JP2009277370A - Membrane electrode assembly - Google Patents

Abstract

A membrane electrode assembly capable of improving the performance of a gas diffusion layer and improving the power generation efficiency of a fuel cell without increasing the thickness of the gas diffusion layer and without changing the material itself. provide.
A membrane electrode assembly 1A in which a catalyst layer 3 is laminated on both surfaces 21 of an electrolyte membrane 2 and a gas diffusion layer 4A containing a hydrophobic resin and conductive fibers is further laminated on both sides 31 of the catalyst layer 3. The gas diffusion layer 4A includes a first gas diffusion layer 41 stacked on the surface of the catalyst layer 3, and a second gas diffusion layer 42 stacked on the surface of the first gas diffusion layer 41. The fiber diameter D2 of the conductive fiber 42b of the second gas diffusion layer 42 is larger than the fiber diameter D1 of the conductive fiber 42a of the first gas diffusion layer 41, and the conductive fiber of the second gas diffusion layer 42 The length L2 of 42b is longer than the length L1 of the conductive fibers 41b of the first gas diffusion layer 41.
[Selection] Figure 1

Description

  The present invention relates to a membrane electrode assembly in which a catalyst layer is laminated on both surfaces of an electrolyte membrane, and a gas diffusion layer containing a hydrophobic resin and conductive fibers is further laminated on both sides of the catalyst layer, and in particular, the gas diffusion layer The present invention relates to a membrane electrode assembly capable of partially controlling the characteristics of the membrane electrode assembly.

  A polymer electrolyte fuel cell using an electrolyte membrane can be operated at a low temperature, and can be reduced in size and weight. Therefore, application to a moving body such as an automobile is being studied. In particular, fuel cell vehicles equipped with polymer electrolyte fuel cells are gaining social interest as ecological cars.

  As shown in FIG. 4, such a polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) 95 as a main component, and includes a fuel (hydrogen) gas passage and an air gas passage. One fuel cell 90 called a single cell is formed by being sandwiched between separators 96 and 96. The membrane electrode assembly 95 includes an anode side electrode (anode catalyst layer) 93a and an anode side gas diffusion layer (anode gas diffusion layer) 94a laminated on one side of an electrolyte membrane 91 which is an ion exchange membrane, and the other side. The cathode side electrode (catalyst layer) 93b and the cathode side gas diffusion layer (cathode gas diffusion layer) 94b are laminated.

  By the way, in the fuel cell, the gas diffusion layer provided on each electrode generally uses carbon fibers formed into a sheet shape such as carbon paper or carbon cloth as a base material, and this base material is used as a catalyst layer. It is formed by laminating. Such a gas diffusion layer enhances the diffusion performance of oxygen gas and air gas, suppresses the occurrence of flatting in the vicinity of the electrode, and does not hinder the conductivity of electrons from the catalyst layer to the separator (electric resistance). Is required).

  Therefore, for example, a membrane electrode assembly has been proposed in which a conductive fiber made of carbon or the like and a layer made of a hydrophobic resin such as PTFE are further provided in the gas diffusion layer (see, for example, Patent Document 1). The membrane electrode assembly can ensure the electronic conductivity of the gas diffusion layer by providing conductive fibers in the gas diffusion layer, and the hydrophobic resin provides the gas diffusion layer forming member with water repellency, thereby providing a catalyst layer. Further, it is possible to reduce the occurrence of flatting due to the retention of moisture in the gas diffusion layer.

JP 2008-027645 A

  However, even when the gas diffusion layer of the membrane electrode assembly described in Patent Document 1 is used, the diffusion performance of oxygen gas and air gas is further improved, and the occurrence of flatting in the vicinity of the electrode is further reduced. In some cases, the thickness of the gas diffusion layer is increased, but the size of the fuel cell itself is increased. In order to reduce the size of the fuel cell, it is not desirable to increase the thickness of the gas diffusion layer.

  It is also possible to change the material of the gas diffusion layer and change the physical properties of the gas diffusion layer itself, but it is easy to control all of the gas diffusion performance, the occurrence of flatting and the prevention of lowering electrical resistance. is not.

  The present invention has been made in view of such problems, and the object of the present invention is to increase the gas diffusion without increasing the thickness of the gas diffusion layer and without changing the material itself. An object of the present invention is to provide a method for producing a membrane electrode assembly capable of improving the performance of a layer and improving the power generation efficiency of a fuel cell.

  As a result of intensive studies, the inventor has controlled the fiber diameter and length of the conductive fibers (carbon fibers) constituting the gas diffusion layer, so that the porosity and electrical properties necessary for the gas diffusion layer are controlled. A new finding was obtained that the resistance can be appropriately controlled.

  That is, when conductive fibers having a short length and a small fiber diameter are used, the conductive fibers in the diffusion layer have a dense structure, the air permeability is lowered, and the electrical resistance value is increased. In this case, it is effective for a dry-up cell. On the other hand, when conductive fibers having a long length and a large fiber diameter are used, the conductive fibers in the diffusion layer have a rough structure, the air permeability is improved, and the electrical resistance is lowered. In this case, it is effective for a cell that seems flat.

  This invention is based on the said new knowledge, The membrane electrode assembly which concerns on this invention laminates | stacks a catalyst layer on both surfaces of an electrolyte membrane, and includes hydrophobic resin and electroconductive fiber on both sides of the said catalyst layer. A membrane electrode assembly in which a gas diffusion layer is further laminated, wherein the gas diffusion layer is laminated on a surface of the catalyst layer and a surface of the first gas diffusion layer. A fiber diameter of the conductive fiber of the second gas diffusion layer is larger than a fiber diameter of the conductive fiber of the first gas diffusion layer, and the second gas diffusion layer The length of the conductive fiber of the diffusion layer is longer than the length of the conductive fiber of the first gas diffusion layer.

  The gas diffusion layer according to the present invention includes a first gas diffusion layer and a second gas diffusion layer. These gas diffusion layers both contain a hydrophobic resin and conductive fibers, and by containing these, the micro diffusion layer is microscopic. It is a porous layer (MPL). As described above, since the second gas diffusion layer having conductive fibers having a larger fiber diameter and a longer fiber length than the first gas diffusion layer has a rough structure, the gas permeability is high. Furthermore, compared with the first gas diffusion layer, the second gas diffusion layer has a high contact area ratio with the hydrophobic resin interposed between the conductive fibers, and thus the electrical resistance is small.

  Since the second gas diffusion layer having such characteristics is arranged on the separator side in contact with the gas, the gas diffusivity can be improved by improving the gas permeability, and the gas diffusion toward the catalyst layer can be achieved. Can be improved. In addition, compared with the first gas diffusion layer, the second gas diffusion layer can improve drainage, and can reduce the flatting of the fuel cell. Furthermore, since the second gas diffusion layer has a lower electrical resistance than the first gas diffusion layer, electrons can be suitably conducted to the separator. In this way, the power generation efficiency of the fuel cell can be increased without increasing the thickness of the gas diffusion layer and without changing the material of the gas diffusion layer.

  Another embodiment is a membrane electrode assembly in which a catalyst layer is laminated on both sides of an electrolyte membrane, and a gas diffusion layer containing a hydrophobic resin and conductive fibers is further laminated on both sides of the catalyst layer, The gas diffusion layer is characterized in that the fiber diameter of the conductive fiber is increased and the fiber length of the conductive fiber is increased as the gas diffusion layer proceeds from the surface of the catalyst layer in the layer thickness direction. .

  According to the present invention, since the fiber diameter of the conductive fibers increases along the layer thickness direction of the catalyst layer, and the fiber length increases, the diffusion layer has finer pores in the vicinity of the catalyst layer surface. In the vicinity of the separator, there is a microporous layer having pores coarser than this, and the porosity from the surface of the catalyst layer toward the layer thickness direction can be increased. As a result, in the portion in contact with the gas on the separator side, the drainage property is enhanced and the diffusibility of the gas toward the catalyst layer can be improved. In this way, the power generation efficiency of the fuel cell can be increased without increasing the thickness of the gas diffusion layer and without changing the material of the gas diffusion layer.

  The membrane / electrode assembly according to the present invention more preferably includes a porous base material layer having conductivity as a surface layer. According to the present invention, by providing this base material layer, in the production stage, a solution containing conductive fibers whose fiber diameter and fiber length are selected on the surface of the base material layer and particles made of a hydrophobic resin The gas diffusion layer forming member is manufactured by applying and baking this, and this can be easily laminated on the catalyst layer on the surface of the electrolyte membrane.

  As another aspect, the membrane electrode assembly according to the present invention comprises an anode catalyst layer laminated on one surface of a denatured membrane, a cathode catalyst layer laminated on the other surface, and the anode catalyst layer and the cathode catalyst. A membrane electrode assembly in which an anode gas diffusion layer and a cathode gas diffusion layer containing a hydrophobic resin and conductive fibers are further laminated on the surface of the layer, and the fiber diameter of the conductive fibers of the cathode gas diffusion layer is: It is larger than the fiber diameter of the conductive fiber of the anode gas diffusion layer, and the length of the conductive fiber of the cathode gas diffusion layer is longer than the length of the conductive fiber of the anode gas diffusion layer. preferable.

  According to the present invention, the cathode gas diffusion layer having conductive fibers having a larger fiber diameter and a longer fiber length than the anode gas diffusion layer has a rough structure and thus has high air permeability. Furthermore, compared with the anode gas diffusion layer, the cathode gas diffusion layer has a high contact area ratio with the hydrophobic resin interposed between the conductive fibers, and therefore has a small electric resistance.

  On the other hand, the anode gas diffusion layer having conductive fibers having a smaller fiber diameter and a shorter fiber length than the cathode gas diffusion layer has a dense structure and thus has low air permeability. Thereby, the water retention of the anode gas diffusion layer and the anode catalyst layer that are easy to dry can be increased.

  As a result, it is possible to suppress the occurrence of cathode-side flatting and increase the water retention on the anode side to improve the proton conductivity, thereby improving the power generation efficiency of the fuel cell. In the present invention, the anode catalyst layer and the anode gas diffusion layer refer to the catalyst layer and the gas diffusion layer formed on the anode electrode side, and the cathode catalyst layer and the cathode gas diffusion layer refer to the cathode electrode side. It refers to the formed catalyst layer and gas diffusion layer.

  According to the present invention, the performance of the gas diffusion layer can be improved and the power generation efficiency of the fuel cell can be improved without increasing the thickness of the gas diffusion layer and without changing the material itself.

  Below, with reference to drawings, it explains based on some embodiments of a membrane electrode assembly concerning the present invention.

  1A and 1B are diagrams for explaining a membrane electrode assembly according to the first embodiment. FIG. 1A is an overall configuration diagram of the membrane electrode assembly, and FIG. 1B is an enlarged view of a portion B in FIG. It is a figure and (c) has shown carbon fiber.

  As shown in FIG. 1, a membrane electrode assembly 1A according to this embodiment includes an electrolyte membrane 2, catalyst layers 3 and 3, and gas diffusion layers 4A and 4A. The electrolyte membrane 2 has an ion exchange function on the polymer electrolyte contained in the electrolyte membrane 2, for example, a perfluoro proton of a fluoroalkyl copolymer having a fluoroalkyl ether side chain and a perfluoroalkyl main chain. Exchange resins are preferably used. For example, Nafion (trade name) manufactured by DuPont, Aciplex (trade name) manufactured by Asahi Kasei, Flemion (trade name) manufactured by Asahi Glass, Gore-Select (trade name) manufactured by Japan Gore-Tex, and the like, Examples thereof include a polymer of trifluorostyrene sulfonic acid and a product obtained by introducing a sulfonic acid group into polyvinylidene fluoride. Further, there are styrene-divinylbenzene copolymer, polyimide resin, etc., which are hydrocarbon proton exchange resins, in which sulfonic acid groups are introduced. These should be appropriately selected according to the use and environment in which the fuel cell is used, but a perfluoro type is preferable from the viewpoint of the life of the fuel cell.

  In addition, the electrolyte membrane 2 may be composed only of an electrolyte, or may be one obtained by impregnating a porous water-repellent polymer resin sheet with the electrolyte described above. Such a polymer resin reinforced sheet can act as a reinforcing material for the electrolyte membrane 2, and further, condensation and retention of water in the polymer electrolyte fuel cell hinder the supply of the electrode reactant and is effective. is there. In particular, fluororesins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) are preferably used because they have high water repellency. It is done. In addition, non-fluorine films such as polyethylene terephthalate, polyethylene, polypropylene, and polyimide can also be used.

  Next, catalyst layers 3 and 3 are laminated on both surfaces 21 and 21 of the electrolyte membrane 2. These two catalyst layers 3 are a catalyst layer on the anode side and a catalyst layer on the cathode side, and correspond to the electrodes of the fuel cell. The catalyst layer 3 is a layer containing platinum-supported carbon and an electrolyte using platinum as a catalyst. In addition, although platinum-supported carbon is given as an example of the catalyst-supporting conductor, the catalyst is not particularly limited as long as it causes a catalytic reaction, and the activation overvoltage in the catalytic reaction is small. Noble metal catalysts such as palladium, ruthenium and iridium are preferably used. Two or more elements such as alloys and mixtures of these noble metal catalysts may be contained. Furthermore, the conductor is not particularly limited as long as it is an electrically conductive substance. For example, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black, and the like has electronic conductivity. And the size of the specific surface area is preferable.

  Gas diffusion layers 4A and 4A are further formed on both sides 31 and 31 of the catalyst layer. As shown in FIG. 1B, the gas diffusion layer 4A is laminated on the first gas diffusion layer 41 laminated on the surface 31 of the catalyst layer 3 and on the surface 41A of the first gas diffusion layer 41. And a second gas diffusion layer 42. Furthermore, the gas diffusion layer 4A further includes a porous base material layer 43 having conductivity as a surface layer.

  Each of the first gas diffusion layer 41 and the second gas diffusion layer 42 includes carbon fibers and a hydrophobic resin. In addition to carbon fibers, there can be mentioned fibers such as metal fibers, and there is no particular limitation as long as the electronic conductivity of the gas diffusion layer 4A can be ensured. Hydrophobic resins include those with hydrophobic properties such as PTFE resin, fluororesin, etc., making the gas diffusion layer water-repellent and preventing flooding due to moisture retention in the catalyst layer and gas diffusion layer. If it can do, it will not specifically limit.

  As shown in FIG.1 (c), the fiber diameter D2 of the carbon fiber 42a of the 2nd gas diffusion layer 42 is larger than the fiber diameter D1 of the carbon fiber 41a of the 1st gas diffusion layer 41, and 2nd gas The length L2 of the carbon fibers 42a of the diffusion layer 42 is longer than the length of the carbon fibers 41a of the first gas diffusion layer 41.

  The base material layer 43 is a porous layer and is a fibrous base material made of carbon fibers formed into a sheet shape, such as carbon paper, carbon cloth, carbon non-woven fabric, and carbon felt. It is a quality layer.

  In particular, by providing the base material layer 43, a solution containing the carbon fiber 41a and the hydrophobic resin is applied to the surface of the base material corresponding to the base material layer 43 in the manufacturing stage, and the carbon fiber 41a is applied to the coating surface. And a solution containing a hydrophobic resin can be further applied. And the apply | coated base material can be baked and a gas diffusion layer forming member can be manufactured. The gas diffusion layer forming member is placed on the surface 31 of the catalyst layer 3, and the gas diffusion layer 4A can be easily laminated on the surface of the catalyst layer 3 by pressurization and heating.

  In addition, depending on selection of the fiber diameter of the second gas diffusion layer 42 (when carbon fiber having a fiber diameter equal to or larger than that of the base material layer is selected), the base material layer 43 is not easily provided. A diffusion layer 4A can be laminated on the substrate.

  In such a gas diffusion layer 4A, compared with the first gas diffusion layer 41, the second gas diffusion layer 42 having carbon fibers 42a having a large fiber diameter and a long fiber length has a rough structure. Therefore, the gas permeability is higher than that of the first gas diffusion layer 41. Furthermore, compared with the first gas diffusion layer 41, the second gas diffusion layer 42 has a high contact area ratio with the hydrophobic resin interposed between the conductive fibers, and therefore has a small electric resistance.

  Since the second gas diffusion layer 42 having such characteristics is disposed on the side of the separator (not shown) in contact with the gas, the gas permeability of the gas diffusion layer 4A through which the gas flows is improved, and the catalyst layer The gas diffusivity toward 3 can be improved.

  Moreover, compared with the 1st gas diffusion layer 41, the 2nd gas diffusion layer 42 can improve drainage, and can aim at reduction of the flatting of a fuel cell. Furthermore, since the second gas diffusion layer 42 has a lower electrical resistance than the first gas diffusion layer 41, it can conduct electrons suitably to the separator. The thus configured membrane electrode assembly 1A can increase the power generation efficiency of the fuel cell without increasing the thickness of the gas diffusion layer 4A and without changing the material of the gas diffusion layer 4A.

  FIG. 2 is an enlarged view of a main part of the membrane electrode assembly according to the second embodiment of the present invention. As shown in FIG. 2, the membrane electrode assembly according to the second embodiment also has a catalyst layer laminated on both sides of the electrolyte membrane, and gas diffusion layers containing hydrophobic resin and conductive fibers on both sides of the catalyst layer. Furthermore, it is a laminated membrane electrode assembly. Therefore, since only the structure of the catalyst layer is different, only that point will be described below, and the structure having the same function as in FIG.

  As shown in FIG. 2, in the membrane electrode assembly 1 </ b> B according to the second embodiment, a gas diffusion layer 4 </ b> B is formed on the surface of the catalyst layer 3. The gas diffusion layer 4 </ b> B includes a microporous layer 44 containing carbon fibers and a hydrophobic resin, and a base material layer 43. In the microporous layer 44, the fiber diameter of the carbon fiber increases and the fiber length of the conductive fiber increases as it proceeds from the surface of the catalyst layer 3 in the layer thickness direction t.

  Thus, the gas diffusion layer 4B of the membrane electrode assembly 1B has a larger fiber diameter and a longer fiber length along the layer thickness direction t. A microporous layer having fine pores is provided, and in the vicinity of the separator, a microporous layer having coarser pores is provided.

  Thus, the porosity from the surface 31 of the catalyst layer 3 toward the layer thickness direction t can be increased. As a result, in the portion that contacts the gas on the separator side, the drainage property is enhanced and the diffusibility of the gas toward the catalyst layer 3 can be improved.

  FIG. 3 is a schematic view of a membrane electrode assembly according to the third embodiment of the present invention. As shown in FIG. 3, the membrane / electrode assembly according to the third embodiment also has a catalyst layer laminated on both surfaces of the electrolyte membrane, and gas diffusion layers containing hydrophobic resin and conductive fibers on both sides of the catalyst layer. Furthermore, it is a laminated membrane electrode assembly. Therefore, since only the structure of the catalyst layer is different, only that point will be described below, and the structure having the same function as in FIG.

  As shown in FIG. 3, in the membrane / electrode assembly 1 </ b> C, the anode catalyst layer 3 </ b> A is laminated on one surface of the electrolyte membrane 2. A cathode catalyst layer 3B is laminated on the other surface of the electrolyte membrane 2. Furthermore, an anode gas diffusion layer 4C and a cathode gas diffusion layer 4D containing a hydrophobic resin and conductive fibers are further laminated on the surfaces of the anode catalyst layer 3A and the cathode catalyst layer 3B.

  The anode gas diffusion layer 4C and the cathode gas diffusion layer 4D are macroporous layers having carbon fibers and a hydrophobic resin. The fiber diameter of the carbon fibers in the cathode gas diffusion layer 4D is determined by the anode gas diffusion layer. It is larger than the fiber diameter of 4C conductive fiber. Further, the length of the carbon fiber of the cathode gas diffusion layer 4D is longer than the length of the conductive fiber of the anode gas diffusion layer 4C.

  In this way, the cathode gas diffusion layer 4D having conductive fibers having a larger fiber diameter and a longer fiber length than the anode gas diffusion layer 4C has a coarser structure than the anode gas diffusion layer 4C. Therefore, the air permeability is high. Furthermore, compared with 4C in the anode gas diffusion layer, the cathode gas diffusion layer 4D has a higher contact area ratio with the hydrophobic resin interposed between the carbon fibers, so that the electric resistance is reduced.

  On the other hand, the anode gas diffusion layer 4C having carbon fibers with a smaller fiber diameter and shorter fiber length than the cathode gas diffusion layer 4D has a dense structure as compared with the cathode gas diffusion layer 4D. Air permeability is low. Thereby, the water retention of the anode gas diffusion layer 4C which is easy to dry can be increased.

  As a result, it is possible to suppress the occurrence of cathode-side flatting and increase the water retention on the anode side to improve the proton conductivity, thereby improving the power generation efficiency of the fuel cell.

  As mentioned above, although embodiment of this invention has been explained in full detail using drawing, a concrete structure is not limited to this embodiment, Even if there is a design change in the range which does not deviate from the gist of the present invention. These are included in the present invention.

  For example, in the third embodiment, the gas diffusion layer is composed of a microporous layer. However, as in the first and second embodiments, a substrate layer may be further provided as a surface layer of the gas diffusion layer.

It is a figure for demonstrating the membrane electrode assembly which concerns on 1st embodiment, (a) is a whole block diagram of a membrane electrode assembly, (b) is the B section enlarged view of (a), (C) is the figure which showed carbon fiber. The principal part enlarged view of the membrane electrode assembly which concerns on 2nd embodiment of this invention. The schematic diagram of the membrane electrode assembly which concerns on 3rd embodiment of this invention. The schematic diagram explaining an example of the conventional solid polymer electrolyte type fuel cell (single cell).

Explanation of symbols

  2: electrolyte membrane, 3: catalyst layer, 3A: anode catalyst layer, 3B: cathode catalyst layer, 4A, 4B: gas diffusion layer, 4C: anode gas diffusion layer, 4D: cathode gas diffusion layer, 41: first gas Diffusion layer, 42: second gas diffusion layer, 43: substrate layer, 41a, 42a: carbon fiber, 44: microporous layer

Claims (4)

A membrane electrode assembly in which a catalyst layer is laminated on both sides of an electrolyte membrane, and a gas diffusion layer containing a hydrophobic resin and conductive fibers is further laminated on both sides of the catalyst layer,
The gas diffusion layer has a first gas diffusion layer laminated on the surface of the catalyst layer, and a second gas diffusion layer laminated on the surface of the first gas diffusion layer,
The fiber diameter of the conductive fiber of the second gas diffusion layer is larger than the fiber diameter of the conductive fiber of the first gas diffusion layer,
The length of the said conductive fiber of said 2nd gas diffusion layer is longer than the length of the said conductive fiber of said 1st gas diffusion layer, The membrane electrode assembly characterized by the above-mentioned. A membrane electrode assembly in which a catalyst layer is laminated on both sides of an electrolyte membrane, and a gas diffusion layer containing a hydrophobic resin and conductive fibers is further laminated on both sides of the catalyst layer,
The gas diffusion layer is characterized in that the fiber diameter of the conductive fiber increases and the fiber length of the conductive fiber increases as it proceeds from the surface of the catalyst layer in the layer thickness direction. Membrane electrode assembly.   The membrane electrode assembly according to claim 1, wherein the gas diffusion layer further includes a porous base material layer having conductivity as a surface layer. An anode catalyst layer is laminated on one surface of the electrolyte membrane, a cathode catalyst layer is laminated on the other surface, and an anode gas diffusion layer containing a hydrophobic resin and conductive fibers on the surfaces of the anode catalyst layer and the cathode catalyst layer. And a membrane electrode assembly in which a cathode gas diffusion layer is further laminated,
The fiber diameter of the conductive fiber of the cathode gas diffusion layer is larger than the fiber diameter of the conductive fiber of the anode gas diffusion layer,
The length of the conductive fiber of the cathode gas diffusion layer is longer than the length of the conductive fiber of the anode gas diffusion layer.

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