Laminated electrolyte membrane, membrane electrode assembly and polymer electrolyte fuel cell

Abstract

To provide a laminate electrolyte membrane having high chemical durability coming from a gas barrier property.SOLUTION: A laminate electrolyte membrane has a sandwich structure including at least three layers of electrolyte membranes. The laminate electrolyte membrane comprises: a first proton-conducting electrolyte membrane disposed on one face; a second proton-conducting electrolyte membrane disposed on the other face; and an intermediate electrolyte membrane disposed between the first and second proton-conducting electrolyte membranes. In the laminate electrolyte membrane, the intermediate electrolyte membrane contains a mixture of a gas barrier polymer and a proton-conducting polymer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrolyte membrane suitable for a polymer electrolyte fuel cell, a membrane electrode assembly using the same, and a polymer electrolyte fuel cell. [Background technology]

[0002] Fuel cell vehicles (FCVs) powered by polymer electrolyte fuel cells (PEFCs) are already commercially available, and their use is expected to expand and become more widespread in trucks, buses, ships, etc. As shown in Figure 1, PEFCs generally use a cell as their basic unit, which has a structure in which a membrane electrode assembly (MEA), in which a pair of electrodes (anode and cathode) are arranged on both sides of a solid polymer electrolyte membrane, is sandwiched between separators with gas flow paths.

[0003] Nafion (registered trademark), a fluorine-based polymer electrolyte, is widely used for the solid polymer electrolyte membrane, but there is room for improvement in durability. As an electrolyte membrane with improved durability, a laminated electrolyte membrane formed by stacking multiple solid polymer electrolyte membranes has been reported. For example, Patent Document 1 reports a laminated electrolyte membrane having a pair of second electrolyte membranes sandwiching a first electrolyte membrane containing a proton-conducting polymer and a synthetic resin from both sides. This laminated electrolyte membrane is said to be able to maintain mechanical strength and have excellent proton conductivity by blending a condensation resin such as polyvinyl acetal resin, polyimide, phenol formaldehyde resin, melamine formaldehyde resin, urea resin, or polyamide into the first electrolyte membrane. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-21549 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the condensation resin blended into the laminated electrolyte membrane of Patent Document 1 contributes to improving the mechanical strength of the first electrolyte membrane (intermediate layer), but does not contribute to improving chemical durability through gas barrier properties. Furthermore, to maintain mechanical strength, the thickness of the first electrolyte membrane, which is the intermediate layer, had to be designed to be larger than the thickness of the outer second electrolyte membrane. Furthermore, there was also the issue of complicated manufacturing processes, such as the need to condense the precursor of the synthetic resin blended into the first electrolyte membrane.

[0006] As described above, the conventional laminated electrolyte membranes have room for improvement in terms of durability. Under these circumstances, an object of the present invention is to provide a laminated electrolyte membrane having high chemical durability due to its gas barrier properties, and a membrane electrode assembly and a polymer electrolyte fuel cell including the same. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the following invention meets the above object, thereby completing the present invention.

[0008] That is, the present invention relates to the following inventions. <1> A laminated electrolyte membrane having a sandwich structure consisting of at least three layers of electrolyte membrane, a first proton-conductive electrolyte membrane disposed on one side, a second proton-conductive electrolyte membrane disposed on the other side, and an intermediate electrolyte membrane disposed between the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane; The intermediate electrolyte membrane is a laminated electrolyte membrane made of a mixture of a gas barrier polymer and a proton conductive polymer. <2> The thickness of the intermediate electrolyte membrane is smaller than the thicknesses of the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane. <1> The laminated electrolyte membrane according to claim 1. <3> The first proton-conducting electrolyte membrane and the second proton-conducting electrolyte membrane are closely attached to each other so as to enclose the intermediate electrolyte membrane. <1> Also <2> The laminated electrolyte membrane according to claim 1. <4> The gas barrier polymer constituting the intermediate electrolyte membrane is polyvinyl alcohol (PVA). <1> from <3> 10. The laminated electrolyte membrane according to claim 9, wherein <5> The proton-conducting polymer constituting the intermediate electrolyte membrane is a proton-conducting polymer having a sulfonic acid group. <1> from <4> 10. The laminated electrolyte membrane according to claim 9, wherein <6> The ratio of the gas barrier polymer and the proton conductive polymer constituting the intermediate electrolyte membrane is 0.5 to 500 parts by mole of the gas barrier polymer per 1 part by mole of the proton conductive polymer. <1> from <5> 10. The laminated electrolyte membrane according to claim 9, wherein <7> The first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane are made of a fluorine-based proton-conductive polymer. <1> from <6> 10. The laminated electrolyte membrane according to claim 9, wherein <8> A membrane electrode assembly having a solid polymer electrolyte membrane, a cathode bonded to one side of the solid polymer electrolyte membrane, and an anode bonded to the other side of the solid polymer electrolyte membrane, wherein the solid polymer electrolyte membrane is <1> from <7> A membrane electrode assembly comprising the laminated electrolyte membrane according to any one of the preceding items. <9> <8> A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 1.

[0009] <1A> <1> from <9> A method for producing a laminated electrolyte membrane according to any one of the above, a step of placing a mask corresponding to the shape and thickness of the intermediate electrolyte membrane on the first proton-conducting electrolyte membrane; applying or spraying an aqueous solution containing the gas barrier polymer and the proton conducting polymer onto the mask and then drying the aqueous solution to form an intermediate electrolyte membrane made of a mixture of the gas barrier polymer and the proton conducting polymer on the first proton conducting electrolyte membrane; a step of removing the mask, and then disposing a second proton-conductive electrolyte membrane on top of the intermediate electrolyte membrane, and sandwiching the intermediate electrolyte membrane between the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane; A manufacturing method comprising the steps of: <2A> The manufacturing method according to <1A>, wherein in the step of sandwiching the intermediate electrolyte membrane between the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane, the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane are brought into close contact with each other so as to encase the intermediate electrolyte membrane.

[0010] According to the present invention, there are provided a laminated electrolyte membrane having high chemical durability due to its gas barrier properties, and a membrane electrode assembly and a polymer electrolyte fuel cell including the same. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a conceptual diagram showing a typical configuration of a polymer electrolyte fuel cell. [Figure 2] 1 is a cross-sectional view showing a laminated electrolyte membrane (first embodiment) of the present invention. [Figure 3] 1 is an explanatory diagram showing the relationship between chemical degradation due to gas permeation through an electrolyte membrane during PEFC operation and gas barrier properties, where (a) is a conventional electrolyte membrane (single layer membrane) and (b) is the laminated electrolyte membrane of the present invention. [Figure 4] 1A and 1B are explanatory views of a laminated electrolyte membrane (second embodiment) of the present invention, where (a) is a schematic cross-sectional view and (b) is a perspective view showing the configuration of the electrolyte membrane in the laminated electrolyte membrane. [Figure 5] 1 is a cross-sectional view of a membrane electrode assembly according to the present invention; [Figure 6] 1 is a conceptual diagram showing the configuration of a polymer electrolyte fuel cell of the present invention. [Figure 7]1A and 1B are diagrams showing the manufacturing process of the laminated electrolyte membrane of Example 1, in which (a) is an explanatory diagram of the process of forming an intermediate electrolyte membrane (PVA-PVS mixture) on a first proton-conductive electrolyte membrane (Nafion membrane), (b) is an explanatory diagram of the process of sandwiching and pressing the formed intermediate electrolyte membrane between the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane (Nafion membrane), and (c) is a cross-sectional schematic diagram of the manufactured laminated electrolyte membrane of Example 1. [Figure 8] 1 is a cross-sectional SEM image of the laminated electrolyte membrane of Example 1. [Figure 9] 1 shows the results of a chemical durability test (OCV retention test) using PEFC on the laminated electrolyte membrane of Example 1 and the electrolyte membrane (Nafion212) of Comparative Example 1. [Figure 10] 1 shows the results of electrochemical evaluation of hydrogen permeation through the laminated electrolyte membrane of Example 1 and the electrolyte membrane (Nafion212) of Comparative Example 1, which serves as an index of membrane degradation. [Figure 11] 1 shows the results of evaluating the oxygen permeability of laminated electrolyte membranes having intermediate electrolyte membranes with different ratios (molar ratios) of PVA and PVS. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples below and can be practiced with any modifications within the scope of the gist of the present invention. In this specification, the symbol "to" is used as an expression including the numerical values or physical quantities before and after it.

[0013] <1. Laminated electrolyte membrane> The present invention relates to a laminated electrolyte membrane having a sandwich structure made of at least three electrolyte membrane layers, the laminated electrolyte membrane having a first proton-conductive electrolyte membrane disposed on one side, a second proton-conductive electrolyte membrane disposed on the other side, and an intermediate electrolyte membrane disposed between the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane, wherein the intermediate electrolyte membrane is made of a mixture of a gas-barrier polymer and a proton-conductive polymer (hereinafter referred to as the "laminated electrolyte membrane of the present invention").

[0014] The first proton-conductive electrolyte membrane, the second proton-conductive electrolyte membrane, and the intermediate electrolyte membrane (gas barrier polymer and proton-conductive polymer) will be described in detail below. In the following, when there is no need to distinguish between the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane, they may be referred to as "proton-conductive electrolyte membrane (outer layer)."

[0015] A conceptual schematic diagram of the laminated electrolyte membrane 1 (first embodiment) of the present invention is shown in Fig. 2. In Fig. 2, in order to facilitate understanding of the structure of the laminated electrolyte membrane of the present invention, the thickness and size of the first proton-conductive electrolyte membrane 2a and the second proton-conductive electrolyte membrane 2b relative to the intermediate electrolyte membrane 3 are shown larger than they actually are.

[0016] 2 is composed of a first proton-conductive electrolyte membrane 2a, a second proton-conductive electrolyte membrane 2b, and an intermediate electrolyte membrane 3, but the laminated electrolyte membrane of the present invention is sufficient as long as it contains at least these three electrolyte membrane layers, and may also contain other electrolyte membranes (for example, electrolyte membranes with higher mechanical strength) within the scope that does not impair the object of the present invention. However, as the number of layers increases, the membrane resistance of the laminated electrolyte membrane increases, and there is a risk of the proton conductivity of the membrane as a whole decreasing. Therefore, it is preferable that the laminated electrolyte membrane of the present invention is composed only of a first proton-conductive electrolyte membrane, a second proton-conductive electrolyte membrane, and an intermediate electrolyte membrane.

[0017] The relationship between chemical degradation due to gas permeation through the electrolyte membrane during PEFC operation and gas barrier properties will be explained with reference to FIG. In a PEFC using a conventional electrolyte membrane made of a fluorinated proton-conducting polymer (typically a Nafion monolayer membrane) as shown in Figure 3(a), radicals are generated through the following mechanism, causing chemical degradation of the electrolyte membrane. (i) Oxygen permeates the membrane and reacts with hydrogen at the anode to form hydrogen peroxide, which then becomes a radical. (ii) Incomplete oxygen reduction reaction at the cathode results in the formation of hydrogen peroxide and its radicals.

[0018] Thus, the main cause of chemical deterioration of electrolyte membranes is radicals, and the mechanism by which radicals are generated involves oxygen permeation through the membrane. If radicals are generated and attack the electrolyte membrane as in this mechanism, then chemical deterioration should be suppressed if oxygen permeation through the membrane can be reduced as close to zero as possible.

[0019] In contrast, in a PEFC using the laminated electrolyte membrane of the present invention shown in Figure 3(b), the gas barrier intermediate electrolyte membrane substantially blocks the permeation of oxygen and hydrogen, thereby suppressing the radical production reaction (i) above. Therefore, the use of the laminated electrolyte membrane of the present invention can provide a PEFC with excellent long-term durability.

[0020] Conventional electrolyte membranes (single layer membranes) use fluorine-based electrolyte materials or aromatic hydrocarbon electrolyte materials that are resistant to attack by radicals. In contrast, the laminated electrolyte membrane of the present invention differs from conventional electrolyte membranes (single layer membranes) in that it has a technical concept of "reducing radical generation and creating an environment that is not susceptible to radical attack" by having an intermediate electrolyte membrane with excellent gas barrier properties in the middle.

[0021] In the laminated electrolyte membrane 1, the intermediate electrolyte membrane 3 has a thickness smaller than that of the first proton-conducting electrolyte membrane 2a and the second proton-conducting electrolyte membrane 2b. The intermediate electrolyte membrane 3 contains a gas barrier polymer that does not have proton conductivity, and therefore has lower proton conductivity than the first proton-conducting electrolyte membrane 2a and the second proton-conducting electrolyte membrane 2b. For this reason, the intermediate electrolyte membrane 3 is made thin (thickness is small) to reduce the resistance due to the intermediate electrolyte membrane 3 and maintain the proton conductivity of the laminated electrolyte membrane 1 as a whole.

[0022] 4 shows a conceptual schematic diagram of a laminated electrolyte membrane 1A (second embodiment) of the present invention. Fig. 4(a) is a cross-sectional schematic diagram, and Fig. 4(b) is a perspective view showing the configuration of the electrolyte membrane in the laminated electrolyte membrane. In Fig. 4, the thickness and size of other components relative to the intermediate electrolyte membrane 3 are shown larger than they actually are in order to facilitate understanding of the structure of the laminated electrolyte membrane of the present invention.

[0023] In the laminated electrolyte membrane 1 of the present invention described above, the intermediate electrolyte membrane 3 and the first proton-conductive electrolyte membrane 2a and the second proton-conductive electrolyte membrane 2b sandwiching it are the same size (in plan view), so the outer edge of the intermediate electrolyte membrane 3 is in contact with the external environment, which may cause the gas barrier polymer or the proton-conductive polymer to elute from the outer edge (especially when the polymer is water-soluble). In contrast, in the laminated electrolyte membrane 1A of the present invention, the first proton-conductive electrolyte membrane 2a and the second proton-conductive electrolyte membrane 2b are tightly attached to encase the intermediate electrolyte membrane 3, and therefore the outer edge of the intermediate electrolyte membrane 3 is not in contact with the external environment. Therefore, the gas barrier polymer and proton-conductive polymer constituting the intermediate electrolyte membrane 3 do not elute from the outer edge, and the membrane can be used stably for a long period of time.

[0024] Furthermore, similar to the laminated electrolyte membrane 1, in the laminated electrolyte membrane 1A, the intermediate electrolyte membrane 3 is smaller in thickness than the first proton-conducting electrolyte membrane 2a and the second proton-conducting electrolyte membrane 2b. The intermediate electrolyte membrane 3 contains a gas barrier polymer that does not have proton conductivity, and therefore has lower proton conductivity than the first proton-conducting electrolyte membrane 2a and the second proton-conducting electrolyte membrane 2b. Therefore, the intermediate electrolyte membrane 3 is made thin (thickness is small) to reduce the resistance due to the intermediate electrolyte membrane 3 and maintain the proton conductivity of the laminated electrolyte membrane 1A as a whole.

[0025] The laminated electrolyte membrane of the present invention will be described in more detail below.

[0026] (Intermediate electrolyte membrane) In the laminated electrolyte membrane of the present invention, the intermediate electrolyte membrane is disposed between the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane, and is made of a mixture of a gas-barrier polymer and a proton-conductive polymer.

[0027] In the present invention, the "gas barrier polymer" is a polymer material that has lower oxygen permeability and hydrogen permeability than Nafion 212 (oxygen permeability (80°C): 10 Barrer) (hydrogen permeability (80°C): 70 Barrer), which is widely used in electrolyte membranes. Note that 1 Barrer = 1 x 10 ‐10 cm 3 cm / (cm 2 ·s·cmHg).

[0028] The gas barrier polymer used in the intermediate electrolyte membrane according to the present invention must have an oxygen permeability at 80° C. of 0.5 Barrer or less, and preferably 0.1 Barrer or less.

[0029] The gas barrier polymer used in the intermediate electrolyte membrane according to the present invention preferably has a hydrogen permeability at 80° C. of 7 Barrers or less, more preferably 3.5 Barrers or less.

[0030] The laminated electrolyte membrane of the present invention is characterized in that the intermediate electrolyte membrane is made of a mixture of a gas barrier polymer and a proton conductive polymer. By using a gas barrier polymer mixed with a proton-conducting polymer without condensing it, the intermediate electrolyte membrane has excellent gas barrier properties (oxygen barrier properties and hydrogen barrier properties) even when it is thin (for example, 10 μm or less). Furthermore, although the gas barrier polymer itself does not have proton conductivity, by mixing it with a proton-conducting polymer, the mixture as a whole has proton conductivity.

[0031] Furthermore, in the laminated electrolyte membrane of the present invention, the gas barrier polymer of the intermediate electrolyte membrane does not need to be condensed or crosslinked, and therefore has the advantage that it can be produced by a simple method in which an aqueous solution containing a gas barrier polymer and a proton-conducting polymer is applied or sprayed onto a first proton-conducting electrolyte membrane and then dried to form an intermediate electrolyte membrane consisting of a mixture of the gas barrier polymer and the proton-conducting polymer on the first proton-conducting electrolyte membrane, and then a second proton-conducting electrolyte membrane is placed on top of the intermediate electrolyte membrane so as to sandwich them. This production method allows the intermediate electrolyte membrane to be made thin, so that even if a non-proton-conducting gas barrier polymer is used, it is possible to avoid impairing the proton conductivity of the entire laminated electrolyte membrane.

[0032] The gas barrier polymer is not particularly limited as long as it does not impair the object of the present invention, and examples thereof include polyvinyl alcohol (PVA), polyglycolic acid (PGA), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), ethylene-vinyl alcohol copolymer (EVOH), etc. These may be used alone or in combination of two or more.

[0033] These gas barrier polymers can be crosslinked, but since this may impair the gas barrier properties of the intermediate electrolyte membrane, it is preferable to use them without crosslinking.

[0034] The gas barrier polymer is preferably a water-soluble or water-dispersible polymer, since water can be used as the solvent. Here, the term "water-soluble or water-dispersible polymer" refers to a polymer that can be completely dissolved or finely dispersed in water at room temperature.

[0035] Among these, polyvinyl alcohol (PVA) is a suitable example. PVA has excellent gas barrier properties (particularly oxygen barrier properties), and by suppressing oxygen permeation, it is possible to suppress radical generation and make chemical degradation less likely to occur in the first place. On the other hand, PVA itself does not have proton conductivity and cannot form an electrolyte membrane by itself. However, as described above, in the laminated electrolyte membrane of the present invention, the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane sandwich the intermediate electrolyte membrane, thereby making it possible to make the intermediate electrolyte membrane thin (for example, 10 μm or less). Therefore, even if a non-proton-conductive gas barrier polymer such as PVA is used, it is possible to avoid impairing the proton conductivity of the entire laminated electrolyte membrane.

[0036] In the conventional examples in which PVA is used as an electrolyte material, the PVA is required to play a role as a chemical cross-linking material, and there have been no examples in which PVA has been used as an intermediate electrolyte membrane having chemical durability derived from high gas barrier properties, as in the laminated electrolyte membrane of the present invention.

[0037] As the proton-conducting polymer, known fluorine-based electrolyte materials and hydrocarbon-based electrolyte materials used as electrolyte materials for PEFCs can be used as long as they do not impair the effects of the present invention.

[0038] As a fluorine-based electrolyte material, a perfluorosulfonic acid-based resin having the following structure can be used. By introducing fluorine atoms with high electronegativity, the material becomes chemically very stable, has a high degree of dissociation of the sulfo group, and achieves high proton conductivity.

[0039] [ka]

[0040] Suitable examples of commercially available products include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and Aquivion (registered trademark, manufactured by Solvay).

[0041] Examples of hydrocarbon-based polymer electrolyte materials include polymers such as polysulfonic acid, polyvinyl sulfonic acid, polystyrene sulfonic acid, polyaryl ether ketone sulfonic acid, polyphenyl sulfonic acid, polybenzimidazole sulfonic acid, polybenzimidazole phosphonic acid, and polyimide sulfonic acid, as well as polymers of these having a side chain such as an alkyl group.

[0042] When a water-soluble polymer is used as the gas barrier polymer, it is preferable that the proton-conducting polymer is also water-soluble. If the gas barrier polymer and the proton-conducting polymer are both water-soluble, water can be used as a solvent, making it easier to form a membrane. Polyvinyl sulfonic acid (PVS) is a suitable example of a water-soluble proton-conducting polymer.

[0043] An example of a suitable combination of a gas barrier polymer and a proton conductive polymer that constitutes the intermediate electrolyte membrane is a mixture of uncrosslinked polyvinyl alcohol (PVA) and polyvinyl sulfonic acid (PVS).

[0044] The blending ratio of the gas barrier polymer and the proton-conducting polymer is determined appropriately within a range that can achieve the desired gas barrier properties and proton conductivity, and is, for example, 0.5 to 500 parts by mole of the gas barrier polymer per 1 part by mole of the proton-conducting polymer.

[0045] The thickness of the intermediate electrolyte membrane is preferably smaller than the thickness of the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane. The specific membrane thickness will vary depending on the types and blending ratios of the gas barrier polymer and proton-conductive polymer used, and the types and membrane thicknesses of the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane, but is preferably as small as possible within the range in which the desired gas barrier properties and proton conductivity are achieved. The thickness of the intermediate electrolyte membrane is usually 10 μm or less, preferably 5 μm or less, and more preferably 2.5 μm or less. If the membrane is too thick, the proton conductivity tends to decrease even if the gas barrier property is improved. Furthermore, if the thickness of the intermediate electrolyte membrane is too small, membrane defects may occur, which may result in gas leakage, so the thickness is usually 0.1 μm or more, and preferably 1 μm or more.

[0046] The intermediate electrolyte membrane can be manufactured by any method, including coating or spraying an aqueous solution containing a gas barrier polymer and a proton-conducting polymer, which are not chemically bonded to each other, followed by drying. This manufacturing method makes it difficult for performance degradation due to gas cross-leakage to occur even when the membrane is thinned due to its high gas barrier properties. At the same time, thinning the membrane reduces the resistance to ion conduction in the electrolyte membrane, thereby preventing a decrease in power generation performance.

[0047] (Proton-conductive electrolyte membrane (outer layer)) The first and second proton-conductive electrolyte membranes (outer layers) are arranged to sandwich the intermediate electrolyte membrane (see FIG. 2). In a preferred embodiment, the first and second proton-conductive electrolyte membranes are in close contact with each other at their outer peripheries so as to encase the intermediate electrolyte membrane (see FIG. 4).

[0048] The first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane may be different types of electrolyte membranes, but typically the same type of electrolyte membrane is used.

[0049] As the proton-conductive electrolyte membrane (outer layer), an electrolyte membrane made of a known fluorine-based electrolyte material used as an electrolyte material for PEFC can be suitably used.

[0050] In the laminated electrolyte membrane of the present invention, the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane, which are outer layers, are set to have a larger thickness than the intermediate electrolyte membrane, and therefore an electrolyte membrane made of a fluorine-based electrolyte material having superior proton conductivity is preferably used. The fluorine-based electrolyte material has been described above in the description of the intermediate electrolyte membrane, and therefore a detailed description thereof will be omitted.

[0051] Suitable examples of commercially available electrolyte membranes made of fluorine-based electrolyte materials include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and Aquivion (registered trademark, manufactured by Solvay).

[0052] It should be noted that, instead of the electrolyte membrane made of a fluorine-based electrolyte material, other electrolyte membranes may also be used for the proton-conductive electrolyte membrane (outer layer).

[0053] For example, the proton-conducting electrolyte membrane (outer layer) may be an electrolyte membrane made of a hydrocarbon-based electrolyte material, such as a polymer of polysulfonic acid, polyvinyl sulfonic acid, polystyrene sulfonic acid, polyaryl ether ketone sulfonic acid, polyphenyl sulfonic acid, polybenzimidazole sulfonic acid, polybenzimidazole phosphonic acid, or polyimide sulfonic acid, or a polymer of any of these having a side chain such as an alkyl group.

[0054] The proton-conductive electrolyte membrane (outer layer) may be a pore-filling electrolyte membrane. Examples of the pore-filling electrolyte membrane include an electrolyte membrane in which various proton-conductive polymer electrolytes are filled into the pores of a porous substrate, such as a polyimide porous membrane or a crosslinked polyolefin membrane, preferably a polyimide porous membrane.

[0055] The first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane may have different thicknesses, but typically they have the same thickness. The thickness of the proton-conductive electrolyte membrane (outer layer) (first proton-conductive electrolyte membrane or second proton-conductive electrolyte membrane) is usually 50 μm or less, and preferably 30 μm or less. If the membrane thickness is too large, the membrane resistance increases, which is not preferable. Furthermore, if the thickness of the proton-conductive electrolyte membrane (outer layer) is too small, the strength cannot be maintained, and membrane defects may occur, which may result in gas leakage. Therefore, the thickness is usually 2 μm or more, and preferably 10 μm or more.

[0056] (Method of manufacturing laminated electrolyte membrane) The method for producing the laminated electrolyte membrane of the present invention described above is not particularly limited as long as the resulting laminated electrolyte membrane functions as an electrolyte membrane for a PEFC, and a suitable method may be selected as appropriate depending on the intermediate electrolyte membrane, the first proton-conductive electrolyte membrane, and the second proton-conductive electrolyte membrane that constitute the laminated electrolyte membrane.

[0057] The laminated electrolyte membrane of the present invention is preferably produced by the production method described below (hereinafter referred to as the "production method of the present invention"), since it can be produced with good reproducibility. The manufacturing method of the present invention is a method for manufacturing the laminated electrolyte membrane of the present invention described above, and is characterized by comprising the steps of: placing a mask corresponding to the shape and thickness of an intermediate electrolyte membrane on a first proton-conducting electrolyte membrane; applying or spraying an aqueous solution containing the gas barrier polymer and a proton-conducting polymer onto the mask and then drying it to form an intermediate electrolyte membrane composed of a mixture of the gas barrier polymer and the proton-conducting polymer on the first proton-conducting electrolyte membrane; and removing the mask, placing a second proton-conducting electrolyte membrane on top of the intermediate electrolyte membrane, and sandwiching the intermediate electrolyte membrane between the first proton-conducting electrolyte membrane and the second proton-conducting electrolyte membrane.

[0058] In the manufacturing method of the present invention, in the step of sandwiching the intermediate electrolyte membrane between the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane, the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane are preferably brought into close contact with each other so as to encase the intermediate electrolyte membrane. This method is employed in the examples described later, and allows for the reproducibility of manufacturing a laminated electrolyte membrane having the structure of the above-mentioned laminated electrolyte membrane 1A (see FIG. 4).

[0059] <2. Membrane electrode assembly (MEA)> The membrane electrode assembly of the present invention is a membrane electrode assembly having the laminated electrolyte membrane of the present invention, a cathode bonded to one surface of the laminated electrolyte membrane, and an anode bonded to the other surface of the laminated electrolyte membrane, wherein at least one of the cathode and the anode is the electrode of the present invention.

[0060] In the following, the cathode conditions of a PEFC refer to the conditions at the cathode during normal operation of the PEFC, where the temperature is between room temperature and approximately 150°C and an oxygen-containing gas such as air is supplied (oxidizing atmosphere), and the anode conditions refer to the conditions at the anode during normal operation of the PEFC, where the temperature is between room temperature and approximately 150°C and an oxygen-containing fuel gas is supplied (reducing atmosphere).

[0061] Fig. 5 is a schematic diagram showing the cross-sectional structure of a membrane electrode assembly according to an embodiment of the present invention. As shown in Fig. 5, the membrane electrode assembly 10 has a structure in which a cathode 4 and an anode 5 are arranged facing a solid polymer electrolyte membrane 6 (the laminated electrolyte membrane of the present invention).

[0062] The membrane electrode assembly (MEA) of the present invention can be suitably used in applications such as polymer electrolyte fuel cells and polymer electrolyte water electrolysis devices. In the membrane electrode assembly of the present invention, the components other than the laminated electrolyte membrane of the present invention are the same as those of known membrane electrode assemblies for polymer electrolyte fuel cells, so detailed description will be omitted and only an outline will be provided below.

[0063] The cathode 4 is composed of an electrode catalyst layer 4a and a gas diffusion layer 4b, and any known cathode can be used as long as it has sufficient durability and electronic conductivity under the cathode conditions of a PEFC (see, for example, Japanese Patent No. 6598159).

[0064] The anode 5 is composed of an electrode catalyst layer 5a and a gas diffusion layer 5b, and any known anode can be used as long as it has sufficient durability and electronic conductivity under the anode conditions of a PEFC (see, for example, Japanese Patent No. 6598159).

[0065] As the solid polymer electrolyte membrane 6 is the laminated electrolyte membrane of the present invention described above, a detailed description thereof will be omitted.

[0066] <3. Polymer electrolyte fuel cell> The polymer electrolyte fuel cell (single cell) of the present invention comprises the membrane electrode assembly of the present invention, and generally has a structure in which the membrane electrode assembly is sandwiched between separators having gas flow paths formed therein.

[0067] 6 is a conceptual diagram showing a typical configuration of a polymer electrolyte fuel cell according to the present invention. As shown in FIG. 6, in a polymer electrolyte fuel cell 20, hydrogen is supplied to the anode 5, and (reaction 1) 2H → 4H + +4e - The protons (H + ) is supplied to the cathode 4 via the solid polymer electrolyte membrane 6 (the laminated electrolyte membrane of the present invention), and the generated electrons are supplied to the cathode 4 via the external circuit 21, resulting in (reaction 2) O2 + 4H + +4e - →2H2O reacts with oxygen to produce water. This electrochemical reaction between the anode 5 and cathode 4 generates a potential difference between the two electrodes.

[0068] Furthermore, in the PEFC according to the present invention, the components other than the membrane electrode assembly of the present invention are the same as those of known solid polymer fuel cells, and therefore detailed description thereof will be omitted (see, for example, Japanese Patent No. 6598159). In practice, a fuel cell stack is formed by stacking the solid polymer fuel cells (single cells) of the present invention in a number corresponding to the power generation performance, and is used by assembling other associated devices such as a gas supply device and a cooling device.

[0069] Although the present invention has been described above with reference to the drawings, the matters disclosed herein are illustrative and not restrictive, except for the fuel cell main body described below. In particular, matters not explicitly disclosed in the matters disclosed herein, such as various parameters, dimensions, weights, and volumes of components, do not deviate from the scope of ordinary practice by a person skilled in the art, and values that can be easily assumed by a person skilled in the art can be used. [Example]

[0070] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0071] <1. Manufacturing of laminated electrolyte membrane> Example 1 The laminated electrolyte membrane of Example 1 was produced by the following procedure. First, polyvinyl alcohol (PVA), a gas barrier polymer, and polyvinyl sulfonic acid (PVS), a proton-conducting polymer, were dissolved in water as a solvent at a molar ratio of PVA:PVS = 100:1 to prepare an aqueous solution (PVA-PVS solution). Next, as shown in FIG. 7(a), a Nafion membrane (Nafion 211.9 cm 2 A mask (1cm thick) corresponding to the shape of the intermediate electrolyte membrane was placed on one side of the membrane. 2 ) and heated with a heater (60°C), the polymer (PVA + PVS) weight was 0.5 mg / cm 2The PVA-PVS solution was sprayed onto the substrate so that the thickness of the substrate was 100 μm and then dried at 60°C for 10 minutes to form an intermediate electrolyte membrane made of a mixture of PVA and PVS. After removing the mask, the intermediate electrolyte membrane (a mixture of PVA and PVS) was placed on a sheet of Nafion membrane (Nafion 211.9 cm ), which was the second proton-conducting electrolyte membrane, as shown in FIG. 7(b). 2 The intermediate electrolyte membrane was sandwiched between two Nafion membranes (25 μm thick), and the two Nafion membranes were hot pressed (132°C, 0.3 kPa, 3 minutes) to encase the intermediate electrolyte membrane, thereby obtaining a laminated electrolyte membrane of Example 1 (see FIG. 7(c)).

[0072] Fig. 8 shows a cross-sectional SEM image of the laminated electrolyte membrane of Example 1. As shown in Fig. 8, it was confirmed that the laminated electrolyte membrane of Example 1 had an intermediate electrolyte membrane of 2.2 µm sandwiched between first and second proton-conductive electrolyte membranes (25 µm).

[0073] From the above, it was confirmed that the laminated electrolyte membrane of Example 1 has a structure in which the intermediate electrolyte membrane (a mixture of PVA and PVS) is sandwiched and integrated between two Nafion membranes, and the outer periphery of the intermediate electrolyte membrane is tightly wrapped by the two Nafion membranes.

[0074] <2. Evaluation> (2-1. Evaluation of gas permeability) The gas permeability of oxygen and hydrogen was evaluated for the laminated electrolyte membrane of Example 1. For comparison, the gas permeability was also evaluated for Nafion212 (membrane thickness: 55 μm), which is a general-purpose electrolyte membrane for PEFCs.

[0075] The gas permeability of the electrolyte membrane was measured using the following method. The electrolyte membrane was sandwiched between aluminum tape with a 1-cm hole on both sides to prepare a measurement sample. The measurement sample was installed in a gas permeability measurement device GTR-11A / 31A (manufactured by GTR Tech), and the gas permeation rate was evaluated using a gas chromatograph G3700T (manufactured by Yanaco). The gas permeation rate was measured under dry conditions at 25°C and 80°C, with the upstream and downstream pressures set at 100 KPa and -100 KPa, respectively, so that the differential pressure between the upstream and downstream sides of the measurement sample was 200 KPa. Hydrogen and oxygen were used as gases. Gas permeability was calculated by dividing the volume of gas permeating the sample by the sample thickness, sample area, measurement time, and differential pressure.

[0076] The oxygen permeability and hydrogen permeability of the electrolyte membrane of Example 1 and Nafion212 of the Reference Example are shown in Table 1 and Table 2, respectively.

[0077] [Table 1]

[0078] [Table 2]

[0079] As shown in Table 1, the laminated electrolyte membrane of Example 1 had a lower oxygen permeability (OP) than Nafion212 at both 25°C and 80°C (25°C: 423 times, 80°C: 286 times). Also, as shown in Table 2, the laminated electrolyte membrane of Example 1 had a lower hydrogen permeability (HP) than Nafion212 at both 25°C and 80°C (25°C: 99 times, 80°C: 44 times). Thus, it was confirmed that the laminated electrolyte membrane of Example 1 has better gas barrier properties for both oxygen and hydrogen than the general-purpose Nafion212.

[0080] (2-2. Chemical durability test using PEFC (OCV retention test)) The laminated electrolyte membrane of Example 1 and the electrolyte membrane of Comparative Example 1 were a Nafion membrane (Nafion 212.9 cm 2A membrane electrode assembly (MEA) was fabricated using a 50 μm thick membrane. An OCV (open circuit voltage) retention test, which is a method for evaluating chemical degradation of electrolyte membranes in fuel cells (PEFC), was conducted to evaluate the effect of gas barrier properties on chemical durability.

[0081] First, a dispersion solution for forming an anode was prepared by dispersing 46.8 wt% Pt / C (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E) in a predetermined organic solvent containing a Nafion solution for the electrolyte membrane of Example 1 or Comparative Example 1. The obtained dispersion solution was spray-printed onto the Nafion membrane to form an anode (electrode catalyst layer) of a predetermined thickness on the electrolyte membrane of Example 1 or Comparative Example 1. Next, a dispersion solution for forming a cathode was prepared in the same manner as for the anode. The resulting dispersion solution was spray-printed on the opposite side of the electrolyte membrane on which the anode had been formed, to form a cathode (electrode catalyst layer) of a predetermined thickness on the electrolyte membrane. The electrode catalyst layer was pressure-bonded to the electrolyte membrane under predetermined conditions (0.12 MPa, 135°C, 180 seconds) to obtain an MEA of Example 1 or Comparative Example 1. The Pt amount in the anode and cathode of the MEAs in Example 1 and Comparative Example 1 was both 0.3 mg / cm 2 is.

[0082] Water-repellent carbon paper (manufactured by Toray Industries, Inc., model number: EC-TP1-060T) was placed as a gas diffusion layer on the MEAs of Example 1 and Comparative Example 1, and the MEAs were sandwiched between a single cell power generation evaluation jig (JARI), after which they were placed in a thermostatic chamber set to 90°C and subjected to an OCV retention test (current density 0 A / cm ) under the following conditions. 2 ) was evaluated. Figure 9 shows the results of the OCV retention test. (anode conditions) Electrode area: 1.0cm 2 Supply gas type: 100% H2 Gas supply rate: 139 mL / min (Cathode conditions) Electrode area: 1.0cm 2 Supply gas type: Air Gas supply rate: 332 mL / min

[0083] As shown in Figure 9, the OCV of the MEA (Nafion212) of Comparative Example 1 dropped to 0.6 V in approximately 200 hours, whereas the OCV of the MEA (laminated electrolyte membrane) of Example 1 maintained 0.6 V or higher for more than 300 hours, demonstrating that the MEA of Example 1 using the laminated electrolyte membrane of Example 1 has high durability. The fact that the membrane thicknesses are almost the same clearly demonstrates that the intermediate electrolyte membrane (a mixture of PVA and PVS) constituting the intermediate electrolyte membrane of the laminated electrolyte membrane of Example 1 suppresses oxygen permeation and suppresses the generation of radicals. These results demonstrate that the gas barrier polymer suppresses the generation of radicals and improves the chemical durability of the polymer electrolyte membrane.

[0084] (2-3. Electrochemical evaluation of hydrogen permeation through membranes) To evaluate the degradation of the membrane, hydrogen permeation through the laminated electrolyte membrane of Example 1 and the electrolyte membrane (Nafion212) of Comparative Example 1 was evaluated electrochemically, and the results are shown in FIG. 10, the amount of hydrogen permeation gradually increases in Comparative Example 1, whereas the gas barrier properties are maintained until just before degradation in Example 1. This also shows that suppressing oxygen permeability suppresses radical generation and degradation of the electrolyte membrane.

[0085] (2-4. Evaluation of oxygen permeability) In the laminated electrolyte membrane of Example 1, the ratio (molar ratio) of PVA and PVS in the intermediate electrolyte membrane was changed to evaluate oxygen permeability. Table 3 shows the PVA and PVS (molar ratio), areal density, and membrane thickness in the intermediate electrolyte membrane of the evaluated laminated electrolyte membrane. The sample named S100 corresponds to the laminated electrolyte membrane of Example 1 above.

[0086] [Table 3]

[0087] FIG. 11 shows the results of oxygen permeability (80° C., dry) of the laminated electrolyte membranes of the examples (S20, S40, S100) and the electrolyte membrane of Comparative Example 1 (Nafion212). As shown in FIG. 11, it was confirmed that the oxygen barrier property of the laminated electrolyte membrane improved as the proportion of PVA increased. [Industrial Applicability]

[0088] According to the present invention, a laminated electrolyte membrane having high chemical durability due to its gas barrier properties can be provided, and is promising as a component of polymer electrolyte fuel cells used in the automotive, electric power, gas, and home appliance industries. [Explanation of symbols]

[0089] 1,1A laminated electrolyte membrane 2a First proton-conducting electrolyte membrane 2b Second proton-conducting electrolyte membrane 3 Intermediate electrolyte membrane 4. Fuel cell electrodes (cathode) 4a Electrode catalyst layer (cathode electrode layer) 4b Gas diffusion layer 5. Fuel cell electrodes (anodes) 5a Electrode catalyst layer (anode electrode layer) 5b Gas diffusion layer 6 Solid polymer electrolyte membrane 10 Membrane electrode assembly (MEA) 20 Polymer electrolyte fuel cell (PEFC) 21 External circuit

Claims

1. A laminated electrolyte membrane having a sandwich structure consisting of at least three layers of electrolyte membrane, a first proton-conductive electrolyte membrane disposed on one side, a second proton-conductive electrolyte membrane disposed on the other side, and an intermediate electrolyte membrane disposed between the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane; the intermediate electrolyte membrane is made of a mixture of a gas barrier polymer and a proton conductive polymer, the gas barrier polymer is mixed with the proton conductive polymer without condensation; the first proton-conducting electrolyte membrane and the second proton-conducting electrolyte membrane are the same type of electrolyte membrane; the thickness of the intermediate electrolyte membrane is smaller than the thicknesses of the first proton-conducting electrolyte membrane and the second proton-conducting electrolyte membrane; a ratio of the gas barrier polymer to the proton conducting polymer constituting the intermediate electrolyte membrane being 0.5 to 500 molar parts of the gas barrier polymer per 1 molar part of the proton conducting polymer.

2. 2. The laminated electrolyte membrane according to claim 1, wherein the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane are closely attached to each other so as to encase the intermediate electrolyte membrane.

3. 3. The laminated electrolyte membrane according to claim 1, wherein the gas barrier polymer constituting the intermediate electrolyte membrane is polyvinyl alcohol (PVA).

4. 4. The laminated electrolyte membrane according to claim 1, wherein the proton-conducting polymer constituting the intermediate electrolyte membrane is a proton-conducting polymer having a sulfonic acid group.

5. 5. The laminated electrolyte membrane according to claim 1, wherein the first proton-conductive electrolyte membrane and the second proton-conductive electrolyte membrane are made of a fluorine-based proton-conductive polymer.

6. 6. A membrane electrode assembly comprising: a solid polymer electrolyte membrane; a cathode bonded to one surface of the solid polymer electrolyte membrane; and an anode bonded to the other surface of the solid polymer electrolyte membrane, wherein the solid polymer electrolyte membrane is the laminated electrolyte membrane according to claim 1.

7. A membrane electrode assembly as described in claim 6 for use in a polymer electrolyte fuel cell or a polymer electrolyte water electrolysis device.

8. A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 6.

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