Fuel cell stack

Abstract

This fuel cell stack comprises: a cell stack body including a first separator and a second separator at an end in a predetermined direction of a cell stacking direction; and a first terminal plate and a second terminal plate disposed adjacent to the first separator and the second separator. The cell stack body is provided with a flow path through which a cooling medium or a reaction gas flows in the predetermined direction, and the first terminal plate is provided with a through hole communicating with the flow path. The peripheral edge of the through hole of the first terminal plate is positioned further inward in the radial direction centered on the center line of the flow path than the peripheral edge of the through hole of a separator constituting the flow path.

Description

Fuel cell stack

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

[0002] In recent years, technical development relating to fuel cells that contribute to improved energy efficiency has been carried out, to enable more people to secure access to affordable, reliable, sustainable and advanced energy. As a technology relating to fuel cell stacks used in such fuel cells, there has been conventionally known a fuel cell stack configured to prevent corrosion of a separator on the high potential side of a cell stack (see, for example, Patent Document 1). The fuel cell stack described in Patent Document 1 includes a sacrificial member made of a material more easily corroded than the separator between the high-potential side separator and a positive terminal, and is configured to suppress corrosion of the separator as corrosion of the sacrificial member progresses.

[0003] Japanese Patent No. 4901169

[0004] However, in the fuel cell stack described in Patent Document 1, since a sacrificial member is provided between the separator and the terminal, the number of components increases, and the size of the fuel cell stack increases accordingly.

[0005] A fuel cell stack according to one aspect of the present invention is configured by alternately laminating membrane electrode structures and metal separators in a predetermined direction, and includes: a cell laminate in which a first separator and a second separator respectively constituting separators are disposed at one end on the high potential side in the predetermined direction and the other end on the low potential side in the predetermined direction; and a first end unit and a second end unit respectively disposed adjacent to the first separator and the second separator in the predetermined direction. The first end unit and the second end unit respectively have a first terminal plate and a second terminal plate disposed adjacent to the first separator and the second separator, the cell laminate is provided with a flow passage through which a cooling medium or reaction gas flows in the predetermined direction, the first terminal plate is provided with a through hole communicating with the flow passage, the first terminal plate has a larger thickness in the predetermined direction than the first separator, and a peripheral edge of the through hole of the first terminal plate is located further inward in a radial direction centered on the flow passage than a peripheral edge of a through hole of the separator that constitutes the flow passage.

[0006] According to the present invention, corrosion of the separator portion along the flow path of the cooling medium or reaction gas can be suppressed without increasing the size of the fuel cell stack.

[0007] A perspective view schematically showing the overall configuration of a fuel cell stack according to an embodiment of the present invention. A perspective view schematically showing the configuration of an integrated electrode assembly included in the fuel cell stack of Figure 1. A cross-sectional view along line III-III in Figure 1. A diagram showing the equivalent circuit of the corrosion current flowing through the fuel cell stack of Figure 1. A diagram showing the corrosion current value obtained by simulation. A perspective view of a terminal plate included in a fuel cell stack as a reference example of this embodiment.

[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 constitutes the main body of the fuel cell. The fuel cell is mounted on a vehicle, for example, and generates 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 a fuel cell stack 100 according to an embodiment of the present invention. 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 up-down direction, and the configuration of each part will be described according to this definition. The longitudinal direction corresponds to the stacking direction of the power generation cells. These directions are not necessarily the same as the longitudinal, left-right, and up-down 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 (UEA) 2 having a membrane electrode assembly containing an electrolyte membrane and an electrode, and a pair of front and rear separators 3, 3 positioned on both the front and rear sides of the UEA 2, 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] The separator 3 has a pair of thin metal plates, front and rear, with a corrugated cross-section (see Figure 3), and is integrally constructed by joining the outer edges of these plates together. The separator 3 is made of a conductive material with excellent corrosion resistance, such as iron, stainless steel, titanium, or titanium alloy. A cooling channel is formed inside the separator 3 (between the pair of thin plates) through which a cooling medium flows, and the power generation surface of the power generation cell 1 is cooled by the flow of the cooling medium. For example, water can be used as the cooling medium. The surface (front and rear) of the separator 3 facing the UEA 2 is made uneven by press molding or the like to form a gas channel between it and the membrane electrode assembly.

[0013] One separator 3 in the forward / backward direction of the UEA2 is the anode-side separator (anode separator), and an anode channel through which fuel gas flows is formed between the anode separator 3 and the membrane power junction. The other separator 3 in the forward / backward direction of the UEA is the cathode-side separator (cathode separator), and a cathode channel through which oxidizer gas flows is formed between the cathode separator 3 and the membrane electrode junction. 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. Sometimes, the fuel gas and oxidizer gas are not distinguished and are simply called reaction gases.

[0014] Figure 2 is a perspective view showing the schematic configuration of UEA2. As shown in Figure 2, UEA2 has a substantially rectangular membrane electrode assembly (MEA: hereinafter referred to as MEA) 20 and a frame 21 that supports MEA20. MEA2 has a front surface 20a and a rear surface 20b, and the frame 21 has a front surface 21a and a rear surface 21b. MEA20 has an electrolyte membrane, an anode electrode provided on one surface of the electrolyte membrane in the front-rear direction, and a cathode electrode provided on the other surface of the electrolyte membrane in the front-rear direction.

[0015] The electrolyte membrane can be, for example, a solid polymer electrolyte membrane, and a thin film of perfluorosulfonic acid containing water can be used. Not only fluorine-based electrolytes, but hydrocarbon-based electrolytes can also be used.

[0016] The anode electrode is formed on one side of the electrolyte membrane in the front-to-back direction and has an electrode catalyst layer that serves as the reaction field for the electrode reaction, and a gas diffusion layer provided on the surface of the electrode catalyst layer that diffuses and supplies fuel gas. The cathode electrode is formed on the other side of the electrolyte membrane in the front-to-back direction and has an electrode catalyst layer that serves as the reaction field for the electrode reaction, and a gas diffusion layer provided on the surface of the electrode catalyst layer that diffuses and supplies oxidizing gas.

[0017] At the anode electrode, fuel gas (hydrogen) supplied through the anode channel 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 through the cathode channel reacts with hydrogen ions introduced from the anode electrode and electrons that have moved from the anode electrode to produce water. The produced water (called generated water) provides appropriate humidity to the electrolyte membrane, and excess water is discharged to the outside of UEA2 along the gas flow.

[0018] The frame 21 is a thin plate having a roughly rectangular shape and is made of an insulating resin or rubber. A roughly rectangular opening 210 is provided in the center of the frame 21. The MEA 20 is provided so as to cover the entire opening 210, and the peripheral edge of the MEA 20 is supported by the frame 21. To the left of the opening 210 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 210, 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 all shown as being roughly rectangular, but the shape and arrangement of the through holes 211 to 216 are not limited to this.

[0019] As shown in Figure 1, the front and rear separators 3 of the UEA2 have through-holes 311 to 316 that penetrate the separators 3 in the front-rear direction, at positions corresponding to the through-holes 211 to 216 of the frame 21. The through-holes 311 to 316 communicate with the through-holes 211 to 216 of the frame 21, respectively. The collection of these interconnected through-holes 211 to 216 and 311 to 316 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 (internal manifolds). Flow paths PA1 to PA6 are connected to an external manifold of the fuel cell stack 100.

[0020] The flow path PA1 (solid arrow) extending forward through through holes 211 and 311 is a fuel gas supply flow path. The flow path PA6 (solid arrow) extending backward through through holes 216 and 316 is a fuel gas discharge flow path. The fuel gas supply flow path PA1 and the fuel gas discharge flow path PA6 are in communication with the anode flow path PAa (Figure 3), which is provided opposite the MEA 20, and as shown by the solid arrow, fuel gas flows from left to right through the anode flow path via the fuel gas supply flow path PA1 and the fuel gas discharge flow path PA6. Communication between the anode flow path and the other flow paths PA2 to PA5 is blocked via a seal (not shown).

[0021] The flow path PA4 (dotted arrow) extending forward through the through holes 214 and 314 is an oxidizer gas supply flow path. The flow path PA3 (dotted arrow) extending backward through the through holes 213 and 313 is an oxidizer gas discharge flow path. The oxidizer gas supply flow path PA4 and the oxidizer gas discharge flow path PA3 are in communication with the cathode flow path PAc (Figure 3) provided opposite the MEA 20, and as shown by the dotted arrow, the oxidizer gas flows from right to left through the cathode flow path via the oxidizer gas supply flow path PA4 and the oxidizer gas discharge flow path PA3. Communication between the cathode flow path and the other flow paths PA1, PA2, PA5, and PA6 is blocked via a seal portion (not shown).

[0022] The flow path PA5 (dotted arrow) extending forward through the through holes 215 and 315 is a cooling medium supply flow path. The flow path PA2 (dotted arrow) extending backward through the through holes 212 and 312 is a cooling medium discharge flow path. The cooling medium supply flow path PA5 and the cooling medium discharge flow path PA2 communicate with the cooling flow path PAw (Figure 3) inside the separator 3, and the cooling medium flows through the cooling flow path via the cooling medium supply flow path PA5 and the cooling medium discharge flow path PA2. Communication between the cooling flow path and the other flow paths PA1, PA3, PA4, PA6 is blocked via a seal portion (not shown).

[0023] The end units 102, positioned on both the front and rear sides of the cell laminate 101, each have a terminal plate 4, an insulating plate 5, and an end plate 6. The front end unit 102 is sometimes called the dry end unit, and the rear end unit 102 is sometimes called the wet end unit. The front and rear pair of terminal plates 4, 4 are positioned on both the front and rear sides of the cell laminate 101. The front and rear pair of insulating plates 5, 5 are positioned on both the front and rear sides of the terminal plates 4, 4. The front and rear pair of end plates 6, 6 are positioned on both the front and rear sides of the insulating plates 5, 5.

[0024] The terminal plate 4 is a roughly rectangular plate-shaped member made of metal and has terminals for extracting the power generated by the electrochemical reaction in the cell laminate 101. The insulating plate 5 is a roughly rectangular plate-shaped member made of non-conductive resin or rubber and electrically insulates the terminal plate 4 from the end plate 6. The end plate 6 is a plate-shaped member made of metal or a high-strength resin, and the front and rear end plates 6, 6 are fixed by bolts to the front and rear ends of a case that surrounds the cell laminate 101, for example, with a predetermined compressive load applied in the front-rear direction. The cell laminate 101 is held in a state of being pressed in the front-rear direction through the case.

[0025] The rear end unit 102 has multiple through holes 102a to 102f that penetrate the end unit 102 in the front-to-back direction. The through holes 102a to 102f include through holes that penetrate the terminal plate 4, through holes that penetrate the insulating plate 5, and through holes that penetrate the end plate 6, respectively, but in Figure 1, for convenience, these are shown collectively as through holes 102a to 102f.

[0026] Through-hole 102a opens on the extension of the fuel gas supply passage PA1 and communicates with the fuel gas supply passage PA1. Through-hole 102b opens on the extension of the cooling medium discharge passage PA2 and communicates with the cooling medium discharge passage PA2. Through-hole 102c opens on the extension of the oxidizer gas discharge passage PA3 and communicates with the oxidizer gas discharge passage PA3. Through-hole 102d opens on the extension of the oxidizer gas supply passage PA4 and communicates with the oxidizer gas supply passage PA4. Through-hole 102e opens on the extension of the cooling medium supply passage PA5 and communicates with the cooling medium supply passage PA5. Through-hole 102f opens on the extension of the fuel gas discharge passage PA6 and communicates with the fuel gas discharge passage PA6.

[0027] More specifically, a fuel gas tank containing high-pressure fuel gas is connected to the through-hole 102a via an ejector, injector, etc., and the fuel gas in the fuel gas tank is supplied to the fuel cell stack 100 through the through-hole 102a. Fuel gas (fuel exhaust gas) is discharged from the through-hole 102f.

[0028] A compressor for supplying oxidant gas is connected to the through-hole 102d, and the oxidant gas compressed by the compressor is supplied to the fuel cell stack 100 through the through-hole 102d. Oxidant gas (oxidant exhaust gas) is discharged from the through-hole 102c.

[0029] A pump for supplying the cooling medium is connected to the through-hole 102e, and the cooling medium is supplied to the fuel cell stack 100 through the through-hole 102e. The cooling medium is discharged from the through-hole 102b. The discharged cooling medium is cooled by heat exchange in the radiator, and ions are removed from the cooling medium via an ion exchanger. Then, it is supplied back to the fuel cell stack 100 through the through-hole 102e.

[0030] The above is a general overview of the fuel cell stack 100. The fuel cell stack 100 is housed in a roughly box-shaped case and mounted on a vehicle. Hereinafter, the cooling medium supply channel PA5 and the cooling medium discharge channel PA2 may be collectively referred to as the refrigerant channel PA0.

[0031] In such a fuel cell stack 100, iron ions may leach from the high-potential separator 3 into the refrigerant flow path PA0, causing corrosion of the separator 3 and the flow of a corrosion current. When corrosion occurs in the separator 3, the seal portion of the separator 3 deteriorates, reducing its sealing performance and potentially causing reaction gases (fuel gas, oxidizer gas) and cooling medium to leak to the outside. Therefore, it is necessary to prevent deterioration of the seal portion of the high-potential separator 3. Similar corrosion currents can occur not only in the refrigerant flow path PA0 but also in the reaction gas flow paths (fuel gas supply flow path PA1, oxidizer gas discharge flow path PA3, oxidizer gas supply flow path PA4, fuel gas discharge flow path PA6) when generated water or condensed water accumulates. The fuel cell stack 100 of this embodiment is configured with this point in mind.

[0032] Figure 3 is a cross-sectional view (a cross-sectional view along line III-III in Figure 1) along the stacking direction of the power generation cell 1, showing the main components of a fuel cell stack 100 according to an embodiment of the present invention. Figure 3 shows a cross-sectional view of the cooling medium supply channel PA5 side as the refrigerant channel PA0, but the cooling medium discharge channel PA2 side is configured in the same way as in Figure 3. As shown in Figure 3, the separator 3 has a front plate 31 and a rear plate 32, which are a pair of thin metal plates with a corrugated cross-section. The front plate 31 has a front surface 31a and a rear surface 31b. The rear plate 32 has a front surface 32a and a rear surface 32b. The outer peripheral edges of the front plate 31 and the rear plate 32 are joined together by welding or the like, thereby forming the separator 3.

[0033] A cooling channel PAw is formed inside the separator 3, which is enclosed by a front plate 31 and a rear plate 32, through which a cooling medium flows. The cooling medium flowing through the refrigerant channel PA0 flows into the cooling channel PAw through the gap between the front plate 31 and the rear plate 32 at the periphery of the through hole 315 of the separator 3. As a result, the cooling medium flows through the cooling channel PAw, and the power generation surface of the power generation cell 1 is cooled. The separator 3 is constructed with an uneven surface by press molding or the like to form a gas channel between it and the UEA 2. More specifically, the front plate 31 and the rear plate 32 each have rib portions 301 that protrude toward the front and rear UEA 2, and recesses 302 that are formed in a concave shape connected to the rib portions 301.

[0034] The rib portion 301 of the rear plate 32 abuts against the front surface of the UEA 2, that is, against the front surface 20a of the MEA 20 and the front surface 21a of the frame 21. The rib portion 301 of the front plate 31 abuts against the rear surface of the UEA 2, that is, against the rear surface 20b of the MEA 20 and the rear surface 21b of the frame 21. A compressive load is applied to the cell stack 101 in the front-rear direction during the assembly of the fuel cell stack 100, and the case and the front and rear end units 102 are fastened in this state. Therefore, after the assembly of the fuel cell stack 100 is completed, the compressive load on the fuel cell stack 100 is maintained. As a result, a predetermined surface pressure acts on the MEA 2 in the front-rear direction via the rib portion 301.

[0035] Between the rear plate 32 of the separator 3 and the front surface 20a of the MEA 20, an anode channel PAa through which fuel gas flows is formed by a recess 302. Between the front plate 31 of the separator 3 and the rear surface 20b of the MEA 20, a cathode channel PAc through which oxidizer gas flows is formed by a recess 302. The cathode channel PAc may be formed between the rear plate 32 of the separator 3 and the MEA 20, or the anode channel PAa may be formed between the front plate 31 of the separator 3 and the MEA 20.

[0036] To distinguish the separator 3 at the front end and the separator 3 at the rear end of the cell laminate 101 from the other separators 3, they are called the front separator 3F and the rear separator 3R, respectively. The front separator 3F abuts against the rear surface of the terminal plate 4 on the dry side (front side). The rear separator 3R abuts against the front surface of the terminal plate 4 on the wet side (rear side). The refrigerant flow path PA0 (cooling medium supply flow path PA5) is formed along the axis CL0 that extends in the front-rear direction.

[0037] Through holes 4a, 5a, and 6a are opened in the wet-side terminal plate 4, insulating plate 5, and end plate 6, respectively, centered on the axis CL0. The through holes 4a, 5a, and 6a communicate with the refrigerant flow path PA0. On the other hand, a through hole 4b is opened in the dry-side terminal plate 4, centered on the axis CL0, but no through holes are opened in the insulating plate 5 and end plate 6. The diameters of the through holes 4a and 4b are the same. The diameter of the through hole 4a may be larger or smaller than the diameter of the through hole 4b.

[0038] The front and rear terminal plates 4 are formed to be thicker in the front-to-back direction than a single separator 3. Specifically, the thickness of the terminal plate 4 is several times (for example, 5 or 10 times) or more the thickness of the separator 3. In the following, to distinguish between the front and rear terminal plates 4, the terminal plate 4 on the wet side (rear side) will be called the rear terminal plate 4R, and the terminal plate 4 on the dry side (front side) will be called the front terminal plate 4F.

[0039] The diameter of the through-hole 315 in the separator 3 is larger than the diameter of the through-hole 215 in the frame 21. Therefore, the periphery of the through-hole 215 in the frame 21 protrudes radially inward around the axis CL0 compared to the periphery of the through-hole 315 in the separator 3. The diameters of the through-holes 4a and 4b in the rear terminal plate 4R and the front terminal plate 4F are the same as the diameter of the through-hole 215 in the frame 21. Therefore, the periphery of the through-holes 4a and 4b in the terminal plates 4 also protrudes radially inward around the axis CL0 compared to the periphery of the through-hole 215 in the separator 3. More specifically, the periphery of the through-holes 4a and 4b in the terminal plates 4 protrudes radially inward around the entire circumference compared to the periphery of the through-hole 215 in the separator 3.

[0040] When power is generated in such a fuel cell stack 100, the wet side (rear side) becomes the high-potential side and the dry side (front side) becomes the low-potential side, creating a potential difference inside the cell stack 101, and an electric current flows inside the cell stack 101. On the other hand, a corrosion current, as shown by arrow A1, flows in the refrigerant flow path PA0 due to the elution of iron ions into the cooling medium.

[0041] Figure 4 is an equivalent circuit diagram schematically showing the current flow in the fuel cell stack 100 according to this embodiment. Figure 4 shows a state in which the power generation cell 1 is used as the power source and the power sources are connected in series. Furthermore, for convenience, the current flow between the separator 3 and the cooling medium is also shown in Figure 4 as the current flowing through the resistor. In the figure, downward arrows indicate corrosion current, and arrows flowing through the resistor indicate reduction current. The magnitude of the current is represented by the length of the arrow.

[0042] As shown in Figure 4, corrosion current occurs on the high-potential side, and reduction current occurs on the low-potential side. The corrosion current is larger at higher potentials, and the reduction current is larger at lower potentials. Corrosion current occurs not only between the separator 3 and the cooling medium, but also between the rear terminal plate 4R and the cooling medium. The current passing through resistor R1 represents the corrosion current occurring at the rear separator 3R. The current passing through resistor R0 represents the corrosion current occurring at the rear terminal plate 4R. The rear terminal plate 4R is located on the highest potential side and has low resistance, so corrosion current flows easily through it.

[0043] FIG. 5 is a diagram showing the magnitude of corrosion current in each part of the fuel cell stack 100. The horizontal axis represents the position in the front-rear direction of the cell stack 101, and the vertical axis represents the magnitude of the corrosion current. A negative current indicates a reduction current. FIG. 5 shows the results of a simulation performed based on the equivalent circuit of FIG. 4. In the figure, the solid line is the result obtained by the fuel cell stack 100 of the present embodiment, and the dotted line is the result obtained by a reference example described later. Point P0 indicates the corrosion current I0 of the rear terminal plate 4R, and point P1 indicates the corrosion current I1 of the rear end separator 3R. Point P3 indicates the reduction current of the front terminal plate 4F, and point P4 indicates the reduction current of the front end separator 3F.

[0044] As shown in FIG. 5, in the present embodiment, the corrosion current I0 flowing through the rear terminal plate 4R is the largest. The peripheral edge of the through hole 4a of the rear terminal plate 4R protrudes radially inward around the axis CL0 more than the peripheral edge of the through hole 315 of the separator 3, and has a larger area in contact with the cooling medium. Therefore, the corrosion current resistance R0 (FIG. 4) between the rear terminal plate 4R and the cooling medium is smaller than the corrosion current resistance R1 between the separator 3 and the cooling medium. As a result, a large amount of corrosion current flows through the rear terminal plate 4R, and accordingly, the flow of corrosion current through the rear end separator 3R is alleviated. This increases the difference between the corrosion current I0 flowing through the rear terminal plate 4R and the corrosion current I1 flowing through the rear end separator 3R.

[0045] When a large amount of corrosion current flows through the rear terminal plate 4R, the peripheral edge of the through hole 4a of the rear terminal plate 4R is prone to corrosion. Regarding this point, the rear terminal plate 4R has a thickness several times or more greater than that of the separator 3, and the volume of the peripheral edge portion of the through hole 4a is large. Therefore, even if a part of the peripheral edge of the through hole 4a of the rear terminal plate 4R is corroded, there is no problem in the function as the terminal plate 4.

[0046] Figure 6 is a perspective view (viewed from the front at an angle) showing the configuration of a rear terminal plate 40R as a reference example of this embodiment. As shown in Figure 6, in the reference example, the rear terminal plate 40R is formed to be smaller than that of Figure 1. That is, the rear terminal plate 40R is provided only inside the through holes 102a to 102f (Figure 1) of the end unit 102, facing the power generation surface of the power generation cell 1. An insulating plate 41 having electrical insulating properties is provided around the rear terminal plate 40R, forming a roughly rectangular frame that surrounds the rear terminal plate 40R. Through holes 104a to 104f corresponding to the through holes 102a to 102f are opened in the insulating plate 41. The through hole 104e is a through hole for supplying a cooling medium, corresponding to the through hole 4a in Figure 3.

[0047] In this example configuration, since a refrigerant flow path PA0 is provided in the insulating plate 41, no corrosion current flows through the insulating plate 41. Instead, as shown by the dotted line in Figure 5, the corrosion current flows through the separator 3 on the high-potential side. In this embodiment, the corrosion current is concentrated in the rear terminal plate 4R, but in the example, the corrosion current is distributed and flows through multiple (several) separators 3 on the high-potential side. In this case, the corrosion power is maximum (I2) at the rear separator 3R. However, the corrosion current I2 at the rear separator 3R is smaller than the corrosion current I0 at the rear terminal plate 4R.

[0048] As described above, in the reference example, since a corrosion current flows through the separator on the high potential side, the peripheral edge of the through hole of the separator is corroded. Therefore, in consideration of this corrosion, it is necessary to provide a sacrificial electrode on the peripheral edge of the through hole. The inner diameter of the through hole needs to be a predetermined size regardless of the presence or absence of the sacrificial electrode. Therefore, when a sacrificial electrode is provided on the peripheral edge of the through hole, the seal portion of the separator around the through hole needs to be shifted radially outward by that amount. As a result, the separator increases in size, making it difficult to reduce the size of the fuel cell stack. In contrast, in the present embodiment, a sacrificial electrode is provided on the peripheral edge of the through hole of the rear terminal plate, so there is no need to provide a sacrificial electrode on the peripheral edge of the through hole of the separator. Therefore, there is no need to increase the size of the separator, and the fuel cell stack can be reduced in size.

[0049] In the present embodiment, not only the rear terminal plate 4R but also the front terminal plate 4F is provided with a through hole 4b communicating with the refrigerant flow path PA0. Therefore, a large amount of reduction current flows through the front terminal plate 4F via the peripheral edge of the through hole 4b (point P3 in FIG. 5), and the reduction current flowing through the front end separator 3F can be suppressed (point P4 in FIG. 5). In the above description, an example in which a sacrificial electrode is provided on the peripheral edge of the through hole 4a of the rear terminal plate 4R that constitutes the refrigerant flow path PA0 has been described, but a sacrificial electrode may similarly be provided on the peripheral edge of the through hole of the terminal plate 4 that constitutes the reaction gas flow path. This eliminates the need to provide a sacrificial electrode around the through hole of the separator 3 through which the reaction gas passes.

[0050] This embodiment provides the following effects: (1) The fuel cell stack 100 is constructed by alternately stacking UEA2 and metal separators 3 in the front-rear direction, and comprises a cell stack 101 with a rear separator 3R and a front separator 3F, which constitute the separator 3, arranged at the rear end on the high-potential side and the front end on the low-potential side, respectively, and a wet-side end unit 102 and a dry-side end unit 102, which are arranged adjacent to the rear separator 3R and the front separator 3F in the front-rear direction, respectively (Figure 1). The wet-side end unit 102 and the dry-side end unit 102 each have a rear terminal plate 4R and a front terminal plate 4F, which are arranged adjacent to the rear separator 3R and the front separator 3F, respectively (Figure 3). The cell stack 101 is provided with a refrigerant flow path PA0 through which a cooling medium flows in the front-rear direction (Figure 3). The rear terminal plate 4R is provided with a through hole 4a that communicates with the refrigerant flow path PA0 (Figure 3). The rear terminal plate 4R is thicker in the front-rear direction than the rear end separator 3R, and the periphery of the through hole 4a of the rear terminal plate 4R is located radially inward from the periphery of the through hole 315 of the separator 3 that constitutes the refrigerant flow path PA0, with respect to the axis CL0 passing through the center of the refrigerant flow path PA0 (Figure 3).

[0051] As a result, the rear terminal plate 4R adjacent to the rear separator 3R functions as a sacrificial electrode, and more corrosion current flows to the rear terminal plate 4R than to the rear separator 3R. Therefore, there is no need to provide a separate sacrificial member in the fuel cell stack 100, nor is there a need to provide a sacrificial electrode in the separator 3. Consequently, corrosion at the periphery of the through-hole 315 of the separator 3 along the refrigerant flow path PA0 can be suppressed without increasing the size of the fuel cell stack 100.

[0052] (2) The refrigerant flow path PA0 includes a cooling medium supply flow path PA5 through which the cooling medium flows from the rear end to the front end of the cell stack 101, and a cooling medium discharge flow path PA2 through which the cooling medium flows from the front end to the rear end of the cell stack 101 (Figure 1). The through holes in the terminal plate 4 include through holes 4a and 102e that allow the cooling medium to flow into the cooling medium supply flow path PA5 from outside the fuel cell stack 100, and through holes 4a and 102b that allow the cooling medium that has flowed through the cooling medium discharge flow path PA2 to flow out to the outside (Figures 1 and 3). This makes it possible to suppress corrosion of the periphery of the through holes 315 of the separator 3 in the respective refrigerant flow paths PA0 for supplying and discharging the cooling medium (cooling medium supply flow path PA5, cooling medium discharge flow path PA2).

[0053] (3) The UEA2 includes an MEA20 having an electrolyte membrane, an anode electrode and a cathode electrode, and a resin frame 21 supporting the periphery of the MEA20 (Figure 2). The periphery of the through hole 4a of the rear terminal plate 4R is located at the same radial position centered on the axis CL0 as the periphery of the through hole 215 of the frame 21 that constitutes the refrigerant flow path PA0 (Figure 3). As a result, the contact area between the cooling medium flowing through the refrigerant flow path PA0 and the rear terminal plate 4R is increased, making it easier for corrosion current to flow through the rear terminal plate 4R, and thereby reducing the corrosion current flowing through the separator 3.

[0054] (4) The periphery of the through hole 4a of the rear terminal plate 4R is located radially inward from the periphery of the through hole 315 of the separator 3, with respect to the axis CL0, along its entire circumference. As a result, corrosion current flows uniformly in the circumferential direction around the periphery of the through hole 4a of the rear terminal plate 4R.

[0055] (5) The front terminal plate 4F is provided with a through hole 4b that communicates with the refrigerant flow path PA0 (Figure 3). This allows a large amount of reduction current to flow through the front terminal plate 4F, thereby reducing the reduction current flowing through the front separator 3F.

[0056] The above embodiment can be modified into various forms. Several modifications are described below. In the above embodiment, the UEA2 (membrane electrode structure) and the separator 3 were stacked in the front-rear direction to form the cell laminate 101, but the predetermined direction for stacking is not limited to the front-rear direction. In the above embodiment, the rear end separator 3R on the wet side was configured as the first separator on the high-potential side, and the front end separator 3F on the dry side was configured as the second separator on the low-potential side, but the wet side may be configured as the low-potential side and the dry side as the high-potential side. Also, in the above embodiment, the end unit 102 (first end unit) on the wet side was configured as the high-potential side, and the end unit 102 (second end unit) on the dry side was configured as the low-potential side, but the wet side may be configured as the low-potential side and the dry side as the high-potential side.

[0057] In the above embodiment, through holes 4a and 4b communicating with the refrigerant flow path PA0 are provided in the rear terminal plate 4R (first terminal plate) and the front terminal plate 4F (second terminal plate), respectively, but the second terminal plate does not need to have a through hole. In the above embodiment, the periphery of the through hole 315 of the rear terminal plate 4R and the periphery of the through hole 215 of the frame 21 (frame member) are located at the same radial position around the axis CL0 (center line), but the periphery of the through hole of the first terminal plate and the periphery of the through hole of the frame member do not need to be at the same radial position, as long as the periphery of the through hole of the first terminal plate is located radially inward than the periphery of the through hole of the separator. For example, the periphery of the through hole of the first terminal plate may be located radially inward than the periphery of the through hole of the frame member.

[0058] In the above embodiment, the periphery of the through hole 4a of the rear terminal plate 4R is positioned radially inward from the periphery of the through hole 315 of the separator 3, centered on the axis CL0, over its entire circumference. However, a portion of the circumferential direction may be positioned radially inward. In the above embodiment, a cooling medium supply channel PA5 (first channel) is provided from the rear end to the front end of the cell stack 101, and a cooling medium discharge channel PA2 (second channel) is provided from the front end to the rear end. However, the configuration of the channels is not limited to those described above. The first channel may be a fuel gas supply channel PA1 and an oxidizer gas supply channel PA4, and the second channel may be a fuel gas discharge channel PA6 and an oxidizer gas discharge channel PA3. Therefore, the above channels may be reaction gas channels instead of refrigerant channels. In the above embodiment, the cooling medium is supplied to the fuel cell stack 100 through through holes 4a and 102e (first through holes) provided in the rear terminal plate 4R, and the cooling medium is discharged from the fuel cell stack 100 through through holes 4a and 102b (second through holes). However, the configuration of the first and second through holes is not limited to that described above. That is, the first and second through holes may be through holes for supplying and discharging reaction gas.

[0059] 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.

[0060] 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.

[0061] 2 Integrated electrode assembly, 3 Separator, 3F Front separator, 3R Rear separator, 4 Terminal plate, 4F Front terminal plate, 4R Rear terminal plate, 4a, 4b Through holes, 20 Membrane electrode assembly, 21 Frame, 100 Fuel cell stack, 101 Cell stack, 102 End unit, 215 Through hole, 315 Through hole, PA0 Refrigerant flow path, PA2 Cooling medium discharge flow path, PA5 Cooling medium supply flow path

Claims

1. A cell laminate comprising a membrane electrode structure and a metal separator stacked alternately in a predetermined direction, with a first separator and a second separator, each constituting the separator, arranged at one end of the predetermined direction on the high-potential side and the other end on the low-potential side of the predetermined direction; a first end unit and a second end unit, each arranged adjacent to the first separator and the second separator in the predetermined direction; the first end unit and the second end unit each having a first terminal plate and a second terminal plate, each arranged adjacent to the first separator and the second separator; the cell laminate is provided with a flow path for a cooling medium or reaction gas to flow in the predetermined direction; the first terminal plate is provided with a through hole communicating with the flow path; and the first terminal plate is configured to be thicker in the predetermined direction than the first separator. A fuel cell stack characterized in that the periphery of the through-hole of the first terminal plate is located radially inward from the periphery of the through-hole of the separator constituting the flow path, with respect to the center line of the flow path.

2. A fuel cell stack according to claim 1, wherein the flow path includes a first flow path through which a cooling medium or reaction gas flows from one end to the other end of the cell stack, and a second flow path through which a cooling medium or reaction gas flows from the other end to the one end of the cell stack, and the through hole includes a first through hole for allowing a cooling medium or reaction gas to flow into the first flow path from outside the fuel cell stack, and a second through hole for allowing the cooling medium or reaction gas that has flowed through the second flow path to flow out to the outside.

3. A fuel cell stack according to claim 1 or 2, wherein the membrane electrode structure comprises a membrane electrode assembly having an electrolyte membrane, an anode electrode and a cathode electrode, and a resin frame member supporting the periphery of the membrane electrode assembly, and the periphery of the through hole of the first terminal plate is located at the same radial position with respect to the center line as the periphery of the through hole of the frame member constituting the flow path, or is located radially inward from the periphery of the through hole of the frame member with respect to the center line.

4. A fuel cell stack according to claim 1 or 2, characterized in that the periphery of the through hole of the first terminal plate is located radially inward from the periphery of the through hole of the separator, with respect to the center line, over its entire circumference.

5. A fuel cell stack according to claim 1 or 2, characterized in that the second terminal plate is provided with a through hole communicating with the flow path.

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