Gas diffusion composites for fuel cells and polymer electrolyte fuel cells

Abstract

The present invention provides a gas diffusion composite material for fuel cells that is thin in structure and exhibits reduced electrical resistance, such as contact resistance. [Solution] A porous substrate sheet made of a conductive or non-conductive material, which is a mesh sheet, punching sheet, expanded sheet, or membrane filter sheet with a thickness of 3 μm to 150 μm, and a microporous carbon layer containing particulate and / or fibrous carbon material and a water-repellent resin, (D1) A structure in which a microporous carbon layer covers one side of a porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, so that the microporous carbon layer reaches from one side to the opposite side of the porous substrate sheet. (D2) A structure in which a microporous carbon layer covers both sides of a porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, so that the microporous carbon layer reaches from one side to the opposite side of the porous substrate sheet. (E) A gas diffusion composite material for fuel cells having a structure in which the entire porous substrate sheet is embedded in a microporous carbon layer.

Description

[Technical Field]

[0001] This invention relates to a gas diffusion composite material for fuel cells and a polymer electrolyte fuel cell. [Background technology]

[0002] A polymer electrolyte fuel cell (PEFC) is constructed with a basic unit consisting of a PEFC single cell, which comprises a membrane electrode assembly (MEA) including an electrolyte membrane and electrodes (anode and cathode) stacked on both sides of the electrolyte membrane, and a gas diffusion layer (GDL) stacked on both sides of the membrane electrode assembly, sandwiched between two separators in which gas channels are formed.

[0003] The gas diffusion layer of a PEFC requires high gas diffusivity to diffuse the gas supplied from the separator to the electrode catalyst layer, high drainage to discharge the water generated by the electrochemical reaction to the separator, and high conductivity to extract the generated current. For this reason, a gas diffusion layer made of a carbon sheet made of carbon fibers is widely used as the gas diffusion layer of a PEFC, with a microporous layer (MPL) made of carbon powder and fluororesin formed on its surface. The MPL is a porous composite material made of conductive carbon material and water-repellent fluororesin, where the carbon material creates a conductive network, and the fluororesin acts as an adhesive and exhibits water repellency.

[0004] As described above, the gas diffusion layer (GDL) requires high gas diffusivity to diffuse the gas supplied from the separator into the electrode catalyst layer. Insufficient gas diffusivity leads to a decrease in power generation performance, especially in the high current density range. Furthermore, in PEFCs, integration efficiency improves as the single cell thickness decreases, but the GDL thickness is only about 150 μm to 1 mm, and the GDL accounts for a large proportion of the total thickness of the PEFC single cell. Therefore, if the gas diffusion layer can be made thinner, the PEFC single cell can be made thinner, improving integration efficiency and potentially increasing output. For example, Patent Document 1 reports a fuel cell in which the thickness of the gas diffusion layer is thinner than that of conventional fuel cells. The technology in Patent Document 1 improves gas diffusion in the high current density range and enhances power generation performance by making the thickness of the gas diffusion layer thinner relative to the rib width of the separator.

[0005] Furthermore, the present inventors have reported a porous metal gas diffusion layer made of a porous metal sheet in Patent Document 2. The porous metal sheet used is a metal mesh sheet made of metal Sn or Sn alloy or stainless steel, or a metal fiber sheet made of metal Ti or Ti alloy. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-11735 [Patent Document 2] Japanese Patent Publication No. 2022-145670 [Overview of the project] [Problems that the invention aims to solve]

[0007] The gas diffusion layer described in Patent Document 1 is self-supporting due to the use of special carbon fibers as a constituent material, and the thickness of the gas diffusion layer in that document is limited to approximately 150 μm. Furthermore, while the porous metal gas diffusion layer described in Patent Document 2 can be made to a thickness of about 30 μm and is useful for thinning PEFC single cells, there was room for improvement in terms of electrical resistance originating from the metal gas diffusion layer, such as contact resistance.

[0008] Under these circumstances, the object of the present invention is to provide a gas diffusion composite material for fuel cells that is thin in thickness and has reduced electrical resistance such as contact resistance, and a polymer electrolyte fuel cell equipped therewith. [Means for solving the problem]

[0009] The inventors of this invention have conducted extensive research to solve the above problems and have found that the following invention is suitable for the above purpose, leading to the present invention.

[0010] In other words, the present invention relates to the following invention. <1> It comprises a porous substrate sheet made of a conductive material, and a microporous carbon layer containing particulate and / or fibrous carbon material and a water-repellent resin, The thickness of the porous substrate sheet is 3 μm or more and 150 μm or less. A gas diffusion composite material for fuel cells having one of the following structures (A) to (E). Structure (A): A structure in which the microporous carbon layer covers one side of the porous substrate sheet. Structure (B): A structure in which the microporous carbon layer covers both sides of the porous substrate sheet. Structure (C): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, wherein the microporous carbon layer does not extend from one side to the opposite side of the porous substrate sheet. Structure (D1): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, wherein the microporous carbon layer extends from one side to the opposite side of the porous substrate sheet. Structure (D2): A structure in which the microporous carbon layer covers both sides of the porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, wherein the microporous carbon layer extends from one side to the opposite side of the porous substrate sheet. Structure (E): A structure in which the entire porous substrate sheet is embedded in the microporous carbon layer. <2> The thickness of the porous substrate sheet is 5 μm or more and 100 μm or less. <1> The gas diffusion composite material described above. <3> The overall thickness is between 10 μm and 300 μm. <1> or <2> The gas diffusion composite material described above. <4> The overall thickness is between 20 μm and 120 μm. <1> from <3> A gas diffusion composite material as described in any of the following. <5> The form of the porous substrate sheet is a mesh sheet, a punched sheet, an expanded sheet, or a membrane filter sheet. <1> from <4> A gas diffusion composite material as described in any of the following. <6> The material of the porous substrate sheet is a carbon material. <1> from <5> A gas diffusion composite material as described in any of the following. <7> The porous substrate sheet is a carbon mesh. <1> from <5> A gas diffusion composite material as described in any of the following. <8> It has one of the structures (C) through (E). <5> from <7> A gas diffusion composite material as described in any of the following. <9> The porous substrate sheet is made of a metal material. <1> from <5> A gas diffusion composite material as described in any of the following. <10> The porous substrate sheet is stainless steel mesh. <1> from <5> A gas diffusion composite material as described in any of the following. <11> It has one of the structures (C) through (E). <10> The gas diffusion composite material described above. <12> The particulate and / or fibrous carbon material constituting the microporous carbon layer is carbon black, carbon nanotubes, and mixtures thereof. <1> from <11> A fuel cell gas diffusion composite material as described in any of the following. <13> A membrane electrode assembly comprising a solid polymer electrolyte membrane, a cathode catalyst layer bonded to one side of the solid polymer electrolyte membrane, and an anode catalyst layer bonded to the other side of the solid polymer electrolyte membrane, a pair of gas diffusion layers laminated on the cathode catalyst layer and the anode catalyst layer, and a pair of separators that sandwich the membrane electrode assembly via the gas diffusion layers, wherein at least one of the pair of gas diffusion layers is <1> from <12> A solid polymer fuel cell which is a gas diffusion composite material for fuel cells as described in any of the following.

[0011] <1a> A porous substrate sheet made of a non-conductive material, and a microporous carbon layer containing particulate and / or fibrous carbon material and a water-repellent resin, The thickness of the porous substrate sheet is 3 μm or more and 150 μm or less. The form of the porous base material sheet is a mesh sheet, a punching sheet, an expanded sheet or a membrane filter sheet, A gas diffusion composite material for a fuel cell having any one of the following structures (D1), structure (D2) and structure (E). Structure (D1): A structure in which the microporous carbon layer covers one surface of the porous base material sheet, and a part of the microporous carbon layer penetrates into the porous base material sheet, and the microporous carbon layer reaches from one surface of the porous base material sheet to the opposite surface Structure (D2): A structure in which the microporous carbon layer covers both surfaces of the porous base material sheet, and a part of the microporous carbon layer penetrates into the porous base material sheet, and the microporous carbon layer reaches from one surface of the porous base material sheet to the opposite surface Structure (E): A structure in which the entire porous base material sheet is embedded in the microporous carbon layer <2a> The gas diffusion composite material according to <1a>, wherein the non-conductive material constituting the porous base material sheet is a fluororesin. <3a> The gas diffusion composite material according to <1a> or <2a>, wherein the thickness of the porous base material sheet is 5 μm or more and 100 μm or less. <4a> The gas diffusion composite material according to any one of <1a> to <3a>, having an overall thickness of 10 μm or more and 300 μm or less. <5a> The gas diffusion composite material according to <4a>, having an overall thickness of 20 μm or more and 120 μm or less. <6a> The gas diffusion composite material according to any one of <1a> to <5a>, having the structure of structure (E). <7a> The gas diffusion composite material for a fuel cell according to any one of <1a> to <6a>, wherein the particulate and / or fibrous carbon material constituting the microporous carbon layer is carbon black, carbon nanotubes, and mixtures thereof. <8a>A solid polymer electrolyte membrane, a cathode catalyst layer joined to one side of the solid polymer electrolyte membrane, and an anode catalyst layer joined to the other side of the solid polymer electrolyte membrane, a membrane electrode assembly having the same, a pair of gas diffusion layers laminated on each of the cathode catalyst layer and the anode catalyst layer, and a pair of separators sandwiching the membrane electrode assembly through the gas diffusion layer, wherein at least one of the pair of gas diffusion layers is a gas diffusion composite material for a fuel cell according to any one of <1a> to <7a>, a solid polymer fuel cell.

Effect of the Invention

[0012] According to the present invention, there are provided a gas diffusion composite material for a fuel cell, which is a thin layer and has reduced electrical resistance such as contact resistance, and a solid polymer fuel cell including the same.

Brief Description of the Drawings

[0013] [Figure 1] It is a schematic diagram of the structure of a solid polymer fuel cell. [Figure 2] It is a schematic diagram of a membrane electrode assembly including a conventional gas diffusion layer. [Figure 3A] It is a schematic diagram of the gas diffusion composite material for a fuel cell of the present invention (Structures (A) to (E)). [Figure 3B] It is a schematic diagram of Structures (D1) and (D2) of the gas diffusion composite material for a fuel cell of the present invention. [Figure 3C] It is a schematic diagram of Structures (E1) and (E2) of a gas diffusion composite material for a fuel cell. [Figure 4] It is a microstructural photograph of the surface of the gas diffusion member 1 (stainless steel mesh sheet, SUS316 977 mesh). [Figure 5] It is a microstructural photograph of the surface of the gas diffusion member 2 (MPL-compounded stainless steel mesh). [Figure 6] It is a microstructural photograph of the cross section of the gas diffusion member 2 (MPL-compounded stainless steel mesh). [Figure 7] It is the result of observing the microstructure of the surface of the gas diffusion member 3 (conventional gas diffusion layer with MPL (reference example)). [Figure 8] This shows the microstructure observation results of the cross-section of the gas diffusion member 3 (conventional MPL-equipped gas diffusion layer (reference example)). [Figure 9] This is a photograph of the external appearance of the gas diffusion member 5 (MPL composite carbon mesh). [Figure 10] This shows the IV characteristics of a PEFC single cell using gas diffusion members 1-3. [Figure 11] This shows the IV characteristics of a PEFC single cell using gas diffusion members 4 and 5. [Figure 12] This shows the IV characteristics of a PEFC single cell using the gas diffusion member 6. [Modes for carrying out the invention]

[0014] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples, and can be modified and implemented as such without departing from the spirit of the invention. In this specification, "~" is used to mean an expression that includes the numerical value or physical quantity before and after it.

[0015] 1. Gas diffusion composite material for fuel cells A first aspect of the present invention is a gas diffusion composite material for fuel cells comprising a porous substrate sheet made of a conductive material, and a microporous carbon layer containing particulate and / or fibrous carbon material and a water-repellent resin, wherein the thickness of the porous substrate sheet is 3 μm or more and 150 μm or less, and the form of the porous substrate sheet is a mesh sheet, a punched sheet, an expanded sheet, or a membrane filter sheet, and the structure is one of the following (A) to (E).

[0016] Structure (A): A structure in which the microporous carbon layer covers one side of the porous substrate sheet. Structure (B): A structure in which the microporous carbon layer covers both sides of the porous substrate sheet. Structure (C): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a portion of it penetrates into the interior of the porous substrate sheet. Structure (D1): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, wherein the microporous carbon layer extends from one side to the opposite side of the porous substrate sheet. Structure (D2): A structure in which the microporous carbon layer covers both sides of the porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, wherein the microporous carbon layer extends from one side to the opposite side of the porous substrate sheet. Structure (E): A structure in which the entire porous substrate sheet is embedded in the microporous carbon layer.

[0017] A second aspect of the present invention is a gas diffusion composite material for fuel cells comprising a porous substrate sheet made of a non-conductive material, and a microporous carbon layer containing particulate and / or fibrous carbon material and a water-repellent resin, wherein the thickness of the porous substrate sheet is 3 μm or more and 150 μm or less, and the form of the porous substrate sheet is a mesh sheet, a punched sheet, an expanded sheet, or a membrane filter sheet, and the composite material has any of the following structures (D1), (D2), and (E).

[0018] Structure (D1): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, wherein the microporous carbon layer extends from one side to the opposite side of the porous substrate sheet. Structure (D2): A structure in which the microporous carbon layer covers both sides of the porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, wherein the microporous carbon layer extends from one side to the opposite side of the porous substrate sheet. Structure (E): A structure in which the entire porous substrate sheet is embedded in the microporous carbon layer.

[0019] Details of the above structures (A) to (E) (including structures (D1) and (D2)) will be described later in "1-3. Arrangement of porous substrate sheet and microporous carbon layer".

[0020] Hereinafter, the gas diffusion composite materials for fuel cells according to the first and second embodiments of the present invention will be collectively referred to as "the gas diffusion composite material of the present invention," and when distinguishing between them, they will be described as "the gas diffusion composite material of the present invention (first embodiment)" and "the gas diffusion composite material of the present invention (second embodiment)."

[0021] The gas diffusion composite material of the present invention is suitable as a gas diffusion layer for polymer electrolyte fuel cells.

[0022] The role of the gas diffusion composite material (gas diffusion layer) in polymer electrolyte fuel cells will be explained below with reference to Figures 1 and 2. Figure 1 is a conceptual diagram showing a typical configuration of a polymer electrolyte fuel cell. In a polymer electrolyte fuel cell, hydrogen is supplied to the fuel electrode (anode), and (reaction 1) 2H2 → 4H + +4e - The resulting proton (H + (The electrons) are supplied to the air electrode (cathode) via a solid polymer electrolyte membrane, and the generated electrons are supplied to the air electrode (cathode) via an external circuit (not shown), (reaction 2) O2 + 4H + +4e - →2H2O reacts with oxygen to produce water. This electrochemical reaction between the fuel electrode (anode) and the air electrode (cathode) generates a potential difference between the two electrodes.

[0023] Figure 2 shows a schematic diagram of a conventional membrane electrode assembly equipped with a gas diffusion member. The main functions required of the gas diffusion component in PEFCs include moisturizing the solid polymer electrolyte membrane (approximately 10 μm thick), draining water from the electrode catalyst layer, conducting electrons between the electrode catalyst layer and the separator, and transporting gas. Conventional gas diffusion components widely use a carbon fiber gas diffusion layer (GDL) and a microporous layer (MPL), which has finer pores, deposited on the surface of the carbon fiber gas diffusion layer in contact with the electrode catalyst layer to improve current collection and water retention. Furthermore, in PEFCs with a thickness of approximately 1 mm, two carbon fiber gas diffusion layers, approximately 200 μm thick, are used adjacent to both electrodes. However, this presents challenges such as a decrease in mechanical strength due to the thinning of the layers and high costs.

[0024] On the other hand, the gas diffusion composite material of the present invention has a structure in which a microporous carbon layer containing particulate and / or fibrous carbon material and a water-repellent resin is supported by a porous substrate sheet with excellent mechanical strength and a thickness of 3 μm to 150 μm (for example, a conductive porous substrate sheet made of metal or carbon, or a non-conductive porous substrate sheet made of resin). Having such a structure, the gas diffusion composite material of the present invention has sufficient mechanical strength derived from the porous substrate sheet and conductivity and water repellency derived from the microporous carbon layer, so that the overall thickness of the gas diffusion composite material can be reduced.

[0025] The gas diffusion composite material of the present invention has excellent surface current collection properties and a microporous carbon layer with low contact resistance. Therefore, by arranging the gas diffusion composite material of the present invention, overvoltage is reduced and power generation characteristics (IV characteristics) are improved compared to using only a porous substrate sheet without a microporous layer.

[0026] Solid polymer fuel cells are typically used as fuel cell stacks by stacking a number of single cells, which are their basic configuration, according to the power generation performance. Therefore, by using the gas diffusion composite material of the present invention, which consists of a porous substrate sheet made of a conductive material and a microporous carbon layer containing particulate and / or fibrous carbon material and a water-repellent resin, as a gas diffusion member for fuel cells instead of conventional gas diffusion members (carbon fiber gas diffusion layers with MPL), and by placing it between the electrode catalyst layer and the separator, it is possible to significantly reduce the thickness of the fuel cell stack.

[0027] The gas diffusion composite material of the present invention can be placed on either the cathode side, the anode side, or both.

[0028] The components of the gas diffusion composite material for fuel cells of the present invention will be described below. In the polymer electrolyte fuel cell according to the present invention, the components other than the gas diffusion composite material for fuel cells of the present invention are the same as those of known polymer electrolyte fuel cells, so their explanation will be omitted.

[0029] (1-1. Porous substrate sheet) The porous substrate sheet constituting the gas diffusion composite material of the present invention is a sheet-like member having a plurality of through holes made of a conductive material (first embodiment) or a non-conductive material (second embodiment).

[0030] The form of the porous substrate sheet is not limited as long as it achieves the effects of the present invention, but examples include mesh sheets, punched sheets, expanded sheets, or membrane filter sheets.

[0031] In this specification, "sheet" refers to a thin, flat structure. Furthermore, in this specification, "through hole" means a hole that completely penetrates from one surface to the other surface. Also, in this specification, "connecting hole" means a hole that connects from one surface to the other surface, and does not necessarily have to "completely penetrate from one surface to the other surface"; it may be curved internally or partially connected.

[0032] In this specification, a "mesh sheet" is a sheet-like member formed by weaving fine wires of the constituent material, and the spaces between the woven fine wires become through spaces (through holes) that penetrate the mesh in the thickness direction. The thickness of the mesh sheet, the diameter of the through holes, the pore density, and the size can be appropriately designed within a range that does not impair the purpose of the present invention and maintains strength.

[0033] In this specification, "perforated sheet" refers to a sheet-like member having numerous through-holes, manufactured by punching holes in a sheet (strip) of constituent material using a punching device. The thickness of the perforated sheet, the diameter of the through-holes, the hole density, and the size can be appropriately designed within a range that does not impair the purpose of the present invention and maintains strength.

[0034] In this specification, "expanded sheet" refers to a sheet-like member obtained by cutting and expanding a sheet of constituent material, making the cuts diamond-shaped, tortoise-shell-shaped, or the like. The expanded diamond-shaped or tortoise-shell-shaped portions become through spaces (through holes) that penetrate the expanded sheet in the thickness direction. The diameter and density of the through holes in the expanded sheet can be appropriately designed according to the diameter of the through holes, within a range that does not impair the purpose of the present invention and maintains strength.

[0035] In this specification, "membrane filter sheet" refers to a membrane-like (sheet-like) member having fine interconnected pores. The diameter and density of the interconnected pores in the membrane filter sheet may be appropriately designed within a range that does not impair the objective of the present invention and maintains strength.

[0036] Among the forms of porous substrate sheets, one preferred embodiment is a mesh sheet (including both conductive porous substrate sheets and non-conductive porous substrate sheets). The mesh sheet has a woven structure. Examples of woven structures include plain weave, twill weave, plain tatami weave, and twill tatami weave. Plain weave is a method of weaving in which warp and weft lines are intersected alternately, one at a time. Twill weave is a method of weaving in which warp and weft lines are intersected every few lines. Plain tatami weave is a method of weaving lines in the same way as tatami mats. Twill tatami weave is a method that applies twill weave to plain tatami weave.

[0037] Furthermore, the number of lines (i.e., linear material) per unit area of ​​a mesh sheet tends to increase in the order of "plain weave < twill weave < plain woven < twill woven". The more lines there are per unit area of ​​the mesh sheet, the better the flatness of the mesh sheet's surface. Improved surface flatness of the mesh sheet increases the contact area of ​​the gas diffusion member with other components in the fuel cell (e.g., electrode catalyst layer and separator), and this increased contact area between components contributes to improved electrical connectivity between them.

[0038] In the case of a non-conductive porous substrate sheet, one preferred embodiment is a membrane filter sheet. Membrane filter sheets include those made from various polymer materials such as polypropylene, nylon, polytetrafluoroethylene (PTFE), and cellulose. They may be used alone or combined with other support materials as needed. Membrane filter sheets can be manufactured using any method; for example, by mechanically stretching a crystalline polymer to form fine pores.

[0039] The thickness of the porous substrate sheet is 3 μm to 150 μm, preferably 5 μm to 100 μm, 20 μm to 100 μm, 5 μm to 80 μm, or 20 μm to 80 μm. With such thicknesses, the gas diffusion composite material of the present invention can be given mechanical strength and can maintain self-support even when a microporous carbon layer is provided. The thickness of the porous substrate sheet can be measured, for example, with a micrometer.

[0040] In the gas diffusion composite material of the present invention, the constituent material of the porous substrate sheet should be a material that has sufficient durability under the operating conditions of a PEFC. In this specification, the operating conditions of a PEFC include both the cathode conditions and anode conditions of the PEFC. The cathode conditions of a PEFC refer to the conditions at the cathode during normal operation of the PEFC, meaning a temperature of room temperature to approximately 150°C and the supply of an oxygen-containing gas such as air (oxidizing atmosphere). The anode conditions refer to the conditions at the anode during normal operation of the PEFC, meaning a temperature of room temperature to approximately 150°C and the supply of a hydrogen-containing fuel gas (reducing atmosphere).

[0041] Specifically, metal materials and carbon materials are selected as constituent materials for the conductive porous substrate sheet in the gas diffusion composite material (first embodiment) of the present invention.

[0042] The metal material is not limited as long as it does not impair the purpose of the present invention, but stainless steel, metallic Ti (titanium), or Ti alloys are preferred.

[0043] Even among porous substrate sheets using metal materials, stainless steel mesh (e.g., SUS304, SUS316, SUS316L, SUS340) is preferred. The thickness of the stainless steel mesh, the diameter of the through holes, the pore density, and the size can be appropriately designed within a range that does not impair the objectives of the present invention and maintains strength.

[0044] You can either make the stainless steel mesh yourself or use a commercially available one.

[0045] Furthermore, carbon mesh is preferred as the porous substrate sheet using carbon material. Carbon mesh is a mesh sheet composed of fibrous carbon and having a network structure containing voids. The thickness of the carbon mesh, the diameter of the through holes, the pore density, and the size can be appropriately designed within a range that does not impair the objectives of the present invention and maintains strength.

[0046] You can either make the carbon mesh yourself or use a commercially available one.

[0047] A resin material is selected as the constituent material of the non-conductive porous substrate sheet in the gas diffusion composite material (second embodiment) of the present invention.

[0048] Furthermore, since the non-conductive porous substrate sheet according to the gas diffusion composite material (second embodiment) of the present invention does not possess electronic conductivity itself, it is necessary that the components constituting the microporous carbon layer (MPL components) have a structure that extends continuously from one side to the opposite side of the porous substrate sheet (structures (D1), (D2), and (E) described later). With such a structure, conductivity is derived from the MPL components that extend continuously from one side to the opposite side of the non-conductive porous substrate sheet, and therefore it can be used as a gas diffusion composite material.

[0049] As the resin material, a resin material that is stable under the operating conditions of the PEFC is selected, and a fluororesin with excellent strength and dimensional stability is preferably selected. Examples of fluororesins include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polytetrafluoroethylene-chlorotrifluoroethylene copolymer, polychlorotrifluoroethylene, polybromotrifluoroethylene, polytetrafluoroethylene-bromotrifluoroethylene copolymer, polytetrafluoroethylene-perfluorovinyl ether copolymer, and polytetrafluoroethylene-hexafluoropropylene copolymer.

[0050] In addition to fluoropolymer resins, other heat-resistant resins such as polyphenylene ether (PEE), polysulfone (PSF), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK) can also be used.

[0051] In the gas diffusion composite material (second embodiment) of the present invention, one preferred form of the non-conductive porous substrate sheet is preferably a mesh sheet or a membrane filter sheet.

[0052] The non-conductive porous substrate sheet may have a highly conductive material fixed to its surface, if necessary. Fixing a highly conductive material to the surface of the non-conductive porous substrate sheet may reduce the resistance originating from the porous substrate sheet. The highly conductive material is not limited as long as it does not impair the objectives of the present invention, and specifically, examples include gold (Au), silver (Ag), copper (Cu), titanium (Ti), tin (Sn), tantalum (Ta), tungsten (W), cobalt (Co), or carbon (C).

[0053] In this specification, "adhesion of the highly conductive material" means that the sheet is fixed to the surface of the constituent material to such an extent that the highly conductive material does not easily detach (peel off). The form of the adhering highly conductive material may be a thin film, island, particulate, etc., as long as it does not impair the purpose of the present invention, but a thin film form is preferred. Furthermore, the amount of highly conductive material fixed is determined within a range that does not impair the objectives of the present invention. If the amount of highly conductive material fixed is too small, there is a risk that the conductivity of the porous substrate sheet and the overvoltage improvement effect will be almost negligible.

[0054] Any method can be used to fix the highly conductive material, as long as it does not impair the objective of the present invention.

[0055] (1-2. Microporous carbon layer) In the gas diffusion composite material of the present invention, the microporous carbon layer comprises particulate and / or fibrous carbon material and a water-repellent resin. The microporous carbon layer has smaller pore diameters, higher density, and superior surface flatness than the porous substrate sheet described above. Therefore, it exhibits excellent electronic conductivity and can reduce contact resistance with the electrode catalyst layer or separator.

[0056] The microporous carbon layer is formed by coating a porous substrate sheet with a coating solution containing the constituent components (MPL components) of the microporous carbon layer. However, the formation of the microporous carbon layer depends not only on the MPL components but also on the structure and material of the porous substrate sheet. Since the surface smoothness and the penetration of the coating solution into the mesh sheet vary depending on the weave structure of the mesh sheet, the mesh sheet should be appropriately selected according to the desired structure.

[0057] Particulate and / or fibrous carbon materials are used as the carbon material constituting the microporous carbon layer. By having a microporous carbon layer incorporating these carbon materials, the gas diffusion composite material of the present invention can be given excellent conductivity.

[0058] A wide range of known or commercially available particulate carbon materials can be used. For example, carbon black such as Ketjenblack and acetylene black; graphite; activated carbon, etc., can be used one or more of these. The average particle size of the particulate carbon material is usually about 5 nm to 200 nm, preferably about 20 to 80 nm.

[0059] Furthermore, by replacing a portion of the particulate carbon material with fibrous carbon material, the current collection and gas diffusion properties can be further enhanced.

[0060] A wide range of known or commercially available fibrous carbon materials can be used. For example, one or more types of carbon nanotubes (CNTs) and carbon fibers (CFs) can be used.

[0061] The particulate and / or fibrous carbon material constituting the microporous carbon layer is preferably carbon black, carbon nanotubes, and mixtures thereof.

[0062] Fluorine-based resins can be used as the water-repellent resin constituting the microporous carbon layer. Examples of fluorine-based resins include polytetrafluoroethylene resin (PTFE), copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), copolymer of tetrafluoroethylene and perfluoropropyl vinyl ether (PFA), and copolymer of tetrafluoroethylene and ethylene (ETFE), and these can be used one or more of them.

[0063] The proportions of particulate and / or fibrous carbon material and water-repellent resin constituting the microporous carbon layer are determined within a range that does not impair the objectives of the present invention.

[0064] Furthermore, one of the features of the microporous carbon layer in the gas diffusion composite material of the present invention is that it can be formed using the same material as the MPL in conventionally known MPL-attached gas diffusion layers. That is, by using a porous substrate sheet as a base, it is possible to form a gas diffusion member (a so-called self-supporting microporous layer) that has sufficient strength to maintain self-supporting properties and is thinned to a thickness similar to that of the MPL in an MPL-attached gas diffusion layer (approximately 20 μm), without using special carbon materials.

[0065] The overall thickness of the gas diffusion composite material for fuel cells of the present invention (hereinafter sometimes simply referred to as "overall thickness") is the sum of the thickness of the porous substrate sheet and the microporous carbon layer. The overall thickness can be measured, for example, with a micrometer. The upper limit of the overall thickness depends on the thickness of the porous substrate sheet, but for example, it is 300 μm or less, preferably 200 μm or less, 150 μm or less, 130 μm or less, 120 μm or less, 110 μm or less, 100 μm or less, or 90 μm or less. The lower limit of the overall thickness depends on the thickness of the porous substrate sheet, but is, for example, 10 μm or more, preferably 20 μm or more, 50 μm or more, 70 μm or more, or 90 μm or more. The above upper and lower limits for the overall thickness can be the upper and lower limits for the range of the overall thickness, respectively. For example, the range of overall thickness is 10 μm to 300 μm, 20 μm to 200 μm, 20 μm to 130 μm, 20 μm to 120 μm, 20 μm to 110 μm, 20 μm to 100 μm, 50 μm to 130 μm, 50 μm to 120 μm, and 50 μm to 100 μm.

[0066] (1-3. Arrangement of porous substrate sheet and microporous carbon layer) As described above, the gas diffusion composite material of the present invention (first embodiment, conductive porous substrate sheet) has one of the following structures (A) to (E). Furthermore, the gas diffusion composite material of the present invention (second embodiment, non-conductive porous substrate sheet) has one of the following structures: structure (D1), structure (D2), and structure (E), as described above.

[0067] Structure (A): A structure in which the microporous carbon layer covers one side of the porous substrate sheet. Structure (B): A structure in which the microporous carbon layer covers both sides of the porous substrate sheet. Structure (C): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, wherein the microporous carbon layer does not extend from one side to the opposite side of the porous substrate sheet. Structure (D1): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, wherein the microporous carbon layer extends from one side to the opposite side of the porous substrate sheet. Structure (D2): A structure in which the microporous carbon layer covers both sides of the porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, wherein the microporous carbon layer extends from one side to the opposite side of the porous substrate sheet. Structure (E): A structure in which the entire porous substrate sheet is embedded in the microporous carbon layer.

[0068] Figure 3A shows schematic diagrams of structures (A) to (E) of the gas diffusion composite material of the present invention. Figure 3B shows schematic diagrams of structures (D1) and (D2) related to structure (D) of the gas diffusion composite material. Figure 3C shows schematic diagrams of structures (E1) and (E2) related to structure (E) of the gas diffusion composite material.

[0069] In the first embodiment of the present invention, when the gas diffusion composite material has a structure (A) in which a microporous carbon layer, as shown in Figure 3A(A), covers one side of a porous substrate sheet, the microporous carbon layer is usually positioned to be in contact with the electrode catalyst layer, thereby reducing the contact resistance between the electrode catalyst layer and the gas diffusion composite material. In the case of structure (A), the microporous carbon layer may also be positioned on the separator side, in which case the contact resistance between the separator and the gas diffusion composite material is reduced.

[0070] In the first embodiment of the present invention, if the gas diffusion composite material has a structure (B) in which a microporous carbon layer, as shown in Figure 3A(B), covers both sides of the porous substrate sheet, the microporous carbon layer is arranged to be in contact with both the electrode catalyst layer side and the separator side, thereby reducing the contact resistance between the electrode catalyst layer and the gas diffusion composite material, and the contact resistance between the separator and the gas diffusion composite material.

[0071] In the first embodiment of the present invention, if the gas diffusion composite material has a structure (C) in which a microporous carbon layer, as shown in Figure 3A(C), covers one side of the porous substrate sheet and a portion of it penetrates into the interior of the porous substrate sheet, then, similar to the case of structure (A), the microporous carbon layer is usually positioned to be in contact with the electrode catalyst layer, thereby reducing the contact resistance between the electrode catalyst layer and the gas diffusion composite material. In the case of structure (C), the microporous carbon layer may also be positioned on the separator side, in which case the contact resistance between the separator and the gas diffusion composite material is reduced.

[0072] Furthermore, as shown in Figure 3A(D) and Figure 3B(D1), in the case of a structure in which a microporous carbon layer covers one side of a porous substrate sheet and a portion of it penetrates into the interior of the porous substrate sheet, and in the case of a structure (D1) in which the microporous carbon layer extends from one side to the opposite side of the porous substrate sheet, the components constituting the microporous carbon layer (MPL components) exhibit excellent conductivity, thereby reducing the electrical resistance in the thickness direction of the gas diffusion composite material.

[0073] Furthermore, as shown in (D2) of Figure 3B, if the structure (D2) is such that the microporous carbon layer covers both sides of the porous substrate sheet and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, and the microporous carbon layer extends from one side to the opposite side of the porous substrate sheet, then the microporous carbon layer is positioned to contact both the electrode catalyst layer side and the separator side, thereby reducing the contact resistance between the electrode catalyst layer and the gas diffusion composite, and between the separator and the gas diffusion composite.

[0074] Furthermore, in the case of the gas diffusion composite material of the present invention having a structure (E) (structure (E1), (E2)) in which the entire porous substrate sheet is embedded in the microporous carbon layer shown in Figure 3A (E) and Figure 3C, the microporous carbon layer is arranged to be in contact with both the electrode catalyst layer side and the separator side, thereby reducing the contact resistance between the electrode catalyst layer and the gas diffusion composite material, and the contact resistance between the separator and the gas diffusion composite material. In addition, since the components constituting the microporous carbon layer (MPL components) exhibit excellent conductivity, the electrical resistance in the thickness direction of the gas diffusion composite material can be reduced.

[0075] Structure (E) involves embedding the entire porous substrate sheet in a microporous carbon layer, and because the components constituting the microporous carbon layer (MPL components) exhibit excellent conductivity, the electrical resistance in the thickness direction of the gas diffusion composite material can be reduced. Therefore, structure (E) is particularly suitable when using a non-conductive porous substrate sheet as the porous substrate sheet.

[0076] The structure shown in Figure 3C (E1) can be formed by coating the MPL component constituting the microporous carbon layer onto one side of a porous substrate sheet and allowing the MPL component to penetrate the entire interior of the porous substrate sheet. Furthermore, the structure shown in Figure 3C (E2) can be formed by coating the MPL components constituting the microporous carbon layer onto both sides of a porous substrate sheet and allowing the MPL components to penetrate the entire interior of the porous substrate sheet.

[0077] In structure (E), the choice between a single-sided coating structure (E1) and a double-sided coating structure (E2) should be made appropriately, taking into consideration the material and shape of the porous substrate sheet used, so that the MPL component penetrates throughout the entire interior of the porous substrate sheet and the thickness of the gas diffusion composite material is within the desired range. For example, if the porous substrate sheet is a mesh sheet, the penetration of the coating liquid into the mesh sheet will change depending on the material, weave structure, and mesh diameter of the mesh sheet. Therefore, as shown in structure (E), the weave structure, pore diameter, etc. of the mesh sheet should be appropriately selected so that the MPL components penetrate sufficiently into the porous substrate sheet. Furthermore, for example, if the porous substrate sheet is a membrane filter sheet, changing the material, manufacturing conditions, etc., of the membrane filter sheet will change the pore size and density of the connecting holes in the membrane filter sheet, and thus change the permeability of the coating liquid into the membrane filter sheet. Therefore, as shown in structure (E), the material, manufacturing conditions, etc., of the membrane filter sheet should be appropriately selected so that the MPL components penetrate sufficiently into the porous substrate sheet.

[0078] Furthermore, the thickness of the non-conductive porous substrate sheet suitable for the gas diffusion composite material of the present invention (second embodiment) is 3 μm or more and 150 μm or less, preferably 5 μm or more and 100 μm or less, 20 μm or more and 100 μm or less, 5 μm or more and 80 μm or less, and 20 μm or more and 80 μm or less. Furthermore, the upper limit of the overall thickness of the gas diffusion composite material (second embodiment) of the present invention depends on the thickness of the non-conductive porous substrate sheet, but is, for example, 300 μm or less, preferably 200 μm or less, 150 μm or less, 130 μm or less, 120 μm or less, 110 μm or less, 100 μm or less, and 90 μm or less. The lower limit of the overall thickness depends on the thickness of the non-conductive porous substrate sheet, but is, for example, 10 μm or more, preferably 20 μm or more, 50 μm or more, 70 μm or more, or 90 μm or more. The above upper and lower limits for the overall thickness can be the upper and lower limits for the range of the overall thickness, respectively. For example, the range of overall thickness is 10 μm to 300 μm, 20 μm to 200 μm, 20 μm to 130 μm, 20 μm to 120 μm, 20 μm to 110 μm, 20 μm to 100 μm, 50 μm to 130 μm, 50 μm to 120 μm, and 50 μm to 100 μm. If the thickness of the non-conductive porous substrate sheet and the overall thickness are within the above range, mechanical strength can be imparted to the gas diffusion composite material of the present invention, and self-supporting properties can be maintained even when a microporous carbon layer is provided. The thickness of the porous substrate sheet made of non-conductive material and the overall thickness can be measured, for example, with a micrometer.

[0079] 2. Components other than polymer electrolyte fuel cells and gas diffusion composites The polymer electrolyte fuel cell of the present invention uses the above-described fuel cell gas diffusion composite material (self-supporting microporous layer) as at least one of the gas diffusion composite materials arranged on the cathode side and the anode side.

[0080] In the present invention, as a gas diffusion composite material for fuel cells, if a microporous carbon layer is present on one side of a porous substrate sheet (structure (A), structure (C), and structure (D1)), the gas diffusion composite material for fuel cells may be arranged such that one side with the microporous carbon layer is in contact with the cathode catalyst layer and / or the anode catalyst layer, and the other side without the microporous carbon layer is in contact with the separator, or it may be arranged so that one side with the microporous carbon layer is in contact with the separator, and the other side without the microporous carbon layer is in contact with the cathode catalyst layer and / or the anode catalyst layer.

[0081] Furthermore, in the case of the gas diffusion composite material for fuel cells of the present invention having microporous carbon layers on both sides of a porous substrate sheet (structure (B), structure (D2), and structure (E) (particularly structure (E2))), the gas diffusion composite material for fuel cells should be arranged such that one side with the microporous carbon layer is in contact with the cathode catalyst layer and / or the anode catalyst layer, and the other side with the microporous carbon layer is in contact with the separator. When arranged in this manner, the side with the microporous carbon layer comes into contact with both the electrode catalyst layer (cathode catalyst layer, anode catalyst layer) and the separator side, resulting in lower contact resistance compared to using a fuel cell gas diffusion composite with a microporous carbon layer fixed to one side. In particular, in the gas diffusion composite material of the present invention using a non-conductive porous substrate sheet (second embodiment), since the porous substrate sheet itself is not conductive, it is preferable that it be structure (E) (especially structure (E2)).

[0082] The following describes the components of the polymer electrolyte fuel cell of the present invention other than the gas diffusion composite material of the present invention. However, since these components are the same as those of known polymer electrolyte fuel cells, they will be described briefly.

[0083] The membrane electrode assembly (MEA) constituting the polymer electrolyte fuel cell of the present invention comprises a polymer electrolyte membrane, a cathode catalyst layer bonded to one side of the polymer electrolyte membrane, and an anode catalyst layer bonded to the other side of the polymer electrolyte membrane.

[0084] Since conventionally known electrode catalyst layers (for example, electrode catalyst layers consisting of a carbon-based support bearing noble metal nanoparticles, an oxide support bearing noble metal nanoparticles, etc.) can be used for the anode catalyst layer and cathode catalyst layer, a detailed explanation will be omitted.

[0085] As the solid polymer electrolyte membrane, any known electrolyte membrane for PEFCs that has proton conductivity and possesses chemical and thermal stability may be used. Examples of electrolyte materials constituting the solid polymer electrolyte membrane include fluorine-based electrolyte materials and hydrocarbon-based electrolyte materials. Electrolyte membranes formed from fluorine-based electrolyte materials are particularly preferred due to their excellent heat resistance and chemical stability.

[0086] As the separator, known separators can be used, such as metal separators and carbon separators.

[0087] The polymer electrolyte fuel cell (single cell) of the present invention is used by forming a fuel cell stack with a number of cells corresponding to the power generation performance, and assembling other associated devices such as a gas supply device and a cooling device.

[0088] While embodiments of the present invention have been described above, the embodiments disclosed herein are illustrative and not restrictive in all respects. In particular, matters not explicitly disclosed in the embodiments disclosed herein, such as the operating conditions of the fuel cell, various parameters, dimensions, weight, and volume of components, do not deviate from what is normally practiced by those skilled in the art, and values ​​that can be easily anticipated by those skilled in the art may be adopted. [Examples]

[0089] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these. In the following examples, gas diffusion composite members (MPL composite porous substrate sheets), porous substrate sheets (not MPL composited), and conventional gas diffusion layers (MPL-coated carbon fiber gas diffusion layers) will be collectively referred to as "gas diffusion members."

[0090] <1. Gas diffusion member> The following gas diffusion members 1 to 6 were used. The thickness of the gas diffusion members was measured five times using a micrometer (Mitutoyo Corporation, Coolant Proof Micrometer MDC-25MX), and the average was used to calculate the thickness.

[0091] Gas diffusion member 1: Stainless steel mesh (porous base sheet) Niraco Co., Ltd. used stainless steel SUS316 / wire mesh (977mesh). This stainless steel mesh sheet is composed of a single layer of twill weave mesh, with a wire diameter of φ13μm and a thickness of 28μm. Figure 4 shows a surface photograph of the gas diffusion member 1 (stainless steel mesh).

[0092] Gas diffusion member 2: MPL composite stainless steel mesh (MPL composite porous base sheet) The MPL composite stainless steel mesh, which is the gas diffusion member 2, was obtained by following the procedure below. A dispersion for MPL formation was obtained by adding 241 mg of high-graphitization carbon black (GCB, Cabot, FCX200), 576 μL of carbon nanotube dispersion (Meijo Nanocarbon Co., Ltd., MWNT INK) (30 mg CNT weight), and 22.5 μL of water-repellent resin (DAIKIN, Polyflon PTFE D-210C) (30 mg PTFE weight) to a mixed solvent of 300 μL (300 mg) of pure water and 1500 μL (1695 mg) of polyethylene glycol (PEG), and mixing until homogeneous. The obtained MPL-forming dispersion was screen printed onto a stainless steel mesh (gas diffusion member 1) using a screen (screen thickness: 30 μm) (single-sided coating). A simple screen printing machine (Print Gocco PG-11, manufactured by RISO KAGAKU CORPORATION) was used for screen printing, and the stainless steel mesh (gas diffusion member 1) was cut slightly larger than the holes in the screen to obtain gas diffusion member 2 (MPL composite stainless steel mesh). The thickness of gas diffusion member 2 was 62 μm.

[0093] Gas diffusion member 3: Carbon fiber gas diffusion layer with MPL (conventional gas diffusion layer) As the gas diffusion member 3, a commercially available MPL-coated gas diffusion layer 22BB (manufactured by SGL Carbon, Germany, with a unit area mass of 70 gm²) made of carbon paper with MPL formed on its surface is used. -2 ) was used. The thickness of the gas diffusion member 3 was 206 μm.

[0094] Gas diffusion member 4: Carbon mesh (porous base sheet) As the gas diffusion member 4, a carbon mesh (bias weave) manufactured by CosmoTec was used. The thickness of the gas diffusion member 4 was 45 μm.

[0095] Gas diffusion member 5: MPL composite carbon mesh (MPL composite porous substrate sheet) The MPL composite carbon mesh, which is the gas diffusion member 5, was obtained by following the procedure below. A dispersion for MPL formation was obtained by adding 241 mg of GCB, a carbon nanotube dispersion (30 mg CNT weight), and 22.5 μL of water-repellent resin (30 mg PTFE weight) to a mixed solvent of 300 μL (300 mg) of pure water and 1500 μL (1695 mg) of PEG, and mixing until homogeneous. The obtained MPL-forming dispersion was screen printed onto a carbon mesh (gas diffusion member 4) using a screen (screen thickness: 30 μm) (single-sided coating). A simple screen printing machine (Print Gocco PG-11, manufactured by Riso Kagaku Corporation) was used for screen printing, and the carbon mesh (gas diffusion member 4) was cut slightly larger than the holes in the screen to obtain a gas diffusion member 5 (MPL composite carbon mesh). The thickness of the gas diffusion member 5 was 87 μm.

[0096] Gas diffusion member 6: MPL composite carbon mesh (MPL composite porous substrate sheet) In the manufacturing method of the gas diffusion member 5 described above, gas diffusion member 6 (MPL composite carbon mesh) was obtained using the same method except that 1400 μL (1400 mg) of pure water, 750 μL (847.5 mg) of PEG, 120.4 mg of GCB, 15 mg of CNT, and 7.12 mg of PTFE were used. The thickness of gas diffusion member 6 was 87 μm.

[0097] <2. Evaluation> 2-1. Observation of the ultrastructure Figure 5 shows a surface SEM image of gas diffusion member 2 (MPL composite stainless steel mesh), and Figure 6 shows a cross-sectional SEM image. For reference, Figure 7 shows a surface SEM image of gas diffusion member 3 (conventional MPL-attached gas diffusion layer), and Figure 8 shows a cross-sectional SEM image. As shown in Figure 5, the gas diffusion member 2 (MPL composite stainless steel mesh) had MPL uniformly supported across its entire surface, similar to the gas diffusion member 3 (conventional MPL-attached gas diffusion layer) shown in Figure 7. The cracks observed on the surface of the gas diffusion member 2 were determined to be due to the drying and hardening of the surface material during heat treatment. Furthermore, as shown in Figure 6, no separation of components occurred in the cross-section of gas diffusion member 2, and it was similar to the cross-section of gas diffusion member 3 shown in Figure 8. Furthermore, MPL components were detected not only on the surface but also on the back side of gas diffusion member 2. Based on the above, it was determined that the gas diffusion member 2 has a structure (D1) (see Figure 3B) in which the MPL component penetrates into the mesh and the MPL component is continuously connected from the surface to the back.

[0098] Figure 9 shows a photograph of the external appearance of the gas diffusion member 5 (MPL composite carbon mesh). As shown in Figure 9, the carbon mesh substrate could not be seen from the surface, confirming that the MPL was evenly held on the surface. Furthermore, although some of the MPL components penetrated into the carbon mesh, they did not reach the back surface, so the structure was determined to be (C) (see Figure 3A). Similarly, with respect to the gas diffusion member 6 (MPL-composite carbon mesh), it was confirmed that MPL was evenly retained on the surface, and although some of the MPL components penetrated into the carbon mesh, they did not reach the back surface. Therefore, it was determined to be structure (C) (see Figure 3A).

[0099] 2-2. Electrochemical evaluation (single cell, initial performance evaluation) A PEFC (single cell) with the following configuration was fabricated, and power generation experiments (IV measurement) were conducted. (solid electrolyte membrane) Nafion film (manufactured by DuPont, Nafion 212, 51 μm thick) (anode) • Electrode catalyst layer: Pt / C catalyst (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) • Gas diffusion layer: Carbon fiber gas diffusion layer (carbon paper) (Cathode) • Electrode catalyst layer: Pt / C catalyst (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) • Gas diffusion layer: Gas diffusion members 1-5

[0100] A single-cell power generation evaluation jig incorporating gas diffusion members 1-5 was placed in a constant temperature chamber set to 80°C, and power generation tests were conducted under the following conditions. A fuel cell evaluation device (Toyo Technica Co., Ltd., model number: PE-8900K) and a potentiometer / galvanostat (Solatron Co., Ltd., model number: SI1287) were used. (Anode condition) Electrode area: 1cm 2 Supply gas type: 100% H2 Gas supply rate: 139 mL / min Supply gas humidification temperature: 80℃ (relative humidity: 100%) (Cathode condition) Electrode area: 1cm 2 Supply gas type: Air Gas supply rate: 332 mL / min Supply gas humidification temperature: 80℃ (relative humidity: 100%)

[0101] (Stainless steel mesh) Figure 10 shows the evaluation results of the current-voltage (IV) characteristics of a PEFC (single cell) using gas diffusion members 1 and 2. For reference, data for a single cell using gas diffusion member 3 (conventional MPL-equipped gas diffusion layer) is also shown.

[0102] As shown in Figure 10, both PEFCs using gas diffusion members 1 and 2 were capable of generating electricity. However, the PEFC using gas diffusion member 2, which incorporates MPL, showed a significant improvement in IV characteristics compared to gas diffusion member 1 without MPL. Gas diffusion member 2 exhibited performance comparable to commercially available gas diffusion member 3 (conventional gas diffusion layer with MPL). Furthermore, gas diffusion member 2 showed performance comparable to gas diffusion member 3 in terms of activation overpotential and resistive overpotential (not shown). From the above, it was confirmed that combining stainless steel mesh with MPL improves power generation performance (IV characteristics).

[0103] (Carbon mesh) Figure 11 shows the evaluation results of the IV characteristics of a PEFC (single cell) using gas diffusion members 4 and 5. As shown in Figure 11, both PEFCs using gas diffusion members 4 and 5 are capable of generating electricity, and the PEFC using gas diffusion member 5, which incorporates MPL, showed improved IV characteristics compared to gas diffusion member 4, which does not have MPL.

[0104] Figure 12 shows the evaluation results of the IV characteristics of a PEFC (single cell) using the gas diffusion member 6. As shown in Figure 12, the PEFC using the gas diffusion member 6 showed improved IV characteristics compared to the gas diffusion member 4 without MPL, and demonstrated performance comparable to the commercially available gas diffusion member 3 (conventional gas diffusion layer with MPL).

[0105] From the above, it was confirmed that combining carbon mesh with MPL improves power generation performance (IV characteristics).

[0106] 2-3. Evaluation of Electrical Resistance and Electrical Resistivity A 1-cm square various gas diffusion member was sandwiched between two pieces of carbon paper (EC-TPI-060T, ElectroChem Inc., Raynhan MA, USA) of the same shape, and was sandwiched in a fixture for full cell evaluation to measure and evaluate the electrical resistivity. First, the electrical resistance of the various gas diffusion members was measured by electrochemical impedance (EIS) measurement using an electrochemical property evaluation apparatus, and the electrical resistivity was calculated based on the thickness of the gas diffusion member. Humidification and temperature increase inside the apparatus were not performed, and all measurements were carried out at room temperature and normal pressure.

[0107] Table 1 shows the measurement results of the electrical resistance of each gas diffusion member (1×1 cm (1 cm 2 )), the thickness of each gas diffusion member, and the electrical resistivity calculated from the electrical resistance and thickness. In addition, carbon paper (EC-TPI-060T, ElectroChem Inc., Raynhan MA, USA) that is widely used as a gas diffusion layer is also shown as a reference example in Table 1.

[0108]

Table 1

[0109] From the comparison between Gas Diffusion Member 1 and Gas Diffusion Member 2 where the porous base material sheet is a stainless steel mesh, it can be seen that the electrical resistivity is reduced to about 1 / 10 by the composite with MPL. As described above, in Gas Diffusion Member 2, the MPL component infiltrated to the back surface, so it is considered that the conductivity was improved by the MPL component. Similarly, it was confirmed that the electrical resistivity is reduced by the composite with MPL in Gas Diffusion Member 4 and Gas Diffusion Member 5 where the porous base material sheet is a carbon mesh.

Industrial Applicability

[0110] The present invention is promising as a component of a solid polymer fuel cell used in the automotive, electric power, gas, and home appliance industries such as passenger cars and commercial vehicles.

Claims

1. It comprises a porous substrate sheet made of a conductive or non-conductive material, and a microporous carbon layer containing particulate and / or fibrous carbon material and a water-repellent resin, The thickness of the porous substrate sheet is 3 μm or more and 150 μm or less. The form of the porous substrate sheet is a mesh sheet, a punched sheet, an expanded sheet, or a membrane filter sheet. A gas diffusion composite material for fuel cells having one of the following structures (D1), (D2), or (E). Structure (D1): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, wherein the microporous carbon layer extends from one side to the opposite side of the porous substrate sheet. Structure (D2): A structure in which the microporous carbon layer covers both sides of the porous substrate sheet, and a portion of the microporous carbon layer penetrates into the interior of the porous substrate sheet, wherein the microporous carbon layer extends from one side to the opposite side of the porous substrate sheet. Structure (E): A structure in which the entire porous substrate sheet is embedded in the microporous carbon layer.

2. The gas diffusion composite material according to claim 1, wherein the porous substrate sheet is composed of a non-conductive material.

3. The gas diffusion composite material according to claim 2, wherein the nonconductive material constituting the porous substrate sheet is a fluororesin.

4. The gas diffusion composite material according to claim 1, wherein the thickness of the porous substrate sheet is 5 μm or more and 100 μm or less.

5. The gas diffusion composite material according to claim 1, wherein the overall thickness is 10 μm or more and 300 μm or less.

6. The gas diffusion composite material according to claim 5, wherein the overall thickness is 20 μm or more and 120 μm or less.

7. A gas diffusion composite material according to claim 1, having the structure of structure (E).

8. The gas diffusion composite material for fuel cells according to claim 1, wherein the particulate and / or fibrous carbon material constituting the microporous carbon layer is carbon black, carbon nanotubes, and mixtures thereof.

9. A polymer electrolyte fuel cell comprising: a membrane electrode assembly having a solid polymer electrolyte membrane; a cathode catalyst layer bonded to one side of the solid polymer electrolyte membrane; and an anode catalyst layer bonded to the other side of the solid polymer electrolyte membrane; a pair of gas diffusion layers laminated on the cathode catalyst layer and the anode catalyst layer, respectively; and a pair of separators that sandwich the membrane electrode assembly via the gas diffusion layers, wherein at least one of the pair of gas diffusion layers is a gas diffusion composite material for fuel cells according to any one of claims 1 to 8.

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