JP2008305755A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell with gas pressure loss reduced and a drainage property improved. <P>SOLUTION: The fuel cell, made by laminating cells structured of a junction body 40 having an electrolyte film equipped with a fuel electrode and an air electrode, and a pair of separators 10 pinching the junction body 40, is provided with a porous flow channel layer arranged between either of the gas diffusion layers 42 each provided at the fuel electrode and the air electrode and the separators 10. The porous flow channel layer consists of a gas diffusion member 20 formed of a metal plate with a plurality of through-holes, and a part of the face of the gas diffusion layer 42 in contact with the gas diffusion member 20 is filled in a concave part 22 of the gas diffusion member 20 existing at an interface of the gas diffusion member 20 and the gas diffusion layer 42. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an improvement of a gas diffusion member, in particular, a fuel cell for facilitating removal of generated water generated during power generation and maintaining and stabilizing the power generation efficiency of the fuel cell.

  For example, in a polymer electrolyte fuel cell, as shown in FIG. 6, a joined body (MEA: Membrane Electrode) in which an electrolyte membrane 62 made of a solid polymer membrane is sandwiched between two electrodes, a fuel electrode 60 and an air electrode 64. Assembly) is a minimum unit of a cell sandwiched between two separators 70, and usually a plurality of cells are stacked to form a fuel cell stack (FC stack) to obtain a high voltage.

In general, the power generation mechanism of the polymer electrolyte fuel cell is such that a fuel gas (anode-side electrode) 60 is a fuel gas, for example, a hydrogen-containing gas, while an air electrode (cathode-side electrode) 64 is an oxidant gas, for example, Is supplied with a gas or air containing oxygen (O ₂ ). The hydrogen-containing gas is supplied to the fuel electrode 60 through the fuel gas flow path, and is decomposed into electrons and hydrogen ions (H ⁺ ) by the action of the electrode catalyst. The electrons move from the fuel electrode 60 to the air electrode 64 through an external circuit, and produce an electric current. On the other hand, hydrogen ions (H ⁺ ) pass through the electrolyte membrane 62 to reach the air electrode 64, and combine with oxygen and electrons that have passed through the external circuit to become reaction water (H ₂ O). Heat generated simultaneously with the bonding reaction of hydrogen (H ₂ ), oxygen (O ₂ ), and electrons is recovered by cooling water. Further, water generated on the cathode side with the air electrode 54 (hereinafter referred to as “generated water”) is discharged from the cathode side.

  As shown in FIG. 6, during the operation of the fuel cell (during power generation), the generated water is generated at a portion in contact with the electrolyte membrane 62 on the surface of the air electrode 64. When the generated water cannot be efficiently discharged out of the fuel cell system along with the operation of the fuel cell, the generated water stays in the space between the diffusion layer of the air electrode 64 and the separator 70. As a result, The diffusion of the reaction gas, particularly the oxidant gas, is hindered and a so-called flatting phenomenon occurs. In such a case, the power generation efficiency of the fuel cell tended to decrease.

  On the other hand, conventionally, the gas flowability in the gas flow path between the separator and the fuel electrode in the fuel cell and the fuel gas and the oxidant gas between the separator and the air electrode has been devised.

  For example, in Patent Document 1, a gas flow path for supplying fuel gas and oxidant gas is formed between a separator body and an electrode layer constituting an electrode structure of a fuel cell, and power is generated by the electrode structure. A fuel cell separator is proposed in which a gas flow path forming member that collects the generated electricity is disposed in a recess in the separator body, and the gas flow path forming member forms streak irregularities on a single plate of expanded metal. Has been.

  Patent Document 2 proposes manufacturing a gas flow path forming member by alternately stacking expanded metals having different opening ratios.

JP 2005-310633 A Special table 2007-26812 gazette

  For example, as shown in FIG. 5, a gas diffusion member 20 made of lath cut metal or expanded metal is disposed between at least one of the gas diffusion layers 52 provided with the fuel electrode and the air electrode and the flat separator 10. In the conventional fuel cell in which the gas diffusion member 20 functions as a porous body flow path, a small gap 24 is formed at the interface between the gas diffusion member 20 and the gas diffusion layer 52. For example, in the low current region where the gas flow rate is low when the fuel cell is low in load, the gas dynamic pressure is small. There is a possibility that the small gap 24 at the interface with the diffusion layer 52 and the concave portion 22 of the gas diffusion member 20 existing at the interface between the gas diffusion member 20 and the gas diffusion layer 52 may remain and be difficult to drain. As a result, a pressure loss (pressure loss) difference occurs, and the gas flows between the gas diffusion member 20 and the flat separator 10 rather than between the gas diffusion member 20 and the gas diffusion layer 52 (in the arrow of FIG. 5). Therefore, gas diffusion is not performed on the joined body (MEA) 40, and power generation may be hindered.

  The present invention has been made in view of the above problems, and provides a fuel cell that discharges generated water from the fuel cell well and maintains and stabilizes the operation efficiency.

  In order to achieve the above object, the fuel cell of the present invention has the following characteristics.

  (1) A fuel cell in which a cell composed of a joined body having a fuel electrode and an air electrode on an electrolyte membrane and a pair of separators sandwiching the joined body is laminated, wherein the fuel electrode and the air electrode Each having a porous channel layer disposed between at least one of the gas diffusion layers provided and the separator, and the porous channel layer is formed of a metal plate having a plurality of through holes. A part of the surface of the gas diffusion layer in contact with the gas diffusion member is filled in the recess of the gas diffusion member existing at the interface between the gas diffusion member and the gas diffusion layer. It is a fuel cell.

  Since a part of the surface of the gas diffusion layer in contact with the gas diffusion member is filled in the recess of the gas diffusion member existing at the interface between the gas diffusion member and the gas diffusion layer, the gas diffusion layer and the gas diffusion member There are no gaps or little gaps at the interface. As a result, at the interface between the gas diffusion layer and the gas diffusion member, the retention of generated water exposed from the gas diffusion layer on the cathode side during power generation of the fuel cell is suppressed. Even in a low current region with a small flow rate, gas diffuses between the gas diffusion member and the gas diffusion layer, and power generation efficiency is maintained.

  (2) The fuel cell according to (1), wherein the separator is a flat separator having a smooth surface on the joined body side surface.

  (3) In the fuel cell according to the above (1) or (2), the gas diffusion member is a fuel cell that is a lath cut metal or an expanded metal.

  By using the gas diffusion member as a lath cut metal or an expanded metal, the through holes can be formed in a mesh shape and can also function as a current collector.

  (4) In the fuel cell according to any one of (1) to (3), the gas diffusion layer has elasticity that can be filled in the recess according to the size of the recess of the gas diffusion member. It is a fuel cell.

  A part of the gas diffusion layer can be embedded in the recess by appropriately selecting the elastic characteristics of the gas diffusion layer according to the size of the recess of the gas diffusion member. Thereby, gap formation at the interface between the gas diffusion layer and the gas diffusion member can be suppressed.

  (5) In the fuel cell according to any one of (1) to (3), the depth of the recess of the gas diffusion member is shorter than the opening diameter of the recess.

  By shallowing the concave portion of the gas diffusion member, a part of the gas diffusion layer can be easily embedded in the shallow concave portion, whereby the formation of a gap at the interface between the gas diffusion layer and the gas diffusion member can be suppressed.

  According to the present invention, the generated water generated during power generation is efficiently discharged out of the fuel cell system, so that a flatting phenomenon hardly occurs and the output characteristics of the fuel cell can be maintained and stabilized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an example of a separator 10 used in the fuel cell of the present embodiment and a gas diffusion member 20 disposed in a power generation region portion of the separator. As shown in FIG. 1, communication holes are provided at both ends of the separator 10. For example, when the separator shown in FIG. 1 is on the cathode side, cooling water is supplied to one end side of the separator 10. The water supply communication hole 12a, the fuel gas supply communication hole 14a for supplying fuel gas, and the oxidizing gas discharge communication hole 16b for discharging the oxidant gas are provided. On the other end side of the separator 10, cooling water is discharged. The cooling water discharge communication hole 12b, the fuel gas discharge communication hole 14b for discharging the fuel gas, and the oxidizing gas supply communication hole 16a for supplying the oxidant gas are provided. Therefore, on the cathode side shown in FIG. 1, the diffusion direction of the oxidant gas in the gas diffusion member 20 is a white arrow direction.

  Moreover, the gas diffusion member 20 shown in FIG. 1 is formed of a metal plate having a number of through holes, and for example, any form of a lath cut metal or an expanded metal can be used.

  Here, in the present embodiment, “lass-cut metal” refers to a plate-like thin metal plate that is processed in a zigzag manner in order and pushes and bends the processed cuts to form a small mesh-shaped through-hole. A hole is formed. In addition, “expanded metal” is a thin metal plate that is formed in a zigzag pattern on a flat thin metal plate, and a small through-hole with a mesh shape is formed by pressing and bending the processed cut. It is processed into a substantially flat plate shape. Since the expanded metal is formed in a substantially flat plate shape, for example, it is not necessary to provide a process for removing unnecessary bending or unevenness in the product after final forming, and the manufacturing cost can be reduced.

  In addition, when the gas diffusion member 20 also serves as a current collector, any metal material can be used as long as it is used for the metal separator. Therefore, a material having a certain degree of rigidity that enables a predetermined gas flow is preferable. For example, titanium and stainless steel are preferable.

  An example of the structure of the gas diffusion member 20 is shown in FIG. The gas diffusion member 20 shown in FIG. 2 has an irregular shape, but is not limited to this, and for example, a hexagonal shape may be used.

<Porous channel layer>
FIG. 3 shows a fuel cell in which a cell composed of a joined body 40 having a fuel electrode and an air electrode on an electrolyte membrane and a pair of separators 10 sandwiching the joined body 40 is laminated. An example of the configuration of one side of the cathode or anode side of a fuel cell having a porous channel layer disposed between at least one of the gas diffusion layers 42 provided for each air electrode and the separator 10 is shown. Yes. In addition, as shown in FIG. 3, the gas diffusion member 20 is disposed between the gas diffusion layer 42 and the separator 10 and used as a porous body flow path layer. 3 is a side view from the same direction as the A viewing direction shown in FIG.

  In the present embodiment, as shown in FIG. 3, the surface of the gas diffusion layer 42 in contact with the gas diffusion member 20 in the recess 22 of the gas diffusion member 20 existing at the interface between the gas diffusion member 20 and the gas diffusion layer 42. Part of it is filled.

  Therefore, no gap is formed at the interface between the gas diffusion layer 42 and the gas diffusion member 20 or there is almost no gap. As a result, at the interface between the gas diffusion layer 42 and the gas diffusion member 20, the retention of the generated water exposed from the gas diffusion layer on the cathode side particularly during power generation of the fuel cell is suppressed, and the generated water is quickly discharged. . Therefore, for example, even in a low current region where the gas flow rate is low when the fuel cell is under a low load, gas is stably diffused between the gas diffusion member 20 and the gas diffusion layer 42, and power generation efficiency is maintained. .

  Here, the gas diffusion layer 42 has elasticity capable of filling the recess 22 according to the size of the recess 22 of the gas diffusion member 20. As a result, the amount of the part of the gas diffusion layer 42 embedded can be equal to or greater than the capacity of the recess 22 (that is, the amount of the part of the gas diffusion layer 42 embedded ≧ the capacity of the recess 22). As a result, a gap at the interface between the gas diffusion layer 42 and the gas diffusion member 20 can be suppressed.

For example, when the gas diffusion member 20 shown in FIG. 3 is made of a lath cut metal or an expanded metal, when the convex width pitch of the lath cut metal or the expanded metal is 0.4 mm, the Young's modulus of the material of the gas diffusion layer 42 is 0.2 MPa. When the gas diffusion layer 42 is partially embedded to a depth of 100 μm and the material of the gas diffusion layer 42 has a Young's modulus of 6.2 MPa, the gas diffusion layer 42 is partially embedded to a depth of 30 μm and the material of the gas diffusion layer 42 is Young. When the rate is 8.7 MPa, the depth at which part of the gas diffusion layer 42 is embedded is 20 μm. Therefore, when the depth h ₁ of the recess 22 of the gas diffusion member 20 is 30 μm, the Young's modulus of the material of the gas diffusion layer 42 is preferably set to 6.2 MPa or less.

  Here, metal separators have been used as fuel cell separators from the viewpoint of durability. However, it is essential for this metal separator to have both corrosion resistance and chargeability. Titanium separators are listed as candidates for achieving both the above corrosion resistance and chargeability. However, since titanium has high rigidity and is not easy to press like stainless steel, the flow path needs to be formed by a method other than pressing. Therefore, a titanium separator is used as a flat separator, and a configuration in which a flow path is formed by a porous body between the flat separator and the gas diffusion layer is devised, and the above-described gas diffusion member 20 is used as the porous body flow path. The configuration used as the pseudo porous channel layer will be described below. Here, the “flat separator” refers to a separator having a smooth surface on the side of the joined body in which the electrolyte membrane composed of the above-described solid polymer membrane is sandwiched between two electrodes, a fuel electrode and an air electrode.

  In the present embodiment, a flat separator has been described as an example of the separator 10. However, the present invention is not limited to this, and for example, a conventional stainless steel separator with a gas supply groove may be used as the separator.

  Moreover, since the porous body flow path layer mentioned above supplies gas to the gas diffusion layer 42 and the electrode of the joined body 40, the gas distribution performance in the direction along the separator surface is required. Therefore, since it is necessary to reduce the pressure loss, both the pore diameter and the porosity need to be larger than those of the gas diffusion layer 42. Therefore, it is preferable that the through holes of the gas diffusion member 20 used for the porous body flow path layer are formed larger than the pores of the carbon-based porous body used for the normal diffusion layer.

  The above-described configuration shown in FIG. 3 is preferably provided at least on the cathode side of the fuel cell in consideration of the generation of generated water, but is not limited to this, and the anode of the fuel cell is not limited thereto. It may also be provided on the side.

In another embodiment, a gas diffusion member 30 shown in FIG. 4 is used instead of the gas diffusion member 20 shown in FIG. As shown in FIG. 4, the depth length h ₂ of the recess 32 of the gas diffusion member 30 is shorter than the opening diameter of the recess 22.

  Accordingly, by making the recess 32 of the gas diffusion member 30 shallow, a part of the gas diffusion layer 52 is easily embedded in the shallow recess 32. Thereby, formation of a gap at the interface between the gas diffusion layer 52 and the gas diffusion member 30 can be suppressed.

  For example, when the gas diffusion member 30 is made of a lath cut metal or an expanded metal, the recess can be made shallow by reducing the cut amount of the lath cut when forming the lath cut metal or the expanded metal.

Further, for example, the depth length h ₂ of the recess 32 of the gas diffusion member 30 shown in FIG. 4 is shorter than the depth length h ₁ of the recess 22 of the gas diffusion member 20 shown in FIG. 3, and the recess 32 is shallow. . Therefore, for example, when the convex width pitch of the lath cut metal or the expanded metal is 0.4 mm, when the Young's modulus of the material of the gas diffusion layer is 6.2 MPa, the depth in which the gas diffusion layer is partially embedded is 30 μm, When the Young's modulus of the material is 8.7 MPa, the depth in which the gas diffusion layer is partially embedded is 20 μm. For example, when the Young's modulus of the material of the gas diffusion layer 52 is 8.7 MPa or more, the gas diffusion layer 52 It is preferable that the depth h ₂ of the recess 32 of the gas diffusion member 30 is appropriately selected within a range of 20 μm or less according to the Young's modulus of the material.

  The configuration shown in FIG. 4 is preferably provided at least on the cathode side of the cell of the fuel cell in consideration of the generation of generated water. However, the configuration is not limited to this, and the cell of the fuel cell is not limited thereto. It may also be provided on the anode side.

  The fuel cell of the present invention is effective for any use as long as it uses a fuel cell, but can be used for a fuel cell for vehicles in particular.

It is a top view explaining an example of composition of a cathode side separator and a porous channel layer in a cell of a fuel cell of the present invention. It is a perspective view which shows an example of the structure of the gas diffusion member used for the fuel cell of this invention. It is a side view explaining an example of the structure of the one side by the side of the cathode or the anode in the cell of the fuel cell of this Embodiment. It is a side view explaining an example of the structure of the one side of the other cathode or anode side in the cell of the fuel cell of this Embodiment. It is a side view explaining an example of the structure by the side of the cathode in the cell of the conventional fuel cell. It is a figure explaining the structure of the cell of a fuel cell, and the mechanism at the time of electric power generation.

Explanation of symbols

  10 separator, 18 generated water, 20, 30 gas diffusion member, 22, 32 recess, 24 gap, 40 joined body, 42, 52 gas diffusion layer.

Claims (5)

A fuel cell in which a cell composed of a joined body having a fuel electrode and an air electrode on an electrolyte membrane, and a pair of separators sandwiching the joined body,
A porous flow path layer disposed between at least one of the gas diffusion layers provided in each of the fuel electrode and the air electrode and the separator;
The porous channel layer is composed of a gas diffusion member formed by a metal plate having a plurality of through holes,
A part of the surface of the gas diffusion layer in contact with the gas diffusion member is filled in a recess of the gas diffusion member existing at the interface between the gas diffusion member and the gas diffusion layer. . The fuel cell according to claim 1, wherein
The fuel cell, wherein the separator is a flat separator having a smooth surface on the joined body side. The fuel cell according to claim 1 or 2,
The fuel cell according to claim 1, wherein the gas diffusion member is a lath cut metal or an expanded metal. The fuel cell according to any one of claims 1 to 3, wherein
The fuel cell according to claim 1, wherein the gas diffusion layer has elasticity capable of filling the recess according to a size of the recess of the gas diffusion member. The fuel cell according to any one of claims 1 to 3, wherein
The depth of the recessed part of the said gas diffusion member is shorter than the opening diameter of a recessed part, The fuel cell characterized by the above-mentioned.

Images