JP2006310104A - Diffusion layer for fuel cell, and the fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffusion layer for a fuel cell and the fuel cell with high degrees of freedom in a gas passage design, small contact resistance between the diffusion layer and the catalyst layer, and capable of achieving high output and a compact size. <P>SOLUTION: The diffusion layers 12b, 13b are provided with reinforcing materials 14, 15 for increasing the rigidity with respect to bending. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a diffusion layer for a fuel cell and a fuel cell using the same.

  Conventionally, a polymer electrolyte fuel cell using a polymer electrolyte membrane is known (for example, Patent Document 1).

JP 2004-152517 A

In the polymer electrolyte fuel cell, as shown in FIG. 6, a polymer electrolyte membrane 91 is sandwiched between catalyst layers 92a and 92b, and the catalyst layers 92a and 92b are sandwiched between diffusion layers 93a and 93b having gas permeability. Yes. Further, the diffusion layers 93a and 93b are sandwiched between separators 95a and 95b serving as current collecting electrodes. The separators 95a and 95b have continuous U-shaped irregularities, and these irregularities form innumerable gas passages 94a and 94b between the diffusion layers 93a and 93b and the separators 95a and 95b.

  In this polymer electrolyte fuel cell, hydrogen gas supplied to the gas passage 94a on the anode side passes through the diffusion layer 93a having gas permeability and is supplied to the catalyst layer 92a. Then, the hydrogen that has reached the catalyst layer 92a is oxidized by an electrochemical reaction and separated into protons and electrons. The electrons thus generated in the anode-side catalyst layer 92a flow through the diffusion layer 93a and the separator 94a to the external circuit.

  On the other hand, the air supplied to the cathode-side gas passage 94b is supplied to the catalyst layer 92b through the diffusion layer 93b having gas permeability. Then, the electrons generated on the anode side are supplied to the cathode catalyst layer 92b through the external circuit, the separator 94b and the cathode diffusion layer 93b, and reduce oxygen which has reached the catalyst layer 92b.

  Thus, the diffusion layers 93a and 93b in the polymer electrolyte fuel cell have a function as a current collecting electrode.

  In order to increase the output of the polymer electrolyte fuel cell, it is desirable to reduce the contact resistance between the diffusion layer and the catalyst layer and the resistance of the diffusion layer itself as much as possible to reduce the internal resistance of the cell. For this purpose, it is necessary to press the diffusion layer against the catalyst layer with as even pressure as possible, so that there is no portion where the contact between the diffusion layer and the catalyst layer becomes poor, and the fibers inside the diffusion layer need to adhere to each other. There is. As a method for that, it is conceivable to increase the contact area between the separator and the diffusion layer. However, this method increases the design limitation on the gas passage. In addition, since the portion where the separator and the diffusion layer come into contact is a dead space that does not contribute to the gas supply, the gas passage provided between the separator and the diffusion layer is narrowed, making it difficult to increase the output and size of the fuel cell. It becomes.

  The present invention has been made in view of the above-described conventional situation, and has a high degree of freedom in gas passage design, a low contact resistance between a diffusion layer and a catalyst layer, and a fuel cell for which high output and miniaturization are possible. The problem to be solved is to provide a diffusion layer and a fuel cell.

  The diffusion layer for a fuel cell according to the present invention includes a base material having gas permeability, and the base material is provided with a reinforcing material for increasing rigidity against bending.

  In the diffusion layer for a fuel cell according to the present invention, a reinforcing material for increasing rigidity is provided on a base material having gas permeability. Therefore, when the diffusion layer is pressed against the catalyst layer, the catalyst is formed by the rigidity of the diffusion layer. Pressure can be applied evenly to the layer. For this reason, when the separator is pressed against the diffusion layer side and the diffusion layer is brought into contact with the catalyst layer, even if the contact area between the separator and the diffusion layer is small, the entire area of the diffusion layer uniformly applies pressure to the catalyst layer. Thus, the contact resistance between the diffusion layer and the catalyst layer and the resistance of the diffusion layer itself can be reduced. For this reason, it becomes possible to allocate a wide area to the gas passage between the separator and the diffusion layer, and the degree of freedom in designing the gas passage is great, and the output of the fuel cell can be increased and the size can be reduced.

The shape of the reinforcing material can be arbitrarily selected as long as the rigidity is enhanced while the gas permeability is secured. In the embodiments described later, a grid-like reinforcing material is used, but a net made of fibers having a predetermined bending rigidity can also be used. Furthermore, fibers having high bending elasticity can be present (without forming a net) in the diffusion layer. Such fibers are preferably arranged in two intersecting directions, but the fibers may be arranged only in a single direction.
The reinforcing material is provided on the entire surface of the diffusion layer, but the installation position is particularly preferably on the separator side, and may be provided on the surface of the diffusion layer. It is also possible for a plurality of reinforcing materials to be present inside and on the surface of the diffusion layer.
The material for forming the reinforcing material is not particularly limited as long as it is a chemically stable material inside the fuel cell, and a corrosion-resistant metal or carbon can be selected. Moreover, it is preferable that the reinforcing material has conductivity.

  As described above, when the diffusion layer of the present invention is used in a fuel cell, the contact resistance between the diffusion layer and the catalyst layer is small, and the fuel cell can be increased in output and size.

  In the fuel cell of the present invention, the cathode-side separator can be a gas-permeable conductor. In this case, gas can be supplied even at the portion where the separator and the diffusion layer are in contact with each other, so that the output of the fuel cell can be further increased and the size can be reduced. Moreover, since the gas can be moved between the gas passages formed by the separator, the pressure loss is small and the gas can be supplied uniformly. Furthermore, even if the separator is made of a gas-permeable conductor, the diffusion layer is provided with a reinforcing material even if the mechanical strength of the separator is reduced, so the contact area between the separator and the diffusion layer is increased. Even without this, the contact resistance between the diffusion layer and the catalyst layer and the resistance of the diffusion layer itself can be reduced.

  Embodiments 1 and 2 embodying the present invention will be described below with reference to the drawings.

Example 1
The fuel cell of Example 1 uses a plurality of cells 1 shown in FIG. Each cell 1 includes a membrane electrode assembly (MEA) 10, an anode side separator 20, and a cathode side separator 21.

  The MEA 10 includes an electrolyte membrane 11 made of Nafion (registered trademark, Nafion (manufactured by Dupon)), an anode electrode 12 integrally joined to one surface of the electrolyte membrane 11, and an integrally joined to the other surface of the electrolyte membrane 11. Cathode electrode 13.

  The anode electrode 12 includes an anode catalyst layer 12a provided on the electrolyte membrane 11 side, and an anode diffusion layer 12b joined to the non-electrolyte membrane side of the anode catalyst layer 12a and diffusing hydrogen into the anode catalyst layer 12a. The anode diffusion layer 12b includes a carbon base material 14a mainly composed of a carbon fiber knitted fabric, an adhesive layer 14c attached to both surfaces of the carbon base material 14a, and a stainless steel lattice attached to the outer adhesive layer 14c. The reinforcing material 14b.

  The cathode 13 includes a cathode catalyst layer 13a provided on the electrolyte membrane 11 side, and a cathode diffusion layer 13b that is bonded to the non-electrolyte membrane side of the cathode catalyst layer 13a and diffuses air into the cathode catalyst layer 13a. Similarly to the anode diffusion layer 12b, the cathode diffusion layer 13b is attached to the carbon base material 15a made of a carbon fiber knitted fabric, the adhesive layer 15c attached to both surfaces of the carbon base material 15a, and the outer adhesive layer 15c. And a stainless steel grid-like reinforcing material 15b.

The anode separator 20 is U-shaped in cross section and has a protrusion 20b protruding toward the anode diffusion layer 12b. The convex portion 20b is pressed against the anode diffusion layer 12b by a pressing jig (not shown), whereby the anode-side separator 20 is joined together with the anode diffusion layer 12b to form a hydrogen chamber 20a for supplying hydrogen. Yes. In the anode separator, the area of the protrusion 20b pressed against the anode diffusion layer 12b can be made larger than the opening area of the hydrogen chamber 20a.
Further, the cathode-side separator 21 has the same cross-sectional shape as the anode-side separator 20 and has a convex portion 21b that protrudes toward the cathode diffusion layer 13b. The convex portion 21b is pressed against the cathode diffusion layer 13b side by a pressing jig (not shown), whereby the cathode side separator 21 is joined integrally with the cathode diffusion layer 13b, and an air chamber 21a for supplying air is formed. Yes.

  By stacking a plurality of the cells 1 described above, a fuel cell stack is formed. A hydrogen cylinder communicating with the hydrogen chamber 20a of each cell 1 via a valve (not shown) and a blower communicating with the air chamber 21a of each cell chamber 1 are connected to the stack.

  This fuel cell is characterized by the diffusion layer 12b and the diffusion layer 13b of the MEA 10. These diffusion layer 12b and diffusion layer 13b can be manufactured by the following manufacturing method.

  First, a stainless steel thin plate is punched into a lattice shape by a press, and further coated with a noble metal, an inorganic compound, a conductive polymer, or the like in order to maintain corrosion resistance and conductivity, to obtain a reinforcing material 14b shown in FIG. In addition, by cutting the carbon fiber knitted fabric into the same size as the reinforcing material 14b, applying a mixture of carbon black powder and PTFE powder, pressing the reinforcing material 14b on one side and integrating them by a hot press method, The diffusion layer 12b shown in FIGS. 3 and 4 is obtained. The diffusion layer 13b can also be obtained by the same method. In addition, as the reinforcing material 14a, a metal net subjected to surface treatment for imparting corrosion resistance and conductivity to the surface, or a carbon fiber having a diameter larger than the fiber diameter of the carbon fiber knitted fabric constituting the carbon base material 15a. The net produced by may be used. Stainless steel, titanium, a titanium alloy, a nickel alloy, a copper alloy, or the like is used as a metal material in the case of using a metal reinforcing material.

  In the fuel cell of Example 1, the convex portion 20b of the anode-side separator 20 shown in FIG. 1 presses the anode diffusion layer 12b, and the anode diffusion layer 12b presses the anode catalyst layer 12a to make electrical contact. Here, since the reinforcing material 14b is inserted on the anode side separator 20 side of the anode diffusion layer 12b, the entire area of the anode diffusion layer 12b presses the anode catalyst layer 12a almost uniformly by its rigidity, and the anode diffusion layer The contact resistance between 12b and the anode catalyst layer 12a and the electrical contact inside the anode diffusion layer 12b are sufficient. For this reason, the contact area of the convex part 20b and the anode diffusion layer 12b can be made small, and a wide area can be allocated to the hydrogen chamber 20a.

  For the same reason, also on the cathode electrode 13 side, the cathode diffusion layer 13b evenly presses the cathode catalyst layer 13a evenly, and the contact resistance between the anode diffusion layer 13b and the anode catalyst layer 13a decreases. For this reason, the contact area of the convex part 21b and the cathode diffusion layer 13b can be made small, and a wide area can be allocated to the air chamber 21a.

Therefore, the fuel cell of Example 1 has a high degree of freedom in designing the gas passage, and the contact resistance between the diffusion layer and the catalyst layer is small, so that the output of the fuel cell can be increased and the size can be reduced.

(Example 2)
The fuel cell of Example 2 uses a plurality of cells 30 shown in FIG. Each cell 30 includes an MEA 40, an anode side separator 50, and a cathode side separator 51. The configurations of the MEA 40 and the anode-side separator 50 are the same as those of the MEA 10 and the anode-side separator 20 of Embodiment 1 shown in FIG. 1, and the same reference numerals are given to the configurations of the respective parts, and detailed description thereof is omitted.

  The cathode-side separator 51 is made of a stainless steel wire mesh, and the shape thereof is the same as that of the anode-side separator 50. The cathode-side separator 51 has a convex portion 51b that protrudes toward the cathode diffusion layer 13b on one side. A stainless steel partition 52 is joined to the other surface of the cathode separator 51. The cathode-side separator 51 is joined integrally with the cathode diffusion layer 13b, and an air chamber 51a for supplying air is formed.

In the fuel cell configured as described above, since the cathode separator 51 is made of a wire mesh through which air can pass, air can move between the adjacent air chambers 51a, and the diffusion of air to the cathode diffusion layer 13b can be achieved. It will be equal. Further, since air can be diffused from the convex portion 51b to the cathode diffusion layer 13b, there is no dead space for air supply, and the fuel cell can be further increased in output and size. Further, since the reinforcing material 15b is inserted into the cathode diffusion layer 13b, the contact resistance between the cathode diffusion layer 13b and the catalyst layer 13a can be achieved without increasing the contact area between the cathode separator 51 and the diffusion layer 13b. In addition, the resistance of the cathode diffusion layer 13b itself can be reduced.
In addition, when the area ratio of the convex part 51b of the cathode side separator 51 is increased, the contact resistance between the cathode diffusion layer and the catalyst layer and the resistance of the cathode diffusion layer itself can be reduced without the reinforcing material 15b. it can.

  On the other hand, since the anode-side separator 50 and the anode electrode 12 have the same structure as that of the first embodiment, the same effects can be obtained.

  The present invention is applicable to a polymer electrolyte fuel cell.

3 is a schematic cross-sectional view of a cell according to Example 1. FIG. It is a top view of a reinforcing material. It is a top view of a diffusion layer. It is sectional drawing of a diffusion layer. 6 is a schematic cross-sectional view of a cell according to Example 2. FIG. It is a schematic cross section of the cell concerning the conventional fuel cell.

Explanation of symbols

14a, 15a ... base material (14a ... carbon base material, 15a ... carbon base material)
14b, 15b ... Reinforcing material 12b, 13b ... Diffusion layer (12b ... Cathode diffusion layer, 13b ... Anode diffusion layer)
20, 21, 51 ... separator

Claims (4)

  A diffusion layer for a fuel cell, characterized by having a gas permeability and a reinforcing material for increasing rigidity against bending.   The diffusion layer according to claim 1, wherein the reinforcing material is made of metal or carbon.   A fuel cell comprising the diffusion layer according to claim 1.   6. The fuel cell according to claim 5, wherein the cathode side separator is made of a conductor that allows gas permeation.

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