.0 A / cm ² during steady operation, it is preferable to supply a methanol amount of 5.0 × 10 ⁻⁴ mol / min per unit electrode area. It is preferable to increase the amount of methanol supplied with the increase. The fuel may be always supplied to the electrode, or when the fuel is insufficient, the fuel may be supplied in an amount corresponding to a predetermined steady operation time.

The amount of the gaseous oxidant such as oxygen supplied is not particularly limited, but is preferably an amount necessary for the electrode reaction during steady operation. For example, when a current density of 0.5 A / cm ² is passed, it is preferable to supply an oxygen amount of 3.8 × 10 ⁻⁴ mol / min per unit electrode area. For example, when increasing the current density to 1.0 A / cm ² during steady operation, it is preferable to supply an oxygen amount of 7.6 × 10 ⁻⁴ mol / min per unit electrode area. Accordingly, it is preferable to increase the oxygen supply amount.

The amount of air to be supplied is not particularly limited, but the amount necessary for the electrode reaction during steady operation is preferable. For example, when a current density of 0.5 A / cm ² is achieved, it is preferable to supply an oxygen amount of 3.8 × 10 ⁻⁴ mol / min per unit electrode area. Furthermore, for example, when the current density is increased to 1.0 A / cm ² during steady operation, the amount of oxygen contained in the air per unit electrode area should be 7.6 × 10 ⁻⁴ mol / min. It is preferable to increase the air supply amount as the current density increases.

  The supply of the oxidizing agent may be always supplied to the electrode, or when the oxidizing agent is insufficient, it may be supplied in an amount corresponding to a predetermined steady operation time.

  The temperature of the supplied fuel and oxidant is not particularly limited, but is preferably 0 ° C. or higher and lower than the decomposition temperature of the polymer electrolyte used in the membrane electrode assembly. When the temperature is lower than 0 ° C., the water contained in the fuel and the oxidant is frozen, and / or the membrane electrode assembly is frozen, which is not preferable. When the temperature is higher than the decomposition temperature of the polymer electrolyte used in the membrane / electrode assembly, the polymer electrolyte used in the membrane / electrode assembly is decomposed.

  The direction in which the fuel and the oxidant used in the present invention are supplied is not particularly limited, and may be a counter flow or a flat alternating current as long as an amount necessary for the electrode reaction can be supplied to the electrode.

  Such a polymer electrolyte fuel cell can be used singly or by stacking a plurality of layers to form a stack, and a fuel cell system incorporating them can also be used.

(Open circuit potential measurement)
By measuring the open circuit potential of the fuel cell thus produced, the characteristics of the membrane electrode assembly used can be evaluated. Specifically, the potential difference between the potential of the electrode supplied with the oxidant and the potential of the electrode supplied with fuel in the single cell of the produced fuel cell is 100 ° C. or less, no load, methanol as the fuel to the anode, and cathode After supplying oxygen or air as an oxidizer, the open circuit potential can be measured by allowing the sample to stand for 1 minute or longer so that each of the oxygen and air can be sufficiently distributed.

  The open circuit potential can be measured, for example, by connecting the fuel cell to an electronic loader, setting the electronic loader to a no-load state, and reading the potential detected by the electronic loader. . The electronic loader may be equipped with a direct-current power supply or a general fuel cell evaluation apparatus.

(Dependence of open circuit potential on methanol concentration)
In the measurement of the open circuit potential, the concentration of methanol supplied to the anode is sequentially measured, for example, as 1 mol / L, 5 mol / L, and 10 mol / L, and then the methanol concentration on the x axis and the open circuit potential on the y axis. And finally, for example, by calculating the slope by the method of least squares, the dependence of the open circuit potential on the methanol concentration can be obtained.

  The membrane electrode assembly of the present invention has a decrease in the open circuit potential of a single cell of a direct methanol fuel cell comprising the assembly with an increase in the concentration of methanol used for fuel, 0.00V / (mol / L) or more, It is preferably 0.02 V / (mol / L) or less. As the methanol concentration increases, the amount of methanol permeated through the polymer electrolyte membrane increases, so the decrease does not fall below 0.00 V / (mol / L). On the other hand, when the decrease in the open circuit potential is larger than 0.02 V / (mol / L), the methanol permeation amount increases as the methanol concentration increases. That is, the power generation characteristics of the fuel cell when high concentration methanol is supplied are not preferable.

  Hereinafter, examples will be shown, and the embodiment of the present invention will be described in more detail. Of course, the present invention is not limited to the following examples. Various details are possible, and various modifications can be made within the scope of the claims, and the technical means disclosed in each of the embodiments can be changed. Embodiments obtained by appropriately combining the above are also included in the technical scope of the present invention.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited at all by these Examples, In the range which does not change the summary, it can change suitably.

Example 1
<Preparation of electrolyte membrane>
First, polyphenylene sulfide (manufactured by Dainippon Ink & Chemicals, Inc., LD10p11) is used as the polymer compound having the aromatic unit, and high-density polyethylene (HI— ZEX 3300F) was used to produce a polymer film.

  Specifically, a pellet mixture obtained by dry blending 50 parts by weight of polyphenylene sulfide pellets and 50 parts by weight of high density polyethylene pellets was set on a T die under the conditions of a screw temperature of 290 ° C. and a T die temperature of 290 ° C. The polymer film was melt-extruded by a twin-screw extruder to prepare a polymer film having a thickness of 84 μm containing 50% by weight of high-density polyethylene in the polymer film. The polymer film thus prepared is actually divided into a polyphenylene sulfide portion which is a polymer compound mainly having an aromatic unit and a high density polyethylene portion which is a polymer compound mainly having no aromatic unit. Phase-separated to form a sea-island structure consisting of a sea composed of a high-density polyethylene portion and an island composed of a polyphenylene sulfide portion.

  Next, a polymer electrolyte membrane was prepared by introducing a sulfonic acid group as a proton conductive group into the polymer film thus prepared. Specifically, first, 905 g of dichloromethane and 18.0 g of chlorosulfonic acid were weighed in a glass container to prepare a 2 wt% chlorosulfonic acid solution, and 2.1 g of the polymer film was added to the chlorosulfonic acid solution. Was allowed to stand at 25 ° C. for 20 hours, whereby sulfonic acid groups were introduced into the aromatic ring of the polyphenylene sulfide portion described above of the polymer film. Thereafter, the polymer film having the sulfonic acid group introduced in this manner is collected and washed with ion-exchanged water until it becomes neutral, and then the polymer film is kept in a constant temperature and humidity chamber adjusted to 23 ° C. The polymer electrolyte membrane was obtained by drying by leaving it for 30 minutes under controlled humidity of 98%, 80%, 60% and 50%, respectively.

<Measurement of softening point>
The softening point of the polymer electrolyte membrane was determined by measuring the storage elastic modulus of dynamic viscoelasticity according to the following procedure. First, the membrane was installed in a dynamic viscoelasticity measuring apparatus (RSA3, manufactured by T.A. Instruments Co., Ltd.), and then measurement conditions (heating from 25 ° C. to 3 ° C./min., Frequency: 1 Hz, The storage elastic modulus of dynamic viscoelasticity was measured at a strain amount of 0.15%), and finally the softening point was obtained from the inflection point of the storage elastic modulus that appeared first. The softening point of the polymer electrolyte membrane produced in Example 1 was 120 ° C.

<Preparation of anode catalyst layer>
First, platinum-ruthenium catalyst-supported carbon powder (TEC61E54, Tanaka Kikinzoku Kogyo Co., Ltd., molar ratio (platinum: ruthenium = 1: 1.5), catalyst-supported amount 54 wt%) 0.463 g in pure water 4.630 g, and After adding 4.123 g of an alcohol solution of Nafion (DE521, 5 wt%, manufactured by DuPont) as an electrolyte solution, the anode catalyst ink was prepared by stirring for 30 minutes using a magnetic stirrer. Next, this anode catalyst ink was sprayed onto a carbon paper diffusion layer (SGL24BA, SGL Carbon Japan, 50 mm × 50 mm) with an air brush until the amount of platinum supported was 1.0 mg / cm ² . Finally, it was vacuum-dried at 150 ° C. for 1 hour, and then cut into a size of 22 mm × 22 mm to obtain an anode catalyst layer forming diffusion layer having a platinum loading of 1.0 mg / cm ² .

<Preparation of cathode catalyst layer>
First, platinum catalyst-supported carbon powder (TEC10E50E, Tanaka Kikinzoku Kogyo Co., Ltd., 50% by weight of catalyst support) 0.250 g of pure water, Nafion alcohol solution (DE521, 5 wt%, manufactured by DuPont) as an electrolyte solution ) After adding 1.840 g, a cathode catalyst ink was prepared by stirring for 30 minutes using a magnetic stirrer. Next, the cathode catalyst ink was sprayed onto a carbon paper diffusion layer (SGL24BA, manufactured by SGL Carbon Japan Co., Ltd., 50 mm × 50 mm) with an air brush until the amount of platinum supported was 1.0 mg / cm ² . Finally, it was dried at 50 ° C. and then cut into a size of 22 mm × 22 mm to obtain a cathode catalyst layer-forming diffusion layer having a platinum loading of 1.0 mg / cm ² .

<Fabrication of membrane electrode assembly for fuel cell>
A membrane / electrode assembly was produced by the following procedure using a heating and pressure welding machine (manufactured by Tester Sangyo Co., Ltd.). SUS plate, polytetrafluoroethylene sheet (100 mm × 100 mm × 0.05 mm), the anode catalyst layer forming diffusion layer (22 mm × 22 mm), the polymer electrolyte membrane, the cathode catalyst layer forming diffusion layer (22 mm × 22 mm), By placing a laminate of polytetrafluoroethylene sheets (100 mm × 100 mm × 0.05 mm) and a SUS plate in this order on a pressure plate heated to 110 ° C., and heat-welding under a condition of 9.8 MPa for 5 minutes A membrane electrode assembly was obtained.

<Fabrication of fuel cell>
The membrane electrode assembly was installed in a commercially available single cell for PEFC (manufactured by Electrochem) to assemble a fuel cell. First, anode side end plate (current collector), gas flow plate (carbon separator), polytetrafluoroethylene gasket (0.15 mm), membrane electrode assembly, polytetrafluoroethylene gasket (0.15 mm), gas flow plate (Carbon separator) and cathode side end plate (current collector) were laminated in this order. Next, a fuel cell was produced by tightening at 2 Nm using M3 bolts.

<Measurement of open circuit potential and power generation characteristics of direct methanol fuel cell>
The open circuit potential and power generation characteristics of the fuel cell thus prepared were measured at a cell temperature of 60 ° C. while supplying an aqueous methanol solution on the anode side and non-humidified air on the cathode side.

The power generation characteristics were measured while supplying a ¹⁰ mol- ¹ methanol aqueous solution to the anode side. The results are shown in FIG.

The open circuit potential was measured after stabilization in each state by changing the concentration of the aqueous methanol solution on the anode side to ¹ mol- ¹ , ¹ , 5 mol- ¹ , and 10 mol- ¹ . The open circuit potential is obtained by connecting the fuel cell to an electronic load (PLZ164WA, manufactured by Kikusui Electronics Co., Ltd.), setting the electronic load to an unloaded state, and reading the potential detected by the electronic load. It was measured. Furthermore, the power generation characteristics were measured by discharging the fuel cell by setting an arbitrary current using the electronic loader.

  As the methanol concentration dependence of the measurement result of the open circuit potential, the methanol concentration was plotted on the x-axis and the open circuit potential was plotted on the y-axis, and the slope when linearly approximated by the least square method was calculated. The results are shown in Table 1. The open circuit potential decreased with increasing methanol concentration.

（比較例１）
高分子電解質膜として膜厚１５０μｍのナフィオン１１５を用いたこと以外は、実施例１と同様にして比較例１の膜電極接合体を作成し、また、実施例１と同様にしてその膜電極接合体を用いた直接メタノール型燃料電池を作成し、メタノール濃度増加に伴う開回路電位低下率、及び発電特性を測定した。結果を表１、及び図１に示す。

(Comparative Example 1)
A membrane / electrode assembly of Comparative Example 1 was prepared in the same manner as in Example 1 except that Nafion 115 having a film thickness of 150 μm was used as the polymer electrolyte membrane. A direct methanol fuel cell using the body was prepared, and the open circuit potential drop rate and the power generation characteristics with increasing methanol concentration were measured. The results are shown in Table 1 and FIG.

(Comparative Example 2)
A membrane / electrode assembly of Comparative Example 2 was prepared in the same manner as in Example 1 except that the temperature of heating and pressure welding was set to 150 ° C., and the open circuit potential reduction rate accompanying the increase in methanol concentration in the direct methanol fuel cell , And power generation characteristics were measured. However, in the direct methanol fuel cell using the membrane electrode assembly of Comparative Example 2, the value of the open circuit potential itself is small, a meaningful value cannot be obtained as the rate of decrease, and the power generation characteristics are also very high. It was a bad result.

  From the comparison of Example 1 in Table 1 and Comparative Example 1, the reduction rate of the open circuit potential of the fuel cell of Example 1 having the membrane electrode assembly of the present invention is smaller than the reduction rate of Comparative Example 1. It was found that the membrane electrode assembly of Example 1 was also suitable for application at a high methanol concentration. This result is considered to be related to the methanol barrier property of the polymer electrolyte membrane used in the membrane electrode assembly of each example.

  Further, from comparison between Example 1 and Comparative Example 1 in FIG. 1, it is clear that the fuel cell provided with the membrane electrode assembly of the present invention exhibits superior power generation characteristics as compared with Comparative Example 1. It was.

  The membrane electrode assembly according to the present invention has various industrial applicability including a fuel cell represented by a direct methanol fuel cell.

The current density-power density curve of the direct methanol type fuel cell using the membrane electrode assembly of the present invention.

Claims (10)

A membrane electrode assembly including a polymer electrolyte membrane and electrodes arranged on both sides thereof, wherein the polymer electrolyte membrane contains two or more polymer compounds, and is the lowest softening point of the polymer compound When the temperature is the lowest softening point, the polymer electrolyte membrane and the electrode are heated and pressed at a heating temperature of the lowest softening point −30 ° C. or more and the lowest softening point + 10 ° C. or less. Membrane electrode assembly. The membrane electrode assembly according to claim 1, wherein the open circuit potential of a single cell of a direct methanol fuel cell including the membrane electrode assembly is 0.00 V / (mol / L) as the concentration of methanol used as fuel increases. ) The membrane electrode assembly is characterized in that it is lowered in the range of 0.02 V / (mol / L) or less. The proton conductive group is introduced into a polymer film in which the polymer electrolyte membrane includes at least a polymer compound having an aromatic unit and a polymer compound having no aromatic unit. 3. The membrane electrode assembly according to either 1 or 2. The polymer compound having an aromatic unit is selected from the group consisting of polystyrene, syndiotactic polystyrene, polyphenylene ether, modified polyphenylene ether, polysulfone, polyethersulfone, polyetheretherketone, polyphenylene sulfide, and derivatives thereof. The membrane / electrode assembly according to claim 3, comprising at least one polymer compound. The membrane electrode assembly according to claim 3 or 4, wherein the polymer compound having no aromatic unit includes one or more polymer compounds selected from polymer compounds represented by the following general formula 1.

(In General Formula 1, X _{1 to} X ₄ are any one selected from the group consisting of H, CH ₃ , Cl, F, OCOCH ₃ , CN, COOH, COOCH ₃ , and OC ₄ H ₉ . , X _{1 to} X ₄ may be the same or different from each other. The polymer compound having no aromatic unit includes at least one polymer compound selected from the group consisting of polyethylene, polypropylene, polymethylpentene, and derivatives thereof. The membrane electrode assembly according to any one of claims. The membrane electrode assembly according to claim 3, wherein the proton conductive group includes a sulfonic acid group. A method for manufacturing a membrane electrode assembly including a polymer electrolyte membrane and electrodes disposed on both sides thereof, wherein the lowest temperature is selected from the softening points of two or more polymer compounds contained in the polymer electrolyte membrane. A membrane electrode assembly, wherein the polymer electrolyte membrane and the electrode are heated and pressure-welded at a heating temperature of a minimum softening point of −30 ° C. or more and a minimum softening point of + 10 ° C. or less when the minimum softening point is used. Production method. A method for producing a membrane electrode assembly according to any one of claims 1 to 7, comprising a method for producing the polymer electrolyte membrane by a process including melt molding. Manufacturing method. A fuel cell comprising the membrane electrode assembly according to claim 1.

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