JP7710138B2 - Fuel cell stack and method for manufacturing the fuel cell stack - Google Patents

Description

The present invention relates to a fuel cell stack and a method for manufacturing a fuel cell stack.

Patent Document 1 discloses a fuel cell that is constructed by stacking multiple unit cells. The unit cell includes a membrane electrode assembly (MEA), a cathode separator that sandwiches the membrane electrode assembly, and an anode separator.

A gas diffusion layer made of expanded metal is provided between the cathode separator and the MEA. On the surface of the cathode separator facing the gas diffusion layer, multiple gas supply grooves for supplying oxidant gas are arranged in a row.

The anode separator has a gas supply groove for supplying fuel gas.

JP 2008-311109 A

In the case of the fuel cell disclosed in Patent Document 1, the oxidant gas flows preferentially through the gas supply grooves, which have a larger flow path cross-sectional area than the holes in the gas diffusion layer made of expanded metal, i.e., have a lower pressure loss. This causes problems such as the oxidant gas not diffusing easily through the gas diffusion layer and the generated water remaining in the gas diffusion layer and being difficult to drain.

In addition, improved cooling performance is also desirable for fuel cells to prevent temperature increases caused by power generation.

The fuel cell stack for solving the above problem is a fuel cell stack formed by stacking a plurality of unit cells, each of which comprises a power generation section, a cathode side separator, an anode side separator that sandwiches the power generation section between the cathode side separator in the stacking direction of the unit cells, and a porous flow path plate provided between the cathode side separator and the power generation section. The cathode side separator has a first cathode surface on which a plurality of groove-shaped oxidant gas flow paths through which an oxidant gas flows are arranged in a row, and a second cathode surface on the side opposite to the first cathode surface on which a plurality of cooling medium flow paths through which a cooling medium flows are arranged in a row. The anode side separator is a fuel cell stack formed by stacking a plurality of unit cells, each of which comprises a power generation section, a cathode side separator, a cathode side separator, and a porous flow path plate provided between the cathode side separator and the power generation section. The fuel gas supply device has a first anode surface on which a plurality of groove-shaped fuel gas flow paths through which the 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. Between the cathode-side separator and the porous flow path plate, a porous sheet having electrical conductivity and flexibility is provided, and the diameter of the holes in the porous sheet is smaller than the diameter of the holes in the porous flow path plate. The porous sheet has 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, abutting against the cathode-side separator, and having a higher density than the low-density parts.

Conventionally, there is a fuel cell stack that is constructed by stacking unit cells each including a flat separator as a cathode side separator and a porous flow passage plate provided between the separator and the power generation section. In this case, if an anode side separator having a first anode surface on which a plurality of groove-shaped fuel gas flow passages are arranged side by side and a second anode surface on which a plurality of groove-shaped cooling medium flow passages through which a cooling medium flows are arranged side by side is used, the following inconvenience occurs. That is, since the flow passage through which the cooling medium flows is composed only of the cooling medium flow passage of the anode side separator, if the cross-sectional area of the cooling medium flow passage is increased to improve cooling performance, the cross-sectional area of the fuel gas flow passage is increased accordingly. As a result, the pressure loss of the fuel gas flowing through the fuel gas flow passage is reduced, and the generated water present in the fuel gas flow passage is less likely to be discharged by the fuel gas.

In this regard, according to the above configuration, the flow path through which the cooling medium flows is formed 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. This improves the drainage of generated water present in the fuel gas flow path while improving cooling performance.

In addition, with the above configuration, the oxidant gas flow path of the cathode separator is filled with the low density portion of the porous sheet, so that the oxidant gas flows through the holes of the porous flow path plate, which has a relatively low pressure loss. This improves the gas diffusion of the oxidant gas.

The generated water in the power generation section moves to the porous sheet through the holes in the porous flow path plate. Here, since the porous sheet has a low density section and a high density section, the generated water that has moved to the porous sheet moves toward the cathode side separator through the holes in the relatively high density section due to capillary action. The generated water present in the low density section moves toward the high density section. The generated water that has moved to the cathode side separator is then discharged toward the downstream side due to the pressure gradient between the upstream and downstream sides of the oxidant gas flow path.

Therefore, gas diffusion, drainage, and cooling properties can be improved.
In the above fuel cell stack, the porous sheet is preferably made of carbon fiber.

According to this configuration, a porous sheet having smaller pores than the pores of the porous flow path plate and having electrical conductivity and flexibility can be easily realized.
In the above fuel cell stack, the porous sheet preferably has a porous substrate and a hydrophilic additive provided on a surface of the substrate.

According to this configuration, the generated water that has migrated to the porous sheet is more likely to collect in the high density portion, thereby further improving the drainage performance.
In the above fuel cell stack, it is preferable that the power generation portion has a membrane electrode assembly and a pair of gas diffusion layers sandwiching the membrane electrode assembly in the stacking direction, and that the rigidity of the porous sheet is lower than the rigidity of the gas diffusion layers.

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

Here, according to the above configuration, the porous sheet is compressed preferentially by the compressive load over the gas diffusion layer. This makes it possible to suppress deformation of the gas diffusion layer caused by bending and deforming the porous sheet to form the low-density portion and the high-density portion.

A method for manufacturing a fuel cell stack to solve the above problem includes the steps of: arranging the cathode-side separator, the anode-side separator, the power generation section, the porous flow plate, and the porous sheet to form the unit cell so that the power generation section is located between the cathode-side separator and the anode-side separator in the stacking direction, the porous flow plate is located between the cathode-side separator and the power generation section, and the porous sheet of uniform density is located between the cathode-side separator and the porous flow plate, and then stacking a plurality of the unit cells to form a stack body; and forming the low-density portion and the high-density portion by applying a compressive load to the stack body in the stacking direction.

According to this method, low-density and high-density sections can be formed by making a simple modification to the conventional process for manufacturing the stack body, such as placing a porous sheet of uniform density between the cathode-side separator and the porous flow path plate.

The method for manufacturing a fuel cell stack to solve the above problem includes the steps of: forming a partial stack in which the cathode-side separator and the porous sheet having a uniform density are stacked together by applying a compressive load to the cathode-side separator and the porous sheet in the stacking direction to form the low-density portion and the high-density portion; forming the unit cell by arranging the partial stack, the anode-side separator, the power generation portion, and the porous flow path plate so that the power generation portion is located between the partial stack and the anode-side separator in the stacking direction, and the porous flow path plate is located between the partial stack and the power generation portion; and forming a stack body by stacking the unit cells.

According to this method, a partial laminate having low-density and high-density sections is first formed, and then a unit cell is formed using the partial laminate. This allows the low-density and high-density sections to be formed with high precision.

The present invention can improve gas diffusion, drainage, and cooling.

FIG. 1 is an exploded perspective view of a fuel cell stack according to a first embodiment. FIG. 2 is a cross-sectional view focusing on one unit cell that constitutes the fuel cell stack of FIG. FIG. 3 is a cross-sectional view of one unit cell that constitutes the fuel cell stack of FIG. FIG. 4 is an enlarged plan view of a porous sheet that constitutes the fuel cell stack of FIG. FIG. 5 is a cross-sectional view showing how a cathode separator and an anode separator are laminated on a power generating section, a porous flow passage plate, and a uniform density porous sheet in a manufacturing process of the fuel cell stack of FIG. FIG. 6 is a cross-sectional view of a unit cell in a state where a compressive load is applied to the stack body in the stacking direction. FIG. 7 is a cross-sectional view focusing on one unit cell that constitutes a fuel cell stack according to a comparative example. FIG. 8 is a cross-sectional view showing how a cathode separator is laminated on a porous sheet of uniform density in the method for manufacturing a fuel cell stack according to the second embodiment. FIG. 9 is a cross-sectional view of a partial laminate. FIG. 10 is a cross-sectional view showing how the partial laminate and the anode-side separator of FIG. 8 are laminated on the power generation section and the porous flow passage plate.

First Embodiment
A first embodiment of a fuel cell stack will now be described with reference to FIGS. 1 to 7. FIG.
As shown in FIG. 1, the fuel cell stack is configured by stacking a plurality of unit cells 10 .

<Single cell 10>
The unit cell 10 includes a power generation section 20, a cathode side separator 40, and an anode side separator 50 that sandwiches the power generation section 20 between the cathode side separator 40 in the stacking direction of the unit cell 10. The unit cell 10 also includes a porous flow path plate 60 provided between the cathode side separator 40 and the power generation section 20, and a porous sheet 70 provided between the cathode side separator 40 and the porous flow path plate 60. The unit cell 10 also includes a resin frame 30 that holds the power generation section 20.

In this embodiment, the unit cell 10 is a rectangular plate having a pair of long sides and a pair of short sides. In the following description, the long side direction of the unit cell 10 is referred to as the length direction X, the short side direction of the unit cell 10 is referred to as the width direction Y, and the stacking direction of the unit cell 10 is referred to as the stacking direction Z.

<Power generation unit 20>
As shown in FIGS. 2 and 3, the power generation section 20 has 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.

The power generating section 20 has a rectangular thin plate shape.
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.

<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 center of the resin frame 30. The hole 30A in this embodiment is rectangular and slightly smaller than the power generation section 20. The inner peripheral edge of the hole 30A is joined to the outer peripheral edge of the power generation section 20 in an overlapping state in the stacking direction Z. The resin frame 30 has an outer peripheral edge that constitutes the outer peripheral edge of the unit cell 10. The resin frame 30 in this embodiment is in the form of a rectangular plate.

At one end of the resin frame 30 in the longitudinal direction X (the left side in FIG. 1), there are a fuel gas exhaust manifold hole 31, a cooling medium supply manifold hole 32, and an oxidizer gas supply manifold hole 33.

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

At the other end side of the resin frame 30 in the longitudinal direction X (the right side in FIG. 1), an oxidizer gas discharge manifold hole 34, a cooling medium discharge manifold hole 35, and a fuel gas supply manifold hole 36 are provided.

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

<Cathode-side separator 40>
As shown in FIG. 1, one end side in the longitudinal direction X of the cathode separator 40 (the left side in FIG. 1) is provided with a fuel gas discharge manifold hole 41, a coolant supply manifold hole 42, and an oxidant gas supply manifold hole 43.

In this embodiment, the fuel gas exhaust manifold hole 41, the cooling medium supply manifold hole 42, and the oxidant gas supply manifold hole 43 are provided in this order from one end side in the width direction Y (the upper side in FIG. 1).

The other end of the cathode separator 40 in the longitudinal direction X (the right side in FIG. 1) is provided with an oxidant gas discharge manifold hole 44, a cooling medium discharge manifold hole 45, and a fuel gas supply manifold hole 46.

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

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 separator 40 is formed by pressing a conductive metal plate material, such as a stainless steel plate or a titanium plate.

The first cathode surface 40a has a plurality of groove-shaped oxidant gas flow paths 47 arranged in a line in the portion overlapping with the power generation unit 20 in the stacking direction Z, through which the oxidant gas flows. The oxidant gas is, for example, air containing oxygen.

The second cathode surface 40b has a number of groove-shaped cooling medium flow paths 48 arranged in a line in the portion overlapping with the power generation unit 20 in the stacking direction Z, through which a cooling medium flows. The cooling medium is, for example, water containing antifreeze.

A coolant flow field 48 is located between adjacent oxygen-containing gas flow fields 47 .
As shown in FIG. 1, the first cathode surface 40 a is provided with an upstream connection flow passage 47 a that connects the oxidizing gas supply manifold hole 43 and the oxidizing gas flow passage 47 .

The first cathode surface 40 a is provided with a downstream connection flow passage 47 b that connects the oxidant gas discharge manifold hole 44 and the oxidant gas flow passage 47 .
<Anode side separator 50>
As shown in FIG. 1, one end side (left side in FIG. 1) of the anode side separator 50 in the longitudinal direction X is provided with a fuel gas discharge manifold hole 51, a cooling medium supply manifold hole 52, and an oxidant gas supply manifold hole 53.

In this embodiment, the fuel gas exhaust manifold hole 51, the cooling medium supply manifold hole 52, and the oxidant gas supply manifold hole 53 are provided in this order from one end side in the width direction Y (the upper side in FIG. 1).

The other end of the anode separator 50 in the longitudinal direction X (the right side in FIG. 1) is provided with an oxidant gas discharge manifold hole 54, a cooling medium discharge manifold hole 55, and a fuel gas supply manifold hole 56.

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

As shown in FIG. 2, the anode-side separator 50 has a first anode surface 50a and a second anode surface 50b which is the surface opposite to the first anode surface 50a.
The anode-side separator 50 is formed by pressing a conductive metal plate material, such as a stainless steel plate or a titanium plate.

The first anode surface 50a has a number of groove-shaped fuel gas flow paths 57 arranged in a line in the portion overlapping with the power generation section 20 in the stacking direction Z, through which fuel gas flows. The fuel gas is, for example, hydrogen.

The second anode surface 50b has a plurality of groove-shaped coolant flow paths 58 arranged side by side in a portion overlapping with the power generation section 20 in the stacking direction Z, through which a coolant flows.
A coolant flow field 58 is located between adjacent fuel gas flow fields 57 .

The width of the cooling medium flow passage 58 is the same as the width of the cooling medium flow passage 48 of the cathode-side separator 40. The cooling medium flow passage 58 and the cooling medium flow passage 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 passage 58 and the cooling medium flow passage 48.

As shown in FIG. 1, the first anode surface 50 a is provided with an upstream connection flow passage 57 a that connects the fuel gas supply manifold hole 56 and a fuel gas flow passage 57 .
The first anode surface 50 a is provided with a downstream connection flow passage 57 b that connects the fuel gas discharge manifold hole 51 and the fuel gas flow passage 57 .

<Porous Flow Channel Plate 60>
1 to 3, the porous flow passage plate 60 is provided between the cathode separator 40 and the power generation section 20. The porous flow passage plate 60 is provided so as to cover the entire power generation section 20. The porous flow passage plate 60 has a large number of holes 61a, 61b formed in a mesh pattern. The porous flow passage plate 60 is made of, for example, lath cut metal or expanded metal.

<Porous sheet 70>
1 to 3, a porous sheet 70 is provided between the cathode separator 40 and the porous flow path 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 path 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 path plate 60.

As shown in Figures 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 passage 47. The high-density portions 74 are located between the low-density portions 73 and abut against the cathode-side separator 40. The high-density portions 74 have a higher density than the low-density portions 73.

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

The rigidity of the porous sheet 70 is preferably lower than the rigidity of the gas diffusion layer 25 .
<Manifold holes 11 to 16 of unit cell 10>
1 , in the unit cell 10, the fuel gas exhaust manifold holes 31, 41, and 51 form a fuel gas exhaust manifold hole 11 that penetrates the unit cell 10 in the stacking direction Z. In addition, the fuel gas exhaust manifold holes 11 of the multiple unit cells 10 form a fuel gas exhaust manifold (not shown) that penetrates the fuel cell stack and exhausts fuel gas.

In the single cell 10, the cooling medium supply manifold holes 32, 42, and 52 form a cooling medium supply manifold hole 12 that penetrates the single cell 10 in the stacking direction Z. In addition, the cooling medium supply manifold holes 12 of multiple single cells 10 form a cooling medium supply manifold (not shown) that penetrates the fuel cell stack and supplies the cooling medium.

In the single cell 10, the oxidant gas supply manifold holes 33, 43, and 53 form an oxidant gas supply manifold hole 13 that penetrates the single cell 10 in the stacking direction Z. In addition, the oxidant gas supply manifold holes 13 of multiple single cells 10 form an oxidant gas supply manifold (not shown) that penetrates the fuel cell stack and supplies oxidant gas.

In the single cell 10, the oxidant gas exhaust manifold holes 34, 44, and 54 form an oxidant gas exhaust manifold hole 14 that penetrates the single cell 10 in the stacking direction Z. In addition, the oxidant gas exhaust manifold holes 14 of multiple single cells 10 form an oxidant gas exhaust manifold (not shown) that penetrates the fuel cell stack and exhausts oxidant gas.

In the single cell 10, the cooling medium discharge manifold holes 35, 45, and 55 form a cooling medium discharge manifold hole 15 that penetrates the single cell 10 in the stacking direction Z. In addition, the cooling medium discharge manifold holes 15 of multiple single cells 10 form a cooling medium discharge manifold (not shown) that penetrates the fuel cell stack and discharges the cooling medium.

In the single cell 10, the fuel gas supply manifold holes 36, 46, and 56 form a fuel gas supply manifold hole 16 that penetrates the single cell 10 in the stacking direction Z. In addition, the fuel gas supply manifold holes 16 of multiple single cells 10 form a fuel gas supply manifold (not shown) that penetrates the fuel cell stack and supplies fuel gas.

Next, a procedure for manufacturing the fuel cell stack of this embodiment will be described.
First, as shown in FIG. 5, the cathode-side separator 40, the anode-side separator 50, the power generation section 20, the porous flow passage plate 60, and the porous sheet 70 are arranged as follows to form a single cell 10. That is, in the stacking direction Z, the power generation section 20 is located between the cathode-side separator 40 and the anode-side separator 50. In addition, in the stacking direction Z, the porous flow passage plate 60 is located between the cathode-side separator 40 and the power generation section 20. In addition, in the stacking direction Z, a porous sheet 70 with a uniform density is located between the cathode-side separator 40 and the porous flow passage plate 60. The porous sheet 70 has a constant thickness. Then, a stack body 80 is formed by stacking a plurality of single cells 10. Note that FIG. 5 shows only one single cell 10 constituting the stack body 80. In addition, the stack body 80 is sandwiched from both sides in the stacking direction Z by two end plates not shown.

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

As a result, as shown in FIG. 6, the porous sheet 70 is compressed by the cathode separator 40 to form a low density portion 73 and a high density portion 74 .
Next, the operation of this embodiment will be described.

In such a fuel cell stack, the oxidant gas is supplied to each unit cell 10 through an oxidant gas supply manifold, and is supplied to the oxidant gas flow passage 47 and the porous flow passage plate 60 through the upstream connection flow passage 47a of the cathode separator 40. The oxidant gas is diffused to the power generation section 20 through the holes 61a and 61b of the porous flow passage plate 60. In addition, a portion of the oxidant gas is discharged to the oxidant gas discharge manifold through the downstream connection flow passage 47b.

The fuel gas is supplied to each unit cell 10 through a fuel gas supply manifold, and is supplied to the fuel gas flow passage 57 through the upstream connection passage 57a of the anode separator 50. The fuel gas flows through the fuel gas flow passage 57 and is diffused to the power generation section 20. In addition, a portion of the fuel gas is discharged to the fuel gas discharge manifold through the downstream connection passage 57b.

In the power generation section 20, the oxidant gas and the fuel gas undergo an electrochemical reaction to generate electricity.
The cooling medium is supplied through a cooling medium supply manifold to cooling medium flow paths 48, 58 formed between adjacent unit cells 10. The cooling medium cools the power generation section 20 by flowing through the cooling medium flow paths 48, 58. The cooling medium is also discharged from the cooling medium flow paths 48, 58 to the fuel gas discharge manifold.

As shown in FIG. 7, the fuel cell stack of the comparative example is constructed by stacking unit cells 110 each including a flat cathode-side separator 140 and a porous flow passage plate 60 provided between the cathode-side separator 140 and the power generation section 20. In this case, if the anode-side separator 150 has the same configuration as the anode-side separator 50 of this embodiment, the following inconvenience occurs. That is, since the flow passage through which the cooling medium flows is composed only of the cooling medium flow passage 158 of the anode-side separator 150, if the cross-sectional area of the cooling medium flow passage 158 is increased to improve cooling performance, the cross-sectional area of the fuel gas flow passage 157 is increased accordingly. As a result, the pressure loss of the fuel gas flowing through the fuel gas flow passage 157 is reduced, and the generated water present in the fuel gas flow passage 157 is less likely to be discharged by the fuel gas.

In this regard, according to the present embodiment, the cooling medium flow paths 48, 58 of both the cathode side separator 40 and the anode side separator 50 form a flow path through which the cooling medium flows. Therefore, the cross-sectional area of the flow paths 48, 58 through which the cooling medium flows can be increased without increasing the cross-sectional area of the fuel gas flow path 57. This allows the cooling performance to be improved while improving the gas diffusion of the fuel gas.

The oxidant gas flow passage 47 of the cathode separator 40 is filled with the low density portion 73 of the porous sheet 70. Therefore, the oxidant gas flows through the holes 61a and 61b of the porous flow passage plate 60, which has a relatively low pressure loss. This improves the gas diffusion of the oxidant gas.

As shown by the arrows in FIG. 3, the generated water in the power generation section 20 moves to the porous sheet 70 through the holes 61a and 61b in the porous flow passage plate 60. Here, since the porous sheet 70 has a low density section 73 and a high density section 74, the generated water that has moved to the porous sheet 70 moves toward the cathode-side separator 40 through the holes in the relatively high density section 74 due to capillary action. The generated water present in the low density section 73 moves toward the high density section 74. The generated water that has moved to the cathode-side separator 40 is then discharged toward the downstream side due to the pressure gradient between the upstream and downstream sides of the oxidant gas flow passage 47.

The effects of this embodiment will be described.
(1-1) The coolant flow field 48 of the cathode side separator 40 and the coolant flow field 58 of the anode side separator 50 form a flow field through which the coolant flows.

According to such a configuration, the above-mentioned effects are achieved, and therefore it is possible to improve the gas diffusion property of the fuel gas and the drainage property of the generated water present in the fuel gas flow channel 57, while improving the cooling property.
The oxidant gas flow channel 47 of the cathode separator 40 is filled with the low density portion 73 of the porous sheet 70 .

With this configuration, the above-mentioned effect is achieved, and therefore the drainage of the generated water present in the oxygen-containing gas flow field 47 can be improved.
(1-2) The porous sheet 70 is made of carbon fiber.

According to this configuration, the porous sheet 70 having holes smaller than the holes 61a, 61b of the porous flow passage plate 60 and having electrical conductivity and flexibility can be easily realized.
(1-3) The porous sheet 70 has a porous substrate 71 and a hydrophilic additive 72 provided on the surface of the substrate 71 .

With this configuration, the generated water that has migrated to the porous sheet 70 is more likely to collect in the high density portion 74. Therefore, the drainage performance can be further improved.
(1-4) The rigidity of the porous sheet 70 is lower than the rigidity of the gas diffusion layer 25 .

With this configuration, when manufacturing a fuel cell stack, the porous sheet 70 is compressed preferentially by the compressive load over the gas diffusion layer 25. This makes it possible to suppress deformation of the gas diffusion layer 25 caused by bending and deforming the porous sheet 70 to form the low-density portion 73 and the high-density portion 74.

(1-5) In the method of manufacturing a fuel cell stack, first, the cathode separator 40, porous sheet 70, porous flow path plate 60, power generation section 20, and anode separator 50 are arranged in this order in the stacking direction Z to form a single cell 10. Then, multiple single cells 10 are stacked in the stacking direction Z to form a stack body 80. Next, a compressive 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.

According to this method, a low-density section 73 and a high-density section 74 can be formed by making a simple modification to the conventional process for manufacturing the stack body 80, such as placing a porous sheet 70 of uniform density between the cathode-side separator 40 and the porous flow path plate 60.

Second Embodiment
A second embodiment of the method for manufacturing a fuel cell stack will now be described with reference to Figures 8 to 10. 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.

First, as shown in FIG. 8, the cathode-side separator 40 and a porous sheet 70 of uniform density are stacked in the stacking direction Z. Next, a compressive load is applied to the cathode-side separator 40 and the porous sheet 70 in the stacking direction Z, so that 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, as shown in FIG. 9. In this way, a partial laminate 90 is formed in which the cathode-side separator 40 and the porous sheet 70 are stacked.

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

Next, a plurality of unit cells 10 are stacked to form a stack body 80 .
The effects of this embodiment will be described.
(2-1) In the method of manufacturing a fuel cell stack, first, the cathode-side separator 40 and the porous sheet 70 are overlapped in the stacking direction Z and a compressive load is applied to form a partial laminate 90, 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 flow path plate 60, the power generation section 20, and the anode-side separator 50 are arranged in this order in the stacking direction Z to form a unit cell 10. Then, a plurality of unit cells 10 are stacked to form a stack body 80.

According to this method, the partial laminate 90 is formed in advance, and then the unit cell 10 is formed using the partial laminate 90. This allows the low-density portion 73 and the high-density portion 74 to be formed with high precision.

<Example of change>
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.

The rigidity of the porous sheet 70 may be the same as the rigidity of the gas diffusion layer 25 or may be higher than the rigidity of the gas diffusion layer 25 .
The additive 72 may be mixed with a carbon material to form the substrate 71. Even in this case, the same effect as the above-mentioned effect (1-3) can be obtained.

The porous sheet 70 does not need to include the additive 72 .
The porous sheet 70 is not limited to being made of carbon fiber, but may be any material as long as it is conductive, flexible, and has the low density portion 73 and the high density portion 74.

Reference Signs List 10: Single cell 11: Fuel gas exhaust manifold hole 12: Cooling medium supply manifold hole 13: Oxidant gas supply manifold hole 14: Oxidant gas exhaust manifold hole 15: Cooling medium exhaust manifold hole 16: Fuel gas supply manifold hole 20: Power generation section 21: MEA
22... Electrolyte membrane 23... Cathode electrode 24... Anode electrode 25... Gas diffusion layer 30... Resin frame 30A... Hole 31... Fuel gas exhaust manifold hole 32... Cooling medium supply manifold hole 33... Oxidant gas supply manifold hole 34... Oxidant gas exhaust manifold hole 35... Cooling medium exhaust manifold hole 36... Fuel gas supply manifold hole 40... Cathode side separator 40a... First cathode surface 40b... Second cathode surface 41... Fuel gas exhaust manifold hole 42... Cooling medium supply manifold hole 43... Oxidant gas supply manifold hole 44... Oxidant gas exhaust manifold hole 45... Cooling medium exhaust manifold hole 46... Fuel gas supply manifold hole 47... Oxidant gas flow path 47a... Upstream connecting flow path 47b... Downstream connecting flow path 48... Cooling medium flow path 50... Anode side separator 50a...First anode surface 50b...Second anode surface 51...Fuel gas exhaust manifold hole 52...Cooling medium supply manifold hole 53...Oxidant gas supply manifold hole 54...Oxidant gas exhaust manifold hole 55...Cooling medium exhaust manifold hole 56...Fuel gas supply manifold hole 57...Fuel gas flow path 57a...Upstream connecting flow path 57b...Downstream connecting flow path 58...Cooling medium flow path 60...Porous flow path plate 61a, 61b...Hole 70...Porous sheet 71...Substrate 72...Additive 73...Low density portion 74...High density portion 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 (6)

A fuel cell stack formed by stacking a plurality of unit cells,
The single cell is
A power generation section;
A cathode-side separator;
an anode-side separator sandwiching the power generation section between the anode-side separator and the cathode-side separator in the stacking direction of the unit cells;
a porous flow path plate provided between the cathode separator and the power generation section,
the cathode-side separator has a first cathode surface on which a plurality of groove-shaped oxidant gas flow paths through which an oxidant gas flows are arranged side by side, and a second cathode surface on the side opposite to 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 has a first anode surface on which a plurality of groove-shaped fuel gas flow paths through which a fuel gas flows are provided side by side, and a second anode surface on the side opposite to the first anode surface, the second anode surface having a plurality of groove-shaped coolant flow paths through which the coolant flows provided side by side,
a porous sheet having electrical conductivity and flexibility is provided between the cathode-side separator and the porous flow path plate;
The diameter of the holes in the porous sheet is smaller than the diameter of the holes in the porous flow path plate,
the porous sheet has a plurality of low-density portions filled in each of the oxidant gas flow channels, and high-density portions located between the low-density portions, abutting against the cathode-side separator, and having a higher density than the low-density portions.
Fuel cell stack. The porous sheet is formed of carbon fiber.
The fuel cell stack of claim 1 . The porous sheet has a porous substrate and a hydrophilic additive provided on a surface of the substrate.
The fuel cell stack according to claim 1 or 2. the power generation section includes a membrane electrode assembly and a pair of gas diffusion layers sandwiching the membrane electrode assembly in the stacking direction,
The rigidity of the porous sheet is lower than the rigidity of the gas diffusion layer.
The fuel cell stack according to claim 1 or 2. A method for manufacturing a fuel cell stack according to claim 1 or 2, comprising the steps of:
a step of forming the unit cell by arranging the cathode-side separator, the anode-side separator, the power generation section, the porous flow plate, and the porous sheet so that, in the stacking direction, the power generation section is located between the cathode-side separator and the anode-side separator, the porous flow plate is located between the cathode-side separator and the power generation section, and the porous sheet having a uniform density is located between the cathode-side separator and the porous flow plate, and then stacking a plurality of the unit cells to form a stack body;
and applying a compressive load to the stack body in the stacking direction to form the low density portion and the high density portion.
A method for manufacturing a fuel cell stack. A method for manufacturing a fuel cell stack according to claim 1 or 2, comprising the steps of:
a step of forming a partial laminate in which the cathode-side separator and the porous sheet having a uniform density are laminated together by applying a compressive load to the cathode-side separator and the porous sheet in the stacking direction to form the low-density portion and the high-density portion, and then forming the unit cell by arranging the partial laminate, the anode-side separator, the power generation portion, and the porous flow passage plate such that the power generation portion is located between the partial laminate and the anode-side separator and the porous flow passage plate is located between the partial laminate and the power generation portion in the stacking direction;
and forming a stack body by stacking a plurality of the unit cells.
A method for manufacturing a fuel cell stack.