Fuel cell and fuel cell unit

Abstract

To suppress deterioration of a catalyst by suppressing generation of negative voltage due to infiltration of liquid water together with fuel gas.SOLUTION: A fuel cell including a membrane electrode assembly including an electrolyte membrane and a catalyst layer, and a separator disposed to face the membrane electrode assembly and forming a fuel gas flow path and an oxidant gas flow path with a diffusion layer interposed between the separator and the catalyst layer; Among the fuel gas flow paths, the fuel gas flow path on the lower side of the fuel cell in the direction of gravity has a reduction region where the catalyst layer in contact with the fuel gas flow path via the diffusion layer is reduced as compared with the fuel gas flow path on the upper side of the fuel cell.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to fuel cells and fuel cell units. [Background technology]

[0002] A fuel cell stack is known in which a fuel gas such as hydrogen and an oxidant gas are supplied to both sides of a solid electrolyte membrane having a catalyst layer on its surface, and electricity is generated by an electrochemical reaction between the hydrogen and oxygen in the electrolyte membrane. In such fuel cell stacks, various measures are taken to prevent the gas flow path from being clogged by liquid water that flows in with the gas.

[0003] For example, in Patent Document 1 listed below, a porous filter is placed inside a through-hole manifold formed by stacking fuel cell cells with openings, in order to disperse liquid water that may flow in along with the fuel gas and avoid blocking of the flow path. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-60717 Summary of the Invention [Problem to be solved by the invention]

[0005] The technique described in Patent Document 1 is excellent for dispersing large droplets of liquid water that flow in together with fuel gas, but the behavior of the inflow of liquid water is not orderly, and even if the arrangement and shape of the porous filter are devised, liquid water can sometimes enter the area where the solid electrolyte membrane of the fuel cell is present (hereinafter referred to as the power generation surface) from the through-hole manifold. When liquid water flows into the fuel gas flow path on the power generation surface, the fuel gas flow path can be blocked by the liquid water, resulting in insufficient fuel gas supply beyond that point, causing a negative voltage on the power generation surface and causing the catalyst in the solid electrolyte membrane to deteriorate. [Means for solving the problem]

[0006] The present disclosure can be realized in the following aspects or applications.

[0007] (1) A first aspect of the present disclosure is a fuel cell. The fuel cell generates electricity by supplying and discharging fuel gas and oxidant gas. The fuel cell includes a membrane electrode assembly (MEA) having an electrolyte membrane and a catalyst layer, a separator facing the MEA and sandwiching a diffusion layer between the MEA and the separator and the catalyst layer to form a fuel gas flow path and an oxidant gas flow path, and a fuel gas exhaust manifold disposed below the MEA in the direction of gravity, with the plane of the MEA being the direction of gravity when the MEA is in use. The fuel gas flow path on the lower side of the MEA has a reduced area in which the catalyst layer in contact with the fuel gas flow path is reduced relative to the fuel gas flow path on the upper side of the MEA. This configuration prevents liquid water from entering the MEA along with the fuel gas and accumulating in the fuel gas flow path, thereby preventing a negative voltage from occurring on the power generation surface of the MEA. This configuration prevents a negative voltage from occurring on the power generation surface, which can lead to deterioration of the catalyst in the electrolyte membrane. (2) In this configuration, the reduction region may be free of the catalyst layer that is in contact with the reduction region via the diffusion layer. In this way, the absence of a catalyst layer prevents catalyst deterioration. (3) In the above configuration, the reduced area may have an area of ​​15% or more of the surface area of ​​the membrane electrode assembly, which can more reliably prevent problems such as accumulation of liquid water. (4) In the above configuration, the region of the fuel gas flow path corresponding to the reduced catalyst region may have higher water repellency than the region of the fuel gas flow path other than the reduced catalyst region. This makes it difficult for liquid water to accumulate in the fuel gas flow path, thereby making it possible to reduce the corresponding reduced catalyst region and easily ensure sufficient power generation. (5) The catalyst layer that contacts the upper fuel gas flow path of the fuel cell via the diffusion layer may have an increased catalyst amount depending on the size of the reduced catalyst area, thereby compensating for the decrease in power generation in the reduced catalyst area. (6) In the above configuration, a fuel cell stack may be provided in which a plurality of the fuel cells are stacked, and a direction intersecting the stacking direction may be used as the direction of gravity. In this way, the direction in which liquid water accumulates can be aligned with the surface direction of the fuel cells, and a catalyst reduction region can be positioned in an appropriate position. (7) Another aspect of the present disclosure is a fuel cell. The fuel cell includes a membrane electrode assembly including an electrolyte membrane and a catalyst layer, and a separator disposed facing the membrane electrode assembly and sandwiching a diffusion layer between the separator and the catalyst layer to form a fuel gas flow path and an oxidant gas flow path. The surface of the fuel cell may be oriented in the direction of gravity when the fuel cell is in use. The fuel gas flow path on the lower side of the fuel cell in the direction of gravity may have a reduced area in which the catalyst layer in contact with the fuel gas flow path via the diffusion layer is reduced compared to the fuel gas flow path on the upper side of the fuel cell. This configuration makes it less likely that the power generation surface of the membrane electrode assembly will become negative voltage even if liquid water infiltrates the fuel cell along with the fuel gas and accumulates in the fuel gas flow path. This reduces the occurrence of problems such as a negative voltage on the power generation surface and deterioration of the catalyst in the electrolyte membrane. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing a fuel cell system including a fuel cell according to an embodiment; [Figure 2] FIG. 2 is an explanatory diagram schematically showing a fuel cell stack and fuel cell units that constitute the fuel cell stack. [Figure 3] FIG. 2 is an explanatory diagram schematically showing the cross-sectional configuration of a fuel cell according to the first embodiment. [Figure 4] FIG. 6 is an explanatory diagram showing the features of a fuel cell according to a second embodiment. [Figure 5]FIG. 10 is an explanatory diagram schematically showing the cross-sectional configuration of a fuel cell according to a second embodiment. [Figure 6] FIG. 10 is an explanatory diagram showing the features of a fuel cell according to a third embodiment. [Figure 7] FIG. 10 is an explanatory diagram schematically showing the cross-sectional configuration of a fuel cell according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] A. First embodiment: (A1) Fuel cell system: As shown in Fig. 1, a fuel cell system 10 of this embodiment is mainly composed of a fuel cell 100, and the power generated by the fuel cell 100 is used to drive a motor 65 via a high-voltage inverter 61. The motor 65 is used, for example, to drive a fuel cell vehicle. Note that the low-voltage power output via a DC / DC converter built into the high-voltage inverter 61 is also used to drive low-voltage accessories 62 and charge a battery 64.

[0010] The fuel cell 100 includes a fuel cell stack 110, which is made up of multiple stacked fuel cell cells 111 (described later). The fuel cell stack 110 includes a fuel gas side end plate 102, which is composed of a current collector plate and an end plate, and an oxidant gas (air) side end plate 104, which is formed at both ends of the stack. The end plate 102 is provided with a fuel gas inlet 91, a cooling water inlet 71, and an oxidant gas outlet 82, while the end plate 104 is provided with a fuel gas outlet 92, a cooling water outlet 72, and an oxidant gas inlet 81. In the figure, the vertical direction of the figure corresponds to the vertical direction when the fuel cell stack 110 is actually placed in use, i.e., the downward direction corresponds to the direction of gravity. This direction of gravity is referred to as the Z direction. The stacking direction of the fuel cell cells 111 is referred to as the Y direction, and the direction perpendicular to the Z direction and the Y direction is referred to as the X direction. These X, Y, and Z directions are the same in other figures and are appropriately indicated in each figure for ease of explanation.

[0011] Hydrogen gas is supplied from the hydrogen gas tank 21 to the fuel gas supply port 91 on the end plate 102 via the main valve 22, pressure regulating valve 24, and injector 26, and introduced into the fuel cell stack 110. The amount of hydrogen gas introduced is adjusted by the opening time of the injector 26. Cooling water is introduced into the cooling water supply port 71. The cooling water is circulated through the fuel cell stack 110 by the cooling water pump 51, and heat accumulated as the cooling water passes through the fuel cell stack 110 is released to the outside as it passes through the radiator 52, maintaining the temperature of the fuel cell stack 110 within a predetermined temperature range. The oxidant gas discharge port 82 is simply open, and surplus air is released directly into the atmosphere.

[0012] Air (oxidant gas) taken in through air filter 41 is sent by pump 43 to gas supply port 81 of end plate 104. Cooling water that has passed through the cooling water passage inside fuel cell stack 110 is discharged from cooling water discharge port 72. As described above, the cooling water is returned to fuel cell stack 110 by cooling water pump 51 via radiator 52 through the circulation passage. Of the hydrogen gas introduced into fuel cell stack 110 by injector 26, hydrogen gas that has not been used for power generation is discharged from fuel gas discharge port 92 and circulated by hydrogen pump 28 to the upstream of injector 26 via circulation passage 93 and gas-liquid separator 30. Generated water and water vapor are also discharged from fuel gas discharge port 92 together with the hydrogen gas. These are separated from the hydrogen gas in gas-liquid separator 30 and discharged as water from drain valve 32 at a predetermined timing.

[0013] A control device (not shown) appropriately controls the above-mentioned high-voltage inverter 61 and low-voltage auxiliary equipment 62, as well as the opening and closing of the main valve 22, the opening time and timing of the injector 26, and the operation of the hydrogen pump 28, pump 43, and cooling water pump 51. The fuel cell 100 generates electricity by utilizing a chemical-electrical reaction between hydrogen in the fuel gas and oxygen in the air, and outputs the required power.

[0014] (A2) Fuel cell stack and fuel cell: Next, the schematic configuration of the fuel cell stack 110 and the fuel cell unit 111 will be described with reference to Figure 2. As shown in the figure, the fuel cell stack 110 is configured by stacking a plurality of fuel cell units 111. The bottom of Figure 2 shows a plan view of one of the plurality of fuel cell units 111 that make up the fuel cell stack 110, with the separator (described below) removed. The fuel cell unit 111 has a power generation area EA in its center and openings on both sides in the longitudinal direction (X direction in the figure). When the fuel cell units 111 are stacked, these openings function as flow paths that pass through the fuel cell stack 110.

[0015] At one end in the X direction, which is the longitudinal direction of the fuel cell 111, there are provided, in order along the Z direction, a fuel gas inlet opening 91P which functions as a fuel gas inlet manifold, a cooling water outlet opening 72P which functions as a cooling water outlet manifold, and an oxidant gas outlet opening 82P which functions as an oxidant gas (air) outlet manifold. On the other hand, at the other end in the -X direction of the fuel cell 111, there are provided, in order from the top in the figure, an oxidant gas inlet opening 81P which functions as an oxidant gas inlet manifold, a cooling water inlet opening 71P which functions as a cooling water inlet manifold, and a fuel gas outlet opening 92P which functions as a fuel gas outlet manifold.

[0016] Fuel gas enters the fuel cell stack 110 through the fuel gas supply port 91, passes through the fuel gas inlet manifold, and diffuses into the power generation area EA through the fuel gas inlet opening 91P in each fuel cell 111. The fuel gas and generated water (including water vapor) that does not contribute to power generation passes through the fuel gas outlet opening 92P and the fuel gas outlet manifold and is discharged from the fuel gas outlet port 92 of the fuel cell stack 110. This process is schematically illustrated by arrow-shaped symbols. Similarly, oxidant gas and coolant water flow in through their respective oxidant gas supply ports 81 and coolant inlets 71, pass through the respective inlet manifolds, pass through the interiors of each stacked fuel cell 111, reach the respective outlet manifolds, and are discharged from the respective oxidant gas outlet ports 82, 72 (see FIG. 1).

[0017] The fuel gas, oxidant gas, and coolant pass through different parts of the fuel cell 111. The structure of the fuel cell 111 and the parts through which the fuel gas and the like pass will be explained using FIG. 3. FIG. 3 is an explanatory diagram schematically showing the III-III cross section in FIG. 2. The fuel cell 111 has a configuration in which a membrane electrode assembly that generates power is sandwiched between an oxidant gas separator 231 and a fuel gas separator 232. The configuration of the power generation body will be described later. When the fuel cell cells 111 are stacked, the oxidant gas separator 231 and the fuel gas separator 232 ensure conductivity between adjacent fuel cell cells 111 and are impermeable to fuel gas and the like. For this reason, the oxidant gas separator 231 and the fuel gas separator 232 are formed from a gas-impermeable, conductive material such as titanium or sintered carbon.

[0018] The power generation unit is configured with a solid polymer electrolyte membrane 200 at its center, and catalyst layers 201, 202, which are electrodes supporting a catalyst such as platinum, are provided on both sides of the solid polymer electrolyte membrane 200. The solid polymer electrolyte membrane 200 and the outer catalyst layers 201, 202 are integrally formed and are also called a membrane electrode assembly (MEA). Diffusion layers 211, 212 are provided on the outer side of the membrane electrode assembly. An oxidant gas channel 221 and a fuel gas channel 222 are provided further outside the diffusion layers 211, 212, respectively. Although described here as separate components, the oxidant gas channel 221 is actually formed integrally with an oxidant gas separator 231, and the fuel gas channel 222 is formed integrally with the fuel gas separator 232.

[0019] As described above, the oxidant gas flows into the oxidant gas flow channel 221 from the oxidant gas inlet opening 81P, and the fuel gas flows into the fuel gas flow channel 222 from the fuel gas inlet opening 91P. The oxidant gas passes from the oxidant gas flow channel 221 through the diffusion layer 211 to one side of the membrane electrode assembly, and the fuel gas passes from the fuel gas flow channel 222 through the diffusion layer 212 to the other side of the membrane electrode assembly. The oxidant gas and fuel gas that have reached the membrane electrode assembly are catalytically acted upon in the catalyst layers 201 and 202 to exchange protons, generating electricity and producing water as a result. The produced water (produced water) and water vapor flow through the fuel gas flow channel 222 and are guided from the fuel gas outlet opening 92P to the fuel gas outlet 92, where they are separated from the fuel gas in the gas-liquid separator 30 and finally discharged to the outside via the drain valve 32. Although not shown in the figure, cooling water is supplied from a cooling water supply port 71, passes through a cooling water flow path provided in both separators 231, 232 from a cooling water inlet opening 71P, reaches a cooling water outlet opening 72P, and is discharged from a cooling water outlet port 72.

[0020] (A3) Features of membrane electrode assembly: In this embodiment, as shown in Figures 2 and 3, on the anode side of the membrane electrode assembly to which the fuel gas is introduced, the catalyst layer 202 is not provided in a predetermined range at the lower end in the Z direction. This range is called a catalyst deficient region 202A. In other words, the fuel gas flow path 222 at the lower end of the fuel cell 111 in the direction of gravity (Z direction) does not have a corresponding catalyst layer. For convenience of explanation, Figure 2 directly shows the range of the catalyst layer 202 and the catalyst deficient region 202A, excluding the fuel gas flow path 222 and the diffusion layer 212.

[0021] When liquid water infiltrates the fuel cell 111 along with the fuel gas, the liquid water tends to accumulate in the lower part of the fuel cell 111, and is therefore likely to collect in the lower part of the fuel gas flow path 222 of the fuel cell 111. In this embodiment, a part of the lower part of the fuel cell 111 is the catalyst deficient region 202A, so even if liquid water accumulates there, it is unlikely that the power generation surface of the membrane electrode assembly will become negative voltage. This prevents problems such as the power generation surface becoming negative voltage and the catalyst in the solid electrolyte membrane being deteriorated. The width of this catalyst deficient region 202A in the Z direction is 10% or more, preferably 15% or more, of the surface area of ​​the membrane electrode assembly, i.e., the area where the catalyst layer would normally be present. In this embodiment, the catalyst deficient region 202A does not have a catalyst layer itself, but it may be provided as a catalyst layer with a reduced catalyst amount, i.e., a reduced catalyst amount region.

[0022] B. Second embodiment: (B1) Characteristic configuration of the second embodiment: Next, a fuel cell 100 according to a second embodiment will be described with reference to FIGS. 4 and 5. The fuel cell 100 according to the second embodiment differs from the first embodiment in that a portion of the configuration of the fuel cell 111B is different, but the remainder is similar to that of the first embodiment. FIG. 4 is an explanatory diagram showing the characteristics of the fuel cell 111B according to the second embodiment, and FIG. 5 is an explanatory diagram showing a schematic cross-sectional configuration of the fuel cell according to the second embodiment as viewed from the arrows VV. Note that FIG. 4 is drawn with the fuel gas separator 232 removed, so that the fuel gas flow path 222 is visible.

[0023] In the fuel cell 100 of the second embodiment, each of the fuel cell cells 111B constituting the fuel cell stack 110 includes a region 222B with enhanced water repellency (hereinafter referred to as the water-repellent flow region) near the Z-direction (downward) end of the fuel gas flow path 222 in the power generation region EA. This water-repellent flow region 222B is formed by forming a coating, such as a fluorine-based coating, on the surface of a component constituting the flow path to enhance water repellency. Therefore, even if moisture enters the power generation region EA along with the fuel gas, liquid water collected in the Z-direction (downward) of the fuel gas flow path 222 does not remain in the water-repellent flow region 222B but quickly moves toward the fuel gas discharge opening 92P and is ultimately discharged from the fuel gas discharge port 92. As a result, as in the first embodiment, accumulated liquid water is less likely to cause insufficient fuel gas supply, resulting in a negative voltage on the power generation surface of the membrane electrode assembly. This reduces the occurrence of problems such as a negative voltage on the power generation surface that could lead to deterioration of the catalyst in the solid electrolyte membrane. The width of the water-repellent-improved flow path region 222B in the Z direction can be determined appropriately based on the expected amount of liquid water and the water-repellent properties. For example, it can be set to about 10% of the area where the catalyst layer would normally be located. The entire area of ​​the fuel gas flow path 222 may be made into the water-repellent-improved flow path region 222B with improved water repellency.

[0024] (B2) Modification: In this embodiment, a predetermined region at the lower end of the fuel gas flow path 222 in the Z direction is designated as the water-repellent flow path region 222B to improve the drainage of liquid water, but conversely, it is also possible to improve the drainage of liquid water by increasing the hydrophilicity of this region. If the surfaces of the components constituting the fuel gas flow path 222 are made superhydrophilic by applying, for example, a polysilicate-based inorganic coating agent, liquid water will be quickly drained without clogging the fuel gas flow path 222. Furthermore, as in the first embodiment, a portion of the catalyst layer 202 corresponding to the water-repellent flow path region 222B may be removed to form a catalyst-deficient region 202A.

[0025] C. Third embodiment: Next, a fuel cell 100 according to a third embodiment will be described with reference to Figures 6 and 7. The fuel cell 100 according to the third embodiment differs from the first embodiment in that a portion of the configuration of the fuel cell 111C is different, but otherwise has the same configuration as the first embodiment. Figure 6 is an explanatory diagram showing the characteristics of the fuel cell 111C according to the third embodiment, and Figure 7 is an explanatory diagram showing a schematic cross-sectional configuration of the fuel cell according to the third embodiment taken along the line VII-VII. Note that the diagram is drawn with the fuel gas separator 232 removed, so that the catalyst layer 202 is visible in the upper half of the power generation area EA, and the fuel gas flow path 222 is visible in the lower half.

[0026] In the fuel cell 100 of the third embodiment, each of the plurality of fuel cell units 111C constituting the fuel cell stack 110 has a region 222C with improved water repellency (hereinafter referred to as water-repellency-improved flow region) near the Z-direction (downward) end of the fuel gas flow channel 222 in the power generation region EA, and also has a region 202C with an increased catalyst amount (hereinafter referred to as catalyst amount-increased region) in a predetermined range at the upper end along the Z direction of the catalyst layer 202. This water-repellency-improved flow region 222C has a configuration similar to that of the water-repellency-improved flow region 222B of the second embodiment.

[0027] In this embodiment, the catalyst amount is increased in a predetermined region near the top of the catalyst layer 202 in the power generation region EA, thereby increasing the amount of power generated in this region. Therefore, even if moisture infiltrates the power generation region EA along with the fuel gas, resulting in a decrease in the amount of power generated in the lower portion of the power generation region EA in the Z direction, the decrease can be compensated for by the amount of power generated in the increased catalyst amount region 202C. Furthermore, liquid water collected in the fuel gas flow path 222 in the Z direction (downward) does not remain in the water-repellency-improved flow path region 222C but quickly moves toward the fuel gas discharge opening 92P and is ultimately discharged through the fuel gas discharge port 92. As in the first and second embodiments, this reduces the likelihood of an insufficient fuel gas supply due to accumulated liquid water, resulting in a negative voltage on the power generation surface of the membrane electrode assembly. Even if liquid water infiltrates the fuel gas flow path 222, sufficient power generation can be ensured. Similar to the first and second embodiments, the effect of suppressing catalyst degradation in the solid electrolyte membrane is achieved. The width of the catalyst-increased region 202C in the Z direction may be determined appropriately based on the expected amount of liquid water and the amount of power generation. For example, it may be approximately 10% of the area where the catalyst layer would normally be located. Alternatively, if a catalyst-deficient region is provided below the catalyst layer 202 in the Z direction, the width of the catalyst-deficient region may be set according to the width of the catalyst-deficient region. Furthermore, the catalyst amount may be increased or the catalyst-increased region may be wide enough to compensate for the decrease in power generation due to the catalyst-deficient region. As long as the presence of the catalyst-increased region 202C can ensure a sufficient amount of power generation, the water-repellency-improved flow path region 222C may be narrow or absent.

[0028] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features of the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate. For example, some of the configurations realized by hardware in the above-described embodiments can be realized by software. [Explanation of symbols]

[0029] 10...fuel cell system, 21...hydrogen gas tank, 22...main valve, 24...pressure regulating valve, 26...injector, 28...hydrogen pump, 30...gas-liquid separator, 32...drain valve, 41...air filter, 43...pump, 51...cooling water pump, 52...radiator, 61...high-voltage inverter, 62...low-voltage auxiliary equipment, 64...battery, 65...motor, 71...cooling water supply port, 71P...cooling water inlet opening, 72...cooling water outlet port, 72P...cooling water outlet opening, 81...oxidizer gas supply port, 81P...oxidizer gas inlet opening, 82...oxidizer gas outlet port, 82P...oxidizer gas outlet opening, 91 ...Fuel gas supply port, 91P...Fuel gas inlet opening, 92...Fuel gas outlet port, 92P...Fuel gas outlet opening, 93...Circulation passage, 100...Fuel cell, 102, 104...End plate, 110...Fuel cell stack, 111, 111B, 111C...Fuel cell, 200...Solid polymer electrolyte membrane, 201, 202...Catalyst layer, 202A...Catalyst deficient region, 202C...Catalyst increased amount region, 211, 212...Diffusion layer, 221...Oxidant gas flow path, 222...Fuel gas flow path, 222B, 222C...Water repellency improved flow path region, 231...Oxidant gas separator, 232...Fuel gas separator, EA...Power generation region

Claims

1. A fuel cell that generates electricity by supplying and discharging a fuel gas and an oxidant gas, a fuel cell comprising a membrane electrode assembly having an electrolyte membrane and a catalyst layer, and a separator disposed facing the membrane electrode assembly and sandwiching a diffusion layer between the separator and the catalyst layer to form a fuel gas flow path and an oxidant gas flow path; a fuel gas discharge manifold that discharges the fuel gas and is provided below the fuel cell in the direction of gravity, with the surface direction of the fuel cell being the direction of gravity when the fuel cell is in use; Equipped with the fuel gas flow path on the lower side of the fuel cell in the direction of gravity has a reduced region in which the catalyst layer in contact with the fuel gas flow path via the diffusion layer is reduced compared to the fuel gas flow path on the upper side of the fuel cell; fuel cell.

2. The fuel cell according to claim 1 , wherein the reduced area is free from the catalyst layer that contacts the reduced area via the diffusion layer.

3. 3. The fuel cell according to claim 2, wherein the reduced area has an area of ​​15% or more of the surface area of ​​the membrane electrode assembly.

4. 2. The fuel cell according to claim 1, wherein a region of the fuel gas flow path corresponding to the reduced area has higher water repellency than a region of the fuel gas flow path other than the reduced area.

5. the catalyst layer, which is in contact with the upper fuel gas flow path of the fuel cell via the diffusion layer, has an increased catalyst amount in accordance with the size of the reduction region; The fuel cell according to claim 1 .

6. 6. The fuel cell according to claim 1, comprising a fuel cell stack in which a plurality of the fuel cell units are stacked, wherein a direction intersecting the stacking direction is used as the direction of gravity.

7. A fuel cell comprising a membrane electrode assembly having an electrolyte membrane and a catalyst layer, and a separator disposed facing the membrane electrode assembly, sandwiching a diffusion layer between the separator and the catalyst layer to form a fuel gas flow path and an oxidant gas flow path, a surface direction of the fuel cell is set to the direction of gravity when the fuel cell is in use, and the fuel gas flow path on the lower side of the fuel cell in the direction of gravity has a reduced region in which the catalyst layer in contact with the fuel gas flow path via the diffusion layer is reduced compared to the fuel gas flow path on the upper side of the fuel cell; Fuel cell.

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