Method for measuring adhesive strength between gas diffusion electrode and electrolyte membrane with catalyst layer

Abstract

To provide a method for highly accurately measuring adhesive strength without peeling off a gas diffusion electrode and an electrolyte membrane with a catalyst layer before testing when the adhesive strength of an interface between the gas diffusion electrode and the electrolyte membrane with the catalyst layer in a membrane electrode assembly of a fuel cell is measured.SOLUTION: There is provided a method for measuring adhesive strength between a gas diffusion electrode and an electrolyte membrane with a catalyst layer. The method includes: a thermal compression bonding step of bonding the gas diffusion electrode and the electrolyte membrane with the catalyst layer by thermo-compression bonding; and a peeling step of peeling the electrolyte membrane with the catalyst layer from the gas diffusing electrode to measure the adhesive strength. The gas diffusion electrode and the electrolyte membrane with the catalyst layer each have a rectangular shape. A length of the gas diffusion electrode in a longitudinal direction is shorter than a length of the electrolyte membrane with the catalyst layer in the longitudinal direction, and a length of the gas diffusion electrode in a short side direction is longer than a length of the electrolyte membrane with the catalyst layer in the short side direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the adhesive strength at the interface between a gas diffusion electrode and an electrolyte membrane with a catalyst layer, which is used in a fuel cell. [Background technology]

[0002] Polymer electrolyte fuel cells generate electromotive force through an electrochemical reaction that occurs at both electrodes by supplying a fuel gas containing hydrogen to the anode and an oxidizing gas containing oxygen to the cathode. Generally, each cell is made up of a separator, gas diffusion electrode, catalyst layer, electrolyte membrane, catalyst layer, gas diffusion electrode, and separator stacked in that order, and are composed of power generation units called stacks in which multiple cells are stacked in series. Here, the three-layer structure of catalyst layer, electrolyte membrane, and catalyst layer is called the catalyst-coated electrolyte membrane, and the five-layer structure including the gas diffusion electrodes placed on both sides of the catalyst-coated electrolyte membrane is called the membrane electrode assembly.

[0003] During normal fuel cell operation, the following reactions take place on the anode side: H2→2H + +2e - (1) On the cathode side, the following reaction takes place: O2+4H + +4e - →2H2O (2).

[0004] The electrochemical reaction between hydrogen and oxygen generates electromotive force as a fuel cell, and water is also produced during this process.

[0005] For the electrochemical reaction to occur efficiently, good electrical conductivity at the interface between the gas diffusion electrode and the catalyst-coated electrolyte membrane, i.e., good adhesion at this interface, is required. Furthermore, good adhesion is also necessary so that the gas diffusion electrode and the catalyst-coated electrolyte membrane can be transported without shifting or peeling after being bonded together in the manufacturing process of the membrane electrode assembly. Thus, the adhesion at the interface between the gas diffusion electrode and the catalyst-coated electrolyte membrane is an important indicator, and a method for accurately evaluating this adhesion is required.

[0006] As a method for evaluating the adhesive strength at the interface between such a gas diffusion electrode and a catalyst layer-coated electrolyte membrane, for example, a method for measuring adhesive strength is known in which the gas diffusion electrode and the catalyst layer-coated electrolyte membrane, which are cut to the same size, are thermocompressed together by a hot press, a weight is attached to a drafting tape attached to the catalyst layer-coated electrolyte membrane, and the weight of the weight at which the catalyst layer peels off is measured (Patent Document 1).

[0007] In addition, a method is known in which an end of a test piece made by bonding an electrolyte membrane with a catalyst layer and a gas diffusion layer is bent to break only the gas diffusion layer, creating a broken portion that serves as a clamping portion, and the broken portion is then grasped to perform interlayer peeling between the catalyst layer and the gas diffusion layer, thereby measuring the adhesive strength between the layers (Patent Document 2). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-137073 [Patent Document 2] Japanese Patent Publication No. 2021-125369 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the measurement method described in Patent Document 1, because the gas diffusion electrode and the catalyst-coated electrolyte membrane are the same size, misalignment during thermocompression bonding can cause the width of the peel interface (Fig. 3) to be uneven, and the way the weight is attached can cause uneven force to be applied to the peel interface, making it difficult to accurately measure the adhesive strength between the gas diffusion electrode and the catalyst-coated electrolyte membrane.In addition, the stress when the starting point of peeling is formed at the start of peeling is generally greater than the stress when peeling is progressing, and there is also a large variation, so it is sometimes impossible to measure the true adhesive strength.

[0010] Furthermore, in the measurement method described in Patent Document 2, when the starting point of peeling is formed in advance by breaking the end of the test piece, uneven stress concentration occurs, which can lead to peeling between the gas diffusion electrode and the catalyst layer of the catalyst-coated electrolyte membrane. [Means for solving the problem]

[0011] In view of the above problems, the present inventors provide the following method for measuring the adhesive strength of fuel cell electrodes. (1) A method for measuring the adhesion between a gas diffusion electrode and a catalyst-coated electrolyte membrane, comprising a thermocompression bonding step of bonding a gas diffusion electrode and a catalyst-coated electrolyte membrane together by thermocompression bonding, and a peeling step of peeling the catalyst-coated electrolyte membrane from the gas diffusion electrode to measure the adhesion between the gas diffusion electrode and the catalyst-coated electrolyte membrane, wherein the gas diffusion electrode and the catalyst-coated electrolyte membrane are both rectangular, the longitudinal length of the gas diffusion electrode is shorter than the longitudinal length of the catalyst-coated electrolyte membrane, and the lateral length of the gas diffusion electrode is longer than the lateral length of the catalyst-coated electrolyte membrane. (2) The method for measuring the adhesion strength between a gas diffusion electrode and a catalyst-coated electrolyte membrane according to (1), wherein the gas diffusion electrode comprises a conductive porous substrate and a microporous layer, and the catalyst-coated electrolyte membrane is bonded to the microporous layer side surface of the gas diffusion electrode in the thermocompression bonding step. (3) The method for measuring the adhesive strength between a gas diffusion electrode and an electrolyte membrane with a catalyst layer according to (1) or (2), wherein the temperature during the thermocompression bonding is 60 to 120° C. and the pressure is 0.2 to 1.5 MPa. (4) The method for measuring the adhesion between a gas diffusion electrode and a catalyst layer-equipped electrolyte membrane according to any one of (1) to (3), wherein in the peeling step, the catalyst layer-equipped electrolyte membrane is peeled from the gas diffusion electrode at a peeling speed of 5 to 50 mm / min and a peeling angle of 150 to 180°. [Effects of the Invention]

[0012] The method of measuring the adhesive strength between a gas diffusion electrode and a catalyst-coated electrolyte membrane of the present invention makes it possible to measure the adhesive strength at the interface between the gas diffusion electrode and the catalyst-coated electrolyte membrane with high precision. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram showing one embodiment of thermocompression bonding in the present invention. [Figure 2] 1 is a schematic diagram showing an embodiment of a method for measuring the adhesive strength between a gas diffusion electrode and an electrolyte membrane with a catalyst layer according to the present invention. [Figure 3] FIG. 1 is a schematic diagram of a peeling interface between a general gas diffusion electrode and an electrolyte membrane with a catalyst layer. DETAILED DESCRIPTION OF THE INVENTION

[0014] The gas diffusion electrode used in the method of measuring the adhesive strength between a gas diffusion electrode and a catalyst-coated electrolyte membrane of the present invention preferably comprises a conductive porous substrate and a microporous layer. The conductive porous substrate in this case will be described below.

[0015] As the conductive porous substrate, a porous substrate containing carbon fiber, such as a carbon fiber fabric, a carbon fiber paper sheet, a carbon fiber nonwoven fabric, carbon felt, carbon paper, or carbon cloth, is preferably used. Here, carbon paper refers to a sheet formed by binding a carbon fiber paper sheet with a resin carbide. Among these, carbon felt, carbon paper, and carbon cloth are preferably used because of their excellent corrosion resistance, and carbon paper is more preferably used because of its excellent "springiness," i.e., ability to absorb dimensional changes in the thickness direction of the electrolyte membrane.

[0016] Examples of carbon fibers include polyacrylonitrile (PAN)-based, pitch-based, and rayon-based fibers. PAN-based and pitch-based carbon fibers are preferred due to their excellent mechanical strength. Also, natural and synthetic fibers, such as rayon, acrylic, and cellulose fibers, may be mixed and used.

[0017] The conductive porous substrate is preferably one that has been treated to have a water-repellent resin attached to the inside. Preferred water-repellent resins include fluororesins with fluoroalkyl chains, such as PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), ETFE (tetrafluoroethylene-ethylene copolymer), PVDF (polyvinylidene fluoride), and PVF (polyvinyl fluoride). PTFE and FEP are preferred because of their high water-repellent properties.

[0018] The thickness of the conductive porous substrate is preferably 90 to 180 μm. Here, the thickness of the conductive porous substrate is the thickness when both surfaces are sandwiched under a pressure of 0.15 MPa. A thickness of 90 μm or more maintains mechanical strength and facilitates handling during the manufacturing process. In addition, the spring properties are enhanced, allowing the gas diffusion electrode to absorb dimensional changes due to the expansion and contraction of the electrolyte membrane during use in the fuel cell, and gas diffusion in the in-plane direction is improved, thereby improving power generation performance. On the other hand, when the thickness of the conductive porous substrate is 180 μm or less, gas diffusion in the perpendicular direction is enhanced, and the conductive path in the perpendicular direction is shortened, improving conductivity, thereby improving power generation performance.

[0019] Next, the microporous layer will be described. The gas diffusion electrode used in the present invention preferably comprises a conductive porous substrate and a microporous layer, and more preferably has a configuration in which the microporous layer is provided on one side of the conductive porous substrate. Roles of the microporous layer include water management such as keeping the electrolyte membrane moist and discharging generated water, reducing the interfacial electrical resistance between the catalyst layer and the gas diffusion electrode, and preventing damage to the electrolyte membrane due to carbon fibers protruding from the conductive porous substrate. The microporous layer is preferably a layer containing carbon fine particles and a water-repellent resin.

[0020] Specific examples of carbon fine particles that can be used include carbon black, carbon nanofibers, carbon nanotubes, graphene, etc. Among these, inexpensive carbon black is preferably used.

[0021] As the water-repellent resin contained in the microporous layer, a fluororesin having a fluoroalkyl chain is preferred from the viewpoints of chemical stability, water repellency, etc., and examples thereof include PTFE, FEP, PFA, and ETFE, which are the same as the fluororesins preferably used in the water-repellent treatment of conductive porous substrates.

[0022] The microporous layer has a basis weight of 10 to 35 g / m 2 It is preferable that the basis weight of the microporous layer is 10 g / m 2 When the thickness is 35 g / m or more, the carbon fibers protruding from the surface of the conductive porous substrate are covered, thereby preventing the carbon fibers from damaging the electrolyte membrane. In addition, the contact resistance between the gas diffusion electrode and the catalyst layer can be reduced, and the electrolyte membrane can be prevented from drying out. In addition, when the basis weight of the microporous layer is 35 g / m or more, the carbon fibers protruding from the surface of the conductive porous substrate are covered, thereby preventing the carbon fibers from damaging the electrolyte membrane. 2 When the weight of the microporous layer is 15 to 25 g / m or less, the drainage property is good. 2 This is more preferable because it enhances these effects.

[0023] The thickness of the gas diffusion electrode used in the present invention is preferably 130 to 190 μm. Here, the thickness of the gas diffusion electrode is the thickness when both surfaces are sandwiched under a pressure of 0.15 MPa. When the thickness of the gas diffusion electrode is 130 μm or more, mechanical strength is maintained and handling during the manufacturing process is easy. On the other hand, when the thickness of the gas diffusion electrode is 190 μm or less, gas diffusibility is increased and electrical resistance is reduced, thereby improving the power generation performance of the fuel cell. The thickness of the gas diffusion electrode can be adjusted by, for example, appropriately adjusting the thickness of the conductive porous substrate and the microporous layer.

[0024] Next, an example of a method for producing a gas diffusion electrode used in the present invention will be described. This example is an example of a method for producing a gas diffusion electrode having a configuration in which a microporous layer is formed on a conductive porous substrate.

[0025] First, carbon fiber bundles cut to a predetermined length are loosened in water to produce a uniformly dispersed carbon fiber dispersion, which is then papered and dried to produce a carbon fiber paper body. Here, a water-soluble resin such as polyvinyl alcohol or polyvinyl acetate may be added to the carbon fiber paper body so that the shape of the carbon fiber paper body can be maintained.

[0026] The obtained carbon fiber paper sheet may be used as the conductive porous substrate of the present invention, but in order to improve mechanical strength and reduce electrical resistance, it is preferable to use a conductive porous substrate in which the intersections of the carbon fibers are bound with a resin carbide.

[0027] For this purpose, for example, a method can be applied in which a carbon fiber paper sheet is impregnated with a resin composition solution and then heated to carbonize the resin component in the resin composition.

[0028] Examples of resin components used in the resin composition solution include thermosetting resins such as phenolic resin, epoxy resin, melamine resin, and furan resin. The resin composition solution may contain, in addition to the resin component and solvent, carbon powder, a surfactant, and the like. Examples of carbon powder include carbon black, graphite, carbon nanotubes, and carbon nanofibers.

[0029] Examples of methods for impregnating the resin composition solution include immersion, spraying, blade coating, die coating, and transfer methods.

[0030] Next, the carbon fiber paper sheet impregnated with the resin composition solution is dried in air at a temperature of 80 to 150° C. Subsequently, it is heated in air at a temperature of 200 to 300° C. to harden the thermosetting resin and decompose and remove the surfactant, etc. At this time, both sides of the carbon fiber paper sheet may be pressed with flat plates to improve flatness and adjust the thickness.

[0031] Furthermore, in order to increase the conductivity of the conductive porous substrate and to enhance its long-term durability, it is preferable to carbonize the cured resin composition in an inert atmosphere such as nitrogen at a temperature of 1,000 to 2,400°C, thereby obtaining a carbon fiber paper body in which the intersections of the carbon fibers are bonded with a resin charcoal.

[0032] A water-repellent treatment may be carried out to improve the drainage of the conductive porous substrate obtained as described above. The method for water-repellent-treating the conductive porous substrate may include immersing the conductive porous substrate in a dispersion of a water-repellent resin, as well as applying a water-repellent resin to the conductive porous substrate by die coating, spray coating, or the like. After the water-repellent treatment, a drying process or a heating process may be added as needed to wet and spread the water-repellent resin throughout the conductive porous substrate. In this way, the conductive porous substrate of the present invention can be obtained.

[0033] Next, a method for forming a microporous layer on a conductive porous substrate will be described.

[0034] The microporous layer can be formed by applying a coating liquid for forming the microporous layer, which is prepared by dispersing fine carbon particles and a water-repellent resin in a dispersion medium such as water, onto the conductive porous substrate, and then subjecting the coating liquid to a heat treatment.

[0035] First, carbon fine particles and a water-repellent resin are mixed with a dispersion medium such as water, and the mixture is kneaded using a homogenizer, planetary mixer, ultrasonic disperser, or the like to obtain a coating liquid for forming a microporous layer.

[0036] When preparing the coating liquid for forming the microporous layer, it is preferable to add a dispersant or a thickener to the liquid, as this improves the dispersion stability of the carbon microparticles and water-repellent resin. As the dispersant, a nonionic surfactant is preferred because it contains little metal components, and an example of such a dispersant is polyoxyethylene octylphenyl ether-based "Triton (registered trademark)" X-100 (manufactured by Nacalai Tesque, Inc.).

[0037] The coating liquid for forming a microporous layer can be applied to the conductive porous substrate using various commercially available coating devices, such as screen printing, gravure printing, spray coating, die coating, bar coating, blade coating, and roll knife coating.

[0038] After the coating liquid for forming the microporous layer is applied to the conductive porous substrate, it is dried at a temperature of 60 to 150°C and then heated at a temperature of 250 to 380°C to promote decomposition and removal of additives such as dispersants and thickeners and melting of the water-repellent resin.

[0039] In this way, a gas diffusion electrode can be obtained in which a microporous layer is formed on a conductive porous substrate.

[0040] The catalyst layer-equipped electrolyte membrane of the present invention has a configuration in which a catalyst layer is formed on an electrolyte membrane.

[0041] The electrolyte membrane preferably has high proton conductivity and oxidation resistance and small gas crossover, and examples thereof include proton-conducting polymers made of fluorine-based polymers and hydrocarbon-based polymers. The catalyst layer is preferably made of a mixture of catalyst-supported carbon particles, in which catalyst fine particles made of noble metals such as platinum, palladium, ruthenium, iridium, and rhodium, or oxides thereof, are supported on carbon particles, and a proton-conducting polymer.

[0042] Next, an example of the method for producing the catalyst layer-equipped electrolyte membrane of the present invention will be described.

[0043] First, a solution of a proton-conducting polymer (a material for the electrolyte membrane, made of a fluoropolymer or hydrocarbon polymer) diluted in a solvent is applied to a substrate such as a glass substrate, PET film, or fluororesin film, and then the solvent is removed by a drying process to produce an electrolyte membrane. The resulting electrolyte membrane is then peeled off from the substrate to obtain a single electrolyte membrane.

[0044] The proton-conductive polymer solution can be applied by a method such as screen printing, gravure printing, spray coating, die coating, bar coating, blade coating, or roll knife coating.

[0045] Suitable solvents include, for example, aprotic polar solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide; ester-based solvents such as γ-butyrolactone and butyl acetate; alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether; alcohol-based solvents such as isopropanol and butanol; water; and mixtures thereof.

[0046] In the drying step, for example, a hot air oven, an infrared heater, etc. The heating temperature range is preferably close to the boiling point of the solvent and equal to or lower than the glass transition temperature of the resulting electrolyte membrane.

[0047] Next, a method for producing a catalyst-coated electrolyte membrane in which a catalyst layer is formed on the surface of the obtained electrolyte membrane will be described.

[0048] The method for forming the catalyst layer is not particularly limited, but a preferred method is to prepare a catalyst layer decal in which the catalyst layer is formed on a substrate in advance, and then transfer the catalyst layer decal onto the electrolyte membrane and dry it, because this method involves simple steps and can reduce process costs.

[0049] In the case of a method of transferring using a catalyst layer decal, first, a catalyst layer coating liquid is applied onto a substrate, and if necessary, a drying step is carried out to prepare a catalyst layer decal.

[0050] The method for applying the catalyst layer coating liquid onto the substrate is not particularly limited as long as it can be applied in the desired shape, and the methods described above in the step of applying the proton-conductive polymer solution can be used.

[0051] The electrolyte membrane is then sandwiched between the catalyst layer decal on the cathode electrode side and the catalyst layer decal on the anode electrode side, and hot-pressed so that the catalyst layer-carrying surfaces of both decals come into contact with the electrolyte membrane, to obtain a catalyst-coated electrolyte membrane. The temperature and pressure of the hot press may be appropriately selected depending on the thickness and moisture content of the electrolyte membrane, and the catalyst layer and decal substrate, but are preferably hot-pressed at a temperature in the range of 40 to 250°C from the viewpoints of industrial productivity and suppression of thermal decomposition of the electrolyte membrane.

[0052] Next, the method for measuring the adhesion between a gas diffusion electrode and a catalyst-coated electrolyte membrane of the present invention will be described in detail. The method for measuring the adhesion between a gas diffusion electrode and a catalyst-coated electrolyte membrane of the present invention measures the adhesion by performing a thermocompression bonding step in which the gas diffusion electrode and the catalyst-coated electrolyte membrane, which are cut to a predetermined size, are bonded together by thermocompression bonding, and then a peeling step in which the catalyst-coated electrolyte membrane is peeled off from the gas diffusion electrode to measure the adhesion. Each step will be described in turn below.

[0053] First, one embodiment of the thermocompression bonding process will be described with reference to Fig. 1. Note that the present invention is not limited in any way by the drawings and explanations referred to below. Furthermore, the explanation of a specific embodiment can also be understood as an explanation of the present invention as a general concept.

[0054] The thermocompression bonding method involves cutting out the gas diffusion electrode and the catalyst-coated electrolyte membrane, then stacking the rubber sheet 5, PTFE sheet 2B, gas diffusion electrode 4, catalyst-coated electrolyte membrane 3, and PTFE sheet 2A in this order from below, and placing them in a heat press to bond them together by thermocompression bonding at a predetermined temperature and pressure. Hereinafter, the gas diffusion electrode 4 and catalyst-coated electrolyte membrane 3 bonded together will be referred to as a test piece.

[0055] The gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3 are both cut out into a rectangular shape, and the longitudinal length of the gas diffusion electrode 4 is required to be shorter than the longitudinal length of the catalyst-coated electrolyte membrane 3, and the lateral length of the gas diffusion electrode 4 is required to be longer than the lateral length of the catalyst-coated electrolyte membrane 3.

[0056] By setting the shapes of the gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3 as described above, the starting point of peeling is formed in advance in the subsequent peeling step. Furthermore, even if the gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3 are misaligned during thermocompression bonding, the width of the peeled interface accurately corresponds to the dimension in the short direction of the catalyst-coated electrolyte membrane 3, allowing for highly accurate measurement.

[0057] The longitudinal length of the gas diffusion electrode 4 is preferably 30 to 150 mm, and the lateral length is preferably 10 mm or more. If the longitudinal length is 30 mm or more, a sufficient area can be secured for stable measurement of the peel force during the peeling step. If the longitudinal length is 150 mm or less, variations in the peeling step due to the device involved can be reduced. On the other hand, if the lateral length is 10 mm or more, the catalyst-coated electrolyte membrane 3 can be prevented from protruding outside the gas diffusion electrode 4 in the lateral direction even if the gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3 are misaligned during thermocompression bonding.

[0058] Furthermore, the longitudinal length of the catalyst layer-equipped electrolyte membrane 3 is preferably 50 to 200 mm, and the lateral length is preferably 10 to 20 mm. If the longitudinal length is 50 mm or more, a sufficient area can be secured for stable measurement of the peeling force during the peeling process. If the longitudinal length is 200 mm or less, variations in the peeling process due to the device involved can be reduced. On the other hand, if the lateral length is 10 to 20 mm, variations in the peeling force during the peeling process can be reduced, allowing for highly accurate measurements.

[0059] The method for cutting out the gas diffusion electrode 4 and the catalyst layer-equipped electrolyte membrane 3 is not particularly limited as long as it is a method that can cut with high precision without causing cracks or chips on the cut surface, and examples of such methods include methods using scissors, a cutter, a cutting machine, a Thomson blade, a laser, etc. In particular, it is preferable to cut out the gas diffusion electrode 4 and the catalyst layer-equipped electrolyte membrane 3 by punching using a Thomson blade, which can easily cut out the electrodes to high-precision dimensions.

[0060] When the gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3 are stacked, they are arranged so that the centers of the gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3 overlap and their longitudinal directions are parallel to each other.

[0061] By arranging the catalyst layer in this manner, both ends of the catalyst layer-equipped electrolyte membrane 3 extend beyond the ends of the gas diffusion electrode 4 in the longitudinal direction, and the catalyst layer-equipped electrolyte membrane 3 is arranged inside both ends of the gas diffusion electrode 4 in the lateral direction. As a result, as described above, measurement variations due to abnormal stress when forming the peel initiation point and peeling when forming the initiation point in advance can be avoided, and the width of the peel interface becomes constant, allowing the peel force to be measured with high precision.

[0062] When the gas diffusion electrode 4 is made of a conductive porous substrate and a microporous layer, it is preferable to arrange and attach the surface of the gas diffusion electrode 4 on the microporous layer side to the catalyst-coated electrolyte membrane 3 so that they come into contact with each other.

[0063] As described above, placing PTFE sheets 2A and 2B above and below the gas diffusion electrode 4 and catalyst-coated electrolyte membrane 3 is preferable because the gas diffusion electrode 4 and catalyst-coated electrolyte membrane 3 do not stick to the upper and lower pressure plates 1A and 1B of the hot press during the thermocompression bonding process. Note that, to prevent misalignment of the bonded portions due to static electricity when placing the gas diffusion electrode 4 and catalyst-coated electrolyte membrane 3 between the PTFE sheets 2A and 2B, it is preferable to remove static electricity from the gas diffusion electrode 4, catalyst-coated electrolyte membrane 3, and PTFE sheets 2A and 2B using an ionizer or the like.

[0064] Furthermore, by placing the rubber sheet 5, it is possible to absorb the in-plane irregularities and steps that occur when the gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3 are sandwiched between the pressure plates 1A and 1B of the heat press, and it is possible to apply pressure and heat uniformly to the contact interface between the gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3.

[0065] The pressure in the thermocompression bonding step is preferably 0.2 to 1.5 MPa. When the pressure is 0.2 MPa or more, the gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3 are uniformly bonded. When the pressure is 1.5 MPa or less, the gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3 can be prevented from shifting from one another during thermocompression bonding.

[0066] The temperature in the thermocompression bonding step is preferably 60 to 120° C. If the temperature is 60° C. or higher, the gas diffusion electrode 4 and the catalyst layer-equipped electrolyte membrane 3 are firmly bonded together. On the other hand, if the temperature is 120° C. or lower, thermal decomposition of the electrolyte membrane can be suppressed.

[0067] Examples of a heat press machine for thermocompression bonding include a high-precision compression bonding device SA-401 (manufactured by Tester Sangyo Co., Ltd.).

[0068] A plurality of gas diffusion electrodes 4 and catalyst-coated electrolyte membranes 3 may be simultaneously thermocompression-bonded. In this case, in order to apply uniform pressure, it is preferable to arrange the test pieces 4 and 3 symmetrically on the pressure plate of the hot press machine in accordance with the number of test pieces to be prepared.

[0069] Next, one embodiment of the peeling step for peeling the catalyst layer-equipped electrolyte membrane 3 from the gas diffusion electrode 4 of the obtained test piece will be described with reference to FIG.

[0070] First, the test piece is attached to the SUS plate 9 using double-sided tape or the like so that the side of the gas diffusion electrode 4 to which the catalyst layer-equipped electrolyte membrane 3 is not attached comes into contact with the SUS plate 9.

[0071] Next, in the test piece laminated on the SUS plate 9, a PET film 8 of sufficient length is attached with tape to one end of the catalyst-coated electrolyte membrane 3 that protrudes from both longitudinal ends of the gas diffusion electrode 4, forming a lead portion for holding with the upper clamp 7A of the tensile tester. When attaching the PET film 8, it is preferable to remove static electricity from the PET film 8 using an ionizer or the like to prevent the catalyst-coated electrolyte membrane 3 from peeling off from the gas diffusion electrode 4 due to static electricity attraction.

[0072] Next, the end of the SUS plate 9 with the test piece attached is clamped in the lower clamp 7B of the tensile tester so that the lead attached to the test piece faces downward. At this time, care is taken to ensure that the lower clamp 7B grips only the SUS plate 9 and does not grip the attached test piece or PET film 8.

[0073] Here, it is preferable to hold the SUS plate 9 so that the longitudinal direction of the catalyst coated electrolyte membrane 3 is parallel to the vertical direction. By doing so, the line of the peeled portion becomes parallel to the lateral direction of the catalyst coated electrolyte membrane 3 during the peeling step, allowing for highly accurate measurement.

[0074] Next, the tips of the lead portions of the PET film 8 are gripped by the upper clamp 7A of the tensile tester, and the upper clamp 7A is then raised to the measurement start position. The measurement start position is the position immediately before tension is applied to the PET film 8 and the gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3 begin to peel off. However, if the adhesive strength between the gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3 is weak, it is preferable not to bend the lead portions of the PET film 8 too much so that peeling does not occur before measurement due to the repulsive force caused by the lead portions of the PET film 8 being bent from bottom to top.

[0075] Next, the upper clamp 7A of the tensile tester is pulled at a predetermined speed to peel the catalyst layer-equipped electrolyte membrane 3 from the gas diffusion electrode 4, and the peeling force at this time is measured.

[0076] After peeling begins, the value when the peel force stabilizes at a steady value is read and divided by the width of the peel interface to calculate the adhesive strength between the gas diffusion electrode 4 and the catalyst-coated electrolyte membrane 3.

[0077] The peel speed is preferably 5 to 50 mm / min. A peel speed of 5 mm / min or more can reduce variations over time in a single measurement due to factors such as the temperature and humidity environment and the device. On the other hand, a peel speed of 50 mm / min or less suppresses zipping during peeling, resulting in a stable measured peel force.

[0078] The peel angle 11 (Figure 3) during the peeling process is preferably 150 to 180°. The peel angle 11 is the angle of the direction in which the edge of the peel target is pulled relative to the plane (fixing surface) on which the test piece is fixed. When the pulling direction is perpendicular to the fixing surface, the peel angle 11 increases as the pulling direction approaches the direction of peel progression, and becomes 180° when the pulling direction and the direction of peel progression coincide. To measure the peel force with good reproducibility, it is necessary to minimize changes in the peel angle 11 during peeling, and the test must be performed while moving the position of the fixing surface relative to the tensile tester. However, a peel angle 11 of 150° or more is preferable because the change in the peel angle 11 is small even without moving the fixing surface, allowing for simple and highly accurate measurements. A peel angle 11 of 180° is even more preferable because the peel angle 11 remains constant even without moving the fixing surface. The tensile tester used in the peeling process can be the precision universal testing machine "Autograph (registered trademark)" AGS-X (manufactured by Shimadzu Corporation). [Example]

[0079] The present invention will be described in more detail below with reference to examples. The performance evaluation methods used in the examples and the methods for preparing materials used in the examples are described below.

[0080] <Method of manufacturing an electrolyte membrane with a catalyst layer> A 10% by mass dispersion of "Nafion (registered trademark)" (manufactured by Sigma-Aldrich), a fluorine-based proton-conducting polymer, was applied to a PET substrate using a 15 cm wide bar coater, dried at 100°C for 4 hours, and then heat-treated at 150°C under nitrogen for 10 minutes. The substrate was then immersed in a 10% by mass aqueous sulfuric acid solution at 95°C for 24 hours to undergo proton substitution and deprotection reactions, after which it was immersed in a large excess of pure water for 24 hours to thoroughly wash, and the membrane was peeled off from the substrate to prepare a 15 cm square electrolyte membrane (film thickness: 10 μm).

[0081] Next, a catalyst coating solution prepared by mixing platinum catalyst-supported carbon particles TEC10E50E (platinum loading rate 50 mass%) manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. and "Nafion (registered trademark)" manufactured by DuPont in a mass ratio of 2:1 was applied to a PET substrate with a platinum content of 0.3 mg / cm. 2The catalyst layer decal (catalyst layer thickness: 8 μm) was prepared by applying the solution using a bar coater so that the thickness of the catalyst layer became 8 μm.

[0082] The catalyst layer decal obtained as described above was cut into a pair of 10 cm squares, and these were stacked facing each other so as to sandwich the electrolyte membrane obtained as described above. These were then hot-pressed at 100°C and 5 MPa for 3 minutes to obtain an electrolyte membrane with a catalyst layer.

[0083] <Method of manufacturing gas diffusion electrode> Toray Industries, Inc.'s polyacrylonitrile carbon fiber "TORAYCA (registered trademark)" T300 (average fiber diameter: 7 μm) was cut to a length of 12 mm, dispersed in water, and continuously made into a paper body. The paper body was then spray-coated with a 10% by mass aqueous solution of polyvinyl alcohol and dried. The weight of the paper body after drying was 30 g / m. 2 The amount of polyvinyl alcohol adhered was 20 parts by mass per 100 parts by mass of the paper body before spray coating.

[0084] Next, a resin composition solution was prepared by mixing flake graphite (average particle size: 5 μm), phenolic resin (a 1:1 mixture of resol-type phenolic resin and novolac-type phenolic resin by mass), and methanol in a mass ratio of 5:10:85. The resin composition solution was then continuously applied to the paper body by spray coating so that the total amount of phenolic resin and flake graphite was 130 parts by mass per 100 parts by mass of carbon fiber in the paper body, and dried at 100°C for 5 minutes.

[0085] Next, the paper sheet with the resin composition attached was sandwiched between upper and lower hot plates in a press molding machine and subjected to a heat compression treatment at 180°C for 5 minutes. Here, release paper was placed between the paper sheet and the hot plates to prevent the hot plates from adhering to the paper sheet, and spacers were placed around the edges of the upper and lower hot plates to adjust the thickness of the paper sheet after heat compression. After that, it was heated to 2,000°C in a nitrogen atmosphere in a heating furnace and carbonized.

[0086] Furthermore, a water-repellent resin dispersion liquid, which is a mixture of 5 parts by mass of a dispersion liquid of PTFE fine particles ("Polyflon (registered trademark)" D-210C manufactured by Daikin Industries, Ltd.) and 95 parts by mass of ion-exchanged water, is spray-coated, and dried at 100°C for 5 minutes to obtain a thickness of 160 μm and a basis weight of 50 g / m at 0.15 MPa. 2 Thus, a conductive porous substrate of 1000 .mu.m was obtained.

[0087] Next, a coating liquid for forming a microporous layer was prepared using acetylene black as the carbon fine particles, PTFE, a fluororesin, as the water-repellent resin, Triton (registered trademark) X-100 (manufactured by Nacalai Tesque, Inc.) as the dispersant, and water as the dispersion medium, with a blending ratio of carbon fine particles / PTFE resin / dispersant = 75 parts by mass / 25 parts by mass / 150 parts by mass, and with the indecomposable components (carbon fine particles and water-repellent resin) accounting for 23% by mass of the total amount. Here, a dispersion of PTFE particles dispersed in water, Polyflon (registered trademark) D-210C (manufactured by Daikin Industries, Ltd.), was used as the PTFE supply source. When preparing the coating liquid, the raw materials were dispersed using a planetary mixer to ensure a uniform coating liquid composition.

[0088] The coating liquid for forming the microporous layer was applied to the conductive porous substrate prepared above using a die coater, dried at 100°C for 10 minutes, and then heated at 350°C for 10 minutes to promote adhesion between the water-repellent resin and the carbon microparticles and to decompose and remove the dispersant, etc., to prepare a gas diffusion electrode. Here, the basis weight of the microporous layer after heating was 20 g / cm. 2 The amount of coating was adjusted so that

[0089] The resulting gas diffusion electrode had a thickness of 180 μm.

[0090] Example 1 The gas diffusion electrode was punched out to a width of 20 mm and a length of 50 mm, and the catalyst-coated electrolyte membrane was punched out to a width of 12 mm and a length of 70 mm using a Thomson blade. The rubber sheet, PTFE sheet, gas diffusion electrode, catalyst-coated electrolyte membrane, and PTFE sheet were stacked from the bottom up so that the microporous layer of the punched gas diffusion electrode and the catalyst layer of the catalyst-coated electrolyte membrane were in contact. Using a high-precision pressure bonding machine SA-401 (manufactured by Tester Sangyo Co., Ltd.), they were thermocompressed for 2 minutes at 80°C and 0.5 MPa to produce a test specimen in which the gas diffusion electrode and catalyst-coated electrolyte membrane were bonded together. Ten test specimens were produced.

[0091] For each test specimen, the side of the gas diffusion electrode not attached to the catalyst-coated electrolyte membrane was attached to a 50 mm wide, 100 mm long stainless steel plate with double-sided tape. A 9–11 mm wide, 250–400 mm long PET film, which had been statically deionized with an ionizer, was attached with tape to one of the portions of the catalyst-coated electrolyte membrane that protruded from both ends of the gas diffusion electrode in the longitudinal direction. The SUS plate with the attached test specimen was clamped with the lower clamp of an Autograph® AGS-X precision universal testing machine (Shimadzu Corporation) so that the PET film was facing downward. The upper clamp then clamped only the tip of the PET film not attached to the catalyst-coated electrolyte membrane, and the upper clamp was raised to the starting position so that the PET film was slightly deflected. The portion of the PET film held by the upper clamp was then raised at a peel speed of 20 mm / min, and the peel process was performed at a peel angle of 180°. Ten test pieces were tested and the average peel force was 0.030 N, with a variation of 10%. By dividing the average peel force by the width of the peel interface (width of the catalyst layer-coated electrolyte membrane: 12 mm), the adhesive strength was calculated to be 2.5 N / m.

[0092] Example 2 A bonded body was produced and a peeling step was carried out in the same manner as in Example 1, except that the temperature for thermocompression bonding was 50° C. The results are shown in Table 1.

[0093] Example 3 The peeling step was carried out in the same manner as in Example 1, except that the peeling speed was 200 mm / min. The results are shown in Table 1.

[0094] (Comparative Example 1) Test specimens were prepared and adhesive strength measurements were performed in the same manner as in Example 1, except that the punched sizes for both the gas diffusion electrode and the catalyst-coated electrolyte membrane were 20 mm wide and 50 mm long. Of the 10 test specimens, three were unable to undergo the peeling process due to significant misalignment between the gas diffusion electrode and the catalyst-coated electrolyte membrane during thermocompression bonding. Furthermore, two of the remaining seven test specimens were unable to undergo the peeling process due to the gas diffusion electrode and the catalyst-coated electrolyte membrane peeling when the PET film was attached to the peeling start point. The average peel strength of the remaining five test specimens was 0.042 N, with a variation of 30% (adhesion strength: 2.1 N). However, even for these test specimens that underwent the peeling process, slight misalignment occurred when the gas diffusion electrode and the catalyst-coated electrolyte membrane were thermocompression bonded. Therefore, the actual width of the peel interface (20 mm) used to calculate the adhesive strength was different, and therefore the calculated adhesive strength was considered to be inaccurate.

[0095] [Table 1] [Explanation of symbols]

[0096] 1A: Pressure plate 1B: Pressure plate 2A: PTFE sheet 2B: PTFE sheet 3: Electrolyte membrane with catalyst layer 4: Gas diffusion electrode 5: Rubber sheet 6: Tensile testing machine 7A: Upper clamp 7B: Lower clamp 8: PET film 9:SUS board 10: Width of peeled interface 11: Peeling angle [Industrial Applicability]

[0097] The method of the present invention for measuring the adhesive strength between a gas diffusion electrode and an electrolyte membrane with a catalyst layer allows for a simple and highly accurate measurement of the adhesive strength between a gas diffusion electrode and an electrolyte membrane with a catalyst layer, which is one of the important indicators for improving the power generation performance and durability of a fuel cell. This will lead to the development of low-cost, high-performance, and highly durable fuel cells, and will contribute to the development of mobility using fuel cell systems, such as automobiles, railways, ships, and UAM, as well as power supply facilities for homes, offices, data centers, etc.

Claims

1. A method for measuring the adhesion between a gas diffusion electrode and a catalyst-coated electrolyte membrane, comprising: a thermocompression bonding step of bonding a gas diffusion electrode and a catalyst-coated electrolyte membrane together by thermocompression bonding; and a peeling step of peeling the catalyst-coated electrolyte membrane from the gas diffusion electrode to measure the adhesion between the gas diffusion electrode and the catalyst-coated electrolyte membrane, wherein the gas diffusion electrode and the catalyst-coated electrolyte membrane are both rectangular, the longitudinal length of the gas diffusion electrode is shorter than the longitudinal length of the catalyst-coated electrolyte membrane, and the lateral length of the gas diffusion electrode is longer than the lateral length of the catalyst-coated electrolyte membrane.

2. 2. The method for measuring adhesion strength between a gas diffusion electrode and a catalyst-coated electrolyte membrane according to claim 1, wherein the gas diffusion electrode comprises a conductive porous substrate and a microporous layer, and the catalyst-coated electrolyte membrane is bonded to the microporous layer side surface of the gas diffusion electrode in the thermocompression bonding step.

3. 2. The method for measuring the adhesive strength between a gas diffusion electrode and a catalyst layer-equipped electrolyte membrane according to claim 1, wherein the temperature during the thermocompression bonding is 60 to 120° C. and the pressure is 0.2 to 1.5 MPa.

4. 2. The method for measuring adhesion between a gas diffusion electrode and a catalyst-coated electrolyte membrane according to claim 1, wherein in the peeling step, a peeling speed when peeling the catalyst-coated electrolyte membrane from the gas diffusion electrode is 5 to 50 mm / min and a peeling angle is 150 to 180°.

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