JP2006120402A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of improving a power generating property. <P>SOLUTION: The fuel cell 10 comprises an electrolyte layer 1, an anode 7 and a cathode 6 arranged on either side of the electrolyte layer 1, and separators 8a, 8b arranged at the outside of the anode 7 and the cathode 6. The anode 7 and the cathode 6 are provided with catalyst layers 2b, 2a, and diffusion layers 3b, 3a. A water repellency of the diffusion layer 3b of the anode is made higher than that of the diffusion layer 3a of the cathode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell, and more particularly to a fuel cell capable of improving power generation performance.

A polymer electrolyte fuel cell (hereinafter referred to as “PEFC (Polymer Electrolyte Fuel Cell)”) can be operated in a low temperature region among various fuel cells and has a high value of 50 to 60%. It shows energy conversion efficiency, has a short start-up time, and has a small and light system, and has attracted attention as an optimal power source for electric vehicles. This PEFC electrolyte uses a cation exchange resin membrane as a cation conductive membrane. The cation conductive membrane of PEFC has proton (hydrogen ion (H ⁺ )) exchange group in the molecule, and shows a specific resistance of 20 Ω · cm or less at room temperature by containing water in a saturated state. It functions as a proton conductive electrolyte. The saturated water content of the electrolyte membrane changes reversibly with temperature. That is, during operation of the PEFC, humidified water added in the form of water vapor in the fuel gas and oxidizing gas to prevent transpiration from the electrolyte membrane, and water generated by an electrochemical reaction on the cathode side By means of this, saturation is always maintained.

  Membrane / electrode assembly (hereinafter referred to as “MEA (Membrane Electrode Assembly)”) is necessary because water needs to be hydrated with protons to move from the anode to the cathode by proton electroosmosis. The proton conductivity of is affected by the amount of water contained. Further, as described above, the gas supplied to each unit cell of the fuel cell is humidified using water vapor, but usually the amount of water vapor contained in these gases is less than the saturated water vapor amount. Therefore, for example, in the vicinity of the gas supply path inlets of the cathode and the anode, moisture is easily taken away by the gas flowing in the supply path, and the moisture content in the MEA is likely to vary. Here, the variation in the moisture content in the MEA also greatly affects the proton conductivity. If there is a region having a low moisture content in the MEA, the proton conductivity in that region is lowered, and the power generation efficiency of the entire fuel cell is lowered. Therefore, in order to improve the power generation performance of PEFC, it is important to keep the MEA moisture content distribution constant.

Several techniques aimed at improving the power generation performance of the fuel cell by means such as suppressing the drying of the electrolyte membrane have been disclosed so far. For example, Patent Document 1 discloses that a region of an anode gas diffusion layer facing the vicinity of the cathode gas inlet along the flow of the cathode gas is a first region, and the other region is a second region. Has disclosed a technology relating to a fuel cell in which the solid polymer membrane is kept uniformly moist throughout the entire region by improving the water permeability of the second region more than the water permeability of the second region. ing. Further, in Patent Document 2, the layer disposed between the catalyst layer and the diffusion layer is configured such that the porosity of the gas inlet side portion is smaller than the gas outlet side portion, thereby preventing the electrolyte membrane from drying. A technique related to a fuel cell obtained is disclosed. Furthermore, in Patent Document 3, the average pore diameter of at least one porous layer that forms the anode gas diffusion layer is made smaller than the average pore diameter of the porous layer that forms the cathode gas diffusion layer. Discloses a technology relating to a fuel cell that can suppress the in-plane distribution of the water content of the part.
JP 2001-236976 A JP 2001-135326 A JP 2001-57218 A

  Here, protons generated at the anode move by electroosmosis from the anode side to the cathode side in the polymer electrolyte membrane in a hydrated state with water. On the other hand, a part of the water generated at the cathode is discharged to the outside of the fuel cell through the gas diffusion layer, and the remaining part is reversely diffused toward the anode due to the concentration gradient. Thus, the moisture content distribution inside the fuel cell is determined by the balance of the opposing water movements as described above. Therefore, it is difficult to keep the moisture content distribution of MEA constant only by the technique disclosed in Patent Document 1 that changes the moisture permeability in the plane of the diffusion layer, and improves the power generation performance of the fuel cell. There was a problem that it was difficult. Further, even with the techniques disclosed in Patent Document 2 and Patent Document 3, it is difficult to keep the moisture content distribution of MEA constant, and there is a problem that it is difficult to improve the power generation performance of the fuel cell.

  Then, this invention makes it a subject to provide the fuel cell which can improve electric power generation performance.

In order to solve the above problems, the present invention takes the following means. That is,
The invention according to claim 1 includes an electrolyte layer, an anode and a cathode provided on both sides of the electrolyte layer, and a separator provided outside the anode and the cathode, and the anode and the cathode are diffused with the catalyst layer. The fuel cell is characterized in that the water repellency of the anode diffusion layer is higher than the water repellency of the cathode diffusion layer.
Here, in the present invention and the invention shown below, the catalyst layer can be, for example, a catalyst layer used in ordinary PEFC, and specific examples thereof include carbon particles supporting a platinum-based catalyst and Examples thereof include a catalyst layer formed by mixing with a proton conductive resin.

According to a second aspect of the present invention, in the fuel cell according to the first aspect, the anode and cathode diffusion layers are a base material and a water repellent layer provided between the base material and the catalyst layers of the anode and the cathode. The water repellency of the water repellent layer of the anode is higher than the water repellency of the water repellent layer of the cathode.
Here, in the present invention and the invention shown below, the base material can be formed if it is formed of a substance that can effectively diffuse reaction gas or the like used in, for example, ordinary PEFC. The substance is not particularly limited, and examples of the substance include a porous body formed of carbon paper or carbon cloth. Furthermore, in the present invention and the invention shown below, the water-repellent layer can be, for example, a water-repellent layer used in ordinary PEFC. Specific examples thereof include carbon particles and polytetrafluoroethylene resin ( And a water repellent layer formed by mixing with a fluororesin such as PTFE).

  According to a third aspect of the present invention, in the fuel cell of the second aspect, the anode base material and the cathode base material are formed of the same material.

According to a fourth aspect of the present invention, in the fuel cell according to the second or third aspect, the water repellent layer of the anode and the cathode includes a water repellent resin and a conductive substance, and the mass A of the water repellent resin and the conductivity When the ratio A / B to the mass B of the substance is X, the X value of the water repellent layer of the anode is larger than the X value of the water repellent layer of the cathode.
Here, in the present invention, the water-repellent resin is not particularly limited as long as it has water repellency and can be used in ordinary PEFC. Specific examples thereof include fluorine such as PTFE. Based resins and the like. On the other hand, in the present invention, the conductive substance is not particularly limited as long as it is a substance that can impart conductivity to the water-repellent resin, and specific examples thereof include carbon particles and metal powder. it can. Further, the form of the conductive substance is not particularly limited, and specific examples include fibrous, particulate, and powdery forms.

  According to the first aspect of the present invention, since the water repellency of the anode diffusion layer is higher than the water repellency of the cathode diffusion layer, the water generated in the cathode catalyst layer easily moves to the anode side. Become. If the water generated in the catalyst layer of the cathode moves to the anode side, the water content of the anode can be kept high, and the water content of the MEA can be kept high. It is also possible to promote despreading. If it becomes possible to promote the reverse diffusion, the moisture content distribution of the MEA can be kept constant, and the high moisture content state of the MEA can be maintained for a long period of time. Therefore, according to the first aspect of the invention, the moisture content distribution of the MEA can be kept constant, and the robustness against the relative humidity can be improved, so that the fuel that can improve the power generation performance A battery can be provided.

  According to the second aspect of the present invention, the water repellency of the water repellent layer of the anode is made higher than the water repellency of the water repellent layer of the cathode, so that the water generated in the catalyst layer of the cathode moves to the anode side. This makes it easier for the water to move to the interface between the anode catalyst layer and the water repellent layer. If the water generated in the cathode catalyst layer moves to the anode catalyst layer, the water content distribution of the MEA can be kept constant. Therefore, by adopting such a configuration, it is possible to improve the robustness with respect to the relative humidity, and thus it is possible to provide a fuel cell that can improve the power generation performance.

  According to the third aspect of the present invention, the anode base material and the cathode base material are formed of the same material. Therefore, with such a configuration, it becomes possible to provide a fuel cell capable of improving the power generation performance at a low cost.

  According to the fourth aspect of the present invention, the water repellency of the water repellent layer of the anode can be made higher than the water repellency of the water repellent layer of the cathode. Therefore, with this configuration, it is possible to improve the robustness against relative humidity, and thus it is possible to easily provide a fuel cell that can improve the power generation performance. In addition, this configuration makes it easy to manufacture the anode and cathode water-repellent layers using the same manufacturing apparatus.

In general, while there is water movement from the anode and generation of water due to electrode reaction at the cathode, water is taken away by electroosmosis and can be supplied only by back diffusion. For this reason, the cathode distribution is dominant in the water distribution in the MEA.
For this reason, in order to keep the MEA moist, it is important to obtain reverse diffusion effectively. In order to promote reverse diffusion, it is necessary to keep the water diffusion coefficient of the MEA itself high, and for this purpose, the water content of the MEA itself is very important. That is, if the moisture content can be kept high, the diffusion coefficient can be kept high. If the water content of the anode, which is inferior in the water distribution, is reduced, water is taken away by electroosmosis, so that the water content of the anode is further reduced, and the water diffusion coefficient is reduced due to the reduction of the water content. As a result, it becomes impossible to receive the supply of water due to reverse diffusion, and the water content of the anode further falls, resulting in a vicious circle.
As a result of the study, the inventor has focused on the fact that the reverse diffusion can be promoted if the moisture content of the anode can be kept high, and has found that the result greatly contributes to the enhancement of the performance of the fuel cell. And in order to give such a moisture content distribution, it discovered that the contribution of the carbon / fluorine ratio of the water-repellent layer in a diffused layer was high. According to the configuration of the present invention, both flooding and dry-up can be eliminated, and a high-performance fuel cell can be obtained in a wide humidified region.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the case where the present invention is applied to PEFC will be described.

  FIG. 1 is a cross-sectional view schematically showing an exemplary embodiment of a unit cell that is to constitute the fuel cell of the present invention. The unit cell 100 according to the first embodiment includes an electrolyte membrane 1, a cathode 6 and an anode 7 provided on both sides of the electrolyte membrane 1, and separators 8a and 8b provided outside the cathode 6 and the anode 7. And. The cathode 6 includes a catalyst layer 2a and a diffusion layer 3a, and the diffusion layer 3a includes a water repellent layer 4a and a base material 5a. On the other hand, the anode 7 includes a catalyst layer 2b and a diffusion layer 3b, and the diffusion layer 3b includes a water repellent layer 4b and a base material 5b. The MEA 10 includes an electrolyte membrane 1 and catalyst layers 2a and 2b. In the separators 8a and 8b provided outside the cathode 6 and the anode 7, reaction gas supply passages 9a, 9a,..., 9b, 9b,. On the side, cooling water passages 9c, 9c,... Are formed. In FIG. 1, the horizontal direction in the figure is the stacking direction of the diffusion layers 3a and 3b.

  In the unit cell 100 shown in FIG. 1, the fuel gas (hereinafter referred to as “hydrogen”) supplied to the diffusion layer 3b from the reaction gas supply paths 9b, 9b,. The material 5b and the water repellent layer 4b are supplied to the catalyst layer 2b on the anode side, and hydrogen is decomposed into hydrogen ions and electrons on the catalyst of the catalyst layer 2b. The hydrogen ions generated in the catalyst layer 2b pass through the electrolyte membrane 1 and reach the cathode catalyst layer 2a. On the other hand, the oxidizing gas (hereinafter sometimes referred to as “oxygen”) supplied from the cathode-side reaction gas supply passages 9a, 9a,. Water (water vapor) is generated by the reaction of hydrogen ions, oxygen and electrons on the catalyst of the catalyst layer 2a through the water layer 4a to the catalyst layer 2a on the cathode side. Here, the unit cell 100 is supplied with humidified hydrogen and oxygen (hereinafter, hydrogen and oxygen may be collectively referred to as “supply gas”), but during normal operation of the fuel cell. In many cases, the water vapor contained in these supply gases is less than the saturated water vapor amount. Therefore, the moisture in the electrolyte membrane 1 is easily taken away by the supply gas supplied into the cathode 6 and the anode 7, and the moisture content in the MEA 10 is likely to vary. Further, it is known that when the inside of the unit cell 100 is in a low humidity environment, the anode 7 side is particularly easy to dry. Therefore, in the present embodiment, the water repellency of the anode-side water-repellent layer 4b is made higher than that of the cathode-side water-repellent layer 4a, and the water-repellent property of the anode-side diffusion layer 3b is made higher than that of the cathode-side diffusion layer 3a. By making it higher than the water repellency, the fuel cell can move the water generated in the catalyst layer 2a on the cathode side to the anode 7 side. With such a configuration, it is possible to suppress drying on the anode 7 side by the generated water in the catalyst layer 2a, and it is possible to keep the moisture content distribution in the MEA 10 constant. Therefore, according to the first embodiment, the moisture content distribution inside the cell 100 can be corrected, and even if the inside of the cell 100 is in a low relative humidity region, the power generation efficiency is reduced due to drying of the electrolyte membrane 1 or the like. Since it becomes possible to suppress, it becomes possible to improve the robustness with respect to relative humidity. That is, according to the first embodiment, it is possible to provide a fuel cell capable of improving the power generation performance.

Hereinafter, the materials constituting each layer and the manufacturing methods thereof will be described in detail.
1. Diffusion layer 1.1. Water-repellent layer In the present embodiment, the water-repellent layers 4 a and 4 b can be formed of a material that has water repellency, good conductivity and air permeability, and can withstand the environment in the fuel cell. Specific examples of such a substance include a mixture of a water repellent resin and a conductive substance. Specific examples of the water-repellent resin that can form the water-repellent layers 4a and 4b according to the first embodiment include polytetrafluoroethylene resin (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP). Fluorine resin can be mentioned. Specific examples of the conductive material that can form the water-repellent layers 4b and 4a according to the present embodiment include carbon black, graphite, metal fibers, and metal fine particles.

When the water-repellent layers 4a and 4b according to the present embodiment include the water-repellent resin and the conductive material, the masses of the water-repellent resin and the conductive material included in the water-repellent layer 4a are Aa and Ba, and the water-repellent layer. When the mass of the water repellent resin and the conductive material contained in 4b is Ab and Bb, and Ab / Bb = Xb, Aa / Ba = Xa,
Xb> Xa (1)
It is preferable to satisfy. If the water repellent layers 4a and 4b are configured so as to satisfy the above formula 1, the water repellency of the water repellent layer 4b on the anode side can be made higher than the water repellency of the water repellent layer 4a on the cathode side. It becomes possible to keep the moisture content distribution of MEA10 constant. Therefore, by adopting a configuration that satisfies the above formula 1, it is possible to provide a high-performance fuel cell with improved robustness against relative humidity. When the water repellent layers 4a and 4b include a water repellent resin and a conductive material, if the mass of the water repellent resin with respect to the conductive material is excessively increased, the current collecting ability of the water repellent layers 4a and 4b may be reduced. There is. Therefore, the mass of the water-repellent resin contained in the water-repellent layers 4a and 4b is set to an amount that does not decrease the power generation efficiency of the fuel cell while paying attention to the current collecting ability of the water-repellent layers 4a and 4b.

1.2. Base Material In the present embodiment, the base materials 5a and 5b can be formed of a material that has good conductivity and air permeability and can withstand the environment in the fuel cell. Specific examples of such substances include electrically conductive porous woven fabrics such as carbon paper, electrically conductive porous nonwoven fabrics such as carbon cloth, foamed metal, sintered metal, or metal produced by plating, foaming methods, etc. Felt etc. can be mentioned. Moreover, although the base materials 5a and 5b concerning 1st Embodiment may each be formed with a separate substance, it is preferable to form with the same substance. With such a configuration, it becomes possible to reduce the manufacturing cost of the fuel cell. In addition, it is preferable that the porosity is 50% or more from the viewpoint that the base materials 5a and 5b formed of such a substance are the base materials 5a and 5b having good air permeability. More preferably, it is 70% or more.

  In the above description, for convenience, a fuel cell having a base material and a water repellent layer is described. However, the present invention can also be applied to a fuel cell having no water repellent layer. When the present invention is applied to the fuel cell according to the embodiment, a method of causing the material constituting the anode-side diffusion layer to contain more water-repellent resin than the material constituting the cathode-side diffusion layer. Thus, the water repellency of the anode-side diffusion layer may be made higher than that of the cathode-side diffusion layer. With such a configuration, it is possible to improve the robustness with respect to the relative humidity, and it is possible to obtain a fuel cell that can improve the power generation performance.

1.3. Method for Producing Diffusion Layer In the fuel cell according to the present embodiment, the method for producing the diffusion layer 3a including the water repellent layer 4a and the base material 5a, and the diffusion layer 3b including the water repellent layer 4b and the base material 5b are particularly It is not limited, The production method of the diffusion layer concerning normal PEFC, etc. can be used conveniently. As a specific example of the manufacturing method of the diffusion layers 3a and 3b according to the first embodiment, the substrate 5a and 5b is coated with the water repellent layers 4a and 4b on the surface of the surface that should face the catalyst layers 2a and 2b, and then dried. The method of making the diffusion layers 3a and 3b according to the present invention by fixing the water-repellent layers 4a and 4b on the surfaces of the base materials 5a and 5b can be exemplified.

2. Other Constituent Members The fuel cell according to the present invention has the electrolyte membrane 1 as another constituent member as long as the water repellency of the anode side diffusion layer is higher than the water repellency of the cathode side diffusion layer. The aspects of the catalyst layers 2a and 2b and the separators 8a and 8b are not particularly limited. Therefore, the constituent materials and production methods of these members will be described below.

2.1. Electrolyte Membrane The constituent material of the electrolyte membrane 1 is not particularly limited as long as it has a polymer that conducts protons (hereinafter sometimes referred to as “proton conducting polymer”). It is preferable to have a polymer having at least one of a sulfonic acid group, a phosphonic acid group, and a phosphoric acid group with a polymer as a skeleton. In addition, a polymer having a hydrocarbon skeleton such as polyolefin may be included. Specific examples of the fluorine-containing polymer that can constitute the electrolyte membrane 1 include 2 containing at least one second group monomer selected from the following first group monomers and the following second group monomers: Examples thereof include a copolymer of seeds or three or more monomers, or a copolymer of at least one or more second group monomers. Examples of the first group monomer include tetrafluoroethylene, trifluoromonochloroethylene, trifluoroethylene, vinylidene fluoride, 1,1-difluoro-2,2-dichloroethylene, 1,1-difluoro-2-chloroethylene, hexafluoro Mention may be made of propylene, 1,1,1,3,3-pentafluoropropylene, octafluoroisobutylene, ethylene, vinyl chloride, and alkyl vinyl esters. In addition, as the second group monomer, the following general formula 2
_{Y- (CF 2) a - (} CFRf) b - (CFR'f) c -O-
- _{[CF (CF 2 X) -CF 2} -O ] _{n-CF = CF 2 (2} )
The monomer represented by these can be mentioned. Here, in the above equation 2,
Y _{is, -SO 2 F, -SO 3 NH} , -COOH, -CN, -COF, -COOR (R is an alkyl group having 1 to 10 carbon _{atoms), - PO 3 H 2,} -PO 3 H,
a and b are integers of 0 to 6, c is 0 or 1, and a + b + c is not 0. Also,
n is an integer of 0 to 6, and X is Cl, Br, F, or a mixture thereof when n> 1. further,
Rf and R′f are independently selected from the group consisting of F, Cl, a fluoroalkyl group having about 1-10 carbon atoms, and a fluorochloroalkyl group having 1-10 carbon atoms.
The electrolyte membrane 1 preferably has a perfluorocarbon polymer having a sulfonic acid group.

  In the electrolyte membrane 1, the polymer may be constituted by bonding two or more molecules of monomers, but the molecular weight is preferably 5000 or more from the viewpoint of durability. Furthermore, when such a polymer and a low molecular weight compound are mixed, the electrolyte membrane 1 having an EW adjusted as described later can be obtained.

  The thickness of the electrolyte membrane 1 is preferably 10 μm or more from the viewpoint of securing sufficient mechanical strength, and preferably 100 μm or less from the viewpoint of suppressing electrical resistance. In addition, the EW of the electrolyte membrane 1 is preferably 500 or more from the viewpoint of ensuring sufficient mechanical strength and suppressing flooding. More preferably, it is 600 or more. On the other hand, from the viewpoint of obtaining an electrolyte membrane 1 that ensures good proton conductivity and can be put to practical use, the EW is preferably 1500 or less. More preferably, it is 1300 or less. Here, EW represents the equivalent weight of the exchange group having proton conductivity. This equivalent weight is the dry weight of the proton conducting polymer per equivalent of ion exchange groups, and is expressed in units of “g / equivalent”.

2.2. Catalyst Layer The catalyst layers 2a and 2b include a proton conductive polymer, a catalyst material, and a conductive substance. In the present invention, the catalyst material is not particularly limited as long as it has a catalytic action on the oxidation reaction of hydrogen and the reduction reaction of oxygen at the anode and the cathode. Specific examples of the catalyst material according to the present invention include metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, or These alloys can be mentioned. In addition, the shape of the catalyst material according to the present invention is not particularly limited, and specific examples of the shape include particles. In the present invention, the particle size of the particulate catalyst is preferably 10 mm or more from the viewpoint of making it possible to produce the catalyst. More preferably, it is 15 mm or more. On the other hand, from the viewpoint of securing good catalyst efficiency and obtaining a high battery voltage, the particle size is preferably 300 mm or less. More preferably, it is 150 mm or less. Further, the amount of the catalyst supported on the catalyst layers 2a and 2b is preferably 0.01 mg / cm ² or more from the viewpoint of making the amount capable of effectively exhibiting the performance of the catalyst. More preferably, it is 0.1 mg / cm ² or more. On the other hand, from the viewpoint of suppressing manufacturing costs and obtaining sufficient cost effectiveness, the supported amount of the catalyst is preferably 5 mg / cm ² or less. More preferably, it is 1 mg / cm ² or less. In the present invention, the presence of the catalyst material is not particularly limited as long as the catalyst material is included in an aspect that can effectively contribute to the oxidation reaction and the reduction reaction. Specific examples of the presence mode of the catalyst material include a mode where the catalyst material is supported on a conductive material.

  In the present invention, the conductive substance contained in the catalyst layers 2a and 2b is not particularly limited as long as it is an electron conductive substance that can withstand the environment in the fuel cell. Specific examples of the conductive material include carbon black such as furnace black, channel black, acetylene black, and ketjen black, activated carbon, graphite, and various metals. Furthermore, in the present invention, the proton conductive polymer contained in the catalyst layers 2 a and 2 b can be the same as the proton conductive polymer contained in the electrolyte membrane 1.

  On the other hand, the method for forming the catalyst layers 2a and 2b containing these substances is not particularly limited. Specific examples of the molding method include a method in which a proton conductive polymer, a catalyst material, and a conductive material are mixed and molded, or a material in which materials other than the proton conductive polymer are mixed and molded in advance. The method of shape | molding a catalyst layer by impregnating a polymer can be mentioned. Here, among proton conductive polymers, proton conductive polymers such as perfluorosulfonic acid have a function as a binder in the polymer itself. Therefore, when such a proton conductive polymer is used, a catalyst layer in which a stable matrix is formed together with the catalyst material and the conductive material can be obtained. In addition, when a catalyst layer having further water repellency is used, a catalyst layer containing a fluorine resin or the like can be used. Such a fluororesin preferably has a melting point of 400 ° C. or lower, and specific examples of the resin include PTFE and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA).

The catalyst layers 2a and 2b according to the present invention can be produced by various generally known methods (a spraying method, a transfer method, a screen printing method, a rolling method, etc.). A specific example of the manufacturing method is described below.
A catalyst dispersion containing a proton conductive polymer, a catalyst material, a conductive substance, and a water-repellent polymer, if necessary, dissolved in a solvent mainly composed of a lower alcohol such as ethanol is sufficiently stirred, and PTFE A catalyst layer is formed by applying and drying the catalyst dispersion on an area of a certain shape on such a smooth sheet (transfer method).
In the catalyst layer thus produced, the EW of the proton conductive polymer may be further inclined between the anode and the cathode, or may be inclined in the same plane. In addition, it is preferable that EW of the proton conductive polymer contained in the catalyst layers 2a and 2b according to the present invention is 500 or more and 1500 or less similarly to the EW of the electrolyte membrane. More preferable EW is 600 or more and 1300 or less.

  The mass of the proton conductive polymer dispersed in the catalyst layer is preferably 0.1 or more in terms of a mass ratio with the catalyst material contained in the catalyst layer from the viewpoint of securing a sufficient catalyst utilization rate. On the other hand, from the viewpoint of effectively diffusing the reaction gas, the mass is preferably 10 or less by mass ratio with the catalyst material.

2.3. Separator The separators 8a and 8b according to the present invention can be formed of a material that can be suitably used in ordinary PEFC. Specific examples of the substance include metals typified by titanium alloys and stainless steel, carbon, conductive resins, and the like. For convenience, in the description of the fuel cell according to the first embodiment, the description has been given of the form in which the reaction gas supply path is formed in the separators 8a and 8b. However, in the present invention, the form applicable to a normal PEFC is described. If it is a separator, it can be used conveniently. FIG. 2 schematically shows another embodiment to which the present invention can be applied. 2, parts having the same configuration as in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. In FIG. 2, the horizontal direction in the figure is the stacking direction of the diffusion layers.
FIG. 2 is a cross-sectional view schematically showing an example of a unit cell that is to constitute the fuel cell of the present invention. The unit cell 200 of the present invention according to the second embodiment is provided on the electrolyte membrane 1, the cathode 6 ′ and the anode 7 ′ provided on both sides of the electrolyte membrane 1, and outside the cathode 6 ′ and the anode 7 ′. Flat type separators 8c and 8d are provided. In the cell 200 according to the present embodiment, the separators 8c and 8d are formed with cooling water passages 9c, 9c,..., But the reaction gas supply passage is not formed, and is formed of a porous body such as sintered metal. The reaction gas is supplied to the diffusion layers 3c and 3d. The diffusion layer 3c according to the present embodiment includes the water repellent layer 4c and the base material 5c, while the diffusion layer 3d includes the water repellent layer 4d and the base material 5d, and the cathode 6 ′ in the cell 20 is the catalyst. A layer 2a and a diffusion layer 3c are provided, and the anode 7 'is provided with a catalyst layer 2b and a diffusion layer 3d. Even in such a unit cell 200, the water content distribution in the MEA 10 can be kept constant by making the water repellency of the anode side diffusion layer 3d higher than the water repellency of the cathode side diffusion layer 3c. become.

3. Manufacturing Method of Fuel Cell The fuel cell according to the present invention can be manufactured by a general manufacturing method of PEFC. A specific example of the production method is schematically described below.
The catalyst layer surface on the sheet on which the catalyst layer is formed is superimposed on both surfaces of the electrolyte membrane 1 with the membrane 1 side, and the catalyst layer is bonded to the electrolyte membrane 1 under pressure and heating, thereby forming the MEA 10. . Here, the pressure and temperature at the time of the joining can be appropriately selected from the conditions under which the electrolyte membrane 1 and the catalyst layers 2a and 2b are given sufficient adhesion to each other. In the case where a perfluorosulfonic acid polymer is used as the electrolyte membrane 1, the temperature is not particularly limited as long as it is equal to or higher than the glass transition temperature. It is preferable that it is 200 degreeC.
Then, the unit cell 100 is obtained by disposing the diffusion layer 3a and the diffusion layer 3b produced by the above method on both sides of the MEA 10 thus produced, and further arranging the separators 8a and 8b on the outside thereof. be able to. Note that, from the viewpoint of reducing the contact resistance in the unit cell 100, normally, in the fuel cell including the unit cell 100, the fastening pressure is applied in the direction from the both sides (end plate side of both ends) toward the inside.

1. Production of test cell 1.1. Production of Example Cell To 40% by mass of platinum catalyst-supporting carbon, a 5% by mass solution of proton type perfluorosulfonic acid polymer resin was added so that the mass ratio of the platinum catalyst to the polymer was 2: 1. The ink was prepared by uniformly dispersing the ink. This ink was applied onto a polytetrafluoroethylene sheet by the doctor blade method, and then dried and fixed at 100 ° C. in an N ₂ atmosphere to obtain a cathode catalyst sheet having a platinum loading of 0.2 mg / cm ² . An anode catalyst sheet was prepared in the same procedure.

  These cathode catalyst sheet and anode catalyst sheet face each other, and a perfluorosulfonic acid membrane having an EW (equivalent weight (g / equivalent) of exchange group having proton conductivity) of 1100 and a thickness of 50 μm is sandwiched therebetween, 150 After hot pressing at ° C. and a pressure of 4.9 MPa, MEA was produced by peeling off the polytetrafluoroethylene sheets on both sides.

  On the other hand, these were added so that the mass ratio of carbon black and PTFE was 4: 6, and the water-repellent ink was adjusted by uniformly dispersing them. This ink was applied on a diffusion layer substrate made of a carbon material by screen printing, and dried to prepare an anode-side diffusion layer having a water-repellent layer. On the other hand, for the diffusion layer on the cathode side provided with the water repellent layer, a water repellent ink adjusted so that the mass ratio of carbon black and PTFE is 8: 2 is used, and the ink is screen-printed. It produced by apply | coating on the diffusion layer base material which consists of carbon materials, and making it dry. Then, the MEA and the diffusion layer produced in this way were incorporated into a fuel cell, and an example cell was produced.

1.2. Preparation of Cell for Comparative Example Using a water repellent ink prepared by adding and uniformly dispersing carbon black and PTFE in a mass ratio of 5: 5, the anode side provided with a water repellent layer was used. A cell according to Comparative Example 1 was produced using the same procedure as the above example cell except that the diffusion layer and the cathode side diffusion layer were produced.
On the other hand, a diffusion layer on the anode side provided with a water repellent layer using a water repellent ink prepared by adding and uniformly dispersing carbon black and PTFE so as to have a mass ratio of 8: 2. A cell according to Comparative Example 2 was produced using the same procedure as the above example cell except that the diffusion layer on the cathode side was produced.

2. Test conditions Hydrogen was used as the fuel gas and air gas was used as the oxidizing gas, and single cell evaluation was performed under the conditions of 2026 hPa and a cell temperature of 80 ° C. The electrode area of the cell concerning an Example and a comparative example is 13 cm < ² >, The gas which humidified at 50-80 degreeC was used for both electrodes. The hydrogen gas flow rate was 1.0 L / min, and the air gas flow rate was 2.0 L / min.

3. Result The result of an Example, the comparative example 1, and the comparative example 2 is shown according to FIG. In FIG. 3, the solid line shows the result of the example, the two-dot chain line shows the result of Comparative Example 1, and the one-dot chain line shows the result of Comparative Example 2. The horizontal axis in FIG. 3 is the temperature at which the gas of both electrodes is humidified (bipolar humidification temperature), and the vertical axis is the limiting current density (A / cm ² ) in each cell of Example, Comparative Example 1, and Comparative Example 2. It is.

  From FIG. 3, the cell according to Comparative Example 1 was excellent in power generation performance in the low humidification region of 50 ° C., but the power generation performance was reduced in the high humidification region of 80 ° C. The decrease in power generation performance in the highly humidified region is considered to be caused by flooding. Moreover, although the cell concerning the comparative example 2 was excellent in the power generation performance in a 80 degreeC high humidification area | region, the power generation performance fell in the 50 degreeC low humidification area | region. The decrease in power generation performance in the low humidification region is considered to be caused by dry-up in the cell. On the other hand, from FIG. 3, the cell according to the example did not lose robustness to the operation in a wide humidified region of 50 to 80 ° C., and was able to generate power stably and showed an excellent limit current density value. . This is because water generated in the cathode catalyst layer moves to the anode side in the high humidification region, and flooding is suppressed by correcting the moisture content distribution, while in the low humidification region, the cathode catalyst layer This is thought to be because the water generated in this way moved to the anode side and the moisture content distribution was corrected to suppress dry-up in the cell. Therefore, according to the present invention, it was confirmed that a fuel cell capable of stably generating power under a wide range of operating conditions can be provided.

It is sectional drawing which shows schematically the unit cell which should comprise the fuel cell of this invention concerning 1st Embodiment. It is sectional drawing which shows roughly the unit cell which should comprise the fuel cell of this invention concerning 2nd Embodiment. It is a figure which shows the relationship between bipolar humidification temperature and a limiting current density.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolyte membrane 2a, 2b Catalyst layer 3a, 3b, 3c, 3d Diffusion layer 4a, 4b, 4c, 4d Water-repellent layer 5a, 5b, 5c, 5d Base material (diffusion layer base material)
6, 6 'Cathode 7, 7' Anode 8a, 8b, 8c, 8d Separator 10 MEA
100, 200 unit cell (fuel cell)

Claims (4)

An electrolyte layer, an anode and a cathode provided on both sides of the electrolyte layer, and a separator provided on the outside of the anode and the cathode,
The anode and the cathode include a catalyst layer and a diffusion layer,
The fuel cell according to claim 1, wherein a water repellency of the anode diffusion layer is higher than a water repellency of the cathode diffusion layer. The anode and cathode diffusion layers comprise a base material, and a water repellent layer provided between the base material and the anode and cathode catalyst layers,
2. The fuel cell according to claim 1, wherein the water repellency of the water repellent layer of the anode is higher than the water repellency of the water repellent layer of the cathode. 3. The fuel cell according to claim 2, wherein the anode base material and the cathode base material are formed of the same material. The water repellent layer of the anode and the cathode contains a water repellent resin and a conductive substance,
When the ratio A / B between the mass A of the water repellent resin and the mass B of the conductive material is X,
4. The fuel cell according to claim 2, wherein the X value of the water repellent layer of the anode is larger than the X value of the water repellent layer of the cathode.

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