Water-repellent layer for fuel cells, gas diffusion layer for fuel cells, and membrane electrode gas diffusion layer assembly

Abstract

To provide a water-repellent layer that can be bonded to a catalyst layer with high bonding strength. [Solution] A water-repellent layer for a fuel cell, wherein a bonding material layer containing a fluoropolymer resin or a fluoropolymer electrolyte is formed on at least one surface.

Description

[Technical Field]

[0001] The present invention relates to a water-repellent layer for fuel cells, a gas diffusion layer for fuel cells, and a membrane electrode gas diffusion layer assembly. [Background technology]

[0002] Fuel cells typically have a membrane electrode gas diffusion layer assembly (MEGA) as their basic unit, in which electrodes containing catalyst layers are bonded to both sides of an electrolyte membrane, and a gas diffusion layer is further bonded to the catalyst layer. In such fuel cells, the gas diffusion layer is used to supply reaction gas and electrons to the catalyst layer, which is the reaction field for the electrode reaction. From the viewpoint of improving the power generation performance of fuel cells, such gas diffusion layers require high gas permeability and high water repellency. Conventionally, gas diffusion layers comprising a porous substrate such as carbon paper or carbon cloth and a water-repellent layer laminated on the surface of this porous substrate have been used. As the water-repellent layer, a water-repellent layer formed by a dry film deposition method using composite particles containing conductive particles such as carbon particles and fluororesin particles such as polytetrafluoroethylene (PTFE) particles is known (for example, Japanese Patent Application Publication No. 2019-121423 (Patent Document 1) and Japanese Patent Application Publication No. 2021-2444 (Patent Document 2)). The gas diffusion layer is then joined to the water-repellent layer and the catalyst layer to form a membrane electrode gas diffusion layer assembly (MEGA). In conventional joining of the water-repellent layer and the catalyst layer, the resin component contained in the water-repellent layer (e.g., water-repellent resin particles) and the ionomer contained in the catalyst layer are melted and softened by hot pressing, and then solidified, thereby directly joining the water-repellent layer and the catalyst layer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-121423 [Patent Document 2] Japanese Patent Publication No. 2021-2444 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in conventional bonding between the water-repellent layer and the catalyst layer, the bonding strength was not always sufficiently high.

[0005] The present invention has been made in view of the problems of the prior art described above, and its first objective is to provide a water-repellent layer that can be bonded with high bonding strength to an adjacent layer (hereinafter also simply referred to as "adjacent layer"), such as a catalyst layer. The second objective of the present invention is to provide a gas diffusion layer that can be bonded with high bonding strength to a membrane electrode assembly. Furthermore, the third objective of the present invention is to provide a membrane electrode gas diffusion layer assembly in which the water-repellent layer and the adjacent layer are bonded with high bonding strength. [Means for solving the problem]

[0006] The inventors of the present invention have conducted extensive research to achieve the above objectives and have found that by forming a layer containing a fluorine-based thermoplastic resin or a fluorine-based polymer electrolyte on at least one surface of the water-repellent layer, a water-repellent layer can be bonded with an adjacent layer such as a catalyst layer with high bonding strength. Furthermore, by forming this water-repellent layer on the surface of a porous substrate, a gas diffusion layer can be bonded with a membrane electrode assembly with high bonding strength. Finally, by bonding this gas diffusion layer to the membrane electrode assembly, a membrane electrode gas diffusion layer assembly can be obtained in which the water-repellent layer and the adjacent layer are bonded with high bonding strength. This discovery has led to the completion of the present invention.

[0007] In other words, the present invention provides the following embodiments. [1] A water-repellent layer for a fuel cell, wherein a bonding material layer containing a fluoropolymer resin or a fluoropolymer electrolyte is formed on at least one surface. [2] The water-repellent layer for a fuel cell according to [1], wherein the bonding material layer is a layer containing a fluoropolymer resin having a melting point of 100 to 330°C or a fluoropolymer electrolyte having a glass transition temperature of 100 to 200°C. [3] The water-repellent layer for fuel cells according to [1] or [2], wherein the bonding material layer is a layer containing polyvinylidene fluoride or perfluorosulfonic acid resin. [4] A gas diffusion layer for a fuel cell, comprising a porous substrate and a water-repellent layer for a fuel cell according to any one of [1] to [3] formed on the surface of the porous substrate. [5] The fuel cell gas diffusion layer according to [4], wherein the bonding material layer is disposed on at least the surface of the fuel cell water-repellent layer opposite to the porous substrate. A fuel cell membrane electrode gas diffusion layer assembly comprising a fuel cell gas diffusion layer as described in [6][4] or [5], and a membrane electrode assembly formed on the fuel cell water-repellent layer of the fuel cell gas diffusion layer. [7] The fuel cell membrane electrode gas diffusion layer assembly according to [6], wherein the bonding material layer is disposed at least at the interface between the water-repellent layer for the fuel cell and the catalyst layer of the membrane electrode assembly.

[0008] Although the reason why the water-repellent layer and the catalyst layer are joined with high bonding strength by this invention is not entirely clear, the inventors speculate as follows: Because the surface roughness of the water-repellent layer and the catalyst layer are different, if the water-repellent layer and the catalyst layer are joined directly, as in conventional joining methods, the contact area between the water-repellent layer and the catalyst layer is small, and it is speculated that sufficient bonding strength cannot be obtained by simply melting, softening, and solidifying the hydrophobic resin in the water-repellent layer and the ionomer in the catalyst layer.

[0009] On the other hand, in the present invention, a bonding material layer containing a fluoropolymer resin or a fluoropolymer electrolyte is formed on at least one surface of the water-repellent layer. When this bonding material layer is formed on the catalyst layer side, the water-repellent layer and the catalyst layer are bonded via this bonding material layer. It is presumed that the bonding material layer containing the fluoropolymer resin or fluoropolymer electrolyte melts, softens, and solidifies, thereby functioning as an adhesive and improving the bonding strength between the water-repellent layer and the catalyst layer.

[0010] Similarly, regarding the reason why the porous substrate and the water-repellent layer are joined with high bonding strength, in the present invention, since the water-repellent layer and the porous substrate are joined through a bonding material layer containing a fluorine-based thermoplastic resin, it is presumed that the bonding material layer containing these functions as an adhesive by melting, softening, and solidifying the fluorine-based thermoplastic resin, thereby improving the bonding strength between the water-repellent layer and the porous substrate. On the other hand, when the water-repellent layer and the porous substrate are directly joined, it is presumed that sufficient bonding strength cannot be obtained only by melting, softening, and solidifying the hydrophobic resin in the water-repellent layer.

Advantages of the Invention

[0011] According to the present invention, it is possible to obtain a water-repellent layer that can be joined to an adjacent layer such as a catalyst layer with high bonding strength, a gas diffusion layer that can be joined to a membrane electrode assembly with high bonding strength, and a membrane electrode gas diffusion layer assembly in which the water-repellent layer and the adjacent layer are joined with high bonding strength.

Brief Description of the Drawings

[0012] [Figure 1A] It is a schematic diagram showing one embodiment of the gas diffusion layer for a fuel cell of the present invention. [Figure 1B] It is a schematic diagram showing another embodiment of the gas diffusion layer for a fuel cell of the present invention. [Figure 1C] It is a schematic diagram showing still another embodiment of the gas diffusion layer for a fuel cell of the present invention. [Figure 2A] It is a schematic diagram showing one embodiment of the membrane electrode gas diffusion layer assembly for a fuel cell of the present invention. [Figure 2B] It is a schematic diagram showing another embodiment of the membrane electrode gas diffusion layer assembly for a fuel cell of the present invention. [Figure 2C] It is a schematic diagram showing still another embodiment of the membrane electrode gas diffusion layer assembly for a fuel cell of the present invention. [Figure 3] It is a graph showing the bonding strength between the water-repellent layer and the catalyst layer of the membrane electrode gas diffusion layer assemblies obtained in the examples and comparative examples.

Modes for Carrying Out the Invention

[0013] The present invention will be described in detail below with reference to its preferred embodiments.

[0014] [Water-repellent coating for fuel cells] First, the water-repellent layer for fuel cells of the present invention will be described. The water-repellent layer for fuel cells of the present invention has a bonding material layer containing a fluorine-based thermoplastic resin or a fluorine-based polymer electrolyte formed on at least one surface.

[0015] There are no particular restrictions on the water-repellent layer, and conventionally known water-repellent layers for fuel cells can be used. However, from the viewpoint of high water repellency and improved strength of the water-repellent layer itself, a layer containing conductive particles and a fluoropolymer resin is preferred.

[0016] (Conductive particles) The conductive particles are not particularly limited as long as they are conductive particles, and examples include carbon particles such as carbon black, carbon nanofibers, carbon nanotubes, carbon nanohorns, and vapor-phase carbon fibers. These conductive particles may be used individually or in combination of two or more types.

[0017] There are no particular restrictions on the average primary particle diameter of such conductive particles, but 1 to 1000 nm is preferred, 10 to 200 nm is more preferred, and 15 to 100 nm is even more preferred. If the average primary particle diameter of the conductive particles falls below the lower limit, the gas diffusivity tends to decrease. On the other hand, if the average primary particle diameter of the conductive particles exceeds the upper limit, the electrical resistance increases, and the power generation performance of the fuel cell tends to decrease.

[0018] Furthermore, when the conductive particles form aggregates, there are no particular restrictions on the average particle diameter (average secondary particle diameter), but it is preferably 0.01 to 10 μm, more preferably 0.05 to 5 μm, and even more preferably 0.08 to 1 μm. When the average particle diameter of the conductive particle aggregates falls below the lower limit, the gas diffusivity tends to decrease. On the other hand, when the average particle diameter of the conductive particle aggregates exceeds the upper limit, the electrical resistance increases, and the power generation performance of the fuel cell tends to decrease.

[0019] (Fluorine-based thermoplastic resin) Examples of the fluorine-based thermoplastic resins include homopolymers and copolymers of ethylene-tetrafluoroethylene (ETFE), perfluoroethylenepropene (FEP), perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVdF). These resins may be used individually or in combination of two or more. Among these, ETFE and PVdF are preferred. Because ETFE and PVdF have low melt viscosity, the molten ETFE and PVdF flow easily, spreading to cover the surface of the conductive particles or flowing into the voids within the aggregates of conductive particles. As a result, the molten ETFE and PVdF act as binder resins in the bonding of conductive particles, and a three-dimensional structure is formed by the bonding of conductive particles by ETFE and PVdF, thereby improving the strength of the water-repellent layer itself.

[0020] The melt viscosity of the aforementioned fluoropolymer thermoplastic resin is 1 × 10⁻¹⁶ when the temperature is 300°C (for ETFE) or 200°C (for PVdF) and the test pressure is 5 MPa using a constant temperature method with a high-efficiency flow tester (Shimadzu Corporation "CFT-100D"). 5 Pa·s or less is preferred, and 1 × 10 4 Pa·s or less is more preferable, 1 × 10 3 A viscosity of 1 Pa·s or less is even more preferable. If the melt viscosity of the fluoropolymer resin exceeds the upper limit, the fluidity of the molten fluoropolymer resin is low, and it is not possible to sufficiently cover the surface of the conductive particles or flow sufficiently into the voids within the aggregates of conductive particles. As a result, the molten fluoropolymer resin does not act as a binder resin in the bonding of the conductive particles, and a three-dimensional structure in which the conductive particles are bonded together by the fluoropolymer resin is not sufficiently formed, which tends to reduce the strength of the water-repellent layer itself. There is no particular lower limit to the melt viscosity of the fluoropolymer resin, but from the viewpoint of preventing excessive segregation of the fluoropolymer resin, 1 Pa·s or more is preferable.

[0021] Furthermore, because the fluoropolymer thermoplastic resin has a low melting point, it can be melted by heating at relatively low temperatures, making it possible to manufacture the water-repellent layer at low cost. The melting point of the fluoropolymer thermoplastic resin is preferably 100 to 330°C, and more preferably 120 to 310°C. If the melting point of the fluoropolymer thermoplastic resin falls below the lower limit, during the subsequent heat-pressing process (120 to 160°C) related to fuel cell cell formation, the fluoropolymer thermoplastic resin tends to melt and penetrate too much into the porous substrate, leading to a decrease in the strength of the water-repellent layer itself and obstruction of the movement of reaction gases and water due to blockage of voids. On the other hand, if the melting point of the fluoropolymer thermoplastic resin exceeds the upper limit, it becomes difficult to melt the fluoropolymer thermoplastic resin by heating at temperatures below 330°C, and a three-dimensional structure in which conductive particles are bound together by the fluoropolymer thermoplastic resin is not sufficiently formed, resulting in a tendency for the strength of the water-repellent layer itself to be low.

[0022] (Water-repellent layer) In a water-repellent layer containing such conductive particles and a fluoropolymer resin, it is preferable that the fluoropolymer resin binds the conductive particles together. By binding the conductive particles together with the fluoropolymer resin, a three-dimensional structure is formed between the conductive particles, thereby improving the strength of the water-repellent layer itself.

[0023] In such a water-repellent layer, the content ratio of conductive particles to the fluoropolymer resin is preferably 97 / 3 to 3 / 97 by mass ratio (conductive particles / fluoropolymer resin), more preferably 95 / 5 to 30 / 70, and even more preferably 90 / 10 to 40 / 60. If the mass ratio (conductive particles / fluoropolymer resin) falls below the lower limit, the proportion of conductive particles decreases, which increases the electrical resistance in the water-repellent layer and tends to reduce the power generation performance of the fuel cell. On the other hand, if the mass ratio (conductive particles / fluoropolymer resin) exceeds the upper limit, the proportion of fluoropolymer resin acting as a binder resin in the bonding of conductive particles decreases, which means that a sufficient three-dimensional structure in which the conductive particles are bonded together by the fluoropolymer resin is not formed, and the strength of the water-repellent layer itself tends to decrease.

[0024] There are no particular restrictions on the thickness of the water-repellent layer, but it is preferably 1 to 100 μm, and more preferably 5 to 50 μm. If the thickness of the water-repellent layer is less than the lower limit, the water-repellent layer cannot be reliably sandwiched between the catalyst layer and the porous substrate, and the surface of the porous substrate tends to be exposed. On the other hand, if the thickness of the water-repellent layer exceeds the upper limit, the electrical resistance increases, and the power generation performance of the fuel cell tends to decrease.

[0025] Furthermore, there are no particular restrictions on the basis weight of the water-repellent layer, but it is generally 0.1 to 20 mg / cm³. 2 Preferably, 0.5 to 5 mg / cm³ 2 This is more preferable. If the basis weight of the water-repellent layer falls below the lower limit, the water-repellent layer cannot be reliably sandwiched between the catalyst layer and the porous substrate, and the surface of the porous substrate tends to be exposed. On the other hand, if the basis weight of the water-repellent layer exceeds the upper limit, the electrical resistance increases, and the power generation performance of the fuel cell tends to decrease.

[0026] (bonding material layer) The bonding material layer is a bonding material layer containing a fluoropolymer resin or a fluoropolymer electrolyte formed on at least one surface of the water-repellent layer. By forming such a bonding material layer on at least one surface of the water-repellent layer, it becomes possible to bond the water-repellent layer and the catalyst layer and / or the porous substrate (i.e., the layer adjacent to the water-repellent layer (adjacent layer)) with high bonding strength.

[0027] (Fluorine-based thermoplastic resin) Examples of the fluorine-based thermoplastic resins include homopolymers and copolymers of ethylene-tetrafluoroethylene (ETFE), perfluoroethylenepropene (FEP), perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVdF). These resins may be used individually or in combination of two or more.

[0028] Furthermore, the melting point of the fluoropolymer resin is preferably 100 to 330°C, and more preferably 120 to 200°C. If the melting point of the fluoropolymer resin falls below the lower limit, the fluoropolymer resin tends to soften at the fuel cell operating temperature, hindering the movement of reaction gases and water due to blockage of the voids in the bonding material layer and its vicinity. On the other hand, if the melting point of the fluoropolymer resin exceeds the upper limit, it becomes necessary to heat the fluoropolymer resin at a high temperature to melt and soften it as the bonding material layer. If the bonding material layer is formed on the catalyst layer side, this tends to cause thermal deformation of the ionomer and electrolyte membrane in the catalyst layer of the bonding membrane electrode assembly.

[0029] Among such fluoropolymer-based thermoplastic resins, PVdF is particularly preferred as a bonding material layer from the viewpoint of its melting point for melting and softening, and its melt viscosity.

[0030] (Fluorine-based polymer electrolytes) Examples of the fluorine-based polymer electrolyte include perfluorosulfonic acid resin, perfluorophosphonic acid resin, perfluorocarboxylic acid resin, and perfluorosulfonimide resin. These resins may be used individually or in combination of two or more.

[0031] Furthermore, the glass transition temperature of the fluorine-based polymer electrolyte is preferably 100 to 200°C, and more preferably 120 to 160°C. If the glass transition temperature of the fluorine-based polymer electrolyte falls below the lower limit, the fluorine-based polymer electrolyte tends to soften at the fuel cell operating temperature, hindering the movement of reaction gases and water due to blockage of voids in the bonding material layer and its vicinity. On the other hand, if the glass transition temperature of the fluorine-based polymer electrolyte exceeds the upper limit, the fluorine-based polymer electrolyte does not soften sufficiently during heat bonding with the membrane electrode assembly, resulting in a tendency for lower bonding strength.

[0032] Among such fluorinated polymer electrolytes, perfluorosulfonic acid resin is more preferred, and perfluorosulfonic acid-polytetrafluoroethylene copolymer is particularly preferred, from the viewpoint of obtaining high bonding strength with the catalyst layer and retaining excess water.

[0033] [Gas diffusion layer for fuel cells] Next, the gas diffusion layer for fuel cells of the present invention will be described. The gas diffusion layer for fuel cells of the present invention comprises a porous substrate and a water-repellent layer for fuel cells of the present invention formed on the surface of the porous substrate.

[0034] The porous substrate is not particularly limited as long as it is used in the gas diffusion layer for fuel cells, and examples include carbon paper and carbon cloth. The thickness of the porous substrate is not particularly limited as long as it is a thickness that can be used in fuel cells, and can be set as appropriate, and is usually 100 to 300 μm.

[0035] One embodiment of the gas diffusion layer for fuel cells of the present invention is, for example, as shown in Figure 1A, a gas diffusion layer in which a porous substrate 1 and the water-repellent layer 4 for fuel cells of the present invention, on which a bonding material layer 3a is formed on one surface of the water-repellent layer 2, are bonded together such that the porous substrate 1 and the water-repellent layer 2 are in contact with each other. In other words, a gas diffusion layer in which the porous substrate 1 and the water-repellent layer 2 are directly bonded and the bonding material layer 3a is provided as the uppermost layer, i.e., the bonding material layer 3a is located on the surface of the water-repellent layer 2 opposite to the porous substrate 1. By bonding a membrane electrode assembly to the surface of such a gas diffusion layer, a membrane electrode gas diffusion layer assembly can be obtained in which the water-repellent layer of the gas diffusion layer and the catalyst layer of the membrane electrode assembly are bonded with high bonding strength.

[0036] Another embodiment of the gas diffusion layer for fuel cells of the present invention is, for example, as shown in Figure 1B, a gas diffusion layer in which a porous substrate 1 and the water-repellent layer 4 for fuel cells of the present invention, on which a bonding material layer 3b is formed on one surface of the water-repellent layer 2, are bonded together such that the porous substrate 1 and the bonding material layer 3b are in contact with each other. In other words, a gas diffusion layer in which the porous substrate 1 and the water-repellent layer 2 are bonded via the bonding material layer 3b, i.e., a gas diffusion layer in which the bonding material layer 3b is located at the interface between the porous substrate 1 and the water-repellent layer 2. In such a gas diffusion layer, the porous substrate and the water-repellent layer are bonded with high bonding strength.

[0037] As yet another embodiment of the gas diffusion layer for fuel cells of the present invention, as shown in Figure 1C, for example, a gas diffusion layer is formed in which a porous substrate 1 and the water-repellent layer 4 for fuel cells of the present invention, which has bonding material layers 3a and 3b formed on both sides of the water-repellent layer 2, are bonded so that the porous substrate 1 and the bonding material layer 3b are in contact with each other. In other words, a gas diffusion layer is formed in which the porous substrate 1 and the water-repellent layer 2 are bonded via the bonding material layer 3b, and the bonding material layer 3a is provided as the outermost layer. That is, the bonding material layer 3a is arranged on the surface of the water-repellent layer 2 opposite to the porous substrate 1, and the bonding material layer 3b is arranged at the interface between the porous substrate 1 and the water-repellent layer 2. By bonding a membrane electrode assembly to the surface of such a gas diffusion layer, a membrane electrode gas diffusion layer assembly is obtained in which the porous substrate, the water-repellent layer of the gas diffusion layer, and the catalyst layer of the membrane electrode assembly are bonded with high bonding strength.

[0038] Furthermore, the gas diffusion layer for fuel cells of the present invention comprises the porous substrate and the water-repellent layer for fuel cells of the present invention laminated on the surface of the porous substrate, but other configurations (for example, other layers other than the porous substrate and the water-repellent layer) and characteristics (for example, conditions such as the BET surface area and pore capacity of the gas diffusion layer as a whole) are not particularly limited.

[0039] [Gas diffusion layer assembly for fuel cell membrane electrodes] Next, the fuel cell membrane electrode gas diffusion layer assembly of the present invention will be described. The fuel cell membrane electrode gas diffusion layer assembly of the present invention comprises the fuel cell gas diffusion layer of the present invention and a membrane electrode assembly formed on the fuel cell water-repellent layer of the fuel cell gas diffusion layer of the present invention.

[0040] There are no particular limitations on the membrane electrode assembly, and conventional membrane electrode assemblies (MEAs) used in fuel cells can be used. For example, an electrolyte membrane electrode assembly having a structure in which an electrolyte membrane is sandwiched between two catalyst layers can be used.

[0041] The electrolyte membrane is not particularly limited, and examples include a solid electrolyte membrane made of a fluorine-based resin having one or more acidic groups such as a sulfonic acid group, a phosphonic acid group, a carboxylic acid group, or a sulfonimide group at its terminal end.

[0042] There are no particular restrictions on the catalyst layer, and examples include a catalyst layer on which a precious metal such as platinum is supported, or a catalyst layer on which an alloy such as platinum or a transition metal is supported.

[0043] Examples of the fuel cell membrane electrode gas diffusion layer assembly of the present invention include, as shown in Figure 2A, a membrane electrode gas diffusion layer assembly in which a porous substrate 1 and a water-repellent layer 2 are directly bonded, and the water-repellent layer 2 of the fuel cell gas diffusion layer 5, which has a bonding material layer 3a as the outermost layer, and the catalyst layer 7a of the membrane electrode assembly 6 are bonded via the bonding material layer 3a. In other words, a membrane electrode gas diffusion layer assembly in which the water-repellent layer 2 is directly placed on the surface of the porous substrate 1 and the bonding material layer 3a is placed at the interface between the water-repellent layer 2 and the catalyst layer 7a. In such a membrane electrode gas diffusion layer assembly, the water-repellent layer of the gas diffusion layer and the catalyst layer of the membrane electrode assembly are bonded with high bonding strength.

[0044] Another embodiment of the fuel cell membrane electrode gas diffusion layer assembly of the present invention is, for example, as shown in Figure 2B, a membrane electrode gas diffusion layer assembly in which the water-repellent layer 2 of a fuel cell gas diffusion layer 5, which is formed by joining a porous substrate 1 and a water-repellent layer 2 via a joining material layer 3b, is directly joined to the catalyst layer 7a of a membrane electrode assembly 6. In other words, the joining material layer 3b is disposed at the interface between the porous substrate 1 and the water-repellent layer 2, and the catalyst layer 7a is directly disposed on the surface of the water-repellent layer 2. In such a membrane electrode gas diffusion layer assembly, the porous substrate and the water-repellent layer of the gas diffusion layer are joined with high bonding strength.

[0045] As yet another embodiment of the fuel cell gas diffusion layer of the present invention, for example, as shown in Figure 2C, a membrane electrode gas diffusion layer assembly is provided in which a porous substrate 1 and a water-repellent layer 2 are joined via a bonding material layer 3b, and the water-repellent layer 2 of the fuel cell gas diffusion layer 5, which has a bonding material layer 3a as the outermost layer, and the catalyst layer 7a of the membrane electrode assembly 6 are joined via a bonding material layer 3a. In other words, a membrane electrode gas diffusion layer assembly is provided in which the bonding material layer 3b is located at the interface between the porous substrate 1 and the water-repellent layer 2, and the bonding material layer 3a is located at the interface between the water-repellent layer 2 and the catalyst layer 7a. In such a membrane electrode gas diffusion layer assembly, the porous substrate, the water-repellent layer of the gas diffusion layer, and the catalyst layer of the membrane electrode assembly are joined with high bonding strength.

[0046] (Method for manufacturing a water-repellent layer for fuel cells, a gas diffusion layer for fuel cells, and a fuel cell membrane electrode gas diffusion layer assembly) The fuel cell water-repellent layer, fuel cell gas diffusion layer, and fuel cell membrane electrode gas diffusion layer assembly of the present invention can be manufactured, for example, by the following method.

[0047] (Method 1) A method for manufacturing the gas diffusion layer for fuel cells shown in Figure 1A and the fuel cell membrane electrode gas diffusion layer assembly shown in Figure 2A is, for example, A step of forming a composite powder of conductive particles and fluorine-based thermoplastic resin powder on the surface of a porous substrate 1 (composite powder layer formation step), The process involves pressurizing the resulting composite powder layer to compact it (compaction process), The process involves firing the compacted composite powder layer to form the water-repellent layer 2 (firing process), The process involves forming a film on the surface of the obtained water-repellent layer 2 with a dispersion solution or powder of a fluoropolymer resin or a dispersion solution or powder of a fluoropolymer electrolyte (bonding material coating layer formation process), The process involves laminating the film electrode assembly 6 onto the surface of the obtained bonding material coating layer, then heating and pressurizing to bond the water-repellent layer 2 and the catalyst layer 7a via the bonding material layer 3a (bonding process). Methods including the following are mentioned.

[0048] Furthermore, in Method 1, the composite powder layer obtained in the composite powder layer formation step may be formed on the surface of the composite powder layer without compaction and firing (i.e., without going through the compaction step and the firing step), and a dispersion solution or powder of a fluoropolymer resin or a dispersion solution or powder of a fluoropolymer electrolyte may be formed on the surface of the composite powder layer (bonding material coating layer formation step). After laminating the membrane electrode assembly 6 on the surface of the obtained bonding material coating layer, the composite powder layer may be compacted (compactment step), fired (firing step), and the water-repellent layer 2 and catalyst layer 7a may be bonded (bonding step) simultaneously by heating and pressurizing.

[0049] By this method, a fuel cell gas diffusion layer (Figure 1A) is obtained in which a porous substrate 1 and a water-repellent layer 2 are directly bonded together and a bonding material layer 3a is provided on the surface, and a fuel cell membrane electrode gas diffusion layer assembly (Figure 2A) is obtained in which the fuel cell gas diffusion layer 5 and the membrane electrode assembly 6 are bonded together via the bonding material layer 3a.

[0050] (Method 2) A method for manufacturing the gas diffusion layer for fuel cells shown in Figure 1B and the fuel cell membrane electrode gas diffusion layer assembly shown in Figure 2B is, for example, A step of forming a film of a dispersion solution or powder of a fluoropolymer resin on the surface of a porous substrate 1 (bonding material coating layer formation step), The process involves applying pressure to the resulting bonding material coating layer (pressurization step), A step of forming a composite powder of conductive particles and fluoropolymer resin powder on the surface of a pressurized bonding material coating layer (composite powder layer formation step), The process involves pressurizing the resulting composite powder layer to compact it (compaction process), The process involves firing a compacted composite powder layer to form a water-repellent layer 2, and then joining the formed water-repellent layer 2 and the porous substrate 1 via a bonding material layer 3b (firing process), The process involves laminating the membrane electrode assembly 6 onto the surface of the obtained water-repellent layer 2, then heating and pressurizing to directly bond the water-repellent layer 2 and the catalyst layer 7a (bonding process). Methods including the following are mentioned.

[0051] Furthermore, in method 2, the bonding material coating layer obtained in the bonding material coating layer formation step may be subjected to pressure without pressurizing it (i.e., without going through the pressurizing step), and a composite powder of the conductive particles and the fluorine-based thermoplastic resin powder may be formed on the surface of the bonding material coating layer (composite powder layer formation step), and then pressurized, thereby simultaneously pressurizing the bonding material coating layer (pressurizing step) and compacting the composite powder layer (compacting step).

[0052] By this method, a fuel cell gas diffusion layer (Figure 1B) is obtained in which a porous substrate 1 and a water-repellent layer 2 are joined via a bonding material layer 3b, and a fuel cell membrane electrode gas diffusion layer assembly (Figure 2B) is obtained in which the fuel cell gas diffusion layer 5 and the membrane electrode assembly 6 are directly joined.

[0053] (Method 3) A method for manufacturing the gas diffusion layer for fuel cells shown in Figure 1C and the fuel cell membrane electrode gas diffusion layer assembly shown in Figure 2C is, for example, A step of forming a film of a dispersion solution or powder of a fluoropolymer resin on the surface of a porous substrate 1 (bonding material coating layer formation step), The process involves applying pressure to the resulting bonding material coating layer (pressurization step), A step of forming a composite powder of conductive particles and fluoropolymer resin powder on the surface of a pressurized bonding material coating layer (composite powder layer formation step), The process involves pressurizing the resulting composite powder layer to compact it (compaction process), The process involves firing a compacted composite powder layer to form a water-repellent layer 2, and then joining the formed water-repellent layer 2 and the porous substrate 1 via a bonding material layer 3b (firing process), The process involves forming a film on the surface of the obtained water-repellent layer 2 with a dispersion solution or powder of a fluoropolymer resin or a dispersion solution or powder of a fluoropolymer electrolyte (bonding material coating layer formation process), The process involves laminating the film electrode assembly 6 onto the surface of the obtained bonding material coating layer, then heating and pressurizing to bond the water-repellent layer 2 and the catalyst layer 7a via the bonding material layer 3a (bonding process). Methods including the following are mentioned.

[0054] Furthermore, in method 3, the bonding material coating layer obtained in the bonding material coating layer formation step may be subjected to pressure without pressurizing it (i.e., without going through the pressurizing step), and a composite powder of the conductive particles and the fluorine-based thermoplastic resin powder may be formed on the surface of the bonding material coating layer (composite powder layer formation step), and then pressurized, thereby simultaneously pressurizing the bonding material coating layer (pressurizing step) and compacting the composite powder layer (compacting step).

[0055] Furthermore, in method 3, the composite powder layer obtained in the composite powder layer formation step may be formed on the surface of the composite powder layer without compaction and firing (i.e., without going through the compaction step and the firing step), and a dispersion solution or powder of a fluoropolymer resin or a dispersion solution or powder of a fluoropolymer electrolyte may be formed on the surface of the composite powder layer (bonding material coating layer formation step). After laminating the membrane electrode assembly 6 on the surface of the obtained bonding material coating layer, the composite powder layer may be compacted (compactment step), fired (firing step), and the water-repellent layer 2 and catalyst layer 7a may be bonded (bonding step) simultaneously by heating and pressurizing.

[0056] By this method, a porous substrate 1 and a water-repellent layer 2 are joined via a bonding material layer 3b, and a fuel cell gas diffusion layer (Figure 1C) having a bonding material layer 3a on its surface is obtained, as well as a fuel cell membrane electrode gas diffusion layer assembly (Figure 2C) in which the fuel cell gas diffusion layer 5 and the membrane electrode assembly 6 are joined via a bonding material layer 3a.

[0057] (Composite powder layer formation process) The composite powder layer formation step involves forming a composite powder of conductive particles and fluoropolymer resin powder on the surface of a porous substrate in Method 1, or on the surface of a pressurized or unpressurized bonding material coating layer in Methods 2 and 3, thereby forming a composite powder layer.

[0058] The fluorine-based thermoplastic resin powder is a powdered fluorine-based thermoplastic resin used in the water-repellent layer. There are no particular restrictions on the average particle size of such fluorine-based thermoplastic resin powder, but values ​​measured by dynamic image analysis are preferably 0.001 to 100 μm, and more preferably 0.01 to 80 μm. If the average particle size of the fluorine-based thermoplastic resin powder falls below the lower limit, the handling properties of the resin powder deteriorate significantly, and productivity tends to decrease. On the other hand, if the average particle size of the fluorine-based thermoplastic resin powder exceeds the upper limit, partial densification and sparseness of the resin occur within the water-repellent layer, and in the sparse areas, the three-dimensional structure of the conductive particles is not sufficiently formed, and the strength of the resulting water-repellent layer itself tends to decrease.

[0059] In the composite powder, the content ratio of the conductive particles to the fluoropolymer resin powder is preferably 97 / 3 to 3 / 97 by mass ratio (conductive particles / fluoropolymer resin powder), more preferably 95 / 5 to 30 / 70, and even more preferably 90 / 10 to 40 / 60. If the mass ratio (conductive particles / fluoropolymer resin powder) falls below the lower limit, the proportion of conductive particles decreases, resulting in increased electrical resistance in the resulting water-repellent layer and a tendency for the power generation performance of the fuel cell to decrease. On the other hand, if the mass ratio (conductive particles / fluoropolymer resin powder) exceeds the upper limit, the proportion of fluoropolymer resin powder acting as a binder resin in the bonding of conductive particles decreases, resulting in insufficient formation of a three-dimensional structure in which the conductive particles are bonded together by the fluoropolymer resin powder, and a tendency for the strength of the resulting water-repellent layer itself to decrease.

[0060] Furthermore, the composite powder may also contain powders made of other components besides the conductive particles and the fluorine-based thermoplastic resin powder, to the extent that they do not impede the function of the resulting water-repellent layer and the effects of the present invention.

[0061] Furthermore, in the composite powder, if the conductive particles form aggregates, the ratio of the average particle diameter of the fluoropolymer resin powder to the average particle diameter of the aggregates of conductive particles (average secondary particle diameter) ([average particle diameter of fluoropolymer resin powder] / [average secondary particle diameter of conductive particles]) is preferably 0.001 μm / 10 μm to 100 μm / 0.01 μm, and more preferably 0.01 μm / 1 μm to 80 μm / 0.08 μm. If the ratio of average particle diameters falls below the lower limit, the coating ratio of the fluoropolymer resin to the conductive particles increases, and the electrical resistance tends to increase. On the other hand, if the ratio of average particle diameters exceeds the upper limit, the distribution of the fluoropolymer resin becomes denser, and a three-dimensional structure is not sufficiently formed in the sparse areas, and the strength of the resulting water-repellent layer tends to decrease.

[0062] The composite powder can be obtained by mixing the conductive particles, the fluoropolymer resin powder, and, if necessary, powders consisting of other components, in a predetermined ratio. There are no particular restrictions on the method of mixing these powders; for example, a known method that allows for sufficiently uniform dispersion and mixing of the conductive particles, the fluoropolymer resin powder, and, if necessary, powders consisting of other components can be appropriately employed, such as a method of stirring and mixing using a commercially available stirrer. There are also no particular restrictions on the stirring conditions, and they can be set as appropriate, but it is preferable to mix under shear conditions (shear mixing).

[0063] In the composite powder layer formation process, it is preferable to form a layer (composite powder layer) consisting of the composite powder by forming a film using a dry film deposition method. By forming the composite powder using a dry film deposition method, the dispersion state of the conductive particles and the fluorine-based thermoplastic resin powder in the composite powder before film deposition can be maintained in the resulting composite powder layer.

[0064] There are no particular restrictions on the dry film formation method, and known dry film formation methods such as electrostatic screen printing, electrostatic coating, and blade coating can be used as appropriate. However, electrostatic screen printing is preferred because it allows for easier coating (film formation) of composite powder having a desired particle size, and moreover, the thickness of the composite powder layer obtained after coating can be more easily adjusted to a desired thickness. Therefore, electrostatic screen printing is preferred in which a screen is placed above a porous substrate or bonding material coating layer on which the coating film is to be formed, the composite powder is placed on the screen, and then the composite powder is rubbed onto the screen using a pressing member (such as a squeegee) to coat and form a film of the composite powder. When electrostatic screen printing is used as the dry film formation method, various film formation conditions such as the type of screen (mesh) and the magnitude of the voltage can be set as appropriate according to the design of the water-repellent layer to be manufactured, and conditions used in known electrostatic screen printing methods can be used as appropriate.

[0065] Furthermore, in the composite powder layer formation step, there are no particular restrictions on the amount of composite powder applied, but the basis weight of the resulting water-repellent layer should be 0.1 to 20 mg / cm². 2 Preferably, 0.5 to 5 mg / cm³ 2 This is more preferable. If the basis weight of the water-repellent layer falls below the lower limit, the water-repellent layer cannot be reliably sandwiched between the catalyst layer and the porous substrate or bonding material layer, and the surface of the porous substrate or bonding material layer tends to be exposed. On the other hand, if the basis weight of the water-repellent layer exceeds the upper limit, the electrical resistance increases, and the power generation performance of the fuel cell tends to decrease.

[0066] (consolidation process) The compaction process is a process of compacting the composite powder layer by applying pressure. There are no particular restrictions on the pressure applied, but 0.2 to 5 MPa is preferred, 0.3 to 4.5 MPa is more preferred, and 0.4 to 4 MPa is even more preferred. If the pressure falls below the lower limit, the composite powder layer cannot be sufficiently compacted, the contact between the conductive particles decreases, the electrical resistance increases, and it tends to become difficult to manufacture a structure of the desired design. On the other hand, if the pressure exceeds the upper limit, the porous substrate, bonding material layer, and water-repellent layer may be destroyed, or voids may collapse, which tends to decrease the strength of the gas diffusion layer and the bonding strength between the porous substrate and the water-repellent layer, and the power generation performance of the fuel cell may decrease.

[0067] There are no particular restrictions on the pressurization time when pressurizing the composite powder layer, but 0.1 to 3600 seconds is preferred, and 0.5 to 600 seconds is more preferred. If the pressurization time falls below the lower limit, the contact between the conductive particles decreases, increasing electrical resistance, and both the strength of the water-repellent layer itself and the power generation performance of the fuel cell tend to decrease. On the other hand, if the pressurization time exceeds the upper limit, the manufacturing cost increases due to the longer pressurization time and the increased energy required for pressurization.

[0068] There are no particular restrictions on the method of pressurizing the composite powder layer; for example, known pressurizing methods (pressing methods) such as flat plate presses and roll presses can be used as appropriate. There are also no particular restrictions on the temperature conditions when pressurizing the composite powder layer. Furthermore, in the present invention, a hot press, in which pressure (pressing) is performed while heating is used as the method of pressurizing the composite powder layer.

[0069] The thickness, porosity, and other conditions of the compacted composite powder layer can be appropriately set according to the type of conductive particles and fluorine-based thermoplastic resin powder, etc., so that the final water-repellent layer has the desired properties. Accordingly, the pressurizing conditions such as the pressure, pressurizing time, and pressurizing temperature during compaction can be appropriately adjusted.

[0070] (Firing process) The firing process involves firing the compacted composite powder layer, thereby forming a water-repellent layer. In addition, in methods 2 and 3, along with the formation of the water-repellent layer, the formed water-repellent layer and the porous substrate are joined via a bonding material layer.

[0071] The firing temperature is preferably within the range of (melting point -50°C) to 400°C (preferably 380°C or less) of the fluoropolymer resin. By firing at a temperature within this range, a water-repellent layer for fuel cells having a three-dimensional structure in which the conductive particles are bonded together by the fluoropolymer resin can be obtained. Furthermore, in methods 2 and 3, the porous substrate and the water-repellent layer are bonded with high bonding strength. If the firing temperature falls below the lower limit, it becomes difficult to sufficiently soften and melt the fluoropolymer resin, and the three-dimensional structure in which the conductive particles are bonded together by the fluoropolymer resin is not sufficiently formed, resulting in a tendency for the strength of the resulting water-repellent layer itself to decrease. Furthermore, in methods 2 and 3, the bonding strength between the porous substrate and the water-repellent layer tends to decrease. On the other hand, if the firing temperature exceeds the upper limit, the manufacturing cost increases due to the increased energy required for firing. In addition, thermal deformation of the resin occurs.

[0072] There are no particular restrictions on the firing time during the firing process, but for example, 0.1 to 120 minutes is preferred, and 0.5 to 60 minutes is more preferred. If the firing time falls below the lower limit, it becomes difficult to sufficiently melt the fluoropolymer thermoplastic resin, and a three-dimensional structure in which conductive particles are bound together by the fluoropolymer thermoplastic resin is not sufficiently formed, resulting in a tendency for the strength of the resulting water-repellent layer itself to decrease. In addition, in methods 2 and 3, the bonding strength between the porous substrate and the water-repellent layer tends to decrease. On the other hand, if the firing time exceeds the upper limit, the manufacturing cost increases due to the longer firing time.

[0073] The gas atmosphere during the firing is not particularly limited. For example, it may be an oxidizing gas atmosphere containing oxygen or an inert gas atmosphere such as nitrogen. However, from the viewpoints of cost reduction and workability improvement, an air atmosphere is preferable. Also, the pressure condition during the firing is not particularly limited, but from the viewpoints of cost reduction and workability improvement, atmospheric pressure (normal pressure) is preferable.

[0074] There is no particular limitation on the heating means used for such firing, and examples thereof include known heating furnaces such as hot blast furnaces and electric furnaces.

[0075] Thus, by firing the composite powder layer after the densification, a water-repellent layer having a three-dimensional structure in which the conductive particles are bound by the fluorine-based thermoplastic resin can be obtained. Also, in the Method 2 and the Method 3, along with the formation of the water-repellent layer, the formed water-repellent layer and the porous base material are joined via a joining material layer.

[0076] There is no particular limitation on the film thickness of the water-repellent layer, but 1 to 100 μm is preferable, and 5 to 50 μm is more preferable. When the film thickness of the water-repellent layer is less than the lower limit, it becomes difficult to reliably sandwich the water-repellent layer between the catalyst layer and the porous base material or the joining material layer. Therefore, the strength of the water-repellent layer itself tends to decrease, and the drainage property becomes insufficient, and the power generation performance of the fuel cell tends to decrease. On the other hand, when the film thickness of the water-repellent layer exceeds the upper limit, the electric resistance increases, and thus the power generation performance of the fuel cell tends to decrease.

[0077] Also, there is no particular limitation on the basis weight of the water-repellent layer, but 0.1 to 20 mg / cm 2 is preferable, and 0.5 to 5 mg / cm 2 is more preferable. When the basis weight of the water-repellent layer is less than the lower limit, the water-repellent layer cannot be reliably sandwiched between the catalyst layer and the porous base material or the joining material layer, and the surface of the porous base material or the joining material layer tends to be exposed. On the other hand, when the basis weight of the water-repellent layer exceeds the upper limit, the electric resistance increases, and thus the power generation performance of the fuel cell tends to decrease.

[0078] (Joining Material Coating Layer Formation Step) The bonding material coating layer formation step involves forming a film on the surface of the water-repellent layer or the uncompacted and unfired composite powder layer in methods 1 and 3 by applying a dispersion solution or powder of a fluoropolymer resin or a dispersion solution or powder of a fluoropolymer electrolyte, and on the surface of the porous substrate in methods 2 and 3 by applying a dispersion solution or powder of a fluoropolymer resin, thereby forming a bonding material coating layer.

[0079] The dispersion solution or powder of the fluoropolymer resin and the dispersion solution or powder of the fluoropolymer electrolyte are dispersion solutions or powders of the fluoropolymer resin and fluoropolymer electrolyte used in the bonding material layer. There are no particular restrictions on the average particle size of the dispersed particles or powder in such a dispersion solution of fluoropolymer resin and fluoropolymer electrolyte, but 0.001 to 100 μm is preferred, and 0.01 to 80 μm is more preferred. If the average particle size of the dispersed particles or powder in the dispersion solution of fluoropolymer resin and fluoropolymer electrolyte falls below the lower limit, the handling properties of the resin powder deteriorate significantly, and productivity tends to decrease. On the other hand, if the average particle size of the dispersed particles or powder in the dispersion solution of fluoropolymer resin and fluoropolymer electrolyte exceeds the upper limit, partial densification of the resin occurs within the bonding material layer, and the bonding strength between the water-repellent layer and the catalyst layer and / or porous substrate tends to decrease.

[0080] In the bonding material coating layer formation step, it is preferable to form a layer (bonding material coating layer) consisting of the dispersion solution or powder of the fluoropolymer resin and / or the dispersion solution or powder of the fluoropolymer electrolyte by forming a film. In particular, by forming a film using the fluoropolymer resin powder and / or the fluoropolymer electrolyte powder by a dry film formation method, a bonding material coating layer in which the resin powder is uniformly dispersed can be obtained.

[0081] There are no particular restrictions on the dry film formation method, and known dry film formation methods such as electrostatic screen printing, electrostatic coating, and blade coating can be used as appropriate. However, electrostatic screen printing is preferred because it allows for easier coating (film formation) of composite powder having a desired particle size, and moreover, the thickness of the bonding material layer obtained after coating can be more easily adjusted to a desired thickness. Therefore, electrostatic screen printing is preferred in which a screen is placed above a porous substrate or the water-repellent layer on which the coating film is to be formed, the resin powder is placed on the screen, and then the resin powder is rubbed onto the screen using a pressing member (such as a squeegee) to coat and form a film with the resin powder. When electrostatic screen printing is used as the dry film formation method, various film formation conditions such as the type of screen (mesh) and the magnitude of the voltage can be set as appropriate according to the design of the water-repellent layer to be manufactured, and conditions used in known electrostatic screen printing methods can be used as appropriate.

[0082] Furthermore, in the bonding material coating layer formation step, if a dispersion solution of the fluorine-based thermoplastic resin and / or the fluorine-based polymer electrolyte is used, the water-repellent layer and / or the uncompacted and unfired composite powder layer and / or the porous substrate may be coated onto the surface using a blade or brush, and then the solvent may be evaporated to form a film.

[0083] Furthermore, in the bonding material coating layer formation step, there are no particular restrictions on the amount of the fluorine-based thermoplastic resin dispersion solution or powder or the fluorine-based polymer electrolyte dispersion solution or powder applied, but the basis weight of the resulting bonding material layer should be 0.005 to 5 mg / cm². 2 Preferably, 0.1-3 mg / cm³ 2 This is more preferable. If the basis weight of the bonding material layer falls below the lower limit, the bonding strength between the water-repellent layer and the catalyst layer and / or porous substrate tends to decrease. On the other hand, if the basis weight of the bonding material layer exceeds the upper limit, the electrical resistance increases, which tends to reduce the power generation performance of the fuel cell.

[0084] (Pressurization process) The pressurization step is the step of pressurizing the bonding material coating layer in Method 2 and Method 3. Typically, in this pressurization step, the bonding material coating layer is pressurized at room temperature or while heated. If pressurized at room temperature, it is heated in the subsequent firing step, and if pressurized while heated, it is converted into a bonding material layer at that time, and the porous substrate and the water-repellent layer are bonded via this bonding material layer.

[0085] There are no particular restrictions on the pressure applied when pressurizing the bonding material coating layer, but 0.2 to 5 MPa is preferred, 0.3 to 4.5 MPa is more preferred, and 0.4 to 4 MPa is even more preferred. If the pressure is below the lower limit, the bonding material powder does not penetrate the substrate well, and sufficient bonding strength tends not to be obtained. On the other hand, if the pressure exceeds the upper limit, the porous substrate, bonding material layer, and water-repellent layer may be damaged, or the voids may collapse, which tends to reduce the strength of the gas diffusion layer and the bonding strength between the porous substrate and the water-repellent layer, and reduce the power generation performance of the fuel cell.

[0086] There are no particular restrictions on the pressurization time of the bonding material coating layer, but it is preferably 0.1 to 60 minutes, and more preferably 0.5 to 10 minutes. If the pressurization time is less than the lower limit, the bonding material powder does not penetrate the substrate well, and sufficient bonding strength tends not to be obtained. On the other hand, if the pressurization time exceeds the upper limit, the manufacturing cost increases due to the longer pressurization time and the increased energy required for pressurization.

[0087] (Joining process) The bonding process involves laminating the film electrode assembly onto the surface of the bonding material coating layer in Method 1 and Method 3, and onto the surface of the water-repellent layer in Method 2, and then applying pressure while heating. As a result, in Method 1 and Method 3, the water-repellent layer of the gas diffusion layer and the catalyst layer of the film electrode assembly are bonded via the bonding material layer, while in Method 2, the water-repellent layer and the catalyst layer are directly bonded.

[0088] In Method 1 and Method 3, the heating temperature of the bonding material coating layer is preferably above the melting point of the fluoropolymer resin (-50°C) or above the glass transition temperature of the fluoropolymer electrolyte. If the heating temperature is below the lower limit, the fluoropolymer resin or the fluoropolymer electrolyte will not soften sufficiently, and the bonding strength tends to be low. Furthermore, the heating temperature of the bonding material coating layer is preferably 200°C or lower, and more preferably 160°C or lower. If the heating temperature exceeds the upper limit, thermal deformation of the ionomer and electrolyte membrane in the catalyst layer of the membrane electrode assembly tends to occur.

[0089] In Method 1 and Method 3, there are no particular restrictions on the pressure used when pressurizing the bonding material coating layer, but 0.2 to 5 MPa is preferred, 0.3 to 4.5 MPa is more preferred, and 0.4 to 4 MPa is even more preferred. If the pressure falls below the lower limit, the bonding between the membrane electrode assembly and the bonding material layer becomes insufficient, reducing the contact between the conductive particles of the catalyst layer and the conductive particles of the water-repellent layer, increasing electrical resistance, and tending to reduce the power generation performance of the fuel cell. On the other hand, if the pressure exceeds the upper limit, the porous substrate, bonding material layer, and water-repellent layer may be damaged or the voids may collapse, reducing the strength of the gas diffusion layer and the bonding strength between the water-repellent layer and the membrane electrode assembly, and tending to reduce the power generation performance of the fuel cell.

[0090] There are no particular restrictions on the pressurization time of the bonding material coating layer in Method 1 and Method 3, but it is preferably 0.1 to 60 minutes, and more preferably 0.5 to 10 minutes. If the pressurization time falls below the lower limit, the bonding between the membrane electrode assembly and the bonding material layer becomes insufficient, reducing the contact between the conductive particles of the catalyst layer and the conductive particles of the water-repellent layer, increasing electrical resistance, and tending to reduce the power generation performance of the fuel cell. On the other hand, if the pressurization time exceeds the upper limit, the ionomer and electrolyte membrane in the catalyst layer of the membrane electrode assembly are held at high temperatures for a long time, and tending to undergo thermal degradation. [Examples]

[0091] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples. The melt viscosity of the fluoropolymer thermoplastic resin was measured using a constant temperature method with a high-efficiency flow tester (Shimadzu Corporation "CFT-100D") at a test pressure of 5 MPa.

[0092] (Example 1) First, acetylene black (Denka Black Granular Product, manufactured by Denka Co., Ltd., average primary particle size: 35 nm) and ethylene-tetrafluoroethylene (ETFE) powder (EC-6520, manufactured by Daikin Industries, Ltd., melting point: 220°C, melt viscosity (240°C): 1000 Pa·s, average particle size (catalog value): 40 μm) were mixed in a mass ratio of 60 / 40. Then, the mixture was further ground and mixed for 5 minutes at a rotation speed of 20,000 rpm using a portable laboratory grinder (LaboMill 2, manufactured by Osaka Chemical Co., Ltd.) to obtain a composite powder.

[0093] Next, the obtained composite powder was applied to the surface of a porous substrate, carbon paper (Toray Industries, Inc.'s "Torayca Carbon Paper," thickness: 200 μm), using electrostatic screen printing (dry film deposition method) to achieve a basis weight of 2 mg / cm². 2 The film was formed in such a manner. The electrostatic screen printing method used involved an electrostatic screen printing apparatus (Berg Industries Co., Ltd. "T-1") and a screen mesh (Berg Industries Co., Ltd. "Electrostatic Screen"), with a distance of 6 mm between the carbon paper and the screen mesh. A voltage of 1.75 kV was applied between them, and the composite powder was placed on the screen mesh and rubbed with a squeegee to cause the composite powder to fall from the mesh onto the carbon paper, thus forming the film.

[0094] Next, the composite powder layer laminated on the surface of the carbon paper was compacted using a flat plate press at room temperature and a pressure of 3 MPa for 1 minute. The compacted composite powder layer was then heated (fired) in a ceramic fiber electric furnace at atmospheric pressure and 260°C for 30 minutes to form a water-repellent layer for fuel cells on the carbon paper, in which the acetylene black particles are bound together by the ETFE, thereby obtaining a laminate of the carbon paper and the water-repellent layer (gas diffusion layer for fuel cells).

[0095] Next, polyvinylidene fluoride (PVdF) powder (Arkema K.K.'s "Kynar Flex 2501," melting point: 120°C, average particle size: 80 μm) is applied to the surface of the water-repellent layer of the fuel cell gas diffusion layer by electrostatic screen printing (dry film deposition) with a basis weight of 2 mg / cm². 2 The material was coated and film-formed to create a PVdF powder layer (bonding material coating layer). The electrostatic screen printing method used was an electrostatic screen printing apparatus (Berg Industries "T-1") and a screen mesh (Berg Industries "Electrostatic Screen"), with a distance of 6 mm between the water-repellent layer and the screen mesh. A voltage of 1.75 kV was applied between them, and the PVdF powder was placed on the screen mesh and rubbed with a squeegee to cause the PVdF powder to fall from the mesh onto the water-repellent layer, thus forming the film.

[0096] Next, a membrane electrode assembly (electrolyte membrane material: perfluorosulfonic acid membrane, catalyst layer material: Pt-supported carbon and perfluorosulfonic acid resin) was loaded onto the PVdF powder layer, preheated at 130°C for 5 minutes using a flat plate press, and then hot-pressed at a pressure of 3 MPa for 5 minutes to obtain a membrane electrode gas diffusion layer assembly in which the water-repellent layer of the gas diffusion layer and the catalyst layer of the membrane electrode assembly were joined via the PVdF layer (joining material layer).

[0097] (Example 2) PVdF powder, basis weight 1 mg / cm 2A membrane electrode gas diffusion layer assembly was obtained in the same manner as in Example 1, except that the coating was applied in such a manner, in which the water-repellent layer of the gas diffusion layer and the catalyst layer of the membrane electrode assembly were joined via a PVdF layer.

[0098] (Example 3) PVdF powder, basis weight 0.5 mg / cm 2 A membrane electrode gas diffusion layer assembly was obtained in the same manner as in Example 1, except that the coating was applied in such a manner, in which the water-repellent layer of the gas diffusion layer and the catalyst layer of the membrane electrode assembly were joined via a PVdF layer.

[0099] (Example 4) PVdF powder, basis weight 0.1 mg / cm 2 A membrane electrode gas diffusion layer assembly was obtained in the same manner as in Example 1, except that the coating was applied in such a manner, in which the water-repellent layer of the gas diffusion layer and the catalyst layer of the membrane electrode assembly were joined via a PVdF layer.

[0100] (Example 5) Instead of PVdF powder, use Nafion dispersion solution (20% Nafion dispersion solution manufactured by Fujifilm Wako Chemical Co., Ltd.) with a solid content of 3 mg / cm³. 2 A membrane electrode gas diffusion layer assembly was obtained in the same manner as in Example 1, except that the coating was applied in such a manner, in which the water-repellent layer of the gas diffusion layer and the catalyst layer of the membrane electrode assembly were joined via a Nafion layer.

[0101] (Comparative Example 1) The membrane electrode assembly was directly loaded onto the water-repellent layer of the fuel cell gas diffusion layer, which was prepared in the same manner as in Example 1. Using a flat plate press, it was preheated at 130°C for 5 minutes, and then hot-pressed at a pressure of 3 MPa for 5 minutes to obtain a membrane electrode gas diffusion layer assembly in which the water-repellent layer of the gas diffusion layer and the catalyst layer of the membrane electrode assembly were directly bonded.

[0102] <Joining strength> For the membrane electrode gas diffusion layer assemblies obtained in the examples and comparative examples, a 90-degree peel test was performed on the membrane electrode assemblies using an electric measuring stand ("MX2-500N-L-FA" manufactured by Imada Corporation). The peel strength (unit: N / m) was measured and defined as the bonding strength between the gas diffusion layer and the membrane electrode assemblies (bonding strength between the water-repellent layer and the catalyst layer). The results are shown in Figure 3.

[0103] As shown in Figure 3, it was found that the membrane electrode gas diffusion layer assembly in which the water-repellent layer and the catalyst layer were joined via a PVdF layer (Examples 1-4) or a Nafion layer (Example 5) resulted in a higher bonding strength between the water-repellent layer and the catalyst layer compared to the membrane electrode gas diffusion layer assembly in which the water-repellent layer and the catalyst layer were directly joined (Comparative Example 1). It is presumed that the PVdF or Nafion present at the interface between the water-repellent layer and the catalyst layer melts and softens due to hot pressing, then solidifies after pressing and functions as an adhesive, resulting in increased bonding strength. [Industrial applicability]

[0104] As described above, the present invention makes it possible to obtain a water-repellent layer for fuel cells that can be bonded to a catalyst layer with high bonding strength. Therefore, the gas diffusion layer for fuel cells of the present invention is useful as a gas diffusion layer for fuel cells that can be bonded to a membrane electrode assembly with high bonding strength because it is equipped with such a water-repellent layer for fuel cells. Furthermore, the membrane electrode gas diffusion layer assembly of the present invention is useful as a highly durable membrane electrode gas diffusion layer assembly in which the water-repellent layer of the gas diffusion layer and the catalyst layer of the membrane electrode assembly are less likely to peel off because they are equipped with such a gas diffusion layer for fuel cells. [Explanation of symbols]

[0105] 1: Porous base material 2: Water-repellent layer 3a, 3b: Bonding material layer 4: Water-repellent layer for fuel cells 5: Gas diffusion layer for fuel cells 6: Membrane electrode assembly 7a, 7b catalyst layer 8: Electrolyte membrane

Claims

1. A water-repellent layer for fuel cells, characterized in that a bonding material layer containing a fluorine-based thermoplastic resin or a fluorine-based polymer electrolyte is formed on at least one of its surfaces.

2. The water-repellent layer for fuel cells according to claim 1, characterized in that the bonding material layer is a layer containing a fluorine-based thermoplastic resin having a melting point of 100 to 330°C or a fluorine-based polymer electrolyte having a glass transition temperature of 100 to 200°C.

3. The water-repellent layer for fuel cells according to claim 1, characterized in that the bonding material layer is a layer containing polyvinylidene fluoride or perfluorosulfonic acid resin.

4. A gas diffusion layer for a fuel cell, characterized by comprising a porous substrate and a water-repellent layer for a fuel cell according to claim 1, formed on the surface of the porous substrate.

5. The fuel cell gas diffusion layer according to claim 4, characterized in that the bonding material layer is disposed on at least the surface of the fuel cell water-repellent layer opposite to the porous substrate.

6. A fuel cell membrane electrode gas diffusion layer assembly, characterized by comprising a fuel cell gas diffusion layer according to claim 4 or 5, and a membrane electrode assembly formed on the fuel cell water-repellent layer of the fuel cell gas diffusion layer.

7. The fuel cell membrane electrode gas diffusion layer assembly according to claim 6, characterized in that the bonding material layer is disposed at least at the interface between the water-repellent layer for the fuel cell and the catalyst layer of the membrane electrode assembly.

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