JP2005174620A - Membrane electrode assembly and fuel cell using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane electrode assembly (MEA) in which a problem that surface unevenness is hard to be controlled conventionally, it is difficult to form unevenness evenly on the membrane surface, and furthermore even in every patent document, the unevenness shape is to be described as a mere peak and valley shape, and the unevenness is larger and the surface area can not be increased, and in order to enhance characteristics of the fuel cell, the electrodes and an electrolyte membrane interface are made to be regularly uneven state, and the joining force of the electrodes and the electrolyte membrane is made stronger, and at the same time the interface is three-dimensional and the reaction surface area is increased, and provide a solid polymer fuel cell using this. <P>SOLUTION: This membrane electrode assembly is constituted by using the polyelectrolyte membrane having minute projection groups formed by plastic working on one face or both faces of the polyelectrolyte membrane. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a novel membrane electrode assembly and a polymer electrolyte fuel cell using the same.

  In recent years, fuel cells using polymer electrolyte membranes have been remarkably improved in performance due to the development of electrolyte membranes and catalyst technology, and are attracting attention as a low-pollution automobile power source and a high-efficiency power generation method. It has a structure in which a reaction layer having an oxidation / reduction catalyst is formed on the surface of a fuel cell using a polymer electrolyte membrane. In this case, it is known that when the surface area is increased by forming irregularities on the surface of the polymer electrolyte membrane, the efficiency of the electrochemical reaction is improved. Examples of such a method include a method for forming irregularities on the film surface by a chemical and mechanical polishing method disclosed in Patent Document 1, and a mixed molding of a solid electrolyte material and a pyrolysis material disclosed in Patent Document 2. There are known a method of firing a body to form irregularities on the surface, a method of pressure bonding a metal foil having irregularities on the surface disclosed in Patent Document 3, and dissolving and removing the metal foil.

JP-A-9-320616 Japanese Patent Laid-Open No. 9-277226 JP 2003-68328 A

  However, in any of the patent documents, it is difficult to control the surface unevenness, and it is difficult to form the unevenness uniformly on the film surface. Further, in any of the patent documents, the shape of the unevenness was only a mountain-valley shape, the unevenness was larger, and the surface area could not be further increased.

  In order to improve the characteristics of a fuel cell, the object of the present invention is to provide a membrane electrode in which the interface between the electrode and the electrolyte membrane is regularly uneven, thereby strengthening the bonding force between the electrode and the electrolyte membrane, and at the same time, the interface is three-dimensional and the reaction surface area is increased. An object of the present invention is to provide an assembly (MEA) and a polymer electrolyte fuel cell using the same.

  The present invention resides in a fuel cell electrolyte membrane characterized by having a group of minute protrusions formed by plastic working on one side or both sides of a polymer electrolyte membrane.

The microprotrusions are formed according to a predetermined planar shape, are columnar, have a diameter of 0.3 μm to 50 μm, a height of 0.3 μm to 50 μm, and an equivalent diameter (D) with respect to the height (H) ) Ratio (H / D) is greater than 1, preferably 5 to 100, and more preferably 5 to 30.

  As the shape of the microprojection group, the equivalent diameter of the tip portion is smaller than the equivalent diameter of the bottom surface portion of the columnar projection group, and has a portion that narrows from the formed root toward the tip portion, and is made of a thermoplastic polymer material. It is preferable to become. In the present invention, the equivalent diameter of the columnar microprotrusions is an equivalent diameter at an intermediate position of the protrusions. The term equivalent diameter is used because the cross section of the protrusion is not necessarily circular, but may be an ellipse, a polygon, an asymmetric shape, and the like.

  The present invention is also directed to a method for producing an electrolyte membrane for a fuel cell, wherein a group of minute protrusions is formed by plastic working on one or both sides of a polymer electrolyte membrane.

  Furthermore, the present invention provides a method of pressing a molding die having a concave portion of a predetermined plane pattern on one or both sides of the polymer electrolyte membrane, and then stretching the convex portion of the polymer electrolyte membrane formed in the concave portion. In the method for producing an electrolyte membrane for a fuel cell, the mold is peeled off from the polymer electrolyte membrane to form a group of minute protrusions. The diameter of the recess is preferably 10 μm or less.

  The present invention includes a polymer electrolyte membrane, different types of catalyst layers formed on both surfaces of the electrolyte membrane supported by a carrier, diffusion layers formed in contact with the respective catalyst layers, In a fuel cell having an anode electrode formed in contact with one of the diffusion layers and a cathode electrode formed in contact with the other diffusion layer, the polymer electrolyte membrane has a group of microprojections formed on its surface. It is formed by processing, and the catalyst is supported on the carrier and formed on the microprojection group.

  It is preferable that the carrier is formed by carbonization of the polymer electrolyte membrane, and the diffusion layer is a carbon sheet.

  In the present invention, the polymer electrolyte membrane is a general term for a polymer film having a polymer having a group having ion exchange ability or a substance having an ion exchange ability contained in the polymer film. It is roughly divided into a cation exchange membrane and an anion exchange membrane. There are also membranes in which both exchange membranes are joined. Examples of the cation exchange membrane include an ion exchange membrane having a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group in the polymer chain in the membrane, and sulfuric acid, sulfonic acids, phosphoric acids, carboxylic acids and solid acids in the polymer membrane. And those containing acidic substances such as fine particles.

  Examples of the anion exchange membrane include a polymer molecule having a basic group such as an amino group, quaternary ammonium hydroxide, and guanidine group, and a membrane in which a solid base is dispersed in the membrane. In addition, there are those in which the acid or base portion in the film is made into a salt, and those in which the salt is impregnated.

  As the most typical ion exchange membrane for fuel cells, a polyperfluorosulfonic acid film is formed, for example, manufactured by DuPont, USA; trade name Nafion, Asahi Glass Co., Ltd .: trade name Flemion, Asahi Kasei Kogyo Co., Ltd. : Product name Aciplex and the like.

  When the polymer electrolyte membrane having a roughened surface produced according to the present invention is used in a fuel cell, the reaction efficiency is improved, and as a result, the performance such as battery output is improved. The reason is considered to be that extremely large irregularities can be formed on the surface of the film, and the surface area of the film is greatly increased. As a result, ions generated by an electrochemical reaction on the film surface can be efficiently dissolved. The polymer electrolyte membrane of the present invention includes a film and a sheet.

  The film or substrate provided with the microprojection group of the present invention is a thermoplastic polymer electrolyte membrane using a micromolding die (precision mold) in which concave portions (hereinafter referred to as pits) having a specific planar shape are formed. To form a pattern according to the type of pit group. When the mold is pulled away from the polymer electrolyte membrane, the thermoplastic resin that has entered the pit is stretched to form a group of microprojections having a desired planar shape. In particular, the height of the protrusion can be adjusted by changing the ratio of the recess area and depth of the mold (molding die), and the position and bottom area of the protrusion can be adjusted by the position and opening area of the recess formed in the mold. it can. The material of the mold (molding die) is not particularly limited, and examples thereof include nickel and silicon that are excellent in workability.

  It is desirable that the projections constituting the microprojection group have a slightly larger equivalent diameter at the bottom surface than the equivalent diameter at the tip, and ensure the self-supporting and self-supporting properties of the resin-made microprojections. Moreover, it is desirable that the microprojections have a portion that becomes narrower from the base of formation toward the tip, and are formed integrally.

  Since the microprojection aggregate of the present invention can have a structure in which microprojections are densely packed, individual microprojections can be made difficult to collapse and difficult to be removed.

  When the aforementioned mold is pressed against the thin film of thermoplastic resin and peeled off, the resin pressed into the pit is stretched to form a group of microprojections slightly smaller than the pit but longer than the pit depth. It is formed. How much equivalent diameter and length of micro-projections varies depending on the type of resin used, physical properties (molecular weight, etc.), and molding conditions (pit depth, temperature, molding pressure, etc.). It is good to confirm by experiment.

  According to the present invention, as the characteristics of the fuel cell, the bonding force between the electrode and the electrolyte membrane is increased to improve the durability, and the unevenness of the reaction surface is large to improve the power generation efficiency.

  The best mode for carrying out the present invention will be described below. In addition, this invention is not limited to the Example shown below.

  FIG. 1 is a view of a projection aggregate formed on one surface of a polymer electrolyte membrane, observed with a scanning electron microscope. As shown in FIG. 1, the projection aggregate is composed of columnar microprojections 101 made of a large number of extremely fine projections. As the polymer electrolyte membrane, a columnar microprojection 101 was formed by press molding using a mold using a Nafion 115 (registered trademark) manufactured by Dubon, USA, cut into a 10 cm square.

  The columnar microprojection 101 is a quadrangle having a height of about 3 μm and a side length of about 0.3 μm at the root. The columnar microprojection 101 has a smooth surface state at the upper portion of about 1 μm, and the root portion has a striped pattern at about 2 μm. The columnar microprojections 101 are arranged with a period (pitch) of 1 μm.

  In addition, it can be seen that the ratio of the height and one side (aspect ratio) of the columnar microprojection 101 is 10, which is sufficiently larger than 1. The cross-sectional area of the tip of the columnar microprojection 101 is smaller than the cross-sectional area of the bottom surface and is divergent, and the shape of the columnar microprojection is a shape that narrows from the root to the tip, but from the root to the tip. It may be a mushroom shape that is thin and has a thick portion at the tip.

  Further, the columnar microprojections 101 are integrated with the polymer electrolyte membrane 102 and have a divergent shape from the front end to the bottom surface portion, and thus are difficult to remove from the base polymer electrolyte membrane.

FIG. 2 is a diagram showing a manufacturing process of the columnar microprojection 101. FIG. 2A shows a process of placing the polymer electrolyte membrane 202 on the metal table 201. The surface of the polymer electrolyte membrane 202 has a predetermined planar shape. Next, FIG. 2B shows a step of press molding with a mold 203 of a concave precision mold in which pits (concave portions) having a depth of 1 μm and a diameter of 0.5 μm are formed on the surface at a pitch of 1 μm. Further, FIG. 2C shows a process of pulling up the mold 203 vertically. Thereby, the columnar microprojection 101 can be formed. A hole can be formed in the electrolyte membrane by using a convex precision mold as the mold 203.

  In this embodiment, the tip of the columnar microprojection 101 is smaller than the bottom of the columnar microprojection, and the columnar microprojection group is the same as the underlying material. It is difficult to remove from the substrate.

  The ratio (H / D) of the equivalent diameter (D) to the height (H) of the columnar microprojection 101 shown in FIG. 1 is about 10, but the depth of the recess of the mold 203 and the hardness of the polymer electrolyte membrane 202 are It is possible to control the diameter and height of the columnar microprojection 101 by adjusting. Furthermore, the size of the bottom of the columnar microprojection 101 can be controlled by increasing the opening area of the recess of the mold 203. By controlling the position of the concave portion of the mold 203, the position where the columnar microprojections 101 are formed can be controlled. Moreover, the shape can be easily controlled by adjusting the temperature when forming the columnar microprojections 101 using the thermoplastic polymer electrolyte membrane 202.

  FIG. 3 shows a membrane electrode assembly (MEA) of the present invention produced using the electrolyte membrane having the columnar microprojections described above. 301 is a polymer electrolyte membrane, and 302 and 303 are electrode layers that serve as a fuel electrode (anode) and an air electrode (cathode).

  As an anode and a cathode, an electrode catalyst in which platinum was supported on carbon black at 50 wt% was used. An electrocatalyst paste was prepared by combining a Nafion solution (concentration: 5 wt%, manufactured by Aldrich) in which NaPoion (registered trademark) of DuPont was dissolved in the electrocatalyst at a ratio of 1: 9 by weight of the electrocatalyst to the Nafion solution. This electrocatalyst paste was applied to both surfaces of an electrolyte membrane having columnar microprojections by an applicator method to produce an MEA of the present invention. In the production of the MEA of the present invention, hot pressing is performed in the range of 100 to 200 ° C. after applying the catalyst as necessary.

  FIG. 4 shows an enlargement of the interface portion between the electrode of F portion and the electrolyte membrane in FIG. As shown in FIG. 4, since the columnar microprojections existing on the surface of the electrolyte membrane are pierced into the electrode layer, the bonding strength between the electrode and the electrolyte membrane is strong and the durability of the MEA is excellent. In addition, the contact area between the electrode and the electrolyte membrane is increased, thereby increasing the reaction area and improving the power generation characteristics.

  The pattern shape of the mold of Example 1 and the precision mold was changed, and a hole having a diameter of about 2 μm and a depth of 5 μm was formed in the electrolyte membrane. Further, in the same manner as in Example 1, an MEA was produced using an electrolyte membrane having holes formed on the surface. FIG. 5 shows an enlarged view of the interface portion between the electrode of the MEA produced in Example 2 and the electrolyte membrane. Since the hole formed in the surface is filled with the electrode catalyst and serves as an anchor for the electrode layer, the bonding strength between the electrode and the electrolyte membrane is strong and the durability of the MEA is excellent. In addition, the contact area between the electrode and the electrolyte membrane is increased, thereby increasing the reaction area and improving the power generation characteristics.

  A composite membrane was produced by applying sulfonated polystyrene as another type of electrolyte material to the electrolyte membrane having columnar microprojections produced in Example 1. Further, an electrode was applied by the applicator method in the same manner as in Example 1 to produce an MEA. Since the interface of the composite film has a structure in which columnar microprojections are pierced, the films do not peel off and the MEA has excellent durability.

The MEA of the present invention was produced by applying the electrolyte membrane having columnar microprojections and the electrode catalyst paste prepared in Example 1 to both surfaces of the electrolyte membrane having columnar microprojections by a spray method. In the spray method, the surface of the electrode layer becomes uneven reflecting the columnar microprojections. Such a structure has good diffusibility of fuel or oxidizing gas and has excellent power generation characteristics.

  In Example 1, the pattern shape of the mold of the precision mold was changed so that the projections and depressions of the columnar microprojections were of two types, a height of about 3 and 1 μm. An MEA was produced in the same manner as in Example 4 using the electrolyte membrane having columnar microprojections produced in Example 5. The electrode layer has large irregularities on the surface, good diffusibility of fuel or oxidizing gas, and has excellent power generation characteristics.

The surface of the electrolyte membrane having columnar microprojections produced in Example 1 was heat-treated and desulfonated to render the columnar microprojections water repellent. An MEA was produced in the same manner as in Example 4 using the electrolyte membrane produced in Example 6. The columnar microprotrusions are water repellent and have excellent power generation characteristics with high discharge of generated water.
[Comparative Example 1]
An MEA was produced in the same manner as in Example 1 using ordinary Nafion 115 (registered trademark) having no columnar microprojections.

  A power generation test was conducted using the MEAs of Examples 1 to 6 and Comparative Example 1. FIG. 10 shows the structure of the fuel cell. Reference numeral 1 denotes a separator provided with a groove for supplying fuel or oxidizing gas. 2 to 4 are MEAs, 2 is an electrolyte membrane, 3 is an anode, and 4 is a cathode. Reference numeral 5 denotes a diffusion layer, which uses water-repellent carbon paper or carbon cloth. 6 is a gasket, and a material excellent in sealing performance and heat resistance is suitable.

A power generation test was conducted using hydrogen as the fuel and air as the oxidizing gas. Table 1 shows a current density of 500 mA /
The generated voltage in cm ² is shown. The MEAs of Examples 1 to 6 had higher power generation voltage than the comparative example and exhibited excellent characteristics. Furthermore, when continuous power generation was performed, the MEA of Examples 1 to 6 showed almost no voltage drop until 1000 hours, whereas the MEA of Comparative Example 1 had a power generation voltage reduced by 50 mV in 200 hours. The MEAs of Examples 1 to 6 are excellent in durability.

  Also, when the fuel was changed from hydrogen to a methanol aqueous solution, the MEA of Examples 1 to 6 produced a higher power generation voltage than that of Comparative Example 1.

The figure observed with the scanning electron microscope which shows the structure of a columnar microprotrusion group. The flowchart which shows the manufacturing process of the columnar microprotrusion group of this invention. MEA of the present invention. Sectional drawing of the interface of the electrode layer and electrolyte membrane of MEA of this invention. Sectional drawing of the interface of the electrode layer and electrolyte membrane of MEA of this invention. Sectional drawing of the interface of the electrode layer and electrolyte membrane of MEA of this invention. Sectional drawing of the interface of the electrode layer and electrolyte membrane of MEA of this invention. Sectional drawing of the interface of the electrode layer and electrolyte membrane of MEA of this invention. Sectional drawing of the interface of the electrode layer and electrolyte membrane of MEA of this invention. The fuel cell of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Separator, 2 ... Electrolyte membrane, 3 ... Anode, 4 ... Cathode, 5 ... Diffusion layer, 6 ... Gasket, 101, 401 ... Columnar microprotrusion, 102, 202, 301, 402 ... Polymer electrolyte membrane, 201 ... Metal base, 203 ... mold, 302, 303,403 ... electrode layer for fuel electrode (anode) and air electrode (cathode), 404 ... hole, 405 ... polymer electrolyte membrane different from base, 406 ... water repellent Columnar microprojections.

Claims (7)

  The membrane electrode assembly using the polymer electrolyte membrane which has the microprotrusion group formed in the single side | surface or both surfaces of the polymer electrolyte membrane by plastic working.   A membrane electrode assembly using a polymer electrolyte membrane having a group of micro holes formed by plastic working on one side or both sides of the polymer electrolyte membrane.   2. The membrane electrode assembly according to claim 1, wherein the microprojection group has a diameter of 0.3 μm to 50 μm and a height of 0.3 μm to 50 μm.   2. The membrane electrode assembly according to claim 1, wherein the solid polymer membrane is composed of two or more kinds of composite membranes.   In a membrane / electrode assembly comprising a polymer electrolyte membrane having a microprojection group formed by plastic working on one or both surfaces of the polymer electrolyte membrane and an electrode layer, irregularities reflecting the microprojection group are formed on the surface of the electrode layer. A membrane electrode assembly, characterized in that it exists.   6. The membrane electrode assembly according to claim 1, wherein the microprojection group is water repellent. A fuel cell using the membrane electrode assembly according to claim 1.

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