Gas diffusion layer, manufacturing method of the same, single fuel battery cell, and fuel battery stack

Abstract

To provide a gas diffusion layer capable of reducing a pressure applied to a portion where a gas diffusion layer and a frame body of a fuel battery overlap each other when the gas diffusion layer is used in the fuel battery.SOLUTION: A gas diffusion layer includes a conductive particle, a conductive fiber, and a polymer resin. When a thickness of at least a part of an outer edge part of the gas diffusion layer is thinner than that of the other part of the outer edge part of the gas diffusion layer, and a part of the outer edge part of the gas diffusion layer having a thin thickness is defined as a region A and the other part of the outer edge part of the gas diffusion layer is defined as a region B, a volume is calculated from a true density calculated from a density and a composition ratio of a material constituting the gas diffusion layer and an area and a film thickness of the region A and the region B of the gas diffusion layer. With respect to the porosity calculated by (the true density - bulk density) / the true density*100 based on the bulk density calculated by dividing the weight by the volume, a difference between a porosity of the region A and a porosity of the region B is within 10%.SELECTED DRAWING: Figure 5A

Description

[Technical Field]

[0001] The present disclosure relates to a gas diffusion layer and a manufacturing method thereof, a single fuel cell, and a fuel cell stack. [Background technology]

[0002] Gas diffusion layers have gas permeability and gas diffusibility and are used, for example, in fuel cells. In a polymer electrolyte fuel cell, one side of a proton-conductive polymer electrolyte membrane is exposed to a fuel gas such as hydrogen, and the other side is exposed to oxygen, synthesizing water through a chemical reaction via the electrolyte membrane, and the reaction energy generated during this process is extracted electrically.

[0003] A single fuel cell includes, for example, an electrolyte membrane, a pair of catalyst layers arranged to sandwich the electrolyte membrane, a pair of gas diffusion layers arranged to sandwich the electrolyte membrane with each catalyst layer interposed therebetween, a pair of separators arranged to sandwich the electrolyte membrane with each gas diffusion layer interposed therebetween, and a resin frame provided around the outer periphery of at least one surface of the electrolyte membrane. The assembly formed by joining the electrolyte membrane, the pair of catalyst layers, and the pair of gas diffusion layers is called a membrane electrode assembly. A fuel cell stack has a structure in which multiple single fuel cell cells are stacked.

[0004] Patent Document 1 discloses a membrane electrode assembly in which the thickness of the inner peripheral portion of the frame covered with the gas diffusion layer is thinner than the thickness of the other portions of the frame, thereby reducing the shear stress applied to the gas diffusion layer and effectively suppressing damage to the gas diffusion layer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-174650 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the membrane electrode assembly described in Patent Document 1, the overlapping portion of the gas diffusion layer and the frame is the thickest part of the membrane electrode assembly, and is subjected to the strongest pressure when the cells are fastened together. This damages the electrolyte membrane. As a result, the pressure applied to the periphery of the power generation portion (the overlapping portion of the electrolyte membrane, catalyst layer, and gas diffusion layer) is reduced, resulting in higher resistance and separator deformation, among other problems.

[0007] The present disclosure has been made in consideration of these circumstances, and aims to provide a gas diffusion layer that, when used in a fuel cell, can reduce the pressure applied to the area where the gas diffusion layer and the frame body overlap. [Means for solving the problem]

[0008] The gas diffusion layer according to the present disclosure is a gas diffusion layer comprising conductive particles, conductive fibers, and a polymer resin, wherein the thickness of at least a portion of the outer edge of the gas diffusion layer is thinner than the remaining portions of the outer edge of the gas diffusion layer, and where the thinner portion of the outer edge of the gas diffusion layer is designated Region A and the remaining portion of the outer edge of the gas diffusion layer is designated Region B, the true density is calculated from the density and composition ratio of the materials constituting the gas diffusion layer, and the bulk density is calculated by calculating the volume from the area and film thickness of Region A and Region B of the gas diffusion layer and dividing the weight by the volume. The porosity is calculated using (true density - bulk density) / true density x 100, and the difference between the porosity of Region A and the porosity of Region B is within 10%.

[0009] The single fuel cell according to the present disclosure is a single fuel cell comprising an electrolyte membrane, a pair of catalyst layers arranged to sandwich the electrolyte membrane, a pair of gas diffusion layers arranged to sandwich the electrolyte membrane between the pair of catalyst layers, a pair of separators arranged to sandwich the electrolyte membrane between the pair of gas diffusion layers and the pair of catalyst layers, and a frame provided around the outer periphery of at least one surface of the electrolyte membrane, wherein at least one of the pair of gas diffusion layers is the gas diffusion layer described above, and the gas diffusion layer is provided on the surface on which the frame is disposed, the inner edge of the frame overlaps with region A of the gas diffusion layer, and the pressure P1 applied to the separator by region A of the gas diffusion layer and the pressure P2 applied to the separator by region B of the gas diffusion layer satisfy the relationship 1≦P1 / P2<3.

[0010] The fuel cell stack according to the present disclosure has a structure in which a plurality of the above-described single fuel cell cells are stacked.

[0011] The method for manufacturing a gas diffusion layer according to the present disclosure includes the steps of: stirring and kneading conductive particles, conductive fibers, and a polymer resin with a dispersion solvent to obtain a kneaded mixture of conductive particles, conductive fibers, and a polymer resin; baking the kneaded mixture at a temperature equal to or higher than the decomposition temperature of the dispersion solvent to obtain a solid product from which the dispersion solvent has been removed; pulverizing the solid product from which the dispersion solvent has been removed to obtain a powder; and rolling the powder with a roll having protruding portions on part of its circumferential direction that extend in the width direction parallel to the rotation axis to form a sheet, and by rotation of the roll, obtaining a gas diffusion layer including a sheet having regions A and B, wherein the thickness of region A corresponding to the protruding portions is thinner than the thickness of region B corresponding to the other parts of the sheet. [Effects of the Invention]

[0012] As described above, when the gas diffusion layer according to the present disclosure is used in a fuel cell, the thickness of the portion where the gas diffusion layer overlaps with the frame of the fuel cell is reduced, thereby reducing the pressure applied to this portion and making it possible to provide a gas diffusion layer, a single fuel cell, and a fuel cell stack that can reduce damage to the electrolyte membrane. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is an exploded perspective view showing the configuration of a fuel cell stack according to a first embodiment of the present disclosure. [Figure 2] 1 is an exploded perspective view showing the configuration of a single fuel cell according to a first embodiment of the present disclosure. [Figure 3A] 1 is a schematic front view showing the overall planar configuration of a gas diffusion layer according to a first embodiment of the present disclosure. [Figure 3B] 3B is a partial cross-sectional view of the gas diffusion layer according to the first embodiment of the present disclosure, viewed in the direction AA of FIG. 3A. [Figure 4] 1 is a schematic diagram illustrating the arrangement of a frame and a cathode-side gas diffusion layer of a single fuel cell according to a first embodiment of the present disclosure. [Figure 5A] 5 is a partial cross-sectional view of the laminate according to the first embodiment of the present disclosure, as viewed in the direction BB in FIG. 4, before being sandwiched between a pair of separators. FIG. [Figure 5B] 5 is a partial cross-sectional view of the laminate according to the first embodiment of the present disclosure sandwiched between a pair of separators, as viewed in the direction BB in FIG. 4. FIG. [Figure 6] FIG. 2 is a schematic enlarged surface view showing the surface configuration of the gas diffusion layer according to the first embodiment of the present disclosure. [Figure 7] 1 is a schematic enlarged view showing an internal structure of a powder for a gas diffusion layer used in a method for manufacturing a gas diffusion layer according to a first embodiment of the present disclosure. [Figure 8] 3 is a flowchart showing a method for manufacturing a gas diffusion layer according to the first embodiment of the present disclosure. [Figure 9A] 1 is a schematic diagram showing a configuration of a manufacturing apparatus for a gas diffusion layer according to a first embodiment of the present disclosure. [Figure 9B] 3 is a schematic cross-sectional view showing a cross-sectional configuration of a second roll constituting the gas diffusion layer manufacturing apparatus according to the first embodiment of the present disclosure, viewed from the axial direction. FIG. [Figure 9C] 3 is a schematic cross-sectional view showing a cross-sectional configuration of a cross section including an axis viewed from a direction perpendicular to the axial direction of a second roll constituting the gas diffusion layer manufacturing apparatus according to the first embodiment of the present disclosure. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] The gas diffusion layer according to the first aspect is a gas diffusion layer comprising conductive particles, conductive fibers, and a polymer resin, wherein the thickness of at least a portion of the outer edge of the gas diffusion layer is thinner than the remaining portion of the outer edge of the gas diffusion layer, and the thinner portion of the outer edge of the gas diffusion layer is designated Region A and the remaining portion of the outer edge of the gas diffusion layer is designated Region B. The true density is calculated from the density and composition ratio of the materials constituting the gas diffusion layer, and the bulk density is calculated by calculating the volume from the area and film thickness of Region A and Region B of the gas diffusion layer and dividing the weight by the volume. The porosity is calculated using (true density - bulk density) / true density x 100, and the difference between the porosity of Region A and the porosity of Region B is within 10%.

[0015] A single fuel cell according to a second aspect is a single fuel cell comprising an electrolyte membrane, a pair of catalyst layers arranged to sandwich the electrolyte membrane, a pair of gas diffusion layers arranged to sandwich the electrolyte membrane between the pair of catalyst layers, a pair of separators arranged to sandwich the electrolyte membrane between the pair of gas diffusion layers and the pair of catalyst layers, and a frame provided around the outer periphery of at least one surface of the electrolyte membrane, wherein at least one of the pair of gas diffusion layers is the gas diffusion layer according to the first aspect, and the gas diffusion layer according to the first aspect is provided on the surface on which the frame is disposed, the inner edge of the frame overlaps with region A of the gas diffusion layer, and a pressure P1 applied by region A of the gas diffusion layer to the separator and a pressure P2 applied by region B of the gas diffusion layer to the separator satisfy the relationship 1≦P1 / P2<3.

[0016] A single fuel cell according to a third aspect may be the same as that of the second aspect, wherein the difference between the total thickness of the frame and region A of the gas diffusion layer and the thickness of region B of the gas diffusion layer is within 10%.

[0017] A fuel cell stack according to a fourth aspect has a structure in which a plurality of the fuel cell units according to the second aspect are stacked.

[0018] A method for producing a gas diffusion layer according to the fifth aspect includes the steps of: stirring and kneading conductive particles, conductive fibers, and a polymer resin with a dispersion solvent to obtain a kneaded mixture of conductive particles, conductive fibers, and a polymer resin; baking the kneaded mixture at a temperature equal to or higher than the decomposition temperature of the dispersion solvent to obtain a solid product from which the dispersion solvent has been removed; pulverizing the solid product from which the dispersion solvent has been removed to obtain a powder; and rolling the powder with a roll having protrusions on part of its circumference that extend in the width direction parallel to the rotation axis to form a sheet, and by rotation of the roll, obtaining a gas diffusion layer including a sheet having regions A and B, wherein the thickness of region A of the sheet corresponding to the protrusions is thinner than the thickness of region B of the sheet corresponding to the areas other than the protrusions.

[0019] Hereinafter, a gas diffusion layer, a fuel cell unit, a fuel cell stack, and a method for manufacturing a gas diffusion layer according to embodiments of the present disclosure will be described with reference to the drawings.

[0020] (Embodiment 1) <Fuel cell stack> 1 is an exploded perspective view showing the configuration of a fuel cell stack 100 in which a plurality of fuel cell units 1 are stacked, which is an example of a fuel cell according to a first embodiment of the present disclosure (hereinafter also referred to as a "polymer electrolyte fuel cell stack"). Note that the first embodiment is not limited to polymer electrolyte fuel cells, and can be applied to various types of fuel cells.

[0021] In the fuel cell stack 100, a gasket (not shown in FIG. 1) is provided between adjacent unit fuel cell cells 1. A current collector plate 110, an insulating plate 120, and a fastening plate 130 are arranged in this order on each of both side ends in the stacking direction of the unit fuel cell 1. A predetermined load is then applied to the fastening plate 130 from both ends in the stacking direction, thereby fastening multiple stacked unit fuel cell cells 1 together to form the fuel cell stack 100.

[0022] Each current collecting plate 110 is provided with a terminal 101a for extracting current. When the single fuel cell 1 generates power, current is extracted from the terminal 110a. Each insulating plate 120 provides insulation between the current collecting plate 110 and the fastening plate 130. The insulating plate 120 may be provided with an inlet and outlet (not shown) for gas or cooling water. A predetermined load is applied to each fastening plate 130 from the outside. In this way, the pair of fastening plates 130 fasten together the stacked multiple single fuel cell cells 1, the pair of current collecting plates 110, and the pair of insulating plates 120. The structure of the single fuel cell 1 will be described in detail below.

[0023] <Fuel cell unit> Fig. 2 is an exploded perspective view showing the configuration of a single fuel cell 1 according to embodiment 1 of the present disclosure. In Fig. 2, the single fuel cell 1 has a structure in which a membrane electrode assembly (MEA) 2, an anode-side sealing member 10A, a cathode-side sealing member 10B, and a frame 6 are sandwiched between a pair of separators 4A and 4B. The MEA 2 is composed of a polymer electrolyte membrane 31, an anode-side catalyst layer 32A, an anode-side gas diffusion layer 40A, a cathode-side catalyst layer 32B, and a cathode-side gas diffusion layer 40B.

[0024] <Gas diffusion layer 40> FIG. 3A is a schematic front view showing the overall planar configuration of the gas diffusion layer 40 according to the first embodiment of the present disclosure. The gas diffusion layer 40 has a portion at its outer periphery (outer edge) that is thinner than the other portions. The thinner portion at the outer periphery is designated Region A, and the other portion at the outer periphery is designated Region B. The width of Region A is preferably 0.5 mm to 20 mm. If it is less than 0.5 mm, there is a possibility that the layer will not overlap with the frame 6 due to misalignment during lamination. On the other hand, if it is 20 mm or more, the thin film thickness will result in low strength, which may result in bending or curling. Note that, while Region A is present on all four sides of the outer periphery of the gas diffusion layer 40 in FIG. 3A, this is not limiting. For example, Region A may be present on at least a portion of the outer periphery (outer edge), preferably on at least one side of the outer periphery.

[0025] FIG. 3B is a partial cross-sectional view of the gas diffusion layer according to the first embodiment of the present disclosure, viewed along the AA direction in FIG. 3A. Let L1 be the membrane thickness in region A, and L2 be the membrane thickness in region B. L1 is preferably 10 μm or more and 100 μm or less. If L1 is less than 10 μm, the force with which region A presses frame 6 against electrolyte membrane 31 is weak, resulting in weak adhesion between the two and the risk of gas leakage. On the other hand, if L1 is greater than 100 μm, the membrane thickness at the portion where region A and frame 6 overlap becomes thicker, reducing the effect of reducing pressure in this portion. Preferably, L2 is 50 μm or more and 500 μm or less. If L2 is less than 50 μm, the flow rate of gas flowing (in the in-plane direction) inside the gas diffusion layer decreases, making it difficult to supply gas to the entire surface of the catalyst layer. On the other hand, if L2 is greater than 500 μm, the resistance (in the membrane thickness direction) of the gas diffusion layer increases, resulting in reduced power generation performance. When the gas diffusion layer is used in a single fuel cell, the difference between the total thickness of the frame of the single fuel cell and region A of the gas diffusion layer and the thickness of region B of the gas diffusion layer may be substantially the same, for example, within 10%. Specifically, the film thickness L1 of region A may be thinner than the film thickness L2 of region B by the thickness of the frame used in the single fuel cell. This reduces the pressure applied to the overlapping portion of the gas diffusion layer and the frame of the fuel cell, thereby reducing damage to the electrolyte membrane.

[0026] Before use in a single fuel cell, i.e., before load application, the difference between the porosity of region A and the porosity of region B of the gas diffusion layer 40 is within 10%. If the porosity of region A is 10% greater than the porosity of region B, region A is likely to become thinner, reducing the force with which region A presses the frame 6 against the electrolyte membrane 31, weakening the adhesion between them and potentially resulting in gas leakage. On the other hand, if the porosity of region A is less than 10% greater than the porosity of region B, region A is unlikely to become thinner, and the thickness of the overlapping portion between region A and the frame 6 is not reduced, reducing the effect of reducing pressure in this portion. Preferably, the porosity of region A and region B are equal. In other words, region A is not thinned by compression, but has a thin thickness while maintaining the same porosity as region B. The porosity of region A and region B of the gas diffusion layer 40 can be calculated using the following formula. Details of the gas diffusion layer and its manufacturing method will be described later. Porosity = (true density - bulk density) / true density x 100 The true density is calculated from the density and composition ratio of the materials that make up the gas diffusion layer 40. The bulk density is calculated by calculating the volume from the areas of region A and region B of the gas diffusion layer and the film thickness, and dividing the weight measured with an electronic balance by the volume.

[0027] Fig. 4 is a schematic diagram of the arrangement of the frame 6 and cathode-side gas diffusion layer 40B of a single fuel cell according to the first embodiment of the present disclosure. Fig. 4 shows a membrane electrode assembly (MEA) 2 sandwiched between a pair of separators 4A, 4B, but for the sake of convenience in explaining the internal arrangement structure of the single fuel cell 1, the separator 4B and the cathode-side seal member 10B are omitted from the illustration. Fig. 4 also shows the cathode-side gas diffusion layer 40B side of the fuel cell 1 as an example. Figs. 5A and 5B are partial cross-sectional views of the frame 6 and cathode-side gas diffusion layer 40B of Fig. 4 as viewed in the direction BB.

[0028] 5A shows the membrane electrode assembly 2 before it is sandwiched between the pair of separators 4A and 4B, and Fig. 5B shows the membrane electrode assembly 2 sandwiched between the pair of separators 4A and 4B. The anode-side separator 4A is disposed on the surface of the anode-side gas diffusion layer 40A opposite to the anode-side catalyst layer 32A, and the cathode-side separator 4B is disposed on the surface of the cathode-side gas diffusion layer 40B opposite to the cathode-side catalyst layer 32B.

[0029] <Frame 6> The frame 6 is a member disposed between the pair of separators 4A, 4B and surrounds the outer periphery of the polymer electrolyte membrane. Therefore, the MEA 2 is housed in a space partitioned by the separators 4A, 4B and the frame 6. As shown in Fig. 4, the frame 6 has a fuel supply manifold 60A, an oxidant discharge manifold 70B, and a cooling water manifold 80 at one end, and a fuel discharge manifold 60B, an oxidant supply manifold 70A, and a cooling water manifold 80 at the other end opposite the one end.

[0030] The frame 6 is injection-molded from polyphenylene ether resin, which has excellent chemical resistance, heat resistance, and insulating properties. However, thermoplastic resins such as polyphenylene sulfide, polypropylene, and polyethylene, and thermosetting resins such as epoxy can also be used. The film thickness of the frame 6 is designated L3. L3 is preferably 10 μm or more and 200 μm or less.

[0031] 5A, the frame 6 may be disposed only between the polymer electrolyte membrane 31 and the cathode-side gas diffusion layer 40B (region A), but is not limited thereto. For example, after region A is formed in the anode-side gas diffusion layer 40A, the frame 6 may be disposed only between the electrolyte membrane 31 and the anode-side gas diffusion layer 40A. Alternatively, two frames may be disposed on both the anode side and the cathode side, stacked one on the other.

[0032] At the contact area between the frame 6 and the polymer electrolyte membrane 31, the anode-side gas diffusion layer 40A and the cathode-side gas diffusion layer 40B are present between the anode-side separator 4A and the cathode-side separator 4B, and by pressing the frame 6 and the electrolyte membrane 31 together, adhesion is enhanced and gas leakage is suppressed.

[0033] <Polymer electrolyte membrane 31> The polymer electrolyte membrane 31 may be a sheet of a polymer electrolyte having hydrogen ion conductivity, but it is preferable that the polymer electrolyte has excellent heat resistance and chemical stability. Examples of the polymer electrolyte include perfluorocarbon sulfonic acid polymers. Examples of the perfluorocarbon sulfonic acid polymer include Nafion (registered trademark).

[0034] <Catalyst layer 32> The catalyst layers 32 (anode-side catalyst layer 32A, cathode-side catalyst layer 32B) contain ion exchange resin, catalyst particles, and, in some cases, carbon particles supporting the catalyst particles. The ion exchange resin in the catalyst layer 32 connects the catalyst particles to the polymer electrolyte membrane 31 and serves to conduct protons between them. This ion exchange resin can be made of the same polymer material as the polymer electrolyte membrane 31. As catalyst particles, for example, Pt or a Pt—Ru alloy can be used as the catalyst metal for the anode-side catalyst layer 32A. For example, Pt or a Pt—Co alloy can be used as the catalyst metal for the cathode-side catalyst layer 32B. Furthermore, for example, acetylene black, ketjen black, carbon nanotubes, or the like can be used as the carbon particles.

[0035] The catalyst layer 32 may have an end portion in contact with the frame 6 as shown in FIG. 5B, or may not have an end portion in contact with the frame 6, or may be sandwiched between the frame 6 and the electrolyte membrane 31.

[0036] <Sealing member 10> The anode-side sealing member 10A and the cathode-side sealing member 10B are each disposed between the frame 6 and the opposing separator. The anode-side sealing member 10A and the cathode-side sealing member 10B are made of elastic material and are pressed into close contact with the frame 6, sealing the outer periphery of the MEA 2 and the outer periphery of the manifold. This prevents leakage of fuel gas, oxidant gas, and coolant. The anode-side sealing member 10A and the cathode-side sealing member 10B may also be formed on the separators 4A and 4B in advance.

[0037] <Separator 4> The separators 4 (anode-side separator 4A, cathode-side separator 4B) mechanically sandwich and fix the membrane electrode assembly 2, i.e., the anode-side gas diffusion layer 40A and the cathode-side gas diffusion layer 40B, and electrically connect adjacent membrane electrode assemblies 2 in series. The separators 4 also serve as paths for supplying gas to the anode-side gas diffusion layer 40A and the cathode-side gas diffusion layer 40B and for carrying away the generated water and excess gas. Fluid channels 5 (anode-side fluid channel 5A, cathode-side fluid channel 5B) for supplying gas are formed on the inner surface of the separator 4 (the surface facing the anode-side gas diffusion layer 40A and the cathode-side gas diffusion layer 40B). The separator 4 also has a cooling water channel (not shown) for cooling the membrane electrode assembly 2 on the surface opposite the membrane electrode assembly 2. The cooling water channel is connected to a cooling water manifold 80.

[0038] Separators 4A and 4B may be made of any material as long as they are airtight, electronically conductive, and electrochemically stable. Although there are no particular limitations on the material, materials with excellent corrosion resistance are suitable, and for example, carbon-based and metal-based materials can be used.

[0039] <Reaction> The following reactions occur in a solid polymer electrolyte fuel cell unit cell 1. When hydrogen gas is supplied as a fuel gas to the anode catalyst layer 32A via the anode gas diffusion layer 40A, the reaction shown in formula (1) below occurs in the anode catalyst layer 32A, and hydrogen is decomposed into protons and electrons. The protons move through the polymer electrolyte membrane 31 toward the cathode catalyst layer 32B. The electrons move to an external circuit (not shown) via the anode gas diffusion layer 40A and separator 4A, and then flow from the external circuit into the cathode catalyst layer 32B via the separator 4B and the cathode gas diffusion layer 40B. When air is supplied as an oxidant gas to the cathode catalyst layer 32B via the cathode gas diffusion layer 40B, the reaction shown in formula (2) below occurs in the cathode catalyst layer 32B, and oxygen in the air reacts with the protons (hydrogen ions) and electrons to form water. As a result, electrons flow from the anode to the cathode in an external circuit, and electric power can be extracted.

[0040] Anode-side catalyst layer 32A: H2→2H + +2e - ···(1) Cathode-side catalyst layer 32B:2H + +(1 / 2)O2+2e - →H2O (2)

[0041] <Assembly> As shown in Fig. 5A, the separators 4 are arranged so that the membrane electrode assembly 2 is interposed between the pair of separators 4. When a predetermined load is applied to the pair of fastening plates 130 (see Fig. 1), the anode side separator 4A and the cathode side separator 4B are displaced in a direction toward each other. The separators 4 (4A, 4B) then press the membrane electrode assembly 2 with a predetermined pressure, resulting in the state shown in Fig. 5B.

[0042] When the membrane electrode assembly 2 is pressed with a predetermined pressure, the pressure exerted by the region A of the gas diffusion layer 40 on the separator 4 (i.e., the pressure exerted by the frame 6 on the polymer electrolyte membrane 31) is defined as P1, and the pressure exerted by the region B of the gas diffusion layer 40 on the separator 4 (i.e., the pressure exerted by the catalyst layer 32 on the polymer electrolyte membrane 31) is defined as P2. 1 ≦ P1 / P2 < 3 The relationship between P1 and P2 is satisfied. During assembly, P1 and P2 can be measured by sandwiching, for example, pressure-sensitive paper (Fujifilm Corporation's Prescale Extra-Low Pressure (LLLW) or Ultra-Low Pressure (LLW)) between the gas diffusion layer 40 and the separator 4 and pressing the paper at a predetermined pressure.

[0043] <Details of the gas diffusion layer 40> The configuration of the gas diffusion layer 40 according to the first embodiment of the present disclosure will be described in detail with reference to FIG. 6. FIG. 6 is a schematic enlarged surface view showing the surface configuration of the gas diffusion layer 40. The gas diffusion layer 40 includes conductive particles 41, conductive fibers 42, and a polymer resin 43. The gas diffusion layer 40 is preferably a free-standing membrane supported by the conductive particles 41, conductive fibers 42, and polymer resin 43. A free-standing membrane refers to a membrane having a self-supporting structure.

[0044] As shown in FIG. 6 , the gas diffusion layer 40 is formed by powder particles 44 containing conductive particles 41, conductive fibers 42, and a polymer resin 43, which are bonded together by the polymer resin 43 present around the powder particles. Therefore, grain boundaries 45 exist between the particles of the powder 44 in the gas diffusion layer 40. The grain boundaries 45 are defined to include both the interfaces where the powder particles 44 are bonded together by the polymer resin 43 and the micro-gaps where the powder particles 44 are not completely bonded together. The gas diffusion layer 40 according to the present disclosure has grain boundaries 45 formed on the surface of the gas diffusion layer 40 by rolling the powder 44 containing conductive particles 41, conductive fibers 42, and a polymer resin 43, and the area ratio of the grain boundaries 45 to the surface area of ​​the gas diffusion layer 40 is 5% or more. The surface of the gas diffusion layer 40 refers to both the surfaces that come into contact with the catalyst layer and the separator.

[0045] Here, we will discuss the role of the grain boundaries 45 between the powder particles 44 that make up the gas diffusion layer 40. Conductive particles 41 and conductive fibers 42 are dispersed within the powder 44 and bound together by a polymer resin 43. Within the powder, there are pores with submicron pore radii (0.1 to 0.3 μm) that form gaps between the conductive particles 41 and the conductive fibers 42. These submicron pores function as diffusion paths for gas and water vapor while preventing water from passing through. Meanwhile, the grain boundaries 45 of the powder 44 are composed of interfaces and minute gaps bound together by the polymer resin 43, some of which are several microns wide. Therefore, the grain boundaries 45 function to expel condensed water generated in the gaps at the interface between the catalyst layer 32 and the gas diffusion layer 40, or condensed water generated by the condensation of water vapor within the submicron pores of the powder 44 inside the gas diffusion layer 40, via capillary action. Therefore, if the grain boundary area ratio of the gas diffusion layer 40 is smaller than 5%, the discharge of condensed water generated at the interface between the catalyst layer 32 and the gas diffusion layer 40 and inside the powder 44 inside the gas diffusion layer 32 will be impaired, particularly during highly humidified power generation, impairing gas diffusion and deteriorating battery performance.

[0046] The particle size of the powder 44, which includes conductive particles, conductive fibers, and a polymer resin and constitutes the gas diffusion layer 40, is, for example, 30 μm to 300 μm. More preferably, it is 50 μm to 150 μm. When the particle size of the powder 44 is smaller than 30 μm, many grain boundaries 45 are present within the gas diffusion layer 40. As described above, the grain boundaries 35 function to drain condensed water. However, when many grain boundaries 45 are present, the grain boundaries 45 inhibit the diffusion of gas and water vapor through the submicron pores within the powder 44, resulting in reduced gas diffusivity and poor battery performance. On the other hand, when the particle size of the powder 44 is larger than 300 μm, the grain boundaries 45 between the powder particles 44 decrease the number of interfaces bonded by the polymer resin and the gaps between the powder particles 34 become too large. This reduces the strength of the gas diffusion layer 40 and makes it unable to exist as a free-standing membrane.

[0047] The arithmetic mean height Sa of the surface of the gas diffusion layer 40 is, for example, 3 μm or less, and more preferably 2 μm or less. If the arithmetic mean height Sa of the surface of the gas diffusion layer 40 is greater than 3 μm, gaps on the order of microns will be generated at the contact surfaces with the catalyst layer and the separator, causing condensed water to accumulate in the gaps, reducing gas diffusibility and deteriorating battery performance.

[0048] The pores inside the gas diffusion layer 40 have multiple functions. The first function is to diffuse the fuel gas and oxidant gas flowing through the separator's gas flow path to the catalyst 32. The second function is to control the water generated by the reaction, retaining moisture in the catalyst layer 32 and the polymer electrolyte membrane 31 while quickly discharging excess water through the pores. The third function is to transport moisture in the humidified fuel gas and oxidant gas to the catalyst layer 32 and the polymer electrolyte membrane 31 under conditions where the catalyst 32 and the polymer electrolyte membrane 31 cannot retain moisture sufficiently with the generated water alone, thereby ensuring proton conductivity. Pores with a pore radius of 0.1 μm to 0.3 μm inside the gas diffusion layer 32 ensure sufficient permeability to water vapor. However, they have poor permeability to condensed water and micromist. Therefore, the catalyst layer 32 and the polymer electrolyte membrane 31 can be maintained in an appropriate moisture content while excess moisture can be quickly discharged as water vapor. The pores with a pore radius of 0.1 μm or more and 0.3 μm or less are formed by gaps between the conductive fibers 42. Therefore, by making the amount of conductive fibers 32 constituting the gas diffusion layer 40 greater than the amount of conductive particles 31, it is possible to form the peak pore radius in the gas diffusion layer 40 in the range of 0.1 μm or more and 0.3 μm or less. Furthermore, the gas diffusion layer 40 has pores with a pore radius of 0.055 μm or more and 0.4 μm or less, with a pore volume of 0.80 mL / g or less. If the pore volume of a pore radius of 0.055 μm or more and 0.4 μm or less exceeds 0.80 mL / g, the amount of water vapor discharge increases, and the water retention of the catalyst layer 32 and the polymer electrolyte membrane 31 decreases, particularly during operation at low humidification, which reduces proton conductivity and deteriorates battery performance.

[0049] In the gas diffusion layer 40, the orientation degree of the conductive fibers 42 is 30% to 70% and the orientation degree of the polymer resin 43 is 5% to 70%. The orientation directions of the conductive fibers 42 and the polymer resin 43 are parallel to the rolling direction (MD) during production of the gas diffusion layer 40. The gas diffusion layer 40 is continuously produced by rolling a powder composed of conductive particles 41, conductive fibers 42, and polymer resin 43. By orienting the conductive fibers 42 and the polymer resin 43 in the rolling direction (MD) during roll rolling and increasing the tensile breaking strength in the orientation direction, it is possible to prevent breakage of the gas diffusion layer during continuous production by roll rolling. If the orientation degree of the conductive fibers 42 is less than 30% or the orientation degree of the polymer resin 43 is less than 5%, the tensile breaking strength of the gas diffusion layer 40 in the rolling direction decreases, making it more likely to break during continuous production. On the other hand, if the orientation degree of the conductive fibers 42 is greater than 70% or the orientation degree of the polymer resin 43 is greater than 70%, the tensile breaking strength in the direction perpendicular to the rolling direction (TD direction) becomes smaller, and cracks become more likely to occur in the gas diffusion layer 40.

[0050] The conductive particles 41 can be made of carbon materials such as carbon black, graphite, and activated carbon. Of these, it is preferable to use carbon black, which has high conductivity and a large pore volume. As carbon black, acetylene black, ketjen black, furnace black, and vulcan can be used. Of these, it is preferable to use acetylene black, which has a low impurity content, or ketjen black, which has a large specific surface area and high conductivity.

[0051] The conductive fibers 42 contribute to improving the electrical conductivity and mechanical strength of the gas diffusion layer 40. The material of the conductive fibers 42 is not particularly limited, but may be, for example, carbon fibers such as carbon nanotubes. The average fiber diameter of the conductive fibers 42 is preferably 50 nm or more and 300 nm or less. When the average fiber diameter of the conductive fibers 42 is 50 nm or more, this more effectively contributes to improving the conductivity of the gas diffusion layer 40, and the mechanical strength of the gas diffusion layer 40 can be further increased, so that the gas diffusion layer 40 can have sufficient strength as a self-supporting membrane. Furthermore, when the average fiber diameter of the conductive fibers 42 is 300 nm or less, the diameter does not become too large, making it easier to ensure a sufficient pore volume in the porous member, and further improving the gas diffusibility of the gas diffusion layer 40. The average fiber length of the conductive fibers 43 is preferably 0.5 μm or more and 50 μm or less. When the average fiber length of the conductive fibers 43 is 0.5 μm or more, this more effectively contributes to improving the conductivity of the gas diffusion layer 40 and can further increase the mechanical strength of the gas diffusion layer 40. Furthermore, when the average fiber length of the conductive fibers 43 is 50 μm or less, the fibers do not become too long, and the conductive fibers 43 are crushed without forming lumps during production, thereby further improving the gas diffusibility of the gas diffusion layer 40.

[0052] Examples of polymer resin 43 include PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PVDF (polyvinylidene fluoride), ETFE (tetrafluoroethylene-ethylene copolymer), PCTFE (polychlorotrifluoroethylene), and PFA (polyfluoroethylene-perfluoroalkyl vinyl ether copolymer). Among these, PTFE is preferred as polymer resin 43 from the viewpoints of heat resistance, water repellency, and chemical resistance. PTFE may be used as a raw material in the form of a dispersion or powder. Among these, dispersion is preferred due to its excellent dispersibility. Polymer resin 43 functions as a binder that binds conductive particles 41 and conductive fibers 42 together. Furthermore, because polymer resin 43 is water-repellent, it also serves to prevent water from accumulating in the pores inside gas diffusion layer 40 and inhibiting gas permeation. Furthermore, in the gas diffusion layer 40, the conductive particles 41 are present in the gaps between the conductive fibers 42, and the conductive fibers 42 and the conductive particles 41 can be well bound together by the fibrous polymer resin 43, so that the gas diffusion layer 40 can have sufficient strength.

[0053] The gas diffusion layer 40 preferably contains 5 wt% or more and less than 35 wt% of conductive particles 41. That is, the content of conductive particles 41 is preferably 5 wt% or more and less than 35 wt% of the entire gas diffusion layer 40. When the content of conductive particles 41 is 5 wt% or more, the amount of conductive particles 41 that fills the gaps between the conductive fibers 42 is sufficient, so the bulk resistance of the gas diffusion layer 40 is unlikely to be high. Furthermore, when the content of conductive particles 41 is less than 35 wt%, the gaps between the conductive fibers 42 are not reduced too much, so water discharge and gas diffusion are further improved.

[0054] The gas diffusion layer 40 preferably contains 35 wt% or more and 80 wt% or less of the conductive fibers 42. That is, the content of the conductive fibers 42 is preferably 35 wt% or more and 80 wt% or less of the entire gas diffusion layer 40. When the content of the conductive fibers 42 is 35 wt% or more, the gaps between the conductive fibers 42 are not reduced too much, resulting in good water discharge properties and gas diffusion properties. Furthermore, when the content of the conductive fibers 42 is 80 wt% or less, the amount of particles filling the gaps between the conductive fibers 42 is sufficient, so the bulk resistance of the gas diffusion layer 40 is unlikely to be high.

[0055] The gas diffusion layer 40 preferably contains 10 wt% or more and 40 wt% or less of the polymer resin 43. That is, the content of the polymer resin 43 is preferably 10 wt% or more and 40 wt% or less of the entire gas diffusion layer 40. When the content of the polymer resin 43 is 10 wt% or more, the polymer resin 43 functions sufficiently as a binder, thereby increasing the tensile breaking strength of the gas diffusion layer 40. Therefore, even when gas pressure or swelling and shrinkage of the electrolyte membrane occurs, the gas diffusion layer 40 is less likely to break, and the durability of a fuel cell using the gas diffusion layer 40 is improved. Furthermore, when the content of the polymer resin 43 is 40 wt% or more, the bulk resistance of the gas diffusion layer 40 is less likely to increase, thereby improving cell performance.

[0056] <Gas diffusion layer powder 46> Next, the gas diffusion layer powder 46 will be described with reference to FIG. 7 . FIG. 7 is a schematic enlarged view showing the internal structure of the gas diffusion layer powder 46 used in the manufacturing method of a gas diffusion layer according to the first embodiment of the present disclosure. The gas diffusion layer powder 46 is a powder before being rolled to manufacture the gas diffusion layer 40 of the present disclosure. A detailed manufacturing method will be described later. As shown in FIG. 7 , the gas diffusion layer powder 46 is a powder containing conductive particles 41, conductive fibers 42, and a polymer resin 43. The shape of the gas diffusion layer powder 46 can be a sphere, an ellipsoid, a cylinder, a cube, a rectangular parallelepiped, or the like. However, a sphere or an ellipsoid is preferable to improve the flowability of the powder. The gas diffusion layer powder 46 has an average particle diameter of, for example, 30 μm to 300 μm, more preferably 50 μm to 150 μm. If the average particle size of the gas diffusion layer powder 46 is smaller than 30 μm, the average particle size of the powder 44 inside the gas diffusion layer 40 manufactured by roll-pressing will also be smaller than 30 μm. Therefore, as described above, many grain boundaries 45 will be present inside the gas diffusion layer 40. The presence of many grain boundaries 45 inhibits the diffusion of gas and water vapor through submicron pores inside the powder 44, resulting in reduced gas diffusivity and poor battery performance. On the other hand, if the average particle size of the gas diffusion layer powder 46 is larger than 300 μm, the average particle size of the powder 44 inside the gas diffusion layer 40 manufactured by roll-pressing will also be larger than 300 μm. Therefore, as described above, the grain boundaries 45 between the powder particles 44 inside the gas diffusion layer 40 will reduce the number of interfaces bonded by the polymer resin and the gaps between the powder particles 44 will become too large, reducing the strength of the gas diffusion layer 40 and making it unable to function as a free-standing membrane.

[0057] Next, the pores inside the gas diffusion layer powder 46 will be described. As described above, the gas diffusion layer 40 is composed of powder 44 containing conductive particles 41, conductive fibers 42, and polymer resin, and grain boundaries between the powder particles. Here, the powder 44 is a powder obtained by rolling the gas diffusion layer powder 46 with a roll to bond the gas diffusion layer powder 46 together. When the gas diffusion layer powder 46 is rolled, pressure and shear force are applied, and the polymer resin is transformed into a fibrous form by the shear force, which becomes the powder 44.

[0058] <Method of manufacturing the gas diffusion layer 40> Next, a method for manufacturing the gas diffusion layer 40 according to the first embodiment of the present disclosure will be described. Fig. 8 is a flowchart showing a method for manufacturing the gas diffusion layer 40. Note that the method for manufacturing the gas diffusion layer 40 according to the present disclosure is not limited to the flowchart of Fig. 8 and the manufacturing method described below, and may be modified within the scope of the present disclosure.

[0059] In step S1, the conductive particles 41, the conductive fibers 42, and the polymer resin 43 are stirred and kneaded in a dispersion solvent to obtain a kneaded mixture of the conductive particles 41, the conductive fibers 42, and the polymer resin 43. For example, a planetary mixer, a hybrid mixer, a kneader, a roll mill, or the like can be used to knead the materials in step S1. In step S1, which is the kneading process, the conductive particles 41, the conductive fibers 42, the surfactant, and the dispersion solvent, excluding the polymer resin 43, are first kneaded and dispersed, and then the polymer resin 43 is added and stirred, thereby achieving a state in which the polymer resin 43 is uniformly dispersed in the kneaded mixture.

[0060] In step S2, the kneaded mixture is fired at a temperature equal to or higher than the decomposition temperature of the dispersion solvent to remove the dispersion solvent and obtain a solid. For example, an IR oven, a hot air oven, or the like can be used for firing in step S2. The firing temperature is set to a temperature higher than the decomposition temperature of the surfactant and lower than the melting temperature of the polymer resin 43. The reason for this is as follows: If the firing temperature is lower than the decomposition temperature of the surfactant, the surfactant remains inside the gas diffusion layer 40, making the interior of the gas diffusion layer 40 hydrophilic and causing water to accumulate, which may reduce the gas permeability of the gas diffusion layer 40. On the other hand, if the firing temperature is higher than the melting point of the polymer resin 43, the polymer resin 43 melts, which may reduce the strength of the gas diffusion layer 40. Specifically, for example, when PTFE is used as the polymer resin 43, the firing temperature is preferably 280°C or higher and 340°C or lower. The firing time is set according to the firing temperature so that the residual dispersion solvent is 1 wt% or less.

[0061] In step S3, the solid material from which the dispersion solvent has been removed is pulverized to obtain gas diffusion layer powder 46. The pulverization in step S3 is not particularly limited as long as it is an apparatus capable of pulverizing to an average particle size of 30 μm to 300 μm, and for example, a cutter mill, a jet mill, a pin mill, or the like can be used. Furthermore, gas diffusion layer powder 46 can also be obtained by classifying the powder particles after pulverization into particles with an average particle size of 30 μm to 300 μm. A vibrating sieve, a rotary sieve, or the like can be used to classify the powder after pulverization.

[0062] In step S4, the pulverized powder is rolled into a sheet to obtain the gas diffusion layer 40. A horizontal roll press with two rolls arranged horizontally can be used for the roll rolling in step S4. The gas diffusion layer powder 46 produced in step S3 is fed between the two rolls using a conveyor, ultrasonic feeder, or the like, and a shear force is applied to the polymer resin 43 with a roll press force of, for example, 0.01 ton / cm to 4 ton / cm to fibrillate the polymer resin 43. The fibrillated polymer resin 43 can produce a gas diffusion layer 40 with high strength. The powder-formed sheet can be re-rolled with rolls one or more times to improve the thickness accuracy and tensile breaking strength of the gas diffusion layer 40. The present disclosure is not limited to the first embodiment, but can be implemented in various other modes.

[0063] <Gas Diffusion Layer 40 Manufacturing Apparatus> 9A is a schematic diagram showing a gas diffusion layer manufacturing apparatus (roll press apparatus) 50 according to the first embodiment of the present disclosure. The gas diffusion layer manufacturing apparatus 50 includes a pair of opposing rolls (a first roll 52 and a second roll 53) for rolling the gas diffusion layer powder 46, a hopper 51 installed at an upper portion on the upstream side between the first roll 52 and the second roll 53, and a gas diffusion layer recovery unit 54 installed below the rolls.

[0064] The powder supply unit comprises a hopper 51 installed above between the first roll 52 and the second roll 53, and a belt conveyor unit (not shown) that supplies the gas diffusion layer powder 46 to the hopper 51. Although not shown, an in-line film thickness measuring device may be installed below the first and second rolls 52 and 53. By controlling the gap and load between the first roll 52 and the second roll 53 based on the measured film thickness, variations in film thickness, porosity, and film strength can be reduced. The first and second rolls 52 and 53 that roll the powder may roll at the same speed or may have different peripheral speeds.

[0065] FIG. 9B is a schematic cross-sectional view showing the cross-sectional configuration of the second roll 53 as viewed from the axial direction. FIG. 9C is a schematic cross-sectional view showing the cross-sectional configuration of the second roll 53 along a cross section including the axis as viewed from a direction perpendicular to the axial direction. The surface of the second roll 53 is provided with protrusions 55 extending parallel to the axial direction, as shown in FIGS. 9B and 9C. During roll pressing, the number of gas diffusion layer powders 46 supplied to the protrusions 55 is reduced, allowing for the creation of thin portions of the gas diffusion layer 40 without changing the porosity of the remaining portions. By cutting unnecessary portions of the gas diffusion layer 40 so that these thin portions become the outer edge, a gas diffusion layer 40 having region A can be created. Changing the shape of the protrusions 55 allows for the creation of gas diffusion layers 40 with region A of various sizes and shapes. The present disclosure is not limited to the above-described embodiment and can be implemented in various other forms.

[0066] [Example] Hereinafter, examples of the present disclosure will be described. (material) The materials used in manufacturing the gas diffusion layers of Example 1 and Comparative Example 1 are as follows. [Conductive particles 31] Li-400 (manufactured by Denka) [Conductive Fiber 32] VGCF (Showa Denko, VGCF-H) [Polymer resin 33] PTFE dispersion (manufactured by Daikin), average particle size 0.25 μm

[0067] (Production of gas diffusion layer of Example 1) The gas diffusion layer of Example 1 was produced by the following method. (1) First, 15 wt% of conductive particles 41, 65 wt% of conductive fibers 42, and 20 wt% of polymer resin 43 were mixed, and then a surfactant and a dispersion solvent were added, followed by kneading using a planetary mixer. (2) Next, the kneaded mixture was baked in a hot air oven at 300°C for 4 hours to remove the surfactant and dispersion solvent. At that time, it was confirmed using TG / DTA that the residual surfactant was 1% or less. (3) After that, the fired mixture was pulverized using a cutter mill to prepare powder 46 for gas diffusion layers.

[0068] (4) Next, the gas diffusion layer powder 46 was placed in a roll press device having protrusions 55 on the surface of a second roll 53, pressed with a pressing force of 0.2 ton / cm, and formed into a sheet. Unnecessary portions were then cut off to produce a gas diffusion layer 40 having region A. At this time, the thickness L1 of region A of the gas diffusion layer was 120 μm, and the thickness of the gas diffusion layer (thickness L2 of region B) was 160 μm. The width of region A was 4 mm, and the porosity of regions A and B of the gas diffusion layer was both 65%.

[0069] (Production of gas diffusion layer of Comparative Example 1) The gas diffusion layer of Comparative Example 1 was produced by the following method. A gas diffusion layer powder 46 was prepared in the same manner as in Example 1. The gas diffusion layer powder 46 was then placed in a roll press device having a second roll with no protrusions on its surface and pressed into a sheet at a pressing force of 0.2 ton / cm to prepare a gas diffusion layer without region A. The thickness of the gas diffusion layer was 160 μm. The porosity of the gas diffusion layer was 65%.

[0070] The relationship between the load and the shrinkage rate of the membrane thickness of the gas diffusion layers in Example 1 and Comparative Example 1 is shown in Table 1.

[0071] [Table 1]

[0072] (Manufacturing of fuel cell units) An ink for forming a cathode catalyst layer was prepared by dispersing a catalyst-supported carbon (TEC10E50E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., 50% by mass of Pt) in which platinum particles were supported on carbon powder as an electrode catalyst, and a polymer electrolyte solution (Nafion dispersion) with hydrogen ion conductivity in a mixed dispersion medium of ethanol and water (mass ratio 1:1). The polymer electrolyte was added so that the mass of the polymer electrolyte in the catalyst layer after coating was 0.4 times the mass of the catalyst-supported carbon.

[0073] The obtained ink for forming a cathode catalyst layer was applied by spraying to one side of a polymer electrolyte membrane (GSII manufactured by Japan Gore-Tex Co., Ltd., 120 mm × 120 mm) so that the platinum loading was 0.3 mg / cm 2 The cathode catalyst layer was formed so that: Next, similar to the cathode electrode, the platinum loading was 0.1 mg / cm 2 The anode catalyst layer was formed so that:

[0074] A polyphenylene sulfide film with a thickness of 40 μm was used as the frame. Carbon paper manufactured by SGL was used as the anode-side gas diffusion layer. The gas diffusion layers of Example 1 and Comparative Example 1 were used as cathode-side gas diffusion layers and joined to a cathode catalyst layer, and the anode-side gas diffusion layer was joined to an anode catalyst layer, thereby obtaining a membrane electrode assembly.

[0075] Next, a single fuel cell was manufactured using the separator with the flow channels formed therein. First, the fabricated membrane electrode assembly was sandwiched between an anode-side separator having a fluid flow path for fuel gas supply and a cooling water flow path, and a cathode-side separator having a gas flow path for oxidant gas supply, and fluororubber gaskets were placed around the cathode and anode to fabricate a single fuel cell. At this time, the clamping pressure of the power generation part of the membrane electrode assembly (the pressure exerted by the catalyst layer on the polymer electrolyte membrane) was 10 kgf / cm. 2 The plates were clamped so that the

[0076] In the fuel cell unit cells of Example 1 and Comparative Example 1, the pressure P1 exerted by region A of the gas diffusion layer 40 on the separator 4 (i.e., the pressure exerted by the frame 6 on the polymer electrolyte membrane 31) was calculated as follows using Table 1. It was assumed that the frame would not deform under load. The film thickness of the frame was 40 μm. In Example 1, the thickness of the gas diffusion layer in region B before load application was 160 μm, and the thickness in region A was 120 μm. In Comparative Example 1, the total thickness before load application was 160 μm. The clamping pressure P2 to region B was 10 kgf / cm 2 Therefore, Table 1 shows that the shrinkage rate is 75.8%. The film thickness of region B after load application is the value multiplied by the shrinkage rate of 75.8%, which is 160 × 0.758 = 121.28 μm. As shown in FIG. 5A, the surface where gas diffusion layer 40B contacts separator 4B is flush, and the thickness of region B is the same as the total thickness of region A and frame 6. Therefore, the thickness of region A after load application is the total thickness minus the thickness of frame 6, which is 121.28 − 40 = 81.28 μm. Since the film thickness of region A before load application is 120 μm and shrinks to 81.28 μm after load application, 81.28 / 120 = 0.6773, and the shrinkage rate is 67.73%. As a result, Table 1 shows that in Example 1, the pressure P1 applied to the separator is approximately 20 kgf / cm 2 It was found that P1 / P2 was 2.0.

[0077] On the other hand, in Comparative Example 1, the gas diffusion layer is only in region B, and the thickness of the gas diffusion layer after the load is applied is 121.28 μm, as in Example 1. Meanwhile, the total thickness of the outer edge of the gas diffusion layer and the frame 6 after the load is applied is also 121.28 μm, and the thickness of the outer edge of the gas diffusion layer after the load is applied is 121.28 - 40 = 81.28 μm, subtracting the thickness of the frame 6 (40 μm). Since the film thickness in region A before the load is applied shrinks to 81.28 μm after the load is applied, the film thickness is 81.28 / 160 = 0.508, and the shrinkage rate is 50.8%. As a result, from Table 1, it can be seen that in Comparative Example 1, the pressure P1 applied to the separator is approximately 50 kgf / cm 2 As a result, P1 / P2 was 5 or more. From this, it was confirmed that by reducing the film thickness at the portion where the gas diffusion layer and the frame overlap, the pressure acting on this portion could be reduced, and it is thought that damage to the polymer electrolyte membrane could be reduced in Example 1. On the other hand, in Comparative Example 1, the pressure P1 acting on the separator at the outer edge portion where the gas diffusion layer and the frame overlap was large, and there was concern about damage to the polymer electrolyte.

[0078] It should be noted that any of the various embodiments or modifications described above can be combined appropriately to achieve the effects of each. In addition, combinations of embodiments, combinations of examples, or combinations of embodiments and examples are possible, and combinations of features of different embodiments or examples are also possible. [Industrial Applicability]

[0079] When the gas diffusion layer according to the present disclosure is used in a fuel cell, the membrane electrode assembly (MEA) is pressed against a pair of separators, and the gas diffusion layer deforms to flow into the gap between the polymer electrolyte membrane and the frame, thereby reducing the pressure at the overlapping portion between the frame and the gas diffusion layer. This increases the adhesion between the frame, the gas diffusion layer, and the polymer electrolyte membrane, thereby providing a fuel cell with a structure that suppresses degradation of the polymer electrolyte membrane. This fuel cell can be used as a power source for a home cogeneration system, a portable power source, or a power source for a vehicle. [Explanation of symbols]

[0080] 1. Fuel cell unit 2 Membrane electrode assembly 4 Separator 4A Anode side separator 4B Cathode side separator 5 Fluid flow path 5A Anode side fluid flow path 5B Cathode side fluid flow path 6 Frame 10 Sealing material 10A Anode seal material 10B Cathode seal member 31 Electrolyte membrane 32 Catalyst layer 32A Anode catalyst layer 32B Cathode catalyst layer 40 Gas diffusion layer 40A anode gas diffusion layer 40B Cathode gas diffusion layer 41 Conductive particles 42 Conductive Fiber 43 Polymer resin 44 Powder containing conductive particles, conductive fibers, and polymer resin 45 Grain boundaries of powder containing conductive particles, conductive fibers, and polymer resin 46 Powder for gas diffusion layers 50 Gas diffusion layer manufacturing equipment 51 Hopper 52 First Roll 53 Second Roll 54 Gas diffusion layer recovery section 55 Protrusion 60A fuel supply manifold 60B Fuel Discharge Manifold 70A Oxidizer Supply Manifold 70B Oxidizer Discharge Manifold 80 Cooling water manifold 100 fuel cell stack 101a terminal 110 Current collector plate 110a terminal 120 Insulating plate 130 Fastening plate

Claims

1. A gas diffusion layer comprising conductive particles, conductive fibers, and a polymer resin, a thickness of at least a part of an outer edge portion of the gas diffusion layer is thinner than a thickness of the other part of the outer edge portion of the gas diffusion layer; a gas diffusion layer in which the part of the outer edge of the gas diffusion layer where the thickness is thinner is designated as region A, and the other part of the outer edge of the gas diffusion layer is designated as region B, and the porosity is calculated by (true density - bulk density) / true density x 100, where true density is calculated from the density and composition ratio of materials constituting the gas diffusion layer, and bulk density is calculated by calculating the volume from the area and film thickness of region A and region B of the gas diffusion layer and dividing the weight by the volume, and the porosity is calculated by (true density - bulk density) / true density x 100, and the difference between the porosity of region A and the porosity of region B is within 10%.

2. an electrolyte membrane; a pair of catalyst layers disposed so as to sandwich the electrolyte membrane; a pair of gas diffusion layers arranged to sandwich the electrolyte membrane with the pair of catalyst layers interposed therebetween; a pair of separators arranged to sandwich the electrolyte membrane with the pair of gas diffusion layers and the pair of catalyst layers interposed therebetween; a frame provided around the outer periphery of at least one surface of the electrolyte membrane; A fuel cell unit cell comprising: At least one of the pair of gas diffusion layers is the gas diffusion layer according to claim 1, and is provided with the gas diffusion layer according to claim 1 on a surface on which the frame is disposed, The inner edge of the frame and region A of the gas diffusion layer overlap with each other, a pressure P1 applied to the separator by the region A of the gas diffusion layer and a pressure P2 applied to the separator by the region B of the gas diffusion layer, 1 ≦ P1 / P2 < 3 A single fuel cell that satisfies the above relationship.

3. 3. The unit fuel cell according to claim 2, wherein a difference between a total thickness of the frame and region A of the gas diffusion layer and a thickness of the region B of the gas diffusion layer is within 10%.

4. A fuel cell stack having a structure in which a plurality of the fuel cell unit cells according to claim 2 are stacked.

5. a step of stirring and kneading conductive particles, conductive fibers, and a polymer resin in a dispersion solvent to obtain a kneaded mixture of the conductive particles, the conductive fibers, and the polymer resin; a step of firing the kneaded product at a temperature equal to or higher than the decomposition temperature of the dispersion solvent to obtain a solid product from which the dispersion solvent has been removed; a step of pulverizing the solid material from which the dispersion solvent has been removed to obtain a powder; a step of rolling the powder with a roll having protruding portions in a width direction parallel to a rotation axis at a part of a circumferential direction to form a sheet, and obtaining a gas diffusion layer including the sheet having the region A and the region B by rotation of the roll, wherein the thickness of the region A of the sheet corresponding to the protruding portions is thinner than the thickness of the region B of the sheet other than the protruding portions; Including, A method for manufacturing a gas diffusion layer.

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