JP2005294101A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell applying no surface pressure to an MEA, having high durability, and capable of easily and inexpensively manufacturing it. <P>SOLUTION: The fuel cell has a separator in which a second member 20 having a prescribed shape is joined to at least one side of a first member 10 formed in a plane shape, and a passage is formed on one side of the first member 10, the first member 10 is made of metal and the second member 20 is made of carbon, a carbon water-repellent film 30 is stuck on the surface on the passage side of the separator, and a catalyst layer 40 and an electrolyte layer 50 are formed on the carbon water-repellent film 30. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell, and more particularly to a fuel cell that has durability, is easy to manufacture, and is inexpensive to manufacture.

  A unit cell of a fuel cell is composed of MEA (membrane / electrode assembly) which is thermocompression bonded with a catalyst layer on both sides of an electrolyte and a diffusion layer on both sides thereof. The theoretical electromotive force of the unit cell is 1.23V. However, such a low electromotive force is not sufficient as a power source for automobiles, etc., and therefore, a module is usually formed by repeatedly stacking unit cells and separators alternately and in series. It is a module laminate. A current collecting plate is disposed at both ends, and an insulating plate having electrical insulation is disposed outside the current collecting plate. Then, the required voltage and power can be obtained by forming a fuel cell having a structure in which the laminate is clamped with a clamping plate, clamped with a clamping plate, a disc spring, and a clamping nut, and held with pressure. Have gained.

  The reason why the laminate is held while being pressed is as follows. That is, the MEA and the separator are configured separately from each other in the conventional fuel cell configuration, and an interface exists between them. Therefore, electricity generated in the fuel cell does not flow unless sufficient surface pressure is applied to the interface from both sides.

With respect to the technical field of the layer configuration of such fuel cells, Patent Document 1 describes an electrolyte, a catalyst layer mainly composed of carbon particles supporting a catalyst, carbon particles and a water-repellent resin, at least on the side opposite to the catalyst layer. And a diffusion layer formed by adhering short carbon fibers in an entangled state with the carbon particles on the surface of the fuel cell assembly. According to this fuel cell assembly, it is said that it is possible to prevent gas diffusivity experienced when using carbon cloth, carbon paper, or the like as an electrode, and deterioration of excess water discharge.
JP-A-8-7897

  However, in the method disclosed in Patent Document 1, the laminate does not generate electric power unless a surface pressure is applied, but this surface pressure reaches the MEA, so that there is a problem that the durability of the electrolyte is lowered.

  Accordingly, an object of the present invention is to provide a fuel cell that does not apply a surface pressure to the MEA, has high durability, can be manufactured at a low cost, and can be manufactured with ease.

  As described above, the conventional fuel cell does not generate power unless a surface pressure is applied to the laminate. However, this surface pressure has a significant adverse effect on the durability of the fuel cell electrolyte. According to the experiment by the present inventor, it has been found that, when the surface pressure is reduced by half, the performance as a fuel cell is lowered, but the durability is increased 10 times. Since the separator and MEA are composed of separate members, the surface pressure is necessary to allow electricity to flow between the two in a good state. Therefore, if this problem is solved, the performance of the fuel cell is maintained. However, the present invention has been completed by conceiving that the durability can be greatly improved.

Thus, in order to solve the above problems, the present invention takes the following means. That is,
The invention according to claim 1 is a separator formed by joining a second member having a predetermined shape to at least one surface side of a first member formed in a flat plate shape and forming a flow path on one surface side of the first member. A fuel cell comprising:

  According to a second aspect of the present invention, in the fuel cell according to the first aspect, the cross-sectional shape of the second member is substantially circular.

  According to a third aspect of the present invention, in the fuel cell according to the first or second aspect, the first member is made of metal and the second member is made of carbon.

  According to a fourth aspect of the present invention, in the fuel cell according to any one of the first to third aspects, at least a part of the second member is a porous body.

  According to a fifth aspect of the present invention, in the fuel cell according to any one of the first to third aspects, at least a part of the second member is a porous body on the cathode downstream side.

  The invention according to claim 6 is the fuel cell according to any one of claims 1 to 5, wherein a carbon water-repellent film is stretched over and joined to the flow path side surface of the separator. It is characterized by that. Here, the “carbon water-repellent film” is obtained by dispersing carbon in a fluorine resin film such as PTFE, and is available in the market.

  Furthermore, according to the invention described in claim 7, in the fuel cell described in claim 6, a catalyst layer and an electrolyte are further formed on the carbon water-repellent film.

  According to the first aspect of the present invention, since the first member and the second member are joined, electricity flows between them, and there is no need to apply a surface pressure between these members. . Moreover, since the first member and the second member are originally separate bodies, they can be made of different materials depending on the purpose.

  According to the second aspect of the present invention, it is possible to raise the temperature of one surface of the first member made of metal to a temperature equal to or higher than the melting point of the metal and to bond the carbon of the second member thereto. The joining of both members can be performed by a method such as plasma fusion joining. With such a configuration, electricity flows between them, and it is not necessary to apply a surface pressure between these members.

  According to the third aspect of the present invention, it is possible to ensure a larger flow path than a normal flow path whose cross-sectional shape is formed in a quadrilateral shape. This is one of the advantages of the present invention that the first member and the second member formed separately from the first member are joined later, so that the cross-sectional shape of the flow path can be determined freely. Such advantages cannot be obtained by a cutting method such as a conventional separator or a processing method such as pressing. In addition, when the flow paths having the same flow rate are sufficient, the thickness of the second member can be reduced. As a result, it becomes possible to reduce the thickness of the separator.

  According to the fourth aspect of the present invention, since the second member is formed of a porous material, the gas flowing in the flow path penetrates also into the surrounding second member, and on the electrode side. A sufficient amount of gas can be supplied. Moreover, the water | moisture content produced | generated by the cathode side can also be discharged | emitted in the gas in a flow path through a 2nd member.

  According to the fifth aspect of the present invention, the effect of the fourth aspect can be obtained particularly on the downstream side of the flow path of the cathode where the generated water becomes rich.

  According to the invention described in claim 6, since the water-repellent film that keeps the humidity of the electrode is joined to the separator side, it is possible to omit a diffusion layer formed of carbon paper, carbon cloth, etc. as in the prior art. . Thus, it is not necessary to apply the surface pressure necessary for flowing electricity between the diffusion layer and the separator in the conventional fuel cell. Therefore, the durability of the fuel cell which has been sacrificed by applying the surface pressure can be dramatically improved. In addition, it is not necessary to use clamping plates, clamping bolts, disc springs, and clamping nuts that have been used in conventional fuel cells to apply surface pressure, reducing the number of parts and reducing the weight of the fuel cell. There is an advantage that it can be realized. Furthermore, since the diffusion layer is not necessary, the cost of the fuel cell can be reduced and the thickness of the cell can be reduced.

  According to the invention described in claim 7, since the electrolyte, the catalyst layer, the water repellent layer, the second member, and the first member constituting the fuel cell are all joined, it is not necessary to apply a surface pressure. It is. Therefore, the durability of the fuel cell can be improved. In addition, the second member, the carbon water repellent film, the catalyst layer, and the electrolyte are joined on the first member so that they can be continuously produced, so that the production process is simple and inexpensive. It is possible to produce at a cost.

  FIG. 1A is a cross-sectional view showing a configuration of a fuel cell 100 of the present invention. For convenience of explanation, FIG. 1 (a) shows only the electrolyte and the anode on one side thereof. Needless to say, when the fuel cell is actually used as a power source of an automobile, for example, the illustrated fuel cell 100 is used as a unit cell in a stacked manner.

  The fuel cell 100 includes a linear or rod-like second member 20, 20,... Joined to the first member 10, and a carbon water-repellent film stretched over and joined to each second member 20, 20,. 30, a catalyst layer 40 bonded on the carbon water-repellent film 30, and an electrolyte 50 bonded on the catalyst layer 40. In FIG. 1A, the catalyst layer 40, the carbon water-repellent film 30, the second member 20, and the first member 10 are disposed on the right side of the electrolyte 50, but these are not shown.

  The first member 10 is a flat plate member made of a metal material. On the other hand, the second member 20 is a carbon linear or rod-shaped member. In order to join the first member 10 and the second member 20, for example, the surface of the first member 10 made of metal may be melted by plasma and the second member 20 may be brought into contact therewith. By simply bringing the second member 20 into contact with the plasma-melted first member 10, sufficient adhesive strength and good electrical conductivity can be obtained between them.

  FIG. 1B is a cross-sectional view of the fuel cell 100 of FIG. The linear or rod-like second members 20, 20,... Are appropriately arranged so as to form the serpentine flow path 60 on the first member 10. In the present invention, the flow path shape is not particularly limited to the serpentine shape shown in FIG. 1 (b), so the second member 20 to be joined on the first member 10 determines its shape as appropriate, For example, a carbon flat plate can be obtained by punching or the like.

  FIG. 2 is a view showing each aspect of the cross-sectional shape of the second member 20 joined on the first member 10. In the present invention, since the first member 10 and the second member 20 that substantially form the flow path 60 are manufactured separately from each other and then joined together, the flow path is cut from one member as in the prior art. Or compared with the case where it forms by press work, the cross-sectional shape of a 2nd member can be determined freely. FIG. 2A shows a second member 20 having a quadrangular cross-sectional shape joined on one surface of the first member 10 in the fuel cell 100 shown in FIG. 2 (b) to 2 (d) show modifications thereof.

  FIG. 2B shows the second member 21 having a circular cross-sectional shape. In this case, there is a view that the first member 10 and the second member 21 are in line contact with each other and there is a concern that the bonding strength is uneasy, but actually, the second member 21 is slightly formed on the surface of the melted first member 10. It has been experienced to obtain sufficient strength and electrical conductivity because the bottom part of the steel bites into and is welded.

  FIG. 2C shows the second member 22 having an anchor-like convex portion at the bottom having a circular cross-sectional shape. According to the second member 22, since the anchor portion firmly bites into the surface of the first member 10 and exhibits the anchor effect, it is possible to obtain sufficient strength and electrical conductivity more reliably.

  FIG. 2D shows the second member 23 whose cross-sectional shape is an inverted triangle. If the second members 21 to 23 having the cross section shown in FIGS. 2B to 2D are bonded onto the first member 10, the second member 20 having a quadrangular cross section is formed on the first member 10. It is possible to form a channel having a larger cross-sectional area than the channels formed by joining. Therefore, it is possible to increase the flow rate of the gas flowing through the flow path.

  The carbon material constituting the second member 20 may be dense, but is porous from the viewpoint of improving the gas supply to the electrode and suppressing flooding due to generated water. Is preferred. In particular, there is a great advantage that the second member 20 is made of a porous carbon material on the downstream side of the cathode flow path where the generated water is rich.

  Returning to FIG. 1A again, the description will be continued. A carbon water-repellent film 30 is stretched over the second members 20, 20,... And joined at the contact surface with the second members 20, 20,. An example of such a bonding method is an ultrasonic bonding method, but the present invention is not limited to this. The carbon water-repellent film 30 is obtained by dispersing carbon particles in a fluorine-based resin and can be obtained in the market. Examples of the fluororesin include polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA), and tetrafluoroethylene. -Ethylene copolymer resin (ETFE), chlorotrifluoroethylene resin (PCTFE), fluorovinylidene resin (PVDF) and the like. Of these, PTFE is preferable. This carbon water-repellent film 30 keeps the humidity on the electrode side composed of the electrolyte 10 and the catalyst layer 20 at almost 100%, and excessive moisture (generated water or humidified moisture is condensed from the outside side to the electrode side). It has a function to prevent intrusion of things). Furthermore, since the carbon water-repellent film 30 has carbon particles and is a good electrical conductor, it does not hinder the flow of electricity from the electrode side to the second member 20 and the first member 10.

  A catalyst layer 40 is disposed between the carbon water repellent layer 30 and the electrolyte 50. The catalyst layer 40 is formed to a thickness of about 10 μm from, for example, a fine particle (3 nm diameter) platinum catalyst supported on carbon particles (30 nm diameter) and a fluororesin having water repellency. It has pores so that gas can diffuse efficiently. Based on the so-called “decal method”, the catalyst layer 40 is obtained by forming a solution of the above material in a solvent such as alcohol on a Teflon (registered trademark) film blank and then on the electrolyte 50 or carbon repellent. By transferring onto the water film 30, it is possible to bond on either layer.

  As the electrolyte 50, a polystyrene-based cation exchange membrane (cation conductive membrane) containing a sulfonic acid group, a membrane obtained by graphitizing trifluoroethylene in a fluorocarbon matrix, and a perfluorocarbonsulfonic acid membrane can be used. As the perfluorocarbon sulfonic acid membrane, for example, “Nafion” manufactured by DuPont, USA, “Flemion” manufactured by Asahi Glass (Japan), “Aciplex” manufactured by Asahi Kasei (Japan), etc. are available in the market. The electrolyte has a proton (hydrogen ion) exchange group in the molecule, and has a specific resistance of 20 Ωcm or less when water is saturated and contained at room temperature, and functions as a proton conductive electrolyte.

  Next, with reference to FIG. 3, an electrochemical reaction process that is a source of electricity generation in the fuel cell 100 will be described. In FIG. 1A, for convenience of explanation, only the left side () anode) of the fuel cell 100 is shown and the right side (cathode) is omitted. However, here, the illustration of the electrolyte 50 is omitted without such omission. “A” is added to the end of the reference number of each member with the left side as the anode side, and the right side of the drawing of the electrolyte 50 is set as the cathode side, and “b” is added to the end of the reference number of each member. . In addition, since the cathode side flow path 60b is formed in the direction orthogonal to the anode side flow path 60a, only the 2nd member 20b is represented by the up-down direction of the figure at the cathode side.

First, hydrogen (H ₂ ) is supplied to the gas flow path 60a formed by the first member 10a and the second member 20a. Hydrogen (H ₂ ) that has passed through the carbon water repellent film 30a from the gas flow path 60a and delivered to the catalyst layer 40a is decomposed into hydrogen ions and electrons in the presence of the catalyst.
Anode side: H ₂ → 2H ⁺ + 2e ⁻
The generated hydrogen ions pass through the electrolyte 50, which is an ionic conductor, and move to the cathode side. Since the electrolyte 50 has a property of allowing only ions to pass therethrough, the generated electrons cannot pass through the electrolyte 50 and move to the cathode side through an external circuit. In the fuel cell 100, electricity is generated by the movement of the electrons. On the other hand, by the gas flow path 60b, oxygen (O ₂ ) circulated in the cathode reacts with hydrogen ions and electrons that have moved to the cathode, thereby generating water.
Cathode side: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O

  The fuel cell 100 of the present invention configured as described above has nothing equivalent to the interface between the diffusion layer and the separator as in the conventional fuel cell, and each component is joined to each other. It is no longer necessary to apply a surface pressure that is necessary for flowing electricity between the diffusion layer and the separator in the conventional fuel cell. Therefore, the durability of the fuel cell which has been sacrificed by applying the surface pressure can be dramatically improved. Further, there is an advantage that it is not necessary to use a clamping plate, a clamping bolt, a disc spring, a clamping nut, and the like, which are conventionally used for a fuel cell to apply a surface pressure. Furthermore, since the diffusion layer is not necessary, the cost of the fuel cell can be reduced and the thickness of the cell can be reduced. In addition, since the second member 20, the carbon water repellent film 30, the catalyst layer 40, and the electrolyte 50 are joined on the first member 10 so that they can be continuously produced, the production process is simplified. Yes, and the cost required for production is low.

(A) is sectional drawing which shows the structure of the fuel cell of this invention. (B) is a BB arrow sectional view of the fuel cell of (a). It is a figure which shows each aspect of the cross-sectional shape of the 2nd member joined on the 1st member. It is a figure explaining the process of the electrochemical reaction in a fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 1st member 20, 21, 22, 23 2nd member 30 Carbon water repellent layer 40 Catalyst layer 50 Electrolyte 60a, 60b Flow path 100 Fuel cell

Claims (7)

A separator formed by joining a second member having a predetermined shape to at least one surface side of the first member formed in a flat plate shape and forming a flow path on one surface side of the first member is provided. Fuel cell. The fuel cell according to claim 1, wherein a cross-sectional shape of the second member is substantially circular. The fuel cell according to claim 1 or 2, wherein the first member is made of metal and the second member is made of carbon. The fuel cell according to claim 1, wherein at least a part of the second member is a porous body. The fuel cell according to any one of claims 1 to 3, wherein at least a part of the second member is a porous body on the downstream side of the cathode. The fuel cell according to any one of claims 1 to 5, wherein a carbon water-repellent film is stretched and joined on a flow path side surface of the separator. The fuel cell according to claim 6, wherein a catalyst layer and an electrolyte are further formed on the carbon water-repellent film.

Images