JP4486540B2 - Method for producing membrane-catalyst layer assembly and method for producing membrane-electrode assembly - Google Patents

Description

  The present invention relates to a method for producing a membrane-catalyst layer assembly and a method for producing a membrane-electrode assembly using the same.

  In a conventional polymer electrolyte fuel cell, a membrane-electrode assembly (MEA) (hereinafter abbreviated as MEA) is formed, for example, in a state of adhering to both main surfaces of the polymer electrolyte membrane. The gas diffusion layer is formed on the outer surface of the catalyst layer. In addition, a structure in which catalyst layers are formed on both main surfaces of the polymer electrolyte membrane is generally called a membrane-catalyst layer assembly (for example, a structure excluding the gas diffusion layer in the MEA). The membrane-catalyst layer assembly is generally produced by spraying, applying, filtering and transferring the catalyst layer forming ink onto the surface of the polymer electrolyte membrane (for example, paragraph [0046] in Patent Document 5). Thru [0050]).

  Further, in the formation of this catalyst layer, a polymer electrolyte fuel cell having a multilayer structure of the catalyst layer has been proposed in order to improve the performance of the polymer electrolyte fuel cell (for example, Patent Documents 1 to 4). 4). In this case, as a method of forming a catalyst layer having a multilayer structure, a method of applying the catalyst layer forming ink a plurality of times is disclosed. Furthermore, it is disclosed that the thickness of each catalyst layer should be adjusted based on the function of each catalyst layer (see, for example, paragraphs 2 to [0052] of Patent Document 2).

On the other hand, during the operation of the polymer electrolyte fuel cell, the reaction gas diffuses into the anode side and the cathode side inside the catalyst layer, and water is generated by an electrochemical reaction. If the generated water inhibits the diffusion of the reaction gas into the catalyst layer, the diffusion of the reaction gas to the entire catalyst layer is inhibited, and the output of the polymer electrolyte fuel cell decreases or becomes unstable. It is known that a phenomenon, a so-called flooding phenomenon occurs. For this reason, the catalyst layer which is excellent in the diffusion of the reaction gas and the discharge of the generated water is required, and Patent Document 6 attempts to obtain the effect of improving the drainage of the catalyst layer when the catalyst layer is formed.
JP 2001-338654 A Japanese Patent Laid-Open No. 2002-8679 JP 2002-8678 A JP 2002-15743 A JP 2002-110202 A JP-A-9-199138

  However, the method of forming a catalyst layer on a polymer electrolyte membrane, that is, the method of producing a membrane-catalyst layer assembly, is considered to be a coating method from the viewpoint of simplicity of operation. There has not been a sufficient study from the viewpoint of improving the required manufacturing time and yield (for example, refer to paragraph [0048] of Patent Document 5). In other words, the manufacturing method of the membrane-catalyst layer assembly does not sufficiently take into account the time required for manufacturing, damage to the polymer electrolyte membrane accompanying the manufacturing method, and defective formation of the catalyst layer. There was room.

  Moreover, in the proposal of patent document 6, since the process of sublimating a pore making agent is required, the required time concerning manufacture of a membrane-electrode assembly will be extended by the said process. Further, in the case of the proposal of Patent Document 6, there is a possibility that the catalyst is poisoned in the precipitation and sublimation processes, and there is room for improvement.

  Therefore, the present invention has been made to solve the above-described problems, and can provide a catalyst layer that can shorten the time required for production and is excellent in diffusibility of reaction gas and discharge of generated water. An object of the present invention is to provide a method for producing a membrane-catalyst layer assembly that can be formed, and a method for producing a membrane-electrode assembly using the same.

  As a result of intensive studies to achieve the above object, the present inventors have made a method for forming a catalyst layer by spraying a catalyst layer forming ink on the main surface of a polymer electrolyte membrane (hereinafter referred to as a spray method). Compared with other methods such as a method of forming a catalyst layer by transferring a pre-formed catalyst layer onto the main surface of the polymer electrolyte membrane (hereinafter referred to as a transfer method), a doctor blade method, etc. It has been found that the output of the electrolyte fuel cell is increased, that is, the performance of the polymer electrolyte fuel cell is improved.

  Although the mechanism by which such a result is obtained has not been clearly clarified, the present inventors presume as follows. In other words, the present inventors have found that the catalyst layer formed by the spraying method is more porous than the catalyst layer formed by the doctor blade method and the transfer method, and the diffusibility of the reaction gas and the discharge of generated water. It is presumed that this improves the performance of the polymer electrolyte fuel cell, thereby improving the performance. That is, according to the spray method, the catalyst layer forming ink is applied and laminated in the form of particles. Since the particles have a large specific surface area, the ink particles are quickly dried. Therefore, the catalyst layer is formed by fixing and laminating so that the particles of the catalyst layer forming ink are deposited. On the other hand, since a pressing force is applied in the transfer method, the pores of the catalyst layer are compressed and the porosity of the catalyst layer is impaired. Further, since the doctor blade method also applies the catalyst layer forming ink, the holes formed in the catalyst layer forming ink are smaller than the spray method. For this reason, the catalyst layer formed by the spray method is more porous than the catalyst layer formed by the doctor blade method and the transfer method. Therefore, the diffusibility of the reaction gas and the generated moisture of the polymer electrolyte fuel cell It is considered that the performance of the polymer electrolyte fuel cell is improved.

  On the other hand, in the spray method, the amount of catalyst layer formation per hour is small, and it takes a considerable time to stack the catalyst-forming ink to a predetermined thickness. On the other hand, the transfer method is a step of placing a catalyst layer on a polymer electrolyte membrane and hot pressing, for example, so that the polymer electrolyte can be obtained in a shorter time than other methods such as a spray method and a doctor blade method. A catalyst layer can be formed on the membrane. Therefore, it is advantageous for shortening the manufacturing time.

Based on these examination results, in order to solve the above-described problems, the method for producing a membrane-catalyst layer assembly of the present invention includes a first catalyst layer formed by transfer on at least one main surface of a polymer electrolyte membrane. forming, and forming a second catalyst layer by spraying a catalyst layer formed ink on the first catalyst layer, and have a thickness of the first catalyst layer, The thickness of the second catalyst layer is not less than one quarter and not more than seven quarters (Claim 1).

  By adopting such a configuration (configuration of the manufacturing method), the time required for manufacturing can be shortened by the step of forming the first catalyst layer by transfer, and the catalyst is formed on the first catalyst layer. The step of spraying the layer forming ink to form the second catalyst layer can enhance the diffusibility of the reaction gas and the discharge of the generated water. That is, the method for producing a membrane-catalyst layer assembly of the present invention can sufficiently reduce the disadvantages of conventional membrane-catalyst layer assembly production methods such as a transfer method, a spray method, and a doctor blade method. This is advantageous for mass production of membrane-catalyst layer assemblies. Further, for example, even when a defect occurs in the first catalyst layer, such as when a crack occurs in the first catalyst layer during transfer, the sprayed catalyst-forming ink penetrates into a defect such as a crack. Therefore, the defect of the first catalyst layer can be repaired by the second catalyst layer, which is advantageous for improving the productivity of the membrane-catalyst layer assembly.

In the present invention, the content ratio of the hydrogen ion conductive polymer electrolyte is preferably higher in the first catalyst layer than in the second catalyst layer. Here, in the present invention, the “content ratio of the hydrogen ion conductive polymer electrolyte in the catalyst layer” refers to [(total mass W _{P of the} hydrogen ion conductive polymer electrolyte contained in the catalyst layer) / (the catalyst Total mass of layer W _L )]. By adopting such a configuration, the density of reaction sites can be increased in the vicinity of the polymer electrolyte membrane, and the diffusibility of the reaction gas and the discharge of generated water can be increased as the distance from the polymer electrolyte membrane increases. The performance of the molecular electrolyte fuel cell can be further improved.

  From the viewpoint of obtaining the effect of the present invention more reliably, the thickness of the first catalyst layer is preferably 3 μm or more and 20 μm or less (Claim 3).

From the viewpoint of obtaining the effect of the present invention more reliably, the first catalyst layer and the second catalyst layer contain platinum, and the amount of platinum contained in the first catalyst layer is the second catalyst layer. It is preferable that it is not less than 1/4 and not more than 7/4 of the amount of platinum contained in the layer (claim 4 ).

The proportion of platinum contained in the first catalyst layer is preferably 0.01 mg / cm ² or more and 1.0 mg / cm ² or less (Claim 5 ). If comprised in this way, the reaction area fall by aggregation of platinum can be prevented, and electric power generation can be advanced without delay.

The catalyst layer forming ink, carbon carrying a catalyst, the hydrogen ion conductive polymer electrolyte, it is preferred to have water, and organic solvent (claim 6). With this configuration, the organic solvent and water can be appropriately mixed to stabilize the ink properties and speed up drying after application.

In the present invention, in the step of forming the second catalyst layer may be formed a second catalytic layer consisting of two or more catalyst layer ink are sequentially sprayed with a plurality of layers (claim 7). With such a configuration, various properties such as “content ratio of hydrogen ion conductive polymer electrolyte” of the catalyst layer forming ink can be adjusted, and the properties of the second catalyst layer can be adjusted more finely. Can do. Here, the “content ratio of the hydrogen ion conductive polymer electrolyte” of the catalyst layer forming ink is [(total mass W _{P of the} hydrogen ion conductive polymer electrolyte contained in the catalyst forming ink) / (the catalyst formation). The total ink mass W _I )].

In the present invention, in the step of forming the second catalyst layer composed of a plurality of layers by sequentially spraying two or more types of catalyst layer forming inks, the lower the content of the hydrogen ion conductive polymer electrolyte, (Claim 8 ). With this configuration, the density of the reaction site is increased on the side close to the polymer electrolyte membrane in the second catalyst layer, and the diffusibility of the reaction gas and the discharge of generated water are increased as the distance from the polymer electrolyte membrane increases. Therefore, the performance of the polymer electrolyte fuel cell can be further improved.

Here, in the present invention, two or more types of catalyst layer forming inks are sequentially sprayed to form the first catalyst layer composed of a plurality of layers. The layer on the side close to the polymer electrolyte membrane is assumed on the assumption that the above catalyst layer forming ink is formed by spraying sequentially. In addition, “the lower layer, the higher the content ratio of the hydrogen ion conductive polymer electrolyte” is, the condition that the second catalyst layer is formed by sequentially spraying two or more types of catalyst layer forming ink, The catalyst layer forming ink used on the side closer to the polymer electrolyte membrane of the catalyst layer where the hydrogen ion conductive polymer electrolyte content ratio (W _P / W _I ) of the catalyst forming ink is farther from the polymer electrolyte membrane The state is finally smaller than the catalyst layer forming ink used in the above. That is, when the formed second catalyst layer is viewed as a whole, the mass ratio (W _P / W _I ) is generally reduced from the side closer to the polymer electrolyte membrane to the side farther from the polymer electrolyte membrane.

For example, the mass ratio (W _P / W _I ) is monotonically decreasing from the side closer to the polymer electrolyte membrane to the side farther from the polymer electrolyte membrane. When three or more types of catalyst-forming inks are used, the catalyst-forming ink used between the lowermost layer and the uppermost layer has a mass ratio (W _P / W) of any of the catalyst-forming inks used before and after. a _I) and the mass ratio of the same value (W _P / W _I) may be. Furthermore, although the catalyst layer forming ink used on the side closer to the polymer electrolyte membrane as a whole is smaller than the catalyst layer forming ink used on the side far from the polymer electrolyte membrane, In some catalyst-forming inks, the mass ratio (W _P / W _I ) of the catalyst-forming ink used on the upper layer side may be larger than the mass ratio (W _P / W _I ) of the catalyst-forming ink used on the lower layer side. May be. However, from the viewpoint of the diffusibility of the reaction gas and the discharge of generated water, the catalyst-forming ink should be used such that the mass ratio (W _P / W _I ) decreases from the lowermost layer to the uppermost layer. The catalyst-forming ink used between the lower layer and the uppermost layer has the same mass ratio (W _P / W _I ) as the mass ratio (W _P / W _I ) of any of the catalyst-forming inks used before and after. This is preferred.

In this invention, you may further have the step of forming one or more 3rd catalyst layers on the said 2nd catalyst layer (Claim 9 ). With such a configuration, various properties such as adjustment of the catalytic reaction area of the catalyst layer of the membrane-catalyst layer assembly, diffusibility of the reaction gas, discharge of generated water, and electronic conductivity can be adjusted. The properties of the catalyst layer 2C can be finely adjusted. Also, it is possible to improve the adhesion between the gas diffusion layer and the second catalyst layer, and to prevent damage to the second catalyst layer and / or polymer electrolyte membrane due to the surface roughness (existence of irregularities) of the gas diffusion layer. it can. Here, in the present invention, as the “third catalyst layer”, for example, a catalyst layer containing at least a catalyst (such as Pt) -supporting carbon (conductive carbon), a hydrogen ion conductive polymer electrolyte, and a catalyst (such as Pt) ) Catalyst layer containing at least supported carbon (conductive carbon), water repellent material and catalyst (such as Pt) Catalyst layer containing at least supported carbon (conductive carbon), water repellent material, hydrogen ion conductive polymer electrolyte and catalyst ( Pt and the like) and a catalyst layer containing at least supported carbon (conductive carbon). Furthermore, in the present invention, the “third catalyst layer” includes a layer made of a water repellent material and conductive carbon (carbon not supporting a catalyst).

Furthermore, in this invention, when it further has the step of forming one or more 3rd catalyst layers on the said 2nd catalyst layer, the content rate of a hydrogen ion conductive polymer electrolyte is so high that it is a lower layer. (Claim 10 ). With this configuration, the density of reaction sites can be increased on the side closer to the polymer electrolyte membrane, and the diffusibility of the reaction gas and the discharge of generated water can be increased as the distance from the polymer electrolyte membrane increases. The performance of the molecular electrolyte fuel cell can be improved.

Here, in the present invention, the “lower layer” in the case of further comprising the step of forming one or more third catalyst layers on the second catalyst layer means that three or more catalyst layers are formed. Is the catalyst layer on the side close to the polymer electrolyte membrane. In addition, “the lower layer has a higher hydrogen ion conductive polymer electrolyte content” state means that three or more catalyst layers are formed, and the hydrogen ion conductive polymer of the formed catalyst layer. The catalyst content rate (W _P / W _L ) near the polymer electrolyte membrane is finally smaller than the catalyst layer far from the polymer electrolyte membrane, and the membrane-catalyst layer junction When viewed as a whole catalyst layer, the mass ratio (W _P / W _L ) of each catalyst layer is generally reduced from the side closer to the polymer electrolyte membrane to the side farther from the polymer electrolyte membrane.

For example, the mass ratio (W _P / W _L ) may be monotonically decreasing from the side closer to the polymer electrolyte membrane to the side farther from the polymer electrolyte membrane. For example, the mass ratio (W _P / W _L ) of some adjacent catalyst layers may be in the same value. Furthermore, when comparing the mass ratio (W _P / W _L ) between some adjacent catalyst layers, the mass ratio (W _P / W _L ) of the upper catalyst layer is equal to the mass ratio of the lower catalyst layer (W _P / W _L ). It may be larger than (W _P / W _L ). However, from the viewpoint of gas diffusibility or drainage, the mass ratio (W _P / W _L ) decreases monotonically from the bottom layer to the top layer, or is disposed between the bottom layer and the top layer Among the layers, it is preferable that the mass ratio (W _P / W _L ) between some adjacent layers has the same value.

Further, the film of the present invention - method of manufacturing an electrode assembly, the membrane of claim 1 to 10 - film produced by the production method of the catalyst layer assembly - over the second catalyst layer of the catalyst layer assembly A gas diffusion layer is disposed on the substrate (claim 11 ). If comprised in this way, since a membrane-electrode assembly is manufactured using the membrane-catalyst layer assembly manufactured by the manufacturing method of the membrane-catalyst layer assembly of the above-mentioned this invention, manufacture of a membrane-electrode assembly The catalyst layer which can shorten the required time concerning this, and is excellent in the diffusibility of a reactive gas and the discharge | emission property of produced | generated water can be formed.

  Here, “disposing the gas diffusion layer above the second catalyst layer of the membrane-catalyst layer assembly” means that when the above-described third catalyst layer is not formed, the gas diffusion layer is the second catalyst layer. It arrange | positions in the state closely_contact | adhered on the catalyst layer. In the case of forming the third catalyst layer, the third catalyst layer is disposed between the second catalyst layer and the gas diffusion layer. In other words, this indicates that the gas diffusion layer is disposed in close contact with the third catalyst layer. Here, “arrange” means a case where adhesion is performed by heat treatment or the like, and a case where adhesion is performed by placing and pressing without adhesion.

  As described above, the method for producing a membrane-catalyst layer assembly of the present invention and the method for producing a membrane-electrode assembly using the same can reduce the time required for production and can also diffuse the reaction gas. In addition, it is possible to form a catalyst layer that is excellent in the ability to discharge generated water.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a partially exploded perspective view showing the structure of a main part of a polymer electrolyte fuel cell produced by a preferred embodiment of a method for producing a membrane-catalyst layer assembly and a method for producing a membrane-electrode assembly of the present invention. FIG.

  As shown in FIG. 1, a polymer electrolyte fuel cell 100 is configured by stacking cells 10.

  Although not shown, a current collector plate, an insulating plate, and an end plate are attached to the outermost layers at both ends of the cell 10, and the cell 10 has a fastening bolt (not shown) and a nut inserted through the bolt hole 11 from both ends. It is constructed by fastening with.

  The cell 10 is configured by sandwiching an MEA-gasket assembly (hereinafter abbreviated as MEA assembly) 7 between a pair of an anode separator 9A and a cathode separator (both are collectively referred to as a separator) 9C. The separator is made of a conductive material and constitutes a part of the cathode side or anode side electrode.

  The MEA assembly 7 is configured by sandwiching a polymer electrolyte membrane extending around the peripheral edge of the MEA 5 between a pair of fluororubber gaskets 6. Therefore, the MEA 5 is exposed on both surfaces of the central opening of the gasket 6.

  In the peripheral portions of the separators 9A and 9C and the MEA assembly 7, a reducing agent gas manifold holes 12, 22, 32 and an oxidizing agent gas are formed to form a pair of manifolds through which the reducing agent gas and the oxidizing agent gas circulate. Manifold holes 13, 23, 33 are formed. In addition, water manifold holes 14, 24, and 34 that form a pair of manifolds through which water flows are also drilled.

  A groove-like reducing agent gas passage 21 is formed on the inner main surface of the anode separator 9A so as to connect the pair of reducing agent gas manifold holes 22 and 22 together.

  On the inner main surface of the cathode separator 9C, a groove-like oxidant gas flow path 31 is formed so as to connect the pair of oxidant gas manifold holes 33, 33.

  Further, in the same manner as the reducing agent gas passage 21 or the oxidizing gas passage 31, grooves are formed on the outer main surface, that is, the rear surface of the separators 9A and 9C so as to connect the pair of water manifold holes 24 and 34. A water channel (not shown) is formed. As a result, when the cell 10 is stacked, these manifold holes are stacked to form a pair of manifolds of oxidant gas, reductant gas, and water. The flow paths of the oxidant gas, the reductant gas, and the water are branched from one manifold, that is, from the supply side manifold to the flow paths 21 and 31 formed in the separator and a water flow path (not shown). , Configured to communicate with each other manifold, that is, the discharge side manifold. The oxidant gas and the reductant gas are exposed to the MEA 5 exposed at the center of the MEA assembly 7 in the reductant gas flow path 21 or the oxidant gas flow path 31, respectively, and cause an electrochemical reaction. Further, since water flows between the back surfaces of the separators 9A and 9C, that is, between the adjacent cells 10, the polymer electrolyte fuel cell is maintained at a predetermined temperature suitable for the electrochemical reaction by the heat transfer capability of water. Can do.

  Here, FIG. 2A is a side view of the MEA, and FIG. 2B is a plan view of the MEA.

  The MEA 5 is mainly composed of a polymer electrolyte membrane 1 made of an ion exchange membrane that selectively permeates hydrogen ions and a carbon powder carrying a platinum group metal catalyst formed so as to sandwich the polymer electrolyte membrane 1. A pair of anode-side catalyst layer 2A and cathode-side catalyst layer 2C, and a pair of anode-side gas diffusion layer 4A and cathode-side gas diffusion layer 4C disposed on the outer surfaces of the pair of catalyst layers 2A, 2C are provided. It is configured. The gas diffusion layers 4A and 4C are configured to have both air permeability and electronic conductivity. For example, it has a porous structure.

  The cathode side catalyst layer 2C, the cathode side gas diffusion layer 4C and the cathode separator 9C constitute the cathode.

  Further, the anode side catalyst layer 2A, the anode side gas diffusion layer 4A and the anode separator 9A constitute an anode.

  Next, the operation of the polymer electrolyte fuel cell 100 configured as described above will be described. An oxidant gas is branched and supplied to each cell 10 via the oxidant flow path 30. In each cell 10, oxidant gas is supplied to the cathode. Here, the cathode side gas diffusion layer 4C is exposed. Similarly, hydrogen or a reducing agent gas containing hydrogen is supplied to the anode. Here, the anode side gas diffusion layer 4 </ b> A is exposed via the reducing agent channel 40. The oxidant gas passes through the cathode side gas diffusion layer 4C and reaches the cathode side catalyst layer 2C. Similarly, the reducing agent gas also passes through the anode side gas diffusion layer 4A and reaches the anode side catalyst layer 2A.

  Here, the cathode-side catalyst layer 2C and the anode-side catalyst layer 2A are electrically connected via the cathode separator 9C, the anode separator 9A, a current collector (not shown), and an external electric circuit (not shown). When the circuit is configured, hydrogen is ionized in the anode catalyst layer 2A. Hydrogen ions permeate the polymer electrolyte membrane 1 and combine with oxygen ions in the cathode side catalyst layer 2C to generate water. Further, electrons generated in the anode side catalyst layer 2A due to hydrogen ionization flow through an external electric circuit (not shown) via the anode side gas diffusion layer 4A to generate an electric output.

  Here, a method for forming the catalyst layers 2A and 2C on the polymer electrolyte membrane 1, that is, a method for producing the membrane-catalyst layer assembly 3 (a preferred embodiment of the method for producing the membrane-catalyst layer assembly of the present invention). Will be described. Here, for the sake of convenience, the manufacturing process of the cathode side catalyst layer 2C is shown and described. The anode side catalyst layer 2A is also formed in the same manner as the cathode side catalyst layer 2C, but the description thereof is omitted here.

  FIG. 3A to FIG. 3D are diagrams schematically showing a manufacturing process of the cathode catalyst layer of the membrane-catalyst layer assembly.

Suitable examples of the polymer electrolyte membrane 1 include a membrane having an ion exchange function of selectively permeating hydrogen ions. Further, as such a membrane, a polymer electrolyte membrane having a structure in which —CF ₂ — is a main chain skeleton and a sulfonic acid group is introduced at the end of a side chain is preferably exemplified. As a membrane having such a structure, for example, a perfluorocarbon sulfonic acid membrane {for example, Nafion 112 (registered trademark) manufactured by DUPONT} is preferably exemplified.

  Further, the catalyst layer forming ink is prepared as follows. The electrode catalyst powder mixed with the catalyst-forming ink for the cathode side catalyst layer 2C, for example, carries 25 wt% of platinum particles having an average particle diameter of about 3 nm on Ketjen Black EC (manufactured by AKZO Chemie). Use catalyst powder. Examples of the electrode catalyst powder mixed with the catalyst-forming ink for the anode side catalyst layer 2A include, for example, ketjen black EC (manufactured by AKZO Chemie, trade name), platinum-ruthenium alloy particles having an average particle diameter of about 3 nm. A catalyst powder supporting 25 wt% (for example, Pt: Ru = 1: 1 by mass ratio) is used. These electrode catalyst powders are dispersed in isopropanol. Next, an ethyl alcohol dispersion (for example, trade name “Flemion FSS-1” manufactured by Asahi Glass Co., Ltd.) of hydrogen ion conductive polymer electrolyte (for example, perfluorocarbon sulfonic acid powder), water and an organic solvent are appropriately mixed with this isopropanol. Is done. Here, the organic solvent is preferably one that does not poison the catalyst-supporting carbon, and examples thereof include acetone, ethanol (ethyl alcohol), isobutyl alcohol, ethylene glycol, butanol, and methanol.

Further, according to the experiences of the inventors so far, when the proportion of platinum in the first catalyst layer 2C1 is less than 0.01 mg / cm ² , the electrochemical reaction of the polymer electrolyte fuel cell is not stable, and power generation May be delayed. Moreover, when the ratio of platinum in the first catalyst layer 2C1 is higher than 1.0 mg / cm ² , the reaction area may be reduced due to aggregation of platinum. Therefore, when the proportion of platinum contained in the first catalyst layer 2C1 is 0.01 mg / cm ² or more and 1.0 mg / cm ² or less, a reduction in reaction area due to aggregation of platinum is prevented, and power generation proceeds smoothly. Can be made.

  As shown in FIG. 3A, the catalyst-forming ink is applied on the transfer substrate P to form the first catalyst layer 2C1. As the transfer substrate P, a PP sheet or a PTEF sheet can be suitably used. In addition, the components do not elute into the catalyst layer due to adhesion of the catalyst layer or hot pressing, and the peelability after transfer is good. Materials can be used.

  And as shown in FIG.3 (b), the 1st catalyst layer 2C1 is accumulated on the main surface of the polymer electrolyte membrane 1, and it hot-presses (for example, conditions of pressure 1MPa, temperature 140 degreeC, time 30 minutes). Thus, the first catalyst layer 2C1 is formed. Then, the transfer substrate P is peeled off, and the first catalyst layer 2C1 is transferred onto the polymer electrolyte membrane 1.

  Next, as shown in FIG. 3C, the catalyst layer forming ink is spray-coated by the spray device 200 to form the second catalyst layer 2C2 on the main surface of the first catalyst layer 2C1. Although not shown, when spray coating is performed, the polymer electrolyte membrane 5A is covered with a mask having an opening having a shape corresponding to the planar shape of the first catalyst layer 2C1, and the catalyst layer is formed except for the required portion. It is protected from ink sticking. Thereby, the catalyst layer 2C in which the first catalyst layer 2C1 and the second catalyst layer 2C2 are joined is formed.

  As described above, the time required for the step of transferring and forming the first catalyst layer 2C1 to the polymer electrolyte membrane 1 is shorter than the time required for the step of forming the entire catalyst layer 2C by spray coating. Therefore, the time for manufacturing the membrane-catalyst layer assembly 3 can be shortened.

  The properties of the ink for forming the catalyst layer of the cathode-side first catalyst layer 2C1 and the cathode-side second catalyst layer 2C2 may not be the same. For example, the catalyst layer forming ink may be prepared so that the content ratio of the hydrogen ion conductive polymer electrolyte in the cathode-side first catalyst layer 2C1 is higher than that in the cathode-side second catalyst layer 2C2. That is, the catalyst layer forming ink in which the mixing ratio of the alcohol dispersion of the hydrogen ion conductive polymer electrolyte is increased as compared with the catalyst layer forming ink used for forming the cathode side second catalyst layer 2C2. It may be used for forming the layer 2C1. Thereby, the density of the reaction sites of the cathode-side first catalyst layer 2C1 can be increased, and the diffusibility of the reaction gas and the generated water can be discharged from the cathode-side second catalyst layer 2C2 (Patent Literature). 2), the performance of the polymer electrolyte fuel cell 100 is improved.

  Further, since no water generated by an electrochemical reaction is generated on the anode side, it is not necessary to discharge water as high as the cathode side. Therefore, on the anode side, the properties of the catalyst layer forming ink of the anode side first catalyst layer 2A1 and the anode side second catalyst layer 2A2 may remain the same.

  As described above, the time required for the step of forming the second catalyst layer 2C2 by transferring it to the first catalyst layer 2C1 is shorter than the time required for the step of forming the entire catalyst layer 2C by spray coating. Since time is sufficient, the time for manufacturing the membrane-catalyst layer assembly 3 can be shortened.

  Further, since the porous second catalyst layer 2C2 is formed by the spraying method, it is possible to improve the diffusibility of the reaction gas of the catalyst layer 2C and the discharge of the generated moisture.

  Next, a method for manufacturing MEA 5 (a preferred embodiment of a method for manufacturing a membrane-electrode assembly of the present invention) will be described.

  The MEA 5 of the present invention is manufactured using the membrane-catalyst layer assembly 3 described above. That is, as shown in FIG. 2A, the MEA 5 is manufactured by forming the gas diffusion layers 4A and 4C on the catalyst layers 2A and 2C.

  The gas diffusion layers 4A and 4C are made of a porous body having a large number of fine pores. As a result, when the gas enters the hole, the gas diffuses and easily reaches the catalyst layers 2A and 2C. Generally, the gas diffusion layers 4A and 4C are produced by applying a water-repellent carbon layer on a conductive carbon fiber substrate (carbon cloth, carbon paper, etc.). As the water-repellent carbon layer, a water-repellent material, conductive carbon (carbon not carrying a catalyst), surfactant, and water mixed ink are coated on a substrate with a bar coater, etc. For example, by baking at 400 ° C. in the air. The stability of the water-repellent carbon layer and the substrate can be improved by firing. That is, the effect that the water-repellent carbon layer and the substrate are stable can be obtained as compared with the case where the water-repellent carbon layer is applied as the third catalyst layer above the second catalyst layer 2C2. In the present embodiment, water-repellent carbon paper (trade name (TGP-H-090) manufactured by TORAY, thickness: 270 μm) is used. The water repellent treatment is performed, for example, by immersing the carbon paper in an aqueous dispersion of polytetrafluoroethylene (PTFE) and then performing a drying treatment. Further, instead of carbon paper, carbon cloth or carbon felt made of carbon fiber, carbon powder, organic binder or the like may be used as the gas diffusion layer. Then, the carbon paper is hot-pressed (for example, pressure 0.5 MPa, temperature 135 ° C., time 5 minutes) so as to be bonded onto the catalyst layers 2A and 2C to form gas diffusion layers 4A and 4C. .

  As described above, in the present invention, the time required for production can be shortened by the step of forming the first catalyst layer by transfer on the polymer electrolyte membrane, and the catalyst layer is formed on the main surface of the first catalyst layer. The step of spraying ink to form the second catalyst layer can enhance the diffusibility of the reaction gas and the discharge of generated water. That is, the present invention sufficiently reduces the disadvantages of conventional membrane-catalyst layer assembly production methods such as the transfer method, spray method, and doctor blade method, and is particularly advantageous for mass production of membrane-catalyst layer assemblies. is there.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and those skilled in the art can use various improvements and alternative means within the scope of the present invention.

For example, in the step of forming the second catalyst layer 2C2, two or more types of catalyst layer forming inks may be sequentially sprayed to form the second catalyst layer 2C2 composed of a plurality of layers. With this configuration, various properties such as “content ratio of hydrogen ion conductive polymer electrolyte” of the catalyst layer forming ink can be adjusted, and the properties of the first catalyst layer can be adjusted more finely. it can. Here, the “content ratio of the hydrogen ion conductive polymer electrolyte” of the catalyst layer forming ink is [(total mass W _{P of the} hydrogen ion conductive polymer electrolyte contained in the catalyst forming ink) / (the catalyst formation). The total ink mass W _I )]. In the step of forming the second catalyst layer 2C2 composed of a plurality of layers by sequentially spraying two or more types of catalyst layer forming inks, the lower the layer, the higher the content ratio of the hydrogen ion conductive polymer electrolyte is. Here, in the present invention, the “lower layer” in the case of forming the second catalyst layer 2C2 composed of a plurality of layers by sequentially spraying two or more kinds of catalyst layer forming inks means that the second catalyst layer 2C2 is: The layer on the side close to the polymer electrolyte membrane is assumed on the assumption that two or more types of ink for forming a catalyst layer are formed by sequentially spraying.

In addition, the state that “the lower layer has a higher content of hydrogen ion conductive polymer electrolyte” means that the second catalyst layer 2C2 is formed by sequentially spraying two or more types of catalyst layer forming inks. In the catalyst layer forming ink, the hydrogen ion conductive polymer electrolyte content ratio (W _P / W _I ) of the catalyst forming ink is used closer to the polymer electrolyte membrane 1 of the catalyst layer. Fig. 5 shows a state where the ink is finally smaller than the catalyst layer forming ink used on the far side. That is, when the formed second catalyst layer 2C2 is viewed as a whole, the mass ratio (W _P / W _I ) is substantially reduced from the side closer to the polymer electrolyte membrane 1 to the side farther from it. .

For example, the mass ratio (W _P / W _I ) is monotonously decreasing from the side closer to the polymer electrolyte membrane 1 to the side farther from it. When three or more types of catalyst-forming inks are used, the catalyst-forming ink used between the lowermost layer and the uppermost layer has a mass ratio (W _P / W) of any of the catalyst-forming inks used before and after. a _I) and the mass ratio of the same value (W _P / W _I) may be. Furthermore, the catalyst layer forming ink used on the side closer to the polymer electrolyte membrane 1 as a whole as the second catalyst layer 2C2 is finally smaller than the catalyst layer forming ink used on the side far from the polymer electrolyte membrane 1. However, in some catalyst forming inks, the mass ratio (W _P / W _I ) of the catalyst forming ink used on the upper layer side is greater than the mass ratio (W _P / W _I ) of the catalyst forming ink used on the lower layer side. May be large. However, from the viewpoint of the diffusibility of the reaction gas and the discharge of generated water, the catalyst-forming ink should be used such that the mass ratio (W _P / W _I ) decreases from the lowermost layer to the uppermost layer. The catalyst-forming ink used between the lower layer and the uppermost layer has the same mass ratio (W _P / W _I ) as the mass ratio (W _P / W _I ) of any of the catalyst-forming inks used before and after. This is preferred.

  With this configuration, in the same manner as described above, in the second catalyst layer 2C2, the density of the reaction sites is increased on the side closer to the polymer electrolyte membrane 1, and the reaction gas flows as the distance from the polymer electrolyte membrane 1 increases. Since the diffusibility and the drainage of generated water can be improved, the performance of the polymer electrolyte fuel cell 100 can be further improved.

  Furthermore, you may further have the step which forms one or more "3rd catalyst layers" (not shown) on the 2nd catalyst layer 2C2 by transfer, spraying, or application | coating. Here, as the “third catalyst layer”, for example, a catalyst layer containing at least a catalyst (such as Pt) -supporting carbon (conductive carbon), a hydrogen ion conductive polymer electrolyte, and a catalyst (such as Pt) are supported. Catalyst layer including at least carbon (conductive carbon), water repellent material and catalyst (such as Pt) supported catalyst layer including at least carbon (conductive carbon), water repellent material, hydrogen ion conductive polymer electrolyte and catalyst (such as Pt) And a catalyst layer containing at least supported carbon (conductive carbon). Furthermore, in the present invention, the “third catalyst layer” includes a layer composed of a water repellent material and conductive carbon (carbon not supporting a catalyst). As a result, various properties such as the adjustment of the catalytic reaction area of the catalyst layer 2C of the membrane-catalyst layer assembly 3, the diffusibility of the reaction gas, the discharge of generated water, and the electronic conductivity can be adjusted. The properties of the catalyst layer 2C can be adjusted. Further, the adhesion between the gas diffusion layer 4C and the second catalyst layer 2C2 is improved, and the damage of the second catalyst layer 2C2 and / or the polymer electrolyte membrane 1 due to the surface roughness (existence of irregularities) of the gas diffusion layer 4C. It can also be prevented. For example, in the “third catalyst layer” that does not include a catalyst, moisture generated by the catalytic reaction is not generated. Accordingly, it is possible to improve the diffusibility of the reaction gas and the discharge of the generated water as the entire catalyst layer 2C. Moreover, as the above-mentioned water repellent material, a substance having high chemical stability is preferable, for example, polytetrafluoroethylene (PTFE) or tetrafluoroethylene / hexafluoropropylene copolymer (FEP).

And when it further has the step of forming one or more "3rd catalyst layers" on the 2nd catalyst layer 2C2, it is good that the content rate of a hydrogen ion conductive polymer electrolyte is so high that it is a lower layer. Here, the “lower layer” in the case of further including a step of forming one or more “third catalyst layers” on the second catalyst layer 2C2 is based on the assumption that three or more layers are formed. The catalyst layer on the side close to the polymer electrolyte membrane 1 is said. In addition, “the lower layer has a higher content of hydrogen ion conductive polymer electrolyte” means that three or more layers are formed on the assumption that the hydrogen ion conductive polymer electrolyte of the formed layer is formed. The layer with the content ratio (W _P / W _L ) closer to the polymer electrolyte membrane 1 is finally smaller than the layer farther from the polymer electrolyte membrane 1, and the membrane-catalyst layer assembly 3 When the catalyst layer 2C as a whole is viewed as a whole, the mass ratio (W _P / W _L ) of each layer is generally reduced from the side closer to the polymer electrolyte membrane 1 to the side farther from it.

For example, the mass ratio (W _P / W _L ) may be monotonically decreasing from the side closer to the polymer electrolyte membrane 1 to the side farther from it. For example, the mass ratio (W _P / W _L ) of some adjacent layers may be in the same value. Furthermore, when comparing the weight ratio between the layers of a part of the adjacent the (W _P / W _L), the mass ratio of the upper layer (W _P / W _L) is the mass ratio of the lower side of the layer (W _P / W _L ) may be larger. However, from the viewpoint of gas diffusibility or drainage, the mass ratio (W _P / W _L ) decreases monotonically from the bottom layer to the top layer, or is disposed between the bottom layer and the top layer Among the layers, it is preferable that the mass ratio (W _P / W _L ) between some adjacent layers has the same value. With this configuration, the density of the reaction sites can be increased on the side closer to the polymer electrolyte membrane 1, and the diffusibility of the reaction gas and the discharge of generated water can be increased as the distance from the polymer electrolyte membrane 1 increases. The performance of the polymer electrolyte fuel cell 100 can be improved.

  Hereinafter, although the manufacturing method of the membrane-electrode assembly of the present invention will be described in more detail with reference to Examples and Comparative Examples, the present invention is not limited to these Examples.

(Example S1) to (Example S7) and (Comparative Example T1)
The membrane-catalyst layer assembly 3 in which the thickness t1 + t2 of the catalyst layer 2C is 20 μm is used in Examples S1 to S7 using the thickness t1 of the first catalyst layer 2C1 and the thickness t2 of the second catalyst layer 2C2 as parameters. Manufactured. Further, as Comparative Example T1, a membrane-catalyst assembly 3 formed only by the transfer method, that is, by forming only the first catalyst layer 2C1 without forming the second catalyst layer 2C2.

[Performance evaluation test]
And each cell 10 was comprised using MEA5 which has the membrane-catalyst assembly 3 of Example S1 thru | or S7 and Comparative Example T1, and the performance evaluation test which measures the output voltage E was done. In the cell 10, gas diffusion layers 4 </ b> A and 4 </ b> C are arranged on both surfaces of the MEA 5 and bonded by hot pressing. A silicon gasket was used as the gasket 6. The MEA 5 and the gasket 6 were sandwiched between the anode separator 9A and the cathode separator 9C and fastened at a pressure of 10 kgf / cm 2.

  The performance test conditions were such that hydrogen was passed through the anode-side reaction gas of the cell 10 and air was passed through the cathode-side reaction gas. The temperature of the cell 10 under test, that is, the operating temperature was maintained at 80 ° C. Hydrogen gas was humidified to a dew point of 80 ° C. and air was humidified to a dew point of 80 ° C. and supplied to the cell 10. Then, the cell 10 was generated with a current density of 1.0 A / cm2. Further, the fuel utilization rate and air utilization rate of the normal polymer electrolyte fuel cell 100 are about 70% and 40%, respectively. However, in this performance test, they were set to 90% and 80%, respectively, so that the diffusibility of the reaction gas and the discharge of the generated water were more or less prominent, that is, a condition where a flooding phenomenon was likely to occur.

  Table 1 is a table showing the catalyst layer thickness ratio, output voltage, and required production time of the membrane-catalyst layer assembly of this example. In the table, the catalyst layer thickness ratio t1 / t2, the output voltage E of the cell 10 as a result of this performance test, and the time required for manufacturing the membrane-catalyst layer assembly 3, that is, the required manufacturing time T are shown. The time required for production T is shown as 1 for the time required for producing Example S1.

  As shown in Table 1, in Examples S1 to S5, voltage drop due to the flooding phenomenon hardly appeared in the output voltage E, and the diffusibility of the reaction gas and the discharge of generated water were excellent. In addition, the required production time T can be shortened, and it has been found that the production method of the membrane-catalyst layer assembly 3 is more suitable. Here, in the membrane-catalyst layer assembly 3 of Examples S1 to S5, as shown in the table, the catalyst layer thickness ratio t1 / t2 was not less than 1/4 and not more than 7/4. Although not shown in the table, the amount of platinum contained in the first catalyst layer 2C1 was about one quarter to seven quarters of the amount of platinum contained in the second catalyst layer 2C2. Further, although not shown in the table, the thickness t1 of the first catalyst layer 2C1 was 3 μm or more and 20 μm or less.

  In the case of the comparative example T1, that is, in the case of the conventional transfer method, although the manufacturing time is short, it is estimated that the decrease in the output voltage E appears remarkably and the voltage decrease due to the flooding phenomenon appears. .

  Further, in the case of the catalyst layer thickness ratio t1 / t2 = 1/6, that is, in the case of Example S6, the second catalyst layer 2C2 is thick. It has been found that the time required for coating by is long and the production time T is remarkably increased.

  Further, in the case of the catalyst layer thickness ratio t1 / t2 = 9/4, that is, in the case of Example S7, the second catalyst layer 2C2 is thin, so that the manufacturing time T is shortened, but the output voltage E is 0.4V. Reduced to: This is presumed that since the first catalyst layer 2C1 is thick, a drop in the output voltage E due to the flooding phenomenon appears as in the comparative example T1.

  The present invention provides a method for producing a membrane-catalyst layer assembly, which can shorten the time required for production and can form a catalyst layer excellent in diffusibility of reaction gas and discharge of generated water, and the same It is useful as a production method of a membrane-electrode assembly using

1 is a partially exploded perspective view showing a structure of a main part of a polymer electrolyte fuel cell produced by a preferred embodiment of a method for producing a membrane-catalyst layer assembly and a method for producing a membrane-electrode assembly of the present invention. 2A is a side view of the MEA, and FIG. 2B is a plan view of the MEA. FIG. 3A to FIG. 3D are diagrams schematically showing a manufacturing process of the cathode catalyst layer of the membrane-catalyst layer assembly.

Explanation of symbols

1 polymer electrolyte membrane 2A anode side catalyst layer 2C cathode side catalyst layer 2A1 (anode side) first catalyst layer 2A2 (anode side) second catalyst layer 2C1 (cathode side) first catalyst layer 2C2 (cathode side) Second catalyst layer 3 Membrane-catalyst layer assembly 4A Anode side gas diffusion layer 4C Cathode side gas diffusion layer 5 Membrane-electrode assembly (MEA)
6 Gasket 7 MEA-Gasket Assembly 9A Anode Separator 9C Cathode Separator 10 Cell 11 Bolt Hole 12, 22, 32 Reductant Gas Manifold Hole 13, 23, 33 Oxidant Gas Manifold Hole 14, 24, 34 Water Manifold Hole 21 Reducing Agent Gas channel 31 Oxidant gas channel 100 Polymer electrolyte fuel cell 200 Spraying device S1 to S7 Example T1 Comparative example t1 First catalyst layer thickness t2 Second catalyst layer thickness t1 / t2 Catalyst layer Thickness ratio E Output voltage T Manufacturing time (the time required for manufacturing Example S1 is 1)
P Transfer base material

Claims (11)

Forming a first catalyst layer by transfer on at least one main surface of the polymer electrolyte membrane;
And have a, and forming a second catalyst layer by spraying a catalyst layer formed ink on the first catalyst layer,
The method for producing a membrane-catalyst layer assembly , wherein the thickness of the first catalyst layer is not less than one quarter and not more than seven quarters of the thickness of the second catalyst layer .   The method for producing a membrane-catalyst layer assembly according to claim 1, wherein the first catalyst layer has a higher content ratio of the hydrogen ion conductive polymer electrolyte than the second catalyst layer.   The method for producing a membrane-catalyst layer assembly according to claim 1 or 2, wherein the thickness of the first catalyst layer is 3 µm or more and 20 µm or less. The first catalyst layer and the second catalyst layer contain platinum, and the amount of platinum contained in the first catalyst layer is ¼ or more of the amount of platinum contained in the second catalyst layer. The method for producing a membrane-catalyst layer assembly according to any one of claims 1 to 3 , which is 7/4 or less. The membrane-catalyst layer bonding according to any one of claims 1 to 4 , wherein a ratio of platinum contained in the first catalyst layer is 0.01 mg / cm ² or more and 1.0 mg / cm ² or less. Body manufacturing method. The membrane-catalyst layer assembly according to any one of claims 1 to 5 , wherein the catalyst layer forming ink includes carbon carrying a catalyst, a hydrogen ion conductive polymer electrolyte, water, and an organic solvent. Manufacturing method. In the step of forming the second catalyst layer are sequentially sprayed two or more catalyst layer ink to form a second catalyst layer comprising a plurality of layers, any one of claims 1 to 6 The manufacturing method of the membrane-catalyst layer assembly as described in 2. The method for producing a membrane-catalyst layer assembly according to claim 7 , wherein the lower layer has a higher content of hydrogen ion conductive polymer electrolyte. The method for producing a membrane-catalyst layer assembly according to any one of claims 1 to 8 , further comprising a step of forming one or more third catalyst layers on the second catalyst layer. The method for producing a membrane-catalyst layer assembly according to claim 9 , wherein the lower layer has a higher hydrogen ion conductive polymer electrolyte content. Film according to any one of claims 1 to 1 0 - catalyst layer assembly film produced by the production method of - above the catalyst layer of the catalyst layer assembly, disposing the gas diffusion layer, film -Manufacturing method of electrode assembly.

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