Fuel cell stack and method for manufacturing a fuel cell stack

Abstract

To provide a fuel cell stack which can be improved in gas diffusibility, drainage and cooled performance and a method of manufacturing the fuel cell stack.SOLUTION: Each of single cells 10 constituting a fuel cell stack comprises a power generation unit 20, a cathode-side separator 40, an anode-side separator 50, and a porous body flow passage plate 60. The cathode-side separator 40 comprises groove-like oxidant gas flow passages 47 and groove-like cooling medium flow passages 48. The anode-side separator 50 comprises groove-like fuel gas flow passages 57 and groove-like cooling medium flow passages 58. An electrically conductive and flexible porous sheet 70 is arranged between the cathode-side separator 40 and the porous body flow passage plate 60. The porous sheet 70 has: a plurality of low-density portions 73 filled in the respective oxidant gas flow passages 47; and a high-density portion 74 which is located between the low-density portions 73, abuts on the cathode-side separator 40 and kas density higher than that of the low-density portions 73.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a fuel cell stack and a method for manufacturing the fuel cell stack.

Background Art

[0002] Patent Document 1 discloses a fuel cell configured by stacking a plurality of single cells. The single cell includes a membrane electrode assembly (hereinafter, MEA), a cathode-side separator sandwiching the membrane electrode assembly, and an anode-side separator.

[0003] A gas diffusion layer made of expanded metal is provided between the cathode-side separator and the MEA. A plurality of gas supply grooves for supplying an oxidant gas are provided side by side on the surface of the cathode-side separator facing the gas diffusion layer.

[0004] The anode-side separator is provided with a gas supply groove for supplying a fuel gas.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the case of the fuel cell disclosed in Patent Document 1, the oxidant gas preferentially flows through the gas supply groove having a larger flow path cross-sectional area, that is, a lower pressure loss, than the pores of the gas diffusion layer made of expanded metal. Therefore, problems such as difficulty in diffusing the oxidant gas through the gas diffusion layer and difficulty in draining the generated water staying in the gas diffusion layer occur.

[0007] In a fuel cell, in order to suppress the temperature rise due to power generation, improvement in coolability is also desired.

Means for Solving the Problems

[0008] A fuel cell stack for solving the above problems is a fuel cell stack formed by laminating a plurality of single cells. The single cell includes a power generation part, a cathode side separator, an anode side separator that sandwiches the power generation part with the cathode side separator in the stacking direction of the single cells, and a porous flow path plate provided between the cathode side separator and the power generation part. The cathode side separator has a first cathode surface provided with a plurality of groove-shaped oxidant gas flow paths through which the oxidant gas flows in parallel, and a second cathode surface on the side opposite to the first cathode surface and provided with a plurality of cooling medium flow paths through which the cooling medium flows in parallel. The anode side separator has a first anode surface provided with a plurality of groove-shaped fuel gas flow paths through which the fuel gas flows in parallel, and a second anode surface on the side opposite to the first anode surface and provided with a plurality of groove-shaped cooling medium flow paths through which the cooling medium flows in parallel. A porous sheet having conductivity and flexibility is provided between the cathode side separator and the porous flow path plate. The pore diameter of the porous sheet is smaller than the pore diameter of the porous flow path plate. The porous sheet has a plurality of low-density portions filled in each of the oxidant gas flow paths, and high-density portions that are located between the low-density portions, contact the cathode side separator, and have a higher density than the low-density portions.

[0009] Conventionally, there has been a fuel cell stack configured by laminating single cells each including a flat separator as a cathode-side separator and a porous flow path plate provided between the separator and a power generation unit. In this case, as the anode-side separator, if one having a first anode surface provided with a plurality of groove-shaped fuel gas flow paths arranged side by side and a second anode surface provided with a plurality of groove-shaped cooling medium flow paths through which a cooling medium flows arranged side by side is used, the following disadvantages occur. That is, since the flow path through which the cooling medium flows is constituted only by the cooling medium flow paths of the anode-side separator, if the cross-sectional area of the cooling medium flow path is increased to improve the cooling performance, the cross-sectional area of the fuel gas flow path increases accordingly. As a result, the pressure loss of the fuel gas flowing through the fuel gas flow path becomes small, making it difficult for the generated water present in the fuel gas flow path to be discharged by the fuel gas.

[0010] In this regard, according to the above configuration, the flow path through which the cooling medium flows is constituted by the cooling medium flow paths of both the cathode-side separator and the anode-side separator. Therefore, the cross-sectional area of the flow path through which the cooling medium flows can be increased without increasing the cross-sectional area of the fuel gas flow path. Thereby, it is possible to enhance the cooling performance while improving the drainage of the generated water present in the fuel gas flow path.

[0011] Also, according to the above configuration, since the low-density portion of the porous sheet is filled in the oxidant gas flow path of the cathode-side separator, the oxidant gas flows through the pores of the porous flow path plate with relatively low pressure loss. Thereby, the gas diffusibility of the oxidant gas can be enhanced.

[0012] In addition, the generated water produced in the power generation section moves to the porous sheet through the pores of the porous flow channel plate. Here, since the porous sheet has a low-density portion and a high-density portion, the generated water that has moved to the porous sheet moves toward the cathode-side separator through the pores of the relatively denser high-density portion due to capillary action. Also, the generated water present in the low-density portion moves toward the high-density portion. Then, the generated water that has moved to the cathode-side separator is discharged toward the downstream side by the pressure gradient between the upstream side and the downstream side of the oxidant gas flow channel.

[0013] Therefore, gas diffusibility, drainage, and coolability can be improved. In the fuel cell stack, it is preferable that the porous sheet is formed of carbon fibers.

[0014] According to the same configuration, a porous sheet having pores smaller than those of the porous flow channel plate and having conductivity and flexibility can be easily realized. In the fuel cell stack, it is preferable that the porous sheet has a porous base material and a hydrophilic additive provided on the surface of the base material.

[0015] According to the same configuration, the generated water that has moved to the porous sheet is more likely to gather in the high-density portion. Therefore, the drainage can be further enhanced. In the fuel cell stack, the power generation section has a membrane electrode assembly and a pair of gas diffusion layers sandwiching the membrane electrode assembly in the stacking direction, and it is preferable that the rigidity of the porous sheet is lower than the rigidity of the gas diffusion layer.

[0016] When manufacturing a fuel cell stack, a single cell is formed by arranging a cathode-side separator, an anode-side separator, a power generation part, a porous flow channel plate, and a porous sheet as follows. That is, in the stacking direction, the power generation part is located between the cathode-side separator and the anode-side separator, the porous flow channel plate is located between the cathode-side separator and the power generation part, and a porous sheet with a uniform density is located between the cathode-side separator and the porous flow channel plate. Next, a plurality of single cells are stacked to form a stack body, and a low-density part and a high-density part are formed by applying a compressive load to the stack body in the stacking direction.

[0017] Here, according to the above configuration, the porous sheet is preferentially compressed by the compressive load rather than the gas diffusion layer. As a result, it is possible to suppress the deformation of the gas diffusion layer due to the bending deformation of the porous sheet to form the low-density part and the high-density part.

[0018] A method for manufacturing a fuel cell stack for solving the above problems includes a step of arranging the cathode-side separator, the anode-side separator, the power generation part, the porous flow channel plate, and the porous sheet so that the power generation part is located between the cathode-side separator and the anode-side separator in the stacking direction, the porous flow channel plate is located between the cathode-side separator and the power generation part, and the porous sheet with a uniform density is located between the cathode-side separator and the porous flow channel plate to form the single cell, and then stacking a plurality of the single cells to form a stack body; and a step of forming the low-density part and the high-density part by applying a compressive load to the stack body in the stacking direction.

[0019] According to the same method, by making a simple change such as arranging a porous sheet with a uniform density between the cathode-side separator and the porous flow channel plate with respect to the process of manufacturing a conventional stack body, a low-density part and a high-density part can be formed.

[0020] A method for manufacturing a fuel cell stack for solving the above problems includes a step of forming a partial laminate in which the cathode-side separator and the porous sheet are laminated by applying a compressive load to the cathode-side separator and the porous sheet in the stacking direction in a state where the porous sheet having the same density as the cathode-side separator is overlapped, thereby forming the low-density portion and the high-density portion, and then, arranging the partial laminate, the anode-side separator, the power generation unit, and the porous body flow path plate such that the power generation unit is positioned between the partial laminate and the anode-side separator in the stacking direction and the porous body flow path plate is positioned between the partial laminate and the power generation unit to form the single cell, and a step of forming a stack body by laminating the single cells.

[0021] According to this method, after forming a partial laminate having a low-density portion and a high-density portion in advance, a single cell is formed using the partial laminate. Therefore, the low-density portion and the high-density portion can be formed with high accuracy.

Effect of the Invention

[0022] According to the present invention, gas diffusibility, drainage, and coolability can be improved.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0024] <First Embodiment> Hereinafter, with reference to FIGS. 1 to 7, a first embodiment of the fuel cell stack will be described. As shown in FIG. 1, the fuel cell stack is configured by laminating a plurality of single cells 10.

[0025] <Single Cell 10> The single cell 10 includes a power generation unit 20, a cathode-side separator 40, and an anode-side separator 50 that sandwiches the power generation unit 20 with the cathode-side separator 40 in the stacking direction of the single cell 10. Further, the single cell 10 includes a porous body flow path plate 60 provided between the cathode-side separator 40 and the power generation unit 20, and a porous sheet 70 provided between the cathode-side separator 40 and the porous body flow path plate 60. Further, the single cell 10 includes a resin frame 30 that holds the power generation unit 20.

[0026] The single cell 10 of the present embodiment is in the shape of a rectangular plate having a pair of long sides and a pair of short sides. Hereinafter, the long side direction of the single cell 10 will be described as the length direction X, the short side direction of the single cell 10 will be described as the width direction Y, and the stacking direction of the single cell 10 will be described as the stacking direction Z.

[0027] <Power generation unit 20> As shown in FIGS. 2 and 3, the power generation unit 20 includes a membrane electrode assembly (hereinafter, MEA 21) and a pair of gas diffusion layers 25 that sandwich the MEA 21 in the stacking direction Z.

[0028] The power generation unit 20 is in the shape of a rectangular thin plate. The MEA 21 includes an electrolyte membrane 22, a cathode electrode 23, and an anode electrode 24. The electrolyte membrane 22 is a solid polymer membrane. The electrolyte membrane 22 is sandwiched between the cathode electrode 23 and the anode electrode 24 in the stacking direction Z.

[0029] <Resin frame 30> As shown in FIG. 1, the resin frame 30 is made of a hard resin having electrical insulation properties. A hole 30A is provided in the central portion of the resin frame 30. The hole 30A in the present embodiment is in a rectangular shape that is slightly smaller than the power generation unit 20. The inner peripheral edge of the hole 30A is joined in a state of overlapping with the outer peripheral edge of the power generation unit 20 in the stacking direction Z. The resin frame 30 has an outer peripheral edge that constitutes the outer peripheral edge of the single cell 10. The resin frame 30 in the present embodiment is in the shape of a rectangular plate.

[0030] On one end side in the length direction X (the left side in FIG. 1) of the resin frame 30, a fuel gas discharge manifold hole 31, a cooling medium supply manifold hole 32, and an oxidant gas supply manifold hole 33 are provided.

[0031] In the present embodiment, the fuel gas discharge manifold hole 31, the cooling medium supply manifold hole 32, and the oxidant gas supply manifold hole 33 are provided in order from one end side in the width direction Y (the upper side in FIG. 1).

[0032] On the other end side in the length direction X (the right side in FIG. 1) of the resin frame 30, an oxidant gas discharge manifold hole 34, a cooling medium discharge manifold hole 35, and a fuel gas supply manifold hole 36 are provided.

[0033] In the present embodiment, an oxidant gas discharge manifold hole 34, a cooling medium discharge manifold hole 35, and a fuel gas supply manifold hole 36 are provided in order from one end side in the width direction Y (the upper side in FIG. 1).

[0034] <Cathode side separator 40> As shown in FIG. 1, a fuel gas discharge manifold hole 41, a cooling medium supply manifold hole 42, and an oxidant gas supply manifold hole 43 are provided at one end side in the length direction X (the left side in FIG. 1) of the cathode side separator 40.

[0035] In the present embodiment, a fuel gas discharge manifold hole 41, a cooling medium supply manifold hole 42, and an oxidant gas supply manifold hole 43 are provided in order from one end side in the width direction Y (the upper side in FIG. 1).

[0036] At the other end side in the length direction X (the right side in FIG. 1) of the cathode side separator 40, an oxidant gas discharge manifold hole 44, a cooling medium discharge manifold hole 45, and a fuel gas supply manifold hole 46 are provided.

[0037] In the present embodiment, an oxidant gas discharge manifold hole 44, a cooling medium discharge manifold hole 45, and a fuel gas supply manifold hole 46 are provided in order from one end side in the width direction Y (the upper side in FIG. 1).

[0038] As shown in FIGS. 2 and 3, the cathode side separator 40 has a first cathode surface 40a and a second cathode surface 40b which is the surface opposite to the first cathode surface 40a. The cathode side separator 40 is formed by pressing a conductive metal plate material. As such a metal plate material, for example, stainless steel or titanium plate is preferable.

[0039] A plurality of groove-shaped oxidant gas flow paths 47 through which the oxidant gas flows are provided side by side on the first cathode surface 40a at a portion overlapping the power generation unit 20 in the stacking direction Z. The oxidant gas is, for example, air containing oxygen.

[0040] On the second cathode surface 40b, a plurality of groove-shaped coolant flow paths 48 through which a coolant flows are provided side by side in a portion overlapping the power generation unit 20 in the stacking direction Z. The coolant is, for example, water containing antifreeze.

[0041] A coolant flow path 48 is located between adjacent oxidant gas flow paths 47. As shown in FIG. 1, on the first cathode surface 40a, an upstream connection flow path 47a that connects the oxidant gas supply manifold hole 43 and the oxidant gas flow path 47 is provided.

[0042] On the first cathode surface 40a, a downstream connection flow path 47b that connects the oxidant gas discharge manifold hole 44 and the oxidant gas flow path 47 is provided. <Anode-side separator 50> As shown in FIG. 1, at one end side (the left side in FIG. 1) in the length direction X of the anode-side separator 50, a fuel gas discharge manifold hole 51, a coolant supply manifold hole 52, and an oxidant gas supply manifold hole 53 are provided.

[0043] In the present embodiment, the fuel gas discharge manifold hole 51, the coolant supply manifold hole 52, and the oxidant gas supply manifold hole 53 are provided in order from one end side in the width direction Y (the upper side in FIG. 1).

[0044] At the other end side (the right side in FIG. 1) in the length direction X of the anode-side separator 50, an oxidant gas discharge manifold hole 54, a coolant discharge manifold hole 55, and a fuel gas supply manifold hole 56 are provided.

[0045] In the present embodiment, the oxidant gas discharge manifold hole 54, the coolant discharge manifold hole 55, and the fuel gas supply manifold hole 56 are provided in order from one end side in the width direction Y (the upper side in FIG. 1).

[0046] As shown in FIG. 2, the anode-side separator 50 has a first anode surface 50a and a second anode surface 50b which is on the side opposite to the first anode surface 50a. The anode-side separator 50 is formed by pressing a conductive metal plate material. As such metal plate materials, for example, those made of stainless steel or titanium plates are preferable.

[0047] On the first anode surface 50a, a plurality of groove-shaped fuel gas flow paths 57 through which fuel gas flows are provided side by side in a portion overlapping with the power generation unit 20 in the stacking direction Z. The fuel gas is, for example, hydrogen.

[0048] On the second anode surface 50b, a plurality of groove-shaped cooling medium flow paths 58 through which a cooling medium flows are provided side by side in a portion overlapping with the power generation unit 20 in the stacking direction Z. A cooling medium flow path 58 is located between adjacent fuel gas flow paths 57.

[0049] The width of the cooling medium flow path 58 is the same as the width of the cooling medium flow path 48 of the cathode-side separator 40. Also, the cooling medium flow path 58 and the cooling medium flow path 48 of the cathode-side separator 40 face each other in the stacking direction Z. The cooling medium flows through the space surrounded by the cooling medium flow path 58 and the cooling medium flow path 48.

[0050] As shown in FIG. 1, on the first anode surface 50a, an upstream connection flow path 57a connecting the fuel gas supply manifold hole 56 and the fuel gas flow path 57 is provided. On the first anode surface 50a, a downstream connection flow path 57b connecting the fuel gas discharge manifold hole 51 and the fuel gas flow path 57 is provided.

[0051] <Porous body flow path plate 60> As shown in FIGS. 1 to 3, the porous flow channel plate 60 is provided between the cathode side separator 40 and the power generation unit 20. The porous flow channel plate 60 is provided so as to cover the entire power generation unit 20. The porous flow channel plate 60 has a large number of holes 61a, 61b formed in a mesh shape. The porous flow channel plate 60 is, for example, lath cut metal or expanded metal.

[0052] <Porous sheet 70> As shown in FIGS. 1 to 3, a porous sheet 70 is provided between the cathode side separator 40 and the porous flow channel plate 60. The diameter of the holes (not shown) of the porous sheet 70 is smaller than the diameter of the holes 61a, 61b of the porous flow channel plate 60. More specifically, the maximum value of the diameter of the holes of the porous sheet 70 is smaller than the minimum value of the diameter of the holes 61a, 61b of the porous flow channel plate 60.

[0053] As shown in FIGS. 2 and 3, the porous sheet 70 has a plurality of low density portions 73 and a plurality of high density portions 74. The low density portions 73 are filled in each oxidant gas flow channel 47. The high density portions 74 are located between the low density portions 73 and are in contact with the cathode side separator 40. The high density portions 74 have a higher density than the low density portions 73.

[0054] As shown in FIG. 4, the porous sheet 70 has, for example, a porous base material 71 and a hydrophilic additive 72 provided on the surface of the base material 71. The base material 71 is formed of, for example, carbon fiber. The additive 72 is formed of, for example, an epoxy resin.

[0055] It is preferable that the rigidity of the porous sheet 70 is lower than the rigidity of the gas diffusion layer 25. <Manifold holes 11 to 16 of single cell 10> As shown in FIG. 1, in the single cell 10, a fuel gas discharge manifold hole 11 penetrating the single cell 10 in the stacking direction Z is formed by fuel gas discharge manifold holes 31, 41, 51. Further, a fuel gas discharge manifold (not shown) that penetrates the fuel cell stack and discharges fuel gas is formed by the fuel gas discharge manifold holes 11 of the plurality of single cells 10.

[0056] In the single cell 10, a cooling medium supply manifold hole 12 penetrating the single cell 10 in the stacking direction Z is formed by cooling medium supply manifold holes 32, 42, 52. Further, a cooling medium supply manifold (not shown) that penetrates the fuel cell stack and supplies cooling medium is formed by the cooling medium supply manifold holes 12 of the plurality of single cells 10.

[0057] In the single cell 10, an oxidant gas supply manifold hole 13 penetrating the single cell 10 in the stacking direction Z is formed by oxidant gas supply manifold holes 33, 43, 53. Further, an oxidant gas supply manifold (not shown) that penetrates the fuel cell stack and supplies oxidant gas is formed by the oxidant gas supply manifold holes 13 of the plurality of single cells 10.

[0058] In the single cell 10, an oxidant gas discharge manifold hole 14 penetrating the single cell 10 in the stacking direction Z is formed by oxidant gas discharge manifold holes 34, 44, 54. Further, an oxidant gas discharge manifold (not shown) that penetrates the fuel cell stack and discharges oxidant gas is formed by the oxidant gas discharge manifold holes 14 of the plurality of single cells 10.

[0059] In the single cell 10, a cooling medium discharge manifold hole 15 penetrating the single cell 10 in the stacking direction Z is formed by cooling medium discharge manifold holes 35, 45, 55. Further, a cooling medium discharge manifold (not shown) that penetrates the fuel cell stack and discharges cooling medium is formed by the cooling medium discharge manifold holes 15 of the plurality of single cells 10.

[0060] In the single cell 10, a fuel gas supply manifold hole 16 penetrating the single cell 10 in the stacking direction Z is formed by the fuel gas supply manifold holes 36, 46, 56. Further, a fuel gas supply manifold (not shown) that penetrates the fuel cell stack and supplies fuel gas is formed by the fuel gas supply manifold holes 16 of the plurality of single cells 10.

[0061] Next, a procedure for manufacturing the fuel cell stack of the present embodiment will be described. First, as shown in FIG. 5, the cathode side separator 40, the anode side separator 50, the power generation unit 20, the porous flow path plate 60, and the porous sheet 70 are arranged as follows to form the single cell 10. That is, in the stacking direction Z, the power generation unit 20 is located between the cathode side separator 40 and the anode side separator 50. Further, in the stacking direction Z, the porous flow path plate 60 is located between the cathode side separator 40 and the power generation unit 20. Further, in the stacking direction Z, the porous sheet 70 having a uniform density is located between the cathode side separator 40 and the porous flow path plate 60. The porous sheet 70 has a certain thickness. Then, a plurality of single cells 10 are stacked to form the stack body 80. Note that FIG. 5 shows only one single cell 10 constituting the stack body 80. Further, the stack body 80 is sandwiched from both sides in the stacking direction Z by two end plates (not shown).

[0062] Next, as shown by the arrow in FIG. 5, a compressive load is applied to the stack body 80 in the stacking direction Z. At this time, for example, a compressive load is applied to the stack body 80 by the axial force of bolts that fasten the stack body 80 and the end plates.

[0063] As a result, as shown in FIG. 6, the porous sheet 70 is compressed by the cathode side separator 40, and the low density portion 73 and the high density portion 74 are formed. Next, the operation of the present embodiment will be described.

[0064] In such a fuel cell stack, the oxidant gas is supplied to each single cell 10 through the oxidant gas supply manifold, and is supplied to the oxidant gas flow path 47 and the porous flow path plate 60 through the upstream connection flow path 47a of the cathode side separator 40. The oxidant gas is diffused into the power generation section 20 through the holes 61a and 61b of the porous flow path plate 60. Also, a part of the oxidant gas is discharged to the oxidant gas discharge manifold through the downstream connection flow path 47b.

[0065] The fuel gas is supplied to each single cell 10 through the fuel gas supply manifold, and is supplied to the fuel gas flow path 57 through the upstream connection flow path 57a of the anode side separator 50. The fuel gas flows through the fuel gas flow path 57 and is diffused into the power generation section 20. Also, a part of the fuel gas is discharged to the fuel gas discharge manifold through the downstream connection flow path 57b.

[0066] In the power generation section 20, power generation is performed by an electrochemical reaction between the oxidant gas and the fuel gas. The cooling medium is supplied to the cooling medium flow paths 48 and 58 formed between adjacent single cells 10 through the cooling medium supply manifold. The cooling medium cools the power generation section 20 by flowing through the cooling medium flow paths 48 and 58. Also, the cooling medium is discharged from the cooling medium flow paths 48 and 58 to the fuel gas discharge manifold.

[0067] Incidentally, as shown in FIG. 7, the fuel cell stack of the comparative example is composed of a single cell 110 including a flat plate-shaped cathode-side separator 140 and a porous flow path plate 60 provided between the cathode-side separator 140 and the power generation unit 20. In this case, if the same configuration as the anode-side separator 50 of the present embodiment is used as the anode-side separator 150, the following disadvantages occur. That is, since the flow path through which the cooling medium flows is constituted only by the cooling medium flow path 158 of the anode-side separator 150, if the cross-sectional area of the cooling medium flow path 158 is increased to improve the cooling performance, the cross-sectional area of the fuel gas flow path 157 increases accordingly. As a result, the pressure loss of the fuel gas flowing through the fuel gas flow path 157 becomes small, making it difficult for the generated water present in the fuel gas flow path 157 to be discharged by the fuel gas.

[0068] In this regard, according to the present embodiment, the flow path through which the cooling medium flows is constituted by the cooling medium flow paths 48 and 58 of both the cathode-side separator 40 and the anode-side separator 50. Therefore, the cross-sectional areas of the flow paths 48 and 58 through which the cooling medium flows can be increased without increasing the cross-sectional area of the fuel gas flow path 57. Thereby, while enhancing the gas diffusibility of the fuel gas, the cooling performance can be enhanced.

[0069] Further, the low-density portion 73 of the porous sheet 70 is filled in the oxidant gas flow path 47 of the cathode-side separator 40. For this reason, the oxidant gas flows through the holes 61a and 61b of the porous flow path plate 60 having a relatively low pressure loss. Thereby, the gas diffusibility of the oxidant gas can be enhanced.

[0070] Further, as shown by the arrow in FIG. 3, the generated water generated in the power generation unit 20 moves to the porous sheet 70 through the holes 61a and 61b of the porous flow path plate 60. Here, since the porous sheet 70 has a low-density portion 73 and a high-density portion 74, the generated water that has moved to the porous sheet 70 moves toward the cathode-side separator 40 through the holes of the high-density portion 74 having a relatively high density due to capillary action. Further, the generated water present in the low-density portion 73 moves toward the high-density portion 74. Then, the generated water that has moved to the cathode-side separator 40 is discharged toward the downstream side by the pressure gradient between the upstream side and the downstream side of the oxidant gas flow path 47.

[0071] The effects of the present embodiment will be described. (1-1) A flow path through which the cooling medium flows is configured by the cooling medium flow path 48 of the cathode-side separator 40 and the cooling medium flow path 58 of the anode-side separator 50.

[0072] According to such a configuration, since the above-described operation is achieved, it is possible to enhance the gas diffusibility of the fuel gas and the drainage of the generated water present in the fuel gas flow path 57 while enhancing the cooling performance. Further, the low-density portion 73 of the porous sheet 70 is filled in the oxidant gas flow path 47 of the cathode-side separator 40.

[0073] According to such a configuration, since the above-described operation is achieved, it is possible to enhance the drainage of the generated water present in the oxidant gas flow path 47. (1-2) The porous sheet 70 is formed of carbon fibers.

[0074] According to such a configuration, it is possible to easily embody the porous sheet 70 having holes smaller than the holes 61a and 61b of the porous flow path plate 60 and having conductivity and flexibility. (1-3) The porous sheet 70 has a porous base material 71 and a hydrophilic additive 72 provided on the surface of the base material 71.

[0075] According to such a configuration, the generated water that has moved to the porous sheet 70 is more likely to gather in the high-density portion 74. Therefore, the drainage performance can be further enhanced. (1-4) The rigidity of the porous sheet 70 is lower than that of the gas diffusion layer 25.

[0076] According to such a configuration, when manufacturing the fuel cell stack, the porous sheet 70 is preferentially compressed rather than the gas diffusion layer 25 by the compression load. As a result, it is possible to suppress deformation of the gas diffusion layer 25 due to bending and deforming the porous sheet 70 to form the low-density portion 73 and the high-density portion 74.

[0077] (1-5) In the method for manufacturing a fuel cell stack, first, the cathode-side separator 40, the porous sheet 70, the porous body flow path plate 60, the power generation unit 20, and the anode-side separator 50 are arranged in this order in the stacking direction Z to form a single cell 10. Then, a plurality of single cells 10 are stacked in the stacking direction Z to form a stack body 80. Next, a compression load is applied to the stack body 80 in the stacking direction Z to form a low-density portion 73 and a high-density portion 74 in the porous sheet 70.

[0078] According to the same method, by making a simple change such as arranging a porous sheet 70 with a uniform density between the cathode-side separator 40 and the porous body flow path plate 60 with respect to the process of manufacturing the conventional stack body 80, the low-density portion 73 and the high-density portion 74 can be formed.

[0079] <Second Embodiment> Hereinafter, a second embodiment of the method for manufacturing a fuel cell stack will be described with reference to FIGS. 8 to 10. Note that the configuration of the fuel cell stack of the second embodiment is the same as that of the fuel cell stack of the first embodiment.

[0080] First, as shown in FIG. 8, a porous sheet 70 having the same density as the cathode-side separator 40 in the stacking direction Z is overlaid. Next, by applying a compressive load to the cathode-side separator 40 and the porous sheet 70 in the stacking direction Z, as shown in FIG. 9, the porous sheet 70 is compressed by the cathode-side separator 40 to form a low-density portion 73 and a high-density portion 74. In this way, a partial laminate 90 in which the cathode-side separator 40 and the porous sheet 70 are laminated is formed.

[0081] Next, as shown in FIG. 10, the partial laminate 90, the anode-side separator 50, the power generation unit 20, and the porous body flow path plate 60 are arranged to form a single cell 10. That is, in the stacking direction Z, the power generation unit 20 is positioned between the partial laminate 90 and the anode-side separator 50, and the porous body flow path plate 60 is positioned between the partial laminate 90 and the power generation unit 20.

[0082] Next, a stack body 80 is formed by stacking a plurality of single cells 10. The operation and effect of this embodiment will be described. (2-1) In the method for manufacturing a fuel cell stack, first, a partial laminate 90 is formed by overlaying the cathode-side separator 40 and the porous sheet 70 in the stacking direction Z and applying a compressive load, and a low-density portion 73 and a high-density portion 74 are formed in the porous sheet 70. Next, the partial laminate 90, the porous body flow path plate 60, the power generation unit 20, and the anode-side separator 50 are arranged in this order in the stacking direction Z to form a single cell 10. Then, a plurality of single cells 10 are stacked to form a stack body 80.

[0083] According to this method, after forming the partial laminate 90 in advance, a single cell 10 is formed using the partial laminate 90. Therefore, the low-density portion 73 and the high-density portion 74 can be formed with high precision.

[0084] <Modification Example> This embodiment can be implemented with the following modifications. This embodiment and the following modification examples can be implemented in combination with each other within a technically non-conflicting range.

[0085] · The rigidity of the porous sheet 70 may be the same as that of the gas diffusion layer 25, or may be higher than that of the gas diffusion layer 25. · The additive 72 may be mixed with the carbon material to form the base material 71. Even in this case, the effects according to the above effects (1-3) can be achieved.

[0086] · The porous sheet 70 may not have the additive 72. · The porous sheet 70 is not limited to being formed of carbon fibers. In short, any material having conductivity and flexibility and having the low density portion 73 and the high density portion 74 may be used.

Explanation of reference numerals

[0087] 10… Single cell 11… Fuel gas discharge manifold hole 12… Cooling medium supply manifold hole 13… Oxidant gas supply manifold hole 14… Oxidant gas discharge manifold hole 15… Cooling medium discharge manifold hole 16… Fuel gas supply manifold hole 20… Power generation unit 21… MEA 22… Electrolyte membrane 23… Cathode electrode 24… Anode electrode 25… Gas diffusion layer 30… Resin frame 30A… Hole 31… Fuel gas discharge manifold hole 32… Cooling medium supply manifold hole 33… Oxidant gas supply manifold hole 34… Oxidant gas discharge manifold hole 35… Cooling medium discharge manifold hole 36… Fuel gas supply manifold hole 40… Cathode side separator 40a… First cathode surface 40b… Second cathode surface 41…Fuel gas discharge manifold hole 42…Cooling medium supply manifold hole 43…Oxidant gas supply manifold hole 44…Oxidant gas discharge manifold hole 45…Cooling medium discharge manifold hole 46…Fuel gas supply manifold hole 47…Oxidant gas flow path 47a…Upstream connection flow path 47b…Downstream connection flow path 48…Cooling medium flow path 50…Anode side separator 50a…First anode surface 50b…Second anode surface 51…Fuel gas discharge manifold hole 52…Cooling medium supply manifold hole 53…Oxidant gas supply manifold hole 54…Oxidant gas discharge manifold hole 55…Cooling medium discharge manifold hole 56…Fuel gas supply manifold hole 57…Fuel gas flow path 57a…Upstream connection flow path 57b…Downstream connection flow path 58…Cooling medium flow path 60…Porous flow path plate 61a,61b…Holes 70…Porous sheet 71…Base material 72…Additive 73…Low density part 74…High density part 80…Stack body 90…Partial laminate 110…Single cell 140…Cathode side separator 150…Anode side separator 157…Fuel gas flow path 158…Cooling medium flow path

Claims

1. A fuel cell stack composed of a plurality of single cells stacked together, wherein each of the single cells has a power generation part, a cathode-side separator, an anode-side separator that sandwiches the power generation part with the cathode-side separator in the stacking direction of the single cells, and a porous flow path plate provided between the cathode-side separator and the power generation part, the cathode-side separator having a first cathode surface on which a plurality of groove-shaped oxidant gas flow paths through which oxidant gas flows are arranged side by side, and a second cathode surface on the opposite side of the first cathode surface, on which a plurality of cooling medium flow paths through which a cooling medium flows are arranged side by side, the anode-side separator having a first anode surface on which a plurality of groove-shaped fuel gas flow paths through which fuel gas flows are arranged side by side, and a second anode surface on the opposite side of the first anode surface, on which a plurality of groove-shaped cooling medium flow paths through which the cooling medium flows are arranged side by side, a porous sheet having conductivity and flexibility is provided between the cathode-side separator and the porous flow path plate, the pore diameter of the porous sheet being smaller than the pore diameter of the porous flow path plate, the porous sheet having a plurality of low-density parts filled in each of the oxidant gas flow paths, and high-density parts located between the low-density parts, contacting the cathode-side separator and having a higher density than the low-density parts, a fuel cell stack.

2. The porous sheet is formed of carbon fibers. The fuel cell stack according to Claim 1.

3. The porous sheet has a porous base material and a hydrophilic additive provided on the surface of the base material. The fuel cell stack according to Claim 1 or Claim 2.

4. The power generation part has a membrane electrode assembly and a pair of gas diffusion layers that sandwich the membrane electrode assembly in the stacking direction, the rigidity of the porous sheet being lower than the rigidity of the gas diffusion layer. The fuel cell stack according to Claim 1 or Claim 2.

5. A method for manufacturing the fuel cell stack according to Claim 1 or Claim 2, The power generation part is located between the cathode-side separator and the anode-side separator in the stacking direction, the porous body flow path plate is located between the cathode-side separator and the power generation part, and the porous sheet with a uniform density is located between the cathode-side separator and the porous body flow path plate. After arranging the cathode-side separator, the anode-side separator, the power generation part, the porous body flow path plate, and the porous sheet to form the single cell, a step of stacking a plurality of the single cells to form a stack body; A step of forming the low-density part and the high-density part by applying a compressive load to the stack body in the stacking direction; A method for manufacturing a fuel cell stack.

6. A method for manufacturing the fuel cell stack according to claim 1 or claim 2, In a state where the cathode-side separator and the porous sheet with a uniform density are overlapped, a compressive load is applied to the cathode-side separator and the porous sheet in the stacking direction to form the low-density part and the high-density part, thereby forming a partially laminated body in which the cathode-side separator and the porous sheet are laminated. After that, the power generation part is located between the partially laminated body and the anode-side separator in the stacking direction, and the porous body flow path plate is located between the partially laminated body and the power generation part. A step of forming the single cell by arranging the partially laminated body, the anode-side separator, the power generation part, and the porous body flow path plate; A step of forming a stack body by stacking a plurality of the single cells; A method for manufacturing a fuel cell stack.

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