Gas diffusion layer for fuel cells

Abstract

To provide a novel gas diffusion layer for fuel cells that has high liquid water discharge performance and minimizes fuel cell performance degradation. [Solution] The gas diffusion layer for fuel cells comprises a porous gas diffusion layer substrate and a non-conductive water-repellent layer formed on the surface of the gas diffusion layer substrate. The non-conductive water-repellent layer contains water-repellent particles A distributed in an island-like manner and does not contain conductive particles. The gas diffusion layer for fuel cells may further comprise a conductive water-repellent layer inserted between the gas diffusion layer substrate and the non-conductive water-repellent layer. The conductive water-repellent layer is preferably composed of a composite of water-repellent particles B and conductive particles B.

Description

[Technical Field]

[0001] The present invention relates to a gas diffusion layer for fuel cells, and more particularly to a gas diffusion layer for fuel cells with high liquid water discharge performance. [Background technology]

[0002] A polymer electrolyte fuel cell (MSF) comprises a membrane electrode assembly (MEA) in which electrodes (catalyst layers) are bonded to both sides of an electrolyte membrane made of a solid polymer electrolyte. In addition, a gas diffusion layer is generally placed outside the catalyst layer in an MSF fuel cell. The gas diffusion layer supplies reaction gases and electrons to the catalyst layer and is made of materials such as carbon paper or carbon cloth. Furthermore, a separator with a gas channel is placed outside the gas diffusion layer. MSF fuel cells typically have a structure (fuel cell stack) in which multiple single cells, each consisting of such an MEA, gas diffusion layer, and separator, are stacked.

[0003] In polymer electrolyte fuel cells, an appropriate water content is necessary for the electrolyte membrane to exhibit good proton conductivity. Therefore, if the fuel cell temperature is high during power generation or if the amount of water in the supply gas is low, the electrolyte membrane dries out, and its performance deteriorates. On the other hand, when generating electricity using a polymer electrolyte fuel cell, water is produced at the cathode due to electrode reactions. Therefore, if the fuel cell temperature is low and the amount of water in the supplied gas is high, liquid water is more likely to form in the gas diffusion layer on the cathode side. Excess liquid water hinders oxygen transport and can cause a decrease in fuel cell performance.

[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, gas diffusion layers generally utilize a microporous layer (a layer containing conductive 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, followed by drying and firing. However, conventional gas diffusion layers do not always have sufficient drainage performance under low-temperature, high-humidity conditions.

[0005] Therefore, various proposals have been made to solve this problem. For example, Patent Document 1 discloses a gas diffusion layer for fuel cells obtained by evaporating polytetrafluoroethylene (PTFE) and depositing PTFE on the surface of a porous substrate. The document states that this method yields a gas diffusion layer in which the degree of hydrophobicity changes with respect to the thickness.

[0006] Patent Document 2 contains: (a) Impregnate carbon paper with a slurry containing dispersed PTFE, and dry the carbon paper at 330°C. (b) Apply a coating solution containing acetylene black and PTFE to one side of the carbon paper, and heat the carbon paper at 350°C. (b) Polish the surface that has not been coated with the coating solution. A gas diffusion layer obtained by this process is disclosed. The document states that by this method, a gas diffusion layer can be obtained in which the ratio of the amount of fluorine on the surface in contact with the catalyst layer to the amount of fluorine on the surface in contact with the separator (polished surface) is between 1.5 and 11.

[0007] Using the method described in Patent Document 1, a gas diffusion layer is obtained in which the hydrophobicity (PTFE load) changes with respect to the thickness direction. Here, the effect of liquid water retention is greatest on the surface in contact with the catalyst layer, and in order to improve drainage performance, it is considered preferable to increase the PTFE load on the surface in contact with the catalyst layer.

[0008] However, Patent Document 1 generates PTFE vapor and deposits PTFE on the surface of a porous substrate. As a result, the PTFE vapor penetrates into the interior of the porous substrate, making it impossible to selectively support PTFE only on the surface of the porous substrate. If more PTFE than necessary is supported on the surface and inside the porous substrate, the electronic conductivity and / or gas permeability of the gas diffusion layer may decrease, potentially reducing the performance of the fuel cell. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2017-059305 [Patent Document 2] Japanese Patent Publication No. 2020-155386 [Overview of the project] [Problems that the invention aims to solve]

[0010] The problem that this invention aims to solve is to provide a novel gas diffusion layer for fuel cells that has high liquid water discharge performance and minimizes degradation of fuel cell performance. [Means for solving the problem]

[0011] To solve the above problems, the gas diffusion layer for fuel cells according to the present invention is A porous gas diffusion layer substrate, A non-conductive water-repellent layer formed on the surface of the gas diffusion layer substrate and Equipped with, The non-conductive water-repellent layer contains water-repellent particles A distributed in an island-like manner, but does not contain conductive particles.

[0012] The gas diffusion layer for a fuel cell includes a conductive water-repellent layer inserted between the gas diffusion layer base material and the non-conductive water-repellent layer and further includes the conductive water-repellent layer may be composed of water-repellent particles B and a composite of the conductive particles B as well.

Advantages of the Invention

[0013] When a non-conductive water-repellent layer in which water-repellent particles A are distributed in an island shape is formed on the surface of the gas diffusion layer base material or the surface of the conductive water-repellent layer, the drainage performance of liquid water is improved. As a result, the retention of liquid water at the interface between the catalyst layer and the gas diffusion layer is suppressed, and the power generation performance in a low-temperature and high-humidity environment is improved. Furthermore, since the water-repellent particles A are distributed in an island shape, it is possible to suppress a decrease in the electron conductivity of the gas diffusion layer and a decrease in the power generation performance of the fuel cell resulting therefrom.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic diagram of a compressor-type nebulizer used for spraying a PTFE dispersion liquid. [Figure 2] It is a diagram showing the relationship between the average luminance value of the surface of the gas diffusion layer and the voltage (@1.5 A / cm2) of a cell using the gas diffusion layer. [Figure 3] It is a diagram showing the current-voltage characteristics of the cells obtained in Examples 1 to 3 and Comparative Example 1.

Modes for Carrying Out the Invention

[0015] [Configuration 1] a porous gas diffusion layer base material, and a non-conductive water-repellent layer formed on the surface of the gas diffusion layer base material and includes the non-conductive water-repellent layer contains water-repellent particles A distributed in an island shape and does not contain conductive particles a gas diffusion layer for a fuel cell.

[0016] [Configuration 2] The aforementioned water-repellent particle A is Polytetrafluoroethylene (PTFE), Tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA), Tetrafluoroethylene-ethylene copolymer (ETFE), and Polyvinylidene fluoride (PVDF) Includes a particle consisting of at least one selected from the group consisting of A gas diffusion layer for a fuel cell as described in Configuration 1.

[0017] [Configuration 3] A conductive water-repellent layer inserted between the gas diffusion layer substrate and the non-conductive water-repellent layer. Furthermore, The conductive water-repellent layer consists of a composite of water-repellent particles B and conductive particles B. A gas diffusion layer for a fuel cell as described in configuration 1 or 2.

[0018] [Structure 4] The water-repellent particles B are Polytetrafluoroethylene (PTFE), Tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA), Tetrafluoroethylene-ethylene copolymer (ETFE), and Polyvinylidene fluoride (PVDF) It includes at least one particle selected from the group consisting of, The conductive particle B is Graphite particles, Carbon black, Carbon nanotubes, and, carbon nanohorns Includes at least one selected from the group consisting of A gas diffusion layer for a fuel cell as described in configuration 3.

[0019] [Composition 5] A gas diffusion layer for a fuel cell, as described in any one of configurations 1 to 4, wherein the average brightness value is 15.2 or higher and 18.6 or lower. however, The aforementioned "average brightness value" refers to, (a) Using a digital camera in an environment with a brightness of 550 Lx, the surface of the non-conductive water-repellent layer was photographed under the following conditions: camera focal length: 28 mm, F-number: 1.8, shutter speed: 1 / 121 sec, ISO sensitivity: 80. (b) Convert the captured photograph into an 8-bit grayscale (256 gradations) digital image, (c) The luminance value (L) of the i-th (1 ≤ i ≤ 256) digital image i ) and the number of pixels (n) that have that brightness value i The sum of the products multiplied by (ΣL i ×n i ) to the total number of pixels (Σn i The value obtained by dividing by (ΣL i ×n i / Σn i ) refers to.

[0020] [Composition 6] A gas diffusion layer for a fuel cell according to configuration 5, wherein the average brightness value is 15.8 or more and 16.7 or less.

[0021] One embodiment of the present invention will be described in detail below. [1. Gas diffusion layer for fuel cells] The gas diffusion layer for fuel cells according to the present invention (hereinafter also simply referred to as the "gas diffusion layer") is A porous gas diffusion layer substrate, A non-conductive water-repellent layer formed on the surface of the gas diffusion layer substrate and It is equipped with. The gas diffusion layer for fuel cells according to the present invention is A conductive water-repellent layer inserted between the gas diffusion layer substrate and the non-conductive water-repellent layer. It would be good to have even more of these features.

[0022] [1.1. Gas Diffusion Layer Substrate] A "gas diffusion layer substrate" refers to a porous sheet-like member that has electronic conductivity and pores of a size that allows gas to diffuse. In the present invention, the material of the gas diffusion layer substrate is not particularly limited, as long as it performs the above-mentioned functions. Examples of materials for the gas diffusion layer substrate include carbon fiber nonwoven fabric, carbon paper, carbon cloth, and porous metal sintered bodies.

[0023] [1.2. Non-conductive water-repellent layer] [1.2.1. Materials] A non-conductive water-repellent layer is formed on the surface of the gas diffusion layer substrate. A "non-conductive water-repellent layer" refers to a layer that contains water-repellent particles A distributed in an island-like pattern, but does not contain conductive particles.

[0024] In the present invention, the material of the water-repellent particle A is not particularly limited, as long as it is capable of imparting water repellency to the gas diffusion layer. The material for the water-repellent particles A is, for example, Polytetrafluoroethylene (PTFE), Tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA), Tetrafluoroethylene-ethylene copolymer (ETFE), Polyvinylidene fluoride (PVDF) These are some examples. The non-conductive water-repellent layer may contain particles consisting of one of these types, or it may contain two or more types of particles.

[0025] [1.2.2. Average particle size of water-repellent particles A] "Average particle size of water-repellent particle A" refers to the average value of the maximum particle size measured for 100 or more randomly selected particles under microscopic observation (optical microscope, scanning electron microscope, etc.).

[0026] If the average particle size of the water-repellent particles A becomes too small, the water-repellent particles A may penetrate the gas diffusion layer substrate, potentially hindering gas movement. Therefore, the average particle size of the water-repellent particles A is preferably 1.0 μm or larger. More preferably, the average particle size is 2.0 μm or larger. On the other hand, if the average particle size of the water-repellent particles A becomes too large, the contact area with the catalyst layer may decrease. Therefore, the average particle size of the water-repellent particles A is preferably 10.0 μm or less, more preferably 8.0 μm or less.

[0027] [1.2.3. Distributed in island form] "The water-repellent particles A are distributed in island form" means that the water-repellent particles A are discretely distributed on the surface of the gas diffusion layer substrate (or, when a conductive water-repellent layer is formed on the surface of the gas diffusion layer substrate, on the surface of the conductive water-repellent layer). As described in Patent Document 1, when using a method of evaporating PTFE and depositing PTFE on the surface of a substrate, PTFE tends to be continuously distributed on the substrate surface. In contrast, when using the method described later, a non-conductive water-repellent layer in which the water-repellent particles A are distributed in island form can be obtained.

[0028] [1.2.4. Average luminance value] "Average luminance value" means (a) Using a digital camera in an environment with a brightness of 550 Lx, photograph the surface of the non-conductive water-repellent layer under the conditions of a camera focal length: 28 mm, F value: 1.8, shutter speed: 1 / 121 second, and ISO sensitivity: 80. (b) Convert the photographed photo into a digital image with 8-bit gray scale (256 gradations). [[ID=2E0]](c) The value obtained by dividing the sum (ΣL i ×n i ) of the product of the luminance value (L i ) of the i-th (1≦i≦256) pixel of the digital image and the number of pixels (n i ) having that luminance value by the total number of pixels (Σn i ) (ΣL i ×n i / Σn i ).

[0029] The average brightness value correlates with the amount of water-repellent particles A, i.e., the drainage performance of the non-conductive water-repellent layer. A low average brightness value indicates a relatively small amount of water-repellent material A. If the average brightness value becomes too low, the drainage performance of the gas diffusion layer may become insufficient. Therefore, an average brightness value of 15.2 or higher is preferable. More preferably, the average brightness value is 15.6 or higher, or 15.8 or higher.

[0030] On the other hand, a high average brightness value indicates a relatively large amount of water-repellent particles A. If the average brightness value becomes too high, the water repellency of the non-conductive water-repellent layer may become excessively high, which may actually reduce the drainage performance of the gas diffusion layer. Also, if the average brightness value becomes too high, the conductivity of the non-conductive water-repellent layer may decrease excessively. Therefore, an average brightness value of 18.6 or less is preferable. More preferably, the average brightness value is 16.7 or less.

[0031] [1.2.5. Thickness] The thickness of the non-conductive water-repellent layer is not particularly limited, and the optimal thickness can be selected according to the purpose. In general, if the thickness of the non-conductive water-repellent layer is too thin, the drainage performance may be insufficient. Therefore, the thickness of the non-conductive water-repellent layer is preferably 1.0 μm or more. More preferably, the thickness is 2.0 μm or more. On the other hand, if the thickness of the non-conductive water-repellent layer becomes too thick, the water repellency may become excessively high, which may actually reduce the drainage performance of the gas diffusion layer. Therefore, the thickness of the non-conductive water-repellent layer is preferably 10.0 μm or less. More preferably, the thickness is 8.0 μm or less.

[0032] [1.3. Conductive water-repellent layer] [1.3.1. Materials] A "conductive water-repellent layer" refers to a layer consisting of a composite of water-repellent particles B and conductive particles B. In the present invention, the material of the water-repellent particles B is not particularly limited, as long as it is capable of imparting water repellency to the conductive water-repellent layer. Similarly, the material of conductive particles B is not particularly limited, as long as it is capable of imparting conductivity to the conductive water-repellent layer.

[0033] Examples of materials for water-repellent particles B include: Polytetrafluoroethylene (PTFE), Tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA), Tetrafluoroethylene-ethylene copolymer (ETFE), Polyvinylidene fluoride (PVDF) These are some examples. The conductive water-repellent layer may contain particles made up of one of these types, or it may contain two or more types. Furthermore, water-repellent particle B may be made of the same material as water-repellent particle A, or it may be made of a different material.

[0034] Examples of conductive particle B include, Graphite particles, Carbon black, Carbon nanotubes, carbon nanohorns These are some examples. The conductive water-repellent layer may contain one of these types, or it may contain two or more types.

[0035] When using carbon black as conductive particle B, the type of carbon black is not particularly limited. For example, the carbon black may be porous and highly conductive Ketjenblack (registered trademark), or it may be non-porous and highly conductive acetylene black.

[0036] [1.3.2. Average particle size of water-repellent particles B] "Average particle size of water-repellent particle B" refers to the average value of the maximum particle size measured for 100 or more randomly selected particles under scanning electron microscopy (SEM) observation.

[0037] If the average particle size of the water-repellent particles B becomes too small, the pore size may become excessively small, making it difficult for gas to flow. Therefore, the average particle size of the water-repellent particles B is preferably 0.01 μm or larger. More preferably, the average particle size is 0.03 μm or larger. On the other hand, if the average particle size of the water-repellent particles B becomes too large, the contact properties of the conductive particles may deteriorate. Therefore, the average particle size of the water-repellent particles B is preferably 0.2 μm or less. More preferably, the average particle size is 0.1 μm or less.

[0038] [1.3.3. Average particle size of conductive particle B] "Average particle size of conductive particle B" refers to the average value of the maximum particle size measured for 100 or more randomly selected particles under scanning electron microscopy (SEM) observation.

[0039] The average particle size of conductive particles B is not particularly limited, and an optimal value can be selected depending on the purpose. Generally, if the average particle size of conductive particles B becomes too small, the gas diffusion resistance may increase. Therefore, the average particle size of conductive particles B is preferably 0.01 μm or larger. More preferably, the average particle size is 0.02 μm or larger. On the other hand, if the average particle size of conductive particles B becomes too large, the water repellency may decrease. Therefore, the average particle size of conductive particles B is preferably 0.2 μm or less. More preferably, the average particle size is 0.1 μm or less.

[0040] [1.3.4. Content of water-repellent particles B] "Water-repellent particle B content" refers to the ratio of the mass of water-repellent particles B to the total mass of the conductive water-repellent layer.

[0041] If the gas diffusion layer includes a conductive water-repellent layer, the content of water-repellent particles B in the conductive water-repellent layer can be selected to an optimal value depending on the purpose. Generally, if the content of water-repellent particles B is too low, the water repellency of the conductive water-repellent layer may become insufficient. Therefore, the content of water-repellent particles B is preferably 5.0 mass% or more. More preferably, the content is 10.0 mass% or more. On the other hand, if the content of water-repellent particles B is excessive, the conductivity of the conductive water-repellent layer may decrease. Therefore, the content of water-repellent particles B is preferably 70.0 mass% or less. More preferably, the content is 60.0 mass% or less.

[0042] [1.3.4. Thickness of the conductive water-repellent layer] The thickness of the conductive water-repellent layer is not particularly limited, and the optimal thickness can be selected according to the purpose. Generally, if the thickness of the conductive water-repellent layer is too thin, the water repellency may be insufficient. Therefore, the thickness of the conductive water-repellent layer is preferably 5.0 μm or more. More preferably, the thickness is 10.0 μm or more. On the other hand, if the thickness of the conductive water-repellent layer becomes too thick, the gas diffusivity and / or electronic conductivity of the conductive water-repellent layer may decrease. Therefore, the thickness of the conductive water-repellent layer is preferably 200.0 μm or less. More preferably, the thickness is 100.0 μm or less.

[0043] [2. Method for manufacturing a gas diffusion layer for fuel cells] The gas diffusion layer for fuel cells according to the present invention is A droplet containing water-repellent particles A is sprayed onto the surface of the gas diffusion layer substrate (or, if a conductive water-repellent layer is formed on the surface of the gas diffusion layer substrate, onto the surface of the conductive water-repellent layer), A gas diffusion layer substrate with droplets sprayed onto its surface is fired. It can be manufactured by doing so.

[0044] [2.1. 1st step] First, droplets containing water-repellent particles A are sprayed onto the surface of the gas diffusion layer substrate. If a conductive water-repellent layer is formed on the surface of the gas diffusion layer substrate, droplets containing water-repellent particles A are sprayed onto the surface of the conductive water-repellent layer.

[0045] The solvent contained in the droplet is not particularly limited, as long as it is capable of dispersing the water-repellent particles A. Examples of solvents include water, isopropyl alcohol, toluene, methyl ethyl ketone, and butyl acetate. The droplet size is not particularly limited, as long as it is capable of forming island-like non-conductive water-repellent layers on the surface of the gas diffusion layer substrate or the conductive water-repellent layer. A droplet size of 1.0 μm to 10.0 μm is preferred.

[0046] The concentration of water-repellent particles A in the droplet is not particularly limited, as long as it is possible to efficiently generate droplets of a predetermined size. A preferred concentration of water-repellent particles A in the droplet is 0.5 mass% to 60.0 mass%. The amount of droplets sprayed is not particularly limited, as long as it is possible to impart the desired drainage performance to the gas diffusion layer. Preferably, the amount of droplets sprayed is selected to be an optimal value depending on the droplet size, the concentration of water-repellent particles A in the droplets, etc.

[0047] [2.2. 2nd process] Next, the gas diffusion layer substrate, on which droplets are sprayed onto the surface, is fired. This yields the gas diffusion layer for fuel cells according to the present invention.

[0048] Firing is performed to further disperse the water-repellent particles A contained in the droplets. If the firing temperature is too low, the dispersion of water-repellent particles A may be insufficient. Therefore, a firing temperature of 300°C or higher is preferable. More preferably, the firing temperature is 310°C or higher, or 320°C or higher. On the other hand, if the firing temperature becomes too high, the water-repellent particles A may decompose. Therefore, a firing temperature of 400°C or lower is preferable. More preferably, the firing temperature is 390°C or lower, or 380°C or lower.

[0049] The firing time should preferably be selected to be optimal according to the firing temperature. Generally, the higher the firing temperature, the shorter the time it takes to disperse the water-repellent particles A in an island-like manner.

[0050] [3. Effect] In fuel cells, the power generation reaction takes place in the catalyst layer. For a continuous reaction, the water product must be quickly removed from the interface between the catalyst layer and the gas diffusion layer. However, if the temperature of the gas diffusion layer is low, the generated water becomes liquid, and this liquid water accumulates at the interface between the catalyst layer and the gas diffusion layer. When liquid water accumulates at the interface, some or all of the diffusion pathways of the reaction gas are blocked. As a result, the supply of gas necessary for the reaction is disrupted, and power generation performance tends to decrease.

[0051] To solve this problem, a microporous layer consisting of a composite of water-repellent and conductive particles is formed on the surface of the gas diffusion layer substrate. However, simply forming a microporous layer on the surface of the gas diffusion layer substrate is not sufficient for power generation performance in low-temperature, high-humidity environments.

[0052] In contrast, forming a non-conductive water-repellent layer on the surface of the gas diffusion layer substrate or the conductive water-repellent layer, in which water-repellent particles A are distributed in an island-like pattern, improves the drainage performance of liquid water. As a result, the accumulation of liquid water at the interface between the catalyst layer and the gas diffusion layer is suppressed, improving power generation performance in low-temperature, high-humidity environments. Furthermore, because the water-repellent particles A are distributed in an island-like pattern, it is possible to suppress the decrease in the electronic conductivity of the gas diffusion layer and the resulting decrease in the power generation performance of the fuel cell. [Examples]

[0053] (Examples 1-3, Comparative Example 1) [1. Sample Preparation] [1.1. Example 1] A commercially available conductive water-repellent gas diffusion layer (AvCarb, GDL3260) was used as the substrate. For the dispersion containing water-repellent particles A, a PTFE dispersion (PTFE31-JR, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.) was used.

[0054] A PTFE dispersion was sprayed onto the surface of a conductive water-repellent layer in droplets approximately 5 μm in size. A compressor-type nebulizer (Omron Corporation, NE-C29) was used for droplet generation and spraying. Figure 1 shows a schematic diagram of the compressor-type nebulizer used for spraying the PTFE dispersion.

[0055] A predetermined amount of dispersion I was filled into the nebulizer kit body D. For spraying, the adapter C for the small inhalation mask was inserted into the nebulizer kit body D. The base material G was fixed by sandwiching it between another cylinder H at a position 45 mm from the end F of a separately prepared cylinder E. At this time, the conductive water-repellent surface of the base material G was facing towards cylinder E. The end F of this cylinder E was connected to the adapter C for the small inhalation mask of the nebulizer. In this state, PTFE mist was sprayed into cylinder E. As a result, almost all of the droplets sprayed into cylinder E adhered to the surface of the conductive water-repellent layer, and only gas permeated through the base material G.

[0056] The spray volume was varied by controlling the amount of liquid supplied to the nebulizer. In Example 1, the volume of dispersion I was 9 mL, and the spraying time was 60 seconds. After spraying, the substrate G was removed from cylinders E and H and fired in air at 370°C for 60 minutes. The firing process further dispersed the PTFE that had adhered to the surface of the water-repellent layer.

[0057] [1.2. Comparative Example 1, Examples 2-3] A gas diffusion layer was prepared in the same manner as in Example 1, except that the PTFE dispersion was not sprayed (Comparative Example 1). In addition, a gas diffusion layer was prepared in the same manner as in Example 1, except that the volume of the PTFE dispersion was 7 mL (Example 2). Furthermore, a gas diffusion layer was prepared in the same manner as in Example 1, except that the volume of the PTFE dispersion was set to 7 mL and the air vent J of the connection between the nebulizer body D and the adapter C for the small inhalation mask was sealed (Example 3).

[0058] [2. Test Method] [2.1. Measurement of PTFE dispersion amount] The surface brightness of the gas diffusion layer after firing was measured using the following procedure. (1) The surface of the gas diffusion layer was photographed using a digital camera in an environment with a brightness of 550 Lx. The camera used was the digital camera included with the iPhone® SE (2nd generation). The focal length was 28 mm, the aperture value was 1.8, and the ISO sensitivity was 80. The exposure time was 1 / 121 second, the distance between the gas diffusion layer and the camera was 26.2 mm, and a 24-bit image with a resolution of 4032 × 3024 pixels was captured without magnification.

[0059] (2) Using the image processing software ImageJ, the captured 24-bit images were converted to 8-bit grayscale images. Then, the brightness of the central 922-pixel diameter area corresponding to the PTFE coated area was measured. A 256-level brightness distribution was created, showing the number of pixels at each brightness value from 0 to 255. (3) Each luminance value (L i ) and the number of pixels (n) that have that brightness value. i The sum of the products multiplied by (ΣL i ×n i ) to the total number of pixels (Σn i The average brightness value was calculated by dividing by ).

[0060] [2.2. Power Generation Performance Evaluation] A catalyst layer was bonded to both sides of a Nafion® film to obtain a membrane-electrode-gas diffusion layer (MEA). Next, both sides of the MEA were sandwiched between two gas diffusion layers to obtain a film-electrode-gas diffusion layer assembly (MEGA). The gas diffusion layers were punched out to a size of 2 mm x 3 mm. The same type of gas diffusion layer was used for the anode-side gas diffusion layer and the card-side gas diffusion layer, respectively. The gas diffusion layers were arranged so that the side with the PTFE dispersion sprayed (Examples 1-3) or the side with the conductive water-repellent layer formed on it (Comparative Example 1) was in contact with the catalyst layer. Furthermore, a cell was obtained by sandwiching both sides of the MEGA with ribs containing flow channels.

[0061] Electricity was generated using the obtained cells. The cell temperature was set to 40°C, the cathode gas was air, and the anode gas was hydrogen gas with a relative humidity of 80%. Under these conditions, the IV curve was measured at a scanning speed of 20 mV / s. The power generation performance was a current density of 1.5 A / cm². 2 The voltage was evaluated at that point.

[0062] [3. Results] [3.1. PTFE dispersion amount] Table 1 shows the average brightness values ​​of the gas diffusion layer surface after firing. Figure 2 shows the average brightness values ​​of the gas diffusion layer surface and the voltage (@1.5A / cm) of the cell using that gas diffusion layer. 2 This shows the relationship with ). From Table 1 and Figure 2, (a) When the average brightness value is 15.2 or higher and 18.6 or lower, the cell voltage is greater than that of Comparative Example 1, and (b) The cell voltage is highest when the average brightness value is between 15.8 and 16.7. You can see that.

[0063] [Table 1]

[0064] [3.2. Power Generation Performance] Figure 3 shows the current-voltage characteristics of the cells obtained in Examples 1-3 and Comparative Example 1. From Figure 3, it can be seen that Examples 1-3 have superior power generation performance in the high current density range compared to Comparative Example 1. This is thought to be because the accumulation of liquid water at the interface between the catalyst layer and the gas diffusion layer is suppressed because island-like non-conductive water-repellent layers are appropriately formed on the surface of the conductive water-repellent layer. In particular, Example 1 showed the highest power generation performance. This is thought to be because the amount of water-repellent particles A attached, i.e., the drainage performance of the non-conductive water-repellent layer, was optimized.

[0065] 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]

[0066] 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 porous gas diffusion layer substrate, A non-conductive water-repellent layer formed on the surface of the gas diffusion layer substrate and Equipped with, The non-conductive water-repellent layer contains water-repellent particles A distributed in an island-like manner, and does not contain conductive particles. Gas diffusion layer for fuel cells.

2. The water-repellent particle A is Polytetrafluoroethylene (PTFE), Tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA), Tetrafluoroethylene-ethylene copolymer (ETFE), and Polyvinylidene fluoride (PVDF) Includes a particle consisting of at least one selected from the group consisting of The gas diffusion layer for fuel cells according to claim 1.

3. A conductive water-repellent layer inserted between the gas diffusion layer substrate and the non-conductive water-repellent layer. Furthermore, The conductive water-repellent layer consists of a composite of water-repellent particles B and conductive particles B. The gas diffusion layer for fuel cells according to claim 1.

4. The water-repellent particles B are Polytetrafluoroethylene (PTFE), Tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA), Tetrafluoroethylene-ethylene copolymer (ETFE), and Polyvinylidene fluoride (PVDF) It includes at least one particle selected from the group consisting of, The conductive particle B is Graphite particles, Carbon black, Carbon nanotubes, and, carbon nanohorns Includes at least one selected from the group consisting of The gas diffusion layer for fuel cells according to claim 3.

5. The gas diffusion layer for a fuel cell according to claim 1, wherein the average brightness value is 15.2 or more and 18.6 or less. however, The aforementioned "average brightness value" refers to, (a) Using a digital camera in an environment with a brightness of 550 Lx, the surface of the non-conductive water-repellent layer was photographed under the following conditions: camera focal length: 28 mm, F-number: 1.8, shutter speed: 1 / 121 sec, ISO sensitivity:

80. (b) Convert the captured photograph into an 8-bit grayscale (256 gradations) digital image, (c) The luminance value (L) of the i-th (1 ≤ i ≤ 256) of the digital image i ) and the number of pixels (n) that have that brightness value i The sum of the products multiplied by (ΣL) i ×n i ) to the total number of pixels (Σn i The value obtained by dividing by (ΣL) i ×n i / Σn i ) refers to.

6. The gas diffusion layer for a fuel cell according to claim 5, wherein the average brightness value is 15.8 or more and 16.7 or less.

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