Fuel cell system

Abstract

To provide a fuel cell that can improve the power generation efficiency.SOLUTION: A fuel cell 10 includes a film electrode joint body 14 including an electrolyte film 11, an anode catalyst layer 12, and a cathode catalyst layer 13, a pair of diffusion layers 21 and 22 stacked on the anode catalyst layer 12 and the cathode catalyst layer 13 in the film electrode joint body 14, and a pair of separators 31 and 32 including flow channels 312 and 322 between a plurality of ribs 311 and 321 at a surface facing the diffusion layers 21 and 22 while clamping these in a stacking direction. A supply material is supplied from the flow channels 312 and 322 of the pair of separators 31 and 32 to the anode catalyst layer 12 and the cathode catalyst layer 13. The ribs 311 and 321 in at least one of the pair of separators 31 and 32 include first compression parts 311a and 321a that press the diffusion layers 21 and 22 in the stacking direction for compression at a first compression ratio, and second compression parts 311b and 321b that press the diffusion layers 21 and 22 in the stacking direction for compression at a second compression ratio that is lower than the first compression ratio.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] A solid polymer electrolyte fuel cell that uses liquid fuel generally has an anode catalyst layer and a diffusion layer laminated on one side of an electrolyte membrane, a cathode catalyst layer and a diffusion layer laminated on the other side, and these sandwiched between a pair of separators in the stacking direction. Liquid fuel is supplied directly to the anode catalyst layer from a flow path formed in the anode separator through the pores of the anode diffusion layer, and an oxidant is supplied from the outside to the cathode catalyst layer from a flow path formed in the cathode separator through the pores of the cathode diffusion layer, resulting in an electrode reaction and generating electricity. Patent Document 1, as an example of such a fuel cell, discloses a configuration in which the flow path of the separator is formed by grooves formed by multiple ribs on the surface facing the diffusion layer, and the separator and the diffusion layer abut against each other at the ribs to exchange electrons. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-210679 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the configuration disclosed in Patent Document 1, the ribs of the separator that contact the diffusion layer are pressed against the diffusion layer, causing compressive deformation in the region of the diffusion layer that contacts the rib, and also in the region that contacts the flow path between the ribs, as adjacent ribs act as beams. When the diffusion layer is compressed and deformed, the pores of the diffusion layer collapse and narrow, impeding the flow of liquid fuel supplied from the flow path in the anode-side diffusion layer and the flow of oxidant supplied from the flow path in the cathode-side diffusion layer. Furthermore, by-products of electrode reactions tend to accumulate in the compressed and deformed regions of both diffusion layers. As a result, power generation efficiency decreases. Furthermore, if the pressing force of the ribs against the diffusion layer is too strong, the electrolyte membrane behind the diffusion layer may be damaged. On the other hand, weakening the pressing force of the ribs against the diffusion layer can reduce the compressive deformation of the diffusion layer, but this increases the resistance within the diffusion layer and the boundary resistance between the diffusion layer and the separator, resulting in reduced power generation efficiency.

[0005] The present invention aims to provide a fuel cell that can improve power generation efficiency. [Means for solving the problem]

[0006] One aspect of the present invention is an electrolyte membrane; a membrane electrode assembly having an anode catalyst layer provided on one surface of the electrolyte membrane and a cathode catalyst layer provided on the other surface of the electrolyte membrane; a pair of diffusion layers laminated on the anode catalyst layer and the cathode catalyst layer of the membrane electrode assembly; a pair of separators that sandwich the membrane electrode assembly and the pair of diffusion layers in a stacking direction, the separators having a plurality of ribs provided on surfaces facing the diffusion layers and flow paths each consisting of a groove formed between the plurality of ribs; a liquid fuel is supplied to the anode catalyst layer from the flow path of the separator provided on the anode catalyst layer side via the diffusion layer on the anode catalyst layer side, and an oxidant is supplied to the cathode catalyst layer from the flow path of the separator provided on the cathode catalyst layer side via the diffusion layer on the cathode catalyst layer side, In a fuel cell, the rib in at least one of the pair of separators includes a first compression section that presses the diffusion layer in the stacking direction and compresses it at a first compression rate, and a second compression section that presses the diffusion layer in the stacking direction and compresses it at a second compression rate that is lower than the first compression rate. [Effects of the Invention]

[0007] In the fuel cell of the above aspect, the diffusion layer is compressed by multiple ribs formed on at least one of the pair of separators. The ribs include first compression sections with a high compression rate and second compression sections with a low compression rate. This reduces compression and deformation of the diffusion layer in contact with the flow path between adjacent ribs compared to when the compression rate of the ribs is uniform. As a result, the flow of the liquid fuel or oxidizer feedstock supplied from the flow path in at least one of the pair of separators is not obstructed, and by-products are prevented from accumulating in the region of the diffusion layer compressed by the ribs. Furthermore, compared to when the ribs compress the diffusion layer at a uniform, high compression rate, the ribs having the second compression sections with a low compression rate can prevent damage to the electrolyte membrane behind the diffusion layer due to the compression of the ribs. Meanwhile, in the region of the diffusion layer compressed by the first compression sections with a high compression rate, the resistance within the diffusion layer and the boundary resistance between the diffusion layer and the separator are maintained low. These factors contribute to improved power generation efficiency.

[0008] As described above, according to the above aspect, it is possible to provide a fuel cell that can improve power generation efficiency. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a conceptual diagram showing the configuration of a fuel cell system according to a first embodiment. [Figure 2] 1 is a conceptual cross-sectional view showing the configuration of a fuel cell according to a first embodiment. [Figure 3] FIG. 3 is an enlarged plan view of a diffusion layer in the first embodiment. [Figure 4] FIG. 3 is an enlarged cross-sectional view of the flow path in FIG. 2. [Figure 5] FIG. 4 is a graph showing the relationship between the compressibility of the diffusion layer and the resistance of the diffusion layer in the first embodiment. [Figure 6] FIG. 10A is a diagram showing the results of a verification test of mean flow pore size versus interference in a compression device, and FIG. 10B is a diagram showing the results of a verification test of bubble point pressure versus interference in a compression device, in the first embodiment. [Figure 7] FIG. 10 is an enlarged cross-sectional view of the vicinity of a flow channel in the second embodiment. [Figure 8] FIG. 11 is an enlarged cross-sectional view of the vicinity of a flow channel in the third embodiment. [Figure 9] FIG. 10 is an enlarged cross-sectional view of the vicinity of the flow path in the first modified embodiment. [Figure 10] FIG. 10 is a conceptual cross-sectional view showing the configuration of a fuel cell according to a fourth embodiment. [Figure 11] FIG. 10 is an enlarged cross-sectional view of the vicinity of a flow channel in a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Embodiment 1) 1. Configuration of fuel cell system 1 In the first embodiment, as shown in FIG. 1 , a fuel cell system 1 includes a fuel cell 10 and a control device 50. A plurality of fuel cells 10 are stacked as unit cells U to form a fuel cell stack 100. The stacked unit cells U in the fuel cell stack 100 are held by a holder H and a bolt B. A first pump 102 that pressurizes and supplies formic acid, which is a liquid fuel stored in a fuel tank 101, is connected to a connection part K1 via a pipe to the fuel cell stack 100. A second pump 104 that pressurizes and supplies oxygen gas as an oxidant (oxidant gas) stored in a gas tank 103 is connected to a connection part K2 via a pipe to the fuel cell stack 100. The control device 50 controls the operations of the first pump 102 and the second pump 104, and outputs electric power to an external load C. In the first embodiment, the liquid fuel and / or the oxidant supplied to the fuel cell 10 for power generation is referred to as a "feedstock."

[0011] 2. Configuration of fuel cell 10 As shown in Fig. 2, the fuel cell 10 includes an electrolyte membrane 11, an anode catalyst layer 12, and a cathode catalyst layer 13. The anode catalyst layer 12 is laminated on one side of the electrolyte membrane 11, and the cathode catalyst layer 13 is laminated on the other side, forming a membrane-electrode-assembly (MEA) 14. The anode catalyst layer 12 and the cathode catalyst layer 13 are formed, for example, by coating each side of the electrolyte membrane 11 with a metal catalyst such as platinum (Pt) or palladium (Pd), carbon to which the metal catalyst has been added, and an electrolyte. The fuel cell 10 is arranged so that the surface direction of the electrolyte membrane 11 is parallel to the vertical direction Y.

[0012] The pair of diffusion layers 21, 22 consists of an anode-side diffusion layer 21 laminated on the anode catalyst layer 12 and a cathode-side diffusion layer 22 laminated on the cathode catalyst layer 13. The materials for the anode-side diffusion layer 21 and the cathode-side diffusion layer 22 are not limited and can be fibrous or porous materials, but carbon cloth is preferred. This is because carbon cloth exhibits high electrical conductivity and has gaps between the carbon fibers or woven yarns that are suitable for the flow of liquid fuel and oxidant. The thickness of each diffusion layer 21, 22 is not limited and can be any desired thickness.

[0013] In the first embodiment, as shown in the enlarged view of FIG. 3, the diffusion layers 21 and 22 are carbon cloths formed into a sheet by spinning warp threads C1 and weft threads C2 made of carbon fiber, and are formed by plain weaving the warp threads C1 and weft threads C2 alternately. As shown in FIG. 3, the carbon cloth has numerous pores R, which are gaps between the warp threads C1 and weft threads C2. Although not shown, the warp threads C1 and weft threads C2 are formed by twisting together carbon fibers, and therefore have numerous pores, which are gaps between the carbon fibers. Note that the weaving method of the carbon cloth is not limited to this, and any desired weaving method can be adopted.

[0014] The pair of separators 31, 32 includes an anode-side separator 31 stacked on the anode-side diffusion layer 21 opposite the anode catalyst layer 12, and a cathode-side separator 32 stacked on the cathode-side diffusion layer 22 opposite the cathode catalyst layer 13. The separators 31, 32 sandwich the membrane electrode assembly 14 and the pair of diffusion layers 21, 22.

[0015] The anode-side separator 31 can be made of, for example, a metal material such as stainless steel, a carbon material, or a conductive resin material. The surface of the anode-side separator 31 facing the anode catalyst layer 12 is provided with a plurality of ribs 311 extending in a width direction Z perpendicular to the stacking direction X and the vertical direction Y, and channels 312 are formed by grooves formed between the ribs 311. Liquid fuel pressurized by the first pump 102 flows through the channels 312. The liquid fuel permeates the channels 312 into the pores R of the anode-side diffusion layer 21. Carbon dioxide, a by-product generated in the anode catalyst layer 12, and unused liquid fuel are discharged through the channels 312.

[0016] The cathode-side separator 32 can have a configuration similar to that of the anode-side separator 31. As shown in FIG. 2, the cathode-side separator 32 has a surface facing the cathode catalyst layer 13 that is provided with a plurality of ribs 321 extending in a width direction Z that is perpendicular to the stacking direction X and the vertical direction Y. Grooves formed between the ribs 321 form flow paths 322. The flow paths 322 are configured to allow oxygen-containing gas, acting as an oxidant, pressurized by the second pump 104 to flow through the flow paths 322. The oxygen-containing gas permeates from the flow paths 322 into the pores R of the cathode-side diffusion layer 22. Water, a by-product generated in the cathode catalyst layer 13, and unused oxygen-containing gas are discharged through the flow paths 322.

[0017] Examples of the liquid fuel supplied to the anode diffusion layer 21 and anode catalyst layer 12 of the fuel cell 10 include formic acid (HCOOH), methanol (CHOH), and ethanol (CHOH). In this embodiment, the fuel cell 10 is a direct formic acid fuel cell (DFAFC) that directly uses formic acid as the liquid fuel. Examples of the oxidant (oxidant gas) supplied to the cathode diffusion layer 22 and cathode catalyst layer 13 of the fuel cell 10 include oxygen (O) gas, air, and other oxygen-containing gases. In this embodiment, the air is used.

[0018] 3. Detailed configuration of ribs 311, 321 and flow channels 312, 322 Next, the ribs 311, 321 provided on the diffusion layers 21, 22 will be described in detail with reference to Figure 4. Note that while the ribs 321 on the cathode diffusion layer 22 will be described below, the ribs 311 on the anode diffusion layer 21 can also have a similar configuration.

[0019] As shown in Fig. 4, a plurality of ribs 321 are erected at equal intervals toward the diffusion layer 22 in a cross section perpendicular to the width direction Z, which is the direction in which the ribs 321 extend. The surface of the rib 321 facing the diffusion layer 22 has a first compression portion 321a and a second compression portion 321b that abut against the diffusion layer 22 and compress the diffusion layer 22. The first compression portion 321a is located closer to the electrolyte membrane 11 than the second compression portion 321b, so that the first compression portion 321a compresses the diffusion layer 22 more than the second compression portion 321b. In other words, the second compression rate, which is the compression rate when the second compression portion 321b compresses the diffusion layer 22, is lower than the first compression rate, which is the compression rate when the first compression portion 321a compresses the diffusion layer 22.

[0020] Here, we will discuss the correspondence relationship between the resistance of the diffusion layers 21, 22 and the compression ratio of the diffusion layers 21, 22. As shown in Figure 5, the correspondence relationship between the contact resistance and compression ratio is such that the higher the compression ratio, the lower the contact resistance. In a low compression region Pa where the compression ratio is relatively low, the correspondence relationship is a first linear relationship with a predetermined rate of change (slope) indicated by dashed line L1. In a high compression region Pb where the compression ratio is relatively high, the correspondence relationship changes to a second linear relationship with a gentler rate of change (slope) indicated by dashed line L2. At an inflection point IP, the correspondence relationship changes from the first linear relationship to the second linear relationship, and an inflection point compression ratio P1, which is the compression ratio indicating the inflection point IP, becomes the boundary value between the low compression region Pa and the high compression region Pb.

[0021] The change in the correspondence relationship between the resistance and the compression ratio is due to the fact that in the low compression region Pa, the resistance is high because there are fewer contact areas between the carbon fibers in the diffusion layer 22, and in the high compression region Pb, the resistance is low because there are more contact areas between the carbon fibers in the diffusion layer 22. At P0, where the compression ratio is 0, the rib 321 is in contact with the diffusion layer 22 but is not pressing against the diffusion layer 22, so that the diffusion layer 22 is in an uncompressed state, and the thickness of the diffusion layer 22 at P0 matches the nominal film thickness of the diffusion layer 22.

[0022] The first compression ratio of the first compression section 321a to the diffusion layer 22 is in a high compression region Pb that is greater than the inflection point compression ratio P1, and the second compression ratio of the second compression section 321b to the diffusion layer 22 is in a low compression region Pa that is smaller than the inflection point compression ratio P1. The second compression ratio is greater than or equal to P0.

[0023] In the first embodiment, the first compression section 321a is formed in a convex shape that protrudes toward the diffusion layer 22. In the cross section shown in FIG. 4, the first compression section 321a has a generally triangular shape along an isosceles triangle with two inclined surfaces and a vertex 321d between them. The vertex 321d of the first compression section 321a is curved. This reduces the concentration of the pressing force of the first compression section 321a on the vertex 321d. The curvature of the vertex 321d is not limited, as long as it can reduce the concentration of the pressing force on the vertex 321d to an extent that the diffusion layer 22, the cathode catalyst layer 13, and the electrolyte membrane 11 are not damaged by the pressing force of the vertex 321d.

[0024] On the other hand, the second compression section 321b is located between the first compression section 321a and the flow path 322 adjacent to the rib 321, and in the first embodiment, the second compression section 321b has a shape in which the two inclined surfaces of the first compression section 321a extend toward the flow path 322. Furthermore, a chamfered portion 321c is formed between the second compression section 321b and the flow path 322 by chamfering the corner of the rib 321. The shape of the chamfered portion 321c is not limited and can be any desired shape for chamfering the corner.

[0025] As described above, the rib 311 in the anode-side diffusion layer 21 also has a first compression portion 311a similar to the first compression portion 321a, a second compression portion 311b similar to the second compression portion 321b, a chamfered portion 311c similar to the chamfered portion 321c, and an apex portion 311d similar to the apex portion 321d.

[0026] 2, flow paths 312 and 322 are formed by grooves between adjacent ribs 311 and 321. Flow path 312 is connected to a supply port 313 and a discharge port 314 for liquid fuel provided in separator 31. Flow path 322 is connected to a supply port 323 and a discharge port 324 for oxidant provided in separator 32.

[0027] 4. Compressive deformation of the diffusion layers 21 and 22 Next, we will describe in detail how the ribs 311 and 321 compress and deform the diffusion layers 21 and 22. While the following describes the compressive deformation of the cathode diffusion layer 22, the anode diffusion layer 21 also undergoes compressive deformation in a similar manner.

[0028] 4, the diffusion layer 22 pressed by the rib 321 is compressed at a first compression rate in the first compression portion 321a and at a second compression rate lower than the first compression rate in the second compression portion 321b. Therefore, the thickness of the region of the diffusion layer 22 that abuts against the rib 321 increases continuously along the shape of the rib 321 from the region in contact with the first compression portion 321a at the center of the rib 321, through the region in contact with the second compression portion 321b, and up to the chamfered portions 321c at both ends of the rib 321.

[0029] Furthermore, because the flow channels 322 are grooves, the region of the diffusion layer 22 facing the flow channels 322 is not directly compressed, but the adjacent ribs 321 act as beams, compressing and deforming the flow channel-facing region 22a of the diffusion layer 22. However, the compression ratio of the flow channel-facing region 22a is lower than in the case of a conventional shape in which the entire rib 321 has a rectangular cross section and presses the diffusion layer 22 at a first compression ratio. The compression ratio of the flow channel-facing region 22a is in the low compression region Pa shown in Figure 5, and can be set to a third compression ratio that is even lower than the second compression ratio and is closer to P0.

[0030] 5. Verification test of mean flow pore size and bubble point pressure in diffusion layers 21 and 22 Next, we conducted a verification test to determine the mean flow pore size and bubble point pressure when the diffusion layers 21 and 22 were compressed. The test method involved first placing the diffusion layers 21 and 22 in an uncompressed state and fully hydrating them. Next, the hydrating diffusion layers 21 and 22 were attached to a compression device via an O-ring while supported by a support screen, and the compression interference of the compression device was varied. The mean flow pore size and bubble point pressure were then measured at each compression interference.

[0031] The mean flow pore diameter is measured by compressing the diffusion layer impregnated with the wetting liquid at each compression interference and applying air pressure according to a predetermined pressure program, and then measuring the pressure at which the wetting liquid is forced out of the pores of the diffusion layer to calculate the mean flow pore diameter.

[0032] The bubble point pressure is measured by obtaining the air pressure when the air first passes through the diffusion layers 21 and 22 during the measurement of the mean flow pore diameter.

[0033] The change in mean flow pore diameter with respect to the compression interference shown in Figure 6(a) showed a similar trend to the change in resistance with respect to the compression ratio of the diffusion layer shown in Figure 5. That is, the rate of decrease in mean flow pore diameter was relatively high up to the compression interference T1, which corresponds to the inflection point compression ratio P1 shown in Figure 5, but the rate of decrease in mean flow pore diameter was relatively low once the compression interference T1 was exceeded. This indicates that the mean flow pore diameter decreases as the compression interference increases, and once the compression interference T1, which corresponds to the inflection point compression ratio P1, is sufficiently small and therefore does not decrease further. Therefore, at compression interferences smaller than the compression interference T1, which corresponds to the inflection point compression ratio P1, the mean flow pore diameter in the diffusion layer 21 is relatively large, ensuring the flow of liquid fuel within the diffusion layer 21. However, at compression interferences greater than the compression interference T1, which corresponds to the inflection point compression ratio P1, the mean flow pore diameter is sufficiently small that the flow of liquid fuel is inhibited. It was also shown that the flow of liquid fuel within the diffusion layer 21 can be ensured by setting the compression ratio of the regions of the diffusion layers 21 and 22 that are in contact with the flow paths 312 and 322 to a third compression ratio that is smaller than the inflection point compression ratio P1.

[0034] 6(b), the change in bubble point pressure with respect to the compression interference indicates that the bubble point pressure increases as the compression interference increases, but once the compression interference exceeds T1, which corresponds to the inflection point compression ratio P1, the bubble point pressure becomes sufficiently large and does not increase further. Therefore, it was inferred that at compression interferences smaller than T1, which corresponds to the inflection point compression ratio P1, the bubble point pressure in the diffusion layer 21 is relatively small, ensuring the flow of oxygen-containing gas within the diffusion layer 22. However, at compression interferences equal to or greater than T1, which corresponds to the inflection point compression ratio P1, the bubble point pressure is sufficiently large, hindering the flow of oxygen-containing gas. Furthermore, it was shown that the flow of oxygen-containing gas within the diffusion layer 22 can be ensured by setting the compression ratio of the region of the diffusion layer 22 in contact with the flow path 322 to a third compression ratio smaller than P1.

[0035] 6. Effects In the fuel cell 10 of the first embodiment, the diffusion layers 21 and 22 are compressed by the plurality of ribs 311 and 321 formed on the separators 31 and 32. However, the ribs 311 and 321 include first compression sections 311a and 321a, which provide a high compression rate for the diffusion layers 21 and 22, and second compression sections 311b and 321b, which provide a low compression rate for the diffusion layers 21 and 22. This reduces compression and deformation of the diffusion layers 21 and 22 in contact with the flow paths 312 and 322 between adjacent ribs 311 and 321 compared to when the compression rate by the ribs 311 and 321 is uniform. As a result, the flow of the feedstock (liquid fuel and oxidant) supplied from the flow paths 312 and 322 is not obstructed, and by-products are prevented from accumulating in the regions of the diffusion layers 21 and 22 compressed by the ribs 311 and 321. Furthermore, compared to when the ribs 311, 321 apply pressure at a uniform, high compression rate, the ribs 311, 321 have second compression sections 311b, 321b with a lower compression rate, which can prevent damage to the electrolyte membrane 11 behind the diffusion layers 21, 22 due to pressure from the ribs 311, 321. Meanwhile, in the regions of the diffusion layers 21, 22 that are pressed by the first compression sections 311a, 321a with a higher compression rate, the resistance within the diffusion layers 21, 22 and the boundary resistance between the diffusion layers 21, 22 and the separators 31, 32 are maintained low. This improves power generation efficiency.

[0036] Furthermore, in the first embodiment, in a cross section perpendicular to the width direction Z, which is the extension direction of the ribs 311 and 321, the second compression sections 311b and 321b are located between the first compression sections 311a and 321a and the flow paths 312 and 322. This allows the compression rate of the diffusion layers 21 and 22 to decrease from the first compression sections 311a and 321a to the flow paths 312 and 322 via the second compression sections 311b and 321b, and also reduces the compression rate of the regions corresponding to the flow paths 312 and 322. As a result, the resistance within the diffusion layers 21 and 22 and the boundary resistance between the diffusion layers 21 and 22 and the separators 31 and 32 are reduced by high compression in the first compression sections 311a and 321a, and the flow of the feedstock and by-products is maintained by low compression in the regions facing the flow paths 312 and 322, thereby further improving power generation efficiency.

[0037] Furthermore, in the first embodiment, in a cross section perpendicular to the width direction Z, which is the extension direction of the ribs 311, 321, the ribs 311, 321 have chamfered portions 311c, 321c formed by chamfering the corners of the ribs 311, 321 at positions adjacent to the flow channels 312, 322, and the second compression portions 311b, 321b are located between the first compression portions 311a, 321a and the chamfered portions 311c, 321c. As a result, in addition to the second compression portions 311b, 321b, the chamfered portions 311c, 321c are formed at the corners of the ribs 311, 321 on the outer side (the side of the adjacent flow channels 312, 322), and therefore, damage to the diffusion layers 21, 22 due to the corners of the ribs 311, 321 is prevented.

[0038] Furthermore, in the first embodiment, the first compression portions 311a and 321a have a convex shape that protrudes toward the diffusion layers 21 and 22. This makes it possible to easily increase the compression rate of the diffusion layers 21 and 22 by the first compression portions 311a and 321a.

[0039] In addition, in the present embodiment 1, the vertices 311d, 321d of the convex shapes of the first compression portions 311a, 321a are curved, which makes it possible to prevent the diffusion layers 21, 22 and the electrolyte membrane 11 from being damaged by the vertices 311d, 321d.

[0040] In addition, in the first embodiment, the first compression ratio is equal to or greater than an inflection-point compression ratio P1, which is the compression ratio at an inflection point IP where the correspondence between the resistance of the diffusion layers 21, 22 and the compression ratio of the diffusion layers 21, 22 changes, and the second compression ratio is smaller than the inflection-point compression ratio P1. This makes it possible to reliably achieve both a reduction in the resistance within the diffusion layers 21, 22 in the first compression sections 311a, 321a and the boundary resistance between the diffusion layers 21, 22 and the separators 31, 32, and a maintenance of the flow of the feedstock or by-products in the regions opposite the second compression sections 311b, 321b and the flow paths 312, 322.

[0041] Furthermore, in this embodiment 1, the diffusion layers 21 and 22 are made of carbon cloth. Carbon cloth can easily increase the difference between the uncompressed and compressed states, allowing the compression ratio of the diffusion layers 21 and 22 to smoothly change from the region compressed by the first compression sections 311a and 321a to the region compressed by the second compression sections 311b and 321b, and to the region facing the flow paths 312 and 322. This makes it easy to simultaneously reduce the resistance within the diffusion layers 21 and 22 in the first compression sections 311a and 321a and the boundary resistance between the diffusion layers 21 and 22 and the separators 31 and 32, while maintaining the flow of the feedstock and by-products in the region facing the second compression sections 311b and 321b and the flow paths 312 and 322.

[0042] In the first embodiment, the first compression sections 311a, 321a and the second compression sections 311b, 321b are provided in both the ribs 311, 321 of the pair of separators 31, 32. However, this is not limiting, and the first compression sections 311a and the second compression sections 311b may be provided only in the rib 311 of the anode-side separator 31, while the cathode-side separator 32 may be provided with ribs of a conventional configuration. Conversely, the first compression sections 321a and the second compression sections 321b may be provided only in the rib 321 of the cathode-side separator 32, while the anode-side separator 31 may be provided with ribs of a conventional configuration. In this case, the separator 31, 32 having the first compression section 311a (321a) and the second compression section 311b (321b) in the pair of separators achieves the effects described above in the first embodiment.

[0043] As described above, according to the above aspect, it is possible to provide a fuel cell that can improve power generation efficiency.

[0044] (Embodiment 2) In the first embodiment, the vertices 311d, 321d are curved. Alternatively, as in the second embodiment shown in FIG. 7, the vertices 311d, 321d may be flat. In the first modified embodiment, the ribs 311, 321 are generally trapezoidal in a cross section perpendicular to the direction in which the ribs 311, 321 extend. In the first modified embodiment, the sloped surfaces forming the side surfaces of the trapezoid form the second compressed portions 311b, 321b. The difference between the length D1 of the vertices 311d, 321d, which form the upper base of the trapezoid, and the bottom width D2 of the ribs 311, 321, which form the lower base, is not limited, but should be large enough to ensure the second compressed portions 311b, 321b, which form the sloped surfaces. Other configurations are the same as those in the first embodiment, and the second embodiment also achieves the same effects as the first embodiment.

[0045] (Embodiment 3) In the first embodiment, the surfaces of the ribs 311, 321 that contact the diffusion layers 21, 22 in a cross section perpendicular to the extension direction of the ribs 311, 321 have a substantially triangular shape along an isosceles triangle as shown in Fig. 4. However, in the third embodiment, as shown in Fig. 8, the surfaces have a substantially triangular shape along a right triangle having a slope, a horizontal plane, and a vertex 321d therebetween. In the third embodiment, the regions from the vertex 321d to the middle of the slope form first compression portions 311a, 321a, and the regions from the middle of the slope to the chamfered portion 321c form second compression portions 311b, 321b. The other configurations are the same as those in the first embodiment, and the third embodiment can achieve the same effects as those in the first embodiment.

[0046] 9, the ribs 311 and 321 may have a shape obtained by inverting the shape of the ribs 311 and 321 of the third embodiment in the vertical direction Y. In this case, the same effects as those of the first embodiment can be achieved.

[0047] (Embodiment 4) In the fuel cell 10 of the fourth embodiment, as shown in Fig. 10, the ribs 321 on the cathode side extend in the width direction Z. As shown in Fig. 11, in a cross section parallel to the width direction Z, which is the extension direction of the ribs 321, the first compression portions 321a and the second compression portions 321b are alternately arranged along the extension direction of the ribs 321. Also, as shown in Fig. 10, the ribs 311 on the anode side have a similar configuration.

[0048] According to the fuel cell 10 of the fourth embodiment, by having the first compression section 321a and the second compression section 321b as described above, compression and deformation of the diffusion layers 21, 22 in contact with the flow paths 312, 322 adjacent to the second compression section 321b are reduced compared to when the compression ratio by the ribs 311, 321 is uniform. As a result, it is possible to prevent the flow of the feedstock supplied from the flow paths 312, 322 from being obstructed, and to prevent by-products from accumulating in the regions of the diffusion layers 21, 22 compressed by the ribs 311, 321. Meanwhile, in the first compression sections 311a, 321a where the compression ratio of the diffusion layers 21, 22 is high, the resistance within the diffusion layers 21, 22 and the boundary resistance between the diffusion layers 21, 22 and the separators 31, 32 are maintained low. This improves power generation efficiency.

[0049] The present invention is not limited to the above-described first to fourth embodiments and modified embodiment 1, and can be applied to various embodiments without departing from the gist of the present invention. [Explanation of symbols]

[0050] 1. Fuel cell system 10 fuel cell 11 Electrolyte membrane 12 Anode catalyst layer 13 Cathode catalyst layer 14 Membrane electrode assembly 21 Anode side diffusion layer (diffusion layer) 22 Cathode side diffusion layer (diffusion layer) 31 Anode side separator (separator) 32 Cathode side separator (separator) 311, 321 Ribs 311a, 321a First compression section 311b, 321b Second compression section 311c, 321c chamfered part 312, 322 flow path

Claims

1. an electrolyte membrane; a membrane electrode assembly having an anode catalyst layer provided on one surface of the electrolyte membrane and a cathode catalyst layer provided on the other surface of the electrolyte membrane; a pair of diffusion layers laminated on the anode catalyst layer and the cathode catalyst layer of the membrane electrode assembly; a pair of separators that sandwich the membrane electrode assembly and the pair of diffusion layers in a stacking direction, the separators having a plurality of ribs provided on surfaces facing the diffusion layers and flow paths each consisting of a groove formed between the plurality of ribs; a liquid fuel is supplied to the anode catalyst layer from the flow path of the separator provided on the anode catalyst layer side via the diffusion layer on the anode catalyst layer side, and an oxidant is supplied to the cathode catalyst layer from the flow path of the separator provided on the cathode catalyst layer side via the diffusion layer on the cathode catalyst layer side, a fuel cell, wherein the rib in at least one of the pair of separators includes a first compression portion that presses the diffusion layer in the stacking direction and compresses it at a first compression rate, and a second compression portion that presses the diffusion layer in the stacking direction and compresses it at a second compression rate that is lower than the first compression rate.

2. 2. The fuel cell according to claim 1, wherein in a cross section perpendicular to the extending direction of the ribs in at least one of the pair of separators, the second compression portion is located between the first compression portion and the flow path.

3. the rib of at least one of the pair of separators has a chamfered portion formed by chamfering a corner of the rib at a position adjacent to the flow path in a cross section perpendicular to an extending direction of the rib, 3. The fuel cell according to claim 2, wherein the second compression portion is located between the first compression portion and the chamfered portion.

4. 2. The fuel cell according to claim 1, wherein the ribs in at least one of the pair of separators are arranged such that the first compression portions and the second compression portions are alternately arranged along the extension direction of the ribs in a cross section parallel to the extension direction of the ribs.

5. 5. The fuel cell according to claim 1, wherein the first compression portion has a convex shape that protrudes toward the diffusion layer.

6. The fuel cell according to claim 5 , wherein the apex of the convex shape of the first compression portion is a curved surface.

7. The fuel cell according to claim 5 , wherein the apex of the convex shape of the first compression portion is a flat surface.

8. the first compression ratio is equal to or greater than an inflection point compression ratio, which is a compression ratio at an inflection point where a correspondence relationship between the resistance value of the diffusion layer and the compression ratio of the diffusion layer changes; 5. The fuel cell according to claim 1, wherein the second compression ratio is smaller than the inflection point compression ratio.

9. 5. The fuel cell according to claim 1, wherein the diffusion layer is made of carbon cloth.

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