Fuel cell stack

Abstract

This fuel cell stack comprises: a cell laminate constituted by laminating, in a predetermined direction, a plurality of power generation cells each having a membrane electrode structure including an electrolyte membrane and an electrode, and a separator; a housing surrounding the cell laminate; and a restriction member which is disposed in a gap between an inner wall surface of the housing and an outer surface of the cell laminate, the surfaces facing each other, and limits movement of the cell laminate in a direction orthogonal to the predetermined direction. The separator has a pair of plates that are joined to each other and form a flow path through which a reaction gas flows, and a flow path through which a cooling medium flows. The pair of plates have, on an outer edge part that is within a predetermined range from an outer edge facing the restriction member, rib parts that protrude in predetermined directions and away from each other. The rib parts extend in a shape of recesses and protrusions along the outer edge when viewed from the laminating direction of the cell laminate.

Description

fuel cell stack

[0001] The present invention relates to a fuel cell stack.

[0002] In recent years, technological developments related to fuel cells that contribute to energy efficiency have been underway to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. As a technology related to fuel cell stacks used in this type of fuel cell, a technology has been known that prevents cell displacement in a fuel cell stack formed by stacking multiple cells when inertial forces act in a direction perpendicular to the stacking direction (see, for example, Patent Document 1). In the fuel cell stack described in Patent Document 1, a restraining member is disposed between the outer surface of the stack and the case, restraining the position of the stack in a direction perpendicular to the stacking direction.

[0003] Patent No. 6870603

[0004] When constructing a fuel cell stack as described in Patent Document 1, it is necessary to increase the strength of the outer surface of the stack that faces the restraining member to prevent deformation of the stack when it comes into contact with the restraining member. However, because the stack is made up of multiple thin plates, it is difficult to sufficiently increase the strength of the outer surface of the stack.

[0005] The fuel cell stack according to one aspect of the present invention includes a cell stack formed by stacking, in a predetermined direction, a plurality of power-generating cells, each having a membrane electrode assembly including an electrolyte membrane and an electrode, and a separator, a housing surrounding the cell stack, and a restricting member disposed in a gap between the opposing inner wall surfaces of the housing and the outer surface of the cell stack, the restricting member restricting movement of the cell stack in a direction perpendicular to the predetermined direction. The separator includes a pair of plates joined together to form a flow path for a reactant gas and a flow path for a coolant, the pair of plates having ribs protruding in a predetermined direction and in directions spaced apart from each other at their outer edges within a predetermined range from the outer edge facing the restricting member, the ribs extending in a wavy or uneven shape along the outer edge when viewed from the stacking direction of the cell stack.

[0006] According to the present invention, the strength of the outer surface of the cell stack can be sufficiently increased.

[0007] Fig. 1 is a perspective view schematically showing the overall configuration of a fuel cell stack according to an embodiment of the present invention. Fig. 2 is a cross-sectional view showing the configuration of a main part of the cell stack of Fig. 1. Fig. 3 is a perspective view showing the schematic configuration of an integrated electrode assembly incorporated into the fuel cell stack of Fig. 1. Fig. 4 is a cross-sectional view taken along line IV-IV of Fig. 1. Fig. 5 is an enlarged view of part VA of Fig. 4. Fig. 5A is an enlarged view of part VB of Fig. 5A. Fig. 5B is a cross-sectional view taken along line VI-VI of Fig. 5B. Fig. 6 is a schematic view showing the shape of the outer edge of a separator.

[0008] Hereinafter, an embodiment of the present invention will be described with reference to Figures 1 to 7. A fuel cell stack according to an embodiment of the present invention is included in a fuel cell as a main component of the fuel cell. The fuel cell is mounted, for example, in a vehicle and can generate power to drive the vehicle. The fuel cell can also be mounted in mobile objects other than vehicles, such as aircraft and ships, robots, and various industrial machines.

[0009] First, the overall configuration of the fuel cell stack will be described. FIG. 1 is a perspective view showing the overall configuration of a fuel cell stack 100 according to an embodiment of the present invention. Hereinafter, for convenience, three mutually orthogonal axial directions as shown in the figure are defined as the front-rear direction, the left-right direction, and the up-down direction, and the configuration of each part will be described according to these definitions. These directions are not necessarily the same as the front-rear direction, the left-right direction, and the up-down direction of a vehicle. The front-rear direction in FIG. 1 is the stacking direction of the fuel cell stack 100, and when assembling the fuel cell stack 100, the stacking direction is aligned with the direction of gravity to form a cell stack.

[0010] 1, the fuel cell stack 100 has a cell stack 10, end units 40 arranged at both front and rear ends of the cell stack 10, and a case 30 arranged around the cell stack 10, and has a generally rectangular parallelepiped shape as a whole. The case 30 and the end units 40 form a housing that surrounds the cell stack 10. The length of the fuel cell stack 100 in the left-right direction is longer than the length in the up-down direction.

[0011] The case 30 has four generally rectangular side walls 300 that face the top, right, bottom, and left sides of the cell stack 10. These four side walls 300 form a generally box-shaped storage space SP0 that is open on the front and back. The case 30 is made of a metal such as aluminum or iron.

[0012] The end unit 40 has a plurality of plates (not shown) stacked in the front-to-rear direction. More specifically, the end unit 40 has a terminal plate arranged on the inside in the front-to-rear direction, an insulating plate arranged on the outside in the front-to-rear direction of the terminal plate, and an end plate arranged on the outside in the front-to-rear direction of the insulating plate. When assembling the fuel cell stack 100, for example, the rear end unit 40 is laid on its side, and a plurality of power-generating cells 1 are stacked on top of it to assemble the cell stack 10, and then the front end unit 40 is mounted on top of the cell stack 10.

[0013] A plurality of guide members 51 (only some of which are shown) are interposed between the cell stack 10 and the side wall 300 of the case 30. The guide members 51 are rod-shaped members extending in the front-rear direction. Both front and rear ends of the guide members 51 are supported by the front and rear end units 40.

[0014] 1 shows a cutaway view of a part of a side wall 300 of the case 30. As shown in part A of Fig. 1, the cell stack 10 is formed by stacking a plurality of power generating cells 1 (for convenience, only a single power generating cell 1 is shown) in the storage space SP0 in the front-to-rear direction (in the up-and-down direction during assembly) while being guided by a guide member 51.

[0015] The power-generating cell 1 includes a unitized electrode assembly (UEA) 2 and separators 3 arranged on both the front and rear sides of the UEA 2 to sandwich the UEA 2. The separators 3 include two types of separators (first separator 31 and second separator 32) that differ in the shape of a portion of their outer edges. The UEA 2 and the separators 3 are arranged alternately in the front-rear direction. The first separator 31 and the second separator 32 are arranged alternately in the front-rear direction with the UEA 2 interposed therebetween. Hereinafter, using an arbitrary UEA 2 as a reference, the separator 3 arranged facing the front surface of the UEA 2 will be defined as the first separator 31, and the separator 3 arranged facing the rear surface of the UEA 2 will be defined as the second separator 32.

[0016] FIG. 2 is a cross-sectional view showing the main configuration of the cell stack 10. As shown in FIG. 2, the separator 3 includes a front plate 3F and a rear plate 3R, which are a pair of front and rear metal thin plates with a corrugated cross section. The front plate 3F extends vertically and horizontally and has a front surface 3Fa and a rear surface 3Fb. The rear plate 3R extends vertically and horizontally and has a front surface 3Ra and a rear surface 3Rb. The opposing rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R are joined at their outer edges by welding or the like. This integrally bonds the front plate 3F and the rear plate 3R to form the separator 3. The separator 3 is made of a conductive material with excellent corrosion resistance, such as stainless steel, titanium, or a titanium alloy.

[0017] A cooling flow path PAw through which a coolant flows is formed inside the separator 3 surrounded by the front plate 3F and the rear plate 3R, that is, between the rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R. The flow of the coolant cools the power generation surface of the power generation cell 1. Water, for example, can be used as the coolant. The surface of the separator 3 facing the UEA 2 (the front surface 3Fa and the rear surface 3Rb) is formed unevenly by press molding or the like to form a gas flow path between the separator 3 and the UEA 2.

[0018] More specifically, an anode flow path PAa through which a fuel gas containing hydrogen flows is formed between the front surface 2a of the UEA 2 and the rear plate 3R of the separator 3 facing this front surface 2a. A cathode flow path PAc through which an oxidizer gas containing oxygen flows is formed between the rear surface 2b of the UEA 2 and the front plate 3F of the separator 3 facing this rear surface 2b. The fuel gas and the oxidizer gas are sometimes referred to as reactant gases without distinction. A compressive load F is applied to the cell stack 10 in the front-to-rear direction during assembly of the fuel cell stack 100, and this compressive load F is maintained after assembly of the fuel cell stack 100 is complete.

[0019] 3 is a perspective view showing a schematic configuration of the UEA 2. The UEA 2 is sometimes called a membrane electrode assembly. As shown in FIG. 3, the UEA 2 has a membrane electrode assembly (MEA) 20 and a frame 21.

[0020] The MEA 20 includes an electrolyte membrane, an anode electrode provided on the front surface of the electrolyte membrane, and a cathode electrode provided on the rear surface of the electrolyte membrane. The electrolyte membrane is, for example, a solid polymer electrolyte membrane. The anode electrode includes an electrode catalyst layer formed on the front surface of the electrolyte membrane and serving as a reaction field for electrode reactions, and a gas diffusion layer provided on the front surface of the electrode catalyst layer and diffusing and supplying a fuel gas. The cathode electrode includes an electrode catalyst layer formed on the rear surface of the electrolyte membrane and serving as a reaction field for electrode reactions, and a gas diffusion layer provided on the rear surface of the electrode catalyst layer and diffusing and supplying an oxidant gas.

[0021] At the anode electrode, fuel gas (hydrogen) supplied via the anode flow channel PAa (FIG. 2) and gas diffusion layer is ionized by the action of a catalyst and moves through the electrolyte membrane to the cathode electrode. The electrons generated at this time pass through an external circuit and are extracted as electrical energy. At the cathode electrode, oxidant gas (oxygen) supplied via the cathode flow channel PAc (FIG. 2) and gas diffusion layer reacts with hydrogen ions introduced from the anode electrode and electrons transferred from the anode electrode to produce water. The produced water provides an appropriate humidity to the electrolyte membrane, and excess water is discharged outside the UEA2.

[0022] The frame 21 is a thin plate having a substantially rectangular shape and is made of insulating resin, rubber, or the like. A substantially rectangular opening 21a is provided in the center of the frame 21. The MEA 20 is provided so as to cover the entire opening 21a, and the outer edge of the MEA 20 is supported by the frame 21. On the left side of the opening 21a in the frame 21, three through-holes 201 to 203 are opened in a vertical line that penetrate the frame 21 in the front-to-rear direction. On the right side of the opening 21a, three through-holes 204 to 206 are opened in a vertical line that penetrate the frame 21 in the front-to-rear direction.

[0023] FIG. 4 is a cross-sectional view (cross-sectional view taken along line IV-IV in FIG. 1) showing the configuration of a main part of the fuel cell stack 100. FIG. 4 includes a rear view of the first separator 31. The first separator 31 and the second separator 32 are configured to have the same shape except for a portion of their outer edges. Therefore, the schematic configuration of the separator 3 will be described using FIG. 4. FIG. 4 shows a center point P0, which is the middle of the separator 3 in the left-right direction and the middle of the separator 3 in the up-down direction. Hereinafter, the side toward the center point P0 will be referred to as the inside of the separator 3, and the side radially away from the center point P0 will be referred to as the outside of the separator 3.

[0024] 4, although not shown in part, an uneven anode flow path PAa (FIG. 2) is formed in the vertical and horizontal central portion of the rear surface 3Rb of the separator 3, facing the front surface 2a of the MEA 20. Although not shown in part, an uneven cathode flow path PAc (FIG. 2) is formed in the vertical and horizontal central portion of the front surface 3Fa of the separator 3, facing the rear surface 2b of the MEA 20.

[0025] The separator 3 has through holes 301 to 306 that penetrate the separator 3 in the front-to-rear direction at positions corresponding to the through holes 201 to 206 ( FIG. 3 ) of the frame 21. The through holes 301 to 306 are connected to the through holes 201 to 206 of the frame 21, respectively. A collection of these through holes 201 to 206 and 301 to 306 that are connected to one another forms a plurality of flow paths that penetrate the cell stack 10 and extend in the front-to-rear direction.

[0026] Although not shown, a rear surface 3Rb of the separator 3 is provided with a seal portion that protrudes rearward to seal against leakage of fuel gas from the anode flow channel PAa. The seal portion is configured to allow communication between the through holes 301 and 306 and the anode flow channel PAa, while a seal rib prevents communication between the other through holes 302 to 305 and the anode flow channel PAa. Similarly, a front surface 3Fa of the separator 3 is provided with a seal portion that protrudes forward to seal against leakage of oxidant gas from the cathode flow channel PAc. The seal portion is configured to allow communication between the through holes 303 and 304 and the cathode flow channel PAc, while the seal portion prevents communication between the other through holes 301, 302, 305, and 306 and the cathode flow channel PAc.

[0027] 1, the rear end unit 40 has a plurality of through holes 401 to 406 that penetrate the end unit 40 in the front-to-rear direction at positions corresponding to the through holes 201 to 206 and 301 to 306. The front end unit 40 does not have the through holes 401 to 406.

[0028] A fuel gas tank storing high-pressure fuel gas is connected to through-hole 401 via an ejector, injector, etc., and the fuel gas is supplied to fuel cell stack 100 via through-hole 401, as shown by the solid arrow. This fuel gas is guided to anode flow path PAa via through-holes 201 and 301. After passing through anode flow path PAa, the fuel gas passes through through-holes 206 and 306 and is discharged from through-hole 406, as shown by the solid arrow.

[0029] An oxidant gas supply compressor is connected to through-hole 404, and as indicated by the dotted arrow, oxidant gas compressed by the compressor is supplied to fuel cell stack 100 via through-hole 404. This oxidant gas is guided to cathode flow path PAc via through-holes 204 and 304. After passing through cathode flow path PAc, the oxidant gas passes through through-holes 203 and 303 and is discharged from through-hole 403 as indicated by the dotted arrow.

[0030] A pump for supplying a cooling medium is connected to through-hole 405, and as shown by the dashed-dotted arrow, the cooling medium is supplied to fuel cell stack 100 through through-hole 405. This cooling medium is guided to cooling flow passage PAw between front plate 3F and rear plate 3R of separator 3 through through-holes 205 and 305. After passing through cooling flow passage PAw, the cooling medium passes through through-holes 202 and 302 and is discharged from through-hole 402 as shown by the dashed-dotted arrow.

[0031] As shown in FIG. 4 , impact receiving members 45 are disposed between the inner surface (case inner surface) 30a of the case 30 and the outer surface 10a of the cell stack 10. Specifically, if the four sides of the separator 3 are defined as an upper side 311, a right side 312, a lower side 313, and a left side 314, a pair of impact receiving members 45 is disposed in the space between the upper side 311 and the case inner surface 30a, the space between the right side 312 and the case inner surface 30a, the space between the lower side 313 and the case inner surface 30a, and the space between the left side 314 and the case inner surface 30a. The pair of impact receiving members 45 is provided near the corners of the cell stack 10. In other words, a pair of impact receiving members 45 is disposed near each of the four corners of the cell stack 10, sandwiching the four corners therebetween.

[0032] The impact receiving member 45 has a substantially rectangular cross section and extends over substantially the entire length of the cell stack 10 in the front-to-rear direction. The multiple impact receiving members 45 have the same cross-sectional shape. The impact receiving member 45 is an elastic material such as resin or rubber, and is made of an insulating material. The impact receiving member 45 is, for example, bonded in advance to the inner surface 30a of the side wall 300 of the case 30, and is provided integrally with the case 30. By providing the impact receiving member 45 near the corner of the cell stack 10, when, for example, a vehicle collides with an obstacle and an impact acts on the case 30 in a direction perpendicular to the stacking direction of the cell stack 10, the vicinity of the corner of the cell stack 10 will abut against the impact receiving member 45 due to inertial force. This effectively prevents the power generating cells 1 from shifting in position.

[0033] The fuel cell stack 100 is constructed by stacking the power generating cells 1 while positioning them via positioning parts. The UEAs 2 are integrated with the separators 3 in advance by welding or the like. For this reason, the separators 3 are provided with positioning parts, but the UEAs 2 are not. The UEAs 2 may be stacked alternately in the front-to-rear direction without being integrated with the separators 3.

[0034] The positioning portions include recesses 501 and 502 provided in the horizontal centers of the long sides of the separator 3, i.e., the upper side 311 and the lower side 313, and recesses 503 and 504 provided in the vertical centers of the short sides of the separator 3, i.e., the right side 312 and the left side 314. Chamfered portions 505 are provided at each of the four corners where the long and short sides intersect.

[0035] A plurality of guide members 51 are arranged inside the case in correspondence with the recesses 501 to 504 of the separator 3. The guide members 51 are configured so that their cross-sectional shape is constant from their lower end to their upper end. The plurality of guide members 51 have the same shape, and the cross-sectional shape is, for example, circular. The lower and upper ends of the plurality of guide members 51 fit into recesses or through-holes provided in the end unit 40, thereby positioning the guide members 51 at predetermined positions inside the case.

[0036] The separators 3 are stacked with the recesses 501 to 504 fitted into the guide members 51. This positions the separators 3 relative to the case 30, allowing the cell stack 10 to be constructed with high precision. The guide members 51 may have a generally L-shaped or T-shaped cross section instead of a circular cross section. The guide members 51 may be supported by the case 30 rather than the end units 40. For example, a guide support portion that supports one end of the generally L-shaped or T-shaped cross section along the cross section of the guide member may be provided on the inner surface 30a of the side wall 300 of the case 30, and the other end of the guide member along the cross section may be engaged with the recesses 501 to 504 of the separators 3.

[0037] This embodiment is characterized by the configuration of the separator 3 facing the impact receiving member 45, i.e., the configuration of the vicinity of the corners of the separator 3. This point will be described below. Fig. 5A is an enlarged view (enlarged view of portion VA in Fig. 4) showing a detailed configuration of the upper left corner of the rear surface 3Rb of the separator 3 (first separator 31), and Fig. 5B is an enlarged view of portion VB in Fig. 5A. Although not shown, the lower left corner, upper right corner, and lower right corner of the separator 3 are also configured in the same manner as in Figs. 5A and 5B.

[0038] 5A , convex bead portions 331 and 332 that seal the reactant gas, i.e., metal bead seals that protrude rearward, are provided double around the through-hole 301 of the separator 3. Although not shown, the inner bead portion 331 surrounds the through-hole 301 for supplying fuel gas ( FIG. 4 ), and the outer bead portion 332 surrounds the entire area through which the reactant gas flows, from the through-hole 301 for supplying fuel gas to the through-hole 304 for supplying oxidant gas, the through-hole 306 for discharging fuel gas, and the through-hole 303 for discharging oxidant gas.

[0039] The region near the outer edge of the separator 3, i.e., the region between the outer edge 33 and the bead portion 332, is referred to as the outer edge portion 34. In FIG. 5A , the outer edge 33 of the first separator 31 is indicated by a solid line, and the outer edge 33 of the second separator 32 is indicated by a two-dot chain line. The upper outer edge 33 of the first separator 31 is cut by punching from the right end of the chamfered portion 505 over a predetermined range AR1 to the right, by a predetermined width W from the outer edge 33 of the first separator 31. The upper outer edge 33 of the second separator 32 is cut by punching from the outer edge 33 of the second separator 32 over a predetermined range AR2 to the right of the predetermined range AR1 over a predetermined width W from the outer edge 33 of the second separator 32. Therefore, the first separator 31 and the second separator 32 do not overlap near the upper outer edges 33 when viewed from the stacking direction.

[0040] The left outer edge 33 of the second separator 32 is cut by punching from the lower end of the chamfered portion 505 to a predetermined range AR3 below the outer edge 33 of the second separator 32 by a predetermined width W. The left outer edge 33 of the first separator 31 is cut by punching from the outer edge 33 of the first separator 31 to a predetermined range AR4 below the predetermined range AR3 by a predetermined width W. Therefore, the first separator 31 and the second separator 32 do not overlap near the left outer edges 33 when viewed from the stacking direction. In other words, the outer edge 33 of the first separator 31 is cut in one of a pair of regions (predetermined ranges AR1, AR3) that sandwich the corner, and the outer edge 33 of the second separator 32 is cut in the other region.

[0041] A predetermined gap GP1 is provided in the left-right direction between the upper outer edge 33 of the separator 3 and the impact receiving member 45 facing this outer edge 33. A predetermined gap GP2 is provided in the up-down direction between the left outer edge 33 of the separator 3 and the impact receiving member 45 facing this outer edge 33. The gaps CL1 and CL2 may be the same value or different values. In this way, when no external impact is applied to the case 30, the predetermined gaps CL1 and CL2 are provided between the separator 3 and the impact receiving member 45. Therefore, the impact receiving member 45 does not have a positioning function when assembling the fuel cell stack 100.

[0042] Ribs 35 protruding forward and rearward from the front plate 3F and the rear plate 3R are provided on the outer edge 34 near the corners of the separator 3, more specifically, on the outer edge 34 in the predetermined ranges AR1 to AR4. The ribs 35 include an inner rib 350 extending seamlessly in the up-down and left-right directions along the outer edge 33 of the separator 3, an outer rib 360 extending substantially parallel to the inner rib 350 on the outside of the inner rib 350, and a plurality of intermediate ribs 370 provided between the inner rib 350 and the outer rib 360.

[0043] As shown in Fig. 5B, the inner rib 350 has a plurality of main rib portions 351 extending generally parallel to the outer edge 33 and a plurality of sub-rib portions 352 extending in a direction perpendicular to the outer edge 33. More specifically, the sub-rib portions 352 are provided so as to protrude inward (toward the through-hole 301) from the main rib portion 351 when viewed in the stacking direction. The inner ends of the pair of sub-rib portions 352 are bent into a generally arc shape and connected to each other at bent portions 353. The main rib portions 351 and the sub-rib portions 352 are provided alternately over a predetermined range AR1 to AR4 in Fig. 5A.

[0044] In other words, the inner rib 350 has a pair of imaginary lines LN1, LN2 parallel to the outer edge 33. The plurality of main rib portions 351 are scattered along the outer imaginary line LN1, and the plurality of bent portions 353 are scattered along the inner imaginary line LN2. The main rib portions 351 are located at offset positions (vertically offset in FIG. 5B ) along the outer edge 33, and the bent portions 353 are connected to both ends of the main rib portions 351 via the sub-rib portions 352. That is, the inner rib 350 alternates between outwardly protruding rib convex portions (main rib portions 351) and inwardly recessed portions (bent portions 353) along the outer edge 33, and extends in an uneven pattern when viewed from the stacking direction. The inner rib 350 may extend in a zigzag pattern or a wavy line when viewed from the stacking direction. In this case, the alternating recesses and protrusions result in an uneven pattern.

[0045] As shown in FIG. 5B , the outer rib 360 has multiple main rib portions 361 extending generally parallel to the outer edge 33 and multiple sub-rib portions 362 extending perpendicular to the outer edge 33. More specifically, the sub-rib portions 362 are provided so as to protrude outward (toward the outer edge 33) from the main rib portion 361 when viewed from the stacking direction, and the outer ends of a pair of sub-rib portions 362 are bent in a generally arc shape and connected to each other. The main rib portions 361 and the sub-rib portions 362 are provided alternately over a predetermined range AR1 to AR4 in FIG. 5A . Therefore, like the inner rib 350, the outer rib 360 extends in an uneven manner when viewed from the stacking direction.

[0046] As shown in FIG. 5B , welds 345 are provided in multiple regions between the outer rib 360 and the outer edge 33 and surrounded in a generally U-shape by the main rib portion 361 and the pair of sub-rib portions 362, 362. At the welds 345, the front plate 3F and the rear plate 3R are joined by laser welding or the like. However, as shown in FIG. 5A , in the predetermined ranges AR1 and AR4, the first separator 31 is cut away near its outer edge together with the welds 345, and in the predetermined ranges AR2 and AR3, the second separator 32 is cut away near its outer edge together with the welds 345. In this regard, in the predetermined ranges AR1 to AR4, the separators 31, 32 may be cut away near their outer edges outside the welds 345.

[0047] 5A and 5B , the main rib portion 361 of the outer rib 360 and the main rib portion 351 of the inner rib 350 are located at the same position in the left-right direction within the predetermined ranges AR1 and AR2, and at the same position in the up-down direction within the predetermined ranges AR3 and AR4. Therefore, the main rib portions 351 and 361 face each other across the intermediate rib 370. A weld 345 is provided near the outer rib 360 (toward the outer edge 33), but no weld is provided near the inner rib 350 (for example, on the side of the through hole 301).

[0048] As shown in FIG. 5B , the intermediate rib 370 has a pair of main rib portions 371 extending generally parallel to the outer edge 33 and a pair of sub-rib portions 372 extending generally perpendicular to the outer edge 33. More specifically, the sub-rib portions 372 are generally semicircular, and the intermediate rib 370 has an oval shape as a whole. The length of the main rib portion 371 of the intermediate rib 370 is equal to or approximately equal to the lengths of the main rib portions 351, 361 of the inner rib 350 and the outer rib 360, with some exceptions. Therefore, as shown in FIG. 5A , the three main rib portions 351, 361, 371 are located at the same position in the left-right direction in the predetermined ranges AR1, AR2, and the three main rib portions 351, 361, 371 are located at the same position in the up-down direction in the predetermined ranges AR3, AR4.

[0049] 5A , the inner rib 350 and the outer rib 360 extend obliquely along the chamfered portion 505 on the inside of the chamfered portion 505. The length (length in a direction parallel to the outer edge 33) of the intermediate rib 370 extending obliquely inside the chamfered portion 505 is longer than the lengths of the other intermediate ribs 370, but the width (length in a direction perpendicular to the outer edge 33) of this intermediate rib 370 is also wider than the widths of the other intermediate ribs 370. Therefore, the length-to-width ratio (aspect ratio) of all intermediate ribs 370 can be kept below a predetermined value.

[0050] As shown in FIG. 5B , the intermediate ribs 370 form an oval closed region AR5. Welds 346 are provided on the inside (closed region AR5) of each of the multiple intermediate ribs 370, and the welds 346 are scattered along the outer edge 33. The front plate 3F and the rear plate 3R are joined at the welds 346 by laser welding or the like. The welds 346 extend substantially parallel to the outer edge 33, except for a portion (inside the chamfered portion 505). As shown in FIG. 5A , a pair of welds 346 extending in a direction substantially perpendicular to the outer edge 33 is provided on the inside of the chamfered portion 505 on the inside of the intermediate rib 370.

[0051] 6 is a cross-sectional view (a cross-sectional view taken along line VI-VI in FIG. 5B) of the outer edge portion 34 of the separator 3. FIG. 6 shows a pair of first separators 31, 31 and a single second separator 32 disposed between the pair of separators 31, 31 via the frame 21 of the UEA 2.

[0052] As shown in Figure 6, an inner rib 350, an outer rib 360, and an intermediate rib 370 are provided on the front plate 3F and the rear plate 3R of each separator 31, 32, protruding in the front-rear direction. The tip surfaces of these ribs 350, 360, and 370 are in contact with the frame 21. As a result, the separator 3 and the frame 21 are pressed together by a compressive load F (Figure 2) in the front-rear direction during assembly of the fuel cell stack 100, and the frame 21 is sandwiched between the pair of front and rear separators 31, 32.

[0053] Providing the ribs 350, 360, and 370 on the outer edge portion 34 of the separator 3 in this manner improves the strength of the separator 3. This makes it possible to suppress deformation of the separator 3 when an external impact acts on the case 30 and the outer edge 33 of the separator 3 abuts against the impact receiving member 45. In particular, as shown in FIG. 5A , the inner rib 350 extends continuously along the outer edge 33, thereby increasing the rigidity of the separator 3 throughout the entire area near the corner of the separator 3. Furthermore, the inner rib 350 has a main rib portion 361 extending in a direction along the outer edge 33, in other words, approximately parallel to the outer edge 33, and a sub-rib portion 362 extending in a direction perpendicular to the outer edge 33, and is configured to have an uneven shape as a whole when viewed from the stacking direction. This makes it possible to configure the outer edge portion 34 more robust.

[0054] Furthermore, since the outer rib 360 is provided near the outer edge 33 of the separator 3, the strength of the outer edge 33 can be improved. Since the welded portion 345 is provided outside the outer rib 360, more specifically between the pair of sub-rib portions 362, 362, facing the main rib portion 361, it is possible to prevent the plates 3F, 3R from being misaligned near the outer rib 360. In FIG. 5A , a portion of the separator 3 is cut near the outer edge 33, so that the outer rib 360 is not continuous but is interrupted midway. However, like the inner rib 350, the outer rib 360 may be provided continuously along the outer edge 33. In this case, the inner rib 350 may be omitted.

[0055] Furthermore, since a plurality of intermediate ribs 370 are provided outside the inner rib 350 along the outer edge 33 of the separator 3, the strength of the outer edge portion 34 near the corners of the separator 3 can be further increased. In particular, each intermediate rib 370 has a pair of main rib portions 371 extending in a direction along the outer edge 33 and a pair of sub-rib portions 372 extending in a direction perpendicular to the outer edge 33, and is formed in a generally elliptical shape as a whole. This improves the bending strength of the separator 3 in the up-down and left-right directions, and can effectively suppress deformation of the outer edge portion 34 when the separator 3 abuts against the impact receiving member 45.

[0056] As shown in Fig. 5B , the intermediate rib 370 has a generally oval shape and defines a closed region AR5. A weld 346 is provided in this closed region AR5, generally parallel to the main rib portion 371. More specifically, as shown in Fig. 6 , a contact portion 347 is provided in the closed region AR5, where the rear end surface of the front plate 3F and the front end surface of the rear plate 3R contact each other, and the weld 346 is provided in the contact portion 347. This facilitates welding the plates 3F, 3R together and prevents misalignment of the plates 3F, 3R near the intermediate rib 370.

[0057] Furthermore, by providing the welded portion 346 in the closed area AR5, it is possible to easily ensure a welding area without interfering with the multiple ribs 350, 360, 370 of the outer edge portion 34. The multiple intermediate ribs 370 are evenly arranged in a direction along the outer edge 33 of the separator 3. Therefore, the welded portion 346 is also evenly arranged, and the plates 3F, 3R can be joined together well over the entire area along the outer edge 33.

[0058] 7 is a diagram of a portion of the outer edge 33 of the first separator 31 and the second separator 32, i.e., the outline of the separator 3 near the corner in FIG. 5A. In the figure, the outline of the frame 21 of the UEA 2 is indicated by hatching. As shown in FIG. 7, in the hatched insulating region AR10, the first separator 31 and the second separator 32 are arranged with the frame 21 sandwiched between them. This insulates the first separator 31 and the second separator 32 from each other.

[0059] On the other hand, the vicinity of the outer edge 33 of the separator 3 protrudes outward from the frame 21, but the separators 31, 32 are arranged so that the vicinity of the outer edges 33 do not overlap each other when viewed from the stacking direction. That is, of a pair of predetermined ranges AR1, AR3 adjacent to the corner, the first separator 31 protrudes outward from the frame 21 in one (upper) predetermined range AR3 but does not protrude in the other (left) predetermined range AR1. Furthermore, of a pair of predetermined ranges AR2, AR4 adjacent to the pair of predetermined ranges AR1, AR3, the first separator 31 protrudes outward from the frame 21 in one predetermined range AR2 but does not protrude in the other predetermined range AR4.

[0060] In contrast to the first separator 31, the second separator 32 protrudes outward from the frame 21 in the predetermined ranges AR1 and AR4 but does not protrude in the predetermined ranges AR2 and AR3. This increases the distance L between the separators 3, 3 (separators 31, 31 in FIG. 6) facing each other outside the frame 21, as shown in FIG. 6. As a result, a sufficient insulation distance can be ensured between the separators 3, 3 while the outer edge 33 of the separator 3 is configured to abut against the impact receiving member 45.

[0061] The present embodiment provides the following advantageous effects. (1) The fuel cell stack 100 includes a cell stack 10 configured by stacking, in the front-to-rear direction, a plurality of power-generating cells 1, each having a UEA 2 including an electrolyte membrane, an anode electrode, and a cathode electrode, and a separator 3; a case 30 surrounding the cell stack 10; and an impact-receiving member 45 disposed in the gap between the opposing inner wall surfaces (case inner surface 30a) of the case 30 and the outer surface 10a of the cell stack 10, to limit movement of the cell stack 10 in directions (left-right and up-down) perpendicular to the stacking direction (FIGS. 1 and 4). The separator 3 includes a pair of plates (a front plate 3F and a rear plate 3R) joined together to form an anode flow path PAa and a cathode flow path PAc through which reactant gas flows, and a cooling flow path PAw through which a coolant flows (FIG. 2). The pair of plates 3F, 3R have ribs 350, 360, 370, particularly the inner rib 350, that protrude in the front-rear direction and away from each other near the outer edge 33 that faces the impact receiving member 45, i.e., on the outer edge portion 34 within a predetermined range from the outer edge 33 (for example, within the range to the through-hole 301) ( FIGS. 5A, 5B, 6 ). The inner rib 350 extends unevenly along the outer edge 33 when viewed from the stacking direction ( FIG. 5A ). In other words, it extends unevenly in the left-right or up-down direction perpendicular to the stacking direction (front-rear direction).

[0062] This effectively improves the strength of the outer edge portion 34 of the separator 3. That is, the inner rib 350 has a component parallel to the outer edge 33 (main rib portion 351) and a component perpendicular to the outer edge 33 (sub-rib portion 352), and extends continuously along the outer edge 33, thereby increasing the rigidity of the separator 3 near the outer edge 33. As a result, deformation of the separator 3 when it abuts against the impact receiving member 45 can be suppressed, and displacement of the power generating cell 1 can be effectively prevented.

[0063] (2) In addition to the inner ribs 350, the pair of plates 3F, 3R further includes intermediate ribs 370 having sub-rib portions 372 extending perpendicular to the outer edge 34 ( FIG. 5A ). This improves the bending strength of the outer edge 34, effectively suppressing deformation of the separator 3.

[0064] (3) The pair of plates 3F, 3R has a plurality of intermediate ribs 370 between the outer edge 33 and the inner rib 350 (FIG. 5A). This can further increase the strength of the outer edge portion 34.

[0065] (4) The pair of plates 3F, 3R have multiple sub-rib portions 372 along the outer edge 33, and multiple abutting portions 347 between the multiple sub-rib portions 372 that abut against each other ( FIGS. 5A and 6 ). Multiple welds 346 that weld the pair of plates 3F, 3R together are provided at the multiple abutting portions 347 ( FIGS. 5A and 6 ). This firmly bonds the pair of plates 3F, 3R near the multiple sub-rib portions 372. This prevents the pair of plates 3F, 3R from shifting relative to each other when the separator 3 abuts against the impact receiving member 45, ensuring stable strength of the separator 3.

[0066] (5) The intermediate ribs 370 are provided so as to surround the welds 346 ( FIG. 5A ). In other words, the welds 346 are provided in the closed area AR5 formed by the intermediate ribs 370 ( FIG. 5B ). This increases the strength of the intermediate ribs 370, and effectively suppresses deformation of the separator 3.

[0067] (6) The separator 3 has a generally rectangular shape ( FIG. 4 ). The impact receiving members 45 are fixed to the inner wall surface of the case 30, and a pair of impact receiving members 45 are disposed on both sides of each corner of the separator 3 (e.g., on the right and bottom sides of the upper left corner) so as to sandwich each corner, with predetermined gaps GP1 and GP2 spaced from the outer edge 33 of the separator 3 ( FIGS. 4 and 5A ). This allows the highly rigid portions of the separator 3 near the corners to abut against the impact receiving members 45, effectively preventing deformation and displacement of the separator 3.

[0068] (7) A chamfered portion 505 is provided at each corner of the separator 3 (FIG. 4). Although stress tends to concentrate at the corners, providing the chamfered portion 505 can prevent the corners from coming into contact with the impact receiving member 45.

[0069] The above embodiment can be modified in various ways. Some modifications will be described below. In the above embodiment, the impact receiving member 45 as a limiting member is bonded to the case inner surface 30a, but the limiting member may be attached by a method other than bonding. In the above embodiment (FIG. 4), the impact receiving member 45 having a substantially rectangular cross section is disposed so as to sandwich the corner of the separator 3. However, the impact receiving member 45 may be configured to be substantially L-shaped so as to face the corner of the separator 3; the shape of the limiting member is not limited to the above. In the above embodiment (FIG. 1), the case 30 is configured in a substantially box shape, but the configuration of the housing is not limited to the above.

[0070] In the above embodiment ( FIG. 5B ), among the multiple ribs 350, 360, 370 (rib portions) of the plates 3F, 3R that protrude away from each other in the front-to-rear direction, the inner rib 350 (first rib portion) is configured to have an uneven shape with multiple main rib portions 351 and sub-rib portions 352 that protrude inward (toward the center point P0) from each main rib portion 351. However, the sub-rib portions 352 may also protrude outward (toward the outer edge 33) from the main rib portions 351, and the configuration of the first rib portion is not limited to that described above. Here, the uneven shape refers to a shape in which multiple convex portions that protrude in a direction perpendicular to the outer edge 33 (left-right or up-down direction) are provided along the outer edge 33 when viewed from the stacking direction, and includes wavy and zigzag shapes.

[0071] In the above embodiment ( FIG. 5A ), multiple intermediate ribs 370 (second rib portions) are provided between the outer edge 33 and the inner rib 350. However, the configuration of the second rib portions is not limited to the above, as long as they have sub-rib portions 352 (orthogonal portions) extending in a direction perpendicular to the outer edge 33. The second rib portions may be substantially rectangular rather than oval. In the above embodiment ( FIG. 1 ), the stack (cell stack 10) is formed by alternately stacking the UEAs 2 and separators 3 as membrane electrode assemblies including an electrolyte membrane and electrodes in the front-rear direction (a predetermined direction). However, the stacking direction is not limited to the front-rear direction and may be the up-down direction.

[0072] The above description is merely an example, and the present invention is not limited to the above-described embodiment and modifications as long as the features of the present invention are not impaired. One or more of the above-described embodiment and modifications can be arbitrarily combined, and modifications can also be combined with each other.

[0073] REFERENCE SIGNS LIST 1 Power generating cell, 2 Integrated electrode assembly, 3 Separator, 10 Cell stack, 30 Case, 31 First separator, 32 Second separator, 33 Outer edge, 34 Outer edge portion, 45 Impact receiving member, 100 Fuel cell stack, 346 Welded portion, 347 Abutment portion, 350 Inner rib, 351 Main rib portion, 352 Second rib portion, 360 Outer rib, 370 Intermediate rib, 371 Main rib portion, 372 Second rib portion, 505 Chamfered portion, GP1, GP2 Gap

Claims

1. A fuel cell stack comprising: a cell stack formed by stacking in a predetermined direction a plurality of power generation cells, each having a membrane electrode structure including an electrolyte membrane and electrodes, and a separator; a housing surrounding the cell stack; and a restricting member disposed in the gap between the opposing inner wall surfaces of the housing and the outer surface of the cell stack, and restricting movement of the cell stack in a direction perpendicular to the predetermined direction; wherein the separator has a pair of plates joined to each other to form a flow path for reactant gas and a flow path for cooling medium, and the pair of plates have rib portions at their outer edges within a predetermined range from the outer edge facing the restricting member, which protrude in the predetermined direction and in directions spaced apart from each other, and the rib portions extend unevenly along the outer edge when viewed from the stacking direction of the cell stack.

2. A fuel cell stack as described in claim 1, characterized in that the rib portion includes a first rib portion extending unevenly along the outer edge, and a second rib portion including an orthogonal portion extending in a direction perpendicular to the outer edge.

3. A fuel cell stack according to claim 2, wherein the pair of plates has a plurality of second rib portions between the outer edges and the first rib portions.

4. A fuel cell stack as claimed in claim 3, wherein the pair of plates have a plurality of orthogonal portions along the outer edges, and a plurality of abutting portions between the plurality of orthogonal portions that abut against each other, and a plurality of welds are provided at the abutting portions to weld the pair of plates together.

5. A fuel cell stack according to claim 4, wherein the second rib portions are arranged so as to surround the welded portions.

6. A fuel cell stack according to any one of claims 1 to 5, wherein the separators are generally rectangular, and the restricting members are fixed to the inner wall surface of the housing and are arranged in pairs on both sides of each corner of the separator, with a predetermined gap from the outer edge of the separator, so as to sandwich the corner.

7. A fuel cell stack according to claim 6, wherein each of the corners of the separator is provided with a chamfer.

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