Gas diffusion layer, gas diffusion electrode, membrane electrode assembly, fuel cell, production method for gas diffusion layer, production method for gas diffusion electrode, and production method for membrane electrode assembly

Abstract

Provided are: a gas diffusion layer comprising a carbon fiber layer and a microporous layer that contains an aromatic polyamide pulp, a water-dispersed resin, and a carbon-based electroconductive substance and is provided upon the carbon fiber layer; a gas diffusion electrode; a membrane electrode assembly; a fuel cell; a production method for the gas diffusion layer; a production method for the gas diffusion electrode; and a production method for the membrane electrode assembly.

Description

Gas diffusion layer, gas diffusion electrode, membrane electrode assembly, fuel cell, method for manufacturing a gas diffusion layer, method for manufacturing a gas diffusion electrode, and method for manufacturing a membrane electrode assembly

[0001] This disclosure relates to a gas diffusion layer, a gas diffusion electrode, a membrane electrode assembly, a fuel cell, a method for manufacturing a gas diffusion layer, a method for manufacturing a gas diffusion electrode, and a method for manufacturing a membrane electrode assembly.

[0002] Fuel cells are broadly classified into four types based on the type of electrolyte used: molten carbonate fuel cells (MCFCs), solid oxide fuel cells (SOFCs), phosphoric acid fuel cells (PAFCs), and polymer electrolyte fuel cells (PEFCs).

[0003] Among the above, solid polymer fuel cells include a membrane electrode assembly (MEA) in which a thin polymer electrolyte membrane is sandwiched between a gas diffusion layer (GDL) via a catalyst layer. The configuration comprising a catalyst layer and a gas diffusion layer is called a gas diffusion electrode (GDE).

[0004] The performance requirements for the gas diffusion layer have traditionally included gas diffusion performance to guide fuel gas or air into the catalyst layer and diffuse the fuel gas into the catalyst layer, water-repellent performance to discharge the generated water produced by the power generation reaction to the separator, high conductivity to extract the generated current to the outside without loss, and resistance to strongly acidic and strongly basic atmospheres caused by the generated ions.

[0005] Typically, a gas diffusion layer comprises a carbon fiber layer, such as a carbon fiber sheet, and a microporous layer (also known as a Micro Porous Layer: MPL, microporous layer, fine porous layer, or water-repellent layer) on the surface of the carbon fiber layer, from the viewpoint of uniformly diffusing fuel gas into the catalyst layer and adjusting the wettability of the membrane electrode assembly.

[0006] Conventional gas diffusion layers are formed by applying a microporous layer-forming coating solution onto a carbon fiber layer, followed by drying and sintering, thereby creating a microporous layer on top of the carbon fiber layer.

[0007] For example, Patent Document 1 describes a method for producing a gas diffusion layer with microporous properties by coating the surface of a carbon fiber sheet with a slurry containing a carbon-based conductive material and a fluororesin at appropriate concentrations using spray or knife coating. Furthermore, Patent Document 2 proposes a method for producing a gas diffusion layer by dispersing a fibril-like material consisting of a conductive carbon material, a fluororesin, and an aromatic polyamide in a solvent, forming a paper mold, hot-pressing the resulting precursor, and then firing it.

[0008] Patent Document 1: Japanese Unexamined Patent Publication No. 7-220734 Patent Document 2: International Publication No. 2012-026498

[0009] However, conventional coating methods are prone to inconsistencies in the thickness and film quality of the resulting microporous layer due to technical factors. As a result, when a catalyst layer is placed on top of the gas diffusion layer to form a gas diffusion electrode, carbon fibers contained in the carbon fiber layer tend to protrude into the microporous layer, damaging the microporous layer and the catalyst layer placed on top of it, thus impairing their properties. Batteries with a gas diffusion layer in which the properties of the microporous layer and catalyst layer have been impaired tend to have reduced battery performance.

[0010] Therefore, this disclosure aims to provide a gas diffusion layer that suppresses roughening of the microporous layer and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber layer, as well as a gas diffusion electrode, a membrane electrode assembly, and a fuel cell equipped therewith. This disclosure also provides a simple method for manufacturing the gas diffusion layer.

[0011] The following embodiments are included as specific means for solving the problem: <1> A gas diffusion layer comprising a carbon fiber layer and a microporous layer provided on the carbon fiber layer, comprising aromatic polyamide pulp, a water-dispersible resin, and a carbon-based conductive material. <2> The gas diffusion layer according to <1>, wherein the microporous layer has a maximum peak in the pore size distribution of 0.1 μm or more and 5.0 μm or less. <3> The gas diffusion layer according to <1>, wherein the microporous layer has a tensile modulus of 300 MPa or more and 900 MPa or less. <4> A gas diffusion electrode comprising a gas diffusion layer according to any one of <1> to <3> and a catalyst layer provided on the microporous layer in the gas diffusion layer. <5> A membrane electrode assembly comprising a polymer electrolyte membrane and a pair of gas diffusion electrodes sandwiching the polymer electrolyte membrane, wherein at least one of the pair of gas diffusion electrodes is the gas diffusion electrode according to <4>. <6> A fuel cell comprising the membrane electrode assembly described in <5> above and a separator. <7> A method for manufacturing a gas diffusion layer, comprising the step of bonding a microporous sheet containing aromatic polyamide pulp, a water-dispersible resin, and a carbon-based conductive material with a carbon fiber sheet to form a laminate. <8> The method for manufacturing a gas diffusion layer according to <7> above, wherein the microporous sheet has a maximum peak in its pore size distribution of 0.1 μm or more and 5.0 μm or less. <9> The method for manufacturing a gas diffusion layer according to <7> or <8> above, wherein the microporous sheet has a tensile modulus of elasticity of 300 MPa or more and 900 MPa or less. <10> The method for manufacturing a gas diffusion layer according to any one of <7> to <9> above, further comprising the step of heating and pressing the laminate from the lamination direction at a temperature of 150°C or more and 400°C or less. <11> A method for manufacturing a gas diffusion electrode, comprising the steps of: manufacturing a gas diffusion layer by the manufacturing method described in any one of <7> to <10> above; and providing a catalyst layer on the microporous sheet side of the manufactured gas diffusion layer. <12> A method for manufacturing a membrane electrode assembly, comprising the steps of: manufacturing a gas diffusion layer by the manufacturing method described in any one of <7> to <10> above; and providing a catalyst layer and a polymer electrolyte membrane in that order on the microporous sheet side of the manufactured gas diffusion layer.<13> A method for manufacturing a membrane electrode assembly according to <12>, wherein a catalyst layer and a polymer electrolyte membrane are provided in this order on the microporous sheet side of the manufactured gas diffusion layer, and the assembly is pressed together in a range of 60°C to 130°C.

[0012] This disclosure provides a gas diffusion layer, a gas diffusion electrode, a membrane electrode assembly, and a fuel cell in which roughening of the microporous layer and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber layer is suppressed. This disclosure also provides a simple method for manufacturing the gas diffusion layer.

[0013] Figure 1 is a schematic cross-sectional view showing an example of the layer configuration of a film electrode assembly according to the present disclosure. Figure 2 is a pore distribution diagram of the gas diffusion layer of Example 1, with the vertical axis representing the [dV / d(logd)(cc / g)] of the microporous layer and the horizontal axis representing the pore diameter (μm) of the microporous layer. Figure 3 is a cross-sectional photograph of the gas diffusion layer of Example 1 in the stacking direction, observed using a scanning electron microscope.

[0014] The following describes an example embodiment of this disclosure. These descriptions and examples are illustrative and do not limit the scope of the invention. In numerical ranges described stepwise in this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Also, in numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with the value shown in the example.

[0015] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if multiple types of the substance corresponding to each component are present in the composition, unless otherwise specified, it refers to the total amount of those multiple types of substances present in the composition.

[0016] When describing embodiments with reference to the drawings, components having substantially the same function will be given the same reference numeral throughout the drawings, and redundant explanations may be omitted.

[0017] <Measurement Methods for Various Physical Properties> The measurement methods used in this specification are as follows. The measurement method for measuring the thickness of the microporous layer is as follows. The thickness of the microporous layer is measured at 10 cm intervals at any five points using a thickness gauge (manufactured by Ono Sokki), and the arithmetic mean is taken as the thickness of the microporous sheet.

[0018] The method for measuring the water contact angle of a microporous layer is as follows: Water is dropped onto the microporous layer, and the contact angle is measured using a contact angle meter (KYOWA DMo-502) at 20°C to 25°C and 65% RH.

[0019] The method for measuring the pore size distribution of a microporous layer is as follows: A fully automated pore size distribution analyzer (Anton Paar PoreMaster 60-GT) is used to measure the pore size distribution of the microporous layer from 0.01 μm to 100 μm. The observed maximum peak value is defined as the maximum peak in the pore size distribution when the vertical axis is [dV / d (log d) (cc / g)] and the horizontal axis is pore size (μm).

[0020] The method for measuring the tensile modulus of a microporous layer is as follows: A 13 cm sample of the microporous layer is taken from the gas diffusion layer to be measured. Using a Tensilon (Orientec RTC-1310A), the breaking strength and elongation at break are measured under the conditions of a chuck distance of 10 cm, a tensile speed of 50 mm / min, a temperature of 20°C to 25°C, and 65% RH, and the tensile modulus is calculated.

[0021] The laminated structure of the laminate and the state of each layer can be confirmed by cutting the gas diffusion layer along the lamination direction and observing the cross-section with a scanning electron microscope (SU3500, Hitachi, Ltd.).

[0022] The carbon fibers, carbon milled fibers, and carbon nanofibers described herein may consist of multiple fibers having different average fiber diameters. The carbon fibers, carbon milled fibers, and carbon nanofibers described herein may consist of multiple fibers having different average fiber lengths. The carbon fibers, carbon milled fibers, and carbon nanofibers described herein may consist of multiple fibers having different average fiber diameters and average fiber lengths.

[0023] <Gas Diffusion Layer> The gas diffusion layer according to this disclosure comprises a carbon fiber layer and a microporous layer provided on the carbon fiber layer, comprising aromatic polyamide pulp, a water-dispersible resin, and a carbon-based conductive material.

[0024] The gas diffusion layer according to this disclosure, having the above configuration, suppresses roughening of the microporous layer and catalyst layer due to the protrusion of carbon fibers contained in the carbon fiber layer. Therefore, even when a battery is equipped with the gas diffusion layer according to this disclosure, the deterioration of battery performance caused by roughening of the microporous layer and catalyst layer is also suppressed.

[0025] [Carbon Fiber Layer] The carbon fiber layer is not particularly limited, and any known carbon fiber layer that can be used as a diffusion layer in a gas diffusion layer can be applied.

[0026] The carbon fiber layer has a specific gravity of 1.10 g / cm³, from the viewpoint of suitably controlling the diffusivity of the gas diffusion layer. ３ 2.00g / cm or more ３ Preferably, it is 1.50 g / cm³. ３ 1.90g / cm or more ３ The following is more preferable:

[0027] The average fiber diameter of the fibers contained in the carbon fiber layer is not particularly limited, but from the viewpoint of suitably controlling the diffusivity of the gas diffusion layer, it is preferably 5.0 μm or more and 50.0 μm or less, and more preferably 5.0 μm or more and 20.0 μm or less.

[0028] The average fiber length of the fibers contained in the carbon fiber layer is not particularly limited, but from the viewpoint of handling, it is preferably 1.0 mm to 15.0 mm, and more preferably 2.0 mm to 10.0 mm.

[0029] The thickness of the carbon fiber layer is not particularly limited, but from the viewpoint of handling, it is preferably 100 μm to 300 μm, and more preferably 120 μm to 250 μm.

[0030] [Microporous layer] The microporous layer (so-called MPL layer) contains aromatic polyamide pulp, a water-dispersible resin, and a carbon-based conductive material. The microporous layer may further contain other materials besides aromatic polyamide pulp, water-dispersible resin, and a carbon-based conductive material.

[0031] The microporous layer is provided on top of the carbon fiber layer. The microporous layer may be provided in contact with the carbon fiber layer, or it may be provided between the microporous layer and the carbon fiber layer with another layer in between. The microporous layer may be provided on a portion of the carbon fiber layer, but it is preferable that it be provided on the entire carbon fiber layer.

[0032] (Aromatic Polyamide Pulp) Aromatic polyamide pulp (hereinafter also referred to as "aramid pulp") is a fiber of aromatic polyamide having amide bonds formed by the dehydration condensation of aromatic diamine and aromatic dicarboxylic acid components, for example, 85 mol% or more of the amide bonds. It is preferable that the fibers of the aramid pulp are highly fibrillated. Examples of aramids include poly(p-phenylene terephthalamide), co(p-phenylene-3,4'-oxydiphenylene-terephthalamide), poly(metaphenylene isophthalamide), poly(p-benzamide), poly(-4,4'-diaminobenzanilide), poly(p-phenylene-2,6-naphthalicamide), co(p-phenylene / 4,4'-(3,3'-dimethylbiphenylene)terephthalamide, poly(-orthophenylene terephthalamide), poly(p-phenylene phthalamide), and poly(metaphenylene isophthalamide).

[0033] Fibrillation refers to a method of randomly forming minute single fibers on the surface of a fiber. In this disclosure, fibrillation of aramid pulp is carried out by known methods. For example, it is carried out by adding a precipitating agent to an organic polymer solution as described in Japanese Patent Publication No. 35-11851 and Japanese Patent Publication No. 37-5752, and mixing them in a system that generates shear force. Alternatively, it can be carried out by applying mechanical shear force, such as beating, to a molded article having molecular orientation formed from an optically anisotropic polymer solution as described in Japanese Patent Publication No. 59-603, thereby randomly imparting minute single fibers.

[0034] The average fiber length of aramid pulp is not particularly limited, but from the viewpoint of high strength and high modulus of elasticity, it is preferably 0.1 mm to 10.0 mm, more preferably 0.2 mm to 5.0 mm, and even more preferably 0.3 mm to 3.0 mm.

[0035] (Water-dispersible resin) The water-dispersible resin only needs to be contained in the microporous layer, and may, for example, be attached to the surface of the aromatic polyamide pulp or fused to the surface of the aromatic polyamide pulp. By including this water-dispersible resin, water-repellent properties are imparted to the microporous layer.

[0036] The water-dispersible resin is not particularly limited, and any known water-dispersible resin used in the gas diffusion layer may be used. The water-dispersible resin may be used alone or in combination of two or more types.

[0037] Examples of water-dispersible resins include fluororesins, water-dispersible acrylic resins, water-dispersible polyester resins, water-dispersible polystyrene resins, and water-dispersible urethane resins. Among these, it is preferable to include fluororesins as the water-dispersible resin from the viewpoint of having excellent water repellency.

[0038] Examples of the fluororesin include ethylene tetrafluoride resin (hereinafter sometimes referred to as "PTFE"), perfluoroalkoxy resin, ethylene tetrafluoride - hexafluoropropylene copolymer resin, ethylene tetrafluoride - ethylene copolymer resin, vinylidene fluoride resin, ethylene chloride trifluoride, and the like. Among these, from the viewpoint of excellent heat resistance and sliding characteristics, it is preferable to contain PTFE as the fluororesin.

[0039] (Carbon - based conductive material) The carbon - based conductive material only needs to be contained in the microporous layer. For example, it may be dispersed between the fibers of aromatic polyamide pulp. By containing this carbon - based conductive material, conductivity is imparted to the microporous layer.

[0040] The carbon - based conductive material is not particularly limited, and known carbon - based conductive materials used for the gas diffusion layer may be adopted. The carbon - based conductive material may be used alone or in combination of two or more.

[0041] From the viewpoint of conductive performance, for example, it is preferable to use a material having a carbon content of 94% by mass or more and a specific resistance of 5 Ω·cm or less as the carbon - based conductive material. Specific examples of the carbon - based conductive material include carbon fiber, carbon black, graphite particles, carbon nanotubes, carbon - milled fiber, carbon nanofiber, carbon nanohorn, graphene, and the like.

[0042] Among these, as the carbon - based conductive material, it is preferably to contain at least one selected from the group consisting of graphite particles, carbon black, carbon fiber, carbon - milled fiber, and carbon nanofiber. More preferably, it contains at least one selected from the group consisting of carbon black, carbon fiber, carbon - milled fiber, and carbon nanofiber. Even more preferably, it contains at least one of carbon - milled fiber and carbon nanofiber. When containing at least one selected from the above group, roughening of the microporous layer and the catalyst layer due to protrusion of carbon fibers contained in the carbon fiber layer is more suppressed.

[0043] - Graphite particles Examples of the graphite particles include flaky graphite, scaly graphite, earthy graphite, artificial graphite, expanded graphite, exfoliated graphite, platelet graphite, massive graphite, and spherical graphite. In particular, spherical or flaky graphite is preferred. The average particle size of the graphite particles is preferably 0.05 μm or more and 300.0 μm or less.

[0044] - Carbon black Examples of the carbon black include acetylene black and Ketjenblack (registered trademark) having a hollow shell structure. In particular, Ketjenblack is preferred.

[0045] The average primary particle size of the carbon black is preferably, for example, 1.0 nm or more and 500.0 nm or less, more preferably 1.0 nm or more and 200.0 nm or less, and even more preferably 10.0 nm or more and 100.0 nm or less. The average secondary particle size of the carbon black is preferably, for example, 0.5 nm or more and 20.0 μm or less. If the average secondary particle size is 0.5 μm or more, aggregation of the carbon black is further suppressed when preparing a dispersion of the carbon black. If the average secondary particle size is 20.0 μm or less, the carbon-based conductive material easily enters the inside of the sheet, improving the conductivity of the sheet.

[0046] - Carbon fibers and carbon milled fibers Examples of the carbon fibers and carbon milled fibers include PAN-based carbon fibers, pitch-based carbon fibers, and phenol-based carbon fibers. Among these, it is preferable to include pitch-based carbon fibers.

[0047] In this specification, the carbon milled fiber refers to a fibrous carbon fiber crushed by a crusher or the like into a powder (milled) state.

[0048] When using at least one of the carbon fibers and / or carbon milled fibers, the average fiber diameter is not particularly limited, but is preferably, for example, 3 μm or more and 20 μm or less, and more preferably 5 μm or more and 13 μm or less.

[0049] The average fiber diameter is a value measured by microscopic observation. When the carbon fiber has a flat cross-section, the arithmetic mean value of the major diameter and the minor diameter is taken as the average fiber diameter.

[0050] When the average fiber diameter is 3 μm or more, the strength of the individual fibers is high, making it easier to improve the strength of the gas diffusion layer. When the average fiber diameter is 20 μm or less, localized lifting of the carbon fiber layer from the microporous layer is suppressed when used as a gas diffusion layer. As a result, the formation of surface irregularities caused by the lifting of the carbon fiber layer is suppressed, resulting in good surface smoothness and lower contact electrical resistance when used as a gas diffusion layer. In other words, it leads to superior battery performance.

[0051] The average fiber length (so-called cut length) of carbon fibers or carbon milled fibers is not particularly limited, but it is preferably 20 mm or less. When the average fiber length is 20 mm or less, the uniform dispersion of the fibers improves, and the strength of the gas diffusion layer tends to improve.

[0052] The carbon content in carbon fibers and carbon milled fibers is preferably, for example, 94% by mass or more. A carbon content of 94% by mass or more improves the electrical conductivity of the sheet. Furthermore, even when a battery incorporating this gas diffusion layer is operated for a long period of time, the deterioration of the sheet is suppressed.

[0053] ・Carbon nanofibers Carbon nanofibers may be single fibers or aggregates. The average fiber diameter of carbon nanofibers (single fibers or aggregates) is preferably, for example, 100 nm or more and 1000 nm or less. If the average fiber diameter of carbon nanofibers is 100 nm or more, handling properties are good, and if it is 1000 nm or less, it is easy to increase the fiber density. The average fiber diameter of carbon nanofibers is preferably 900 nm or less, more preferably 800 nm or less, even more preferably 600 nm or less, even more preferably 500 nm or less, even more preferably 450 nm or less, and even more preferably 400 nm or less. The average fiber diameter of carbon nanofibers is preferably 110 nm or more, more preferably 120 nm or more, even more preferably 150 nm or more, and even more preferably 200 nm or more.

[0054] The average fiber length of the carbon nanofibers is preferably 1 μm or more, and more preferably 10 μm or more. If the average fiber length is 1 μm or more, it is possible to suppress a decrease in conductivity, strength, and liquid retention. Furthermore, if the average fiber length is 100 μm or less, the dispersibility of the carbon fibers is less likely to be impaired, and the carbon fibers are less likely to orient in the in-plane direction of the gas diffusion layer. As a result, it is easier to form conductive paths in the thickness direction of the gas diffusion layer. From the viewpoint of sheet strength, for example, the average fiber length of the carbon nanofibers is preferably 10 μm or more and 100 μm or less, and more preferably 12 μm or more and 80 μm or less.

[0055] Carbon nanofibers can be produced, for example, by the method disclosed in International Publication No. 2020 / 045243. Specifically, a method for producing a carbon fiber aggregate includes: (1) a fibrous step of obtaining resin composite fibers by molding a resin composition consisting of a thermoplastic resin and 30 to 150 parts by mass of mesophase pitch per 100 parts by mass of the thermoplastic resin in a molten state to fibrose the mesophase pitch; (2) a stabilization step of stabilizing the resin composite fibers to obtain resin composite stabilized fibers; (3) a thermoplastic resin removal step of removing the thermoplastic resin from the resin composite stabilized fibers to obtain stabilized fibers; and (4) a carbonization and calcination step of heating the stabilized fibers in an inert atmosphere to carbonize or graphitize them to obtain a carbon fiber aggregate.

[0056] (Content of various materials) The content of aromatic polyamide pulp is preferably 1% by mass or more and 20% by mass or less, and more preferably 2% by mass or more and 15% by mass or less, relative to the total solid content of the microporous layer. When the content of aromatic polyamide pulp is 1% by mass or more, roughening of the microporous layer and catalyst layer due to the protrusion of carbon fibers contained in the carbon fiber layer is further suppressed. In addition, the durability of the gas diffusion layer is improved. When the content of aromatic polyamide pulp is 20% by mass or less, the relative decrease in the proportion of carbon-based conductive materials and water-dispersible resins is suppressed, so roughening of the microporous layer and catalyst layer due to the protrusion of carbon fibers contained in the carbon fiber layer is further suppressed. In addition, this results in improved battery performance.

[0057] The content of the water-dispersible resin is preferably 10% to 30% by mass, and more preferably 15% to 25% by mass, relative to the total solid content of the microporous layer. When the content of the water-dispersible resin is 10% by mass or more, roughening of the microporous layer and catalyst layer due to the protrusion of carbon fibers contained in the carbon fiber layer is further suppressed. Furthermore, water repellency is improved. When the content of the water-dispersible resin is 30% by mass or less, the relative decrease in the proportion of aromatic polyamide pulp and carbon-based conductive material is suppressed, so roughening of the microporous layer and catalyst layer due to the protrusion of carbon fibers contained in the carbon fiber layer is further suppressed. Furthermore, the decrease in the porosity of the microporous layer due to excessive water-dispersible resin is suppressed. Furthermore, these factors result in improved battery performance.

[0058] The content of the carbon-based conductive material is preferably 50% to 85% by mass, and more preferably 55% to 80% by mass, relative to the total solid content of the microporous layer. When the content of the carbon-based conductive material is 50% by mass or more, roughening of the microporous layer and catalyst layer due to the protrusion of carbon fibers contained in the carbon fiber layer is further suppressed. Furthermore, conductivity is improved. When the content of the carbon-based conductive material is 85% by mass or less, the relative decrease in the proportion of aromatic polyamide pulp and water-dispersible resin is suppressed, so roughening of the microporous layer and catalyst layer due to the protrusion of carbon fibers contained in the carbon fiber layer is further suppressed. Furthermore, this results in better battery performance.

[0059] The mass ratio of aromatic polyamide pulp to carbon-based conductive material (aromatic polyamide pulp / carbon-based conductive material) is not particularly limited, but is preferably in the range of 1 / 99 to 50 / 50, and more preferably in the range of 3 / 97 to 40 / 60. When the above mass ratio is 1 / 99 or higher, the reinforcing effect is better due to the aromatic polyamide pulp. When the above mass ratio is 50 / 50 or lower, the conductivity is better due to the carbon-based conductive material. In particular, when the carbon-based conductive material contains at least one of carbon fibers and carbon milled fibers, when the above mass ratio is above the lower limit, roughening of the microporous layer and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber layer is further suppressed.

[0060] The mass ratio of aromatic polyamide pulp to water-dispersible resin (aromatic polyamide pulp / water-dispersible resin) is not particularly limited, but is preferably in the range of 10 / 90 to 70 / 30, and more preferably in the range of 20 / 80 to 60 / 40. When the mass ratio is 10 / 90 or higher, the reinforcing effect is better due to the aromatic polyamide pulp. On the other hand, when the mass ratio is 70 / 30 or lower, the water-dispersible resin is better due to the water-dispersible resin.

[0061] (Other materials) The microporous layer may further contain other materials other than aromatic polyamide pulp, water-dispersible resin, and carbon-based conductive material. Examples of other materials include electrode catalysts and ionomer resins.

[0062] As the electrode catalyst, catalysts used in known fuel cells such as polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), and biobatteries can be used. The type and content of the electrode catalyst can be selected according to the application of the gas diffusion layer, and examples include platinum catalysts, iridium catalysts, carbon catalysts, and enzymes.

[0063] (Characteristics of the microporous layer) The microporous layer preferably has a maximum peak in the pore size distribution of 0.1 μm to 5.0 μm, more preferably 0.2 μm to 3.0 μm, and even more preferably 0.3 μm to 2.0 μm. When the maximum peak is 0.1 μm to 5.0 μm, roughening of the microporous layer and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber layer is further suppressed. Furthermore, when a battery is equipped with a gas diffusion layer, the battery performance is superior.

[0064] The microporous layer preferably has a tensile modulus of 200 MPa to 900 MPa, more preferably 300 MPa to 700 MPa, and even more preferably 300 MPa to 500 MPa. When the tensile modulus of the microporous layer is 200 MPa or higher, roughening of the microporous layer and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber layer is further suppressed. Furthermore, the strength of the gas diffusion layer is superior. When the tensile modulus of the microporous layer is 900 MPa or lower, roughening of the microporous layer and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber layer is further suppressed.

[0065] The microporous layer preferably has a water contact angle of 130° to 160°, and more preferably 140° to 150°. When the water contact angle is within the above range, roughening of the microporous layer and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber layer is further suppressed.

[0066] The thickness of the microporous layer may be, for example, 170 μm or more and 250 μm or less. Preferably, the thickness of the microporous layer is 50 μm or more and 150 μm or less, and more preferably 50 μm or more and 100 μm or less. The thickness of the microporous layer is usually 170 μm or more, from the viewpoint of avoiding a decrease in battery performance due to carbon fibers contained in the carbon fiber layer protruding and roughening the microporous layer and catalyst layer. In contrast, in the gas diffusion layer according to this disclosure, even if the thickness of the microporous layer is thinner than conventional methods, such as 50 μm or more and 150 μm or less, the carbon fibers contained in the carbon fiber layer are less likely to protrude, and roughening of the microporous layer and catalyst layer is suppressed.

[0067] [Characteristics of the gas diffusion layer] The overall thickness of the gas diffusion layer can be controlled during the manufacturing process by adjusting the basis weight of the carbon fiber layer, which consists of carbon fiber sheets (described later), and the microporous layer, which consists of microporous sheets, as well as the temperature and pressure during hot pressing.

[0068] The applications of the gas diffusion layer according to this disclosure are not particularly limited and can be applied to known devices that use a gas diffusion layer, such as electrolysis, flow batteries, and fuel cells, but its use in fuel cells is preferred. A fuel cell equipped with the gas diffusion layer according to this disclosure has reduced deterioration of the catalyst layer and superior battery performance.

[0069] The method for manufacturing the gas diffusion layer according to this disclosure is not particularly limited, but it is preferable, for example, to manufacture it using the method for manufacturing the gas diffusion layer according to this disclosure described later.

[0070] <Gas Diffusion Electrode> The gas diffusion electrode according to this disclosure comprises a gas diffusion layer according to this disclosure and a catalyst layer provided on a microporous layer in the gas diffusion layer. According to the gas diffusion electrode according to this disclosure, roughening of the microporous layer and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber layer is suppressed. Furthermore, a decrease in battery performance caused by the aforementioned roughening is also suppressed.

[0071] The catalyst layer is not particularly limited, and known catalyst layers used in gas diffusion electrodes can be employed. Examples of catalyst layers include electrode catalysts and carbon-based conductive materials.

[0072] <Membrane Electrode Assembly> The membrane electrode assembly according to this disclosure comprises a polymer electrolyte membrane and a pair of gas diffusion electrodes that sandwich the polymer electrolyte membrane, wherein at least one of the pair of gas diffusion electrodes is the gas diffusion electrode according to this disclosure. According to the membrane electrode assembly according to this disclosure, a decrease in battery performance caused by roughening of the microporous layer or catalyst layer due to the protrusion of carbon fibers contained in the carbon fiber layer is suppressed.

[0073] Figure 1 is a schematic cross-sectional view showing an example of the layer configuration of a membrane electrode assembly according to the present disclosure. The membrane electrode assembly 100 shown in Figure 1 comprises a polymer electrolyte membrane 10 and a pair of gas diffusion electrodes 20 sandwiching the polymer electrolyte membrane 10. As shown in Figure 1, the gas diffusion electrode 20 is a laminate in which a catalyst layer 30 and a gas diffusion layer 40 are stacked in that order from the polymer electrolyte membrane 10 side. The catalyst layer 30 contains an electrode catalyst C. The gas diffusion layer 40 is a laminate in which a microporous layer 42 and a carbon fiber layer 44 are stacked in that order from the catalyst layer 30 side. Of the pair of gas diffusion electrodes 20, one is the cathode electrode and the other is the anode electrode. Hydrogen is supplied to the anode electrode, and an oxidation reaction of hydrogen occurs in the catalyst layer. Air containing oxygen is supplied to the cathode electrode, and an oxygen reduction reaction occurs. Protons generated at the anode electrode are then conducted to the cathode electrode via the polymer electrolyte membrane 10, and electrons are extracted in this process to generate electricity. Water is generated at the cathode electrode, and this water wets the polymer electrolyte membrane 10, increasing its proton conductivity.

[0074] In the membrane electrode assembly, at least one of the pair of gas diffusion electrodes is a gas diffusion electrode according to the present disclosure, and from the viewpoint of further suppressing the deterioration of battery performance caused by roughening of the catalyst layer on the microporous layer side, it is preferable that both of the pair of gas diffusion electrodes are gas diffusion electrodes according to the present disclosure.

[0075] The applications of the membrane electrode assembly relating to this disclosure are not particularly limited, but for example, it can be used in fuel cells and water electrolysis devices.

[0076] <Fuel Cell> The fuel cell according to this disclosure comprises a membrane electrode assembly and a separator. According to the fuel cell according to this disclosure, a decrease in battery performance caused by roughening of the microporous layer and catalyst layer due to the protrusion of carbon fibers contained in the carbon fiber layer is suppressed.

[0077] The separator is not particularly limited, and any known separator applicable to water electrolysis devices or fuel cells can be used.

[0078] <Method for manufacturing a gas diffusion layer> The method for manufacturing a gas diffusion layer according to this disclosure includes a step of forming a laminate by bonding a microporous sheet containing aromatic polyamide pulp, a water-dispersible resin, and a carbon-based conductive material with a carbon fiber sheet (hereinafter referred to as the laminate formation step).

[0079] Conventional gas diffusion layers are formed by applying a microporous layer-forming coating solution onto a carbon fiber layer, followed by drying and sintering to create a microporous layer on top of the carbon fiber layer. However, this coating method is prone to inconsistencies in the thickness and film quality of the resulting microporous layer due to technical factors. As a result, carbon fibers contained in the carbon fiber layer may protrude from the carbon fiber layer during compression, which can easily damage the microporous layer and the catalyst layer provided on top of it.

[0080] According to this disclosure, a gas diffusion layer, which is a laminate, is obtained by a simple operation of bonding a microporous sheet and a carbon fiber sheet. Therefore, unevenness in the thickness and film quality of the microporous layer obtained due to technical factors is suppressed. As a result, carbon fibers contained in the carbon fiber layer protrude from the carbon fiber layer during compression or other processes, and roughening of the microporous layer and the catalyst layer provided on top of the microporous layer is suppressed. Furthermore, a decrease in battery performance caused by roughening of the microporous layer and catalyst layer is suppressed.

[0081] [Laminate Formation Process] In the laminate formation process, a microporous sheet containing aromatic polyamide pulp, a water-dispersible resin, and a carbon-based conductive material is bonded to a carbon fiber sheet to form a laminate.

[0082] The microporous sheet may be a commercially available product or may be manufactured, as long as it contains aromatic polyamide pulp, a water-dispersible resin, and a carbon-based conductive material, and is water-repellent.

[0083] The method for producing the microporous sheet is not particularly limited, and known methods for producing microporous layers can be applied. When producing a microporous sheet, for example, a slurry for forming a microporous sheet may be paper-formed to obtain a precursor for the microporous sheet, and the microporous sheet may be produced by calcining the precursor.

[0084] As for the aromatic polyamide pulp, water-dispersible resin, and carbon-based conductive material in the microporous sheet, those similar to the aromatic polyamide pulp, water-dispersible resin, and carbon-based conductive material exemplified in the gas diffusion layer according to this disclosure are preferred, from the viewpoint of more effectively suppressing roughness on the microporous sheet side of the catalyst layer.

[0085] As for the carbon fiber sheet, from the viewpoint of more effectively suppressing the protrusion of carbon fibers contained in the carbon fiber sheet and the resulting roughening of the microporous sheet or catalyst layer, a carbon fiber sheet similar to the one exemplified in the gas diffusion layer according to this disclosure is preferred.

[0086] The microporous sheet preferably has a peak diameter in its pore size distribution of 0.1 μm to 5.0 μm, more preferably 0.2 μm to 3.0 μm, and even more preferably 0.3 μm to 2.0 μm. When the maximum peak is between 0.1 μm and 5.0 μm, roughening of the microporous sheet and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber sheet is further suppressed. Furthermore, when the battery is equipped with a gas diffusion layer, the battery performance is superior.

[0087] The microporous sheet preferably has a tensile modulus of 200 MPa to 900 MPa, more preferably 300 MPa to 700 MPa, and even more preferably 300 MPa to 500 MPa. When the tensile modulus of the microporous sheet is 200 MPa or higher, roughening of the microporous sheet and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber sheet is further suppressed. Furthermore, the strength of the gas diffusion layer is superior. When the tensile modulus of the microporous sheet is 900 MPa or lower, roughening of the microporous sheet and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber sheet is further suppressed.

[0088] In the laminate formation process, it is preferable to heat the carbon fiber sheet and the microporous sheet when bonding them together, from the viewpoint of further improving the adhesion between the carbon fiber sheet and the microporous sheet. The heating temperature in the laminate formation process is not particularly limited and can be appropriately designed according to the materials of the carbon fiber sheet and the microporous sheet. The pressurizing temperature is preferably in the range of 100°C to 400°C, more preferably in the range of 150°C to 400°C, and even more preferably in the range of 150°C to 250°C.

[0089] In the laminate formation process, it is preferable to apply pressure when bonding the carbon fiber sheet and the microporous sheet, from the viewpoint of further improving the adhesion between the carbon fiber sheet and the microporous sheet. The pressure applied in the laminate formation process is not particularly limited and can be appropriately designed according to the materials of the carbon fiber sheet and the microporous sheet. As an example of the pressure applied (surface pressure), from the viewpoint of further reducing the damage caused by the carbon fibers in the carbon fiber sheet to the catalyst layer, 10 kgf / cm² is preferred. ２ More than 60kgf / cm ２ Preferably, it is 20 kgf / cm². ２ More than 50kgf / cm ２ The following is more preferable:

[0090] The laminate formation process preferably further includes a step of heating and pressing the laminate from the lamination direction, from the viewpoint of further improving the adhesion between the carbon fiber sheet and the microporous sheet, and more preferably further includes a step of heating and pressing in a range of 150°C to 400°C (more preferably a range of 150°C to 300°C, and particularly preferably a range of 150°C to 250°C).

[0091] The method for bonding the carbon fiber sheet and the microporous sheet is not particularly limited, and known methods can be applied. From the viewpoint of preventing slippage between layers and achieving superior adhesion, the bonding method is preferably a calendering method.

[0092] In one embodiment, the laminate formation process may involve bonding a carbon fiber sheet and a microporous sheet using a laminate calender and then pressing the two together to form a laminate. In this case, the roll speed is preferably 1 m / min to 10 m / min, for example, from the viewpoint of preventing misalignment during bonding.

[0093] [Sintering Process] The method for manufacturing a gas diffusion layer according to this disclosure may further include a sintering process. In the sintering process, the laminate obtained in the laminate formation process is heated and sintered. Including the sintering process results in superior water repellency, which in turn improves battery performance.

[0094] The sintering method is not particularly limited, and known sintering methods for sintering gas diffusion layers can be applied.

[0095] The sintering temperature is not particularly limited and can be appropriately designed depending on the material of the carbon fiber sheet and the microporous sheet, but for example, it may be between 300°C and 500°C.

[0096] The sintering time is not particularly limited and can be appropriately designed depending on the material of the carbon fiber sheet and the microporous sheet, but for example, it may be in the range of 30 minutes to 5 hours or in the range of 30 minutes to 2 hours.

[0097] [Other Processes] The method for manufacturing a gas diffusion layer according to this disclosure may further include other processes other than the laminate formation process and the sintering process. Examples of other processes include a crimping process for pressing the laminates together; a processing process such as cutting; and a packaging process for packaging the obtained gas diffusion layer. Each process may be performed simultaneously with the laminate formation process or separately.

[0098] In one embodiment, the method for manufacturing a gas diffusion layer according to the present disclosure may include a laminate formation step of forming a laminate by bonding a microporous sheet containing aromatic polyamide pulp, a water-dispersible resin, and a carbon-based conductive material with a carbon fiber sheet and then heating and pressurizing the bonded sheet, and a sintering step of sintering the laminate.

[0099] <Method for manufacturing a gas diffusion electrode> The method for manufacturing a gas diffusion electrode according to the present disclosure includes the step of providing a catalyst layer on the microporous sheet side of the gas diffusion layer manufactured by the method for manufacturing a gas diffusion layer according to the present disclosure.

[0100] According to this disclosure, roughening of the microporous layer and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber layer is suppressed. As a result, the deterioration of battery performance caused by the aforementioned roughening is suppressed.

[0101] The method for forming the catalyst layer is not particularly limited, and known methods for forming catalyst layers used in gas diffusion electrodes can be applied.

[0102] <Method for manufacturing a membrane electrode assembly> The method for manufacturing a membrane electrode assembly according to the present disclosure includes the steps of manufacturing a gas diffusion layer by the method for manufacturing a gas diffusion layer according to the present disclosure, and providing a catalyst layer and a polymer electrolyte membrane in that order on the microporous sheet side surface of the manufactured gas diffusion layer.

[0103] According to this disclosure, roughening of the microporous layer and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber layer in the film electrode assembly is suppressed. As a result, the deterioration of battery performance caused by the aforementioned roughening is suppressed.

[0104] From the viewpoint of more efficiently manufacturing a membrane electrode assembly and suppressing roughness of the microporous layer and catalyst layer, the manufacturing method according to this disclosure preferably involves providing the catalyst layer and the polymer electrolyte membrane in this order on the microporous sheet side surface of the manufactured gas diffusion layer and pressing them together in a range of 60°C to 130°C (more preferably 65°C to 130°C, and even more preferably 70°C to 125°C).

[0105] The method for forming the catalyst layer is not particularly limited, and known methods for forming catalyst layers used in gas diffusion electrodes can be applied.

[0106] The present disclosure will be described in more detail below with reference to examples, but the invention of the present disclosure is not limited to these examples.

[0107] <Fabrication of Gas Diffusion Layer: Example 1> 10 parts by mass of aromatic polyamide pulp (manufactured by Teijin Limited, pulp of Twaron (registered trademark) 1094), 20 parts by mass of PTFE (manufactured by AGC Inc., AD911E; water-dispersible resin), 10 parts by mass of Ketjen black (manufactured by Lion Corporation, EC600JD), and 60 parts by mass of pitch-based ultra-fine carbon fiber (manufactured by Teijin Limited, average fiber length 10 μm to 28 μm; carbon-based conductive material) were used to produce a microporous sheet (thickness 69 μm, pore diameter 0.7 μm, elastic modulus 347 MPa). Subsequently, carbon fiber (manufactured by Teijin Limited, average fiber diameter 7 μm, specific gravity 1.76) cut to an average fiber length of 3 mm was dispersed in water, and a carbon fiber sheet (thickness 120 μm) which is wet-laid was produced. Then, the microporous sheet and the carbon fiber sheet were pressure-bonded in the thickness direction using a laminating calendar. At this time, the roll temperature was 200 °C (shown as the calendar pressure-bonding temperature in Table 1), the roll pressure was 40 kgf / cm ２ , and the roll speed was 2 m / min. Further, it was sintered in an oven under the conditions of 400 °C for 1 hour to obtain a laminate (gas diffusion layer) composed of a microporous layer and a porous carbon fiber layer.

[0108] Fig. 2 shows a pore size distribution diagram when [dV / d(log d) (cc / g)] of the microporous layer in the gas diffusion layer of Example 1 is taken as the vertical axis and the pore diameter (μm) of the microporous layer is taken as the horizontal axis. As shown in Fig. 2, the microporous layer of Example 1 has a maximum peak in the pore size distribution within the range of 0.2 μm or more and 5.0 μm or less.

[0109] <Fabrication of Gas Diffusion Layer: Example 2> A gas diffusion layer was fabricated in the same manner as in Example 1, except that a microporous layer with a thickness of 64 μm, a maximum peak in the pore size distribution of 1.0 μm, and a tensile elastic modulus of 443 MPa was used.

[0110] <Fabrication of Gas Diffusion Layer: Example 3> A gas diffusion layer was fabricated in the same manner as in Example 1, except that a microporous layer with a thickness, a maximum peak in the pore size distribution, and a tensile elastic modulus shown in Table 1 respectively was used.

[0111] <Preparation of Gas Diffusion Layer: Comparative Example 1> 7.5 parts by mass of Ketjenblack, 2.5 parts by mass of PTFE, 7.5 parts by mass of surfactant (DT-100, manufactured by Toyo Chemical), and 82.5 parts by mass of water were mixed in a mixer. The mixture was applied to the carbon fiber layer with a die coater and dried in an oven at 100°C for 1 hour to obtain a gas diffusion layer of a laminate consisting of a microporous layer and a carbon fiber layer. In the evaluation of the protrusion of the carbon fiber layer, carbon fibers contained in the porous carbon fiber layer protruded into the microporous layer, and cracks were observed in the microporous layer.

[0112] <Preparation of Gas Diffusion Layer: Example 4> Using the method of Example 1, a microporous sheet and a carbon fiber sheet were prepared, consisting of aromatic polyamide pulp, PTFE (water-dispersible resin), Ketjenblack, and pitch-based ultrafine carbon fibers (carbon-based conductive material). The microporous sheet was sintered in an oven at 400°C for 1 hour. The microporous sheet and the carbon fiber sheet were then pressed together in the thickness direction using a laminate calender to obtain a laminate (gas diffusion layer). At this time, the roll temperature was 200°C and the roll pressure was 40 kgf / cm. ２ The roll speed was set to 2 m / min.

[0113] <Preparation of Gas Diffusion Layer: Example 5> A laminate (gas diffusion layer) was obtained in the same manner as in Example 1, except that the roll temperature of the laminate calender was set to 350°C.

[0114] <Preparation of Gas Diffusion Layer: Example 6> A microporous sheet (thickness 87 μm, pore diameter 2.5 μm, elastic modulus 416 MPa) was prepared from 9 parts by mass of aromatic polyamide pulp (Teijin Limited, pulp of Twaron® 1094), 5 parts by mass of PTFE (AGC Inc., AD911E; water-dispersible resin), 30 parts by mass of Ketjenblack (Lion Corporation, EC600JD), 35 parts by mass of pitch-based ultrafine carbon fibers (Teijin Limited, average fiber length 10 μm to 28 μm; carbon-based conductive material), and 21 parts by mass of carbon fibers (Teijin Limited, average fiber diameter 7 μm, specific gravity 1.76) cut to an average fiber length of 3 mm. The sheet was pressed and sintered with the carbon fiber sheet using the method described in Example 1 to obtain a laminate (gas diffusion layer).

[0115] <Fabrication of Membrane Electrode Assembly: Example 7> A microporous sheet was fabricated as described in Example 6. A membrane electrode assembly was fabricated by pressing a catalyst-containing polymer electrolyte membrane (fuel cell.com) and the microporous sheet together using a press machine. The pressing temperature was 80°C, the pressure was 0.5 MPa, and the pressing time was 6 minutes.

[0116] <Fabrication of film electrode assembly: Example 8> A film electrode assembly was fabricated in the same manner as in Example 7, except that the pressing temperature was set to 120°C.

[0117] <Physical Properties of Gas Diffusion Layer and Membrane Electrode Assembly> For the microporous layer in the gas diffusion layer of each example, the thickness of the microporous layer, the maximum peak value of the pore size distribution, the tensile modulus, and the contact angle were measured using the measurement method described above. The results are shown in Table 1. Items marked with [-] in the table indicate that they were not measured. In the table, items where the microporous sheet and carbon fiber sheet were pressed together and then sintered are indicated as [After Pressing], and items where the microporous sheet and carbon fiber sheet were sintered before pressing together are indicated as [Before Pressing]. In the table, the temperature at which the polymer electrolyte membrane with the catalyst layer is pressed against the gas diffusion layer is indicated as [Press Pressing Temperature].

[0118] <Evaluation of Microporous Layers and Membrane Electrode Assemblies> The gas diffusion layers prepared in Examples 1 to 5 and Comparative Example 1 were evaluated by observing cross-sectional images taken with a scanning electron microscope. The evaluation indicated that no roughness was observed in the microporous layer, and that roughness was observed in the microporous layer due to carbon fibers contained in the porous carbon fiber layer protruding into the microporous layer, which was indicated as [NG]. In addition, for the membrane electrode assemblies of Examples 7 and 8, the condition of the catalyst layer after pressing was observed with a scanning electron microscope, and that no roughness was observed was indicated as [OK], and that roughness was observed was indicated as [NG].

[0119]

[0120] Figure 3 is a cross-sectional photograph of the gas diffusion layer of Example 1 in the stacking direction, observed using a scanning electron microscope. As shown in Figure 3, it can be seen that in the gas diffusion layer of Example 1, the microporous layer (upper layer) and the porous carbon fiber layer (lower layer) are in close contact to form a laminate. Also, as shown in Figure 3, in the gas diffusion layer of Example 1, the carbon fibers contained in the porous carbon fiber layer do not protrude from the carbon fiber layer, and no roughness is observed in the microporous layer.

[0121] The gas diffusion layers of Example 2 and Comparative Example 1 were also examined in the same manner as the gas diffusion layer of Example 1 to confirm the protrusion of carbon fibers contained in the porous carbon fiber layer into the microporous layer and the presence or absence of resulting roughening of the microporous layer. The results are shown in Table 1.

[0122] As shown in Table 1, the gas diffusion layer of the example was found to suppress roughening of the microporous layer and catalyst layer due to protrusion of carbon fibers contained in the carbon fiber layer, compared to the gas diffusion layer of the comparative example.

[0123] The disclosure of Japanese Patent Application No. 2024-229276, filed on 25 December 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

[0124] (Explanation of symbols) 100 Membrane electrode assembly 10 Polymer electrolyte membrane 20 Gas diffusion electrode 30 Catalyst layer 40 Gas diffusion layer C Electrode catalyst 42 Microporous layer 44 Carbon fiber layer

Claims

1. A gas diffusion layer comprising a carbon fiber layer and a microporous layer provided on the carbon fiber layer, the microporous layer comprising aromatic polyamide pulp, a water-dispersible resin, and a carbon-based conductive material.

2. The gas diffusion layer according to claim 1, wherein the microporous layer has a maximum peak in the pore size distribution of 0.1 μm or more and 5.0 μm or less.

3. The gas diffusion layer according to claim 1, wherein the microporous layer has a tensile modulus of 300 MPa or more and 900 MPa or less.

4. A gas diffusion electrode comprising: a gas diffusion layer according to any one of claims 1 to 3; and a catalyst layer provided on the microporous layer in the gas diffusion layer.

5. A membrane electrode assembly comprising a polymer electrolyte membrane and a pair of gas diffusion electrodes that sandwich the polymer electrolyte membrane, wherein at least one of the pair of gas diffusion electrodes is the gas diffusion electrode described in claim 4.

6. A fuel cell comprising the membrane electrode assembly described in claim 5, and a separator.

7. A method for producing a gas diffusion layer, comprising the step of bonding a microporous sheet containing aromatic polyamide pulp, a water-dispersible resin, and a carbon-based conductive material with a carbon fiber sheet to form a laminate.

8. The method for producing a gas diffusion layer according to claim 7, wherein the microporous sheet has a maximum peak in the pore size distribution of 0.1 μm or more and 5.0 μm or less.

9. The method for manufacturing a gas diffusion layer according to claim 7, wherein the microporous sheet has a tensile modulus of 300 MPa or more and 900 MPa or less.

10. The method for manufacturing a gas diffusion layer according to claim 7, further comprising the step of heating and pressing the laminate in the lamination direction at a temperature of 150°C to 400°C.

11. A method for manufacturing a gas diffusion electrode, comprising the steps of: manufacturing a gas diffusion layer by the manufacturing method described in any one of claims 7 to 10; and providing a catalyst layer on the microporous sheet side of the manufactured gas diffusion layer.

12. A method for manufacturing a membrane electrode assembly, comprising the steps of: manufacturing a gas diffusion layer by the manufacturing method described in any one of claims 7 to 10; and providing a catalyst layer and a polymer electrolyte membrane in that order on the microporous sheet side surface of the manufactured gas diffusion layer.

13. A method for manufacturing a membrane electrode assembly according to claim 12, wherein a catalyst layer and a polymer electrolyte membrane are provided in this order on the microporous sheet side of the manufactured gas diffusion layer, and the assembly is pressed together at a temperature of 60°C to 130°C.

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