JP2004220843A - Membrane electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the durability of a membrane electrode assembly by suppressing the damage of an electrolyte membrane caused by the fuzzing or breakdown of a diffusion layer. <P>SOLUTION: The membrane electrode assembly is formed by joining the diffusion layer with a solid polymer electrolyte membrane through a catalyst layer, and the catalyst layer comprises a composite of a first phase comprising a catalyst and a first solid polymer electrolyte for giving and receiving protons and of a reinforcing material for suppressing the damage of the solid polymer electrolyte membrane by the diffusion layer. The reinforcement material is preferable to be a porous membrane, a fibrous material, fine particles, a binder, a sputtered membrane, or a carbon layer. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００８５】
比較例１で得られたＭＥＡの場合、乾燥状態におけるセル抵抗は、０．１５×１０^３Ω・ｍ^２であった。これに対し、実施例１〜４で得られたＭＥＡの場合、乾燥状態におけるセル抵抗は、２．０〜１．１×１０^３Ω・ｍ^２であり、比較例１の７．３〜１３．３倍であった。表１より、触媒層内に補強材を加えることによって、固体高分子電解質膜の損傷が抑制されることがわかる。
【００８６】
以上、本発明の実施の形態について詳細に説明したが、本発明は上記実施の形態に何ら限定されるものではなく、本発明の要旨を逸脱しない範囲内で種々の改変が可能である。
【００８７】
例えば、上記実施例においては、本発明に係る膜電極接合体を固体高分子型燃料電池に適用した例について説明したが、本発明の用途はこれに限定されるものではなく、固体高分子型燃料電池以外の各種電気化学デバイスに用いられる膜電極接合体としても使用することができる。
【００８８】
また、本発明に係る膜電極接合体を構成する補強材を備えた触媒層は、その外側に拡散層を接合して使用する場合に特に好適であるが、補強材を備えた触媒層の用途はこれに限定されるものではなく、固体高分子電解質膜に対して触媒層のみを接合して使用する膜電極接合体に対しても適用することができる。
【００８９】
【発明の効果】
本発明に係る膜電極接合体は、触媒層内に補強材が含まれているので、拡散層の毛羽立ち、破損等に起因する固体高分子電解質膜の損傷を抑制できるという効果がある。
【図面の簡単な説明】
【図１】図１（ａ）は、セパレータのリブで押圧される前の膜電極接合体の断面模式図であり、図２（ｂ）は、セパレータのリブで押圧された後の膜電極接合体の断面模式図である。
【符号の説明】
１０ 膜電極接合体
１２ 固体高分子電解質膜
１４、１６ 電極
１４ａ、１６ａ 触媒層
１４ｂ 拡散層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a membrane electrode assembly, and more particularly, to a polymer electrolyte fuel cell, a water electrolysis device, a hydrohalic acid electrolysis device, a salt electrolysis device, an oxygen and / or hydrogen concentrator, a humidity sensor, a gas sensor, and the like. The present invention relates to a membrane electrode assembly used for various electrochemical devices.
[0002]
[Prior art]
A polymer electrolyte fuel cell generally has a structure in which electrodes are bonded to both sides of a polymer electrolyte membrane to form a membrane electrode assembly (MEA), and both sides of the MEA are sandwiched by ribbed separators. The solid polymer electrolyte membrane generally includes a perfluorinated electrolyte membrane having excellent oxidation resistance (for example, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation)), Flemion (registered trademark) Trademark, manufactured by Asahi Glass Co., Ltd.).
[0003]
Further, the electrode generally has a two-layer structure of a catalyst layer bonded to the surface of the solid polymer electrolyte membrane and a diffusion layer bonded outside the catalyst layer. The diffusion layer is for supplying a reaction gas and transferring electrons to and from the catalyst layer, and generally uses carbon cloth, carbon paper, or the like. In addition, the catalyst layer is a part to be a reaction field of an electrode reaction, and is generally made of a composite of carbon carrying a catalyst such as platinum and a solid polymer electrolyte.
[0004]
The polymer electrolyte fuel cell has advantages that other fuel cells do not have, such as no problem of electrolyte dissipation, can be started at room temperature, and can be reduced in size and weight (high power density). . However, the conventional polymer electrolyte fuel cell has a problem that sufficient durability for practical use has not been obtained.
[0005]
The reason why the durability of the polymer electrolyte fuel cell is low is that the electrolyte membrane is damaged by carbon fibers contained in the diffusion layer, locally existing protrusions, corners of the diffusion layer, etc., and the electrolyte membrane starts from there. It is considered that the deterioration of is promoted. Therefore, various proposals have conventionally been made to solve this problem.
[0006]
For example, in Patent Document 1, a water-repellent carbon layer is formed on the surface of a carbon cloth, the carbon cloth is subjected to hot pressing to flatten the surface, and a catalyst layer is formed on the surface of the water-repellent carbon layer. There is disclosed a method for manufacturing a polymer electrolyte fuel cell in which a fuel cell and an ion exchange membrane are joined.
[0007]
Patent Document 2 discloses that when carbon paper is used as a diffusion layer (catalyst support member), the solid polymer electrolyte membrane is prevented from being broken due to the edge portion of the diffusion layer biting into the solid polymer electrolyte membrane. In order to achieve this, it is described that the edge of carbon paper is chamfered.
[0008]
[Patent Document 1]
JP 2001-085019 A (paragraph number “0008”)
[Patent Document 2]
JP 2001-243963 A (paragraph number “0023”)
[0009]
[Problems to be solved by the invention]
In the case where carbon cloth is used as the diffusion layer, if the diffusion layer is hot-pressed before joining, the carbon fibers on the surface of the diffusion layer can be flattened. Therefore, damage to the electrolyte membrane due to the carbon fibers during bonding can be suppressed to some extent. However, when the MEA is incorporated in the cell, the MEA is pressed by the ribbed separator, so that a part of the flattened carbon fiber is fluffed again. As a result, the fluffed carbon fibers may damage the electrolyte membrane, and may not have sufficient durability for practical use.
[0010]
In addition, carbon paper has higher rigidity than carbon cloth. Therefore, when carbon paper is used as the diffusion layer, if the MEA is pressed by the ribbed separator, the carbon paper may be damaged. When the carbon paper is broken, fibers and fragments contained in the carbon paper may damage the electrolyte membrane, and may not have sufficient durability for practical use.
[0011]
The problem to be solved by the present invention is to suppress the damage to the electrolyte membrane due to the fluffing, breakage, and the like of the diffusion layer, and to improve the durability of the membrane electrode assembly.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a membrane electrode assembly in which a diffusion layer is joined to a solid polymer electrolyte membrane via a catalyst layer, wherein the catalyst layer has a catalyst and a second catalyst for transferring protons to the catalyst. The gist of the present invention is to provide a composite including a first phase made of a solid polymer electrolyte of No. 1 and a reinforcing material for suppressing damage of the solid polymer electrolyte membrane by the diffusion layer.
[0013]
When a reinforcing material is added to the catalyst layer, the mechanical strength of the catalyst layer is improved. Therefore, damage to the electrolyte membrane due to fluffing, breakage, and the like of the diffusion layer is suppressed, and the durability of the membrane electrode assembly is improved.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail. The membrane / electrode assembly according to the present invention includes a solid polymer electrolyte membrane and electrodes joined to both surfaces of the solid polymer electrolyte membrane.
[0015]
In the present invention, the material of the solid polymer electrolyte membrane is not particularly limited, and may be selected from solid polymer electrolytes having various compositions and various molecular structures (eg, linear, branched, etc.). Thus, the present invention can be applied.
[0016]
That is, the solid polymer electrolyte constituting the membrane includes (1) a perfluorinated electrolyte containing a C—F bond in the polymer chain and not containing a C—H bond, and (2) a C—F in the polymer chain. A partially fluorinated electrolyte containing both F bonds and C—H bonds, or (3) a hydrocarbon-based electrolyte containing no C—F bonds in the polymer chain and containing C—H bonds, Is also good.
[0017]
Also, the type of the electrolyte group contained in the solid polymer electrolyte is not particularly limited. Specific examples of the electrolyte group include a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, and a sulfonimide group. The solid polymer electrolyte may include only one of these electrolyte groups, or may include two or more of these electrolyte groups.
[0018]
As the solid polymer electrolyte constituting the membrane, specifically,
(1) Perfluorocarbon sulfonic acid (for example, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.)), etc.
(2) a polystyrene-graft-ethylenetetrafluoroethylene copolymer or a polystyrene-graft-polytetrafluoroethylene copolymer having an electrolyte group such as a sulfonic acid group introduced into any of the polymer chains;
(3) Polyether ether ketone, polyether ketone, polyphenylene, polyphenylene ether, polycarbonate, polyphenylene sulfide polyamide, polyacetal, polyethylene, polypropylene, acrylic resin having an electrolyte group such as a sulfonic acid group introduced into any of the polymer chains , Polyester, polysulfone, polyether, polystyrene, polyamideimide, polyimide, polyetherimide, polyethersulfone, or polycarbonate, or
(4) these derivatives,
Is a preferred example.
[0019]
Further, the solid polymer electrolyte membrane may be constituted by any one of the above-mentioned solid polymer electrolytes, or may be constituted by two or more kinds. Further, the solid polymer electrolyte membrane may be composed of only one or more of the solid polymer electrolytes described above, or may be composed of one or more solid polymer electrolytes and another material. May be a complex.
[0020]
Among these, a solid polymer electrolyte having a sulfonic acid group is suitable as an MEA electrolyte membrane because of its high electric conductivity. Further, partially fluorine-based electrolytes, especially perfluorinated electrolytes, are excellent in oxidation resistance, and thus are suitable as electrolyte membranes for MEAs used under severe conditions, such as polymer electrolyte fuel cells and water electrolysis devices. It is.
[0021]
The electrode has a two-layer structure of a catalyst layer and a diffusion layer, and the diffusion layer is joined to the solid polymer electrolyte membrane via the catalyst layer. The material of the diffusion layer is not particularly limited, and various materials such as carbon cloth and carbon paper can be used. The thickness, porosity, etc. of the diffusion layer are not particularly limited, and an optimum one is selected according to the use of the MEA, required characteristics, and the like.
[0022]
The catalyst layer comprises a first phase composed of a catalyst and a first solid polymer electrolyte for transferring protons to and from the catalyst (hereinafter, this is referred to as “electrolyte in the catalyst layer”), and a solid polymer electrolyte membrane formed by a diffusion layer. And a reinforcing material for suppressing damage to the material.
[0023]
In general, platinum black, platinum or a platinum alloy, or carbon carrying these or the like is used as the catalyst. The amount of the catalyst contained in the catalyst layer is not particularly limited, and an optimum amount is selected according to the type of the catalyst, the application and / or required characteristics of the MEA, the type of the electrode (anode or cathode), and the like.
[0024]
The electrolyte in the catalyst layer has an action of promoting the transfer of protons between the solid polymer electrolyte membrane and the catalyst, and is arranged so as to surround the periphery of the catalyst. As the electrolyte in the catalyst layer, the same material as that of the above-described solid polymer electrolyte membrane is usually used, but a different material may be used. The amount of the electrolyte in the catalyst layer contained in the catalyst layer is not particularly limited, and is optimal according to the type of the electrolyte in the catalyst layer, the application and / or required characteristics of the MEA, the type of the electrode (anode or cathode), and the like. The right amount.
[0025]
The reinforcing material is for improving the mechanical strength of the catalyst layer, and various materials and forms can be used. Specific examples of the reinforcing material include the following.
[0026]
A first specific example of the reinforcing member is made of a porous film. The porous film may be made of an insulating material, or may be made of a conductive material. When the porous membrane is made of an insulating material, the porous membrane is preferably disposed inside the catalyst layer (that is, the inside of the pores of the porous membrane is filled with the first phase composed of the catalyst and the electrolyte in the catalyst layer). . On the other hand, when the porous membrane is made of a conductive material, the porous membrane may be disposed inside the catalyst layer, or at the interface between the first phase formed in a layer on the surface of the solid polymer electrolyte membrane and the diffusion layer. It may be arranged.
[0027]
As the porous film made of an insulating material, specifically, a fluorinated polymer (specifically, polytetrafluoroethylene, polyhexafluoropropylene, ethylene tetrafluoroethylene copolymer, ethylene hexafluoropropylene copolymer, A suitable example is a porous film of tetrafluoroethylene hexafluoropropylene copolymer). Further, as a porous film made of a conductive material, specifically, a carbon porous film is mentioned as a preferred example.
[0028]
For the thickness, porosity, average pore diameter, etc. of the porous film, optimal values are selected according to the material of the porous film, the application of the MEA, the characteristics required for the MEA, and the like. In general, as the thickness of the porous membrane increases, the mechanical strength of the catalyst layer increases, so that the electrolyte layer can be prevented from being damaged by the diffusion layer, but the electric resistance of the catalyst layer tends to increase.
[0029]
In addition, as the porosity and / or the average pore diameter of the porous membrane increases, the amount of the catalyst and the electrolyte in the catalyst layer filled in the pores increases, so that the electric resistance of the catalyst layer tends to decrease. The mechanical strength of the layers tends to decrease.
[0030]
When a porous film made of an insulating material is used as a reinforcing material, the thickness of the porous film is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, in order to obtain MEA with excellent durability. . The porosity of the porous membrane is preferably 20% or more and 95% or less, and more preferably 50% or more and 90% or less. Further, the average pore diameter of the porous membrane is preferably 0.01 μm or more and 20 μm or less, and more preferably 0.1 μm or more and 10 μm or less.
[0031]
When a porous film made of a conductive material is used as the reinforcing material, the thickness of the porous film is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, in order to obtain MEA with excellent durability. It is. The porosity of the porous film is preferably 20% or more and 95% or less, and more preferably 30% or more and 90% or less. Further, the average pore diameter of the porous membrane is preferably 0.05 μm or more and 20 μm or less, and more preferably 0.1 μm or more and 10 μm or less.
[0032]
A second specific example of the reinforcing member is made of a fibrous material. The fibrous material may be made of an insulating material, or may be made of a conductive material. When the fibrous material is made of an insulating material, it is preferable that the fibrous material be disposed inside the catalyst layer (that is, dispersed in the first phase). On the other hand, when the fibrous material is made of a conductive material, the fibrous material may be disposed inside the catalyst layer, or the first layer formed on the surface of the solid polymer electrolyte membrane in a layered manner and the diffusion layer may be used. It may be arranged at the interface. Further, in order to ensure the supply of gas to the three-phase interface, it is preferable that the fibrous materials are arranged in parallel to the membrane surface of the solid polymer electrolyte membrane and in random directions.
[0033]
Specific examples of suitable fibrous materials include carbon fiber yarns, carbon fibers, and carbon cut fibers.
[0034]
The length and diameter of the fibrous material, the weight of the fiber per unit area (hereinafter referred to as “dispersion density”), etc., depend on the material of the fibrous material, the application of the MEA, the characteristics required for the MEA, and the like. To select the best value. Generally, the shorter the length of the fibrous material, the higher the dispersion density can be. However, it is difficult to arrange the fibrous material in parallel with the surface of the solid polymer electrolyte membrane.
[0035]
In addition, as the diameter of the fibrous material decreases, the flexibility of the fibrous material increases, so that damage to the solid polymer electrolyte membrane due to breakage of the fibrous material can be suppressed, but the mechanical strength of the catalyst layer tends to decrease. There is. Further, as the dispersion density increases, the mechanical strength of the catalyst layer increases, but the electrical resistance of the catalyst layer tends to increase.
[0036]
When a fibrous material made of an insulating material is used as the reinforcing material, the length of the fibrous material is preferably 0.1 mm or more and 100 mm or less, more preferably 1 mm or more, in order to obtain MEA with excellent durability. It is 50 mm or less. Further, the diameter of the fibrous material is preferably 0.5 μm or more and 100 μm or less, and more preferably 1 μm or more and 10 μm or less. Further, the dispersion density of the fibrous material is 0.01 g / cm. ² 0.5g / cm or more ² The following is preferred, and more preferably 0.01 g / cm ² More than 0.05g / cm ² It is as follows.
[0037]
When a fibrous material made of a conductive material is used as the reinforcing material, the length of the fibrous material is preferably 0.1 mm or more and 100 mm or less, more preferably 1 mm or more, in order to obtain MEA with excellent durability. It is 50 mm or less. Further, the diameter of the fibrous material is preferably 0.5 μm or more and 100 μm or less, more preferably 1 μm or more and 20 μm or less. Further, the dispersion density of the fibrous material is 0.01 g / cm. ² 0.5g / cm or more ² The following is preferred, and more preferably 0.01 g / cm ² 0.2g / cm or more ² It is as follows.
[0038]
A third specific example of the reinforcing material is made of fine particles. The fine particles may be made of an insulating material, or may be made of a conductive material. Further, the fine particles are preferably arranged inside the catalyst layer (that is, dispersed inside the first phase).
[0039]
As the fine particles, specifically, layered clay particles, metal particles (for example, platinum, palladium, gold, copper, etc.), ceramic particles (for example, Al ₂ O ₃ Particles, SiO ₂ Particles, TiO ₂ Particles. ) Is a preferred example.
[0040]
As the average particle diameter (average value of the maximum dimension), the amount of addition, the shape, and the like of the fine particles, optimal values are selected according to the material of the fine particles, the application of the MEA, the characteristics required for the MEA, and the like. In general, as the average particle size increases, damage to the solid polymer electrolyte membrane due to fuzzing, breakage, and the like of the diffusion layer can be suppressed, but the fine particles themselves may damage the solid polymer electrolyte membrane. Also, as the amount of added fine particles increases, the mechanical strength of the catalyst layer improves, but the electric resistance of the catalyst layer tends to increase. Further, as the number of the fine particles having a plate-like shape and the plate surface thereof is arranged in parallel with the film surface of the solid polymer electrolyte membrane increases, the damage of the solid polymer electrolyte membrane can be suppressed. .
[0041]
In the case where fine particles made of an insulating material are used as the reinforcing material, the average particle diameter of the fine particles is preferably 0.1 μm or more and 50 μm or less, more preferably 1 μm or more and 10 μm or less, in order to obtain MEA having excellent durability. is there. The amount of the fine particles added to the entire catalyst layer is preferably 2% by weight or more and 80% by weight or less, more preferably 5% by weight or more and 50% by weight or less.
[0042]
In the case where fine particles made of a conductive material are used as the reinforcing material, the average particle diameter of the fine particles is preferably 0.1 μm or more and 50 μm or less, more preferably 1 μm or more and 20 μm or less, in order to obtain MEA having excellent durability. is there. The addition amount of the fine particles to the entire catalyst layer is preferably 2% by weight or more and 90% by weight or less, more preferably 5% by weight or more and 80% by weight or less.
[0043]
A fourth specific example of the reinforcing material is made of a binder for binding between the catalysts. Generally, the catalyst is in a state of being bound by the electrolyte in the catalyst layer, but the binding force by the electrolyte in the catalyst layer is relatively weak. Therefore, the mechanical strength of the catalyst layer can be improved by newly adding a binder having a stronger binding force than the electrolyte in the catalyst layer to the catalyst layer.
[0044]
A specific example of a preferable binder is a polyimide adhesive.
[0045]
As the amount of the binder to be added, an optimal value is selected according to the material of the binder, the use of the MEA, the characteristics required for the MEA, and the like. In general, as the amount of the binder added increases, the mechanical strength of the catalyst layer increases, so that damage to the solid polymer electrolyte membrane due to fluffing, breakage, etc. of the diffusion layer can be suppressed. Tends to be large.
[0046]
In order to obtain an MEA with excellent durability, the amount of the binder added to the entire catalyst layer is preferably 0.5% by weight or more and 50% by weight or less, more preferably 1% by weight or more and 30% by weight or less. is there.
[0047]
A fifth specific example of the reinforcing member is formed of a sputtered film. For the sputtered film, a material having acid resistance and electrical conductivity is used. The sputtered film is formed at the interface between the first phase and the diffusion layer formed in a film on the surface of the solid polymer electrolyte membrane.
[0048]
Preferable examples of the sputtered film include a platinum sputtered film, a palladium film, and a gold film.
[0049]
The optimum thickness of the sputtered film is selected according to the material of the sputtered film, the application of the MEA, the characteristics required for the MEA, and the like. In general, as the thickness of the sputtered film increases, the mechanical strength of the catalyst layer improves, so that damage to the solid polymer electrolyte membrane due to fuzzing, breakage, etc. of the diffusion layer can be suppressed, but the electrical resistance of the catalyst layer increases. They tend to be large and costly.
[0050]
In order to obtain an MEA with excellent durability, the thickness of the sputtered film is preferably 0.01 μm or more and 30 μm or less, and more preferably 0.05 μm or more and 10 μm or less.
[0051]
A sixth specific example of the reinforcing material is a carbon layer made of a composite containing carbon and the second solid polymer electrolyte. The material of the second solid polymer electrolyte contained in the carbon layer may be the same as or different from the electrolyte in the catalyst layer (first solid polymer electrolyte) or the solid polymer electrolyte membrane. Further, the carbon layer is formed at the interface between the first phase formed in a film shape on the surface of the solid polymer electrolyte membrane and the diffusion layer.
[0052]
The thickness of the carbon layer, the ratio of carbon contained in the carbon layer and the second solid polymer electrolyte, and the like depend on the material of the second solid polymer electrolyte, the application of the MEA, the characteristics required for the MEA, and the like. Choose the best one. In general, as the thickness of the carbon layer increases, the mechanical strength of the catalyst layer improves, so that damage to the solid polymer electrolyte membrane due to fuzzing, breakage, etc. of the diffusion layer can be suppressed, but the electrical resistance of the catalyst layer increases. Tends to be larger.
[0053]
Further, as the amount of the second solid polymer electrolyte contained in the carbon layer increases, the carbon particles are bound by the second solid polymer electrolyte, so that the mechanical strength of the catalyst layer is improved. Has a tendency to increase.
[0054]
In order to obtain an MEA with excellent durability, the thickness of the carbon layer is preferably 1 μm or more and 500 μm or less, and more preferably 1 μm or more and 100 μm or less. The amount of the second solid polymer electrolyte contained in the carbon layer is preferably from 10% by weight to 250% by weight, and more preferably from 20% by weight to 150% by weight.
[0055]
Further, the carbon layer may be a composite composed of only carbon and the second solid polymer electrolyte, or a binder such as the above-described porous membrane, fibrous material, fine particles and / or a polyimide adhesive ( Hereinafter, these may be referred to as “porous membranes or the like”. When the carbon layer further contains a porous film or the like, the point that the physical properties of the porous film or the like, the amount added, etc. can be selected according to the material, the application of the MEA, the characteristics required for the MEA, and the like. This is the same as the case where the first phase is combined with the porous membrane and the like.
[0056]
The various reinforcing materials described above may be used alone or in combination of two or more. Further, the reinforcing material may be included in the catalyst layer of one electrode, or may be included in the catalyst layers of both electrodes.
[0057]
Next, a method for producing a membrane / electrode assembly according to the present invention will be described. The membrane / electrode assembly according to the present invention can be manufactured by the following method.
[0058]
For example, when the reinforcing material is made of a porous film, the porous film is placed on a substrate, and a solution containing a catalyst and an electrolyte in a catalyst layer (hereinafter, referred to as “catalyst ink”) is applied to the surface of the porous film. Form a catalyst layer. Next, the catalyst layer is transferred to the surface of the solid polymer electrolyte membrane by hot pressing, and a diffusion layer is further bonded thereon by hot pressing to obtain a membrane electrode assembly according to the present invention.
[0059]
In this case, the catalyst layer in which the catalyst and the electrolyte in the catalyst layer are uniformly filled in the pores of the porous film by optimizing the material of the porous film, the porosity and the average pore diameter, the composition of the catalyst ink, the application conditions, and the like. Alternatively, any of the catalyst layers in which the first phase composed of the catalyst and the electrolyte in the catalyst layer is formed in a layer on the surface of the porous membrane can be produced.
[0060]
Further, for example, when the reinforcing material is a fibrous material, first, the fibrous material is dispersed in an appropriate solvent, and this is applied onto a substrate. After evaporating the solvent, a catalyst ink is applied to the surface of the fibrous material applied on the substrate to form a catalyst layer. Next, the catalyst layer is transferred to the surface of the solid polymer electrolyte membrane by hot pressing, and a diffusion layer is further bonded thereon by hot pressing to obtain a membrane electrode assembly according to the present invention.
[0061]
In this case, the fibrous material was uniformly dispersed in the first phase by optimizing the material, length and diameter of the fibrous material, the dispersion density of the fibrous material, the composition of the catalyst ink, and the application conditions. The catalyst layer or the catalyst layer in which the first phase composed of the catalyst and the electrolyte in the catalyst layer is formed in a layer on the surface of the uniformly dispersed fibrous material can be produced.
[0062]
Further, for example, when the reinforcing material is fine particles or a binder, first, fine particles or a binder are dispersed in catalyst ink, and this is applied on a substrate to form a catalyst layer. Next, the catalyst layer is transferred to the surface of the solid polymer electrolyte membrane by hot pressing, and a diffusion layer is further bonded thereon by hot pressing to obtain a membrane electrode assembly according to the present invention. When the fine particles have a flat shape, the flat fine particles can be easily oriented parallel to the substrate surface by applying a catalyst ink having the fine particles dispersed on the substrate.
[0063]
Further, for example, when the reinforcing material is a sputtered film, first, a catalyst ink is applied on a substrate to form a layered first phase. Next, the first phase is transferred to the surface of the solid polymer electrolyte membrane by hot pressing. Next, a sputtered film is formed on the surface of the first phase according to a conventional method, and a diffusion layer is further bonded thereon by hot pressing to obtain a membrane electrode assembly according to the present invention.
[0064]
Further, for example, when the reinforcing material is a carbon layer, first, a catalyst ink and a solution containing carbon and a second solid polymer electrolyte (hereinafter, referred to as “carbon ink”) are respectively applied to the substrate. To form a layered first phase and a carbon layer. Next, the first phase and the carbon layer are transferred to the surface of the solid polymer electrolyte membrane by hot pressing in this order, and the diffusion layer is further bonded thereon by hot pressing, whereby the membrane electrode assembly according to the present invention is obtained. can get. The carbon layer further including a porous film or the like can be manufactured by the same method as the first phase including the porous film or the like.
[0065]
Next, the operation of the membrane / electrode assembly according to the present invention will be described. FIG. 1 shows a schematic cross-sectional view of the membrane electrode assembly. In FIG. 1A, a membrane electrode assembly 10 includes a solid polymer electrolyte membrane 12 and electrodes 14 and 16 bonded to both surfaces thereof. The electrodes 14 and 16 are respectively composed of catalyst layers 14 a and 16 a formed on the surface of the solid polymer electrolyte membrane 12 and a diffusion layer 14 b formed outside thereof (a diffusion layer on the electrode 16 side is not shown). It has).
[0066]
Normally, carbon cloth is used for the diffusion layer 14b. The carbon cloth is made of carbon fiber fabric having a diameter of about 5 to 10 μm, and its surface is often fluffy. Therefore, when such a carbon cloth is directly bonded to the solid polymer electrolyte membrane 12, the solid polymer electrolyte membrane 12 may be damaged by the fluffed carbon fibers.
[0067]
On the other hand, as described in Patent Document 1 described above, when the surface of the carbon cloth before bonding is subjected to a flattening process, damage to the solid polymer electrolyte membrane 12 due to fuzzing of carbon fibers during bonding is suppressed to some extent. Can be.
[0068]
However, the membrane electrode assembly 10 is usually used while being sandwiched by ribbed separators. Therefore, even when a carbon cloth subjected to a flattening process is used as the diffusion layer 14b, when the membrane electrode assembly 10 is pressed by the ribs 18 of the separator as shown in FIG. The carbon fibers 14c in the diffusion layer 14b may be fluffed again, and the fluffed carbon fibers 14c may pierce the solid polymer electrolyte membrane 12.
[0069]
If a hole is formed in the solid polymer electrolyte membrane 12 due to the penetration of the carbon fiber 14c, the reaction gas cross-leak through the hole, which causes a problem of fuel loss. Further, when a cross leak of the reaction gas occurs, there is a problem that the fuel gas burns on the surface of the polymer electrolyte membrane 12, and the heat of combustion burns the polymer electrolyte membrane 12.
[0070]
Further, such damage of the solid polymer electrolyte membrane 12 by the diffusion layer 14b may occur even when carbon paper is used as the diffusion layer 14b. In particular, since carbon paper has higher rigidity than carbon cloth, if it is broken by being pressed by the ribs 18 of the separator, the solid polymer electrolyte membrane 12 may be damaged more by broken pieces or fibers contained in the carbon paper. There is.
[0071]
On the other hand, when a reinforcing material is added to the catalyst layer 14a and / or the catalyst layer 16a, the mechanical strength of the catalyst layers 14a and 16a is improved. Therefore, it is possible to suppress such fluffing of the carbon fibers 14c, damage to the solid polymer electrolyte membrane 12 due to breakage of the diffusion layer 14b, and fuel loss and deterioration of the solid polymer electrolyte membrane 12 caused thereby. .
[0072]
【Example】
(Example 1)
(1) Preparation of catalyst ink.
10 g of platinum-supported carbon (platinum-supported density 30%, carbon: Vulcan XC72R) was dispersed in 50 g of water. 100 g of a 10% Nafion solution was added to this dispersion to prepare a catalyst ink.
[0073]
(2) Preparation of catalyst layer.
A porous PTFE membrane (MICRO-TEX NF1026, manufactured by Nitto Denko Corporation) is placed on a polytetrafluoroethylene (hereinafter referred to as “PTFE”) sheet, and the catalyst ink is applied thereon using a doctor blade. Worked. After air drying, vacuum drying was performed at 60 ° C. to form a catalyst layer. The amount of platinum carried on the obtained catalyst layer was 0.17 mg / cm. ² Met. The thickness of the catalyst layer was 26 μm.
[0074]
(3) Preparation of MEA for cell resistance measurement.
The prepared catalyst layer (4 cm × 4 cm) was hot pressed (120 ° C., 50 kg / cm). ² (4.9 MPa) for 20 minutes) to join both surfaces of the Nafion (registered trademark) 111 film. After peeling off the PTFE sheet, the diffusion layer (E-TEK carbon cloth, 4 cm × 4 cm) was hot pressed (120 ° C., 50 kg / cm) from above both catalyst layers. ² (4.9 MPa) for 20 minutes.
[0075]
(Example 2)
A polyimide porous film (manufactured by Ube Industries, Ltd., film thickness 18 μm) was treated at 2000 ° C. in a nitrogen atmosphere to obtain a carbon porous film. Next, the process of immersing the carbon porous film in the catalyst ink prepared in Example 1 for 5 minutes and air-drying was repeated a total of 10 times. After the last immersion and air drying were completed, vacuum drying was performed at 60 ° C. to form a catalyst layer. The amount of platinum carried on the obtained catalyst layer was 0.07 g / cm. ² Met. The thickness of the catalyst layer was 20 μm.
[0076]
Next, using the obtained catalyst layer, an MEA for cell resistance measurement was produced. The manufacturing conditions of the cell resistance measurement MEA were the same as those in Example 1 except that the hot pressing temperature of the diffusion layer was set at 140 ° C.
[0077]
(Example 3)
Using an ultrasonic washer, 10 g of carbon fibers (trade cut fiber T010-24, manufactured by Toray Industries, Inc.) cut to a fiber length of 24 mm and having a diameter of 24 mm were dispersed in 1000 g of water / ethanol (50 vol./50 vol.). . 3 × 10 3 ^-2 g / cm ² Was applied to a PTFE sheet at a dispersion density of, and air-dried. The catalyst ink prepared in Example 1 was placed on the PTFE sheet on which the carbon fibers were spread, and was applied using a doctor blade. After air drying, vacuum drying was performed at 60 ° C. to form a catalyst layer. The amount of platinum carried on the obtained catalyst layer was 0.14 mg / cm. ² Met. The thickness of the catalyst layer was 18 μm.
[0078]
Next, using the obtained catalyst layer, an MEA for cell resistance measurement was manufactured in the same procedure as in Example 1.
[0079]
(Example 4)
(1) Preparation of the first phase.
The catalyst ink prepared in Example 1 was applied on a PTFE sheet using a doctor blade. After air drying, vacuum drying was performed at 60 ° C. to produce a layered first phase. The platinum loading of the obtained first phase was 0.14 mg / cm ² Met. The thickness of the first phase was 16 μm.
[0080]
(2) Preparation of carbon layer.
A carbon ink containing a carbon and a Nafion solution was applied on a PTFE sheet using a doctor blade. After air drying, drying was performed at 60 ° C. to form a carbon layer. The thickness of the carbon layer was 18 μm.
[0081]
(3) Preparation of MEA for cell resistance measurement.
The produced first phase (4 cm × 4 cm) is hot pressed (120 ° C., 50 kg / cm). ² (4.9 MPa) for 20 minutes) to join both surfaces of the Nafion (registered trademark) 111 film. After peeling off the PTFE sheet, the carbon layer was hot-pressed (120 ° C., 50 kg / cm ² (4.9 MPa) for 10 minutes. After removing the PTFE sheet, the diffusion layer (E-TEK carbon cloth, 4 cm × 4 cm) was further hot-pressed (120 ° C., 50 kg / cm) from above both carbon layers. ² (4.9 MPa) for 20 minutes. The thickness of the catalyst layer was 32 μm.
[0082]
(Comparative Example 1)
The catalyst ink prepared in Example 1 was applied on a PTFE sheet using a doctor blade. After air drying, vacuum drying was performed at 60 ° C. to form a catalyst layer. The amount of supported platinum is 0.14 mg / cm ² Met. The thickness of the catalyst layer was 18 μm. Next, using the obtained catalyst layer, an MEA for cell resistance measurement was manufactured in the same procedure as in Example 1.
[0083]
The cell resistance was evaluated using the MEA for cell resistance measurement obtained in Examples 1 to 4 and Comparative Example 1. That is, the MEA for cell resistance measurement was incorporated into a fuel cell evaluation cell, and the cell resistance was measured at room temperature while flowing dry nitrogen gas. Note that the cell resistance is an index of micro short (electron short) due to penetration of carbon fibers, and the smaller the cell resistance, the larger the amount of micro short. Table 1 shows the cell resistance.
[0084]
[Table 1]

[0085]
In the case of the MEA obtained in Comparative Example 1, the cell resistance in a dry state was 0.15 × 10 ³ Ω ・ m ² Met. On the other hand, in the case of the MEAs obtained in Examples 1 to 4, the cell resistance in the dry state was 2.0 to 1.1 × 10 ³ Ω ・ m ² Which was 7.3 to 13.3 times that of Comparative Example 1. Table 1 shows that the addition of the reinforcing material in the catalyst layer suppresses the damage of the solid polymer electrolyte membrane.
[0086]
As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.
[0087]
For example, in the above embodiment, an example in which the membrane electrode assembly according to the present invention is applied to a polymer electrolyte fuel cell has been described, but the application of the present invention is not limited to this. It can also be used as a membrane electrode assembly used for various electrochemical devices other than fuel cells.
[0088]
Further, the catalyst layer provided with a reinforcing material constituting the membrane electrode assembly according to the present invention is particularly suitable when a diffusion layer is bonded to the outside thereof and used, but the use of the catalyst layer provided with a reinforcing material is preferred. However, the present invention is not limited to this, and can be applied to a membrane / electrode assembly in which only a catalyst layer is joined to a solid polymer electrolyte membrane.
[0089]
【The invention's effect】
The membrane-electrode assembly according to the present invention has an effect of suppressing damage to the solid polymer electrolyte membrane due to fluffing, breakage, and the like of the diffusion layer since the catalyst layer contains a reinforcing material.
[Brief description of the drawings]
1A is a schematic cross-sectional view of a membrane electrode assembly before being pressed by ribs of a separator, and FIG. 2B is a cross-sectional view of the membrane electrode assembly after being pressed by ribs of a separator. It is a cross-sectional schematic diagram of a body.
[Explanation of symbols]
10 Membrane electrode assembly
12. Solid polymer electrolyte membrane
14, 16 electrodes
14a, 16a catalyst layer
14b Diffusion layer

Claims (3)

In a membrane electrode assembly in which a diffusion layer is joined to a solid polymer electrolyte membrane via a catalyst layer,
The catalyst layer includes a first phase including a catalyst and a first solid polymer electrolyte for transferring protons to and from the catalyst;
A membrane / electrode assembly comprising a composite including a reinforcing material for suppressing damage of the solid polymer electrolyte membrane by the diffusion layer. The reinforcing material is
A porous membrane disposed inside the first phase or at an interface between the first phase and the diffusion layer;
A fibrous material disposed inside the first phase or at an interface between the first phase and the diffusion layer;
Fine particles dispersed inside the first phase,
A binder for binding the catalysts,
A sputtered film formed at an interface between the first phase and the diffusion layer; and a carbon formed at an interface between the first phase and the diffusion layer and made of a composite containing carbon and a second solid polymer electrolyte. The membrane electrode assembly according to claim 1, which is at least one of the layers. The membrane / electrode assembly according to claim 2, wherein the reinforcing material is a porous membrane made of polytetrafluoroethylene disposed inside the first phase.

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