JP7444748B2 - How to design a gas diffusion layer - Google Patents

Description

The present disclosure relates to a method for designing a gas diffusion layer.

Conventionally, there is a fuel cell in which a pair of separators forming a gas flow path are arranged on both sides of a membrane electrode gas diffusion layer assembly. An electrochemical reaction is performed by the fuel gas, which is a reactive gas, and the oxidizing gas supplied from the gas flow path, and water generated by the electrochemical reaction is discharged to the outside together with the discharged reactive gas. In conventional fuel cells, it is known that electrochemical reactions are promoted when the diffusibility of a reaction gas supplied from a gas flow path to a gas diffusion layer is improved (for example, Patent Document 1).

Japanese Patent Application Publication No. 2013-125744

When the diffusivity of the reaction gas is improved, the electrochemical reaction is promoted. On the other hand, if the diffusivity increases too much, excessive water produced by the reaction gas will be discharged to the outside, which may cause the electrolyte membrane to dry up.

The present disclosure can be realized as the following forms.
According to one embodiment of the present disclosure, a method for designing a gas diffusion layer included in a fuel cell is provided. The fuel cell includes a membrane electrode gas diffusion layer assembly in which an electrolyte membrane, a catalyst electrode layer, and the gas diffusion layer are laminated, and a separator laminated on the membrane electrode gas diffusion layer assembly, a) A first channel that is recessed in a first direction away from the membrane electrode gas diffusion layer assembly, extends along the membrane surface of the membrane electrode gas diffusion layer assembly, and forms a primary flow path for supplying a reaction gas. (b) a secondary groove formed concave in the first direction, extending along the membrane surface in line with the first groove, into which the reaction gas that has passed through the membrane electrode gas diffusion layer assembly flows; a second groove forming a side flow path; (c) a rib provided between the first groove and the second groove and in contact with the membrane electrode gas diffusion layer assembly; and (d) a flow path. a separator having a constricted portion serving as a resistance, the constricted portion being predetermined in the first groove portion and the second groove portion, respectively, along the extending direction of the first groove portion and the second groove portion. A plurality of gas diffusion layers are provided at intervals such that their positions in the stretching direction do not overlap with each other, and the porosity of the gas diffusion layer is 70%. The design method includes determining the permeability of the gas diffusion layer as K [m ² ], the thickness of the gas diffusion layer as t [m], the pressure of the reaction gas flowing in the primary flow path, and the secondary flow. ΔP [Pa] is the differential pressure between the pressure of the reaction gas flowing through the channel, μ [Pa·s] is the viscosity of water at the operating temperature of the polymer electrolyte fuel cell, and is the first groove portion and the second groove portion. Assuming that the width of the rib portion at the position where the throttle portion is not provided in either of the groove portions is w [m], the following formula: Convection flow rate [cc/min] = K x t x ΔP/μ/w x 60 x 10 ⁶
the current density of the current generated by the fuel cell under predetermined power generation conditions, and the amount of liquid water that is the proportion of liquid water present in the gas diffusion layer that is in contact with the rib portion; Based on the above, the gas diffusion layer is designed such that the convection flow rate is larger than a first value and smaller than a second value, and the first value and the second value are 0 cc/min. The value is larger than 20 cc/min and is a value used for suppressing dry-up of the electrolyte membrane while the gas diffusion layer improves the diffusivity of the reaction gas and promotes the electrochemical reaction. The first value and the second value are a plurality of plot points corresponding to a plurality of samples having different convective flow rates, and the convective flow rate is plotted on the horizontal axis, and the current density and the liquid water amount are plotted on the horizontal axis. It is a value obtained from a graph including a plurality of plot points, each of which is plotted as a vertical axis, and in a range where the convective flow rate is larger than the second value, than in a range where the convective flow rate is smaller than the second value. The rate of decrease of the amount of liquid water with respect to the convection flow rate is small, and the second value is represented by the slope of a straight line connecting two adjacent plot points among the plurality of plot points with the vertical axis being the amount of liquid water. The rate of decrease is a value corresponding to the convective flow rate that changes significantly, and in a range where the convective flow rate is smaller than the first value, the convective flow rate is lower than in a range where the convective flow rate is larger than the first value. the rate of increase in the current density relative to the current density is large, the first value is smaller than the second value, and two adjacent plot points among the plurality of plot points with the vertical axis representing the current density are This is a value greater than or equal to the convective flow rate at which the rate of increase, which is indicated by the slope of the connecting straight line, changes significantly.

According to one embodiment of the present disclosure, a method for designing a gas diffusion layer included in a fuel cell is provided. The fuel cell includes a membrane electrode gas diffusion layer assembly in which an electrolyte membrane, a catalyst electrode layer, and the gas diffusion layer are laminated, and a separator laminated on the membrane electrode gas diffusion layer assembly, a) A first channel that is recessed in a first direction away from the membrane electrode gas diffusion layer assembly, extends along the membrane surface of the membrane electrode gas diffusion layer assembly, and forms a primary flow path for supplying a reaction gas. (b) a secondary groove formed concave in the first direction, extending along the membrane surface in line with the first groove, into which the reaction gas that has passed through the membrane electrode gas diffusion layer assembly flows; a separator having a second groove portion forming a side flow path; and (c) a rib portion provided between the first groove portion and the second groove portion and in contact with the membrane electrode gas diffusion layer assembly; The design method is characterized in that the permeability of the gas diffusion layer is K [m ² ], the thickness of the gas diffusion layer is t [m], the pressure of the reaction gas flowing through the primary flow path and the secondary The differential pressure that is the difference between the pressure of the reaction gas flowing through the next flow path is ΔP [Pa], the viscosity of water is μ [Pa・s], and the width of the rib portion is w [m], and the following equation is expressed as: Flow rate [cc/min] = K×t×ΔP/μ/w×60×10 ⁶
In this design method, the gas diffusion layer is designed so that the convective flow rate determined by . According to this design method, it is possible to provide a fuel cell that has good power generation efficiency and suppresses dry-up of the electrolyte membrane.
Note that the present disclosure can be realized in various forms, and in addition to the above-described form, it can be realized in the form of a fuel cell or the like including a gas diffusion layer designed using the above-described design method.

FIG. 1 is a schematic configuration diagram of a fuel cell. FIG. 4 is a sectional view taken along line II-II in FIG. 3, and is a partial sectional view of the fuel cell. FIG. 3 is a plan view of a cathode-side separator. These are the results of liquid water volume and current density with respect to convection flow rate.

A. Embodiment:
FIG. 1 is a schematic configuration diagram of a fuel cell 100 in an embodiment of the present disclosure. The fuel cell 100 uses fuel gas and oxidizing gas as reaction gases to generate electricity through an electrochemical reaction. In this embodiment, air is used as the oxidizing gas. The fuel cell 100 includes a cell stack 10 in which a plurality of fuel cells 60 are stacked, a positive electrode terminal 20, and a negative electrode terminal 30. In the fuel cell 60, a cathode separator 91 and an anode separator 92 are arranged on both sides of the membrane electrode gas diffusion layer assembly 80 (see FIG. 2). Cooling water manifolds 11a, 11b, oxidizing gas manifolds 12a, 12b, and fuel gas manifolds 13a, 13b are formed in the negative electrode terminal 30 and the cell stack 10, which penetrate in the stacking direction of the fuel cells 60. There is. Cooling water manifolds 11a, 11b, oxidizing gas manifolds 12a, 12b, and fuel gas manifolds 13a, 13b are used to supply and discharge cooling water, oxidizing gas, and fuel gas to and from the cell stack 10, respectively. The cooling water manifold 11a, the oxidizing gas manifold 12a, and the fuel gas manifold 13a are for supply, and the cooling water manifold 11b, the oxidizing gas manifold 12b, and the fuel gas manifold 13b are for discharging. The positive terminal 20 and the negative terminal 30 collect power generated by the fuel cell 60. The collected power is supplied to an external load via the positive terminal 20 and the negative terminal 30.

FIG. 2 is a partial cross-sectional view of the fuel cell 60, and is a cross-sectional view taken along the line II--II in FIG. FIG. 3 is a plan view of the cathode side separator 91. As shown in FIG. 2, the fuel cell 60 includes a membrane electrode gas diffusion layer assembly 80, a cathode separator 91, and an anode separator 92. The cathode side separator 91 and the anode side separator 92 are arranged on both sides of the membrane electrode gas diffusion layer assembly 80, respectively. The membrane electrode gas diffusion layer assembly 80 includes a membrane electrode assembly 70 and two gas diffusion layers 74 arranged on each of both surfaces of the membrane electrode assembly 70. The membrane electrode assembly 70 includes an electrolyte membrane 71 and two catalyst electrode layers 72 disposed on each side of the electrolyte membrane 71. The electrolyte membrane 71 is a solid polymer membrane, for example, a proton-conducting ion exchange membrane made of a fluororesin such as perfluorocarbon sulfonic acid polymer. The catalyst electrode layer 72 contains a catalyst that promotes electrochemical reactions, such as a platinum catalyst or a platinum alloy catalyst made of platinum and another metal. The gas diffusion layer 74 is a layer for diffusing oxidizing gas or fuel gas, and includes a gas diffusion layer base material 74a, a permeation layer 74b, and an MPL (Micro Porous Layer) 74c. The gas diffusion layer base material 74a is made of carbon fiber, for example. Note that the gas diffusion layer base material 74a is not limited to carbon fiber, and may be a metal porous body such as a metal mesh or foamed metal. The MPL74c is formed by containing, for example, carbon powder and a water-repellent resin such as polytetrafluoroethylene (PTFE). Note that the water-repellent resin is not limited to polytetrafluoroethylene, and may also be polyethylene, polypropylene, or the like. Specifically, the MPL 74c is formed by applying an MPL paste containing a mixture of carbon powder, water-repellent resin, adhesive, water, etc. to the gas diffusion layer base material 74a. The permeation layer 74b is a layer formed by permeating the MPL paste into the gas diffusion layer base material 74a. The two gas diffusion layers 74 are arranged on each of both sides of the membrane electrode assembly 70 such that the MPL 74c is in contact with the membrane electrode assembly 70.

The cathode side separator 91 and the anode side separator 92 are formed, for example, by pressing a metal plate member. The cathode separator 91 has a plurality of grooves 91a, ribs 91b, and a constricted portion 91c that serves as flow path resistance. The plurality of groove portions 91a are formed to be recessed toward a first direction away from the membrane electrode gas diffusion layer assembly 80 that is in contact with the groove portions 91a. Further, the plurality of groove portions 91a extend along the direction from the front to the back of the paper in FIG. 2, among the directions along the membrane surface of the membrane electrode gas diffusion layer assembly 80. The rib portion 91b is provided between adjacent groove portions 91a and is in contact with the membrane electrode gas diffusion layer assembly 80. Like the groove portion 91a, the constricted portion 91c is formed to be recessed toward the first direction away from the membrane electrode gas diffusion layer assembly 80. As shown in FIG. 3, in this embodiment, a plurality of grooves 91a having the same width are arranged at equal intervals in a direction perpendicular to the stretching direction. A plurality of narrowed portions 91c are arranged at predetermined intervals in the extending direction of the groove portion 91a. Further, the constricted portions 91c arranged in adjacent groove portions 91a are arranged so that the positions in the extending direction of the groove portions 91a do not overlap with each other. Specifically, in this embodiment, the constricted portion 91c of the adjacent groove portion 91a is disposed approximately at the center of two adjacent constricted portions 91c disposed in the same groove portion 91a. The constriction portion 91c is provided to obstruct the flow of oxidizing gas. The flow passage cross-sectional area of the throttle portion 91c is smaller than the flow passage cross-sectional area of the groove portion 91a. In this embodiment, the width of the constricted portion 91c is narrower than the width of the groove portion 91a. Further, in this embodiment, as shown in FIG. 2, the depth of the constricted portion 91c is smaller than the depth of the groove portion 91a. The space surrounded by the groove portion 91a and the membrane electrode gas diffusion layer assembly 80 is the oxidizing gas flow path 41. The anode side separator 92 is formed similarly to the cathode side separator 91. The anode side separator 92 has a groove portion 92a and a rib portion 92b. A space surrounded by the groove portion 92a and the membrane electrode gas diffusion layer assembly 80 is the fuel gas flow path 42. A space surrounded by the rib portions 91b, 92b and groove portions 91a, 92a of the cathode side separator 91 and the anode side separator 92, which are adjacent to each other in the stacking direction of the membrane electrode gas diffusion layer assembly 80, is the cooling water flow path 43.

As shown in FIG. 3, the cathode side separator 91 has connection parts 91d and 91e and openings 911 to 916 in addition to the above-described configuration. The openings 911 to 916 are through holes formed at the outer edge of the cathode side separator 91, and each form a part of the various manifolds 11a, 11b, 12a, 12b, 13a, and 13b shown in FIG. The openings 911, 913, 915 and the openings 912, 914, 916 are arranged facing each other with the groove 91a in between. The connecting portion 91d is recessed in the same direction as the groove portion 91a so as to connect the plurality of groove portions 91a and the opening portion 913. Thereby, the oxidizing gas flowing in from the opening 913 forming the manifold 12a flows through the oxidizing gas flow path 41 formed by the groove 91a. Similarly, the connecting portion 91e is recessed in the same direction as the groove portion 91a so as to connect the plurality of groove portions 91a and the opening portion 914. As a result, the oxidizing gas flowing through the oxidizing gas flow path 41 formed by the groove 91a flows out from the opening 914 forming the manifold 12b.

The arrows drawn in the groove 91a in FIG. 3 indicate the flow of the oxidizing gas, and the magnitude of the flow rate is expressed by the magnitude of the arrow. Since the flow passage cross-sectional area of the constricted portion 91c is smaller than the flow passage cross-sectional area of the groove portion 91a, the flow of the oxidizing gas flowing through the groove portion 91a is blocked by the constricted portion 91c. The circulating oxidizing gas becomes difficult to move straight before the constricted portion 91c, so it sneaks into the gas diffusion layer 74 and flows to the adjacent groove portion 91a via the gas diffusion layer 74. The reason why the water flows to the adjacent groove portion 91a is that the adjacent groove portion 91a does not have a constriction portion 91c on the downstream side and has less flow resistance and thus flows easily. The arrows drawn in FIG. 2 indicate the flow of oxidizing gas. The oxidizing gas whose flow is blocked by the constricted portion 91c diffuses toward the catalyst electrode layer 72, is partially consumed by an electrochemical reaction, and flows into the adjacent groove portion 91a. Here, for convenience, the oxidizing gas flow path 41 through which the oxidizing gas flows out to the gas diffusion layer 74 due to the presence of the constriction part 91c will be referred to as the primary side flow path 41a, and the presence of the constriction part 91c will refer to the oxidizing gas flow path 41 as the primary side flow path 41a. The oxidizing gas flow path 41 into which the oxidizing gas flows from 74 is referred to as a secondary flow path 41b. Furthermore, the groove 91a forming the primary flow path 41a is referred to as a first groove 191a, and the groove 91a forming the secondary flow path 41b is referred to as a second groove 291a. More specifically, as shown in FIG. 3, when the groove portions 91a are divided in the stretching direction at intervals of the constricted portions 91c, the section where the constricted portions 91c are present is the first groove portion 191a, and the section where the constricted portions 91c are not present. The section is the second groove portion 291a.

Arrows a, b, and c shown in FIG. 2 indicate the flow of oxidizing gas. Arrow a indicates a flow that diffuses from the primary flow path 41a toward the catalyst electrode layer 72. Arrow b indicates a flow from the primary flow path 41a to the adjacent secondary flow path 41b. Arrow c indicates the flow drawn into the secondary flow path 41b. Water generated by the electrochemical reaction (hereinafter referred to as generated water) is discharged from the secondary flow path 41b to the outside together with the oxidizing gas flowing toward the secondary flow path 41b, as shown by arrows b and c. is discharged. When the diffusivity of the oxidizing gas to the gas diffusion layer 74 improves, the electrochemical reaction is promoted, and thus the power generation efficiency is improved. On the other hand, if the diffusivity of the oxidizing gas increases too much, the discharge of generated water is also promoted, so the electrolyte membrane 71 dries, hydrogen ion conductivity decreases, and power generation performance decreases, resulting in so-called dry-up. There is a risk. Therefore, the inventors conducted experiments to find an appropriate flow rate of the oxidizing gas flowing from the primary flow path 41a to the secondary flow path 41b. In the following description, the flow from the primary flow path 41a toward the secondary flow path 41b, indicated by arrow b, will be referred to as "convection", and the flow rate of this convection will be referred to as "convection flow rate".

The following equation (1) was used to calculate the convection amount.
Convection flow rate [cc/min] = K×t×ΔP/μ/w×60×10 ⁶ ...Equation (1)
The parameters in equation (1) are as follows.
K: permeability of gas diffusion layer 74 [m ² ]
t: Thickness of gas diffusion layer base material 74a [m]
ΔP: Differential pressure between the pressure in the primary flow path 41a and the pressure in the secondary flow path 41b [Pa]
μ: Viscosity of produced water [Pa・s]
w: Width of rib portion 91b [m]
In this embodiment, the thickness of the gas diffusion layer base material 74a is used as the thickness of the gas diffusion layer 74. The differential pressure ΔP is a value obtained by subtracting the pressure in the secondary flow path 41b from the pressure in the primary flow path 41a determined by simulation. The simulation was performed using the three-dimensional flow path structure of the primary flow path 41a and the secondary flow path 41b, power generation conditions, and the like as input conditions. Specifically, a range of flow path structures including the primary flow path 41a and the secondary flow path 41b was used for the simulation. The power generation conditions include, for example, current density, flow rates of oxidizing gas and fuel gas, and temperature. Specifically, a value calculated by the following method was used for the rib width w. The intersection points CP1 and CP2 of the line indicating the position of half the depth of the groove portion 91a shown by the broken line in FIG. The distance between the intersection points CP1 and CP2 of the groove portion 91a was defined as the rib width w.

In order to investigate the relationship between the convection flow rate, the current density, and the amount of liquid water contained in the gas diffusion layer 74, various fuel cells 100 were fabricated so as to have various convection flow rates. Specifically, a plurality of cathode-side separators 91 were manufactured in which the flow path cross-sectional areas of the constricted portions 91c had various cross-sectional areas so that the differential pressure ΔP in equation (1) had various values. Furthermore, two types of gas diffusion layers 74 different from each other were used as the gas diffusion layer 74. FIG. 4 shows the results of current density and liquid water amount versus convective flow rate. Here, the amount of liquid water refers to the proportion of liquid water present in the gas diffusion layer base material 74a that is in contact with the rib portion 91b, and the state in which all the voids in the gas diffusion layer base material 74a are filled with liquid water. This is a value calculated with 100%. Note that in this embodiment, a gas diffusion layer base material 74a with a porosity of about 70% is used. The amount of liquid water was measured using X-ray radiography. The current density was measured under constant power generation conditions. Sample A and sample B in FIG. 4 correspond to two different types of gas diffusion layers 74, respectively.

As shown in FIG. 4, regardless of the type of gas diffusion layer 74, the current density and the amount of liquid water exhibit the same behavior with respect to changes in the convective flow rate. If there is liquid water in the gas diffusion layer 74, the supply of oxidizing gas from the gas diffusion layer 74 to the catalyst electrode layer 72 will be inhibited, so the amount of liquid water is preferably small. The liquid water amount decreases significantly with respect to the convection flow rate in a range where the convection flow rate is greater than 0 [cc/min] and smaller than 7 [cc/min]. However, in a range larger than 7 [cc/min], the rate of decrease in the amount of liquid water relative to the convection flow rate is smaller than in a range smaller than 7 [cc/min]. In a range where the convection flow rate is greater than 7 [cc/min], even if the convection flow rate is increased, the amount of liquid water does not decrease much. In this embodiment, in order to increase the convection flow rate, the cross-sectional area of the flow path of the constriction part 91c is made small, so that the pressure loss in the primary side flow path 41a increases as the convection flow rate increases. In view of the above, when the convection flow rate is made larger than 7 [cc/min], it is thought that the disadvantage of increasing pressure loss in the primary flow path 41a becomes greater than the advantage of decreasing the amount of liquid water. .

The larger the convection amount, the larger the current density. This is considered to be because the larger the convection flow rate, the more liquid water is discharged from the gas diffusion layer 74, the more easily the oxidizing gas is supplied, and the more diffusivity of the oxidizing gas improves. In particular, the rate of increase in current density relative to the convection flow rate is high in a range where the convection flow rate is greater than 0 [cc/min] and smaller than 4 [cc/min]. In other words, when the convection flow rate becomes smaller than 4 [cc/min], the current density suddenly becomes smaller. Accordingly, it is considered that the convection flow rate is preferably larger than 4 [cc/min]. Furthermore, in a range where the convection flow rate is greater than 7 [cc/min], the rate of increase in current density relative to the convection flow rate is greater than the rate of increase in the range where the convection flow rate is greater than 4 [cc/min] and smaller than 7 [cc/min]. also decreases. As mentioned above, in a range where the convection flow rate is greater than 7 [cc/min], the amount of liquid water does not decrease much. Therefore, in a range where the convection flow rate is greater than 7 [cc/min], the disadvantage of increasing pressure loss in the primary flow path 41a becomes greater than the advantage of decreasing the amount of liquid water and increasing the current density. It is thought that it will be put away. Moreover, if the convection flow rate is set to a range smaller than 7 [cc/min], discharge of excessive generated water is suppressed, and therefore dry-up of the electrolyte membrane 71 is suppressed. To summarize the above, it is considered that it is good to design the gas diffusion layer 74 so that the convection flow rate is greater than 4.0 [cc/min] and smaller than 7.0 [cc/min].

According to the embodiment described above, the gas diffusion layer 74 is designed so that the convective flow rate calculated by equation (1) is greater than 4.0 [cc/min] and smaller than 7.0 [cc/min]. By doing so, it is possible to provide a fuel cell 100 that has good power generation efficiency and suppresses dry-up of the electrolyte membrane 71.

B. Other embodiments:
(B1) In the embodiment described above, in the cathode side separator 91, the narrowed portions 91c are arranged in the grooves 91a at equal intervals in all the grooves 91a. However, the present invention is not limited to this, and for example, the arrangement interval and number of the narrowed portions 91c may be different between the center portion and the outer edge portion of the cathode side separator 91. Even in this case, by designing the gas diffusion layer 74 for each portion, the fuel cell 100 can have good power generation efficiency and suppress dry-up of the electrolyte membrane 71.

(B2) In the above embodiment, the design method for the cathode side separator 91 has been described, but the design method of the present disclosure can also be applied to the design of the anode side separator 92.

(B3) In the above embodiment, all the grooves 91a of the cathode side separator 91 are connected to both the opening 913 and the opening 914, and due to the arrangement of the throttle part 91c, one groove 91a is connected to the primary flow path. 41a and a secondary flow path 41b. In contrast, the grooves 91a connected only to the opening 913 and the grooves 91a connected only to the opening 914 are arranged alternately, and the grooves 91a connected to the opening 913 are connected to the primary flow path. The design method of the present disclosure can also be applied to the cathode separator 91 having a configuration in which the groove 91a connected to the opening 914 functions as the secondary flow path 41b.

The present disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from the spirit thereof. For example, the technical features of the embodiments corresponding to the technical features in each form described in the column of the summary of the invention may be Alternatively, in order to achieve all of the above, it is possible to perform appropriate replacements or combinations. Further, unless the technical feature is described as essential in this specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10... Cell stacked body, 11a, 11b... Cooling water manifold, 12a, 12b... Oxidizing gas manifold, 13a, 13b... Fuel gas manifold, 20... Positive electrode terminal, 30... Negative electrode terminal, 41... Oxidizing gas flow path, 41a... Primary Side channel, 41b... Secondary channel, 42... Fuel gas channel, 43... Cooling water channel, 60... Fuel cell, 70... Membrane electrode assembly, 71... Electrolyte membrane, 72... Catalyst electrode layer, 74 ... Gas diffusion layer, 74a... Gas diffusion layer base material, 74b... Penetration layer, 74c... MPL, 80... Membrane electrode gas diffusion layer assembly, 91... Cathode side separator, 91a, 92a... Groove, 91b, 92b... Rib part, 91c...diaphragm part, 91d, 91e...connection part, 92...anode side separator, 100...fuel cell, 191a...first groove part, 291a...second groove part, 911-916...opening part

Claims (1)

A method for designing a gas diffusion layer of a fuel cell, the method comprising:
The fuel cell includes:
A membrane electrode gas diffusion layer assembly in which an electrolyte membrane, a catalyst electrode layer, and the gas diffusion layer are laminated;
A separator laminated on the membrane electrode gas diffusion layer assembly, the separator being (a) recessed in a first direction away from the membrane electrode gas diffusion layer assembly, the separator having a membrane surface of the membrane electrode gas diffusion layer assembly; (b) a first groove extending along the membrane surface and forming a primary flow path for supplying the reaction gas; (c) a second groove portion forming a secondary flow path into which the reaction gas flowing through the membrane electrode gas diffusion layer assembly flows; and (c) a second groove portion provided between the first groove portion and the second groove portion; A separator having a rib portion in contact with the membrane electrode gas diffusion layer assembly, and (d) a constriction portion serving as flow path resistance,
A plurality of the narrowed portions are arranged in the first groove portion and the second groove portion at predetermined intervals along the stretching direction of the first groove portion and the second groove portion so that the positions in the stretching direction do not overlap with each other. It is provided,
The porosity of the gas diffusion layer is 70%,
The design method includes:
The permeability of the gas diffusion layer is K [m ² ], the thickness of the gas diffusion layer is t [m], the pressure of the reaction gas flowing through the primary flow path and the reaction flowing through the secondary flow path. The differential pressure that is the difference between the gas pressure and the gas pressure is ΔP [Pa], the viscosity of water at the operating temperature of the polymer electrolyte fuel cell is μ [Pa・s], and both the first groove part and the second groove part The width of the rib portion at the position where the throttle portion is not provided is w [m], and the following formula is used: Convection flow rate [cc/min] = K x t x ΔP/μ/w x 60 x 10 ⁶
the current density of the current generated by the fuel cell under predetermined power generation conditions, and the amount of liquid water that is the proportion of liquid water present in the gas diffusion layer that is in contact with the rib portion; Based on the above, the gas diffusion layer is designed such that the convection amount is larger than a first value and smaller than a second value,
The first value and the second value are larger than 0 cc/min and smaller than 20 cc/min, and the gas diffusion layer improves the diffusivity of the reaction gas and promotes the electrochemical reaction. , is a value used to suppress dry-up of the electrolyte membrane,
The first value and the second value are a plurality of plot points corresponding to a plurality of samples having different convective flow rates, wherein the convective flow rate is plotted on the horizontal axis, and the current density and the liquid water amount are plotted on the horizontal axis, respectively. It is a value obtained from a graph containing multiple plot points plotted as the vertical axis,
In a range where the convection flow rate is larger than the second value, a decreasing rate of the liquid water amount with respect to the convection flow rate is smaller than in a range where the convection flow rate is smaller than the second value,
The second value corresponds to the convective flow rate at which the rate of decrease, which is indicated by the slope of a straight line connecting two adjacent plot points among the plurality of plot points with the liquid water amount on the vertical axis, changes significantly. is the value of
In a range where the convection amount is smaller than the first value, the rate of increase in the current density with respect to the convection amount is greater than in a range where the convection amount is larger than the first value,
The first value is smaller than the second value, and the rate of increase is represented by the slope of a straight line connecting two adjacent plot points among the plurality of plot points with the vertical axis representing the current density. The design method is a value greater than or equal to the convection flow rate that changes significantly .

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