Gas diffusion composite material for fuel cells and polymer electrolyte fuel cells

Abstract

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 polymer electrolyte fuel cell including the same are provided. The present invention has a porous substrate sheet made of a conductive material and a microporous carbon layer containing a particulate and / or fibrous carbon material and a water-repellent resin, A gas diffusion composite material for a fuel cell having any 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 part of the layer penetrates into the porous substrate sheet. Structure (D): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a part of the microporous carbon layer penetrates into the porous substrate sheet, and the microporous carbon layer reaches from one side of the porous substrate sheet to the opposite side. Structure (E): A structure in which the porous substrate sheet is entirely embedded in the microporous carbon layer.

Description

[Technical field]

[0001] (Citation of Related Application) This application claims the benefit and priority of a Japanese patent application (Patent Application No. 2023-42109) filed on March 16, 2023. Priority to the aforementioned patent application is expressly claimed, and the entire disclosure of that application is incorporated herein by reference for all purposes. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] The present invention relates to a gas diffusion composite material for a fuel cell and a polymer electrolyte fuel cell. [Background technology]

[0003] A polymer electrolyte fuel cell (PEFC) is constructed as a basic unit in which a PEFC unit cell, which is made up of a membrane electrode assembly (MEA) including an electrolyte membrane and electrodes (anode and cathode) laminated on both sides of the electrolyte membrane, and gas diffusion layers (GDLs) laminated on both sides of the membrane electrode assembly, is sandwiched between two separators with gas flow paths formed therein.

[0004] The gas diffusion layer of a PEFC needs to have 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, the gas diffusion layer of a PEFC is widely used in which a microporous layer (MPL) made of carbon powder and fluororesin is formed on the surface of a carbon sheet made of carbon fiber as a substrate layer. The MPL is a layer made of a porous composite material of a conductive carbon material and a water-repellent fluororesin, where the carbon material creates a conductive network and the fluororesin acts as an adhesive and also exhibits water repellency.

[0005] As described above, the GDL is required to have high gas diffusivity to diffuse the gas supplied from the separator to the electrode catalyst layer, and insufficient gas diffusivity reduces the power generation performance, especially in the high current density region. In addition, in a PEFC, the thinner the unit cell, the better the integration, but the thickness of the GDL is about 150 μm to 1 mm, and the proportion of the GDL in the total thickness of the PEFC unit cell is large. Therefore, if the gas diffusion layer can be made thinner, the PEFC unit cell can be made thinner, which improves integration and is expected to improve output. For example, Patent Document 1 reports a fuel cell with a thinner gas diffusion layer than conventional ones. The technology of Patent Document 1 improves gas diffusivity 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.

[0006] The present inventors have also 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, a Sn alloy, or stainless steel, or a metal fiber sheet made of metal Ti or a Ti alloy. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2022-11735 [Patent Document 2] JP 2022-145670 A Summary of the Invention [Problem to be solved by the invention]

[0008] The gas diffusion layer in Patent Document 1 is self-supporting due to the use of special carbon fibers as a constituent material, and the gas diffusion layer in this document can be thinned to a thickness of approximately 150 μm. In addition, the porous metal gas diffusion layer of Patent Document 2 can be made thicker than about 30 μm, which is useful for thinning the PEFC single cell. However, there is room for improvement in terms of electrical resistance, such as contact resistance, derived from the metal gas diffusion layer.

[0009] Under these circumstances, an object of the present invention is to provide 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 polymer electrolyte fuel cell including the same. [Means for solving the problem]

[0010] As a result of intensive research aimed at solving the above problems, the present inventors discovered that the following invention meets the above object, and thus completed the present invention.

[0011] That is, the present invention relates to the following inventions. <1> The present invention has a porous substrate sheet made of a conductive material, and a microporous carbon layer containing a 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 a fuel cell, having any 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): The microporous carbon layer covers one side of the porous substrate sheet, and a part of the microporous carbon layer penetrates into the porous substrate sheet. Structure (D): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a part of the microporous carbon layer penetrates into the porous substrate sheet, and the microporous carbon layer reaches 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 according to claim 1. <3> The overall thickness is between 3μm and 150μm. <1> or <2> The gas diffusion composite material according to claim 1. <4> The overall thickness is between 20μm and 100μm. <1> from <3> 2. The gas diffusion composite material according to claim 1 . <5> The porous substrate sheet is in the form of a mesh sheet, a punched sheet or an expanded sheet. <1> from <4> 2. The gas diffusion composite material according to claim 1 . <6> The porous substrate sheet is made of a carbon material. <1> from <5> 2. The gas diffusion composite material according to claim 1 . <7> The porous substrate sheet is a carbon mesh. <1> from <5> 2. The gas diffusion composite material according to claim 1 . <8> Having any of the structures (C) to (E) <5> from <7> 2. The gas diffusion composite material according to claim 1 . <9> Having the structure (C) <7> The gas diffusion composite material according to claim 1. <10> The porous base sheet is made of a metal material. <1> from <5> 2. The gas diffusion composite material according to claim 1 . <11> The porous base sheet is a stainless steel mesh. <1> from <5> 2. The gas diffusion composite material according to claim 1 . <12> Having any of the structures (C) to (E) <11> The gas diffusion composite material according to claim 1. <13> Having the structure (D) <11> The gas diffusion composite material according to claim 1. <14> The present invention has a porous substrate sheet made of a non-conductive material, and a microporous carbon layer containing a 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 for a fuel cell having either of the following structures (D) and (E). Structure (D): A structure in which the microporous carbon layer covers one side of the porous substrate sheet made of the non-conductive material, and a part of the microporous carbon layer penetrates into the porous substrate sheet made of the non-conductive material, and the microporous carbon layer reaches from one side to the opposite side of the porous substrate sheet made of the non-conductive material. Structure (E): A structure in which the entire porous substrate sheet is embedded in the microporous carbon layer. <15> The particulate and / or fibrous carbon material constituting the microporous carbon layer is carbon black, carbon nanotubes, or a mixture thereof. <1> from <14> 2. The gas diffusion composite material for a fuel cell according to claim 1 . <16> 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 sandwiching the membrane electrode assembly via the gas diffusion layers, wherein at least one of the pair of gas diffusion layers is <1> from <15> 2. A solid polymer electrolyte fuel cell comprising the gas diffusion composite material for a fuel cell according to claim 1 . 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 polymer electrolyte fuel cell including the same. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing the structure of a polymer electrolyte fuel cell. [Diagram 2] FIG. 1 is a schematic diagram of a membrane electrode assembly including a conventional gas diffusion layer. [Diagram 3] FIG. 1 is a schematic diagram of a gas diffusion composite material for a fuel cell of the present invention (porous substrate sheet: (A) MPL laminated on one side, (B) MPL laminated on both sides, (C) partially embedded in MPL (not reaching the back side), (D) MPL partially embedded (reaching the back side), (E) completely embedded in MPL). [Figure 4] 1 is a photograph of the microstructure of the surface of a gas diffusion member 1 (stainless steel mesh sheet, SUS316 977mesh). [Diagram 5] 1 is a photograph of the microstructure of the surface of a gas diffusion member 2 (MPL composite stainless steel mesh). [Figure 6]1 is a photograph of the microstructure of a cross section of a gas diffusion member 2 (MPL composite stainless steel mesh). [Figure 7] 1 shows the results of observation of the microstructure of the surface of gas diffusion member 3 (gas diffusion layer with MPL (reference example)). [Figure 8] 1 shows the results of observation of the microstructure of a cross section of gas diffusion member 3 (gas diffusion layer with MPL (reference example)). [Figure 9] 1 is a photograph showing the appearance of a gas diffusion member 5 (MPL composite carbon mesh). [Figure 10] 4 shows the IV characteristics of a PEFC unit cell using gas diffusion members 1 to 3. [Figure 11] 4 shows the IV characteristics of a single PEFC cell using gas diffusion members 4 and 5. [Figure 12] 4 shows the IV characteristics of a single PEFC cell using gas diffusion member 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 as desired without departing from the gist of the present invention. In this specification, the word "to" is used as an expression including the numerical value or physical quantity before and after it.

[0015] 1. Gas diffusion composites for fuel cells The present invention relates to a gas diffusion composite material for a fuel cell (hereinafter, sometimes referred to as "the gas diffusion composite material of the present invention") which comprises a porous substrate sheet made of a conductive material, and a microporous carbon layer containing a 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 has any of the following structures (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): The microporous carbon layer covers one side of the porous substrate sheet, and a part of the microporous carbon layer penetrates into the porous substrate sheet. Structure (D): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a part of the microporous carbon layer penetrates into the porous substrate sheet, and the microporous carbon layer reaches 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] Details of structures (A) to (E) will be described later in "1-3. Arrangement of porous substrate sheet and microporous carbon layer."

[0018] The gas diffusion composite material of the present invention is suitable as a gas diffusion layer for a polymer electrolyte fuel cell.

[0019] Hereinafter, the role of the gas diffusion composite material (gas diffusion layer) in a polymer electrolyte fuel cell will be described with reference to FIGS. FIG. 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 protons (H + ) is supplied to the air electrode (cathode) through a solid polymer electrolyte membrane, and the generated electrons are supplied to the air electrode (cathode) through an external circuit (not shown), resulting in (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) creates a potential difference between the two electrodes.

[0020] FIG. 2 shows a schematic diagram of a membrane electrode assembly equipped with a conventional gas diffusion member. The main functions required for PEFC gas diffusion materials are moisture retention for the solid polymer electrolyte membrane (approximately 10 μm thick), drainage from the electrode catalyst layer, electronic conduction between the electrode catalyst layer and the separator, and gas transport. Conventional gas diffusion materials widely used are carbon fiber gas diffusion layers (GDLs) and those with finer pores, called microporous layers (MPLs), formed on the surface of the carbon fiber gas diffusion layer that comes into contact with the electrode catalyst layer to improve current collection and water retention. In particular, in PEFCs with a thickness of about 1 mm, two carbon fiber gas diffusion layers with a thickness of about 200 μm are used adjacent to each electrode, but these have issues such as a decrease in mechanical strength due to the thinning and high costs.

[0021] 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 (e.g., a conductive porous substrate sheet made of metal or carbon) having a thickness of 3 μm to 150 μm and excellent in mechanical strength. By having such a structure, the gas diffusion composite material of the present invention has sufficient mechanical strength and conductivity derived from the porous substrate sheet and conductivity and water repellency derived from the microporous carbon layer, so that the total thickness of the gas diffusion composite material can be reduced to 150 μm or less (preferably 100 μm or less, 60 μm or less).

[0022] The gas diffusion composite material of the present invention has a microporous carbon layer on its surface which has excellent current collection properties and low contact resistance. Therefore, by disposing the gas diffusion composite material of the present invention, overvoltage is reduced and the power generation characteristics (IV characteristics) are excellent compared to when only a porous substrate sheet without a microporous layer is used.

[0023] A solid polymer fuel cell is normally used as a fuel cell stack by stacking a number of unit cells, which are its basic component, 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 a particulate and / or fibrous carbon material and a water-repellent resin, as the gas diffusion member for the fuel cell instead of the conventional gas diffusion member (carbon fiber-based gas diffusion layer with MPL) and placing this between the electrode catalyst layer and the separator, it is possible to significantly reduce the thickness of the fuel cell stack.

[0024] The gas diffusion composite of the present invention may be located on either or both of the cathode and anode sides.

[0025] The components of the gas diffusion composite material for a fuel cell 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 a fuel cell according to the present invention are the same as those in known polymer electrolyte fuel cells, and therefore a description thereof will be omitted.

[0026] (1-1. Porous base sheet) The porous substrate sheet constituting the gas diffusion composite material of the present invention is a sheet-like member made of a conductive material and having a plurality of through holes.

[0027] The form of the porous substrate sheet is not limited as long as the effects of the present invention are achieved, and examples thereof include a mesh sheet, a punched sheet, and an expanded sheet.

[0028] In this specification, a "mesh sheet" refers to a sheet-like member formed by weaving thin wires of a constituent material, and the spaces between the woven thin wires become through spaces (through holes) that penetrate the mesh in the thickness direction. The thickness of the mesh sheet and the diameter, density, and size of the through holes may be appropriately designed within a range that does not impair the object of the present invention and maintains strength.

[0029] In this specification, the term "punched sheet" refers to a sheet-like member with many through holes, which is produced by punching a sheet (strip) of a constituent material with a punching device. The thickness of the punched sheet and the diameter, density, and size of the through holes may be appropriately designed within a range that does not impair the object of the present invention and maintains strength.

[0030] In this specification, an "expanded sheet" refers to a sheet-like member in which a sheet of a constituent material is cut and expanded to form the cuts into a diamond or tortoiseshell shape, and the diamond or tortoiseshell shape formed by expanding the cuts becomes a through space (through hole) that penetrates the expand in the thickness direction. The hole diameter and density of the through holes in the expanded sheet may be appropriately designed according to the hole diameter of the through hole within a range that does not impair the object of the present invention and maintains strength.

[0031] Among the forms of the porous substrate sheet, a mesh sheet is preferred. The mesh sheet has a weave such as a plain weave, a twill weave, a plain tatami weave, and a twill tatami weave. "Plain weave" is a weaving method in which vertical and horizontal lines cross each other alternately. "Twill weave" is a weaving method in which vertical and horizontal lines cross every few lines. "Plain tatami weave" is a method of weaving lines like the covering of a tatami mat. "Twill tatami weave" is a method that applies twill weave to plain tatami weave.

[0032] The number of lines (i.e., linear materials) per unit area of ​​the mesh sheet tends to increase in the following order: plain weave < twill weave < plain tatami weave < twill tatami weave. The more lines per unit area of ​​the mesh sheet, the more flat the surface of the mesh sheet is. Improving the flatness of the surface of the mesh sheet can increase the contact area of ​​the gas diffusion member with other components in the fuel cell (e.g., the electrode catalyst layer and the separator), and the increased contact area between the components can contribute to improving the electrical connectivity between the components.

[0033] 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 60 μm, or 20 μm to 60 μm. Such a thickness can impart mechanical strength to the gas diffusion composite material of the present invention, and can provide self-supporting properties even when a microporous carbon layer is provided. The thickness of the porous substrate sheet can be measured, for example, with a micrometer.

[0034] In the gas diffusion composite material of the present invention, the material for the porous substrate sheet may be selected from materials having both sufficient durability and electronic conductivity under the operating conditions of the PEFC. Specifically, metal materials and carbon materials are selected as the material for the porous substrate sheet.

[0035] 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 conditions at the cathode during normal operation of the PEFC, where the temperature is from room temperature to about 150° C. and an oxygen-containing gas such as air is supplied (oxidizing atmosphere), while the anode conditions refer to conditions at the anode during normal operation of the PEFC, where the temperature is from room temperature to about 150° C. and an oxygen-containing fuel gas is supplied (reducing atmosphere).

[0036] There is no limitation on the metal material as long as it does not impair the object of the present invention, but preferable examples include stainless steel, metallic Ti (titanium) and Ti alloys.

[0037] Among the porous base sheets using metal materials, stainless steel mesh (e.g., SUS304, SUS316, SUS316L, SUS340) is preferred. The thickness of the stainless steel mesh and the diameter, density, and size of the through holes may be appropriately designed within a range that does not impair the object of the present invention and maintains strength.

[0038] The stainless steel mesh may be homemade or a commercially available product may be used.

[0039] In addition, a carbon mesh is preferable as a porous substrate sheet using a carbon material. The carbon mesh is a mesh sheet made of fibrous carbon and has a mesh structure including voids. The thickness of the carbon mesh and the diameter, density, and size of the through holes may be appropriately designed within a range that does not impair the object of the present invention and maintains strength.

[0040] The carbon mesh may be homemade or a commercially available product may be used.

[0041] If necessary, the porous substrate sheet may have a conductive material fixed to the surface.

[0042] The microporous carbon layer is formed by applying a coating liquid containing the constituent components of the microporous carbon layer (MPL components) to a porous substrate sheet, but how the microporous carbon layer is formed 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 permeability of the coating liquid into the mesh sheet vary depending on the weave structure of the mesh sheet, an appropriate mesh sheet can be selected depending on the desired structure (structures (A) to (E)).

[0043] (1-2. Microporous carbon layer) In the gas diffusion composite material of the present invention, the microporous carbon layer contains a particulate and / or fibrous carbon material and a water-repellent resin. The microporous carbon layer has a smaller pore size, higher density, and better surface flatness than the above-mentioned porous substrate sheet. Therefore, it has excellent electronic conductivity and can reduce contact resistance with the electrode catalyst layer or the separator.

[0044] As the carbon material constituting the microporous carbon layer, a particulate and / or fibrous carbon material is used. By having a microporous carbon layer containing such a carbon material, it is possible to impart excellent electrical conductivity to the gas diffusion composite material of the present invention.

[0045] As the particulate carbon material, a wide variety of known or commercially available materials can be used. For example, one or more of carbon blacks such as Ketjen Black and Acetylene Black, graphite, activated carbon, etc. can be used. The average particle size of the particulate carbon material is usually about 5 nm to 200 nm, preferably about 20 to 80 nm.

[0046] Moreover, by replacing a part of the particulate carbon material with a fibrous carbon material, the current collecting property and the gas diffusing property can be further improved.

[0047] As the fibrous carbon material, a wide variety of known or commercially available materials can be used, for example, carbon nanotubes (CNTs), carbon fibers (CFs), etc. can be used alone or in combination of two or more kinds.

[0048] The particulate and / or fibrous carbon material constituting the microporous carbon layer is preferably carbon black, carbon nanotubes, or a mixture thereof.

[0049] The water-repellent resin constituting the microporous carbon layer can be a fluororesin, such as polytetrafluoroethylene resin (PTFE), a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), a copolymer of tetrafluoroethylene and perfluoropropyl vinyl ether (PFA), a copolymer of tetrafluoroethylene and ethylene (ETFE), etc., which can be used alone or in combination of two or more.

[0050] The proportions of the particulate and / or fibrous carbon material and the water-repellent resin that constitute the microporous carbon layer are determined within a range that does not impair the object of the present invention.

[0051] 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 the conventionally known gas diffusion layer with MPL. 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 its independence without using a special carbon material and that is thinned to the same thickness as the MPL in the gas diffusion layer with MPL (about 20 μm).

[0052] In the gas diffusion composite material for fuel cells of the present invention, the total thickness 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 60 μm or less, or 20 μm or more and 60 μm or less. Here, the "total thickness" is the total thickness of the porous substrate sheet and the microporous carbon layer. The total thickness can be measured, for example, with a micrometer.

[0053] (1-3. Arrangement of porous substrate sheet and microporous carbon layer) As described above, the gas diffusion composite material of the present invention has any 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): The microporous carbon layer covers one side of the porous substrate sheet, and a part of the microporous carbon layer penetrates into the porous substrate sheet. Structure (D): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a part of the microporous carbon layer penetrates into the porous substrate sheet, and the microporous carbon layer reaches 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.

[0054] 3(A) to (E) show structures (A) to (E) of the gas diffusion composite material of the present invention, respectively.

[0055] When the gas diffusion composite material of the present invention has structure (A) in which a microporous carbon layer covers one side of a porous substrate sheet as shown in Fig. 3(A), the microporous carbon layer is usually arranged so as to be in contact with the electrode catalyst layer side, thereby reducing the contact resistance between the electrode catalyst layer and the gas diffusion composite material. Note that, even in the case of structure (A), the microporous carbon layer may be arranged on the separator side, in which case the contact resistance between the separator and the gas diffusion composite material is reduced.

[0056] When the gas diffusion composite material of the present invention has structure (B) in which the microporous carbon layers cover both sides of the porous substrate sheet as shown in FIG. 3(B), the microporous carbon layers are arranged so as to be in contact with both the electrode catalyst layer side and the separator side, and 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 are reduced.

[0057] In the case of the gas diffusion composite material of the present invention, in which the microporous carbon layer shown in Fig. 3(C) covers one side of the porous substrate sheet and part of the microporous carbon layer penetrates into the porous substrate sheet, the microporous carbon layer is usually arranged so as to be in contact with the electrode catalyst layer, as in the case of structure (A), so that the contact resistance between the electrode catalyst layer and the gas diffusion composite material is reduced. In the case of structure (C), the microporous carbon layer may also be arranged on the separator side, in which case the contact resistance between the separator and the gas diffusion composite material is reduced.

[0058] Furthermore, as shown in FIG. 3(D), in the case of a structure (D) 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 porous substrate sheet and the microporous carbon layer reaches from one side of the porous substrate sheet to the opposite side, the component constituting the microporous carbon layer (the MPL component) exhibits excellent electrical conductivity, so that the electrical resistance in the thickness direction of the gas diffusion composite can be reduced. When the porous base sheet is a mesh sheet, the permeability of the coating liquid into the mesh sheet varies depending on the weave structure and mesh diameter of the mesh sheet. Therefore, the weave structure, pore size, etc. of the porous base sheet can be appropriately selected so that the MPL components are regularly distributed inside the porous base sheet, as in the structure shown in Figure 3(D).

[0059] Furthermore, when the gas diffusion composite material of the present invention has a structure (E) in which the entirety of the porous substrate sheet is embedded in the microporous carbon layer as shown in FIG. 3(E), the microporous carbon layer is arranged so as to be in contact with both the electrode catalyst layer side and the separator side, 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 component constituting the microporous carbon layer (MPL component) exhibits superior conductivity to the porous substrate sheet, the electrical resistance in the thickness direction of the gas diffusion composite material can be reduced.

[0060] In addition, when the gas diffusion composite material has structure (D) or structure (E), the component constituting the microporous carbon layer (MPL component) is continuous from one side to the other side of the porous substrate sheet and exhibits electrical conductivity due to the microporous carbon layer, so that a non-conductive porous substrate sheet (e.g., a fluororesin) can be used instead of a conductive porous substrate sheet (metal or carbon).

[0061] That is, another aspect of the present invention is a gas diffusion composite for a fuel cell, comprising a porous substrate sheet made of a non-conductive material, and a microporous carbon layer containing a 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 gas diffusion composite has either of the following structures (D) and (E). Structure (D): A structure in which the microporous carbon layer covers one side of the porous substrate sheet made of the non-conductive material, and a part of the microporous carbon layer penetrates into the porous substrate sheet made of the non-conductive material, and the microporous carbon layer reaches from one side to the opposite side of the porous substrate sheet made of the non-conductive material. Structure (E): A structure in which the entire porous substrate sheet is embedded in the microporous carbon layer.

[0062] The thickness of the porous substrate sheet made of a non-conductive material is 3 μm to 150 μm, preferably 5 μm to 100 μm, 5 μm to 50 μm. The total thickness is 3 μm to 150 μm, preferably 5 μm to 100 μm, 20 μm to 100 μm, 5 μm to 60 μm, 20 μm to 60 μm. Such a thickness can impart mechanical strength to the gas diffusion composite material of the present invention, and can provide self-supporting properties even when a microporous carbon layer is provided. The thickness and total thickness of the porous substrate sheet made of a non-conductive material can be measured, for example, with a micrometer.

[0063] 2. Components other than polymer electrolyte fuel cells and gas diffusion composites The polymer electrolyte fuel cell of the present invention uses the above-mentioned gas diffusion composite material for fuel cells (self-supporting microporous layer) of the present invention as at least one of the gas diffusion composite materials arranged on the cathode side and the anode side.

[0064] When the gas diffusion composite material for fuel cells of the present invention has a microporous carbon layer on one side of the porous substrate sheet (structure (A), structure (C) and structure (D)), the gas diffusion composite material for fuel cells may be arranged so that the side having the microporous carbon layer is in contact with the cathode catalyst layer and / or the anode catalyst layer and the other side not having the microporous carbon layer is in contact with the separator, or the one side having the microporous carbon layer is in contact with the separator and the other side not having the microporous carbon layer is in contact with the cathode catalyst layer and / or the anode catalyst layer.

[0065] Furthermore, when the gas diffusion composite material for a fuel cell of the present invention has a microporous carbon layer on both sides of a porous substrate sheet (structure (B) and structure (E)), the gas diffusion composite material for a fuel cell may be arranged so that one side having the microporous carbon layer contacts the cathode catalyst layer and / or the anode catalyst layer, and the other side having the microporous carbon layer contacts the separator. When arranged in this manner, the surface with the microporous carbon layer is in contact with both the electrode catalyst layer (cathode catalyst layer, anode catalyst layer) and the separator, resulting in lower contact resistance compared to when a gas diffusion composite for fuel cells is used that has a microporous carbon layer adhered to one side.

[0066] Hereinafter, the components of the polymer electrolyte fuel cell of the present invention other than the gas diffusion composite material of the present invention will be described. However, since the components other than the gas diffusion composite material of the present invention are the same as those of known polymer electrolyte fuel cells, they will be described briefly.

[0067] The membrane electrode assembly (MEA) constituting the solid polymer electrolyte fuel cell of the present invention has 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.

[0068] The anode catalyst layer and the cathode catalyst layer can be conventionally known electrode catalyst layers (e.g., an electrode catalyst layer made of a carbon-based support carrying precious metal particles, an oxide support carrying precious metal particles, etc.), so detailed explanations are omitted.

[0069] As the solid polymer electrolyte membrane, a known electrolyte membrane for PEFC may be used as long as it has proton conductivity, chemical stability, and thermal stability. Examples of electrolyte materials constituting the solid polymer electrolyte membrane include fluorine-based electrolyte materials and hydrocarbon-based electrolyte materials. In particular, an electrolyte membrane formed of a fluorine-based electrolyte material is preferable because of its excellent heat resistance, chemical stability, and the like.

[0070] As the separator, a known separator can be used, for example, a metal separator, a carbon separator, etc.

[0071] The polymer electrolyte fuel cell (single cell) of the present invention is stacked in the number appropriate for power generation performance to form a fuel cell stack, which is used by assembling other associated devices such as a gas supply device and a cooling device.

[0072] Although the embodiments of the present invention have been described above, the embodiments disclosed herein are illustrative in all respects and are not restrictive. In particular, matters not explicitly disclosed in the embodiments disclosed herein, such as the operating conditions of the fuel cell, various parameters, dimensions, weights, volumes of components, etc., do not deviate from the scope of ordinary practice by a person skilled in the art, and values ​​that can be easily assumed by a person skilled in the art can be adopted. EXAMPLES

[0073] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. In the following examples, the gas diffusion composite member (MPL-composite porous substrate sheet), the porous substrate sheet (not composited with MPL), and the conventional gas diffusion layer (carbon fiber-based gas diffusion layer with MPL) are collectively referred to as "gas diffusion member".

[0074] <1. Gas diffusion materials> The following were used as gas diffusion members 1 to 6. The thickness of the gas diffusion member was measured five times with a micrometer (Mitutoyo Corporation, Coolant Proof Micrometer MDC-25MX) and calculated from the average.

[0075] Gas diffusion material 1: Stainless steel mesh (porous base sheet) We used stainless steel SUS316 / wire mesh (977 mesh) manufactured by Nilaco Co., Ltd. The stainless steel mesh sheet is made of a single layer of twill mesh with a wire diameter of φ13 μm and a thickness of 28 μm. Figure 4 shows a surface photograph of the gas diffusion member 1 (stainless steel mesh).

[0076] Gas diffusion material 2: MPL composite stainless steel mesh (MPL composite porous base sheet) An MPL composite stainless steel mesh serving as the gas diffusion member 2 was obtained by the following procedure. A dispersion for forming MPL was obtained by adding 241 mg of highly graphitized carbon black (GCB, Cabot Corporation, FCX200), 576 μL (CNT weight 30 mg) of carbon nanotube dispersion (Meijo Nano Carbon Co., Ltd., MWNT INK), and 22.5 μL (PTFE weight 30 mg) of water-repellent resin (DAIKIN Corporation, Polyflon PTFE D-210C) to a mixed solvent of 300 μL (300 mg) of pure water and 1500 μL (1695 mg) of polyethylene glycol (PEG), and mixing until homogenous. The obtained MPL-forming dispersion was screen-printed onto a stainless steel mesh (gas diffusion member 1) using a screen (screen thickness: 30 μm). A simple screen printer (PRINT GOKKO PG-11, manufactured by Riso Kagaku Corporation) was used for the screen printing, and the stainless steel mesh (gas diffusion member 1) cut slightly larger than the holes in the screen was used to obtain a gas diffusion member 2 (MPL composite stainless steel mesh). The thickness of the gas diffusion member 2 was 62 μm.

[0077] Gas diffusion material 3: Carbon fiber gas diffusion layer with MPL (conventional gas diffusion layer) As the gas diffusion member 3, a commercially available gas diffusion layer with MPL 22BB (manufactured by SGL Carbon, Germany, unit area mass 70 gm) made of carbon paper with MPL formed on the surface was used. -2 ) was used. The thickness of the gas diffusion member 3 was 206 μm.

[0078] Gas diffusion material 4: Carbon mesh (porous substrate sheet) Carbon mesh (bias weave) manufactured by Cosmotec was used as the gas diffusion member 4. The thickness of the gas diffusion member 4 was 45 μm.

[0079] Gas diffusion material 5: MPL composite carbon mesh (MPL composite porous substrate sheet) An MPL composite carbon mesh serving as the gas diffusion member 5 was obtained by the following procedure. 241 mg of GCB, a carbon nanotube dispersion (CNT weight: 30 mg), and 22.5 μL of water-repellent resin (PTFE weight: 30 mg) were added to a mixed solvent of 300 μL (300 mg) of pure water and 1500 μL (1695 mg) of PEG, and mixed until homogenous to obtain a dispersion for forming MPL. The obtained MPL forming dispersion was screen printed on a carbon mesh (gas diffusion member 4) using a screen (screen thickness: 30 μm). A simple screen printer (PRINT GOKKO PG-11, manufactured by Riso Kagaku Corporation) was used for the screen printing, and the carbon mesh (gas diffusion member 4) cut slightly larger than the holes in the screen was used to obtain a gas diffusion member 5 (MPL composite carbon mesh). The thickness of the gas diffusion member 5 was 87 μm.

[0080] Gas diffusion material 6: MPL composite carbon mesh (MPL composite porous substrate sheet) A gas diffusion member 6 (MPL composite carbon mesh) was obtained in the same manner as in the manufacturing method of the gas diffusion member 5, 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 the gas diffusion member 6 was 87 μm.

[0081] <2. Evaluation> 2-1. Microstructural observation A surface SEM image of gas diffusion member 2 (MPL composite stainless steel mesh) is shown in Fig. 5, and a cross-sectional SEM image is shown in Fig. 6. For reference, a surface SEM image of gas diffusion member 3 (conventional gas diffusion layer with MPL) is shown in Fig. 7, and a cross-sectional SEM image is shown in Fig. 8. As shown in Figure 5, in gas diffusion member 2 (MPL composite stainless steel mesh), MPL was supported uniformly over the entire surface, similar to gas diffusion member 3 (conventional gas diffusion layer with MPL) shown in Figure 7. The cracks seen on the surface of gas diffusion member 2 were determined to be caused by the surface material drying and hardening during heat treatment. 6, no separation of components occurred in the cross section of gas diffusion member 2, which was similar to the cross section of gas diffusion member 3 shown in FIG. Furthermore, in gas diffusion member 2, the MPL component was confirmed not only on the front surface but also on the back surface. From the above, it was determined that the gas diffusion member 2 has a structure (D) (see FIG. 3) in which the MPL component permeates into the mesh and is continuously connected from the front surface to the back surface.

[0082] FIG. 9 shows a photograph of the appearance of the gas diffusion member 5 (MPL composite carbon mesh). As shown in Figure 9, the carbon mesh base material could not be seen from the surface, and it was confirmed that MPL was evenly held on the surface. In addition, some of the MPL components had permeated into the carbon mesh, but had not reached the back surface, so it was determined to be structure (C) (see Figure 3). Similarly, it was confirmed that the gas diffusion member 6 (MPL composite carbon mesh) had MPL evenly distributed on its surface, and some of the MPL components had penetrated into the carbon mesh but not reached the rear surface. As a result, it was determined to have structure (C) (see Figure 3).

[0083] 2-2. Electrochemical evaluation (single cell, initial performance evaluation) A PEFC (single cell) with the following configuration was fabricated and a power generation experiment (IV measurement) was performed. (solid electrolyte membrane) Nafion membrane (DuPont, Nafion 212, thickness 51 μm) (anode) Electrode catalyst layer: Pt / C catalyst (Tanaka Kikinzoku Kogyo Co., Ltd.) Gas diffusion layer: Carbon fiber gas diffusion layer (carbon paper) (Cathode) Electrode catalyst layer: Pt / C catalyst (Tanaka Kikinzoku Kogyo Co., Ltd.) Gas diffusion layer: Gas diffusion members 1 to 5

[0084] The single cell power generation evaluation jig incorporating the gas diffusion members 1 to 5 was placed in a thermostatic chamber set at 80° C., and a power generation test was performed under the following conditions: A fuel cell evaluation device (manufactured by Toyo Corporation, model number: PE-8900K) and a potentio / galvanostat (manufactured by Solatron, model number: SI1287) were used. (Anode conditions) Electrode area: 1cm 2 Supply gas type: 100% H2 Gas supply rate: 139mL / min Supply gas humidification temperature: 80℃ (relative humidity: 100%) (Cathode conditions) Electrode area: 1cm 2 Supply gas type: Air Gas supply rate: 332mL / min Supply gas humidification temperature: 80℃ (relative humidity: 100%)

[0085] (Stainless steel mesh) Figure 10 shows the evaluation results of the current-voltage (IV) characteristics of PEFC (single cell) using gas diffusion materials 1 and 2. For reference, data for a single cell using gas diffusion material 3 (a conventional gas diffusion layer with MPL) is also shown.

[0086] As shown in Figure 10, both PEFCs using gas diffusion materials 1 and 2 were able to generate electricity, but the PEFC using gas diffusion material 2 composited with MPL showed a significant improvement in IV characteristics compared to gas diffusion material 1 without MPL. Gas diffusion material 2 showed performance equivalent to that of commercially available gas diffusion material 3 (a conventional gas diffusion layer with MPL). Gas diffusion material 2 also showed performance comparable to that of gas diffusion material 3 in activation overvoltage and resistance overvoltage (not shown). From the above, it was confirmed that the power generation performance (IV characteristics) was improved by combining stainless steel mesh with MPL.

[0087] (Carbon mesh) FIG. 11 shows the results of evaluation of the IV characteristics of a PEFC (single cell) using the gas diffusion members 4 and 5. As shown in FIG. 11, both PEFCs using gas diffusion materials 4 and 5 were capable of generating electricity, and the PEFC using gas diffusion material 5 incorporating MPL was found to have improved IV characteristics compared to gas diffusion material 4 without MPL.

[0088] FIG. 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 gas diffusion material 6 showed improved IV characteristics compared to gas diffusion material 4 without MPL, and demonstrated performance comparable to that of commercially available gas diffusion material 3 (a conventional gas diffusion layer with MPL).

[0089] From the above, it was confirmed that the power generation performance (IV characteristics) was improved by combining carbon mesh with MPL.

[0090] 2-3.Evaluation of electrical resistance and electrical resistivity Various gas diffusion materials measuring 1 cm square were sandwiched between two sheets of carbon paper of the same shape (EC-TPI-060T, ElectroChem Inc., Raynhan MA, USA), and then sandwiched in a full-cell evaluation jig to measure and evaluate the electrical resistivity. First, the electrical resistance of various gas diffusion materials was measured by electrochemical impedance (EIS) measurement using an electrochemical property evaluation device, and the electrical resistivity was calculated based on the thickness of the gas diffusion material. The inside of the device was not humidified or heated, and all measurements were performed at room temperature and pressure.

[0091] Table 1 shows the dimensions of each gas diffusion material (1 × 1 cm (1 cm 2 The electrical resistance of each gas diffusion member is shown in Table 1. The electrical resistance of each gas diffusion member is shown in Table 1. The electrical resistivity of each gas diffusion member is shown in Table 1. The electrical resistivity of each gas diffusion member is shown in Table 1. The electrical resistivity of each gas diffusion member is shown in Table 1. The electrical resistivity of each gas diffusion member is shown in Table 1.

[0092] [Table 1]

[0093] Comparing gas diffusion member 1 and gas diffusion member 2, in which the porous base sheet is stainless steel mesh, it can be seen that the electrical resistivity is reduced to about 1 / 10 by combining with MPL. As described above, since the MPL component had infiltrated into the back surface of gas diffusion member 2, it is considered that the electrical conductivity was improved by the MPL component. It was also confirmed that the electrical resistivity of gas diffusion members 4 and 5, in which the porous substrate sheet is a carbon mesh, was reduced by combining with MPL. [Industrial Applicability]

[0094] The present invention is promising as a component of polymer electrolyte fuel cells used in automobiles such as passenger cars and commercial vehicles, as well as in the electric power, gas and home appliance industries.

Claims

1. A gas diffusion composite material for a fuel cell, comprising: a porous substrate sheet made of a conductive material; and a microporous carbon layer containing a particulate and / or fibrous carbon material and a water-repellent resin, The porous base sheet is a sheet-like member made of a conductive material and having a plurality of through holes, The material of the porous base sheet is a carbon material, The porous substrate sheet is in the form of a mesh sheet, a punched sheet or an expanded sheet, The thickness of the porous substrate sheet is 5 μm or more and 100 μm or less, The total thickness of the gas diffusion composite material for a fuel cell is 5 μm or more and 100 μm or less, A gas diffusion composite material for a fuel cell, having any 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 part of the microporous carbon layer penetrates into the porous substrate sheet, and the microporous carbon layer does not reach from one side to the opposite side of the porous substrate sheet. Structure (D): A structure in which the microporous carbon layer covers one side of the porous substrate sheet, and a part of the microporous carbon layer penetrates into the porous substrate sheet, and the microporous carbon layer reaches 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. 2. The gas diffusion composite material according to claim 1, wherein the porous substrate sheet has a thickness of 5 μm or more and 60 μm or less.

3. 2. The gas diffusion composite material according to claim 1, wherein the porous substrate sheet is a carbon mesh.

4. 2. The gas diffusion composite material according to claim 1, having any one of structures (C) to (E).

5. 2. The gas diffusion composite material according to claim 1, having a structure (C).

6. 2. The gas diffusion composite material for a fuel cell according to claim 1, wherein the particulate and / or fibrous carbon material constituting the microporous carbon layer is carbon black, carbon nanotubes, or a mixture thereof.

7. 7. 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 sandwiching the membrane electrode assembly via the gas diffusion layer, wherein at least one of the pair of gas diffusion layers is the gas diffusion composite material for a fuel cell according to any one of claims 1 to 6.

Images