Gas diffusion layer and method for manufacturing the same

Abstract

To provide a new gas diffusion layer with high liquid water discharge performance and a manufacturing method thereof.SOLUTION: A gas diffusion layer includes a base material, and a carbon nanotube film formed on the surface of the base material. The base material is made of a conductive porous material. The carbon nanotube film includes in-plane oriented carbon nanotubes. The thickness of the base material is preferably 90 μm or more and 250 μm or less. The thickness of the carbon nanotube film is preferably 0.1 μm or more and 30 μm or less. Furthermore, the contact angle of water on the surface of the carbon nanotube film is preferably 40° or more and 140° or less.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a gas diffusion layer and a method for manufacturing the same, and more particularly to a gas diffusion layer having high liquid water discharge performance and a method for manufacturing the same.

Background Art

[0002] A solid polymer fuel cell includes a membrane electrode assembly (MEA) in which electrodes (catalyst layers) are joined to both surfaces of an electrolyte membrane made of a solid polymer electrolyte. Also, in a solid polymer fuel cell, a gas diffusion layer is generally disposed outside the catalyst layer. The gas diffusion layer is for supplying a reaction gas and electrons to the catalyst layer, and carbon paper, carbon cloth, etc. are used. Further, a separator having a gas flow path is disposed outside the gas diffusion layer. A solid polymer fuel cell usually has a structure (fuel cell stack) in which a plurality of single cells each composed of such an MEA, a gas diffusion layer, and a separator are stacked.

[0003] In a solid polymer fuel cell, an appropriate water content is required for the electrolyte membrane to exhibit good proton conductivity. Therefore, when the temperature of the fuel cell during power generation is high or the amount of moisture contained in the supply gas is small, the electrolyte membrane dries out and the performance deteriorates. On the other hand, when power generation is performed using a solid polymer fuel cell, water is generated by an electrode reaction on the cathode side. Therefore, when the temperature of the fuel cell is low and the amount of moisture in the supply gas is large, liquid water is likely to occur in the gas diffusion layer on the cathode side. Excessive liquid water inhibits oxygen transport and causes a decrease in the performance of the fuel cell.

[0004] To suppress performance degradation under high humidity conditions, the gas diffusion layer needs to possess not only high gas permeability but also high water repellency. Therefore, the gas diffusion layer generally uses a microporous layer (a layer containing conductive particles and water-repellent particles, with fine pores) formed on the surface of a porous substrate such as carbon paper. The microporous layer is generally formed by applying a paste containing conductive and water-repellent particles to the surface of a porous substrate, drying, and firing it. However, the method of applying and drying the paste is a complicated process.

[0005] Therefore, various proposals have been made to solve this problem. For example, Patent Document 1 discloses a membrane electrode assembly comprising a gas diffusion layer made solely of carbon nanotube film. The document states: (A) Because carbon fiber paper has an uneven distribution of carbon fibers, when used as a gas diffusion layer, it is not possible to diffuse the reaction gas uniformly, and (B) Carbon nanotube films have a uniformly distributed microporous structure, so when used as a gas diffusion layer, they allow for uniform diffusion of the reaction gas. It is stated.

[0006] Patent Document 2 contains: (a) A catalyst stack is formed by depositing thin films of Fe (2 nm) / Ti (5 nm) / Al (2 nm) / Fe (1 nm) in this order on the surface of carbon paper. (b) Using the CVD method, a CNT mat is formed on the surface of the catalyst stack. (c) Place the carbon paper on which the CNT mat has been formed onto the carbon paper impregnated with polytetrafluoroethylene. A multilayer structure obtained by this process is disclosed.

[0007] The document states: (A) By this method, a CNT mat can be formed consisting of carbon nanotubes that are substantially parallel to each other and oriented perpendicular to a carbon fiber-based support, and (B) Such a multilayer structure can be used as a diffusion layer for solid polymer electrolytes. It is stated.

[0008] Patent Document 1 discloses a gas diffusion layer consisting solely of carbon nanotube film and not containing a substrate made of a conductive material. However, when a fuel cell is fabricated using a gas diffusion layer consisting solely of carbon nanotube film, the load applied to the MEA is not balanced when the entire fuel cell is fastened, causing stress to concentrate in a part of the MEA. This leads to a problem where the electrolyte membrane becomes more prone to rupture, resulting in reduced durability.

[0009] On the other hand, Patent Document 2 discloses a diffusion layer having a multilayer structure. However, a diffusion layer having a multilayer structure is unsuitable for mass production. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2009-117354 [Patent Document 2] Japanese Patent Publication No. 2019-079796 [Overview of the project] [Problems that the invention aims to solve]

[0011] The problem that this invention aims to solve is to provide a novel gas diffusion layer with high liquid water discharge performance and a method for manufacturing the same. Another problem that the present invention aims to solve is to provide a novel gas diffusion layer suitable for mass production and a method for manufacturing the same. [Means for solving the problem]

[0012] To solve the above problems, the gas diffusion layer according to the present invention has the following configuration. (1) The gas diffusion layer includes a base material and a carbon nanotube film formed on the surface of the base material. (2) The base material is made of a conductive porous material. (3) The carbon nanotube film includes carbon nanotubes oriented in-plane.

[0013] The method for manufacturing the gas diffusion layer according to the present invention includes a first step of forming a carbon nanotube film including carbon nanotubes oriented in-plane on the surface of a base material made of a conductive porous material.

Advantages of the Invention

[0014] When a gas diffusion layer having a two-layer structure including a base material and a carbon nanotube film including carbon nanotubes oriented in-plane is applied to a solid polymer fuel cell, flooding is suppressed and the power generation performance under high-humidity conditions is improved. This is presumably because the carbon nanotube film has appropriate water repellency, and thus water transport from the catalyst layer to the base material is promoted under high-humidity conditions. Furthermore, such a gas diffusion layer can be manufactured, for example, by transferring a carbon nanotube film onto the surface of the base material. Therefore, the process of applying and drying the paste becomes unnecessary, and the manufacturing process can be simplified.

Brief Description of the Drawings

[0015] [Figure 1] It is a cross-sectional view of a nano-CT image of an in-plane oriented CNT film. [Figure 2] It is a schematic cross-sectional view of the fuel cells of Examples 1 to 8. [Figure 3] It is a diagram showing the relationship between the contact angle of water on the surface of the carbon nanotube film and the current density. [Figure 4] It is a diagram showing the relationship between the thickness of the carbon nanotube film and the current density.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, an embodiment of the present invention will be described in detail. [1. Gas Diffusion Layer] The gas diffusion layer according to the present invention comprises a base material and a carbon nanotube film formed on the surface of the base material and.

[0017] [1.1. Base Material] [1.1.1. Material] The base material is made of a conductive porous material. Here, the "conductive porous material" refers to a material having electronic conductivity and pores of a size capable of diffusing gas. In the present invention, the material of the base material is not particularly limited as long as it is a conductive porous material, and an optimal material can be selected according to the purpose. Examples of the material of the base material include carbon fiber non-woven fabric, carbon paper, carbon cloth, porous metal sintered body, etc.

[0018] [1.1.2. Water-Repellent Substance A] [A. Material] The base material may consist only of a conductive porous material such as non-woven fabric or carbon paper, or may further contain a water-repellent substance A in addition to the conductive porous material. When the base material contains the water-repellent substance A, the drainage performance of the liquid water in the gas diffusion layer may be further improved. When the base material contains the water-repellent substance A, the type of the water-repellent substance A is not particularly limited, and an optimal material can be selected according to the purpose. Examples of the water-repellent substance A include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene·hexafluoropropylene copolymer (FEP), etc.

[0019] [B. Content] When the substrate contains water-repellent substance A, the content of water-repellent substance A is not particularly limited, and an optimal content can be selected depending on the purpose. Generally, the higher the content of water-repellent substance A, the better the water repellency of the substrate. To obtain such an effect, it is preferable that the content of water-repellent substance A is greater than 0 mass%. More preferably, the content is 5 mass% or more, and even more preferably, 10 mass% or more. On the other hand, if the content of water-repellent substance A is excessive, the gas permeability and / or electronic conductivity of the substrate may decrease. Therefore, the content of water-repellent substance A is preferably 50 mass% or less. More preferably, the content is 40 mass% or less, and even more preferably, 30 mass% or less.

[0020] [1.1.3. Thickness] The thickness of the substrate is not particularly limited, and the optimal thickness can be selected according to the purpose. Generally, if the substrate is too thin, the springiness decreases, which may lead to assembly defects when assembling it into a fuel cell. Also, if the substrate is too thin, flooding may increase. This is because heat dissipation through the ribs is promoted, and the temperature of the substrate decreases. Therefore, a substrate thickness of 90 μm or more is preferable. A substrate thickness of 100 μm or more is even more preferable. On the other hand, if the substrate thickness becomes too thick, the drainage resistance of the liquid water and the gas diffusion resistance increase, which may reduce the output of the fuel cell. Therefore, the substrate thickness is preferably 250 μm or less. More preferably, the substrate thickness is 200 μm or less.

[0021] [1.1.4. Porosity] The porosity of the substrate in its incompressible state is not particularly limited, and the optimal porosity can be selected according to the purpose. Generally, if the porosity in the incompressible state becomes too small, the temperature may drop due to heat dissipation, which can cause flooding. Therefore, a porosity of 65% or higher is preferable. On the other hand, if the porosity in the incompressible state becomes too large, the electrical conductivity of the substrate may be insufficient. Therefore, a porosity of 85% or less is preferable.

[0022] [1.2. Carbon Nanotube Films] [1.2.1. Materials] A carbon nanotube film is formed on the surface of the substrate. In this invention, "carbon nanotube film" refers to a film containing in-plane oriented carbon nanotubes (CNTs). Carbon nanotube films in which CNTs are in-plane oriented can be fabricated by various methods. The carbon nanotube film may consist of a single film obtained in a single fabrication step, or it may be a laminated film obtained by stacking multiple films obtained in a single fabrication step.

[0023] "In-plane orientation" refers to the arrangement of CNTs such that their longitudinal directions are approximately parallel to the surface of the film. In this case, the CNTs do not necessarily need to be arranged parallel to each other. Furthermore, the longitudinal direction of each CNT does not need to be perfectly parallel to the surface of the film; it may be tilted. However, if the average tilt angle of the CNTs (the average value of the angle between the longitudinal direction of the CNTs and the planar direction of the film) becomes too large, the surface irregularities of the CNT layer will increase, which may lead to poor adhesion to the catalyst layer and gas diffusion layer substrate, and an increase in electronic resistance. Therefore, an average tilt angle of 10° or less is preferable. More preferably, the average tilt angle is 5° or less, and even more preferably, 3° or less.

[0024] The type of carbon nanotube (CNT) that makes up the carbon nanotube film is not particularly limited, and the most suitable type can be selected depending on the purpose. For example, the CNTs may be single-walled (WW) or multi-walled (WW) CNTs. Furthermore, the diameter and length of the CNTs are not particularly limited and can be selected to be optimal for the purpose. Specifically, the diameter of the CNTs is preferably between 10 nm and 40 nm. Specifically, the length of the CNTs is preferably between 100 μm and 2 mm.

[0025] [1.2.2. Water repellent substance B] [A. Materials] The carbon nanotube membrane may consist solely of CNTs, or it may contain CNTs in addition to a water-repellent substance B. When the carbon nanotube membrane contains water-repellent substance B, the drainage performance of the liquid water in the gas diffusion layer may be further improved. When a carbon nanotube film contains water-repellent substance B, the type of water-repellent substance B is not particularly limited, and the most suitable material can be selected depending on the purpose. Furthermore, when the substrate contains water-repellent substance A, water-repellent substance B may be the same material as water-repellent substance A, or it may be a different material. Other aspects concerning water-repellent substance B are the same as those concerning water-repellent substance A, so their explanation will be omitted.

[0026] [B. Content] When a carbon nanotube film contains water-repellent substance B, the content of water-repellent substance B is not particularly limited, and an optimal content can be selected depending on the purpose. Generally, the higher the content of water-repellent substance B, the better the water repellency of the carbon nanotube film. To obtain such an effect, it is preferable that the content of water-repellent substance B is greater than 0 mass%. More preferably, the content is 3 mass% or more, and even more preferably, 5 mass% or more. On the other hand, if the content of water-repellent substance B is excessive, the gas permeability and / or electronic conductivity of the carbon nanotube film may decrease. Therefore, the content of water-repellent substance B is preferably 40 mass% or less. More preferably, the content is 30 mass% or less, and even more preferably, 20 mass% or less.

[0027] [1.2.3. Thickness] The thickness of the carbon nanotube film is not particularly limited, and the optimal thickness can be selected depending on the purpose. Generally, if the carbon nanotube film is too thin, the substrate of the gas diffusion layer may penetrate the electrolyte film, reducing the durability of the electrolyte film. Therefore, a carbon nanotube film thickness of 0.1 μm or more is preferred. More preferably, the thickness is 1 μm or more, and even more preferably, 3 μm or more. On the other hand, if the thickness of the carbon nanotube film becomes too thick, the gas permeability of the carbon nanotube film may decrease. Therefore, the thickness of the carbon nanotube film is preferably 30 μm or less. More preferably, the thickness is 15 μm or less.

[0028] [1.2.4. Contact angle] The surface of carbon nanotubes (CNTs) contained in a carbon nanotube film immediately after manufacturing is typically hydrophobic. By applying various treatments to this carbon nanotube film, its surface can be made hydrophilic, or its hydrophobicity can be further enhanced.

[0029] The degree of water repellency or hydrophilicity of a carbon nanotube membrane can be expressed by the contact angle of water on the surface of the carbon nanotube membrane. If the contact angle becomes too small, liquid water tends to accumulate within the carbon nanotube membrane, reducing the drainage performance of the liquid water. Therefore, a contact angle of 40° or higher is preferable. More preferably, the contact angle is 45° or higher, and even more preferably, 50° or higher. On the other hand, if the contact angle becomes too large, the water generated in the catalyst layer will have difficulty permeating through the carbon nanotube membrane, which will actually reduce the drainage performance of the liquid water. Therefore, a contact angle of 140° or less is preferable. More preferably, the contact angle is 135° or less, and even more preferably, 120° or less.

[0030] [2. Method for manufacturing a gas diffusion layer] The method for producing a gas diffusion layer according to the present invention comprises a first step of forming a carbon nanotube film containing in-plane oriented carbon nanotubes on the surface of a substrate made of a conductive porous material. The method for producing a gas diffusion layer according to the present invention may further include a second step after the first step, in which a treatment is performed to adjust the hydrophilicity and hydrophobicity of the surface of the carbon nanotube film.

[0031] [2.1. 1st step] First, a carbon nanotube film containing in-plane oriented carbon nanotubes is formed on the surface of a substrate made of a conductive porous material (first step).

[0032] [2.1.1. Preparation of Substrate] The base material may consist solely of a conductive porous material, or it may further contain water-repellent material A. When the substrate contains water-repellent substance A, the method of adding water-repellent substance A to the substrate is not particularly limited, and the most suitable method can be selected depending on the purpose. Methods for adding water-repellent substance A include, for example, applying a dispersion of water-repellent substance A in a solvent to the surface of a substrate, or impregnating the substrate with the dispersion and drying the substrate (water-repellent treatment). In this case, the treatment conditions such as the concentration of the dispersion and the drying temperature are not particularly limited, and the optimal conditions can be selected according to the purpose.

[0033] [2.1.2. Formation of carbon nanotube films on substrate surfaces] The method for forming a carbon nanotube film on the substrate surface is not particularly limited, and the most suitable method can be selected depending on the purpose. For example, a method for forming carbon nanotube films is: (a) A method for fabricating a carbon nanotube film in which carbon nanotubes are oriented in plane by peeling off CNTs from a CNT array grown on a CNT growth substrate, and transferring this film to the surface of a substrate made of a conductive porous material. (b) A method of applying a CNT dispersion to the surface of a substrate made of a conductive porous material and drying it. These are some examples.

[0034] [2.2. 2nd process] The method for producing a gas diffusion layer according to the present invention may further include a second step after the first step, in which a treatment is performed to adjust the hydrophilicity and hydrophobicity of the surface of the carbon nanotube film. There are various methods for adjusting the hydrophilicity and hydrophobicity of the surface of a carbon nanotube film. In this invention, any of these treatment methods may be used.

[0035] For example, treatments to adjust hydrophilicity / hydrophobicity include: (a) A process of firing the carbon nanotube film in air, (b) The carbon nanotube film is coated or impregnated with a dispersion containing water-repellent substance B, and the carbon nanotube film is dried. These are some examples.

[0036] [2.2.1. Firing Process] The process for adjusting the hydrophilicity / hydrophobicity may be a process of firing the carbon nanotube film in air. When a carbon nanotube film is fired in air, oxygen-containing functional groups are introduced to the CNT surface, increasing its hydrophilicity.

[0037] The firing temperature affects the water contact angle (i.e., the degree of hydrophobicity or hydrophilicity) of the carbon nanotube film surface. Generally, if the firing temperature is too low, the carbon nanotube film may become excessively hydrophobic, reducing the drainage performance of liquid water. Therefore, a firing temperature of 200°C or higher is preferable. A firing temperature of 250°C or higher is even more preferable. On the other hand, if the firing temperature is too high, the carbon nanotube film may become excessively hydrophilic, which can reduce the drainage performance of the liquid water. Therefore, a firing temperature of 350°C or lower is preferable. More preferably, the firing temperature is 300°C or lower.

[0038] [2.2.2. Impregnation Treatment] The process of adjusting the hydrophilicity / hydrophobicity may involve coating or impregnating the carbon nanotube membrane with a dispersion containing water-repellent substance B, and then drying the carbon nanotube membrane. In this case, the treatment conditions such as the concentration of the dispersion and the drying temperature are not particularly limited, and the optimal conditions can be selected according to the purpose.

[0039] [3. Effect] When a gas diffusion layer having a two-layer structure consisting of a substrate and a carbon nanotube film containing in-plane oriented carbon nanotubes is applied to a polymer electrolyte fuel cell, flooding is suppressed and power generation performance under high humidity conditions is improved. This is thought to be because the carbon nanotube film has appropriate water repellency, which promotes water transport from the catalyst layer to the substrate under high humidity conditions. Furthermore, such a gas diffusion layer can be manufactured, for example, by transferring the carbon nanotube film to the surface of the substrate. Therefore, the paste coating and drying process is unnecessary, and the manufacturing process can be simplified. [Examples]

[0040] (Examples 1-8, Comparative Examples 1-3) [1. Sample Preparation] [1.1. Base material] The substrate for the gas diffusion layer is (a) SGL Corporation, 29BA (hereinafter referred to as "Substrate A"), or (b) SGL Corporation, 39BA (hereinafter referred to as "substrate B") I used it.

[0041] Substrates A and B were subjected to testing without forming a microporous layer (water-repellent layer) on their surfaces. However, some of substrate A was treated by impregnating it with a dispersion of polytetrafluoroethylene, drying it in the air, and volatilizing the solvent (water-repellent treatment). Hereinafter, substrate A that has undergone water-repellent treatment will be referred to as "water-repellent treated substrate A".

[0042] [1.2. Carbon Nanotube Films] Carbon nanotube films in which carbon nanotubes are oriented in-plane (hereinafter also referred to as "in-plane oriented CNT films") were fabricated by peeling carbon nanotubes from a vertically oriented carbon nanotube array. Figure 1 shows a cross-sectional view of the nano-CT image of the in-plane oriented CNT film. In Figure 1, the white areas are CNTs. From Figure 1, it was found that the thickness of the in-plane oriented CNT film was 3 μm. Such in-plane oriented CNT films were pressed and bonded to the surface of substrate A or substrate B, and then subjected to necessary processing. In addition, for some samples, 2, 3, or 10 layers of in-plane oriented CNT films were bonded to the substrate surface.

[0043] Hereinafter, an untreated single-layer in-plane oriented CNT film bonded to the surface of a substrate will also be referred to as a "CNT film." Furthermore, an untreated two- or three-layer in-plane oriented CNT film bonded to the surface of a substrate will also be referred to as a "double CNT film" or a "triple CNT film," respectively. In addition, an untreated ten-layer in-plane oriented CNT film bonded to the surface of a substrate will also be referred to as a "30 μm CNT film."

[0044] Some of the in-plane oriented CNT films underwent a hydrophilization treatment by firing them at a predetermined temperature (200°C to 350°C) for 1 hour in an atmospheric environment after bonding them to the substrate surface. Hereinafter, the in-plane oriented CNT films that have undergone the hydrophilization treatment will also be referred to as "fired CNT films." Furthermore, some other in-plane oriented CNT films were subjected to a treatment (water-repellent treatment) in which, after bonding to the substrate surface, a dispersion of polytetrafluoroethylene was impregnated, and then dried in the air to volatilize the solvent. Hereinafter, in-plane oriented CNTs that have undergone water-repellent treatment will also be referred to as "water-repellent treated CNT films."

[0045] [1.3. Fuel Cell] [1.3.1. Examples 1-8] Figure 2 shows schematic cross-sectional diagrams of fuel cell cells from Examples 1 to 8. A MEA was fabricated by coating both sides of a Nafion® film with catalyst layers. For the cathode-side gas diffusion layer, a bond was used between an in-plane oriented CNT film (untreated, hydrophilized, or hydrophobic) and a substrate. For the anode-side gas diffusion layer, a commercially available gas diffusion layer with a hydrophobic layer (microporous layer) was used. Both sides of the MEA were sandwiched between the cathode-side gas diffusion layer and the anode-side gas diffusion layer, respectively, with a separator (not shown) placed on the outside. The separator was fabricated from resin-impregnated graphite material.

[0046] [1.3.2. Comparative Examples 1-3] Fuel cell cells were fabricated in the same manner as in Examples 1 to 8, except that the cathode-side gas diffusion layer was either substrate A only (Comparative Example 1), substrate B only (Comparative Example 2), or a single layer of in-plane oriented CNT film only (Comparative Example 3).

[0047] [2. Test Method] [2.1. Contact angle] Water droplets were dropped onto a carbon nanotube film, and the contact angle was measured. [2.2. Power Generation Performance] Current-voltage characteristics were obtained using a fuel cell. The power generation conditions were: cell temperature of 40°C, cathode supply gas of 21% O2 (N2 balanced) gas, relative humidity of 120% RH, and flow rate of 300 cm³. 3 The current was supplied at a rate of / min. The power generation performance of each fuel cell was evaluated by the current density at a voltage of 0.1V.

[0048] [3. Results] [3.1. Power Generation Performance] Table 1 shows the power generation performance of the fuel cell cells obtained in Examples 1-8 and Comparative Examples 1-3. Figure 3 shows the relationship between the water contact angle on the carbon nanotube film surface and the current density. Figure 4 shows the relationship between the thickness of the carbon nanotube film and the current density. From Table 1 and Figures 3-4, the following can be seen.

[0049] (1) Performance improvements were confirmed by controlling the hydrophilicity, hydrophobicity, and thickness of the carbon nanotube membrane to a specific range. This is thought to be because the carbon nanotube membrane promoted drainage from the catalyst layer without inhibiting O2 diffusion, thereby suppressing flooding. (2) The contact angle of the carbon nanotube film is preferably 40° to 140°, more preferably 45° to 135°, and even more preferably 50° to 120° (see Figure 3). (3) The thickness of the in-plane oriented CNT film is preferably 0.1 μm or more and 30 μm or less, and more preferably 1 μm or more and 17 μm or less (see Figure 4).

[0050] [Table 1]

[0051] Although embodiments of the present invention have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. [Industrial applicability]

[0052] The gas diffusion layer according to the present invention can be used in solid polymer fuel cells, polymer electrolyte membrane water electrolysis devices, and the like.

Claims

1. A gas diffusion layer having the following configuration: (1) The gas diffusion layer is Substrate and A carbon nanotube film formed on the surface of the substrate and It is equipped with. (2) The substrate is made of a conductive porous material. (3) The carbon nanotube film contains carbon nanotubes that are oriented in plane.

2. The gas diffusion layer according to claim 1, wherein the thickness of the substrate is 90 μm or more and 250 μm or less.

3. The gas diffusion layer according to claim 1 or 2, wherein the substrate comprises a water-repellent substance A.

4. The gas diffusion layer according to any one of claims 1 to 3, wherein the thickness of the carbon nanotube film is 0.1 μm or more and 30 μm or less.

5. The gas diffusion layer according to any one of claims 1 to 4, wherein the water contact angle on the surface of the carbon nanotube film is 40° or more and 140° or less.

6. The carbon nanotube film is a gas diffusion layer according to any one of claims 1 to 5, wherein the carbon nanotube film does not contain water-repellent substance B.

7. The carbon nanotube film comprises a water-repellent substance B, as described in any one of claims 1 to 5, for the gas diffusion layer.

8. A method for manufacturing a gas diffusion layer, comprising a first step of forming a carbon nanotube film containing in-plane oriented carbon nanotubes on the surface of a substrate made of a conductive porous material.

9. The method for producing a gas diffusion layer according to claim 8, wherein the substrate comprises a water-repellent substance A.

10. A method for producing a gas diffusion layer according to claim 8 or 9, further comprising a second step of performing a treatment to adjust the hydrophilicity and hydrophobicity of the surface of the carbon nanotube film after the first step.

11. The second step is, (a) A process of firing the carbon nanotube film in air, (b) A process in which the carbon nanotube film is coated with or impregnated with a dispersion containing water-repellent resin B, and the carbon nanotube film is dried. A method for producing a gas diffusion layer according to claim 10, including the following:

Images