Fuel battery

Abstract

To suppress the increase in the volume of a fuel battery while equalizing the cell surface pressure.SOLUTION: A fuel battery includes a fuel battery stack formed by stacking a plurality of fuel battery unit cells having a longitudinal direction and a lateral direction, and having a longitudinal end face along the longitudinal direction and a lateral end face along the lateral direction, a pair of end plates arranged to sandwich the fuel battery stack in the stacking direction, a plurality of tie rods that fasten the end plates in a direction bringing them closer to each other on the outside of the fuel battery stack to hold the fuel battery stack and the end plates, and an external manifold attached to the longitudinal end face of the fuel battery stack and supplying gas to the fuel battery stack. The external manifold is arranged between the tie rods and the longitudinal end face of the fuel battery stack in the lateral direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a fuel cell.

Background Art

[0002] A fuel cell is a power generation device that generates power by supplying a fuel gas such as hydrogen and an oxidant gas such as air. In particular, a polymer electrolyte fuel cell that applies a proton-conductive ion exchange membrane as an electrolyte of a fuel cell unit cell that constitutes a fuel cell is known. Such a fuel cell includes a fuel cell stack in which a plurality of fuel cell unit cells are stacked, and a pair of end plates arranged so as to sandwich the fuel cell stack in the stacking direction. The fuel cell stack and the end plates are held by tightening the end plates in a direction approaching each other outside the fuel cell stack with a plurality of tie rods.

[0003] Especially in the case of a fuel cell for mobility applications, increasing the output density of the fuel cell is important. For this reason, a method of reducing the volume of the fuel cell while improving the performance of the fuel cell has been sought. From the viewpoint of performance improvement, in order to reduce the contact resistance of the fuel cell unit cells in the fuel cell stack, development has been promoted to increase the tightening pressure by tie rods. Although four tie rods are arranged on the four sides of the end plate in consideration of the installation space of the external manifold, as the tightening pressure increases, the end plate bends in all directions. For this reason, the surface pressure (cell surface pressure) applied to the fuel cell unit cells becomes non-uniform, and in some cases, the fuel cell unit cells may be damaged.

[0004] For fuel cells for mobility applications, there are limitations in the mounting space, especially in terms of height. Therefore, as a fuel cell unit cell, a rectangular fuel cell unit cell having a longitudinal direction and a lateral direction may be used. In this case, when the clamping pressure by the four tie rods is increased as described above, the deflection of the end plate in the longitudinal direction becomes particularly large. To address this problem, a method of increasing the thickness of the end plate to enhance the rigidity can be considered, but in this case, the volume of the fuel cell increases.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In view of the above, an object of the present invention is to provide a fuel cell that can suppress an increase in the volume of the fuel cell while equalizing the cell surface pressure.

Means for Solving the Problems

[0007] A fuel cell according to an embodiment is a fuel cell stack in which a plurality of fuel cell unit cells having a longitudinal direction and a lateral direction are stacked, the fuel cell stack having a longitudinal end face along the longitudinal direction and a lateral end face along the lateral direction, a pair of end plates arranged so as to sandwich the fuel cell stack in the stacking direction, a plurality of tie rods for clamping the end plates in a direction approaching each other outside the fuel cell stack to hold the fuel cell stack and the end plates, and an external manifold attached to the longitudinal end face of the fuel cell stack for supplying gas to the fuel cell stack. The external manifold is arranged between the tie rod and the longitudinal end face of the fuel cell stack in the lateral direction.

[0008] Further, the fuel cell according to the embodiment includes a fuel cell stack formed by stacking a plurality of fuel cell unit cells, a pair of end plates arranged to sandwich the fuel cell stack in the stacking direction, and a plurality of tie rods that tighten the end plates in a direction approaching each other outside the fuel cell stack to hold the fuel cell stack and the end plates. The end plate has an inner end plate that contacts the fuel cell stack, an outer end plate that is arranged outside the inner end plate in the stacking direction, and a central end plate that is arranged between the inner end plate and the outer end plate. The inner end plate includes four recesses formed at the four corners of the inner end plate.

Advantages of the Invention

[0009] According to the present invention, it is possible to suppress an increase in the volume of the fuel cell while equalizing the cell surface pressure.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

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Figure 8

Figure 9

Figure 10

Figure 11

[0011] Hereinafter, with reference to FIGS. 1 to 11, a fuel cell according to an embodiment of the present invention will be described.

[0012] The fuel cell 1 is configured to generate power using a fuel gas and an oxidant gas. The fuel cell 1 can be applied to mobility (mobile bodies) such as automobiles, railway vehicles, airplanes, and ships, for example. As shown in FIGS. 1 and 2, the fuel cell 1 includes a fuel cell stack 10, a pair of end plates 20, a plurality of tie rods 30, and an external manifold 40.

[0013] As shown in FIG. 2, the fuel cell stack 10 is configured by stacking a plurality of fuel cell unit cells 11 in the stacking direction Z. The fuel cell unit cell 11 generates power by an electrochemical reaction between a fuel gas and an oxidant gas. The fuel cell unit cell 11 is the minimum unit of the fuel cell stack 10 and may be simply called a unit cell or a cell.

[0014] The fuel cell unit cell 11 has a rectangular shape when viewed along the stacking direction Z. That is, the fuel cell unit cell 11 has a longitudinal direction X and a short side direction Y. The longitudinal direction X and the short side direction Y are orthogonal to each other. Both the longitudinal direction X and the short side direction Y are orthogonal to the stacking direction Z. In this case, the fuel cell stack 10 has a longitudinal end face 10a along the longitudinal direction X and a short side end face 10b along the short side direction Y.

[0015] As shown in FIG. 3, the fuel cell unit cell 11 includes an electrolyte membrane 12, a fuel electrode 13a and an oxidant electrode 13b, a fuel electrode flow field plate 14, and an oxidant electrode flow field plate 16. The electrolyte membrane 12 is, for example, a solid polymer electrolyte membrane. The electrolyte membrane 12 has a first main surface 12a and a second main surface 12b located on the side opposite to the first main surface 12a. The fuel electrode 13a is disposed on the first main surface 12a of the electrolyte membrane 12. The oxidant electrode 13b is disposed on the second main surface 12b of the electrolyte membrane 12. That is, the fuel electrode 13a and the oxidant electrode 13b are disposed so as to sandwich the electrolyte membrane 12.

[0016] The fuel electrode flow field plate 14 has a first main surface 14a and a second main surface 14b located on the side opposite to the first main surface 14a. The first main surface 14a of the fuel electrode flow field plate 14 faces the side opposite to the electrolyte membrane 12. The second main surface 14b of the fuel electrode flow field plate 14 faces the first main surface 12a of the electrolyte membrane 12. The first main surface 14a of the fuel electrode flow field plate 14 is formed in a flat shape. On the other hand, fuel gas flow channels (not shown) are formed on the second main surface 14b of the fuel electrode flow field plate 14. The fuel gas flow channels face the fuel electrode 13a. The fuel gas supplied to the fuel cell stack 10 flows through these fuel gas flow channels.

[0017] The oxidant electrode flow field plate 16 has a first main surface 16a and a second main surface 16b located on the side opposite to the first main surface 16a. The first main surface 16a of the oxidant electrode flow field plate 16 faces the second main surface 12b of the electrolyte membrane 12. The second main surface 16b of the oxidant electrode flow field plate 16 faces the side opposite to the electrolyte membrane 12. Oxidant gas flow channels 17 are formed on the first main surface 16a of the oxidant electrode flow field plate 16. The oxidant gas flow channels 17 face the oxidant electrode 13b. The oxidant gas supplied to the fuel cell stack 10 flows through these oxidant gas flow channels 17. On the other hand, cooling water flow channels (not shown) are formed on the second main surface 16b of the oxidant electrode flow field plate 16. The cooling water supplied to the fuel cell stack 10 flows through these cooling water flow channels.

[0018] These multiple fuel cell unit cells 11 generate electricity through the reaction shown in Chemical Formula 1 below. More specifically, the fuel gas is, for example, a hydrogen-containing gas. The fuel gas flows through the fuel gas flow path grooves of the fuel electrode flow path plate 14 and is supplied to the fuel electrode 13a to cause a fuel electrode reaction. The oxidant gas is, for example, air (atmosphere). The oxidant gas flows through the oxidant gas flow path groove 17 of the oxidant electrode flow path plate 16 and is supplied to the oxidant electrode 13b to cause an oxidant electrode reaction. The fuel cell 1 generates electrical energy using these electrochemical reactions. The generated electrical energy is taken out from current terminals (not shown). Also, the cooling water flows through the cooling water flow path grooves of the oxidant electrode flow path plate 16 to cool each fuel cell unit cell 11 that has generated heat during power generation.

[0019] (Chemical Formula 1) Fuel electrode reaction: H2 → 2H + + 2e - Oxidant electrode reaction: 1 / 2O2 + 2H + +2e - → H2O

[0020] As shown in FIGS. 2 and 4, a pair of end plates 20 are arranged to sandwich the fuel cell stack 10 in the stacking direction Z. That is, the pair of end plates 20 are arranged on both sides of the fuel cell stack 10 in the stacking direction Z. The end plate 20 has, in order from the side of the fuel cell stack 10, an inner end plate 22, a central end plate 24, and an outer end plate 26. The end plate 20 may be composed of three end plates, namely, the inner end plate 22, the central end plate 24, and the outer end plate 26.

[0021] The inner end plate 22 contacts the fuel cell stack 10. The inner end plate 22 may be formed in a plate shape. The inner end plate 22 may include four recesses 23 formed at the four corners of the inner end plate 22. The description of the recesses 23 will be given later. The inner end plate 22 may have conductivity. The inner end plate 22 may be made of a metal material.

[0022] The central end plate 24 is disposed between the inner end plate 22 and the central end plate 24. The central end plate 24 may be formed in a plate shape. The central end plate 24 may have insulation. The central end plate 24 may be made of a resin material.

[0023] The outer end plate 26 is disposed outside the inner end plate 22 and the central end plate 24 in the stacking direction Z. The outer end plate 26 may be disposed at the outermost side of the end plate 20. The outer end plate 26 may be formed in a plate shape. The outer end plate 26 may have a larger planar area than the fuel cell stack 10, the inner end plate 22, and the central end plate 24. That is, when viewed along the stacking direction Z, the outer edge of the fuel cell stack 10, the outer edge of the inner end plate 22, and the outer edge of the central end plate 24 may be located inside the outer edge of the outer end plate 26. As shown in FIGS. 1 and 2, the outer end plate 26 has four protruding portions 37 protruding in the short-side direction Y from the vicinity of the four corners of the outer end plate 26. A tie rod attachment portion 28 to which the tie rod 30 is attached is provided on each protruding portion 37. The outer end plate 26 may be made of a metal material or a resin material.

[0024] As shown in FIGS. 1 and 2, a plurality of tie rods 30 are located outside the fuel cell stack 10. The tie rods 30 hold the fuel cell stack 10 and the end plates 20 by tightening the end plates 20 in a direction approaching each other outside the fuel cell stack 10. The tie rods 30 have a rod-like shape extending in the stacking direction Z. The plurality of tie rods 30 may include four tie rods 30. Each tie rod 30 is disposed near the four corners of the fuel cell stack 10. Each tie rod 30 is attached to the tie rod attachment portions 28 of a pair of outer end plates 26, respectively. Each tie rod 30 is fixed by a nut or the like at the tie rod attachment portion 28. Each tie rod 30 faces the longitudinal end face 10a of the fuel cell stack 10 in the short side direction Y. That is, each tie rod 30 is arranged so as to overlap the fuel cell stack 10 when viewed along the short side direction Y. Each tie rod 30 may be made of a metal material.

[0025] As shown in FIGS. 1 and 5, the external manifold 40 is attached to the end face (side face) of the fuel cell stack 10. The external manifold 40 includes two external manifolds 40a attached to the longitudinal end face 10a of the fuel cell stack 10 and two external manifolds 40b attached to the short side end face 10b of the fuel cell stack 10. The external manifold 40 is a member for supplying a gas such as a fuel gas or an oxidant gas to the fuel cell stack 10. The external manifold 40 has a gas chamber for accommodating the gas inside. The external manifold 40 also has a connection pipe 42 connected to an external pipe. A gas such as a fuel gas or an oxidant gas is supplied from the external pipe through this connection pipe 42 to the gas chamber inside the external manifold 40. Alternatively, the gas inside the gas chamber is discharged to the external pipe through this connection pipe 42.

[0026] In the illustrated example, the external manifold 40a attached to the longitudinal end face 10a of the fuel cell stack 10 has one connection pipe 42. This connection pipe 42 is disposed at the center of the external manifold 40a in the longitudinal direction X. More specifically, the connection pipe 42 is formed so as to extend from the center of the external manifold 40a to one side (the upper side in FIG. 1) in the stacking direction Z.

[0027] Also, the external manifold 40b attached to the short-side end face 10b of the fuel cell stack 10 has two connection pipes 42. These connection pipes 42 are disposed at the center of the external manifold 40b in the short-side direction Y. More specifically, the connection pipes 42 are formed so as to extend from the center of the external manifold 40b to one side (the upper side in FIG. 1) in the stacking direction Z.

[0028] In the present embodiment, the external manifold 40a is disposed between the tie rod 30 and the longitudinal end face 10a of the fuel cell stack 10 in the short-side direction Y. For this reason, the thickness of the external manifold 40a (the thickness at the position where the connection pipe 42 is not disposed) is equal to or less than the distance between the tie rod 30 and the longitudinal end face 10a of the fuel cell stack 10. In particular, the thickness of the external manifold 40a may be equal to or less than half of the distance between the tie rod 30 and the longitudinal end face 10a of the fuel cell stack 10.

[0029] Also, in the present embodiment, as shown in FIG. 5, when viewed along the stacking direction Z, the tie rods 30 are arranged at equal intervals on the circumference of a circle C centered on the center point O of the fuel cell stack 10. This center point O is the center of the fuel cell unit cell 11 when viewed along the stacking direction Z. In the example shown in FIG. 5, four tie rods 30 are arranged on the circumference of the circle C at equal intervals, that is, at equal distances in the circumferential direction.

[0030] Further, in the present embodiment, the external manifold 40a is configured to be attachable to the longitudinal end face 10a of the fuel cell stack 10 by being inserted obliquely between two adjacent tie rods 30 in the longitudinal direction X and between the tie rod 30 and the longitudinal end face 10a of the fuel cell stack 10.

[0031] More specifically, first, as shown in FIG. 6, an end portion on one side (the right side in the figure) of the external manifold 40a in the longitudinal direction X is inserted obliquely between two adjacent tie rods 30 in the longitudinal direction X and between the tie rod 30 on one side in the longitudinal direction X and the longitudinal end face 10a of the fuel cell stack 10.

[0032] Next, as shown in FIG. 7, the external manifold 40a is slid obliquely to further move an end portion on one side of the external manifold 40a in the longitudinal direction X to one side in the longitudinal direction X. As a result, the end portion on the other side (the left side in the figure) of the external manifold 40a in the longitudinal direction X also comes to be positioned between the tie rod 30 and the longitudinal end face 10a of the fuel cell stack 10 in the short direction Y.

[0033] Thereafter, as shown in FIG. 8, the end portion on the other side of the external manifold 40a in the longitudinal direction X is moved to the other side in the longitudinal direction X and positioned between the tie rod 30 on the other side in the longitudinal direction X and the longitudinal end face 10a of the fuel cell stack 10. In this way, the external manifold 40a is attached to the longitudinal end face 10a of the fuel cell stack 10.

[0034] Such a configuration of the external manifold 40a can be realized, for example, by arranging the connecting pipe 42 of the external manifold 40a at the central portion of the external manifold 40a in the longitudinal direction X and making the thickness of the external manifold 40a equal to or less than half of the distance between the tie rod 30 and the longitudinal end face 10a of the fuel cell stack 10.

[0035] Further, in the present embodiment, as shown in FIG. 9, the inner end plate 22 includes four recesses 23 formed at the four corners of the inner end plate 22. The inner end plate 22 includes an inner surface 22a and an outer surface 22b located on the side opposite to the inner surface 22a. The inner surface 22a faces the fuel cell stack 10. The inner surface 22a is in contact with the fuel cell stack 10. The inner surface 22a is formed in a flat shape. The outer surface 22b faces the central end plate 24. The outer surface 22b is in contact with the central end plate 24. The outer surface 22b is generally formed in a flat shape, but the four recesses 23 are formed in the outer surface 22b. That is, the four recesses 23 are formed at the four corners of the outer surface 22b of the inner end plate 22.

[0036] The four recesses 23 are spaced apart from each other. That is, there is a region where no recess 23 of the inner end plate 22 is formed between two adjacent recesses 23 in the longitudinal direction X, and there is a region where no recess 23 of the inner end plate 22 is formed between two adjacent recesses 23 in the short transverse direction Y. The recess 23 is disposed in the vicinity of the tie rod 30. The recess 23 is disposed so as to face the tie rod 30 in the short transverse direction Y. That is, the recess 23 is disposed at a position overlapping the tie rod 30 when viewed along the short transverse direction Y. The shape of the recess 23 is arbitrary. In the example shown in FIG. 9, the recess 23 has a triangular shape when viewed along the stacking direction Z. However, the present invention is not limited to this, and the recess 23 may have a rectangular shape or other shapes when viewed along the stacking direction Z.

[0037] Next, the operation and effects of the present embodiment will be described.

[0038] As a comparative example, a general fuel cell 101 will be described. As shown in FIG. 10, a general fuel cell 101 also includes a fuel cell stack 110, a pair of end plates (not shown in FIG. 10), four tie rods 130, and an external manifold 140. The fuel cell stack 110 is formed by stacking a plurality of fuel cell unit cells having a longitudinal direction X and a lateral direction Y. Each tie rod 130 is disposed outside the four corners of the fuel cell stack 10. More specifically, each tie rod 130 is disposed at a position outside the longitudinal end face 110a of the fuel cell stack 110 and outside the lateral end face 110b of the fuel cell stack 110. The external manifold 140 includes two external manifolds 140a attached to the longitudinal end face 110a of the fuel cell stack 110 and two external manifolds 140b attached to the lateral end face 110b of the fuel cell stack 110.

[0039] Here, in the general fuel cell 101, the external manifold 140a is not disposed between the tie rod 130 and the longitudinal end face 110a of the fuel cell stack 110 in the lateral direction Y, but is disposed between two adjacent tie rods 130 in the longitudinal direction X. For this reason, the thickness of the external manifold 140a is larger than the distance between the tie rod 130 and the longitudinal end face 110a of the fuel cell stack 110. Also, the distance between two adjacent tie rods 130 in the longitudinal direction X is larger than the distance between two adjacent tie rods 30 in the lateral direction Y. The external manifold 140a is attached to the longitudinal end face 110a of the fuel cell stack 110 by moving straight in the lateral direction Y from between two adjacent tie rods 130 in the longitudinal direction X.

[0040] When the end plates are tightened toward each other by the tie rods 130, the end plates are deformed (bent) into an arch shape by the tightening force of the tie rods 130 and the reaction force of the fuel cell stack 110. In particular, in the case of the above-described configuration, the end plates are greatly bent in the longitudinal direction X. For this reason, particularly in the longitudinal direction, the surface pressure (cell surface pressure) applied to the fuel cell unit cells becomes non-uniform. In some cases, there is a risk that the fuel cell unit cells may be damaged. To address this problem, a method of increasing the thickness of the end plates to increase the rigidity can be considered. However, in this case, the volume of the fuel cell 101 increases.

[0041] On the other hand, according to the present embodiment, the external manifold 40a is disposed between the tie rod 30 and the longitudinal end face 10a of the fuel cell stack 10 in the short direction Y. As a result, the distance between two adjacent tie rods 30 in the longitudinal direction X can be reduced. For this reason, the bending of the end plate 20 in the longitudinal direction X can be suppressed. As a result, while suppressing an increase in the volume of the fuel cell 1, the cell surface pressure can be made uniform. Further, breakage of the fuel cell unit cell 11 can be prevented.

[0042] In particular, according to the present embodiment, when viewed along the stacking direction Z, the tie rods 30 are arranged at equal intervals on the circumference of a circle C centered on the center point O of the fuel cell stack 10. As a result, the arrangement intervals of the respective tie rods 30 can be equalized. For this reason, the bending of the end plate 20 in the longitudinal direction X can be further suppressed.

[0043] Further, according to the present embodiment, the external manifold 40a is configured to be attachable to the longitudinal end face 10a of the fuel cell stack 10 by being inserted obliquely between two adjacent tie rods 30 in the longitudinal direction X from between the tie rod 30 and the longitudinal end face 10a of the fuel cell stack 10. As a result, even in a configuration in which the external manifold 40a is disposed between the tie rod 30 and the longitudinal end face 10a of the fuel cell stack 10 in the short direction Y, the external manifold 40a can be easily attached to the longitudinal end face 10a of the fuel cell stack 10.

[0044] Also, according to the present embodiment, the connecting pipe 42 connected to the external pipe is disposed at the central portion of the external manifold 40a in the longitudinal direction X, and the thickness of the external manifold 40a is equal to or less than half of the distance between the tie rod 30 and the longitudinal end face 10a of the fuel cell stack 10. With such a configuration, it becomes possible to dispose the external manifold 40a between the tie rod 30 and the longitudinal end face 10a of the fuel cell stack 10 in the short direction Y. Further, with such a configuration, the gas distribution to the fuel cell stack 10 can be made uniform in each direction.

[0045] Next, the inner end plate 122 according to the comparative example will be described. As shown in FIG. 11, the inner end plate 122 according to the comparative example includes two recesses 123. The two recesses 123 are formed on both sides of the inner end plate 122 in the short direction Y. That is, one recess 123 is formed along the long side on one side (the upper left side in FIG. 11) of the inner end plate 122 in the short direction Y. Further, the other recess 123 is formed along the long side on the other side (the lower right side in FIG. 11) of the inner end plate 122 in the short direction Y. The inner end plate 122 includes an inner surface 122a and an outer surface 122b located on the side opposite to the inner surface 122a. The inner surface 122a faces the fuel cell stack. The inner surface 122a contacts the fuel cell stack. The outer surface 122b faces the central end plate. The outer surface 122b contacts the central end plate. The two recesses 123 are formed on this outer surface 122b. That is, the two recesses 123 are formed on both sides of the outer surface 122b of the inner end plate 122 in the short direction Y.

[0046] In the case of such a configuration, a gap is provided between the inner end plate 122 and the central end plate due to the recess 123 formed in the inner end plate 122. This can suppress the variation in surface pressure on the inner end plate 122 caused by the deflection of the outer end plate (see, for example, Patent Document 1). However, when focusing on the vicinity of the tie rod attachment portion of the outer end plate, due to the presence of the gap, the structure becomes such that the distance between the fulcrum and the force point in the cantilever beam increases, and the deflection of the outer end plate can be promoted.

[0047] On the other hand, according to the present embodiment, the inner end plate 22 includes four recesses 23 formed at the four corners of the inner end plate 22. As a result, the range of the gap provided between the inner end plate 22 and the central end plate 24 is limited, and the portion where the distance between the fulcrum and the force point in the cantilever beam increases can be reduced. Therefore, the deflection of the outer end plate 26 can be suppressed. As a result, while suppressing the increase in the volume of the fuel cell 1, the cell surface pressure can be made uniform. Also, damage to the fuel cell unit cell 11 can be prevented.

[0048] Also, according to the present embodiment, the recesses 23 are formed at the four corners of the outer surface 22b of the inner end plate 22. Thereby, a gap can be provided between the inner end plate 22 and the central end plate 24. Therefore, the variation in surface pressure on the inner end plate 22 caused by the deflection of the outer end plate 26 can be effectively suppressed.

[0049] Also, according to the present embodiment, with the above-described configuration, the tightening pressure by the tie rod 30 can be increased, and the performance of the fuel cell 1 can be improved. Also, the thickness and size of the end plate can be reduced, and the volume of the fuel cell 1 can be reduced. Therefore, a high output density of the fuel cell 1 can be realized.

[0050] According to the embodiment described above, while suppressing the increase in the volume of the fuel cell, the cell surface pressure can be made uniform.

[0051] As described above, some embodiments of the present invention have been explained. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0052] 1: Fuel cell, 10: Fuel cell stack, 10a: Longitudinal end face, 10b: Lateral end face, 11: Fuel cell unit cell, 20: End plate, 22: Inner end plate, 22a: Inner surface, 22b: Outer surface, 23: Recess, 24: Central end plate, 26: Outer end plate, 30: Tie rod, 40, 40a, 40b: External manifold, 42: Connecting pipe, C: Circle, O: Center point, X: Longitudinal direction, Y: Lateral direction, Z: Stacking direction

Claims

1. A fuel cell stack formed by stacking a plurality of fuel cell unit cells having a longitudinal direction and a lateral direction, the fuel cell stack having a longitudinal end face along the longitudinal direction and a lateral end face along the lateral direction, A pair of end plates arranged to sandwich the fuel cell stack in the stacking direction, A plurality of tie rods for tightening the end plates in a direction approaching each other outside the fuel cell stack to hold the fuel cell stack and the end plates, An external manifold attached to the longitudinal end face of the fuel cell stack for supplying gas to the fuel cell stack, and comprising: The external manifold is arranged between the tie rod and the longitudinal end face of the fuel cell stack in the lateral direction, a fuel cell.

2. The tie rod is arranged at equal intervals on the circumference of a circle centered on the center point of the fuel cell stack when viewed along the stacking direction, the fuel cell according to claim 1.

3. The external manifold is configured to be attachable to the longitudinal end face of the fuel cell stack by being slid obliquely in a direction between two adjacent tie rods in the longitudinal direction and inserted between the tie rod and the longitudinal end face of the fuel cell stack, the fuel cell according to claim 1.

4. The external manifold has a connecting pipe connected to an external pipe, The connecting pipe is arranged at the center of the external manifold in the longitudinal direction, The thickness of the external manifold is not more than half of the distance between the tie rod and the longitudinal end face of the fuel cell stack, the fuel cell according to claim 1.

5. The end plate has an inner end plate in contact with the fuel cell stack, an outer end plate arranged outside the inner end plate in the stacking direction, and a central end plate arranged between the inner end plate and the outer end plate, The inner end plate includes four recesses formed at the four corners of the inner end plate, the fuel cell according to any one of claims 1 to 4.

6. The inner end plate includes an inner surface in contact with the fuel cell stack and an outer surface located on the side opposite to the inner surface in the stacking direction, The fuel cell according to claim 5, wherein the concave portion is formed on the outer surface of the inner end plate. **Claim 7** A fuel cell stack formed by stacking a plurality of fuel cell unit cells; A pair of end plates arranged to sandwich the fuel cell stack in the stacking direction; A plurality of tie rods that tighten the end plates in a direction approaching each other outside the fuel cell stack to hold the fuel cell stack and the end plates. The end plate includes an inner end plate that contacts the fuel cell stack, an outer end plate that is disposed outside the inner end plate in the stacking direction, and a central end plate that is disposed between the inner end plate and the outer end plate. The fuel cell, wherein the inner end plate includes four concave portions formed at four corners of the inner end plate. **Claim 8** The inner end plate includes an inner surface that contacts the fuel cell stack and an outer surface that is located on the opposite side of the inner surface in the stacking direction. The fuel cell according to claim 7, wherein the concave portion is formed on the outer surface of the inner end plate.

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