WO2007105072A2

WO2007105072A2 - Fuel cell

Info

Publication number: WO2007105072A2
Application number: PCT/IB2007/000601
Authority: WO
Inventors: Kazunari Moteki; Tsuguhiro Fujita
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2006-03-15
Filing date: 2007-03-13
Publication date: 2007-09-20
Also published as: JP2007250297A; WO2007105072A3

Abstract

A gas passage (28) is formed by stacking a first expand metal member (30) and a second expand metal member (31). The directions in which the major axes of meshes extend differ by 90 degrees between the first expand metal member (30) and the second expand metal member (31). The reaction gas impinges on bond portions (302) of the first expand metal member (30) and strand portions (311) of the second expand metal member (31), while flowing through openings (303) of the first expand metal member (30), and openings (313) of the second expand metal member (31) in the plane direction. Due to such impingement, the reaction gas flows in the normal-line direction, thereby diffusing into an MEGA (25). The difference in the directions of the major axes minimizes formation of partition walls, which would occur if the meshes of the successive expand metal members coincide with each other. Accordingly, the gas flows more efficiently and the fuel cell generates electric power more efficiently.

Description

FUELCELL

FIELD OF THE INVENTION

[0001] The invention relates generally to a fuel cell, and, more specifically to the structure of a passage through which fuel gas flows.

BACKGROUND OF THE INVENTION

[0002] In recent years, fuel cells that generate electric power by the electrochemical reaction between hydrogen gas and oxygen draw widespread attention as energy sources. An example of such fuel cells is a polymer electrolyte fuel cell. A polymer electrolyte fuel cell is formed by stacking multiple cells. Each cell is formed by integrally combining a membrane electrode assembly in which catalyst electrode layers are formed on the respective faces of a polymer electrolyte membrane, separators, and members in which gas passages, which are arranged between the membrane electrode assembly and the respective separators. The gas passages guide the reaction gases used for electric power generation by the fuel cell, for example, hydrogen gas and air to the membrane electrode assembly.

[0003] Such gas passage is formed by stacking multiple expand metal members each of which is formed by regularly forming uniformly-shaped through-holes in a metal plate. Portions of the expand metal member, which define the through-holes will be referred to as strand portions, and portions at which the strand portions cross each other will be referred to as bond portions. The gas passage guides the reaction gas in the direction in which the expand metal member extends (hereinafter, referred to as the "plane direction") from the through-hole of one expand metal member to the through-hole of the successive expand metal member. The reaction gas flowing through the gas passage impinges on the strand portions and the bond portions of the expand metal members, thereby diffusing into the catalyst electrode layers.

[0004] Japanese Patent Application Publication No. 2004-511067 (JP-A-2004-511067), Japanese Patent Application Publication No. 08-138701 (JP-A-08-138701), and Japanese Patent Application Publication No. 11-162480 (JP-A-11-162480) each describe such a fuel cell.

[0005] However, if multiple expand metal members having uniformly-shaped i through-holes are stacked on top of each other in a manner in which the through-holes of one expand metal member coincides with the through-holes of the successive expand metal member, partition walls are formed by the strand portions and the bond portions of the through-holes of the stacked expand metal members, which may interrupt the flow of the reaction gas in the plane direction. Even if the expand metal members are stacked

I on top of each other in a manner in which the through-holes of the successive expand metal members are offset from each other in the longitudinal direction and/or the lateral direction of the expand metal members, the through-holes of the successive expand metal members may coincide with each other. This is because the shapes of the through-holes vary due to production errors. Therefore, partition walls may eventually be formed, and, therefore, the flow of the reaction gas may be interrupted.

[0006] Such inconvenience occurs not only in the gas passage formed by stacking the expand metal members on top of each other but also in any gas passages formed by stacking members in which uniformly-shaped through-holes are regularly formed.

DISCLOSURE OF THE INVENTION

[0007] The invention allows reaction gas to flow and diffuse more efficiently in a gas passage formed by stacking members in which through-holes are regularly formed.

[0008] An aspect of the invention relates of a fuel cell. The fuel cell has a gas passage formed by stacking multiple metal plates in which through-holes are formed. These through-holes form the gas passage. The fuel cell includes a separator; a membrane electrode assembly in which catalyst electrode layers are formed on the respective faces of an electrolyte membrane; a first metal plate which is arranged between the membrane electrode assembly and the separator, and in which uniformly-shaped first gas passage forming-holes that form the gas passage are regularly formed in multiple rows that extend in the first direction; and a second metal plate which is arranged between the membrane electrode assembly and the first metal plate, and in which second gas passage forming-holes that have identical shape with the first gas passage forming-holes are regularly formed in multiple rows that extend in the second direction which differs from the first direction.

[0009] In the fuel cell according to the aspect of the invention, the orientation of the gas passage-forming holes of the first metal plate differs from the orientation of the gas passage-forming holes of the second metal plate. Accordingly, the coincidence of the gas passage-forming holes of the first metal plate with the gas passage-forming holes of the second metal plate is minimized. As a result, the reaction gas flows in the plane direction of the metal plates more efficiently, and diffuses into the membrane electrode assembly more efficiently.

[0010] In the fuel cell according to the aspect of the invention, each of the first gas passage forming-hole and the second gas passage forming-hole may have a major axis and a minor axis, the major axis of the first gas passage forming-hole may extend in the first direction, and the major axis of the second gas passage forming-hole may extend in the second direction. In the fuel cell having such configuration, the gas passage-forming holes of the successive metal plates are less likely to coincide with each other, because each of the first gas passage forming-hole and the second gas passage-forming hole has the major axis and the minor axis, and the directions in which the major axes extend differ between the successive metal plates.

[0011] In the fuel cell according to the aspect of the invention, each of the first gas passage forming-hole and the second gas passage forming-hole may be shaped in a parallelogram.

[0012] In the fuel cell according to the aspect of the invention, each of the first gas passage forming-hole and the second gas passage forming-hole may be shaped in a rhombus. With this configuration, the gas passage-forming holes may be easily formed.

[0013] In the fuel cell according to the aspect of the invention, each of the first gas passage forming-hole and the second gas passage forming-hole may be shaped in a rectangle.

[0014] In the fuel cell according to the aspect of the invention, each of the first gas passage forming-hole and the second gas passage forming-hole may be shaped in an ellipse.

[0015] In the fuel cell according to the aspect of the invention, each of the first gas passage forming-hole and the second gas passage forming-hole may be shaped in a square.

[0016] In the fuel cell according to the aspect of the invention, the second direction may be at an angle of 90 degrees with respect to the first direction. With this configuration, the formation of partition walls, which would occur if the through-holes of the successive metal plates coincide with each other, is suppressed highly reliably, because the orientations of the gas passage-forming holes differ by 90 degrees between the successive metal plates.

[0017] In the fuel cell according to the aspect of the invention, the second direction is at an angle of 45 degrees with respect to the first direction.

[0018] In the fuel cell according to the aspect of the invention, a third metal plate may be further provided. The third metal plate is arranged between the second metal plate and the membrane electrode assembly. In the third metal plate, third gas passage forming-holes that have identical shape with the second gas passage forming-holes are regularly formed in multiple rows that extend in the third direction which differs from the second direction.

[0019] In the fuel cell having such configuration, the reaction gas diffuses more efficiently because the number of the metal plates arranged between the membrane electrode assembly and the separator is increased.

[0020] In the fuel cell according to the aspect of the invention, a fourth metal plate may be further provided. The fourth plate is arranged between the second metal plate and the membrane electrode assembly. In the fourth metal plate, fourth gas passage forming-holes that are geometrically similar to and smaller than the second gas passage forming-holes are regularly formed in multiple rows that extend in the fourth direction which differs from the second direction.

[0021] In the fuel cell having such configuration, the gas diffuse into the membrane electrode assembly further efficiently, because the fourth gas passage-forming holes of the fourth metal plate provided adjacent to the membrane electrode assembly are smaller than those of the other metal members.

[0022] In the fuel cell according to the aspect of the invention, a gas diffusion layer may be further provided. The gas diffusion layer is arranged between the membrane electrode assembly and the second metal plate, and formed of a porous member having electric conductivity.

[0023] In the fuel cell having such configuration, the gas diffuses into the membrane electrode assembly further efficiently, because the gas diffusion layer is arranged between the membrane electrode assembly and the second metal plate.

[0024] In the fuel cell according to the aspect of the invention, the separator may be a three-layer separator that is formed by stacking three conductive metal plates having electric conductivity on top of each other. With this configuration, the gas flow efficiency is increased without forming a gas passage in the separator, because the gas passage is formed by the metal plates.

[0025] In the fuel cell according to the aspect of the invention, each metal plate may be an expand metal member. Expand metal members are light and rigid, and produced at low cost. Accordingly, employing such configuration makes it possible to provide rigid gas passages at low cost.

[0026] In the invention, the above-described configurations may be appropriately combined with each other, or may be partially omitted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The forgoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein the same or corresponding portions will be denoted by the same reference numerals and wherein: FIG. 1 is the view schematically showing the structure of a fuel cell according to a first embodiment of the invention;

FIG. 2 is the cross-sectional view showing a cell according to the first embodiment of the invention;

FIG. 3 is the perspective view showing an expand metal member according to the first embodiment of the invention;

FIG. 4 is the perspective view showing another expand metal member according to the first embodiment of the invention;

FIG. 5 is the schematic diagram illustrating the directions in which the major axes of meshes extend;

FIG. 6 is the view illustrating the mesh of the expand metal member according to the first embodiment of the invention;

FIG. 7 is the schematic diagram illustrating a gas passage according to the first embodiment of the invention;

FIG. 8 is the schematic diagram illustrating the flow of the reaction gas according to the first embodiment of the invention.

FIG. 9 is the schematic diagram illustrating a gas passage according to a comparative example, which is compared with the gas passage according to the first embodiment of the invention;

FIG. 10 is the graph showing the relationship between the output current and the output voltage of the fuel cell according to the first embodiment of the invention;

FIG. 11 is the cross-sectional diagram schematically showing the structure of a gas passage and the flow of the reaction gas according to a second embodiment of the invention;

FIG. 12 is the cross-sectional diagram schematically showing the structure of a gas passage and the flow of the reaction gas according to a third embodiment of the invention; and

FIG. 13 is the cross-sectional diagram schematically showing the structure of a gas passage and the flow of the reaction gas according to a modified example of the embodiments of the invention.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS [0028] Hereafter, example embodiments of the invention will be described with 5 reference to the accompanying drawings.

[0029] A. First embodiment: Al. Schematic structure of fuel cell:

The schematic structure of a fuel cell 1000 according to a first embodiment of the invention will be described with reference to FIGs. 1 and 2. FIG. 1 schematically

) illustrates the structure of the fuel cell 1000 according to the first embodiment of the invention. FIG. 2 is the cross-sectional view taken along the line II-II in FIG. 1, and illustrates a cell 10 according to the first embodiment of the invention. The fuel cell

1000 is a polymer electrolyte fuel cell that is supplied with fuel gas containing hydrogen and oxidizing gas containing oxygen, and generates electric power by the electrochemical i reaction between the fuel gas and the oxidizing gas.

[0030] As shown in FIG. 1, the fuel cell 1000 is formed by stacking multiple cells 10, and then placing end plates 85 and 86 at the respective ends of the cell stack. Formed in the end plate 85 are: a through-hole 85a through which anode gas is supplied to the fuel cell 1000; a through-hole 85b through which cathode gas is supplied to the fuel cell 1000; a through-hole 85c through which anode off-gas is discharged from the fuel cell 1000; a through-hole 85d through which cathode off-gas is discharged from the fuel cell 1000; a through-hole 85e through which coolant is supplied to the fuel cell 1000; and a through-hole 85f through which coolant is discharged from the fuel cell 1000. The anode gas is supplied from a fuel gas tank (not shown) through the through-hole 85a to the fuel cell 1000. The cathode gas is compressed by a compressor (not shown), and then supplied through the through-hole .85b to the fuel cell 1000. The coolant is cooled by a radiator (not shown), and then supplied through the through-hole 85e to the fuel cell 1000.

[0031] As shown in FIG. 2, the cell 10 includes an MEA (Membrane Electrode Assembly) 24, gas diffusion layers 23a and 23b, members in which gas passages 28 and 29 are formed, a seal gasket 26, and separators 40. The gas diffusion layers 23a and 23b are formed on the respective faces of the MEA 24. The member formed of the MEA 24, the gas diffusion layer 23a and the gas diffusion layer 23b will be referred to as a MEGA

5 25. The members in which the gas passages 28 and 29 are formed are arranged between the MEGA 25 and the respective separators 40. The MEGA 25 and the members in which the gas passages 28 and 29 are formed are integrated with the seal gasket 26 in a manner in which the MEGA 25 is surrounded by the seal gasket 26. The separators 40 are placed on the respective faces of the member formed by integrally combining the

) MEGA 25, the members in which the gas passages 28 and 29 are formed, and the seal gasket 26.

[0032] In the MEA 24, a cathode catalyst electrode layer 22a and an anode catalyst electrode layer 22b are formed on the respective faces of an electrolyte membrane 21. The electrolyte membrane 21 is a thin membrane made of a polymer electrolyte material i that has proton conductivity and that exhibits good electric conductivity in a wet condition. The electrolyte membrane 21 is shaped in a rectangle that is smaller than the separator 40 and larger than the outline of the member in which the gas passage is formed. For example, Nafion is used as the electrolyte membrane 21. The cathode catalyst electrode layer 22a and the anode catalyst electrode layer 22b formed on the respective faces of the electrolyte membrane 21 support catalysts that promote the electrochemical reaction, for example, platinum.

[0033] The gas diffusion layers 23a and 23b are made of carbon porous bodies having a porosity of approximately 20 %. The gas diffusion layers 23a and 23b are made, for example, of carbon cloth or carbon paper. The gas diffusion layers 23a and 23b are jointed with the MEA 24 to form the MEGA 25. The gas diffusion layer 23a is arranged on the cathode side of the MEA 24, and the gas diffusion layer 23b is arranged on the anode side of the MEA 24. The gas diffusion layer 23a diffuses the cathode gas in the thickness direction thereof to supply the cathode gas to all over the cathode catalyst electrode layer 22a. The gas diffusion layer 23b diffuses the anode gas in the thickness direction thereof to supply the anode gas to all over the anode catalyst electrode layer 22b. Because the gas diffusion layers 23a and 23b are arranged mainly to diffuse the gas in the thickness direction thereof, the porosity thereof is relatively low.

[0034] Each of the gas passages 28 and 29 is formed by stacking two expand metal 5 members on top of each other. Each expand metal member is a metal plate in which uniformly-shaped through-holes are regularly formed. The expand metal member is made of conductive metal, for example, stainless steel, titanium, or a titanium alloy. Each expand metal member is shaped in a substantial rectangle that is slightly smaller than the MEGA 25. The structure of the expand metal member will be described later. ) The two expand metal members are joined to each other by, for example, diffusion joining or resistance welding. Joining the two expand metal members to each other reduces the interface between the two expand metal members stacked on top of each other. As a result, it is possible to minimize entry of the water produced by the electrochemical reaction into the interface. Accordingly, it is possible to minimize corrosion of the expand metal members.

[0035] The gas passage 28 is formed at a position between the cathode side of the MEGA 25 (the cathode side of the MEA 24) and the separator 40. The gas passage 28 guides the oxidizing gas supplied through the separator 40 downward as shown in FIG. 1 to supply the oxidizing gas to the cathode side of the MEGA 25.

[0036] The gas passage 29 is formed at a position between the anode side of the MEGA 25 (the anode side of the MEA 24) and the separator 40. The gas passage 29 guides the fuel gas supplied through the separator 40 downward as shown in FIG. 1 to supply the fuel gas to the anode side of the MEGA 25.

[0037] The reaction gas flowing through the gas passage 28 and the reaction gas flowing through the gas passage 29 are supplied to the MEGA 25 while flowing through these gas passages, diffused into the cathode catalyst electrode layer 22a and the anode catalyst electrode layer 22b through the gas diffusion layers 23a and 23b of the MEGA 25, and then used for the electrochemical reaction. The electrochemical reaction is an exothermic reaction. Accordingly, in order to operate the fuel cell 1000 at a temperature _1Q

in a predetermined temperature range, coolant is supplied in the fuel cell 1000.

[0038] The seal gasket 26 is made of an elastic rubber insulating resin material such as silicon rubber, butyl rubber or fluoro-rubber. Such insulating resin material is injected onto the circumferential portions of the MEGA 25 and the expand metal members in which the gas passages 28 and 29 are formed so that the seal gasket 26 is integrated with the MEGA 25 and the expand metal members in which the gas passages 28 and 29 are formed. The seal gasket 26 is made, for example, of fluoro-rubber.

[0039] The seal gasket 26 is formed in a substantial rectangle having the same outer shape as the separator 40. As shown in FIG. 1, holes 20a to 2Of are formed in the seal gasket 26 along the four sides thereof. In order to distinguish the holes 20a to 2Of, which are used as part of manifolds and formed in the seal gasket 26, from the holes, which are used as part of manifolds and formed in the separator 40, the holes 20a to 2Of formed in the seal gasket 26 will be referred to as the communication-holes 20a to 2Of. Each of the communication-holes 20a to 2Of is used as a part of the manifold through which the fluid (fuel gas, oxidizing gas, coolant) in the fuel cell 100 flows. The communication-hole 20a forms a part of the anode gas manifold, and the communication-hole 20b forms a part of the cathode gas manifold. The communication-hole 20c forms a part of the anode off-gas manifold, the communication-hole 2Od forms a part of the cathode off-gas manifold, the communication-hole 2Oe forms a part of the coolant supply manifold, and the communication-hole 2Of forms a part of the coolant discharge manifold.

[0040] On the seal gasket 26, convex portions 26a that surround the respective communication-holes and that extend in the thickness direction. The convex portions 26a are sandwiched between the separators 40, receive the fastening force applied in the direction in which the cells 10 are stacked (hereinafter, referred to as the "stacked direction"), and then compressed and deformed in the stacked direction. As a result, the convex portions 26a form seal lines SL that minimize leakage of the fluid (fuel gas, oxidizing gas, coolant) from the respective manifolds, as shown in FIG. 2.

[0041] Next, the separator 40 that collects electricity generated by the electrochemical reaction will be described. The separator 40 is a three-layer separator that is formed by stacking three thin metal plates on top of each other. More specifically, the separator 40 is formed of a cathode plate 41 that contacts the gas passage 28 through which the oxidizing gas flows, an anode plate 43 that contacts the gas passage 29 through which the fuel gas flows, and an intermediate plate 42 which is sandwiched between the cathode plate 41 and the anode plate 43 and in which a passage mainly for the coolant is formed.

[0042] Each of the three plates has a flat face in which concave/convex portions used for passages are not formed in the thickness direction thereof (namely, the face which contacts the gas passages 28 or 29 is flat). Each of the three plates is made of an electric conductive metal material such as stainless steel, titanium, or a titanium alloy.

[0043] In each of the three plates, through-holes, which are used as the part of the various manifolds described above, are formed. More specifically, as shown in FIG. 1, a through-hole 41a through which the oxidizing gas is supplied and a through-hole 41b through which the oxidizing gas is discharged are formed along the respective long sides of the substantially rectangular separator 40. A through-hole 41c through which the fuel gas is supplied and a through-hole 41d through which the fuel gas is discharged are formed along the respective short sides of the separator 40. In addition, a through-hole 41e through which the coolant is supplied and a through-hole 41f through which the coolant is discharged are formed along the respective short sides of the separator 40.

[0044] In the cathode plate 41, in addition to the above-described through-holes which are used as part of the manifolds, holes 45 and 46 through which the oxidizing gas is supplied to/discharged from the gas passage 28 are formed. Similarly, in the anode plate 43, in addition to the above-described through-holes which are used as part of the manifolds, multiple holes (not shown) through which the fuel gas is supplied to/discharged from the gas passage 29 are formed.

[0045] Among multiple through-holes which are used as part of the manifolds and formed in the intermediate plate 42, through-holes 42a, which are used as part the manifolds and through which the oxidizing gas flows, are formed so as to communicate with the respective holes 45 formed in the cathode plate 41. The through-holes 42b, which are used as part of the manifolds and through which the fuel gas flows, are formed so as to communicate with respective holes (not shown) formed in the anode plate 43.

[0046] In the intermediate plate 42, multiple notches are formed along the direction in which the long sides of the substantially rectangular intermediate plate 42 extend. The both ends of the respective notches communicate with the through-holes used as part of the manifolds through which the coolant flows.

[0047] Using the separators 40 formed by stacking such flat plates together with the expand metal members in which the gas passages 28 and 29 are formed eliminates the need to form the grooves used as the passages, which would be formed by a complicated method such as etching, in the separators 40.

[0048] Hereafter, the fuel gas and the oxidizing gas will be collectively referred to as the reaction gas in the first embodiment of the invention.

[0049] A2. Expand metal members

The expand metal members in which the gas passages 28 and 29 are formed will be described with reference to FIGs. 3 to 6. Because first expand metal members 30 and 34 have the same structure, the first expand metal 30 will be described. Because second expand metal members 31 and 33 have the same structure, the second expand metal member 31 will be described. Also, the structure of the gas passage 28, and the flow of the reaction gas through the gas passage 28 will be described with reference to FIGs. 7 and 8. FIG. 3 is the perspective view showing the first expand metal member 30 according to the first embodiment of the invention. FIG. 4 is the perspective view showing the second expand metal member 31 according to the first embodiment of the invention. FIG. 5 is the schematic diagram illustrating the directions in which the major axes (i.e., long diagonals) of the respective meshes extend according to the first embodiment of the invention. FIG. 6 is the view illustrating one mesh of the first expand metal member 30. FIG. 6 is the partially enlarged view showing the portion indicated by the dashed-line circle Z in FIG 3. FIG. 7 is the schematic diagram illustrating the gas passage 28 according to the first embodiment of the invention. FIG. 8 is the schematic diagram showing the flow of the gas according to the first embodiment of the invention. FIG. 8 is the enlarged view showing the portion indicated by the circle Y in FIG. 2.

[0050] As shown in FIG. 3, the first expand metal member 30 is a metal plate in which multiple rhomboid-shaped through-holes 300 having uniform shape are regularly formed in multiple rows. Hereafter, the through-holes 300 will be referred to as meshes 300 in the first embodiment of the invention. Each mesh 300 has a major axis (i.e., long diagonal) and a minor axis (i.e., short diagonal). The meshes 300 are formed so that the major axes thereof extend parallel to the first direction. The first direction in the first embodiment of the invention is parallel to the short sides of the first expand metal member 30. The lateral size LWl indicates the size of the mesh 300 in the lateral direction of the first expand metal member 30. The longitudinal size SWl indicates the size of the mesh 300 in the longitudinal direction of the first expand metal member 30. As shown in FIG. 3, the lateral size LWl of the mesh 300 is x (LWl = x), and the longitudinal size SWl of the mesh 300 is y (SWl = y (x > y)). The mesh 300 is a laterally-long rhombus where the length of the major axis is x and the length of the minor axis is y. The major axis and the minor axis of the mesh 300 cross each other at right angles. The first expand metal member 30 is a flat-type expand metal member formed by skin pass rolling.

[0051] Next, the second expand metal member 31 will be described. As shown in FIG. 4, the second expand metal member 31 is a metal plate in which multiple rhomboid-shaped through-holes 310 having uniform shape are regularly formed in multiple rows. The through-hole 310 has a major axis and a minor axis. The through-holes 310 are formed so that the major axes thereof extend parallel to the second direction. The second direction in the first embodiment of the invention is parallel to the long sides of the second expand metal member 31. Like the first expand metal member 30, the second expand metal member 31 is a flat-type expand metal member formed by skin pass rolling. In the first embodiment of the invention, the through-holes 310 will be referred to as the meshes 310, and the second direction will be referred to as the direction in which the major axes of the meshes 310 of the second expand metal member 31 extend. The lateral size LW2 of the mesh 310 is y (LW2 = y), and the vertical size SW2 of the mesh 310 is x (S W2 = x). The mesh 300 is a longitudinally long rhombus where the length of the major axis is x and the length of the minor axis is y. The major axis and the minor axis of the mesh 310 cross each other at right angles.

[0052] As shown in FIG. 5, the direction in which the major axes of the meshes 310 of the second expand metal member 31 extend and the direction in which the major axes of the meshes 300 of the first expand metal member 30 extend are perpendicular to each other, namely, they are different from each other by 90 degrees.

[0053] A3. Structure of mesh

The structure of the mesh according to the first embodiment of the invention will be described using the mesh 300 of the first expand metal member 30 as an example, with reference to FIG. 6. As shown in FIG. 6, the mesh 300 of the first expand metal member 30 has strand portions 301, bond portions 302 and an opening 303. The strand portions 301 correspond to the four sides of the mesh 300. The strand portions 301 cross each other at the bond portions 302. The opening 303 is a through-hole that is defined by the strand portions 301 and the bond portions 302. As described above, the size of the mesh 300 in the lateral direction of the first expand metal 30 is x (LWl = x), and the size of the mesh 300 in the longitudinal direction of the first expand metal 30 is y (SWl = y) (x > y).

[0054] The mesh 300 and the mesh 310 are though-holes that have the same shape. The direction in which the major axes of the meshes 300 extend is at an angle of 90 degrees with respect to the direction in which the major axes of the meshes 310 extend. Accordingly, it is possible to stack the first expand metal member 30 and the second expand metal member 31 on top of each other while minimizing the coincidence of the strand portions 301 of the meshes 300 with the strand portions 311 of the meshes 310 and the coincidence of the bond portions 302 of the meshes 300 with the bond portions of the meshes 310.

[0055] The ends of the first expand metal member 30 and the second expand metal member 31 are kept in the state obtained when they are cut, and the first expand metal member 30 and the second expand metal member 31 are not provided with frames, etc. The major axis of each mesh 300 of the first expand metal member 30 and each mesh 310 of the second expand metal member 31 is 0.1 millimeters to 0.5 millimeters.

[0056] A4. Structure of gas passage and electric power generation performance

The structure of the gas passage 28 formed by stacking the first expand metal member 30 and the second expand metal member 31 on top of each other will be described with reference to FIG. 7. In a schematic diagram 400 in FIG. 7, the plan view of the gas passage 28 and the cross-sectional view of the gas passage 28, which is taken along the line VII-VII in the plan view are shown. In the schematic diagram 400, the corresponding portions in the plan view and the cross-sectional view are shown at the same positions in the direction in which the major axes of the meshes 300 extend. In the schematic diagram 400, the strand portions and the bond portions of the meshes 300 and the meshes 310 are indicated by hatched patterns. In the plan view in the schematic diagram 400, the direction in which the major axes of the meshes 300 extend and the direction in which the major axes of the meshes 310 extend are also shown.

[0057] As shown in the plan view in the schematic diagram 400, in the gas passage 28 formed by stacking the first expand metal member 30 and the second expand metal member 31 on top of each other, the direction in which the major axes of the meshes 310 of the second expand metal member 31 extend is at an angle of 90 degrees with respect to the direction in which the major axes of the meshes 300 of the first expand metal member 30 extend.

[0058] Because the direction in which the major axes of the meshes 300 extend is at an angle of 90 degrees with respect to the direction in which the major axes of the meshes 310 extend, as shown in the cross-sectional view in the schematic diagram 400, it is possible to minimize the coincidence of the strand portions 301 and the bond portions

302 of the first expand metal 30 with the strand portions 311 and the bond portions 312 of the second expand metal member 30. Accordingly, in the gas passage 28, the openings

303 of the first expand metal member 30 and the openings 313 of the second expand metal member 31 efficiently communicate with each other. As a result, the reaction gas flows through the gas passage 28 smoothly.

[0059] The flow of the reaction gas through the gas passage 28 is indicated by the heavy-line arrow in FIG. 8. In the first embodiment of the invention, the reaction gas flows in the plane direction (from right-hand side to the left-hand side in the sheet on

) which FIG. 8 is drawn) while diffusing in the normal-line direction (upward in the sheet on which FIG. 8 is drawn). As shown in FIG. 8, the reaction gas supplied from the separator 40 impinges on the bond portions 302 of the first expand metal member 30 and the strand portions 311 of the second expand metal member 31, while flowing through the openings 303 of the first expand metal member 30, and the openings 313 of the

• second expand metal member 31 in the plane direction. By impinging on the bond portions 302 of the first expand metal member 30 and the strand portions 311 of the second expand metal member 31, the reaction gas flows in the normal-line direction, thereby diffusing into the MEGA 25. In the gas passage 28, it is possible to minimize the formation of the partition walls, which would be formed if the meshes 300 of the first expand metal member 30 coincide with the meshes 310 of the second expand metal member 31. Accordingly, the gas passage 28 appropriately guides the reaction gas in the plane direction.

[0060] Hereafter, a gas passage 270 according to a comparative example will be described with reference to FIG. 9. The gas passage 270 according to the comparative example will be compared with the gas passage 28 according to the first embodiment of the invention. The gas passage 270 is formed by staking expand metal members having the meshes which have the same shape and of which the major axes extend in the same direction, in a manner in which the metal members are offset from each other in the lateral direction and/or the longitudinal direction. The gas passage 270 is formed by stacking the expand metal members so that the meshes of the respective expand metal members coincide with each other. FIG. 9 is the schematic diagram showing the gas passage 270 formed by stacking two expand metal members having the meshes which have the same shape and of which the major axes extend in the same direction. In a schematic diagram 410, the plan view of the gas passage 270 and the cross sectional view of the gas passage 270, which is taken along the line IX-IX in the plan view are shown. In the schematic diagram 410, the corresponding portions in the plan view and the cross-sectional view are shown at the same positions in the plane direction. The strand portions and the bond portions of the first expand metal member 30 and a third expand i metal member 35, in which the gas passage 270 is formed, are indicated by hatched patterns. In the cross-sectional view in the schematic diagram 410, the flow of the reaction gas is indicated by the heavy-line arrow.

[0061] The gas passage 270 is formed by stacking the first expand metal member 30 and the third expand metal member 35 on top of each other. The positions of the

¹ meshes 300 of the first expand metal member 30 and the positions of meshes 350 of the third expand metal member 35 are offset from each other by an amount of approximately one-fourths of the major axis of the mesh in the direction in which the major axes of the meshes 300 extend.

[0062] The expand metal members have some manufacturing errors in the shapes and sizes of the meshes. Even if such error is minor, as shown in FIG. 9, a mesh 300a, which is one of the meshes 300 of the first expand metal member 30, may coincides with a mesh 350a, which is one of the meshes 350 of the third expand metal member 35, because the size of the mesh is considerably small, namely, the major axis of the mesh is 0.1 millimeters to 0.5 millimeters. If the mesh 300a coincides with the mesh 350 a, as shown in the cross-sectional view in FIG. 9, the bond portion 302 of the mesh 300a coincides with the bond portion 352 of the mesh 350a. As a result, a partition wall 600 is formed.

[0063] If the partition wall 600 is formed, as shown by the heavy-line arrow in FIG. 9, the flow of the reaction gas is interrupted by the partition wall 600. As a result, the reaction gas flows in the plane direction and diffuses into the MEGA less efficiently.

[0064] The electric power generation performance of the fuel cell 1000 in which the gas passage 28 is used and the electric power generation performance of a fuel cell in which the gas passage 270 is used (hereinafter, such fuel cell will be referred to as the "fuel cell 1000a") will be compared with each other with reference to FIG. 10. FIG. 10 is the graph showing the relationship between the output voltage and the output current of the fuel cell 1000 and the relationship between the output voltage and the output current of the fuel cell 1000a. In the graph 500, the vertical axis represents the output voltage, and the lateral axis represents the output current. In the graph 500, a solid line 510 indicates the relationship between the output voltage V and the output current I of the fuel cell 1000, in which the gas passage 28 is used, according to the first embodiment of the invention. A dashed line 520 indicates the relationship between the output voltage V and the output current I of the fuel cell 1000a in which the gas passage 270 described above is used.

[0065] As shown in the graph 500, as the output current I increases, the output voltage V of the fuel cell 1000a decreases more quickly than the output voltage V of the fuel cell 1000 does. For example, at the output current II, the output voltage V of the fuel cell 1000 is Vl, and the output voltage V of the fuel cell 1000a is V2. At the output current II, the output voltage V of the fuel cell 1000 is higher than the output voltage V of the fuel cell 1000a. The reasons for this will be described below.

[0066] The sizes of the meshes of the expand metal member vary. Accordingly, in the gas passage formed by stacking the expand metal members having the meshes which have the same shape and of which the major axes extend in the same direction in a manner in which the expand metal members are offset from each other in the longitudinal direction and/or the lateral direction, the meshes of the respective stacked expand metal members are highly likely to coincide with each other, and the partition walls are highly likely to be formed by the strand portions and the bond portions of the expand metal members. The formation of the partition walls interrupts the flow of the reaction gas, causing the reaction gas to flow and diffuse less efficiently.

[0067] In contrast, in the gas passage 28 according to the first embodiment of the invention, the directions in which the major axes of the meshes extend differ between the expand metal members stacked on top of each other. Accordingly, it is possible to minimize the coincidence of the strand portions and the bond portions of the stacked expand metal members. As a result, the formation of the partition walls is minimized. Accordingly, in the gas passage 28, the reaction gas flows more appropriately and diffuses into the MEGA more efficiently than in the gas passage 270. Therefore, concentration overvoltage in the fuel passage 28 is lower than that in the gas passage 270. Accordingly, the electric power generation efficiency of the fuel cell 1000 is higher than that of the fuel cell 1000a by approximately 10 %.

[0068] In the fuel cell according to the first embodiment of the invention, the gas passage is formed by stacking the expand metal members having the meshes of which the major axes extend in the directions different between these expand metal members. Accordingly, it is possible to minimize the coincidence of the strand portions and the bond portions of the successive expand metal members. As a result, it is possible to minimize the formation of the partition walls, which would be formed due to coincidence of the strand portions and the bond portions. Therefore, the reaction gas flows and diffuses more efficiently. Accordingly, the fuel cell generates electric power more efficiently.

[0069] In the fuel cell according to the first embodiment of the invention, the mesh of the expand metal has the major axis and the minor axis, and the directions in which the major axes of the meshes extend differ by 90 degrees between the successive expand metal members. Accordingly, it is possible to easily and highly accurately minimize the formation of the partition walls, which would occur if the meshes of the respective expand metal members coincide with each other.

[0070] In the fuel cell according to the first embodiment of the invention, the gas passage is formed by stacking the expand metal members on top of each other. Accordingly, the fuel cell is produced easily and at low cost. In addition, the quality of the fuel cell is easily controlled.

[0071] In the fuel cell according to the first embodiment of the invention, the gas diffusion layers are formed between the respective members in which the gas passage is formed and the MEA. Accordingly, the reaction gas flows through the gas passage and diffuses into the MEA more efficiently.

[0072] B. Second embodiment In the first embodiment of the invention described above, the gas passage is formed by stacking two expand metal members on top of each other. In contrast, in a second embodiment of the invention, the gas passage is formed by stacking three expand metal members on top of each other.

[0073] Bl. Structure of gas passage

A gas passage 260 according to the second embodiment of the invention will be described with reference to FIG. 11. FIG. 11 is the cross-sectional diagram schematically showing the structure of the gas passage 260 and the flow of the reaction gas according to the second embodiment of the invention. The gas passage 260 according to the second embodiment of the invention is formed by arranging a fourth expand metal member 32 between the members in which the gas passage 28 is formed according to the first embodiment of the invention and the MEGA 25. The fourth expand metal member 32 is the same as the first expand metal member 30. Namely, the direction in which the major axes of the meshes of the fourth expand metal member 32 extend is at an angle of 90 degrees with respect to the direction in which the major axes of the meshes 310 of the second expand metal member 31 extend. In the gas passage 260 formed by the three expand metal members, the directions in which the major axes of the meshes extend differ between the successive expand metal members. Accordingly, it is possible to minimize the formation of the partition walls, which would occur due to coincidence of the meshes of the successive expand metal members.

[0074] The flow of the reaction gas is indicated by the solid-line arrow in FIG. 11. The reaction gas supplied through the separator 40 impinges on the bond portions and the strand portions of the expand metal members, while flowing in the plane direction. By impinging on the bond portions and the strand portions of the expand metal members, the reaction gas flows in the normal-line direction, thereby diffusing into the MEGA 25.

[0075] Increasing the number of the expand metal members allows the reaction gas to diffuses more efficiently. Accordingly, in the gas passage 260 according to the second embodiment of the invention, the gas diffuses more efficiently than in the gas passage 28 according to the first embodiment of the invention. However, an increase in the number of the expand metal members increases the size of the fuel cell 1000. Therefore, the number of the expand metal members that forms the gas passage is preferably three in order to allow the gas to flow efficiently while minimizing an increase in the size of the fuel cell 1000. Note that, the number of the expand metal members that form the gas passage may be four or more.

[0076] C. Third embodiment

In a third embodiment of the invention, the gas passage is formed by arranging an expand metal member, which have the meshes that are smaller than the meshes of the other expand metal members, adjacent to the MEGA.

[0077] Cl. Structure of gas passage

A gas passage 261 according to the third embodiment of the invention will be described with reference to FIG. 12. FIG. 12 is the cross-sectional diagram schematically showing the structure of the gas passage and the flow of the reaction gas according to the third embodiment of the invention. The gas passage 261 is formed by arranging a fifth expand metal member 32a between the gas passage 28 according to the first embodiment of the invention and the MEGA 25. The major axes of the meshes of the fifth expand metal member 32a extend in the same direction as the direction in which the major axes of the meshes of the first expand metal member 30 extend. The mesh of the fifth expand metal member 32a is similar to and smaller than the mesh of the first expand metal member 30.

[0078] The flow of the reaction gas is indicated by the wave-like solid-line arrow. As shown in FIG. 12, the reaction gas supplied from the separator 40 impinges on the strand portions and the bond portions of the expand metal members, while flowing in the plane direction. By impinging on strand portions and the bond portions of the expand metal members, the reaction gas flows in the normal-line direction, thereby diffusing into the MEGA 25. Because the meshes of the fifth expand metal member 32a are smaller than the meshes of the first expand metal member 30 and the second expand metal member 31, the reaction gas diffuses into the MEGA 25 more efficiently than when the fifth expand metal member 32a is not arranged. [0079] With the gas passage 261 according to the third embodiment of the invention, the meshes of the fifth expand metal member 32a successive to the MEGA 25 are smaller than the meshes of the other expand metal members, and the directions in which the major axes of the meshes extend differ by 90 degrees between the successive expand metal members. Accordingly, the gas flows and diffuses into the MEGA more efficiently.

[0080] D. Modified example

According to the first to third embodiments of the invention described above, the gas passage is formed by stacking the expand metal members so that directions in which the major axes of the meshes extend differ by 90 degrees between the successive expand metal members. Alternatively, as shown in FIG. 13, the gas passage may be formed by stacking the expand metal members on top of each other so that the directions in which the major axes of the meshes extend differ by 45 degrees between the successive expand metal members.

[0081] FIG. 13 is the schematic diagram illustrating a gas passage 280 according to a modified example of the embodiments of the invention. In a schematic diagram 450, the plan view of the gas passage 280 and the cross sectional view of the gas passage 280, which is taken along the line XIII-XIII in the plan view are shown. In the schematic diagram 450, the corresponding portions in the plan view and the cross-sectional view are shown at the same positions in the direction in which the major axes of the meshes 300 extend. The gas passage 280 in the schematic diagram 450 is formed by stacking the first expand metal member 30 and a sixth expand metal member 36 on top of each other. The strand portions and the bond portions of the meshes 300 of the first expand metal member 30 and meshes 360 of the sixth expand metal member 36 are indicated by hatched patterns.

[0082] In the plan view in the schematic diagram 450, the direction in which the major axes of the meshes 300 extend and the direction in which the major axes of the meshes 360 extend are shown. In the gas passage 280 formed by stacking the first expand metal member 30 and the sixth expand metal member 36 on top of each other, the direction in which the major axes of the meshes 360 of the sixth expand metal member 36 extend is at an angle of 45 degrees with respect to the direction in which the major axes of the meshes 300 of the first expand metal member 30 extend.

[0083] Because the direction in which the major axes of the meshes 300 extend is at an angle of 45 degrees with respect to the direction in which the major axes of the meshes 360 extend, as shown in the cross-sectional view in the schematic diagram 450, the bond portions 302 of the first expand metal member 30 and the strand portions 361 of the sixth expand metal member 36 overlap with each other by a small amount. As a result, in the gas passage 280, communication is appropriately provided between the openings 303 and the openings 363, which allows the gas to flow efficiently.

[0084] The flow of the reaction gas in the gas passage 280 is shown by the heavy-line arrow in FIG. 13. As shown in FIG. 13, the reaction gas supplied from the separator 40 impinges on the bond portions 302 of the first expand metal member 30 and the strand portions 361 of the sixth expand metal member 36, while flowing through the openings 303 of the first expand metal member 30 and the openings 363 of the sixth expand metal member 36 in the plane direction. By impinging on the bond portions 302 of the first expand metal member 30 and the strand portions 361 of the sixth expand metal member 36, the reaction gas flows in the normal-line direction, thereby diffusing into the MEGA 25.

[0085] In the gas passage 280, it is possible to minimize the formation of the partition walls 600, which would occur if the meshes 300 of the first expand metal member 30 and the meshes 360 of the sixth expand metal member 36 coincide with each other. As a result, the reaction gas flows in the plane direction more efficiently, like the gas passage 28 according to the first embodiment of the invention. In addition, the reaction gas diffuses in the normal-line direction more efficiently.

[0086] According to the modified example of the embodiments of the invention, the direction in which the major axes of the meshes 360 extend is at an angle of 45 degrees with respect to the direction in which the major axes of the meshes 300. However, the angle is not limited to 45 degrees. If the directions in which the major axes of the meshes extend differ only by a small amount between the successive expand metal members, the gas diffuses efficiently.

[0087] According to the first embodiment of the invention, the flat-type expand metal members are used. Alternatively, for example, standard-type expand metal members that have not been rolled may be used.

[0088] According to the embodiments of the invention described above, the shape of the mesh of the expand metal members is rhomboid. Alternatively, the mesh may be, for example, parallelogram or testudinal.

[0089] According to the first embodiment of the invention, the expand metal members are used to form the gas passage. Alternatively, punching metal members formed by forming multiple through-holes in each metal plate may be used. In this case, the through-hole preferably has a shape having a major axis (major axis) and a minor axis (minor axis), for example, a rectangle or an ellipse.

[0090] According to the first embodiment of the invention, the outline of the expand metal member is rectangular. Alternatively, the outline of the expand metal member may be a shape that have equal axes (diameters), for example, a square or a circle. In this case, multiple expand metal members having the meshes which have the same shape and of which the major axes extend in the same direction are prepared. Then, the expand metal members are stacked on top of each other so that the orientations of the respective expand metal members differ by 90 degrees. Thus, it is possible to easily form the gas passage where the directions in which the major axes of the meshes extend between the successive expand metal members.

[0091] According to the first to third embodiments of the invention, the gas passage is formed by stacking multiple expand metal members. Alternatively, the gas passage may be formed by stacking multiple metal plates having uniformly-shaped through-holes therein.

[0092] According to the second embodiment of the invention, among the three expand metal members stacked on top of each other, the first expand metal member 30 and the fourth expand metal member 32 have the same characteristics. However, the first expand metal member 30 and the fourth expand metal member 32 need not have the same characteristics as long as the direction in which the major axes of the meshes of the fourth expand metal member 32 extend differs from the direction in which the major axes of the meshes of the second expand metal member 31 extend. For example, the direction in which the major axes of the meshes of the fourth expand metal member 32 extend may be at an angle of 45 degrees with respect to the direction in which the major axes of the meshes of the second expand metal member 31 extend.

[0093] While the invention has been described with reference to what are considered to be example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. On the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the described invention are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.

Claims

1. A fuel cell, comprising: a separator; a membrane electrode assembly in which catalyst electrode layers are formed on respective faces of an electrolyte membrane; a first metal plate which is arranged between the membrane electrode assembly and the separator, and in which uniformly-shaped first gas passage forming-holes that form a gas passage are regularly formed in multiple rows that extend in a first direction; and a second metal plate which is arranged between the membrane electrode assembly and the first metal plate, and in which second gas passage forming-holes that have identical shape with the first gas passage forming-holes are regularly formed in multiple rows that extend in a second direction which differs from the first direction.

2. The fuel cell according to claim 1, wherein each of the first gas passage forming-hole and the second gas passage forming-hole has a major axis and a minor axis, the major axis of the first gas passage forming-hole extends in the first direction, and the major axis of the second gas passage forming-hole extends in the second direction.

3. The fuel cell according to claim 2, wherein each of the first gas passage forming-hole and the second gas passage forming-hole is shaped in a parallelogram.

4. The fuel cell according to claim 2, wherein each of the first gas passage forming-hole and the second gas passage forming-hole is shaped in a rhombus.

5. The fuel cell according to claim 2, wherein each of the first gas passage forming-hole and the second gas passage forming-hole is shaped in a rectangle.

6. The fuel cell according to claim 2, wherein each of the first gas passage forming-hole and the second gas passage forming-hole is shaped in an ellipse.

7. The fuel cell according to claim 1, wherein each of the first gas passage forming-hole and the second gas passage forming-hole is shaped in a square.

8. The fuel cell according to any one of claims 1 to 7, wherein the second direction is at an angle of 90 degrees with respect to the first direction.

9. The fuel cell according to any one of claims 1 to 7, wherein

. the second direction is at an angle of 45 degrees with respect to the first direction.

10. The fuel cell according to any one of claims 1 to 9, further comprising: a third metal plate which is arranged between the second metal plate and the membrane electrode assembly, and in which third gas passage forming-holes that have identical shape with the second gas passage forming-holes are regularly formed in multiple rows that extend in a third direction which differs from the second direction.

11. The fuel cell according to any one of claims 1 to 10, further comprising: a fourth metal plate which is arranged between the second metal plate and the membrane electrode assembly, and in which fourth gas passage forming-holes that are geometrically similar to and smaller than the second gas passage forming-holes are regularly formed in multiple rows that extend in a fourth direction which differs from the second direction.

12. The fuel cell according to any one of claims 1 to 11, further comprising: a gas diffusion layer that is arranged between the membrane electrode assembly and the second metal plate, and that is formed of a porous member having electric conductivity.

13. The fuel cell according to any one of claims 1 to 12, wherein the separator is a three-layer separator that is formed by stacking three conductive metal plates having electric conductivity on top of each other.

14. The fuel cell according to any one of claims 1 to 13, wherein each of the metal plates is an expand metal member.