Gas diffusion layer

Abstract

Provided is a gas diffusion layer for use in a fuel cell, which has excellent gas diffusibility, electrical conductivity, and current collection properties, and can be designed and manufactured so as to systematically ensure drainage properties. [Solution] A gas diffusion layer for a fuel cell, the gas diffusion layer being made of a non-carbon material, having a plurality of openings penetrating the gas diffusion layer, and having a plurality of drainage slots on one side of the gas diffusion layer extending in one direction parallel to the surface.

Description

[Technical Field]

[0001] The present invention relates to a gas diffusion layer used in a fuel cell. [Background technology]

[0002] A polymer electrolyte fuel cell (PEFC) is a fuel cell that uses a polymer membrane as an electrolyte, and is capable of generating energy with high efficiency while also having a low environmental impact. For this reason, polymer electrolyte fuel cells are being used in a variety of applications, such as as a power source (energy source) for automobiles. At the same time, in order to further popularize polymer electrolyte fuel cells as automobile fuel cells, there is a demand for improved performance of the components that make up the fuel cell and, therefore, for increased output from the fuel cell.

[0003] In a typical configuration of such a polymer electrolyte fuel cell, in order to efficiently react a fuel gas (anode gas) and an oxidizing gas (cathode gas), a gas diffusion layer (GDL) that guides the fuel gas or oxidizing gas supplied from the gas flow path of the separator is placed adjacent to a catalyst layer that supports a catalyst such as platinum and where the electrochemical reaction takes place. Such a gas diffusion layer is used to improve the diffusibility of the reactant gas (fuel gas or oxidizing gas). Specifically, such a gas diffusion layer serves to diffuse (gas diffusibility, gas permeability) the fuel gas or oxidizing gas supplied from the gas flow path of the separator to the adjacent catalyst layer.

[0004] The gas diffusion layer is also required to have a conductive function and a current collecting function for efficiently transferring electrons necessary for the electrochemical reaction.

[0005] Gas diffusion layers include those based on carbon (see, for example, Patent Document 2), those based on metal (see, for example, Patent Document 3), and those based on a composite material of carbon and metal (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-5571 [Patent Document 2] Patent Publication No. 2021-141072 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-257928 Summary of the Invention [Problem to be solved by the invention]

[0007] Woven fabrics, nonwoven fabrics, felt-like materials, and carbon paper have been developed as carbon-based gas diffusion layers. However, carbon-based gas diffusion layers have problems such as low strength and susceptibility to breakage due to impacts. In addition, carbon substrates absorb moisture and expand, which can reduce gas permeability and power generation performance. In order to suppress moisture absorption, a microporous layer using a water-repellent polymer has been provided on the carbon substrate. However, such a microporous layer reduces the conductivity and current collection of the gas diffusion layer.

[0008] On the other hand, as a gas diffusion layer based on a metal, various materials have been developed, including net-like members, mesh-like members, expanded members, felt-like members, foam metal members, and sintered metal members. Metal-based gas diffusion layers tend to have high strength and excellent electrical conductivity and current collection properties. However, while metal-based gas diffusion layers are less susceptible to moisture absorption, mesh-like members have very low internal electrical conductivity, requiring measures such as the deposition of an expensive metal film on the surface. Furthermore, with porous metals, including foam metals, it is difficult to uniformly control the diameter of the micropores and ensure the intended continuity of the micropores, making it difficult to reliably ensure gas permeability.

[0009] In addition to the above, to improve the power generation performance and ensure stable power generation in fuel cells, it is important to quickly discharge excess reaction product water and condensed water generated by the electrochemical reaction of hydrogen and oxygen in the catalyst layer. Therefore, the gas diffusion layer, which also serves as a water passageway, must be able to prevent the phenomenon of water clogging its micropores (i.e., flooding). In other words, the gas diffusion layer must have drainage properties (water repellency, moisture permeability, and moisture diffusibility). However, it has been difficult to fabricate conventional gas diffusion layers in a way that systematically and intentionally ensures drainage from the design stage.

[0010] Therefore, an object of the present invention is to provide a gas diffusion layer for use in fuel cells such as polymer electrolyte fuel cells, which has excellent electrical conductivity and current collection properties, and can be designed and manufactured to systematically ensure gas diffusion properties and drainage properties. [Means for solving the problem]

[0011] That is, the gist of the present invention for solving the above problems is as follows.

[0012] [1] A gas diffusion layer for a fuel cell, The gas diffusion layer is It is made of non-carbon materials, a plurality of openings extending through the gas diffusion layer; a plurality of drainage slots extending in one direction parallel to one surface of the gas diffusion layer; A gas diffusion layer characterized by: Such a gas diffusion layer has excellent electrical conductivity and current collection properties, and can be designed and manufactured so as to systematically ensure gas diffusion and drainage properties.

[0013] [2] The gas diffusion layer according to [1], having a thickness of 200 μm or less. Such gas diffusion layers use non-carbon materials, and can be designed with desired openings and drainage slots in mind, even at the design stage. They are also configured to perform current collection and distribution functions, making it possible to make the layers even thinner.

[0014] [3] The gas diffusion layer is composed of a plate-shaped base portion having a plurality of openings and finger portions disposed on one surface of the base portion, The gas diffusion layer according to [1] or [2], wherein the finger portion has a plurality of spaced portions extending in a direction parallel to the surface of the gas diffusion layer, and the plurality of spaced portions form the drainage slots. In a fuel cell, such a gas diffusion layer allows the base portion to contact the electrode and the finger portion to contact the catalyst layer, thereby further improving conductivity and current collection (or distribution). Furthermore, the configuration of the openings and drainage slots in the gas diffusion layer is one that can be easily formed systematically and intentionally from the design stage.

[0015] [4] The base portion includes a plurality of lines extending in a first direction X of the surface direction of the gas diffusion layer, The gas diffusion layer according to [3], wherein the finger portions are composed of a plurality of main lines provided continuously in the first direction X and a plurality of sub-lines provided intermittently. Such a gas diffusion layer allows openings and drainage slots to be formed in a planned and intentional manner, and also allows for improved electrical conductivity and current collection (or distribution) properties.

[0016] [5] The width of each line constituting the base portion is 20 μm or more and 100 μm or less, The gas diffusion layer according to [4], wherein the width of the main lines and sub-lines constituting the finger portions is 5 μm or more and 60 μm or less. Such a gas diffusion layer ensures sufficient strength while increasing the opening ratio on the catalyst layer side of the gas diffusion layer, thereby further improving gas diffusibility.

[0017] [6] The base portion has an opening ratio of 50% or more in a plan view, The gas diffusion layer according to any one of [3] to [5], wherein the finger portions have an opening ratio of 80% or more in a plan view. Such a gas diffusion layer can further improve gas diffusibility.

[0018] [7] The gas diffusion layer according to any one of [1] to [6], wherein the width of the drainage slot is 10 μm or more and 500 μm or less. Such a gas diffusion layer can effectively discharge water vapor generated in the catalyst layer during power generation in the fuel cell, thereby providing sufficiently good drainage properties. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a gas diffusion layer for use in fuel cells such as polymer electrolyte fuel cells, which has excellent electrical conductivity and current collection properties and can be designed and manufactured so as to systematically ensure gas diffusion properties and drainage properties. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic cross-sectional view of a single cell constituting a polymer electrolyte fuel cell to which the gas diffusion layer of the present invention can be applied. [Figure 2] FIG. 2 is a schematic perspective view of a gas diffusion layer according to one embodiment of the present invention. [Figure 3A] 3 is a cross-sectional view of the gas diffusion layer of FIG. 2 taken along the line 3-3. [Figure 3B] 4 is a cross-sectional view of the gas diffusion layer of FIG. 2 taken along line 4-4. [Figure 4] FIG. 3 is a diagram showing the gas inflow direction and the water discharge direction when the gas diffusion layer of FIG. 2 is incorporated into a fuel cell. [Figure 5] FIG. 10 is a schematic perspective view of a gas diffusion layer according to another embodiment of the present invention, showing the gas inflow direction and the water discharge direction when the gas diffusion layer is incorporated into a fuel cell. [Figure 6A]FIG. 4 is a schematic plan view of a gas diffusion layer according to another embodiment of the present invention. [Figure 6B] FIG. 4 is a schematic plan view of a gas diffusion layer according to another embodiment of the present invention. [Figure 6C] FIG. 4 is a schematic plan view of a gas diffusion layer according to another embodiment of the present invention. [Figure 7] FIG. 1 is a diagram showing the results of impedance measurements in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present invention (gas diffusion layer) will be described with reference to the drawings. Note that components indicated by the same reference numerals in each drawing are the same or similar components. Furthermore, duplicated descriptions and reference numerals may be omitted in the embodiments described below. Furthermore, all drawings used in the following description are schematic, and the dimensional relationships, ratios, etc. of the elements shown in the drawings do not necessarily match those of reality. Furthermore, the dimensional relationships, ratios, etc. of the elements do not necessarily match between multiple drawings.

[0022] In the present specification, in the numerical ranges described in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present specification, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.

[0023] (fuel cell) First, a fuel cell to which the gas diffusion layer of the present invention can be applied will be described. FIG. 1 is a schematic cross-sectional view of a unit cell constituting a fuel cell to which the gas diffusion layer of the present invention can be applied. In FIG. 1, the fuel cell 1 is a solid polymer fuel cell. FIG. 1 shows one of the cells constituting the fuel cell, i.e., a unit cell (hereinafter, a unit cell may also be referred to as a "fuel cell"). In a solid polymer fuel cell, multiple unit cells are electrically connected in series. In the fuel cell 1 of FIG. 1, a membrane-electrode-gas diffusion layer assembly 5 (MEGA: Membrane-Electrode-Gas Diffusion Layer Assembly) is composed of a polymer electrolyte membrane 2 (ion-conductive solid polymer electrolyte membrane), catalyst layers 3A and 3B, gas diffusion layers 10 (10A and 10B), a cathode (+) electrode 4A, and an anode (-) electrode 4B.

[0024] The polymer electrolyte membrane 2 selectively allows specific ions to pass through. The catalyst layers 3A and 3B are provided on both sides of the polymer electrolyte membrane 2 and are made of a conductive material such as carbon carrying a catalyst such as platinum, and an ion exchange resin. The gas diffusion layers 10A and 10B are disposed on the outside of the catalyst layers 3A and 3B and constitute the electrodes of the single cell. The cathode (+) electrode 4A and the anode (-) electrode 4B are disposed on the outside of the gas diffusion layers 10A and 10B. The cathode (+) electrode 4A is electrically connected to the catalyst layer 3A. The anode (-) electrode 4B is electrically connected to the catalyst layer 3B.

[0025] Separators 6A and 6B are disposed on the outer sides of the gas diffusion layers 10A and 10B. That is, the membrane / electrode assembly 5 is sandwiched between the separators 6A and 6B. Gas flow channels 6A1, 6A2, 6B1, and 6B2 are formed in the separators 6A and 6B to supply fuel gas (anode gas) or oxidizing gas (cathode gas) and to discharge product gas and excess gas. The peripheries of the catalyst layers 3A and 3B and the gas diffusion layers 10A and 10B are sealed with gaskets 7A and 7B.

[0026] Gas diffusion layers 10A and 10B constitute electrodes of a single cell and diffuse reactant gases (fuel gas or oxidizing gas) (indicated by arrows in FIG. 1) supplied from gas flow channels 6A1 and 6B1 of separators 6A and 6B to adjacent catalyst layers 3A and 3B. Gas diffusion layers 10A and 10B are disposed between separators 6A and 6B and catalyst layers 3A and 3B.

[0027] Oxidizing gas (oxygen) is introduced from the gas flow path 6A1 of the separator 6A into the space 6A3 of the cathode (+) electrode 4A and reaches the gas diffusion layer 10A. Excess reaction product water and condensed water produced by the electrochemical reaction between the fuel gas (hydrogen) and the oxidizing gas (oxygen) during power generation, as well as unreacted oxidizing gas, are discharged from the space 6A3 through the gas flow path 6A2 of the separator 6A (arrows in FIG. 1).

[0028] Fuel gas (hydrogen) is introduced from the gas flow path 6B1 of the separator 6B into the space 6B3 of the anode (-) side electrode 4B, passes through the gas diffusion layer 10B, and reaches the catalyst layer 3B. Unreacted fuel gas is discharged from the space 6B3 through the gas flow path 6B2 of the separator 6B (arrow in FIG. 1).

[0029] By stacking a plurality of such unit cells (fuel cell 1), the power generation capacity of the polymer electrolyte fuel cell can be further improved.

[0030] In the fuel cell 1, the gas diffusion layer of the present invention can be applied as the gas diffusion layers 10A and 10B.

[0031] (gas diffusion layer) The gas diffusion layer of the present invention is a gas diffusion layer used in fuel cells, including polymer electrolyte fuel cells. The gas diffusion layer of the present invention is characterized by being made of a non-carbon material, having a plurality of openings penetrating the gas diffusion layer, and having a plurality of drainage slots on one side of the gas diffusion layer, the drainage slots extending in a direction parallel to the surface. Thus, the gas diffusion layer of the present invention has a predetermined 3D structure.

[0032] The gas diffusion layer has a plurality of openings penetrating the gas diffusion layer, allowing gas to pass through the plurality of openings. Furthermore, since the gas diffusion layer is made of a non-carbon material, there is no risk of deterioration in gas permeability due to moisture absorption and expansion, as occurs with carbon substrates. Therefore, the gas diffusion layer can stably exhibit high gas diffusivity due to the stable shape of the plurality of openings.

[0033] Furthermore, carbon materials generally tend to have high electrical resistivity, whereas the gas diffusion layer is made of a non-carbon material and therefore has excellent electrical conductivity and current collection properties.

[0034] Furthermore, one surface of the gas diffusion layer is formed with a plurality of drainage slots extending in one direction parallel to the surface. These drainage slots can prevent the openings of the gas diffusion layer from becoming clogged with water (i.e., flooding). In other words, the gas diffusion layer has excellent drainage properties. Furthermore, the configuration of the openings and drainage slots, while still providing excellent electrical conductivity and current collection, can be planned and intentionally formed from the design stage. Therefore, in this respect as well, the gas diffusion layer of the present invention is superior to conventional gas diffusion layers.

[0035] As described above, the gas diffusion layer of the present invention has excellent electrical conductivity and current collection properties, and can be designed and produced so as to systematically ensure gas diffusion properties and drainage properties.

[0036] When the gas diffusion layer of the present invention is applied to a fuel cell 1 as shown in FIG. 1, it is important to assemble the layer so that the surface on which the drainage slots are formed faces the catalyst layers 3A and 3B, and the surface on which the drainage slots are not formed faces the separators 6A and 6B (electrodes 4A and 4B).

[0037] The gas diffusion layer of the present invention, which includes a predetermined number of drainage slots, can be produced by controlling the 3D configuration. Specifically, when the gas diffusion layer of the present invention is produced using a metal, it can be produced by a manufacturing method using a known metal processing technique (e.g., laser processing, etching, plating, electroforming, etc.). Therefore, the gas diffusion layer of the present invention can be customized three-dimensionally (3D) to match the specifications of various types of catalysts, separators, bipolar plates, etc., or stack output.

[0038] Furthermore, the gas diffusion layer of the present invention can be produced with reduced production energy, production costs, and / or CO2 emissions. Furthermore, since the gas diffusion layer of the present invention can be produced using a production process that utilizes renewable energy (e.g., laser processing, plating, electroforming, etc.), the gas diffusion layer 10 of the present invention can be a zero-emission material.

[0039] Next, a gas diffusion layer according to one embodiment of the present invention (hereinafter, sometimes referred to as "the gas diffusion layer of this embodiment") will be specifically described with reference to the drawings. However, the gas diffusion layer of the present invention is not limited to the gas diffusion layer of this embodiment.

[0040] FIG. 2 is a schematic perspective view of a gas diffusion layer according to this embodiment. In FIG. 2, the gas diffusion layer 10 is composed of a plate-shaped base portion 16 having a plurality of openings and finger portions 14 disposed on one surface of the base portion 16. The "base portion" can also be referred to as a "busbar portion." The plurality of openings in the base portion 16 correspond to the openings 12 in the gas diffusion layer 10. The base portion 16 typically functions to collect and distribute current on the electrode side (separator side), while the finger portions 14 typically function to collect and distribute current on the catalyst layer side. Because the gas diffusion layer 10 is thus composed of the base portion 16 and the finger portions 14, the base portion 16 can contact the electrodes 4A and 4B, and the finger portions 14 can contact the catalyst layers 3A and 3B in the fuel cell 1, thereby further improving electrical conductivity and current collection (or distribution).

[0041] In FIG. 2, the plurality of openings in the base portion 16 (the plurality of openings 12 in the gas diffusion layer 10) have a quadrangular shape in a planar view. Specifically, the base portion 16 has a plurality of lines 16X extending in a first direction X among the surface directions of the gas diffusion layer 10. The base portion 16 also has a plurality of lines 16B other than the lines 16X (in FIG. 2, a plurality of lines extending in a second direction Y intersecting with the first direction X among the surface directions). That is, in FIG. 2, the lines 16X and the lines 16B intersect. The plurality of lines 16X and the plurality of lines 16B are aligned to form a grid, and thus a matrix of a plurality of openings each having a quadrangular shape in a planar view is formed in the base portion 16.

[0042] The angle between the first direction X and the second direction Y is typically orthogonal (90°) or approximately orthogonal, but does not have to be orthogonal. For example, the angle (acute angle side) between the first direction X and the second direction Y may be 70° or more and 90° or less.

[0043] 2, the finger portions 14 are arranged on the side of the base portion 16 in the direction Z, which is perpendicular to a plane including the first direction X and the second direction Y. More specifically, the finger portions 14 are arranged with a plurality of main lines 14X extending continuously in the first direction X and a plurality of sub-lines 14B intersect with each other in the second direction Y. In the gas diffusion layer 10 of FIG. 2, the main lines 14X and the sub-lines 14B basically intersect with each other. Furthermore, the sub-lines 14B adjacent to each other in the second direction Y are spaced apart from each other in the second direction Y (see also FIG. 3A, which is a cross-sectional view taken along the arrow 3-3 in FIG. 2). As a result, in the finger portions 14, a plurality of spaces formed by the spaces between adjacent sub-lines 14B are arranged in the first direction X, and these spaces form drainage slots 14S extending in the first direction X. The drainage slots 14S can have the function of discharging water vapor and the like generated from the catalyst layer. However, the drainage slots 14S can contribute not only to the discharge of water vapor and the like but also to the diffusion of gas in the first direction X. The drainage slots 14S are also referred to as flow paths.

[0044] 3A, dotted lines are shown, but these dotted lines are imaginary, and the base portion 16 and the finger portions 14 are integrally configured.

[0045] Fig. 3B is a cross-sectional view taken along the line 4-4 in Fig. 2. In the view of Fig. 3B, the line 16X constituting the base portion 16 and the main line 14X of the finger portion 14 arranged thereon are adjacent to each other in the second direction Y, with the opening 12 in between.

[0046] 4 is a diagram showing the gas inflow direction and water discharge direction when the gas diffusion layer of FIG. 2 is incorporated into a fuel cell 1. Referring to FIG. 4, in a fuel cell incorporating a gas diffusion layer, a catalyst layer 3A is located on the side of the gas diffusion layer 10 (10A) on which the drainage slots 14S are formed (upper side in FIG. 4), and an electrode 4A is located on the side of the gas diffusion layer 10 (10A) on which the drainage slots 14S are not formed (lower side in FIG. 4). The same applies to the gas diffusion layer 10 (10B).

[0047] FIG. 5 is a schematic perspective view of a gas diffusion layer, and like FIG. 4, it also shows the gas inflow direction and water discharge direction when the gas diffusion layer is incorporated into a fuel cell 1. Note that, for ease of explanation, FIG. 5 partially shows the base portion 16 and finger portions 14. With reference to FIG. 5, in a fuel cell incorporating a gas diffusion layer, the catalyst layer 3A is located on the side of the gas diffusion layer 10 (10A) on which the drainage slots 14S are formed (the lower side in FIG. 5), and the electrode 4A is located on the side of the gas diffusion layer 10 (10A) on which the drainage slots 14S are not formed (the upper side in FIG. 5). The same applies to the gas diffusion layer 10 (10B).

[0048] When the fuel cell 1 generates electricity, an oxidizing gas is supplied to the gas diffusion layer 10 (10A). The oxidizing gas passes through the openings 12 in the gas diffusion layer 10 (10A) in the direction of the arrow IN (see FIGS. 4 and 5), is diffused, and reaches the catalyst layer 3A. This allows the gas diffusion layer 10 to exhibit excellent gas diffusibility.

[0049] Furthermore, when power is generated in the fuel cell 1, an electrochemical reaction between the fuel gas and the oxidizing gas generates current and water. The excess water vapor, reaction product water, and / or condensed water are discharged in the direction of the arrow OUT (see FIGS. 4 and 5) through the drainage slots 14S in the gas diffusion layer 10. This prevents the openings of the gas diffusion layer from becoming clogged with water (i.e., flooding), thereby preventing performance degradation.

[0050] 6A, 6B, and 6C (hereinafter collectively referred to as FIG. 6) are each a schematic plan view of a gas diffusion layer 10 according to another embodiment of the present invention. The gas diffusion layer 10 in FIG. 6 is composed of a plate-shaped base portion 16 having a plurality of openings 12 and finger portions 14 arranged on one surface of the base portion 16.

[0051] 6, the base portion 16 has a plurality of lines extending in a first direction X among the surface directions of the gas diffusion layer 10. In the gas diffusion layer 10 of FIG. 6, the finger portion 14 is composed of a plurality of main lines 14X provided continuously in the first direction X and a plurality of sub-lines 14B provided intermittently. In the gas diffusion layer 10 of FIG. 6, the finger portion 14 has a plurality of spaced portions extending in one direction parallel to the surface of the gas diffusion layer 10 (i.e., the first direction X), and the plurality of spaced portions form the drainage slots 14S.

[0052] 6, oxidizing gas supplied during power generation passes through the plurality of openings 12. In addition, in the gas diffusion layer 10 of FIG. 6, excess water vapor, reaction product water, and / or condensed water are discharged in the direction of the arrow through the drainage slots 14S.

[0053] As shown in Figures 2 and 6, the finger portions 14 are preferably arranged only at positions on one surface of the base portion 16 that overlap the lines (16X, 16B) that constitute the base portion 16 in a planar view. In other words, the finger portions 14 are preferably arranged at positions on one surface of the base portion 16 that do not overlap the openings of the base portion 16 in a planar view. Furthermore, the center line of the line 16X that constitutes the base portion 16 and the center line of the main line 14X that constitutes the finger portions 14 preferably coincide or substantially coincide in a planar view. Similarly, the center line of the line 16B that constitutes the base portion 16 and the center line of the sub-line 14B that constitutes the finger portions 14 preferably coincide or substantially coincide in a planar view.

[0054] In the gas diffusion layer 10 as shown in FIGS. 2 and 6, the width of each line (16X, 16B) constituting the base portion 16 is preferably 20 μm or more and 100 μm or less.

[0055] In the gas diffusion layer 10 shown in FIGS. 2 and 6, the height (also referred to as thickness) of each line (16X, 16B) constituting the base portion 16 is preferably 10 μm or more and 100 μm or less.

[0056] In each line (16X, 16B) constituting the base portion 16 in the gas diffusion layer 10 as shown in FIGS. 2 and 6, the ratio of height to width (height / width) is preferably 0.1 or more and 0.5 or less.

[0057] In the gas diffusion layer 10 shown in Figures 2 and 6, the width (W) of each line (main line 14X and sub-line 14B) constituting the finger portion 14 is preferably 5 µm or more and 60 µm or less. If the width (W) is 5 µm or more and 60 µm or less, the strength of the gas diffusion layer 10 is sufficiently ensured, while the opening ratio on the catalyst layer side of the gas diffusion layer 10 is further increased, thereby further improving gas diffusibility. From the same viewpoint, the width (W) of each line constituting the finger portion 14 is more preferably 10 µm or more, more preferably 40 µm or less, and even more preferably 30 µm or less.

[0058] In the gas diffusion layer 10 shown in FIGS. 2 and 6, the height (H) of each line (main line 14X and sub-line 14B) constituting the finger portion 14 is, for example, 10 μm or more and 100 μm or less. Furthermore, it is more preferable that the height (H) of each line constituting the finger portion 14 is 50 μm or less.

[0059] In each line (main line 14X and sub-line 14B) constituting the finger portion 14 in the gas diffusion layer 10 as shown in FIGS. 2 and 6, the ratio of height to width (height / width) is preferably 0.5 or more and 1.5 or less.

[0060] 2 and 6, in the gas diffusion layer 10 composed of the base portion 16 and the finger portions 14, the base portion 16 preferably has an opening ratio (the ratio of the open area per unit area, or the ratio of the area per unit area where no non-carbon material is present; the same applies hereinafter) of 50% or more in a plan view. In this case, gas diffusibility can be further improved.

[0061] 2 and 6, in the gas diffusion layer 10 composed of the base portion 16 and the finger portions 14, the finger portions 14 preferably have an opening ratio of 80% or more in a plan view, which can further improve gas diffusibility.

[0062] When applying the gas diffusion layer 10 shown in FIGS. 2 and 6 to the fuel cell 1 shown in FIG. 1, it is essential that the surface on which the finger portions 14 are arranged faces the catalyst layers 3A and 3B, and the surface on which the finger portions 14 are not arranged faces the separators 6A and 6B (electrodes 4A and 4B).

[0063] In the gas diffusion layer 10 as shown in FIGS. 2 and 6, the other surface of the base portion 16 (the surface on which the finger portions 14 are not arranged) can constitute the outermost surface of the gas diffusion layer 10.

[0064] As shown in FIGS. 4, 5, and 6, the direction in which the drainage slots 14S in the gas diffusion layer 10 extend is preferably the first direction X.

[0065] As shown in FIGS. 4, 5, and 6A, the drainage slots 14S in the gas diffusion layer 10 are preferably formed so as to cross the opening 12 in a plan view.

[0066] Next, specific or preferred embodiments of the gas diffusion layer of the present invention other than those described above will be described.

[0067] As described above, the gas diffusion layer of the present invention is made of a non-carbon material. Preferably, the non-carbon material is a highly conductive material, particularly one with higher conductivity (electrical resistivity (0°C)) than carbon materials. The use of a highly conductive material can further improve conductivity and current collection. Examples of highly conductive materials include metals, including, but not limited to, metals such as Ni, Cu, Ru, and Au, and alloys such as Au-Ag and Ni-Pd. In addition to the above metals, metals that can be formed into films using known metal processing techniques (e.g., laser processing, etching, plating, electroforming, etc.) may also be used. Using a metal as the non-carbon material can improve the stability of the shape of the openings because it is not affected by moisture. Furthermore, metals can be recovered and reused, reducing the environmental impact of manufacturing the gas diffusion layer. Polymers (highly conductive polymers) can also be used as highly conductive materials.

[0068] The electrical resistivity (0°C) [Ω·m] of major materials is as follows: Carbon (graphite): 1375.0 x 10 -6 Ni: 6.84 × 10 -8 Cu: 6.2.3 x 10 -8 Au: 2.35 × 10 -8 The performance of the gas diffusion layer affects the electron transfer rate, electrical resistance, etc. As can be seen from the above, highly conductive materials such as metals have much better properties than carbon materials, and can therefore effectively contribute to improving the conductivity as well as the current collection and distribution properties.

[0069] Furthermore, the above-mentioned highly conductive materials have the advantage that they are hardly affected by poisoning from hydrogen peroxide, hydrates, radicals, carbon monoxide, etc., compared to carbon materials.

[0070] The gas diffusion layer of the present invention is preferably integrally constructed. In other words, the gas diffusion layer of the present invention is preferably not constructed by assembling each component (for example, the base portion 16 and the finger portion 14 in FIG. 2 ) that is produced separately. The integral construction of the gas diffusion layer of the present invention can further improve the strength, particularly compared to gas diffusion layers based on carbon.

[0071] For example, the gas diffusion layer of the present invention may be composed of an integral metal crystal.

[0072] The planar shape of the plurality of openings in the gas diffusion layer of the present invention is not limited to a rectangle, and may be, for example, a perfect circle, an ellipse, a polygon, or the like.

[0073] The thickness of the gas diffusion layer of the present invention (represented by T in FIG. 2, also referred to as the maximum thickness) is preferably 200 μm or less. Conventional gas diffusion layers, particularly those based on carbon, have limitations on how thin they can be. However, the gas diffusion layer of the present invention uses a non-carbon material, allows for the planned and intentional formation of desired openings and drainage slots from the design stage, and has a configuration that enables current collection and distribution functions, allowing for even thinner layers. The thickness of the gas diffusion layer of the present invention can be 180 μm or less, 150 μm or less, 120 μm or less, 100 μm or less, 80 μm or less, or 60 μm or less. On the other hand, the thickness of the gas diffusion layer of the present invention is preferably 15 μm or more, and more preferably 30 μm or more, from the viewpoint of ensuring sufficient strength. The gas diffusion layer of the present invention can generate output equivalent to or greater than that of a carbon-based gas diffusion layer (such as carbon paper) while being less than half the thickness. Therefore, the gas diffusion layer of the present invention makes it possible to reduce the size of the fuel cell stack while maintaining the output.

[0074] The gas diffusion layer of the present invention preferably has an opening ratio of 50% or more in a plan view, which can further improve gas diffusibility.

[0075] In the gas diffusion layer of the present invention, the width of the drainage slot (in FIGS. 4 and 6A, the width of the gap formed by the sub-lines 14B spaced apart in the second direction Y; in FIGS. 6B and 6C, the width of the gap formed by the main line 14X and the sub-line 14B spaced apart in the second direction Y) is preferably 10 μm or more and 500 μm or less. In this case, water vapor generated in the catalyst layer during power generation in the fuel cell can be effectively discharged, and sufficiently good drainage can be achieved.

[0076] The gas diffusion layer of the present invention preferably has a contact surface smoothness of 300 nm or less when laminated on another member (e.g., catalyst layer, electrode, etc.). In this case, it is possible to increase the contact area with the contact object compared to gas diffusion layers based on carbon (carbon paper, carbon cloth, etc.). From the same viewpoint, the smoothness of the gas diffusion layer of the present invention is more preferably 60 nm or less. The smoothness can be measured in accordance with JIS B 0601.

[0077] The above describes one example of an embodiment of the present invention, but the embodiment of the present invention is not limited to the above, and it goes without saying that various modifications can be made without departing from the spirit of the present invention. [Example]

[0078] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to the following examples and can be modified as appropriate within the scope of the present invention.

[0079] Example 1 (Preparation of gas diffusion layer) A gas diffusion layer 10 having the configuration shown in FIG. 2 was fabricated using Ni (nickel) using a known metal processing technique. The fabricated gas diffusion layer had drainage slots, which were intentionally formed from the design stage. The details of the fabricated gas diffusion layer are as follows. The electrical conductivity, surface resistivity, and volume resistivity of the gas diffusion layer were measured, and the results are shown in Table 1. Thickness: 40μm Width of each line (16X, 16B) that constitutes the base portion 16: 60 μm Height of each line (16X, 16B) that constitutes the base part 16: 20 μm Width of each line (main line 14X and sub-line 14B) constituting the finger portion 14: 20 μm Height of each line (main line 14X and sub-line 14B) constituting the finger portion 14: 20 μm ·Smoothness of the contact surface with the adjacent layer: 60nm or less Drainage slot width: 60μm ·Opening ratio: 75% or more Aperture shape: Square with sides of 150 μm

[0080] Catalyst synthesis Pt40% activated carbon Vulvan Catalyst ink synthesis (ethanol ionomer catalyst) Ink application (spray coating) MEA (Membrane Electrode Assembly) manufacturing (hot press bonding) Physical properties of each material: conductivity, resistivity Performance evaluation Electric output Fuel cell Mouvik experimental single cell fuel cell Power generation area: 25cm 2

[0081] (Catalyst synthesis) Aqueous nitric acid solution was added to activated carbon (VULCAN, "CV-XC72R") and stirred for 30 minutes to disperse and wet the activated carbon. Aqueous chloroplatinic acid solution was then added and stirred for 30 minutes. Ethanol was then added as a reducing agent and stirred for 15 minutes, followed by heating and stirring at 90°C for 3 hours to precipitate Pt particles onto the activated carbon. The mixture was then filtered and washed. The filtrate and washings were collected separately, and the Pt concentration in the filtrate was measured by ICP measurement to confirm that Pt was successfully supported. The resulting Pt catalyst was then heated and vacuum dried at 80°C for 15 hours using a vacuum dryer. The Pt content in the catalyst was 40%.

[0082] (Production of MEA (electrolyte membrane + catalyst layer)) The Pt catalyst (Pt 40%) obtained above, ethanol, and a 10% Nafion aqueous solution were mixed in a weight ratio of 1:6:4 and stirred using an ultrasonic disperser to obtain a catalyst ink. The catalyst ink was spray-coated onto the center of a 10 cm square electrolyte membrane (Nafion N212) with an area of ​​5 cm × 5 cm and a catalyst amount of 0.5 mg Pt / cm. 2 The coating was applied to both sides of the electrolyte membrane. After drying indoors, the membrane was pressed at 80°C and 1.8N / 25cm using a hot press. 2 The pressure bonding was performed for 2 minutes, thereby producing a membrane electrode assembly (MEA).

[0083] (Fuel cell construction) The MEA fabricated as described above was sandwiched between the gas diffusion layers described above and set in a single-cell experimental fuel cell manufactured by Maubic. This single-cell fuel cell had the configuration shown in Figure 1. Next, air was introduced at 0.5 L / min through gas flow path 6A1 in Figure 1 using an air pump. Furthermore, hydrogen humidified by bubbling with pure water was introduced at 0.5 L / min through gas flow path 6B1 in Figure 1. The electrical output at this time was measured using a HIOKI digital multimeter "DT4253." The results are shown in Tables 1 and 2. Impedance was also measured. The results are shown in Figure 7.

[0084] <Comparative Example 1> A single-cell fuel cell was produced in the same manner as in Example 1, except that a carbon paper ("TGP-H-060" manufactured by Toray Industries, Inc., which had been treated with a 5% water-repellent coating (manufactured by Maubic Co., Ltd., thickness: 190 μm) was used as the gas diffusion layer. The electrical conductivity, surface resistivity, and volume resistivity of the gas diffusion layer were measured, and the results are shown in Table 1. Then, the electrical output was measured in the same manner as in Example 1. The results are shown in Table 2. The impedance was also measured. The results are shown in FIG. 7.

[0085] <Comparative Example 2> A single-cell fuel cell was fabricated in the same manner as in Example 1, except that a carbon cloth (Carbon Cloth CC4 Plain, manufactured by Fuel Cell Earth, thickness: 500 μm) was used as the gas diffusion layer. The electrical conductivity, surface resistivity, and volume resistivity of the gas diffusion layer were measured, and the results are shown in Table 1. The carbon cloth used in Comparative Example 2 was too thick and therefore not very advantageous as a gas diffusion layer.

[0086] [Table 1]

[0087] [Table 2]

[0088] As can be seen from Table 1, the gas diffusion layer of Example 1 had higher electrical conductivity and lower surface resistivity and volume resistivity than the gas diffusion layers of Comparative Examples 1 and 2. Furthermore, as can be seen from Fig. 7, the fuel cell using the gas diffusion layer of Example 1 had lower internal resistance than the fuel cell using the gas diffusion layer of Comparative Example 1. This shows that the gas diffusion layer of Example 1 is excellent in electrical conductivity and therefore in current collection.

[0089] Furthermore, Table 2 shows that the fuel cell using the gas diffusion layer of Example 1 had improved current and voltage values ​​compared to the fuel cell using the gas diffusion layer of Comparative Example 1. Therefore, it is clear that the fuel cell using the gas diffusion layer of Example 1 has superior performance.

[0090] Furthermore, the gas diffusion layer of Example 1 was able to form multiple openings using a non-carbon material, and was able to form drainage slots as planned from the design stage. Therefore, it can be determined that the gas diffusion layer of Example 1 has sufficiently excellent gas diffusion properties and drainage properties. [Explanation of symbols]

[0091] 1 Fuel cell (single cell) 2 Polymer electrolyte membrane 3A,3B Catalyst layer 4A cathode (+) electrode 4B Anode (-) electrode 5 Membrane / electrode assembly 6A, 6B separator 7A, 7B gaskets 6A1, 6A2, 6B1, 6B2 Gas flow path 6A3,6B3 Space 10, 10A, 10B Gas diffusion layer 12 Opening 14 Finger section 14X Main line that makes up the finger section 14B Sub-lines that make up the finger section 14S Drainage slot 16 Base 16X, 16B Base line H Finger height T is the thickness of the gas diffusion layer W: Width of the line that makes up the finger

Claims

1. A gas diffusion layer for a fuel cell, comprising: The gas diffusion layer is It is made of metal material, a plurality of openings extending through the gas diffusion layer; a plurality of drainage slots extending in a first direction X parallel to one surface of the gas diffusion layer; the gas diffusion layer is composed of a plate-shaped base portion having a plurality of openings and finger portions disposed on one surface of the base portion; the base portion includes a plurality of lines extending in a first direction X among the surface directions of the gas diffusion layer, the finger portion is composed of a plurality of main lines continuously provided in the first direction X and a plurality of sub-lines intermittently provided in the first direction X so as to form a plurality of spaced portions, The plurality of spaced apart portions constitute the drainage slot. A gas diffusion layer characterized by:

2. The gas diffusion layer according to claim 1 , having a thickness of 200 μm or less.

3. The width of each line constituting the base portion is 20 μm or more and 100 μm or less, The gas diffusion layer according to claim 1 , wherein the width of the main lines and sub-lines constituting the finger portions is 5 μm or more and 60 μm or less.

4. the base portion has an opening ratio of 50% or more in a plan view, The gas diffusion layer according to claim 1 , wherein the finger portions have an opening ratio of 80% or more in a plan view.

5. The gas diffusion layer according to claim 1 , wherein the drainage slots have a width of 10 μm or more and 500 μm or less.

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