Fuel cell stack

Abstract

The present invention forms a flow path between a first plate part and a second plate part of a separator constituting a fuel cell stack. This flow path includes: a power generation region flow path through which a cooling medium flows along a power generation region of the separator; a supply flow path that guides the cooling medium supplied via a supply hole passing through the separator to the power generation region flow path; a bypass flow path that guides air bubbles contained in the cooling medium supplied via the supply hole to the downstream side of the power generation region flow path by bypassing the power generation region flow path; and a connection flow path that connects the supply flow path and the bypass flow path. The supply flow path has a first throttling part and a second throttling part downstream thereof which are positioned downstream of a connection position where the connection flow path is connected thereto. The first throttling part is configured so as to have a flow path resistance which is greater than that of the second throttling part.

Description

fuel cell stack

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

[0002] In recent years, technological developments related to fuel cells that contribute to energy efficiency have been underway to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. One known technology related to this type of fuel cell is one that discharges air bubbles that flow in through a coolant supply hole via a bypass flow path that bypasses the power generation unit (see, for example, Patent Document 1). In the fuel cell stack described in Patent Document 1, the upper end of the coolant supply hole and the bypass flow path are connected via a bubble discharge flow path.

[0003] Patent No. 7297805

[0004] However, simply providing a bypass flow path that bypasses the power generation section, as in the fuel cell stack described in Patent Document 1, makes it difficult to sufficiently reduce the amount of bubbles supplied to the power generation section.

[0005] A fuel cell stack according to one embodiment of the present invention is constructed by alternately stacking membrane electrode assemblies and separators in a predetermined direction. The membrane electrode assembly includes a membrane electrode assembly having an electrolyte membrane and electrodes, and a frame member supporting the peripheral edge of the membrane electrode assembly. The separator includes a first plate portion having an uneven shape disposed opposite a first surface of the membrane electrode assembly and defining a first gas flow path between the separator and the membrane electrode assembly for a first gas to flow, and a second plate portion having an uneven shape disposed opposite a second surface of the membrane electrode assembly and defining a second gas flow path between the separator and the membrane electrode assembly for a second gas to flow. The first plate portion and the second plate portion have a flow path forming portion that forms a flow path through which the coolant flows between the first plate portion and the second plate portion, the flow path including a power generation region flow path through which the coolant flows along the power generation region of the separator facing the membrane electrode assembly, a supply flow path that guides the coolant supplied through a supply hole that penetrates the separator to the power generation region flow path, a bypass flow path that guides bubbles contained in the coolant supplied through the supply hole to a downstream side of the power generation region flow path, bypassing the power generation region flow path, and a communication flow path that communicates the supply flow path with the bypass flow path. The supply flow path has multiple throttle portions downstream of a connection position where the communication flow path is connected, which shorten the height of the gap between the first plate portion and the second plate portion, the multiple throttle portions including a first throttle portion and a second throttle portion downstream of the first throttle portion, and the first throttle portion is configured to have a higher flow path resistance than the second throttle portion.

[0006] According to the present invention, the amount of bubbles supplied to the power generation section can be sufficiently reduced.

[0007] 7 is a perspective view schematically showing the overall configuration of a fuel cell stack according to an embodiment of the present invention; a cross-sectional view taken along line II-II in FIG. 1; a perspective view showing the schematic configuration of an integrated electrode assembly included in the fuel cell stack of FIG. 1; a front view of a separator included in the fuel cell stack of FIG. 1; a view showing a pair of guide portions at the end of the separator of FIG. 4 overlapping each other; a cross-sectional view taken along line VI-VI in FIG. 4; an enlarged view of part VII in FIG. 4; a cross-sectional view taken along line VIII-VIII in FIG. 7;

[0008] Hereinafter, an embodiment of the present invention will be described with reference to Figures 1 to 8. A fuel cell stack according to an embodiment of the present invention is one of the main components of a fuel cell. The fuel cell is mounted, for example, in a vehicle and can generate electric power to drive the vehicle. First, the overall configuration of the fuel cell stack will be described in brief.

[0009] FIG. 1 is a perspective view showing a schematic view of the overall configuration of a fuel cell stack 100 according to this embodiment. For convenience, the three mutually orthogonal axial directions 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 in accordance with these definitions. The downward direction in the up-down direction corresponds to the direction of gravity or approximately the direction of gravity. The front-rear direction corresponds to the stacking direction of the fuel cell stack 100. The front-rear direction and the left-right direction are not necessarily the same as the front-rear direction and the left-right direction of a vehicle.

[0010] As shown in Fig. 1, the fuel cell stack 100 has a cell stack 101 formed by stacking a plurality of power-generating cells 1 in the front-rear direction, and end units 102 arranged at both front-rear ends of the cell stack 101, and has a generally rectangular parallelepiped shape as a whole. Although not shown, the cell stack 101 is surrounded by a generally rectangular parallelepiped case. The length of the cell stack 101 in the left-right direction is longer than the length in the up-down direction. For convenience, only a single power-generating cell 1 is shown in Fig. 1.

[0011] The power-generating cell 1 includes a unitized electrode assembly 2 (hereinafter referred to as UEA) having an assembly including an electrolyte membrane and electrodes, and separators 3, 3 arranged on both sides of the UEA 2 in the front-rear direction to sandwich 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] FIG. 2 is a cross-sectional view (a cross-sectional view taken along line II-II in FIG. 1 ) of a main portion of the power generation region at the center in the left-right direction 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 extends vertically and horizontally and has a front surface 3Fa and a rear surface 3Fb. The rear plate 3R extends vertically and horizontally and has a front surface 3Ra and a rear surface 3Rb. The opposing rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R are joined at their outer peripheral edges by welding or the like. This integrally bonds 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. Water, for example, can be used as the coolant. The surface of the separator 3 facing the UEA 2 (the front surface 3Fa and the rear surface 3Rb) is formed unevenly by press molding or the like to form a gas flow path between the separator 3 and the UEA 2. More specifically, the separator 3 has a pair of front and rear protrusions 31 protruding toward the UEA 2 and a pair of front and rear recesses 32 formed in a concave shape and connected to the pair of front and rear protrusions 31.

[0014] The pair of front and rear protrusions 31 abut against the rear surface 2b and front surface 2a of the UEA 2. A compressive load F is applied to the cell stack 101 in the front-rear direction during assembly of the fuel cell stack 100, and this compressive load F is maintained after assembly of the fuel cell stack 100 is complete. As a result, a predetermined surface pressure due to the compressive load F acts on the UEA 2 in the front-rear direction via the protrusions 31.

[0015] Between the front surface 2a of the UEA 2 and the rear plate 3R of the separator 3 facing this front surface 2a, an anode flow path PAa through which fuel gas flows is formed by a recess 32. Between the rear surface 2b of the UEA 2 and the front plate 3F of the separator 3 facing this rear surface 2b, a cathode flow path PAc through which oxidizer gas flows is formed by a recess 32. The fuel gas is a gas containing hydrogen, and hydrogen gas can be used, for example. The oxidizer gas is a gas containing oxygen, and air can be used, for example. The fuel gas and the oxidizer gas are sometimes referred to as reactant gases without distinction between them.

[0016] 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 (hereinafter referred to as MEA) 20 and a frame 21 that supports the MEA 20. The MEA 20 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. It is not limited to a fluorine-based electrolyte membrane, but a hydrocarbon-based electrolyte membrane can also be used. The anode electrode is formed on the front surface of the electrolyte membrane and has an electrode catalyst layer that serves as a reaction field for the electrode reaction, and a gas diffusion layer that is provided on the front surface of the electrode catalyst layer and diffuses and supplies the fuel gas. The cathode electrode is formed on the rear surface of the electrolyte membrane and has an electrode catalyst layer that serves as a reaction field for the electrode reaction, and a gas diffusion layer that is provided on the rear surface of the electrode catalyst layer and diffuses and supplies the oxidant gas.

[0018] At the anode electrode, fuel gas (hydrogen) supplied via the anode flow path PAa in FIG. 2 is ionized by the action of a catalyst and moves through the electrolyte membrane to the cathode electrode side. The electrons generated at this time pass through an external circuit and are extracted as electrical energy. At the cathode electrode, oxidant gas (oxygen) supplied via the cathode flow path PAc in FIG. 2 reacts with hydrogen ions introduced from the anode electrode and electrons transferred from the anode electrode to generate water. The generated water (referred to as generated water) provides an appropriate humidity to the electrolyte membrane, and excess water is discharged to the outside of the UEA2 along the gas flow.

[0019] 3 , the frame 21 is a substantially rectangular frame member made of insulating resin, rubber, or the like. A substantially rectangular opening 21 a is provided in the center of the frame 21. The MEA 20 is provided to cover the entire opening 21 a, and the peripheral edge of the MEA 20 is supported by the frame 21.

[0020] Three through holes 211 to 213 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 214 to 216 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 211 to 216 are shown as being substantially rectangular, but the shape and arrangement of the through holes 211 to 216 are not limited to this.

[0021] As shown in FIG. 1 , the front and rear separators 3 of the UEA 2 are provided with through-holes 301-306 that penetrate the separators 3 in the front-rear direction at positions corresponding to the through-holes 211-216 of the frame 21. The through-holes 301-306 are connected to the through-holes 211-216 of the frame 21, respectively. The interconnected through-holes 211-216 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.

[0022] 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. That is, 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.

[0023] A plurality of through holes 102a to 102f that penetrate the end unit 102 in the front-to-rear direction are opened in the rear end unit 102 at positions corresponding to the through holes 211 to 216 and 301 to 306 of the cell stack 101. For convenience, the through holes 102a to 102f are all shown as being substantially rectangular, but the positions and shapes of the through holes 102a to 102f are not limited to this.

[0024] The through-hole 102a is a fuel gas supply port, and the fuel gas is supplied to the fuel cell stack 100 through the through-hole 102a. This fuel gas is guided to the anode flow path PAa between the UEA 2 and the rear plate 3R of the separator 3 through the through-holes 211 and 301. After passing through the anode flow path PAa, the fuel gas flows rearward through the through-holes 216 and 306 and is discharged from the through-hole 102f.

[0025] The through-hole 102d is an oxidant gas supply port, and the oxidant gas is supplied to the fuel cell stack 100 through the through-hole 102d. This oxidant gas is guided to the cathode flow path PAc between the UEA 2 and the front plate 3F of the separator 3 through the through-holes 214 and 304. After passing through the cathode flow path PAc, the oxidant gas flows rearward 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 to the cooling flow path PAw between the front plate 3F and the rear plate 3R of the separator 3 through the through-holes 215 and 305. After passing through the cooling flow path PAw, the cooling medium flows rearward through the through-holes 212 and 302 and is discharged from the through-hole 102b. The above is a schematic configuration of the fuel cell stack 100.

[0027] The structure of the separator 3 will be described in more detail. FIG. 4 is a front view (viewed from the front) of the separator 3, with the left-right direction reversed compared to FIG. 1 . That is, FIG. 4 shows the front surface 3Fa (FIG. 2) of the separator 3 facing the cathode electrode on the rear surface 2b of the UEA 2. In FIG. 4 , the shape and arrangement of the through-holes 301-306 are slightly changed from those in FIG. 1 . Specifically, the through-holes 302 and 305 through which the coolant passes are located laterally outward of the through-holes 301 and 306 through which the fuel gas passes and the through-holes 303 and 304 through which the oxidizer gas passes. Positioning portions (e.g., engagement recesses) for positioning the separator 3 are provided on the periphery of the separator 3, but are not shown in FIG. 4 . The left-right and up-down directions in FIG. 4 correspond to the longitudinal and lateral directions of the separator 3, respectively.

[0028] In Figure 4, the region AR1 in the center in the left-right direction, which faces the MEA 20 of the UEA 2, i.e., the region AR1 indicated by the two-dot chain line facing the power generation surface, is called the active region of the separator 3. The region AR2 on the outside of the active region AR1 in the left-right direction is called the inactive region. The inactive region AR2 of the separator 3 faces the frame 21 of the UEA 2. The active region AR1 corresponds to the power generation region where power generation occurs.

[0029] 2 and 4 , a plurality of protrusions 31 are provided protruding forward at equal intervals in the vertical direction across substantially the entire active region AR1 of the separator 3, although some of the protrusions are not shown. Each of the plurality of protrusions 31 extends in the horizontal direction, and a recess 32 is provided between adjacent protrusions 31 in the vertical direction. A cathode flow path PAc is formed between the plurality of recesses 32 and the rear surface of the MEA 20. As indicated by the arrow Ca in FIG. 4 , oxidant gas flows from right to left through the cathode flow path PAc.

[0030] As shown in FIG. 4 , the front surface 3Fa of the separator 3 (front plate 3F) is provided with a plurality of bead portions, i.e., metal bead seals, that protrude forward toward the frame 21. The plurality of bead portions includes an outer bead portion 331 and a plurality of individual bead portions 332. The plurality of bead portions protrude forward by the same amount. The plurality of bead portions extend with a predetermined width, but for convenience, the bead portions are indicated by thick lines in FIG. 4 . Although not shown, a plurality of bead portions are also provided on the rear plate 3R, similar to the front plate 3F.

[0031] The individual bead portions 332 extend along the peripheries of the through holes 301 to 306, respectively, and individually surround the through holes 301 to 306. The outer bead portions 331 extend in the left-right direction above and below the active region AR1 along the upper and lower edges of the separator 3, and also extend along the left-right outer sides of the individual bead portions 332 around the through holes 301, 303, 304, and 306, and along the left-right inner sides of the individual bead portions 332 around the through holes 302 and 305.

[0032] In the inactive region AR2 of the separator 3 (front plate 3F), a plurality of guide portions 333 are provided to protrude toward the front frame 21, from the through-hole 304 over the entire vertical area of ​​the inlet at the right end of the cathode flow channel PAc, and from the entire vertical area of ​​the outlet at the left end of the cathode flow channel PAc over the through-hole 303. The plurality of guide portions 333 extend at equal intervals and approximately parallel to one another.

[0033] A plurality of tunnel portions 41 are provided between the through holes 304 and the guide portions 333, and between the through holes 303 and the guide portions 333, protruding forward and crossing the individual bead portions 332. The amount of forward protrusion of the tunnel portions 41 is smaller than the amount of forward protrusion of the individual bead portions 332. Although not shown, tunnel portions 41 are also provided on the rear plate 3R, symmetrically to the front plate 3F in the front-rear direction.

[0034] One end of the tunnel portion 41 communicates with the through holes 303, 304. The other end of the tunnel portion 41 communicates with the space in front of the separator 3 (front plate 3F) (the space between the separator 3 and the frame 21 in front of it). In the right inactive region AR2, a cathode supply flow path PA11 is formed between vertically adjacent guide portions 333, 333. In the left inactive region AR2, a cathode discharge flow path PA12 is formed between vertically adjacent guide portions 333, 333. As a result, the through hole 304 and the cathode supply flow path PA11, and the through hole 303 and the cathode discharge flow path PA12, are each communicated via the tunnel portion 41.

[0035] Separator 3 is further provided with tunnel portion 42 extending from through holes 301 and 306, and tunnel portion 43 extending from through holes 302 and 305. One end of tunnel portion 42 communicates with through holes 301 and 306, and the other end communicates with the space behind separator 3 (rear plate 3R). One end of tunnel portion 43 communicates with through holes 302 and 305, and the other end communicates with the space between front plate 3F and rear plate 3R (see FIG. 6 ).

[0036] The oxidant gas supplied through the through-hole 304 passes through the tunnel portion 41 and flows into the cathode supply flow path PA11 at the inlet of the guide portion 333. The oxidant gas then flows leftward or diagonally downward to the left along the guide portion 333 and is led to the cathode flow path PAc. The oxidant gas that has flowed through the cathode flow path PAc flows into the cathode discharge flow path PA12 at the inlet of the guide portion 333. The oxidant gas then flows leftward or diagonally downward to the left along the guide portion 333 and flows through the tunnel portion 41 to the through-hole 303.

[0037] By providing the guide portion 333, the oxidant gas can be guided evenly throughout the entire area of ​​the cathode flow channel PAc in the vertical direction. Instead of or in addition to the guide portion 333, a plurality of embossed portions each having a generally cylindrical shape and protruding forward may be provided. The metal bead seal (outer bead portion 331, individual bead portion 332), guide portion 333, tunnel portions 41 to 43, etc. are formed by pressing the front plate 3F.

[0038] Although not shown, a plurality of protrusions 31 and recesses 32, metal bead seals (outer bead portions 331 and individual bead portions 332), guide portions 333, and tunnel portions 41 to 43 are similarly formed on the rear surface 3Rb of the separator 3 (rear plate 3R) by press working the rear plate 3R. As a result, fuel gas is guided from the through hole 301 to the anode flow path PAa via the tunnel portion 42 and guide portion 333. The fuel gas that has flowed through the anode flow path PAa is discharged from the through hole 306 via the guide portion 333 and tunnel portion 42.

[0039] 5 is a diagram showing the guide portion 333 (solid line) of the front plate 3F and the guide portion 333 (dotted line) of the rear plate 3R superimposed on each other on the right side (left side in the figure) of the separator 3. In Fig. 5, the flow direction of the oxidant gas in the cathode flow channel PAc is indicated by a solid arrow Ca, and the flow direction of the fuel gas in the anode flow channel PAa is indicated by a dotted arrow An.

[0040] 5 , in the inactive region AR2 of the separator 3 (rear plate 3R), a plurality of guide portions 333 are provided to protrude from the entire vertical area of ​​the right-end outlet of the anode flow channel PAa to the through-hole 306 toward the rear frame 21. The guide portions 333 extend at equal intervals and generally parallel to one another. Therefore, the guide portions 333 (dotted lines) of the rear plate 3R and the guide portions 333 (solid lines) of the front plate 3F extend so as to intersect with one another.

[0041] The flow of the coolant will now be described. Figure 6 is a cross-sectional view taken along line VI-VI in Figure 4, showing the configuration of the tunnel portion 43 connected to the through hole 305. Figure 6 also shows frames 21 disposed in front and behind the separator 3. As shown in Figure 6, the front end surfaces of the individual bead portions 332 and the front surface of the outer bead portion 331, which protrude forward from the front plate 3F of the separator 3, abut against the rear surface of the frame 21 via sealants 334. The rear end surfaces of the individual bead portions 332 and the rear end surface of the outer bead portion 331, which protrude rearward from the rear plate 3R of the separator 3, abut against the front surface of the frame 21 via sealants 334.

[0042] The tunnel portion 43 extends rightward from the through hole 305, passing over the individual bead portion 332 and the outer bead portion 331. The tunnel portion 43 has a front tunnel portion 431 that bulges forward from the front plate 3F, and a rear tunnel portion 432 that bulges rearward from the rear plate 3R. A coolant supply flow path PA13 is formed between the front tunnel portion 431 and the rear tunnel portion 432, and the coolant flows from right to left through the coolant supply flow path PA13, as shown by the arrow in FIG. 6 .

[0043] The coolant supply flow path PA13 includes an inner space SP12 of the individual bead portion 332 and an inner space SP11 of the outer bead portion 331. The inner space SP12 extends in the up-down and left-right directions along the individual bead portion 332, and the inner space SP11 extends in the approximately up-down direction along the outer bead portion 331 (see FIG. 5 ). Although not shown, the cross-sectional shape of the tunnel portion 43 perpendicular to the coolant supply flow path PA13 (the cross-sectional shape of the tunnel portion 43 excluding the bead portions 331 and 332 in FIG. 6 ) is approximately polygonal (for example, approximately rectangular), approximately elliptical, or approximately oval.

[0044] 4 shows multiple tunnels 43, but the configurations of the multiple tunnels 43 are identical or substantially identical. The cooling medium that has passed through the multiple tunnels 43 flows to the right through the back side (rear side) of the guide portion 333, as indicated by the dotted arrow A1 in FIG. 4, and flows into the cooling flow path PAw ( FIG. 2 ) in the active region AR1. The cooling medium further flows to the right along the cooling flow path PAw ( FIG. 2 ), and then flows to the right through the back side (rear side) of the guide portion 333, as indicated by the dotted arrow A2, and reaches the through-hole 302 via the tunnels 43.

[0045] Fig. 7 is an enlarged view of portion VII in Fig. 4. As shown in Fig. 7, one end (lower end) of the upper tunnel portion 44 is connected to the upper edge of the through hole 305 for supplying a coolant. The upper tunnel portion 44 traverses the individual bead portion 332 around the through hole 305, and the other end (upper end) is connected to the outer bead portion 331. This allows the through hole 305 to communicate with the inner space SP11 (Fig. 6) of the outer bead portion 331.

[0046] 4, one end of the upper tunnel portion 45 is connected to the upper end of the through hole 302 for discharging the coolant. The upper tunnel portion 45 traverses the individual bead portion 332 around the through hole 302, and the other end of the upper tunnel portion 45 is connected to the outer bead portion 331. This allows the through hole 302 to communicate with the inner space SP11 (FIG. 6) of the outer bead portion 331.

[0047] After the fuel cell stack 100 is assembled, a cooling medium is injected into the fuel cell stack 100 through the through-hole 102e (FIG. 1). At this time, the air in the cooling flow path PAw moves upward and flows along the cooling flow path PAw and flow paths PA5 and PA2 together with the cooling medium. Furthermore, if air is mixed in the cooling medium supplied through the through-hole 102e, this air also flows along the cooling flow path PAw and flow paths PA5 and PA2 together with the cooling medium.

[0048] When air (air bubbles) are contained in the coolant supplied to the through-hole 305, the air bubbles B1 move upward as indicated by arrow A3 in FIG. 7 and enter the inner space SP13 of the upper tunnel 44. The air bubbles B1 pass through the inner space SP13 and then enter the inner space SP11 of the outer bead 331 as indicated by arrow A4. The air bubbles in the inner space SP11 pass through the inner space SP11 of the outer bead 331 above the active region AR1 as indicated by arrows A5 and A6 in FIG. 4, and are then guided to the through-hole 302 via the inner space of the upper tunnel 45 as indicated by arrow A7, and are then discharged to the outside via the through-hole 302.

[0049] In this way, the inner space SP13 of the upper tunnel 44, the inner space SP11 of the outer bead 331, and the inner space of the upper tunnel 45 constitute a bypass flow path PAb that bypasses the active region AR1 and leads from the through-hole 305 to the through-hole 302. This allows bubbles in the through-hole 305 to flow around the cooling flow path PAw via the bypass flow path PAb. This suppresses the flow of bubbles B1 into the cooling flow path PAw via the coolant supply flow path PA13 ( FIG. 6 ), thereby enhancing the cooling effect of the coolant flow in the active region AR1. Note that not only bubbles but also refrigerant can flow through the bypass flow path PAb.

[0050] In this fuel cell stack 100, not all of the bubbles contained in the coolant supplied to the through-holes 305 are necessarily guided to the bypass flow path PAb, but some are guided to the coolant supply flow path PA13. The bubbles that flow to the active region AR1 via the coolant supply flow path PA13 flow above the active region AR1, which may reduce the cooling efficiency above. Therefore, in order to increase the cooling efficiency due to the flow of the coolant, it is preferable to reduce the amount and size of the bubbles guided to the active region AR1 via the coolant supply flow path PA13. Taking this into consideration, the fuel cell stack 100 of this embodiment is configured as follows.

[0051] 8 is a cross-sectional view taken along line VIII-VIII in FIG. 7 , i.e., a cross-sectional view of the coolant supply channel PA13 cut along the coolant flow direction. As shown in FIGS. 7 and 8 , a plurality of guide portions 333 that are generally parallel to one another protrude forward from the front plate 3F of the separator 3. A recess 335 is provided between adjacent guide portions 333 in the left-right direction. The recesses 335 form the cathode supply channel PA11 ( FIG. 4 ) in front of the front plate 3F, extending from the tunnel portion 41 to the active region AR1 ( FIG. 4 ). The rear plate 3R of the separator 3 does not have guide portions 333 in this region, and the rear plate 3R is flat (see FIG. 5 ).

[0052] The multiple recesses 335 include multiple recesses 335a each having a predetermined width W1 and a single wide recess 335b having a predetermined width W2. The width W2 is wider than the width W1, for example, the width W2 is at least twice the width W1. The wide recess 335b is located upstream of the multiple recesses 335a in the direction of coolant flow. For example, the first recess 335 or the second recess 335 beyond the tunnel portion 43 is the wide recess 335b.

[0053] The upper tunnel portion 44 and the tunnel portion 43 are connected via an outer bead portion 331 outside the through hole 305. The outer bead portion 331 between the upper tunnel portion 44 and the tunnel portion 43 is referred to as a connection flow path portion 331a. One end (lower end) of the connection flow path portion 331a is connected to the tunnel portion 43, and the other end (upper end) is connected to a connection portion 338 that connects the upper tunnel portion 44 and the outer bead portion 331. The coolant supply flow path PA13 branches at the tunnel portion 43 and communicates with the bypass flow path PAb via a communication flow path PAs inside the connection flow path portion 331a.

[0054] As shown in FIG. 8 , with respect to the height of the coolant supply channel PA13, i.e., the distance from the rear surface 3Fb of the front plate 3F to the front surface 3Ra of the rear plate 3R, the height H1 of the wide recess 335b is the same as the height of the multiple recesses 335a. The height H1 is also lower than the height H2 of the guide portion 333. For example, the height H1 is equal to or less than half the height H2. Furthermore, the height H1 is lower than the height of the bypass channel PAb, for example, equal to or less than half the height of the bypass channel PAb. The channel area of ​​the coolant supply channel PA13 is narrowed by the recess 335. Therefore, the recess 335 constitutes a throttle portion. Hereinafter, the back side (rear side) of the recess 335a of the coolant supply channel PA13 will be referred to as the throttle portion 336a, and the back side (rear side) of the wide recess 335b will be referred to as the wide throttle portion 336b.

[0055] As shown in Fig. 7 , a weld 337 extending in the left-right direction is provided below the tunnel portion 41, and the front plate 3F and the rear plate 3R are welded via the weld 337. Therefore, the opening at the upper end of the wide recess 335b is closed by the weld 337. As shown in Fig. 4 , the lower end of the wide recess 335b is located near the lower end of the active region AR1. Therefore, the wide recess 335b extends across the entire coolant supply flow path PA13 (arrow A1 in Fig. 4 ) upstream of the active region AR1.

[0056] In this fuel cell stack 100 configuration, when a coolant is supplied through the through-holes 305, the bubbles contained in the coolant are reduced in size as they pass through the wide throttle portion 336b. In particular, because the length of the wide throttle portion 336b is longer than the length of the throttle portion 336a, the reduction in size is promoted in the wide throttle portion 336b. The reduced bubbles dissolve as the refrigerant flows, gradually reducing in size. This reduces the amount and size of bubbles flowing into the active region AR1 via the coolant supply flow path PA13.

[0057] The flow resistance of the wide throttle portion 336b of the coolant supply flow path PA13 is greater than the flow resistance of the throttle portion 336a. Therefore, bubbles that cannot pass through the wide throttle portion 336b tend to flow to the bypass flow path PAb via the communication flow path PAs. This promotes the flow of bubbles in the bypass flow path PAb and suppresses the flow of bubbles toward the active area AR1. In contrast, if the wide throttle portion 336b were not present, the number of bubbles passing through the throttle portion 336a would increase, and the number of bubbles flowing toward the active area AR1 would also increase.

[0058] The wide throttle portion 336b extends across the entire coolant supply flow path PA13. Therefore, all of the coolant flowing into the active region AR1 passes through the wide throttle portion 336b. This effectively prevents bubbles from bypassing the wide throttle portion 336b and flowing into the active region AR1. Furthermore, because the wide recess 335b has a large cross-sectional area, the flow rate of the oxidant gas flowing through the wide recess 335b increases. This also allows a sufficient amount of oxidant gas to be supplied via the wide recess 335b to the inlet at the bottom of the cathode flow path PAc, which is farthest from the through-hole 304.

[0059] This embodiment provides the following advantageous effects. (1) The fuel cell stack 100 is constructed by alternately stacking UEAs 2 and separators 3 as membrane electrode assemblies in a front-to-rear direction (a predetermined direction) ( FIG. 1 ). The UEA 2 includes an MEA 20 having an electrolyte membrane, an anode electrode, and a cathode electrode, and a frame 21 supporting the periphery of the MEA 20 ( FIG. 3 ). The separator 3 includes an uneven rear plate 3R disposed opposite the front surface 2a of the UEA 2 and defining an anode flow path PAa through which fuel gas flows between the rear plate 3R and the separator 2. The uneven front plate 3F disposed opposite the rear surface 2b of the UEA 2 and defining a cathode flow path PAc through which oxidizer gas flows between the rear plate 3R and the separator 2F ( FIG. 2 ). The rear plate 3R and the front plate 3F have flow path forming portions, such as a tunnel portion 43, a recessed portion 32, and an outer bead portion 331, that define a flow path between the rear plate 3R and the front plate 3F ( FIGS. 4 and 5 ). The flow paths include a cooling flow path PAw that flows along the active region AR1 of the separator 3 facing the MEA 20, a cooling medium supply flow path PA13 that guides the cooling medium supplied through the through-holes 305 through the separator 3 to the cooling flow path PAw, a bypass flow path PAb that guides bubbles contained in the cooling medium supplied through the through-holes 305 to the cooling flow path PAw, bypassing the cooling flow path PAw, and a communication flow path PAs that connects the cooling medium supply flow path PA13 to the bypass flow path PAb ( FIGS. 4 and 7 ). The cooling medium supply flow path PA13 has multiple throttle portions 336 a, 336 b downstream of the tunnel portion 43 to which the communication flow path PAs is connected ( FIG. 7 ). The multiple throttle portions include a wide throttle portion 336 b and a throttle portion 336 a downstream of the wide throttle portion 336 b ( FIGS. 7 and 8 ). The wide narrowed portion 336b is configured to have a larger flow resistance than the narrowed portion 336a (FIG. 8).

[0060] With this configuration, if the coolant supplied through the through-holes 305 contains bubbles, the bubbles can be refined by the wide throttle portion 336b. The refined bubbles dissolve as the coolant flows, gradually reducing in size. This sufficiently reduces the amount of bubbles supplied to the active region AR1 through the coolant supply flow path PA13. In contrast, if the wide throttle portion 336b were not present, the bubbles would easily pass through the throttle portion 336a and flow into the active region AR1.

[0061] (2) The length (width W2) of the wide constricted portion 336b along the coolant flow direction is longer than the length (width W1) of the constricted portion 336a ( FIGS. 7 and 8 ). By increasing the length of the wide constricted portion 336b in this way, the flow resistance increases, making it easier to break down clumps of bubbles into smaller pieces.

[0062] (3) The size (height H1) of the gap in the wide throttle portion 336b is smaller than the size of the gap in the communication flow path PAs ( FIG. 8 ). As a result, bubbles that cannot pass through the wide throttle portion 336b tend to flow to the bypass flow path PAb via the communication flow path PAs upstream of the wide throttle portion 336b. This promotes the flow of bubbles in the bypass flow path PAb and prevents bubbles from flowing into the active area AR1.

[0063] (4) The wide throttle portion 336b extends in a direction intersecting the flow direction of the coolant, i.e., across the entire width of the coolant supply flow path PA13 ( FIGS. 4 and 7 ). As a result, all of the coolant flowing toward the active area AR1 passes through the wide throttle portion 336b, effectively preventing air bubbles from bypassing the wide throttle portion 336b and flowing toward the active area AR1.

[0064] The above embodiment can be modified in various ways. Some modifications are described below. In the above embodiment, the rear plate 3R of the separator 3 serving as the first plate portion is disposed opposite the front surface 2a (first surface) of the UEA 2 serving as the membrane electrode assembly, and is configured unevenly to form an anode flow path PAa (first gas flow path) through which a fuel gas (first gas) flows between the rear plate 3R and the UEA 2. The front plate 3F of the separator 3 serving as the second plate portion is disposed opposite the rear surface 2b (second surface) of the UEA 2, and is configured unevenly to form a cathode flow path PAc (second gas flow path) through which an oxidizer gas (second gas) flows between the rear plate 3R and the UEA 2. However, the configurations of the first plate portion and the second plate portion are not limited to those described above.

[0065] In the above embodiment, the flow path forming portion defines a flow path for the coolant and bubbles contained in the coolant between the rear plate 3R and the front plate 3F. That is, the recess 32 defines a cooling flow path PAw (power generation region flow path) that flows along the power generation region of the separator 3 facing the MEA 20. The tunnel portion 43 and the throttle portions 336a and 336b define a coolant supply flow path PA13 (supply flow path) that guides the coolant supplied through the through holes 305 (supply holes) to the cooling flow path PAw. The upper tunnel portion 44 and the outer bead portion 331 define a bypass flow path PAb that guides the bubbles contained in the coolant supplied through the through holes 305 to a downstream side of the cooling flow path PAw, bypassing the cooling flow path PAw. The outer bead portion 331 defines a communication flow path PAs that connects the coolant supply flow path PA13 and the bypass flow path PAb. However, the configuration of the flow path forming portion is not limited to the above.

[0066] In the above embodiment, the length (width W2) of the wide throttling portion 336b as the first throttling portion is longer than the length (width W1) of the throttling portion 336a as the second throttling portion. However, the configurations of the first throttling portion and the second throttling portion are not limited to those described above as long as the flow path resistance of the first throttling portion is configured to be greater than the flow path resistance of the second throttling portion. For example, the size of the throttling of the first throttling portion may be smaller than the size of the throttling of the second throttling portion. The widthwise lengths of the first throttling portion and the second throttling portion are also not limited to those described above. In the above embodiment, the communicating flow path PAs is connected to the tunnel portion 43. However, the connection position of the communicating flow path PAs to the coolant supply flow path PA13 is not limited to this.

[0067] 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.

[0068] 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.

[0069] 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, 31 Convex portion, 32 Concave portion, 43 Tunnel portion, 44 Upper tunnel portion, 305 Through hole, 336a Constricted portion, 336b Wide constricted portion, 100 Fuel cell stack, PAa Anode flow path, Pac Cathode flow path, PAw Cooling flow path, PA13 Cooling medium supply flow path, PAb Bypass flow path, PAs Communication flow path, AR1 Active area, W1, W2 Width, H1 Height

Claims

1. A fuel cell stack constructed by alternately stacking membrane electrode assemblies and separators in a predetermined direction, wherein the membrane electrode assembly comprises a membrane electrode assembly having an electrolyte membrane and electrodes, and a frame member supporting the peripheral edge of the membrane electrode assembly, wherein the separator comprises: a first plate portion having an uneven shape, disposed opposite a first surface of the membrane electrode assembly, and forming a first gas flow path between the separator and the membrane electrode assembly, through which a first gas flows; and a second plate portion having an uneven shape, disposed opposite a second surface of the membrane electrode assembly, and forming a second gas flow path between the separator and the membrane electrode assembly, through which a second gas flows; wherein the first plate portion and the second plate portion have flow path forming portions that form a flow path between the first plate portion and the second plate portion, and the flow path comprises: a power generation region flow path through which a cooling medium flows along a power generation region of the separator facing the membrane electrode assembly; and a supply flow path that guides the cooling medium supplied via a supply hole penetrating the separator to the power generation region flow path. a bypass flow path that guides bubbles contained in the cooling medium supplied through the supply hole downstream of the power generation area flow path, bypassing the power generation area flow path; and a communication flow path that connects the supply flow path and the bypass flow path, wherein the supply flow path has a plurality of throttling portions downstream of a connection position where the communication flow path is connected, which shortens the height of a gap between the first plate portion and the second plate portion, and the plurality of throttling portions include a first throttling portion and a second throttling portion downstream of the first throttling portion, and the first throttling portion is configured to have a greater flow path resistance than the second throttling portion.

2. A fuel cell stack according to claim 1, characterized in that the length of the first throttling portion along the direction of flow of the cooling medium is longer than the length of the second throttling portion.

3. A fuel cell stack according to claim 2, wherein the size of the gap in the first throttle portion is smaller than the size of the gap in the communication flow path.

4. A fuel cell stack according to any one of claims 1 to 3, characterized in that the first narrowed portion extends across the entire width of the supply flow path, which crosses the flow direction of the cooling medium.

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