Gas diffusion layer for fuel cell, and method of manufacturing gas diffusion layer for fuel cell

Abstract

To improve gas diffusion properties, conductivity and spring properties.SOLUTION: A gas diffusion layer 10 for a fuel cell comprises: a carbon sheet laminate 11 in which a plurality of carbon sheets 12 mainly formed from a carbon fiber nonwoven fabric with a fiber diameter of not less than 500 nm and not more than 1 μm is stacked; and a large number of conductive assistant particles 13 that are arranged between the carbon sheets 12 adjacent to each other. The carbon sheets 12 are coupled together via the conductive assistant particles 13.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gas diffusion layer for a fuel cell and a method for producing a gas diffusion layer for a fuel cell. [Background technology]

[0002] A solid polymer electrolyte fuel cell includes a fuel cell stack formed by stacking a plurality of unit cells. Each unit cell has a membrane electrode assembly including a solid polymer electrolyte membrane (hereinafter referred to as electrolyte membrane) and a pair of catalyst layers sandwiching the electrolyte membrane, a pair of gas diffusion layers sandwiching the membrane electrode assembly, and an anode separator and a cathode separator sandwiching the pair of gas diffusion layers.

[0003] An example of such a gas diffusion layer is the gas diffusion electrode disclosed in Patent Document 1. The gas diffusion electrode disclosed in Patent Document 1 includes a sheet-like porous substrate and a microporous layer disposed in contact with one surface of the porous substrate. The porous substrate is carbon paper, carbon cloth, carbon nonwoven fabric, or the like. The microporous layer is formed by applying a paste-like coating liquid in which conductive fine particles, a binder, a solvent, a thickener, and the like are mixed and dispersed on one surface of the porous substrate. The conductive particles are carbon black such as acetylene black having an average particle size of 20 to 150 nm. The binder is, for example, polytetrafluoroethylene (PTFE). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-42074 A Summary of the Invention [Problem to be solved by the invention]

[0005] In such a gas diffusion layer for a fuel cell, there is a demand for improved gas diffusibility, electrical conductivity, and springiness. There is also a demand for a gas diffusion layer having excellent gas diffusibility, electrical conductivity, and springiness to be easily manufactured. [Means for solving the problem]

[0006] A gas diffusion layer for a fuel cell to solve the above problems comprises a carbon sheet laminate in which a plurality of carbon sheets, each formed of a carbon fiber nonwoven fabric having a fiber diameter of 500 nm or more and 1 μm or less, are laminated together, and a large number of conductive additive particles are disposed between adjacent carbon sheets, and the carbon sheets are bonded together via the conductive additive particles.

[0007] According to this configuration, a carbon sheet laminate is formed by stacking multiple carbon sheets, and a gas diffusion layer is formed by disposing a large number of conductive additive particles between adjacent carbon sheets to bond the carbon sheets together.

[0008] Here, when the carbon sheet is made of a nonwoven carbon fiber fabric mainly having a fiber diameter smaller than 500 nm, the porosity of the carbon sheet is small, and the gas diffusivity is deteriorated, whereas when the carbon sheet is made of a nonwoven carbon fiber fabric mainly having a fiber diameter larger than 1 μm, the thickness of the carbon sheet is large, and the gas diffusivity is deteriorated.

[0009] In this respect, according to the above configuration, the carbon sheet is mainly formed of a carbon fiber nonwoven fabric having a fiber diameter of 500 nm or more and 1 μm or less, so the porosity of the carbon sheet is large and the thickness of the carbon sheet is small. This allows the thickness of the gas diffusion layer to be smaller than that of a conventional gas diffusion layer having a substrate formed of a carbon fiber nonwoven fabric having a fiber diameter of several μm and a microporous layer superimposed on the surface of the substrate. The large porosity of the carbon sheet and the small thickness of the gas diffusion layer allow for improved gas diffusibility.

[0010] Furthermore, according to the above-mentioned configuration, since the adjacent carbon sheets are bonded to each other via a large number of conductive assistant particles, the electrical conductivity of the gas diffusion layer can be increased. Furthermore, according to the above-described configuration, spaces are formed between the carbon sheets to allow the carbon sheets to flex, thereby improving the spring properties.

[0011] Furthermore, the thickness of the gas diffusion layer can be adjusted by appropriately setting the number of carbon sheets constituting the carbon sheet laminate. In addition, since the fiber diameter of the carbon fiber nonwoven fabric constituting the carbon sheet is 500 nm or more and 1 μm or less, the firing temperature can be lower than when forming the carbon sheet by firing a substrate constituting a conventional gas diffusion layer, that is, a substrate formed from a carbon fiber nonwoven fabric having a fiber diameter of several μm.

[0012] Therefore, gas diffusibility, electrical conductivity, and spring properties can be improved. A method for manufacturing a gas diffusion layer for a fuel cell to solve the above problems includes a precursor sheet preparation step of preparing a precursor sheet, which is a precursor of the carbon sheet, by spinning a raw material containing polyacrylonitrile using an electrospinning method, a stacking arrangement step of forming a precursor sheet laminate by stacking a plurality of the precursor sheets and arranging a large number of the conductive assistant particles between the precursor sheets, a pressing step of pressing the precursor sheet laminate, and a firing step of firing the precursor sheet laminate to form the carbon sheet laminate.

[0013] According to this method, the gas diffusion layer according to claim 1 can be easily manufactured. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view of a gas diffusion layer for a fuel cell according to one embodiment. [Diagram 2] FIG. 2 is a flow chart showing a manufacturing procedure of the gas diffusion layer of FIG. [Diagram 3]3(a) to 3(d) are cross-sectional views sequentially illustrating the stacking arrangement process of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, one embodiment of a gas diffusion layer for a fuel cell (hereinafter, gas diffusion layer 10) and a method for manufacturing the gas diffusion layer 10 will be described with reference to FIGS. The gas diffusion layers 10 are disposed between the anode side surface of the membrane electrode assembly and the anode side separator, and between the cathode side surface of the membrane electrode assembly and the cathode side separator (both not shown).

[0016] As shown in FIG. 1, the gas diffusion layer 10 includes a carbon sheet laminate 11 in which a plurality of carbon sheets 12 formed of carbon fiber nonwoven fabric are laminated, and a large number of conductive additive particles 13 arranged between adjacent carbon sheets 12. The carbon fiber nonwoven fabric has a fiber diameter of 500 nm or more and 1 μm or less. The carbon sheets 12 are bonded to each other via the conductive additive particles 13. FIG. 1 is a schematic diagram showing the cross-sectional structure of the gas diffusion layer 10. In the gas diffusion layer 10, there may be a portion in which the carbon sheets 12 are directly bonded to each other.

[0017] It is preferable that there are three or more carbon sheets 12. The carbon sheet laminate 11 of the present embodiment includes five carbon sheets 12, for example. The conductive assistant particles 13 are located between adjacent carbon sheets 12 in all of the carbon sheets 12 .

[0018] The conductive assistant particles 13 are preferably fine carbon particles. The conductive assistant particles 13 of this embodiment are, for example, acetylene black. The particle size of the primary particles of the conductive assistant particles 13 is preferably, for example, 500 nm or more and 2000 nm or less.

[0019] Next, a manufacturing procedure for the gas diffusion layer 10 will be described with reference to FIGS. As shown in FIG. 2, the method for producing the gas diffusion layer 10 includes a precursor sheet preparation step, a lamination arrangement step, a pressing step, and a firing step.

[0020] <Precursor sheet preparation process> In the precursor sheet preparation step, a precursor sheet 22, which is a precursor of the carbon sheet 12, is prepared by spinning a raw material containing polyacrylonitrile by an electrospinning method. The precursor sheet 22 is a so-called nanofiber nonwoven fabric. As the raw material, a homopolymer in which only the structural unit of one type of monomer is polymerized, or a copolymer in which two or more types of monomers are copolymerized may be used.

[0021] <Stacking arrangement process> In the stacking and arranging step, a plurality of precursor sheets 22 are stacked to form a precursor sheet stack 21, and a large number of conductive assistant particles 13 are arranged between the precursor sheets 22.

[0022] In detail, first, as shown in FIG. 3(a), one precursor sheet 22 is placed on a workbench. Subsequently, a large number of conductive assistant particles 13 are arranged on the precursor sheet 22 as shown in FIG. 3(b).

[0023] Next, as shown in FIG. 3( c ), a precursor sheet 22 is placed on the conductive assistant particles 13 . By repeating these steps, a precursor sheet laminate 21 is formed as shown in FIG. 3(d).

[0024] <Pressing process> As shown in FIG. 3(d), in the pressing step, the precursor sheet laminate 21 is pressed to adjust the thickness of the precursor sheet laminate 21.

[0025] <Firing process> In the firing step, the precursor sheet laminate 21 is fired to form the carbon sheet laminate 11. In the firing step, the precursor sheet laminate 21 is fired at a temperature of, for example, 1000° C. or higher and 2400° C. or lower. As a result, the precursor sheets 22 are graphitized to form the carbon sheets 12, and the carbon sheets 12 and the conductive assistant particles 13 are bonded to each other.

[0026] Next, the operation of this embodiment will be described. A carbon sheet laminate 11 is formed by stacking multiple carbon sheets 12, and a gas diffusion layer 10 is formed by arranging a large number of conductive additive particles 13 between adjacent carbon sheets 12 to bond the carbon sheets 12 together.

[0027] Here, when the carbon sheet 12 is formed mainly from a carbon fiber nonwoven fabric having a fiber diameter smaller than 500 nm, the gas diffusibility deteriorates due to a small porosity of the carbon sheet 12. On the other hand, when the carbon sheet 12 is formed mainly from a carbon fiber nonwoven fabric having a fiber diameter larger than 1 μm, the thickness of the carbon sheet 12 increases, resulting in a deterioration of the gas diffusibility.

[0028] In this regard, according to the gas diffusion layer 10 of the present embodiment, the carbon sheet 12 is formed mainly of a carbon fiber nonwoven fabric having a fiber diameter of 500 nm or more and 1 μm or less, so that the porosity of the carbon sheet 12 is large and the thickness of the carbon sheet 12 is small. As a result, the thickness of the gas diffusion layer 10 can be made smaller than that of a conventional gas diffusion layer having a substrate formed of a carbon fiber nonwoven fabric having a fiber diameter of several μm and a microporous layer superimposed on the surface of the substrate. As a result of the large porosity of the carbon sheet 12 and the small thickness of the gas diffusion layer 10, the gas diffusibility can be improved.

[0029] Furthermore, according to the gas diffusion layer 10 of this embodiment, the adjacent carbon sheets 12 are bonded to each other via a large number of conductive assistant particles 13, so that the electrical conductivity can be increased. Furthermore, according to the gas diffusion layer 10 of the present embodiment, a space is formed between the carbon sheets 12 allowing the carbon sheets 12 to bend, thereby improving the springiness.

[0030] Furthermore, the thickness of the gas diffusion layer 10 can be adjusted by appropriately setting the number of carbon sheets 12 that constitute the carbon sheet laminate 11. In addition, since the fiber diameter of the carbon fiber nonwoven fabric constituting the carbon sheet 12 is 500 nm or more and 1 μm or less, the firing temperature can be lower than when a substrate constituting a conventional gas diffusion layer, that is, a substrate formed from a carbon fiber nonwoven fabric having a fiber diameter of several μm, is fired to form the carbon sheet 12.

[0031] Next, the effects of this embodiment will be described. (1) The gas diffusion layer 10 includes a carbon sheet laminate 11 in which a plurality of carbon sheets 12 formed mainly from a carbon fiber nonwoven fabric having a fiber diameter of 500 nm or more and 1 μm or less are laminated, and a large number of conductive additive particles 13 disposed between adjacent carbon sheets 12. The carbon sheets 12 are bonded to each other via the conductive additive particles 13.

[0032] According to this method, the above-mentioned effects are achieved, and therefore gas diffusibility, electrical conductivity, and spring properties can be improved. By improving gas diffusivity in this way, it is possible to reduce the concentration overvoltage of the fuel cell. Also, by improving electrical conductivity, it is possible to reduce the resistance overvoltage of the fuel cell. Also, by improving springiness, it is possible to improve the conformability to the shape of the anode side separator or the cathode side separator rib, thereby reducing the resistance overvoltage of the fuel cell. Therefore, it is possible to improve the power generation performance of the fuel cell.

[0033] (2) There are three or more carbon sheets 12. The conductive assistant particles 13 are located between adjacent carbon sheets 12 in all of the carbon sheets 12. With this configuration, the springiness of the gas diffusion layer 10 can be further improved.

[0034] (3) The conductive assistant particles 13 are carbon fine particles. With this configuration, the conductive assistant particles 13 are made of inexpensive carbon fine particles, which can reduce the cost of the fuel cell.

[0035] (4) The method for producing the gas diffusion layer 10 includes a precursor sheet preparation step, a lamination arrangement step, a pressing step, and a firing step. According to this method, the gas diffusion layer 10 can be easily produced.

[0036] <Modification> This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that there is no technical contradiction.

[0037] The conductive assistant particles 13 are not limited to acetylene black. For example, other carbon particles such as Ketjen black, i.e., carbon black, can also be used. Furthermore, the conductive assistant particles 13 are not limited to carbon particles, and ceramic materials with excellent conductivity such as titanium nitride can also be used.

[0038] The carbon sheet laminate 11 may include two, three, four, or six or more carbon sheets 12 . <Additional Notes> Each of the above embodiments includes the configurations described in the following supplementary notes.

[0039] [Appendix 1] A gas diffusion layer for a fuel cell, comprising: a carbon sheet laminate in which a plurality of carbon sheets, each formed of a carbon fiber nonwoven fabric having a fiber diameter of 500 nm or more and 1 μm or less, are laminated; and a large number of conductive additive particles disposed between adjacent carbon sheets, wherein the carbon sheets are bonded to each other via the conductive additive particles.

[0040] [Appendix 2] 2. A gas diffusion layer for a fuel cell as described in claim 1, wherein the carbon sheets are three or more, and the conductive additive particles are located between adjacent carbon sheets for all of the carbon sheets.

[0041] [Appendix 3] 3. The gas diffusion layer for a fuel cell according to claim 1, wherein the conductive assistant particles are carbon fine particles.

[0042] [Appendix 4] A method for producing a gas diffusion layer for a fuel cell according to any one of Supplementary Note 1 to Supplementary Note 3, comprising: a precursor sheet preparation step of preparing a precursor sheet, which is a precursor of the carbon sheet, by spinning a raw material containing polyacrylonitrile by an electrospinning method; a stacking and arranging step of stacking a plurality of the precursor sheets to form a precursor sheet laminate and arranging a large number of the conductive assistant particles between the precursor sheets; a pressing step of pressing the precursor sheet laminate; and a firing step of firing the precursor sheet laminate to form the carbon sheet laminate. [Explanation of symbols]

[0043] 10… 10...Gas diffusion layer 11...Carbon sheet laminate 12…Carbon sheet 13...Conductive additive particles 21... precursor sheet laminate 22…Precursor sheet

Claims

1. a carbon sheet laminate including a plurality of carbon sheets formed of carbon fiber nonwoven fabrics having a fiber diameter of 500 nm or more and 1 μm or less; and a number of conductive assistant particles disposed between adjacent carbon sheets, The carbon sheets are bonded to each other via the conductive assistant particles. Gas diffusion layer for fuel cells.

2. The carbon sheets are three or more, The conductive assistant particles are located between adjacent carbon sheets for all of the carbon sheets. The gas diffusion layer for a fuel cell according to claim 1 .

3. The conductive assistant particles are carbon fine particles. The gas diffusion layer for a fuel cell according to claim 1 .

4. A method for producing a gas diffusion layer for a fuel cell according to any one of claims 1 to 3, comprising the steps of: a precursor sheet preparation step of preparing a precursor sheet, which is a precursor of the carbon sheet, by spinning a raw material containing polyacrylonitrile by an electrospinning method; a lamination arrangement step of laminating a plurality of the precursor sheets to form a precursor sheet laminate and arranging a large number of the conductive assistant particles between the precursor sheets; a pressing step of pressing the precursor sheet laminate; and a firing step of firing the precursor sheet laminate to form the carbon sheet laminate. A method for manufacturing a gas diffusion layer for a fuel cell.

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