JP2013225398A - Fuel cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell stack which has had functional improvement achieved in the relationship between the thickness of a catalyst layer and the direction of a reaction gas flow.SOLUTION: A fuel cell stack (10) comprises: a membrane-catalyst layer assembly (26) including an anode side catalyst layer (38), a cathode side catalyst layer (42), and a polymer electrolyte membrane (32); an anode side gas diffusion layer (40) and a cathode side gas diffusion layer (44); an anode side separator (28) and a cathode side separator (30); a fuel gas passage (29); and an oxidant gas passage (31). The direction of an overall (macroscopic) fuel gas flow in the fuel gas passage and the direction of an overall (macroscopic) oxidant gas flow in the oxidant gas passage are parallel. The thickness of the anode side catalyst layer is formed to monotonously change from an upstream end toward a downstream end of the overall fuel gas flow in the fuel gas passage, and the thickness of the cathode side catalyst layer is formed to monotonously change from an upstream end toward a downstream end of the overall oxidant gas flow in the oxidant gas passage.

Description

  The present invention relates to a fuel cell stack, and more particularly to a structure of a membrane-catalyst layer assembly.

  A conventional fuel cell stack has a MEA (Membrane-Electrode-Assembly: membrane-electrode stack) composed of a polymer electrolyte membrane and a pair of gas diffusion electrodes, and a pair of separators sandwiching the MEA. . These separators are provided with a reaction gas flow path on the main surface that comes into contact with the gas diffusion electrode (see, for example, Patent Document 1).

JP 2004-87311 A

  However, in the conventional fuel cell stack described above, the relationship between the thickness of the catalyst layer and the flow direction of the reaction gas has not been sufficiently studied.

  The present invention has been made to solve such problems, and provides a fuel cell stack in which the function is improved compared to the prior art in relation to the thickness of the catalyst layer and the flow direction of the reaction gas. The purpose is to do.

  According to an aspect of the present invention, a fuel cell stack includes an anode-side catalyst layer, a cathode-side catalyst layer, and a membrane-catalyst layer junction having a polymer electrolyte membrane sandwiched between the anode-side catalyst layer and the cathode-side catalyst layer. An anode side gas diffusion layer and a cathode side gas diffusion layer facing each other with the membrane-catalyst layer assembly sandwiched therebetween, an anode side separator facing each other with the anode side gas diffusion layer and the cathode side gas diffusion layer sandwiched therebetween, and A cathode side separator, a fuel gas flow path provided between the anode side separator and the anode side gas diffusion layer, and an oxidant gas flow provided between the cathode side separator and the cathode side gas diffusion layer. An overall (macroscopic) fuel gas flow direction of the fuel gas flow path and an overall (macroscopic) of the oxidant gas flow path. The oxidant gas flow direction is parallel, and the thickness of the anode catalyst layer is monotonous from the upstream end to the downstream end in the overall fuel gas flow in the fuel gas flow path. And the thickness of the cathode-side catalyst layer monotonously changes from the upstream end to the downstream end in the overall oxidant gas flow of the oxidant gas flow path. Formed as follows.

  The present invention has an effect of improving the function of the fuel cell stack in relation to the thickness of the catalyst layer and the flow direction of the reaction gas.

  The above object, other objects, features, and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments with reference to the accompanying drawings.

1 is a functional block diagram showing a configuration of a fuel cell system including a fuel cell stack according to Embodiment 1 of the present invention. It is sectional drawing which shows typically the fuel cell stack shown in FIG. FIG. 2 is a schematic diagram illustrating an example of a flow of reaction gas in the fuel cell stack of FIG. 1. FIG. 6 is a schematic diagram showing another example of the flow of reaction gas in the fuel cell stack of FIG. 1. It is a schematic diagram which shows the manufacturing system of the membrane-catalyst layer assembly shown in FIG. It is a graph which shows the relationship between the discharge pressure detected by the 1st pressure gauge in the manufacturing system of FIG. 4, and time. It is a graph which shows the relationship between the weight per unit area (catalyst weight) of the catalyst contained in the catalyst layer manufactured by the manufacturing system of FIG. 4, and the position of the X direction in a catalyst layer. It is a graph which shows the relationship between the weight per unit area (catalyst weight) of the catalyst contained in a cathode side catalyst layer, and a cell voltage. It is sectional drawing which shows typically the fuel cell stack which concerns on Embodiment 2 of this invention. It is sectional drawing which shows typically the fuel cell stack which concerns on Embodiment 3 of this invention. It is sectional drawing which shows typically the fuel cell stack which concerns on Embodiment 4 of this invention.

  The fuel cell stack according to the first aspect of the present invention includes an anode-side catalyst layer, a cathode-side catalyst layer, and a membrane-catalyst layer having a polymer electrolyte membrane sandwiched between the anode-side catalyst layer and the cathode-side catalyst layer. An anode-side gas diffusion layer and a cathode-side gas diffusion layer facing each other so as to sandwich the membrane-catalyst layer assembly, and an anode-side separator facing each other so as to sandwich the anode-side gas diffusion layer and the cathode-side gas diffusion layer And a cathode side separator, a fuel gas flow path provided between the anode side separator and the anode side gas diffusion layer, and an oxidant gas provided between the cathode side separator and the cathode side gas diffusion layer An overall (macroscopic) fuel gas flow direction of the fuel gas channel and an overall (macroscopic) of the oxidant gas channel. The oxidant gas flow direction is parallel, and the thickness of the anode catalyst layer is monotonous from the upstream end to the downstream end in the overall fuel gas flow in the fuel gas flow path. And the thickness of the cathode-side catalyst layer monotonously changes from the upstream end to the downstream end in the overall oxidant gas flow of the oxidant gas flow path. It is formed as follows.

  According to this configuration, there is an effect that the function is improved in the relationship between the thickness of the catalyst layer and the flow direction of the reaction gas.

  In the fuel cell stack according to the second aspect of the present invention, in the first aspect, the anode-side catalyst layer has a thickness from the upstream end to the downstream end in the overall fuel gas flow of the fuel gas flow path. The cathode-side catalyst layer has a thickness that monotonously decreases toward the portion, and the thickness of the cathode-side catalyst layer monotonically increases from the upstream end to the downstream end in the overall oxidant gas flow of the oxidant gas flow path. It may be formed to be larger.

  According to this configuration, the voltage generated by the fuel cell stack can be improved. Further, the deterioration of the function of the fuel cell stack due to the ammonia contained in the fuel gas is suppressed.

  In the fuel cell stack according to the third aspect of the present invention, in the first aspect, the thickness of the anode side catalyst layer is such that the upstream end portion to the downstream end in the entire fuel gas flow in the fuel gas flow path. The cathode-side catalyst layer has a thickness that increases monotonously toward the portion, and the thickness of the cathode-side catalyst layer monotonously increases from the upstream end to the downstream end in the overall oxidant gas flow of the oxidant gas flow path. It may be formed to be smaller.

  According to this configuration, deterioration of the function of the fuel cell stack due to contaminants in the air is suppressed. Moreover, the deterioration of the function of the fuel cell stack due to the pollutants contained in the reverse diffusion water is suppressed.

  In the fuel cell stack according to the fourth aspect of the present invention, in the first aspect, the anode catalyst layer has a thickness from the upstream end to the downstream end in the overall fuel gas flow in the fuel gas flow path. The cathode-side catalyst layer has a thickness that monotonously decreases toward the portion, and the thickness of the cathode-side catalyst layer monotonically increases from the upstream end to the downstream end in the overall oxidant gas flow of the oxidant gas flow path. It may be formed to be smaller.

  According to this configuration, deterioration of the function of the fuel cell stack due to contaminants in the air is suppressed. Further, the deterioration of the function of the fuel cell stack due to the ammonia contained in the fuel gas is suppressed.

  In the fuel cell stack according to the fifth aspect of the present invention, in the first aspect, the anode-side catalyst layer has a thickness from the upstream end to the downstream end in the entire fuel gas flow in the fuel gas flow path. The cathode-side catalyst layer has a thickness that increases monotonously toward the portion, and the thickness of the cathode-side catalyst layer monotonously increases from the upstream end to the downstream end in the overall oxidant gas flow of the oxidant gas flow path. It may be formed to be larger.

  According to this configuration, the voltage generated by the fuel cell stack can be improved. Moreover, the deterioration of the function of the fuel cell stack due to the pollutants contained in the reverse diffusion water is suppressed.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

  In the following description, the same or corresponding elements are denoted by the same reference symbols throughout all the drawings, and redundant description thereof is omitted.

(Embodiment 1)
[Configuration of fuel cell system]
FIG. 1 is a functional block diagram showing configurations of a fuel cell stack 10 and a fuel cell system 12 including the fuel cell stack 10 according to the first embodiment.

  The fuel cell system 12 includes a fuel cell stack (hereinafter referred to as “stack”) 10, an oxidant gas supply device 14, a raw material gas supply device 16, a reformer 18, a combustor 20, and a controller 22.

  The oxidant gas supply unit 14 is connected to the stack 10 via the oxidant gas supply path, and supplies the oxidant gas to the stack 10. Examples of the oxidant gas include air and oxygen. For the oxidant gas supply device 14, for example, a blower such as a fan or a blower for blowing air, an oxygen cylinder, or the like is used. The oxidant gas supply unit 14 has a flow rate adjusting function for adjusting the flow rate of sending the oxidant gas in accordance with a control signal from the controller 22.

  The raw material gas supplier 16 is connected to the reformer 18 via the raw material gas supply path, and supplies the raw material gas to the reformer 18. The raw material gas supplier 16 includes, for example, a raw material gas cylinder, a booster connected to the raw material gas supply infrastructure, an on-off valve, a flow rate adjusting valve, and the like. The raw material gas supplier 16 has a function of supplying a raw material gas and a function of adjusting a flow rate of the raw material gas. Examples of the source gas include hydrocarbon gases such as natural gas, other hydrocarbon gases such as propane gas, hydrocarbon fuels that are liquid at room temperature such as kerosene, and organic fuels other than hydrocarbons such as methanol. Can be mentioned.

  The reformer 18 is connected to the stack 10 via a fuel gas supply path. The reformer 18 is supplied with the source gas from the source gas supply unit 16. Further, the reformer 18 is supplied with oxygen-containing gas such as steam and / or air through a supply path (not shown) according to a reforming method (steam reforming method, partial oxidation method, or autothermal method). For example, in the case of the steam reforming method, the reformer 18 is disposed in the vicinity of the combustor 20, reforms the raw material gas using heat from these, and generates a fuel gas containing hydrogen. Then, this fuel gas is supplied to the stack 10.

  As will be described later, the stack 10 generates power by causing an oxidation-reduction reaction (power generation reaction) between the fuel gas and the oxidant gas. The stack 10 is provided with a temperature detector (not shown). The temperature in the stack 10 detected by the temperature detector is output to the controller 22.

  The combustor 20 is connected to the stack 10 through a power generation gas discharge path, and power generation exhaust gas is supplied to the combustor 20 from the stack 10. The power generation exhaust gas includes a fuel gas and an oxidant gas that are not used in the power generation reaction, and water (steam) generated by the power generation reaction. The combustor 20 is disposed in the vicinity of the reformer 18 and heats the reformer 18 by burning the power generation exhaust gas. The combustion exhaust gas generated by the combustion in the combustor 20 is discharged to the outside of the fuel cell system 12 through a discharge path (not shown).

  The controller 22 only needs to have an arithmetic processing function. Examples of the control device include a microcontroller, CPU, MPU, logic circuit, PLC (Programmable Logic Controller), and the like. The controller 22 controls the raw material gas supplier 16 and the oxidant gas supplier 14 based on the temperature of the stack 10 detected by the temperature detector. A humidifier (not shown) may be provided in at least one of the oxidant gas supply path and the fuel gas supply path.

[Stack structure]
FIG. 2 is a schematic diagram showing the membrane-catalyst layer assembly 26 included in the stack 10. FIG. 3A is a schematic diagram illustrating an example of the flow of the reaction gas in the stack 10. FIG. 3B is a schematic diagram illustrating another example of the flow of the reactive gas in the stack 10. In FIG. 3A and FIG. 3B, the fuel gas channel 29 and the oxidant gas channel 31 are indicated by lines. I represent.

  The stack 10 is formed by stacking a plurality of cells 24. The cell 24 is sandwiched between an anode side separator 28 and a cathode side separator 30 facing each other. The cell 24 includes a membrane-catalyst layer assembly 26 and an anode-side gas diffusion layer 40 and a cathode-side gas diffusion layer 44 that are opposed to each other so as to sandwich the membrane-catalyst layer assembly 26. The membrane-catalyst layer assembly 26 includes an anode side catalyst layer 38, a cathode side catalyst layer 42, and a polymer electrolyte membrane (hereinafter referred to as "electrolyte membrane") disposed between the anode side catalyst layer 38 and the cathode side catalyst layer 42. .) 32. The anode side catalyst layer 38 and the anode side gas diffusion layer 40 constitute an anode. In addition, the cathode side catalyst layer 42 and the cathode side gas diffusion layer 44 constitute a cathode.

  The electrolyte membrane 32 is preferably a polymer membrane having hydrogen ion conductivity in a wet state. In the present embodiment, the electrolyte membrane 32 has a substantially rectangular shape. The material of the electrolyte membrane 32 is not particularly limited as long as it selectively moves hydrogen ions. The electrolyte membrane 32 is, for example, a fluorine-based electrolyte membrane made of perfluorocarbon sulfonic acid (for example, Nafion (registered trademark) manufactured by DuPont, USA, Aciplex (registered trademark) manufactured by Asahi Kasei Co., Ltd., and Flemion manufactured by Asahi Glass Co., Ltd. (Registered trademark, etc.) and various hydrocarbon electrolyte membranes can be used.

  Each of the catalyst layers 38 and 42 is preferably a layer containing a catalyst for a redox reaction of hydrogen or oxygen. Each catalyst layer 38, 42 is not particularly limited as long as it has conductivity and has a catalytic ability for a redox reaction of hydrogen and oxygen. Each catalyst layer 38, 42 has a substantially rectangular shape in the present embodiment. Each of the catalyst layers 38 and 42 is composed of a porous member mainly composed of, for example, carbon powder carrying a platinum group metal catalyst and a polymer material having proton conductivity. The proton conductive polymer material used for each of the catalyst layers 38 and 42 may be the same as or different from the electrolyte membrane 32.

  The thickness of the anode catalyst layer 38 changes monotonously in the X direction shown in FIG. 2 from the upstream end 29a to the downstream end 29b in the entire fuel gas flow in the fuel gas passage 29. It is formed. Here, for example, the thickness is formed so as to monotonously decrease from the upstream end 29 a to the downstream end 29 b of the fuel gas channel 29.

  The thickness of the cathode side catalyst layer 42 also monotonously changes in the X direction shown in FIG. 2 from the upstream end 31a to the downstream end 31b in the entire oxidant gas flow in the oxidant gas flow path 31. Formed. Here, for example, the thickness is formed so as to increase monotonously from the upstream end portion 31 a to the downstream end portion 31 b of the oxidant gas flow path 31.

  Each gas diffusion layer 40, 44 is preferably a porous member having electrical conductivity. Each gas diffusion layer 40, 44 is plate-shaped and has a substantially rectangular shape. Each gas diffusion layer 40, 44 is not particularly limited as long as it has conductivity and can diffuse the reaction gas. Each gas diffusion layer 40, 44 uses a conductive base material having a porous structure made of carbon fine powder, pore former, carbon paper, carbon cloth or the like in order to give gas permeability. be able to. Further, in order to give the gas diffusion layers 40 and 44 drainage properties, a water-repellent polymer such as a fluororesin may be dispersed in the gas diffusion layers 40 and 44. Furthermore, in order to give the gas diffusion layers 40 and 44 electronic conductivity, the gas diffusion layers 40 and 44 may be made of an electron conductive material such as carbon fiber, metal fiber, or carbon fine powder. In addition, a water repellent carbon layer composed of a water repellent polymer and carbon powder may be provided on the surfaces of the gas diffusion layers 40 and 44 that are in contact with the catalyst layers 38 and 42. In addition, for each gas diffusion layer 40, 44, for example, a porous member that is mainly composed of conductive particles and a polymer resin may be used without using carbon fiber as a base material. The anode side gas diffusion layer 40 and the cathode side gas diffusion layer 44 may be made of the same material or different materials.

  Examples of the conductive particle material include carbon materials such as graphite, carbon black, and activated carbon. Examples of carbon black include acetylene black (AB), furnace black, ketjen black, Vulcan, and the like. These materials may be used alone, or a plurality of materials may be used in combination. In addition, the raw material form of the carbon material may be any shape such as powder, fiber, and granule.

  In addition, as the polymer resin, PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene / hexafluoropropylene copolymer), PVDF (polyvinylidene fluoride), ETFE (tetrafluoroethylene / ethylene copolymer), Examples thereof include PCTFE (polychlorotrifluoroethylene) and PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer). PTFE is advantageous from the viewpoints of heat resistance, water repellency and chemical resistance. As a raw material of PTFE, there are a dispersion and a powdery shape. Dispersion is advantageous from the viewpoint of workability. The polymer resin functions as a binder that binds the conductive particles. In addition, since the polymer resin has water repellency, it also has a function (water retention) to confine water in the system inside the fuel cell.

  The gas diffusion layers 40 and 44 that do not use carbon fiber as a base material are manufactured by kneading, extruding, rolling, and firing a mixture containing a polymer resin and conductive particles. Specifically, carbon, which is conductive particles, a dispersion solvent, and a surfactant are charged into a stirrer / kneader, and then kneaded, pulverized, and granulated to disperse the carbon in the dispersion solvent. Next, the fluororesin, which is a polymer resin, is further dropped into a stirrer / kneader to stir and knead to disperse the carbon and the fluororesin. The obtained kneaded material is rolled to form a sheet, and fired to remove the dispersion solvent and the surfactant, whereby a sheet for forming each gas diffusion layer 40, 44 is manufactured.

  The anode side gas diffusion layer 40 is disposed on the anode side catalyst layer 38, and the cathode side gas diffusion layer 44 is disposed on the cathode side catalyst layer 42. Thereby, the anode side gas diffusion layer 40 and the cathode side gas diffusion layer 44 are arranged so as to face each other so as to sandwich the membrane-catalyst layer assembly 26.

  Each separator 28 and 30 is preferably a member for mechanically fixing the membrane-electrode assembly and electrically connecting adjacent membrane-electrode assemblies to each other in series. The membrane-electrode assembly is composed of an anode, a cathode, and an electrolyte membrane 32 sandwiched therebetween. Thereby, the anode side separator 28 and the cathode side separator 30 are disposed so as to face each other so as to sandwich the anode side gas diffusion layer 40 and the cathode side gas diffusion layer 44.

  Each of the separators 28 and 30 is preferably made of a material containing carbon or a material containing metal. When each separator 28 and 30 is comprised with the material containing carbon, each separator 28 and 30 supplies the raw material powder which mixed carbon powder and the resin binder to the metal mold | die, and uses the raw material powder supplied to the metal mold | die. It is formed by applying pressure and heat. Moreover, when each separator 28 and 30 is comprised with the material containing a metal, each separator 28 and 30 may consist of a metal plate. The separators 28 and 30 may be made of a plate made of titanium or stainless steel with gold plating. Each separator 28, 30 may be formed of a porous plate having conductivity.

  Each separator 28, 30 is formed of, for example, a substantially rectangular flat plate. As shown in FIG. 3, grooves that are reaction gas flow paths 29 and 31 are formed on one main surface (electrode surface) of each separator 28 and 30. Moreover, the groove | channel which is a cooling medium flow path (not shown) is formed in the other main surface (cooling surface). The groove is formed in each separator 28, 30 by an appropriate method (for example, molding using a press machine or cutting using a cutting machine or the like). The reaction gas passages 29 and 31 and the cooling medium passage may not be provided in each separator 28 and 30. In this case, each flow path 29, 31 may be provided in a member different from each separator 28, 30, or a member adjacent to each separator 28, 30, such as each gas diffusion layer 40, 44, etc. It may be provided.

  Each separator 28, 30 is provided with each manifold hole 29c, 29d, 31c, 31d. The manifold hole 29c is connected to the inflow side of the fuel gas passage 29, and the manifold hole 29d is connected to the outflow side of the fuel gas passage 29. The manifold hole 31c is connected to the inflow side of the oxidant gas flow path 31, and the manifold hole 31d is connected to the outflow side of the oxidant gas flow path 31. These manifold holes 29c, 29d, 31c, 31d are formed at positions corresponding to each other in the separators 28, 30, and penetrate the separators 28, 30. Therefore, in the separators 28 and 30 stacked in the thickness direction, the manifold holes 29c, 29d, 31c, and 31d are connected to each other, and the fuel gas inflow manifold, the fuel gas outflow manifold, the oxidant gas inflow manifold, and the oxidant gas outflow manifold. Is formed.

  The anode side separator 28 is disposed on the anode side gas diffusion layer 40 so that the fuel gas flow path 29 faces the anode side gas diffusion layer 40. As a result, the fuel gas channel 29 is provided between the anode separator 28 and the anode gas diffusion layer 40. The fuel gas that has flowed from the fuel gas inflow manifold into the upstream end portion 29 a of the fuel gas channel 29 flows through the fuel gas channel 29 so as to contact the anode side gas diffusion layer 40. At this time, the fuel gas is supplied to the anode side catalyst layer 38 via the anode side gas diffusion layer 40. Then, the surplus water in the stack 10 and the unused surplus gas that has not been used for the power generation reaction are discharged from the downstream end 29b of the fuel gas passage 29 to the fuel gas outflow manifold.

  The cathode-side separator 30 is disposed on the cathode-side gas diffusion layer 44 so that the oxidant gas flow path 31 faces the cathode-side gas diffusion layer 44. Thereby, the oxidant gas flow path 31 is provided between the cathode side separator 30 and the cathode side gas diffusion layer 44. The oxidant gas that has flowed from the oxidant gas inflow manifold into the upstream end 31 a of the oxidant gas flow path 31 flows through the oxidant gas flow path 31 so as to be in contact with the cathode-side gas diffusion layer 44. At this time, the oxidant gas is supplied to the cathode side catalyst layer 42 via the cathode side gas diffusion layer 44. Unused surplus gas that has not been used for the power generation reaction is discharged from the downstream end portion 31b of the oxidant gas flow path 31 to the oxidant gas outflow manifold together with the generated water generated by the power generation reaction.

  The fuel gas channel 29 and the oxidant gas channel 31 are formed in, for example, a broken line shape that curves in the X direction while extending in the Y direction shown in FIG. 3A. Partially (microscopically), the direction of the oxidant gas passage 31 extending in the Y direction and the direction of the fuel gas passage 29 extending in the Y direction are opposite to each other. However, the overall (macroscopic) fuel gas flow direction 51 of the fuel gas flow path 29 and the overall (macroscopic) oxidant gas flow direction 52 of the oxidant gas flow path 31 are both shown in FIG. The X direction shown in FIG. Thus, these overall (macroscopic) flow directions are parallel, as shown in FIG. The fuel gas channel 29 and the oxidant gas channel 31 may be formed in a plurality of straight lines parallel to each other as shown in FIG. 3B, for example. That is, the fuel gas channel 29 and the oxidant gas channel 31 are not particularly limited as long as the overall gas flow directions 51 and 52 are parallel to each other.

  A cooling medium such as water or antifreeze flows through a cooling medium flow path formed on the cooling surface of each separator 28, 30. As a result, heat generated during power generation of the membrane-electrode assembly is removed.

[Configuration of membrane-electrode assembly manufacturing apparatus]
FIG. 4 is a schematic diagram showing a manufacturing system 50 for the membrane-catalyst layer assembly 26.

  The manufacturing system 50 of the membrane-catalyst layer assembly 26 includes a roll 51, a die 52, a pump 53, first and second valves 54 and 55, and first and second pressure gauges 56 and 57.

  The roll 51 is, for example, a cylindrical member. The roll 51 is disposed between an unwinding portion (not shown) of the original fabric of the support sheet and a product winding portion (not shown). An electrolyte membrane 32 is affixed to the outer surface of the support sheet that spans the roll 51. The X direction of the electrolyte membrane 32 is aligned with the longitudinal direction of the original sheet of the support sheet.

  The die 52 is, for example, a slot die that can be applied in a thin film shape. The die 52 is disposed at a position facing the roll 51. The die 52 discharges the catalyst ink for forming the catalyst layers 38 and 42 toward the roll 51.

  The catalyst ink is a catalyst ink in which carbon fine particles supporting a platinum-based metal catalyst and a proton conductive polymer are mixed with a solvent. As the metal catalyst, for example, platinum, ruthenium, rhodium, iridium and the like can be used. As the carbon powder, carbon black, ketjen black, acetylene black and the like can be used. As the solvent, organic solvents such as water, ethanol, n-propanol, alcohols such as n-butanol, and ethers, esters, and fluorines can be used. By drying the solvent of the platinum-based metal catalyst ink, it is possible to form the catalyst layers 38 and 42 mainly composed of carbon powder carrying the metal catalyst.

  The pump 53 is connected to a catalyst ink supply unit (not shown) such as a tank via a supply path 58. The pump 53 monotonously delivers a constant flow of catalyst ink from the catalyst ink supply unit to the supply path 58.

  The supply path 58 branches into a discharge path 59 and a recovery path 60. As a result, the supply path 58 guides the catalyst ink to the discharge path 59 and the recovery path 60.

  The discharge path 59 is connected to the die 52 and guides the catalyst ink supplied by the pump 53 via the supply path 58 to the die 52.

  The first valve 54 is provided in the discharge path 59, and shuts off or communicates the discharge path 59 by opening and closing. When the first valve 54 is opened, the catalyst ink from the supply path 58 is supplied to the die 52 through the discharge path 59.

  The first pressure gauge 56 is provided in the discharge path 59 between the first valve 54 and the die 52, and detects the pressure of the catalyst ink passing through the discharge path 59. Based on the detection value of the first pressure gauge 56, the pressure supplied to the die 52 by the pump 53, that is, the pressure of the catalyst ink discharged from the die 52 (discharge pressure) is obtained.

  The second valve 55 is provided in the recovery path 60, and shuts off or communicates with the recovery path 60 by opening and closing. The second valve 55 opens alternately with the first valve 54. Thus, when the first valve 54 is opened and the second valve 55 is closed, the catalyst ink from the supply path 58 flows into the discharge path 59. On the other hand, when the first valve 54 is closed and the second valve 55 is opened, the catalyst ink from the supply path 58 flows into the recovery path 60. The second valve 55 adjusts the flow rate of the catalyst ink in the collection path 60 by changing the opening degree. For this reason, the smaller the opening of the second valve 55, the smaller the flow rate of the catalyst ink in the recovery path 60. Thus, when the second valve 55 is closed and the first valve 54 is opened, the flow rate flowing through the discharge path 59 is increased.

  The collection path 60 has an upstream end connected to the second valve 55 and a downstream end connected to a collection unit (not shown) such as a collection tank or a catalyst ink supply unit. For this reason, the catalyst ink that has passed through the collection path 60 is collected by the collection unit.

  The second pressure gauge 57 is provided in the recovery path 60 between the second valve 55 and the recovery unit, and detects the pressure of the catalyst ink passing through the recovery path 60.

[Method for producing membrane-electrode assembly]
FIG. 5 is a graph showing the relationship between the discharge pressure detected by the first pressure gauge 56 and time. In addition, the vertical axis | shaft has shown the discharge pressure which normalized the measured value of the discharge pressure with the predetermined value. FIG. 6 is a graph showing the relationship between the weight per unit area (catalyst weight) of the catalyst contained in the catalyst layer and the position in the X direction in the catalyst layer. In addition, the vertical axis | shaft has shown the catalyst basis weight which normalized the measured value of the catalyst basis weight with the predetermined value.

  Here, a case where the cathode side catalyst layer 42 is formed after the anode side catalyst layer 38 is formed will be described. However, the order of forming these catalyst layers 38 and 42 may be reversed.

  The support sheet is pulled out from the original sheet of the support sheet by the unwinding portion. The original sheet of the support sheet is supported on the roll 51 by being laid over the roll 51 so that the inner surface thereof is on the roller side. The electrolyte membrane 32 attached to the outer surface of the support sheet moves on the roll 51. At this time, the X direction and the moving direction of the electrolyte membrane 32 coincide with each other.

  Until the electrolyte membrane 32 reaches a position facing the die 52, for example, between ta and tb and between tc and td shown in FIG. 5, the second valve 55 is opened and the first valve 54 is closed. . As a result, the catalyst ink flows from the supply path 58 to the recovery path 60 and is recovered. For this reason, the catalyst ink does not flow into the discharge path 59 from the supply path 58, and the pressure detected by the first pressure gauge 56, that is, the pressure of the catalyst ink in the discharge path 59 becomes zero.

  When the electrolyte membrane 32 reaches a position facing the die 52, for example, at tb and td shown in FIG. 5, the second valve 55 is closed and the first valve 54 is opened. As a result, the catalyst ink flows from the supply path 58 to the discharge path 59. The pressure of the catalyst ink in the discharge path 59 at this time is the second until the first valve 54 is opened, that is, while the first valve 54 is closed and the second valve 55 is opened (ta to tb, tc to td). It depends on the opening of the valve 55.

That is, when the opening degree of the second valve 55 is, for example, level 2, as shown in FIG. 5, the catalyst ink in the discharge path 59 is opened slightly after opening the first valve 54 (tb1) (tb1). the pressure became _{P 1.} Thereafter, the pressure of the catalyst ink was maintained almost constant.

For example, when the opening degree of the second valve 55 is level 3 smaller than level 2, the amount of catalyst ink flowing from the supply path 58 to the recovery path 60 is small. For this reason, as shown in FIG. 5, the pressure of the catalyst ink in the discharge path 59 suddenly increases a little after the first valve 54 is opened (tb) (tb1). Then, the catalyst ink of the discharge passage 59 with the discharged from the die 52, the pressure of the catalyst ink in the discharge passage 59 becomes P ₁ gradually decreases.

On the other hand, when the opening degree of the second valve 55 is, for example, level 1 greater than level 2, the amount of catalyst ink flowing from the supply path 58 to the recovery path 60 is large. For this reason, as shown in FIG. 5, when the first valve 54 is opened, the pressure of the catalyst ink in the discharge path 59 is low. Then, the catalyst ink according to flows from the supply passage 58 to the discharge passage 59, the pressure of the catalyst ink in the discharge passage 59 increases and becomes P ₁ gradually.

  Thus, the catalyst ink that has passed through the discharge path 59 is discharged from the die 52 toward the electrolyte membrane 32, and the catalyst ink is applied onto the electrolyte membrane 32. Since the electrolyte membrane 32 moves, a thin film is formed on the electrolyte membrane 32. Then, the electrolyte membrane 32 coated with the catalyst ink is dried by a drying device (not shown), and an anode side catalyst layer 38 is formed on the electrolyte membrane 32.

  The thickness of the anode side catalyst layer 38 on the electrolyte membrane 32 depends on the pressure of the catalyst ink in the discharge path 59. That is, as the pressure of the catalyst ink is higher, the amount of the catalyst ink discharged from the die 52 is increased, the thickness of the catalyst ink applied on the electrolyte membrane 32 is increased, and the anode side catalyst layer 38 is increased. Therefore, as shown in FIG. 5, when the pressure of the catalyst ink in the discharge path 59 changes according to the discharge time, the thickness of the anode side catalyst layer 38 in the X direction is accordingly changed as shown in FIG. Varies with position. The thickness of the anode side catalyst layer 38 is substantially proportional to the weight per unit area (catalyst weight) of the catalyst contained in the catalyst layer. For this reason, the greater the weight of the catalyst, the greater the thickness of the anode side catalyst layer 38. The thickness of the cathode side catalyst layer 42 is the same as the thickness of the anode side catalyst layer 38.

  For example, when the opening degree of the second valve 55 is level 2, as shown in FIG. 5, the pressure of the catalyst ink in the discharge path 59 is substantially constant while the first valve 54 is open. For this reason, as shown in FIG. 6, the basis weight of the catalyst, that is, the thickness of the anode catalyst layer 38 is substantially constant with respect to the position in the X direction.

  When the opening degree of the second valve 55 is level 3, as shown in FIG. 5, the pressure of the catalyst ink in the discharge path 59 decreases with time while the first valve 54 is open. For this reason, as shown in FIG. 6, the basis weight of the catalyst, that is, the thickness of the anode catalyst layer 38 also decreases as the position in the X direction advances.

  On the other hand, when the opening degree of the second valve 55 is level 1, as shown in FIG. 5, while the first valve 54 is open, the pressure of the catalyst ink in the discharge path 59 gradually increases with time. To increase. For this reason, as shown in FIG. 6, the basis weight of the catalyst, that is, the thickness of the anode side catalyst layer 38 increases as the position in the X direction advances.

  After the anode side catalyst layer 38 is formed on the outer surface of the electrolyte membrane 32 in this way, a shape maintaining sheet is stuck on the anode side catalyst layer 38. A laminate in which the anode side catalyst layer 38 and the electrolyte membrane 32 are sandwiched between the shape maintaining sheet and the support sheet is formed. Then, this laminated body is wound up by a winding part.

  Next, the wound laminate is drawn out from the unwinding unit and is laid over the roll 51. On this roller, the shape maintaining sheet, the anode side catalyst layer 38, the electrolyte membrane 32, and the support sheet are laminated in this order. Then, the electrolyte membrane 32 moves on the roll 51 in the X direction of the electrolyte membrane 32. Accordingly, the support sheet is peeled off from the inner surface of the electrolyte membrane 32, and the inner surface of the electrolyte membrane 32 appears outside. Then, the cathode side catalyst layer 42 is formed on the inner surface of the electrolyte membrane 32 in the same manner as the anode side catalyst layer 38 described above. Thereby, the membrane-catalyst layer assembly 26 is manufactured.

[Function and effect]
According to the membrane-catalyst layer assembly 26 configured as shown in FIG. 2, the thickness of the cathode-side catalyst layer 42 increases from the upstream end 31 a to the downstream end 31 b of the oxidant gas channel 31. And is formed so as to increase monotonously. Thus, as the cathode side catalyst layer 42 becomes thicker toward the downstream side (downstream end portion 31b) of the oxidant gas flow path 31, the amount of catalyst contained in the cathode side catalyst layer 42 increases. For this reason, as shown in FIG. 7, the voltage of the cell 24 in which the catalyst basis weight (the thickness of the catalyst layer) increases toward the downstream side of the oxidant gas flow path 31 indicates that the catalyst weight is downstream of the oxidant gas flow path 31. For example, it becomes 10 mV larger than the voltage of the cell 24 that decreases toward the side. At this time, the thickness of the cathode side catalyst layer 42 increasing toward the downstream side of the oxidant gas flow path 31 is 5 to 12 μm in the upstream portion and 8 to 15 μm in the downstream portion. Moreover, the thickness of the cathode side catalyst layer 42 decreasing toward the downstream side of the oxidant gas flow path 31 is 8 to 15 μm at the upstream portion and 5 to 12 μm at the downstream portion. Such a voltage difference is caused by uneven distribution of the current density distribution of the cell 24. In other words, in the low humidification operation, the downstream side of the oxidant gas flow path 31 has a higher water content and a higher current density. As the current density increases, the amount of catalyst in the cathode side catalyst layer 42 increases, so that the catalyst is effectively utilized.

  Further, the anode-side catalyst layer 38 is formed so that the thickness thereof monotonously decreases from the upstream end 29a to the downstream end 29b of the fuel gas channel 29. Thus, as the anode-side catalyst layer 38 becomes thicker toward the upstream side (upstream end portion 29a) of the fuel gas channel 29, the amount of catalyst contained in the anode-side catalyst layer 38 increases, so that the fuel gas Deterioration of the function of the stack 10 due to the ammonia contained in is suppressed. That is, city gas, propane gas, or the like is used as the source gas that is the source of the fuel gas, and the source gas may contain nitrogen. In this case, a small amount of ammonia is generated by the reforming reaction of the raw material gas and is contained in the fuel gas. When this ammonia is supplied to the anode side catalyst layer 38 through the fuel gas passage 29, the ammonia is adsorbed on the anode side catalyst and poisoned. This ammonia tends to adhere to the upstream anode catalyst. However, since there are many anode side catalysts on the upstream side of the fuel gas flow path 29, even if a part of the anode side catalyst layer 38 is poisoned, an active anode side catalyst remains. Thereby, the activity of the anode side catalyst is maintained over the entire length of the anode side catalyst layer 38 in the X direction, and a decrease in the voltage and durability of the stack 10 is suppressed.

(Embodiment 2)
FIG. 8 is a schematic diagram showing the membrane-catalyst layer assembly 26 according to the second embodiment.

  The thickness of the cathode side catalyst layer 42 is monotonous from the upstream end 31a to the downstream end 31b in the overall oxidant gas flow of the oxidant gas flow path 31, that is, in the X direction of FIG. It is formed to be smaller.

  The thickness of the anode catalyst layer 38 increases monotonously from the upstream end 29a to the downstream end 29b in the overall fuel gas flow in the fuel gas flow path 29, that is, in the X direction of FIG. Formed as follows.

  According to the membrane-catalyst layer assembly 26 configured as described above, the cathode side catalyst layer 42 becomes thicker toward the upstream side (upstream end portion 31a) of the oxidant gas flow path 31. As a result, the amount of the catalyst contained in the cathode side catalyst layer 42 increases, so that the deterioration of the function of the stack 10 due to contaminants in the air is suppressed. That is, the air supplied to the cathode side catalyst layer 42 contains contaminants such as nitrogen oxides. The cathode side catalyst is more likely to be poisoned toward the upstream side by this contaminant. However, since there are more cathode side catalysts on the upstream side of the oxidant gas flow path 31, an active cathode side catalyst remains even if some of the cathode side catalysts are poisoned. Thereby, the activity of the cathode side catalyst is maintained over the entire length of the cathode side catalyst layer 42 in the X direction, and the voltage and durability of the stack 10 are suppressed from being lowered.

  Further, the anode side catalyst layer 38 becomes thicker toward the downstream side (downstream end portion 29 b) side of the fuel gas passage 29. Accordingly, the amount of the catalyst contained in the anode side catalyst layer 38 is increased, so that the deterioration of the function of the stack 10 due to the reverse diffusion water is suppressed. That is, since water is generated by the power generation reaction, the amount of moisture at the cathode increases toward the downstream side. For this reason, in the low humidification operation, the rate at which downstream water moves to the anode side catalyst layer 38 via the electrolyte membrane 32 by reverse diffusion increases. When contaminants such as nitrogen oxides accompany the back-diffused water and reach the anode side catalyst layer 38, the contaminants poison the anode side catalyst. However, since there are many anode side catalysts in the downstream of the fuel gas flow path 29, an active anode side catalyst remains even if some anode side catalyst layers 38 are poisoned. Thereby, the activity of the anode side catalyst is maintained over the entire length of the anode side catalyst layer 38 in the X direction, and a decrease in the voltage and durability of the stack 10 is suppressed.

(Embodiment 3)
FIG. 9 is a schematic diagram showing the membrane-catalyst layer assembly 26 according to Embodiment 3. As shown in FIG.

  The thickness of the cathode-side catalyst layer 42 is monotonous from the upstream end 31a to the downstream end 31b in the overall oxidant gas flow of the oxidant gas flow path 31, that is, in the X direction of FIG. It is formed to be smaller.

  The thickness of the anode catalyst layer 38 decreases monotonously from the upstream end 29a toward the downstream end 29b in the overall fuel gas flow in the fuel gas passage 29, that is, in the X direction of FIG. Formed as follows.

  According to the membrane-catalyst layer assembly 26 configured as described above, the cathode side catalyst layer 42 becomes thicker toward the upstream side (upstream end portion 31a) of the oxidant gas flow path 31. As a result, the amount of the catalyst contained in the cathode side catalyst layer 42 increases, so that the function deterioration of the stack 10 due to contaminants in the air is suppressed as in the second embodiment.

  Further, the anode-side catalyst layer 38 is formed so that the thickness thereof monotonously decreases from the upstream end 29a to the downstream end 29b of the fuel gas channel 29. As described above, as the anode-side catalyst layer 38 becomes thicker toward the upstream side (upstream end portion 29a) of the fuel gas flow path 29, the amount of the catalyst contained in the anode-side catalyst layer 38 increases. As in the first mode, the deterioration of the function of the stack 10 due to the ammonia contained in the fuel gas is suppressed.

(Embodiment 4)
FIG. 10 is a schematic diagram showing the membrane-catalyst layer assembly 26 according to Embodiment 4. As shown in FIG.

  The thickness of the cathode-side catalyst layer 42 is monotonous from the upstream end 31a to the downstream end 31b in the overall oxidant gas flow in the oxidant gas flow path 31, that is, in the X direction of FIG. It is formed to be large.

  The thickness of the anode side catalyst layer 38 increases monotonously from the upstream end 29a to the downstream end 29b in the entire fuel gas flow in the fuel gas passage 29, that is, in the X direction of FIG. Formed as follows.

  According to the membrane-catalyst layer assembly 26 configured as described above, the thickness of the cathode side catalyst layer 42 is formed so as to increase monotonously from the upstream end portion 31a to the downstream end portion 31b of the oxidant gas flow channel 31. Is done. As described above, the cathode side catalyst layer 42 becomes thicker toward the downstream side (downstream end portion 31 b) side of the oxidant gas flow path 31. As a result, the amount of the catalyst contained in the cathode side catalyst layer 42 increases, so that the voltage in the stack 10 increases as in the first embodiment.

  Further, the anode side catalyst layer 38 becomes thicker toward the downstream side (downstream end portion 29 b) side of the fuel gas passage 29. As a result, the amount of the catalyst contained in the anode side catalyst layer 38 is increased, so that the deterioration of the function of the stack 10 due to the contaminant contained in the back diffusion water is suppressed as in the second embodiment.

  In all the embodiments described above, as shown in FIG. 3, one polygonal fuel gas channel 29 is provided in the anode-side separator 28, and one polygonal oxidant gas channel 31 is the cathode. Provided on the side separator 30. However, the number and shape provided in each separator 28, 30 of the fuel gas channel 29 and the oxidant gas channel 31 are not limited to this. For example, the separators 28 and 30 in the plurality of linear fuel gas passages 29 and oxidant gas passages 31 may be provided.

  Further, all the above embodiments may be combined with each other as long as they do not exclude each other.

  From the foregoing description, many modifications and other embodiments of the present invention are apparent to persons skilled in the art. Accordingly, the foregoing description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and / or function may be substantially changed without departing from the spirit of the invention.

  The fuel cell stack 10 of the present invention is useful as a fuel cell stack 10 or the like whose function is improved in the relationship between the thickness of the catalyst layer and the flow direction of the reaction gas.

DESCRIPTION OF SYMBOLS 10 Stack 26 Membrane-catalyst layer assembly 28 Anode side separator 29 Fuel gas flow path 29a Upstream end part 29b Downstream end part 30 Cathode side separator 31 Oxidant gas flow path 31a Upstream end part 31b Downstream end part 32 Electrolyte membrane 38 Anode side Catalyst layer 40 Anode side gas diffusion layer 42 Cathode side catalyst layer 44 Cathode side gas diffusion layer

Claims (5)

A membrane-catalyst layer assembly having an anode side catalyst layer, a cathode side catalyst layer, and a polymer electrolyte membrane sandwiched between the anode side catalyst layer and the cathode side catalyst layer;
An anode-side gas diffusion layer and a cathode-side gas diffusion layer facing each other so as to sandwich the membrane-catalyst layer assembly,
An anode-side separator and a cathode-side separator facing each other so as to sandwich the anode-side gas diffusion layer and the cathode-side gas diffusion layer;
A fuel gas flow path provided between the anode separator and the anode gas diffusion layer;
An oxidant gas flow path provided between the cathode side separator and the cathode side gas diffusion layer,
An overall (macroscopic) fuel gas flow direction in the fuel gas flow path and an overall (macroscopic) oxidant gas flow direction in the oxidant gas flow path are parallel,
The anode-side catalyst layer is formed so that the thickness thereof monotonously changes from the upstream end portion toward the downstream end portion in the overall fuel gas flow of the fuel gas flow path,
And,
A fuel cell stack formed such that the thickness of the cathode side catalyst layer monotonously changes from an upstream end to a downstream end in the overall oxidant gas flow of the oxidant gas flow path. The anode-side catalyst layer is formed so that the thickness thereof monotonously decreases from the upstream end to the downstream end in the overall fuel gas flow of the fuel gas flow path,
The thickness of the said cathode side catalyst layer was formed so that it might increase monotonically toward the downstream end part from the upstream end part in the flow of the whole oxidizing gas of the said oxidizing gas flow path. The fuel cell stack described. The anode catalyst layer is formed so that the thickness thereof monotonously increases from the upstream end portion toward the downstream end portion in the overall fuel gas flow of the fuel gas flow path,
The thickness of the said cathode side catalyst layer was formed so that it might become monotonically small toward the downstream end part from the upstream end part in the flow of the whole oxidizing agent gas flow path of the said oxidizing agent gas flow path. The fuel cell stack described. The anode-side catalyst layer is formed so that the thickness thereof monotonously decreases from the upstream end to the downstream end in the overall fuel gas flow of the fuel gas flow path,
The thickness of the said cathode side catalyst layer was formed so that it might become monotonically small toward the downstream end part from the upstream end part in the flow of the whole oxidizing agent gas flow path of the said oxidizing agent gas flow path. The fuel cell stack described. The anode catalyst layer is formed so that the thickness thereof monotonously increases from the upstream end portion toward the downstream end portion in the overall fuel gas flow of the fuel gas flow path,
The thickness of the said cathode side catalyst layer was formed so that it might increase monotonically toward the downstream end part from the upstream end part in the flow of the whole oxidizing gas of the said oxidizing gas flow path. The fuel cell stack described.

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