JP2009140854A - Membrane-electrode assembly and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane-electrode assembly which can control a drop of an output of a fuel cell and a gas leakage of an electrolyte membrane, and to provide a fuel cell including the same. <P>SOLUTION: The membrane-electrode assembly comprises a catalyst layer containing a hydrogen ion conductive electrolyte. The catalyst layer contains metal ions coordinating with an ion exchange group in the hydrogen ion conductive electrolyte, wherein a content of the metal ions has an upper limit of the number of mols equivalent to that of the ion exchange group in the hydrogen ion conductive electrolyte. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to membrane-electrode assemblies and fuel cell technologies.

  In general, a fuel cell includes a membrane-electrode assembly including an anode catalyst layer and a cathode catalyst layer sandwiching both sides of an electrolyte membrane, a pair of diffusion layers sandwiching both sides of the membrane-electrode assembly, and both diffusion layers. And a fuel cell separator sandwiching the outside. During power generation of the fuel cell, when the anode gas supplied to the anode electrode catalyst layer is hydrogen gas and the cathode gas supplied to the cathode electrode catalyst layer is oxygen gas, the anode electrode catalyst layer undergoes a reaction to form hydrogen ions and electrons. Hydrogen ions pass through the electrolyte membrane to the cathode catalyst layer, and electrons reach the cathode catalyst layer through an external circuit. On the other hand, in the cathode electrode catalyst layer, a reaction in which hydrogen ions, electrons and oxygen gas react to generate moisture is performed, and energy is released.

The electrolyte membrane has hydrogen ion conductivity and transports hydrogen ions generated in the anode electrode catalyst layer to the cathode electrode catalyst layer. The catalyst layer also contains a hydrogen ion conductive electrolyte. Actually, hydrogen ions generated in the anode catalyst layer hydrate with the water absorbed by the hydrogen ion conductive electrolyte and the electrolyte membrane and move in the form of H ₃ O ⁺ .

  If the water absorbed by the electrolyte and the electrolyte membrane remains in the electrolyte and the electrolyte membrane even when the fuel cell is not generating electricity, the reaction gas in the fuel cell may permeate (leak) the electrolyte membrane. is there. When gas leakage of the electrolyte membrane occurs, the voltage of the fuel cell rises and the durability of the fuel cell may be reduced.

  Although not for suppressing gas leakage of the electrolyte membrane, for example, in Patent Documents 1 to 3, in order to suppress a decrease in the catalytic activity of the anode electrode catalyst layer and the cathode electrode catalyst layer, other than hydrogen storage alloy or platinum group A membrane-electrode assembly to which these metals are added has been proposed.

In order not by way of suppressing a gas leak of the electrolyte membrane, for example, Patent Document 4, to decompose H ₂ O ₂ was radicalized generated in the anode catalyst layer and cathode catalyst layer, H ₂ O A membrane-electrode assembly to which a metal or metal oxide having _two resolutions is added has been proposed.

Among the metals added to the membrane-electrode assemblies of Patent Documents 1 to 4, there are also metals that can suppress gas leakage of the electrolyte membrane. However, in order to decompose the radicalized H ₂ O ₂ in order to suppress a decrease in catalytic activity, it is necessary to add more metal in order to suppress gas leakage of the electrolyte membrane. Therefore, the output of the fuel cell to which metal is added may be lower than the output of the fuel cell to which no metal is added.

JP-A-10-74523 JP-A-11-329452 JP 2002-110180 A JP 2006-269133 A

  An object of the present invention is to provide a membrane-electrode assembly capable of suppressing a decrease in output of a fuel cell and gas leakage of an electrolyte membrane, and a fuel cell including the membrane-electrode assembly.

  The present invention is a membrane-electrode assembly having a catalyst layer containing a hydrogen ion conductive electrolyte, the catalyst layer containing a metal ion coordinated to an ion exchange group in the hydrogen ion conductive electrolyte, The upper limit of the ion content is the number of moles equal to the number of moles of ion exchange groups in the hydrogen ion conductive electrolyte.

  In the membrane-electrode assembly, the metal ion content is preferably in the range of 80 mol% to 100 mol% with respect to the number of moles of ion exchange groups in the hydrogen ion conductive electrolyte.

  In the membrane-electrode assembly, the catalyst layer is preferably only on the anode electrode catalyst layer side.

  In the membrane-electrode assembly, the metal ion is preferably added as a metal oxide.

  In the membrane-electrode assembly, the metal species of the metal ion is preferably at least one of iron, nickel, aluminum, silicon, cerium, and manganese.

  The present invention also provides a fuel cell comprising a membrane-electrode assembly having a catalyst layer containing a hydrogen ion conductive electrolyte, wherein the catalyst layer is a metal coordinated to an ion exchange group in the hydrogen ion conductive electrolyte. The upper limit of the content of the metal ions including ions is equal to the number of moles of ion-exchange groups in the hydrogen ion conductive electrolyte.

  According to the present invention, the catalyst layer constituting the membrane-electrode assembly includes a metal ion coordinated to an ion exchange group of the hydrogen ion conductive electrolyte in the catalyst layer, and the content of the metal ion is a hydrogen ion conductive electrolyte. Membrane-electrode assembly capable of suppressing reduction in fuel cell output and gas leakage of electrolyte membrane by setting the upper limit to the number of moles equal to the number of moles of ion exchange groups therein, and a fuel cell including the membrane-electrode assembly Can be provided.

  Embodiments of the present invention will be described below.

  FIG. 1 is a schematic diagram showing an example of the configuration of a fuel cell according to an embodiment of the present invention. As shown in FIG. 1, the fuel cell 1 sandwiches both sides of an electrolyte membrane 10 between an anode electrode catalyst layer 12 and a cathode electrode catalyst layer 14, and both outer sides of the membrane electrode assembly 16. It has a pair of diffusion layers 18a and 18b and a pair of fuel cell separators 20a and 20b that sandwich both outer sides of the diffusion layers 18a and 18b. Further, the fuel cell according to the present embodiment may be a stack of a plurality of fuel cells 1 as unit cells.

  The anode electrode catalyst layer 12 and the cathode electrode catalyst layer 14 include a metal catalyst, a carrier supporting the metal catalyst, and a hydrogen ion conductive electrolyte. Further, at least one of the anode electrode catalyst layer 12 and the cathode electrode catalyst layer 14 contains a metal ion coordinated to an ion exchange group in the hydrogen ion conductive electrolyte.

  The metal catalyst used for the anode electrode catalyst layer 12 and the cathode electrode catalyst layer 14 may have any catalytic activity for the hydrogen reduction reaction in the anode electrode catalyst layer 12 and the oxygen oxidation reaction in the cathode electrode catalyst layer 14. There is no particular limitation, and for example, platinum, palladium, iridium, rhodium, a platinum alloy, or the like can be used.

  The carrier for supporting the metal catalyst is not particularly limited as long as it is a conductive material. For example, conductive carbon such as carbon black, graphite, activated carbon, conductive ceramic, or the like can be used.

The hydrogen ion conductive electrolyte is not particularly limited as long as it is an electrolyte having an ion exchange group that realizes hydrogen ion conductivity. Examples of the hydrogen ion conductive electrolyte include a fluorine-based electrolyte and a hydrocarbon-based electrolyte having SO ₃ ⁻ , COO ⁻ , PO ₃ ^— or the like as an ion exchange group. From the viewpoint of high durability and high hydrogen ion conductivity, a fluorine-based electrolyte having SO ₃ ^— is preferable, and examples thereof include perfluorocarbon sulfonic acid resin.

  The content of metal ions coordinated to ion exchange groups in the hydrogen ion conductive electrolyte (hereinafter sometimes simply referred to as “metal ions”) is determined by the ion exchange groups in the hydrogen ion conductive electrolyte contained in the catalyst layer. The upper limit is the number of moles of metal ions equal to the number of moles.

  A more preferable metal ion content is in the range of 80 mol% to 100 mol% with respect to the number of moles of ion exchange groups in the hydrogen ion conductive electrolyte contained in the catalyst layer. When the content of the metal ions is lower than 80 mol%, gas leakage of the electrolyte membrane 10 cannot be sufficiently suppressed, and the durability of the fuel cell 1 may be lowered. When the content is higher than 100 mol%, the fuel cell 1 may be reduced.

  In the present embodiment, it is sufficient that at least one of the anode electrode catalyst layer 12 and the cathode electrode catalyst layer 14 includes a metal ion coordinated to an ion exchange group in the hydrogen ion conductive electrolyte. However, since the reaction rate of the oxidation-reduction reaction in the catalyst layer is slower in the oxidation reaction on the cathode electrode catalyst layer 14 side, the output of the fuel cell 1 is increased by adding the metal ions to the cathode electrode catalyst layer 14. May decrease. Therefore, it is preferable that the anode electrode catalyst layer 12 contains a metal ion coordinated with an ion exchange group in the hydrogen ion conductive electrolyte, in that a decrease in the output of the fuel cell 1 can be effectively suppressed.

  The metal ions are added to the catalyst layer (the anode electrode catalyst layer 12 or the cathode electrode catalyst layer 14) as a metal oxide, metal salt, metal complex, semiconductor, simple metal, or an alloy containing two or more kinds of metals. Just do it. However, the metal ions are catalyst as metal oxides in that they are easily coordinated to ion exchange groups in the hydrogen ion conductive electrolyte and can be stably present in the catalyst layer during power generation of the fuel cell 1. It is preferable to be added in the layer.

  The metal species of the metal ion coordinated to the ion exchange group in the electrolyte membrane 10 is, for example, at least one of Fe, Ni, Cr, Al, Mn, Si, Ce, Pb, alkali metal, alkaline earth metal, and the like. Species are mentioned. Moreover, the valence of the metal ion selected from the metal species is not particularly limited.

However, the metal species of the metal ions coordinated to the ion exchange group in the hydrogen ion conductive electrolyte are iron, nickel, aluminum, silicon, cerium, It is preferably at least one of manganese. Further, the metal ion metal coordinated to the ion exchange group in the hydrogen ion conductive electrolyte in terms of suppression of gas leakage of the electrolyte membrane 10, durability of the fuel cell 1, environmental load, material supply stability, and the like. More preferably, the seed is at least one of Ce and Mn. For example, when Ce and Mn are present as a metal oxide or the like in the catalyst layer, dicerium trioxide Ce ₂ O ₃ (having trivalent cerium ions), manganese dioxide MnO ₂ (divalent manganese ions) Preferably).

  Next, an example of a mechanism for suppressing gas leakage of the electrolyte membrane 10 will be described.

  FIG. 2 (a) is a diagram showing an example of the structure of the hydrogen ion conductive electrolyte in the catalyst layer, and FIG. 2 (b) is an example of the structure of the hydrogen ion conductive electrolyte membrane during power generation of the fuel cell. FIG. 2C is a diagram showing an example of the structure of the hydrogen ion conductive electrolyte membrane when the fuel cell is not generating electricity. The hydrogen ion conductive electrolyte shown in FIG. 2A is a perfluorocarbon sulfonic acid resin, and Rf is an abbreviation for perfluorocarbon.

As shown in FIG. 2 (b), when the perfluorocarbon sulfonic acid resin is placed in the presence of water, the sulfonic acid groups in the perfluorocarbon sulfonic acid resin are ionized to form SO ₃ ⁻ (ion exchange described above). Group). Then, SO ₃ ⁻ gather to form a cluster.

Since SO ₃ ⁻ is hydrophilic, water is usually drawn around SO ₃ ⁻ when the fuel cell 1 is not generating power. When water is attracted around SO ₃ ⁻ when the fuel cell 1 is not generating power, the reaction gas in the fuel cell 1 easily passes through the electrolyte membrane 10. This is because when water is attracted around SO ₃ ⁻ , the structure of the hydrogen ion conductive electrolyte is changed and gaps are easily formed, and gas is easily transmitted through the attracted water. When the gas leak of the electrolyte membrane 10 occurs, the voltage of the fuel cell 1 rises and the durability of the fuel cell 1 is likely to be lowered.

In the present embodiment, as shown in FIG. 2C, the metal ions in the catalyst layer are coordinated to an ion exchange group (for example, SO ₃ ⁻ ) when the fuel cell is not generating electricity. When the metal ions are coordinated, the hydrophilicity of SO ₃ ⁻ is lowered and water can be prevented from being drawn to the surroundings, so that gas leakage of the electrolyte membrane 10 can be suppressed. In the present embodiment, the content of metal ions is limited to the number of moles equal to the number of moles of ion exchange groups (for example, SO ₃ ⁻ ) of the hydrogen ion conductive electrolyte, and therefore, more metals than SO ₃ ⁻ It is possible to prevent ions from being present in the catalyst layer and to suppress a decrease in the output of the fuel cell 1.

The preferred metal ion content is in the range of 80 mol% to 100 mol% with respect to the number of moles of ion exchange groups (for example, SO ₃ ⁻ ) of the hydrogen ion conductive electrolyte. When the amount is less than 80 mol% with respect to the number of ion exchange groups (for example, SO ₃ ⁻ ) of the conductive electrolyte, water exists around SO ₃ ⁻ due to the presence of SO ₃ ⁻ in which metal ions are not coordinated. May be attracted and gas leakage of the electrolyte membrane 10 may not be sufficiently suppressed. Further, when the amount is more than 100 mol% with respect to the number of moles of ion exchange groups of the hydrogen ion conductive electrolyte, SO ₃ ⁻ more metal ions exist in the catalyst layer, and the output of the fuel cell 1 is It tends to decrease.

Further, the metal ions coordinated to SO ₃ ⁻ during the non-power generation are dissociated from SO ₃ ⁻ due to a potential difference generated between the anode electrode and the cathode electrode during power generation of the fuel cell 1, and return to the original state. . As described above, by setting the content of metal ions in the above range, it is possible to suppress the gas leak of the electrolyte membrane 10 and the decrease of the output of the fuel cell 1.

The electrolyte membrane 10 is not particularly limited as long as it is a membrane composed of an electrolyte having an ion exchange group that realizes hydrogen ion conductivity. The electrolyte used for the electrolyte membrane and the electrolyte used for the anode catalyst layer and the cathode catalyst layer may be the same or different. The electrolyte membrane 10 is preferably a membrane composed of a fluorine-based electrolyte having SO ₃ ^{− in} terms of high durability and high hydrogen ion conductivity, and examples thereof include a perfluorocarbon sulfonic acid resin membrane. Specific examples include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like.

Next, an example of a method for manufacturing the membrane-electrode assembly 16 will be described. At least one of the anode electrode catalyst layer 12 and the cathode electrode catalyst layer 14 includes, for example, carbon carrying a metal catalyst such as platinum described above, a hydrogen ion conductive electrolyte, and the metal oxide described above. And mix. At this time, a solvent such as alcohol that can dissolve the hydrogen ion conductive electrolyte may be added. The above-described metal oxide or the like is added so that the metal ion such as the metal oxide is, for example, 100 mol% with respect to the number of moles of the ion exchange group (for example, SO ₃ ⁻ ) of the hydrogen ion conductive electrolyte. . A membrane-electrode assembly 16 is obtained by forming a mixture of these substances on the electrolyte membrane 10.

  The diffusion layers 18a and 18b are not particularly limited as long as they have conductivity and can supply a reaction gas (anode gas, cathode gas) to the anode electrode catalyst layer 12 and the cathode electrode catalyst layer 14. Absent. The diffusion layers 18a and 18b are, for example, carbonaceous porous bodies such as carbon paper, carbon cloth, and carbon felt, aluminum, copper, nickel, nickel-chromium alloy, copper and its alloys, silver, aluminum alloy, zinc alloy, Examples thereof include a metal mesh or a metal porous body made of a metal such as lead alloy, titanium, niobium, tantalum, iron, stainless steel, gold, and platinum.

  The fuel cell separators 20a and 20b are not particularly limited as long as they have gas impermeability and electronic conductivity, and include metal plates and carbon plates. The fuel cell separators 20a and 20b are formed with reaction gas flow paths 22a and 22b through which a reaction gas flows.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples unless the gist thereof is changed.

Example 1
<Adjustment of catalyst layer ink>
Platinum catalyst-supported carbon, ethanol, perfluorocarbon sulfonic acid resin, and Ce ₂ O ₃ (the content of Ce ions is 40 mol% with respect to the number of moles of SO ₃ ⁻ in the perfluorocarbon sulfonic acid resin) are mixed with a stirrer. Thus, an anode catalyst layer ink was prepared. Further, platinum catalyst-supported carbon, ethanol, and Nafion were mixed with a stirrer to prepare a cathode electrode catalyst layer ink.

<Fabrication of fuel cell>
The anode electrode catalyst layer ink was spray-coated on one surface side of the electrolyte membrane (membrane pressure 50 μm), and the cathode electrode catalyst layer ink was spray-coated on the other surface side, and the ink was volatilized and dried to prepare a membrane-electrode assembly. Carbon paper as a diffusion layer was arranged on both outer sides of the produced membrane-electrode assembly, and a fuel cell separator having gas flow paths formed on both outer sides of the carbon paper was arranged to produce a fuel cell.

(Example 2)
Platinum catalyst-supported carbon, ethanol, perfluorocarbon sulfonic acid resin, Ce ₂ O ₃ (the content of Ce ions is 80 mol% with respect to the number of moles of SO ₃ ⁻ in the perfluorocarbon sulfonic acid resin) are mixed with a stirrer. Thus, an anode catalyst layer ink was prepared. A fuel cell was produced in the same manner as in Example 1 except for the above.

(Example 3)
Platinum catalyst-supported carbon, ethanol, perfluorocarbon sulfonic acid resin, Ce ₂ O ₃ (the Ce ion content is 100 mol% with respect to the number of moles of SO ₃ ⁻ in the perfluorocarbon sulfonic acid resin) are mixed with a stirrer. Thus, an anode catalyst layer ink was prepared. A fuel cell was produced in the same manner as in Example 1 except for the above.

(Comparative Example 1)
Platinum catalyst-supported carbon, ethanol, perfluorocarbon sulfonic acid resin, Ce ₂ O ₃ (the Ce ion content is 110 mol% with respect to the number of moles of SO ₃ ⁻ in the perfluorocarbon sulfonic acid resin) are mixed with a stirrer. Thus, an anode catalyst layer ink was prepared. A fuel cell was produced in the same manner as in Example 1 except for the above.

(Comparative Example 2)
Platinum catalyst-supported carbon, ethanol, and perfluorocarbon sulfonic acid resin were mixed with a stirrer to prepare an anode electrode catalyst layer ink (without Ce ions). A fuel cell was produced in the same manner as in Example 1 except for the above.

<Measurement of fuel cell output>
First, the fuel cells of Examples 1 to 3 and Comparative Examples 1 and 2 were generated under the following conditions. Hydrogen gas was used as the anode gas, and air was used as the cathode gas. The fuel cell of the above-mentioned examples and comparative examples was made by setting the fuel cell temperature to 80 ° C., the anode gas utilization rate of 60%, and the cathode gas utilization rate of 40%, and passing the anode gas and cathode gas through the bubbler at 80 ° C. Was made to generate electricity. The output (V · A / cm ² ) of the fuel cell when the current density during power generation was 0.6 mA / cm ² was measured. The outputs of the fuel cells of Examples 1 to 3 and Comparative Example 1 in Table 1 are expressed as a ratio when the output of the fuel cell of Comparative Example 2 (without addition of CeO ₃ ) is 1.

<Measurement of gas permeability coefficient of electrolyte membrane>
After power generation under the above conditions, the electrolyte membrane was taken out from the fuel cells of Examples 1 to 3 and Comparative Examples 1 and 2, and the gas permeability coefficient was measured. The gas used for the measurement of the gas permeability coefficient is hydrogen. The gas permeability coefficients of the electrolyte membranes of Examples 1 to 3 and Comparative Example 1 in Table 1 were expressed as a ratio when the gas permeability coefficient of the electrolyte membrane of Comparative Example 2 (without addition of CeO ₃ ) was 10.

<Durability test of fuel cell>
The durability of Examples 1 to 3 and Comparative Example 1 in Table 1 was expressed as a ratio when the durability of Comparative Example 2 (without addition of CeO ₃ ) was 1. In addition, the outputs of the fuel cells of Examples 1 to 3 and Comparative Example 1 in Table 1 are expressed as a ratio when the output of the fuel cell of Comparative Example 2 (without addition of CeO ₃ ) is 1.

  As can be seen from the results in Table 1, it can be seen that the gas permeability coefficients of the electrolyte membranes of Examples 1 to 3 are lower than those of Comparative Example 2. In particular, the gas permeability coefficient of the electrolyte membranes of Examples 2 and 3 was reduced by about 80% compared with the gas permeability coefficient of Comparative Example 2. Moreover, even if the output of Examples 1-3 compared with the output of the comparative example 2, the fall was hardly seen. Further, the durability of Examples 2 and 3 increased by about 4 times compared to the durability of Comparative Example 2.

  On the other hand, the gas permeability coefficient of the electrolyte membrane of Comparative Example 1 is about 80% lower than the gas permeability coefficient of Comparative Example 2, but the output of the fuel cell is compared with the output of Comparative Example 2. About 18%.

  As described above, the fuel cell according to the present embodiment includes a metal ion coordinated to an ion exchange group in the hydrogen ion conductive electrolyte in the catalyst layer, and the content of the metal ion in the ion in the hydrogen ion conductive electrolyte. By setting the upper limit to the number of moles equal to the number of moles of the exchange group, it was possible to suppress a decrease in the output of the fuel cell and gas leakage of the electrolyte membrane. In particular, by setting the content of metal ions in the range of 80 mol% to 100 mol% relative to the number of moles of ion exchange groups in the hydrogen ion conductive electrolyte, gas leakage of the electrolyte membrane can be further suppressed, and the fuel The durability of the battery could be improved and the durability of the fuel cell could be improved.

  The fuel cell according to the present embodiment can be used as, for example, a small power source for mobile devices such as a mobile phone and a portable personal computer, a power source for automobiles, a household power source, and the like.

It is a schematic diagram which shows an example of a structure of the fuel cell which concerns on embodiment of this invention. (A) is a diagram showing an example of the structure of the electrolyte membrane, (B) is a diagram showing an example of the structure of the electrolyte membrane during power generation of the fuel cell, and (C) is a diagram showing an unpowered state of the fuel cell. It is a figure which shows an example of the structure of the electrolyte membrane at the time.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Fuel cell, 10 Hydrogen ion conductive electrolyte membrane, 12 Anode electrode catalyst layer, 14 Cathode electrode catalyst layer, 16 Membrane-electrode assembly, 18a, 18b Diffusion layer, 20a, 20b Fuel cell separator, 22a, 22b Reaction gas flow Road.

Claims (6)

A membrane-electrode assembly having a catalyst layer comprising a hydrogen ion conducting electrolyte, comprising:
The catalyst layer includes a metal ion coordinated to an ion exchange group in the hydrogen ion conductive electrolyte, and the content of the metal ion is equal to the number of moles of the ion exchange group in the hydrogen ion conductive electrolyte. A membrane-electrode assembly, characterized in that the upper limit is the number.   2. The membrane-electrode assembly according to claim 1, wherein the metal ion content is in a range of 80 mol% to 100 mol% with respect to the number of moles of ion exchange groups in the hydrogen ion conductive electrolyte. Feature membrane-electrode assembly.   3. The membrane-electrode assembly according to claim 1, wherein the catalyst layer is only on the anode electrode catalyst layer side.   The membrane-electrode assembly according to any one of claims 1 to 3, wherein the metal ion is added as a metal oxide.   5. The membrane-electrode assembly according to claim 1, wherein a metal species of the metal ion is at least one of iron, nickel, aluminum, silicon, cerium, and manganese. Feature membrane-electrode assembly. A fuel cell comprising a membrane-electrode assembly having a catalyst layer comprising a hydrogen ion conducting electrolyte, comprising:
The catalyst layer includes a metal ion coordinated to an ion exchange group in the hydrogen ion conductive electrolyte, and the content of the metal ion is a mole equal to the number of moles of the ion exchange group in the hydrogen ion conductive electrolyte. A fuel cell characterized in that the upper limit is the number.

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