fuel cell

Abstract

To provide a fuel battery cell which can enlarge a contact surface of a rib with a gas diffusion layer without increasing a width of the rib, and which can also prevent degradation in efficiency for discharging water from the gas diffusion layer to the outside of a fuel battery.SOLUTION: A fuel battery cell comprises a membrane-electrode gas diffusion layer assembly 12 and a separator 15. The separator 15 has a rib 21 and a groove 22 which are adjacent to each other and extend parallel to each other. The rib 21 is in contact with a gas diffusion layer 20 of the membrane-electrode gas diffusion layer assembly 12. The groove 22 defines a passage 25 for flowing a fluid between the groove and the gas diffusion layer 20. A contact surface 21a of the rib 21 with the gas diffusion layer 20 has such a shape that a recess 27 and a protrusion 28 are alternately repeated along an extension direction of the rib 21. An inner shape of the groove 22 is formed such that a circulation cross section of the fluid in the passage 25 may be smaller at a portion corresponding to the protrusion 28 than at a portion corresponding the recess 27 on the contact surface 21a of the rib 21.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] As shown in Patent Document 1, a fuel cell stack is formed by stacking fuel cells in the thickness direction. Each fuel cell includes a membrane electrode gas-diffusion assembly (MEGA) and a separator.

[0003] The membrane electrode gas diffusion layer assembly includes an electrolyte membrane, an anode electrode layer, a cathode electrode layer, and a gas diffusion layer, and is formed in a sheet shape. The anode electrode layer is bonded to one of the two sides in the thickness direction of the electrolyte membrane. A gas diffusion layer is bonded to one of the two sides in the thickness direction of the anode electrode layer opposite to the side bonded to the electrolyte membrane. This gas diffusion layer is the anode side gas diffusion layer in the membrane electrode gas diffusion layer assembly. The cathode electrode layer is bonded to the other of the two sides in the thickness direction of the electrolyte membrane. A gas diffusion layer is bonded to the other of the two sides in the thickness direction of the cathode electrode layer opposite to the side bonded to the electrolyte membrane. This gas diffusion layer is the cathode side gas diffusion layer in the membrane electrode gas diffusion layer assembly.

[0004] The separators are made of a conductive material such as metal. Two separators are arranged to sandwich the membrane electrode gas diffusion layer assembly from both sides in the thickness direction. The separators have adjacent ribs and grooves extending parallel to each other. The ribs are in contact with the gas diffusion layer of the membrane electrode gas diffusion layer assembly. The grooves form a flow path between the separator and the gas diffusion layer for the flow of a fuel gas such as hydrogen or an oxidizing gas such as air. Specifically, fuel gas flows through the flow path between the separator groove in contact with the gas diffusion layer on the anode electrode layer side and the gas diffusion layer, i.e., the anode side flow path. Meanwhile, oxidizing gas flows through the flow path between the separator in contact with the gas diffusion layer on the cathode electrode side and the gas diffusion layer, i.e., the cathode side flow path.

[0005] The fuel gas flows from the anode-side flow channel to the anode-side gas diffusion layer, where it is diffused by the gas diffusion layer and then supplied to the anode electrode layer. The oxidizing gas flows from the cathode-side flow channel to the cathode-side gas diffusion layer, where it is diffused by the gas diffusion layer and then supplied to the cathode electrode layer. Power generation is then generated by a reaction between the fuel gas and the oxidizing gas in the membrane-electrode-gas diffusion layer assembly. During this process, water is produced in the cathode electrode layer of the membrane-electrode-gas diffusion layer assembly. The water thus produced flows to the cathode-side gas diffusion layer and is then discharged from the gas diffusion layer to the outside of the fuel cell by utilizing the flow of oxidizing gas in the cathode-side flow channel. The water produced in the cathode electrode layer also flows to the anode side of the membrane-electrode-gas diffusion layer assembly. This water flows to the anode-side gas diffusion layer and is then discharged from the gas diffusion layer to the outside of the fuel cell by utilizing the flow of fuel gas in the anode-side flow channel. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5500096 Summary of the Invention [Problem to be solved by the invention]

[0007] The reaction between fuel gas and oxidizing gas in the membrane-electrode-gas diffusion layer assembly is affected by the electrical resistance between the membrane-electrode-gas diffusion layer assembly and the separator. To reduce this effect, it is effective to increase the contact area between the ribs and the gas diffusion layer, for example by increasing the width of the separator ribs. Increasing the contact area between the ribs and the gas diffusion layer in this way can reduce the electrical resistance. However, increasing the width of the ribs to increase the contact area makes it more difficult for water at the location of the gas diffusion layer corresponding to the contact area to flow into the flow path. As a result, the efficiency of discharging water from the gas diffusion layer to the outside of the coulomb cell decreases.

[0008] Patent Document 1 also describes forming irregularities on the contact surface of the rib. Forming irregularities on the contact surface in this way makes it possible to increase the contact surface without increasing the width of the rib. However, the convex portions of the contact surface further compress the gas diffusion layer, reducing the air permeability of the gas diffusion layer at the points pressed by the convex portions. This makes it difficult for water present at the points pressed by the convex portions of the gas diffusion layer to flow into the flow channels. As a result, the efficiency of discharging water from the gas diffusion layer to the fuel cell decreases. [Means for solving the problem]

[0009] The means for solving the above problems and their effects will be described below. A fuel cell that solves the above problems includes a membrane electrode gas diffusion layer assembly and a separator. The membrane electrode gas diffusion layer assembly is formed in a sheet shape. The separators are arranged to sandwich the membrane electrode gas diffusion layer assembly from both sides in the thickness direction, and include ribs and grooves that extend adjacent to each other and in parallel. The ribs are in contact with the gas diffusion layer of the membrane electrode gas diffusion layer assembly. The grooves form flow paths for fluid flow between the ribs and the gas diffusion layer. The contact surfaces of the ribs with the gas diffusion layer have a shape in which recesses and protrusions are alternately repeated along the extension direction of the ribs. The inner shape of the grooves is formed so that the cross-sectional flow area of ​​the fluid in the flow path is smaller at locations corresponding to the protrusions on the contact surfaces of the ribs than at locations corresponding to the recesses.

[0010] According to the above configuration, the ribs of the separator contact the gas diffusion layer of the membrane electrode gas diffusion layer assembly. The contact surface of the rib with the gas diffusion layer has a shape in which concave portions and convex portions alternate along the extension direction of the rib. This allows the contact surface of the rib with the gas diffusion layer to be increased without increasing the width of the rib. Furthermore, the fluid flow cross-sectional area in the grooves corresponding to the convex portions of the rib contact surface is smaller than that in the concave portions. This allows the fluid to flow faster in the grooves corresponding to the convex portions of the rib contact surface than in the concave portions. As a result, the convex portions of the rib contact surface compress the gas diffusion layer more than the concave portions. Even if the gas permeability of the gas diffusion layer at the convex portions is reduced at the convex portions, water present in the convex portions can easily flow into the flow channels. The water is then discharged to the outside of the fuel cell by utilizing the fluid flowing through the flow channels in the grooves. This allows the contact surface of the rib with the gas diffusion layer to be increased without increasing the width of the rib, and prevents a decrease in the efficiency of water discharge from the gas diffusion layer to the outside of the fuel cell. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a cross-sectional view showing a fuel cell. [Figure 2] FIG. 2 is a perspective view showing a separator. [Figure 3] FIG. 3 is an enlarged perspective view of a portion of the separator of FIG. 2. [Figure 4] 4 is a cross-sectional view showing the separator as viewed in the direction of arrows IV-IV in FIG. 3. FIG. [Figure 5] 5 is a cross-sectional view showing the separator as viewed in the direction of arrow VV in FIG. 4. FIG. [Figure 6] FIG. 4 is a perspective view showing another example of the separator. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of a fuel cell will be described below with reference to FIGS. As shown in Fig. 1, a fuel cell stack is formed by stacking a plurality of fuel cell units 11 in the thickness direction. Each fuel cell unit 11 includes a membrane electrode gas diffusion layer assembly 12 and separators 14 and 15. The membrane electrode gas diffusion layer assembly 12 is formed in a sheet shape. The separators 14 and 15 sandwich the membrane electrode gas diffusion layer assembly 12 from both sides in the thickness direction.

[0013] <Membrane electrode gas diffusion layer assembly 12> The membrane electrode gas diffusion layer assembly 12 includes an electrolyte membrane 16, an anode electrode layer 17, a cathode electrode layer 18, and gas diffusion layers 19 and 20, and is formed in a sheet shape. The anode electrode layer 17 is bonded to one of the two thickness-wise sides of the electrolyte membrane 16, i.e., the lower side in FIG. 1. A gas diffusion layer 19 is bonded to one of the two thickness-wise sides of the anode electrode layer 17 opposite the side bonded to the electrolyte membrane 16, i.e., the lower side in FIG. 1. The cathode electrode layer 18 is bonded to the other thickness-wise side of the electrolyte membrane 16, i.e., the upper side in FIG. 1. A gas diffusion layer 20 is bonded to one of the thickness-wise sides of the cathode electrode layer 18 opposite the side bonded to the electrolyte membrane 16, i.e., the upper side in FIG. 1.

[0014] <Separators 14, 15> The separators 14 and 15 are disposed between adjacent membrane electrode gas diffusion layer assemblies 12 in the cell stack. The separator 14 and the separator 15 are adjacent to each other between adjacent fuel cell cells 11. The separator 14 is in contact with the anode-side gas diffusion layer 19 of the membrane electrode gas diffusion layer assembly 12. The separator 15 is in contact with the cathode-side gas diffusion layer 20 of the membrane electrode gas diffusion layer assembly 12. The separators 14 and 15 may be made of metals such as titanium, stainless steel, and aluminum, or may be made of non-metallic materials such as carbon.

[0015] The separators 14 and 15 have a plurality of ribs 21 extending in parallel. The ribs 21 are formed by bending the plate-shaped separators 14 and 15. The ribs 21 of the separator 14 protrude toward the gas diffusion layer 19 and are in contact with the gas diffusion layer 19. The ribs 21 of the separator 15 protrude toward the gas diffusion layer 20 and are in contact with the gas diffusion layer 20. The separators 14 and 15 have a plurality of grooves 22 and 23. The grooves 22 are located between the plurality of ribs 21. These grooves 22 are adjacent to the ribs 21 of the separators 14 and 15 and extend parallel to the ribs 21. The grooves 23 are located on the side of the ribs 21 of the separators 14 and 15 opposite to the contact surfaces 21a with the gas diffusion layers 19 and 20.

[0016] The grooves 22 of the separator 14 form flow paths 24 between the separator 14 and the gas diffusion layer 19 on the anode side of the membrane electrode gas diffusion layer assembly 12. These flow paths 24 are for the flow of fuel gas such as hydrogen. The grooves 22 of the separator 15 form flow paths 25 between the separator 15 and the gas diffusion layer 20 on the cathode side of the membrane electrode gas diffusion layer assembly 12. These flow paths 25 are for the flow of oxidizing gas such as air. The grooves 23 of the separators 14 and 15 form flow paths 26 between the separators 14 and 15. These flow paths 26 are for the flow of refrigerant such as cooling water.

[0017] Next, power generation by the cell stack of the fuel cell will be described. This power generation is performed using a fuel gas and an oxidizing gas. That is, the fuel gas flows through a flow path 24 on the anode side of the fuel cell 11, and the oxidizing gas flows through a flow path 25 on the cathode side of the fuel cell 11. As the fuel gas passes through the flow path 24, it is diffused in the anode-side gas diffusion layer 19 and then supplied to the anode electrode layer 17. As the oxidizing gas passes through the flow path 25, it is diffused in the cathode-side gas diffusion layer 20 and then supplied to the cathode electrode layer 18. Power generation is then performed based on the reaction between the fuel gas and the oxidizing gas in the membrane electrode gas diffusion layer assembly 12. In addition, cooling water flows through the flow path 26 of the fuel cell 11. This cooling water removes heat from the fuel cell 11, which is generated during power generation, thereby cooling the fuel cell 11.

[0018] During power generation based on the reaction between fuel gas and oxidizing gas in the membrane electrode gas diffusion layer assembly 12, water is produced in the cathode electrode layer 18. The water produced in this manner flows to the cathode-side gas diffusion layer 20 and is then discharged from the gas diffusion layer 20 to the outside of the fuel cell 11 by utilizing the flow of oxidizing gas in the cathode-side flow path 25. The water produced in the cathode electrode layer 18 also flows to the anode side of the membrane electrode gas diffusion layer assembly 12. This water flows to the anode-side gas diffusion layer 19 and is then discharged from the gas diffusion layer 19 to the outside of the fuel cell 11 by utilizing the flow of fuel gas in the anode-side flow path 24.

[0019] Next, a detailed description will be given of the ribs 21 and grooves 22 of the separators 14 and 15. Since the separators 14 and 15 have the same structure, the following will describe the separator 15 in detail, and a detailed description of the separator 14 will be omitted.

[0020] As shown in Figures 2 and 3, a plurality of ribs 21 and grooves 22 are arranged side by side and alternately adjacent to each other. Figure 4 shows the rib 21 and groove 22 as viewed from the direction of arrows IV-IV in Figure 3, and Figure 5 shows the rib 21 as viewed from the direction of arrows VV in Figure 4. As can be seen from Figures 4 and 5, the contact surface 21a of the rib 21 with the gas diffusion layer 20 has a shape in which recesses 27 and protrusions 28 are alternately repeated along the extension direction of the rib 21. The length of each recess 27 in the extension direction of the rib 21 is constant for each recess 27 in the rib 21. Furthermore, the length of each protrusion 28 in the extension direction of the rib 21 is constant for each protrusion 28 in the rib 21.

[0021] The inner shape of the groove 22 is formed so that the cross-sectional area of ​​fluid flow in the groove 22 (flow path 25) is smaller at locations corresponding to the convex portions 28 on the contact surface 21a of the rib 21 than at locations corresponding to the concave portions 27. More specifically, the bottom surface 22a of the groove 22 is shaped so that concave portions 29 and convex portions 30 are alternately repeated along the direction in which the groove 22 extends. The convex portions 30 on the bottom surface 22a are positioned corresponding to the convex portions 28 on the contact surface 21a of the rib 21, and the concave portions 29 on the bottom surface 22a are positioned corresponding to the concave portions 27 on the contact surface 21a. As a result, the cross-sectional area of ​​fluid flow in the groove 22 (flow path 25) is smaller at locations corresponding to the convex portions 28 on the contact surface 21a than at locations corresponding to the concave portions 27. The length of each of the concave portions 29 in the direction in which the groove 22 extends is constant for each of the concave portions 29 in the groove 22. Furthermore, the length of each of the convex portions 30 in the groove 22 in the direction in which the groove 22 extends is constant.

[0022] It is possible to appropriately change the lengths of the recessed portions 27 and the protruding portions 28. In this case, the lengths of the recessed portions 29 and the protruding portions 30 are adjusted to match the lengths of the recessed portions 27 and the protruding portions 28.

[0023] Of both longitudinal ends of groove 22 in separator 15, end 22A located on the left side in Fig. 5 serves as an inlet of flow path 25, and end 22B located on the right side in Fig. 5 serves as an outlet of flow path 25. Note that both longitudinal ends of groove 22 in separator 14 (Fig. 1) serve as an inlet and an outlet of flow path 24.

[0024] Next, the effects of the fuel cell 11 will be described. The reaction between the fuel gas and the oxidizing gas in the membrane electrode gas diffusion layer assembly 12 is affected by the electrical resistance between the membrane electrode gas diffusion layer assembly 12 and the separators 14, 15. In order to reduce this effect, it is effective to increase the contact area 21a of the ribs 21 in the separators 14, 15 with the gas diffusion layers 19, 20, thereby reducing the electrical resistance.

[0025] However, if the width of the rib 21, i.e., the length of the rib 21 in the left-right direction in FIG. 4, is increased to increase the contact surface 21a, the gas diffusion layers 19, 20 come into contact with a wider area of ​​the contact surface 21a. This makes it more difficult for water in the gas diffusion layers 19, 20 at locations corresponding to the contact surface 21a to flow into the flow paths 24, 25. As a result, the efficiency of discharging water from the gas diffusion layers 19, 20 to the outside of the fuel cell 11 decreases.

[0026] In this regard, the contact surface 21a of the rib 21 with the gas diffusion layers 19, 20 of the fuel cell 11 is shaped so that recesses 27 and protrusions 28 are alternately repeated along the extension direction of the rib 21. Therefore, the contact surface 21a of the rib 21 with the gas diffusion layers 19, 20 can be increased without increasing the width of the rib 21.

[0027] Furthermore, by forming the recesses 27 and the protrusions 28 on the contact surface 21a, the protrusions 28 further compress the gas diffusion layers 19, 20. This reduces the breathability of the areas of the gas diffusion layers 19, 20 that are pressed by the protrusions 28. This makes it difficult for water present in the areas of the gas diffusion layers 19, 20 that are pressed by the protrusions 28 to flow into the grooves 22 (flow paths 25). As a result, the efficiency of discharging water from the gas diffusion layers 19, 20 to the outside of the fuel cell 11 may decrease.

[0028] However, at the locations of the grooves 22 that correspond to the convex portions 28 of the contact surfaces 21a of the ribs 21, the cross-sectional area of ​​the fluid flow in the grooves 22 (flow paths 25) is smaller than at the locations that correspond to the concave portions 27. Therefore, the fluid flows faster at the locations of the grooves 22 that correspond to the convex portions 28 of the contact surfaces 21a of the ribs 21 than at the locations that correspond to the concave portions 27. As a result, even if the air permeability of the gas diffusion layer 20 at the locations pressed by the convex portions 28 decreases, water present at those locations tends to flow into the grooves 22 (flow paths 25). Then, the water is discharged to the outside of the fuel cell 11 by utilizing the fluid flowing through the flow paths 25 in the grooves 22.

[0029] According to the present embodiment described above in detail, the following effects can be obtained. (1) The contact surface 21a of the rib 21 with the gas diffusion layers 19, 20 can be increased without increasing the width of the rib 21, and a decrease in the efficiency of discharging water from the gas diffusion layers 19, 20 to the outside of the fuel cell 11 can be suppressed.

[0030] (2) The bottom surface 22a of the groove 22 has a shape in which the recessed portions 29 and the protruding portions 30 are alternately repeated. Therefore, the cross-sectional area of ​​the fluid flow in the flow path 25 in the groove 22 is smaller at the locations of the groove 22 corresponding to the protruding portions 28 than at the locations of the recessed portions 29. The protruding portions 30 of the bottom surface 22a are positioned corresponding to the protruding portions 28 of the contact surface 21a of the rib 21, and the recessed portions 29 of the bottom surface 22a are positioned corresponding to the recessed portions 27 of the contact surface 21a. Therefore, simply by forming the bottom surface 22a of the groove 22 as described above, the cross-sectional area of ​​the fluid flow in the groove 22 (flow paths 24, 25) corresponding to the protruding portions 28 of the contact surface 21a of the rib 21 can be easily made smaller than the cross-sectional area of ​​the fluid flow in the groove 22 corresponding to the recessed portions 27 of the contact surface 21a of the rib 21.

[0031] (3) The ribs 21 and the grooves 22 are arranged alternately and adjacently in multiple rows, so that the grooves 22 are disposed on both sides of each rib 21. The convex portions 30 on the bottom surfaces 22a of the grooves 22 are located on both sides of the width of the rib 21 at locations corresponding to the convex portions 28 on the contact surfaces 21a of the ribs 21 with the gas diffusion layers 19, 20. Therefore, the flow velocity of the fluid in each groove 22 (flow passage 25) is increased on both sides of the locations corresponding to the convex portions 28 on the contact surfaces 21a of the ribs 21. As a result, water at locations on the gas diffusion layers 19, 20 that are pushed by the convex portions 28 on the contact surfaces 21a of the ribs 21 can easily flow to the grooves 22 (flow passages 25) located on both sides of the rib 21. This allows water to be more efficiently discharged from the gas diffusion layers 19, 20 to the fuel cell 11.

[0032] The above embodiment can be modified as follows, for example: The above embodiment and the following modifications can be combined and implemented within the scope of technical compatibility. The shapes of the contact surfaces 21a of the ribs 21 and the bottom surfaces 22a of the grooves 22 in the separators 14 and 15 may be changed to the shapes shown in FIG.

[0033] In this case, a protrusion 31 narrower than the rib 21 is formed at the end of the rib 21 in the protruding direction (the upper end in FIG. 6). This protrusion 31 protrudes upward in FIG. 6, and the upper surface of the protrusion 31 in FIG. 6 functions as part of the contact surface 21a. Then, a recess 27 and a protrusion 28 are formed on the contact surface 21a including the upper surface of the protrusion 31 of the rib 21. The protrusion 31 may be located at the center in the width direction of the rib 21, or may be shifted from the center in the width direction.

[0034] Furthermore, a protrusion 32 narrower than the groove 22 is formed at the bottom of the groove 22 (the lower end in FIG. 6). This protrusion 32 protrudes upward in FIG. 6, and the upper surface of the protrusion 32 in FIG. 6 functions as part of the bottom surface 22a of the groove 22. A recess 29 and a protrusion 30 are formed on the bottom surface 22a of the groove 22, including the upper surface of the protrusion 32. The protrusion 32 may be located at the center of the groove 22 in the width direction, or may be shifted from the center in the width direction.

[0035] The lengths of the recesses 27 and the protrusions 28 in the direction in which the ribs 21 extend may be changed as appropriate. For example, the lengths of the recesses 27 in the direction in which the ribs 21 extend may be shorter for recesses 27 closer to the outlets of the flow paths 24, 25 between the gas diffusion layers 19, 20 in the grooves 22. In this case, the lengths of the recesses 27 and the protrusions 28 in the direction in which the grooves 22 extend are adjusted to match the lengths of the recesses 27 and the protrusions 28 described above.

[0036] According to this configuration, in the groove 22 adjacent to the rib 21, the cross-sectional area of ​​the fluid flow in the flow paths 24, 25 becomes smaller more frequently toward the downstream of the flow paths 24, 25. As a result, the locations where the fluid flow velocity in the flow paths 24, 25 becomes faster occur more frequently toward the downstream of the flow paths 24, 25.

[0037] The water in the gas diffusion layers 19, 20 is diverted downstream along with the flow of fluid in the flow paths 24, 25. Therefore, at the locations of the gas diffusion layers 19, 20 corresponding to the contact surfaces 21a of the ribs 21, water tends to accumulate more easily the closer to the outlets of the flow paths 24, 25.

[0038] However, even if water tends to accumulate in the areas of the gas diffusion layers 19, 20 corresponding to the contact surfaces 21a of the ribs 21 and close to the outlets of the flow paths 24, 25, the water can be made to flow easily into the grooves 22 (flow paths 24, 25). This is because, as described above, areas where the flow velocity of the fluid in the flow paths 24, 25 becomes faster occur more frequently downstream of the flow paths 24, 25.

[0039] It is not necessary to align the positions of the recesses 27 and protrusions 28 on the contact surface 21a among multiple ribs 21. In this case, it is sufficient to align the positions of the recesses 27 and protrusions 28 on the contact surface 21a with the recesses 29 and protrusions 30 on the bottom surface 22a, with each rib 21 and its adjacent groove 22 being treated as a set.

[0040] As long as the recesses 27 and the protrusions 28 correspond to the recesses 29 and the protrusions 30, the length of the recesses 27 and the protrusions 28 in the direction in which the ribs 21 extend does not necessarily have to be the same as the length of the recesses 29 and the protrusions 30 in the direction in which the grooves 22 extend.

[0041] By forming recesses 29 and protrusions 30 on the bottom surface 22a of the groove 22, the cross-sectional area of ​​fluid flow in the groove 22 (flow paths 24, 25) is reduced at the locations corresponding to the protrusions 30. Alternatively, the cross-sectional area of ​​fluid flow in the flow paths 24, 25 may be reduced at those locations by forming locations where the width of the groove 22 is narrowed. [Explanation of symbols]

[0042] 11...Fuel cell 12...Membrane electrode gas diffusion layer assembly 14,15...Separator 16...Electrolyte membrane 17...Anode electrode layer 18...Cathode electrode layer 19, 20...Gas diffusion layer 21...Rib 21a…Contact surface 22A, 22B...end 22...Groove 22a…Bottom surface 23…Groove 24~26...Flow path 27...recess 28...Convex part 29...recess 30...Convex part 31,32...projection part

Claims

1. a membrane electrode gas diffusion layer assembly and a separator; The membrane electrode gas diffusion layer assembly is formed into a sheet shape, the separators are arranged to sandwich the membrane electrode-gas diffusion layer assembly from both sides in a thickness direction thereof, and have ribs and grooves extending adjacent to each other and in parallel, the rib is in contact with the gas diffusion layer of the membrane electrode gas diffusion layer assembly, In a fuel cell, the groove forms a flow path for allowing a fluid to flow between the groove and the gas diffusion layer, a contact surface of the rib with the gas diffusion layer has a shape in which recesses and protrusions are alternately repeated along an extension direction of the rib; an inner surface of the recess and an end surface of the protrusion in a protruding direction are in contact with the gas diffusion layer, A fuel cell in which the inner shape of the groove is formed so that the cross-sectional area of ​​the fluid flowing through the flow path is smaller at the locations corresponding to the convex portions on the contact surface of the rib than at the locations corresponding to the concave portions.

2. The bottom surface of the groove has a shape in which recesses and protrusions are alternately repeated along the extension direction of the groove, 2. The fuel cell according to claim 1, wherein the convex portions of the bottom surface are positioned corresponding to the convex portions of the contact surface of the rib, and the concave portions of the bottom surface are positioned corresponding to the concave portions of the contact surface, thereby making the flow cross-sectional area of ​​the fluid in the flow path smaller at the points corresponding to the convex portions of the contact surface than at the points corresponding to the concave portions.

3. The fuel cell according to claim 2 , wherein a plurality of the ribs and the grooves are arranged adjacent to each other and alternate with each other.

4. 4. The fuel cell according to claim 1, wherein the length of the recessed portion of the contact surface in the direction in which the rib extends is shorter as the recessed portion is closer to the outlet of the flow path.

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