JP2005078870A - Fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell which enhances its output by raising catalyst efficiency on the interface of an electrode and an electrolyte, and also to provide its manufacturing method. <P>SOLUTION: Metal films 17 having openings are provided on the electrolyte film 11 side of the fuel cell electrode 12 and on the electrolyte film 11 side of the oxygen electrode 13. The opening area percentage of the metal film 17 in a surface perpendicular to the direction in which the fuel cell electrode 12 faces the oxygen electrode 13 is 25 % or more, and electron conductivity of the fuel electrode 12 and the oxygen electrode 13 is enhanced while securing the contact area where the fuel electrode 12 and the oxygen electrode 13 are brought into contact with the electrolyte film 11. The metal film 17 is preferably formed of noble metal such as Pt or Au, and its thickness is preferably not less than 0.10 μm and not more than 10 μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell in which a fuel electrode and an oxygen electrode are arranged to face each other via an electrolyte membrane, and a method for manufacturing the same.

  In recent years, the need for alternative clean energy sources that can replace fossil fuels such as petroleum has increased, and for example, hydrogen (gas) fuel or methanol fuel has attracted attention. Hydrogen is a clean and inexhaustible ideal energy source because it contains a large amount of chemical energy per unit mass and does not release harmful substances or global warming gases when used. Further, lower alcohols typified by methanol are attracting attention as direct methanol fuel cells because they exhibit a reaction potential close to that of hydrogen.

  In a fuel cell, a fuel electrode and an oxygen electrode are arranged with an electrolyte membrane in between, a fuel such as hydrogen is supplied to the fuel electrode, and oxygen is supplied to the oxygen electrode to cause a cell reaction and obtain an electromotive force. is there. The electrode contains a catalyst for causing a battery reaction, but this catalyst is usually carried on a carrier having a large specific surface area such as carbon black. This is because if the support is not used, the catalyst particles are enlarged due to the sintering phenomenon and cannot be stably present.

  However, since the electrode formed of the catalyst supported on the carrier is an aggregate of particles, the contact resistance between the particles is larger than that of metal or the like. The electrode also contains a polymer for conducting ions such as fluorocarbons having a sulfonic group, but the electronic conductivity of this polymer is close to that of an insulator, and it is bound so as to enclose the carrier carrying the catalyst. Exist. Therefore, the electronic conductivity as the whole electrode is low.

  Further, at the interface between the electrode and the electrolyte membrane, the polymer constituting the electrolyte membrane has digged into the electrode and has intervened between the particles of the carrier carrying the catalyst, thereby inactivating the catalyst at the interface. Therefore, in order to improve the catalyst efficiency, it is necessary to improve the electron conductivity at the interface between the electrode and the electrolyte membrane.

Therefore, conventionally, for example, it has been proposed to form a metal film made of platinum (Pt) on the surface of the electrolyte film (see, for example, Non-Patent Document 1 and Patent Document 1).
S. Y. SYCha, 1 other, “Performance of Proton Exchange Membrane Fuel Cell Electrodes Prepared by Direct Deposition Ultrathin Platinum on the Membrane Surface) ", Journal of the Electrochemical Society (USA), The Electrochemical Society, November 1999, 146, 11 , P. 4055-4060 JP 2002-75384 A

  However, if a metal film is formed on the electrolyte membrane as in the past, the contact area between the catalyst particles and the electrolyte membrane at the interface between the electrode and the electrolyte membrane is reduced due to the rigidity of the metal, and the output is extremely reduced. There was a problem of doing.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a fuel cell capable of increasing the catalyst efficiency at the interface between the electrode and the electrolyte membrane and improving the output, and a method for manufacturing the same. .

  A fuel cell according to the present invention is a fuel cell in which a fuel electrode and an oxygen electrode are arranged to face each other through an electrolyte membrane, and includes a noble metal element on at least one of the fuel electrode and the electrolyte membrane side of the oxygen electrode. The metal film has an opening, and the opening area ratio in a plane perpendicular to the opposing direction of the fuel electrode and the oxygen electrode is 25% or more.

  A method of manufacturing a fuel cell according to the present invention is a method of manufacturing a fuel cell in which a fuel electrode and an oxygen electrode are arranged to face each other with an electrolyte membrane, wherein a noble metal element is placed on at least one of the fuel electrode and the oxygen electrode. Including a step of forming a metal film.

  In the fuel cell according to the present invention, a metal film containing a noble metal element having an opening area ratio of 25% or more is provided on the electrolyte membrane side of the fuel electrode, the electrolyte membrane side of the oxygen electrode, or both. The metal film suppresses inactivation of the electrode at the interface with the electrolyte membrane, and ensures contact between the electrode and the electrolyte membrane through the opening. Therefore, the catalyst efficiency is improved.

  In the fuel cell manufacturing method according to the present invention, a metal film containing a noble metal element is formed on the fuel electrode, the oxygen electrode, or both. Therefore, an opening is formed in the metal film, and an opening area ratio in a plane perpendicular to the film forming direction is 25% or more.

  According to the fuel cell of the present invention, the metal electrode having the opening with an opening area ratio of 25% or more is provided on at least one of the fuel electrode and the electrolyte membrane side of the oxygen electrode. The electron conductivity of the fuel electrode or the oxygen electrode can be improved while ensuring the contact area between the electrode and the electrolyte membrane. Therefore, the catalyst efficiency of the fuel electrode or oxygen electrode can be increased, and the output can be improved.

  Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 shows the configuration of a fuel cell according to an embodiment of the present invention. This fuel cell has a fuel electrode 12 and an oxygen electrode 13 which are arranged to face each other with an electrolyte membrane 11 interposed therebetween. The electrolyte membrane 11, the fuel electrode 12, and the oxygen electrode 13 are housed inside the exterior member 14. Inside the exterior member 14, a fuel chamber 15 is provided adjacent to the fuel electrode 12, and an oxygen chamber 16 is provided adjacent to the oxygen electrode 13. The fuel chamber 15 is connected to a fuel supply unit (not shown) through circulation holes 14A and 14B provided in the exterior member 14, and liquid fuel containing hydrogen, methanol, ethanol, dimethyl ether, or the like is supplied from the fuel supply unit. It has come to be. The oxygen chamber 16 communicates with the outside through a circulation hole 14 </ b> C provided in the exterior member 14, and supplies air, that is, oxygen to the oxygen electrode 13 by natural ventilation.

The electrolyte membrane 11 is made of, for example, a proton conductor. Examples of the proton conductor include many perfluorocarbon polymers having a sulfonic acid group (—SO ₃ H), H ₃ Mo ₁₂ PO ₄₀ · 29H ₂ O, and Sb ₂ O ₅ · 5.4H ₂ O. Examples include polymolybdic acids or oxides having hydration water. These have high proton conductivity in a wet state. Protons react with water to generate oxonium ions (H ₃ O ⁺ ), and these oxonium ions move.

In addition, proton conductors having completely different conduction mechanisms may be used. As what has another conduction mechanism, the thing which made the base the carbonaceous material which has carbon as a main component, and introduce | transduced the proton dissociative group into this is mentioned, for example. This is because protons move through a proton dissociable group. Here, the “proton dissociable group” means a functional group capable of leaving a proton (H +) by ionization. Specific examples of the proton dissociable group include —OH, —OSO ₃ H, —SO ₃ H, —COOH, —OP (OH) _{2, and the} like. As the base carbonaceous material, any material having carbon as a main component can be used. However, after introducing a proton-dissociable group, ion conductivity is higher than electron conductivity. It is necessary to be.

  The fuel electrode 12 and the oxygen electrode 13 have a configuration in which a catalyst layer containing a catalyst such as platinum (Pt) or ruthenium (Ru) is formed on a current collector made of, for example, carbon paper. The catalyst layer is composed of, for example, a carrier in which a catalyst is supported, such as carbon black, dispersed in a proton conductive material.

  This fuel cell also has a metal film 17 on the electrolyte membrane 11 side of the fuel electrode 12 and on the electrolyte membrane 11 side of the oxygen electrode 13. FIG. 2 is a schematic enlarged view of the vicinity of the interface between the electrolyte membrane 11 and the fuel electrode 12 or the oxygen electrode 13. The metal film 17 is formed to have irregularities following the irregularities on the surfaces of the fuel electrode 12 and the oxygen electrode 13, that is, the irregularities of the supports 12B and 13B carrying the catalysts 12A and 13A, and has a large number of openings 17A. doing. The opening area ratio in the plane perpendicular to the opposing direction of the fuel electrode 12 and the oxygen electrode 13 of the metal film 17 is 25% or more. Thereby, in this fuel cell, the contact area between the fuel electrode 12 and the oxygen electrode 13 and the electrolyte membrane 11 can be increased while the electron conductivity of the fuel electrode 12 and the oxygen electrode 13 is increased. .

  This opening area ratio is the ratio of the area S2 of the opening in the same plane to the area (including the area of the opening) S1 of the surface perpendicular to the facing direction of the fuel electrode 12 and the oxygen electrode 13 of the metal film 17 (S2 / S1). The opening area ratio is more preferably 40% or more, and further preferably 45% or more. Moreover, it is preferable that this opening area ratio is 80% or less. This is because if the opening area ratio is too large, the electron conductivity of the fuel electrode 12 and the oxygen electrode 13 cannot be sufficiently improved.

  Since the metal film 17 is in contact with the electrolyte film 11 that is a strong acid of sulfuric acid or more, it is preferable that the metal film 17 includes a noble metal element that does not react with the electrolyte film 11, the fuel electrode 12, and the oxygen electrode 13. For example, it is preferably configured to include at least one member selected from the group consisting of platinum, gold (Au), silver (Ag), palladium (Pd), iridium (Ir), and ruthenium (Ru). More preferably, it is composed of at least one of them. Of these, platinum or gold is particularly preferable. The thickness of the metal film 17 is preferably 0.10 μm or more and 10 μm or less. If the thickness is smaller than 0.10 μm, the electron conductivity of the fuel electrode 12 and the oxygen electrode 13 cannot be sufficiently improved. If the thickness is larger than 10 μm, the metal film 17 has a low ionic conductivity, and is generated at the fuel electrode 12. This is because it becomes difficult for the protons to reach the electrolyte membrane 11 and the characteristics of the fuel cell deteriorate.

  This fuel cell can be manufactured, for example, as follows.

  First, the electrolyte membrane 11, the fuel electrode 12, and the oxygen electrode 13 made of the above-described materials are prepared, and the above-described materials are deposited on the surfaces of the catalyst layers of the fuel electrode 12 and the oxygen electrode 13 by vapor deposition, sputtering, chemical reduction, or the like. A metal film 17 made of the thickness and material is formed. Thereby, an opening 17A is formed in the metal film 17 following the irregularities of the catalyst layer of the fuel electrode 12 and the oxygen electrode 13, and the opening area ratio is 25% or more.

  Next, the fuel electrode 12 and the oxygen electrode 13 on which the metal film 17 is formed, and the electrolyte film 11 are laminated with the metal film 17 side as the electrolyte film 11 side, and are joined by, for example, hot pressing. Subsequently, the laminated electrolyte membrane 11, fuel electrode 12, and oxygen electrode 13 are accommodated in the exterior member 14. Thereby, the fuel cell shown in FIG. 1 is completed.

  The metal film 17 is not formed on the surfaces of the fuel electrode 12 and the oxygen electrode 13, but is formed on the surface of the electrolyte film 11 by vapor deposition, sputtering, chemical reduction, or the like, and then an opening is formed. The opening area ratio may be 25% or more. In this method, after the surface roughness of the electrolyte membrane 11 is increased by bringing it into contact with a rough surface film or the like, a film is formed thereon by vapor deposition, sputtering, chemical reduction, or the like, and the opening area ratio is 25. % Or more. However, it is preferable to form them on the surfaces of the fuel electrode 12 and the oxygen electrode 13 because a good metal film 17 can be easily formed with a small number of manufacturing steps.

  In this fuel cell, fuel is supplied to the fuel electrode 12, and protons and electrons are generated by the reaction. Protons move to the oxygen electrode 13 through the electrolyte membrane 11 and react with electrons and oxygen to generate water. At that time, protons move between the electrolyte membrane 11 and the fuel electrode 12 and between the electrolyte membrane 11 and the oxygen electrode 13 mainly through the opening 17A of the metal membrane 17, and the fuel electrode 12 and the oxygen electrode. The movement of electrons in 13 is mainly performed through the metal film 17. Therefore, the catalyst efficiency is improved.

  Thus, according to the present embodiment, the metal film 17 having the opening 17A having an opening area ratio of 25% or more is provided on the electrolyte membrane 11 side of the fuel electrode 12 and the electrolyte membrane 11 side of the oxygen electrode 13. Since it did in this way, the electronic conductivity of the fuel electrode 12 and the oxygen electrode 13 can be improved, ensuring the contact area of the fuel electrode 12 and the oxygen electrode 13, and the electrolyte membrane 11. FIG. Therefore, the catalyst efficiency of the fuel electrode 12 and the oxygen electrode 13 can be increased, and the output can be improved.

  In particular, if the metal film 17 includes at least one of the group consisting of platinum, gold, silver, palladium, iridium, and ruthenium, and further includes at least one of these, Above all, if it is made of platinum or gold, the reaction of the metal film 17 can be suppressed, and a higher effect can be obtained.

  Moreover, if the thickness of the metal film 17 is in the range of 0.10 μm or more and 10 μm or less, the electron conductivity and the ion conductivity can be further increased, and a higher effect can be obtained.

  Furthermore, specific examples of the present invention will be described. In the following examples, a fuel cell having the same configuration as that shown in FIG. 1 was produced and the characteristics were evaluated. Therefore, the following embodiments will be described using the same reference numerals with reference to FIG.

(Examples 1-8)
First, 20% by mass of a platinum catalyst supported on a carbon support (manufactured by Electrochemical Co., Ltd.) is mixed with a commercially available Nafion solution (manufactured by Furuuchi Chemical Co., Ltd .; 5 wt%), and carbon paper (manufactured by Electrochemical Co., Ltd.) is mixed. The fuel electrode 12 and the oxygen electrode 13 were produced. Next, a metal film 17 made of platinum was formed on the surfaces of the fuel electrode 12 and the oxygen electrode 13 by vapor deposition. Vapor deposition was conducted until a 0.5φ platinum wire was heated to red hot current until the wire was cut. At that time, the thickness of the metal film 17 was changed by changing the current value and the deposition time in Examples 1 to 8, 0.05 μm in Example 1, 0.1 μm in Example 2, and 0.2 μm in Example 3. Example 4 was 0.3 μm, Example 5 was 1.0 μm, Example 6 was 5.0 μm, Example 7 was 10.0 μm, and Example 8 was 15 μm. The thickness of the metal film 17 was visually observed with an SEM (Scanning Electron Microscope). Hitachi S-8000 (made by Hitachi, Ltd.) was used for SEM. The error in film thickness is ± 0.01 μm.

  When the opening area ratio was investigated by SEM about the obtained metal film 17 of Examples 1-8, all were 45% or more. FIG. 3 shows an SEM photograph of the metal film 17 of Example 2 as a representative. Further, for the obtained fuel electrode 12 and oxygen electrode 13 of Examples 1 to 8, the interfacial resistance on the metal film 17 side was measured by the four-terminal method shown in FIG. The obtained results are shown in FIGS.

Subsequently, a perfluorocarbon polymer film having a sulfonic acid group is used as the electrolyte film 11, and the fuel electrode 12, the electrolyte film 11, and the oxygen electrode 13 are laminated so that the metal film 17 is in contact with the electrolyte film 11. Then, they were integrated by a hot press method to produce a power generator. The hot press conditions were a pressurization time of 15 minutes, a pressure of 70 kgf / cm ² , and a temperature of 130 ° C. Thus, fuel cells of Examples 1 to 8 were obtained.

  About the obtained fuel cell of Examples 1-8, output characteristics were evaluated using the evaluation apparatus by Toyo Technica Co., Ltd. At that time, 50 ml / min of dry hydrogen was supplied to the fuel electrode 12 and 100 ml / min of dry air was supplied to the oxygen electrode 13 to measure the battery output at a closed circuit voltage of 0.3V. The temperature of the fuel cell at the time of evaluation was 20 ° C to 24 ° C. The obtained results are shown in FIGS.

  Further, as Comparative Example 1 for this example, a fuel cell was fabricated in the same manner as in Examples 1 to 8, except that no metal film was formed. Also in Comparative Example 1, the interface resistance and the battery output of the fuel electrode and the oxygen electrode were measured in the same manner as in Examples 1-8. The obtained results are shown in FIG. 5 and FIG.

Furthermore, as Comparative Example 2 for this example, a metal film made of platinum having a thickness of 0.1 μm is formed on an electrolyte film whose surface is not roughened by vapor deposition, and is integrated with a fuel electrode and an oxygen electrode on which no metal film is formed. A fuel cell was fabricated in the same manner as in Examples 1 to 8 except that. When the opening area ratio of the metal film of Comparative Example 2 was examined in the same manner as in Examples 1 to 8, it was as low as 24%. FIG. 7 shows an SEM photograph of the metal film of Comparative Example 2. Further, when the battery output of the fuel cell of Comparative Example 2 was examined in the same manner as in Examples 1 to 8, the battery output at 0.3 V was as extremely low as 100 mA / cm ² .

  As described above, from the results of Examples 1 to 8 and Comparative Example 1, by providing the metal film 17, the interface resistance between the fuel electrode 12 and the oxygen electrode 13 can be lowered and the battery output can be improved. I understood. From the results of Examples 1 to 8 and Comparative Example 2, the fuel electrode 12 can be obtained by setting the opening area ratio of the metal film 17 to 25% or more, further 40% or more, more preferably 45% or more. It was also found that the battery output can be improved while lowering the interface resistance of the oxygen electrode 13. Further, it has been found that if the metal film 17 is formed on the fuel electrode 12 and the oxygen electrode 13, the opening area ratio can be easily increased.

  In addition, as can be seen from the comparison of Examples 1 to 8, in Example 1 in which the thickness of the metal film 17 was thinner than 0.1 μm, the interface resistance of the metal film 17 was increased, and the battery output was also low. . In Example 8 in which the thickness of the metal film 17 was 15 μm, although the interface resistance of the metal film 17 was low, the battery output was low. That is, it has been found that if the thickness of the metal film 17 is 1 μm or more and 10 μm or less, the interface resistance of the metal film 17 can be lowered and the battery output can be improved, which is preferable.

  The present invention has been described with reference to the embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above embodiment and example, the metal film 17 is provided on the fuel electrode 12 and the oxygen electrode 13 on the side of the electrolyte film 11. The metal film 17 may be provided only on one side of the electrolyte film 11 side. However, it is preferable to provide both of them because a higher effect can be obtained.

  Moreover, in the said embodiment and Example, although the structure of the electrolyte membrane 11, the fuel electrode 12, and the oxygen electrode 13 was demonstrated concretely, you may make it comprise with another structure or another material.

  Further, in the above-described embodiments and examples, fuel is supplied to the fuel electrode 12 from a fuel supply unit (not shown). However, the fuel chamber may be a sealed type, and fuel may be supplied as necessary. .

  In addition, in the above-described embodiments and examples, the supply of air to the oxygen electrode 13 is natural ventilation, but may be forcibly supplied using a pump or the like. In that case, oxygen or a gas containing oxygen may be supplied instead of air.

  Furthermore, in the above-described embodiments and examples, the single cell type fuel cell has been described. However, the present invention can also be applied to a stacked type in which a plurality of cells are stacked.

It is sectional drawing showing the structure of the fuel cell which concerns on one embodiment of this invention. FIG. 2 is an enlarged cross-sectional view illustrating the vicinity of an interface between the electrolyte membrane illustrated in FIG. 1 and a fuel electrode or an oxygen electrode. It is a microscope picture of the metal film which concerns on Example 2 of this invention. It is a top view showing the 4-terminal method used when measuring interface resistance in the Example and comparative example of this invention. It is a characteristic view showing the result of the Example and comparative example of this invention. It is a characteristic view showing the result of the Example and comparative example of this invention. 6 is a micrograph of a metal film according to Comparative Example 4.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Electrolyte membrane, 12 ... Fuel electrode, 13 ... Oxygen electrode, 14 ... Exterior member, 14A, 14B, 14C ... Flow hole, 15 ... Fuel chamber, 16 ... Oxygen chamber, 17 ... Metal film, 17A ... Opening.

Claims (5)

A fuel cell in which a fuel electrode and an oxygen electrode are arranged to face each other through an electrolyte membrane,
A metal film containing a noble metal element is provided on at least one of the fuel electrode and the electrolyte film side of the oxygen electrode,
The metal film has an opening, and an opening area ratio in a plane perpendicular to a facing direction of the fuel electrode and the oxygen electrode is 25% or more.   The metal film includes at least one selected from the group consisting of platinum (Pt), gold (Au), silver (Ag), palladium (Pd), iridium (Ir), and ruthenium (Ru). The fuel cell according to claim 1.   The fuel cell according to claim 1, wherein the metal film is made of platinum or gold.   The fuel cell according to claim 1, wherein the metal film has a thickness of 0.10 μm to 10 μm. A method of manufacturing a fuel cell in which a fuel electrode and an oxygen electrode are arranged to face each other through an electrolyte membrane,
A method for producing a fuel cell, comprising a step of forming a metal film containing a noble metal element on at least one of a fuel electrode and an oxygen electrode.

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