JP2009021224A - Membrane electrode assembly for fuel cell and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane electrode assembly having a catalyst layer excellent in joining with an electrolyte membrane comprising a hydrocarbon polymer compound having proton conductivity and excellent in proton conductivity; and to provide a fuel cell using the membrane electrode assembly. <P>SOLUTION: The membrane electrode assembly is equipped with a fuel electrode having a catalyst layer 11, an oxidant electrode having a catalyst layer 14, and a hydrocarbon electrolyte membrane 17 interposed between the catalyst layer 11 of the fuel electrode and the catalyst layer 14 of the oxidant electrode. At least one catalyst layer 11 (or 14) of the fuel electrode and the oxidant electrode contains a fluorine system proton conductor 23 and a hydrocarbon system proton conductor 21, and the hydrocarbon system proton conductor 23 is unevenly distributed on the electrolyte membrane 17 side. The fuel cell is equipped with this kind of membrane electrode assembly. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a membrane electrode assembly for a fuel cell and a fuel cell.

  In recent years, attempts have been made to use a fuel cell as a power source for portable electronic devices such as notebook computers and mobile phones so that they can be used for a long time without being charged. A fuel cell is characterized in that it can generate electric power simply by supplying fuel and air, and can generate electric power continuously for a long time if fuel is replenished. For this reason, if the fuel cell can be reduced in size, it can be said that the system is extremely advantageous as a power source for portable electronic devices.

  A direct methanol fuel cell (DMFC) is promising as a power source for portable electronic devices because it can be miniaturized and can easily handle fuel.

  The DMFC includes a membrane electrode assembly (fuel cell) having a structure in which an electrolyte membrane is sandwiched between a fuel electrode and an air electrode. The fuel electrode and the air electrode each have a gas diffusion layer and a catalyst layer. The catalyst layer is in contact with the electrolyte membrane. The catalyst layers of the fuel electrode and the air electrode are formed by, for example, integrating catalyst particles obtained by supporting a catalyst such as Pt on a porous carrier with a polymer binder having proton conductivity.

  In such a DMFC, when fuel methanol is introduced into the fuel electrode, the methanol reaches the catalyst layer through the gas diffusion layer, and protons, electrons, and carbon dioxide are generated by the catalytic action. Protons move from the catalyst layer to the electrolyte membrane by the action of the polymer binder having proton conductivity, and further move to the catalyst layer on the air electrode side. On the other hand, when air is introduced into the air electrode, the air reaches the catalyst layer through the gas diffusion layer. In this catalyst layer, oxygen in the air, protons moving from the fuel electrode side, and electrons supplied from the fuel electrode through an external circuit react to generate water, and electric power is generated by electrons passing through the external circuit. Is supplied.

  Conventionally, as the polymer binder having proton conductivity of the electrolyte membrane and each catalyst layer, a fluorine-based polymer compound having a sulfonic acid group, for example, Nafion (trade name) manufactured by DuPont has been used for proton conductivity. Widely used because of its superiority. However, there is a problem that this fluorine-based polymer compound is very expensive.

  Therefore, it has been proposed to use a hydrocarbon-based polymer compound having proton conductivity as an inexpensive material instead of the fluorine-based polymer compound (see, for example, Patent Document 1).

  However, this electrolyte membrane formed of a hydrocarbon-based polymer compound having proton conductivity is poor in bonding with a catalyst layer using a conventional fluorine-based polymer compound having a sulfonic acid group as a binder, There was a problem that peeling occurred. This is due to the low compatibility between the fluorine-based polymer compound and the hydrocarbon-based polymer compound. When interfacial delamination occurs, the mobility of protons to the electrolyte membrane is impaired, causing a decrease in output. . In addition, durability is reduced.

In order to solve this problem, it has been studied to use a hydrocarbon-based polymer compound having proton conductivity as a binder for the catalyst layer (see, for example, Patent Documents 2 and 3). However, in this case, although the bondability between the electrolyte membrane and the catalyst layer is improved, the polymer compound having hydrocarbon proton conductivity has lower proton conductivity than the fluorine polymer compound. Decreases.
US Pat. No. 5,403,675 JP 2002-164055 A JP 2002-298855 A

  The present invention relates to a membrane electrode assembly for a fuel cell having a catalyst layer that has good adhesion to an electrolyte membrane made of a hydrocarbon-based polymer compound having proton conductivity and also has excellent proton conductivity, and An object of the present invention is to provide a fuel cell comprising such a fuel cell membrane electrode assembly, inexpensive and excellent in output performance.

  A membrane electrode assembly for a fuel cell according to an aspect of the present invention includes a fuel electrode provided with a catalyst layer, an oxidant electrode provided with a catalyst layer, a catalyst layer of the fuel electrode, and a catalyst layer of the oxidant electrode. A membrane electrode assembly for a fuel cell comprising a hydrocarbon electrolyte membrane sandwiched between at least one of the fuel electrode and the oxidant electrode, wherein the catalyst layer of at least one of the fuel electrode and the oxidant electrode comprises a fluorine proton conductor and a hydrocarbon proton conductor. And the hydrocarbon proton conductor is unevenly distributed on the electrolyte membrane side.

  A fuel cell according to an aspect of the present invention includes the above-described membrane electrode assembly for a fuel cell.

  The membrane electrode assembly for a fuel cell according to one aspect of the present invention has a catalyst layer that has good bondability with an electrolyte membrane made of a hydrocarbon-based polymer compound having proton conductivity and is also excellent in proton conductivity. By using this, it becomes possible to obtain a fuel cell having excellent output performance at low cost. In addition, since the fuel cell according to one embodiment of the present invention includes such a membrane electrode assembly for a fuel cell, the fuel cell has low cost and excellent output performance.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. Although the description will be made based on the drawings, the drawings are provided for illustration only, and the present invention is not limited to the drawings.

  FIG. 1 is a cross-sectional view showing a main configuration of a fuel cell according to an embodiment of the present invention. As shown in FIG. 1, the fuel cell of the present embodiment includes an anode (fuel electrode) 13 having an anode catalyst layer 11 and an anode gas diffusion layer 12, a cathode having a cathode catalyst layer 14 and a cathode gas diffusion layer 15. A membrane / electrode assembly (MEA) comprising an (air electrode / oxidant electrode) 16 and a proton (hydrogen ion) conductive electrolyte membrane 17 sandwiched between the anode catalyst layer 11 and the cathode catalyst layer 14. Assembly) 18.

  The electrolyte membrane 17 is a hydrocarbon electrolyte membrane, that is, an electrolyte membrane made of a hydrocarbon proton conductor. Examples of the hydrocarbon proton conductor include those in which an ion exchange group such as a sulfonic acid group, a phosphonic acid group, or a carboxylic acid group is introduced in order to impart proton conductivity to a polymer whose main chain is composed of hydrocarbon. . Here, “the ion exchange group is introduced into the polymer” means “the ion exchange group is introduced into the polymer skeleton via a chemical bond”. The main chain may be interrupted by a hetero atom such as an oxygen atom. Among these, those having an aromatic ring in the main chain and having a sulfonic acid group and / or a phosphonic acid group introduced as an ion exchange group are preferable. Preferable specific examples of the hydrocarbon proton conductor include, for example, polycarbonate, polyetheretherketone, polysulfone, polyethersulfone, poly (arylene ether), polyphosphazene, polyimide, poly (4-phenoxybenzoyl-1,4). -Phenylene), polyphenylene sulfide, polyphenylquinoxalene and the like each having a sulfonic acid group introduced therein, arylsulfonated polybenzimidazole, alkylsulfonated polybenzimidazole, alkylphosphonated polybenzimidazole, Examples thereof include phosphonated poly (phenylene ether).

  The anode catalyst layer 11 and the cathode catalyst layer 14 are each composed of a catalyst, a conductive material that functions as an electron conductive path between the catalysts, and a proton conductor that functions as a proton conductive path between the catalyst and the electrolyte membrane 17. It is configured.

  Examples of the catalyst contained in the anode catalyst layer 11 and the cathode catalyst layer 14 include simple substances of platinum group elements such as Pt, Ru, Rh, Ir, Os, and Pd, alloys containing these platinum group elements, and the like. . The anode catalyst layer 11 is preferably made of an alloy such as Pt—Ru or Pt—Mo that has strong resistance to methanol, carbon monoxide, or the like. The cathode catalyst layer 14 is preferably made of an alloy such as Pt or Pt—Ni. However, the catalyst is not limited to these, and various substances having catalytic activity can be used. Examples of the conductive substance include particulate or fibrous carbon materials such as conductive carbon black, activated carbon, and graphite. The above-described catalyst may be supported on such a carbon material and contained.

  Furthermore, examples of the proton conductor include (a) a hydrocarbon proton conductor and (b) a fluorine proton conductor. Examples of the hydrocarbon proton conductor (a) and preferred examples thereof include the same materials as those exemplified as the material of the electrolyte membrane 17. The fluorine-based proton conductor (b) includes a sulfonic acid group, a phosphonic acid group, a carboxylic acid group, etc. for imparting proton conductivity to a polymer whose main chain is a hydrocarbon substituted with fluorine. In which an ion exchange group is introduced. Here again, “an ion exchange group is introduced into the polymer” means “an ion exchange group is introduced into the polymer skeleton via a chemical bond”. Specific examples of (b) fluorine-based proton conductors include, for example, perfluorocarbon sulfonic acid, perfluoroalkyl polymer having a phosphonic acid group, polytrifluorostyrene sulfonic acid, polytrifluorostyrene phosphonic acid, and the like. Perfluorocarbon sulfonic acid is preferred. Examples of commercially available perfluorocarbon sulfonic acids include Nafion (trade name, manufactured by DuPont) and Flemion (trade name, manufactured by Asahi Glass).

  In the present invention, at least one, preferably both, of the anode catalyst layer 11 and the cathode catalyst layer 14 contains (a) a hydrocarbon proton conductor and (b) a fluorine proton conductor as proton conductors, and , (A) The hydrocarbon proton conductor is unevenly distributed on the electrolyte membrane 17 side. (B) Fluorine-based proton conductor is superior to (a) hydrocarbon-based proton conductor in proton conductivity, while (a) hydrocarbon-based proton conductor is (b) fluorine-based proton conductive. Compared to the body, the bonding property to the electrolyte membrane 17 is excellent. Therefore, a catalyst layer containing (a) a hydrocarbon proton conductor and (b) a fluorine proton conductor as proton conductors, and (a) a hydrocarbon proton conductor unevenly distributed on the electrolyte membrane 17 side. Is excellent in bondability with the electrolyte membrane 17 while having good proton conductivity. Here, “the hydrocarbon proton conductor is unevenly distributed on the electrolyte membrane 17 side” means that (a) the content of the hydrocarbon proton conductor of the anode catalyst layer 11 in the cross section in the thickness direction is In this case, it means that the electrolyte membrane 17 side is increased from the anode gas diffusion layer 12 side and the cathode catalyst layer 14 side from the cathode catalyst layer 15 side.

  In addition, although a proton conductor is normally mix | blended about 30-70 volume% in a catalyst layer. In the catalyst layer containing (a) a hydrocarbon proton conductor and (b) a fluorine proton conductor as the proton conductor, and (a) the hydrocarbon proton conductor being unevenly distributed on the electrolyte membrane 17 side, The proportion of the (a) hydrocarbon proton conductor in the total proton conductor is preferably in the range of 5 to 60% by volume, more preferably in the range of 5 to 40% by volume. (A) When the proportion of the hydrocarbon-based proton conductor is less than 5% by volume, the bondability with the electrolyte membrane 17 is lowered, and conversely, when it exceeds 60% by volume, the proton conductivity is lowered and the use efficiency of the catalyst is reduced. descend. You may mix | blend proton conductors other than (a) hydrocarbon type proton conductor and (b) fluorine type proton conductor in this catalyst layer in the range which does not inhibit the effect of this invention.

  In addition, the area ratio of the (a) hydrocarbon proton conductor on the surface in contact with the electrolyte membrane 17 is preferably in the range of 5 to 40% of the total surface area, and in the range of 15 to 30%. It is more preferable. (A) When the ratio of the hydrocarbon proton conductor to the total area of the surface is less than 5%, the bonding property with the electrolyte membrane 17 is lowered. Conversely, when the proportion exceeds 40% by weight, the proton conductivity is lowered, Usage efficiency decreases.

  From the viewpoint of improving the bondability of the catalyst layer to the electrolyte membrane 17, as shown schematically in FIG. 2 as an example, at least on the surface in contact with the electrolyte membrane 17, (a) the hydrocarbon proton conductor is bulky. 21 is preferably present. The bulk 21 preferably has an average particle size of 10 μm or more, and more preferably 10 to 100 μm. The bulk 21 is preferably dispersed as uniformly as possible over the entire surface. In FIG. 2, 22 indicates catalyst particles supported on a conductive material, and 23 indicates (b) a fluorine-based proton conductor.

  The area of the (a) hydrocarbon proton conductor on the surface in contact with the electrolyte membrane 17 and the size of the bulk 21 are determined by the electron microanalyzer (EPMA: surface of the catalyst layer in contact with the electrolyte membrane 17). It can be determined by Electron-probe Microanalyzer analysis.

  The anode gas diffusion layer 12 laminated on the anode catalyst layer 11 functions as a current collector that uniformly supplies fuel to the anode catalyst layer 11 and efficiently transmits electrons generated in the anode catalyst layer 11 to the outside. It also has functions. The cathode gas diffusion layer 15 laminated on the cathode catalyst layer 14 has a function of uniformly supplying an oxidant to the cathode catalyst layer 14 and also efficiently collects electrons supplied from the outside to the cathode catalyst layer 14. It also has a function as a body. Both the anode gas diffusion layer 12 and the cathode gas diffusion layer 15 are formed of a porous substrate formed of a conductive material.

  As the porous substrate, it is preferable to use a conductive fiber that has been processed into a sheet shape, such as carbon cloth or carbon paper formed of carbon fiber or the like. Carbon paper or carbon cloth made of carbon fibers of about 1 μm or more and having a porosity of 50% or more can be used. The porous substrate may be a sintered body, and a sintered metal or metal oxide (tin oxide, titanium oxide, etc.) can be used. However, since the proton conductors contained in the anode gas diffusion layer 12 and the cathode gas diffusion layer 15 are generally strongly acidic materials, it is preferable to select materials with high acid resistance when using metal materials.

  When forming the anode catalyst layer 11 and the cathode catalyst layer 14 on the anode gas diffusion layer 12 and the cathode gas diffusion layer 15, respectively, the porous base materials for forming the anode gas diffusion layer 12 and the cathode gas diffusion layer 15 are used. In addition, a catalyst paste obtained by dispersing a catalyst and a conductive material (or a catalyst previously supported on a conductive material) and a proton conductor in a solvent is applied once or multiple times by a coater or spray. It can be formed by drying. The catalyst layer contains (a) a hydrocarbon proton conductor and (b) a fluorine proton conductor as proton conductors, and (a) a catalyst in which the hydrocarbon proton conductors are unevenly distributed on the electrolyte membrane 17 side. In the case of a layer, (a) a plurality of catalyst pastes having different hydrocarbon-based proton conductor contents are prepared, and (a) coating formation is performed so that the hydrocarbon-based proton conductor is unevenly distributed on the electrolyte membrane 17 side. do it. Further, in this case, in order for the above-described (a) hydrocarbon proton conductor to exist in the form of the bulk 21, the mixing time of each component when preparing the catalyst paste may be adjusted. If there is too much application amount of the catalyst paste at one time, cracking may occur in the catalyst layer due to volume change when the solvent volatilizes. It is preferable to apply it in small portions and dry it.

  Thus, the anode (fuel electrode) 13 having the anode catalyst layer 11 formed on the anode gas diffusion layer 12 and the cathode (air electrode / oxidant electrode) having the cathode catalyst layer 14 formed on the cathode gas diffusion layer 15. 16 and the electrolyte membrane 17 are overlapped on both surfaces of the electrolyte membrane 17 so that the anode catalyst layer 11 and the cathode catalyst layer 15 are in contact with each other, and heated and pressed to form a membrane electrode assembly 18. A conductive layer may be formed on the surface of the anode gas diffusion layer 12 opposite to the anode catalyst layer 11 and the surface of the cathode gas diffusion layer 15 opposite to the cathode catalyst layer 14 as necessary. . As these conductive layers, for example, a mesh, a porous film, a thin film, or the like made of a conductive metal material such as Au is used.

In the fuel cell including the membrane electrode assembly 18 configured as described above, the fuel is supplied to the anode (fuel electrode) 13 while the cathode (air electrode / oxidant electrode) 16 is oxidized with air, oxygen, or the like. Sex gas is introduced. The fuel diffuses through the anode gas diffusion layer 12 and is supplied to the anode catalyst layer 11. When methanol fuel is used as the fuel, an internal reforming reaction of methanol shown in the following formula (1) occurs in the anode catalyst layer 11. When pure methanol is used as the methanol fuel, the water generated in the cathode catalyst layer 14 or the water in the electrolyte membrane 17 is reacted with methanol to cause the internal reforming reaction of the formula (1). Alternatively, the internal reforming reaction is caused by another reaction mechanism that does not require water.
CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)

Electrons (e ⁻ ) generated by this reaction are guided to the outside, and are operated as so-called electricity, and are then guided to the cathode (air electrode) 16 after operating a portable electronic device or the like. Further, protons (H ⁺ ) generated by the internal reforming reaction of the formula (1) are guided to the cathode 16 through the electrolyte membrane 17. Electrons (e ⁻ ) and protons (H ⁺ ) that have reached the cathode 16 react with oxygen in the cathode catalyst layer 14 according to the following formula (2), and water is generated in accordance with this reaction.
6e ⁻ + 6H ⁺ + (3/2) O ₂ → 3H ₂ O (2)

  In the power generation reaction of the fuel cell described above, in order to increase the power to be generated, it is important to efficiently move protons generated by the catalytic reaction from the anode catalyst layer 11 through the electrolyte membrane 17 to the cathode catalyst layer 14. . The proton conductivity of the anode catalyst layer 11, the electrolyte membrane 17 and the cathode catalyst layer 14 is low, or the adhesion and bonding between the anode catalyst layer 11 and the electrolyte membrane 17 and between the electrolyte membrane 17 and the cathode catalyst layer 14 are poor. When it is, the mobility of a proton will fall and an output will fall. Further, interfacial peeling occurs between the anode catalyst layer 11 and the electrolyte membrane 17 and between the electrolyte membrane 17 and the cathode catalyst layer 14, and durability is reduced.

  In the fuel cell of the present embodiment, as described above, at least one of the anode catalyst layer 11 and the cathode catalyst layer 14 has (a) a hydrocarbon proton conductor and (b) a fluorine proton conductor as proton conductors. And the hydrocarbon proton conductor (a) is unevenly distributed on the electrolyte membrane 17 side. The catalyst layer configured as described above is excellent in proton conductivity, and also has good adhesion and bonding properties with the electrolyte membrane 7. For this reason, it is possible to suppress a decrease in output and durability.

  The present invention can be widely applied to various solid polymer fuel cells having a polymer electrolyte membrane, but is generally applied to a fuel cell using a liquid fuel such as methanol fuel. Fuel cells using liquid fuel can be broadly divided into active fuel cells and passive fuel cells depending on the fuel supply system, and any of them can be applied. Incidentally, an active fuel cell forcibly supplies liquid fuel, air, etc. to the anode and cathode electrodes of the membrane electrode assembly, respectively, while a passive fuel cell supplies vaporized liquid fuel. While supplying naturally to the anode pole of a membrane electrode assembly, outside air is naturally supplied to a cathode pole. Furthermore, the present invention can also be applied to a fuel cell of a type called a semi-passive in which a pump or the like is partially used for fuel supply. In the semi-passive type fuel cell, the fuel supplied from the fuel storage part to the membrane electrode assembly is used for the power generation reaction, and is not circulated thereafter and returned to the fuel storage part. The semi-passive type fuel cell is different from the conventional active method because it does not circulate the fuel, and does not impair the downsizing of the device. Moreover, a pump is used to supply fuel, which is different from a pure passive system such as a conventional internal vaporization type. For this reason, this fuel cell is called a semi-passive system as described above. In this semi-passive type fuel cell, a fuel cutoff valve may be arranged in place of the pump as long as fuel is supplied from the fuel storage portion to the membrane electrode assembly. In this case, the fuel cutoff valve is provided to control the supply of liquid fuel through the flow path.

  As the liquid fuel, methanol fuel such as methanol aqueous solution, pure methanol, ethanol aqueous solution, ethanol fuel such as pure ethanol, propanol fuel such as propanol aqueous solution and pure propanol, glycol fuel such as glycol aqueous solution and pure glycol, formic acid, Examples include dimethyl ether. In any case, liquid fuel corresponding to the fuel cell is used. It should be noted that the liquid fuel vapor supplied to the MEA may be all supplied as a liquid fuel vapor, but the present invention can be applied even when a part of the liquid fuel vapor is supplied in a liquid state.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples at all. In the following description, “part” means “part by weight” unless otherwise specified.

[Preparation of catalyst paste]
20 parts of perfluorocarbon sulfonic acid (trade name Nafion manufactured by DuPont) was dissolved in 80 parts of 1-propanol to obtain a 20 wt% fluorine-based solution. Moreover, 20 parts of sulfonated polyetheretherketone was dissolved in 80 parts of N, N-dimethylformaldehyde (DMF) to obtain a 20 wt% hydrocarbon-based solution. These fluorine-based solution and hydrocarbon-based solution, Pt-Ru-supported carbon particles (Pt-Ru content 60% by weight), ion-exchanged water and methoxypropanol were mixed with a stirrer / mixer as shown in Table 1. To obtain catalyst pastes (I) to (X).

[Manufacture of membrane electrode assemblies for fuel cells and fuel cells]
Example 1
The catalyst paste (I), the catalyst paste (I), and the catalyst paste (II) are arranged in this order on one side of a porous substrate (thickness 200 μm, area 12 cm ² , porosity 70 volume%) made of water-repellent carbon paper. The catalyst layer was formed by applying and drying.

  The porous base material on which the catalyst layer is formed is used as an anode and a cathode, and the catalyst layers are superimposed on both sides of the electrolyte membrane made of sulfonated polyetheretherketone, and 150 ° C., 4 MPa A membrane electrode assembly was produced by heating and pressing for 10 minutes, and a passive DMFC was produced using the membrane electrode assembly.

(Examples 2-6, Comparative Examples 1 and 2)
A membrane / electrode assembly was prepared in the same manner as in Example 1 except that the type and order of the catalyst paste applied on the porous substrate were changed as shown in Table 2, and further this was used as a passive type. DMFC was produced.

  Area ratio of hydrocarbon proton conductor (sulfonated polyetheretherketone) on the surface of the membrane electrode assembly produced in each of the above Examples and Comparative Examples in contact with the electrolyte membrane of the catalyst layer (ratio to the total area of the surface) ) And the average bulk diameter were measured by the methods shown below. Further, the uneven distribution of the hydrocarbon proton conductor in the catalyst layer was observed by the following method. Further, 10 ml of pure methanol was injected into the liquid fuel tank of the passive type DMFC prepared in each of the above examples and comparative examples, and after measuring 1 kHz AC impedance, the temperature was 25 ° C. and the relative humidity was 50%. The maximum output per unit area was measured by changing the current value. These measurement results are shown in Table 2. Regarding the uneven distribution of the hydrocarbon proton conductor in the catalyst layer, it was confirmed that the hydrocarbon proton conductor was unevenly distributed on the electrolyte membrane side in Examples 1 to 6 and Comparative Example 2.

[Measurement of area ratio, uneven distribution and average bulk diameter of hydrocarbon proton conductor]
The area ratio and average bulk diameter of the hydrocarbon-based proton conductor were determined by immersing the membrane electrode assembly in boiling water for about 1 hour, separating the catalyst layer from the electrolyte membrane, and analyzing the elemental map analysis of the separation surface. This was determined by EPMA (JXA-8900) manufactured under the conditions of an acceleration voltage of 15 kV and an irradiation current of 20 nA. Specifically, first, an element map analysis is performed in an observation range of 50 μm × 50 μm, a map for each element of C, F, and Pt is prepared, a region containing F is made a fluorine-based proton conductor, and C is contained. A region not containing Pt was a hydrocarbon proton conductor, and a region containing Pt was a supported catalyst. Next, the above 50 μm × 50 μm range is divided into 5 squares × 5 laterals, a total of 25 squares each consisting of a 10 μm square, and from the top to the left end of the first row, the central part, The area ratio of the hydrocarbon proton conductor and the same bulk diameter in each of the nine cells in the right end, the left end of the third row, the central portion, the right end, the left end, the central portion, and the right end of the fifth row The average value was calculated, and the area ratio of the hydrocarbon proton conductors in the nine squares and the average value of the same bulk diameter were obtained. Here, the bulk diameter means an average value (a + b) / 2 of the major axis a and the minor axis b of the bulk region.

  In addition, the hydrocarbon proton conductor is unevenly distributed by cutting the catalyst layer vertically with a cutter, and performing element map analysis of the cut surface under the same conditions as above using EPMA (JXA-8900) manufactured by JEOL Ltd. Went and examined. Specifically, the area of 10 μm × 10 μm is observed in order from the position close to the electrolyte membrane in the catalyst layer to the position close to the gas diffusion layer, and the area of the specified hydrocarbon proton conductor is measured in the same manner as described above. And compared the values.

  As is apparent from Table 2, the area ratio of the hydrocarbon proton conductor on the surface of the catalyst layer in contact with the electrolyte membrane is in the range of 5 to 40%, and the average bulk diameter of the hydrocarbon proton conductor is 10 μm. In the example described above, particularly good results have been obtained, and this is presumed to be due to improved bondability between the catalyst layer and the electrolyte membrane.

  In the implementation stage, the present invention can be embodied by modifying the constituent elements without departing from the scope of the invention. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

It is sectional drawing which shows the structure of the membrane electrode assembly for fuel cells by one Embodiment of this invention. FIG. 2 is a cross-sectional view schematically showing an example of a catalyst layer in the fuel cell membrane electrode assembly shown in FIG. 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Anode catalyst layer, 12 ... Anode gas diffusion layer, 13 ... Anode (fuel electrode), 14 ... Cathode catalyst layer, 15 ... Cathode gas diffusion layer, 16 ... Cathode (air electrode), 17 ... Electrolyte membrane, 18 ... Membrane Electrode assembly, 21 ... bulk made of hydrocarbon proton conductor, 22 ... supported catalyst particles, 23 ... fluorine proton conductor.

Claims (6)

A fuel cell comprising a fuel electrode having a catalyst layer, an oxidant electrode having a catalyst layer, and a hydrocarbon-based electrolyte membrane sandwiched between the catalyst layer of the fuel electrode and the catalyst layer of the oxidant electrode A membrane electrode assembly,
At least one of the catalyst layers of the fuel electrode and the oxidant electrode includes a fluorine-based proton conductor and a hydrocarbon-based proton conductor, and the hydrocarbon-based proton conductor is unevenly distributed on the electrolyte membrane side. A membrane electrode assembly for a fuel cell.   2. The fuel cell membrane electrode assembly according to claim 1, wherein an area ratio of the hydrocarbon proton conductor in a surface of the at least one catalyst layer in contact with the electrolyte membrane is 5 to 40%.   3. The membrane electrode assembly for a fuel cell according to claim 1, wherein the hydrocarbon proton conductor is present in a bulk form at least on a surface in contact with the electrolyte membrane.   The membrane electrode assembly for a fuel cell according to claim 3, wherein the bulk has an average particle size of 10 µm or more.   The hydrocarbon proton conductor and the hydrocarbon electrolyte membrane are made of a polymer compound having an aromatic ring in the main chain and having a sulfonic acid group and / or a phosphonic acid group introduced therein. The membrane electrode assembly for a fuel cell according to any one of claims 1 to 4.   A fuel cell comprising the membrane electrode assembly for a fuel cell according to any one of claims 1 to 5.

Images