JP2014160579A - Fuel cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell stack which improves power generation performance of end unit cells arranged at both ends in a lamination direction in a simple configuration and enables the excellent power generation performance to be obtained in the entire unit cells even when normally operated within an operating temperature range.SOLUTION: In a fuel cell stack 10 in which a plurality of unit cells 12 having an electrolyte film/electrode structure 34 in which porous layers 56 and 62 are interposed between electrode catalyst layers 52 and 58 and gas diffusion layers 54 and 60 of each of a pair of electrodes 48 and 50 are laminated, end unit cells 12a arranged at both ends in a lamination direction show at least one of characteristic in which percolation pressure of a superposition 64 and 68 formed of the gas diffusion layers 54 and 60 and the porous layers 56 and 62 is smaller than that of the other unit cell 12b and characteristic in which steam discharge speed is larger than that of the other unit cell 12b.

Description

  The present invention includes an electrode having an electrode catalyst layer and a gas diffusion layer on each side of a solid polymer electrolyte membrane, and at least one of the electrodes includes a porous layer between the electrode catalyst layer and the gas diffusion layer. The present invention relates to a fuel cell stack configured by laminating a plurality of unit cells each having an electrolyte membrane / electrode structure intervening.

  In recent years, various types of fuel cells have been developed. For example, it is known to use a polymer electrolyte fuel cell that operates at about 70 to 100 ° C. for in-vehicle applications. This polymer electrolyte fuel cell is usually used as a fuel cell stack in which a predetermined number of unit cells are stacked and end plates are provided at both ends in the stacking direction in order to obtain a desired power generation.

  In such end unit cells arranged at both ends in the stacking direction of the fuel cell stack, heat is radiated to the outside of the fuel cell stack via the end plate or the like, and is arranged at the center in the stacking direction. There is a concern that the temperature is likely to decrease as compared with other unit cells, and sufficient power generation performance cannot be obtained.

  By the way, when starting a fuel cell stack from a stop state, it is known that the temperature of the fuel cell stack is raised to the above operating temperature by, for example, warming up by self-heating by a power generation reaction. However, since the end unit cell has a large amount of heat radiation to the outside as described above, it takes a long time for the temperature to rise compared to other unit cells. As a result, for example, in the end unit cell, if the vapor pressure of generated water or the like generated by the power generation reaction does not sufficiently increase, water stays in the pores forming the reaction gas flow path and flooding occurs. It tends to occur. As a result, the power generation reaction is hindered, and there is a concern that it is difficult to start the fuel cell stack well. In particular, when the fuel cell stack is used in a vehicle, it is assumed that the fuel cell stack is started in a cold environment below freezing. However, in this case, the accumulated water in the end unit cell freezes, and the fuel cell stack is further started. There are concerns that it will be difficult.

  Therefore, for the purpose of suppressing flooding generated in the end unit cell when starting the fuel cell stack in a low temperature region such as below freezing point, that is, for improving the low temperature startability of the fuel cell stack, for example, Patent Document 1 Has proposed a fuel cell stack in which the calorific value of the end unit cell is larger than that of other unit cells. Patent Document 2 proposes a fuel cell system including a fuel cell stack in which the water absorption capacity of the end unit cell is larger than that of other unit cells.

JP 2006-196220 A JP-T-2006-526271

  However, as described above, the fuel cell stack described in Patent Document 1 is intended to improve low temperature startability, and during normal operation after the fuel cell stack reaches the operating temperature, the end unit cell It does not consider improving the power generation performance. In this fuel cell stack, as long as power generation is performed, the amount of heat generated by the end unit cells always increases. For this reason, at the time of normal operation, there is a concern that the end unit cell becomes excessively high in temperature and the power generation performance deteriorates due to drying of the electrolyte membrane. Therefore, during normal operation, it is necessary to cool the end unit cell more than other cells. If the cooling is insufficient, the power generation performance of the end unit cell, and thus the entire fuel cell stack, There was a problem that the power generation performance deteriorated.

  On the other hand, in the fuel cell system of Patent Document 2, even during normal operation, in order to suppress a decrease in power generation performance due to flooding of the end unit cell, etc. A control device for adjusting and supplying humidity is provided. However, in this fuel cell system, a control device such as a microcomputer is required in addition to the fuel cell stack.

  The present invention solves this type of problem, and can improve the power generation performance of the end unit cells arranged at both ends in the stacking direction with a simple configuration even during normal operation within the operating temperature range. As a result, an object of the present invention is to provide a fuel cell stack exhibiting excellent power generation performance in the entire unit cell.

To achieve the above object, the present invention provides an electrolyte membrane / electrode structure in which an electrolyte membrane made of a solid polymer membrane is sandwiched between an anode electrode and a cathode electrode, and the electrolyte membrane / electrode structure A fuel cell stack configured by stacking a plurality of unit cells having separators disposed on both sides,
Each of the anode electrode and the cathode electrode has an electrode catalyst layer facing the electrolyte membrane, and a gas diffusion layer,
At least one of the anode electrode or the cathode electrode further has a porous layer interposed between the electrode catalyst layer and the gas diffusion layer,
Among the plurality of unit cells, end unit cells arranged at both ends in the stacking direction are superposed bodies in which the porous layer and the gas diffusion layer are superposed as compared with other unit cells. The hydraulic pressure is small.

  In the fuel cell stack, the hydraulic pressure of the superimposed body of the end unit cell is 10.0 to 30.0 kPa, and the hydraulic pressure of the superimposed body of the other unit cell is 30.0 to 120.0 kPa. It is preferable that

The present invention also provides an electrolyte membrane / electrode structure in which an electrolyte membrane made of a solid polymer membrane is sandwiched between an anode electrode and a cathode electrode, and a separator disposed on both sides of the electrolyte membrane / electrode structure A fuel cell stack configured by stacking a plurality of unit cells having
Each of the anode electrode and the cathode electrode has an electrode catalyst layer facing the electrolyte membrane, and a gas diffusion layer,
At least one of the anode electrode or the cathode electrode further has a porous layer interposed between the electrode catalyst layer and the gas diffusion layer,
Among the plurality of unit cells, end unit cells arranged at both ends in the stacking direction are superposed bodies in which the porous layer and the gas diffusion layer are superposed as compared with other unit cells. It is characterized by a high water vapor discharge rate.

In the fuel cell stack, the water vapor discharge rate of the superposed body of the end unit cell is 18.0 to 20.0 mg / cm ² · min, and the water vapor discharge speed of the superposed body of the other unit cell is It is preferably 15.0 to 18.0 mg / cm ² · min.

Furthermore, the present invention provides an electrolyte membrane / electrode structure in which an electrolyte membrane made of a solid polymer membrane is sandwiched between an anode electrode and a cathode electrode, and a separator disposed on both sides of the electrolyte membrane / electrode structure A fuel cell stack configured by stacking a plurality of unit cells having
Each of the anode electrode and the cathode electrode has an electrode catalyst layer facing the electrolyte membrane, and a gas diffusion layer,
At least one of the anode electrode or the cathode electrode further has a porous layer interposed between the electrode catalyst layer and the gas diffusion layer,
Among the plurality of unit cells, end unit cells arranged at both ends in the stacking direction are superposed bodies in which the porous layer and the gas diffusion layer are superposed as compared with other unit cells. The water permeability is low and the water vapor discharge rate is high.

In the above fuel cell stack, the water permeability of the superposed body of the end unit cell is 10.0 to 30.0 kPa and the water vapor discharge rate is 18.0 to 20.0 mg / cm ² · min. The water permeability of the superposed body of the unit cell is preferably 30.0 to 120.0 kPa, and the water vapor discharge rate is preferably 15.0 to 18.0 mg / cm ² · min.

  In the fuel cell stack according to the present invention, a porous layer is interposed between the electrode catalyst layer and the gas diffusion layer of each unit cell constituting the fuel cell stack, and the porous layer and the gas diffusion layer are overlapped. As described above, the end unit cell and the other unit cell are set so as to exhibit different characteristics with respect to at least one of the body hydraulic pressure and the water vapor discharge rate. As a result, the power generation performance of both the end unit cell and other unit cells can be improved. In particular, the end unit cell has a large amount of heat radiation to the outside and the temperature is likely to be lower than other cells. The power generation performance can be significantly improved.

  That is, the end unit cell easily discharges water and water vapor as compared with other unit cells. For this reason, flooding hardly occurs even when the temperature is lower than that of other unit cells. Therefore, even if the temperature of the end unit cell is lowered, the flooding can be suppressed by discharging excess water while maintaining the electrolyte membrane of the end unit cell in a wet state. Thereby, good proton conductivity can be expressed in the electrolyte membrane, and the diffusibility of the reaction gas can be improved to promote the power generation reaction, and the power generation performance of the end unit cell can be improved. As a result, the power generation performance of the entire fuel cell stack including this end unit cell can be improved.

  Here, the end unit cell is not limited to two unit cells disposed at the extreme ends (endmost portions) on both sides in the stacking direction of the fuel cell stack. The end unit cell may be composed of all of several (2 to 5) unit cells respectively disposed at both ends of the fuel cell stack or one or more selected from the unit cells. . That is, the end unit cell may be configured not to include the two unit cells disposed at the extreme end, and in this case, the two unit cells disposed at the extreme end may be fuel. You may have the characteristic similar to the unit cell (other unit cell) arrange | positioned at the center part of a battery stack.

  In this fuel cell stack, the water permeability between the anode electrode and the cathode electrode and the cathode electrode in each of the end unit cell and the other unit cell are set to the above values by setting the water permeability and water vapor discharge speed of the superposed body, respectively. The balance of drainage can be more appropriately achieved, and better power generation performance can be obtained.

In the fuel cell stack, it is preferable that the end unit cell has a smaller electric resistance in the stacking direction of the electrolyte membrane / electrode structure than the other unit cell. More preferably, when the superposed body of the end unit cell is pressurized at 15 kgf / cm ² in the stacking direction, the through resistance of the superposed body is 4.0 to 5.0 mΩ · cm ² . When the superposed body of the unit cell is pressurized at 15 kgf / cm ² in the stacking direction, the through resistance of the superposed body is 5.0 to 7.0 mΩ · cm ² .

  In this case, for each of the end unit cells and the other unit cells, a balance between water retention and drainage between the anode electrode and the cathode electrode can be more appropriately achieved, so that a fuel cell stack having better power generation performance can be obtained. Can be obtained.

  According to the present invention, the temperature of the superposed body of the end unit cells is adjusted by adjusting at least one of reducing the water permeation pressure and increasing the water vapor discharge rate compared to other unit cells. Also for the end unit cell that tends to be lowered, it is possible to efficiently discharge the surplus water and to diffuse the reaction gas well while maintaining the electrolyte membrane in a wet state. Thus, even during normal operation, the power generation performance of the end unit cell can be improved with a simple configuration, and the power generation performance of the entire fuel cell stack can be improved.

It is a perspective explanatory view of the fuel cell stack concerning the embodiment of the present invention. FIG. 2 is a schematic vertical sectional view of a main part of the fuel cell stack shown in FIG. 1. It is a graph which shows the preparation conditions of a porous layer, and the physical-property value of a superimposition about unit cell A1, A2, B1-B4 for measurement samples. It is a schematic block diagram of the apparatus which measures the water vapor | steam discharge speed | velocity | rate of a superimposition body. It is a graph which shows the average voltage difference of the whole average voltage and a center part unit cell, and an end unit cell about the fuel cell stack of Examples 1-5 and Comparative Examples 1-5.

  Hereinafter, preferred embodiments of a fuel cell stack according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a perspective explanatory view of the fuel cell stack 10, and FIG. 2 is a schematic vertical sectional view of a main part of the fuel cell stack 10.

  In the fuel cell stack 10, a plurality of unit cells 12 are stacked in the direction of arrow A, and end plates 18, 18 are interposed at both ends in the stacking direction via terminal plates 14, 14 and insulating plates 16, 16. Is arranged (see FIG. 2).

  Also, as shown in FIG. 1, an oxidant gas inlet for supplying an oxidant gas such as an oxygen-containing gas to one end edge of the fuel cell stack 10 in the direction of arrow B and communicating with each other in the direction of arrow A A communication hole 20, a cooling medium inlet communication hole 22 for supplying a cooling medium such as pure water or ethylene glycol, and a fuel gas outlet communication hole 24 for discharging a fuel gas such as a hydrogen-containing gas are provided.

  In addition, the other end edge of the fuel cell stack 10 in the direction of arrow B communicates with each other in the direction of arrow A, a fuel gas inlet communication hole 26 for supplying fuel gas, and an oxidation for discharging oxidant gas. An agent gas outlet communication hole 30 and a cooling medium outlet communication hole 28 for discharging the cooling medium are provided.

  The end plates 18, 18 are fastened in the stacking direction by a plurality of tie rods 32, for example. The end plate 18 disposed on the distal end side of the tie rod 32 is formed with a screw hole (not shown) that is screwed with the male screw of the tie rod 32. Alternatively, a through hole may be formed in the end plate 18 instead of the screw hole, and a nut (not shown) may be screwed onto the tip of the tie rod 32.

  Further, a clamping load may be applied by adjusting a distance between the end plates 18 and 18 by interposing a plate (not shown) between the end plates 18 and 18. Further, a load may be applied between the end plate 18 and the insulating plate 16 with a disc spring (not shown) interposed therebetween.

  As shown in FIG. 2, each unit cell 12 is configured by stacking an electrolyte membrane / electrode structure 34, an anode side separator 36, and a cathode side separator 38 in a standing posture, for example. As the anode side separator 36 and the cathode side separator 38, for example, a carbon separator is used, but a metal separator may be used instead.

  A fuel gas passage 40 communicating with the fuel gas inlet communication hole 26 and the fuel gas outlet communication hole 24 is provided in a horizontal direction (arrow B direction) on the surface of the anode separator 36 facing the electrolyte membrane / electrode structure 34. It is provided to extend.

  Similarly, an oxidant gas passage 42 communicating with the oxidant gas inlet communication hole 20 and the oxidant gas outlet communication hole 30 is horizontally provided on the surface facing the electrolyte membrane / electrode structure 34 of the cathode side separator 38. It is provided to extend.

  Cooling that communicates with the cooling medium inlet communication hole 22 and the cooling medium outlet communication hole 28 between the surfaces of the anode side separator 36 and the cathode side separator 38 that face each other when a plurality of unit cells 12 are stacked. A medium flow path 44 is integrally formed.

  The electrolyte membrane / electrode structure 34 includes an electrolyte membrane 46 made of a solid polymer membrane, and an anode electrode 48 and a cathode electrode 50 that sandwich the electrolyte membrane 46. The outer dimension (surface area) of the electrolyte membrane 46 is set larger than the outer dimensions of the anode electrode 48 and the cathode electrode 50. As a result, the reaction gas supplied to one of the anode electrode 48 and the cathode electrode 50 passes through the electrolyte membrane 46 and moves to the other electrode, or from the electrolyte membrane / electrode structure 34 to the outside. Can be prevented from leaking (outleak).

  As the electrolyte membrane 46, for example, a film formed of a polymer that belongs to a cation exchange resin and has proton conductivity can be used. Examples of the cation exchange resin include sulfonated products of vinyl polymers such as polystyrene sulfonic acid, heat-resistant polymers such as perfluoroalkyl sulfonic acid polymer, perfluoroalkyl carboxylic acid polymer, polybenzimidazole, and polyether ether ketone. Examples thereof include a polymer having a sulfonic acid group or a phosphoric acid group introduced therein, a rigid polyphenylene obtained by polymerizing an aromatic compound having a phenylene chain as a main component, and a polymer having a sulfonic acid group introduced thereto.

  The anode electrode 48 includes a first electrode catalyst layer 52, a first gas diffusion layer 54, and a first porous layer 56. On the other hand, the cathode electrode 50 includes a second electrode catalyst layer 58, a second gas diffusion layer 60, and a second porous layer 62.

  The first electrode catalyst layer 52 includes carbon particles supporting a catalyst metal. As the carbon particles, carbon black can be used. In addition to this, for example, graphite, carbon fiber, activated carbon and the like, pulverized products thereof, and carbon compounds such as carbon nanofiber and carbon nanotube can be adopted. . On the other hand, as a catalyst metal, metals such as platinum, ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum are used alone or in combination. Can be used in combination.

  The first electrode catalyst layer 52 is provided so as to be joined to the electrolyte membrane 46, and the outer dimension is set smaller than that of the electrolyte membrane 46.

  The first gas diffusion layer 54 is made of, for example, carbon paper formed by containing a large number of fibrous carbons in cellulosic material. For example, a water-repellent resin made of FEP (tetrafluoroethylene / hexafluoropropylene copolymer) or the like may be contained in the base material. The outer dimension of the first gas diffusion layer 54 is set larger than that of the first electrode catalyst layer 52.

  The first porous layer 56 is a porous layer containing an electron conductive substance and a water repellent resin, and exhibits conductivity based on the electron conductive substance. Suitable examples of the electron conductive material include furnace black (“Ketjen Black EC” and “Ketjen Black ECP600JD” manufactured by Ketjen Black International, “Vulcan XC-72” manufactured by Cabot, and Tokai Carbon Co., Ltd. “Toka Black”, “Asahi AX” manufactured by Asahi Carbon Co., Ltd .; all trade names), acetylene black (“Denka Black” produced by Denki Kagaku Kogyo Co., Ltd .; trade names), crushed products of glassy carbon, vapor grown carbon fiber ("VGCF" and "VGCF-H" manufactured by Showa Denko KK; both are trade names), carbon nanotubes, and powders obtained by graphitizing them, or a mixture of two or more thereof.

  One water-repellent resin material is ETFE (tetrafluoroethylene / ethylene copolymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), ECTFE (chlorotrifluoroethylene / ethylene copolymer), PTFE. (Polytetrafluoroethylene), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer), crystalline fluororesins such as FEP, “Lumiflon” and “Cytop” manufactured by Asahi Glass Co., Ltd. ) And the like, and silicone resins and the like can be exemplified, and these can be used alone or in combination of two or more.

  The outer dimension of the first porous layer 56 is set to be approximately equal to the outer dimension of the first gas diffusion layer 54, and the first porous layer 56 and the first gas diffusion layer 54 are overlapped to form a first superimposed body. 64 is configured.

  The first superimposed body 64 can set its water permeation pressure and water vapor discharge rate by appropriately adjusting the maximum pore diameter and thickness, the type and amount of the water repellent resin in the first porous layer 56, and the like. it can. Specific physical property values will be described later.

  As described above, the outer dimensions of the first electrode catalyst layer 52 are set smaller than those of the electrolyte membrane 46 and the first gas diffusion layer 54. For this reason, the outer peripheral edge of the electrolyte membrane 46 is exposed to the outside from the outer periphery of the first electrode catalyst layer 52, and the first porous layer 56 is between the exposed portion and the first gas diffusion layer 54. Intervenes. That is, the first porous layer 56 is interposed between the first electrode catalyst layer 52 and the first gas diffusion layer 54 and between the electrolyte membrane 46 and the first gas diffusion layer 54. As a result, the fibers constituting the first gas diffusion layer 54 can be prevented from piercing the electrolyte membrane 46 (particularly, the outer peripheral edge portion of the electrolyte membrane 46), and thus the physical deformation of the electrolyte membrane 46 can be suppressed.

  In addition, a frame-shaped first insulating sheet 66 is applied to the surface of the outer peripheral edge of the electrolyte membrane 46 that is exposed to the anode separator 36 from the outer periphery of the first superimposed body 64. It is provided to touch.

  The first insulating sheet 66 has gas impermeability, and is formed of, for example, a substantially flat film made of PEN (polyethylene naphthalate). In addition, since the thickness of the first insulating sheet 66 and the thickness of the first superimposed body 64 are substantially equal, the surfaces of the first insulating sheet 66 and the first superimposed body 64 (first gas diffusion layer 54) are flush with each other. In this state, it is in contact with the anode separator 36.

  Thus, by providing the 1st insulating sheet 66, it can avoid effectively that a reaction gas moves and mixes between the anode electrode 48 and the cathode electrode 50, and an out leak arises.

  The second electrode catalyst layer 58, the second gas diffusion layer 60, the second porous layer 62, the second superposed body 68 and the second insulating sheet 70 in the cathode electrode 50 are composed of the first electrode catalyst layer 52, the first gas described above. The diffusion layer 54, the first porous layer 56, the first superimposed body 64, and the first insulating sheet 66 are configured in the same manner. For this reason, the detailed description about the structure of the cathode electrode 50 is abbreviate | omitted. In the following description, when the first electrode catalyst layer 52 and the second electrode catalyst layer 58 are not particularly distinguished from each other, they are collectively referred to as an electrode catalyst layer. Similarly, the first porous layer 56 and the second porous layer 62 are also referred to as porous layers, and the first superimposed body 64 and the second superimposed body 68 are also referred to as superimposed bodies.

  The anode side separator 36 and the cathode side separator 38 are provided with sealing members 72 and 72 so as to surround the edges of the first gas diffusion layer 54 and the second gas diffusion layer 60, respectively. Outleak can be effectively prevented by these seal members 72, 72.

  Next, a method for producing the above-described electrolyte membrane / electrode structure 34 will be described. In producing the electrolyte membrane / electrode structure 34, first, the electrolyte membrane 46 is produced in the shape of a rectangular sheet made of a polymer selected from the polymers belonging to the cation exchange resin and having proton conductivity.

  Then, the first electrode catalyst layer 52 is formed on one surface of the electrolyte membrane 46, and the second electrode catalyst layer 58 is formed on the other surface. Specifically, first, a catalyst paste is prepared by mixing the catalyst particles and an ionomer solution.

  Next, a predetermined amount of this catalyst paste is applied onto one surface of a film formed from PTFE or the like. Then, the surface of the film to which the catalyst paste is applied is thermocompression bonded to one surface of the electrolyte membrane 46. Thereafter, when the film is peeled off, the catalyst paste is transferred to one surface of the electrolyte membrane 46. Thereby, the first electrode catalyst layer 52 can be formed. Further, the second electrode catalyst layer 58 can be formed by transferring the catalyst paste to the other surface of the electrolyte membrane 46 in the same manner.

  Separately, the first porous layer 56 is formed on the first gas diffusion layer 54 to obtain the first superimposed body 64, and the second porous layer 62 is formed on the second gas diffusion layer 60. A second superimposed body 68 is obtained.

  Specifically, for example, the porous layer paste is prepared by mixing the electron conductive substance and the water repellent resin in an organic solvent such as ethanol, propanol, or ethylene glycol. And after apply | coating the predetermined amount of this paste for porous layers on the 1st gas diffusion layer 54, the 1st porous layer 56 is formed by heat-processing. Thereby, the first superimposed body 64 can be obtained.

  Similarly, after applying a predetermined amount of the porous layer paste on the second gas diffusion layer 60, the second porous layer 62 is formed by heat treatment. Thereby, the second superimposed body 68 can be obtained. In addition, the 1st superimposed body 64 and the 2nd superimposed body 68 may have a mutually different characteristic by being formed from the paste for porous layers adjusted so that it may mutually differ.

  Here, for example, the coating amount of the porous layer paste applied on the first gas diffusion layer 54 and the second gas diffusion layer 60, the electron conductive substance and the water repellent resin with respect to the organic solvent of the porous layer paste By adjusting the concentration (solid content concentration) and the like, the water permeation pressure and the water vapor discharge rate of the first superimposed body 64 and the second superimposed body 68 can be adjusted. Furthermore, in order to adjust the physical property values of the first superposed body 64 and the second superposed body 68, the physical property values of the base materials constituting the first gas diffusion layer 54 and the second gas diffusion layer 60 and the base material are impregnated. You may adjust the density | concentration etc. of the water-repellent resin to make.

  Instead of the above production method, the first porous layer 56 and the second porous layer 62 may be obtained as a sheet-like molded body. In this case, by preparing the porous layer paste so that the concentration (solid content concentration) of the electron conductive material and the water-repellent resin with respect to the organic solvent is increased, the solvent is extracted and subjected to stretching treatment, etc. The 1st porous layer 56 and the 2nd porous layer 62 are formed as a sheet-like molded object.

  Then, the first porous layer 56 and the second porous layer 62 obtained as a sheet-like molded body are superimposed on each of the first gas diffusion layer 54 and the second gas diffusion layer 60. In this state, by applying pressure and heating (hot pressing), the first gas diffusion layer 54 and the first porous layer 56 can be thermocompression bonded to obtain the first superimposed body 64, and the second gas diffusion can be obtained. The second superposed body 68 can be obtained by thermocompression bonding the layer 60 and the second porous layer 62.

  The first superposed body 64 and the second superposed body 68 obtained as described above, the first porous layer 56 and the second porous layer 62 are respectively the first electrode catalyst layer 52 and the second electrode catalyst layer 58. Are integrated so as to face each other by thermocompression bonding. Thereby, the electrolyte membrane / electrode structure 34 is obtained.

  At this time, as described above, the porous layer is interposed between the gas diffusion layer and the electrode catalyst layer, and between the gas diffusion layer 54 and the electrolyte membrane 46. Accordingly, even if a load due to thermocompression bonding is applied to the superposed body, it is possible to avoid the fibers of the gas diffusion layer 54 from being pierced into the electrolyte membrane 46 and to suppress physical deformation of the electrolyte membrane 46.

  The unit cell 12 is configured by sandwiching the electrolyte membrane / electrode structure 34 between the anode side separator 36 and the cathode side separator 38.

  Therefore, the fuel cell stack 10 is configured by stacking, for example, 10 or more unit cells 12 configured as described above, and sandwiching both end portions between the end plates 18 and 18 as described above. The number of unit cells 12 to be stacked can be set so that a desired power generation can be obtained by the fuel cell stack 10. That is, when the fuel cell stack 10 is mounted on, for example, a fuel cell vehicle, the fuel cell stack 10 is configured by stacking a number of unit cells 12 that can generate electric power necessary for driving the vehicle. Can do.

  Here, as shown in FIG. 2, among the plurality of unit cells 12, the end unit cells 12 a arranged at both ends in the stacking direction are connected to the end plate 18 via the terminal plate 14 and the insulating plate 16. In contact. For this reason, the end unit cell 12a is radiated to the outside of the fuel cell stack 10 through the end plate 18, and the other unit cells (center unit cell) 12b disposed in the center in the stacking direction In comparison, the temperature tends to decrease.

  Therefore, in the fuel cell stack 10, the water permeability of the superimposed body is set so that the value of the end unit cell 12a is smaller than that of the central unit cell 12b. In this embodiment, the hydraulic pressure of the superposed body of the end unit cell 12a is adjusted to 10.0 to 30.0 kPa, and the hydraulic pressure of the superposed body of the center unit cell 12b is adjusted to 30.0 to 120.0 kPa. It is carried out. In this case, as described later, the power generation performance of the end unit cell 12a can be improved more favorably. These hydraulic pressures can be determined using, for example, a palm porometer manufactured by PMI (Porous Material, Inc).

Further, in this fuel cell stack 10, the value of the end unit cell 12a is set to be larger than the central unit cell 12b with respect to the water vapor discharge speed of the superposed body. In the present embodiment, the water vapor discharge rate of the superposed body of the end unit cell 12a is 18.0 to 20.0 mg / cm ² · min, and the water vapor discharge speed of the superposed body of the central unit cell 12b is 15.0 to 18 It is adjusted to be 0.0 mg / cm ² · min. In this case, as described later, the power generation performance of the end unit cell 12a can be improved more favorably. These water vapor discharge rates can be determined using, for example, a measuring device 74 shown in FIG. 4 described later.

Further, in the fuel cell stack 10, the electric resistance in the stacking direction of the electrolyte membrane / electrode structure 34 is set so that the value of the end unit cell 12a is smaller than that of the central unit cell 12b. . In the present embodiment, for the superposed body in the electrolyte membrane / electrode structure 34, the penetration resistance obtained by multiplying the electrical resistance with respect to the stacking direction by a contact area described later is adjusted as follows. The electrical resistance in the stacking direction of the structures 34 is set as described above. That is, when the superposed body of the end unit cell 12a is pressurized at 15 kgf / cm ² in the stacking direction, the penetration resistance is 4.0 to 5.0 mΩ · cm ² , and the superposed body of the central unit cell 12b is the same. Further, the penetration resistance when pressurized at 15 kgf / cm ² is adjusted to 5.0 to 7.0 mΩ · cm ² . In this case, as described later, the power generation performance of the end unit cell 12a can be improved more favorably.

  Regarding the penetration resistance, the coating amount of the porous layer paste applied on the gas diffusion layer, the concentration and type of the electron conductive substance and the water-repellent resin with respect to the organic solvent of the porous layer paste, and the gas diffusion layer are configured. By adjusting the physical property value of the base material to be adjusted, the concentration of the water-repellent resin impregnated in the base material, and the like, it can be set to the above value. A method for obtaining the penetration resistance will be described later.

  In the present embodiment, the physical property values of both the first superimposed body 64 and the second superimposed body 68 are set as described above, but at least one of the physical property values of the first superimposed body 64 and the second superimposed body 68 is set. May be set as described above.

  As described above, by setting the physical property values of the end unit cell 12a and the central unit cell 12b, for example, when starting the fuel cell stack 10 or during normal operation operating at about 70 to 100 ° C. Even if the temperature of the end unit cell 12a is lower than that of the central unit cell 12b, the power generation performance of the end unit cell 12a can be improved. This effect will be described below together with the operation of the fuel cell stack 10 during normal operation.

  When generating power in the fuel cell stack 10, the oxidant gas is supplied to the oxidant gas inlet communication hole 20 and the fuel gas is supplied to the fuel gas inlet communication hole 26. Further, the cooling medium is supplied to the cooling medium inlet communication hole 22.

  The cooling medium supplied to the cooling medium inlet communication hole 22 is introduced into a cooling medium flow path 44 formed between the anode side separator 36 and the cathode side separator 38. In the cooling medium flow path 44, the cooling medium moves in the direction of gravity (the direction of arrow C in FIG. 1). Therefore, the cooling medium is cooled over the entire power generation surface of the electrolyte membrane / electrode structure 34 and then discharged to the cooling medium outlet communication hole 28.

  The oxidant gas is introduced from the oxidant gas inlet communication hole 20 into the oxidant gas flow path 42 of the cathode side separator 38. The oxidant gas flows in the direction of arrow B along the oxidant gas flow path 42 and moves along the cathode electrode 50 of the electrolyte membrane / electrode structure 34.

  On the other hand, the fuel gas is introduced from the fuel gas inlet communication hole 26 into the fuel gas flow path 40 of the anode side separator 36. In the fuel gas channel 40, the fuel gas flows in the direction of arrow B, and moves along the anode electrode 48 of the electrolyte membrane / electrode structure 34.

  Therefore, in the electrolyte membrane / electrode structure 34, the fuel gas supplied to the anode electrode 48 and passed through the first gas diffusion layer 54 and the first porous layer 56, and supplied to the cathode electrode 50 and the second gas diffusion layer. 60 and the oxidant gas that has passed through the second porous layer 62 are consumed by the electrochemical reaction (electrode reaction) in the first electrode catalyst layer 52 and the second electrode catalyst layer 58, respectively, and electricity is generated.

More specifically, after the fuel gas supplied to the anode electrode 48 has passed through the first gas diffusion layer 54 and the first porous layer 56 via the fuel gas flow path 40, the hydrogen gas in the fuel gas is changed. The first electrode catalyst layer 52 is ionized to generate protons (H ⁺ ) and electrons. Electrons are taken out as electric energy for energizing an external load (not shown) electrically connected to the fuel cell stack 10, while protons are electrolyte membranes constituting the electrolyte membrane / electrode structure 34. The cathode electrode 50 is reached via 46. The proton moves from the anode electrode 48 side to the cathode electrode 50 side along with water contained in the electrolyte membrane 46.

  In the second electrode catalyst layer 58 of the cathode electrode 50, the protons, the electrons reaching the cathode electrode 50 after energizing an external load, and the second gas diffusion layer 60 and the second gas supplied to the cathode electrode 50 are supplied. The oxygen gas in the oxidant gas that has passed through the porous layer 62 is combined. As a result, water is generated. Hereinafter, this water is also referred to as generated water.

  In the electrolyte membrane / electrode structure 34, as described above, the first superposed body 64 is formed by interposing the first porous layer 56 between the electrolyte membrane 46 and the first gas diffusion layer 54, and the electrolyte membrane. A second superposed body 68 is formed by interposing a second porous layer 62 between 46 and the second gas diffusion layer 60. Due to the presence of the first porous layer 56 and the second porous layer 62, it is possible to appropriately achieve a balance between water retention and drainage in the anode electrode 48 and the cathode electrode 50 during the above electrode reaction.

  That is, in this embodiment, since the values of the water permeability and the water vapor discharge rate of the superposed body in the end unit cell 12a and the center unit cell 12b are set as described above, the end unit cell 12a has more water vapor. Ejects easily. For this reason, flooding hardly occurs. In addition, in this case, the water vapor contained in the fuel gas at the anode electrode 48 and the generated water at the cathode electrode 50 excessively permeate the first porous layer 56 or the second porous layer 62 or are excessively blocked. This is because it is avoided.

  Accordingly, in the fuel cell stack 10 during normal operation, both the end unit cell 12a whose temperature is likely to decrease and the central unit cell 12b whose temperature is unlikely to decrease are both water retentive for maintaining the electrolyte membrane 46 in a wet state. In addition, the drainage for diffusing the reaction gas quickly becomes sufficient. For this reason, proton conduction easily proceeds in the electrolyte membrane 46, and the occurrence of flooding in the anode electrode 48 and the cathode electrode 50 is avoided, and the reaction gas diffuses easily. That is, good proton conductivity can be exhibited in the electrolyte membrane 46, and the diffusibility of the reaction gas can be improved to promote the electrode reaction.

  Thereby, the generated voltage of each of the end unit cell 12a and the central unit cell 12b can be increased. In particular, since the temperature is likely to be lower than that of the central unit cell 12b during normal operation of the fuel cell stack 10, the fuel cell stack 10 also has the power generation performance with respect to the end unit cell 12a whose power generation performance is likely to be reduced. It is possible to improve without lowering. As a result, the terminal voltage of the fuel cell stack 10 increases, in other words, the power generation performance can be improved. This effect is more remarkable when the water permeability, water vapor discharge speed, and penetration resistance of the superposed body of the end unit cell 12a and the central unit cell 12b are within the above numerical ranges.

  In addition, this invention is not specifically limited to above-described embodiment, A various deformation | transformation is possible in the range which does not deviate from the summary.

  For example, in the above embodiment, the electrolyte membrane / electrode structure 34 having the first porous layer 56 and the second porous layer 62 is illustrated, but the first porous layer 56 and the second porous layer 62 are illustrated. There is no need to provide both of them, and only one of them may be provided. In particular, it is preferable to provide the second porous layer 62 on the cathode electrode 50 side where water is generated by an electrode reaction.

  In the above embodiment, the end unit cell 12a is composed of the two unit cells 12 arranged at the extreme ends (endmost parts) on both sides in the stacking direction of the fuel cell stack 10. The invention is not particularly limited to this. The end unit cell is composed of all of several (2 to 5) unit cells 12 respectively disposed at both ends of the fuel cell stack 10 or one or more selected from the unit cells 12. May be. In other words, the end unit cell may be configured without including the two unit cells (end unit cell 12a) disposed at the extreme end.

  As unit cells for the measurement sample, unit cells A1, A2, and B1 to B4 were produced as follows based on the production conditions of the porous layer shown in FIG.

[Unit cell A1]
(1) The gas diffusion layer is a dispersion of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) manufactured by Mitsui-DuPont Fluorochemical Co., Ltd. on carbon paper having a bulk density of 0.31 g / m ² and a thickness of 190 μm. The liquid “FEP 120-JRB Dispersion” (trade name) was impregnated and dried at 120 ° C. for 30 minutes to perform a water repellent treatment. At this time, the carbon paper was impregnated in the dispersion so that the dry weight of FEP with respect to the carbon paper was 2.4% by weight.

  (2) For the porous layer paste, 12 g of vapor phase growth carbon “VGCF” (trade name) manufactured by Showa Denko KK and FEP dispersion (solid content concentration 54%) “FEP120JRB” manufactured by Mitsui DuPont Fluorochemical Co., Ltd. (Trade name) 12 g and ethylene glycol 200 g were prepared by stirring and mixing with a ball mill. That is, the weight ratio (C / F ratio) of the water repellent resin (F) to the electron conductive substance (C) was 1.0.

  (3) Screen printing was performed on the gas diffusion layer prepared in (1) above using the porous layer paste prepared in (2) as an ink so that the thickness of the porous layer was 22.3 μm. . And the porous layer was formed by performing the heat processing for 30 minutes at 380 degreeC, and the superimposed body was obtained.

  (4) The catalyst paste is such that the weight ratio of the platinum catalyst “LSA” (trade name) made by BASF is 0.1 with respect to the ion conductive polymer solution “DE2020CS” (trade name) made by DuPont. Further, it was prepared by stirring and mixing with a ball mill.

(5) After applying the catalyst paste prepared in the above (4) on a PTFE sheet so that the weight of platinum is 0.4 mg / cm ² , a heat treatment is performed at 120 ° C. for 60 minutes, whereby an electrode catalyst is obtained. A sheet for transferring the layer to one side and the other side of the electrolyte membrane was prepared.

  (6) The catalyst paste application side of the sheet prepared in (5) above is thermocompression bonded to the surface of a fluorine-based electrolyte membrane having a thickness of 24 μm and an ion exchange capacity of 1.05 meq / g, and then the PTFE sheet is peeled off did. That is, an electrode catalyst layer was formed on one surface and the other surface of the electrolyte membrane by a decal method.

(7) The electrode catalyst layer formed on the electrolyte membrane prepared in (6) above is heated with the porous layer on the gas diffusion layer prepared in (3) above at 120 ° C. and a surface pressure of 15 kgf / cm ^2. Crimped. By the above method, each of the anode electrode and the cathode electrode was produced in the same manner to obtain an electrolyte membrane / electrode structure.

  (8) The electrolyte membrane / electrode structure produced in (7) was sandwiched between separators to produce unit cell A1.

[Unit cell A2]
Instead of the step (3), the porous layer thickness is 52.2 μm on the gas diffusion layer prepared in (1) above, using the porous layer paste prepared in (2) as an ink. Screen printing was performed. Other than that was carried out similarly to unit cell A1, and obtained unit cell A2.

[Unit cell B1]
Instead of the step (3), the porous layer paste prepared in (2) above is applied onto the gas diffusion layer prepared in (1) so as to have a thickness of 14.3 μm. It applied using. Other than that was carried out similarly to unit cell A1, and obtained unit cell B1.

[Unit cell B2]
Instead of the step (3), the porous layer paste prepared in (2) above is applied to the gas diffusion layer prepared in (1) so as to have a thickness of 31.4 μm. It applied using. Other than that was carried out similarly to unit cell A1, and obtained unit cell B2.

[Unit cell B3]
Instead of the step (3), the porous layer paste prepared in (2) above is applied onto the gas diffusion layer prepared in (1) so as to have a thickness of 40.9 μm. It applied using. Other than that was carried out similarly to unit cell A1, and obtained unit cell B3.

[Unit cell B4]
Instead of the step (3), the porous layer paste prepared in (2) above is applied onto the gas diffusion layer prepared in (1) so as to have a thickness of 48.2 μm. It applied using. Other than that was carried out similarly to unit cell A1, and obtained unit cell B4.

The above unit cell A1, A2, for B1 to B4, water penetration pressure [kPa] and the steam discharge rate of one of the piled body of the anode electrode and the cathode electrode and the ^{[mg / cm 2 · min]} , at 15 kgf / cm ² The penetration resistance [mΩ · cm ² ] of the superposed body when pressurized was determined. The results are shown in FIG. 3 together with the conditions for producing the porous layer.

  The water permeation pressure of the superimposed body was measured using a palm porometer manufactured by PMI (Porous Material, Inc). Specifically, first, the superimposed body is punched into a circular shape having a diameter of 1 inch to produce a measurement sample. On the porous layer of the measurement sample, pure water is dropped to form a water film, and air pressure is gradually applied to the water film by a palm porometer. Then, the water permeation pressure of the superimposed body is calculated by measuring the minimum pressure required for pure water to begin to permeate the measurement sample.

  The water vapor discharge speed of the superposed body was obtained using a measuring device 74 shown in FIG. The measuring device 74 includes an air supply unit 76 that supplies dry air, a sample storage container 80 that stores a measurement sample 78, and a water supply unit 82 that supplies pure water to the sample storage container 80. In the following description, dry air is also referred to as air and pure water is also referred to as water.

  The air supply unit 76 includes a cylinder 84 that stores air, and a supply pipe 86 that extends from the cylinder 84 to the sample storage container 80. The supply pipe 86 is provided with a regulator 88 and a mass flow controller (MFC) 90 for adjusting the mass flow rate of air.

  The sample storage container 80 includes a storage tank 92 and a lid member 94 that closes the upper open end of the storage tank 92, and a water supply hole 96 is formed at the bottom of the storage tank 92 therein. The water supply unit 82 supplies water into the sample storage container 80 through the water supply hole 96.

  The stored water W is stored in the storage tank 92, and the punching metal 98, the nonwoven fabric 100, and the measurement sample 78 are stacked in this order above the stored water W.

  A plurality of through holes 102 are formed in the punching metal 98. A measurement sample 78 is placed on the punching metal 98 through the nonwoven fabric 100. This measurement sample 78 is manufactured by punching the superposed body into a square shape having a side of 4.2 cm.

  The lid member 94 covers the upper end of the opening of the storage tank 92, and the flow path portion 104 is formed on the surface in contact with the measurement sample 78. The flow path portion 104 imitates the fuel gas flow path 40 formed in the anode side separator 36 constituting the fuel cell stack 10 or the oxidant gas flow path 42 formed in the cathode side separator 38. The supply pipe 86 and the discharge pipe 106 are communicated with each other. The lid member 94 is heated by a heater (not shown) or the like, and the temperature is maintained at 70 ° C.

  The water supply unit 82 stores water and is connected to the water supply hole 96 of the storage tank 92 through the water supply pipe 108, the water level sensor 112 that detects the water level in the tank 110, and the detection of the water level sensor 112. Based on the result, a pump 114 for supplying water into the tank 110 from a pure water supply source (not shown) is provided to keep the water level in the tank 110 constant.

  In the measuring device 74 configured as described above, first, the air stored in the cylinder 84 is supplied via the supply pipe 86. The pressure of the air is adjusted by passing through the regulator 88, the flow rate is adjusted to 5 L / min by the MFC 90, and the temperature is adjusted to 70 ° C. by a heater (not shown). It is supplied into the flow path part 104.

  As described above, the air at 70 ° C. is supplied to the flow path portion 104 and the temperature of the lid member 94 is maintained at 70 ° C., so that heat is transmitted to the stored water W in the storage tank 92. As a result, the stored water W evaporates and steam is generated. The generated water vapor rises through the through-hole 102 of the punching metal 98, is diffused by the nonwoven fabric 100, and is then supplied to one surface of the measurement sample 78.

  The water vapor further passes through the measurement sample 78 along the film thickness direction, and is discharged from the other surface of the measurement sample 78 and then reaches the flow path portion 104. The water vapor that has reached the flow path portion 104 is discharged from the discharge pipe 106 to the outside of the sample storage container 80 together with the air supplied from the air supply portion 76.

  At this time, each time the stored water W passes through the pores of the measurement sample 78 as water vapor and is discharged to the outside, the same amount of water lost as water vapor is supplied from the tank 110 to the water supply pipe 108 and the water supply. It is supplied into the storage tank 92 through the hole 96. Corresponding to this supply, the water level in the tank 110 falls according to the speed at which water vapor is discharged from the measurement sample 78.

  When the water level in the tank 110 falls below a predetermined threshold preset in the water level sensor 112, the sequence control functions and the pump 114 is energized. As a result, new water is supplied into the tank 110. The amount of water supplied at this time is an amount corresponding to the amount of water vapor discharged from the measurement sample 78. Therefore, the water vapor discharge speed of the measurement sample 78 is calculated based on the supply amount and the time from the start of the supply of air to the start of the supply of water to the tank 110.

The penetration resistance of the superposed body is measured by the four probe method. Specifically, the superposed body is sandwiched between metal plates from both sides in the stacking direction, and pressurized at 15 kgf / cm ² . In this state, a constant current in the penetration direction (stacking direction) is passed between the metal plates so that a current corresponding to 1.5 A / cm ² flows through the superposed body, and the resistance R is obtained by measuring the voltage. . By multiplying the resistance R by the contact area between the metal plate and the superimposed body, the penetration resistance of the superimposed body is calculated.

  One of the unit cells A1 and A2 produced as described above is selected as an end unit cell, and one of the unit cells B1 to B4 is selected as a central unit cell. Then, the unit cells selected as the end unit cells are stacked on both ends of the eight unit cells selected as the center unit cells, that is, the sum of the two end unit cells and the eight unit cell units. Ten fuel cells were stacked to produce fuel cell stacks of Examples 1 to 5. Further, any one of the unit cells A1, A2, B1 to B4 was selected, and the selected 10 unit cells were stacked to produce fuel cell stacks of Comparative Examples 1 to 5.

  That is, in the fuel cell stacks of Examples 1 to 5, the end unit cell and the central unit cell are composed of different unit cells, and in the fuel cell stacks of Comparative Examples 1 to 5, the end unit cell and the central unit A cell is composed of similar unit cells. Specifically, as shown in FIG. 5, fuel cell stacks of Examples 1 to 5 and Comparative Examples 1 to 5 were obtained by selecting an end unit cell and a center unit cell, respectively.

  About these Examples 1-5 and Comparative Examples 1-5, it is two from the average voltage (average voltage of a fuel cell stack) of a total of ten unit cells laminated | stacked, and the average voltage of eight center part unit cells. Values obtained by subtracting the average voltage of the end unit cells (average voltage difference) were obtained and shown in FIG.

The average voltage and average voltage difference of the fuel cell stack shown in FIG. 5 are values obtained from the measurement results during normal operation of the fuel cell stack at 70 ° C. As other operating conditions, the output current density is 0.5 A / cm ² , the relative humidity (RH) of the fuel gas and the oxidant gas is 100%, the gas utilization is 70% for the fuel gas, and 50% for the oxidant gas. The gas pressure of the fuel gas and the oxidant gas was set to 100 kPaG.

  4 and 5, it can be seen that in Examples 1 to 5, the average voltage of the fuel cell stack is large and the average voltage difference is relatively small compared to Comparative Examples 1 to 5. Here, in Examples 1 to 5, as compared with the central unit cell, the water permeability of the superposed body of the end unit cell is small and the water vapor discharge rate is large, and the penetration resistance (in the stacking direction of the electrolyte membrane / electrode structure) Electric resistance is small. On the other hand, in Comparative Examples 1 to 5, the above-described characteristics of the overlapping unit of the center unit cell and the end unit cell are the same.

  That is, in the fuel cell stack during normal operation, particularly by setting the hydraulic pressure, the water vapor discharge speed, and the penetration resistance of the superposed bodies of the center unit cell and the end unit cell as in the first to fifth embodiments. The power generation performance of the unit cell was improved, and the power generation performance of the entire fuel cell stack could be improved.

  Furthermore, in Examples 1-4, compared with Example 5 and Comparative Examples 1-5, the average voltage of a fuel cell stack is still larger, and an average voltage difference is still smaller. Therefore, the average voltage of the fuel cell stack, particularly the end unit, is set by setting the water permeation pressure, the water vapor discharge rate and the penetration resistance of the superposed bodies of the central unit cell and the end unit cell as in Examples 1-4. It can be seen that the average voltage of the cell can be further increased.

That is, the hydraulic pressure of the superposed body of the end unit cell is 10.0 to 30.0 kPa, the water vapor discharge rate is 18.0 to 20.0 mg / cm ² · min, and the hydraulic pressure of the superposed body of the central unit cell is 30.0 to 120.0 kPa, the water vapor discharge rate is set to 15.0 to 18.0 mg / cm ² · min, and the penetration resistance of the superposed body of the end unit cell is set to 4.0 to 5.0 mΩ · cm ² , By setting the penetration resistance of the superposed body of the central unit cell to 5.0 to 7.0 mΩ · cm ² , the power generation performance of the end unit cell of the fuel cell stack during normal operation can be further improved. As a result, the power generation performance of the entire fuel cell stack could be further improved.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell stack 12 ... Unit cell 12a ... End unit cell 12b ... Center unit cell 14 ... Terminal plate 16 ... Insulating plate 18 ... End plate 20 ... Oxidant gas inlet communication hole 22 ... Cooling medium inlet communication hole 24 ... Fuel gas outlet communication hole 26 ... Fuel gas inlet communication hole 28 ... Cooling medium outlet communication hole 30 ... Oxidant gas outlet communication hole 32 ... Tie rod 34 ... Electrolyte membrane / electrode structure 36 ... Anode side separator 38 ... Cathode side separator 40 ... Fuel gas flow path 42 ... Oxidant gas flow path 44 ... Cooling medium flow path 46 ... Electrolyte membrane 48 ... Anode electrode 50 ... Cathode electrode 52 ... First electrode catalyst layer 54 ... First gas diffusion layer 56 ... First porous layer 58 ... second electrode catalyst layer 60 ... second gas diffusion layer 62 ... second porous layer 64 ... first superposed body 66 ... first insulating sheet 68 ... second superposed body 70 ... 2nd insulating sheet 72 ... Seal member 74 ... Measuring device

Claims (8)

A unit cell having an electrolyte membrane / electrode structure in which an electrolyte membrane made of a solid polymer membrane is sandwiched between an anode electrode and a cathode electrode, and separators disposed on both sides of the electrolyte membrane / electrode structure. A fuel cell stack configured by stacking a plurality of fuel cells,
Each of the anode electrode and the cathode electrode has an electrode catalyst layer facing the electrolyte membrane, and a gas diffusion layer,
At least one of the anode electrode or the cathode electrode further has a porous layer interposed between the electrode catalyst layer and the gas diffusion layer,
Among the plurality of unit cells, the end unit cells arranged at both ends in the stacking direction are transparent in a superposed body in which the porous layer and the gas diffusion layer are overlapped as compared with other unit cells. A fuel cell stack characterized by low water pressure.   2. The fuel cell stack according to claim 1, wherein a hydraulic pressure of the superposed body of the end unit cell is 10.0 to 30.0 kPa, and a hydraulic pressure of the superposed body of the other unit cell is 30.0. A fuel cell stack, which is ˜120.0 kPa. A unit cell having an electrolyte membrane / electrode structure in which an electrolyte membrane made of a solid polymer membrane is sandwiched between an anode electrode and a cathode electrode, and separators disposed on both sides of the electrolyte membrane / electrode structure. A fuel cell stack configured by stacking a plurality of fuel cells,
Each of the anode electrode and the cathode electrode has an electrode catalyst layer facing the electrolyte membrane, and a gas diffusion layer,
At least one of the anode electrode or the cathode electrode further has a porous layer interposed between the electrode catalyst layer and the gas diffusion layer,
Among the plurality of unit cells, the end unit cells arranged at both ends in the stacking direction are superposed water vapors in which the porous layer and the gas diffusion layer are superposed as compared with other unit cells. A fuel cell stack characterized by a high discharge rate. 4. The fuel cell stack according to claim 3, wherein a water vapor discharge rate of the superposed body of the end unit cell is 18.0 to 20.0 mg / cm ² · min, and the superposed body of the other unit cell A fuel cell stack having a water vapor discharge rate of 15.0 to 18.0 mg / cm ² · min. A unit cell having an electrolyte membrane / electrode structure in which an electrolyte membrane made of a solid polymer membrane is sandwiched between an anode electrode and a cathode electrode, and separators disposed on both sides of the electrolyte membrane / electrode structure. A fuel cell stack configured by stacking a plurality of fuel cells,
Each of the anode electrode and the cathode electrode has an electrode catalyst layer facing the electrolyte membrane, and a gas diffusion layer,
At least one of the anode electrode or the cathode electrode further has a porous layer interposed between the electrode catalyst layer and the gas diffusion layer,
Among the plurality of unit cells, the end unit cells arranged at both ends in the stacking direction are transparent in a superposed body in which the porous layer and the gas diffusion layer are overlapped as compared with other unit cells. A fuel cell stack having a low water pressure and a high water vapor discharge rate. 6. The fuel cell stack according to claim 5, wherein a water permeation pressure of the superposed body of the end unit cell is 10.0 to 30.0 kPa, and a water vapor discharge rate is 18.0 to 20.0 mg / cm ² · min. The fuel cell stack, wherein the superposed body of the other unit cell has a water permeation pressure of 30.0 to 120.0 kPa and a water vapor discharge rate of 15.0 to 18.0 mg / cm ² · min.   The fuel cell stack according to any one of claims 1 to 6, wherein the end unit cell has a smaller electric resistance in the stacking direction of the electrolyte membrane / electrode structure than the other unit cell. A fuel cell stack characterized by that. 8. The fuel cell stack according to claim 7, wherein when the superposed body of the end unit cell is pressurized at 15 kgf / cm ² in the stacking direction, the through resistance of the superposed body is 4.0 to 5.0 mΩ · cm ^2. The penetration resistance of the superposed body when the superposed body of the other unit cell is pressurized at 15 kgf / cm ² in the stacking direction is 5.0 to 7.0 mΩ · cm ^2. Fuel cell stack.

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