Gas diffusion layer, gas diffusion electrode, membrane electrode assembly, water electrolysis device, composition for forming a microporous layer, method for manufacturing a gas diffusion layer, method for manufacturing a gas diffusion electrode

Abstract

To provide a gas diffusion layer, gas diffusion electrode, membrane electrode assembly, and water electrolysis device that suppress the degradation of the catalyst layer and polymer electrolyte membrane and have excellent battery performance; to provide a microporous layer forming composition that can form a gas diffusion layer that suppresses the degradation of the catalyst layer and polymer electrolyte membrane and has excellent battery performance even when mounted on a water electrolysis device, etc.; and to provide a simple method for manufacturing a gas diffusion layer and a method for manufacturing a gas diffusion electrode equipped therewith. [Solution] A gas diffusion layer; gas diffusion electrode; membrane electrode assembly; water electrolysis device; composition for forming a microporous layer; method for manufacturing a gas diffusion layer; and method for manufacturing a gas diffusion electrode, comprising a carbon fiber layer and a microporous layer provided on the carbon fiber layer, wherein a portion of the microporous layer is embedded within the carbon fiber layer.

Description

[Technical Field]

[0001] This disclosure relates to a gas diffusion layer, a gas diffusion electrode, a membrane electrode assembly, a water electrolysis apparatus, a composition for forming a microporous layer, a method for manufacturing a gas diffusion layer, and a method for manufacturing a gas diffusion electrode. [Background technology]

[0002] A water electrolysis device is a device that generates hydrogen and oxygen from water through a chemical reaction mediated by a catalyst. For example, a water electrolysis device includes 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 both a catalyst layer and a gas diffusion layer is called a gas diffusion electrode (GDE).

[0003] 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 discharge fuel gas into the catalyst layer, water-repellent performance to discharge generated water from 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.

[0004] 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 or water-repellent layer) on the surface of the carbon fiber layer, from the viewpoints of suppressing damage to the ion exchange membrane by the fibers contained in the carbon fiber layer, uniformly diffusing the fuel gas into the catalyst layer, and adjusting the wettability of the membrane electrode assembly.

[0005] For example, Patent Document 1 discloses a gas diffusion layer for a water electrolysis cell that includes a mesh structure having a filtration accuracy of 80 μm or less. For example, Patent Document 2 discloses an anion exchange membrane gas diffusion layer for water electrolysis, which includes a film in which carbon nanofibers are in a network form, and the carbon nanofibers have a diameter of 500 nm or less.

[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. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-72818 [Patent Document 2] Special Publication No. 2024-542274 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] When a gas diffusion electrode, which has a catalyst layer on top of a gas diffusion layer, is used as a hydrogen generation electrode, conventionally, the carbon fiber layer has been made of carbon fiber nonwoven fabric, which is made by firing a nonwoven fabric of staple fibers, which are carbon fiber precursors, or carbon fiber paper, which is made by firing a sheet formed by solidifying carbon fiber cut yarn (for example, carbon fibers cut to 3 to 20 mm) with resin.

[0009] The charge necessary for the catalytic reaction is supplied from the voids in the carbon fiber layer via the catalyst layer. However, there is a difference in the length of electron transfer between the areas where the carbon fiber layer and the catalyst layer are in direct contact and the voids, making it easy for electrical loads to occur in the voids. This can lead to localized accelerated catalyst degradation, damage to the polymer electrolyte membrane, and a shortened lifespan of the membrane electrode assembly.

[0010] In conventional technology, in order to extend the maintenance cycle of the polymer electrolyte membrane in a water electrolysis device, it is necessary to take measures such as increasing the thickness of the polymer electrolyte membrane or increasing the amount of catalyst coating. However, increasing the thickness of the polymer electrolyte membrane tends to reduce ionic conductivity and increase power consumption. Furthermore, since precious metals are typically used as catalysts, increasing the amount of catalyst coating raises concerns about increased costs.

[0011] In view of the above circumstances, this disclosure aims to provide a gas diffusion layer that suppresses the degradation of the catalyst layer and polymer electrolyte membrane and has excellent battery performance, a gas diffusion electrode equipped therewith, a membrane electrode assembly, and a water electrolysis device. Furthermore, this disclosure provides a microporous layer-forming composition that can suppress the degradation of the catalyst layer and polymer electrolyte membrane and form a gas diffusion layer with excellent battery performance, even when installed in a water electrolysis device or the like. Furthermore, this disclosure also provides a simple method for manufacturing a gas diffusion layer and a method for manufacturing a gas diffusion electrode equipped therewith. [Means for solving the problem]

[0012] The above problems will be solved by the following means. <1> A carbon fiber layer, A microporous layer provided on the carbon fiber layer comprises aromatic polyamide pulp, fluororesin, and carbon-based conductive material, It has, A gas diffusion layer in which a portion of the aforementioned microporous layer is embedded within the carbon fiber layer. <2> A portion of the microporous layer penetrates to a depth of 10% or more of the thickness of the microporous layer from the interface between the carbon fiber layer and the microporous layer, <1> The gas diffusion layer described above. <3> The microporous layer has a maximum peak in the pore size distribution of 0.1 μm or more and 5.0 μm or less. <1> or <2> The gas diffusion layer described above. <4> The above-mentioned, which is for water electrolysis. <1> ~ <3> A gas diffusion layer as described in any one of the following. <5> The aforementioned <1> ~ <4> A gas diffusion layer described in any one of the following, A catalyst layer provided on the microporous layer in the gas diffusion layer, A gas diffusion electrode having <6> Polymer electrolyte membrane, A pair of gas diffusion electrodes sandwiching the polymer electrolyte membrane, The membrane electrode assembly, wherein at least one of the pair of gas diffusion electrodes is the gas diffusion electrode according to <5>. <7> The membrane electrode assembly according to <6>, A separator, And a water electrolysis device. <8> A composition for forming a microporous layer containing aromatic polyamide pulp, a fluororesin, and a carbon-based conductive material. <9> A method for producing a gas diffusion layer, including a step of applying a liquid for a microporous layer containing aromatic polyamide pulp, a fluororesin, and a carbon-based conductive material onto a carbon fiber layer. A method for producing a gas diffusion layer. <10> A method for producing a gas diffusion electrode, including a step of providing a catalyst layer on the surface on the microporous layer side of the gas diffusion layer produced by the production method according to <9>.

Advantages of the Invention

[0013] According to one embodiment of the present disclosure, there are provided a gas diffusion layer that suppresses deterioration of a catalyst layer and a polymer electrolyte membrane and has excellent battery performance, a gas diffusion electrode including the same, a membrane electrode assembly, and a water electrolysis device. According to one embodiment of the present disclosure, there is provided a composition for forming a microporous layer that can form a gas diffusion layer that suppresses deterioration of a catalyst layer and a polymer electrolyte membrane and has excellent battery performance even when mounted in a water electrolysis device or the like. According to another embodiment of the present disclosure, there are also provided a simple method for producing a gas diffusion layer and a method for producing a gas diffusion electrode including the same.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of the layer structure of a membrane electrode assembly according to the present disclosure. [Figure 2] FIG. 2 is a cross-sectional photograph in the lamination direction of the gas diffusion layer of Example 1 observed by a scanning electron microscope.

Modes for Carrying Out the Invention

[0015] The following describes an example of an embodiment of this disclosure. These descriptions and examples are illustrative and do not limit the scope of the invention. In numerical ranges described stepwise within 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. Furthermore, in numerical ranges described within this specification, the upper or lower limit of that range may be replaced with the values ​​shown in the examples.

[0016] Each component may contain multiple types of the relevant substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition.

[0017] 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.

[0018] <Methods for measuring various physical properties> The measurement methods used in this specification are as follows: The 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 five arbitrary points using a thickness gauge (manufactured by Ono Sokki), and the arithmetic mean of these measurements is taken as the thickness of the microporous layer.

[0019] The method for measuring the water contact angle of a microporous layer is as follows. Water is dropped onto a 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.

[0020] The method for measuring the pore size distribution of a microporous layer is as follows: A fully automated pore size distribution analyzer (Anton Paar PoreMaster60-GT) is used to measure the pore size distribution in a microporous layer, ranging from 0.01 μm to 100 μm. The observed maximum peak value is then defined as the maximum peak in the pore size distribution, with the vertical axis being [dV / d(logd)(cc / g)] and the horizontal axis being pore size (μm). Note that "dV / d(logd)" represents the cumulative pore volume distribution.

[0021] The method for measuring the tensile modulus of a microporous layer is as follows. A microporous layer was collected from the gas diffusion layer to be measured, and a 13 cm sample was obtained. Using a Tensilon (Orientec RTC-1310A), the breaking strength and elongation at break were measured with a chuck distance of 10 cm, a tensile speed of 50 mm / min, at 20°C to 25°C, and 65% RH conditions, and the tensile modulus was calculated.

[0022] The layer structure of the gas diffusion layer can be confirmed by cutting the gas diffusion layer along the stacking direction and observing the cross-section with a scanning electron microscope (SU3500, Hitachi, Ltd.).

[0023] 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.

[0024] <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, which includes aromatic polyamide pulp, fluororesin, and a carbon-based conductive material, with a portion of the microporous layer penetrating into the carbon fiber layer.

[0025] In the gas diffusion layer according to this disclosure, a portion of the microporous layer is embedded within the carbon fiber layer. This reduces the size of the porous voids on the surface in contact with the catalyst layer, thereby reducing the region where charge supplied from the gas diffusion layer is difficult to propagate. As a result, the uniformity of charge supply to the catalyst is increased, and local degradation of both the catalyst layer and the polymer electrolyte membrane is further suppressed. Furthermore, the gas diffusion layer according to this disclosure includes a microporous layer containing a carbon fiber layer, aromatic polyamide pulp, fluororesin, and a carbon-based conductive material. Therefore, the microporous layer that penetrates the carbon fiber layer also exhibits excellent conductive pathways and gas diffusion properties. These synergistic effects suppress the degradation of the catalyst layer and polymer electrolyte membrane, resulting in superior battery performance.

[0026] Furthermore, the gas diffusion layer according to this disclosure, having the above configuration, exhibits superior catalytic activity because fine conductive paths are formed in the region where the microporous layer penetrates the carbon fiber layer. Therefore, the amount of catalyst coating (e.g., 0.1 mg / cm³) is lower than in conventional materials. 2 The following can be reduced:

[0027] [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. Examples of carbon fiber layers include woven fabrics, nonwoven fabrics, felt-like materials, and carbon paper.

[0028] The carbon fiber layer has a specific gravity of 0.2 g / cm³, which is desirable for effectively controlling the diffusivity of the gas diffusion layer. 3 Preferably, it is 0.3 g / cm³ or more. 3 It is more preferable that the above conditions are met. The carbon fiber layer has a specific gravity of 0.9 g / cm³, from the viewpoint of suitably controlling the diffusivity of the gas diffusion layer and suitably controlling the degree of penetration into the microporous layer. 3 Preferably, it is 0.6 g / cm³. 3 The following is more preferable:

[0029] 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 4.0 μm to 30.0 μm, and more preferably 5.0 μm to 20.0 μm.

[0030] When the carbon fiber layer is of a paper type such as carbon paper, the average fiber length of the carbon fiber layer is preferably 1.0 mm or more and 30.0 mm or less, and more preferably 3.0 mm or more and 20.0 mm or less, from the viewpoint of handling.

[0031] When the carbon fiber layer is a nonwoven fabric (for example, a nonwoven fabric produced by carbonizing and firing a carbon fiber precursor (e.g., acrylic oxide fibers such as Pyromex® manufactured by Teijin Limited) in an inert atmosphere), the average fiber length of the carbon fiber layer is preferably 30 mm or more and 80 mm or less from the viewpoint of productivity and handling of the carbon fiber layer.

[0032] 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.

[0033] [Microporous layer] The microporous layer (so-called MPL layer) contains aromatic polyamide pulp, fluororesin, and carbon-based conductive material. The microporous layer may further contain other materials besides aromatic polyamide pulp, fluororesin, and carbon-based conductive materials.

[0034] The microporous layer is provided on top of the carbon fiber layer, with a portion of the microporous layer penetrating into the carbon fiber layer. The microporous layer only needs to be partially embedded in the carbon fiber layer; it may be embedded throughout the entire carbon fiber layer.

[0035] (Aromatic polyamide pulp) Aromatic polyamide pulp (hereinafter also referred to as "aramid pulp") is, for example, a fiber of aromatic polyamide having amide bonds in which 85 mol% or more of the amide bonds are formed by the dehydration condensation of aromatic diamine components and aromatic dicarboxylic acid components. It is preferable that the aramid pulp has fibers that are highly fibrillated. Examples of aramids include poly(p-phenylene terephthalamide), copoly(p-phenylene-3,4'-oxydiphenylene-terephthalamide), poly(metaphenylene isophthalamide), poly(p-benzuamide), poly-4,4'-diaminobenzanilide, poly(p-phenylene-2,6-naphthalicamide), copoly(p-phenylene / 4,4'-(3,3'-dimethylbiphenylene)terephthalamide, poly(orthophenylene terephthalamide), poly(p-phenylene phthalamide), and poly(metaphenylene isophthalamide).

[0036] 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.

[0037] 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, even more preferably 0.3 mm to 3.0 mm, and particularly preferably 0.2 mm to 1.0 mm.

[0038] (Fluororesin) The fluororesin may be contained within the microporous layer, for example, attached to the surface of the aromatic polyamide pulp, or fused to the surface of the aromatic polyamide pulp. The inclusion of this fluororesin imparts water repellency to the microporous layer.

[0039] The fluororesin is not particularly limited, and any known fluororesin used in the gas diffusion layer may be used. The fluororesin may be used alone or in combination of two or more types.

[0040] Examples of fluororesins include tetrafluoroethylene resin (hereinafter sometimes referred to as "PTFE"), perfluoroalkoxy resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, tetrafluoroethylene-ethylene copolymer resin, vinylidene fluoride resin, trifluoroethylene chloride, and the like. Among the above, PTFE is preferred as the fluororesin from the viewpoint of having excellent heat resistance.

[0041] (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. The inclusion of this carbon-based conductive material imparts conductivity to the microporous layer.

[0042] The carbon-based conductive material is not particularly limited, and any known carbon-based conductive material used in the gas diffusion layer may be used. The carbon-based conductive material may be used alone or in combination of two or more types.

[0043] As a carbon-based conductive material, it is preferable to use a material that has a carbon content of 94% by mass or more and a resistivity of 5 Ω·cm or less, from the viewpoint of conductive performance. Specific examples of carbon-based conductive materials include carbon fibers, carbon black, graphite particles, carbon nanotubes, carbon milled fibers, carbon nanofibers, carbon nanohorns, and graphene.

[0044] Among the above, the carbon-based conductive material preferably includes at least one selected from the group consisting of graphite particles, carbon black, carbon fibers, carbon milled fibers, and carbon nanofibers; more preferably includes at least one selected from the group consisting of carbon black, carbon fibers, carbon nanofibers, and carbon milled fibers; and even more preferably includes carbon nanofibers. When the carbon-based conductive material includes at least one selected from the above group, degradation of the catalyst layer and polymer electrolyte membrane is suppressed, resulting in excellent battery performance. In addition, the risk of contamination by metal species is low, and electrochemical stability is also excellent.

[0045] • Graphite particles Examples of graphite particles include flaky graphite, scale-like graphite, clay-like graphite, artificial graphite, expanded graphite, expanded graphite, leaf-like graphite, nodular graphite, and spheroidal graphite. Spheroidal and flaky graphite are particularly preferred. The average particle size of the graphite particles is preferably between 0.05 μm and 50.00 μm.

[0046] • Carbon Black Examples of carbon black include acetylene black and Ketjenblack (registered trademark), which has a hollow shell structure. Ketjenblack is particularly preferred.

[0047] The average primary particle size of the carbon black is preferably, for example, 1.0 nm to 500.0 nm, more preferably 1.0 nm to 200.0 nm, and even more preferably 10.0 nm to 100.0 nm. The average secondary particle diameter of the carbon black is preferably, for example, 0.5 nm to 20.0 μm. If the average secondary particle diameter is 0.5 μm or more, further aggregation of the carbon black is suppressed when preparing the carbon black dispersion. If the average secondary particle diameter is 20.0 μm or less, the carbon-based conductive material can easily penetrate into the gas diffusion layer, improving the conductivity of the gas diffusion layer.

[0048] • Carbon fiber and carbon milled fiber Examples of carbon fibers and carbon milled fibers include PAN-based carbon fibers, pitch-based carbon fibers, and phenol-based carbon fibers, and among these, it is preferable to include pitch-based carbon fibers.

[0049] In this specification, "carbon milled fiber" refers to fibrous carbon fiber that has been ground into a powder (milled) form using a pulverizer or the like.

[0050] When using at least one of carbon fibers and / or carbon milled fibers, the average fiber diameter is not particularly limited, but is preferably, for example, 3 μm to 20 μm, and more preferably 4 μm to 13 μm.

[0051] The average fiber diameter is a value measured by microscopic observation. If the carbon fiber has a flattened cross-section, the arithmetic mean of the major and minor axes is used as the average fiber diameter.

[0052] 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.

[0053] The average fiber length (so-called cut length) of carbon fibers or carbon milled fibers is not particularly limited, but it is preferable to have an average fiber length of 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.

[0054] 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 conductivity of the gas diffusion layer. Furthermore, even when a battery incorporating this gas diffusion layer is operated for a long period of time, the degradation of the gas diffusion layer is suppressed.

[0055] • Carbon nanofibers Carbon nanofibers may be single fibers or aggregates. The average fiber diameter of the 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 easier to increase the fiber density. The average fiber diameter of the 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 the 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.

[0056] 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. The average fiber length of the carbon nanofibers is preferably 10 μm to 100 μm, and more preferably 12 μm to 80 μm, from the viewpoint of the strength of the gas diffusion layer.

[0057] Carbon nanofibers can be produced, for example, by the method disclosed in International Publication No. 2020 / 045243. Specifically, (1) A fiberization step to obtain 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, thereby fiberizing the mesophase pitch. (2) A stabilization step to stabilize the resin composite fiber and obtain a resin composite stabilized fiber, (3) A thermoplastic resin removal step to obtain a stabilized fiber by removing the thermoplastic resin from the resin composite stabilizing fiber, (4) A carbonization and calcination step in which the stabilized fibers are heated in an inert atmosphere to carbonize or graphitize them to obtain a carbon fiber aggregate, A method for producing a carbon fiber aggregate containing carbon fiber is also mentioned.

[0058] (Content of various materials) The aromatic aramid pulp content 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 aromatic aramid pulp content is 1% by mass or more, the degradation of the catalyst layer and polymer electrolyte membrane is suppressed, resulting in superior battery performance. Furthermore, the durability and water repellency of the gas diffusion layer are maintained more effectively. When the aromatic aramid pulp content is 20% by mass or less, the relative decrease in the proportion of carbon-based conductive materials and fluororesins is suppressed, thereby suppressing the degradation of the catalyst layer and polymer electrolyte membrane and resulting in superior battery performance.

[0059] The fluororesin content is preferably 1% by mass or more and 30% by mass or less, and more preferably 2% by mass or more and 25% by mass or less, relative to the total solid content of the microporous layer. When the fluororesin content is 1% by mass or more, the degradation of the catalyst layer and polymer electrolyte membrane is suppressed, resulting in superior battery performance. Furthermore, it provides superior water repellency. When the fluororesin content is 30% by mass or less, the relative decrease in the proportion of aromatic aramid pulp and carbon-based conductive materials is suppressed, thereby suppressing the degradation of the catalyst layer and polymer electrolyte membrane and resulting in superior battery performance. In addition, the reduction in the porosity of the microporous layer due to excessive fluororesin is suppressed.

[0060] The content of the carbon-based conductive material is preferably 50% to 98% by mass, and more preferably 55% to 95% by mass, relative to the total solid content of the microporous layer. When the carbon-based conductive material content is 50% by mass or more, the degradation of the catalyst layer and polymer electrolyte membrane is suppressed, resulting in superior battery performance. Furthermore, conductivity is also improved. When the carbon-based conductive material content is 98% by mass or less, the relative decrease in the proportion of aromatic aramid pulp and fluororesin is suppressed, thereby suppressing the degradation of the catalyst layer and polymer electrolyte membrane and resulting in superior battery performance.

[0061] The mass ratio of aromatic aramid pulp to fluororesin (aromatic aramid pulp / fluororesin) 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 above mass ratio is 10 / 90 or higher, the reinforcing effect is superior due to aromatic aramid pulp. On the other hand, when the above mass ratio is 70 / 30 or lower, the water repellency is superior due to fluororesin.

[0062] The mass ratio of aromatic aramid pulp to carbon-based conductive material (aromatic aramid 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 superior due to aromatic aramid pulp. When the above mass ratio is 50 / 50 or lower, the conductivity is superior due to carbon-based conductive material. In particular, when the carbon-based conductive material contains at least one of carbon fiber and carbon-milled fiber, when the above mass ratio is above the lower limit, the degradation of the catalyst layer and polymer electrolyte membrane is suppressed, resulting in superior battery performance.

[0063] (Other materials) The microporous layer may further contain other materials besides aromatic aramid pulp, fluororesin, and carbon-based conductive materials. Examples of other materials include electrode catalysts and ionomer resins.

[0064] The microporous layer preferably further contains an electrode catalyst. As the electrode catalyst, catalysts used in known fuel cells such as polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), and biobatteries, as well as water electrolysis devices, can be used. The type and content of the electrode catalyst may be appropriately selected depending on the application of the gas diffusion layer. Examples of electrode catalysts include carbon catalysts, platinum catalysts, iridium catalysts, and enzymes. Among the above, it is preferable to include a platinum catalyst as the electrode catalyst from the viewpoint of battery performance.

[0065] (Characteristics of microporous layers) 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 5.0 μm or less, the problem of excessively large void sizes in the porous material hindering the propagation of charge supplied from the gas diffusion layer is suppressed. As a result, the charge supply to the catalyst is improved, the degradation of the catalyst layer and polymer electrolyte membrane is suppressed, and the battery performance is superior.

[0066] The microporous layer has a maximum peak in the pore size distribution of 0.1 μm or larger, preferably 0.2 μm or larger, and more preferably 0.3 μm or larger. When the maximum peak is 0.1 μm or higher, degradation of the catalyst layer and polymer electrolyte membrane is suppressed, resulting in superior battery performance.

[0067] The microporous layer has a maximum peak in the pore size distribution of 5.0 μm or less, preferably 3.0 μm or less, and more preferably 2.0 μm or less. When the maximum peak is 5.0 μm or less, degradation of the catalyst layer and polymer electrolyte membrane is suppressed, resulting in superior battery performance. Furthermore, excessive pore size enlargement is suppressed, leading to excellent water repellency. Additionally, when applied to a membrane electrode assembly, excessive increase in wettability is suppressed. As a result, battery performance is further improved.

[0068] 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. If the tensile modulus of the microporous layer is 200 MPa or higher, degradation of the catalyst layer and polymer electrolyte membrane is suppressed, resulting in superior battery performance. Furthermore, the strength of the gas diffusion layer is also superior. If the tensile modulus of the microporous layer is 900 MPa or lower, degradation of the catalyst layer and polymer electrolyte membrane is suppressed, resulting in superior battery performance.

[0069] The water contact angle of the microporous layer is not particularly limited, but is preferably 130° to 160°, and more preferably 140° to 150°. When the water contact angle is within the above range, the degradation of the catalyst layer and polymer electrolyte membrane is suppressed, resulting in superior battery performance.

[0070] The thickness of the microporous layer may be, for example, 170 μm or more and 250 μm or less. The thickness of the microporous layer is preferably 50 μm to 150 μm, and more preferably 50 μm to 100 μm, from the viewpoint of further suppressing the degradation of the catalyst layer and the polymer electrolyte membrane. The thickness of the microporous layer refers to the shortest distance from the side where the microporous layer is located to the point where it penetrates deepest in the direction of the carbon fiber layer.

[0071] [Characteristics of the gas diffusion layer] In the gas diffusion layer, a portion of the microporous layer penetrates into the carbon fiber layer.

[0072] The gas diffusion layer only needs to have a portion of the microporous layer embedded within the carbon fiber layer, or the entire area of ​​the microporous layer (i.e., an area of ​​100% or more of the total area of ​​the microporous layer) may be embedded within the carbon fiber layer.

[0073] Preferably, the gas diffusion layer has a portion of the microporous layer that penetrates to a depth of 10% or more of the thickness of the microporous layer from the interface between the carbon fiber layer and the microporous layer, more preferably to a depth of 20% or more, and even more preferably to a depth of 30% or more. In the gas diffusion layer, it is preferable that a portion of the microporous layer penetrates from the interface between the carbon fiber layer and the microporous layer to a depth of 100% or less of the thickness of the microporous layer. When the material penetrates to a depth of 10% or more, fine conductive paths are more easily formed by carbon-based conductive materials in the penetration region, resulting in superior battery performance. Furthermore, it exhibits excellent resistance to peeling of the microporous layer from the carbon fiber layer. When the material penetrates to a depth of 100% or less, the decrease in gas diffusion in the penetration region is suppressed, resulting in superior battery performance. This is also preferable from the standpoint of manufacturing costs.

[0074] The method for controlling the degree to which the above-mentioned microporous layer penetrates is not particularly limited, but examples include using a microporous layer-forming composition as described later in this disclosure.

[0075] The method for confirming the degree of penetration of the above-mentioned microporous layer is as follows. (1) The gas diffusion layer to be measured is cut in the direction of stacking, and the cut surface is observed using a scanning electron microscope manufactured by JEOL Ltd. at a magnification of 100 to 500 times. (2) From the observation surface, determine the shortest straight-line distance X from the end of the carbon fiber layer on the interface side with the microporous layer to the end in the thickness direction (i.e., the end opposite to the end on the interface side with the microporous layer). (3) From the end on the interface side with the microporous layer, a point is determined that is 1% of the straight-line distance X in the thickness direction. (4) On the observation surface, it is determined whether at least one component contained in the microporous layer (for example, aromatic polyamide pulp, fluororesin, carbon-based conductive material, etc.) has penetrated into the region from the edge on the interface side with the microporous layer to a point that is 1% of the straight-line distance X in the thickness direction.

[0076] The overall thickness of the gas diffusion layer is not particularly limited, but may be, for example, 100 μm to 5000 μm. The thickness of the gas diffusion layer can be controlled by adjusting the basis weight of the carbon fiber layer and the microporous layer, as well as the temperature and pressure during hot pressing, when manufacturing the gas diffusion layer.

[0077] [Uses of gas diffusion layers] The applications of the gas diffusion layer relating to this disclosure are not particularly limited and can be applied to known devices that use a gas diffusion layer, such as hydrogen electrodes, water electrolysis devices, electrolysis equipment, flow batteries, and fuel cells, but it is preferable to use it for water electrolysis.

[0078] [Method for manufacturing a gas diffusion layer] 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.

[0079] <Gas Diffusion Electrode> The gas diffusion electrode according to this disclosure comprises a gas diffusion layer relating to this disclosure and a catalyst layer provided on a microporous layer in the gas diffusion layer. According to the gas diffusion electrode described herein, when incorporated into a membrane electrode assembly, it suppresses the degradation of the catalyst layer and the polymer electrolyte membrane, resulting in superior battery performance.

[0080] 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.

[0081] <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. The membrane electrode assembly according to this disclosure suppresses the degradation of the catalyst layer and the polymer electrolyte membrane, resulting in superior battery performance.

[0082] 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 that sandwich 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 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. When this membrane electrode assembly is installed in a water electrolysis device, as shown below, water is electrolyzed by applying a voltage to the anode and cathode electrodes, generating oxygen at the anode electrode and hydrogen at the cathode electrode. The hydrogen generated at the cathode electrode then conducts to the cathode electrode through the polymer electrolyte membrane 10, extracting electrons in this process and generating electricity. Water is generated at the anode electrode, and this water wets the polymer electrolyte membrane 10, increasing its proton conductivity.

[0083] Anode: H2O → 1 / 2O2 + 2H++2e - Cathode: 2H++2e - →H2

[0084] 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.

[0085] 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.

[0086] <Water electrolysis device> The water electrolysis apparatus according to this disclosure comprises a membrane electrode assembly according to this disclosure and a separator. The fuel cell described herein suppresses the degradation of the catalyst layer and polymer electrolyte membrane, resulting in superior battery performance.

[0087] The separator is not particularly limited, and any known separator applicable to water electrolysis devices or fuel cells can be used.

[0088] <Composition for forming microporous layer> The composition for forming a microporous layer according to this disclosure comprises aromatic polyamide pulp, fluororesin, and carbon-based conductive material. According to the microporous layer forming composition of this disclosure, when a gas diffusion layer having a microporous layer is formed using it, the degradation of the catalyst layer and the polymer electrolyte membrane is suppressed, resulting in excellent battery performance.

[0089] Preferred embodiments of the aromatic polyamide pulp, fluororesin, and carbon-based conductive material in the microporous layer forming composition according to this disclosure are the same as the preferred embodiments exemplified in the gas diffusion layer according to this disclosure.

[0090] The microporous layer-forming composition according to this disclosure may further contain other materials besides aromatic polyamide pulp, fluororesin, and carbon-based conductive material. Preferred embodiments of the other materials include those similar to those exemplified in the gas diffusion layer according to this disclosure.

[0091] The method for forming a microporous layer using the microporous layer-forming composition according to this disclosure is not particularly limited, and known methods for forming a microporous layer, such as papermaking lamination (for example, passing the microporous layer-forming composition onto a carbon fiber layer), impregnation, spray coating, and drop method, can be applied. Among the above, papermaking lamination and spray coating methods are preferred as methods for forming a microporous layer, from the viewpoint of allowing the microporous layer to penetrate the carbon fiber layer and further suppressing the occurrence of localized electrical loads in the gas diffusion layer.

[0092] <Method for manufacturing a gas diffusion layer> The method for manufacturing a gas diffusion layer according to this disclosure includes a step of coating a microporous layer on a carbon fiber layer using a microporous layer forming composition containing aromatic polyamide pulp, fluororesin, and carbon-based conductive material (hereinafter also referred to as the microporous layer coating step).

[0093] According to the method for manufacturing a gas diffusion layer described herein, when the obtained gas diffusion layer is used in a water electrolysis device or the like, the degradation of the catalyst layer and polymer electrolyte membrane is suppressed, resulting in superior battery performance.

[0094] The preferred embodiments of the aromatic polyamide pulp, fluororesin, and carbon-based conductive material in the method for manufacturing the gas diffusion layer according to this disclosure are the same as the preferred embodiments exemplified in the gas diffusion layer according to this disclosure. The preferred embodiment of the carbon fiber layer in the method for manufacturing the gas diffusion layer according to this disclosure is the same as the preferred embodiment illustrated in the gas diffusion layer according to this disclosure.

[0095] The method for manufacturing the gas diffusion layer according to this disclosure may further include other materials other than aromatic polyamide pulp, fluororesin, and carbon-based conductive material. Preferred other materials include those similar to those exemplified in the gas diffusion layer according to this disclosure.

[0096] The method for applying the microporous layer onto the carbon fiber layer is not particularly limited as long as the microporous layer-forming composition is used, and known methods for forming a microporous layer such as papermaking lamination (for example, applying the microporous layer-forming composition onto the carbon fiber layer and then rolling up the paper), impregnation, spray coating, and drop method can be applied.

[0097] In the microporous layer formation process, a microporous layer is applied onto the carbon fiber layer using a microporous layer formation composition containing aromatic polyamide pulp, fluororesin, and a carbon-based conductive material. From the viewpoint of suppressing the degradation of the catalyst layer and polymer electrolyte membrane and achieving excellent battery performance, the microporous layer formation composition according to the present disclosure described above is preferred as the microporous layer formation composition containing aromatic polyamide pulp, fluororesin, and a carbon-based conductive material.

[0098] The method for manufacturing a gas diffusion layer according to this disclosure may further include other steps besides the microporous layer formation step. Examples of other steps include a sintering step, a pressurizing step, a crimping step, a machining step such as cutting, and a packaging step. Each step may be performed simultaneously in combination with the laminate formation step, or separately.

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

[0100] According to this disclosure, when the obtained gas diffusion electrode is used in a water electrolysis device or the like, it suppresses the degradation of the catalyst layer and polymer electrolyte membrane, resulting in superior battery performance.

[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. [Examples]

[0102] 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.

[0103] - Fabrication of a gas diffusion layer - <Example 1> On one side of a carbon fiber nonwoven fabric (Freudenberg H23, 210 μm thick, 95 g / m² basis weight), a mixed slurry of PotenCia®, a carbon-based conductive material, and aromatic polyamide pulp (mass ratio: carbon-based conductive material / aromatic aramid pulp = 95 / 5) was applied using a papermaking process, at a rate of 25 g / m². 2 The layers were stacked in such a manner to create a gas diffusion layer of the embodiment having a microporous layer and a carbon fiber layer.

[0104] The content and ratio of each material relative to the total solid content of the microporous layer in Example 1 are as follows. • Total amount of carbon-based conductive material: 90% by mass • Aromatic aramid pulp content: 5% by mass • Fluororesin content: 5% by mass • Mass ratio (aromatic aramid pulp / carbon-based conductive material): 5 / 90 • Mass ratio (aromatic aramid pulp / fluororesin): 50 / 50 • Microporous layer: More than 10% of the total area of ​​the microporous layer is embedded in the carbon fiber layer.

[0105] -Physical properties of the gas diffusion layer- For the microporous layer in the gas diffusion layer of Example 1, the thickness of the microporous layer, the maximum peak value of the pore size distribution, the tensile modulus, the water contact angle, and the penetration rate into the carbon fiber layer were measured using the measurement method described above. The results are shown in Table 1. Items marked with [-] in the table indicate that the measurement was not performed. In the table, the item [Penetration rate into carbon fiber layer] refers to the percentage of the microporous layer that penetrates to the depth in the thickness direction of the carbon fiber layer from the interface between the carbon fiber layer and the microporous layer.

[0106] <Rating> The gas diffusion layer prepared in Example 1 was examined using a scanning electron microscope to observe cross-sectional images and evaluate the state of the microporous layer. Figure 2 is a cross-sectional photograph of the gas diffusion layer of Example 1 observed by a scanning electron microscope in the stacking direction. As shown in Figure 2 and Table 1, it can be seen that in the gas diffusion layer of Example 1, a part of the microporous layer penetrates from the interface between the carbon fiber layer and the microporous layer to a depth of 30% or more in the thickness direction of the carbon fiber layer.

[0107]

Table 1

[0108] <Evaluation of Battery Performance> The gas diffusion layer of Example 1 was used as the gas diffusion layer on the anode (positive electrode: oxygen electrode) side to fabricate a cell for water electrolysis. The cell has the configuration shown in Figure 1. Using the cell, the cell voltage was measured at a cell temperature of 80° and a current density of 0 to 6 A / cm 2 and current density-voltage curves were obtained respectively. The cell voltage when the current density obtained from the current density-voltage curve in the cell is 1 A / cm 2 is shown in Table 1.

[0109] The details of the device environment are as follows. ·Separator: JARI-2, 0.3 mm / 0.3 mm straight 1 cm 2 ·Gas diffusion layer: size 1 cm × 1 cm ·Humidifier: cathode 80°C / anode 75°C ·Gas supply: anode (oxygen electrode) is 0.4 L / min, cathode (hydrogen electrode) is 0.95 L / min ·Back pressure: anode 100 KPa / cathode 100 KPa ·Ion exchange membrane (CCM) coated with an electrode catalyst (platinum-supported carbon) ·Catalyst amount (i.e., platinum amount) on the anode (cathode: oxygen electrode) side 0.1 mg / cm 2 ·Catalyst amount (i.e., platinum amount) on the cathode (anode: hydrogen electrode) side 0.4 mg / cm 2 ·Anode (cathode: oxygen electrode): A conductive and water-repellent carbon fiber layer was used as the cathode (gas diffusion electrode) by coating carbon fiber paper (SGL25BC, water-repellent, with PTFE content of 5% by mass) manufactured by SGL Carbon Japan Co., Ltd. with a mixed paste (a mixed paste in which the solid content of PTFE is 23% by mass and the solid content of carbon black is 77% by mass). The carbon fiber layer has a maximum peak in the pore size distribution in the range of 0.1 μm to less than 0.2 μm.

[0110] As shown in Table 1, the gas diffusion layer in the example was found to have excellent battery performance. In other words, the gas diffusion layer in the example was found to suppress the degradation of the catalyst layer and the polymer electrolyte membrane. [Explanation of Symbols]

[0111] 100 Membrane electrode assembly 10 Polymer electrolyte membrane 20 Gas diffusion electrode 30 Catalyst layer 40 Gas diffusion layer C Electrocatalyst 42 Microporous layer 44 Carbon fiber layer

Claims

1. A carbon fiber layer, A microporous layer provided on the carbon fiber layer comprises aromatic polyamide pulp, fluororesin, and carbon-based conductive material, It has, A gas diffusion layer in which a portion of the aforementioned microporous layer is embedded within the carbon fiber layer.

2. The gas diffusion layer according to claim 1, wherein a portion of the microporous layer penetrates to a depth of 10% or more of the thickness of the microporous layer from the interface between the carbon fiber layer and the microporous layer.

3. The gas diffusion layer according to claim 1 or claim 2, 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.

4. A gas diffusion layer according to claim 1 or claim 2, for use in water electrolysis.

5. A gas diffusion layer according to claim 1 or claim 2, A catalyst layer provided on the microporous layer in the gas diffusion layer, A gas diffusion electrode having

6. Polymer electrolyte membrane, The system comprises a pair of gas diffusion electrodes that sandwich the polymer electrolyte membrane, A membrane electrode assembly wherein at least one of the pair of gas diffusion electrodes is the gas diffusion electrode described in claim 5.

7. The membrane electrode assembly according to claim 6, Separator and, A water electrolysis device equipped with the following features.

8. A composition for forming a microporous layer, comprising aromatic polyamide pulp, fluororesin, and carbon-based conductive material.

9. The process includes applying a microporous layer liquid containing aromatic polyamide pulp, fluororesin, and carbon-based conductive material onto a carbon fiber layer. A method for manufacturing a gas diffusion layer.

10. A method for manufacturing a gas diffusion electrode, comprising the step of providing a catalyst layer on the microporous layer side of a gas diffusion layer manufactured by the manufacturing method described in claim 9.

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