Fuel cell stack

Abstract

This fuel cell stack comprises a layered body formed by alternately layering membrane electrode structures and separators in a prescribed direction. Each separator has: a first plate member having a first rib provided protruding toward a membrane electrode structure so as to form, between the first plate member and the membrane electrode structure, a first gas flow path through which a first reaction gas flows; and a second plate member having a second rib provided protruding toward the membrane electrode structure so as to form, between the second plate member and the membrane electrode structure, a second gas flow path through which a second reaction gas flows. A cooling flow path through which a cooling medium flows is formed between the first plate member and the second plate member. The first gas flow path has an enlarged portion in which the flow path width is enlarged, and in plan view of the separator from the layering direction, the second rib is disposed in the enlarged portion of the first gas flow path.

Description

Fuel cell stack

[0001] The present invention relates to a fuel cell stack including a laminate of a plurality of power generation cells.

[0002] In recent years, technological development has been carried out on fuel cells that contribute to improving energy efficiency, in order to enable more people to secure access to affordable, reliable, sustainable and advanced energy. As a technology related to fuel cell stacks used for this type of fuel cell, there has been conventionally known a separator in which ribs are provided protruding from the surface of the separator, and a gas flow path or a cooling medium flow path is formed along the ribs (see, for example, Patent Document 1). Patent Document 1 describes that the separator may be provided with a gas flow path on one surface and a cooling medium flow path on the other surface.

[0003] Japanese Unexamined Patent Publication No. 2006-172924

[0004] However, when the separator is configured such that a gas flow path is provided on one surface of the separator and a cooling medium flow path is provided on the other surface, there is a possibility that a region where cooling by the flow of the cooling medium becomes insufficient, such as a region where the width of the gas flow path changes, may occur.

[0005] A fuel cell stack according to one aspect of the present invention comprises a laminate formed by alternately stacking a membrane electrode structure including an electrolyte membrane and an electrode, and a separator, in a predetermined direction. The separator has a first plate member having a first surface and a first back surface opposite to the first surface, and a second plate member having a second back surface facing the first back surface and a second surface opposite to the second back surface, and is configured such that a cooling channel is formed between the first back surface and the second back surface through which a cooling medium flows, from a refrigerant supply hole on one end of the separator that penetrates the separator, to a refrigerant discharge hole on the other end of the separator that also penetrates the separator. The first plate member has a first rib protruding from the first surface toward the membrane electrode structure so as to form a first gas channel through which a first reaction gas flows between the first surface and the membrane electrode structure facing the first surface. The second plate member has a second rib protruding from the second surface toward the membrane electrode structure so as to form a second gas channel through which a second reaction gas flows between the second surface and the membrane electrode structure facing the second surface. The first gas channel has an enlarged portion where the channel width is increased, and the second rib is positioned in the enlarged portion of the first gas channel in a plan view when the separators are viewed from the stacking direction.

[0006] According to the present invention, cooling by the flow of a cooling medium can be performed effectively.

[0007] Figure 1 shows a schematic perspective view illustrating the overall configuration of a fuel cell stack according to an embodiment of the present invention. Figure 2 shows a cross-sectional view illustrating the main components of the cell stack in Figure 1. Figure 3 shows a schematic perspective view illustrating the integrated electrode assembly incorporated into the fuel cell stack in Figure 1. Figure 4 shows an enlarged view of section V in Figure 4. Figure 5A shows a reference example. Figure illustrating the cooling effect due to the flow of the cooling medium.

[0008] Embodiments of the present invention will be described below with reference to Figures 1 to 6. The fuel cell stack according to the embodiment of the present invention is the main component of the fuel cell and constitutes the body of the fuel cell. The fuel cell can be mounted on a vehicle, for example, and generate electricity for driving the vehicle. First, the overall configuration of the fuel cell stack will be described in general terms. Note that the fuel cell stack is sometimes simply referred to as a fuel cell.

[0009] Figure 1 is a schematic perspective view showing the overall configuration of the fuel cell stack 100 according to this embodiment. For convenience, the three mutually orthogonal axial directions shown in the figure will be defined as the longitudinal direction, the left-right direction, and the vertical direction, and the configuration of each part will be described according to this definition. The downward direction in the vertical direction corresponds to the direction of gravity or approximately the direction of gravity. The longitudinal direction corresponds to the stacking direction of the fuel cell stack 100. The longitudinal and left-right directions are not necessarily the same as the longitudinal and left-right directions of a vehicle.

[0010] As shown in Figure 1, the fuel cell stack 100 has a cell stack 101 formed by stacking multiple power generation cells 1 in the front-to-back direction, and end units 102 positioned at both ends of the cell stack 101 in the front-to-back direction, and the whole has a substantially rectangular parallelepiped shape. Although not shown in the figure, the cell stack 101 is covered by a substantially rectangular parallelepiped case. The length of the cell stack 101 in the left-to-right direction is longer than the length in the up-to-down direction. Therefore, the left-to-right direction is the long dimension, and the up-to-down direction is the short dimension. For convenience, a single power generation cell 1 is shown in Figure 1.

[0011] The power generation cell 1 includes a unitized electrode assembly 2 (hereinafter referred to as UEA) having a joint containing an electrolyte membrane and an electrode, and separators 3, 3 arranged on both sides of the UEA 2 in the front-rear direction and sandwiching the UEA 2. The UEA 2 and the separators 3 are arranged alternately in the front-rear direction. The UEA 2 can also be called a membrane electrode structure or membrane electrode member.

[0012] Figure 2 is a cross-sectional view of the main part of the power generation region in the center of the cell stack 101 in the left-right direction (a cross-sectional view along the line II-II in Figure 1). As shown in Figure 2, the separator 3 has a front plate 3F and a rear plate 3R, which are a pair of thin metal plates with a corrugated cross-section. The front plate 3F extends in the vertical, horizontal, and lateral directions and has a front surface 3Fa and a rear surface 3Fb. The rear plate 3R extends in the vertical, horizontal, and lateral directions and has a front surface 3Ra and a rear surface 3Rb. The rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R, which face each other, are joined at their outer edges by welding or the like. This integrally connects 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 titanium alloy.

[0013] A cooling channel PAw is formed inside the separator 3, which is enclosed by the front plate 3F and the rear plate 3R, specifically between the rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R, through which a cooling medium flows. The flow of the cooling medium cools the power generation surface of the power generation cell 1. For example, water can be used as the cooling medium. The surfaces of the separator 3 facing the UEA 2 (front surface 3Fa and rear surface 3Rb) are formed to be uneven by press molding or the like so as to form a gas flow channel between them and the UEA 2. More specifically, the separator 3 has a pair of front and rear ribs 31 that protrude toward the UEA 2, and a pair of front and rear recesses 32 that are recessed and connected to the pair of front and rear ribs 31.

[0014] A pair of front and rear ribs 31 abut the rear surface 2b and front surface 2a of the UEA2. A compressive load F is applied to the cell stack 101 in the front-rear direction during the assembly of the fuel cell stack 100, and this compressive load F is maintained after the assembly of the fuel cell stack 100 is completed. Therefore, a predetermined surface pressure due to the compressive load F acts on the UEA2 in the front-rear direction via the ribs 31.

[0015] Between the front surface 2a of the UEA2 and the rear plate 3R of the separator 3 facing the front surface 2a, a recess 32 forms an anode channel PAa through which the fuel gas flows. Between the rear surface 2b of the UEA2 and the front plate 3F of the separator 3 facing the rear surface 2b, a recess 32 forms a cathode channel PAc through which the oxidizer gas flows. The fuel gas is a gas containing hydrogen, for example, hydrogen gas can be used. The oxidizer gas is a gas containing oxygen, for example, air can be used. The fuel gas and oxidizer gas are sometimes referred to collectively as reaction gases without distinction.

[0016] Figure 3 is a perspective view showing the schematic configuration of the UEA2. As shown in Figure 3, the UEA2 has a substantially rectangular membrane electrode assembly (MEA; hereinafter referred to as MEA) 20 and a frame 21 that supports the MEA20. The MEA20 has an electrolyte membrane, an anode electrode provided on the front surface of the electrolyte membrane, and a cathode electrode provided on the rear surface of the electrolyte membrane.

[0017] The electrolyte membrane is, for example, a solid polymer electrolyte membrane, and a thin film of a water-containing perfluorosulfonic acid polymer can be used. Not limited to fluorine-based electrolyte membranes, hydrocarbon-based electrolyte membranes can also be used. The anode electrode has an electrode catalyst layer formed on the front surface of the electrolyte membrane, which serves as the reaction field for the electrode reaction, and a gas diffusion layer provided on the front surface of the electrode catalyst layer, which diffuses and supplies the fuel gas. The cathode electrode has an electrode catalyst layer formed on the rear surface of the electrolyte membrane, which serves as the reaction field for the electrode reaction, and a gas diffusion layer provided on the rear surface of the electrode catalyst layer, which diffuses and supplies the oxidizing gas.

[0018] At the anode electrode, fuel gas (hydrogen) supplied via the anode channel PAa in Figure 2 is ionized by the action of a catalyst and moves to the cathode electrode side through the electrolyte membrane. The electrons generated at this time pass through an external circuit and are extracted as electrical energy. At the cathode electrode, oxidizing gas (oxygen) supplied via the cathode channel PAc in Figure 2 reacts with hydrogen ions introduced from the anode electrode and electrons that have moved from the anode electrode to produce water. The generated water (called generated water) provides appropriate humidity to the electrolyte membrane, and excess water is discharged to the outside of the integrated electrode assembly 2 along the gas flow.

[0019] As shown in Figure 3, the frame 21 is a substantially rectangular frame member and is made of a thin, plate-like film or sheet material such as resin or rubber that has insulating properties. A substantially rectangular opening 21a is provided in the center of the frame 21. The MEA 20 is provided so as to cover the entire opening 21a, and the peripheral edge of the MEA 20 is supported by the frame 21. The frame 21 can also be called a film or a sheet.

[0020] To the left of the opening 21a of the frame 21, three through holes 211 to 213 are opened vertically, penetrating the frame 21 in the front-to-back direction. To the right of the opening 21a, three through holes 214 to 216 are opened vertically, penetrating the frame 21 in the front-to-back direction. For convenience, the through holes 211 to 216 are shown as being approximately rectangular in shape, but the shape and arrangement of the through holes 211 to 216 are not limited to this.

[0021] As shown in Figure 1, through holes 301 to 306 are opened in the front and rear separators 3 of the UEA2 at positions corresponding to the through holes 211 to 216 of the frame 21, respectively, and the through holes 301 to 306 penetrate the separators 3 in the front-rear direction. The through holes 301 to 306 communicate with the through holes 211 to 216 of the frame 21, respectively. The collection of these mutually communicating through holes 211 to 216 and 301 to 306 forms flow paths PA1 to PA6 (indicated by arrows for convenience) that penetrate the cell stack 101 and extend in the front-rear direction. Flow paths PA1 to PA6 are sometimes called manifolds. Flow paths PA1 to PA6 are connected to a manifold outside the fuel cell stack 100.

[0022] Although not shown in the diagram, the front and rear end units 102 of the cell stack 101 each have multiple plates arranged in a stacked manner in the front-to-back direction. That is, the end unit 102 has a terminal plate arranged adjacent to the cell stack 101, an insulating plate arranged outside the terminal plate in the front-to-back direction, and an end plate arranged outside the insulating plate in the front-to-back direction.

[0023] The rear end unit 102 has multiple through holes 102a to 102f that penetrate the end unit 102 in the front-to-back direction, at positions corresponding to the through holes 211 to 216 and 301 to 306 of the cell laminate 101. For convenience, the through holes 102a to 102f are all shown as roughly rectangular in shape, but the position and shape of the through holes 102a to 102f are not limited to this.

[0024] The through-hole 102a is a fuel gas supply port, and fuel gas is supplied to the fuel cell stack 100 through the through-hole 102a. This fuel gas is guided through the through-holes 211 and 301 to the anode flow path PAa between the UEA2 and the rear plate 3R of the separator 3. After passing through the anode flow path PAa, the fuel gas flows backward through the through-holes 216 and 306 and is discharged from the through-hole 102f.

[0025] The through-hole 102d is an oxidizer gas supply port, and oxidizer gas is supplied to the fuel cell stack 100 through the through-hole 102d. This oxidizer gas is guided through the through-holes 214 and 304 to the cathode flow path PAc between the UEA2 and the front plate 3F of the separator 3. After passing through the cathode flow path PAc, the oxidizer gas flows backward through the through-holes 213 and 303 and is discharged from the through-hole 102c.

[0026] The through-hole 102e is a supply port for the cooling medium, and the cooling medium is supplied to the fuel cell stack 100 through the through-hole 102e. This cooling medium is guided through the through-holes 215 and 305 to the cooling channel PAw between the front plate 3F and the rear plate 3R of the separator 3. After passing through the cooling channel PAw, the cooling medium flows backward through the through-holes 212 and 302 and is discharged from the through-hole 102b. The above is a general overview of the fuel cell stack 100.

[0027] The configuration of separator 3 will be described in more detail. Figure 4 is a front view (viewed from the rear) showing the schematic configuration of separator 3, that is, a view of the rear surface 3Rb of separator 3. As shown in Figure 4, on the rear surface 3Rb of separator 3, a plurality of (Na0) anode flow paths PAa (referred to as anode central flow paths PAa0) are provided at equal intervals in the vertical direction in the central region AR0, which is a predetermined distance to the right of the through-hole 301 for fuel gas supply and a predetermined distance to the left of the through-hole 306 for fuel gas discharge. The plurality of anode flow paths PAa may be provided at different intervals in the vertical direction.

[0028] In the central region AR0, multiple anode central channels PAa0 extend horizontally from the left end 41 to the right end 42 of the central region AR0. The anode central channels PAa0 are formed by multiple ribs 31 that extend substantially parallel to each other in the horizontal direction, and extend horizontally while maintaining a predetermined width without merging or branching.

[0029] To the left of the central region AR0, a left-side region AR1 is provided between the through-hole 301 and the central region AR0. In the left-side region AR1 of the rear surface 3Rb, multiple vertical ribs 31 extend from the through-hole 301 to the entire vertical area of ​​the left end 41 of the central region AR0, and multiple (1 Na) anode flow channels PAa (referred to as anode supply channels PAa1) for fuel gas supply are formed between the ribs 31, 31. The region where the anode supply channels PAa1 are provided gradually expands to the right.

[0030] A branch of the anode supply channel PAa1 is provided in the left-side region AR1 of the rear surface 3Rb. Therefore, the number of anode supply channels PAa1 Na1 increases towards the right, and the number of anode supply channels PAa1 Na1 near the through hole 301 is less than the number of anode central channel PAa0 Na0. Although detailed illustrations are omitted, the rib 31 of the left-side region AR1 of the rear surface 3Rb extends in a straight line, a curved line, or a bent line. Therefore, the rib 31 of the left-side region AR1 includes portions that extend to the right, diagonally downward to the right, and downward.

[0031] To the right of the central region AR0, a right-side region AR2 is provided between the through-hole 306 and the central region AR0. In the right-side region AR2 of the rear surface 3Rb, a rib 31 extends from the entire vertical area of ​​the right end 42 of the central region AR0 to the through-hole 306, and multiple (2 Na) anode flow channels PAa (referred to as anode discharge flow channels PAa2) for fuel gas discharge are formed between the ribs 31, 31. The area where the anode discharge flow channels PAa2 are provided gradually decreases towards the right.

[0032] A confluence of anode discharge channels PAa2 is provided in the right-side region AR2 of the rear surface 3Rb. Therefore, the number of anode discharge channels PAa2 Na2 decreases towards the right, and the number of anode discharge channels PAa2 Na2 near the through hole 306 is less than the number of anode central channels PAa0 Na0. Although detailed illustrations are omitted, the ribs 31 in the right-side region AR2 of the rear surface 3Rb extend in a straight line, a curved line, or a bent line, similar to the ribs 31 in the left-side region AR1. Therefore, the ribs 31 in the right-side region AR2 include portions that extend to the right, diagonally downward to the right, and downward. As described above, the anode channel PAa is composed of ribs 31, which are sometimes called anode ribs.

[0033] The front surface 3Fa of the separator 3 is provided with a central region AR0, a left-side region AR1, and a right-side region AR2, all within the same area as the rear surface 3Rb. Furthermore, the front surface 3Fa of the separator 3 is also provided with cathode flow paths PAc, namely a central cathode flow path PAc0, a cathode supply flow path PAc1, and a cathode discharge flow path PAc2, similar to the rear surface 3Rb.

[0034] More specifically, multiple (Nc0) cathode central channels PAc0 are provided at equal intervals in the vertical direction in the central region AR0 of the front surface 3Fa. The multiple cathode channels PAc may be provided at different intervals in the vertical direction. The cathode central channels PAc0 are formed by multiple ribs 31 that extend substantially parallel to each other in the left-right direction, and extend in the left-right direction from the left end 41 to the right end 42 of the central region AR0 without merging or branching. The number of cathode central channels PAc0 Nc0 may be the same as or different from the number of anode central channels PAa0 Na0.

[0035] In the right-side region AR2 of the front surface 3Fa, multiple vertical ribs 31 extend from the through-hole 304 to the entire vertical area of ​​the right end 42 of the central region AR0, and multiple (Nc1) cathode flow channels PAc (referred to as cathode supply channels PAc1) for supplying oxidant gas are formed between the ribs 31, 31. The region where the cathode supply channels PAc1 are provided gradually expands toward the left. A branching section of the cathode supply channels PAc1 is provided in the right-side region AR2 of the front surface 3Fa. Therefore, the number of cathode supply channels PAc1 Nc1 increases toward the left, and the number of cathode supply channels PAc1 Nc1 near the through-hole 304 is less than the number of cathode central channels PAc0 Nc0.

[0036] In the left-side region AR1 of the front surface 3Fa, ribs 31 extend from the entire vertical area of ​​the left end 41 of the central region AR0 to the through hole 303, and multiple (Nc2) cathode flow channels PAc (referred to as cathode discharge channels PAc2) for oxidizer gas discharge are formed between the ribs 31, 31. The area where cathode discharge channels PAc2 are provided gradually decreases towards the left. A confluence of cathode discharge channels PAc2 is provided in the left-side region AR1 of the front surface 3Fa. Therefore, the number of cathode discharge channels PAc2 Nc2 decreases towards the left, and the number of cathode discharge channels PAc2 Nc2 near the through hole 303 is less than the number of cathode central channels PAc0 Nc0.

[0037] Although detailed illustrations are omitted, the ribs 31 in the right-side region AR2 and left-side region AR1 of the front surface 3Fa extend in a straight line, curved line, or bent shape, similar to the ribs 31 on the rear surface 3Rb. Therefore, the ribs 31 in the right-side region AR2 and left-side region include portions that extend to the left, diagonally downward to the left, and downward. As described above, the cathode flow path PAc is composed of ribs 31, which are sometimes called cathode ribs.

[0038] In a portion of the left region AR1, the anode channel PAa (anode supply channel PAa1) and the cathode channel PAc (cathode discharge channel PAc2) overlap in a plan view when the separator 3 is viewed from the stacking direction. Similarly, in a portion of the right region AR2, the anode channel PAa (anode discharge channel PAa2) and the cathode channel PAc (cathode supply channel PAc1) overlap in a plan view when the separator 3 is viewed from the stacking direction.

[0039] In the central region AR0, where the anode central channel PAa0 and the cathode central channel PAc0 are provided, the MEA20 is positioned. Furthermore, in this embodiment, the MEA20 extends in the left-right direction, as shown by the dashed line in Figure 4, to the region where the anode supply channel PAa1 and the cathode discharge channel PAc2 overlap, and the region where the anode discharge channel PAa2 and the cathode supply channel PAc1 overlap. Therefore, the power generation region AR3, where power is generated, expands outward in the left-right direction from the central region AR0. That is, the power generation region AR3 includes an expanded region AR4 that extends outward in the left-right direction from the central region AR0.

[0040] The cooling medium flows through the cooling channel PAw (Figure 2) inside the separator 3, from the through-hole 305 on the right to the through-hole 302 on the left. The cooling channel PAw is in contact with the MEA 20 via the rib 31. Therefore, when the fuel cell generates electricity, heat is transferred from the MEA 20 to the rib 31 and the cooling medium due to the flow of the cooling medium, causing the MEA 20 to absorb heat (also called heat dissipation). This suppresses the temperature rise of the MEA 20.

[0041] Incidentally, since the cooling medium flows from right to left, the temperature of the cooling medium rises towards the left. For this reason, the temperature of the separator 3 on the left side tends to rise. In particular, when the power generation region AR13 expands to a part of the left region AR1, a branching section for the fuel gas and a confluence section for the oxidizer gas are provided in the expanded region AR4. At the branching and confluence sections, the flow width of the reaction gas increases, and the density of the ribs 31 decreases. As a result, the amount of heat absorbed by the flow of the cooling medium decreases, and the temperature of the MEA20 (e.g., electrolyte membrane) may exceed the upper limit temperature. Therefore, in this embodiment, in order to keep the temperature of the MEA20 below the upper limit temperature, the separator 3 is configured as follows.

[0042] FIG. 5A is an enlarged view of section V in FIG. 4 in an enlarged region AR4 on the left side of the separator 3, and FIG. 5B is a diagram showing a reference example of FIG. 5A. In the figure, the ribs 31 (anode ribs 31a) forming the anode supply flow path PAa1 on the rear surface 3Rb of the separator 3 are indicated by solid lines, and the ribs 31 (cathode ribs 31c) forming the cathode discharge flow path PAc2 on the front surface of the separator 3 are indicated by dotted lines.

[0043] First, the reference example will be described. FIG. 5B shows three cathode ribs 31c in the vertical direction extending in the left-right direction, namely, an upper cathode rib 31c1, an intermediate cathode rib 31c2, and a lower cathode rib 31c3. Among these, the intermediate cathode rib 31c2 is interrupted midway while extending from the right to the left, and the flow path width of the cathode discharge flow path PAc2 increases on the left side of the end 310 of the intermediate cathode rib 31c2. The portion where the flow path width is enlarged is referred to as an enlarged portion. FIG. 5B shows a confluence portion PAc3 as the enlarged portion where the flow path width of the cathode discharge flow path PAc2 is enlarged.

[0044] FIG. 5B also shows three anode ribs 31a in the left-right direction extending in the vertical direction, namely, a left anode rib 31a1, an intermediate anode rib 31a2, and a right anode rib 31a3. These anode ribs 31a extend in parallel with each other without interruption. For this reason, there is no branch portion of the anode supply flow path PAa1 in the region of FIG. 5B.

[0045] In the example of FIG. 5B, the left anode rib 31a1 and the intermediate anode rib 31a2 are positioned overlapping the confluence portion PAc3 of the cathode discharge flow path PAc2 in a plan view viewed from the stacking direction. Therefore, the left anode rib 31a1 and the intermediate anode rib 31a2 intersect the upper cathode rib 31c1 and the lower cathode rib 31c3 via the MEA 20. On the other hand, the right anode rib 31a3 intersects the upper cathode rib 31c1, the intermediate cathode rib 31c2, and the lower cathode rib 31c3 via the MEA 20.

[0046] FIG. 5B shows an inscribed circle C1 (two-dot chain line) in contact with an end 310 of an intermediate cathode rib 31c2, an upper cathode rib 31c1, and a lower cathode rib 31c3. In FIG. 5B, when a reference line L1 extending in the vertical direction passing through the center P0 of the inscribed circle C1 is defined, the reference line L1 is positioned midway between a left anode rib 31a1 and an intermediate anode rib 31a2. That is, in the reference example, the anode rib 31a is positioned offset from the reference line L1.

[0047] The center P0 of the inscribed circle C1 is the center of the merging portion PAc3. For this reason, the MEA 20 tends to reach a high temperature in the vicinity of the center P0. In particular, since the cathode side is the power generation side, the temperature tends to be higher than that on the anode side, and the MEA 20 reaches the highest temperature near the center of the inscribed circle C1 where there is no heat dissipation from the cathode rib 31c. In this regard, in the present embodiment, as shown in FIG. 5A, the anode rib 31a (intermediate anode rib 31a2) is positioned on the reference line L1. By arranging the anode rib 31a along the reference line L1 in this manner, heat can be favorably absorbed from the high-temperature region of the MEA 20 via the anode rib 31a by the flow of the cooling medium.

[0048] FIG. 6 is a diagram showing the temperature distribution in the left-right direction of the MEA 20 centered on the reference line L1. The solid line in the figure is the temperature distribution obtained according to the present embodiment (FIG. 5A), and the dotted line is the temperature distribution obtained according to the reference example (FIG. 5B). In FIG. 6, positions corresponding to the left anode rib 31a1 and the right anode rib 31a3 in FIG. 5A are indicated by P1 and P2.

[0049] As shown in FIG. 6, in the reference example (dotted line), the temperature of the portion along the reference line L1 of the MEA 20 rises sharply, reaching a temperature T1. Therefore, the temperature difference between the portion along the reference line L1 and other portions (e.g., positions P1, P2) is large. On the other hand, in the present embodiment (solid line), the temperature rise of the portion along the reference line L1 of the MEA 20 is gradual, and the temperature becomes T2 which is lower than T1. Therefore, the temperature difference between the portion along the reference line L1 and other portions is generally small overall.

[0050] The temperature of the MEA20 in contact with the anode rib 31a is lower than the temperature of the parts not in contact with the anode rib 31a. Therefore, as in this embodiment, by placing the anode rib 31a in the center of the confluence PAc3 where the cathode rib 31c is absent (Figure 5A), the temperature of the MEA20 can be effectively reduced.

[0051] This embodiment provides the following advantages and effects: (1) The fuel cell stack 100 comprises a cell stack 101 formed by alternately stacking a UEA 2 containing an electrolyte membrane and electrodes, and a separator 3 in a predetermined direction (front-to-back direction) (Figure 1). The separator 3 has a front plate 3F having a front surface 3Fa and a rear surface 3Fb, and a rear plate 3R having a front surface 3Ra and a rear surface 3Rb facing the rear surface 3Fb. A cooling channel PAw is formed between the rear surface 3Fb and the front surface 3Ra, through which a cooling medium flows from a through-hole 305 for supplying refrigerant on the right side that penetrates the separator 3, to a through-hole 302 for discharging refrigerant on the left side that penetrates the separator 3 (Figures 1 and 2). The front plate 3F has a rib 31 (cathode rib 31c) projecting from the front surface 3Fa toward the UEA2 so as to form a cathode channel PAc through which oxidizer gas flows between the front surface 3Fa and the UEA2 facing the front surface 3Fa (Figure 2). The rear plate 3R has a rib 31 (anode rib 31a) projecting from the rear surface 3Rb toward the UEA2 so as to form an anode channel PAa through which fuel gas flows between the rear surface 3Rb and the UEA2 facing the rear surface 3Rb (Figures 2, 4). The cathode channel PAc (cathode discharge channel PAc2) has a confluence section PAc3 where the channel width is increased (Figure 5A). The anode rib 31a is positioned in the confluence section PAc3 of the cathode channel PAc in a plan view when the separator 3 is viewed from the stacking direction (Figure 5A). That is, it is positioned within the range of the confluence section PAc3.

[0052] In the confluence section PAc3 of the cathode flow path PAc, where the flow path width is increased, a cathode rib 31c is not placed. As a result, the amount of heat absorbed from the MEA20 via the cathode rib 31c is small, and the MEA20 tends to become hot. In this regard, by placing an anode rib 31a on top of the confluence section PAc3, heat can be absorbed from the high-temperature region of the MEA20 via the anode rib 31a, and the MEA20 can be kept below the lower limit temperature. Therefore, the MEA20 can be cooled effectively by the flow of the cooling medium, and the deterioration of the MEA20 can be suppressed.

[0053] (2) The UEA2 has an MEA20 that constitutes the power generation surface and a frame 21 that supports the MEA20 (Figure 3). The confluence PAc3 is provided opposite the MEA20, that is, it is provided within the power generation region AR3 (Figure 4). When the confluence PAc3 is provided in the power generation region AR3, the temperature of the MEA20 tends to rise, but in this embodiment, the temperature rise in this case can be suppressed well.

[0054] (3) The cathode rib 31c includes an intermediate cathode rib 31c2 having an end 310 where the cathode rib 31c is discontinuous, and an upper cathode rib 31c1 and a lower cathode rib 31c3 extending so as to sandwich the end 310 of the intermediate cathode rib 31c2 (Figure 5A). The confluence PAc3 is provided between the end 310 and the upper cathode rib 31c1 and the lower cathode rib 31c3 (Figure 5A). The anode rib 31a passes inside the inscribed circle C1 that is in contact with the end 310 and the upper cathode rib 31c1 and the lower cathode rib 31c3, and extends in the direction of the flow width of the cathode flow path PAc, i.e., in the vertical direction (Figure 5A). This allows for good heat absorption from the parts of the MEA 20 that tend to get hot by the flow of the cooling medium.

[0055] (4) The anode rib 31a passes through the center P0 of the inscribed circle C1 (Figure 5A). This positions the anode rib 31a adjacent to the hottest part of the MEA 20, allowing for an efficient reduction of the peak temperature of the MEA 20.

[0056] (5) The anode rib 31a has an intermediate anode rib 31a2 that intersects the upper cathode rib 31c1 and the lower cathode rib 31c3 and extends so as to overlap with the confluence PAc3 in a plan view from the stacking direction, and a left anode rib 31a1 and a right anode rib 31a3 that extend on both sides of the intermediate anode rib 31a2 substantially parallel to the intermediate anode rib 31a2 (Figure 5A). This makes it possible to hold the MEA20 well between the multiple anode ribs 31a and the multiple cathode ribs 31c while suppressing the temperature rise of the MEA20 (electrolyte membrane, etc.).

[0057] (6) The cathode flow path PAc is formed from the right-side through-hole 304 for supplying oxidant gas that penetrates the separator 3, through the central region AR0 in the center of the separator 3 where the flow path width is uniform, and from the central region AR0 to the left-side through-hole 303 for discharging oxidant gas that penetrates the separator 3 (Figure 4). The confluence section PAc3 is provided between the central region AR0 and the through-hole 303 (Figure 4). For this reason, the confluence section PAc3 is downstream of the cooling flow path PAw and tends to become hot, but by arranging the anode rib 31a as in this embodiment, the temperature rise of the MEA20 in the confluence section PAc3 can be effectively suppressed.

[0058] The above embodiment can be modified into various forms. Several modifications will be described below. In the above embodiment, the separator 3 is configured such that a cooling channel PAw is formed between the rear surface 3Fb and the front surface 3Ra by a front plate 3F as a first plate member having a front surface 3Fa (first surface) and a rear surface 3Fb (first back surface), and a rear plate 3R as a second plate member having a front surface 3Ra (second back surface) and a rear surface 3Rb (second surface). That is, a cooling channel PAw is formed from a through hole 305 (refrigerant supply hole) at the right end (one end) of the separator 3 that penetrates the separator 3 to a through hole 302 (refrigerant discharge hole) at the left end (other end) of the separator 3 that penetrates the separator 3, but the configuration of the cooling channel PAw is not limited to the above. For example, the cooling channel PAw may be configured such that a cooling medium flows from the through hole 302 to the through hole 305.

[0059] In the above embodiment, a cathode rib 31c (first rib) is provided projecting from the front surface 3Fa of the front plate 3F toward the UEA2 so as to form a cathode channel PAc (first gas channel) through which an oxidizing gas (first reaction gas) flows between the front plate 3F and the UEA2, and an anode rib 31a (second rib) is provided projecting from the rear surface 3Rb of the rear plate 3R toward the UEA2 so as to form an anode channel PAa (second gas channel) through which a fuel gas (second reaction gas) flows between the rear plate 3R and the UEA2. However, the configuration of the first plate member and the second plate member is not limited to those described above. The first gas channel and the second gas channel may be formed in the first plate member and the second plate member so that the first reaction gas is the fuel gas and the second reaction gas is the oxidizing gas.

[0060] In the above embodiment (Figure 5A), the configuration of the anode rib 31a at the confluence PAc3 of the cathode flow path PAc has been described, but the anode rib 31a may also be arranged in the same way as in Figure 5A at the branching section of the cathode flow path PAc. Furthermore, at the confluence and branching sections of the anode flow path PAa, the anode rib 31a and cathode rib 31c in Figure 5A may be swapped. Therefore, the enlarged section where the flow path width of the first gas flow path is expanded is not limited to the confluence PAc3 of the cathode flow path PAc, but may be any or all of the branching section of the cathode flow path PAc, the confluence section of the anode flow path PAa, or the branching section of the anode flow path PAa. In the above embodiment, the enlarged section of the gas flow path (confluence PAc3) was provided facing the MEA20, which is the power generation surface, but the enlarged section does not have to face the MEA20.

[0061] In the above embodiment, the cathode rib 31c as the first rib is formed by the intermediate cathode rib 31c2 (intermediate rib) and the upper cathode ribs 31c1 and lower cathode ribs 31c3 (a pair of outer ribs) on both sides thereof, and the anode rib 31a as the second rib is formed by passing through the center P0 of the inscribed circle C1 that is tangent to the end 310 of the intermediate cathode rib 31c2 and the upper cathode ribs 31c1 and lower cathode ribs 31c3 in a plan view from the stacking direction, but the second rib may pass through a position other than the center inside the inscribed circle. In the above embodiment, the anode rib 31a is formed by the intermediate anode rib 31a2 (first intersecting rib) that extends so as to overlap with the confluence PAc3 in a plan view from the stacking direction, and the left anode rib 31a1 and right anode rib 31a3 (a pair of second intersecting ribs) on both sides of the intermediate anode rib 31a2, but the configuration of the second rib is not limited to that described above.

[0062] In the above embodiment, a cathode flow path PAc was formed as the first gas flow path, extending from the through hole 304 (gas supply hole) at one end of the separator 3 to the central region AR0 and the through hole 303 (gas discharge hole) at the other end. However, the configuration of the first gas flow path is not limited to that described above. For example, the first gas flow path may also be an anode flow path PAa. Therefore, the gas supply hole may be the through hole 301, and the gas discharge hole may be the through hole 306.

[0063] In the above embodiment, an example of applying the fuel cell stack 100 to a vehicle was described, but the fuel cell stack having the power generation cell of the present invention can also be applied to mobile bodies other than vehicles such as aircraft and ships, robots, and various industrial machines.

[0064] The above description is merely an example, and the present invention is not limited by the embodiments and modifications described above, as long as the features of the present invention are not impaired. It is also possible to arbitrarily combine one or more of the above embodiments and modifications, and to combine modifications with each other.

[0065] 2. Integrated electrode assembly, 3. Separator, 3F. Front plate, 3Fa. Front surface, 3Fb. Rear surface, 3R. Rear plate, 3Ra. Front surface, 3Rb. Rear surface, 20. Membrane electrode assembly, 31. Rib, 31a. Anode rib, 31a1. Left anode rib, 31a2. Intermediate anode rib, 31a3. Right anode rib, 31c. Cathode rib, 31c1. Upper cathode rib, 31c2. Intermediate cathode rib, 31c3. Lower cathode rib, 100. Fuel cell stack, 302-305. Through hole, PAc. Cathode flow path, PAc3. Confluence section, PAw. Cooling flow path, C1. Inscribed circle, P0. Center, AR0. Central region.

Claims

1. A fuel cell stack comprising a laminate formed by alternately stacking membrane electrode structures including an electrolyte membrane and an electrode, and a separator, in a predetermined direction, wherein the separator has a first plate member having a first surface and a first back surface opposite to the first surface, and a second plate member having a second back surface facing the first back surface and a second surface opposite to the second back surface, and is configured such that a cooling channel is formed between the first back surface and the second back surface through which a cooling medium flows, from a refrigerant supply hole on one end of the separator that penetrates the separator, to a refrigerant discharge hole on the other end of the separator that penetrates the separator, and the first plate member has a first rib protruding from the first surface toward the membrane electrode structure so as to form a first gas channel through which a first reaction gas flows between the first surface and the membrane electrode structure facing the first surface, The fuel cell stack is characterized in that the second plate member has a second rib protruding from the second surface toward the membrane electrode structure so as to form a second gas channel through which a second reaction gas flows between the second surface and the membrane electrode structure facing the second surface, the first gas channel has an enlarged portion in which the channel width is increased, and the second rib is arranged in the enlarged portion of the first gas channel in a plan view when the separator is viewed from the stacking direction.

2. A fuel cell stack according to claim 1, wherein the membrane electrode structure comprises a membrane electrode assembly constituting a power generation surface and a frame supporting the membrane electrode assembly, and the enlarged portion is provided opposite the membrane electrode assembly.

3. A fuel cell stack according to claim 1, wherein the first rib includes an intermediate rib having an end that is discontinuous to the first rib, and a pair of outer ribs extending so as to sandwich the end of the intermediate rib, the enlarged portion is provided between the end and the pair of outer ribs, and the second rib passes through the interior of an inscribed circle that is tangent to the end and the pair of outer ribs, and extends in the direction of the flow path width of the first gas flow path.

4. A fuel cell stack according to claim 3, characterized in that the second rib passes through the center of the inscribed circle.

5. A fuel cell stack according to claim 3 or 4, wherein the second rib comprises a first intersecting rib that intersects the pair of outer ribs and extends so as to overlap with the enlarged portion in a plan view, and a pair of second intersecting ribs that extend substantially parallel to the first intersecting rib on both sides of the first intersecting rib.

6. A fuel cell stack according to claim 1, wherein the first gas flow path is formed from a gas supply hole on one end of the separator that penetrates the separator, through a central region in the center of the separator where the flow path width is uniform, and from the central region to a gas discharge hole on the other end of the separator that penetrates the separator, and the enlarged portion is provided between the central region and the gas discharge hole.

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