JP2003068328A - Method of manufacturing polymer electrolytic film with roughened surface and electrochemical device and fuel cell using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing the polyelectrolyte film which has a large surface area by making its surface shape extremely complicated and sculptured for dissolving the problem, which a method of forming an unevenness surface of a conventional polyelectrolyte film has, that a pinhole is easy to make and a film is easy to break, and improving the efficiency of an electrochemical device of a fuel cell and so forth. SOLUTION: The method of manufacturing the polyelectrolyte film with roughened surface is characterized by including a step of bonding with pressure a rough surface of the metallic foil having the roughened surface on one surface or both sides of the polyelectrolyte electrolyte film and a step of dissolving and removing the metal foil.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polymer electrolyte membrane having a roughened surface, and the membrane is particularly excellent for use in electrochemical devices such as fuel cells.

[0002]

2. Description of the Related Art A fuel cell, which is a type of electrochemical device using a polymer electrolyte membrane, has been remarkably improved in performance in recent years due to the development of electrolyte membrane and catalyst technology, and has been used as a low-pollution automobile power source and a highly efficient power generation method. It is getting attention. An electrochemical device using a polymer electrolyte membrane is oxidized on the surface of the membrane,
It has a structure in which a reaction layer having a reduction catalyst is formed.
In this case, it has been known that the efficiency of the electrochemical reaction is improved by forming irregularities on the surface of the polymer electrolyte membrane to increase the surface area. As such a method, JP-A-56-
A method for making unevenness on the film surface by a polishing method disclosed in No. 139974, and a method for making unevenness on the surface by pressing a metal plate (press jig) having unevenness on the surface disclosed in JP-A-3-167752. A method has been known in which a reaction layer film having the same is prepared in advance, and the reaction layer film is press-bonded to form irregularities on the polymer electrolyte membrane.

However, the polishing method is difficult to control the surface irregularities, and it is difficult to uniformly form the irregularities on the surface of the film. Further, the film is rubbed with a polishing paper or the like or the sandy particles are collided with the pin, so There are problems that holes are generated and the film is easily damaged. In addition, when the polymer electrolyte membrane is applied to an electrochemical device such as a fuel cell, it is common to form a catalyst or an electrode in the center of the membrane and to have a gasket function in the peripheral portion of the membrane. . On the other hand, the polishing method has a problem in that the gas sealing property is deteriorated because irregularities are easily formed even on the outer peripheral portion of the film. On the other hand, in the method of pressing a metal plate having unevenness, it is necessary to physically peel off the metal plate after pressing, but there is a problem that the surface having unevenness is easily damaged at this time. Further, in both of the above two methods, the shape of the concavo-convex shape is only a mountain-valley shape as shown in the left side of FIG. 1, but it has been desired to form a more complicated shape such as the right side in which the surface area is further increased.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above problems of the method for forming a rough surface of a polymer electrolyte membrane, such as easy formation of pinholes and easy breakage of the membrane, and fuel consumption. In order to improve the efficiency of electrochemical devices such as batteries, the present inventors have conducted studies to provide a polymer electrolyte membrane having an extremely complicated surface shape, a three-dimensional shape, and a large surface area with a high yield.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have pressure-bonded a metal foil having a roughened surface to a polymer electrolyte membrane, and then melted the metal foil. The present invention has been completed by finding that the above problems can be solved by removing them, that the membrane is not damaged at all and that a polymer electrolyte membrane having a complicated surface shape can be easily obtained.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the polymer electrolyte membrane is a polymer film having a polymer having a group having ion-exchange ability in the polymer skeleton, or a substance having ion-exchange ability in the polymer membrane. Is a general term for what is included, and is roughly classified into a cation exchange membrane and an anion exchange membrane. There is also a membrane 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, sulfuric acid, sulfonic acids, phosphoric acids, carboxylic acids and solid acid in the polymer membrane. Examples thereof include those containing an acidic substance such as the above fine particles. Examples of the anion exchange membrane include polymer membranes having a basic group such as amino group, quaternary ammonium hydroxide and guanidine group, and membranes in which a solid base is dispersed. In addition, there are those in which the acid or base moiety in the film is salted, and those in which the salt is impregnated. The most typical ion exchange membranes for fuel cells are known to have polyperfluorosulfonic acid formed into a film, for example, DuPont USA: Nafion, trade name; Asahi Glass Co., Ltd .: Flemion, Asahi Kasei. Industrial Co., Ltd .: trade name Aciplex and the like can be mentioned.

The metal foil used in the present invention is a metal foil prepared by a method such as plating or rolling, which has a rough surface with fine irregularities on at least one surface. The type of metal is not particularly limited, but typical examples are copper, nickel,
Examples of the metal foil include aluminum, zinc, tin, iron or alloys thereof. The method for forming unevenness on the surface is not particularly limited, but a preferred example is used for applications such as a metal foil-clad laminate for printed wiring boards, a metal foil having an uneven surface formed by electrolytic plating or a metal corrosive agent on the surface. Is mentioned. The metal foil for laminated metal foils for printed wiring boards has been subjected to electrolytic plating to form extremely complicated irregularities evenly on one or both sides of the metal foil in order to increase the adhesive strength with the resin that serves as an insulator. Is something
It is easily available. A method of corroding the surface of a metal foil to form complex irregularities is also known, and as a metal corrosive agent, for example, MEC Co., Ltd .: trade name MEC Etch Bond CZ8100, CZ5480, or a mixture of sulfuric acid and hydrogen peroxide. Metal corrosion agents of

The roughness of the metal foil having a rough surface as described above is not particularly specified, but when the difference in height between the apex of the convex portion and the bottom of the concave portion is defined as the roughness, the roughness is 0.5 μm. -10
The range is preferably 0 μm, more preferably 1 μm to 5
It is 0 μm. Further, within the above preferred range, the usable range is different depending on whether the thickness or pressure-bonding surface of the polymer electrolyte membrane to be used is one side or both sides. On the other hand, a metal foil having a roughness of 1/2 or less can be preferably used, and when pressure-bonded on one side, a metal foil having a roughness of 4/5 or less with respect to the thickness of the polymer electrolyte membrane can be preferably used. If a metal foil rougher than this is used, the film is partially thinned too much, and substances on both sides of the film are likely to permeate, which is not preferable.

Further, a metal foil having a rough surface whose shape is processed according to a desired place on the polymer electrolyte membrane or a metal foil having a part of the surface roughened according to the desired place is formed. By pressing the rough surface of these metal foils onto the polymer electrolyte membrane and melting the metal foil, the metal foil having the rough surface is adhered, or the roughened metal foil is adhered. It is possible to roughen only the part that was left. When the polymer electrolyte membrane is applied to an electrochemical device such as a fuel cell, it is common that a catalyst, an electrode and the like are formed in the central portion of the membrane and a peripheral portion of the membrane also serves as a gasket. According to the manufacturing method of the present invention, the surface can be roughened except for the outer peripheral portion of the film, so that the peripheral portion has no irregularities, and the deterioration of the gas sealing property can be prevented.

In the present invention, the step of pressure-bonding the metal foil to the polymer electrolyte membrane includes a method such as pressing and roll laminating, and it is preferable to heat and pressure-bond the polymer foil to a temperature at which the polymer electrolyte membrane becomes flexible. The preferable temperature for heating varies depending on the material of the film, but it is preferable that the film material is in a softened, semi-molten or molten state at the time of pressure bonding and lower than the decomposition temperature. However, even if the temperature is higher than the decomposition temperature, there is no problem if the pressure bonding step is extremely short. For example, for a perfluorosulfonic acid-based polymer electrolyte membrane, it is preferable to carry out at 50 ° C to 200 ° C. The pressure bonding may be performed in a dry state of the film or in a state of being swollen with water, a solvent or the like. Furthermore, when the film swells due to water etc. when used as an electrochemical device and the size changes, the film is swollen in advance and then pressure is applied, or the dimensional change of the film is calculated in advance, and the size of the metal foil is calculated. You may decide the size. Further, thermocompression bonding using a hard roll made of metal, ceramic or the like is preferable in that irregularities on the metal foil can be transferred evenly and continuous production can be facilitated.

In the present invention, the step of dissolving and removing the metal foil is essential. When the metal foil that three-dimensionally digs into the film in the crimping process is peeled off, the film is very often deformed or damaged, and in many cases, problems such as metal foil fragments remaining in the film occur. By dissolving and removing the metal foil in the process, the three-dimensional shape of the metal foil can be transferred as it is without damaging the film or mixing metal impurities. The solution that can be used in this step is not particularly limited as long as it can dissolve the metal,
A solution such as an acid, an alkali, ferric chloride, cupric chloride, or a mixed solution of sulfuric acid and hydrogen peroxide can be used. However,
As is generally known, the type of metal may limit the usable liquid. For example, copper foil is soluble in ferric chloride aqueous solution and mixed solution of sulfuric acid and hydrogen peroxide,
Does not dissolve in alkali or sulfuric acid at room temperature. The aluminum foil is soluble in both acid and alkali.

When the metal foil is melted in the above steps, impurities such as metal ions remain in the film, impeding the transport of ions when used in an electrochemical device, or causing metal in the film during operation as an electrochemical device. May be deposited and short-circuited. In the present invention, in order to prevent this, it is preferable to include a film washing step with an acid, which can remove ionic impurities. Further, in order to wash the acid, a step of washing the film with pure water or the like may be added.

The above-mentioned metal dissolving step and acid cleaning step can be carried out by immersing the film in a liquid, but if a conveyor type spray atomizer is used, it can be combined with the roll-bonding step of the metal foil in a continuous production line. Are more preferable because high productivity can be obtained.

[0014]

When the polymer electrolyte membrane having a roughened surface produced by the present invention is used in an electrochemical device such as a fuel cell, the reaction efficiency is improved and, as a result, the performance such as battery output is improved. The reason for this is that an extremely complicated uneven shape can be formed on the surface of the film, and the film surface area is greatly increased.
This is probably because the ions generated by the electrochemical reaction on the film surface can be efficiently dissolved.

[0015]

Example 1 (Method for producing a polymer electrolyte membrane having a roughened surface) Nafion 115 manufactured by DuPont, USA, cut out into 10 cm square was used as a polymer electrolyte membrane, and 5 were provided at the center portions on both sides thereof.
A copper foil (cm-square, CF-T9, thickness: 35 μm) with one side roughened cut into cm squares was overlaid so that the rough side was on the electrolyte membrane side, and the metal heat was applied. Roll lamination was performed at 130 ° C. using a roll, and the metal foil was pressure bonded. Next, the copper foil was completely dissolved and removed through a conveyor-type etching device capable of spraying a ferric chloride aqueous solution.
This membrane was passed through a conveyor type atomizer capable of spraying a 1N hydrochloric acid aqueous solution, then sprayed with distilled water using the same conveyor type atomizer to wash it, and a polymer electrolyte membrane having irregularities formed on the surface within a 5 cm square area of the central portion. Got An electron micrograph of the roughened surface of the polymer electrolyte membrane tilted by 30 degrees is shown in FIG. Comparing with the electron micrograph (FIG. 3) in which the rough surface of the copper foil used was also tilted by 30 degrees, it was found that the complex irregularities on the copper foil were completely transferred onto the polymer electrolyte membrane. .

Example 2 (Fuel Cell) Carbon black supporting platinum as a catalyst (manufactured by Tanaka Kikinzoku Kogyo KK), polytetrafluoroethylene suspension and polymer electrolyte solution (manufactured by DuPont, USA:
Nafion (trade name) 5% solution) in solid content of 6: 2: 2
The ink prepared above was mixed at a ratio of 1 to each of two sheets of carbon paper water-repellent treated with polytetrafluoroethylene so that the platinum amount was 0.5 mg / cm ² and dried. Next, two sheets of this carbon paper were superposed on both sides of the surface-roughened polymer electrolyte membrane prepared in Example 1 so that the ink-printed surface was on the inside, and the temperature was 120 ° C.
A membrane electrode assembly (MEA) for a fuel cell was prepared by hot pressing under the condition of 1 minute. When this was incorporated into a fuel cell single cell and operated under the conditions described below to create a current density-voltage curve, a higher voltage was obtained on the high current density side compared to Comparative Example 1 described below as shown in FIG. It was found that the performance was higher than that of Example 1.

Comparative Example 1 Nafion 1 manufactured by DuPont, USA as a polymer electrolyte membrane
A fuel cell membrane electrode assembly (MEA) was produced in the same manner as in Example 2 except that 15 was used as it was. This was incorporated into a fuel cell single cell and operated under the conditions described below to prepare a current density-voltage curve. As a result, it looks like Figure 4.
Compared with Example 2, the voltage on the high current density side was low and the performance was inferior.

(Fuel Cell Performance Evaluation Method) The operating conditions when the MEA prepared in Example 2 and Comparative Example 1 were incorporated into the fuel cell single cell were as follows. The fuel gas and oxidant gas are pure hydrogen and pure oxygen, respectively, and each gas is 90% at 60 ° C.
The above humidity was maintained. The cell temperature was 60 ° C. Current and voltage were measured while changing the load with an electronic loader. A current density-voltage curve was created based on this value.

[0019]

EFFECTS OF THE INVENTION The method of roughening a polymer electrolyte membrane according to the present invention can form extremely complicated uneven shapes uniformly on the surface of the polymer electrolyte membrane and causes problems such as pinholes and tears. It has the feature that there is no Further, since only a necessary portion can be roughened, when used by incorporating it into a fuel cell or the like, the gas sealing property and the film strength which are problems in the conventional roughening method are not reduced. Further, continuous production is possible by pressing the metal foil with a hot roll. The surface-roughened polymer electrolyte membrane obtained by the present invention is extremely useful as an electrochemical device such as a fuel cell.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the state of the surface of a conventional polymer electrolyte membrane and a desirable polymer electrolyte membrane.

FIG. 2 is an electron micrograph of a roughened surface of a polymer electrolyte membrane.

FIG. 3 is an electron micrograph of a roughened surface of a copper foil used.

FIG. 4 is a graph of current density-voltage curves of Example 2 and Comparative Example 1.

Claims (5)

[Claims] 1. A rough surface comprising a step of pressure-bonding the rough surface of a metal foil having a rough surface to one or both surfaces of a polymer electrolyte membrane, and a step of dissolving and removing the metal foil. Of producing a polymerized polymer electrolyte membrane. 2. A membrane is contacted with an acidic solution after a step of pressure-bonding the rough surface of a metal foil having a rough surface to one or both sides of the polymer electrolyte membrane and a step of dissolving and removing the metal foil. A method for producing a polymer electrolyte membrane having a roughened surface, comprising the steps of: 3. A metal foil having a rough surface, the shape of which is processed according to a desired location on the polymer electrolyte membrane, or the surface of which is partially roughened according to the desired location. The method for producing a polymer electrolyte membrane having a roughened surface according to claim 1 or 2, wherein 4. An electrochemical device using a polymer electrolyte membrane having a roughened surface produced by the method according to any one of claims 1 to 3. 5. A fuel cell using the polymer electrolyte membrane having a roughened surface produced by the method according to any one of claims 1 to 3.