Fuel cell stack

Abstract

To provide a fuel cell stack in which a power generation efficiency is improved by promoting a movement of a fluid from a serpentine-type flow path to an electrode side in a flow path.SOLUTION: In a separator 30 of a fuel cell stack, a groove-shaped anode-side flow path 31 is formed on a surface 30a on an anode catalyst layer side, and a groove-shaped cathode-side flow path 32 is formed on a surface 30b on a cathode catalyst layer side. At least one of the anode-side flow path 31 and the cathode-side flow path 32 is a meandering flow path, and has a serpentine shape including a connection portion that connects an inflow-side end portion of one of a straight portions 311 and 312 and an outflow-side end portion of the other thereof that are adjacent to each other in parallel. At least one of the anode-side flow path 31 and the cathode-side flow path 32 includes small cross-sectional area regions 311 and 321 each having a small flow path cross-section, and large cross-sectional area regions 312 and 322 each having a larger cross-sectional area than the small cross-sectional area regions 311 and 321.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] A solid polymer electrolyte fuel cell stack using liquid fuel is generally formed by alternately stacking electrode assemblies, each having an anode catalyst layer laminated on one side of an electrolyte membrane and a cathode catalyst layer laminated on the other side, and separators with diffusion layers interposed between them. Liquid fuel is directly supplied from a flow path formed in the anode separator to the anode catalyst layer through the pores in the anode diffusion layer, and an oxidant is supplied from the outside to the cathode catalyst layer through the pores in the cathode diffusion layer from the flow path formed in the cathode separator, thereby causing an electrode reaction and generating electricity. Patent Document 1, as an example of such a fuel cell, discloses a configuration in which a separator is formed into a corrugated shape to form a single serpentine groove on both sides of the separator, thereby providing an anode-side flow path and a cathode-side flow path. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-277273 Summary of the Invention [Problem to be solved by the invention]

[0004] In such a fuel cell stack, it is necessary to efficiently move liquid fuel and oxidant from the separator flow channels to the electrode side. However, in the configuration disclosed in Patent Document 1, the cross-sectional area of ​​the grooves formed in the separator is constant for each flow channel, so that in a single serpentine flow channel, there is little change in the pressure of the flowing fluid, and the movement of the fluid from the flow channel to each electrode side is sometimes insufficient. Therefore, there is room for improvement in improving the power generation efficiency of fuel cells.

[0005] The present invention provides a fuel cell stack in which power generation efficiency is improved by promoting the movement of fluid from a serpentine-shaped flow channel to the electrode side. [Means for solving the problem]

[0006] One aspect of the present invention is A fuel cell stack in which a membrane electrode assembly having an electrolyte membrane between an anode catalyst layer and a cathode catalyst layer and separators are alternately stacked with diffusion layers interposed therebetween, the separator is provided with a groove-shaped anode-side flow path on its surface facing the anode catalyst layer, for supplying a liquid fuel to the anode catalyst layer, and a groove-shaped cathode-side flow path on its surface facing the cathode catalyst layer, for supplying an oxidant to the cathode catalyst layer; at least one of the anode-side flow path and the cathode-side flow path is a single flow path that snakes from an inlet to an outlet, and is of a serpentine type that includes a plurality of straight portions that are arranged in parallel to each other and a connection portion that connects an inlet-side end of one of the straight portions and an outlet-side end of the other of the adjacent straight portions; At least one of the anode-side flow path and the cathode-side flow path is in a fuel cell stack and includes a small cross-sectional area region having a small flow path cross section and a large cross-sectional area region having a cross-sectional area larger than the small cross-sectional area region. [Effects of the Invention]

[0007] In the fuel cell stack of the above aspect, at least one of the anode-side flow path and the cathode-side flow path formed in the separator is serpentine-shaped, and the at least one flow path includes a small cross-sectional area region having a small cross-sectional area and a large cross-sectional area region having a larger cross-sectional area than the small cross-sectional area region. This increases the pressure within the flow path due to the small cross-sectional area included in the flow path, making it easier for the feedstock flowing through the flow path to move from the flow path to the electrode side, thereby promoting the electrode reaction. This improves the power generation efficiency of the fuel cell stack.

[0008] As described above, according to the above aspect, it is possible to provide a fuel cell stack in which power generation efficiency is improved by promoting the movement of fluid from the serpentine-shaped flow channel to the electrode side. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a conceptual diagram showing the configuration of a battery system including a fuel cell stack according to a first embodiment. [Figure 2] FIG. 1 is a conceptual cross-sectional view showing the configuration of a fuel cell stack in a first embodiment. [Figure 3] FIG. 2 is a plan view of the anode side of the separator in the first embodiment. [Figure 4] FIG. 2 is a plan view of the cathode side of the separator in the first embodiment. [Figure 5] Cross-sectional view taken along line VV in Figure 3. [Figure 6] FIG. 2 is a partially enlarged perspective view of the anode side of the separator in the first embodiment. [Figure 7] 1A is a perspective view of a separator of Example 1, FIG. 1B is a perspective view of a separator of Comparative Example 1, and FIG. 1C is a perspective view of a separator of Comparative Example 2 in Verification Test 1 of Embodiment 1. [Figure 8] FIG. 1A is a plan view of Example 1 in Verification Test 1 of Embodiment 1, and FIG. 1B is a cross-sectional view taken along line VIIIb-VIIIb in FIG. [Figure 9] 9A is a plan view of Comparative Example 1 in Verification Test 1 of Embodiment 1, and FIG. 9B is a cross-sectional view taken along line IXb-IXb in FIG. 9A. [Figure 10] 1A is a plan view of Comparative Example 2 in Verification Test 1 of Embodiment 1, and FIG. 1B is a cross-sectional view taken along line Xb-Xb in FIG. 1A. [Figure 11] 1A shows the test results of Example 1, FIG. 1B shows the test results of Comparative Example 1, and FIG. 1C shows the test results of Comparative Example 2 in Verification Test 1 of Embodiment 1. FIG. [Figure 12] FIG. 10A is a diagram showing the test results of Examples 1 to 3 in Verification Test 2 of Embodiment 1, and FIG. 10B is a partially enlarged view of (a). [Figure 13] FIG. 10 is a partial cross-sectional view of a separator in a first modified embodiment. [Figure 14] FIG. 10 is a partial cross-sectional view of a separator in a second modified embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Embodiment 1) 1. Overview of fuel cell stack 1 In the first embodiment, as shown in FIG. 1 , the fuel cell stack 1 is formed by stacking a plurality of single cells U and holding them together with a holder H and bolts 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 pipe connection part K1 in the fuel cell stack 1. 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 pipe connection part K2 in the fuel cell stack 1. A control device 50 controls the operation 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 oxidant supplied to the fuel cell stack 1 for power generation is referred to as a "feed material."

[0011] 2. Configuration of fuel cell stack 1 2, the fuel cell stack 1 is formed by alternately stacking membrane electrode assemblies 14 and separators 30 with diffusion layers 21, 22 interposed therebetween. In this embodiment, the stacking direction in the fuel cell stack 1 is designated X, the vertical direction is designated Y, and the width direction perpendicular to the stacking direction X and the vertical direction Y is designated Z. The membrane electrode assembly 14 is a membrane-electrode-assembly (MEA) formed by an electrolyte membrane 11, an anode catalyst layer 12 stacked on one side of the electrolyte membrane 11, and a cathode catalyst layer 13 stacked on the other side of the electrolyte membrane 11.

[0012] The anode catalyst layer 12 and the cathode catalyst layer 13 are formed by coating, for example, a metal catalyst such as platinum (Pt) or palladium (Pd), carbon to which the metal catalyst has been added, and an electrolyte on each surface of the electrolyte membrane 11. The fuel cell stack 1 is arranged so that the surface direction of the electrolyte membrane 11 is parallel to the vertical direction Y.

[0013] 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. Both the anode-side diffusion layer 21 and the cathode-side diffusion layer 22 have numerous pores. 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. The thickness of each diffusion layer 21, 22 is not limited and can be any desired thickness.

[0014] Separators 30 are laminated on the anode diffusion layer 21 and the cathode diffusion layer 22, respectively, to separate adjacent cells U. As a result, one surface 30a of the separator 30 faces and contacts the anode diffusion layer 21 of one cell, and the other surface 30b of the separator 30 faces and contacts the cathode diffusion layer 22 of the adjacent cell. The separator 30 can be made of, for example, a metal material such as stainless steel, a carbon material, or a conductive resin material.

[0015] 2-1. Anode-side flow path 31 and cathode-side flow path 32 2 and 3, an anode-side flow path 31 is formed on the surface of the separator 30 facing the anode catalyst layer 12, and a cathode-side flow path 32 is formed on the surface facing the cathode catalyst layer 13. The anode-side flow path 31 is groove-shaped and is configured to allow liquid fuel pressurized by the first pump 102 shown in FIG. 1 to flow through it. The liquid fuel permeates from the anode-side flow path 31 into the pores 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 anode-side flow path 31.

[0016] 2 and 3, the cathode-side flow path 32 is groove-shaped and configured to allow oxygen-containing gas as an oxidant pressurized by the second pump 104 shown in FIG. 1 to flow through it. The oxygen-containing gas permeates from the cathode-side flow path 32 into the pores of the cathode-side diffusion layer 22. Water, which is a by-product generated in the cathode catalyst layer 13, and unused oxygen-containing gas are discharged through the cathode-side flow path 32.

[0017] Examples of the liquid fuel supplied to the anode-side flow path 31 include formic acid (HCOOH), methanol (CHOH), and ethanol (CHOH), and in this embodiment 1, the fuel cell stack 1 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-side flow path 32 include oxygen (O) gas, air, and other oxygen-containing gases, and in this embodiment 1, air is used.

[0018] At least one of the anode-side flow path 31 and the cathode-side flow path 32 has a serpentine shape, and in this embodiment, both the anode-side flow path 31 and the cathode-side flow path 32 have a serpentine shape as shown in Figures 3, 4, and 5. In this specification, a "serpentine" flow path refers to, in the case of the anode-side flow path 31 shown in Figure 3 as an example, a single flow path that snakes from the inlet 314 to the outlet 315, and has a shape that includes a plurality of straight sections 311 (312) arranged in parallel to each other, and a connection section 313 that connects the inlet end of one straight section 311a (312a) of adjacent straight sections 311 to the outlet end of the other straight section 311b (312b). In this embodiment, the multiple straight portions 311 (312) extend in the width direction Z, and as shown in FIG. 3, a total of 18 straight portions 311 (312) are provided at equal intervals in the vertical direction Y in the anode side flow path 31.

[0019] Similarly, the case of the cathode-side flow path 32 shown in FIG. 4 will be described. The cathode-side flow path 32 is a single flow path that meanders from the inlet 324 to the outlet 325, and includes a plurality of straight portions 321(322) arranged parallel to each other, and a connection portion 323 that connects the inflow-side end portion of one straight portion 321a(322a) of the adjacent straight portions 321 to the outflow-side end portion of the other straight portion 321b(322b). The straight portions 321(322) extend in the width direction Z. As shown in FIG. 4, in the cathode-side flow path 32, a total of 18 straight portions 321(322) are provided at equal intervals in the vertical direction Y. And, in a plan view, the cathode-side flow path 32 shown in FIG. 4 has a shape obtained by horizontally inverting the anode-side flow path 31 shown in FIG. 3. Also, when the anode-side flow path 31 and the cathode-side flow path 32 are projected in the thickness direction of the separator 30, the straight portions 311, 312, 321, 322 of each other will overlap.

[0020] 2-2. Flow path cross section of anode-side flow path 31 and cathode-side flow path 32 As shown in FIG. 5, the plurality of straight portions 311, 312 in the anode-side flow path 31 include a small cross-sectional area region 311 with a small cross-sectional area of the flow path and a large cross-sectional area region 312 with a large cross-sectional area of the flow path. In the present embodiment, the widths W of the plurality of straight portions 311, 312 are the same as each other, and the depth D1 of the straight portion 311 is shallower than the depth D2 of the straight portion 312, so that the straight portion 311 becomes a small cross-sectional area region with a small cross-sectional area of the flow path, and the straight portion 312 becomes a large cross-sectional area region. Further, the straight portion 311 that becomes the small cross-sectional area region has a depth D1 throughout its entire area, and the straight portion 312 that becomes the large cross-sectional area region has a depth D2 throughout its entire area. The magnitudes of D1 and D2 are not limited as long as D1<D2 is satisfied, but in the present embodiment, D1 is shallower than the central position 30c in the thickness direction of the separator 30, and D2 is deeper than the central position 30c.

[0021] 6, in this embodiment, connecting portion 313 connecting straight portion 311, which becomes the small cross-sectional area region, and straight portion 312, which becomes the large cross-sectional area region, has the same depth D2 as straight portion 312, which becomes the large cross-sectional area region, and step 316 is formed between connecting portion 313 and straight portion 311, which becomes the small cross-sectional area region. Note that instead of providing step 316, the bottom surface of connecting portion 313 may be tapered to smoothly connect straight portion 311, which becomes the small cross-sectional area region, and straight portion 312, which becomes the large cross-sectional area region.

[0022] In this embodiment, among the multiple straight portions 311, 312, a pair of adjacent straight portions 311a, 311b is defined as a first group, and a pair of adjacent straight portions 312a, 312b that is not included in the first group is defined as a second group. The first group includes small cross-sectional area regions, and the second group includes large cross-sectional area regions. The first and second groups are arranged alternately in the flow direction of the anode-side flow path 31.

[0023] The cathode-side flow path 32 is formed in the same manner as the anode-side flow path 31. However, as shown in Fig. 5 , the straight section 321, which forms the small cross-sectional area region in the cathode-side flow path 32, and the straight section 322, which forms the large cross-sectional area region, are arranged in the reverse order to those in the anode-side flow path 31. As a result, the straight section 311, which forms the small cross-sectional area region of the anode-side flow path 31, and the straight section 322, which forms the large cross-sectional area region of the cathode-side flow path 32, overlap each other in the stacking direction X, and the straight section 312, which forms the large cross-sectional area region of the anode-side flow path 31, and the straight section 321, which forms the small cross-sectional area region of the cathode-side flow path 32, overlap each other in the stacking direction X.

[0024] 2-3. Pressure of fluid in the anode side flow path 31 and the cathode side flow path 32 As described above, the anode-side flow path 31 and the cathode-side flow path 32 include small cross-sectional area regions 311, 321 and large cross-sectional area regions 312, 322. This changes the flow velocity of the fluid (liquid fuel, oxidant) flowing through the anode-side flow path 31 and the cathode-side flow path 32, and also changes the pressure loss of the fluid flowing through the anode-side flow path 31 and the cathode-side flow path 32. The flow velocity is expressed by the following formula (1), and the pressure loss is expressed by the following formula (2).

[0025]

number

[0026]

number

[0027] Based on the above formulas (1) and (2), the pressure loss ΔP is proportional to the square of the flow velocity, and the flow velocity is inversely proportional to the cross-sectional area. Therefore, a difference occurs in the pressure of the fluid (liquid fuel, oxidant) flowing through the anode-side flow path 31 and the cathode-side flow path 32 between the small cross-sectional area regions 311, 321 and the large cross-sectional area regions 312, 322. This pressure difference promotes the movement of the fluid from the anode-side flow path 31 and the cathode-side flow path 32 to the adjacent diffusion layers 21, 22, respectively.

[0028] 3-1. Verification test 1 The following simulation test was conducted as verification test 1 on the flow velocity and pressure loss in a flow path having a small cross-sectional area region and a large cross-sectional area region. First, test specimens 71, 81, and 82 of Example 1, Comparative Example 1, and Comparative Example 2 shown in Figures 7(a) to 7(c) were prepared.

[0029] 8(a), the specimen 71 of Example 1 shown in Fig. 7(a) has a serpentine-type flow path including seven straight portions 711-717 and six connecting portions 718 that connect the seven straight portions 711-717 to form a single flow path. The seven straight portions 711-717 are numbered first to seventh straight portions 711-717 in order from bottom to top in the vertical direction Y, and extend parallel to each other in the width direction Z, with the width W of each flow path being the same.

[0030] 8(b), the first to third straight portions 711-713 and the sixth to seventh straight portions 716, 717 form large cross-sectional area regions with a depth D2, while the fourth and fifth straight portions 714, 715 form small cross-sectional area regions with a depth D1. The depths of the first to third straight portions 711-713 and the sixth to seventh straight portions 716, 717 are all D2, while the depths of the fourth and fifth straight portions 714-715 are all D1. A step 718 is formed at a connection 718 between the second and sixth straight portions 712, 716 and the fourth and fifth straight portions 714-715.

[0031] The specimen 81 of Comparative Example 1 shown in FIG. 7(b) has a serpentine-type flow path as shown in FIG. 9(a), which includes seven straight sections 811-817 and six connecting sections 818 that connect these sections to form a single flow path. The seven straight sections 811-817 are designated as the first to seventh straight sections 811-817 in order from bottom to top in the vertical direction Y, and extend parallel to each other in the width direction Z, with the width W of the flow path being the same. As shown in FIG. 9(b), the first to seventh straight sections 811-817 have a constant depth D2. The specimen 81 does not have any steps in its flow path.

[0032] The specimen 82 of Comparative Example 2 shown in FIG. 7(c) has a parallel-type flow path as shown in FIG. 10(a), including seven straight sections 821-827, a first connection section 828 connecting one end of the straight sections 821-827 so that the straight sections 821-827 are connected in parallel with each other, and a second connection section 829 connecting the other end of the straight sections 821-827. The seven straight sections 821-827 are numbered first to seventh straight sections 821-827 in order from one side in the width direction Z, and extend parallel to each other in the vertical direction Y. The widths W of the flow paths are the same for all of them. Furthermore, as shown in FIG. 10(b), the depths D2 of the first to seventh straight sections 821-827 are constant. The specimen 82 does not have any steps in its flow paths.

[0033] In this simulation test, each of the test specimens 71, 81, and 82 was a rectangle with length and width of 15 mm in plan view, with the length L of each straight section being 13 mm, the width W of the flow path being 1.0 mm, and the depths D1 and D2 being 0.25 mm. A fluid was supplied at a predetermined flow rate and flow velocity from inlet position S, which was the lower end in the vertical direction Y and one end in the width direction Z, into the flow path of each of the test specimens 71, 81, and 82, and discharged from outlet position E, which was the upper end in the vertical direction Y and the other end in the width direction Z. The flow velocity and pressure loss occurring at the center position and outlet position E of each straight section were calculated based on the above formulas (1) and (2).

[0034] According to the calculation results of Example 1, the flow velocity in the fourth straight section 714 and the fifth straight section 715, which are small cross-sectional area regions, was approximately three times the flow velocity in the first to third straight sections 711 to 713 and the sixth to seventh straight sections 716 and 717, which are large cross-sectional area regions. As shown in FIG. 11(a), the pressure difference between the fourth straight section 714 and the fifth straight section 715, which are small cross-sectional area regions, was sufficiently larger than the pressure difference between the fourth straight section 714 and the fifth straight section 715 in the calculation results of Comparative Example 1 shown in FIG. 11(b). Furthermore, the total pressure loss, which is the pressure loss at the outflow position E in Example 1 shown in FIG. 11(a), was sufficiently larger than the pressure loss at the outflow position E in Comparative Example 1 shown in FIG. 11(b). Comparing the calculation results of Example 1 with those of the parallel-type flow path of Comparative Example 2, both the flow velocity and the pressure loss were sufficiently larger.

[0035] This simulation test confirmed that providing a flow path with a small cross-sectional area region increases the flow velocity, increases the pressure difference between the flow paths, and increases the total pressure loss.

[0036] 3-2. Verification test 2 Regarding the depth of the flow path having a small cross-sectional area region and a large cross-sectional area region, the following simulation test was conducted as Verification Test 2. In this simulation test, as shown in Table 1 below, a test specimen 71 of Example 1 shown in Figure 7(a) having a depth D1 of 0.75 mm and a depth D2 of 0.25 mm, a test specimen of Example 2 in which the depth D1 of test specimen 71 was changed to 0.9 mm and the depth D2 was changed to 0.1 mm, and a test specimen of Example 3 in which the depth D1 of test specimen 71 was changed to 0.6 mm and the depth D2 was changed to 0.4 mm were prepared, and the pressure loss was calculated by simulation in the same manner as in Verification Test 1, and the calculation results are shown in Figures 12(a) and 12(b).

[0037] [Table 1]

[0038] As shown in FIG. 12(a), in Example 2, the total pressure loss, which is the pressure loss at the outflow position E, was excessively large. Furthermore, in Example 3, as shown in FIG. 12(b), the pressure difference between the fourth straight section 714 and the fifth straight section 715 was small, and the total pressure loss was also small. On the other hand, in Example 1, as shown in FIG. 12(b), the pressure difference between the fourth straight section 714 and the fifth straight section 715 was sufficiently large, and as shown in FIG. 12(a), the total pressure loss was prevented from becoming excessively large. This verification confirmed that a good balance between the pressure difference and the total pressure loss was achieved in Example 1.

[0039] 4. Effects In the fuel cell stack 1 of this embodiment, at least one of the anode-side flow path 31 and the cathode-side flow path 32 formed in the separator 30 is serpentine-shaped, and the at least one flow path in the fuel cell stack 1 includes small cross-sectional area regions 311, 321 having a small flow path cross section and large cross-sectional area regions 312, 322 having a larger cross-sectional area than the small cross-sectional area regions 311, 321. As a result, the small cross-sectional area regions 311, 321 included in the flow path increase the pressure within the flow path, making it easier for the feedstock, which is the fluid flowing through the flow path, to move from the flow path to the electrode side, thereby promoting the electrode reaction. This improves the power generation efficiency of the fuel cell stack 1.

[0040] In this embodiment, both the anode-side flow path 31 and the cathode-side flow path 32 are serpentine-shaped, and each includes small cross-sectional area regions 311, 321 and large cross-sectional area regions 312, 322. This facilitates the movement of the feedstock from the flow path to the electrode on both the anode and cathode sides, further promoting the electrode reaction. This further improves the power generation efficiency of the fuel cell stack 1.

[0041] Furthermore, in this embodiment, when the anode-side flow path 31 and the cathode-side flow path 32 are projected in the thickness direction of the separator 30, the multiple straight portions 311, 312 in the anode-side flow path 31 and the multiple straight portions 321, 322 in the cathode-side flow path 32 at least partially overlap with each other. This allows the lengths of the anode-side flow path 31 and the cathode-side flow path 32 to be increased. As a result, the feed material can more easily move from the flow path to the electrode side, improving the power generation efficiency of the fuel cell stack 1.

[0042] Furthermore, in this embodiment, when the anode-side flow path 31 and the cathode-side flow path 32 are projected in the thickness direction of the separator 30, the small cross-sectional area region 311 in the anode-side flow path 31 overlaps with the large cross-sectional area region 322 in the cathode-side flow path 32, and / or the large cross-sectional area region 312 in the anode-side flow path 31 overlaps with the small cross-sectional area region 321 in the cathode-side flow path 32. This makes it possible to increase the lengths of the anode-side flow path 31 and the cathode-side flow path 32 while preventing the thickness of the separator 30 from increasing. This allows for both a compact fuel cell stack 1 and improved power generation efficiency.

[0043] In this embodiment, the multiple straight portions 311, 312, 321, 322 include first straight portions 311b, 321b and second straight portions 312a, 322a that are adjacent to each other, with small cross-sectional area regions provided in the first straight portions 311b, 321b and large cross-sectional area regions provided in the second straight portions 312a, 322a. This makes it easier to generate a pressure difference in the flow paths, thereby improving the power generation efficiency of the fuel cell stack 1.

[0044] In this embodiment, the multiple straight portions 311, 312, 321, and 322 include first groups 311 and 321 each consisting of a pair of adjacent straight portions, and second groups 312 and 322 each consisting of a pair of adjacent straight portions that are not included in the first groups 311 and 321. The pairs of straight portions 311a, 311b, 321a, and 321b included in the first groups 311 and 321 include small cross-sectional area regions, and the pairs of straight portions 312a, 312b, 322a, and 322b included in the second groups 312 and 322 include large cross-sectional area regions. This makes it easy to form small cross-sectional area regions and large cross-sectional area regions while increasing the length of the anode-side flow path 31 or the cathode-side flow path 32.

[0045] In this embodiment, the first groups 311, 321 and the second groups 312, 322 are alternately arranged in the flow direction of the anode-side flow path 31 or the cathode-side flow path 32. This makes it easier to create a pressure difference in the anode-side flow path 31 or the cathode-side flow path 32, thereby improving the power generation efficiency of the fuel cell stack 1.

[0046] In this embodiment, the depth D1 of the grooves forming the small cross-sectional area regions is shallower than the depth D2 of the grooves forming the large cross-sectional area regions. This makes it easy to form the small cross-sectional area regions and the large cross-sectional area regions simply by changing the depth of the grooves forming the anode side flow path 31 and the cathode side flow path 32.

[0047] In addition, in this embodiment, the depth D1 of the grooves forming the small cross-sectional area regions is shallower than the depth D2 of the grooves forming the large cross-sectional area regions, but instead, the width of the grooves forming the small cross-sectional area regions may be narrower than the width of the grooves forming the large cross-sectional area regions. In this case, it becomes easy to form the small cross-sectional area regions and the large cross-sectional area regions simply by changing the width of the grooves forming the anode-side flow path 31 and the cathode-side flow path 32.

[0048] In this embodiment, the liquid fuel contains formic acid, which can improve the power generation efficiency in a direct formic acid fuel cell (DFAFC) that directly uses formic acid as the liquid fuel.

[0049] In this embodiment, as shown in FIG. 5 , both the anode-side flow path 31 and the cathode-side flow path 32 are configured to include both the small cross-sectional area regions 311, 321 and the large cross-sectional area regions 312, 322. However, instead of this, as shown in Modified Example 1 shown in FIG. 13 , the anode-side flow path 31 may be configured to include only the small cross-sectional area region 311 without including the large cross-sectional area region. Furthermore, although not shown, the cathode-side flow path 32 may be configured to include only the small cross-sectional area region 321 without including the large cross-sectional area region. Furthermore, as shown in Modified Example 2 shown in FIG. 14 , the cathode-side flow path 32 may be configured to not include a small cross-sectional area region. Furthermore, as shown in Modified Example 2 shown in FIG. 14 , when the anode-side flow path 31 and the cathode-side flow path 32 are projected in the thickness direction of the separator 30, the straight portions of the anode-side flow path 31 and the cathode-side flow path 32 do not have to overlap with each other in part or in whole.

[0050] In this embodiment, the straight portions 311, 312, 321, and 322 of the anode-side flow path 31 and the cathode-side flow path 32 all have a constant depth, but this is not limiting, and the straight portions 311 and 321 may be provided with shallower depths in part so that only parts of the straight portions 311 and 321 have small cross-sectional area regions. Furthermore, the bottoms of the grooves may be tapered so that the depth of part or all of the straight portions 311 and 321 changes continuously, thereby forming shallow small cross-sectional area regions.

[0051] As described above, according to this embodiment and its modified form, a fuel cell stack 1 can be provided in which the power generation efficiency is improved by promoting the movement of fluid from the serpentine-shaped flow path to the electrode side.

[0052] The present invention is not limited to the above-described embodiment and modified forms, and can be applied to various embodiments without departing from the spirit of the present invention. [Explanation of symbols]

[0053] 1. Fuel cell stack 11 Electrolyte membrane 12 Anode catalyst layer 13 Cathode catalyst layer 14 Membrane electrode assembly 21 Anode side diffusion layer 22 Cathode side diffusion layer 30 Separator 31 Anode side flow path 32 Cathode side flow path 50 Control device 101 Fuel Tank 102 First Pump 103 Gas Tank 104 Second Pump 311, 311a, 311b Straight section (first group, small cross-sectional area) 312, 312a, 312b Straight section (second group, large cross-sectional area) 313 Connection 314 Inlet 315 Outlet 316 Step 321, 321a, 321b Straight section (first group, small cross-sectional area) 322, 322a, 322b Straight section (second group, large cross-sectional area) 323 Connection 324 Inlet 325 Outlet 711~717 Straight section (1st~7th straight section) 718 steps 718 Connection 811~817 Straight section (1st to 7th straight sections) 818 Connection 821~827 Straight section (1st to 7th straight sections) 828 First Connection 829 Second connection part S Inflow position E Outflow position U Cell

Claims

1. A fuel cell stack in which a membrane electrode assembly having an electrolyte membrane between an anode catalyst layer and a cathode catalyst layer and separators are alternately stacked with diffusion layers interposed therebetween, the separator is provided with a groove-shaped anode-side flow path on its surface facing the anode catalyst layer, for supplying a liquid fuel to the anode catalyst layer, and a groove-shaped cathode-side flow path on its surface facing the cathode catalyst layer, for supplying an oxidant to the cathode catalyst layer; at least one of the anode-side flow path and the cathode-side flow path is a single flow path that snakes from an inlet to an outlet, and is of a serpentine type that includes a plurality of straight portions that are arranged in parallel to each other and a connection portion that connects an inlet-side end of one of the straight portions and an outlet-side end of the other of the adjacent straight portions; a small cross-sectional area region having a small flow path cross section and a large cross-sectional area region having a cross-sectional area larger than that of the small cross-sectional area region;

2. 2. The fuel cell stack according to claim 1, wherein both the anode side flow path and the cathode side flow path are serpentine-shaped, and both the anode side flow path and the cathode side flow path include the small cross-sectional area region and the large cross-sectional area region.

3. 3. The fuel cell stack according to claim 2, wherein, when the anode-side flow path and the cathode-side flow path are projected in a thickness direction of the separator, a plurality of straight portions in the anode-side flow path and a plurality of straight portions in the cathode-side flow path at least partially overlap with each other.

4. 4. The fuel cell stack according to claim 3, wherein, when the anode-side flow path and the cathode-side flow path are projected in a thickness direction of the separator, the small cross-sectional area region in the anode-side flow path and the large cross-sectional area region in the cathode-side flow path overlap, and / or the large cross-sectional area region in the anode-side flow path and the small cross-sectional area region in the cathode-side flow path overlap.

5. 5. The fuel cell stack according to claim 1, wherein the plurality of straight portions include a first straight portion and a second straight portion adjacent to each other, the small cross-sectional area region being provided in the first straight portion, and the large cross-sectional area region being provided in the second straight portion.

6. the plurality of straight portions include a first group consisting of a pair of adjacent straight portions and a second group consisting of a pair of adjacent straight portions among the straight portions not included in the first group, 5. The fuel cell stack according to claim 1, wherein the pair of straight portions included in the first group include the small cross-sectional area region, and the pair of straight portions included in the second group include the large cross-sectional area region.

7. 7. The fuel cell stack according to claim 6, wherein the first groups and the second groups are alternately arranged in a flow direction in the anode-side flow passage or the cathode-side flow passage.

8. 5. The fuel cell stack according to claim 1, wherein the depth of the grooves forming the small cross-sectional area regions is shallower than the depth of the grooves forming the large cross-sectional area regions.

9. 5. The fuel cell stack according to claim 1, wherein the width of the groove that forms the small cross-sectional area region is narrower than the width of the groove that forms the large cross-sectional area region.

10. 5. The fuel cell stack according to claim 1, wherein the liquid fuel contains formic acid.

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