Fuel cell

Abstract

To provide a technology for equalizing the distribution of a moisture content in the in-plane direction of a membrane electrode assembly.SOLUTION: In a projection view obtained by projecting an oxidant gas flow path 50 and a refrigerant flow path 60 onto a plane perpendicular to the thickness direction of an electrolyte membrane 12, an overlapping portion 70 between the oxidant gas flow path 50 and the refrigerant flow path 60 exists. The overlapping portion 70 includes a matching portion 71 in which the flow direction of an oxidant gas in the oxidant gas flow path 50 coincides with the flow direction of a refrigerant in the refrigerant flow path 60, In the projection view, the ratio of the area of the matching portion 71 to the area of the oxidant gas flow path 50 is 0.8 or more.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to fuel cells. [Background technology]

[0002] Further improvements in fuel cell performance are required to effectively utilize hydrogen, one of the next-generation energy sources. In order to improve fuel cell performance, it is important to increase the power generated per unit cell. One method for increasing the power generated per unit cell is to uniformly distribute the current density in the in-plane direction of the unit cell.

[0003] Patent Document 1 describes that the cross-sectional area of ​​the oxidant gas flow channel increases from the end to the center of the separator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-174648 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a technique for making the distribution of the moisture content uniform within the surface of a membrane electrode assembly. [Means for solving the problem]

[0006] The present disclosure provides: an anode separator; a cathode separator; and a membrane electrode assembly including an anode, a cathode, and an electrolyte membrane, the membrane electrode assembly being disposed between the anode separator and the cathode separator; a fuel gas flow channel provided between the anode and the anode separator; an oxidant gas flow channel provided between the cathode and the cathode separator; a coolant flow channel provided so as to be separated from the oxidant gas flow channel by the cathode separator; Equipped with the fuel gas flow path, the oxidant gas flow path, and the coolant flow path are each a serpentine flow path, Satisfy at least one of the following requirements (a) and (b): A fuel cell is provided. (a) In a projection obtained by projecting the fuel gas flow path and the refrigerant flow path onto a plane perpendicular to the thickness direction of the electrolyte membrane, there is an overlapping portion between the fuel gas flow path and the refrigerant flow path, the overlapping portion includes a coincident portion where the flow direction of the fuel gas in the fuel gas flow path and the flow direction of the refrigerant in the refrigerant flow path coincide, and in the projection, the ratio of the area of ​​the coincident portion to the area of ​​the fuel gas flow path is 0.8 or more. (b) In a projection obtained by projecting the oxidant gas flow path and the refrigerant flow path onto a plane perpendicular to the thickness direction of the electrolyte membrane, there is an overlapping portion between the oxidant gas flow path and the refrigerant flow path, the overlapping portion includes a coincident portion where the flow direction of the oxidant gas in the oxidant gas flow path and the flow direction of the refrigerant in the refrigerant flow path coincide, and in the projection, the ratio of the area of ​​the coincident portion to the area of ​​the oxidant gas flow path is 0.8 or more. [Effects of the Invention]

[0007] According to the present disclosure, the distribution of the moisture content within the surface of the membrane electrode assembly can be made uniform. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view of a fuel cell stack according to a first embodiment. [Figure 2] First plan view of the anode separator [Figure 3] Plan view of the cathode separator [Figure 4] Second plan view of the anode separator [Figure 5] A projection diagram obtained by projecting the oxidant gas flow path and the refrigerant flow path onto a plane perpendicular to the thickness direction of the electrolyte membrane. [Figure 6A] FIG. 1 is a diagram illustrating the effects obtained by the configuration of this embodiment. [Figure 6B] FIG. 10 is a diagram illustrating an example in which the flow direction of the oxidant gas and the flow direction of the refrigerant do not match. [Figure 7A] A diagram explaining the rules for calculating the area of ​​the matching portion in the projection drawing of FIG. [Figure 7B] Another diagram explaining the rules for calculating the area of ​​the matching portion in the projection of FIG. 5. [Figure 8] Figure 1 shows additional configurations that can contribute to a more uniform relative humidity distribution. [Figure 9] FIG. 1 is a diagram showing a schematic configuration of a cathode separator according to Modification 1. [Figure 10] FIG. 2 is a second plan view of an anode separator according to Modification 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Findings that formed the basis of this disclosure) To improve the power generation efficiency of a fuel cell, it is important to efficiently supply hydrogen and oxygen to the entire membrane electrode assembly. Specifically, it is important to appropriately control the moisture content of the electrolyte membrane and catalyst layer and reduce the resistance throughout the entire surface of the membrane electrode assembly so that a state of high proton conductivity and high oxygen diffusivity is achieved.

[0010] On the other hand, because the reaction in a fuel cell is exothermic, it is necessary to cool the fuel cell. For example, if a fuel cell stack is provided with a coolant channel, the temperature of the fuel cell stack can be controlled to an appropriate temperature by circulating a coolant through the coolant channel. In this case, a temperature distribution occurs from upstream to downstream of the coolant channel. Since the amount of saturated water vapor changes depending on the gas temperature, in order to control the moisture content of the membrane electrode assembly to a desired value from upstream to downstream in the gas flow direction, it is necessary to appropriately control not only the temperature distribution on the surface of the membrane electrode assembly but also the moisture content in the gas.

[0011] For example, if the proton conduction resistance is high due to a lack of water downstream of the refrigerant flow path, where the temperature is relatively high, one possible solution is to increase the amount of water vapor supplied to the gas flow path along with oxygen. However, increasing the amount of water vapor supplied to the gas flow path may result in an excess of water upstream of the refrigerant flow path, where the temperature is relatively low. In this case, oxygen diffusion resistance increases, which actually reduces power generation performance. Therefore, it is not easy to appropriately control the water content throughout the entire surface of the membrane electrode assembly.

[0012] Under these circumstances, the inventors came up with the idea of ​​utilizing the water produced as a by-product of power generation, and focused on the phenomenon in which the produced water flows downstream through the gas flow path, which led to the subject matter of the present disclosure.

[0013] The present disclosure aims to homogenize the distribution of moisture content within the surface of a membrane electrode assembly by aligning the gas flow direction with the refrigerant flow direction in the overlapping region between the refrigerant flow channel and the gas flow channel.

[0014] Hereinafter, embodiments will be described in detail with reference to the drawings. However, unnecessary detailed description may be omitted. For example, detailed description of already well-known matters or redundant description of substantially the same configuration may be omitted.

[0015] The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0016] (Embodiment 1) Hereinafter, the first embodiment will be described with reference to FIGS.

[0017] [1-1.Configuration] 1 is a schematic cross-sectional view of a fuel cell stack 200 according to Embodiment 1. The fuel cell stack 200 includes a plurality of fuel cells 100 stacked one on top of the other.

[0018] The fuel cell 100 includes a membrane electrode assembly 10, an anode separator 20, and a cathode separator 30. The membrane electrode assembly 10 is disposed between the anode separator 20 and the cathode separator 30. The fuel cell 100 is, for example, a polymer electrolyte fuel cell.

[0019] The membrane electrode assembly 10 can also be used in other electrochemical devices, such as a hydrogen purification device for purifying hydrogen.

[0020] The membrane electrode assembly 10 includes an anode 13, an electrolyte membrane 12, and a cathode 16. The anode 13 is bonded to one surface of the electrolyte membrane 12. The cathode 16 is bonded to the other surface of the electrolyte membrane 12.

[0021] The membrane electrode assembly 10 may include a frame 19. The frame 19 is disposed around the membrane electrode assembly 10 so that the anode separator 20 and the cathode separator 30 do not come into contact with each other, and fixes the membrane electrode assembly 10 between the anode separator 20 and the cathode separator 30. The frame 19 maintains airtightness around the membrane electrode assembly 10. The frame 19 prevents the fuel gas (anode gas) and the oxidant gas (cathode gas) from mixing, and electrically separates the anode separator 20 and the cathode separator 30. The frame 19 is insulating, gas permeation resistant, and water vapor permeation resistant. An insulating member can be used as the frame 19. The frame 19 may be, for example, a resin member.

[0022] The electrolyte membrane 12 is disposed between the anode 13 and the cathode 16. The electrolyte membrane 12 is made of a polymer material having proton conductivity. For example, the electrolyte membrane 12 is a membrane made of a perfluorocarbon sulfonic acid-based polymer material having sulfonic acid groups, or a hydrocarbon-based polymer material.

[0023] The anode 13 includes an anode catalyst layer 14 and an anode gas diffusion layer 15. The anode catalyst layer 14 is disposed between the electrolyte membrane 12 and the anode gas diffusion layer 15. The cathode 16 includes a cathode catalyst layer 17 and a cathode gas diffusion layer 18. The cathode catalyst layer 17 is disposed between the electrolyte membrane 12 and the cathode gas diffusion layer 18.

[0024] The anode catalyst layer 14 has a function of promoting an electrochemical reaction that dissociates hydrogen molecules into protons. The anode catalyst layer 14 includes an electrode catalyst and a polymer electrolyte. The anode catalyst layer 14 may include, as the electrode catalyst, carbon particles carrying catalyst particles and a polymer electrolyte.

[0025] The anode gas diffusion layer 15 has the function of supplying fuel gas to the anode catalyst layer 14 and the function of receiving electrons from the anode catalyst layer 14. The anode gas diffusion layer 15 is made of a gas-permeable and electrically conductive material. The anode gas diffusion layer 15 has, as its main material, for example, an electrically conductive porous body. An example of the porous body is a carbon fiber aggregate such as carbon paper.

[0026] The cathode catalyst layer 17 has a function of promoting an electrochemical reaction that produces water from protons and oxygen. The cathode catalyst layer 17 includes an electrode catalyst and a polymer electrolyte. The cathode catalyst layer 17 may include, as the electrode catalyst, carbon particles carrying catalyst particles and a polymer electrolyte. The carbon particles may be mesoporous carbon particles. The cathode catalyst layer 17 may further include conductive fibers.

[0027] The cathode gas diffusion layer 18 has the function of supplying an oxidant gas to the cathode catalyst layer 17 and the function of transferring electrons to the cathode catalyst layer 17. The cathode gas diffusion layer 18 is made of a gas-permeable and electrically conductive material. The cathode gas diffusion layer 18 contains, for example, an electrically conductive porous body as its main material. An example of the porous body is a carbon fiber aggregate such as carbon paper.

[0028] An example of the fuel gas is a hydrogen-containing gas. The hydrogen-containing gas may be a gas produced from hydrocarbons by steam reforming, or may be pure hydrogen gas with a hydrogen concentration of 99% or more. An example of the oxidant gas is air.

[0029] A fuel gas flow channel 40 is provided between the anode 13 and the anode separator 20. Fuel gas is supplied to the anode 13 through the fuel gas flow channel 40. In this embodiment, a groove is provided in the anode separator 20 as the fuel gas flow channel 40. However, the fuel gas flow channel 40 may be formed of a member separate from the anode separator 20.

[0030] An oxidant gas flow channel 50 is provided between the cathode 16 and the cathode separator 30. An oxidant gas is supplied to the cathode 16 through the oxidant gas flow channel 50. In this embodiment, a groove is provided in the cathode separator 30 as the oxidant gas flow channel 50. However, the oxidant gas flow channel 50 may be formed of a member separate from the cathode separator 30.

[0031] The anode separator 20 and the cathode separator 30 are each made of a conductive material such as carbon or metal, and may be provided with a corrosion-resistant coating such as resin or plating to prevent corrosion.

[0032] The fuel cell 100 further includes a coolant flow channel 60 separated from the oxidant gas flow channel 50 by the cathode separator 30. A coolant such as brine or water is supplied to the coolant flow channel 60. In this embodiment, the anode separator 20 is provided with grooves as the coolant flow channel 60. That is, the fuel gas flow channel 40 is provided on a first surface of the anode separator 20, and the coolant flow channel 60 is provided on a second surface of the anode separator 20. The first and second surfaces of the anode separator 20 refer to the two main surfaces of the plate-like anode separator 20. The surface in contact with the anode 13 is the first surface, and the surface in contact with the cathode separator 30 is the second surface.

[0033] The coolant flow path 60 may be provided in the cathode separator 30, or may be provided in both the anode separator 20 and the cathode separator 30, or may be formed by a member separate from the anode separator 20. The coolant flow path 60 may be disposed between the anode separator 20 and the cathode separator 30 of adjacent fuel cells 100.

[0034] The fuel gas flow channel 40 and the oxidant gas flow channel 50 are configured so that the fuel gas and the oxidant gas flow, respectively, from the first side to the second side of the membrane electrode assembly 10. Similarly, the coolant flow channel 60 is configured so that the coolant flows from the first side to the second side of the membrane electrode assembly 10. The flow of the fuel gas and the flow of the coolant form parallel flows in the vertical direction of the membrane electrode assembly 10. The flow of the oxidant gas and the flow of the coolant form parallel flows in the vertical direction of the membrane electrode assembly 10. With this configuration, the relative humidity distribution of the fuel gas in the fuel gas flow channel 40 is easily made uniform, and the relative humidity distribution of the oxidant gas in the oxidant gas flow channel 50 is easily made uniform. If the relative humidity distribution of the gas can be made uniform, the distribution of the moisture content within the surface of the membrane electrode assembly 10 can be made uniform.

[0035] The fuel gas flow path 40 has an inlet 40a and an outlet 40b. The oxidant gas flow path 50 has an inlet 50a and an outlet 50b. The coolant flow path 60 has an inlet 60a and an outlet 60b. The inlet 40a of the fuel gas flow path 40, the inlet 50a of the oxidant gas flow path 50, and the inlet 60a of the coolant flow path 60 are located on a first side of the membrane electrode assembly 10. The outlet 40b of the fuel gas flow path 40, the outlet 50b of the oxidant gas flow path 50, and the outlet 60b of the coolant flow path 60 are located on a second side of the membrane electrode assembly 10.

[0036] In this embodiment, the membrane electrode assembly 10 and the fuel cell 100 have a rectangular shape in a plan view. A first side of the membrane electrode assembly 10 and the fuel cell 100 is the side on which one of a pair of sides positioned in a direction perpendicular to the thickness direction of the membrane electrode assembly 10 is located. A second side of the fuel cell 100 is the side on which the other of the pair of sides positioned in a direction perpendicular to the thickness direction of the membrane electrode assembly 10 is located. In the example of FIG. 1 , the X direction is the thickness direction of the membrane electrode assembly 10. The Y direction and the Z direction are each perpendicular to the thickness direction of the membrane electrode assembly 10.

[0037] The Z direction is, for example, a direction parallel to the vertical direction. The X direction is, for example, a direction parallel to the horizontal direction. The Y direction is, for example, a direction parallel to the horizontal direction and perpendicular to the thickness direction of the membrane electrode assembly 10. The first side of the membrane electrode assembly 10 and the fuel cell 100 may be the upper side in the vertical direction. The second side of the membrane electrode assembly 10 and the fuel cell 100 may be the lower side in the vertical direction. In this case, the fuel gas, the oxidant gas, and the coolant flow from the upper side to the lower side in the vertical direction.

[0038] In this embodiment, an inlet 40a of the fuel gas flow channel 40 is provided at one end of the fuel cell 100 in the Z direction. An outlet 40b of the fuel gas flow channel 40 is provided at the other end of the fuel cell 100 in the Z direction. The inlet 40a and outlet 40b of the fuel gas flow channel 40 penetrate the anode separator 20 and the cathode separator 30 in the thickness direction. The inlets 40a of adjacent fuel cells 100 are connected to each other. The outlets 40b of adjacent fuel cells 100 are connected to each other. This allows fuel gas to be supplied to the fuel gas flow channel 40 from outside the fuel cell stack 200, and allows unconsumed fuel gas to be discharged from the fuel gas flow channel 40 to outside the fuel cell stack 200.

[0039] In this embodiment, an inlet 50a of the oxidant gas flow channel 50 is provided at one end of the fuel cell 100 in the Z direction. An outlet 50b of the oxidant gas flow channel 50 is provided at the other end of the fuel cell 100 in the Z direction. The inlet 50a and outlet 50b of the oxidant gas flow channel 50 penetrate the anode separator 20 and the cathode separator 30 in the thickness direction. The inlets 50a of adjacent fuel cells 100 are connected to each other. The outlets 50b of adjacent fuel cells 100 are connected to each other. This allows the oxidant gas to be supplied to the oxidant gas flow channel 50 from outside the fuel cell stack 200, and allows unconsumed oxidant gas and water vapor to be discharged from the oxidant gas flow channel 50 to outside the fuel cell stack 200.

[0040] In this embodiment, an inlet 60a of the refrigerant flow path 60 is provided at one end of the fuel cell 100 in the Z direction. An outlet 60b of the refrigerant flow path 60 is provided at the other end of the fuel cell 100 in the Z direction. The inlet 60a and outlet 60b of the refrigerant flow path 60 penetrate the anode separator 20 and the cathode separator 30 in the thickness direction. The inlets 60a of adjacent fuel cells 100 are connected to each other. The outlets 60b of adjacent fuel cells 100 are connected to each other. This allows a refrigerant to be supplied to the refrigerant flow path 60 from outside the fuel cell stack 200, and allows the refrigerant to be discharged from the refrigerant flow path 60 to outside the fuel cell stack 200.

[0041] FIG. 2 is a first plan view of the anode separator 20. The first plan view is a plan view of the surface 20p that contacts the anode 13. In this embodiment, the fuel gas flow field 40 is a serpentine flow field. Specifically, the fuel gas flow field 40 includes a plurality of first straight portions 41, a plurality of second straight portions 42, and a plurality of turned-back portions 43. The second straight portions 42 are parallel to the first straight portions 41. The flow direction of the fuel gas in the first straight portions 41 is 180 degrees opposite to the flow direction of the fuel gas in the second straight portions 42. The turned-back portions 43 are portions that connect the first straight portions 41 and the second straight portions 42. The first straight portions 41 and the second straight portions 42 extend in directions (-Y direction and +Y direction) perpendicular to the direction from the first side to the second side of the membrane electrode assembly 10 (-Z direction). The folded portion 43 extends in a direction (-Z direction) from the first side to the second side of the membrane electrode assembly 10. The folded portion 43 may have an arc shape in a plan view. With this configuration, the fuel gas can be supplied to every corner of the anode 13.

[0042] 1 and 2, the anode separator 20 has a plurality of ribs 22 that contact the membrane electrode assembly 10 and perform a current collecting function. In this embodiment, the plurality of ribs 22 give the fuel gas flow channel 40 a serpentine shape.

[0043] FIG. 3 is a plan view of the cathode separator 30. In this embodiment, the oxidant gas flow field 50 is a serpentine flow field. Specifically, the oxidant gas flow field 50 includes a plurality of first straight portions 51, a plurality of second straight portions 52, and a plurality of turn-back portions 53. The second straight portions 52 are parallel to the first straight portions 51. The flow direction of the oxidant gas in the first straight portions 51 is 180 degrees opposite to the flow direction of the oxidant gas in the second straight portions 52. The turn-back portions 53 connect the first straight portion 51 and the second straight portion 52. The first straight portion 51 and the second straight portion 52 extend in directions (+Y direction and −Y direction) perpendicular to the direction (−Z direction) from the first side to the second side of the membrane electrode assembly 10. The turn-back portions 53 extend in the direction (−Z direction) from the first side to the second side of the membrane electrode assembly 10. The folded portion 53 may have an arc shape in a plan view. With this configuration, the oxidant gas can be supplied to every corner of the cathode 16.

[0044] 1 and 2, the cathode separator 30 has a plurality of ribs 32 that contact the membrane electrode assembly 10 and perform a current collecting function. In this embodiment, the plurality of ribs 32 give the oxidant gas flow field 50 a serpentine shape.

[0045] 2 and 3, the flow direction of the fuel gas in the fuel gas flow field 40 is parallel to the flow direction of the oxidant gas in the oxidant gas flow field 50. This configuration makes it easier for the electrochemical reaction in the membrane electrode assembly 10 to proceed efficiently.

[0046] 2 and 3 , when the fuel cell 100 is viewed in a direction parallel to the thickness direction of the membrane electrode assembly 10, the flow direction of the fuel gas in the first straight portion 41 of the fuel gas flow field 40 is opposite to the flow direction of the oxidant gas in the first straight portion 51 of the oxidant gas flow field 50. The flow direction of the fuel gas in the second straight portion 42 of the fuel gas flow field 40 is opposite to the flow direction of the oxidant gas in the second straight portion 52 of the oxidant gas flow field 50. With this configuration, the arrangement of the inlet 40a of the fuel gas flow field 40, the outlet 40b of the fuel gas flow field 40, the inlet 50a of the oxidant gas flow field 50, and the outlet 50b of the oxidant gas flow field 50 is less likely to be restricted. As a result, the design freedom of the fuel cell stack 200 is increased.

[0047] However, when the fuel cell 100 is viewed in a direction parallel to the thickness direction of the membrane electrode assembly 10, the flow direction of the fuel gas in the first straight portion 41 of the fuel gas flow field 40 may be parallel to the flow direction of the oxidant gas in the first straight portion 51 of the oxidant gas flow field 50. The flow direction of the fuel gas in the second straight portion 42 of the fuel gas flow field 40 may be parallel to the flow direction of the oxidant gas in the second straight portion 52 of the oxidant gas flow field 50.

[0048] The fuel cell stack 200 is installed, for example, so that the Z direction is parallel to the vertical direction. In this case, the first straight portion 41 of the fuel gas flow field 40, the second straight portion 42 of the fuel gas flow field 40, the first straight portion 51 of the oxidant gas flow field 50, and the second straight portion 52 of the oxidant gas flow field 50 are each parallel to the horizontal direction.

[0049] FIG. 4 is a second plan view of the anode separator 20. The second plan view is a plan view of the surface 20q opposite to the surface 20p (FIG. 2) that contacts the anode 13. In this embodiment, the refrigerant flow path 60 is a serpentine flow path. Specifically, the refrigerant flow path 60 includes a plurality of first straight portions 61, a plurality of second straight portions 62, and a plurality of turned-back portions 63. The second straight portions 62 are parallel to the first straight portions 61. The refrigerant flow direction in the first straight portions 61 is 180 degrees opposite to the refrigerant flow direction in the second straight portions 62. The turned-back portions 63 are portions that connect the first straight portions 61 and the second straight portions 62. The first straight portions 61 and the second straight portions 62 extend in directions (+Y direction and −Y direction) perpendicular to the direction from the first side to the second side of the membrane electrode assembly 10 (−Z direction). The folded portion 63 extends in a direction (-Z direction) from the first side to the second side of the membrane electrode assembly 10. The folded portion 63 may have an arc shape in a plan view. With this configuration, the entire membrane electrode assembly 10 can be uniformly cooled and the efficiency of exhaust heat recovery can be improved.

[0050] 1 and 4, the anode separator 20 has a plurality of ribs 122 for imparting a serpentine shape to the refrigerant flow path 60. The plurality of ribs 122 are in contact with the cathode separator 30, which is a member adjacent to the anode separator 20.

[0051] FIG. 5 is a projection obtained by projecting the oxidant gas channel 50 and the refrigerant channel 60 onto a plane perpendicular to the thickness direction of the electrolyte membrane 12. The projection in FIG. 5 is a projection within the range of a rectangular region K where the cathode catalyst layer 17 is present. In other words, the projection in FIG. 5 does not show a part of the oxidant gas channel 50 in the section from the inlet 50a of the oxidant gas channel 50 to the rectangular region K where the cathode catalyst layer 17 is present, nor a part of the oxidant gas channel 50 in the section from the rectangular region where the cathode catalyst layer 17 is present to the outlet 50b of the oxidant gas channel 50. Similarly, the projection in FIG. 5 does not show a part of the refrigerant channel 60 in the section from the inlet 60a of the refrigerant channel 60 to the rectangular region K where the cathode catalyst layer 17 is present, nor a part of the refrigerant channel 60 in the section from the rectangular region K where the cathode catalyst layer 17 is present to the outlet 60b of the refrigerant channel 60.

[0052] In the projection of Fig. 5, the ribs 22 of the anode separator 20 are considered to be part of the fuel gas flow path 40. Similarly, in the projection of Fig. 5, the ribs 32 of the cathode separator 30 are considered to be part of the oxidant gas flow path 50. In the projection of Fig. 5, the ribs 122 of the anode separator 20 are considered to be part of the refrigerant flow path 60.

[0053] In the projection view of FIG. 5 , there is an overlapping portion 70 between the oxidant gas flow field 50 and the coolant flow field 60. In FIG. 5 , the overlapping portion 70 is indicated by solid diagonal lines and dashed diagonal lines. The overlapping portion 70 includes a matching portion 71 where the flow direction of the oxidant gas in the oxidant gas flow field 50 and the flow direction of the coolant in the coolant flow field 60 match. In the projection view of FIG. 5 , the ratio (S2 / S1) of the area S2 of the matching portion 71 to the area S1 of the oxidant gas flow field 50 is 0.8 or more. In the example shown in FIG. 5 , the overlapping portion 70 completely matches the matching portion 71. However, in many cases, the flow field width and number of the oxidant gas flow fields 50 differ from the flow field width and number of the coolant flow fields 60. In such cases, part of the overlapping portion 70 becomes the matching portion 71.

[0054] 6A is a diagram illustrating the effects obtained by the configuration of this embodiment. The moisture content of the oxidant gas flowing through the oxidant gas flow channel 50 increases from upstream to downstream of the oxidant gas flow channel 50 in the order of Position H1, Position H2, Position H3, and Position H4. This is because water generated by power generation flows from upstream to downstream along with the oxidant gas. When the oxidant gas flow channel 50 and the coolant flow channel 60 overlap and the flow direction of the oxidant gas and the coolant are aligned as in this embodiment, the temperature of the oxidant gas flowing through the oxidant gas flow channel 50 also increases from upstream to downstream of the coolant flow channel 60 in the order of Position H1, Position H2, Position H3, and Position H4. This is because the flow path of the coolant in the coolant flow channel 60 increases from upstream to downstream. As the temperature of the oxidant gas increases, the amount of saturated water vapor in the oxidant gas also increases. Therefore, the relative humidities of the oxidant gas at multiple positions H1, H2, H3, and H4 along the flow direction of the oxidant gas flow channel 50 approach each other. In one example, it is desirable for the relative humidity of the oxidant gas at each of positions H1, H2, H3, and H4 to be approximately equal.

[0055] As described above, the present embodiment aims to homogenize the relative humidity distribution of the oxidant gas in the oxidant gas flow field 50 by aligning the flow direction of the refrigerant with the flow direction of the oxidant gas in the overlapping region between the oxidant gas flow field 50 and the refrigerant flow field 60. If the relative humidity distribution of the oxidant gas can be homogenized, the distribution of the moisture content within the surface of the membrane electrode assembly 10 can be homogenized. As a result, the current density distribution within the surface of the membrane electrode assembly 10 can be homogenized, thereby improving the power generation efficiency of the fuel cell 100.

[0056] FIG. 6B is a diagram illustrating an example in which the flow direction of the oxidant gas and the flow direction of the coolant do not match. In the configuration shown in FIG. 6B, the flow direction of the oxidant gas in the oxidant gas flow path 501 does not match the flow direction of the coolant in the coolant flow path 60. In this case, the relative humidity of the oxidant gas at each of positions H1, H2, H3, and H4 varies for the following reason. For example, because position H2 is located downstream of position H1, the moisture content of the oxidant gas at position H2 is relatively large. However, because position H2 corresponds to the vicinity of the inlet of the coolant flow path 60, the temperature of the oxidant gas at position H2 is low. As a result, the relative humidity of the oxidant gas at position H2 becomes excessively high. The same explanation applies to positions H1, H3, and H4.

[0057] FIG. 7A is a diagram illustrating a rule for calculating the area of ​​the overlapping portion 71 in the projection of FIG. 5. In FIG. 7A, the flow direction of the oxidant gas G in the first straight portion 51 of the oxidant gas flow field 50 is the +Y direction. The flow direction of the oxidant gas G in the second straight portion 52 is the −Y direction. The flow direction of the oxidant gas G in the turn-back portion 53 is the −Z direction. The boundary between the first straight portion 51 and the turn-back portion 53 is determined by a reference line L that passes through the tip of the rib 32 of the cathode separator 30 and is perpendicular to the first straight portion 51 or the second straight portion 52. In other words, the position corresponding to the tip of the rib 32 is the end point of the first straight portion 51 and the start point of the second straight portion 52. The area of ​​the overlapping portion 71 shown in the projection of FIG. 5 is calculated according to this rule. Similar rules apply to the fuel gas flow field 40 and the refrigerant flow field 60.

[0058] As described above, in the projection view of FIG. 5 , the rib 32 of the cathode separator 30 is considered to be part of the oxidant gas flow field 50. Specifically, as shown in FIG. 7A , the rib 32 includes a first portion 32a adjacent to the first straight portion 51 of the oxidant gas flow field 50, a second portion 32b adjacent to the second straight portion 52 of the oxidant gas flow field 50, and a third portion 32c adjacent to the turned portion 53 of the oxidant gas flow field 50. The first portion 32a and the second portion 32b have equal areas. The third portion of the rib 32 is a base portion of the rib 32 and is defined by the reference line L. The first portion 32a of the rib 32 is considered to be part of the first straight portion 51 of the oxidant gas flow field 50. The second portion 32b of the rib 32 is considered to be part of the second straight portion 52 of the oxidant gas flow field 50. The third portion 32c of the rib 32 is considered to be part of the turned portion 53 of the oxidant gas flow field 50. These rules are also applied when calculating the area of ​​the fuel gas flow path 40 in the projection drawing, and are also applied when calculating the area of ​​the refrigerant flow path 60 in the projection drawing.

[0059] FIG. 7B is another diagram illustrating the rules for calculating the area of ​​the overlapping portion in the projection view of FIG. 5. As shown in FIG. 7B, at least one rib 33 may be provided in the oxidant gas flow field 50. In this case, the rib 33 is also considered to be part of the oxidant gas flow field 50. Specifically, the rib 33 includes at least one first portion 33a that separates the first straight portion 51, at least one second portion 33b that separates the second straight portion 52, and at least one third portion 33c that separates the turned portion 53. In the example shown in FIG. 7B, multiple ribs 33 are provided in the oxidant gas flow field 50. The first portion 33a of the rib 33 is considered to be part of the first straight portion 51 of the oxidant gas flow field 50. The second portion 33b of the rib 33 is considered to be part of the second straight portion 52 of the oxidant gas flow field 50. The third portion 33c of the rib 33 is considered to be part of the turned portion 53 of the oxidant gas flow field 50. These rules are also applied when calculating the area of ​​the fuel gas flow path 40 in the projection drawing, and are also applied when calculating the area of ​​the refrigerant flow path 60 in the projection drawing.

[0060] A large area of ​​the overlapping portion 70 between the oxidant gas flow path 50 and the refrigerant flow path 60 is desirable from the viewpoint of achieving the effect described with reference to FIG. 6A. Therefore, the upper limit of the ratio (S2 / S1) is not particularly limited. However, taking into consideration the arrangement of the inlet 50a of the oxidant gas flow path 50 and the inlet 60a of the refrigerant flow path 60, the upper limit of the ratio (S2 / S1) is, for example, 0.95. When the upper limit of the ratio (S2 / S1) is such a value, the arrangement of the inlet 50a of the oxidant gas flow path 50 and the inlet 60a of the refrigerant flow path 60 is not easily restricted. As a result, the degree of freedom in designing the fuel cell stack 200 is increased.

[0061] 8 is a diagram showing an additional configuration that can contribute to uniforming the relative humidity distribution. As shown in FIG. 8, a heat conduction suppression section 80 that separates the first straight portion 51 and the second straight portion 52 of the oxidant gas flow field 50 may be provided between the first straight portion 51 and the second straight portion 52 of the oxidant gas flow field 50. The heat conduction suppression section 80 suppresses heat conduction from the oxidant gas flowing through the first straight portion 51 to the oxidant gas flowing through the second straight portion 52. As a result, the temperature distribution of the oxidant gas flowing through the oxidant gas flow field 50 is likely to be formed along the flow direction of the refrigerant in the coolant flow field 60. In this case, the relative humidity distribution of the oxidant gas in the oxidant gas flow field 50 is likely to be more uniform.

[0062] The heat conduction suppression portion 80 may be made of, for example, a material having a lower thermal conductivity than the anode separator 20 and the cathode separator 30. This configuration tends to suppress heat conduction from the oxidant gas flowing through the first straight portion 51 to the oxidant gas flowing through the second straight portion 52. The heat conduction suppression portion 80 may be part of the rib 32 (see FIG. 7A ) of the cathode separator 30 in which the oxidant gas flow field 50 is provided. For example, if the anode separator 20 and the cathode separator 30 are made of a composite material of resin and carbon, the resin content of the portion corresponding to the heat conduction suppression portion 80 is higher than the resin content of the other portions. This reduces the thermal conductivity of the portion corresponding to the heat conduction suppression portion 80. Alternatively, the heat conduction suppression portion 80 can be formed by forming a coating of a material such as resin on the surface of the rib 32 of the cathode separator 30.

[0063] 8 may be applied to the refrigerant flow path 60. That is, a heat conduction suppression section 80 may be provided between the first straight portion 61 of the refrigerant flow path 60 and the second straight portion 62 of the refrigerant flow path 60, separating the first straight portion 61 and the second straight portion 62. The heat conduction suppression section 80 suppresses heat conduction from the refrigerant flowing through the first straight portion 61 to the refrigerant flowing through the second straight portion 62. This may contribute to making the relative humidity distribution of the oxidant gas in the oxidant gas flow path 50 uniform.

[0064] [1-2. Operation] The operation and function of the fuel cell stack 200 configured as above will be described below with reference to FIG.

[0065] A fuel gas, an oxidant gas, and a coolant are supplied to the fuel gas flow passage 40, the oxidant gas flow passage 50, and the coolant flow passage 60, respectively. The oxidant gas is typically air.

[0066] At the anode 13, hydrogen (H2) is converted into protons (H + ) and electrons (e - ) The protons move from the anode 13 to the cathode 16 by conduction through the electrolyte membrane 12. The electrons move from the anode 13 to the cathode 16 through an external circuit. At the cathode 16, water (H2O) is produced by an electrochemical reaction of the protons, oxygen (O2), and electrons, as expressed by the following formula (2):

[0067] H2→2H + +2e - (1) 4H + +O2+2e - →2H2O(2)

[0068] The moisture content of the oxidant gas flowing through the oxidant gas flow field 50 increases from upstream to downstream of the oxidant gas flow field 50. This is because water produced by power generation flows from upstream to downstream along with the oxidant gas. When the oxidant gas flow field 50 and the refrigerant flow field 60 overlap and the flow direction of the oxidant gas and the refrigerant are aligned as in the present embodiment, the temperature of the oxidant gas flowing through the oxidant gas flow field 50 increases from upstream to downstream of the refrigerant flow field 60. This is because the flow path of the refrigerant in the refrigerant flow field 60 increases from upstream to downstream. As the temperature of the oxidant gas increases, the amount of saturated water vapor in the oxidant gas also increases. Therefore, the relative humidity of the oxidant gas at multiple positions along the flow direction of the oxidant gas flow field 50 approaches each other. In other words, the relative humidity distribution of the oxidant gas in the oxidant gas flow field 50 can be made uniform. If the relative humidity distribution of the oxidant gas can be made uniform, the distribution of the moisture content within the surface of the membrane electrode assembly 10 can be made uniform. As a result, the current density distribution within the surface of the membrane electrode assembly 10 can be made uniform, and the power generation efficiency of the fuel cell 100 is improved.

[0069] (Variation 1) 9 is a diagram showing a schematic configuration of a cathode separator 130 according to Modification 1. In this modification, the length L1 of the cathode separator 130 in the direction parallel to the vertical direction (-Z direction) from the first side to the second side is shorter than the length L2 of the cathode separator 130 in the horizontal direction (Y direction) perpendicular to the vertical direction. With this configuration, the height of the fuel cell 100 and the fuel cell stack 200 can be reduced.

[0070] The configuration shown in Fig. 9 also applies to the anode separator. That is, the length of the anode separator in the direction parallel to the vertical direction from the first side to the second side is shorter than the length of the anode separator in the horizontal direction perpendicular to the vertical direction.

[0071] The heat conduction suppressing section 80 described with reference to Fig. 8 is suitable for the configuration shown in Fig. 9. In the configuration shown in Fig. 9, the first straight portion 51 and the second straight portion 52 are each long, so the influence of heat conduction from the first straight portion 51 to the second straight portion 52 is large. In this case, the effect of the heat conduction suppressing section 80 in uniformizing the relative humidity distribution is further enhanced.

[0072] (Variation 2) Fig. 10 is a second plan view of the anode separator 120 according to Modification 2. As can be seen from a comparison of Fig. 4 and Fig. 10, the refrigerant flow direction in the anode separator 20 shown in Fig. 4 is opposite in the Y direction by 180 degrees to the refrigerant flow direction in the anode separator 120 shown in Fig. 10. When the anode separator 120 shown in Fig. 10 is applied to the fuel cell 100 instead of the anode separator 20 shown in Fig. 4, the following configuration is established.

[0073] That is, in a projection diagram obtained by projecting the fuel gas flow channel 40 and the refrigerant flow channel 60 onto a plane perpendicular to the thickness direction of the electrolyte membrane 12, there may be an overlapping portion between the fuel gas flow channel 40 and the refrigerant flow channel 60. The overlapping portion includes a portion where the flow direction of the fuel gas in the fuel gas flow channel coincides with the flow direction of the refrigerant in the refrigerant flow channel 60. In the projection diagram, the ratio of the area of ​​the overlapping portion to the area of ​​the fuel gas flow channel 40 is 0.8 or more. That is, the configurations of the oxidant gas flow channel 50 and the refrigerant flow channel 60 can also be applied to the fuel gas flow channel 40 and the refrigerant flow channel 60. This homogenizes the relative humidity distribution of the fuel gas in the fuel gas flow channel 40. If the relative humidity distribution of the fuel gas can be homogenized, the distribution of the moisture content within the surface of the membrane electrode assembly 10 can be homogenized. As a result, the current density distribution within the surface of the membrane electrode assembly 10 can be homogenized, thereby improving the power generation efficiency of the fuel cell 100.

[0074] 8 may be applied to the fuel gas flow field 40. That is, a heat conduction suppression section 80 may be provided between the first straight portion 41 of the fuel gas flow field 40 and the second straight portion 42 of the fuel gas flow field 40, separating the first straight portion 41 and the second straight portion 42. The heat conduction suppression section 80 suppresses heat conduction from the fuel gas flowing through the first straight portion 41 to the fuel gas flowing through the second straight portion 42. This may contribute to uniforming the relative humidity distribution of the fuel gas in the fuel gas flow field 40.

[0075] The configuration of Modification 2 that defines the overlap between the fuel gas flow path 40 and the refrigerant flow path 60 can be realized simultaneously with the configuration of Embodiment 1 that defines the overlap between the oxidant gas flow path 50 and the refrigerant flow path 60. This is because the position of the inlet 40a of the fuel gas flow path 40 and the position of the inlet 50a of the oxidant gas flow path 50 can be made sufficiently close to each other so that the flow of the fuel gas and the flow of the oxidant gas form parallel flows in the Y direction.

[0076] [1-3. Supplementary Notes] The above description of the embodiments discloses the following techniques.

[0077] (Technology 1) an anode separator; a cathode separator; and a membrane electrode assembly including an anode, a cathode, and an electrolyte membrane, the membrane electrode assembly being disposed between the anode separator and the cathode separator; a fuel gas flow channel provided between the anode and the anode separator; an oxidant gas flow channel provided between the cathode and the cathode separator; a coolant flow channel provided so as to be separated from the oxidant gas flow channel by the cathode separator; Equipped with the fuel gas flow path, the oxidant gas flow path, and the coolant flow path are each a serpentine flow path, Satisfy at least one of the following requirements (a) and (b): fuel cell. (a) In a projection obtained by projecting the fuel gas flow path and the refrigerant flow path onto a plane perpendicular to the thickness direction of the electrolyte membrane, there is an overlapping portion between the fuel gas flow path and the refrigerant flow path, the overlapping portion includes a coincident portion where the flow direction of the fuel gas in the fuel gas flow path and the flow direction of the refrigerant in the refrigerant flow path coincide, and in the projection, the ratio of the area of ​​the coincident portion to the area of ​​the fuel gas flow path is 0.8 or more. (b) In a projection obtained by projecting the oxidant gas flow path and the refrigerant flow path onto a plane perpendicular to the thickness direction of the electrolyte membrane, there is an overlapping portion between the oxidant gas flow path and the refrigerant flow path, the overlapping portion includes a coincident portion where the flow direction of the oxidant gas in the oxidant gas flow path and the flow direction of the refrigerant in the refrigerant flow path coincide, and in the projection, the ratio of the area of ​​the coincident portion to the area of ​​the oxidant gas flow path is 0.8 or more.

[0078] According to the present disclosure, the distribution of the moisture content within the surface of the membrane electrode assembly can be made uniform.

[0079] (Technology 2) The fuel cell according to Technology 1, which satisfies the requirement (b).The present disclosure provides significant effects when applied to an oxidant gas flow path and a coolant flow path.

[0080] (Technology 3) The fuel cell according to Technology 1 or 2, wherein the fuel gas flow path includes a first straight portion, a second straight portion parallel to the first straight portion, and a return portion connecting the first straight portion and the second straight portion, the flow direction of the fuel gas in the first straight portion is opposite to the flow direction of the fuel gas in the second straight portion by 180 degrees, and a heat conduction suppression portion is provided between the first straight portion and the second straight portion to separate the first straight portion from the second straight portion. The heat conduction suppression portion suppresses heat conduction from the fuel gas flowing in the first straight portion to the fuel gas flowing in the second straight portion.

[0081] (Technology 4) The fuel cell according to any one of techniques 1 to 3, wherein the oxidant gas flow field includes a first straight portion, a second straight portion parallel to the first straight portion, and a return portion connecting the first straight portion and the second straight portion, wherein the flow direction of the oxidant gas in the first straight portion is opposite to the flow direction of the oxidant gas in the second straight portion by 180 degrees, and a heat conduction suppression portion is provided between the first straight portion and the second straight portion to separate the first straight portion from the second straight portion. The heat conduction suppression portion suppresses heat conduction from the oxidant gas flowing in the first straight portion to the oxidant gas flowing in the second straight portion.

[0082] (Technology 5) The fuel cell according to any one of techniques 1 to 4, wherein the refrigerant flow path includes a first straight portion, a second straight portion parallel to the first straight portion, and a folded portion connecting the first straight portion and the second straight portion, wherein the flow direction of the refrigerant in the first straight portion is opposite to the flow direction of the refrigerant in the second straight portion by 180 degrees, and a heat conduction suppression portion that separates the first straight portion from the second straight portion is provided between the first straight portion and the second straight portion. The heat conduction suppression portion suppresses heat conduction from the refrigerant flowing in the first straight portion to the refrigerant flowing in the second straight portion.

[0083] (Technology 6) The fuel cell according to any one of techniques 3 to 5, wherein the heat conduction suppressing portion is made of a material having a lower thermal conductivity than the anode separator and the cathode separator. With this configuration, heat conduction from the first straight portion to the second straight portion is easily suppressed.

[0084] (Technology 7) The fuel cell according to any one of Techniques 1 to 6, wherein the fuel gas flow path, the oxidant gas flow path, and the coolant flow path are configured so that the fuel gas, the oxidant gas, and the coolant flow path flow from the first side to the second side of the membrane electrode assembly, respectively. With this configuration, the relative humidity distribution of the fuel gas in the fuel gas flow path is easily made uniform, and the relative humidity distribution of the oxidant gas in the oxidant gas flow path is easily made uniform.

[0085] (Technology 8) The fuel cell according to any one of techniques 1 to 7, wherein the lengths of the anode separator and the cathode separator in a direction parallel to a longitudinal direction from the first side to the second side are shorter than the lengths of the anode separator and the cathode separator in a lateral direction perpendicular to the longitudinal direction. With this configuration, the height of the fuel cell and the fuel cell stack can be reduced. [Industrial Applicability]

[0086] The techniques of the present disclosure are useful in fuel cells. [Explanation of symbols]

[0087] 10 Membrane electrode assembly 12 Electrolyte membrane 13 Anode 14 Anode catalyst layer 15 Anode gas diffusion layer 16 cathode 17 Cathode catalyst layer 18 Cathode gas diffusion layer 19 Frame 20,120 Anode separator 20p,20q side 30,130 Cathode separator 22, 32, 33, 122 Ribs 32a, 33a First part of rib 32b, 33b Second part of rib 32c, 33c Third part of rib 40 fuel gas flow path 50 oxidant gas flow path 60 refrigerant flow path Entrance to 40a, 50a, 60a 40b,50b,60b exit 41,51,61 1st straight line section 42,52,62 2nd straight line section 43, 53, 63 Folded parts 70 Overlapping part 71 Match part 80 Heat conduction suppression section 100 fuel cell 200 fuel cell stack

Claims

1. an anode separator; a cathode separator; and a membrane electrode assembly including an anode, a cathode, and an electrolyte membrane, the membrane electrode assembly being disposed between the anode separator and the cathode separator; a fuel gas flow channel provided between the anode and the anode separator; an oxidant gas flow channel provided between the cathode and the cathode separator; a coolant flow channel provided so as to be separated from the oxidant gas flow channel by the cathode separator; Equipped with the fuel gas flow path, the oxidant gas flow path, and the coolant flow path are each a serpentine flow path, Satisfy at least one of the following requirements (a) and (b): fuel cell. (a) In a projection obtained by projecting the fuel gas flow path and the refrigerant flow path onto a plane perpendicular to the thickness direction of the electrolyte membrane, there is an overlapping portion between the fuel gas flow path and the refrigerant flow path, the overlapping portion includes a coincident portion where the flow direction of the fuel gas in the fuel gas flow path and the flow direction of the refrigerant in the refrigerant flow path coincide, and in the projection, the ratio of the area of ​​the coincident portion to the area of ​​the fuel gas flow path is 0.8 or more. (b) In a projection obtained by projecting the oxidant gas flow path and the refrigerant flow path onto a plane perpendicular to the thickness direction of the electrolyte membrane, there is an overlapping portion between the oxidant gas flow path and the refrigerant flow path, the overlapping portion includes a coincident portion where the flow direction of the oxidant gas in the oxidant gas flow path and the flow direction of the refrigerant in the refrigerant flow path coincide, and in the projection, the ratio of the area of ​​the coincident portion to the area of ​​the oxidant gas flow path is 0.8 or more.

2. Satisfies the requirement (b), The fuel cell according to claim 1 .

3. the fuel gas flow field includes a first straight portion, a second straight portion parallel to the first straight portion, and a turning portion connecting the first straight portion and the second straight portion, a flow direction of the fuel gas in the first straight portion is opposite to a flow direction of the fuel gas in the second straight portion by 180 degrees, a heat conduction suppressing portion that separates the first straight portion from the second straight portion is provided between the first straight portion and the second straight portion; The fuel cell according to claim 1 .

4. the oxidant gas flow field includes a first straight portion, a second straight portion parallel to the first straight portion, and a turning portion connecting the first straight portion and the second straight portion, a flow direction of the oxidant gas in the first straight portion is opposite to a flow direction of the oxidant gas in the second straight portion by 180 degrees, a heat conduction suppressing portion that separates the first straight portion from the second straight portion is provided between the first straight portion and the second straight portion; The fuel cell according to claim 1 .

5. the refrigerant flow path includes a first straight portion, a second straight portion parallel to the first straight portion, and a folded portion connecting the first straight portion and the second straight portion, the flow direction of the refrigerant in the first straight portion is opposite to the flow direction of the refrigerant in the second straight portion by 180 degrees; a heat conduction suppressing portion that separates the first straight portion from the second straight portion is provided between the first straight portion and the second straight portion; The fuel cell according to claim 1 .

6. the heat conduction suppressing portion is made of a material having a lower thermal conductivity than the anode separator and the cathode separator; 6. The fuel cell according to claim 3.

7. the fuel gas flow path, the oxidant gas flow path, and the coolant flow path are configured so that the fuel gas, the oxidant gas, and the coolant flow, respectively, from a first side to a second side of the membrane electrode assembly. The fuel cell according to claim 1 .

8. a length of each of the anode separator and the cathode separator in a direction parallel to a longitudinal direction from the first side to the second side is shorter than a length of each of the anode separator and the cathode separator in a lateral direction perpendicular to the longitudinal direction; The fuel cell according to claim 1 .

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