Fuel cell and operation method of same

Abstract

A fuel cell 100 according to the present disclosure comprises: an anode separator 20; a cathode separator 30; a membrane electrode assembly 10 that includes an anode 13, a cathode 16, and an electrolyte membrane 12 and that is disposed between the anode separator 20 and the cathode separator 30; a fuel gas flow path 40 that is provided between the anode 13 and the anode separator 20; and an oxidant gas flow path 50 that is provided between the cathode 16 and the cathode separator 30. The difference between the temperature of the oxidant gas and the dew point of the oxidant gas is 2°C or less at an outlet 50b of the oxidant gas flow path 50.

Description

Fuel cell and its operating method

[0001] The present disclosure relates to fuel cells and methods of operating the same.

[0002] To effectively utilize hydrogen, one of the next-generation energy sources, further improvements in fuel cell performance are required. To improve fuel cell performance, it is important to increase the power generated per unit cell. One way to increase the power generated per unit cell is to uniformly distribute the current density across the surface of the unit cell.

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

[0004] Japanese Patent Application Laid-Open No. 2005-174648

[0005] An object of the present disclosure is to provide a technique for achieving uniform current density distribution in a fuel cell.

[0006] The present disclosure provides a fuel cell comprising: an anode separator; a cathode separator; a membrane electrode assembly including an anode, a cathode, and an electrolyte membrane and disposed between the anode separator and the cathode separator; a fuel gas flow channel provided between the anode and the anode separator; and an oxidant gas flow channel provided between the cathode and the cathode separator, wherein the difference between the temperature of the oxidant gas and the dew point of the oxidant gas at an outlet of the oxidant gas flow channel is 2°C or less.

[0007] In another aspect, the present disclosure provides a fuel cell comprising: an anode separator; a cathode separator; a membrane electrode assembly including an anode, a cathode, and an electrolyte membrane and 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; and a coolant flow channel provided so as to be separated from the oxidant gas flow channel by the cathode separator, wherein the fuel gas flow channel and the oxidant gas flow channel are configured so that a fuel gas and an oxidant gas flow respectively flow from a first side to a second side of the membrane electrode assembly, and the coolant flow channel is configured so that a coolant flows from the second side to the first side of the membrane electrode assembly.

[0008] In another aspect, the present disclosure provides a method for operating a fuel cell, the fuel cell comprising: an anode separator; a cathode separator; a membrane electrode assembly including an anode, a cathode, and an electrolyte membrane and disposed between the anode separator and the cathode separator; a fuel gas flow channel provided between the anode and the anode separator; and an oxidant gas flow channel provided between the cathode and the cathode separator, the method comprising cooling the membrane electrode assembly so that a difference between a temperature of the oxidant gas and a dew point of the oxidant gas at an outlet of the oxidant gas flow channel is 2°C or less.

[0009] According to the present disclosure, it is possible to achieve a more uniform current density distribution in a fuel cell.

[0010] Schematic cross-sectional view of a fuel cell stack in Embodiment 1. First plan view of an anode separator. Plan view of a cathode separator. Second plan view of an anode separator. Second plan view of an anode separator showing another shape of a refrigerant channel. Graph showing the relationship between the difference between the temperature and dew point of an oxidant gas and the performance of a fuel cell.

[0011] (Knowledge, etc., that Forms the Basis of the Present Disclosure) When the present inventors arrived at the present disclosure, it was believed that improving the gas diffusion property of the cathode catalyst layer would lead to improved fuel cell performance from the perspective of oxygen supply. In recent years, it has been discovered that excessively improving the gas diffusion property of the cathode catalyst layer dries out the electrolyte membrane and cathode catalyst layer, resulting in reduced performance. For this reason, it has been common to adjust the physical properties of the cathode gas diffusion layer to control the moisture content of the cathode catalyst layer. However, changing the physical properties of the cathode gas diffusion layer changes the moisture content of the cathode catalyst layer across the entire surface of the membrane electrode assembly. Therefore, it has not been easy to increase the efficiency of the electrochemical reaction across the entire cathode catalyst layer. Improving the gas diffusion property of the cathode catalyst layer conflicts with improving the moisture content of the cathode catalyst layer to improve proton conductivity, making it difficult to achieve both goals using conventional thinking.

[0012] Under these circumstances, the inventors came up with the idea of ​​increasing the humidity of the oxidant gas and the water content of the cathode gas diffusion layer to improve the proton conductivity of the cathode catalyst layer facing the downstream region of the oxidant gas flow channel. By improving the proton conductivity of the cathode catalyst layer facing the downstream region of the oxidant gas flow channel, it is possible to make the current density distribution in the in-plane direction of the membrane electrode assembly uniform.

[0013] 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.

[0014] 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.

[0015] First Embodiment Hereinafter, a first embodiment will be described with reference to FIGS. 1 to 5. FIG.

[0016] 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.

[0017] 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.

[0018] The membrane electrode assembly 10 can also be used in other electrochemical devices, such as a hydrogen purification device that purifies hydrogen.

[0019] 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.

[0020] The membrane electrode assembly 10 may include a frame 19. The frame 19 is disposed around the membrane electrode assembly 10 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 may be a metal member, a resin member, or a member made by combining these.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] The anode gas diffusion layer 15 has a function of supplying a fuel gas (anode gas) to the anode catalyst layer 14 and a 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.

[0025] 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.

[0026] The technology of the present disclosure is particularly useful when mesoporous carbon particles are used as catalyst particle supports. Generally, mesoporous carbon particles have a larger particle diameter than solid carbon particles. The particle diameter of mesoporous carbon particles tends to be larger than the particle diameter of carbon particles contained in, for example, the cathode gas diffusion layer 18. Therefore, when mesoporous carbon particles are used in the cathode catalyst layer 17, water tends to accumulate in the voids between the mesoporous carbon particles. Specifically, the capillary pressure P, which serves as the driving force for water migration, is expressed by the following formula (A), so water easily migrates from the cathode gas diffusion layer 18 to the cathode catalyst layer 17 throughout the entire surface. This makes it difficult to appropriately adjust the moisture content of the cathode catalyst layer 17 facing the downstream region of the oxidant gas flow field 50.

[0027] P = 2σ cos θ / r (A) σ: surface tension of liquid water θ: contact angle of liquid water r: radius of pore

[0028] The average particle diameter of the mesoporous carbon particles is, for example, in the range of 100 nm to 3 μm. When mesoporous carbon particles are used, the thickness of the cathode catalyst layer 17 is, for example, in the range of 5 μm to 50 μm.

[0029] The particle diameter of the mesoporous carbon particles and the thickness of the cathode catalyst layer 17 can be measured by the following method. Specifically, a cross section of the cathode catalyst layer 17 in the thickness direction is formed using a focused ion beam (FIB). The cross section is then observed using a scanning electron microscope (SEM). The thickness is measured at any number of positions (e.g., three or more), and the average of the measured values ​​can be regarded as the thickness of the cathode catalyst layer 17. The average particle diameter of the mesoporous carbon particles can be calculated, for example, by image processing the areas of multiple mesoporous carbon particles (e.g., 10 or more) that appear in an SEM image. The diameter (equivalent diameter) of a circle having an area equal to the average of the calculated areas can be regarded as the average particle diameter of the mesoporous carbon particles.

[0030] The cathode gas diffusion layer 18 has a function of supplying an oxidant gas (cathode gas) to the cathode catalyst layer 17 and a 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.

[0031] 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.

[0032] 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.

[0033] An oxidant gas flow field 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 field 50. In this embodiment, a groove is provided in the cathode separator 30 as the oxidant gas flow field 50. However, the oxidant gas flow field 50 may be formed of a member separate from the cathode separator 30.

[0034] 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.

[0035] 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, a groove is provided in the anode separator 20 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 that contacts the anode 13 is the first surface, and the surface that contacts the cathode separator 30 is the second surface.

[0036] The coolant flow path 60 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.

[0037] 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. The coolant flow channel 60 is configured so that the coolant flows from the second side to the first side of the membrane electrode assembly 10. That is, the fuel gas flows counter to the coolant, and the oxidant gas flows counter to the coolant. This configuration can strengthen cooling of the downstream regions of the fuel gas flow channel 40 and the oxidant gas flow channel 50 and increase the humidity of the fuel gas and the oxidant gas in the downstream regions. Increasing the humidity of the oxidant gas in the downstream regions increases the moisture content of the cathode gas diffusion layer 18 facing the downstream region of the oxidant gas flow channel 50 and improves the proton conductivity of the cathode catalyst layer 17. As a result, the current density in the downstream region of the oxidant gas flow channel 50 can be increased, and ultimately, the current density distribution in the in-plane direction of the membrane electrode assembly 10 can be made uniform.

[0038] The fuel gas flow field 40 has an inlet 40a and an outlet 40b. The oxidant gas flow field 50 has an inlet 50a and an outlet 50b. The coolant flow field 60 has an inlet 60a and an outlet 60b. The inlet 40a of the fuel gas flow field 40, the inlet 50a of the oxidant gas flow field 50, and the outlet 60b of the coolant flow field 60 are located on a first side of the membrane electrode assembly 10. The outlet 40b of the fuel gas flow field 40, the outlet 50b of the oxidant gas flow field 50, and the inlet 60a of the coolant flow field 60 are located on a second side of the membrane electrode assembly 10. With this configuration, the coolant flow can be directed opposite the flows of the fuel gas and the oxidant gas. This increases the degree of cooling in the downstream regions of the fuel gas flow field 40 and the oxidant gas flow field 50, and increases the humidity of the fuel gas and the oxidant gas in the downstream regions.

[0039] 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.

[0040] 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 and the oxidant gas flow from the upper side to the lower side in the vertical direction, and the coolant flows from the lower side to the upper side in the vertical direction.

[0041] 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.

[0042] 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 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.

[0043] In this embodiment, an outlet 60b of the coolant flow path 60 is provided at one end of the fuel cell 100 in the Z direction. An inlet 60a of the coolant 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 coolant 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 coolant to be supplied to the coolant flow path 60 from outside the fuel cell stack 200, and allows the coolant to be discharged from the coolant flow path 60 to outside the fuel cell stack 200.

[0044] 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 including a plurality of first portions 41 and a plurality of second portions 42. The first portions 41 extend in a direction from the first side (upper side in the figure) of the membrane electrode assembly 10 toward the second side (lower side in the figure). The first portions 41 may have an arc shape in plan view. The second portions 42 extend in a direction perpendicular to the direction from the first side to the second side of the membrane electrode assembly 10. This configuration allows fuel gas to be supplied to every corner of the anode 13.

[0045] 3 is a plan view of the cathode separator 30. In this embodiment, the oxidant gas flow field 50 is a serpentine flow field including a plurality of first portions 51 and a plurality of second portions 52. The first portions 51 extend in a direction from the first side (upper side in the figure) of the membrane electrode assembly 10 to the second side (lower side in the figure). The first portions 51 may have an arc shape in a plan view. The second portions 52 extend in a direction perpendicular to the direction from the first side to the second side of the membrane electrode assembly 10. With this configuration, the oxidant gas can be supplied to every corner of the cathode 16.

[0046] 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 to efficiently advance the electrochemical reaction in the membrane electrode assembly 10.

[0047] 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 second portion 42 of the fuel gas flow field 40 is opposite to the flow direction of the oxidant gas in the second portion 52 of the oxidant gas flow field 50. This configuration makes it easier to efficiently advance the electrochemical reaction in the membrane electrode assembly 10.

[0048] The fuel cell stack 200 is installed such that the Z direction is parallel to the vertical direction, for example. In this case, the second portion 42 of the fuel gas flow field 40 and the second portion 52 of the oxidant gas flow field 50 are 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 including a plurality of first portions 61 and a plurality of second portions 62. The first portions 61 extend in a direction from the second side (lower side in the figure) of the membrane electrode assembly 10 toward the first side (upper side in the figure). The first portions 61 may have an arc shape in plan view. The second portions 62 extend in a direction perpendicular to the direction from the second side to the first side of the membrane electrode assembly 10. This configuration enables uniform cooling of the membrane electrode assembly 10 and improves the efficiency of exhaust heat recovery.

[0050] Figure 5 is a second plan view of the anode separator 20, showing another shape of the refrigerant flow path 60. In the example shown in Figure 5, the refrigerant flow path 60 is not serpentine, but has multiple portions extending in a direction from the second side (the lower side in the figure) of the membrane electrode assembly 10 to the first side (the upper side in the figure). With this configuration, the pressure loss in the refrigerant flow path 60 can be reduced, allowing the refrigerant to flow smoothly through the refrigerant flow path 60.

[0051] [1-2. Operation] The operation and function of the fuel cell stack 200 configured as above will be described below with reference to FIG.

[0052] 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.

[0053] At the anode 13, hydrogen (H) 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):

[0054] H2 → 2H+ +2e - (1) 4H + + O2 + 2e - → 2H2O (2)

[0055] In this embodiment, the difference between the temperature of the oxidant gas and the dew point of the oxidant gas at the outlet 50b of the oxidant gas flow field 50 is 2° C. or less. In other words, the membrane electrode assembly 10 is cooled by flowing a refrigerant through the refrigerant flow field 60 so that the difference is 2° C. or less.

[0056] In the upstream regions of the fuel gas flow channel 40 and the oxidant gas flow channel 50, the fuel gas and the oxidant gas are easily supplied to the membrane electrode assembly 10, so that the membrane electrode assembly 10 tends to exhibit a high current density in these upstream regions.

[0057] It would seem preferable to have the coolant flow in the opposite direction to that of this embodiment, that is, from the first side (upper side) to the second side (lower side), because this would allow preferential cooling of the areas exhibiting high current density. However, as a result of further investigations using computer simulations, the inventors of the present invention found that the moisture content of the cathode gas diffusion layer is low and the current density is also low in the downstream regions of the fuel gas flow path and the oxidant gas flow path.

[0058] In this embodiment, the coolant flows from the second side (lower side) to the first side (upper side), opposite to the flow directions of the fuel gas and the oxidant gas. This configuration enhances cooling of the downstream regions of the fuel gas flow channel 40 and the oxidant gas flow channel 50, thereby increasing the humidity of the fuel gas and the oxidant gas in the downstream regions. Increasing the humidity of the oxidant gas in the downstream regions increases the moisture content of the cathode gas diffusion layer 18 facing the downstream region of the oxidant gas flow channel 50, thereby improving the proton conductivity of the cathode catalyst layer 17. As a result, the current density in the downstream region of the oxidant gas flow channel 50 can be increased, thereby uniforming the current density distribution in the in-plane direction of the membrane electrode assembly 10. Uniformizing the current density distribution can improve the power generation of the fuel cell 100.

[0059] To sufficiently increase the moisture content of the cathode gas diffusion layer 18 facing the downstream region of the oxidant gas flow field 50, it is desirable that the relative humidity of the oxidant gas at the outlet 50b of the oxidant gas flow field 50 be approximately 95% or higher. When the fuel cell 100 is a polymer electrolyte fuel cell, it is unlikely that the temperature of various gases will exceed 100°C. Therefore, it is assumed that the upper limit of the temperature of the oxidant gas at the outlet 50b of the oxidant gas flow field 50 is 100°C. The dew point of air at a temperature of 100°C and a relative humidity of 95% is 98.6°C. Considering factors such as oxidant gas pressure fluctuations, the moisture content of the cathode gas diffusion layer 18 can be sufficiently increased by ensuring that the difference between the temperature of the oxidant gas at the outlet 50b of the oxidant gas flow field 50 and the dew point of the oxidant gas is 2°C or less. The dew point can be determined from the dry-bulb temperature and wet-bulb temperature of the oxidant gas at the outlet 50b of the oxidant gas flow field 50. The temperature and dew point of the oxidant gas at the outlet 50b of the oxidant gas flow path 50 can be measured by inserting a temperature and humidity sensor into the outlet 50b.

[0060] If the difference between the temperature of the oxidant gas at the oxidant gas outlet 50b and the dew point of the oxidant gas exceeds 2°C, the difference can be kept below 2°C by lowering the refrigerant temperature, increasing the refrigerant flow rate, or a combination of these.

[0061] The relative humidity of the oxidant gas is preferably 95% or more, and more preferably 100%, at the outlet 50b of the oxidant gas flow field 50. With this configuration, the moisture content of the cathode catalyst layer 17 facing the downstream region of the oxidant gas flow field 50 can be more sufficiently increased.

[0062] The difference between the refrigerant temperature T1 at the inlet 60a of the refrigerant flow channel 60 and the refrigerant temperature T2 at the outlet 60b of the refrigerant flow channel 60 is, for example, 10°C or less. With this configuration, it is possible to more sufficiently increase the moisture content of the cathode catalyst layer 17 facing the downstream region of the oxidant gas flow channel 50. The lower limit of the difference between the temperatures T1 and T2 is not particularly limited and is, for example, 5°C.

[0063] [1-3. Supplementary Notes] The above description of the embodiments discloses the following techniques.

[0064] (Technology 1) A fuel cell comprising: an anode separator; a cathode separator; a membrane electrode assembly including an anode, a cathode, and an electrolyte membrane and disposed between the anode separator and the cathode separator; a fuel gas flow channel provided between the anode and the anode separator; and an oxidant gas flow channel provided between the cathode and the cathode separator, wherein the difference between the temperature of the oxidant gas and the dew point of the oxidant gas at an outlet of the oxidant gas flow channel is 2°C or less.

[0065] With this configuration, the current density distribution in the fuel cell can be made uniform.

[0066] (Technology 2) The fuel cell according to Technology 1, further comprising a coolant flow path separated from the oxidant gas flow path by the cathode separator, wherein the difference between the temperature of the coolant at an inlet of the coolant flow path and the temperature of the coolant at an outlet of the coolant flow path is 10° C. or less. With this configuration, it is possible to more sufficiently increase the moisture content of the cathode catalyst layer facing the downstream region of the oxidant gas flow path.

[0067] (Technology 3) A fuel cell comprising: an anode separator; a cathode separator; a membrane electrode assembly including an anode, a cathode, and an electrolyte membrane and disposed between the anode separator and the cathode separator; a fuel gas flow path provided between the anode and the anode separator; an oxidant gas flow path provided between the cathode and the cathode separator; and a coolant flow path provided so as to be separated from the oxidant gas flow path by the cathode separator, wherein the fuel gas flow path and the oxidant gas flow path are configured so that a fuel gas and an oxidant gas flow, respectively, flow from a first side to a second side of the membrane electrode assembly, and the coolant flow path is configured so that a coolant flows from the second side to the first side of the membrane electrode assembly.

[0068] With this configuration, the current density distribution in the fuel cell can be made uniform.

[0069] (Technology 4) A fuel cell according to Technology 3, wherein the inlet of the fuel gas flow path, the inlet of the oxidant gas flow path, and the outlet of the coolant flow path are located on the first side of the membrane electrode assembly, and the outlet of the fuel gas flow path, the outlet of the oxidant gas flow path, and the inlet of the coolant flow path are located on the second side of the membrane electrode assembly. With this configuration, the flow of the coolant can be made to oppose the flows of the fuel gas and the oxidant gas.

[0070] (Technology 5) The fuel cell according to Technology 3 or 4, wherein the flow direction of the fuel gas in the fuel gas flow field is parallel to the flow direction of the oxidant gas in the oxidant gas flow field. With this configuration, it is easy to efficiently proceed the electrochemical reaction in the membrane electrode assembly.

[0071] (Technology 6) The fuel cell according to any one of Technologies 3 to 5, wherein at the outlet of the oxidant gas flow path, the difference between the temperature of the oxidant gas and the dew point of the oxidant gas is 2° C. or less. With this configuration, the current density distribution in the fuel cell is likely to be uniform.

[0072] (Technology 7) The fuel cell according to any one of Technologies 3 to 6, wherein the difference between the temperature of the refrigerant at the inlet of the refrigerant channel and the temperature of the refrigerant at the outlet of the refrigerant channel is not more than 10° C. With this configuration, it is possible to more sufficiently increase the moisture content of the cathode catalyst layer facing the downstream region of the oxidant gas channel.

[0073] (Technology 8) The fuel cell according to any one of Techniques 3 to 7, wherein the fuel gas flow field and the oxidant gas flow field are serpentine flow fields each including a plurality of first portions extending in a direction from the first side to the second side and a plurality of second portions extending in a direction perpendicular to the direction from the first side to the second side, and when the fuel cell is viewed from a direction parallel to a thickness direction of the membrane electrode assembly, the flow direction of the fuel gas in the second portions of the fuel gas flow field is opposite to the flow direction of the oxidant gas in the second portions of the oxidant gas flow field. This configuration makes it easy to efficiently proceed with an electrochemical reaction in the membrane electrode assembly.

[0074] (Technology 9) The fuel cell according to any one of Technologies 1 to 8, wherein the relative humidity of the oxidant gas at the outlet of the oxidant gas flow field is 95% or more. With this configuration, it is possible to more sufficiently increase the moisture content of the cathode catalyst layer facing the downstream region of the oxidant gas flow field.

[0075] (Technology 10) The fuel cell according to any one of Technologies 1 to 8, wherein the relative humidity of the oxidant gas at the outlet of the oxidant gas flow field is 100%. With this configuration, it is possible to more sufficiently increase the moisture content of the cathode catalyst layer facing the downstream region of the oxidant gas flow field.

[0076] (Technology 11) A method for operating a fuel cell, the fuel cell comprising: an anode separator; a cathode separator; a membrane electrode assembly including an anode, a cathode, and an electrolyte membrane and disposed between the anode separator and the cathode separator; a fuel gas flow path provided between the anode and the anode separator; and an oxidant gas flow path provided between the cathode and the cathode separator, the method comprising cooling the membrane electrode assembly so that a difference between a temperature of the oxidant gas and a dew point of the oxidant gas at an outlet of the oxidant gas flow path is 2°C or less.

[0077] The change in performance of the fuel cell 100 (see FIGS. 1 to 4) when the difference (°C) between the oxidant gas temperature and the oxidant gas dew point was changed was examined by simulation. The software used in the simulation was "ANSYS-X (FLUENT)" manufactured by ANSYS, Inc. The conditions for the fuel gas, oxidant gas, and electrolyte membrane 12 were set as follows:

[0078] (Inlet 40a of fuel gas flow path 40) Fuel gas flow rate 1 NLM (Normal Litter / Min), temperature 60°C, relative humidity 90% (Inlet 50a of oxidant gas flow path 50) Oxidant gas flow rate 3 NLM (Normal Litter / Min), temperature 60°C, relative humidity 90% (Electrolyte membrane 12) The temperature of the top edge (Z direction side) of the electrolyte membrane 12 was set to 65°C, and the temperature of the bottom edge (-Z direction side) of the electrolyte membrane 12 was set to 70°C to 80°C. The temperature was changed linearly and at equal intervals between the top edge and bottom edge of the electrolyte membrane 12.

[0079] The temperatures of the fuel gas, the oxidant gas, and the electrolyte membrane 12 were all increased in the -Z direction. The temperature and dew point at the outlet 50b of the oxidant gas flow field 50 were calculated when the temperature of the bottom edge of the electrolyte membrane 12 was changed from 70°C to 80°C. The difference between the temperature and the dew point at the outlet 50b of the oxidant gas flow field 50 at this time was defined as the "difference between the temperature and dew point of the oxidant gas."

[0080] Under the above conditions, the voltage of the fuel cell 100 was output, and the relationship between the difference between the temperature of the oxidant gas and the dew point was examined. The results are shown in FIG.

[0081] FIG. 6 is a graph showing the relationship between the difference between the temperature and dew point of the oxidant gas and the performance of the fuel cell. The vertical axis shows the voltage difference from the reference voltage. Specifically, the vertical axis shows the value obtained by subtracting the reference voltage from the cell voltage of each example. The horizontal axis shows the difference between the temperature and dew point of the oxidant gas. The cell voltage of Example 4 was used as the reference voltage. Example 4 shows the results of a simulation in which the difference between the temperature of the oxidant gas at the outlet of the oxidant gas flow channel and the dew point of the oxidant gas was set to 3.5°C. As shown in FIG. 6, the voltage difference tended to increase as the difference between the temperature of the oxidant gas at the outlet of the oxidant gas flow channel and the dew point of the oxidant gas decreased. In particular, when the difference between the temperature of the oxidant gas and the dew point of the oxidant gas was 2°C or less (Examples 1, 2, and 3), the voltage difference was sufficiently large.

[0082] The technology of the present disclosure is useful for electrochemical devices such as secondary batteries, fuel cells, and hydrogen purification devices.

Claims

1. An anode separator, a cathode separator, 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 path provided between the anode and the anode separator, an oxidant gas flow path provided between the cathode and the cathode separator, and the difference between the temperature of the oxidant gas and the dew point of the oxidant gas being 2°C or less at the outlet of the oxidant gas flow path. A fuel cell.

2. The fuel cell according to claim 1, further comprising a refrigerant flow path provided so as to be separated from the oxidant gas flow path by the cathode separator, and the difference between the temperature of the refrigerant at the inlet of the refrigerant flow path and the temperature of the refrigerant at the outlet of the refrigerant flow path being 10°C or less.

3. An anode separator, a cathode separator, 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 path provided between the anode and the anode separator, an oxidant gas flow path provided between the cathode and the cathode separator, a refrigerant flow path provided so as to be separated from the oxidant gas flow path by the cathode separator, the fuel gas flow path and the oxidant gas flow path being configured such that the fuel gas and the oxidant gas each flow from the first side to the second side of the membrane electrode assembly, and the refrigerant flow path being configured such that the refrigerant flows from the second side to the first side of the membrane electrode assembly. A fuel cell.

4. The inlet of the fuel gas flow path, the inlet of the oxidant gas flow path, and the outlet of the refrigerant flow path are located on the first side of the membrane electrode assembly, and the outlet of the fuel gas flow path, the outlet of the oxidant gas flow path, and the inlet of the refrigerant flow path are located on the second side of the membrane electrode assembly. The fuel cell according to claim 3.

5. The fuel cell according to claim 3, wherein the flow direction of the fuel gas in the fuel gas flow path is parallel to the flow direction of the oxidant gas in the oxidant gas flow path.

6. The fuel cell according to claim 3, wherein the difference between the temperature of the oxidant gas and the dew point of the oxidant gas is 2°C or less at the outlet of the oxidant gas flow path.

7. The fuel cell according to claim 3, wherein a difference between the temperature of the refrigerant at the inlet of the refrigerant flow path and the temperature of the refrigerant at the outlet of the refrigerant flow path is 10°C or less.

8. The fuel gas flow path and the oxidant gas flow path are each a meandering flow path including a plurality of first portions extending in a direction from the first side toward the second side and a plurality of second portions extending in a direction perpendicular to the direction from the first side toward the second side. When the fuel cell is viewed from a direction parallel to the thickness direction of the membrane electrode assembly, the flow direction of the fuel gas in the second portion of the fuel gas flow path is opposite to the flow direction of the oxidant gas in the second portion of the oxidant gas flow path. The fuel cell according to claim 3.

9. The fuel cell according to claim 1 or 3, wherein the relative humidity of the oxidant gas at the outlet of the oxidant gas flow path is 95% or more.

10. The fuel cell according to claim 1 or 3, wherein the relative humidity of the oxidant gas at the outlet of the oxidant gas flow path is 100%.

11. A method for operating a fuel cell, the fuel cell including an anode separator, a cathode separator, an anode, a cathode, and an electrolyte membrane, a membrane electrode assembly disposed between the anode separator and the cathode separator, a fuel gas flow path provided between the anode and the anode separator, and an oxidant gas flow path provided between the cathode and the cathode separator. The method for operating the fuel cell includes cooling the membrane electrode assembly such that a difference between the temperature of the oxidant gas and the dew point of the oxidant gas at the outlet of the oxidant gas flow path is 2°C or less.

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