JP2005100748A - Electrolyte membrane electrode bonded laminate, its manufacturing method as well as solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte membrane electrode bonded laminate in which the diffusion performance and durability of a diffusion layer in the electrode are improved and which can be manufactured with high reproducibility, and its manufacturing method, and a solid polymer fuel cell using the same. <P>SOLUTION: The diffusion layer 6 is formed into a sheet state having flexibility by mixing conductive carbon and a hydrophobic polymer and structured to serve also as an electrode substrate. Furthermore, the diffusion layer 6 is structured by laminating a plurality of unit layers which are formed into a sheet by properly selecting and mixing the conductive carbons of different shapes and sizes and the hydrophobic polymers of different kinds. Thereby, the diffusion performances of a reactant and a product and mechanical strength, which are necessary as a property of the diffusion layer, can be improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrolyte membrane electrode assembly using a polymer as an electrolyte membrane, a method for producing the same, and a solid polymer fuel cell having the electrolyte membrane electrode assembly as a constituent element.

  A fuel cell is essentially a generator and takes out electricity using the reverse reaction of water electrolysis. And since electric energy can be taken out with high efficiency compared with the conventional power generation method, various technical development is made | formed and put into practical use from a viewpoint of resource saving.

  The basic structure of a fuel cell consists of an electrolyte membrane that allows hydrogen ions to pass through, an electrode composed of a fuel electrode and an oxygen electrode arranged on both sides of the electrolyte membrane, a current collector that extracts electricity from the electrode, and fuel and air supply to the electrode It consists of a separator that partitions the path and configures the above-described elements as cell units and electrically connects the cell units.

  And it is classified into a molten carbonate type, a solid oxide type, a phosphoric acid type, and a solid polymer type according to the kind of material constituting the electrolyte membrane. The operating temperature is a characteristic that determines these applications, and the solid polymer type is particularly noted for its low operating temperature of about 80 ° C., and is likely to be used for mobile devices and the like.

  FIG. 8 is a perspective view showing the structure of a basic conventional polymer electrolyte fuel cell. In FIG. 8, 1 is an electrolyte membrane, and 21 is an electrode, which are joined by sandwiching the electrolyte membrane 1 from both sides to constitute an electrolyte membrane electrode assembly (hereinafter referred to as MEA). The electrode 21 in the MEA is obtained by laminating a catalyst layer and a diffusion layer. When fuel and oxygen are supplied, an electrochemical reaction occurs and electric power is obtained.

  Reference numeral 22 denotes a separator, and a groove is provided on the entire surface. The separator 22 sandwiches the MEA from both sides, is fixed by applying pressure, and has functions of supplying reactants, discharging products, and collecting current. Since the material needs to be conductive, graphite or stainless steel is used, and the reactant is supplied and the product is discharged through the groove. The arrow indicates the direction in which fuel or oxygen is supplied.

  In general, the MEA in a polymer electrolyte fuel cell is produced by joining an electrode and a proton conductive solid polymer electrolyte membrane by hot pressing. The electrode is coated with a paste in which conductive carbon and hydrophobic polymer are mixed and dispersed as a diffusion layer on an electrode base material made of conductive paper or the like, and a noble metal catalyst is supported thereon. A paste obtained by mixing conductive carbon and an electrolyte solution is obtained by applying as a catalyst layer. Moreover, as the electrolyte solution, a polymer solution constituting the solid electrolyte membrane is often used.

  In the polymer electrolyte fuel cell, fuel and oxygen supplied to the MEA from the outside pass through the electrode base material and the diffusion layer, cause an electrochemical reaction in the catalyst layer, and generate electric power. On the contrary, water and carbon dioxide generated by the reaction are discharged from the catalyst layer to the outside through the diffusion layer and the electrode substrate. In this case, supply and discharge are performed without delay, leading to improvement of power generation characteristics, and on the electrode base material, particularly the oxygen electrode side, which is the passage route, the diffusion layer is required to have a performance of smoothly discharging water. .

  Thus, the main performance required for the electrode substrate and the diffusion layer is to provide a route for rapidly supplying and discharging the reactants and products, water repellency, electronic conductivity, and chemical stability. . In order to satisfy such requirements, various studies have been made on electrode base materials and diffusion layers.

  Examples of technologies corresponding to this are disclosed in the following Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5.

  Patent Document 1 and Patent Document 2 include a technique for producing a diffusion layer and an electrode by carbonizing a paper body made of cellulose fibers and polyvinyl alcohol, or a sheet obtained by binding carbonized paper bodies with a pitch or the like by heat treatment. It is disclosed. However, the diffusion layer and the electrode by this technique have a problem that the binder is also carbonized, so that it is fragile and durability and workability are lowered. In addition, if a catalyst layer is formed directly on the diffusion layer having such a configuration by a direct coating method, there is a problem that it becomes difficult to form a required catalyst layer due to penetration.

  Patent Document 3 and Patent Document 4 disclose examples of the material configuration and formation method of the diffusion layer. Since the diffusion layer disclosed in these is formed by applying a paste in which conductive carbon and a hydrophobic polymer are mixed to the electrode base as described above, its physical properties are utilized. It depends on the properties of the electrode substrate.

  Therefore, when a fibrous carbon sheet made of carbon fiber or the like is used for the electrode base material, the structure tends to be easily damaged. Depending on the material used, cracks may occur in the coating film, which cannot be produced with good reproducibility, and because the bondability with the electrode substrate is poor, the electrical properties at the interface between the diffusion layer and the electrode substrate There are problems such as increased resistance.

  Patent Document 5 discloses a sheet-like diffusion layer and a manufacturing method thereof. In this example, the problem is that the thickness of the diffusion layer is thick, and as the conductive carbon constituting the diffusion layer, granular carbon and fibrous carbon are used, but they are simply mixed and formed into a sheet, There is a problem that the improvement of the diffusion effect is insufficient.

  As described above, the conventional MEA has a carbon fiber bonded with carbon in the electrode base material itself, is brittle and has low durability, and has a large electric resistance at the interface between the diffusion layer and the electrode base material. For these reasons, there is room for study to improve the performance of fuel cells. In addition, in the manufacturing process, when polytetrafluoroethylene (hereinafter referred to as PTFE) is used as the hydrophobic polymer, cracking may not occur if only a paste in which conductive carbon and hydrophobic polymer are dispersed is applied. There is a problem that it is difficult to obtain a film having a large number of occurrences and uniform reproducibility. Furthermore, since PTFE is more fibrous in terms of water repellency, its properties cannot be fully utilized by simply applying it.

  Further, as described above, the reaction between the fuel and oxygen prevents the diffusion process of the reactants to the catalyst layer from becoming rate-limiting, and the product is discharged quickly, which improves the performance of the polymer electrolyte fuel cell. It becomes a factor. For this purpose, it is necessary to improve the diffusion layer, and the structure of the conductive carbon and hydrophobic polymer to be used needs further investigation.

Japanese Patent Laid-Open No. 7-220735 JP 2002-141071 A JP 2001-216773 A JP 2003-109611 A JP-A-7-220734

  Accordingly, an object of the present invention is to improve the mechanical strength of the MEA used in the polymer electrolyte fuel cell, speed up the supply and discharge of the reactants and products, and also configure the MEA as a component. It is to improve the reliability of the polymer electrolyte fuel cell and to improve the performance.

  The present invention has been made as a result of reexamination of materials used for the diffusion layer of MEA and the structure thereof in order to solve the above-mentioned problems.

  That is, the present invention relates to a fuel electrode and oxygen including a diffusion layer having a structure in which a plurality of unit layers made of a sheet including conductive carbon and a hydrophobic polymer and having flexibility, and a catalyst layer in contact with the diffusion layer. An electrolyte membrane electrode assembly of a polymer electrolyte fuel cell having an electrode and a solid electrolyte membrane, wherein the conductive carbon contained in the unit layer has a different shape and size for each layer It is MEA characterized by these.

  In the present invention, the conductive carbon contained in the unit layer on the side close to the catalyst layer is granular conductive carbon, and the conductive carbon contained in the unit layer on the side away from the catalyst layer is a fiber. The conductive carbon and the carbon layer disposed at a position further away from the catalyst layer are characterized in that the average fiber length and average fiber diameter of the fibrous conductive carbon contained are larger, Said MEA.

  Further, the present invention is the above MEA, wherein the type of the hydrophobic polymer and the mixing ratio of the hydrophobic polymer and the conductive carbon are different for each unit layer.

  Moreover, this invention is said MEA, The said diffusion layer functions as a base material which comprises an electrode.

  Further, the present invention is characterized in that, on the fuel electrode side, as a substitute for the diffusion layer, a sheet in which an infiltration prevention layer and a catalyst layer are formed on a fibrous conductive carbon papermaking body is used. MEA.

  The present invention also includes a step of preparing a unit layer by mixing conductive carbon and hydrophobic child molecules and forming a sheet, and using the unit layer as a diffusion layer as it is, or laminating a plurality of the unit layers. The unit membrane is formed of a conductive polymer shape and size, and a hydrophobic polymer material. The method includes a step of manufacturing a diffusion layer having a multilayer structure. The MEA manufacturing method is characterized in that at least one of them differs for each unit layer.

  The present invention also provides a polymer electrolyte fuel cell comprising the MEA.

  In the MEA of the present invention, there is no diffusion layer formed by applying a paste in which conductive carbon and a hydrophobic polymer are mixed to the electrode base material as in the past, and the conductive carbon is dispersed in the hydrophobic polymer. It is a flexible sheet formed from the blend. For this reason, there is no brittleness as in the prior art, and it has conductivity due to conductive carbon, so there is no need to provide a separate electrode base material, and there is no contact resistance between the diffusion layer and the electrode base material. It is characterized in that the conductivity can be improved.

  Further, since the diffusion layer is formed in a sheet shape, a uniform diffusion layer with good reproducibility can be obtained without causing cracks as in the coating method. Furthermore, when PTFE is used as the hydrophobic polymer, the PTFE particles are stretched and fiberized when processed into a sheet shape by a roll, so that an effect of imparting sufficient hydrophobicity to the diffusion layer can be obtained.

  In addition, the diffusion layer sheet has a multi-layer structure by integrating a plurality of sheets of different material configurations using different types of conductive carbon and different hydrophobic polymers, thereby improving diffusibility and strength. It is characterized by improvement.

  In the MEA of the present invention, granular conductive carbon and fibrous conductive carbon are used for the diffusion layer sheet. The granular conductive carbon preferably has a particle diameter of 0.02 to 10 μm, more preferably 0.02 to 1 μm, and the fibrous conductive carbon has a fiber diameter of 0.05 to 20 μm and fibers. Those having a length of 10 μm to 10 mm are preferred.

  As the granular conductive carbon, acetylene black, ketjen black, furnace black, thermal black, etc. can be used. As the fibrous conductive carbon, carbon fibers such as cellulose, polyacrylonitrile, pitch can be used. is there. Moreover, carbon nanofibers obtained by a vapor phase method or the like can also be used.

  As the hydrophobic polymer, PTFE, polyvinylidene fluoride (hereinafter referred to as PVDF), hexafluoropropylene-tetrafluoroethylene copolymer (hereinafter referred to as FEP), or the like can be used. Moreover, it is also possible to mix and use these. In the case of these hydrophobic polymers, it is preferable to use a dispersion in which fine powder having an average particle size of 0.1 to 0.2 μm is dispersed in water by 50 to 60% by weight in PTFE and FEP. It is preferable to use a solution dissolved in a solvent such as cyclohexanone or dimethylformamide.

  As for the mixing ratio of these conductive carbon and hydrophobic polymer, when the amount of hydrophobic polymer is large, the hydrophobicity is improved, but the electronic conductivity is lowered. On the other hand, if the amount is small, the decrease in electron conductivity is suppressed, but the hydrophobicity is decreased. Considering these, the mixing ratio of the hydrophobic polymer is preferably 5 to 30% by weight, and more preferably 10 to 20% by weight.

  In an actual manufacturing process, conductive carbon and a dispersion or solution of a hydrophobic polymer are weighed, mixed and dispersed to produce a paste so as to have the above mixing ratio, and processed into a sheet. However, when PTFE is used as the hydrophobic polymer, it is mixed, dispersed, filtered and dried to obtain a composite powder composed of conductive carbon and a hydrophobic polymer, and the composite powder is used as a solvent naphtha or the like. There is also a method of forming a sheet using a solvent. For those that require firing, heating and compression are performed using a muffle furnace or a hot press.

  The thickness of the sheet thus prepared is preferably 50 to 200 μm, and more preferably 50 to 150 μm. The reason is that if the thickness is smaller than this range, the diffusibility and electron conductivity are high, but the strength is reduced. If the thickness is thicker than this range, the strength is improved, but the diffusivity and electron conductivity are decreased. Because.

  FIG. 1 is a diagram schematically showing a cross section of an example of the MEA of the present invention. In FIG. 1, 1 is an electrolyte membrane, 2 is a catalyst layer, 3 is a first unit layer containing granular conductive carbon, 4 is a second unit layer containing fibrous conductive carbon, and 5 is a fibrous unit. A third unit layer containing conductive carbon, 6 is a diffusion layer, and 7 is an electrode. The first unit layer 3, the second unit layer 4, and the third unit layer 5 are integrated to form a diffusion layer 6, and the fiber diameter and length of the fibrous conductive carbon is the second The third unit layer 5 is larger than the unit layer 4.

  Further, the granular conductive carbon constituting the first unit layer 3 is used for coating in the step of forming the catalyst layer 2 by a coating method by making the particle size distribution such that the gaps between the particles are as small as possible. It is possible to extremely reduce the penetration of the paste into the inside. Thereby, a required catalyst layer can be easily formed, and the first unit layer 3 can function as a permeation preventing layer.

  A method for producing such a diffusion layer sheet having a multi-layer structure is not particularly limited. As described above, a pace in which conductive carbon is mixed and dispersed in a dispersion or solution of a hydrophobic polymer is used. By coating on a substrate and forming a film, a sheet of each unit layer is produced, and a single diffusion layer sheet can be obtained by overlapping and compressing them.

  As the catalyst, a PtRu-supported carbon catalyst is used for the fuel electrode, and a Pt-supported carbon catalyst is used for the oxygen electrode, and these catalysts are mixed with a solution of a solid electrolyte that functions as a proton conduction path and a catalyst layer binder. The electrode 7 can be produced by applying and drying the diffusion layer as a paste for forming the catalyst layer, and the MEA of the present invention can be obtained.

Note that polyperfluorosulfonic acid can be used as the solid electrolyte, and specific examples include Nafion (registered trademark) manufactured by DuPont. In the MEA of the present invention, the coating amount of the catalyst, the oxygen electrode is 1 mg / cm ^2, the fuel electrode is 2-4 mg / cm ^2, but is not particularly limited to this range.

  The solid electrolyte membrane was sandwiched between a pair of electrodes for the fuel electrode and oxygen electrode produced in this way, and joined by hot pressing to obtain an MEA. Note that the Nafion has excellent characteristics and can be suitably used as a solid electrolyte membrane. Moreover, the conditions of hot press are pressure 10MPa, temperature 130 degreeC, time 1 minute, and the magnitude | size of MEA are 35x35 mm. The size of the solid electrolyte membrane, hot press conditions, and MEA is not particularly limited.

  The evaluation of the obtained MEA is a direct methanol fuel cell system in which methanol and water, which are currently attracting the most attention as portable fuel cells, are reacted directly in the catalyst layer, and without using a pump, fuel, oxygen The method of supplying Particularly at the oxygen electrode, the output is likely to decrease due to the flooding phenomenon in which the generated water accumulates, and the effect of the diffusion layer is important. However, the MEA of the present invention can also be applied when hydrogen or other fuel is used, and is not limited to when methanol is used as the fuel.

  Hereinafter, the present invention will be described with specific examples.

  In order to prepare a sheet of the diffusion layer, granular conductive carbon and a dispersion of PTFE of a hydrophobic polymer were weighed and mixed so that the solid content of PTFE was 20% by weight. After sufficiently stirring this, it was filtered and dried to prepare a composite powder of conductive carbon and PTFE. Solvent naphtha was added to the composite powder to form a sheet having a thickness of 120 μm, which was baked by heating at 320 ° C. for 10 minutes using a muffle furnace to obtain a diffusion layer.

  Here, EC600JD made by Lion Corporation was used as Ketjen Black, and D-1 made by Daikin Corporation was used as a PTFE dispersion. However, any material having the same characteristics and properties can be used as well. Of course.

On the surface of this diffusion layer, a catalyst layer forming paste in which a Pt-supported carbon catalyst and a Nafion solution were mixed was applied so that the amount of Pt was 1 mg / cm ² to produce an electrode for an oxygen electrode. Similarly, a catalyst layer forming paste in which a PtRu-supported carbon catalyst and a Nafion solution were mixed was applied so that the amount of PtRu was 4 mg / cm ² to produce an electrode for a fuel electrode.

  A sheet of Nafion 117 was sandwiched between the fuel electrode and the oxygen electrode thus produced, and hot pressing was performed at 10 MPa at 130 ° C. for 1 minute to obtain MEA. FIG. 2 is a view showing a cross section of the MEA of the present embodiment. In FIG. 2, 1 is an electrolyte membrane, 2 is a catalyst layer, 8 is a diffusion layer, 9 is an electrode on the oxygen electrode side, and 10 is an electrode on the fuel electrode side. In this case, since the electrode structure is the same for both the oxygen electrode and the fuel electrode, they are compatible.

  This MEA was incorporated into an evaluation cell, and discharge characteristics were measured for evaluation. In the evaluation cell used here, oxygen was supplied from the air by exposing the oxygen electrode to the atmosphere, and the fuel was a methanol aqueous solution having a concentration of 2 mol / L, and a tank was provided near the fuel electrode. It supplied without using a pump. The cell temperature at the time of evaluation was room temperature.

  In the diffusion layer sheet in Example 1, only ketjen black, which is granular conductive carbon, was used as the conductive carbon. Here, however, the fibrous conductive carbon further has a fiber diameter of about 0.5 μm, A layer using carbon fibers having a fiber length of about 13 μm was provided to form a two-layer diffusion layer. Specifically, as a carbon fiber, a pitch-type carbon fiber, Donacabo Mild S-243 (registered trademark) manufactured by Donac Co., Ltd. was used. it can.

  This was joined to an electrolyte membrane to produce an MEA. FIG. 3 is a diagram schematically showing a cross section of the MEA of the present embodiment. In FIG. 3, 11 is a first unit layer containing granular conductive carbon, 12 is a second unit layer containing fibrous conductive carbon, 13 is a diffusion layer, and 14 is an electrode. By adopting such a structure, the characteristics as the diffusion layer, that is, the diffusibility is improved, and the durability is also improved.

  Here, both the first unit layer 11 and the second unit layer 12 were prepared in the same manner as in Example 1, the mixing ratio of PTFE was 20% by weight, and the respective thicknesses were set to 120 μm before firing. . The two sheets were stacked and compressed by a roll to form a single sheet having a thickness of 120 μm. This was fired under the same conditions as in Example 1 to obtain a diffusion layer 13. The production conditions and evaluation conditions of the MEA were the same as in Example 1, and the discharge characteristics were measured.

  In Example 2, the diffusion layer has a two-layer structure, but this example further includes fibrous conductive carbon obtained by a vapor phase method having a fiber diameter and fiber length smaller than those used in Example 2. A unit layer was formed to have a three-layer structure. In this case, the cross section is the same as that in FIG. 1 and will be described with reference to FIG. In FIG. 1, the first unit layer 3 is a layer containing granular conductive carbon prepared in the same manner as in Example 1, and the third unit layer 5 is a fibrous conductive material prepared in the same manner as in Example 2. This is a layer containing carbon.

  The fibrous conductive carbon contained in the second unit layer 4 is vapor grown carbon fiber, and has a fiber diameter of about 150 nm and a fiber length of about 16 μm. Specifically, VGCF (registered trademark) manufactured by Showa Denko Co., Ltd. was used, but any carbon fiber having similar characteristics can be used. Also in the second unit layer, the hydrophobic polymer used is PTFE, and the contained ratio is 20% by weight.

  The conditions from the production of the unit layer to the production of the MEA are the same as in Example 2. With such a structure, the performance of the MEA is further improved. The evaluation conditions were the same as in Example 1, and the discharge characteristics were measured.

  In Example 2, the hydrophobic polymer used in the diffusion layer was PTFE in both layers, and was prepared with the same mixing ratio. However, in this example, in the unit layer containing fibrous conductive carbon, FEP was used as the hydrophobic polymer and the mixing ratio was 10% by weight. The conditions from the production of the unit layer to the production of the MEA are the same as in Example 2. The evaluation conditions were the same as in Example 1, and the discharge characteristics were measured.

  In Example 3, the hydrophobic polymer used in the diffusion layer was PTFE in all three layers, and was prepared with the same mixing ratio. However, in this example, the third unit layer, that is, pitch-based carbon was used. The hydrophobic polymer of the unit layer containing fibers is FEP, the mixing ratio is 10% by weight, the hydrophobic polymer of the second unit layer, that is, the unit layer containing vapor grown carbon fibers, is PTFE, and the mixing ratio is 15%. %, The hydrophobic polymer of the first unit layer, that is, the unit layer containing ketjen black, which is granular conductive carbon, was PTFE and the mixing ratio was 20 wt%. The conditions from the production of the unit layer to the production of the MEA are the same as in Example 2. The evaluation conditions were the same as in Example 1, and the discharge characteristics were measured.

  In Examples 1 to 5, both the fuel electrode and the oxygen electrode used diffusion layers prepared from conductive carbon and a hydrophobic polymer, but in this example, such a structure is formed only on the oxygen electrode side. A paste prepared by mixing ketjen black and ethanol as a permeation preventive layer on one side of a fibrous conductive carbon papermaking body on the fuel electrode side is applied to a thickness of 10 μm and dried. What applied the paste for forming a catalyst layer on it was used.

  Specifically, carbon paper manufactured by Toray Industries, Inc., TGP-H030, was used as the paper body of fibrous conductive carbon, but any paper having the same characteristics can be used. In addition, the diffusion layer similar to Example 1 was used for the oxygen electrode side. FIG. 4 is a view showing a cross section of the MEA of the present embodiment. In FIG. 4, 15 is a penetration preventing layer, 16 is a fibrous conductive carbon papermaking body, 9 is an electrode on the oxygen electrode side, and 17 is an electrode on the fuel electrode side. The evaluation conditions were the same as in Example 1, and the discharge characteristics were measured.

  For comparison, an MEA was produced by a general method using a coating method. The diffusion layer was formed by mixing and dispersing Ketjen Black and PTFE dispersion so that the mixing ratio of PTFE was 20% by weight in a fixed portion, and the fibrous conductive carbon paper body used in Example 6 was used. Is applied, dried and then fired so that the thickness of the surface becomes 30 μm. The firing conditions and the MEA manufacturing method were the same as in Example 1.

  FIG. 5 is a diagram showing a cross section of the MEA of the comparative example. In FIG. 5, 18 is a diffusion layer formed by a coating method, 19 is an electrode on the oxygen electrode side, and 20 is an electrode on the fuel electrode side. The evaluation conditions were the same as in Example 1, and the discharge characteristics were measured.

The object of the present invention is to improve the diffusion layer, and the current-voltage characteristics in the range where the current density where the influence of the diffusion greatly appears is large. Table 1 summarizes the current-voltage characteristics of the example and the comparative example. Moreover, FIG. 6 is a figure which shows the change of the voltage with respect to the accumulation operation time when constant current discharge is carried out with a current density of 25 mA / cm ^{2 in the} example and the comparative example.

  By comparing these results with Example 1 and the comparative example, the current-voltage characteristics are almost the same, but the voltage drop with respect to the cumulative operation time is smaller in Example 1 and the improvement in characteristics is recognized. It is done.

  Further, when Example 2 and Example 3 are compared with Example 1 and Comparative Example, the voltage drop with respect to the current-voltage characteristics and the cumulative operation time is smaller in Examples 2 and 3 and the characteristics are improved. Is recognized. This is considered to be because by providing a unit layer containing fibrous conductive carbon, the porosity was increased and the diffusibility was improved, and the strength was improved by the fibrous conductive carbon.

  When Example 4 and Example 5 are compared with Example 2 and Example 3, respectively, it is recognized that the voltage drop with respect to the current-voltage characteristics and the accumulated operation time is slightly reduced. In this example, it is considered that this is caused by the difference in the type and mixing ratio of the hydrophobic polymer, and further improvement of characteristics is expected by further study.

  Example 6 shows excellent results in current-voltage characteristics as compared with Examples 1 to 5 and Comparative Example, and it is recognized that the diffusibility is improved. This is presumably because the diffusibility of the fuel was increased by not providing the hydrophobic diffusion layer because the methanol aqueous solution was used as the fuel in this example. However, the voltage drop with respect to the cumulative operation time showed the same value as in Example 1 and the comparative example.

In the sheet-like diffusion layers of Examples 1 to 6, the generation of cracks, which was generated by the method of applying the paste to the electrode substrate as in the conventional method to form the diffusion layer, was not observed. FIG. 7 shows the results of measuring the voltage when five samples were prepared and discharged at a current density of 110 mA / cm ² for Example 1, Example 2, and Comparative Example. From this figure, it can be said that Example 1 and Example 2 in which the diffusion layer is formed into a sheet form have less variation and higher reproducibility than the comparative example.

  As described above, the method using the sheet-like diffusion layer of the present invention causes cracks in the diffusion layer compared to the conventional method of forming a diffusion layer by applying paste to an electrode substrate. And a uniform diffusion layer could be obtained with good reproducibility. In addition, a diffusion layer having a multilayer structure, which is considered difficult to realize by a conventional manufacturing method, was formed on a single sheet, and diffusion characteristics and durability could be improved. Furthermore, since the MEA of the present invention does not use an electrode base material, the manufacturing cost can be reduced, and at the same time, the characteristics of a polymer electrolyte fuel cell using the same can be improved and the manufacturing cost can be reduced.

The schematic diagram of the cross section of an example of MEA of this invention. 1 is a cross-sectional view of an MEA of Example 1. FIG. Sectional drawing of MEA of Example 2. FIG. Sectional drawing of MEA of Example 6. FIG. MEA sectional drawing of a prior art example and a comparative example. The figure which shows the change of the voltage with respect to the accumulation operation time when constant current discharge is carried out. The result of measuring the voltage when discharged at a current density of 110 mA / cm ² . The perspective view which shows the structure of the conventional polymer electrolyte fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolyte membrane 2 Catalyst layer 3,11 1st unit layer 4 containing a granular conductive carbon 2nd unit layer 5 containing a fibrous conductive carbon 3rd unit containing a fibrous conductive carbon Layers 6, 8, 13, 18 Diffusion layers 7, 14, 21 Electrodes 9, 19 Oxygen electrode side electrodes 10, 17, 20 Fuel electrode side electrode 15 Infiltration prevention layer 16 Fibrous conductive carbon paper body 22 Separator

Claims (7)

  A diffusion layer having a structure in which at least one unit layer including a conductive carbon and a hydrophobic polymer and having flexibility is laminated, and a fuel electrode and an oxygen electrode including a catalyst layer in contact with the diffusion layer; An electrolyte membrane electrode assembly of a polymer electrolyte fuel cell having a solid electrolyte membrane, wherein the conductive carbon contained in the unit layer is different in shape and size for each unit layer. Electrolyte membrane electrode assembly.   The conductive carbon contained in the unit layer on the side close to the catalyst layer is granular conductive carbon, and the conductive carbon contained in the unit layer on the side away from the catalyst layer is fibrous conductive carbon, The unit layer disposed at a position further away from the catalyst layer has a larger average fiber length and average fiber diameter of the fibrous conductive carbon contained therein. Electrolyte membrane electrode assembly.   3. The electrolyte membrane electrode joint according to claim 1, wherein a kind of the hydrophobic polymer and a mixing ratio of the hydrophobic polymer and the conductive carbon are different for each unit layer. 4. body.   The electrolyte membrane electrode assembly according to any one of claims 1 to 3, wherein the diffusion layer functions as a base material constituting an electrode.   5. The sheet according to claim 1, wherein a sheet having a permeation preventing layer and a catalyst layer formed on a fibrous paper made of fibrous conductive carbon is used as an alternative to the diffusion layer on the fuel electrode side. The electrolyte membrane electrode assembly according to any one of the above.   A step of preparing a unit layer by mixing conductive carbon and a hydrophobic child molecule and forming a sheet, and using the unit layer as a diffusion layer as it is, or laminating and integrating a plurality of unit layers to form a multilayer structure A method for producing an electrolyte membrane electrode assembly including a step of producing a diffusion layer, wherein the unit layer includes at least one of a shape and size of conductive carbon contained therein and a material of a hydrophobic polymer. 6. The method for producing an electrolyte membrane electrode assembly according to claim 1, wherein the method is different for each layer.   A polymer electrolyte fuel cell comprising the electrolyte membrane electrode assembly according to any one of claims 1 to 5.

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