Water-repellent layer and gas diffusion layer with water-repellent layer

Abstract

To provide a water-repellent layer with excellent drainage performance, and a gas diffusion layer with the water-repellent layer. [Solution] The water-repellent layer contains composite particles. The composite particles include carbon particles and a water-repellent coating consisting of a first water-repellent molecule that covers the surface of the carbon particles. The carbon particles are preferably carbon black. The water-repellent layer may further contain a water-repellent binder consisting of a second water-repellent molecule. The gas diffusion layer with a water-repellent layer comprises a gas diffusion layer substrate and the water-repellent layer formed on the surface of the gas diffusion layer substrate.

Description

Technical Field

[0001] The present invention relates to a water-repellent layer and a gas diffusion layer with a water-repellent layer, and more particularly to a water-repellent layer having excellent drainage performance and a gas diffusion layer with a water-repellent layer using the same.

Background Art

[0002] A solid polymer fuel cell includes a membrane electrode assembly (MEA) in which catalyst layers are joined to both sides of a solid polymer electrolyte membrane. A gas diffusion layer is usually disposed outside the catalyst layer. The catalyst layer is a portion that serves as a reaction field for an electrode reaction and generally consists of a composite of carbon supporting an electrode catalyst such as platinum and a catalyst layer ionomer. The gas diffusion layer is for supplying / discharging gas to / from the catalyst layer and for transferring electrons with the catalyst layer. Usually, a porous substrate such as carbon paper or carbon cloth is used for the gas diffusion layer.

[0003] In addition to high gas permeability, the gas diffusion layer of a solid polymer fuel cell is required to have high water repellency. Therefore, generally, a gas diffusion layer having a water-repellent layer (also called a "microporous layer (MPL)") formed on the surface of a porous substrate such as carbon paper is used. Further, the water-repellent layer is generally formed by applying a paste containing conductive particles and water-repellent particles to the surface of a porous substrate and drying and firing it.

[0004] When forming a water-repellent layer on the surface of a porous substrate, optimizing the structure of the water-repellent layer can enhance the drainage performance while maintaining high gas permeability. Therefore, various proposals have been made for such a water-repellent layer and a gas diffusion layer with a water-repellent layer.

[0005] For example, in Patent Document 1, (a) A granule in which second particles are bonded to the surface of first particles made of spherical graphite via a water-repellent polymer, and (b) A water-repellent layer obtained by applying such granules to the surface of a substrate and heat-treating them are disclosed. The document states that the water-repellent layer obtained in this way has excellent gas permeability, water repellency, and conductivity because it is equipped with small pores originating from the gaps between the second particles and large pores originating from the gaps between adjacent granules.

[0006] The method described in Patent Document 1 yields a water-repellent layer with excellent gas permeability and water repellency. However, the water-repellent layer described in that document has limitations in improving drainage performance because the surface of the second particle is not coated with a water-repellent polymer. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2021-002444 [Overview of the project] [Problems that the invention aims to solve]

[0008] The problem that this invention aims to solve is to provide a water-repellent layer with excellent drainage performance, and a gas diffusion layer with a water-repellent layer equipped therewith. [Means for solving the problem]

[0009] To solve the above problems, the water-repellent layer according to the present invention has the following configuration. (1) The water-repellent layer contains composite particles. (2) The composite particles are Carbon particles and A water-repellent coating consisting of a first water-repellent molecule that covers the surface of the carbon particles, Includes.

[0010] The gas diffusion layer with a water-repellent layer according to the present invention is Gas diffusion layer substrate, The water-repellent layer according to the present invention is formed on the surface of the gas diffusion layer substrate. It is equipped with. [Effects of the Invention]

[0011] When forming composite particles by creating a water-repellent coating on the surface of carbon particles, optimizing the film formation conditions allows for the formation of a thin and uniform water-repellent coating on the surface of the carbon particles. Subsequently, if necessary, a water-repellent binder is added to the composite particles, and then the composite particles or a mixture of composite particles and the water-repellent binder is sprayed and pressed onto the substrate surface to form a precursor layer. When the precursor layer is heated, the water-repellent layer according to the present invention is obtained. The water-repellent layer obtained in this way has superior drainage performance compared to conventional water-repellent layers.

[0012] this is, (A) By forming a thin and uniform water-repellent coating on the surface of the carbon particles, the water repellency of the carbon particle surface is increased, but the pores (gaps between carbon particles, or between primary particles constituting the carbon particles) remain unblocked, and, (B) Because the drainage of liquid water through the remaining pores without blockage is promoted. It is thought that... [Brief explanation of the drawing]

[0013] [Figure 1] These are SEM images and an F element map superimposed image of the composite particles (PTFE content: 2.8 mass%) obtained in Example 7 after stirring. [Figure 2] These are SEM images and an overlay image of the fluorine element map of the composite particles (PTFE content: 0.8 mass%) obtained in Example 1 after stirring. [Figure 3] These are the SEM image and the superimposed fluorine map image of the carbon black after stirring obtained in Comparative Example 3.

[0014] [Figure 4] This shows the time-dependent changes in the TEM image of the composite particles (PTFE content 2.8 mass%) obtained in Example 7 after stirring. [Figure 5] This figure shows the relationship between the amount of PTFE (first water-repellent molecule) contained in the composite particles and the electronic resistance of the gas diffusion layer with a water-repellent layer. [Figure 6]Isotherm of water vapor adsorption of carbon black (CB) and composite particles (PTFE-CB) obtained by subjecting carbon black to plasma PVD treatment with PTFE (Example 1, PTFE amount: 0.8 mass%).

[0015] [Figure 7] It is a figure showing the influence of the amount of PTFE (first hydrophobic molecule) on the BET specific surface area and pore volume of the composite particles. [Figure 8] Liquid water permeation amount of the water repellent layer obtained in Examples 1 to 3 and Comparative Examples 1 to 3. [Figure 9] Optical microscope photographs of the water repellent layer obtained in Examples 1 to 3 and Comparative Examples 1 to 3. [Figure 10] Pore size distribution of the base material. [Figure 11] Pore size distribution of the water repellent layer / base material obtained in Examples 1 to 3 and Comparative Examples 1 to 3.

[0016] [Figure 12] [ Pore size distribution of Examples 1 to 3, which is an enlarged view near a pore size of 0.1 μm in the pore size distribution shown in FIG. 11. [Figure 13] Pore size distribution of Comparative Examples 1 to 3, which is an enlarged view near a pore size of 0.1 μm in the pore size distribution shown in FIG. 11. [Figure 14] It is a figure showing the relationship between the amount of PTFE (second water repellent molecule) contained in the water repellent layer and the electrical resistance of the gas diffusion layer with the water repellent layer. [Embodiment for Carrying Out the Invention]

[0017] Hereinafter, an embodiment of the present invention will be described in detail. [1. Water Repellent Layer] The water repellent layer according to the present invention has the following configuration.

[0018] [Configuration 1] A water repellent layer having the following configuration. (1) The water repellent layer contains composite particles. (2) The composite particles are carbon particles and A water-repellent coating consisting of a first water-repellent molecule that covers the surface of the carbon particles, Includes.

[0019] [Configuration 2] The water-repellent layer according to configuration 1, wherein the carbon particles are carbon black.

[0020] [Configuration 3] The water-repellent layer according to configuration 1 or 2, wherein the carbon particles have an average particle diameter of less than 5.0 μm.

[0021] [Structure 4] The water-repellent layer according to any one of configurations 1 to 3, wherein the first water-repellent molecule comprises one or more selected from the group consisting of polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), and ethylenetetrafluoroethylene copolymer (ETFE).

[0022] [Composition 5] The water-repellent layer according to any one of configurations 1 to 4, wherein the coverage rate of the water-repellent film is 5.0% or more. However, the "coverage rate of the water-repellent coating" refers to the ratio of the surface area of ​​the carbon particles covered with the water-repellent coating to the total surface area of ​​the carbon particles, assuming that the water-repellent coating consists of a single atomic layer of the first water-repellent molecule.

[0023] [Composition 6] The water-repellent coating is a water-repellent layer according to any one of configurations 1 to 5, wherein the thickness is 2.0 nm or less.

[0024] [Composition 7] A water-repellent layer according to any one of configurations 1 to 6, further comprising a water-repellent binder consisting of a second water-repellent molecule.

[0025] [Structure 8] The water-repellent layer according to composition 7, wherein the second water-repellent molecule comprises one or more selected from the group consisting of polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), and ethylenetetrafluoroethylene copolymer (ETFE).

[0026] [Composition 9] The water-repellent layer according to composition 7 or 8, wherein the content of the water-repellent binder is 50.0 mass% or less. However, the "content of the water-repellent binder" refers to the ratio of the mass of the water-repellent binder to the total mass of the composite particles and the water-repellent binder.

[0027] [Configuration 10] A water-repellent layer according to any one of the configurations 1 to 9, wherein the average pore size is 0.1 μm or more and 1.0 μm or less.

[0028] [1.1. Composite particles] The water-repellent layer consists of layers in which composite particles are bonded to each other, or to composite particles and a water-repellent binder. The composite particles also include carbon particles and a water-repellent coating consisting of a first water-repellent molecule that covers the surface of the carbon particles.

[0029] [1.1.1. Carbon Particles] [A. Materials] In this invention, the type of carbon particles is not particularly limited, and the most suitable material can be selected depending on the purpose. Examples of carbon particles include acetylene black and carbon black such as Ketjenblack. The composite particles may contain one of these carbon particles, or they may contain two or more of these.

[0030] Carbon black has a structure in which primary particles are linked together in a chain-like fashion, and there are many voids (pores) between the primary particles. When a thin, uniform water-repellent coating is formed on the surface of such carbon black to create composite particles, and a water-repellent layer is made using these particles, the drainage performance of the water-repellent layer is improved.

[0031] [B. Average particle size] "Average particle diameter" refers to the volume-based median diameter (D) measured by laser diffraction / scattering. 50 ) refers to.

[0032] In the present invention, the average particle size of the carbon particles is not particularly limited, and an optimal value can be selected depending on the purpose. However, if the average particle size of the carbon particles becomes too large, the number of contact points between the carbon particles decreases when a water-repellent layer is formed, which may increase the electronic resistance. Therefore, the average particle size of the carbon particles is preferably 5.0 μm or less. More preferably, the average particle size is 4.0 μm or less, and even more preferably, 3.0 μm or less.

[0033] [1.1.2. Water-repellent coating] [A. Materials] The water-repellent coating consists of a first water-repellent molecule. In this invention, the type of the first water-repellent molecule is not particularly limited, and the most suitable material can be selected depending on the purpose. Examples of the first water-repellent molecules include polytetrafluoroethylene (PTFE), perfluoroalkoxyalkanes (PFA), and ethylenetetrafluoroethylene copolymer (ETFE). The water-repellent coating may consist of one of these first water-repellent molecules, or it may consist of two or more of these first water-repellent molecules.

[0034] Among these, PTFE is preferred as the first water-repellent molecule. Since PTFE has higher water repellency compared to other first water-repellent molecules, using it as the first water-repellent molecule allows for high water repellency to be imparted to composite particles with only a small amount of addition.

[0035] [B. Coverage Rate] "Coverage rate of the water-repellent coating (%)" refers to the ratio of the surface area of ​​the carbon particles covered with the water-repellent coating to the total surface area of ​​the carbon particles, assuming that the water-repellent coating consists of a single atomic layer of the first water-repellent molecule.

[0036] Generally, the higher the coverage rate of the water-repellent coating, the better the drainage performance of the water-repellent layer. To obtain this effect, a coverage rate of 5.0% or higher is preferable. Preferably, the coverage rate is 10.0% or higher, and more preferably, 20.0% or higher. Furthermore, while the electronic resistance of the water-repellent layer increases with increasing coverage, it does not significantly increase even at 100% coverage. This is thought to be due to multilayer adsorption of the first water-repellent molecules. However, if the coverage becomes too high, the electronic resistance may increase excessively. Therefore, a coverage of 200% or less is preferable.

[0037] [C. Load] "Amount of water-repellent coating (mass%)" refers to the ratio of the mass of the water-repellent coating to the total mass of the composite particles.

[0038] Generally, the greater the amount of water-repellent coating, the better the drainage performance of the water-repellent layer. To obtain this effect, the amount of water-repellent coating is preferably 0.125 mass% or more. Preferably, the amount is 0.25 mass% or more, and more preferably 0.50 mass% or more. On the other hand, increasing the amount of water-repellent coating beyond what is necessary is pointless because it saturates the drainage performance. Therefore, the amount of water-repellent coating is preferably 3.0 mass% or less. Preferably, the amount is 2.8 mass% or less, and more preferably 2.6 mass% or less.

[0039] [D. Thickness] "Water-repellent coating thickness" refers to the value measured by observing composite particles using TEM.

[0040] Generally, the greater the amount of water-repellent coating supported, the easier it becomes for the primary water-repellent molecules to adsorb in multiple layers onto the surface of the carbon particles. If multilayer adsorption proceeds excessively, the thickness of the water-repellent coating may become excessively thick, and the electronic resistance of the water-repellent layer may increase. Therefore, the thickness of the water-repellent coating is preferably 2 nm or less. The thickness is preferably 1.5 nm or less, and more preferably 1.0 nm or less.

[0041] [1.2. Water-repellent binders] [1.2.1. Materials] The water-repellent layer may further contain a water-repellent binder consisting of a second water-repellent molecule in addition to the composite particles. When a water-repellent binder is added to the water-repellent layer, a water-repellent layer is obtained in which the composite particles are bound together by the water-repellent binder.

[0042] In this invention, the type of the second water-repellent molecule is not particularly limited, and the most suitable material can be selected depending on the purpose. Examples of secondary hydrophobic molecules include polytetrafluoroethylene (PTFE), perfluoroalkoxyalkanes (PFA), and ethylenetetrafluoroethylene copolymer (ETFE). The hydrophobic binder may consist of one of these secondary hydrophobic molecules, or it may consist of two or more secondary hydrophobic molecules.

[0043] Among these, PTFE is preferred as the second water-repellent molecule. Since PTFE has higher water repellency compared to other second water-repellent molecules, using it as the second water-repellent molecule allows for high water repellency to be imparted to composite particles with only a small amount of addition.

[0044] [1.2.2. Content] "Water-repellent binder content (mass%)" refers to the ratio of the mass of the water-repellent binder to the total mass of the water-repellent layer.

[0045] The water-repellent layer according to the present invention exhibits high drainage performance even without a water-repellent binder. However, if the water-repellent layer further contains a water-repellent binder, the adhesive strength between carbon particles, between the water-repellent layer and the substrate, or between the water-repellent layer and the catalyst layer may be improved. On the other hand, if the content of the water-repellent binder is excessive, the electronic resistance of the gas diffusion layer with the water-repellent layer may increase. Therefore, the content of the water-repellent binder is preferably 50.0 mass% or less. Preferably, the content is 45.0 mass% or less, and more preferably 40.0 mass% or less.

[0046] [1.3. Characteristics of the water-repellent layer] [1.3.1. Average pore diameter] "Average pore diameter of the water-repellent layer" refers to the mode diameter of pores originating from the water-repellent layer, measured using the mercury intrusion method.

[0047] The average pore size of the water-repellent layer affects its drainage performance. Generally, if the average pore size of the water-repellent layer becomes too small, liquid water may have difficulty permeating through the layer, potentially reducing drainage performance. Therefore, an average pore size of 0.1 μm or larger is preferable for the water-repellent layer. On the other hand, if the average pore size of the water-repellent layer becomes too large, the drainage performance may actually decrease. Therefore, the average pore size of the water-repellent layer is preferably 1.0 μm or less.

[0048] [1.3.2. Thickness of the water-repellent layer] In this invention, the thickness of the water-repellent layer is not particularly limited, and an optimal thickness can be selected depending on the purpose. Generally, if the water-repellent layer is too thin, the drainage performance may decrease. Therefore, a water-repellent layer thickness of 150 μm or more is preferable. Preferably, the thickness is 200 μm or more, and more preferably 250 μm or more. On the other hand, if the water-repellent layer becomes too thick, the gas diffusion resistance of the water-repellent layer may increase. Therefore, the thickness of the water-repellent layer is preferably 450 μm or less. Preferably, the thickness is 400 μm or less, and more preferably 350 μm or less.

[0049] [2. Gas diffusion layer with water-repellent coating] The gas diffusion layer with a water-repellent layer according to the present invention has the following configuration.

[0050] [Composition 11] Gas diffusion layer substrate, A water-repellent layer according to any one of configurations 1 to 10 is formed on the surface of the gas diffusion layer substrate. A gas diffusion layer with a water-repellent layer.

[0051] [2.1. Gas Diffusion Layer Substrate] The gas diffusion layer substrate is made of a conductive porous material. Here, "conductive porous material" refers to a material that has electron 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 is a conductive porous material, and the most suitable material can be selected depending on the purpose. Examples of materials for the gas diffusion layer substrate include carbon fiber nonwoven fabric, carbon paper, carbon cloth, and porous metal sintered bodies.

[0052] [2.2. Water-repellent layer] A water-repellent layer is formed on the surface of the gas diffusion layer substrate. The water-repellent layer may contain only composite particles, or it may contain composite particles and a water-repellent binder. Details of the water-repellent layer are as described above and will not be explained further.

[0053] [3. Method for manufacturing a water-repellent layer and a gas diffusion layer with a water-repellent layer] The water-repellent layer according to the present invention is (a) Prepare composite particles, (b) If necessary, a water-repellent binder is mixed with the composite particles to form a mixed powder. (c) Form a precursor layer on the substrate surface by scattering and pressing composite particles or mixed powder onto the substrate surface, (d) Sinter the precursor layer. It can be manufactured by doing so. Furthermore, if a gas diffusion layer substrate is used as the base material, a gas diffusion layer with a water-repellent layer can be obtained by the method described above.

[0054] [3.1. 1st step] First, composite particles are prepared. The method for forming a water-repellent coating on the surface of the carbon particles is not particularly limited, and the most suitable method can be selected depending on the purpose. One method for forming a water-repellent coating is to use a target made of a primary water-repellent molecule (e.g., PTFE) to perform plasma PVD treatment on carbon particles.

[0055] [3.2. 2nd process] Next, if necessary, a water-repellent binder is mixed with the composite particles to form a mixed powder. The mixing ratio of the water-repellent binder is not particularly limited, and the optimal value can be selected according to the purpose. Furthermore, the mixing method of the composite particles and the water-repellent binder is not particularly limited, and the optimal method can be selected according to the purpose.

[0056] [3.3. Third step] Next, composite particles or mixed powder are scattered and pressed onto the substrate surface to form a precursor layer on the substrate surface. The method for forming the precursor layer is not particularly limited, and the most suitable method can be selected depending on the purpose. For example, the method for forming the precursor layer is as follows: (a) A method of depositing composite particles or mixed powder onto the surface of a substrate using an electrostatic screen printing method, and pressing the layer of composite particles or mixed powder at room temperature. (b) Dry film formation methods such as electrostatic coating, These are some examples.

[0057] [3.4. 4th step] Next, the precursor layer is calcined. This yields the water-repellent layer or the gas diffusion layer with a water-repellent layer according to the present invention. The firing temperature can be selected to the optimal temperature depending on the purpose. Generally, if the firing temperature is too low, the bonding between the composite particles, or between the composite particles and the water-repellent binder, will be insufficient. Therefore, a firing temperature of 250°C or higher is preferable. Preferably, the firing temperature is 300°C or higher, and more preferably, 350°C or higher. On the other hand, if the firing temperature becomes too high, the first water-repellent molecule and / or the second water-repellent molecule may undergo thermal decomposition. Therefore, a firing temperature of 500°C or lower is preferable. Preferably, the firing temperature is 450°C or lower, and more preferably, 400°C or lower.

[0058] [4. Effect] When forming composite particles by creating a water-repellent coating on the surface of carbon particles, optimizing the film formation conditions allows for the formation of a thin and uniform water-repellent coating on the surface of the carbon particles. Subsequently, if necessary, a water-repellent binder is added to the composite particles, and then the composite particles or a mixture of composite particles and the water-repellent binder is sprayed and pressed onto the substrate surface to form a precursor layer. When the precursor layer is heated, the water-repellent layer according to the present invention is obtained. The water-repellent layer obtained in this way has superior drainage performance compared to conventional water-repellent layers.

[0059] this is, (A) By forming a thin and uniform water-repellent coating on the surface of the carbon particles, the water repellency of the carbon particle surface is increased, but the pores (gaps between carbon particles, or between primary particles constituting the carbon particles) remain unblocked, and, (B) Because the drainage of liquid water through the remaining pores without blockage is promoted. It is thought that... [Examples]

[0060] (Examples 1-7, Comparative Examples 1-3) [1. Sample Preparation] Carbon black (Acetylene Black manufactured by Denka Co., Ltd., product name: Li400, average particle size: 4 μm, average primary particle size: 48 nm) (hereinafter abbreviated as "CB") was used as the carbon particles. Using PTFE (first hydrophobic molecule) as a target, composite particles were obtained by subjecting carbon particles to plasma-coated PVD treatment. The treatment time was: (a) CB (17g) for 1 hour (Examples 1-3), (b) CB (6.8g) for 0.5 hours (Example 4), (c) CB (6.8g) for 1 hour (Example 5), (d) CB (6.8g) for 2 hours (Example 6), or (e) CB (6.8g) for 4 hours (Example 7) That's what I decided.

[0061] Next, the composite particles and a water-repellent binder (second water-repellent molecule) were blended in a predetermined ratio and mixed using a stirrer. PTFE powder with an average particle size of 0.2 μm was used as the water-repellent binder. The stirrer used was Osaka Chemical Co., Ltd., product name: LAB MILL II, model number: OML-2. Furthermore, stirring was performed under the same conditions regardless of the presence or absence of the water-repellent binder. Next, the mixed powder was deposited onto the surface of the substrate using electrostatic screen printing. Carbon paper was used as the substrate. Furthermore, the deposited layer of mixed powder was pressed for 1 minute at room temperature and 3 MPa to obtain a precursor layer / substrate laminate. Finally, the laminate was held in an electric furnace at atmospheric pressure and 350°C for 30 minutes to obtain a water-repellent layer / substrate laminate. Table 1 shows the content of the first water-repellent molecule and the mixing ratio (mass ratio) of the composite particles and the second water-repellent molecule.

[0062] [Table 1]

[0063] [2. Test Method] [2.1. Evaluation of composite particles] [2.1.1. PTFE Coverage Rate] Quantitative analysis of fluorine atoms was performed using combustion ion chromatography (IC) on CB and composite particles (PTFE-CB) obtained by plasma PVD treatment of CB with PTFE. The amount of PTFE (first hydrophobic molecule) was calculated from the amount of fluorine atoms. Furthermore, the PTFE coverage rate was calculated assuming that the surface of CB was coated with a single layer of PTFE.

[0064] [2.1.2. SEM and TEM observations] SEM and TEM observations were performed on the composite particles.

[0065] [2.1.3. Electronic Resistance - Influence of the Content of the First Hydrophobic Molecule -] For gas diffusion layers with a water-repellent layer containing only composite particles (Examples 1, 4-7), the electronic resistance in the film thickness direction of the gas diffusion layer with a water-repellent layer was measured using a two-terminal method.

[0066] [2.1.4. Water vapor adsorption measurement] Water vapor adsorption measurements were performed on CB and PTFE-CB. Anton Paar Japan Co., Ltd.'s AUTOSORB-IQ was used for the measurements.

[0067] [2.1.5. N2 adsorption measurement] N2 adsorption measurements were performed on CB and PTFE-CB.

[0068] [2.2. Evaluation of the water-repellent layer] [2.2.1. Liquid water permeation amount] The laminate of the water-repellent layer and the substrate was sandwiched between flanges with the water-repellent layer facing upwards, and a water pressure of approximately 250 kPa was applied to the water-repellent layer. The amount of liquid water permeated from the water-repellent layer to the substrate side over a 5-minute period was detected by mass spectrometry.

[0069] [2.2.2. Observation with an optical microscope] The surface of the water-repellent layer was observed using an optical microscope.

[0070] [2.2.3. Average pore diameter] The average pore size of the substrate and the water-repellent layer / substrate laminate was measured using the mercury intrusion method.

[0071] [2.2.4. Electronic Resistance - Influence of the Blending Ratio of the Second Hydrophobic Molecule -] For gas diffusion layers with a water-repellent layer (Examples 1-3, Comparative Examples 1-3) that had water-repellent layers with different mixing ratios of the second hydrophobic molecule, the electronic resistance in the film thickness direction of the gas diffusion layer with the water-repellent layer was measured using a two-terminal method.

[0072] [3. Results] [3.1. Evaluation of composite particles] [3.1.1. PTFE Coverage Rate] Table 2 shows the relationship between the amount of PTFE (primary water-repellent molecule) and the PTFE coverage rate. From Table 2, it can be seen that the PTFE coverage rate increases as the PTFE content increases. Furthermore, it can be seen that the PTFE coverage rate exceeds 100% when the PTFE content reaches 2.8%. This is thought to indicate that multilayer adsorption of PTFE is occurring.

[0073] [Table 2]

[0074] [3.1.2. SEM and TEM Observation] [A. SEM observation] Figure 1 shows the SEM image and F element map overlay of the stirred composite particles (PTFE content: 2.8 mass%) obtained in Example 7. Figure 2 shows the SEM image and F element map overlay of the stirred composite particles (PTFE content: 0.8 mass%) obtained in Example 1. Furthermore, Figure 3 shows the SEM image and F element map overlay of the stirred carbon black obtained in Comparative Example 3. From Figures 1 to 3, it can be seen that the PTFE containing element F is uniformly dispersed in all of the composite particles.

[0075] [B. TEM image] Figure 4 shows the time-dependent changes in the TEM image of the composite particles (PTFE content 2.8 mass%) obtained in Example 7 after stirring. TEM observation of the composite particles revealed areas where the shape of the deposits on the surface of the CB changed over time (the central region of the composite particles) and areas where the shape did not change over time (the upper right region of the composite particles). Areas where the shape of the deposits has changed over time are thought to be areas where volatilization and deposition of contaminants other than PTFE have occurred due to electron beam irradiation. On the other hand, areas where the shape has not changed over time are thought to be areas where PTFE has been deposited. The thickness of the PTFE coating measured from the areas where the shape has not changed over time was estimated to be 2.0 nm.

[0076] [3.1.3. Electronic Resistance - Influence of the Content of the First Hydrophobic Molecule -] Figure 5 shows the relationship between the amount of PTFE (first water-repellent molecule) contained in the composite particles and the electronic resistance of the gas diffusion layer with a water-repellent layer. From Figure 5, it can be seen that the electronic resistance of the gas diffusion layer with a water-repellent layer increases as the amount of PTFE (first water-repellent molecule) increases, but even when the PTFE coverage exceeds 100% (Example 7), the electronic resistance does not become excessively high.

[0077] [3.1.4. Water vapor adsorption measurement] Figure 6 shows the water vapor adsorption isotherms for carbon black (CB) and composite particles obtained by plasma PVD treatment of carbon black with PTFE (PTFE-CB) (Example 1, PTFE content: 0.8 mass%). The amount of water vapor adsorbed by PTFE-CB decreased compared to untreated CB. From Figure 6, it can be concluded that PTFE-CB became water-repellent.

[0078] [3.1.5. N2 adsorption measurement] Figure 7 shows the effect of PTFE (first hydrophobic molecule) content on the BET specific surface area and pore volume of composite particles. While the BET specific surface area and pore volume of the composite particles (PTFE-CB) tended to decrease as the amount of PTFE (first hydrophobic molecule) increased, the decrease was not dramatic. Figure 7 demonstrates that plasma PVD treatment does not cause pore blockage in CB.

[0079] [3.2. Evaluation of the water-repellent layer] [3.2.1. Liquid water permeation amount] Figure 8 shows the liquid water permeability of the water-repellent layers obtained in Examples 1-3 and Comparative Examples 1-3. From Figure 8, when comparing water-repellent layers with the same ratio of water-repellent binder (Example 1 vs. Comparative Example 1, Example 2 vs. Comparative Example 2, Example 3 vs. Comparative Example 3), it can be seen that the water-repellent layer containing PTFE-CB has a higher liquid water permeability than the water-repellent layer containing untreated CB. From this result, it was found that the water-repellent effect of the PTFE coating is effective in improving liquid water permeability (drainage). Furthermore, it was found that whether or not plasma PVD-treated composite particles are used is more important than the ratio of the water-repellent binder in increasing liquid water permeability.

[0080] [3.2.2. Observation with an optical microscope] Figure 9 shows optical microscope images of the water-repellent layers obtained in Examples 1-3 and Comparative Examples 1-3. From Figure 9, it was confirmed that none of Examples 1-3 or Comparative Examples 1-3 showed any cracks or other defects. This result indicates that the difference in liquid water permeability is not due to the presence or absence of cracks or other defects.

[0081] [3.2.3. Average pore diameter] Figure 10 shows the pore size distribution of the substrate. In Figure 10, "CP" represents untreated carbon paper, and "PTFE / CP" represents carbon paper treated with 5 mass% PTFE for water repellency. Figure 11 shows the pore size distribution of the water-repellent layer / substrate obtained in Examples 1-3 and Comparative Examples 1-3. Figure 12 shows the pore size distribution of Examples 1-3, specifically a magnified view of the pore size distribution shown in Figure 11 near a pore size of 0.1 μm. Figure 13 shows the pore size distribution of Comparative Examples 1-3, specifically a magnified view of the pore size distribution shown in Figure 11 near a pore size of 0.1 μm.

[0082] As shown in Figures 10 to 13, peaks near a pore diameter of 0.1 μm were observed in all three examples (1 to 3) and comparative examples (1 to 3). Since the peak near 0.1 μm is not observed in Figure 10, it can be concluded that this peak originates from the water-repellent layer and not from the substrate. Furthermore, since the mode diameters of Examples 1 to 3 are almost the same as those of Comparative Examples 1 to 3, it can be concluded that the pores of the CB are not blocked by the formation of the water-repellent coating.

[0083] [3.2.4. Electronic Resistance - Influence of the Mixing Ratio of the Second Hydrophobic Molecule -] Figure 14 shows the relationship between the amount of PTFE (secondary hydrophobic molecule) contained in the water-repellent layer and the electronic resistance of the gas diffusion layer with the water-repellent layer. From Figure 14, it can be seen that the electronic resistance tends to increase as the PTFE (secondary hydrophobic molecule) content increases, and that even when 40 mass% of PTFE (secondary hydrophobic molecule) is added, the increase in electronic resistance is relatively small. Furthermore, the water-repellent layers of Examples 1-3 exhibit higher electronic resistance compared to the water-repellent layers of Comparative Examples 1-3. However, since the increase in electronic resistance is slight, the influence of PTFE (the first water-repellent molecule) on the performance of the water-repellent layer is considered to be small.

[0084] 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]

[0085] The water-repellent layer according to the present invention can be used as a water-repellent layer formed on the surface of a gas diffusion layer substrate used in a fuel cell.

Claims

1. A water-repellent layer having the following configuration: (1) The water-repellent layer contains composite particles. (2) The composite particles are Carbon particles and A water-repellent coating consisting of a first water-repellent molecule that covers the surface of the carbon particles, Includes.

2. The water-repellent layer according to claim 1, wherein the carbon particles are carbon black.

3. The water-repellent layer according to claim 1, wherein the carbon particles have an average particle diameter of less than 5.0 μm.

4. The water-repellent layer according to claim 1, wherein the coverage rate of the water-repellent film is 5.0% or more. However, the "coverage rate of the water-repellent coating" refers to the ratio of the surface area of ​​the carbon particles covered with the water-repellent coating to the total surface area of ​​the carbon particles, assuming that the water-repellent coating consists of a single atomic layer of the first water-repellent molecule.

5. The water-repellent layer according to claim 1, wherein the water-repellent coating has a thickness of 2.0 nm or less.

6. The water-repellent layer according to claim 1, further comprising a water-repellent binder consisting of a second water-repellent molecule.

7. The water-repellent layer according to claim 6, wherein the content of the water-repellent binder is 50.0 mass% or less. However, the "content of the water-repellent binder" refers to the ratio of the mass of the water-repellent binder to the total mass of the composite particles and the water-repellent binder.

8. The water-repellent layer according to claim 1, wherein the average pore diameter is 0.1 μm or more and 1.0 μm or less.

9. Gas diffusion layer substrate, A water-repellent layer according to any one of claims 1 to 8, formed on the surface of the gas diffusion layer substrate, A gas diffusion layer with a water-repellent layer.

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