Power generation cell

Abstract

According to the present invention, a first separator is disposed along the outer edge part of a membrane electrode structure and has a plurality of first protrusions that protrudes toward the opposite side of a first surface. A second separator is disposed along the outer edge part of the membrane electrode structure and has a plurality of second protrusions that protrudes toward the opposite side of a second surface. The plurality of first protrusions each have an elongated shape that extends along a plurality of first center lines, which are parallel to each other, with a first width that is orthogonal to the plurality of first center lines, and the plurality of second protrusions each have an elongated shape that extends along a plurality of second center lines, which are parallel to each other, with a second width that is orthogonal to the plurality of second center lines. In a plan view viewed from a direction that is perpendicular to the first surface, the first center lines and the second center lines are substantially parallel to each other, and the first width is narrower than the second width.

Description

Power generation cell

[0001] The present invention relates to a power generating cell for a fuel cell.

[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. One known technology related to power generation cells used in this type of fuel cell is a power generation cell that has multiple protrusions along the longitudinal periphery of the separator, protruding from the side opposite the electrolyte membrane (see, for example, Patent Document 1). In the power generation cell described in Patent Document 1, multiple first protrusions protruding from a first separator facing one side of the electrolyte membrane and multiple second protrusions protruding from a second separator facing the other side of the electrolyte membrane are configured to intersect at a predetermined angle and abut against each other.

[0003] Patent No. 7238761

[0004] However, when a power generation cell is constructed so that multiple first convex portions and multiple second convex portions intersect at a predetermined angle and abut against each other, as described in Patent Document 1, it is not possible to ensure sufficient contact area between the convex portions, and there is a risk that the separator will deform.

[0005] One aspect of the power generation cell of the present invention includes a membrane electrode assembly having an electrolyte membrane and a first electrode and a second electrode provided on both sides of the electrolyte membrane, respectively, and a frame member that supports the outer edge of the membrane electrode assembly. The membrane electrode assembly and the frame member are integrally formed into a membrane electrode structure. A first separator and a second separator are disposed opposite to the first surface and the second surface opposite to the first surface of the membrane electrode structure, respectively, and form gas flow paths through which reaction gases flow between the first electrode and the second electrode. The first separator is disposed along the outer edge of the membrane electrode structure and has a plurality of first convex portions protruding to the opposite side of the first surface. The second separator is disposed along the outer edge of the membrane electrode structure and has a plurality of second convex portions protruding to the opposite side of the second surface. The plurality of first convex portions are elongated and extend along a plurality of first center lines parallel to each other with a first width perpendicular to the plurality of first center lines. The plurality of second convex portions are elongated and extend along a plurality of second center lines parallel to each other with a second width perpendicular to the plurality of second center lines. In a plan view seen from a direction perpendicular to the first surface, the first center line and the second center line are substantially parallel to each other, and the first width is narrower than the second width.

[0006] According to the present invention, deformation of a pair of separators where the convex portions contact each other can be suppressed.

[0007] Perspective view schematically showing the overall configuration of a fuel cell stack having a power generation cell according to an embodiment of the present invention. Cross-sectional view taken along line II-II of FIG. 1. Perspective view showing the schematic configuration of an integrated electrode assembly constituting a power generation cell according to an embodiment of the present invention. Front view showing the schematic configuration of a separator constituting a power generation cell according to an embodiment of the present invention. Enlarged view of part V in FIG. 4 on the front surface of the separator. Enlarged view of the corresponding part in FIG. 5A on the rear surface of the separator. Cross-sectional view taken along line VI-VI of FIG. 5A. Cross-sectional view taken along line VII-VII of FIG. 5A. Cross-sectional view taken along line VIII-VIII of FIG. 5A. Diagram for explaining the positional relationship between the main part of the separator and the integrated electrode assembly. Cross-sectional view taken along line X-X of FIG. 5A. Front view of the main part of a separator different from FIG. 5A.

[0008] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 11. A power-generating cell according to an embodiment of the present invention is a power generating element that constitutes a fuel cell stack included in a fuel cell. The fuel cell is mounted on, for example, a vehicle and generates electric power for driving the vehicle. First, the overall configuration of a fuel cell stack will be described in brief. A fuel cell stack may also be simply called a fuel cell.

[0009] FIG. 1 is a perspective view showing a schematic view of the overall configuration of a fuel cell stack 100. 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. In other words, the front-rear direction in FIG. 1 may be the front-rear direction, the left-right direction, or the up-down direction of a vehicle.

[0010] 1 , the fuel cell stack 100 has a cell stack 101 formed by stacking a plurality of power-generating cells 1 in the front-to-rear direction, and end units 102 disposed at both front-to-rear ends of the cell stack 101, and has a generally rectangular parallelepiped shape as a whole. Although not shown, a generally box-shaped case with open front and rear faces is disposed around the cell stack 101. The front end face of the case and the front end unit 102, and the rear end face of the case and the rear end unit 102 are fastened together with bolts.

[0011] The power-generating cell 1 includes a unitized electrode assembly (UEA) 2 having a membrane electrode assembly including an electrolyte membrane and electrodes, and a pair of front and rear separators 3, 3 arranged on both the front and rear sides of the UEA 2 and sandwiching the UEA 2. The UEA 2 and the separators 3 are arranged alternately in the front-rear direction. The UEA 2 is a membrane electrode structure, which may also be called a membrane electrode member. Point P in FIG. 1 is the center point of the power-generating cell 1 in the vertical and horizontal directions. Hereinafter, the side of center point P may be referred to as the inner side or inside, and the outer edge side of the power-generating cell 1 (the side opposite center point P) may be referred to as the outer side or outside.

[0012] FIG. 2 is a cross-sectional view (a cross-sectional view taken along line II-II in FIG. 1 ) showing a schematic configuration of the power generation region of the cell stack 101. 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 is a substantially rectangular plate member extending in the vertical and horizontal directions and has a front surface 3Fa and a rear surface 3Fb. The rear plate 3R is a substantially rectangular plate member extending in the vertical and horizontal directions and has a front surface 3Ra and a rear surface 3Rb. The outer peripheral edge of the rear surface 3Fb of the front plate 3F and the outer peripheral edge of the front surface 3Ra of the rear plate 3R, which face each other, are joined by welding or the like, thereby integrating the front plate 3F and the rear plate 3R. The separator 3 is made of a conductive material with excellent corrosion resistance, such as stainless steel, titanium, or a titanium alloy.

[0013] 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, i.e., 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. The surfaces of the separator 3 facing the UEA 2 (the front surface 3Fa and the rear surface 3Rb) are formed unevenly by press molding or the like to form gas flow paths between the separator 3 and the UEA 2. More specifically, the front plate 3F and the rear plate 3R each have a protrusion 31 that protrudes toward the front and rear UEA 2, and a recess 32 that is formed concave and convex and continuous with the protrusion 31.

[0014] The rear end surface (contact surface) 310a of the rear convex portion 31 abuts against the front surface 2a of the UEA 2. The front end surface (contact surface) 310c of the front convex portion 31 abuts against the rear surface 2b of the UEA 2. A compressive load F is applied to the cell stack 101 in the front-to-rear direction when the fuel cell stack 100 is assembled, and in this state, the cases surrounding the cell stack 101 are fastened to the front and rear end units 102. Therefore, after assembly of the fuel cell stack 100 is complete, the compressive load F is maintained on the cell stack 101, and a predetermined surface pressure acts on the UEA 2 in the front-to-rear direction via the convex portion 31.

[0015] Between the front surface 2a of the UEA 2 and the rear plate 3R of the separator 3, an anode flow channel PAa through which fuel gas flows is formed by a recess 32. The anode flow channel PAa has a generally trapezoidal cross section and includes a bottom surface 320a of the recess 32 and a pair of inclined surfaces 320b extending obliquely upward and downward from both upper and lower ends of the bottom surface 320a to the abutment surface 310a. The width of the anode flow channel PAa (the vertical length of the recess 32) gradually increases from the bottom surface 320a to the abutment surface 310a. The rear plate 3R is sometimes referred to as the anode separator.

[0016] Between the rear surface 2b of the UEA 2 and the front plate 3F of the separator 3, a cathode flow channel PAc through which oxidant gas flows is formed by a recess 32. The cathode flow channel PAc has a generally trapezoidal cross section and includes a bottom surface 320c of the recess 32 and a pair of inclined surfaces 320d extending obliquely upward and downward from both the upper and lower ends of the bottom surface 320c to the abutment surface 310c. The width of the cathode flow channel PAc (the vertical length of the recess 32) gradually increases from the bottom surface 320c to the abutment surface 310c. The front plate 3F is sometimes referred to as a cathode separator. The fuel gas and the oxidant gas are sometimes referred to as reactant gases without distinction. In FIG. 2, the anode flow channel PAa and the cathode flow channel PAc are depicted as having the same vertical position and flow channel width, but in reality, they are different (see FIG. 4).

[0017] Fig. 3 is a perspective view showing a schematic configuration of the UEA 2. As shown in Fig. 3, the UEA 2 has a substantially rectangular membrane electrode assembly (MEA) 20 and a frame 21 that supports the MEA 20. Fig. 2 also includes a cross-sectional view of the MEA 20 as a cross-sectional view of the UEA 2. As shown in the detailed view of portion A in Fig. 2, the MEA 20 has an electrolyte membrane 23, an anode electrode 24 provided on a front surface 23f of the electrolyte membrane 23, and a cathode electrode 25 provided on a rear surface 23r of the electrolyte membrane 23.

[0018] The electrolyte membrane 23 is, for example, a solid polymer electrolyte membrane, and a thin film of a perfluorosulfonic acid polymer containing water can be used. The electrolyte membrane 23 is not limited to a fluorine-based electrolyte membrane, and a hydrocarbon-based electrolyte membrane can also be used.

[0019] The anode 24 is formed on the front surface 23f of the electrolyte membrane 23 and includes an electrode catalyst layer 241 that serves as a reaction field for an electrode reaction, and a gas diffusion layer 242 that is provided on the front surface of the electrode catalyst layer 241 and diffuses and supplies a fuel gas. The cathode 25 is formed on the rear surface 23r of the electrolyte membrane 23 and includes an electrode catalyst layer 251 that serves as a reaction field for an electrode reaction, and a gas diffusion layer 252 that is provided on the rear surface of the electrode catalyst layer 251 and diffuses and supplies an oxidizer gas. An intermediate layer (base layer) may be provided between the electrode catalyst layers 241, 251 and the gas diffusion layers 242, 252.

[0020] The electrode catalyst layers 241, 251 contain a catalytic metal that promotes an electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas, a proton-conductive electrolyte (e.g., ionomer), and electron-conductive carbon particles, etc. The gas diffusion layers 242, 252 are made of a gas-permeable conductive material, such as a porous carbon material.

[0021] At the anode electrode 24, the fuel gas (hydrogen) supplied through the anode flow path PAa is ionized by the action of a catalyst and moves toward the cathode electrode side through the electrolyte membrane 23. The electrons generated at this time pass through an external circuit and are extracted as electrical energy. At the cathode electrode 25, the oxidizer gas (oxygen) supplied through the cathode flow path PAc reacts with the hydrogen ions introduced from the anode electrode 24 and the electrons transferred from the anode electrode 24 to generate water. The generated water (referred to as "generated water") provides an appropriate humidity to the electrolyte membrane 23, and excess water is discharged to the outside of the UEA 2 along the gas flow. The generated water on the cathode side also flows toward the anode side by back diffusion through the electrolyte membrane 23. Therefore, both the fuel gas and the oxidizer gas contain generated water. Condensed water is also contained in the fuel gas and the oxidizer gas.

[0022] As shown in FIG. 3 , the frame 21 is a thin plate having a substantially rectangular shape and is made of insulating and gas-impermeable resin, rubber, or the like. Examples of materials that can be used include PEN (polyethylene naphthalate) and PPS (polyphenylene sulfide). A substantially rectangular opening 21a is formed in the center of the frame 21, and the MEA 20 is provided to cover the entire opening 21a. The frame 21 has a substantially rectangular outer edge 221 and an inner edge 222. The outer edge 221 refers to the outer edge of the frame 21 and its surrounding area, and the inner edge 222 refers to the inner edge of the frame 21 (the edge of the opening 21a) and its surrounding area.

[0023] Three through holes 201 to 203 are aligned vertically and penetrate the frame 21 in the front-to-rear direction on the left side of the opening 21a of the frame 21. Three through holes 204 to 206 are aligned vertically and penetrate the frame 21 in the front-to-rear direction on the right side of the opening 21a. For convenience, the through holes 201 to 206 are shown as being substantially rectangular, but the shapes and positions of the through holes 201 to 206 are not limited to this.

[0024] As shown in FIG. 1 , the front and rear separators 3 of the UEA 2 are provided with through-holes 301-306, respectively, that penetrate the separators 3 in the front-rear direction at positions corresponding to the through-holes 201-206 in the frame 21. The through-holes 301-306 are connected to the through-holes 201-206 in the frame 21, respectively. The interconnected through-holes 201-206 and 301-306 collectively form flow paths PA1-PA6 (indicated by arrows for convenience) that penetrate the cell stack 101 and extend in the front-rear direction. The flow paths PA1-PA6 are sometimes called manifolds. The flow paths PA1-PA6 are connected to a manifold external to the fuel cell stack 100.

[0025] Although not shown in the figure, the front and rear end units 102 of the cell stack 101 each have a plurality of plates stacked in the front-to-rear direction. Specifically, the end unit 102 has a terminal plate arranged adjacent to the cell stack 101, an insulating plate arranged on the outer side of the terminal plate in the front-to-rear direction, and an end plate arranged on the outer side of the insulating plate in the front-to-rear direction.

[0026] The rear end unit 102 is a wet-side end unit through which the reactant gas and the cooling medium pass, and the front end unit 102 is a dry-side end unit through which the reactant gas and the cooling medium do not pass. The rear end unit 102 has a plurality of through-holes 102a-102f that penetrate the end unit 102 in the front-rear direction at positions corresponding to the through-holes 201-206, 301-306 of the cell stack 101. For convenience, the through-holes 102a-102f are shown as being substantially rectangular, but the shape of the through-holes 102a-102f is not limited to this.

[0027] Flow paths PA1 and PA6 (solid arrows) are flow paths for supplying and discharging fuel gas, respectively. Flow paths PA1 and PA6 communicate with an anode flow path PAa ( FIG. 2 ) provided opposite the front surface of the MEA 20, and as shown by the solid arrows, fuel gas flows to the right through the anode flow path PAa via flow paths PA1 and PA6. Communication between the anode flow path PAa and the other flow paths PA2 to PA5 is blocked by a seal portion (not shown).

[0028] The flow paths PA4 and PA3 (dotted arrows) are flow paths for supplying and discharging oxidant gas, respectively. The flow paths PA4 and PA3 communicate with the cathode flow path PAc ( FIG. 2 ) provided opposite the rear surface of the MEA 20, and as shown by the dotted arrows, the oxidant gas flows leftward through the cathode flow path PAc via the flow paths PA4 and PA3. The communication between the cathode flow path PAc and the other flow paths PA1, PA2, PA5, and PA6 is blocked by a seal (not shown).

[0029] Flow paths PA5 and PA2 (indicated by dashed-dotted arrows) are flow paths for supplying and discharging the cooling medium, respectively. The flow paths PA5 and PA2 communicate with a cooling flow path PAw (FIG. 2) provided inside the separator 3, and the cooling medium flows through the cooling flow path PAw via the flow paths PA5 and PA2. Communication between the cooling flow path PAw and the other flow paths PA1, PA3, PA4, and PA6 is blocked by a seal portion (not shown).

[0030] The power generating cell 1 of this embodiment is characterized by the configuration of the separator 3. The configuration of the separator 3 will be described in more detail below. FIG. 4 is a front view (viewed from the front) showing the schematic configuration of the separator 3. More specifically, it is a diagram showing the front surface 3Fa (FIG. 3) of the separator 3 (front plate 3F) facing the cathode electrode 25 on the rear surface 2b of the UEA 2. The region AR1 in the figure is the region where power generation occurs in the MEA 20 of the UEA 2 facing the separator 3, and is called the active region (power generation region). The region AR2 outside the active region AR1 (outside in the left-right and up-down directions) is the region where power generation does not occur, and is called the inactive region (non-power generation region).

[0031] As shown in FIG. 4 , a plurality of protrusions 31 ( FIG. 2 ) are provided in the active region AR1 of the front plate 3F of the separator 3, some of which are not shown, and are protruding forward at equal intervals in the vertical direction across almost the entire area. Each of the plurality of protrusions 31 extends in the left-right direction, and recesses 32 ( FIG. 2 ) are provided between adjacent protrusions 31 in the vertical direction. A cathode flow path PAc is formed between the recesses 32 and the rear surface 2b ( FIG. 2 ) of the MEA 20. Although not shown, a plurality of protrusions 31 ( FIG. 2 ) are also provided in the active region AR1 of the rear plate 3R of the separator 3, and are protruding rearward at equal intervals in the vertical direction. Recesses 32 ( FIG. 2 ) are provided between adjacent protrusions 31 in the vertical direction, and an anode flow path PAa is formed between the recesses 32 and the front surface 2a ( FIG. 2 ) of the MEA 20.

[0032] The detailed view of section B in FIG. 4 shows the detailed configuration of each gas flow channel PAc, PAa. In this detailed view, the boundary where the bottom surface 320c ( FIG. 2 ) of the cathode flow channel PAc intersects with the inclined surface 320d is indicated by a solid line, and the boundary where the bottom surface 320a ( FIG. 2 ) of the anode flow channel PAa behind the cathode flow channel PAc intersects with the inclined surface 320b is indicated by a dotted line. As shown in the detailed view of section B in FIG. 4 , the cathode flow channel PAc (solid line) extends in a wavy shape in the left-right direction while meandering up and down. The anode flow channel PAa (dotted line) also extends in a wavy shape in the left-right direction while meandering up and down. That is, each gas flow channel PAc, PAa is formed by alternating upwardly convex bends (mountain bends) PAc1, PAa1 and downwardly convex bends (valley bends) PAc2, PAa2 in the left-right direction.

[0033] The peak-side bend PAc1 of the cathode flow channel PAc and the valley-side bend PAa2 of the anode flow channel PAa are located at the same position in the left-right direction, as are the valley-side bend PAc2 of the cathode flow channel PAc and the peak-side bend PAa1 of the anode flow channel PAa. Therefore, the longitudinal pitch of the cathode flow channel PAc (the length from the bend PAc1 to the bend PAc1 adjacent to each other in the left-right direction) and the longitudinal pitch of the anode flow channel PAa (the length from the bend PAa1 to the bend PAa1 adjacent to each other in the left-right direction), which correspond to the wavelength of the waveform, are equal to each other, and the gas flow channels PAc and PAa are formed with a half-pitch offset from each other in the left-right direction. In other words, the phase difference between the gas flow channels PAa and PAc is π, and the gas flow channels PAa and PAc are formed in opposite phases.

[0034] On the other hand, the pitch Pc (the distance between the cathode channels PAc, PAc) between the vertically aligned cathode channels PAc is shorter than the widthwise pitch Pa (the distance between the anode channels PAa, PAa) between the vertically aligned anode channels PAa. Therefore, the total area of ​​the cathode channel PAc is larger than the total area of ​​the anode channel PAa. This is because the oxidant gas has a large pressure loss and is difficult to flow.

[0035] In the inactive area AR2 on the front surface 3Fa of the front plate 3F of the separator 3, a plurality of sealing bead portions, i.e., metal bead seals, are provided by press molding and protrude forward toward the frame 21. The plurality of bead portions include a plurality of end bead portions 331 that individually surround the through holes 301, 302, 305, and 306, and outer bead portions 332 that surround the active area AR1, the inactive areas AR2 above and below it, and the through holes 303 and 304 through which the oxidizer gas flows.

[0036] A resin sealant ( FIG. 6 ) is fixed to the tops of the bead portions 331, 332. The bead portions 331, 332 are in close contact with the rear surface 2b of the UEA 2 (frame 21) via the sealant, thereby forming a flow space through which oxidizer gas flows, sealed from the outside, from the through-hole 304 to the cathode flow channel PAc and the through-hole 303. The sealant may be omitted, and the tops of the bead portions 331, 332 may be directly abutted against the rear surface of the frame 21. End bead portions 331 may be provided inside the outer bead portion 332 and around the through-holes 303, 304. In this case, a tunnel portion may be provided that intersects the end bead portion 331 and bulges rearward from the front surface 3Fa of the front plate 3F, and the inside and outside of the end bead portion 331 may be connected via the tunnel portion.

[0037] Although not shown, multiple bead portions for sealing, i.e., metal bead seals, protruding rearward toward the frame 21 are similarly formed by press molding in the inactive region AR2 on the rear surface 3Rb of the rear plate 3R of the separator 3. The multiple bead portions include multiple end bead portions that individually surround the through holes 302-305, as well as outer bead portions that surround the active region AR1, the inactive regions AR2 above and below it, and the through holes 301 and 306 through which the fuel gas flows. The end bead portions may be provided around the through holes 301 and 306 together with tunnel portions. These bead portions are in close contact with the front surface 2a of the UEA2 (frame 21), with or without a sealing material, thereby forming a flow space through which the fuel gas flows, sealed from the outside, from the through hole 301 to the anode flow channel PAa and the through hole 306.

[0038] The front plate 3F and rear plate 3R of the separator 3 are welded together at welds 333. As shown by dotted lines in Fig. 4 , the welds 333 extend along the outer edges of the plates 3F and 3R, outside the outer bead portions 332 and the end bead portions 331. Although not shown, welds that weld the front plate 3F and rear plate 3R together are also provided outside the through holes 301, 303, 304, and 306 (outside the end bead portions 331) so as to individually surround the entire through holes 301, 303, 304, and 306.

[0039] A plurality of generally cylindrical protrusions 334 are provided inside the outer bead portion 332 on the left and right sides of the active region AR1 on the front surface 3Fa of the separator 3, protruding toward the front UEA2. Although not shown, a plurality of generally cylindrical protrusions are also provided inside the outer bead portion 332 on the left and right sides of the active region AR1 on the rear surface 3Rb of the separator 3, protruding toward the rear UEA2. These protrusions 334 form buffer portions for uniforming the flow of oxidant gas between the through holes 303, 304 and the cathode flow channel PAc, and the flow of fuel gas between the through holes 301, 306 and the anode flow channel PAa.

[0040] Instead of the protrusion 334, a guide portion may be provided so as to form a flow path from the through hole 304 to the entire cathode flow path inlet and from the entire cathode flow path outlet to the through hole 303. Furthermore, a guide portion may be provided so as to form a flow path from the through hole 301 to the entire anode flow path inlet and from the entire anode flow path outlet to the through hole 306.

[0041] On the front surface 3Fa of the separator 3, bypass suppression portions 350 are provided across the left and right between the active region AR1 and the outer bead portions 332 above and below it. Similarly, on the rear surface 3Rb of the separator 3, bypass suppression portions 360 are provided across the left and right between the active region AR1 and the outer bead portions 332 above and below it. The bypass suppression portions 350 have a function of suppressing the flow of oxidant gas that bypasses the cathode flow channel PAc without passing through it. The bypass suppression portions 360 have a function of suppressing the flow of fuel gas that bypasses the anode flow channel PAa without passing through it.

[0042] The configuration of the bypass suppression portions 350, 360 will be described in detail. FIG. 5A is an enlarged view of portion V in FIG. 4 showing the configuration of the bypass suppression portion 350 on the front surface 3Fa of the separator 3, and FIG. 5B is an enlarged view of the opposite side of portion V in FIG. 4 (rear surface 3Rb) showing the configuration of the bypass suppression portion 360 on the rear surface 3Rb of the separator 3. Hereinafter, the rear side of the front plate 3F and the front side of the rear plate 3R, i.e., the side facing the coolant (opposite side from UEA2), will be referred to as the coolant side. Furthermore, the front side of the front plate 3F and the rear side of the rear plate 3R, i.e., the gas flow path PAa, PAc side (UEA2 side), will sometimes be referred to as the gas side.

[0043] In the following description, the gas side is mainly used as the reference, and when viewed from the gas side, the portion protruding toward the gas side is called a convex portion, and the portion protruding toward the cooling medium side is called a concave portion. If the cooling medium surface side is used as the reference, the relationship between the concave portion and the convex portion is reversed.

[0044] 5A and 5B , the outer bead portion 332 below (outside) the bypass suppression portions 350, 360 extends in the left-right direction while meandering in the up-down direction while maintaining a predetermined vertical width W. That is, the outer bead portion 332 is formed in a wavy shape by alternating upwardly convex bends (peak-side bends) 332 a and downwardly convex bends (valley-side bends) 332 b in the left-right direction.

[0045] The pitch in the longitudinal direction (left-right direction) of the outer bead portion 332, which corresponds to the wavelength of the waveform, is half the pitch in the longitudinal direction of the gas flow paths PAa and PAc. Therefore, the valley-side bend portion 332b is located at the same left-right position as the crest-side bend portions PAc1 and PAa1 and the valley-side bend portions PAc2 and PAa2 of the gas flow paths PAc and PAa. The crest-side bend portion 332a is located midway between the crest-side bend portions PAc1 and PAa1 and the valley-side bend portions PAc2 and PAa2 of the gas flow paths PAc and PAa.

[0046] The weld 333 extends in the left-right direction while meandering up and down so as to be substantially parallel to the outer bead 332. Because the width (vertical length) of the weld 333 is very small, the weld 333 is shown by a solid line in Fig. 5A. A flange 335 is provided on the outside of the weld 333 (the lower side in Fig. 5A ), extending in the left-right direction while meandering up and down so as to be substantially parallel to the outer bead 332. The outer bead 332 protrudes toward the gas side, the weld 333 protrudes toward the coolant side, and the flange 335 protrudes toward the gas side (see Fig. 6 ).

[0047] 5A , the bypass suppression section 350 includes a flat portion 351 that is generally flat in the vertical and horizontal directions, and a plurality of vertically elongated recesses 352 and a plurality of horizontally elongated recesses 353 that are recessed from the flat portion 351 toward the coolant, i.e., protrude toward the coolant. Each of the vertically elongated recesses 352 has an elongated shape in the vertical direction and is arranged side by side at equal intervals in the horizontal direction. Specifically, a predetermined number (six in the figure) of vertically elongated recesses 352 are arranged at equal intervals between adjacent mountain-side bend portions PAc1, PAc1 in the horizontal direction of the cathode flow path PAc.

[0048] The vertically elongated recess 352 has a bottom surface 352a and an inclined surface 352b that rises from the bottom surface 352a toward the gas side, and the width (left-right length) and length (up-down length) gradually increase from the bottom surface 352a to the flat portion 351. The upper and lower ends of the vertically elongated recess 352 are formed in a substantially arc shape. The width of the vertically elongated recess 352 is substantially constant over the entire vertical length. The widths of the multiple vertically elongated recesses 352 are the same.

[0049] On the other hand, the lengths of the multiple vertically elongated recesses 352 are not the same. Specifically, of the vertically elongated recess 3521 facing the mountain-side bending portion PAc1, the vertically elongated recess 3522 facing the valley-side bending portion PAc2, the vertically elongated recesses 3523 on the left and right sides of the vertically elongated recess 3521, and the vertically elongated recesses 3524 on the left and right sides of the vertically elongated recess 3522, the vertically elongated recess 3521 is the longest and the vertically elongated recess 3524 is the shortest. The multiple vertically elongated recesses 352 are provided symmetrically with respect to the vertically elongated recess 3521.

[0050] The upper ends of the vertically elongated recesses 3521, 3523 are located at the same vertical position, and the upper end of the vertically elongated recess 3524 is located below (outside) the upper ends of the vertically elongated recesses 3521, 3523, and the upper end of the vertically elongated recess 3522 is located below (outside) the upper end of the vertically elongated recess 3524. That is, the positions of the upper ends of the vertically elongated recesses 352 gradually shift downward from the crest-side bend portion PAc1 to the valley-side bend portion PAc2 of the cathode flow channel PAc. This allows for the formation of a flat portion 351 that is continuous and uninterrupted in the left-right direction and has a vertical length equal to or greater than a predetermined length between the multiple vertically elongated recesses 352 and the recess 320 that constitutes the lowest cathode flow channel PAc.

[0051] The bottom ends of the vertically elongated recesses 3521 and 3522 are positioned at the same vertical position, and the bottom ends of the vertically elongated recesses 3523 and 3524 are also positioned at the same vertical position. The bottom ends of the vertically elongated recesses 3521 and 3522 are positioned lower (outside) than the bottom ends of the vertically elongated recesses 3523 and 3524. The left-right positions of the vertically elongated recesses 3521 and 3522 are the same as the left-right position of the valley-side bend portion 332b of the outer bead portion 332.

[0052] The horizontally elongated recesses 353 are provided between the vertically elongated recesses 352 and the outer bead portion 332. More specifically, the horizontally elongated recesses 353 are continuous with the peak-side bend 332a of the outer bead portion 332 and extend in a generally arc-like shape in the left-right direction around the peak-side bend 332a. The horizontally elongated recesses 353 have a bottom surface 353a and an inclined surface 353b that rises from the bottom surface 353a toward the gas side, and the width (vertical length) and length (left-right length) gradually increase from the bottom surface 353a to the flat portion 351.

[0053] The width of the horizontally elongated recess 353 is substantially constant over the entire length in the left-right direction. The horizontally elongated recesses 353 are provided symmetrically with respect to the position of the mountain-side bending portion PAc1. For example, on the right side of the mountain-side bending portion PAc1, the left end of the horizontally elongated recess 353 is located between the vertically elongated recess 3521 and the vertically elongated recess 3523 and near the vertically elongated recess 3521. The right end of the horizontally elongated recess 353 is located between the vertically elongated recess 3522 and the vertically elongated recess 3524 and near the vertically elongated recess 3522.

[0054] The lower (outer) edge of the flat portion 351 has an arc portion 351a extending in a substantially arc shape along the horizontally elongated recess 353, and a protruding portion 351b protruding toward the valley-side bend 332b between the horizontally adjacent horizontally elongated recesses 353, 353. In an area AR10 between the protruding portion 351b and the valley-side bend 332b of the outer bead portion 332 below the protruding portion 351b, the front surface 3Fa of the separator 3 extends downward (outward) at an incline toward the gas side, and then extends downward substantially parallel to the rear surface 2b of the UEA 2.

[0055] Furthermore, the front surface 3Fa of the separator 3 extends from the left end of the horizontally elongated recess 353 on the right side of the protrusion 351b and the right end of the horizontally elongated recess 353 on the left side of the protrusion 351b toward the protrusion 351b, slanting toward the gas side, and then extends in the left-right direction approximately parallel to the rear surface 2b of the UEA 2 in the left-right intermediate part of the region AR10. Therefore, in the region AR10, the front surface 3Fa of the separator 3 protrudes toward the gas side beyond the flat portion 351.

[0056] 5B , the bypass suppression section 360 includes a flat portion 361 that is generally flat in the up-down and left-right directions, and a plurality of vertically elongated recesses 362 and a plurality of horizontally elongated recesses 363 that are recessed from the flat portion 361 toward the coolant side, in other words, that protrude toward the coolant side. Each of the vertically elongated recesses 362 has an elongated shape in the up-down direction and is arranged side by side at equal intervals in the left-right direction. Specifically, a predetermined number (six in the figure) of vertically elongated recesses 362 are arranged at equal intervals between mountain-side bend portions PAa1, PAa1 that are adjacent in the left-right direction of the anode flow channel PAa.

[0057] The vertically elongated recess 362 has a bottom surface 362a and an inclined surface 362b that rises from the bottom surface 362a toward the gas side, and the width (left-right length) and length (up-down length) gradually increase from the bottom surface 362a to the flat portion 361. The upper and lower ends of the vertically elongated recess 362 are formed in a substantially arc shape. The width of the vertically elongated recess 362 is substantially constant over the entire vertical length. The widths of the multiple vertically elongated recesses 362 are the same.

[0058] On the other hand, the lengths of the multiple vertically elongated recesses 362 are not the same. Specifically, of the vertically elongated recess 3621 facing the mountain-side bending portion PAa1, the vertically elongated recess 3622 facing the valley-side bending portion PAa2, the vertically elongated recesses 3623 on the left and right sides of the vertically elongated recess 3621, and the vertically elongated recesses 3624 on the left and right sides of the vertically elongated recess 3622, the vertically elongated recess 3621 is the longest and the vertically elongated recess 3622 is the shortest. The multiple vertically elongated recesses 362 are provided symmetrically with respect to the vertically elongated recess 3621.

[0059] The upper end of the vertically elongated recess 3621 is located at the uppermost position (innermost), the upper end of the vertically elongated recess 3623 is located below (outside) the upper end of the vertically elongated recess 3621, the upper end of the vertically elongated recess 3624 is located below (outside) the upper end of the vertically elongated recess 3623, and the upper end of the vertically elongated recess 3622 is located below (outside) the upper end of the vertically elongated recess 3624. In other words, the positions of the upper ends of the vertically elongated recesses 362 gradually shift downward from the crest-side bend portion PAa1 to the valley-side bend portion PAa2 of the anode flow channel PAa. This allows for the formation of a flat portion 361 that is continuous and uninterrupted in the left-right direction between the multiple vertically elongated recesses 362 and the recess 320 that constitutes the lowest anode flow channel PAa, and that has a vertical length of at least a predetermined length.

[0060] The bottom ends of the vertically elongated recesses 3621 and 3622 are positioned at the same vertical position, and the bottom ends of the vertically elongated recesses 3623 and 3624 are also positioned at the same vertical position. The bottom ends of the vertically elongated recesses 3621 and 3622 are positioned slightly lower (outside) than the bottom ends of the vertically elongated recesses 3623 and 3624. The left-right positions of the vertically elongated recesses 3621 and 3622 are the same as the left-right position of the valley-side bend portion 332b of the outer bead portion 332.

[0061] The horizontally elongated recesses 363 are provided between the vertically elongated recesses 362 and the outer bead portion 332. More specifically, the horizontally elongated recesses 363 are continuous with the peak-side bend 332a of the outer bead portion 332 and extend in a generally arc-like shape in the left-right direction around the peak-side bend 332a. The horizontally elongated recesses 363 have a bottom surface 363a and an inclined surface 363b that rises from the bottom surface 363a toward the gas side, and the width (vertical length) and length (left-right length) gradually increase from the bottom surface 363a to the flat portion 361.

[0062] The width of the horizontally elongated recess 363 is substantially constant over the entire length in the left-right direction. The multiple horizontally elongated recesses 363 are provided symmetrically with respect to the position of the mountain-side bending portion PAa1. For example, on the right side of the mountain-side bending portion PAa1, the left end of the horizontally elongated recess 363 is located between the vertically elongated recess 3621 and the vertically elongated recess 3623 and near the vertically elongated recess 3621. The right end of the horizontally elongated recess 363 is located between the vertically elongated recess 3622 and the vertically elongated recess 3624 and near the vertically elongated recess 3622.

[0063] The lower (outer) edge of the flat portion 361 has an arc portion 361a extending in a substantially arc shape along the horizontally elongated recess 363, and a protruding portion 361b protruding slightly toward the valley-side bend 332b between the horizontally adjacent horizontally elongated recesses 363, 363. In an area AR20 between the protruding portion 361b and the valley-side bend 332b of the outer bead portion 332 below the protruding portion 361b, the rear surface 3Rb of the separator 3 extends downward (outward) at an incline toward the gas side, and then extends downward substantially parallel to the front surface 2a of the UEA2.

[0064] Furthermore, the rear surface 3Rb of the separator 3 extends obliquely toward the gas side from the left end of the horizontally elongated recess 363 on the right side of the protrusion 361b and the right end of the horizontally elongated recess 363 on the left side of the protrusion 361b toward the protrusion 361b, and then extends in the left-right direction approximately parallel to the front surface 2a of the UEA2 in the left-right intermediate portion of the region AR20. Therefore, in the region AR20, the rear surface 3Rb of the separator 3 protrudes toward the gas side beyond the flat portion 351. The protrusion amount of the anode-side protrusion 361b is very small, and the protrusion 361b may be omitted.

[0065] The multiple vertically elongated recesses 352 (3521 to 3524) of the front plate 3F and the multiple vertically elongated recesses 362 (3621 to 3624) of the rear plate 3R are located at the same positions relative to one another in the left-right direction. Therefore, the rear end surfaces of the multiple vertically elongated recesses 352 and the front end surfaces of the multiple vertically elongated recesses 362 abut against one another. Specifically, the vertically elongated recess 3521 abuts against the vertically elongated recess 3622, the vertically elongated recess 3522 abuts against the vertically elongated recess 3621, the vertically elongated recess 3523 abuts against the vertically elongated recess 3624, and the vertically elongated recess 3524 abuts against the vertically elongated recess 3623, respectively. At this time, the rear end surface of the horizontally elongated recess 353 abuts against the front end surface of the horizontally elongated recess 363.

[0066] The cross-sectional shape of the power-generating cell 1 will now be described. Fig. 6 is a cross-sectional view of the power-generating cell 1 taken along line VI-VI in Figs. 5A and 5B, and Fig. 7 is a cross-sectional view of the power-generating cell 1 taken along line VII-VII in Figs. 5A and 5B. Figs. 6 and 7 schematically show the configuration of a single power-generating cell 1, i.e., the configuration from a boundary surface SF1 that defines the rear end surface of the front plate 3F to a boundary surface SF2 that defines the front end surface of the rear plate 3R. The boundary surfaces SF1 and SF2 extend in the up-down and left-right directions, and the boundary surfaces SF1 and SF2 of power-generating cells 1, 1 adjacent in the front-rear direction coincide with each other. For convenience, the scale of some of the configuration (such as thickness) is appropriately changed from the actual scale in Figs. 6 and 7.

[0067] As shown in Figures 6 and 7, the frame 21 of the UEA 2 is composed of a front frame 21F and a rear frame 21R. An adhesive (not shown) is applied between the rear surface 21Fb of the front frame 21F and the front surface 21Ra of the rear frame 21R, and the front frame 21F and the rear frame 21R are joined together via the adhesive. The inner edge 222 (Figure 3) of the front frame 21F extends upward (inward) than the inner edge 222 of the rear frame 21R. Therefore, the inner edge of the front frame 21F is located above the inner edge of the rear frame 21R.

[0068] The electrolyte membrane 23 and the anode-side electrode catalyst layer 241 are disposed inside the inner edge of the front frame 21F. The outer edges of the electrolyte membrane 23 and the electrode catalyst layer 241 are positioned at the same vertical position, and the electrolyte membrane 23 and the electrode catalyst layer 241 are disposed with a predetermined gap from the inner edge of the front frame 21F. The cathode-side electrode catalyst layer 251 is disposed inside the inner edge of the rear frame 21R. The electrode catalyst layer 251 extends downward (outside) beyond the inner edge of the front frame 21F, and the electrode catalyst layer 251 is disposed with a predetermined gap from the inner edge of the rear frame 21R.

[0069] The anode-side gas diffusion layer 242 extends downward (outward) beyond the outer edges of the electrolyte membrane 23 and electrode catalyst layer 241 and the inner edge of the front frame 21F. The lower end of the gas diffusion layer 242, i.e., the outer edge 242a, overlaps the inner edge 222 of the front frame 21F and is disposed in close contact with the front surface 21Fa of the front frame 21F. The cathode-side gas diffusion layer 252 extends downward (outward) beyond the outer edge of the electrode catalyst layer 251 and the inner edge of the rear frame 21R. The lower end of the gas diffusion layer 252, i.e., the outer edge 252a, overlaps the rear frame 21R and is disposed in close contact with the rear surface 21Rb of the rear frame 21R. The outer edges of the gas diffusion layers 242, 252 are positioned at the same vertical position.

[0070] The gas flow paths PAa and PAc are sealed by the gas diffusion layers 242 and 252 being in close contact with the frames 21F and 21R in this manner, which prevents the reaction gas and generated water from leaking from the gas flow paths PAa and PAc to the space SP1 formed between the gas diffusion layers 242 and 252, the outer bead portion 332, and the separator 3 through the contact surfaces between the UEA2 and the separator 3.

[0071] The rear end surface 32r of the recess 32 forming the cathode flow path PAc, the rear end surface 352r of the vertically elongated recess 352 ( FIG. 7 ), the rear end surface 353r of the horizontally elongated recess 353 ( FIG. 6 ), and the rear end surface 333r of the rib portion 333a (where the welded portion 333 is provided) provided below (outside) the outer bead portion 332 each protrude rearward by a predetermined length and are located on boundary surface SF1. The front end surface 32f of the recess 32 forming the anode flow path PAa, the front end surface 362f of the vertically elongated recess 362 ( FIG. 7 ), the front end surface 363f of the horizontally elongated recess 363 ( FIG. 6 ), and the front end surface 333f of the rib portion 333b (where the welded portion 333 is provided) provided below (outside) the outer bead portion 332 each protrude forward by a predetermined length and are located on boundary surface SF2.

[0072] The rear end surface 32r of the recess 32 forming the cathode flow path PAc and the front end surface 32f of the recess 32 forming the anode flow path PAa abut against each other (see the detailed view of part B in FIG. 4). The rear end surface 352r of the vertically elongated recess 352 abuts against the front end surface 362f of the vertically elongated recess 362. The rear end surface 353r of the horizontally elongated recess 353 abuts against the front end surface 363f of the horizontally elongated recess 363. The rear end surface 333r of the rib portion 333a abuts against the front end surface 333f of the rib portion 333b. Welds 333 are provided on the abutting surfaces of the ribs 333a and 333b.

[0073] The front end surface (contact surface 310c) of the protrusion 31 protruding forward from the cathode flow path PAc and the surface (front end surface) of the flat portion 351 of the bypass suppression portion 350 are located on an imaginary plane SF10 extending forward of and substantially parallel to the boundary surface SF1. The contact surface 310c and the surface of the flat portion 351 are pressed against the rear end surface of the gas diffusion layer 252, thereby sealing the cathode flow path PAc.

[0074] The front end surfaces of the outer bead portion 332 and the flange portion 335 of the front plate 3F are located forward of the imaginary plane SF10. A sealant 336 is fixed to the front end surface of the outer bead portion 332, and the outer bead portion 332 is pressed against the outer edge portion 221 (near the outer edge) of the rear frame 21R via the sealant 336. The flange portion 335 abuts against the outer edge portion 221 of the rear frame 21R without the sealant. Therefore, the front end surface of the flange portion 335 is located forward of the front end surface of the outer bead portion 332 by the thickness of the sealant 336.

[0075] The rear end surface (contact surface 310a) of the protrusion 31 protruding rearward from the anode flow path PAa and the surface (rear end surface) of the flat portion 361 of the bypass suppression portion 360 are located on an imaginary plane SF20 that extends rearward of and substantially parallel to the boundary surface SF2. The contact surface 310a and the surface of the flat portion 361 are pressed against the front end surface of the gas diffusion layer 242, thereby sealing the anode flow path PAa.

[0076] The rear end surface of the outer bead portion 332 of the rear plate 3R and the rear end surface of the flange portion 335 are located rearward of the imaginary plane SF20. A sealant 336 is fixed to the rear end surface of the outer bead portion 332, and the outer bead portion 332 is pressed against the outer edge portion 221 (near the outer edge) of the front frame 21F via the sealant 336. The flange portion 335 abuts against the front frame 21F without the sealant. Therefore, the rear end surface of the flange portion 335 is located rearward of the rear end surface of the outer bead portion 332 by the thickness of the sealant 336.

[0077] 7, the front plate 3F has a bulging portion 354 that bulges forward from the flat portion 351 between the flat portion 351 below the vertically elongated recess 352 and the outer bead portion 332 (area AR10 in FIG. 5A). The gap between the bulging portion 354 and the rear frame 21R is smaller than the gap between the flat portion 351 and the rear frame 21R. The bulging portion 354 may be flush with the front end surface of the outer bead portion 332, or may be located rearward of the front end surface of the outer bead portion 332.

[0078] The rear plate 3R also has a bulging portion 364 that bulges rearward from the flat portion 361, located between the flat portion 361 below the vertically elongated recess 362 and the outer bead portion 332 (region AR20 in FIG. 5B ). The gap between the bulging portion 364 and the front frame 21F is smaller than the gap between the flat portion 361 and the front frame 21F. The bulging portion 364 may be flush with the rear end surface of the outer bead portion 332, or may be located forward of the rear end surface of the outer bead portion 332.

[0079] FIG. 8 is a cross-sectional view of the power-generating cell 1 taken along line VIII-VIII in FIG. 5A. As shown in FIG. 8, the spaces between the rear frame 21R and the horizontally elongated recesses 353 arranged side by side in the left-right direction are connected via gaps between the bulges 354 and the rear frame 21R. As a result, a bypass flow path PAb (cathode-side bypass flow path PAb1) is formed between the front plate 3F of the separator 3 and the rear frame 21R, bypassing the cathode flow path PAc ( FIG. 5A ) via the horizontally elongated recesses 353 and the bulges 354. Oxidant gas flows from right to left through the cathode-side bypass flow path PAb1, as indicated by the arrow in FIG. 8. However, because the bypass flow path PAb1 is narrowed by the bulges 354, the flow of oxidant gas is restricted.

[0080] Furthermore, the spaces between the front frame 21F and the horizontally elongated recesses 363 arranged side by side in the left-right direction are connected via gaps between the bulges 364 and the front frame 21F. As a result, a bypass flow path PAb (anode-side bypass flow path PAb2) that bypasses the anode flow path PAa ( FIG. 5B ) is formed between the rear plate 3R of the separator 3 and the front frame 21F via the horizontally elongated recesses 363 and the bulges 364. Fuel gas flows from left to right through the anode-side bypass flow path PAb2, as shown by the arrow in FIG. 8 . However, because the bypass flow path PAb2 is narrowed by the bulges 364, the flow of fuel gas is restricted.

[0081] As shown in Fig. 6 , the outer bead portion 332 is located below (outside) the lower ends (outer edges) of the gas diffusion layers 242, 252. The horizontally elongated recesses 353, 363 of the separator 3 are also located below the lower ends of the gas diffusion layers 242, 252. As shown in Fig. 7 , the upper ends of the vertically elongated recesses 352, 362 of the separator 3 are located above (inside) the lower ends of the gas diffusion layers 242, 252, and the lower ends of the vertically elongated recesses 352, 362 are located below (outside) the lower ends of the gas diffusion layers 242, 252. In other words, the lower ends of the gas diffusion layers 242, 252 are located midway between the vertically elongated recesses 352, 362.

[0082] This embodiment is characterized by the positional relationship, particularly in the vertical direction, between the bypass suppression units 350, 360 and the UEA 2. Fig. 9 is a diagram showing the positional relationship between the bypass suppression unit 350 of the front plate 3F and the UEA 2. Although not shown, the positional relationship between the bypass suppression unit 360 of the rear plate 3R and the UEA 2 is also the same as that shown in Fig. 9.

[0083] As shown in Figure 9, the lower end face SF11, which is the outer edge of the electrolyte membrane 23 and the anode-side electrode catalyst layer 241, is located above (inside) the lower end of the cathode flow path PAc. The lower end face SF12, which is the outer edge of the cathode-side electrode catalyst layer 251, is located near the upper end of the vertically elongated recess 352. The lower end face SF13, which is the outer edge of the gas diffusion layers 242, 252, is located near the lower end of the vertically elongated recess 352. The power generation cell 1 is capable of generating power in an active region AR1 where the electrolyte membrane 23, anode electrode 24, and cathode electrode 25 overlap. In this embodiment, the active region AR1 does not overlap any of the multiple vertically elongated recesses 352 and is located above (inside) the vertically elongated recesses 352.

[0084] Dimensional errors and assembly errors occur in each part of the power-generating cell 1. As a result, the positions of the bottom end faces SF11 of the electrolyte membrane 23 and the electrode catalyst layer 241 relative to the separator 3 may be shifted within a predetermined range ΔSF11. Also, the position of the bottom end face SF12 of the electrode catalyst layer 251 relative to the separator 3 may be shifted within a predetermined range ΔSF12. Furthermore, the position of the bottom end faces SF13 of the gas diffusion layers 242, 252 relative to the separator 3 may be shifted within a predetermined range ΔSF13.

[0085] Even if the bottom end surfaces SF11 of the electrolyte membrane 23 and the electrode catalyst layer 241 were shifted downward to their maximum extent, the bottom end surfaces SF11 would not overlap the cathode-side vertically elongated recess 352 and the anode-side vertically elongated recess 362. In other words, the connection line LN1 obtained by sequentially connecting the upper ends of the multiple vertically elongated recesses 352, 362 in the left-right direction is located outside the active area AR1 defined by the bottom end surface SF11. This prevents water generated in the active area AR1 from accumulating in the vertically elongated recesses 352, 362.

[0086] Furthermore, even if the bottom end surfaces SF13 of the gas diffusion layers 242, 252 are shifted upward to the maximum extent, the bottom end surfaces SF13 overlap the cathode-side vertically elongated recesses 352 and the anode-side vertically elongated recesses 362. In other words, the connection line LN1 is covered over its entire length by the gas diffusion layers 242, 252. Therefore, at least the region AR3 (hatched in FIG. 9 ) of the flat portions 351, 361 between the vertically elongated recesses 352, 362 and the gas flow paths PAc, PAa is entirely covered by the gas diffusion layers 252, 242. This prevents the gas flow paths PAc, PAa from communicating with the vertically elongated recesses 352, 362 through the gap between the UEA2 and the separator 3.

[0087] Furthermore, even if the bottom end surfaces SF13 of the gas diffusion layers 242, 252 are displaced downward to the maximum extent, the bottom end surfaces SF13 do not overlap with the cathode-side horizontally elongated recesses 353 and the anode-side horizontally elongated recesses 363. Therefore, the bypass flow paths PAb formed along the multiple horizontally elongated recesses 353, 363 can be prevented from being blocked by the gas diffusion layers 242, 252.

[0088] The main operation of the power-generating cell 1 according to this embodiment will now be described. When fuel gas is supplied to the anode flow path PAa via the flow path PA1 and through-hole 301 shown in FIG. 1 and oxidant gas is supplied to the cathode flow path PAc via the flow path PA4 and through-hole 304 shown in FIG. 1 , power generation occurs in the active region AR1. At this time, water is generated in the active region AR1, but the vertically elongated recesses 352 and 362 do not face the active region AR1. Therefore, the water is not guided to the vertically elongated recesses 352 and 362, thereby preventing the water from accumulating in the vertically elongated recesses 352 and 362. Furthermore, iron ions eluted from the separator 3 can be prevented from reaching the electrolyte membrane 23, thereby preventing deterioration of the electrolyte membrane 23.

[0089] A portion of the reactant gas supplied through the through holes 301, 304 bypasses the gas flow paths PAa, PAc, but this bypass flow is suppressed by the bypass suppression portions 350, 360. The bypass suppression portions 350, 360 not only suppress the bypass flow but also abut the front plate 3F and the rear plate 3R of the separator 3 to bear a compressive load. In particular, in this embodiment, the bypass suppression portions 350, 360 are provided with multiple vertically elongated recesses 352, 362 that protrude toward the coolant side, so that the bypass suppression portions 350, 360 (flat portions 351, 361) abut against the gas diffusion layers 242, 252 over a wide area. This reduces the flow path area for the bypass flow compared to when protrusions protruding toward the gas side are provided, thereby effectively suppressing the bypass flow.

[0090] The reactant gas that bypasses the gas flow paths PAa and PAc flows laterally through the bypass flow path PAb, as shown in FIGS. 8 and 9. The bypass suppression portions 350 and 360 have protruding portions 351b and 361b (FIGS. 5A and 5B) that protrude toward the bypass flow path PAb and bulging portions 354 and 364 (FIG. 8) that bulge toward the bypass flow path PAb. Therefore, the area of ​​the bypass flow path PAb is reduced between the horizontally adjacent horizontally elongated recesses 353, 353, thereby suppressing the bypass flow.

[0091] If stagnant water exists in the area facing the bypass suppression portions 350, 360, the bypass flow of reactant gas flowing through the bypass flow path PAb can suck the stagnant water. In particular, the bypass flow path PAb is provided with a throttle portion formed by the protrusions 351b, 361b and the bulges 354, 364. This creates a pressure difference between the bypass flow path PAb and the vertically elongated recesses 352, 362, enhancing the effectiveness of suctioning stagnant water. Lateral bypass flow of reactant gas can also occur in the space SP1 outside the UEA2, inside the bypass flow path PAb, which is formed by the horizontally elongated recesses 353, 363 and the bulges 354, 364, and outside the gas diffusion layers 242, 252. However, because the horizontally elongated recesses 353, 363 extending in the horizontal direction are provided in the bypass flow path PAb, bypass flow is more likely to occur there than in other areas.

[0092] The reaction gas that bypasses the gas flow paths PAa and PAc contains moisture such as generated water and condensed water. The reaction gas containing moisture may accumulate in the vertically elongated recesses 352 and 362 and the horizontally elongated recesses 353 and 363 and become retained water containing iron ions that have eluted from the separator 3 into the bypass suppression portions 350 and 360. If this retained water reaches the gas flow paths PAa and PAc, it will cause deterioration of the electrolyte membrane 23. Therefore, it is necessary to prevent the retained water from flowing into the gas flow paths PAa and PAc.

[0093] In this regard, in the present embodiment, the flat portions 351, 361 are provided continuously and uninterruptedly across the left-right direction in the region AR3 (hatched in FIG. 9 ) between the gas flow paths PAa, PAc and the vertically elongated recesses 352, 362 of the separator 3. Therefore, when the gas diffusion layers 242, 252 and the flat portions 351, 361 are pressed against each other, the gas flow paths PAa, PAc and the vertically elongated recesses 352, 362 can be reliably separated from each other. This makes it possible to prevent the flow of accumulated water from the bypass suppression portions 350, 360 to the gas flow paths PAa, PAc, and suppress deterioration of the electrolyte membrane 23.

[0094] This embodiment provides the following advantageous effects. (1) The power-generating cell 1 includes a UEA 2 formed by integrating an MEA 20 having an electrolyte membrane 23 and an anode electrode 24 and a cathode electrode 25 provided on a front surface 23f and a rear surface 23r of the electrolyte membrane 23, a frame 21 supporting the outer edge of the MEA 20, and a pair of separators 3, 3 (a rear plate 3R and a front plate 3F) disposed opposite the front surface 2a and the rear surface 2b of the UEA 2, respectively, to form gas flow paths PAa, PAc through which reactant gases flow between the anode electrode 24 and the cathode electrode 25 ( FIGS. 1 to 3 ). An outer bead 332 and a sealant 336 are provided at the contact portion between the outer edge 221 of the frame 21 and the pair of separators 3, 3 as a seal to prevent reactant gas leakage ( FIGS. 5A and 5B ). The separator 3 has bypass suppression portions 350, 360 formed in an uneven shape toward the UEA2 between the gas flow paths PAa, PAc and the outer bead portion 332, and outside the active area AR1 (power generation area) where the anode electrode 24, the electrolyte membrane 23, and the cathode electrode 25 overlap (Figures 6, 7, and 9). The bypass suppression portions 350, 360 are formed in an uneven shape toward the UEA2 so as to suppress the flow of reaction gas that bypasses the gas flow paths PAa, PAc.

[0095] By arranging the uneven bypass suppression portions 350, 360 outside the active region AR1 in this manner, it is possible to prevent the generated water in the active region AR1 from accumulating in the vertically elongated recesses 352, 362 of the separator 3. As a result, the amount of water containing iron ions eluted from the separator 3 into the generated water is small, and this water is prevented from penetrating the electrolyte membrane 23, thereby suppressing deterioration of the electrolyte membrane 23. The cathode-side electrode catalyst layer 251 and gas diffusion layers 242, 252 are arranged outside the active region AR1 (the lower side in FIG. 9 ). In other words, because the bottom end faces SF11, SF12, SF13 are arranged with their positions offset in the up-down direction, there is little change in the thickness of the ends of the MEA 20. By arranging the vertically elongated recesses 352, 362 in such an area where the thickness change is small, the flat portions 351, 361 and the MEA 20 are brought into good close contact with each other, and the sealing performance between the UEA 2 and the separator 3 can be easily ensured.

[0096] (2) The bypass suppression portions 350, 360 have multiple vertically elongated recesses 352, 362 arranged along the outer edge portions 242a, 252a of the MEA 20 (gas diffusion layer) ( FIGS. 5A , 5B , 6 , and 7 ). The connection lines LN1 obtained by sequentially connecting the ends of the multiple vertically elongated recesses 352, 362 on the active region AR1 side are located outside the active region AR1 ( FIG. 9 ). This prevents the multiple vertically elongated recesses 352, 362 from communicating with the active region AR1 over their entire width in the left-right direction, effectively preventing water from flowing between the gas flow paths PAa, PAc and the vertically elongated recesses 352, 362.

[0097] (3) The bypass suppression portions 350, 360 have flat portions 351, 361 facing the UEA 2 and multiple vertically elongated recesses 352, 362 recessed from the flat portions 351, 361 toward the opposite side of the UEA 2 ( FIGS. 5A , 5B , 6 , and 7 ). As a result, the bypass suppression portions 350, 360 come into contact with the UEA 2 (mainly the gas diffusion layers 242, 252) over a wide area via the flat portions 351, 361, thereby effectively suppressing the bypass flow of reactant gas.

[0098] (4) The separator 3 (bypass suppression portion 350, 360) further includes horizontally elongated recesses 353, 363 and bulges 354, 364 between the outer bead portion 332 and the plurality of vertically elongated recesses 352, 362, which form a bypass flow path PAb through which the reactant gas bypasses the gas flow paths PAa, PAc ( FIG. 8 ). This provides a throttle portion in the bypass flow path PAb, thereby suppressing the bypass flow of the reactant gas. Furthermore, the flow of the reactant gas through the bypass flow path PAb allows suction and discharge of accumulated water in the bypass suppression portion 350, 360.

[0099] (5) The separator 3 has recesses 32 that form gas flow paths PAa and PAc that meander vertically and extend horizontally ( FIGS. 5A and 5B ). Flat portions 351 and 361 extend between the vertically elongated recesses 352 and 362 and the recess 32, respectively, to block communication between the vertically elongated recesses 352 and 362 and the gas flow paths PAa and PAc ( FIGS. 5A and 5B ). This effectively seals the gap between the UEA2 and the separator 3 via the flat portions 351 and 361. As a result, even when meandering gas flow paths PAa and PAc approaching the bypass suppression portions 350 and 360, water generated in the active region AR1 can be reliably prevented from entering the vertically elongated recesses 352 and 362.

[0100] (6) From a different perspective from that described above, in this embodiment, the separator 3 has flat portions 351, 361 that are located between the gas flow paths PAa, PAc and the outer bead portion 332 and that abut seamlessly from one end to the other end of the gas flow paths PAa, PAc on the front surface 2a and rear surface 2b of the UEA2 outside the active area AR1 (power generation area) where the anode electrode 24, the electrolyte membrane 23, and the cathode electrode 25 overlap ( FIGS. 6 , 7 , and 9 ).

[0101] This configuration makes it possible to prevent the accumulated water from reaching the gas flow paths PAa and PAc when accumulated water containing iron ions eluted from the separator 3 occurs in the bypass suppression portions 350 and 360 outside the active region AR1. As a result, it is possible to prevent the accumulated water from entering the electrolyte membrane 23 via the gas flow paths PAa and PAc, and to suppress deterioration of the electrolyte membrane 23.

[0102] (7) The anode electrode 24 and the cathode electrode 25 each have a gas-permeable gas diffusion layer 242, 252 disposed opposite a pair of separators 3, 3 ( FIG. 2 ). The flat portions 351, 361 abut against the surfaces of the gas diffusion layers 242, 252 ( FIGS. 6 and 7 ). This allows the abutting surfaces between the flat portions 351, 361 and the gas diffusion layers 242, 252 to be sealed without gaps, reliably preventing water from flowing from the gas flow paths PAa, PAc to the space SP1 ( FIGS. 6 and 7 ) outside the UEA2 and from the space SP1 to the gas flow paths PAa, PAc. Furthermore, because the gas diffusion layers 242, 252 are compressed by a load F in the front-rear direction, sufficient sealing can be ensured between the gas diffusion layers 242, 252 and the flat portions 351, 361 even when thickness variations occur in the various portions due to stack misalignment of the power-generating cell 1 or manufacturing errors.

[0103] (8) The separator 3 has a plurality of vertically elongated recesses 352, 362 arranged along the outer edge 242a, 252a of the MEA 20 (gas diffusion layer) between the flat portion 351, 361 and the outer bead portion 332 and recessed toward the UEA 2 ( FIGS. 5A , 5B , 6 , and 7 ). The connecting line LN1 obtained by sequentially connecting the ends of the vertically elongated recesses 352, 362 on the active region AR1 side is covered by the gas diffusion layer 242, 252 along the entire length of the connecting line LN1 ( FIG. 9 ). By covering at least the entire length of the connecting line LN1 with the gas diffusion layer 242, 252 in this manner, the vertically elongated recesses 352, 362 do not communicate with the active region AR1 along their entire width, reliably preventing water from flowing between the gas flow paths PAa, PAc and the vertically elongated recesses 352, 362. That is, the gas flow paths PAa, PAc and the space SP1 of the bypass suppression portions 350, 360 are reliably separated, and water can be prevented from passing between the gas flow paths PAa, PAc and the space SP1.

[0104] As described above, in this embodiment, the vertically elongated recesses 352, 362 of the pair of separators 3 abut against each other, i.e., the rear end faces 352r ( FIG. 7 ) of the vertically elongated recesses 352 of the front plate 3F abut against the front end faces 362f ( FIG. 7 ) of the vertically elongated recesses 362 of the rear plate 3R. Also, the horizontally elongated recesses 353, 363 abut against each other, i.e., the rear end faces 353r ( FIG. 6 ) of the horizontally elongated recesses 353 of the front plate 3F abut against the front end faces 363f ( FIG. 6 ) of the horizontally elongated recesses 363 of the rear plate 3R. The vertically elongated recesses 352, 362 and the horizontally elongated recesses 353, 363 protrude toward the coolant. Therefore, when the cooling medium side is used as a reference (when viewed from the cooling medium side), as shown in Figures 6 and 7, the vertically elongated recesses 352 and 362 form vertically elongated protrusions 3520 and 3620, and the horizontally elongated recesses 353 and 363 form horizontally elongated protrusions 3530 and 3630.

[0105] 2, a load F is applied in the front-to-rear direction to the contact surfaces (rear end surface 352r, front end surface 362f) of the vertically elongated protrusions 3520, 3620 and the contact surfaces (rear end surface 353r, front end surface 363f) of the horizontally elongated protrusions 3530, 3630 during assembly of the fuel cell stack 100. At this time, there is a risk that the left-to-right center position of the vertically elongated protrusion 3520 and the left-to-right center position of the vertically elongated protrusion 3620 may be misaligned due to assembly errors of the power generation cell 1 and the fuel cell stack 100, dimensional errors of individual components, etc.

[0106] If the centers of the vertically elongated protrusions 3520 and 3620 are misaligned, the rear end surface 352r of the vertically elongated protrusion 3520 and the front end surface 362f of the vertically elongated protrusion 3620 may not abut against each other, and one of the protrusions (e.g., the vertically elongated protrusion 3520) may enter the space between the other of the protrusions (e.g., the vertically elongated protrusions 3620 and 3620) (the space facing the flat portion 361). Alternatively, even if the rear end surface 352r and the front end surface 362f abut against each other, if the abutment area is insufficient, the vertically elongated protrusions 3520 and 3620 may be deformed, causing one of the vertically elongated protrusions 3520 to enter the space between the other of the vertically elongated protrusions 3620 and 3620.

[0107] As a result, when a compressive load F is applied in the front-rear direction, the separator 3 may be deformed and damaged. Therefore, in order to prevent damage to the separator 3 due to such misalignment of the centers of the vertically elongated convex portions 3520 and 3620, in this embodiment, the separator 3 is further configured as follows.

[0108] 10 is a cross-sectional view taken along line XX in FIG. 5A (a cross-sectional view including gas diffusion layers 242, 252), and for convenience, shows multiple power-generating cells 1 stacked in the front-to-rear direction. As shown in FIGS. 5A and 5B , the multiple vertically elongated protrusions 3520 (vertically elongated recesses 352) and the multiple vertically elongated protrusions 3620 (vertically elongated recesses 362) all extend in the up-down direction. Therefore, a center line CLc extending in the longitudinal direction (up-down direction) through the center in the width direction (left-right direction) of each of the multiple vertically elongated protrusions 3520 and a center line CLa extending in the longitudinal direction through the center in the width direction of each of the multiple vertically elongated protrusions 3620 are parallel to each other.

[0109] 10 shows a state in which the center line CLc of the vertically elongated protrusion 3520 and the center line CLa of the vertically elongated protrusion 3620 are aligned. At this time, the center lines CLc and CLa overlap in a plan view ( FIG. 4 ) of the power generating cell 1. In this state, the entire rear end surface 352r of the cathode-side vertically elongated protrusion 3520, which has a generally trapezoidal cross section, abuts against the front end surface 362f of the vertically elongated protrusion 3620, which also has a generally trapezoidal cross section.

[0110] When the fuel cell is generating electricity, the pressure of the oxidant gas constantly acts on the cathode flow path PAc. Meanwhile, fuel gas is injected by the injector when electricity generation is required, so the pressure of the fuel gas acts intermittently on the anode flow path PAa. Therefore, the pressure of the oxidant gas in the cathode flow path PAc is generally greater than the pressure of the fuel gas in the anode flow path PAa. In the bypass suppression units 350 and 360, the pressure acting from the oxidant gas (Ca) on the vertically elongated convex portion 3520 is also greater than the pressure acting from the fuel gas (An) on the vertically elongated convex portion 3620. Wa in FIG. 10 represents a coolant (water).

[0111] As shown in FIG. 10 , the width Wc (horizontal length) of the cathode-side vertically elongated protrusion 3520 is smaller than the width Wa (horizontal length) of the anode-side vertically elongated protrusion 3620. This allows the entire rear end surface 352r of the vertically elongated protrusion 3520 to abut against the front end surface 362f of the vertically elongated protrusion 3620, even if the center lines CLa and CLc of the vertically elongated protrusions 3520 and 3620 are misaligned relative to each other in the horizontal direction. As a result, deformation and damage to the separator 3 can be prevented. The vertically elongated protrusions 3520 and 3620 have an elongated shape extending vertically ( FIGS. 5A and 5B ). Therefore, even if the positions of the vertically elongated protrusions 3520 and 3620 are misaligned relative to each other in the vertical direction, the vertically elongated protrusions 3520 and 3620 can maintain sufficient abutment.

[0112] Furthermore, by making the width Wc of the vertically elongated protrusion 3520 on the cathode side smaller than the width Wa of the vertically elongated protrusion 3620 on the anode side, the area on the contact surface between the vertically elongated protrusions 3520, 3620 on which the pressure of the oxidant gas on the high-pressure side acts is limited. This allows the pressure of the oxidant gas acting on the vertically elongated protrusion 3520 to be well received by the opposing vertically elongated protrusion 3620. Contrary to the above, the width Wc of the vertically elongated protrusion 3520 may be larger than the width Wa of the vertically elongated protrusion 3620.

[0113] 6 , the rear end surface 353r of the horizontally elongated protrusion 3530 on the cathode side abuts against the front end surface 363f of the horizontally elongated protrusion 3630 on the anode side of the adjacent power generating cell 1. As a result, the protrusions of the pair of plates 3F, 3R abut against each other also below (outside of) the vertically elongated protrusions 3520, 3620. By abutting the vertically elongated protrusions 3520, 3620 and the horizontally elongated protrusions 3530, 3630 against each other in this manner, the pair of plates 3F, 3R abut against each other over a wide range, and therefore the load in the front-to-rear direction can be well distributed and borne across the entire separator. The horizontally elongated convex portions 3530, 3630 (horizontally elongated recesses 353, 363) extend in the left-right direction perpendicular to the vertically elongated convex portions 3520, 3620 (vertically elongated recesses 352, 362), thereby preventing the bypass suppression portions 350, 360 from becoming elongated in the vertical direction.

[0114] In addition to the above, this embodiment can also achieve the following advantageous effects. (1) The power-generating cell 1 includes a UEA 2 formed by integrating an MEA 20 having an electrolyte membrane 23 and an anode electrode 24 and a cathode electrode 25 provided on both sides of the electrolyte membrane 23, a frame 21 supporting the outer edge of the MEA 20, and a pair of separators 3, 3 (a rear plate 3R and a front plate 3F) disposed opposite the front surface 2a and rear surface 2b of the UEA 2, respectively, and forming gas flow paths PAa and PAc through which reactant gases flow between the anode electrode 24 and the cathode electrode 25 ( FIGS. 1 to 3 ). The front plate 3F is disposed along the outer edge 221 of the UEA 2 (frame 21) and has multiple vertically elongated protrusions 3520 protruding from the opposite side of the rear surface 2b of the UEA 2 ( FIGS. 5A , 7 , and 10 ). The rear plate 3R is disposed along the outer edge 221 of the UEA 2 and has multiple vertically elongated protrusions 3620 protruding from the opposite side of the front surface 2a of the UEA 2 ( FIGS. 5B , 7 , and 10 ). The multiple vertically elongated protrusions 3520 have elongated shapes extending along multiple parallel center lines CLc, each with a predetermined width Wc perpendicular to the center lines CLc ( FIGS. 5A and 10 ). The multiple vertically elongated protrusions 3620 have elongated shapes extending along multiple parallel center lines CLa, each with a predetermined width Wa perpendicular to the center lines CLa ( FIGS. 5B and 10 ). In a plan view from the front-rear direction perpendicular to the front surface 2a of the UEA 2, the center lines CLc and CLa are approximately parallel to each other, and the width Wc is narrower than the width Wa ( FIG. 10 ).

[0115] With this configuration, even if the center line CLc of the vertically elongated protrusion 3520 of the front plate 3F is misaligned in the left-right direction and does not overlap with the center line CLa of the vertically elongated protrusion 3620 of the rear plate 3R during assembly of the fuel cell stack 100 due to assembly errors, dimensional errors, etc., the entire rear end surface 352r of the vertically elongated protrusion 3520 can abut against the front end surface 362f of the vertically elongated protrusion 3620. This ensures a sufficient contact area between the vertically elongated protrusions 3520, 3620, and prevents deformation and damage to the separator 3.

[0116] (2) The front plate 3F is a cathode separator that forms a cathode flow path PAc through which oxidant gas flows between the front plate 3F and the cathode electrode 25, and the rear plate 3R is an anode separator that forms an anode flow path PAa through which fuel gas flows between the front plate 3F and the cathode electrode 25 ( FIGS. 2 and 10 ). The pressure of the oxidant gas in the cathode flow path PAc is greater than the pressure of the fuel gas in the anode flow path PAa. However, by making the width Wc of the cathode-side vertically elongated protrusion 3520 smaller than the width Wa of the anode-side vertically elongated protrusion 3620, the area where the pressure of the high-pressure oxidant gas acts at the contact portion between the plates 3F and 3R is limited. This allows the opposing vertically elongated protrusions 3620 to effectively receive the pressure of the oxidant gas.

[0117] (3) At the contact points between the outer edge 221 of the frame 21 and the front and rear plates 3F and 3R, outer bead portions 332 and sealing materials 336 are provided as seals to prevent leakage of reactant gas ( FIGS. 6 and 7 ). The front plate 3F further includes horizontally elongated protrusions 3530 between the vertically elongated protrusions 3520 and the outer bead portion 332, protruding from the opposite side of the rear surface 2b of the UEA 2 ( FIGS. 5A and 6 ). The rear plate 3R further includes horizontally elongated protrusions 3630 between the vertically elongated protrusions 3620 and the outer bead portion 332, protruding from the opposite side of the front surface 2a of the UEA 2 ( FIGS. 5B and 6 ). Each of the horizontally elongated protrusions 3530 and each of the horizontally elongated protrusions 3630 extends elongatedly in a direction (left-right direction) substantially perpendicular to the center lines CLc and CLa ( FIGS. 5A and 5B ). As a result, the pair of plates 3F, 3R abut against each other even on the outsides of the vertically elongated protrusions 3520, 3620. Therefore, the pair of plates 3F, 3R abut against each other over a wide range, and the entire separator can effectively bear the load in the front-rear direction.

[0118] (4) The center lines CLc and CLa extend in a direction (vertical direction) substantially perpendicular to the flow direction (horizontal direction) of the reactant gas along the gas flow paths PAc and PAa ( FIGS. 5A and 5B ). Because the oxidizer gas and the fuel gas flow in opposite directions in the bypass suppression portions 350 and 360, if the center lines CLc and CLa were tilted in the horizontal direction, the tilt directions of the center lines CLc and CLa would be opposite to each other, and the vertically elongated convex portions 3520 and 3620 would intersect with each other. However, by providing the center lines CLc and CLa without tilting them, the vertically elongated convex portions 3520 and 3620 would overlap with each other in the vertical direction without intersecting with each other, thereby increasing the contact area of ​​the vertically elongated convex portions 3520 and 3620.

[0119] (5) The gas flow path includes a cathode flow path PAc and an anode flow path PAa ( FIG. 2 ). The cathode flow path PAc and the anode flow path PAa are each formed in a wavy shape in plan view and in opposite phases to each other ( FIG. 4 ). This allows the rear end surface 32r ( FIG. 6 ) of the recess 32 in the front plate 3F that constitutes the cathode flow path PAc and the front end surface 32f ( FIG. 6 ) of the recess 32 in the rear plate 3R that constitutes the anode flow path PAa to intersect with each other and abut evenly across the entire active region AR1.

[0120] In this embodiment, the accumulated water in the bypass suppression units 350, 360 can be drained by flowing the reactant gas along the bypass flow path PAb, which bypasses the gas flow paths PAa, PAc, as described above. That is, the accumulated water in the space SP1 is sucked into the bypass flow along the bypass flow path PAb, and the accumulated water can be discharged. In this regard, in order to improve the drainage performance, the bypass suppression units 350, 360 can be further configured as follows.

[0121] FIG. 11 is a front view of an example of a bypass suppression portion 350 configured to enhance drainage, showing the front plate 3F as viewed from the front. This FIG. 11 corresponds to a modification of FIG. 5A . As shown in FIG. 11 , the center line CLc of the vertically elongated recess 352 extends downward and leftward at a predetermined angle. That is, it extends obliquely toward the flow direction of the reactant gas in the bypass flow passage PAb. If the angle θ is defined as the angle between the vertical axis CL0 and the center line CLc, the angle θ is greater than 0° and less than 90°, e.g., 45°. The angle θ may be greater than 45° (e.g., approximately 60°) or less (e.g., approximately 30°).

[0122] The lower end of the vertically elongated recess 352 extends until it intersects with the horizontally elongated recess 353, and the vertically elongated recess 352 and the horizontally elongated recess 353 are connected via a connecting portion 355. More specifically, as the connecting portion 355, a notch 355a having the same width as the vertically elongated recess 352 is provided on the inclined surface 353b of the horizontally elongated recess 353, and the vertically elongated recess 352 and the horizontally elongated recess 353 are connected via the notch 355a. The depth (length in the front-to-rear direction) of the notch 355a is equal to the depth of the vertically elongated recess 352. The depth of the notch 355a may be shallower than the depth of the vertically elongated recess 352.

[0123] The vertically elongated recess 362 of the rear plate 3R is configured symmetrically to the vertically elongated recess 352 of the front plate 3F. That is, as shown partially by the dotted line in FIG. 11 , the vertically elongated recess 362 extends downward and to the right at a predetermined angle θ. That is, it extends obliquely toward the flow direction of the reactant gas in the bypass flow channel PAb. The vertically elongated recess 362 and the horizontally elongated recess 363 are connected via a connecting portion 365, more specifically, via a notch 365a in the horizontally elongated recess 363.

[0124] In this way, by connecting the vertically elongated recesses 352, 362 and the horizontally elongated recesses 353, 363 via the connecting portions 355, 365 (notches 355 a, 365 a), the accumulated water in the vertically elongated recesses 352, 362 can be easily sucked along the gas flow in the bypass flow path PAb. As a result, even if accumulated water occurs in the vertically elongated recesses 352, 362, the accumulated water will not remain for a long time and can be easily discharged.

[0125] Furthermore, because the vertically elongated recesses 352, 362 extend at an angle toward the flow direction of the bypass flow path PAb, when a bypass flow occurs in the bypass flow path PAb, the accumulated water in the vertically elongated recesses 352, 362 is likely to flow toward the bypass flow path PAb. This facilitates the discharge of accumulated water from the vertically elongated recesses 352, 362. In this case, because the vertically elongated recesses 352, 362 are disposed so as to intersect with each other, sufficient contact between the vertically elongated recesses 352, 362 can be maintained even if the center line CLc is misaligned in the left-right direction with respect to the center line CLa, provided that the widths Wc, Wa ( FIG. 10 ) of the vertically elongated recesses 352, 362 are the same.

[0126] To summarize the above, this embodiment can further achieve the following advantageous effects. (1) The power-generating cell 1 includes a UEA 2 formed by integrating an MEA 20 having an electrolyte membrane 23 and an anode electrode 24 and a cathode electrode 25 provided on a front surface 23f and a rear surface 23r of the electrolyte membrane 23, and a frame 21 supporting the outer edge of the MEA 20, and a pair of separators 3, 3 (a rear plate 3R and a front plate 3F) disposed opposite the front surface 2a and the rear surface 2b of the UEA 2, respectively, and forming gas flow paths PAa, PAc through which reactant gas flows between the anode electrode 24 and the cathode electrode 25 ( FIGS. 1 to 3 ). An outer bead portion 332 and a sealant 336 are provided at the contact portion where the outer edge portion 221 of the frame 21 and the pair of separators 3, 3 contact each other as a seal to prevent reactant gas leakage ( FIGS. 5A and 5B ). The separator 3 has bypass suppression sections 350, 360 (particularly vertically elongated recesses 352, 362) formed unevenly toward the UEA2 between the gas flow paths PAc, PAa and the outer bead section 332 to suppress the flow of reaction gas bypassing the gas flow paths PAc, PAa, and horizontally elongated recesses 353, 363 and bulges 354, 364 as bypass flow path forming sections provided between the vertically elongated recesses 352, 362 and the outer bead section 332 to form a bypass flow path PAb through which reaction gas flows, bypassing the gas flow paths PAc, PAa (Figures 6A and 6B).

[0127] In this way, the reactant gas flows through the bypass flow path PAb outside the vertically elongated recesses 352, 362, thereby making it possible to suck and discharge the accumulated water in the vertically elongated recesses 352, 362. As a result, iron ions eluted from the separator 3 into the accumulated water can be prevented from penetrating the electrolyte membrane 23, and deterioration of the electrolyte membrane 23 can be suppressed.

[0128] (2) The bypass suppression sections 350, 360 are arranged along the outer edge of the MEA 20 and have multiple vertically elongated recesses 352, 362 recessed toward the opposite side of the UEA 2 ( FIGS. 5A and 5B ). The bypass flow path forming sections are recessed toward the opposite side of the UEA 2 and have multiple horizontally elongated recesses 353, 363 intermittently formed along the outer bead section 332 ( FIGS. 5A and 5B ). By providing multiple vertically elongated recesses 352, 362 and horizontally elongated recesses 353, 363 between the gas flow paths PAa, PAc and the outer bead section 332 in this manner, not only is the drainage of stagnant water improved, but the bypass flow of reactant gas can also be effectively suppressed.

[0129] (3) The bypass flow passage forming portion has a plurality of bulging portions 354, 364 arranged alternately with a plurality of horizontally elongated recesses 353, 363 along the outer bead portion 332 ( FIGS. 5A and 5B ). The depth of the horizontally elongated recesses 353, 363 (the amount of protrusion toward the coolant) is greater than the depth of the bulging portions 354, 364 ( FIG. 8 ). This configuration allows the bulging portions 354, 364 to function as throttle portions, thereby enhancing the suction effect of accumulated water.

[0130] (4) The vertically elongated recesses 352, 362 are formed in an elongated shape so as to intersect with the horizontally elongated recesses 353, 363, and have connecting portions 355, 365 at the ends of the vertically elongated recesses 352, 362 that connect to the horizontally elongated recesses 353, 363 ( FIG. 11 ). This allows the accumulated water in the vertically elongated recesses 352, 362 to be easily discharged along the gas flow in the bypass flow path PAb.

[0131] (5) The vertically elongated recesses 352, 362 extend at an angle toward the flow direction of the reactant gas in the bypass flow passage PAb ( FIG. 11 ). This makes it easier for accumulated water in the vertically elongated recesses 352, 362 to flow toward the bypass flow passage PAb, thereby facilitating the discharge of accumulated water from the vertically elongated recesses 352, 362.

[0132] The above-described embodiment can be modified in various ways. Some modifications are described below. In the above-described embodiment, the bulging portions 354, 364 are disposed closer to the gas side than the flat portions 351, 361. However, they may be disposed closer to the coolant side. That is, the height of the bulging portions 354, 364 is higher than the height of the flat portions 351, 361. However, they may be lower. The bulging portions 354, 364 and the flat portions 351, 361 may be set to the same height. In the above-described embodiment (FIGS. 6 and 7), the electrolyte membrane 23 is shown disposed at the center of the thickness of the power-generating cell 1 in the front-rear direction for convenience. However, the electrolyte membrane 23 may be disposed shifted in one direction (e.g., forward) from the center. In this case, the depth (front-rear length) of the anode flow channel PAa is shallower than the depth of the cathode flow channel PAc. In the above embodiment, the multiple vertically elongated recesses 352, 362 and the multiple horizontally elongated recesses 353, 363 are included in the bypass suppression sections 350, 360, but the multiple horizontally elongated recesses 353, 363 may also be included in a bypass flow path forming section separate from the bypass suppression sections 350, 360.

[0133] In the above embodiment, the UEA 2 is configured as a membrane electrode assembly by integrating the MEA 20 having the electrolyte membrane 23, the anode electrode 24 as a first electrode, and the cathode electrode 25 as a second electrode, with the frame 21 as a frame member supporting the outer edge portions 242a, 252a of the MEA 20. However, the configuration of the electrolyte membrane 23, the anode electrode 24, and the cathode electrode 25 (e.g., the positional relationship of their respective outer edge portions) is not limited to the above. In the above embodiment, the frame member is configured by a pair of front and rear frames 21F, 21R, but the frame member may also be configured by a single frame 21.

[0134] In the above embodiment, the separator 3 is configured to form gas flow paths PAa, PAc (recesses 32) through which the reactant gas flows between the rear surface 2b (first surface) of the UEA 2 and the front plate 3F (first separator), and between the front surface 2a (second surface) of the UEA 2 and the rear plate 3R (second separator), respectively. However, the configuration of the separator 3 is not limited to the above. In the above embodiment, the outer bead portion 332 and the seal material 336 are provided as a seal portion at the contact portion where the outer edge portion 221 of the frame 21 and the separator 3 contact. However, the configuration of the seal portion is not limited to this.

[0135] In the above embodiment ( FIG. 10 ), the front plate 3F has a plurality of vertically elongated protrusions 3520 (first protrusions) protruding from the opposite side of the rear surface 2 b of the UEA 2, and the rear plate 3R has a plurality of vertically elongated protrusions 3620 (second protrusions) protruding from the opposite side of the front surface 2 a of the UEA 2. More specifically, the plurality of vertically elongated protrusions 3520 have an elongated shape extending by a predetermined width Wc (first width) in the left-right direction along a plurality of parallel center lines CLc (first center lines) extending in the front-rear direction, and the plurality of vertically elongated protrusions 3620 have an elongated shape extending by a predetermined width Wa (second width) in the left-right direction along a plurality of parallel center lines CLa (second center lines) extending in the front-rear direction. Here, the separator 3 may have any configuration as long as the center lines CLc and CLa are substantially parallel to each other in a plan view (FIGS. 5A and 5B) viewed from the front-rear direction and the width Wc is narrower than the width Wa. The width Wa may be narrower than the width Wc.

[0136] In the above embodiment ( FIG. 6 ), the front plate 3F further has a plurality of horizontally elongated protrusions 3530 (third protrusions) that protrude from the opposite side of the rear surface 2 b of the UEA 2 between the plurality of vertically elongated protrusions 3520 and the outer bead portion 332, and the rear plate 3R further has a plurality of horizontally elongated protrusions 3630 (fourth protrusions) that protrude from the opposite side of the front surface 2 a of the UEA 2 between the plurality of vertically elongated protrusions 3620 and the outer bead portion 332. However, these horizontally elongated protrusions 3530 and 3630 may be omitted. In the above embodiment ( FIG. 4 ), the cathode flow channel PAc (first gas flow channel) and the anode flow channel PAa (second gas flow channel) are formed in a wavy shape and in opposite phases to each other in a plan view. However, the configuration of the first flow channel and the second flow channel is not limited to the above, and may be formed, for example, in a linear shape.

[0137] In the above embodiment, an example of applying the fuel cell stack 100 to a vehicle has been described, but a fuel cell stack having the power generation cells of the present invention can also be applied to moving bodies other than vehicles, such as aircraft and ships, robots, and various industrial machines.

[0138] 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.

[0139] 1 Power generation cell, 2 Integrated electrode assembly, 2a Front surface, 2b Rear surface, 3 Separator, 3F Front plate, 3R Rear plate, 20 Membrane electrode assembly, 21 Frame, 23 Electrolyte membrane, 24 Anode electrode, 25 Cathode electrode, 32 Recess, 100 Fuel cell stack, 242, 252 Gas diffusion layer, 332 Outer bead portion, 336 Sealing material, 352, 362 Vertically elongated recess, 353, 363 Horizontally elongated recess, 3520, 3620 Vertically elongated convex portion, 3530, 3630 Horizontally elongated convex portion, PAa Anode flow channel, PAc Cathode flow channel, Wa, Wc Width, CLa, CLc Center line

Claims

1. A membrane electrode assembly formed by integrating a membrane electrode assembly having an electrolyte membrane and a first electrode and a second electrode provided on each side of the electrolyte membrane, and a frame member supporting the outer edge of the membrane electrode assembly; and a first separator and a second separator respectively disposed opposite a first surface and a second surface opposite the first surface of the membrane electrode assembly, forming gas flow paths through which reactant gases flow between the first electrode and the second electrode, wherein the first separator is disposed along the outer edge of the membrane electrode assembly and has a plurality of first protrusions protruding on the side opposite to the first surface, and the second separator is disposed along the outer edge of the membrane electrode assembly and has a plurality of second protrusions protruding on the side opposite to the second surface, and the first protrusions each have an elongated shape extending along a plurality of first center lines parallel to each other, with a first width perpendicular to the first center lines, the plurality of second protrusions each have an elongated shape extending along a plurality of second center lines parallel to each other, with a second width perpendicular to the plurality of second center lines, and in a plan view seen from a direction perpendicular to the first surface, the first center lines and the second center lines are approximately parallel to each other, and the first width is narrower than the second width.

2. A power generation cell according to claim 1, wherein the first separator is a cathode separator that forms a cathode flow path between the first electrode and the second separator, through which oxidant gas flows, and the second separator is an anode separator that forms an anode flow path between the second electrode and the second separator, through which fuel gas flows.

3. A power generation cell as defined in claim 1 or 2, wherein a seal is provided at the contact portion where the outer edge of the frame member contacts the first separator and the second separator to prevent leakage of reaction gas, the first separator further has a plurality of third convex portions between the plurality of first convex portions and the seal portion and protruding on the opposite side of the first surface, and the second separator further has a plurality of fourth convex portions between the plurality of second convex portions and the seal portion and protruding on the opposite side of the second surface, and each of the plurality of third convex portions and each of the plurality of fourth convex portions extends in an elongated manner in a direction approximately perpendicular to the first center line and the second center line.

4. A power generating cell according to claim 1 or 2, wherein the first center line and the second center line extend in a direction substantially perpendicular to the flow direction of the reactant gas along the gas flow path.

5. A power generation cell according to claim 1 or 2, wherein the gas flow path includes a first gas flow path and a second gas flow path, and the first gas flow path and the second gas flow path are each formed in a wavy shape in the plan view and in opposite phases to each other.

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