JP2009252666A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell having a structure capable of preventing the damage of an electrolyte film by a diffusion layer substrate without increasing the manufacturing cost concerning a fuel cell in which a gas diffusion layer consisting of a current collection layer and a diffusion layer substrate is joined with a membrane-electrode assembly. <P>SOLUTION: A catalyst layer 2 narrower than an electrolyte film 1 comes in contact with the electrolyte film 1, and a current collection layer 3 surrounds the catalyst layer 2 and comes in contact with the electrolyte film 1 at the outside from the catalyst layer 2. A diffusion layer substrate 4 is formed on the opposite side of the catalyst layer 2 at the current collection layer 3, and the current collection layer 3 has a relatively thin center region 32 where the current collection layer 3 comes in contact with the catalyst layer 2, and a relatively thick outer circumferential region 31 where the current collection layer 3 comes in contact with the electrolyte film 1. For a lateral side of the diffusion layer substrate 4 in contact with the current collection layer 3, the diffusion layer substrate 4 has a relatively thin outer circumferential region 41 to correspond to the shape of the current collection layer 3, and a relatively thick center region 42 of the diffusion layer substrate 4 brought in contact with the center region 31 of the current collection layer 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell, and more particularly to the structure of a gas diffusion layer comprising a current collecting layer and a diffusion layer substrate.

  A single cell of a polymer electrolyte fuel cell has a membrane electrode assembly (an electrode-permeable electrolyte membrane, an anode side catalyst layer (electrode layer) and a cathode side catalyst layer (electrode layer) sandwiching the electrolyte membrane) MEA: Membrane Electrode Assembly, a gas diffusion layer (GDL) for providing fuel gas or oxidant gas to the membrane electrode assembly and collecting electricity generated by an electrochemical reaction, and a separator At least. This separator defines each single cell and becomes a gas flow path layer. There is also a so-called flat type separator in which this gas flow path layer is separated from the separator. The fuel cell stack is formed by stacking a predetermined number of single cells according to required power.

  In the fuel cell described above, hydrogen gas or the like is provided as a fuel gas to the anode electrode, oxygen or air is provided as the oxidant gas to the cathode electrode, and each electrode is faced by a unique gas flow path layer (or separator). Gas flows inward, and then the gas diffused in the gas diffusion layer is guided to the electrode catalyst layer to cause an electrochemical reaction.

  As a form of the gas diffusion layer described above, a gas diffusion layer composed of a diffusion layer base material and a current collecting layer (MPL: Micro Porous Layer) is generally known. The gas diffusion layer and the membrane electrode assembly are bonded by thermocompression bonding such as hot pressing, and generally a fastening pressure is applied to reduce the contact resistance. Since this thermocompression bonding is performed by heating to the vicinity of the glass transition point of the electrolyte membrane, the electrolyte membrane is likely to be damaged during the compression bonding.

  Furthermore, while the central region of the electrolyte membrane is protected by the catalyst layer thereabove, the diffusion layer substrate penetrates the thin MPL layer in the end region of the electrolyte membrane not protected by the catalyst layer, and the electrolyte The phenomenon of piercing the membrane often occurs. In the region of the electrolyte membrane pierced by the diffusion layer base material, the surface pressure received by the fuel cell stack is lower than that in the central region of the electrolyte membrane in a state where the fastening pressure is applied, and sufficient adhesion cannot be obtained. This is inevitable, and this causes gas cross-leakage to be promoted in this piercing region. It is easy to understand that the power generation performance of the fuel cell deteriorates due to gas cross leak. A fuel cell including a gas diffusion layer having the structure referred to here is disclosed in Patent Document 1.

  In order to solve the above problems, a gasket is provided between the diffusion layer base material and the electrolyte membrane at the peripheral edge of the membrane electrode assembly, more specifically, the peripheral edge of the catalyst layer and the MPL layer, and the diffusion layer base material. A configuration that can prevent the diffusion layer base material from being stuck between the (end region) and the electrolyte membrane (a gasket separate from a general sealing gasket surrounding a gas supply or gas exhaust manifold) Form). This structure will be described with reference to FIG. 3 showing only the electrolyte membrane, the cathode-side catalyst layer, and the gas diffusion layer. The catalyst layer b is narrower (smaller in area) than the electrolyte membrane a on the upper surface of the electrolyte membrane a. And a MPL layer c, a diffusion layer base material d is provided outside the MPL layer c, and the periphery of the catalyst layer b and the MPL layer c is made of resin between the electrolyte membrane a and the diffusion layer base material d. The gasket e is interposed. In the form having the gasket shown in the figure, the manufacturing cost increases due to the increase in the number of parts and the assembly process of the gasket, and the increase in the manufacturing cost becomes remarkable with the mass production of the fuel cell. The actual situation is that there is a problem that the peripheral portion is damaged by the gasket provided in such a portion.

JP 2007-184129 A

  The present invention has been made in view of the above-described problems, and relates to a fuel cell in which a gas diffusion layer composed of a current collecting layer and a diffusion layer base material is bonded to a membrane electrode assembly, and increases manufacturing costs. It aims at providing the fuel cell which exhibited the structure which can prevent the damage of the electrolyte membrane by a diffusion layer base material.

  In order to achieve the above object, a fuel cell according to the present invention is a fuel cell in which a gas diffusion layer comprising a current collecting layer (MPL) and a diffusion layer substrate is bonded to a membrane electrode assembly having at least an electrolyte membrane. The electrolyte membrane is in contact with a catalyst layer that is narrower than the electrolyte membrane, and the current collector layer surrounds the catalyst layer and is in contact with the electrolyte membrane outside the catalyst layer. The diffusion layer base material is formed on the opposite side of the electrode layer from the catalyst layer, and the current collecting layer has a relatively thin central region where the current collecting layer is in contact with the catalyst layer. The thickness of the outer peripheral region in contact with the current collecting layer of the diffusion layer base material is relatively thick, and the side surface of the diffusion layer base material in contact with the current collecting layer corresponds to the shape of the current collecting layer. Is relatively thin and the thickness of the central region of the diffusion layer base material in contact with the central region of the current collecting layer There is one that is relatively thick.

  In the fuel cell according to the present invention, the thickness of the current collecting layer (MPL layer) constituting the gas diffusion layer is made relatively thin in the central region where it is in contact with the catalyst layer, and the end region is in direct contact with the electrolyte membrane. The electrolyte membrane that is not protected by the catalyst layer is formed by making the thickness of the diffusion layer base material relatively thin and the thickness of the end region of the diffusion layer base material relatively thin so as to correspond to the shape of the current collecting layer. The distance between the end region and the diffusion layer substrate is set to be as long as possible so that the diffusion layer substrate can effectively prevent the electrolyte membrane from being stuck to the electrolyte membrane.

  The MPL layer is bonded to a diffusion layer base material whose end region is a thin layer in advance, that is, the central region has a shape protruding toward the MPL layer and the side surface opposite to the MPL layer is flat. The end region of the MPL layer is not protected by the catalyst layer by thermocompression bonding with an electrolyte membrane and a catalyst layer having a smaller area, that is, a catalyst layer having a smaller area, by hot pressing. Bonded to the end region of the electrolyte membrane.

  Here, the area of both the central region of the diffusion layer base material and the catalyst layer is the same or substantially the same, and it is preferable that both are opposed to each other through the current collecting layer without being shifted. This means that the projecting portion in the vertical direction of the end region of the MPL layer, that is, the projecting portion toward the diffusion layer substrate side and the projecting portion toward the electrolyte membrane side have substantially the same width. That means. According to this embodiment, when a plurality of single cells are stacked to form a stack and compressed from both sides to form a fuel cell, the projecting region of the diffusion layer base material corresponding to the entire region of the catalyst layer A uniform pressure acts from the (central region), and an in-plane uniform pressure environment can be imparted to the catalyst layer.

  According to the fuel cell of the present invention described above, the piercing from the diffusion layer base material to the electrolyte membrane is effectively prevented by an extremely simple structure in which the shape of the diffusion layer base material and the shape of the current collecting layer are adjusted. It is possible to effectively suppress gas cross-leakage caused by this. In addition, as described above, there is no need to interpose a gasket or the like between the electrolyte membrane and the diffusion layer base material, resulting in an increase in material costs due to additional materials (members) and an increase in manufacturing costs accompanying an increase in processes. There is no. This effect becomes more prominent as the fuel cell production increases. Furthermore, according to the preferable fuel cell configuration described above, the in-plane uniform pressure always acts on the catalyst layer, and a fuel cell excellent in power generation efficiency and power generation performance can be obtained.

  As can be understood from the above description, according to the fuel cell of the present invention, the manufacturing cost is increased by applying the electrode body structure having both the shape of the diffusion layer base material and the current collecting layer which is not in the conventional structure. Therefore, it is possible to effectively prevent the diffusion layer substrate from sticking to the electrolyte membrane, thereby effectively suppressing gas cross-leakage.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram in which a part of the structure of the fuel cell of the present invention is disassembled, in which only the catalyst layer and the gas diffusion layer on the cathode side are extracted and shown in FIG. FIG. Of course, the structure on the anode side is the same as the structure on the cathode side shown in the figure.

  A single cell constituting a fuel cell has a membrane electrode assembly (MEA) formed of an electrolyte membrane 1, a cathode-side catalyst layer 2 sandwiching the electrolyte membrane 1, and an anode-side catalyst layer (not shown). An electrode body (MEGA) is formed from the sandwiched cathode-side gas diffusion layer 5 and the anode-side gas diffusion layer (not shown), and this electrode body is formed into a cathode-side gas flow path layer and anode-electrode-side gas (not shown). A single cell is configured by sandwiching the flow path layer and further sandwiching the gas flow path layer by a flat type separator. In addition to the flat type separator, a conventional general separator provided with a concavo-convex separator having a gas flow path action, a current collecting action, and a defining action with adjacent cells may be used.

  In an actual fuel cell, a single cell is stacked in a predetermined stage according to a desired power generation amount to form a fuel cell stack. Further, the fuel cell stack includes an end plate, a tension plate, and the like on the outermost side, and a compressive force is applied between the tension plates at both ends to form a fuel cell.

  A fuel cell system mounted on an electric vehicle or the like includes this fuel cell, various tanks for storing hydrogen gas and air, a blower for supplying these gases to the fuel cell, a radiator for cooling the fuel cell, a fuel The battery is generally composed of a battery that stores electric power generated by the battery, a drive motor that is driven by the electric power, and the like.

  As shown in FIG. 1, a catalyst layer 2 having a narrower area, that is, a smaller flat area, is bonded above the electrolyte membrane 1, and a gas formed by bonding the current collecting layer 3 and the diffusion layer base material 4 to each other. The structure on the cathode side of the electrode body is formed by thermocompression bonding of the diffusion layer 5 with a hot press (X direction).

  Here, the side surface of the diffusion layer base material 4 on the side of the current collecting layer 3 has the same area as the catalyst layer 2 and both of the catalyst layer 2 and the catalyst layer 2 when being bonded to the catalyst layer 2 and the electrolyte membrane 1 as shown in FIG. It is composed of a central region 42 protruding at a position where the entire surface can be opposed (a position where both are not shifted), and an end region 41 on the outer periphery thereof, and the other surface of the diffusion layer substrate 4 is a flat surface. It has become.

  1, the current collecting layer 3 having a flat lower surface is thermocompression bonded to the electrolyte membrane 1 or the like as shown in FIG. 2, so that the lower surface of the current collecting layer 3 is the upper surface of the catalyst layer 2 protruding upward from the electrolyte membrane 1. And the upper surface of the end region of the electrolyte membrane 1 on the outer periphery thereof. As is apparent from FIG. 2 showing the posture in which the cathode-side electrode body is formed, in the current collecting layer 3, the thickness of the central region 32 sandwiched between the catalyst layer 2 and the central region 42 of the diffusion layer base material 4. Is relatively thin, and the thickness of the outer end region 31 is relatively large.

  By forming the electrode body having the shape (structure) shown in the figure, the catalyst layer 2 receives a uniform compressive force from the central region 42 of the diffusion layer base 4 that has the same area and the entire area when the stack is formed. This means that the uniform compressive force is constantly applied over the life of the fuel cell.

  Furthermore, the separation between the end region 41 of the diffusion layer base material 4 and the end region of the electrolyte membrane 1 facing this is set longer in the thick end region 31 of the current collecting layer 3, In the posture of FIG. 2, the possibility that the diffusion layer base material 4 pierces the end region of the electrolyte membrane 1 that is not protected by the catalyst layer 2 can be remarkably reduced, or such piercing can be completely eliminated.

  Therefore, in a fuel cell having a conventional structure, the diffusion layer base material pierces the end region of the electrolyte membrane, and gas cross-leakage is promoted starting from this, thereby reducing the power generation efficiency and power generation performance of the fuel cell. The problem can be solved effectively.

[Experiment and results of verifying leakage current and cycle durability between the fuel cell of the present invention (Example) and the conventional fuel cell (Comparative Examples 1 and 2)]
The inventors of the present invention manufactured a fuel cell in which a predetermined number of single cells each having the same anode-side structure as the cathode-side electrode body shown in FIG. A fuel cell having a conventional structure was manufactured as Comparative Examples 1 and 2, and both leakage currents (specifically, the short-circuit leakage current value at the time of electrode preparation) were measured and the cycle durability of both was verified. . In Comparative Example 1 relating to the conventional fuel cell, a diffusion layer is manufactured using a diffusion layer substrate having a uniform thickness, and a reinforcing film or the like is provided between end regions of both the diffusion layer substrate and the electrolyte membrane. 3 is a structure without the gasket (a structure without the gasket e in FIG. 3), and the comparative example 2 has a gasket (reinforcing film) as shown in FIG.

A list of short circuit current leakage values is shown in Table 1 below, and experimental results on cycle durability are shown in Table 2. In addition, regarding this cycle durability, when the cell temperature is 80 ° C. and the energization current density is 0.1 A / cm ² , the durability time until the cross leak exceeds a predetermined standard value is measured.

  As can be seen from Table 1, in the fuel cell according to the example, a remarkable decrease in the short-circuit current (reduction to about 1/3) was recognized as compared with the fuel cell of Comparative Example 1 that does not have the gasket.

  Further, in contrast to the fuel cell according to Comparative Example 1, the fuel cell according to the Example has a leakage current comparable to that of the fuel cell according to Comparative Example 2 in which the reinforcing film (gasket) is provided between the diffusion layer base material and the electrolyte membrane. It was proved that the reduction effect of the value can be expected.

  Further, from Table 2, the cross-leak endurance time of the fuel cell according to the example is about 1.6 times longer than that of the fuel cell of Comparative Example 1, which is the same as that of the fuel cell of Comparative Example 2 including the reinforcing film. It was proved to have a degree of durability performance.

  From the experimental results shown in Tables 1 and 2, the fuel cell of the example according to the present invention is not provided with a gasket or the like between the diffusion layer base material and the electrolyte membrane, and the conventional fuel cell having the gasket is provided. It was proved that the same level of performance can be demonstrated. This indicates that a fuel cell with high cross-leak durability can be obtained while avoiding the extension of the manufacturing process and the increase in manufacturing cost caused by the work process of assembling the gasket and the like to the electrode body.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

It is the schematic diagram which decomposed | disassembled a part of structure of the fuel cell of this invention, Comprising: It is the figure which extracted and showed only the catalyst layer and gas diffusion layer by the side of a cathode. FIG. 2 is a schematic view in which the exploded structure of FIG. 1 is integrated. It is the schematic diagram which showed a part of structure of the conventional fuel cell.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane, 2 ... (cathode side) catalyst layer, 3 ... (cathode side) current collection layer, 31 ... end region, 32 ... center region, 4 ... (cathode side) diffusion layer base material, 41 ... end Region, 42 ... central region, 5 ... (cathode side) gas diffusion layer

Claims (2)

In a fuel cell formed by bonding a gas diffusion layer comprising a current collecting layer (MPL) and a diffusion layer base material to a membrane electrode assembly including at least an electrolyte membrane,
A catalyst layer narrower than the electrolyte membrane is in contact with the electrolyte membrane, and the current collecting layer surrounds the catalyst layer and is in contact with the electrolyte membrane outside the catalyst layer,
The diffusion layer base material is formed on the side of the current collecting layer opposite to the catalyst layer,
The current collecting layer has a relatively thin central region where the current collecting layer is in contact with the catalyst layer, and a relatively thick outer peripheral region is in contact with the electrolyte membrane,
The side surface of the diffusion layer base that is in contact with the current collecting layer has a relatively thin outer peripheral region corresponding to the shape of the current collecting layer, and is relatively in contact with the central region of the current collecting layer. A fuel cell in which a thickness of a central region of the diffusion layer base in contact with the base material is relatively thick.   2. The fuel according to claim 1, wherein the areas of both the central region and the catalyst layer of the diffusion layer base material are the same or substantially the same, and both face each other without being shifted through the current collecting layer. battery.

Images