JP2006114397A - Membrane electrode assembly and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell excellent in durability.
SOLUTION: A membrane electrode assembly 10 in which a polymer electrolyte membrane 11 having ion conductivity is sandwiched between a pair of electrodes composed of a fuel electrode 12 supplied with fuel and an oxidant electrode 13 supplied with an oxidant. The electrode is provided with gas diffusion layers 12b and 13b containing a fibrous conductor and catalyst layers 12a and 13a containing a catalyst, and the outer dimension in the surface direction of the polymer electrolyte membrane 11 is the outer diameter in the surface direction of the electrode. A membrane electrode assembly and a fuel cell, characterized in that a protective means 12c is provided, which is larger and prevents the fibrous conductor protruding from the end faces of the gas diffusion layers 12b and 13b from piercing the polymer electrolyte membrane 11. .
[Selection] Figure 1

Description

  The present invention relates to a fuel cell.

  A solid polymer fuel cell has a membrane electrode assembly in which a polymer electrolyte membrane having ionic conductivity is sandwiched between a fuel electrode and an oxidant electrode and is joined as a basic element. A separator having a fuel supply path is brought into contact with the fuel electrode, and fuel is supplied to the fuel electrode through the fuel supply path. A separator having an oxidant supply path is brought into contact with the oxidant electrode, and the oxidant is supplied to the oxidant electrode through the oxidant supply path. As the fuel, gas such as hydrogen and reformed gas containing hydrogen is generally used. A gas such as air is generally used as the oxidizing agent. These gases are called reaction gases.

At the fuel electrode, the following reaction occurs when hydrogen in the fuel comes into contact with the catalyst.
2H ₂ → 4H ⁺ + 4e ⁻
H ⁺ moves through the polymer electrolyte membrane, reaches the catalyst of the oxidant electrode, and reacts with oxygen in the oxidant to become water.
4H ⁺ + 4e ⁻ + O ₂ → 2H ₂ O
The above reaction generates electricity by electrochemical reaction using hydrogen and oxygen. The polymer electrolyte membrane has a role of conducting hydrogen ions and blocking reaction gas. One of the causes of the deterioration of the power generation characteristics of the fuel cell due to aging is a phenomenon called cross leak in which the reaction gas permeates through the polymer electrolyte membrane to the opposite side during power generation.

One of the causes of the cross leak is a pinhole originally present in the polymer electrolyte membrane. As a method for solving this problem, Patent Document 1 discloses a method of shifting the pinhole position by laminating a plurality of polymer electrolyte membranes. Patent Document 2 discloses a method for preventing pinholes by modifying the surface of a polymer electrolyte membrane by plasma treatment or crosslinking treatment. However, there are very few pinholes originally present, and the resulting hydrogen gas permeability coefficient is 9 to 10 × 10 ⁻¹³ (cm ³ · cm · cm ⁻² · sec ⁻¹ · Pa ⁻¹ ), which is a very small amount. .

The electrode (fuel electrode, oxidant electrode) constituting the membrane electrode assembly has a structure having a catalyst layer on one surface of a gas diffusion layer having a fibrous conductor such as carbon fiber as a main component. Another cause of the cross leak is a pinhole in the polymer electrolyte membrane due to the puncture of the fibrous conductor of the gas diffusion layer. Since this pinhole has a large amount of cross leak (especially hydrogen gas permeation), it is more problematic than an existing pinhole. As a method for solving this problem, Patent Document 3 discloses that a reinforcing material (porous membrane, fibrous material, fine particles, binder) is disposed in the catalyst layer in order to suppress damage to the polymer electrolyte membrane due to the gas diffusion layer. However, it is disclosed that a reinforcing material (porous film, fibrous material, sputtered film, carbon layer) is disposed between the catalyst layer and the gas diffusion layer.
JP-A-6-84528 (paragraph [0010]) JP 2003-272663 A (paragraphs [0010] to [0011]) JP, 2004-220843, A (Claims 1, 2) However, the methods of Patent Documents 1 and 2 are measures against pinholes originally present in the polymer electrolyte membrane, but gas diffusion with more cross leaks. It is not a countermeasure against pinholes due to piercing with fibrous conductors in the layers. On the other hand, it has been found that Patent Document 3 is not sufficient as a countermeasure against cross leaks, which is a countermeasure against pinholes caused by piercing with the fibrous conductor of the gas diffusion layer.

  An object of the present invention is to elucidate the cause of cross leak, to realize a sufficient cross leak countermeasure, and to provide a membrane electrode assembly and a fuel cell excellent in durability.

  In order to solve the above technical problem, in the invention of claim 1, a polymer electrolyte membrane having ionic conductivity by a pair of electrodes comprising a fuel electrode supplied with fuel and an oxidant electrode supplied with an oxidant. A membrane electrode assembly, wherein at least one of the fuel electrode and the oxidant electrode is provided with a gas diffusion layer containing a fibrous conductor and a catalyst layer containing a catalyst, and the surface direction of the polymer electrolyte membrane The outer dimension of the electrode is larger than the outer diameter dimension in the surface direction of the electrode, and protective means for preventing the fibrous conductor protruding from the end face of the gas diffusion layer from piercing the polymer electrolyte membrane is provided. The membrane electrode assembly is characterized.

    The invention according to claim 2 is the membrane electrode assembly according to claim 1, wherein the protection means is a first protection layer covering an end face of the gas diffusion layer.

  According to a third aspect of the present invention, a second protective layer is provided between the gas diffusion layer and the catalyst layer to prevent the fibrous conductor of the gas diffusion layer from piercing the polymer electrolyte membrane. The membrane electrode assembly according to claim 1 or 2, wherein the membrane electrode assembly is provided.

  In the invention of claim 4, carbon particles and a polymer electrolyte are contained as at least one component of the first protective layer and the second protective layer. This membrane electrode assembly is used.

  According to a fifth aspect of the present invention, there is provided a fuel cell using the membrane electrode assembly according to the first to fourth aspects.

    According to the first aspect of the present invention, since the protective means for preventing the fibrous conductor protruding from the end face of the gas diffusion layer from piercing the polymer electrolyte membrane is provided, the reaction gas is passed through the polymer electrolyte membrane. Can be prevented from cross leaking, and a membrane electrode assembly excellent in durability can be obtained.

    According to invention of Claim 2, since the 1st protective layer is provided in the end surface of the gas diffusion layer, it can prevent that reactive gas cross-leaks through a polymer electrolyte membrane, and is a film | membrane excellent in durability An electrode assembly can be formed.

    According to the invention of claim 3, since the second protective layer for preventing the fibrous conductor of the gas diffusion layer from sticking into the polymer electrolyte membrane is provided between the gas diffusion layer and the catalyst layer, the catalyst layer The membrane electrode assembly can be prevented from being pierced through the polymer electrolyte membrane, more effectively preventing the reactant gas from cross leaking, and having excellent durability.

    According to the invention of claim 4, by forming the first protective layer and the second protective layer with carbon particles and a polymer electrolyte, a protective layer excellent in puncture prevention and corrosion resistance can be obtained.

    According to the invention of claim 5, since the membrane electrode assembly excellent in durability is used, a fuel cell excellent in durability can be obtained.

  The present inventor has investigated the cause of the method of Patent Document 3 being insufficient as a countermeasure against cross leak and has reached the present invention.

  FIG. 7 is an explanatory sectional view of a general membrane electrode assembly. The membrane electrode assembly 50 is formed by laminating a fuel electrode 52, a polymer electrolyte membrane 51, and an oxidant electrode 53 in this order and joining them by hot pressing. The fuel electrode 52 is provided with a catalyst layer 52a on one surface of the gas diffusion layer 52b. The oxidant electrode 53 is provided with a catalyst layer 53a on one surface of the gas diffusion layer 53b. The fuel electrode 52 and the oxidant electrode 53 are disposed so that the catalyst layer 52a and the catalyst layer 53a are in contact with the polymer electrolyte membrane 51, respectively. The sizes of the surfaces of the fuel electrode 52 and the oxidant electrode 53 that are in contact with the polymer electrolyte membrane 51 are substantially the same. The size of the surface of the polymer electrolyte membrane 51 that contacts the fuel electrode 52 and the oxidant electrode 53 is larger than the size of the fuel electrode 52 and the oxidant electrode 53. This is because the polymer electrolyte membrane 51 serves as a sealing material that prevents mixing of the fuel supplied to the fuel electrode 52 and the oxidant supplied to the oxidant electrode 53.

  The inventor manufactures a membrane electrode assembly 50 in which carbon layers (reinforcing materials referred to in Patent Document 3) are provided between the catalyst layer 52a and the gas diffusion layer 52b and between the catalyst layer 53a and the gas diffusion layer 53b, respectively. Then, a power generation experiment of a single fuel cell using this was conducted. Although it was confirmed that the durability of the fuel cell was improved by providing the carbon layer, it was not sufficient. The inventor investigated the cause. As the thickness of the carbon layer is increased, the durability is improved. However, when the thickness exceeds the predetermined thickness, the durability is not further improved. From this, it is considered that if the carbon layer has a predetermined thickness, the polymer electrolyte membrane piercing by the fibrous conductor of the gas diffusion layer is eliminated. However, there was still a cross leak, which affected the durability of the fuel cell. This amount of cross leak cannot be explained by the pinhole originally existing in the polymer electrolyte membrane.

  Therefore, as a result of studying the cause of the cross leak, the present inventor has thought that the cause is a fibrous conductor present on the end face of the gas diffusion layer. Here, the end surface of the gas diffusion layer refers to a surface other than the flat surface facing the polymer electrolyte membrane and its back surface. The gas diffusion layer is used by cutting a carbon fiber sheet such as carbon paper obtained by solidifying carbon fibers into a sheet or carbon cloth which is a woven fabric of carbon fibers into a predetermined shape as an electrode. In the inventor's test, carbon paper made into a predetermined shape by punching was used. At the time of this cutting, the carbon fiber on the end face of the gas diffusion layer becomes fuzzy or falls off. Since the carbon fibers pierce the polymer electrolyte membrane, resulting in pinholes, the amount of cross leak is large. In some cases, the carbon fibers on the end face may pierce the polymer electrolyte membrane through the catalyst layer, but this can be almost prevented by the carbon layer between the catalyst layer and the gas diffusion layer. However, it is impossible to prevent the carbon fibers on the end face of the gas diffusion layer from being stuck into the polymer electrolyte membrane existing around the electrode. This is the cause of the cross leak remaining even when the carbon layer is provided.

  The inventor considered the cause of the cross leak as described above. Based on this consideration, the present invention has been reached in which a protective means for preventing the carbon fiber on the end face of the gas diffusion layer from piercing the polymer electrolyte membrane is provided. That is, according to the present invention, in the membrane / electrode assembly provided with the polymer electrolyte membrane having the outer dimension in the surface direction larger than the outer dimension in the surface direction of the electrode, the carbon fiber on the end surface of the gas diffusion layer pierces the polymer electrolyte membrane. Is provided with a protection means to prevent.

  Examples of the protective means include providing a first protective layer on the end surface of the gas diffusion layer, and providing a third protective layer that protects the peripheral portion of the polymer electrolyte membrane existing outside the bonding surface with the electrode. . In addition to the first protective layer or the third protective layer, a second protective layer may be provided between the gas diffusion layer and the catalyst layer.

  Since the material of the first protective layer and the third protective layer does not need electrical conductivity in this portion, the polymer electrolyte can be prevented from being pierced by the fibrous conductor, and can be formed in the relevant portion, so that the fuel cell is not adversely affected. Any material can be used. As described later, in the examples, a mixture of carbon particles and an electrolyte material was used. The carbon particles have an effect of preventing the puncture of the fibrous conductor. Instead of carbon particles, inorganic particles or plastic particles may be used. The electrolyte material also has an effect of preventing the puncture of the fibrous conductor, but has the role of an adhesive between the carbon particles and a protective layer and a gas diffusion layer or an adhesive between the protective layer and the polymer electrolyte membrane. Instead of the electrolyte material, an epoxy-based, silicon-based, or fluorine-based polymer resistant to heat and water may be used. Moreover, the organic material which has a stab prevention effect and an adhesive effect can also be used by 1 type, or 2 or more types of mixtures, without using a carbon particle and its substitute. For example, an epoxy-based, silicon-based, or fluorine-based polymer that is resistant to heat and water can be used. Particularly in the case of the third protective layer, a polymer electrolyte membrane may be used to join the portion by hot pressing or the like.

  The material of the second protective layer needs to have conductivity and gas permeability in addition to the properties required for the first protective layer and the third protective layer. As described later, in the examples, a mixture of carbon particles and an electrolyte material was used in the same manner as in the first protective layer and the third protective layer. Since the carbon particles have conductivity, they satisfy the necessary requirements. Other conductive particles may be used in place of the carbon particles. However, using carbon particles is also used for the catalyst layer, which is preferable in terms of handling and cost. If the same material as that used for the second protective layer is used as the material for the first protective layer and the third protective layer, it is preferable in terms of handling and cost.

  FIG. 1 is an explanatory view illustrating a membrane electrode assembly according to the first embodiment. The membrane electrode assembly 10 is formed by laminating a fuel electrode 12, a polymer electrolyte membrane 11, and an oxidant electrode 13 in this order and joining them by hot pressing. The fuel electrode 12 includes a gas diffusion layer 12b including a fibrous conductor, a first protective layer 12c provided on an end surface of the gas diffusion layer 12b, and a second protective layer 12d provided on one surface of the gas diffusion layer 12b. And a gas diffusion layer 12b of the second protective layer 12d and a catalyst layer 12a provided on the back surface. The first protective layer 12 c and the second protective layer 12 d are protective layers for preventing the fibrous conductor of the gas diffusion layer 12 b from sticking into the polymer electrolyte membrane 11. The oxidant electrode 13 includes a gas diffusion layer 13b containing a fibrous conductor, a first protective layer 13c provided on an end surface of the gas diffusion layer 13b, and a second protective layer provided on one surface of the gas diffusion layer 13b. 13d and a gas diffusion layer 13b of the second protective layer 13d and a catalyst layer 13a provided on the back surface. The first protective layer 13 c and the second protective layer 13 d are protective layers for preventing the fibrous conductor of the gas diffusion layer 13 b from sticking into the polymer electrolyte membrane 11.

  The fuel electrode 12 and the oxidant electrode 13 are disposed so that the catalyst layer 12a and the catalyst layer 13a are in contact with the polymer electrolyte membrane 11, respectively. The sizes of the surfaces of the fuel electrode 12 and the oxidant electrode 13 that are in contact with the polymer electrolyte membrane 11 are substantially the same. The size of the surface of the polymer electrolyte membrane 11 in contact with the fuel electrode 12 and the oxidant electrode 13 (outside dimension in the surface direction) is the size of the surface of the fuel electrode 12 and oxidant electrode 13 (outside dimension in the surface direction). It is getting bigger. This is because the polymer electrolyte membrane 11 serves as a sealing material that prevents mixing of the fuel supplied to the fuel electrode 12 and the oxidant supplied to the oxidant electrode 13. The first protective layer 12c and the first protective layer 13c are provided over the entire end face of the gas diffusion layer 12b and the gas diffusion layer 13b, that is, over the entire circumference, respectively. The fuel electrode 12 is manufactured by first forming the first protective layer 12c on the gas diffusion layer 12b, then forming the second protective layer 12d, and then forming the catalyst layer 12a on the second protective layer 12d. Similarly, the oxidant electrode 13 first forms the first protective layer 13c on the gas diffusion layer 13b, then forms the second protective layer 13d, and then forms the catalyst layer 13a on the second protective layer 13d. To manufacture.

  FIG. 2 is an explanatory view illustrating a membrane electrode assembly according to the second embodiment. The membrane electrode assembly 20 is formed by laminating a fuel electrode 22, a polymer electrolyte membrane 21, and an oxidizer electrode 23 in this order and joining them by hot pressing. The fuel electrode 22 includes a gas diffusion layer 22b including a fibrous conductor, a first protective layer 22c provided on an end surface of the gas diffusion layer 22b, and a second protective layer 22d provided on one surface of the gas diffusion layer 22b. And a gas diffusion layer 22b of the second protective layer 22d and a catalyst layer 22a provided on the back surface. The first protective layer 22 c and the second protective layer 22 d are protective layers for preventing the fibrous conductor of the gas diffusion layer 22 b from sticking into the polymer electrolyte membrane 21. The oxidizer electrode 23 includes a gas diffusion layer 23b including a fibrous conductor, a first protective layer 23c provided on an end surface of the gas diffusion layer 23b, and a second protective layer provided on one surface of the gas diffusion layer 23b. 23d and a gas diffusion layer 23b of the second protective layer 23d and a catalyst layer 23a provided on the back surface. The first protective layer 23c and the second protective layer 23d are protective layers for preventing the fibrous conductor of the gas diffusion layer 23b from piercing the polymer electrolyte membrane 21.

  The fuel electrode 22 and the oxidant electrode 23 are disposed so that the catalyst layer 22a and the catalyst layer 23a are in contact with the polymer electrolyte membrane 21, respectively. The sizes of the surfaces of the fuel electrode 22 and the oxidant electrode 23 that are in contact with the polymer electrolyte membrane 21 are substantially the same. The size of the surface of the polymer electrolyte membrane 21 that contacts the fuel electrode 22 and the oxidant electrode 23 (surface dimension in the surface direction) is the size of the surface of the fuel electrode 22 and oxidant electrode 23 (the dimension in the surface direction). It is getting bigger. This is because the polymer electrolyte membrane 21 serves as a sealing material that prevents mixing of the fuel supplied to the fuel electrode 22 and the oxidant supplied to the oxidant electrode 23. The first protective layer 22c and the first protective layer 23c are provided over the entire end face of the gas diffusion layer 22b and the gas diffusion layer 23b, that is, around the entire circumference. The fuel electrode 22 is manufactured by first forming the second protective layer 22d on the gas diffusion layer 22b, then forming the first protective layer 22c, and then forming the catalyst layer 22a on the second protective layer 22d. Similarly, the oxidant electrode 23 is formed by first forming the second protective layer 23d in the gas diffusion layer 23b, then forming the first protective layer 23c, and then forming the catalyst layer 23a on the second protective layer 23d. To manufacture. The second embodiment differs from the first embodiment in the order of forming the first protective layer and the second protective layer.

  FIG. 3 is an explanatory view for explaining the membrane electrode assembly of the third embodiment. The membrane electrode assembly 30 is formed by laminating a fuel electrode 32, a polymer electrolyte membrane 31, and an oxidizer electrode 33 in this order and joining them by hot pressing. The fuel electrode 32 covers the entire surface of the gas diffusion layer 32b in order to prevent the fibrous conductor of the gas diffusion layer 32b including the fibrous conductor and the fibrous conductor of the gas diffusion layer 32b from piercing the polymer electrolyte membrane 31. The protective layer 32 c provided and the catalyst layer 32 a provided on the protective layer 32 c on one surface of the fuel electrode 32 are provided. The portion of the protective layer 32c that covers the end face of the gas diffusion layer 32b is the first protective layer 32c1, and the portion of the protective layer 32c between the gas diffusion layer 32b and the catalyst layer 32a is the second protective layer 32c2. ing. The oxidizer electrode 33 covers the entire surface of the gas diffusion layer 33b in order to prevent the fibrous conductor of the gas diffusion layer 33b and the fibrous conductor of the gas diffusion layer 33b from piercing the polymer electrolyte membrane 31. And a catalyst layer 33 a provided on the protective layer 33 c on one surface of the oxidant electrode 33. The portion of the protective layer 33c covering the end surface of the gas diffusion layer 33b is the first protective layer 33c1, and the portion of the protective layer 33c between the gas diffusion layer 33b and the catalyst layer 33a is the second protective layer 33c2. ing.

  The fuel electrode 32 and the oxidant electrode 33 are disposed so that the catalyst layer 32a and the catalyst layer 33a are in contact with the polymer electrolyte membrane 31, respectively. The sizes of the surfaces of the fuel electrode 32 and the oxidant electrode 33 that are in contact with the polymer electrolyte membrane 31 are substantially the same. The size of the surface of the polymer electrolyte membrane 31 that contacts the fuel electrode 32 and the oxidant electrode 33 (surface dimension in the surface direction) is the size of the surface of the fuel electrode 32 and oxidant electrode 33 (the dimension in the surface direction). It is getting bigger. This is because the polymer electrolyte membrane 31 serves as a sealing material that prevents mixing of the fuel supplied to the fuel electrode 32 and the oxidant supplied to the oxidant electrode 33. The fuel electrode 32 is manufactured by forming a protective layer 32c so as to cover the entire surface of the gas diffusion layer 32b. Similarly, the oxidant electrode 33 is manufactured by forming a protective layer 33c so as to cover the entire surface of the gas diffusion layer 33b. As a method for forming the protective layers 32c and 33c, a material for forming the protective layer is made into a paste or liquid coating material using a dispersion medium, and the gas diffusion layer is dipped, pulled up and dried in the coating material, coating There is a method of applying a material by spraying or the like. According to these methods, the manufacturing cost for forming the protective layer can be reduced.

  FIG. 4 is an explanatory view for explaining the membrane electrode assembly of the fourth embodiment. The membrane electrode assembly 40 is formed by laminating a fuel electrode 42, a polymer electrolyte membrane 41, and an oxidizer electrode 43 in this order and joining them by hot pressing. The fuel electrode 42 includes a gas diffusion layer 42b including a fibrous conductor and a catalyst layer 42a provided on one surface of the gas diffusion layer 42b. The oxidant electrode 43 includes a gas diffusion layer 43b including a fibrous conductor and a catalyst layer 43a provided on one surface of the gas diffusion layer 43b.

  The fuel electrode 42 and the oxidant electrode 43 are disposed so that the catalyst layer 42a and the catalyst layer 43a are in contact with the polymer electrolyte membrane 41, respectively. The sizes of the surfaces of the fuel electrode 42 and the oxidant electrode 43 that are in contact with the polymer electrolyte membrane 41 are substantially the same. The size of the surface of the polymer electrolyte membrane 41 in contact with the fuel electrode 42 and the oxidant electrode 43 (outside dimension in the surface direction) is the size of the surface of the fuel electrode 42 and oxidant electrode 43 (outside dimension in the surface direction). It is getting bigger. This is because the polymer electrolyte membrane 41 serves as a sealing material that prevents mixing of the fuel supplied to the fuel electrode 42 and the oxidant supplied to the oxidant electrode 43. The fibrous conductors of the gas diffusion layer 42b and the gas diffusion layer 43b pierce the polymer electrolyte membrane 41 in the peripheral portion of the polymer electrolyte membrane 41 existing outside the joint surface between the fuel electrode 42 and the oxidant electrode 43. A third protective layer 44 for preventing the above is provided. As a manufacturing method of the membrane electrode assembly 40, the fuel electrode 42, the polymer electrolyte membrane 41, and the oxidant electrode 43 are laminated in this order and bonded by hot pressing, and then the periphery of the polymer electrolyte membrane 41 protruding from the bonded surface A third protective layer 44 is formed on the portion. As shown in FIG. 4, the third protective layer 44 may be provided on the entire periphery of the polymer electrolyte membrane 41, but as long as it is provided at least on the inner side (center side of the polymer electrolyte membrane 41) from the seal portion. Good.

  Example 1 is an example corresponding to Embodiment 1, and will be described with reference to FIG.

(Formation of gas diffusion layer)
To 1000 g of water, 300 g of carbon black (conductive substance) was mixed, and stirred with a stirrer for 10 minutes. 250 g of a dispersion stock solution (trade name: POLYFLON D1 grade) containing 60% of tetrafluoroethylene (hereinafter referred to as PTFE) manufactured by Daikin Industries, Ltd. was added to the mixed solution, and the mixture was stirred for 10 minutes to carbon. An ink was prepared. Carbon paper (Toray Industries, Ltd., trading card TGP-060, thickness 180 μm), which is a base material for the gas diffusion layer, was put into the carbon ink. After carbon paper was sufficiently impregnated with carbon ink, the carbon paper was lifted from the carbon ink, and excess water in the carbon paper was evaporated in a drying furnace maintained at a temperature of 80 ° C. Thereafter, PTFE was sintered at a sintering temperature of 390 ° C. for 60 minutes to produce two water-repellent carbon papers. This was punched with a punching die so that the surface shape was a predetermined shape, and a gas diffusion layer 12b for the fuel electrode and a gas diffusion layer 13b for the oxidant electrode were obtained. The size of the gas diffusion layer 12b and the gas diffusion layer 13b is 100 mm × 130 mm × thickness 180 μm.

(Formation of first protective layer)
120 g of carbon black (conductive substance) was mixed with 12 g of an ion exchange resin solution (SS-1080, manufactured by Asahi Kasei Kogyo Co., Ltd.) having a concentration of 5 wt%, and stirred with a stirrer for 10 minutes to prepare a carbon paste. This carbon paste was applied with a brush to the entire periphery of the end surfaces of the gas diffusion layer 12b and the gas diffusion layer 13b and to a flat portion 5 mm from the end surfaces. The reason why it is applied also to the end of the flat portion is to form a protective layer on the corners of the end surface and the flat portion. The thickness of the first protective layer was about 40 μm. When the thickness of the 1st protective layer was measured, it was 30-50 micrometers.

(Formation of second protective layer)
The same carbon paste used for the first protective layer was applied to one side of the gas diffusion layer 12b and the gas diffusion layer 13b by the doctor blade method to form the second protective layer 12d and the second protective layer 13d, respectively. The thicknesses of the second protective layer 12d and the second protective layer 13d were set to 10 μm.

(Preparation of catalyst paste)
The platinum-supporting carbon is a carbon minute body (conductive minute body) carrying platinum as a catalyst. TEC10E60E (platinum support concentration: 55 wt%) manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. was used as the platinum support carbon. 12 g of platinum-supporting carbon, 127 g of an ion exchange resin solution having a concentration of 5 wt% (SS-1100, manufactured by Asahi Kasei Kogyo Co., Ltd.), 23 g of water, and 23 g of isopropyl alcohol as a molding aid are sufficiently mixed and oxidized. A catalyst paste for the agent electrode was prepared. The ion exchange resin solution used is mainly composed of a fluorocarbon electrolyte polymer (glass transition temperature: 120 ° C) with ion conductivity (proton conductivity), which is a mixture of water and ethanol as a liquid medium. It is dissolved or dispersed in a solution. Specifically, according to the present example, the fluorocarbon electrolyte polymer contains perfluorosulfonic acid as a main component.

  Further, a catalyst paste for a fuel electrode was prepared using platinum (supporting concentration 30 wt%), ruthenium (supporting concentration 23 wt%) alloy supporting carbon (TEC61E54, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) instead of platinum supporting carbon. The platinum-ruthenium alloy-supported carbon is a carbon minute body (conductive minute body) supporting platinum and ruthenium. Then, a fuel electrode catalyst paste was prepared by the same method as that for the oxidant electrode catalyst paste except that the platinum ruthenium alloy-supported carbon was used.

(Production of catalyst layer)
The catalyst paste for the oxidant electrode is applied to a tetrafluoroethylene sheet (hereinafter referred to as PTFE sheet) by a doctor blade method so that the amount of platinum supported is 0.6 mg / cm ² and dried to form a PTFE sheet. A catalyst layer 13a for the oxidant electrode was prepared. Similarly, a fuel electrode catalyst paste is applied to a PTFE sheet by a doctor blade method so that the amount of platinum supported is 0.6 mg / cm ² and dried to form a fuel electrode catalyst layer 12a formed on the PTFE sheet. Produced.

(Production of membrane electrode assembly)
As the polymer electrolyte membrane 11, Nafion 111 (trade name) manufactured by DuPont having a thickness of 25 μm was used. A PTFE sheet with a catalyst layer 13a is arranged so that the catalyst layer 13a abuts on one surface of the polymer electrolyte membrane 11, and a PTFE sheet with a catalyst layer 12a so that the catalyst layer 12a abuts on the other surface of the polymer electrolyte membrane 11 Arranged. Thereafter, pressure is applied from the outside of both PTFE sheets, hot pressing is performed under the conditions of a temperature of 120 ° C., a pressure of 8 MPa, and a time of 1 minute, the catalyst layers 12a and 13a are transferred to the polymer electrolyte membrane 11, and the PTFE sheets are peeled off. An intermediate laminate was produced in which the catalyst layers 12a and 13a were joined to the molecular electrolyte membrane.

  Next, the gas diffusion layer 12b with a protective layer was disposed so that the second protective layer 12d was in contact with the catalyst layer 12a of the intermediate laminate. A gas diffusion layer 13b with a protective layer was arranged so that the second protective layer 13d was in contact with the catalyst layer 13a of the intermediate laminate. Thereafter, pressure was applied from the outside of the gas diffusion layers 12b and 13b, and hot pressing was performed under the conditions of a temperature of 140 ° C., a pressure of 8 MPa, and a time of 3 minutes, and the membrane electrode assembly 10 was produced.

(Performance evaluation)
A power generation performance test and a cross leak test were performed using the produced membrane electrode assembly 10.

FIG. 5 is a cross-sectional view of a single cell used in the power generation performance test. A single cell 100 was fabricated by sandwiching the membrane electrode assembly 10 between the separator 4 and the separator 5 so that the separator 5 was in contact with the fuel electrode 12 and the separator 4 was in contact with the oxidant electrode 13. The separator 4 is provided with an oxidant gas supply port 4a, an oxidant gas flow groove 4b, and an oxidant gas discharge port 4c. The separator 5 is provided with a fuel gas supply port 5a, a fuel gas flow groove 5b, and a fuel gas discharge port 5c. 1. 2.5 atm of air from the oxidant gas supply port 4a to the oxidant electrode 1 through the oxidant gas flow groove 4b, and 2. from the fuel gas supply port 5a to the fuel electrode 2 through the fuel gas flow groove 5b. 5 atm of hydrogen was supplied. Moisture humidification was performed by humidifying both air and hydrogen by a bubbling method. Electricity generated from the electric terminals of the separator 4 and the separator 5 was taken out, the resistance was changed by the external variable resistor 6, and the single cell voltage of the single cell 100 was measured at a current density of 0.5 A / cm ² . The measurement was performed up to 1000 hours of operation time to evaluate the durability.

  The cross leak test was performed as follows. Power generation was stopped after 300 hours, 500 hours, and 1000 hours of operation time during the power generation performance test, and purged by flowing nitrogen gas through the oxidant gas flow groove 4b and the fuel gas flow groove 5b. Next, nitrogen gas was supplied to the fuel gas flow groove 5b and sealed at a pressure of 20 kPa (gauge pressure), and the oxidant gas flow groove 4b was opened to the atmosphere. The pressure in the fuel gas flow groove 5b after 1 minute was measured, and the differential pressure between both electrodes was measured.

  A membrane / electrode assembly 10 was produced in the same manner as in Example 1 except that the thickness of the second protective layer 13d was 30 μm. The performance evaluation was also performed in the same manner as in Example 1.

  A membrane / electrode assembly 10 was produced in the same manner as in Example 1 except that the thickness of the second protective layer 13d was 50 μm. The performance evaluation was also performed in the same manner as in Example 1.

Comparative Example 1

  A membrane / electrode assembly was produced in the same manner as in Example 1 except that the first protective layer was not provided. The thickness of the second protective layer is 10 μm. The performance was evaluated in the same manner as in Example 1.

Comparative Example 2

  A membrane / electrode assembly was produced in the same manner as in Example 2 except that the first protective layer was not provided. The thickness of the second protective layer is 30 μm. The performance was evaluated in the same manner as in Example 1.

Comparative Example 3

  A membrane / electrode assembly was produced in the same manner as in Example 3 except that the first protective layer was not provided. The thickness of the second protective layer is 50 μm. The performance was evaluated in the same manner as in Example 1.

Comparative Example 4

  A membrane / electrode assembly was produced in the same manner as in Example 1 except that the first protective layer and the second protective layer were not provided. This membrane electrode assembly corresponds to that described in FIG. The performance was evaluated in the same manner as in Example 1.

(Evaluation results)
FIG. 6 is a graph showing the results of the power generation performance test. In Examples 1 to 3 provided with the first protective layer, the decrease in output is less than that of the corresponding Comparative Examples 1 to 3 in which the thickness of the second protective layer is the same. Table 1 shows the results of the cross leak test. In the cross leak test, the lower the differential pressure between both electrodes, the greater the leak. In Examples 1 to 3 provided with the first protective layer, the decrease in the differential pressure is smaller than in the corresponding Comparative Examples 1 to 3 in which the thickness of the second protective layer is the same. In the case of Comparative Example 4, the power generation performance was remarkably reduced, the cross leak was greatly increased, and the operation longer than the operation time of 500 h could not be performed.

  These results indicate that the durability of the fuel cell power generation performance can be improved by providing the first protective layer. In particular, in Examples 2 and 3 in which the thickness of the second protective layer is 30 μm or more, the power generation performance does not deteriorate after 1000 hours of operation, and there is no cross leak. The reason seems to be that the first protective layer prevents the polymer electrolyte membrane from being pierced by the carbon fibers on the end face of the gas diffusion layer. In particular, it is considered that the second protective layer is provided and the thickness thereof is 30 μm or more, so that the polymer electrolyte membrane piercing by the carbon fiber is almost prevented.

Explanatory drawing explaining the membrane electrode assembly of 1st Embodiment Explanatory drawing explaining the membrane electrode assembly of 2nd Embodiment Explanatory drawing explaining the membrane electrode assembly of 3rd Embodiment Explanatory drawing explaining the membrane electrode assembly of 4th Embodiment Cross section of single cell used for power generation performance test Graph diagram showing power generation performance test results Cross-sectional view of a general membrane electrode assembly

Explanation of symbols

10, 20, 30, 40 ... Membrane electrode assembly 11, 21, 31, 41 ... Polymer electrolyte membrane 12, 22, 32, 42 ... Fuel electrode 12a, 22a, 32a, 42a ... Catalyst layer (for fuel electrode)
12b, 22b, 32b, 42b ... Gas diffusion layer (for fuel electrode)
12c, 22c, 32c1 ... 1st protective layer (for fuel electrodes)
12d, 22d, 32c2 ... second protective layer (for fuel electrode)
13, 23, 33, 43 ... oxidant electrode 13a, 23a, 33a, 43a ... catalyst layer (for oxidant electrode)
13b, 23b, 33b, 43b ... Gas diffusion layer (for oxidant electrode)
13c, 23c, 33c1... First protective layer (for oxidant electrode)
13d, 23d, 33c2 ... second protective layer (for oxidant electrode)
32c ... Protective layer (for fuel electrode)
33c ... Protective layer (for oxidant electrode)
44. Third protective layer

Claims (5)

A membrane electrode assembly in which a polymer electrolyte membrane having ionic conductivity is sandwiched between a pair of electrodes consisting of a fuel electrode supplied with fuel and an oxidant electrode supplied with an oxidant,
At least one of the fuel electrode and the oxidant electrode is provided with a gas diffusion layer containing a fibrous conductor and a catalyst layer containing a catalyst, and the outer dimension in the surface direction of the polymer electrolyte membrane is outside the surface direction of the electrode. A membrane electrode assembly, wherein a protective means for preventing a fibrous conductor larger than the diameter size and protruding from an end face of the gas diffusion layer from being pierced into the polymer electrolyte membrane is provided. The membrane electrode assembly according to claim 1, wherein the protection means is a first protection layer covering an end surface of the gas diffusion layer. 2. A second protective layer is provided between the gas diffusion layer and the catalyst layer to prevent the fibrous conductor of the gas diffusion layer from piercing the polymer electrolyte membrane. Or the membrane electrode assembly of Claim 2. The membrane electrode assembly according to any one of claims 1 to 3, wherein carbon particles and a polymer electrolyte are contained as at least one component of the first protective layer and the second protective layer. A fuel cell using the membrane electrode assembly according to claim 1.

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