Fuel cell and fuel cell system

Abstract

To provide a fuel cell and a fuel cell system, each having excellent power generation performance and / or high potential durability in low humidity environment.SOLUTION: A fuel cell includes as a cathode catalyst, a first electrode catalyst in which first catalyst particles are carried on the surface of a first support made of tin oxide particles, and a second electrode catalyst having second catalyst particles carried on the surface of a second support made of carbon particles, and the content of the first electrode catalyst in the upstream region of the cathode flow path is more than that in the downstream region of a cathode flow path. The fuel cell system includes the above-mentioned fuel cell, an anode gas supply device supplying fuel gas, a cathode gas supply device supplying oxidant gas, and a purge device for purging the anode flow path with air. Each of the anode flow path and the cathode flow path has counterflow structure or parallel flow structure, and the purge device includes a device for supplying air in direction opposite to or the same as that of the fuel gas.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fuel cell and a fuel cell system, and more particularly to a fuel cell having excellent power generation performance in a low humidity environment and / or high potential durability, and a fuel cell system including such a fuel cell. [Background technology]

[0002] A polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) in which catalyst layers containing catalyst particles are bonded to both sides of an electrolyte membrane. A gas diffusion layer is usually disposed on the outside of the catalyst layer. Furthermore, a separator (also called a current collector) having a gas flow path is disposed on the outside of the gas diffusion layer. A polymer electrolyte fuel cell usually includes a structure (fuel cell stack) in which multiple unit cells each consisting of such an MEA, a gas diffusion layer, and a current collector are stacked.

[0003] The catalyst layer generally consists of a mixture of an electrode catalyst in which catalyst particles such as platinum or a platinum alloy are supported on the surface of a carrier, and a catalyst layer ionomer. When a fuel (e.g., hydrogen) and an oxidant (e.g., air) are supplied to the anode and cathode of a fuel cell having such a structure, an electrode reaction proceeds and electricity can be obtained.

[0004] However, when air is supplied to a long and narrow cathode flow channel, the oxygen concentration decreases toward the downstream side as the electrode reaction proceeds. At the same time, the concentration of water vapor, which is a reaction product, increases toward the downstream side of the cathode flow channel. Therefore, in an electrode with a uniform structure along the gas flow direction, the power generation performance may decrease.

[0005] In order to solve this problem, various proposals have been made in the past. For example, Patent Document 1 states: The present invention provides a catalyst layer including catalyst particles made of catalyst-supporting carbon, a fibrous material having an average fiber length of 1 μm or more and 15 μm or less, and a polymer electrolyte, The mass ratio of the fibrous material to the carbon particles on the gas outlet side (second electrode catalyst portion) is greater than that on the gas inlet side (first electrode catalyst portion). A membrane electrode assembly for a fuel cell is disclosed.

[0006] The same document states: (A) As the mass ratio of the fibrous material to the carbon particles increases, the number of pores formed in the catalyst layer by the fibrous material increases, and water removal is promoted; and (B) When the mass ratio at the gas outlet side is made larger than that at the gas inlet side, the water retention is increased at the gas inlet side, while the water removal is promoted at the gas outlet side. is stated.

[0007] In Patent Document 2, A catalyst layer is transferred onto the surface of the electrolyte membrane. Of the transferred catalyst layer, only the gas inlet side portion is further pressurized or heated. A method for manufacturing a membrane electrode assembly is disclosed.

[0008] The same document states: (A) The greater the pore volume of the catalyst layer, the greater the promotion of water removal; (B) When only the gas inlet side portion of the catalyst layer is pressurized or heated, the pore volume at the gas inlet side becomes smaller than that at the gas outlet side; and (C) This increases water retention at the gas inlet side, while facilitating water removal at the gas outlet side. is stated.

[0009] Patent Document 3 states: A catalyst layer including catalyst-supporting particles and a polymer electrolyte is provided. The ion exchange capacity of the polymer electrolyte contained in the gas inlet side (first electrode catalyst portion) is greater than that of the polymer electrolyte contained in the gas outlet side (second electrode catalyst portion). A membrane electrode assembly for a fuel cell is disclosed.

[0010] The same document states: (A) The larger the ion exchange capacity of the polymer electrolyte contained in the catalyst layer, the higher the water retention capacity; and (B) When the ion exchange capacity of the polymer electrolyte at the gas inlet side is made larger than that at the gas outlet side, the water retention is increased at the gas inlet side, while the water removal is promoted at the gas outlet side. is stated.

[0011] Furthermore, Patent Document 4 states: The cathode catalyst includes a first electrode catalyst including catalyst particles (A) whose surfaces are coated with a carbon film, and a second electrode catalyst including catalyst particles (B) whose surfaces are not coated with a carbon film, The content of the first electrode catalyst contained in the upstream region of the cathode flow channel is greater than the content of the first electrode catalyst contained in the downstream region of the cathode flow channel. A fuel cell is disclosed.

[0012] The same document states: (A) When the content of the first electrode catalyst in the upstream region of the cathode flow path is made larger than that in the downstream region of the cathode flow path, the power generation performance of the entire fuel cell in a low humidity environment is improved compared to when only one of the first electrode catalyst or the second electrode catalyst is used as the cathode catalyst; and (B) The oxygen transfer resistance of the entire catalyst layer does not decrease excessively, improving the power generation performance of the entire fuel cell in a high humidity environment. is stated.

[0013] In an automobile fuel cell system, if hydrogen gas remains in the anode flow path when the system is shut down, hydrogen may cross over to the cathode side, causing deterioration of the electrolyte membrane. In addition, impurities contained in the remaining fuel gas may poison the anode catalyst. For this reason, in automobile fuel cell systems, the anode flow path is purged with air when the system is shut down. On the other hand, when air purging is performed while the fuel cell is stopped, an area where the potential exceeds 1.5 V is generated in part of the cathode catalyst layer. This is believed to be due to the formation of a local cell inside the fuel cell. Therefore, when a carbon support is used as the catalyst support for the cathode catalyst, the carbon support is oxidized and deteriorated due to this abnormal potential (see Non-Patent Document 1). Furthermore, the occurrence of such abnormal potential and the resulting oxidized deterioration of the carbon support also occur immediately after the fuel cell is started up.

[0014] As disclosed in Patent Documents 1 to 4, by arranging an electrode catalyst with high water retention on the upstream side of the cathode flow path and an electrode catalyst with high drainage on the downstream side of the cathode flow path, it is possible to suppress the deterioration of power generation performance caused by changes in water vapor concentration. However, in Patent Documents 1 to 4, a carbon support is used as the catalyst support for the cathode catalyst, and therefore durability against abnormal potential (hereinafter also referred to as "high potential durability") is low.

[0015] Furthermore, in the case of fuel cells for automobiles, there is a demand for humidifier-free and compact radiators in order to reduce costs and improve power density. As a result, the temperature inside the cell becomes higher and the humidity inside the cell becomes lower. Under such conditions, an electrode catalyst that can obtain high power generation performance at low humidity without relying on generated water, or a catalyst layer using this, is required. However, there have been no examples of fuel cells proposed that take into consideration both power generation performance in a low humidity environment and high potential durability. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] JP 2019-083112 A [Patent Document 2] JP 2017-174600 A [Patent Document 3] JP 2018-060715 A [Patent Document 4] Patent Publication No. 2021-089874 [Non-patent literature]

[0017] [Non-Patent Document 1] A.Reiser et al., Electrochem. Solid-State Lett., 2005, 8, A273 Summary of the Invention [Problem to be solved by the invention]

[0018] An object of the present invention is to provide a fuel cell that is excellent in power generation performance in a low humidity environment and / or high potential durability. Another object of the present invention is to provide a fuel cell system including such a fuel cell. [Means for solving the problem]

[0019] In order to solve the above problems, a fuel cell according to the present invention has the following configuration. (1) The fuel cell is a membrane electrode assembly in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode catalyst layer; an anode separator disposed on the outer side of the anode-side gas diffusion layer and having an anode flow channel; a cathode separator disposed on the outer side of the cathode-side gas diffusion layer and having a cathode flow channel; It is equipped with: (2) The cathode catalyst layer contains, as a cathode catalyst, a first electrode catalyst in which first catalyst particles are supported on the surface of a first support made of tin oxide-based particles; a second electrode catalyst in which second catalyst particles are supported on the surface of a second support made of carbon particles; Including, The content of the first electrode catalyst contained in the upstream region of the cathode flow channel is greater than the content of the first electrode catalyst contained in the downstream region of the cathode flow channel.

[0020] A fuel cell system according to a first embodiment of the present invention comprises: A fuel cell according to the present invention; an anode gas supply device for supplying a fuel gas to an anode flow channel of the fuel cell; a cathode gas supply device that supplies an oxidant gas to a cathode flow passage of the fuel cell; a purge device that supplies air to the anode flow path when the fuel cell is stopped; Equipped with The anode flow channel and the cathode flow channel have a counter-flow structure or a parallel-flow structure, The purge system may include a system for supplying the air in a direction opposite to or in the same direction as the fuel gas.

[0021] Furthermore, a fuel cell system according to a second embodiment of the present invention has the following configuration. (1) The fuel cell system comprises: Fuel Cells and an anode gas supply device for supplying a fuel gas to an anode flow channel of the fuel cell; a cathode gas supply device that supplies an oxidant gas to a cathode flow passage of the fuel cell; a purge device that supplies air to the anode flow path when the fuel cell is stopped; Equipped with The anode flow channel and the cathode flow channel have a counter-flow structure or a parallel-flow structure, The purge system may include a system for supplying the air in a direction opposite to or in the same direction as the fuel gas. However, this does not include a case where the anode flow path and the cathode flow path have a counterflow structure and the purge device includes a device that supplies the air in a direction opposite to that of the fuel gas. (2) The fuel cell is a membrane electrode assembly in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode catalyst layer; an anode separator provided with the anode flow channel and disposed on the outer side of the anode-side gas diffusion layer; a cathode separator disposed on the outer side of the cathode-side gas diffusion layer and including the cathode flow channel; It is equipped with: (3) The cathode catalyst layer contains, as a cathode catalyst, a first electrode catalyst in which first catalyst particles are supported on the surface of a first support made of tin oxide-based particles; a second electrode catalyst in which second catalyst particles are supported on the surface of a second support made of carbon particles; Including, The content of the first electrode catalyst contained in the downstream region of the cathode flow channel is greater than the content of the first electrode catalyst contained in the upstream region of the cathode flow channel. Effect of the Invention

[0022] Tin oxide particles are more hydrophilic and have higher oxidation resistance against electric potential than carbon particles, so the first electrode catalyst using tin oxide particles as a carrier has poor drainage but is excellent in water retention (power generation performance under low humidity conditions) and high electric potential durability. On the other hand, carbon particles have lower oxidation resistance to electric potential compared to tin oxide particles, but are highly conductive and hydrophobic. Therefore, a second electrode using carbon particles as a carrier has poor water retention and high electric potential durability, but is excellent in drainage (power generation performance under high humidity conditions).

[0023] By optimizing the arrangement of the first electrode catalyst and the second electrode catalyst, which have such different properties, within the cathode catalyst layer and optimizing the gas flow, it is possible to improve the power generation performance in a low humidity environment and / or the high potential durability. Specifically, when the content of the first electrode catalyst in the upstream region of the cathode flow channel is made greater than that in the downstream region of the cathode flow channel, power generation performance in a low humidity environment is improved. Furthermore, by relatively increasing the content of the first electrode catalyst in the region of the cathode catalyst layer corresponding to the downstream region of the fuel gas flow, the high potential durability immediately after start-up is improved. Furthermore, by relatively increasing the content of the first electrode catalyst in the region of the cathode catalyst layer corresponding to the upstream region of the purge gas (air) flow, the high potential durability immediately after stopping is improved. [Brief description of the drawings]

[0024] [Figure 1] 1 shows an example of the configuration of a fuel cell system, and an example of gas flows during operation, immediately after shutdown, during shutdown, and immediately after startup of the fuel cell system. [Diagram 2] 1 is a schematic diagram of a fuel cell system according to a first embodiment of the present invention. [Diagram 3] FIG. 4 is a schematic diagram of a fuel cell system according to a second embodiment of the present invention. [Figure 4] IV performance under high humidity conditions (60° C., 80% RH) of the cells obtained in Reference Example 1 (Pt / Sb—SnO 2 ) and Reference Example 2 (Pt / C).

[0025] [Diagram 5] IV performance under low humidity conditions (82° C., 30% RH) of the cells obtained in Reference Example 1 (Pt / Sb—SnO 2 ) and Reference Example 2 (Pt / C). [Figure 6] 1 shows the ECSA retention rates before and after a high potential cycle test (2000 cycles) of the cells obtained in Reference Example 2 (Pt / C) and Reference Example 3 (Pt / Sb-SnO2). [Figure 7] FIG. 1 is a schematic diagram of assumptions used to predict power generation performance when low humidity gas is supplied to a fuel cell. [Figure 8] 1 shows the current density at 0.6 V (IR loss corrected) obtained by simple calculation for the fuel cells of Example 1 and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] [Configuration 1] A fuel cell comprising: (1) The fuel cell is a membrane electrode assembly in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode catalyst layer; an anode separator disposed on the outer side of the anode-side gas diffusion layer and having an anode flow channel; a cathode separator disposed on the outer side of the cathode-side gas diffusion layer and having a cathode flow channel; It is equipped with: (2) The cathode catalyst layer contains, as a cathode catalyst, a first electrode catalyst in which first catalyst particles are supported on the surface of a first support made of tin oxide-based particles; a second electrode catalyst in which second catalyst particles are supported on the surface of a second support made of carbon particles; Including, The content of the first electrode catalyst contained in the upstream region of the cathode flow channel is greater than the content of the first electrode catalyst contained in the downstream region of the cathode flow channel.

[0027] [Configuration 2] The tin oxide particles are SnO doped with at least one element selected from the group consisting of Sb, Nb, Ta, and W. 2 2. The fuel cell according to claim 1, comprising:

[0028] [Configuration 3] 3. The fuel cell according to configuration 1 or 2, wherein the tin oxide based particles have a structure in which primary particles are fused together in a beaded shape (a beaded structure).

[0029] [Configuration 4] The tin oxide particles have a specific surface area of ​​60 m 2 / g or more.

[0030] [Configuration 5] 5. The fuel cell according to any one of configurations 1 to 4, wherein the tin oxide based particles are porous particles having pores with a pore diameter of 5 nm or more and 8 nm or less.

[0031] [Configuration 6] 6. The fuel cell according to any one of configurations 1 to 5, wherein the carbon particles are porous particles having pores with a pore diameter of 3 nm or more and 30 nm or less.

[0032] [Configuration 7] A fuel cell according to any one of configurations 1 to 6; an anode gas supply device for supplying a fuel gas to an anode flow channel of the fuel cell; a cathode gas supply device that supplies an oxidant gas to a cathode flow passage of the fuel cell; a purge device that supplies air to the anode flow path when the fuel cell is stopped; Equipped with The anode flow channel and the cathode flow channel have a counter-flow structure or a parallel-flow structure, The purge device includes a device for supplying the air in a direction opposite to or in the same direction as the fuel gas. Fuel cell system.

[0033] [Configuration 9] A fuel cell system comprising: (1) The fuel cell system comprises: Fuel Cells and an anode gas supply device for supplying a fuel gas to an anode flow channel of the fuel cell; a cathode gas supply device that supplies an oxidant gas to a cathode flow passage of the fuel cell; a purge device that supplies air to the anode flow path when the fuel cell is stopped; Equipped with The anode flow channel and the cathode flow channel have a counter-flow structure or a parallel-flow structure, The purge system may include a system for supplying the air in a direction opposite to or in the same direction as the fuel gas. However, this does not include a case where the anode flow path and the cathode flow path have a counterflow structure and the purge device includes a device that supplies the air in a direction opposite to that of the fuel gas. (2) The fuel cell is a membrane electrode assembly in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode catalyst layer; an anode separator provided with the anode flow channel and disposed on the outer side of the anode-side gas diffusion layer; a cathode separator disposed on the outer side of the cathode-side gas diffusion layer and including the cathode flow channel; It is equipped with: (3) The cathode catalyst layer contains, as a cathode catalyst, a first electrode catalyst in which first catalyst particles are supported on the surface of a first support made of tin oxide-based particles; a second electrode catalyst in which second catalyst particles are supported on the surface of a second support made of carbon particles; Including, The content of the first electrode catalyst contained in the downstream region of the cathode flow channel is greater than the content of the first electrode catalyst contained in the upstream region of the cathode flow channel.

[0034] An embodiment of the present invention will be described in detail below. [1. First electrode catalyst] The fuel cell according to the present invention contains a first electrode catalyst as a cathode catalyst. Here, the "first electrode catalyst" refers to an electrode catalyst including a first support made of tin oxide-based particles and first catalyst particles supported on the surface of the first support.

[0035] [1.1. First catalyst particles] [1.1.1. Materials] In the present invention, the material of the first catalyst particles is not particularly limited. (a) Precious metals (Pt, Au, Ag, Pd, Rh, Ir, Ru, Os), (b) An alloy containing two or more precious metal elements; (c) Alloys containing one or more precious metal elements and one or more base metal elements (e.g., Fe, Co, Ni, Cr, V, Ti, etc.); etc.

[0036] Among these, the first catalyst particles are preferably made of Pt or a Pt alloy, since they have high activity in the electrode reaction of the fuel cell. Examples of Pt alloys include Pt-Fe alloys, Pt-Co alloys, Pt-Ni alloys, Pt-Pd alloys, Pt-Cr alloys, Pt-V alloys, Pt-Ti alloys, Pt-Ru alloys, and Pt-Ir alloys.

[0037] [1.1.2. Particle size] The particle size of the first catalyst particles is not particularly limited, and the most suitable particle size can be selected according to the purpose. In general, if the particle size of the first catalyst particles is too small, the first catalyst particles tend to dissolve. Therefore, the particle size of the first catalyst particles is preferably 1 nm or more. On the other hand, if the particle size of the first catalyst particles is too large, the mass activity decreases. Therefore, the particle size of the first catalyst particles is preferably 20 nm or less. The particle size of the first catalyst particles is more preferably 10 nm or less, or 5 nm or less.

[0038] [1.2. First carrier] [1.2.1. Materials] The first support is for supporting the first catalyst particles. In the present invention, tin oxide particles are used for the first support. Here, "tin oxide particles" refers to SnO 2 or SnO containing a dopant. 2 The term refers to particles consisting of: In the present invention, the type of dopant is not particularly limited. Examples of dopants include Sb, Nb, W, Ta, and Al. SnO 2 may contain any one of these dopants, or may contain two or more of them.

[0039] Among these, the tin oxide particles are SnO doped with at least one element selected from the group consisting of Sb, Nb, Ta, and W. 2 is preferred. In particular, tin oxide particles are Sb-doped SnO 2 Sb-doped SnO is preferred. 2 is SnO containing other dopants 2 Since the conductivity is higher than that of the first catalyst particles, it is suitable as a catalyst support for supporting the first catalyst particles.

[0040] Sb doped SnO 2 In the above, the higher the doping amount of Sb, the higher the electrical conductivity. To obtain such an effect, the doping amount of Sb is preferably 2.5 at % or more. The doping amount of Sb is more preferably 5.0 at % or more. On the other hand, if the doping amount of Sb is excessive, the carrier concentration becomes excessive and the electrical conductivity may decrease. Therefore, the doping amount of Sb is preferably 15.0 at% or less. The doping amount of Sb is more preferably 10.0 at% or less.

[0041] [1.2.2. Specific surface area] In general, the larger the specific surface area of ​​the tin oxide particles, the more highly dispersed the first catalyst particles can be supported, and the higher the ORR mass activity. Therefore, the larger the specific surface area of ​​the tin oxide particles, the better. In order to obtain high ORR mass activity, the specific surface area of ​​the tin oxide particles should be 30 m 2 / g or more. More preferably, the specific surface area is 50 m 2 / g or more, 60m 2 / g or more, 90m 2 / g or more, or 100m 2 / g or more.

[0042] [1.2.3. Pore diameter] The tin oxide particles may be porous particles having pores with a pore size of 50 nm or less (hereinafter also referred to as "mesopores") therein, or may be solid particles having no mesopores. The tin oxide particles are particularly preferably porous particles having mesopores therein. Here, "mesopores" generally refer to pores having a diameter of 2 nm or more and 50 nm or less. However, in the present invention, unless otherwise specified, "mesopores" includes pores having a diameter of less than 2 nm (so-called "micropores") in addition to pores having a diameter of 2 nm or more and 50 nm or less.

[0043] "Pore size" refers to the average diameter of the mesopores. The pore diameter can be obtained by analyzing the adsorption side data of the nitrogen adsorption isotherm of the tin oxide particles by the BJH method and determining the pore diameter at which the pore volume is maximum (the most frequent peak value or the mode pore diameter).

[0044] In the case where the tin oxide-based particles have mesopores, when the first catalyst particles are supported on the tin oxide-based particles, the proportion of the first catalyst particles present in the mesopores increases. Therefore, when the first catalyst particles are supported in the mesopores of the tin oxide-based particles to form a first electrode catalyst, and a catalyst layer is produced using such a first electrode catalyst and an ionomer, it is possible to suppress poisoning of the first catalyst particles by the ionomer and the resulting performance degradation.

[0045] When the tin oxide particles have mesopores, the pore diameter (size of the mesopores) affects the performance of the electrode catalyst. In general, if the pore diameter is too small, it becomes difficult to support the first catalyst particles in the mesopores. As a result, when a catalyst layer is produced using the first electrode catalyst according to the present invention and an ionomer, the first catalyst particles may be poisoned by the ionomer. Therefore, the pore diameter is preferably 1 nm or more. The pore diameter is more preferably 2 nm or more, and even more preferably 5 nm or more.

[0046] On the other hand, if the pore size is too large, the ionomer may enter the mesopores and the first catalyst particles supported in the mesopores may be poisoned by the ionomer. Therefore, the pore size is preferably 20 nm or less. The pore size is more preferably 10 nm or less, and even more preferably 8 nm or less. In particular, the tin oxide particles are preferably porous particles having pores with a pore size of 5 nm or more and 8 nm or less.A first electrode catalyst using such tin oxide particles as a catalyst support exhibits high catalytic activity.

[0047] [1.2.4. Shape] In the present invention, the shape of the tin oxide based particles is not particularly limited as long as the above-mentioned conditions are satisfied. The tin oxide based particles may be isolated particles or may have a beaded structure. Here, the term "beaded structure" refers to a structure in which primary particles are fused together in a beaded shape. The primary particles may be porous particles or solid particles. In order to obtain high catalytic activity, the primary particles are preferably porous particles.

[0048] By using the method described below, it is possible to obtain tin oxide-based particles whose primary particles are porous and have a beaded structure. In particles with a beaded structure (i.e., secondary particles), the primary particles are loosely connected to each other, so there are relatively large gaps between the primary particles. Therefore, when an electrode catalyst is produced using tin oxide-based particles with a beaded structure and a catalyst layer is produced using this and an ionomer, appropriate gaps are formed in the catalyst layer. As a result, the gas diffusion resistance of the catalyst layer is reduced. In addition, because the primary particles are made up of an aggregate of minute crystallites, there are relatively minute voids (mesopores) inside the primary particles, and therefore, when these are used as catalyst supports, it is possible to suppress poisoning of the first catalyst particles by the ionomer.

[0049] The shape of the primary particles is not particularly limited. When tin oxide-based particles are produced using the method described below, the primary particles are usually not perfectly spherical, but have an irregular shape with an aspect ratio of about 1.1 to 3.

[0050] [1.2.5. Average particle size of primary particles] The term "average particle size of primary particles" refers to the average value of the maximum dimension of primary particles measured by observation with a scanning electron microscope (SEM). The average particle size of the primary particles of the tin oxide based particles is not particularly limited, and an optimal value can be selected depending on the purpose.

[0051] Generally, if the average particle size of the primary particles is too small, it becomes difficult to support the first catalyst particles. Therefore, the average particle size of the primary particles is preferably 0.05 μm or more. The average particle size is more preferably 0.06 μm or more, and even more preferably 0.07 μm or more. On the other hand, if the average particle size of the primary particles is too large, the thickness of the catalyst layer becomes large, and the ionic resistance and electronic resistance in the catalyst layer may become large. Therefore, the average particle size of the primary particles is preferably 2 μm or less. The average particle size is more preferably 1 μm or less, and more preferably 0.5 μm or less.

[0052] [1.2.6. Catalyst loading] The term "catalyst loading amount" refers to the ratio of the mass of the first catalyst particles to the total mass of the first electrode catalyst. In the present invention, the catalyst loading amount of the first electrode catalyst is not particularly limited, and an optimal loading amount can be selected depending on the purpose.

[0053] Generally, if the amount of catalyst supported is too small, sufficient activity cannot be obtained. Therefore, the amount of catalyst supported is preferably 5 mass% or more. The amount of catalyst supported is more preferably 10 mass% or more, or 20 mass% or more. On the other hand, even if the catalyst loading amount is more than necessary, there is no difference in the effect and no practical benefit. Therefore, the catalyst loading amount of the first electrode catalyst is preferably 70 mass% or less. The catalyst loading amount is more preferably 60 mass% or less, or 50 mass% or less.

[0054] [1.2.7. Manufacturing method of tin oxide particles] The tin oxide based particles can be produced by a variety of methods. Examples of methods for producing tin oxide particles include (a) Co-precipitation method (Reference 1), (b) A method in which a precursor is sprayed into a flame (Reference 2), (b) Precipitating tin oxide in the pores of the template and then removing the template (Reference 3) etc. [Reference 1] F. Takasaki et al., J. Electrochem. Soc., 2011, 158, B1270 [Reference 2] K. Kakinuma et al., ACS Appl. Mater. Interfaces, 2019, 11, 34957 [Reference 3] JP 2022-077821 A

[0055] Among these, the method described in Reference 3 can be used to produce tin oxide particles whose primary particles are porous and have a beaded structure. Specifically, tin oxide particles having a beaded structure and made of porous primary particles can be produced using mesoporous carbon as a template. Mesoporous carbon is produced using mesoporous silica as a template. Mesoporous silica is usually synthesized by condensation polymerization of a silica source in a reaction solution containing a silica source, a surfactant, and a catalyst.

[0056] In synthesizing mesoporous silica, when the concentrations of the surfactant and the silica source in the reaction solution are each limited to a specific range, mesoporous silica having a beaded structure and specific ranges of specific surface area, pore size, etc. can be obtained. When such mesoporous silica having a beaded structure is used as a first template, carbon is precipitated in the first template, and the first template is removed, mesoporous carbon having a beaded structure is obtained. When mesoporous carbon having a beaded structure is used as a second template, tin oxide is precipitated in the second template, and the second template is removed, tin oxide particles having a beaded structure are obtained.

[0057] [2. Second electrode catalyst] The fuel cell according to the present invention further comprises a second electrode catalyst as a cathode catalyst. Here, the "second electrode catalyst" refers to an electrode catalyst including a second support made of carbon particles and second catalyst particles supported on the surface of the second support.

[0058] [2.1. Second catalyst particles] [2.1.1. Materials] In the present invention, the material of the second catalyst particles is not particularly limited, and the details of the material of the second catalyst particles are the same as those of the first catalyst particles, so the explanation is omitted.

[0059] [2.1.2. Particle size] The particle size of the second catalyst particles is not particularly limited, and an optimal particle size can be selected depending on the purpose. The details of the particle size of the second catalyst particles are the same as those of the first catalyst particles, so the explanation is omitted.

[0060] [2.2. Second Carrier] [2.2.1. Materials] The second support is for supporting the second catalyst particles. In the present invention, carbon particles are used as the second support. The carbon particles may be porous particles having mesopores or may be solid particles having no mesopores, but in order to obtain high catalytic activity, the carbon particles are preferably porous particles having mesopores.

[0061] Examples of carbon particles include: (a) Mesoporous carbon; (b) Carbon black, carbon nanotubes, carbon nanohorns, activated carbon, natural graphite, mesocarbon microbeads, glassy carbon powder etc.

[0062] [2.2.2. Specific surface area] The specific surface area of ​​the carbon particles is not particularly limited, and an optimal value can be selected depending on the purpose. In general, the larger the specific surface area of ​​the carbon particles, the more highly dispersed the first catalyst particles can be supported.

[0063] [2.2.3. Pore diameter] When the carbon particles are porous particles, the pore size is not particularly limited, and an optimal value can be selected depending on the purpose. Note that the definition of the pore size and the method of measuring the pore size are the same as those of the tin oxide particles, and therefore the explanation is omitted.

[0064] In the case where the carbon particles are porous particles, if the pore size is too small, it may be difficult to support the second catalyst particles in the mesopores. Therefore, the pore size is preferably 3 nm or more. The pore size is more preferably 5 nm or more. On the other hand, if the pore diameter is too large, the ionomer easily penetrates into the mesopores. Therefore, the pore diameter is preferably 30 nm or less. The pore diameter is more preferably 25 nm or less, 20 nm or less, or 15 nm or less.

[0065] [2.2.4. Shape] In the present invention, the shape of the carbon particles is not particularly limited as long as it satisfies the above-mentioned conditions. The carbon particles may be isolated particles or may have a beaded structure. Other points regarding the shape of the carbon particles are the same as those of the tin oxide particles, so the description will be omitted.

[0066] [2.2.5. Average particle size of primary particles] The average particle size of the primary particles of the carbon particles is not particularly limited, and an optimal value can be selected depending on the purpose. Details of the average particle size of the primary particles of the carbon particles are the same as those of the tin oxide particles, so a description thereof will be omitted.

[0067] [2.2.5. Catalyst loading] In the present invention, the amount of catalyst carried by the second electrode catalyst is not particularly limited, and an optimal amount can be selected depending on the purpose. The details of the amount of catalyst carried by the second electrode catalyst are the same as those of the first electrode catalyst, so the explanation is omitted.

[0068] [3. Fuel cell] The fuel cell according to the present invention comprises: a membrane electrode assembly in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode catalyst layer; an anode separator disposed on the outer side of the anode-side gas diffusion layer and having an anode flow channel; a cathode separator disposed on the outer side of the cathode-side gas diffusion layer and having a cathode flow channel; It is equipped with:

[0069] [3.1. Components of a fuel cell] [3.1.1. Electrolyte membrane] In the present invention, the material of the electrolyte membrane is not particularly limited, and an optimum material can be selected depending on the purpose. Examples of the electrolyte material include: (a) perfluorocarbon sulfonic acid polymers such as Nafion®, Flemion®, Aciplex®, and Aquivion®; (b) Hydrocarbon polymers such as sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, and sulfonated polyphenylene; etc.

[0070] [3.1.2. Anode catalyst layer] The anode catalyst layer is bonded to one side of the electrolyte membrane and includes an anode catalyst and a catalyst layer ionomer. In the present invention, the materials of the anode catalyst and the catalyst layer ionomer, and the contents thereof are not particularly limited, and an optimum material can be selected depending on the purpose.

[0071] [3.1.3. Cathode catalyst layer] The cathode catalyst layer is bonded to the other surface of the electrolyte membrane. The cathode catalyst layer includes a cathode catalyst and a catalyst layer ionomer. Among these, the material of the catalyst layer ionomer and its content are not particularly limited, and an optimum one can be selected depending on the purpose.

[0072] On the other hand, the fuel cell according to the present invention contains, as a cathode catalyst, a first electrode catalyst in which first catalyst particles are supported on the surface of a first support made of tin oxide-based particles; a second electrode catalyst in which second catalyst particles are supported on the surface of a second support made of carbon particles; This is different from the conventional method. The details of the first electrode catalyst and the second electrode catalyst are as described above, and therefore will not be described here. The contents of the first electrode catalyst and the second electrode catalyst contained in the cathode catalyst layer will be described later.

[0073] [3.1.4. Anode side gas diffusion layer, cathode side gas diffusion layer] An anode-side gas diffusion layer is disposed on the outer side of the anode catalyst layer, and a cathode-side gas diffusion layer is disposed on the outer side of the cathode catalyst layer. In the present invention, the materials and structures of the anode side gas diffusion layer and the cathode side gas diffusion layer are not particularly limited, and the optimum materials and structures can be selected depending on the purpose.

[0074] [3.1.5. Anode separator and cathode separator] An anode separator is disposed on the outside of the anode-side gas diffusion layer. A cathode separator is disposed on the outside of the cathode-side gas diffusion layer. The anode separator has an anode flow path for allowing fuel gas to flow in a specific direction. Similarly, the cathode separator has a cathode flow path for allowing oxidant gas to flow in a specific direction.

[0075] In the present invention, the material of the separator is not particularly limited, and an optimum material can be selected depending on the purpose. Examples of the separator material include stainless steel and carbon.

[0076] The structure of the gas flow channels (anode flow channel and cathode flow channel) is not particularly limited, and an optimal structure can be selected depending on the purpose. For example, the gas flow channel may extend linearly from one end to the other end of the separator. Alternatively, the gas flow channel may be bent or curved within the plane of the separator.

[0077] In order to improve the high potential durability, the anode flow channel and the cathode flow channel preferably have a counter flow structure or a parallel flow structure. When the anode flow channel and the cathode flow channel have a counter flow structure or a parallel flow structure, the high potential durability may be improved by optimizing the direction of the gas flow. This will be described later.

[0078] Here, the term "counterflow structure" refers to a structure in which the flow direction of the fuel gas and the flow direction of the oxidant gas are opposite to each other. The term "parallel flow structure" refers to a structure in which the flow direction of the fuel gas and the flow direction of the oxidant gas are the same. In this case, the anode flow channel and the cathode flow channel may be straight flow channels or may be bent or curved flow channels, so long as they have a counter-flow structure or a parallel-flow structure.

[0079] [3.2. Cathode catalyst content] [3.2.1. Definition] In the fuel cell according to the present invention, the content of the first electrode catalyst in the upstream region of the cathode flow channel is greater than the content of the first electrode catalyst in the downstream region of the cathode flow channel. This point is different from the conventional one. Here, the "upstream region of the cathode flow channel" refers to the region from the inlet of the cathode flow channel to the midpoint between the inlet and outlet of the cathode flow channel. The "downstream region of the cathode flow channel" refers to the region from the midpoint to the outlet of the cathode flow channel. "Content of the first electrode catalyst" refers to the mass (W 1 ) and the mass of the second electrode catalyst (W 2 ) the mass ratio of the first electrode catalyst to the sum of (= W 1 ×100 / (W 1 +W 2 ))

[0080] The "content of the first electrode catalyst contained in the upstream region" refers to the average content of the first electrode catalyst contained in the upstream region, and does not necessarily mean that the content of the first electrode catalyst contained in the upstream region is uniform regardless of location. For example, the content of the first electrode catalyst may decrease stepwise or continuously from the inlet of the cathode flow channel to the midpoint. Similarly, the "content of the first electrode catalyst contained in the downstream region" refers to the average content of the first electrode catalyst contained in the downstream region, and does not necessarily mean that the content of the first electrode catalyst contained in the downstream region is uniform regardless of location. For example, the content of the first electrode catalyst may decrease stepwise or continuously from the midpoint toward the outlet of the cathode flow channel.

[0081] [3.2.2. Content of first electrode catalyst in the upstream region] The first electrode catalyst contains tin oxide particles. Tin oxide particles are more hydrophilic and have higher oxidation resistance against electric potential than carbon particles. Therefore, the first electrode catalyst using tin oxide particles as a carrier has poor drainage, but has excellent water retention (power generation performance under low humidity conditions) and high electric potential durability. On the other hand, in the upstream region of the cathode flow channel, the oxygen concentration is generally high and the humidity is generally low. In general, catalyst poisoning by ionomers increases at low humidity, where the adsorptive power of the ionomers is strong.

[0082] Therefore, when the content of the first electrode catalyst is relatively increased in the upstream region where humidity is low, water retention is improved and power generation performance is improved. In addition, when the tin oxide particles are porous and the first catalyst particles are supported in the pores of the tin oxide particles, catalyst poisoning by the ionomer can be suppressed. Furthermore, when the upstream region of the cathode flow path corresponds to the "region where abnormal potential occurs", high potential durability is improved by relatively increasing the content of the first electrode catalyst in the upstream region. To obtain such an effect, the content of the first electrode catalyst in the upstream region is preferably 50% or more. The content is preferably 60% or more, 70% or more, 80% or more, or 90% or more.

[0083] [3.2.3. Content of first electrode catalyst in downstream region] The second electrode catalyst contains carbon particles. Compared to tin oxide particles, carbon particles have low oxidation resistance against electric potential, but high electrical conductivity and hydrophobicity. Therefore, the second electrode catalyst using carbon particles as a carrier has poor water retention and high electric potential durability, but is excellent in drainage (power generation performance under high humidity conditions). On the other hand, in the downstream region of the cathode flow channel, the oxygen concentration is generally low and the humidity is high.

[0084] Therefore, by relatively reducing the content of the first electrode catalyst in the downstream region where humidity is high, drainage and power generation performance are improved. Furthermore, when the downstream region of the cathode flow path does not correspond to the "region where abnormal potential occurs", high potential durability is not excessively reduced even if the second electrode catalyst is placed in the downstream region of the cathode flow path. To obtain such an effect, the content of the first electrode catalyst in the downstream region is preferably less than 50%. The content is preferably less than 40%, less than 30%, less than 20%, or less than 10%.

[0085] [4. Fuel Cell Systems (1)] A fuel cell system according to a first embodiment of the present invention comprises: A fuel cell according to the present invention; an anode gas supply device for supplying a fuel gas to an anode flow channel of the fuel cell; a cathode gas supply device that supplies an oxidant gas to a cathode flow passage of the fuel cell; a purge device that supplies air to the anode flow path when the fuel cell is stopped; It is equipped with:

[0086] Furthermore, in the fuel cell system according to the present embodiment, The anode flow channel and the cathode flow channel have a counter-flow structure or a parallel-flow structure, The purge system may include a system for supplying the air in a direction opposite to or in the same direction as the fuel gas.

[0087] [4.1. Components of a fuel cell system] [4.1.1. Fuel cell] The fuel cell system according to the present embodiment includes a fuel cell according to the present invention. In the present embodiment, the anode flow path and the cathode flow path of the fuel cell have a counter-flow structure or a parallel flow structure. Other points regarding the fuel cell are as described above, and therefore will not be described here.

[0088] [4.1.2. Anode gas supply device] The anode gas supply device is for supplying fuel gas to the anode flow channel of the fuel cell. In the present embodiment, the anode gas supply device is not particularly limited, and an optimal one can be selected depending on the purpose.

[0089] [4.1.3. Cathode gas supply device] The cathode gas supply device is for supplying an oxidant gas to the cathode flow passage of the fuel cell. In the present embodiment, the cathode gas supply device is not particularly limited, and an optimum one can be selected depending on the purpose.

[0090] [4.1.4. Purging device] The purge device is for supplying air (purge gas) to the anode flow path when the fuel cell is stopped. If fuel gas remains in the anode flow path when the fuel cell is stopped, degradation of the electrolyte membrane due to crossover of the fuel gas and poisoning of the anode catalyst due to impurities contained in the fuel gas may occur. Therefore, it is preferable to purge the anode flow path with air immediately after the fuel cell is stopped and discharge the remaining fuel gas from the anode flow path. The purge device may be equipped with a device for supplying air in the opposite direction to the fuel gas, or may be equipped with a device for supplying air in the same direction as the fuel gas. It is preferable to select the optimal direction of the purge gas flow depending on the purpose.

[0091] [4.2. Methods to avoid oxidative deterioration of supports due to abnormal potential] [4.2.1. Configuration of fuel cell system] An example of the configuration of a fuel cell system and an example of the gas flows during operation, immediately after shutdown, during shutdown, and immediately after startup of the fuel cell system are shown in Fig. 1. In Fig. 1, the fuel cell system 10a includes a fuel cell 20, an anode gas supply device 40, a cathode gas supply device 50, and a purging device 60.

[0092] The fuel cell 20 comprises an electrolyte membrane 22, an anode 24 bonded to one side of the electrolyte membrane 22, a cathode 26 bonded to the other side of the electrolyte membrane 22, an anode separator 28 arranged on the outside of the anode 24, and a cathode separator 30 arranged on the outside of the cathode 26.

[0093] The anode 24 is made of a laminate of an anode catalyst layer (not shown) and an anode-side gas diffusion layer (not shown). In the example shown in Fig. 1, a support made of carbon particles (carbon support) is used as the catalyst support of the anode catalyst. The cathode 26 is composed of a laminate of a cathode catalyst layer (not shown) and a cathode-side gas diffusion layer (not shown). In the example shown in Fig. 1, a carrier made of tin oxide particles (oxide carrier) is used for the catalyst carrier of the cathode catalyst arranged in the upstream region 26a of the cathode flow path. On the other hand, a carbon carrier is used for the catalyst carrier of the cathode catalyst arranged in the downstream region 26b of the cathode flow path.

[0094] In the example shown in Fig. 1, the anode flow path provided in the anode separator 28 and the cathode flow path provided in the cathode separator 30 have a counter-flow structure. Fuel gas (hydrogen) is supplied from the left side to the right side of Fig. 1. Meanwhile, oxidant gas (air) is supplied from the right side to the left side of Fig. 1. Furthermore, purge gas (air) is supplied in the opposite direction to the fuel gas, that is, from the right side to the left side of Fig. 1.

[0095] 4.2.2. Gas flow [A. During driving] The upper diagram in Fig. 1 shows the flow of fuel gas and oxidant gas during operation. When low-humidity air is supplied to the cathode flow passage of the cathode separator 30 in the fuel cell system 10a having the above-mentioned configuration to generate power, the upstream region 26a of the cathode flow passage is in a dry environment, whereas the downstream region 26b of the cathode flow passage is in a wet environment. Therefore, by arranging a first electrode catalyst containing an oxide carrier in the upstream region 26a of the cathode flow passage and arranging a second electrode catalyst containing a carbon carrier in the downstream region 26b of the cathode flow passage, high power generation performance can be obtained even when low-humidity oxidant gas is supplied.

[0096] [B. Immediately after stopping] The second diagram from the top in Fig. 1 shows the flow of purge gas immediately after shutdown. The purge device 60 is equipped with a device that supplies purge gas (air) in the opposite direction to the fuel gas. The purge device 60 also has a switching valve 62 for supplying purge gas at the outlet of the anode flow path. Immediately after shutdown (during air purging), the switching valve 62 switches from the outlet side of the anode flow path to the inlet flow path side for supplying purge gas.

[0097] When stopping the fuel cell 20 having a counterflow structure, if a purge gas (air) is made to flow in the opposite direction to the fuel gas, (a) in a region of the anode flow channel corresponding to upstream region 26a of the cathode flow channel, hydrogen is replaced with air; and (b) Hydrogen remains in the region of the anode flow channel corresponding to the downstream region 26b of the cathode flow channel. Furthermore, air remains in the cathode flow passage.

[0098] If such a state occurs temporarily in the fuel cell 20, a local cell is formed in the fuel cell 20, and the potential of the upstream region 26a of the cathode flow path exceeds 1.5 V. Therefore, if a second electrode catalyst containing a carbon support is placed in the upstream region 26a of the cathode catalyst layer, the carbon support will be oxidized and deteriorated due to the abnormal potential. In contrast, if a first electrode catalyst containing an oxide support is placed in the region where the abnormal potential occurs, it is possible to avoid the oxidized deterioration of the support caused by the abnormal potential.

[0099] [C. When stopped] 1 shows the state inside the fuel cell when it is stopped. When it is stopped, the flow valve 42 of the anode gas supply device 40 is closed, and the anode is maintained in an air environment. Purging the anode flow path with air when it is stopped can suppress deterioration of the electrolyte membrane caused by hydrogen crossover and poisoning of the anode catalyst by impurities.

[0100] [D. Immediately after startup] The lower diagram in Figure 1 shows the flow of fuel gas and oxidant gas immediately after startup. Immediately after startup, hydrogen is once again supplied to the anode flow path and air is expelled. At this time, (a) in a region of the anode flow channel corresponding to downstream region 26b of the cathode flow channel, air is replaced with hydrogen, and (b) Air remains in the region of the anode flow channel that corresponds to the upstream region 26a of the cathode flow channel.

[0101] As a result, immediately after startup, an abnormal potential occurs in the upstream region 26a of the cathode flow path, just as immediately after shutdown. Therefore, by disposing a first electrode catalyst having an oxide support in the upstream region 26a of the cathode flow path, it is possible to avoid oxidative deterioration of the support caused by the abnormal potential.

[0102] [4.3. Specific examples of fuel cell systems] 2 shows a schematic diagram of fuel cell systems 10a to 10d according to a first embodiment of the present invention. In each of the fuel cell systems 10a to 10d, a first electrode catalyst containing an oxide support is disposed in an upstream region 26a of the cathode flow path, and a second electrode catalyst containing a carbon support is disposed in a downstream region 26b of the cathode flow path. However, the fuel cell systems 10a to 10d differ from each other in the way that the fuel gas and the purge gas flow.

[0103] [4.3.1. Case 1] The upper diagram in Fig. 2 shows Case 1. The fuel cell system 10a in Case 1 has the same configuration as the fuel cell system 10a shown in Fig. 1. That is, the fuel cell system 10a has the following configuration: (a) the cathode flow channel and the anode flow channel have a counter-flow structure; and (b) The purge device 60 is provided with a device for supplying air in the opposite direction to the fuel gas.

[0104] The fuel cell system 10a exhibits high power generation performance in a low humidity environment. In addition, the fuel cell system 10a has excellent high potential durability immediately after startup because the first electrode catalyst is disposed in the region of the cathode catalyst layer corresponding to the downstream region of the anode gas flow (i.e., the region where abnormal potential occurs immediately after startup). Furthermore, the fuel cell system 10a has excellent high potential durability immediately after shutdown because the first electrode catalyst is disposed in the region of the cathode catalyst layer corresponding to the upstream region of the purge gas flow (i.e., the region where abnormal potential occurs immediately after shutdown).

[0105] [4.3.2. Case 2] The second diagram from the top in FIG. 2 shows Case 2. The fuel cell system 10b of Case 2 has the following features: (a) the cathode flow channel and the anode flow channel have a parallel flow structure; and (b) The purge device 60 is provided with a device for supplying air in the opposite direction to the fuel gas.

[0106] The fuel cell system 10b exhibits high power generation performance in a low humidity environment. However, the fuel cell system 10b has poor high potential durability immediately after startup because the first electrode catalyst is not disposed in the region of the cathode catalyst layer corresponding to the downstream region of the anode gas flow (i.e., the region where abnormal potential occurs immediately after startup). Similarly, the fuel cell system 10b has poor high potential durability immediately after shutdown because the first electrode catalyst is not disposed in the region of the cathode catalyst layer corresponding to the upstream region of the purge gas flow (i.e., the region where abnormal potential occurs immediately after shutdown).

[0107] [4.3.3. Case 3] The third diagram from the top in FIG. 2 shows Case 3. The fuel cell system 10c of Case 3 has the following features: (a) the cathode flow channel and the anode flow channel have a counter-flow structure; and (b) The purge device 60 is equipped with a device that supplies air in the same direction as the fuel gas.

[0108] The fuel cell system 10c exhibits high power generation performance in a low humidity environment. In addition, the fuel cell system 10c has excellent high potential durability immediately after startup because the first electrode catalyst is disposed in the region of the cathode catalyst layer corresponding to the downstream region of the anode gas flow (i.e., the region where abnormal potential occurs immediately after startup). However, the fuel cell system 10c has poor high potential durability immediately after shutdown because the first electrode catalyst is not disposed in the region of the cathode catalyst layer corresponding to the upstream region of the purge gas flow (i.e., the region where abnormal potential occurs immediately after shutdown).

[0109] [4.3.4. Case 4] The lower diagram of FIG. 2 shows Case 4. The fuel cell system 10d of Case 4 has the following features: (a) the cathode flow channel and the anode flow channel have a parallel flow structure; and (b) The purge device 60 is equipped with a device that supplies air in the same direction as the fuel gas.

[0110] The fuel cell system 10d exhibits high power generation performance in a low humidity environment. However, the fuel cell system 10d has poor high potential durability immediately after startup because the first electrode catalyst is not disposed in the region of the cathode catalyst layer corresponding to the downstream region of the anode gas flow (i.e., the region where abnormal potential occurs immediately after startup). On the other hand, the fuel cell system 10c has excellent high potential durability immediately after shutdown because the first electrode catalyst is disposed in the region of the cathode catalyst layer corresponding to the upstream region of the purge gas flow (i.e., the region where abnormal potential occurs immediately after shutdown).

[0111] [5. Fuel Cell Systems (2)] A fuel cell system according to a second embodiment of the present invention comprises: Fuel Cells and an anode gas supply device for supplying a fuel gas to an anode flow channel of the fuel cell; a cathode gas supply device that supplies an oxidant gas to a cathode flow passage of the fuel cell; a purge device that supplies air to the anode flow path when the fuel cell is stopped; It is equipped with:

[0112] Furthermore, in the fuel cell system according to the present embodiment, The anode flow channel and the cathode flow channel have a counter-flow structure or a parallel-flow structure, The purge system may include a system for supplying the air in a direction opposite to or in the same direction as the fuel gas. However, this does not include a case where the anode flow path and the cathode flow path have a counterflow structure and the purge device includes a device that supplies the air in a direction opposite to that of the fuel gas.

[0113] [5.1. Components of a fuel cell system] In this embodiment, the content of the first electrode catalyst in the downstream region of the cathode flow channel is greater than the content of the first electrode catalyst in the upstream region of the cathode flow channel, i.e., the catalyst arrangement in this embodiment is reversed from that in the first embodiment. Furthermore, this embodiment excludes a fuel cell system in which the anode flow passage and the cathode flow passage have a counterflow structure and the purge device has a device that supplies air in the opposite direction to the fuel gas. Other aspects of the fuel cell system are similar to those of the first embodiment, so a description thereof will be omitted.

[0114] [5.2. Specific examples of fuel cell systems] 3 is a schematic diagram of fuel cell systems 10e to 10h according to a second embodiment of the present invention. In each of the fuel cell systems 10e to 10h, a second electrode catalyst containing a carbon support is disposed in an upstream region 26a of the cathode flow path, and a first electrode catalyst containing an oxide support is disposed in a downstream region 26b of the cathode flow path. However, the fuel cell systems 10e to 10h differ from each other in the way that the fuel gas and purge gas are allowed to flow.

[0115] [5.2.1. Case 5] The upper diagram in FIG. 3 shows Case 5. The fuel cell system 10e of Case 5 has the following features: (a) the cathode flow channel and the anode flow channel have a counter-flow structure; and (b) The purge device 60 is provided with a device for supplying air in the opposite direction to the fuel gas.

[0116] The fuel cell system 10e has poor power generation performance in a low humidity environment because a first electrode catalyst containing an oxide support is not disposed in the upstream region 26a of the cathode flow path. In addition, the fuel cell system 10e has poor high potential durability immediately after startup because the first electrode catalyst is not disposed in the region of the cathode catalyst layer corresponding to the downstream region of the anode gas flow (i.e., the region where abnormal potential occurs immediately after startup). Furthermore, the fuel cell system 10e has poor high potential durability immediately after shutdown because the first electrode catalyst is not disposed in the region of the cathode catalyst layer corresponding to the upstream region of the purge gas flow (i.e., the region where abnormal potential occurs immediately after shutdown). Therefore, case 5 is excluded from the present invention.

[0117] [5.2.2. Case 6] The second diagram from the top in FIG. 3 shows Case 6. The fuel cell system 10f of Case 6 has the following features: (a) the cathode flow channel and the anode flow channel have a parallel flow structure; and (b) The purge device 60 is provided with a device for supplying air in the opposite direction to the fuel gas.

[0118] The fuel cell system 10f has low power generation performance in a low humidity environment. However, the fuel cell system 10f has excellent high potential durability immediately after startup because the first electrode catalyst is disposed in the region of the cathode catalyst layer corresponding to the downstream region of the anode gas flow (i.e., the region where abnormal potential occurs immediately after startup). Furthermore, the fuel cell system 10f has excellent high potential durability immediately after shutdown because the first electrode catalyst is disposed in the region of the cathode catalyst layer corresponding to the upstream region of the purge gas flow (i.e., the region where abnormal potential occurs immediately after shutdown).

[0119] [5.2.3. Case 7] The third diagram from the top in FIG. 3 shows Case 7. The fuel cell system 10g of Case 7 has the following features: (a) the cathode flow channel and the anode flow channel have a counter-flow structure; and (b) The purge device 60 is equipped with a device that supplies air in the same direction as the fuel gas.

[0120] The fuel cell system 10g has low power generation performance in a low humidity environment. In addition, the fuel cell system 10g has poor high potential durability immediately after startup because the first electrode catalyst is not disposed in the region of the cathode catalyst layer corresponding to the downstream region of the anode gas flow (i.e., the region where abnormal potential occurs immediately after startup). However, the fuel cell system 10g has excellent high potential durability immediately after shutdown because the first electrode catalyst is disposed in the region of the cathode catalyst layer corresponding to the upstream region of the purge gas flow (i.e., the region where abnormal potential occurs immediately after shutdown).

[0121] [5.2.4. Case 8] The lower diagram of FIG. 3 shows Case 8. The fuel cell system 10h of Case 8 is as follows: (a) the cathode flow channel and the anode flow channel have a parallel flow structure; and (b) The purge device 60 is equipped with a device that supplies air in the same direction as the fuel gas.

[0122] The fuel cell system 10h has low power generation performance in a low humidity environment. However, the fuel cell system 10g has excellent high potential durability immediately after startup because the first electrode catalyst is disposed in the region of the cathode catalyst layer corresponding to the downstream region of the anode gas flow (i.e., the region where abnormal potential occurs immediately after startup). On the other hand, the fuel cell system 10g has poor high potential durability immediately after shutdown because the first electrode catalyst is not disposed in the region of the cathode catalyst layer corresponding to the upstream region of the purge gas flow (i.e., the region where abnormal potential occurs immediately after shutdown).

[0123] [6. Effect] The principle of the abnormal potential occurring immediately after the start-up of a fuel cell is reported in Non-Patent Document 1. When hydrogen is introduced into the anode of a fuel cell that has been purged with air during shutdown, the anode catalytic potential (V m a ), cathode catalytic potential (V m c ) and electrolyte potential (F). In addition, because the hydrogen / oxygen concentration distributions are different in the anode flow channel, the voltage distribution change at startup may be different between the downstream and upstream regions of the cathode flow channel.

[0124] Assuming that hydrogen is introduced into the anode that is purged with air, the voltage distribution change immediately after start-up is as follows. (1) Before start-up, the anode and cathode are held in air. Here, the potential of the cathode catalyst layer is at equilibrium potential, and the cell voltage is net zero. (2) Immediately after startup, hydrogen gas flows from the inlet to the outlet of the anode flow channel. At this time, the potential of the upstream region of the anode flow channel becomes the equilibrium potential of hydrogen due to hydrogen oxidation, and the cell voltage becomes 0.85 V.

[0125] (3) At the same time that hydrogen supply begins, the air that had been stagnating in the upstream region of the anode flow channel is pushed out to the downstream region of the anode flow channel. Due to the influence of remaining oxygen in the downstream region of the anode flow channel, the potential difference between the electrolyte and the anode in the downstream region of the anode flow channel becomes close to the oxygen equilibrium potential. Due to the effect of a drop in the electrolyte potential, the potential of the region of the cathode flow channel corresponding to the downstream region of the anode flow channel becomes higher than the oxygen equilibrium potential, and the cell voltage increases to 1.443 V. This abnormal potential that occurs immediately after startup can cause the carbon support in the cathode catalyst layer to oxidize and deteriorate. (4) This phenomenon also occurs when the hydrogen on the anode side is purged with air immediately after shutdown.

[0126] In contrast, tin oxide particles are more hydrophilic and have higher oxidation resistance to electric potential than carbon particles, and therefore a first electrode catalyst using tin oxide particles as a carrier has poor drainage but is excellent in water retention (power generation performance under low humidity conditions) and high electric potential durability. On the other hand, carbon particles have lower oxidation resistance to electric potential compared to tin oxide particles, but are highly conductive and hydrophobic. Therefore, a second electrode using carbon particles as a carrier has poor water retention and high electric potential durability, but is excellent in drainage (power generation performance under high humidity conditions).

[0127] By optimizing the arrangement of the first electrode catalyst and the second electrode catalyst, which have such different properties, within the cathode catalyst layer and optimizing the gas flow, it is possible to improve the power generation performance in a low humidity environment and / or the high potential durability. Specifically, when the content of the first electrode catalyst in the upstream region of the cathode flow channel is made greater than that in the downstream region of the cathode flow channel, power generation performance in a low humidity environment is improved. Furthermore, by relatively increasing the content of the first electrode catalyst in the region of the cathode catalyst layer corresponding to the downstream region of the fuel gas flow, the high potential durability immediately after start-up is improved. Furthermore, by relatively increasing the content of the first electrode catalyst in the region of the cathode catalyst layer corresponding to the upstream region of the purge gas (air) flow, the high potential durability immediately after stopping is improved. EXAMPLES

[0128] (Reference examples 1~3) [1. Sample preparation] [1.1. Preparation of electrode catalyst] [1.1.1. Reference Examples 1 and 3: Sb-SnO 2 Preparation of the carrier] [A. Preparation of starburst silica (radial pores)] To a mixed solvent of 4.6 g of methanol (MeOH) and 4.6 g of ethylene glycol (EG), 56.3 g of 30 mass% aqueous cetyltrimethylammonium chloride solution was added and stirred at room temperature. 8.8 g of 1 M NaOH was added and heated to 50° C. Hereinafter, this is referred to as the “first solution.” Next, 12.3 g of tetraethoxysilane (TEOS) was dissolved in a mixed solvent of 6.5 g of MeOH and 6.5 g of EG, hereinafter referred to as "second solution."

[0129] The second solution was added to the first solution heated to 50°C. After the mixture became cloudy, heating was stopped and the mixture was stirred for an additional 4 hours or more. Filtration and redispersion in purified water were repeated twice, and then the mixture was dried at 45°C. The dried powder was then calcined in air at 550°C for 6 hours to obtain mesoporous silica in which primary particles with radial pores are connected in a rosary shape (hereinafter referred to as "Connected Starburst Silica (CSS)").

[0130] [B. Preparation of starburst carbon with radial pores] 0.5g of CSS was placed in a PFA container, and furfuryl alcohol (FA) was added in an amount equal to the pore volume of the CSS, allowing it to penetrate into the pores of the CSS. This was heat-treated at 150°C for 24 hours to polymerize the FA. This was then heat-treated in a nitrogen atmosphere for 6 hours at 500°C to advance the carbonization of the FA. This was repeated twice, and then further heat-treated in a nitrogen atmosphere for 6 hours at 900°C to obtain a CSS / carbon composite.

[0131] This composite was immersed in a 12% HF solution for 4 hours to dissolve the silica component. After dissolution, it was repeatedly filtered and washed, and then dried at 45°C to obtain mesoporous carbon in which primary particles with radial pores are connected in a string-like shape (hereinafter referred to as "connected starburst carbon (CSC)"). The obtained porous body had a BET specific surface area of ​​2122 m 2 / g, pore volume: 1.3 mL / g, and pore diameter: 2.2 nm.

[0132] [C. Bead-like mesoporous Sb-SnO 2 Preparation of Concentrated hydrochloric acid (35 mass%, Fujifilm Wako Pure Chemical Industries, Ltd.): SbCl in 12 mL (Reference Example 1) or 4 mL (Reference Example 3) 3 (99.9 mass%, Fujifilm Wako Pure Chemical Industries, Ltd.): 90.2 mg (Reference Example 1) or 120 mg (Reference Example 3) was dissolved to obtain solution A. Next, solution A was diluted with purified water: 108 mL (Reference Example 1) or 36 mL (Reference Example 3) to obtain solution B. Furthermore, SnCl was added to solution B. 2 (99.9 mass%, Fujifilm Wako Pure Chemical Industries, Ltd.): 15.0 g (Reference Example 1) or 5.0 g (Reference Example 3) was further added and dissolved to obtain solution C.

[0133] 0.3 g (Reference Example 1) or 0.1 g (Reference Example 3) of CSC was added to solution C and dispersed, followed by stirring in air at room temperature for 2 hours. After that, 600 mL (Reference Example 1) or 200 mL (Reference Example 3) of purified water was added to this dispersion, followed by stirring in air for an additional 4 hours. Then, filtration and redispersion in purified water were repeated twice, and the mixture was dried at 85°C for 2 h to obtain the bead-like Sb-SnO 2 A carbon composite was obtained.

[0134] This rhomboid Sb-SnO 2 The carbon composite was treated in an air atmosphere at 320℃ for 24 hours to obtain blue mesoporous Sb-SnO 2 obtained. The bead-like mesoporous Sb-SnO of Reference Example 1 2 The Sb doping amount was 2.5 at%. 2 The mode pore diameter (mode) determined from the adsorption measurements was 5.8 nm and the pore volume was 0.218 cc / g. The bead-like mesoporous Sb-SnO of Reference Example 3 2 The Sb doping amount was 2.5 at%. 2 The mode pore diameter (mode) determined from the adsorption measurements was 5.7 nm and the pore volume was 0.230 cc / g.

[0135] [D. Bead-like mesoporous Sb-SnO 2 Pt loading on The bead-like mesoporous Sb-SnO prepared above 2 Pt nanoparticles were supported on the Pt / Sb-SnO 2 obtained. First, 16 mL (Reference Example 1) or 6 mL (Reference Example 3) of 0.4 M NaOH / EG solution and 0.04 mM H 2 PtCl 6 (FUJIFILM Wako Pure Chemical Industries, Ltd.) / EG solution: 16 mL (Reference Example 1) or 6 mL (Reference Example 3) was mixed. This mixture was heated at 160° C. for 3 minutes while stirring in a microwave synthesis apparatus (Monowave 400, manufactured by Anton Paar) to obtain a Pt nanoparticle colloidal solution.

[0136] Next, 22.4 mL (Reference Example 1) or 10 mL (Reference Example 3) of the Pt nanoparticle colloidal solution was mixed with Sb-SnO 2 Powder: 350 mg (Reference Examples 1 and 3) was added and stirred at room temperature overnight. 3 0.2 mL (Reference Example 1) or 0.25 mL (Reference Example 3) was added and stirred at room temperature for 1 hour. This operation was repeated twice. Furthermore, 1M HNO 3 2.8 mL (Reference Example 1) or 0.625 mL (Reference Example 3) was added, and the mixture was stirred at room temperature for 1 hour. After that, filtration and redispersion in purified water were repeated twice. Finally, the solid was vacuum dried at 70 °C to obtain Pt / Sb-SnO 2 The Pt loading rate in Reference Example 1 was 20 mass %, and the Pt loading rate in Reference Example 3 was 30 mass %.

[0137] [1.1.2. Reference example 2] A commercially available Pt / C (30 mass% Pt / TEC10V30E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was used for the test as it was.

[0138] [1.2. Preparation of cathode catalyst layer] [1.2.1. Reference examples 1 and 3] Pt / Sb-SnO2 Purified water, ethanol, propylene glycol, and an ionomer dispersion were added to the mixture. The mixture was subjected to alternating shaking (Digital Disruptor Genie, 3000 rpm, 2 min) and ultrasonic dispersion (Bioruptor, 5 min) three times each to prepare a catalyst ink. The obtained catalyst ink was applied to a polytetrafluoroethylene (PTFE) sheet using an applicator (gap height: 4 mils), and vacuum dried at 80°C for 3 hours to obtain a cathode catalyst layer. The ratio (I / S) of the mass of the ionomer to the mass of the oxide support in Reference Examples 1 and 3 was 0.26.

[0139] [1.2.2. Reference example 2] Purified water, ethanol, and an ionomer dispersion were added to Pt / C. A cathode catalyst layer was obtained in the same manner as in Reference Examples 1 and 3. The ratio of the mass of the ionomer to the mass of the carbon support (I / C) in Reference Example 2 was set to 1.0.

[0140] [1.3. Preparation of MEA] Table 1 shows the specifications of the cathode catalyst layer, electrolyte membrane, and anode catalyst layer of Reference Examples 1 to 3. The cathode catalyst layer and the anode catalyst layer were each cut into a 1 cm square. Next, the catalyst layer was transferred to a Nafion (registered trademark) membrane (NR211) by hot pressing to obtain an MEA. The hot pressing conditions were: temperature: 120°C, pressure: 0.89 kN / cm 2 , time: 5 min.

[0141] [Table 1]

[0142] 2. Test Method [2.1. Cell performance evaluation] The MEA prepared above is divided into 1 cm 2The evaluation was performed using a rectangular cell for solar cells. Carbon paper with a microporous layer was used for the diffusion layer. After a break-in period, the resulting cell was examined for power generation performance under low humidity (cell temperature: 83°C, humidity: 30% RH) and high humidity (cell temperature: 60°C, humidity: 80% RH).

[0143] The type and flow rate of gas used was hydrogen / 500sccm on the anode side and air / 1000sccm on the cathode side. The gas flow rates were in excess of the reaction consumption in both cases, so the humidity at the cell inlet and outlet sides was almost the same. The gas back pressure was atmospheric pressure for both electrodes. The cell resistance for IR correction was the value of high frequency resistance (10kHz).

[0144] [2.2. High potential cycle test] The MEA prepared above is divided into 1 cm 2 The evaluation was performed using a rectangular cell for use in a battery. Carbon paper with a microporous layer was used for the diffusion layer. After a break-in period, the obtained cell was subjected to a high-potential cycle test at a cell temperature of 80°C and a humidity of 100% RH.

[0145] The type and flow rate of the gas used was 10% hydrogen / 500sccm on the anode side and nitrogen / 1000sccm on the cathode side. RHE to 1.5V RHE The potential was swept at 0.5 V / s for 2000 cycles. Cyclic voltammetry (CV) (0.1 to 1.0 V) was performed before and after the potential cycle. RHE , 3 cycles) were performed. The third cycle of the obtained CV UPD From the peak (desorption side), conversion coefficient: 210 μC / cm 2 was used to estimate the electrochemical surface area (ECSA) of Pt.

[0146] [3. Results] [3.1. Cell performance evaluation] FIG. 4 shows the results of the reference example 1 (Pt / Sb-SnO 25 shows the IV performance under high humidity conditions (60° C., 80% RH) of the cells obtained in Reference Example 1 (Pt / Sb-SnO 2 3 shows the IV performance under low humidity conditions (82° C., 30% RH) of the cell obtained in Example 1 (Pt / C) and Reference Example 2 (Pt / C).

[0147] The power generation performance at 80% RH in Reference Example 2 was higher in the entire current range than in Reference Example 1. The reason for this is thought to be that the carbon support is more hydrophobic than the tin oxide support, and therefore the effect of flooding is less than that of the tin oxide support under operating conditions in a high humidity environment. On the other hand, at 30% RH, the performance of Reference Example 1 was higher than that of Reference Example 2. The reason for this is thought to be that under low humidity operating conditions, the tin oxide support has a higher water retention capacity than the carbon support, thereby reducing the effect of ohmic loss.

[0148] [3.2. High potential cycle test] FIG. 6 shows the results of the comparison of the Pt / C and Pt / Sb-SnO 2 ) shows the ECSA retention rate of the cell before and after the high potential cycle test (2000 cycles). The ECSA retention rate of Reference Example 2 was 37%. On the other hand, the ECSA retention rate of Reference Example 3 was 113%, which was about three times that of Reference Example 2. It has been reported that immediately after the start-up of a fuel cell with a counterflow structure, the abnormal potential is maximized near the inlet of the cathode flow channel (see Non-Patent Document 1). Therefore, by arranging the oxide support in this region, high durability against abnormal potentials that occur when the fuel cell is started up and stopped can be expected.

[0149] (Example 1, Comparative Examples 1-2) [1. Test method] In the experiments shown in Figures 4 and 5, a large amount of supply gas is flowing, so the humidity on the upstream and downstream sides of the gas is almost the same. However, in an actual fuel cell, the flow rate of the supply gas is restricted, so even if the humidity of the supply gas is low, the humidity on the downstream side will be high due to water generated during power generation. Therefore, we predicted the power generation performance of a fuel cell that uses different catalysts in the upstream and downstream regions of the cathode flow path.

[0150] Example 1 was a fuel cell in which only the electrode catalyst (Pt / Sb-SnO2) of Reference Example 1 was arranged in the upstream region of the cathode flow channel, and only the electrode catalyst (Pt / C) of Reference Example 2 was arranged in the downstream region. In Comparative Example 1, the electrode catalyst (Pt / Sb-SnO 2 ) was placed in the fuel cell. In Comparative Example 2, a fuel cell was prepared in which only the electrode catalyst (Pt / C) of Reference Example 2 was disposed in the upstream and downstream regions of the cathode flow channel.

[0151] FIG. 7 shows a schematic diagram of the assumptions used to predict the power generation performance when a low humidity gas is supplied to the fuel cell. 2 The surface area ratio of Pt / C and Pt / C was set to half and half. When low-humidity gas is supplied to the fuel cell, the humidity gradually increases from the inlet to the outlet of the cathode flow channel due to water produced during power generation. In order to simply represent this situation, it was assumed that the humidity in the upstream region of the cathode flow channel (first half) was 30% RH, and that in the downstream region of the cathode flow channel (second half) was 80% RH. The power generation performance of the entire cell was then calculated using the power generation performance in Figure 4 for the first half and the power generation performance in Figure 5 for the second half.

[0152] 8 shows the current density at 0.6 V (IR loss corrected) obtained by simple calculation for the fuel cells of Example 1 and Comparative Examples 1 and 2. It can be seen from FIG. 8 that Example 1 has higher power generation performance than Comparative Examples 1 and 2.

[0153] In this calculation, Pt / Sb-SnO 2 The area ratio of the region containing only Pt / C and the region containing only Pt / Sb was set to half and half, but the optimal area ratio varies depending on the operating conditions of the cell. For example, in the case of a fuel cell operated under conditions of low humidity throughout the cell, the area ratio of Pt / Sb-SnO 2 On the other hand, in the case of a fuel cell operated under conditions where the humidity of the entire cell is relatively high, it is desirable to increase the area ratio of the region containing only Pt / Sb-SnO 2 It is desirable to reduce the area ratio of the region containing only the fluorescein.

[0154] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the present invention. [Industrial Applicability]

[0155] The fuel cell system according to the present invention can be used as an in-vehicle power source, a small stationary power generator, and the like.

Claims

1. A fuel cell comprising: (1) The fuel cell comprises: a membrane electrode assembly in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode catalyst layer; an anode separator disposed on the outer side of the anode-side gas diffusion layer and having an anode flow channel; a cathode separator disposed on the outer side of the cathode-side gas diffusion layer and having a cathode flow channel; It is equipped with: (2) The cathode catalyst layer contains, as a cathode catalyst, a first electrode catalyst in which first catalyst particles are supported on the surface of a first support made of tin oxide-based particles; a second electrode catalyst in which second catalyst particles are supported on the surface of a second support made of carbon particles; Including, The content of the first electrode catalyst contained in the upstream region of the cathode flow channel is greater than the content of the first electrode catalyst contained in the downstream region of the cathode flow channel.

2. The tin oxide particles are SnO doped with at least one element selected from the group consisting of Sb, Nb, Ta, and W. 2 2. The fuel cell according to claim 1, comprising:

3. 2. The fuel cell according to claim 1, wherein the tin oxide based particles have a structure in which primary particles are fused together in a beaded shape (a beaded structure).

4. The tin oxide particles have a specific surface area of ​​60 m 2 2. The fuel cell according to claim 1, wherein the molecular weight is 1 / g or more.

5. 2. The fuel cell according to claim 1, wherein the tin oxide based particles are porous particles having pores with a pore diameter of 5 nm or more and 8 nm or less.

6. 2. The fuel cell according to claim 1, wherein the carbon particles are porous particles having pores with a pore diameter of 3 nm or more and 30 nm or less.

7. A fuel cell according to claim 1; an anode gas supply device for supplying a fuel gas to an anode flow channel of the fuel cell; a cathode gas supply device that supplies an oxidant gas to a cathode flow passage of the fuel cell; a purge device that supplies air to the anode flow path when the fuel cell is stopped; Equipped with The anode flow channel and the cathode flow channel have a counter-flow structure or a parallel-flow structure, The purge device includes a device for supplying the air in a direction opposite to or in the same direction as the fuel gas. Fuel cell system.

8. A fuel cell system comprising: (1) The fuel cell system comprises: Fuel Cells and an anode gas supply device for supplying a fuel gas to an anode flow channel of the fuel cell; a cathode gas supply device that supplies an oxidant gas to a cathode flow passage of the fuel cell; a purge device that supplies air to the anode flow path when the fuel cell is stopped; Equipped with The anode flow channel and the cathode flow channel have a counter-flow structure or a parallel-flow structure, The purge system may include a system for supplying the air in a direction opposite to or in the same direction as the fuel gas. However, this does not include a case where the anode flow path and the cathode flow path have a counterflow structure and the purge device includes a device that supplies the air in a direction opposite to that of the fuel gas. (2) The fuel cell is a membrane electrode assembly in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode catalyst layer; an anode separator provided with the anode flow channel and disposed on the outer side of the anode-side gas diffusion layer; a cathode separator disposed on the outer side of the cathode-side gas diffusion layer and including the cathode flow channel; It is equipped with: (3) The cathode catalyst layer contains, as a cathode catalyst, a first electrode catalyst in which first catalyst particles are supported on the surface of a first support made of tin oxide-based particles; a second electrode catalyst in which second catalyst particles are supported on the surface of a second support made of carbon particles; Including, The content of the first electrode catalyst contained in the downstream region of the cathode flow channel is greater than the content of the first electrode catalyst contained in the upstream region of the cathode flow channel.

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