JP2005190750A - Membrane electrode assembly for fuel cell, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane electrode assembly for a fuel cell which prevents an output reduction as the fuel cell by preventing damage of a proton conductive solid polymer membrane due to a gas diffusion layer, and easily positions an electrode catalyst. <P>SOLUTION: A porous material 5 which functions as a reinforcing layer are interposed between a gas diffusion layer 4 in a membrane electrode assembly 1 consisting of: a proton conductive solid polyelectrolyte membrane 2; an electrode catalyst layer 3; and a gas diffusion layer 4, and the polyelectrolyte membrane 2. The electrode catalyst layer 3 is formed inside of this porous material, and the outer brim part 5a of the porous material 5 is arranged and installed so that it is arranged farther outside than the outer brim part 4a of the gas diffusion layer 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polymer electrolyte fuel cell (PEFC) using a proton conductive solid polymer membrane such as a fluororesin polymer as an electrolyte, and more particularly, a proton conductive solid polymer membrane and A membrane electrode assembly (MEA) for a fuel cell comprising a pair of electrode catalyst layers sandwiching the solid polymer membrane and a pair of gas diffusion layers sandwiching these from the outside, and a membrane electrode assembly (MEA) The present invention also relates to a production method, and further to a polymer electrolyte fuel cell using such a membrane electrode assembly.

Solid polymer fuel cells using proton-conducting solid polymer membranes operate at lower temperatures than other types of fuel cells, and are expected to be used as power sources for mobile vehicles such as automobiles. Progressing.
In such a polymer electrolyte fuel cell, a hydrogen-containing fuel gas and an oxygen-containing oxidizing gas are respectively applied to a pair of electrodes (oxygen electrode and fuel electrode) with a proton conductive solid polymer membrane interposed therebetween. By supplying, the reaction represented by the following formula occurs, and electric energy is taken out.
Cathode reaction (oxygen electrode): 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O
Anode reaction (fuel electrode): H ₂ → 2H ⁺ + 2e ⁻

Gas diffusion electrodes used in polymer electrolyte fuel cells consist of catalyst-supported carbon particles coated with an ion exchange resin (polymer electrolyte) of the same or different type from polymer electrolyte membranes (proton conductive solid polymer membranes). Containing an electrode catalyst layer and a gas diffusion layer that supplies a reaction gas to the catalyst layer and collects charges generated in the catalyst layer, and the electrode catalyst layer side of the gas diffusion layer faces the polymer electrolyte membrane In this state, the membrane / electrode assembly is formed by bonding by hot pressing. The gas diffusion layer is generally made of carbon paper, woven fabric, or non-woven fabric made using carbon fibers.
And a fuel cell is comprised by laminating | stacking many such membrane electrode assemblies through the separator (gas flow path formation member) provided with the gas flow path.

In such a polymer electrolyte fuel cell, since the proton conductive solid polymer membrane is flexible, the proton conductive solid polymer membrane is easily damaged at the contact portion with the gas diffusion layer (especially the end portion), and gas cross-leakage may occur. However, since some reinforcement is necessary, for example, in Patent Document 1, the peripheral portion of the proton conductive solid polymer membrane is covered with a reinforcing member (carbonized resin-based resin sheet). It is described that the mechanical strength of a molecular film is improved.
Patent Document 2 discloses that a proton conductive solid polymer membrane itself is reinforced by filling a perfluorosulfonic acid resin into a porous body made of PTFE (polytetrafluoroethylene).
JP-A-10-308228 JP 2003-142122 A

However, in the polymer electrolyte fuel cell described in Patent Document 1, when the peripheral portion of the proton conductive polymer membrane is reinforced, the positioning of the opening of the reinforcing member (carbonized resin sheet) and the electrode catalyst layer is performed. Therefore, when the two interfere with each other (the reinforcing member overlaps the electrode catalyst layer), there is a problem that the contact state between the electrode catalyst layer and the gas diffusion layer is deteriorated. In addition, when the gap between the two is increased in order to avoid such interference, there is a problem that the end of the gas diffusion layer comes into contact with the proton conductive solid polymer membrane and causes damage.
On the other hand, as described in Patent Document 2, when the proton conductive solid polymer membrane itself is reinforced by the porous body made of PTFE, the proton conductive solid polymer membrane is protected, but the electrode catalyst layer is weak. Because of the state, the electrode catalyst layer is in contact with the gas diffusion layer and is damaged, resulting in a problem that the output is reduced.

  The present invention has been made by paying attention to the above-mentioned problems in conventional membrane electrode assemblies for fuel cells. The object of the present invention is to facilitate positioning of the electrode catalyst layer and to produce protons from the gas diffusion layer. Membrane electrode assembly for fuel cell and method for producing the same, further preventing damage of conductive solid polymer membrane and electrode catalyst layer and preventing output decrease as fuel cell, and such membrane electrode An object of the present invention is to provide a high-performance polymer electrolyte fuel cell using a joined body.

  In order to achieve the above object, the present inventor has intensively studied the material and structure of the gas diffusion electrode, and as a result, the porous conductive material made of an inorganic material or an organic material is interposed between the proton conductive solid polymer membrane and the electrode catalyst layer. It is found that the polymer electrolyte membrane can be prevented from being damaged by the edge portion of the gas diffusion layer or the tip portion of the carbon fiber by arranging the electrode body and forming the electrode catalyst layer therein. The present invention has been completed.

  That is, the present invention is based on the above knowledge, and the membrane electrode assembly for a fuel cell of the present invention is a membrane electrode assembly for a fuel cell in which a proton conductive solid polymer membrane is sandwiched between an electrode catalyst layer and a gas diffusion layer. The electrode catalyst layer is formed inside the porous body, and the outer edge portion of the porous body is disposed outside the outer edge of the gas diffusion layer.

  The method for producing a membrane electrode assembly for a fuel cell of the present invention is preferably used for the production of the membrane electrode assembly of the present invention, and a porous body is disposed on a proton conductive solid polymer membrane. A structure including a step, a step of including a solution containing a catalyst, a proton conductive polymer resin, and a solvent in the polymorph, and a step of removing the solvent of the solution included in the porous body, or a gas A step of disposing a porous body in the diffusion layer; a step of including a similar solution in the multi-molecular body; a step of disposing a porous body integral with the gas diffusion layer in the proton conductive solid polymer membrane; Including a step of removing the solvent of the solution, a step of disposing a porous body on the base material sheet, a step of including the same solution in the multi-material body, and a porous body integrated with the base material sheet To place the body on a proton conducting solid polymer membrane When is characterized in that the arrangement comprising the step of removing the solvent from the solution, the step of removing the base sheet of a porous material which is integrated with the solid polymer membrane.

  The polymer electrolyte fuel cell of the present invention is characterized in that a plurality of the membrane electrode assemblies of the present invention are stacked via a gas flow path forming member.

  In the fuel cell membrane electrode assembly of the present invention, since the electrode catalyst layer is provided inside the porous body functioning as a reinforcing member, the electrode catalyst layer can be easily positioned. The contact state with the gas diffusion layer is improved. In addition, since the outer edge of the porous body is located outside the outer edge of the gas diffusion layer, the edge portion at the end of the gas diffusion layer does not come into contact with the proton conductive solid polymer membrane. An excellent effect is obtained that the breakage of the conductive polymer film can be reliably prevented.

  According to the method for producing a membrane / electrode assembly of the present invention, a step of arranging a porous body on a proton conductive solid polymer membrane, a gas diffusion layer, or a base sheet, a catalyst and a proton conductive Since it comprises a step of including a solution containing a polymer resin and a solvent, a step of removing the solvent in the solution contained in the porous body, the membrane electrode assembly for a fuel cell of the present invention It can be applied to manufacturing.

  Furthermore, in the polymer electrolyte fuel cell of the present invention, a plurality of the membrane electrode assemblies of the present invention are used, and these membrane electrode assemblies are laminated together with a gas flow path forming member that functions as a separator. Therefore, the contact resistance between the electrode catalyst layer and the gas diffusion layer is good, and the proton conductive polymer membrane is not damaged, and a high-performance fuel cell can be obtained.

  Hereinafter, the membrane electrode contact assembly for fuel cell of the present invention and the production method thereof will be described in more detail.

FIGS. 1A and 1B are a plan view and a cross-sectional view, respectively, showing the structure of a fuel cell membrane electrode assembly of the present invention. The fuel cell membrane electrode assembly 1 shown in FIG. In addition, the proton conductive solid polymer membrane 2 as an electrolyte has a structure sandwiched by a gas diffusion electrode composed of an electrode catalyst layer 3 and a gas diffusion layer 4, and the electrode catalyst layer 3 is composed of the polymer electrolyte membrane. 2 and the gas diffusion layer 4 are formed inside the porous body 5.
At this time, the porous body 5 is disposed such that the outer edge portion 5a is outside the outer edge portion 4a of the gas diffusion layer 4, whereby the end edge portion of the gas diffusion layer 4 is a polymer. Even if pressure is applied to the membrane / electrode assembly 1 during bonding by hot pressing or battery operation, there is no direct contact with the electrolyte membrane 2. Stress concentration is avoided and damage to the polymer electrolyte membrane 2 is prevented.

Then, a separator made of a conductive material having a gas flow path provided on the outer side of the membrane electrode assembly 1, that is, a gas flow path forming member (not shown), is arranged, and a plurality of membrane electrode assemblies 1 are formed. By laminating, the solid oxide fuel cell of the present invention is formed.
In the above structural example, the size of the porous body 5 is smaller than that of the proton conductive solid polymer membrane 2, and the outer edge portion 5a of the porous body 5 is the outer edge of the solid polymer membrane 2. A gasket 6 is disposed on the exposed portion of the outer peripheral portion of the solid polymer film 2 so as to be gas sealed.

  The porous body 5 can be made of an inorganic material such as silica or an organic material such as polyimide, cross-linked polyethylene, or PTFE. As described above, the end edge of the gas diffusion layer 4 can be used. Strength (rigidity), porosity and thickness sufficient to prevent the carbon fibers forming the gas diffusion layer 4 from reaching the proton-conducting solid polymer membrane 2 while relieving stress concentration due to the shaped portion. It is necessary to be.

The electrode catalyst layer 3 contains the same or different polymer electrolyte (proton conductive solid polymer resin) and catalyst particles as the polymer electrolyte membrane 2, and the center of the porous body 5 leaving the peripheral portion. The portion is impregnated with a solution (slurry) containing a proton conductive solid polymer resin, a catalyst, and a solvent, and then dried to remove the solvent to form the porous body 5.
At this time, it is desirable to impregnate the region where the electrode catalyst layer 3 is formed inside the porous body 5 so as to be inside the outer edge 4a of the gas diffusion layer 4, whereby the electrode catalyst layer 3 has its function. It will be installed only in the part which can fully exhibit, and the usage-amount of an expensive catalyst will be reduced.

FIGS. 2A and 2B are a plan view and a cross-sectional view, respectively, showing another structural example of the membrane electrode assembly for a fuel cell of the present invention, in the membrane electrode assembly 1 for a fuel cell shown in the drawing. The porous body 5 has substantially the same size as the polymer electrolyte membrane 2, and a sealing layer made of a polymer resin on the outer peripheral portion of the porous body 5 outside the region where the electrode catalyst layer 3 is formed. Except for this point, it has basically the same structure as the membrane electrode assembly shown in FIG.
By forming such a seal layer 7, the gas is blocked at the outer edge of the porous body 5, and the outflow of the gas passing through the electrode catalyst layer 3 is suppressed without damaging the polymer electrolyte membrane 2. Will be.

  The polymer resin material constituting the sealing layer 7 is not particularly limited as long as it exhibits a gas sealing function, but the polymer electrolyte membrane 2 and the electrode catalyst layer 3 are not limited. It is desirable to use a resin material of the same type as these polymer resins so as not to cause an adverse effect due to a reaction to the constituent resin material.

Examples of the catalyst component contained in the electrode catalyst layer 3 include Pt (platinum), Ir (iridium), gold (Au), silver (Ag), Pd (palladium), Ru (ruthenium), rhodium (Rh), and the like. These metals and their alloys can be selected.
These catalytic metal particles are usually used in a state where they are supported on a conductive carrier such as carbon black or graphite, and as described above, together with a proton conductive solid polymer resin or, if necessary, a water repellent polymer. The electrode catalyst layer 3 is configured.

  The fuel cell membrane electrode assembly 1 having such a structure is, for example, a structure in which a porous body 5 is disposed on both surfaces of a proton conductive solid polymer membrane 2 and then a central portion of the multi-molecular body 5. A solution containing a catalyst, a proton conductive polymer resin, and a solvent is contained in a region narrower than the range in which the gas diffusion layer 4 is disposed, and the solvent is removed from the solution by evaporation to dry the porous body. The electrode catalyst layer 3 is formed inside 5 and the resulting laminate is hot pressed to obtain a joined body. A gas diffusion layer 4 made of carbon paper, carbon woven fabric or non-woven fabric is installed on both sides.

  Further, after the porous body 5 is placed on the gas diffusion layer 4, the porous body 5 is impregnated with the solution containing the catalyst in the same manner, and this is disposed on both surfaces of the proton conductive solid polymer membrane 2. Similarly, it is possible to dry, remove the solvent, form the electrode catalyst layer 3 inside the porous body 5, and form a bonded body by hot pressing.

Alternatively, the porous body 5 is disposed on the base material sheet, and the polycrystalline body 5 is impregnated with the catalyst solution in the same manner, and then dried to remove the solvent from the catalyst solution. It can also be manufactured by hot pressing in a state of being disposed on both surfaces of the film 2 and peeling off the substrate sheet from the obtained laminate.
In addition, as said base material sheet, PTFE can be used, for example.

  Further, as shown in FIGS. 2A and 2B, in order to form the seal layer 7 on the outer peripheral portion of the porous body 5, the porous body 5 is impregnated with the catalyst solution, The outer portion of the impregnation region is impregnated with the polymer material as described above. The timing may be after impregnation with the catalyst solution or after hot pressing.

  Hereinafter, the present invention will be specifically described based on examples. Needless to say, the present invention is not limited to these examples. In this example, “%” means mass percentage unless otherwise specified.

(Example 1)
First, as a catalyst solution (slurry) for forming the electrode catalyst layer 3 in the porous body 5, carbon black powder (Vulcan XC72) carrying Pt (platinum) fine particles as a catalyst metal and a proton conductive solid Using a polymer resin solution (5% solution of Nafion (registered trademark)), an alcohol solution as a solvent and water, the amount of Pt used is 0.3 mg / cm ² , and the catalyst-supported carbon black powder and polymer after drying A slurry in which the mass ratio of the resin was 1: 1 was prepared.

  Next, Nafion 112 is used as the proton conductive solid polymer membrane, and the porous body 5 (thickness: 18 μm, porosity: 85%) made of polyimide is placed on the solid polymer membrane 2. The slurry is impregnated in the central portion of the porous body 5 and inside the region where the gas diffusion layer 4 described later is disposed, and the same is applied to the back side of the solid polymer membrane 2 as well. After the porous body 5 was placed and similarly impregnated with the slurry, it was dried to remove the solvent component from the slurry, and the electrode catalyst layer 3 was formed inside the porous body 5.

  Furthermore, after the gas diffusion layer 4 made of carbon paper is installed on both sides of the above-mentioned laminate in which the solid polymer membrane 2 is sandwiched by the porous body 5 provided with the electrode catalyst layer 3, the temperature of 140 ° C., 10 MPa These were joined by hot pressing for 120 seconds under a pressure of 1 to obtain a membrane electrode assembly 1 as shown in FIG.

The membrane electrode assembly 1 thus obtained was sandwiched between a gas flow path forming member and a current collector (not shown) to form a single cell of a fuel cell.
Subsequently, in order to evaluate the performance of this single cell, the output voltage at 1 A / cm ² was measured.

(Example 2)
The porous body 5 is placed on the carbon paper as the gas diffusion layer 4 used in Example 1, and the slurry is similarly impregnated in the central portion of the porous body 5 and then dried. Thus, the solvent component contained in the slurry was removed, and the electrode catalyst layer 3 was formed inside the porous body 5.

  Next, a laminate composed of the porous body 5 provided with the gas diffusion layer 4 and the electrode catalyst layer 3 thus prepared was installed on both sides of the same proton conductive solid polymer membrane 2 as in Example 1, These were joined by hot pressing under the same conditions to obtain a membrane electrode assembly 1 as shown in FIG.

  In the same manner as in Example 1, a single cell of the fuel cell was formed using the gas flow path forming member and the current collector, and the output voltage of this single cell was measured in the same manner.

(Example 3)
A base sheet made of PTFE was prepared, and the porous body 5 similar to that of the above example was placed on the base sheet, and the slurry was similarly impregnated in the central portion of the porous body 5. After that, the electrode catalyst layer 3 was formed inside the porous body 5 by drying.

  Next, a laminate of the porous body 5 and the base sheet provided with such an electrode catalyst layer 3 was placed on both sides of the proton conductive solid polymer membrane 2 and hot-pressed under the same conditions. After that, the base sheet was peeled off, and carbon paper as the gas diffusion layer 4 was installed on both sides thereof, and these were joined to obtain a membrane electrode assembly 1 as shown in FIG.

  As in the above example, a single cell of the fuel cell was formed using the gas flow path forming member and the current collector, and the output voltage of this single cell was measured in the same manner.

Example 4
Similarly to Example 2 above, the slurry was similarly impregnated in the central portion of the porous body 5 placed on the carbon paper as the gas diffusion layer 4 and then dried to remove the solvent component contained in the slurry. The electrode catalyst layer 3 was formed inside the porous body 5 by removing.
Next, the outer surface of the porous body 5 where the electrode catalyst layer 3 was formed was impregnated with a Nafion solution as a polymer resin material to form a seal layer 7 on the outer periphery of the porous body 5.

  Next, the laminate of the gas diffusion layer 4 thus obtained and the porous body 5 provided with the electrode catalyst layer 3 and the seal layer 7 was placed on both sides of the proton conductive solid polymer membrane 2, and the same These were joined by hot pressing to obtain a membrane electrode assembly 1 as shown in FIG.

  In the same manner as in the above example, a single cell of the fuel cell was formed using the gas flow path forming member and the current collector, and the output voltage of this single cell was measured in the same manner.

(Comparative example)
Without using the porous body 5, hot pressing is performed on both surfaces of the Nafion 112, which is a proton conductive solid polymer membrane, with the electrode catalyst layer attached to the carbon paper (gas diffusion layer) using the slurry. Thus, a membrane electrode assembly of the comparative example was obtained.
And similarly, it was set as the single cell of a fuel cell using the gas flow path formation member and the electrical power collector, and the output voltage of this single cell was measured similarly.

〔Measurement result〕
FIG. 3 shows the voltage measurement results at the open end of the single fuel cell using the membrane electrode assemblies according to Examples 1 to 4 and the comparative example.

  As is apparent from the results of FIG. 3, in a single cell using a membrane electrode assembly of a comparative example in which an electrode catalyst layer is directly formed between a polymer electrolyte membrane and a gas diffusion layer without using a porous body. The polymer electrolyte membrane is damaged at the time of joining by hot pressing by the edge portion of the gas diffusion layer and the carbon fiber constituting the gas diffusion layer, and the damage to the electrolyte membrane is extended even during the operation of the cell. Therefore, it was considered that gas cross-leak occurred, the initial voltage was low, and the phenomenon that the output voltage decreased with the passage of operation time was recognized.

  In contrast, in a single cell using the membrane electrode assembly of the present invention in which a porous body is interposed between the polymer electrolyte membrane and the gas diffusion layer and an electrode catalyst layer is provided inside the porous body, Since the attack to the polymer electrolyte membrane by the gas diffusion layer is mitigated and damage to the electrolyte membrane is avoided, not only the initial voltage is high, but also the performance deterioration width with time is small, especially the outer peripheral portion of the porous body In the membrane / electrode assembly of Example 4 provided with a sealing layer, the gas seal becomes more complete, so that there is very little deterioration over time, and good battery performance can be maintained over a long period of time. confirmed.

(A) And (b) is sectional drawing and a top view which respectively show the structure of the membrane electrode assembly for fuel cells of this invention. (A) And (b) is sectional drawing and a top view which show the other structure of the membrane electrode assembly for fuel cells of this invention, respectively. It is a graph which compares and shows the time-dependent change of the output voltage of the fuel cell single cell using the membrane electrode assembly concerning an Example and a comparative example.

Explanation of symbols

1 Fuel Cell Membrane / Electrode Assembly 2 Proton Ion Conductive Solid Polymer Membrane (Polymer Electrolyte Membrane)
3 Electrocatalyst layer 4 Gas diffusion layer
5 Porous material 7 Seal layer

Claims (8)

  In a membrane electrode assembly for a fuel cell comprising a proton conductive solid polymer membrane, an electrode catalyst layer, and a gas diffusion layer, the electrode catalyst layer is formed inside the porous body, and the outer edge of the porous body Is located outside the outer edge of the gas diffusion layer, a fuel cell membrane electrode assembly.   2. The membrane electrode assembly for a fuel cell according to claim 1, wherein a region in which the electrode catalyst layer is formed in the porous body is located inside an outer edge of the gas diffusion layer.   The membrane electrode assembly for a fuel cell according to claim 1 or 2, wherein a sealing layer made of a polymer resin is formed outside a region where the electrode catalyst layer is formed in the porous body.   A method for producing a membrane electrode assembly for a fuel cell according to any one of claims 1 to 3, comprising a step of disposing a porous body on a proton conductive solid polymer membrane; A method for producing a membrane electrode assembly for a fuel cell, comprising the steps of: adding a solution containing a catalyst, a proton conductive polymer resin, and a solvent; and removing the solvent from the solution.   A method for producing a membrane electrode assembly for a fuel cell according to any one of claims 1 to 3, comprising a step of disposing a porous body in a gas diffusion layer, and a catalyst and a proton in the polymorphic body. Including a step of including a solution containing a conductive polymer resin and a solvent, a step of disposing the gas diffusion layer and the porous body on the proton conductive solid polymer membrane, and a step of removing the solvent from the solution. A method for producing a membrane electrode assembly for a fuel cell.   A method for producing a membrane electrode assembly for a fuel cell according to any one of claims 1 to 3, comprising a step of disposing a porous body on a base sheet, and a catalyst and a proton on the polymorphic body. A step of including a solution containing a conductive polymer resin and a solvent, a step of placing the base sheet and the porous body on a proton conductive solid polymer membrane, a step of removing the solvent from the solution, The manufacturing method of the membrane electrode assembly for fuel cells characterized by including the process of removing a base material sheet from a porous body.   The membrane electrode assembly for a fuel cell according to any one of claims 4 to 6, further comprising a step of including a polymer resin outside the region containing the solution in the porous body. Manufacturing method.   A polymer electrolyte fuel cell comprising a plurality of fuel cell membrane electrode assemblies according to any one of claims 1 to 3 and a plurality of gas flow path forming members.

Images