JP2002203569A - Solid high polymer type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid high polymer type fuel cell by which humidifying of an electrolyte by auxiliary machine is reduced or made needless, and high output is obtained steady under a condition of not humidifying. SOLUTION: In the solid high polymer type fuel cell equipped with a film-electrode zygote 10 which electrodes are joined to both sides of a solid high polymer electrolyte film 20, at least a cathode 30 is made into a two-layer structure of a catalyst layer 34 and a diffusion layer 32, and a gaseous phase side surface of an electrolyte 40 in the catalyst layer is covered with water repellant layer 42 which has oxygen permeability. The water repellant layer 42 is obtained by a method of making the gaseous phase side surface of the electrolyte 40 in a catalyst layer, which is applied a hydrophobic metaloxan precursor, polycondensation, a method of carrying out acid base reaction of an ion exchange group, which has come out to the gaseous phase side surface of the electrolyte 40 in a catalyst layer, and a base, and a method of carrying out gaseous phase deposit of an water-repellent material to the gaseous phase side surface of the electrolyte 40 in a catalyst layer. Moreover, the water-repellent material 42 is obtained also by a method of using what has a hydrophobic segment in an end of a main chain or a side chain as the electrolyte 40 in a catalyst layer, and making the hydrophobic segment unevenly distributed on the gaseous phase side surface of the catalyst layer 34.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer electrolyte fuel cell, and more particularly, to a polymer electrolyte fuel cell suitable as a small portable power source, a vehicle power source, a cogeneration system, and the like.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell is a fuel cell using a polymer electrolyte membrane as an electrolyte. Solid polymer electrolytes used in polymer electrolyte fuel cells include:
Non-crosslinked perfluoro-based electrolytes and various hydrocarbon-based electrolytes such as Nafion (registered trademark, manufactured by DuPont) are known, but all of them require water to exhibit ionic conductivity. And Therefore, when the operating condition of the fuel cell becomes a dry condition, the water content of the solid polymer electrolyte membrane decreases and the ionic conductivity decreases, so-called dry-up occurs, which causes a decrease in the output of the fuel cell.

In a conventional polymer electrolyte fuel cell,
In order to solve this problem, it is common to use a method of externally supplying water to the electrolyte membrane using an auxiliary machine.
As a method of supplying water to the electrolyte membrane, specifically,
There are known a method of humidifying a reaction gas using a bubbler, a mist generator, and the like, a method of directly injecting moisture into a reaction gas flow path formed inside a separator, and the like.

A polymer electrolyte fuel cell is generally
A structure in which a pair of electrodes are joined to both surfaces of a solid polymer electrolyte membrane to form a membrane electrode assembly, and both sides thereof are sandwiched between separators. In order for the battery reaction to proceed, it is necessary to ensure a three-phase interface in which the three phases of the electrolyte, the catalyst, and the reaction gas coexist in the electrode. Therefore, the electrode generally has a porous structure including the catalyst and the electrolyte. ing.

On the other hand, in the case of a polymer electrolyte fuel cell, water is generated at the cathode by a cell reaction. When protons move from the anode side to the cathode side, water also moves to the cathode side by electroosmosis. Therefore, when the operating condition of the fuel cell is a wet condition, excess water tends to stay, particularly at the cathode. If this water is left, pores in the electrodes are closed with water, so that the supply of the reaction gas is obstructed, that is, so-called flooding occurs, which causes a decrease in the output of the fuel cell.

In a conventional polymer electrolyte fuel cell,
In order to solve this problem, it is general to use a method of optimizing the electrode structure. For example, there is known a method in which an electrode has a two-layer structure of a diffusion layer and a catalyst layer provided on a surface in contact with a solid polymer electrolyte membrane in order to increase a three-phase interface. The diffusion layer is a layer for supplying a reaction gas to the catalyst layer and transferring electrons, and is generally made of a porous and electron conductive material. The catalyst layer is a layer that serves as a reaction field of a battery reaction, and generally includes a catalyst supported on a catalyst or a carrier and an electrolyte having the same components as the solid polymer electrolyte membrane (electrolyte in the catalyst layer). .

For example, Japanese Patent Application Laid-Open No. 5-36418 discloses that in order to increase the number of reaction sites with respect to the electrodes,
A porous electrode is disclosed in which a catalyst-supporting carbon whose surface is coated with a solid polymer electrolyte is bound with a fluororesin.

Further, Japanese Patent Application Laid-Open No. 9-320611 discloses carbon black carrying a platinum catalyst, a fluorine-based ion-exchange resin and an ion-exchange group in order to uniformly impart water repellency to a porous electrode. An electrode for a polymer electrolyte fuel cell obtained by applying a mixed solution of a solvent-soluble fluoropolymer which is not used to a polymer electrolyte membrane is disclosed.
In addition, the same publication discloses that a porous film is obtained by kneading and stretching a mixture of carbon black carrying a platinum catalyst and polytetrafluoroethylene, and a fluorine-based ion exchange resin and a solvent-soluble fluorine having no ion exchange group. An electrode for a polymer electrolyte fuel cell obtained by impregnating a polymer is disclosed.

[0009]

In order to humidify the electrolyte using the auxiliary equipment, a water tank for storing water for humidification, a humidifier, and a condenser for collecting water discharged from the fuel cell are required. Various components such as vessels are required. Therefore, there is a problem that the entire fuel cell system becomes complicated and large. Further, humidification of the electrolyte using the auxiliary equipment requires extra auxiliary power, which may cause a reduction in the power generation efficiency of the fuel cell.

On the other hand, in the case of the polymer electrolyte fuel cell, as described above, water is generated by the cell reaction on the cathode side. If this generated water can be directly used for humidifying the electrolyte, the humidification of the electrolyte by the auxiliary equipment can be reduced or made unnecessary, and a reduction in the size, weight, and efficiency of the entire fuel cell system can be expected.

However, the conventional electrode used in the polymer electrolyte fuel cell has a problem in that water remaining in the electrode is reduced by, for example, performing a water-repellent treatment on the inner surface of the pores of the electrode in order to suppress a decrease in output due to flooding. Generally, it is easy to discharge water, and the structure is not suitable for effective use of generated water.

For example, an electrode for a polymer electrolyte fuel cell disclosed in Japanese Patent Application Laid-Open No. 9-320611 discloses a solvent-soluble fluorine-containing polymer having no ion-exchange group at least a part of the inner surface of the pores of the electrode. It aims at coating and imparting water repellency. However, it is difficult to coat all the ion-exchange groups exposed on the gas phase side surface with a solvent-soluble fluoropolymer thinly and uniformly by using the disclosed method. Therefore, most of the water generated by the battery reaction is discharged from the inside of the pores to the outside of the electrode, and is not effectively used for humidification of the electrolyte. Has become.

An object of the present invention is to provide a polymer electrolyte fuel cell capable of reducing or eliminating humidification of an electrolyte by an auxiliary machine and stably providing a high output even under non-humidified conditions. is there.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a polymer electrolyte fuel cell having a membrane / electrode assembly having electrodes joined to both sides of a polymer electrolyte membrane. At least one comprises a catalyst layer comprising a catalyst or a catalyst supported on a carrier and an electrolyte in the catalyst layer, and the gas phase side surface of the electrolyte in the catalyst layer is covered with a water-repellent layer having a reaction gas permeability. The point is that

When the gas-phase surface of the electrolyte in the catalyst layer is covered with a water-repellent layer having a reaction gas permeability, the diffusion of the reaction gas into the catalyst layer is not hindered and the water from the catalyst layer to the diffusion layer side is not hindered. Emissions are suppressed. As a result, part of the water generated by the battery reaction stays inside the catalyst layer. Further, the water retained inside the catalyst layer is returned to the solid polymer electrolyte membrane by diffusion, and is reused for humidifying the solid polymer electrolyte membrane. Therefore, even under low or no humidification conditions, the water content of the solid polymer electrolyte membrane can be maintained at a level required for stable operation, and a high output can be obtained stably.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. The polymer electrolyte fuel cell according to the present invention includes a membrane / electrode assembly in which electrodes are joined to both surfaces of a polymer electrolyte membrane. Further, at least one of the electrodes includes a catalyst layer containing a catalyst supported on a catalyst or a carrier and an electrolyte in the catalyst layer, and the electrolyte in the catalyst layer has a water-repellent gas-phase surface having a reactive gas permeability. Characterized by being coated with a layer.

The water-repellent layer may be provided on either the cathode or the anode. However, in the case of a polymer electrolyte fuel cell, since more water is generally discharged from the cathode side, it is preferable to provide a water-repellent layer at least on the cathode side. Further, since a part of water is discharged from the anode side, it is more preferable to provide a water-repellent layer on both the cathode and the anode when the dry condition is remarkable.

FIG. 1 shows an example of a cross-sectional view of such a membrane electrode assembly 10 on the cathode side. In FIG. 1, a membrane electrode assembly 10 includes a solid polymer electrolyte membrane 20 and a cathode 30 joined to one surface thereof.

In the present invention, the solid polymer electrolyte membrane 2
For 0, various materials can be used, and there is no particular limitation. That is, the solid polymer electrolyte membrane 20
May be a fluorinated polymer in which all or part of the polymer skeleton is fluorinated and provided with an ion exchange group, or a hydrocarbon polymer containing no fluorine in the polymer skeleton and the ion exchange group It may be provided.

The ion exchange groups contained in these polymers are not particularly limited. That is, the ion exchange group may be any of sulfonic acid, carboxylic acid, phosphonic acid, phosphonous acid and the like. Also,
These polymers may contain one kind of ion exchange group, or may contain two or more kinds of ion exchange groups.

As the solid polymer electrolyte in which all or a part of the polymer skeleton is fluorinated, specifically, perfluorocarbon sulfonic acid-based polymers such as Nafion (registered trademark), perfluorocarbon phosphonic acid-based polymers, Styrene sulfonic acid polymers, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymers and the like are mentioned as preferable examples.

Specific examples of the hydrocarbon-based solid polymer electrolyte containing no fluorine include polysulfonesulfonic acid, polyaryletherketonesulfonic acid, polybenzimidazolealkylsulfonic acid, and polybenzimidazolealkylphosphonic acid. Is a preferred example.

The cathode 30 comprises a diffusion layer 32 and a catalyst layer 3
4 and a water-repellent layer 42. The diffusion layer 32 is a layer for supplying an oxidizing gas to the catalyst layer 34 and transferring electrons, and is provided on the gas phase side of the cathode 30. The material is not particularly limited as long as it is porous and has electronic conductivity. Generally, a porous carbon cloth, carbon paper, or the like is used.

The catalyst layer 34 is a layer serving as a reaction field for a battery reaction, and is provided on a surface in contact with the solid polymer electrolyte membrane 20. The catalyst layer 34 includes a carrier 36, a catalyst 38 supported on the carrier 36, and an electrolyte 40 in the catalyst layer. The materials of the carrier 36 and the catalyst 38 are not particularly limited, and various materials can be used depending on the application. Generally, carbon is used for the carrier 36 and Pt or a Pt alloy is used for the catalyst 38. The catalyst 3
As shown in FIG. 1, 8 may be contained in the catalyst layer 34 while being supported on the carrier 36, or the catalyst 38 may be contained alone in the catalyst layer 34.

The catalyst layer electrolyte 40 is added to impart ionic conductivity to the catalyst layer 34. The material of the electrolyte 40 in the catalyst layer is not particularly limited, and various materials can be used depending on the application. Usually, an electrolyte having the same component as the solid polymer electrolyte membrane 20 is used, but an electrolyte having a different component may be used. Further, the water-repellent layer 4
In order to form 2, a solid polymer electrolyte having a hydrophobic segment at the end of the main chain or a side chain may be used alone or as a mixture with another electrolyte as the electrolyte 40 in the catalyst layer. This will be described later.

The water-repellent layer 42 is provided so as to cover the gas-phase side surface of the electrolyte 40 in the catalyst layer. The material of the water-repellent layer 42 is oxygen permeability capable of supplying oxygen contained in the oxidizing gas to the catalyst layer 34,
Any material can be used as long as the material has water repellency capable of suppressing the discharge of water to 2, and is not particularly limited.

The thickness of the water-repellent layer 42 can be arbitrarily selected according to the material as long as it has the required oxygen permeability and water repellency. For example, the water-repellent layer 42 may be a monomolecular layer as long as it has sufficient water-repellency. Further, for example, the water-repellent layer 42 may be a polymer layer having a predetermined thickness as long as the layer has sufficient oxygen permeability.

The larger the area of the water-repellent layer 42 is, the better. As the area of the water repellent layer 42 covering the gas phase side surface of the electrolyte 40 in the catalyst layer increases, the diffusion layer 3
This is because the discharge of water to 2 is efficiently suppressed. However, in order to transfer electrons between the catalyst layer 34 and the diffusion layer 32, both need to be electrically continuous. Therefore, the water-repellent layer 42 is a substantially continuous layer that covers a portion other than a portion where the catalyst 38 or the carrier 36 is in contact with the diffusion layer 32 in the gas-phase side surface of the electrolyte 40 in the catalyst layer. Preferably, there is.

Specific examples of the water-repellent layer 42 include a polycondensate layer obtained by polycondensation of a hydrophobic metalloxane precursor and an ion exchange layer on the gas-phase side surface of the electrolyte 40 in the catalyst layer. Preferable examples include a base layer obtained by performing an acid-base reaction between a group and a base, and a deposited layer in which a water-repellent material is deposited on the gas-phase side surface of the electrolyte 40 in the catalyst layer via a gas phase. In addition, instead of forming a heterogeneous material on the gas-phase side surface of the electrolyte 40 in the catalyst layer, the water-repellent layer 42 has a hydrophobic segment bonded to the terminal or side chain of the main chain as at least a part of the electrolyte 40 in the catalyst layer. An unevenly distributed layer obtained by unevenly distributing the hydrophobic segment to the gas-phase side surface of the electrolyte 40 in the catalyst layer using the solid polymer electrolyte described above may be used.

The same applies to the case where the anode has a two-layer structure of a catalyst layer and a diffusion layer, and a water-repellent layer is formed on the surface of the electrolyte in the catalyst layer. That is, the water-repellent layer on the anode side can be made of various materials having an arbitrary thickness as long as it has the required hydrogen permeability and water repellency. Further, the water-repellent layer on the anode side is preferably a continuous layer as long as conduction between the diffusion layer and the catalyst layer is ensured. Further, the above-mentioned polycondensate layer, base layer,
Both the deposition layer and the unevenly distributed layer can be used as a water-repellent layer on the anode side.

When a water-repellent layer is provided on the anode side,
The material of the water-repellent layer is particularly preferably a fluorine-based material containing a C—F bond in the molecule. Since the thin layer of the fluorine-based material has high water repellency and low CO gas permeability, if this is used as the water repellent layer on the anode side, CO poisoning of the catalyst on the anode side is reduced. This has the advantage of being suppressed and improving the durability of the electrode.

The membrane / electrode assembly 1 having such a water-repellent layer
No. 0 is used in a state where both surfaces thereof are sandwiched by a separator provided with a reaction gas flow path for supplying a reaction gas, similarly to the conventional membrane electrode assembly.

Next, the operation of the polymer electrolyte fuel cell according to the present embodiment will be described. In FIG. 1, when a fuel gas containing hydrogen is supplied to the anode (not shown) side of the membrane electrode assembly 10, protons and electrons are generated from the hydrogen at the anode, and the generated protons pass through the solid polymer electrolyte membrane 20. To the cathode 30. The generated electrons are carried from the load (not shown) to the catalyst layer 34 through the diffusion layer 32 on the cathode 30 side.

On the other hand, when an oxidizing gas containing oxygen is supplied to the cathode 30 side, oxygen passes through the diffusion layer 32 and
Reach two surfaces. Since the water-repellent layer 42 has oxygen permeability, the diffusion of oxygen is not hindered, and oxygen passes through the water-repellent layer 42 as it is and reaches the catalyst 38 in the catalyst layer 34.

On the surface of the catalyst 38, water is generated from protons, oxygen, and electrons. At this time, since the water-repellent layer 42 has high water repellency, a part of the water generated in the catalyst layer 34 stays in the catalyst layer 34 without being discharged to the diffusion layer 32 side. The water retained in the catalyst layer 34 is returned to the solid polymer electrolyte membrane 20 by diffusion, and is reused for humidifying the solid polymer electrolyte membrane 20. Therefore, the water content of the solid polymer electrolyte membrane 20 is maintained at a level required for stable operation even without externally replenishing water using an auxiliary machine.
High output is obtained stably.

A part of the water returned into the solid polymer electrolyte membrane 20 diffuses to the anode side. At this time, if the gas-phase surface of the electrolyte in the catalyst layer on the anode side is covered with the water-repellent layer, the amount of water discharged from the fuel electrode also decreases. Therefore, the total amount of water discharged from the membrane electrode assembly 10 decreases, and the non-humidifying operation is further facilitated.

In the above-described example, the electrode has a two-layer structure including a catalyst layer in which the gas-phase surface of the electrolyte in the catalyst layer is covered with a water-repellent layer, and a diffusion layer provided outside the catalyst layer. However, the electrode may have a single-phase structure composed of only the catalyst layer in which the gas-phase surface of the electrolyte in the catalyst layer is covered with the water-repellent layer. When the electrode has a single-phase structure, the water-repellent layer is preferably a continuous layer except for a portion where the catalyst or the carrier is in contact with the separator.

Next, a specific example of the water-repellent layer 42 will be described in detail. The first specific example of the water-repellent layer 42 includes a polycondensate layer obtained by applying a solution containing a hydrophobic metalloxane precursor to the gas-phase side surface of the electrolyte 40 in the catalyst layer and performing polycondensation. Here, the hydrophobic metalloxane precursor refers to a monomer or an oligomer having a hydrophobic group and producing a metalloxane bond by polycondensation by a sol-gel method. The hydrophobic metalloxane monomer can be represented by the following chemical formula 1. Further, the hydrophobic metalloxane oligomer refers to a 2- to 200-mer of a hydrophobic metalloxane monomer represented by the formula (1).

[0039]

Embedded image X _4-n M (OR) _n

In the formula 1, n is an integer of 1 to 3. M is a tetravalent metalloid or metal element;
Suitable examples include silicon, titanium, zirconium, and the like. OR is an alkoxyl group. Specifically, a methoxy group, an ethoxy group, a propoxy group, a butoxy group and the like are mentioned as preferable examples.

In addition, at least one of X bonded to the element M may be a hydrophobic group. As the hydrophobic group, those in which at least one hydrogen bonded to carbon in an alkyl group, a cycloalkyl group, an allyl group, an aryl group or the like is replaced by fluorine are particularly preferable. Further, the hydrophobic group may be a hydrocarbon group having strong hydrophobicity (for example, a phenyl group, an alkyl group, an allyl group, etc.). Further, when two or more hydrophobic groups are bonded to the element M, the respective hydrophobic groups may be the same or different.

As such a hydrophobic metalloxane precursor, specifically, (3,3,3-trifluoropropyl) trimethoxysilane, (tridecafluoro-1,
Suitable examples include 1,2,2-tetrahydrooctyl) triethoxysilane, (heptadecafluoro-1,1,2,2-tetrahydrodecyl) triethoxysilane, and oligomers thereof.

When a solution containing a hydrophobic metalloxane precursor is applied to the gas phase surface of the electrolyte 40 in the catalyst layer, the solution may contain one kind of hydrophobic metalloxane precursor, or More than one type of hydrophobic metalloxane precursor may be included. Further, the type and concentration of the hydrophobic metalloxane precursor contained in the solution, the amount of the solution to be applied, etc. are determined by the thickness of the polycondensate layer to be formed, the reaction gas permeability required for the polycondensate layer, and the water repellency. What is necessary is just to adjust suitably according to etc.

In the present invention, "coating" refers to uniformly covering the gas-phase surface of the electrolyte 40 in the catalyst layer with a solution, and specifically, dripping, brushing, spraying, steam contact, etc. Is a preferred example. Furthermore, the method of polycondensation of the hydrophobic metalloxane precursor is a method of heating,
Various methods such as a method of reacting with an acid or an alkali can be used and are not particularly limited.

When the ion-exchange groups are exposed on the gas-phase side surface of the electrolyte 40 in the catalyst layer, water is easily discharged to the diffusion layer 32 side through the ion-exchange groups. On the other hand, when the gas-phase side surface of the electrolyte 40 in the catalyst layer is covered with the polycondensate layer of the hydrophobic metalloxane precursor, the diffusion layer 3
2 is suppressed. In particular, the water present in the portion where the ion exchange group which is likely to serve as a water discharge port is exposed, and the water repellent layer can be selectively formed by the catalytic action of the ion exchange group itself, so that the water discharge is efficiently suppressed. . Moreover,
Since such a polycondensate layer has a reaction gas permeability, diffusion of the reaction gas to the catalyst layer 34 is not hindered. Therefore, a fuel cell that operates stably even under non-humidified conditions can be obtained.

Next, a second specific example will be described. The second specific example of the water-repellent layer 42 includes a base layer obtained by performing an acid-base reaction between a base and an ion exchange group on the gas-phase side surface of the electrolyte 40 in the catalyst layer. As a preferable example of the base to be reacted with the ion exchange group, a quaternary ammonium salt represented by the following chemical formula 2 is given.

[0047]

Embedded image (R ₄ N) Y

In the formula (2), R is generally an alkyl group, an allyl group, an aryl group or the like, but in the present invention, the structure of R is not particularly limited, and various quaternary ammonium compounds may be used. Salt can be used. Further, in order to impart high water repellency to the base layer, R is a hydrophobic group in which at least one hydrogen bonded to carbon in the above-mentioned alkyl group, allyl group, aryl group or the like is substituted with fluorine. Particularly preferred. In addition, each R bonded to the nitrogen atom may be the same or different. Y is an anion, and its type is not particularly limited.

Specific examples of suitable bases include dodecyltrimethylammonium chloride, distearyldimethylammonium chloride, and 3,3,3-trifluorotripropyltrimethylammonium chloride.

In order to cause an acid-base reaction between the ion exchange group on the gas phase side surface of the electrolyte 40 in the catalyst layer and the base, a solution containing a base may be applied to the gas phase side surface of the catalyst layer 34. In this case, the kind of the base contained in the solution, the concentration of the solution, the amount of the solution applied, and the like may be appropriately adjusted according to the reaction gas permeability, water repellency, and the like required for the base layer.

When an ion-exchange group on the gas-phase side surface of the electrolyte 40 in the catalyst layer is subjected to an acid-base reaction with the base, the ion-exchange group is blocked by the base, and the diffusion layer 3
2 is suppressed. In particular, when a base having a hydrophobic group is used, high water repellency is imparted to the base layer by the hydrophobic group in addition to the block of the ion exchange group. Moreover, since such a base layer has a reaction gas permeability,
The diffusion of the reaction gas into the catalyst layer 34 is not hindered. Of course, only the ion-exchange groups on the gas-phase side surface are selectively made water-repellent, so that the original role of proton conductivity is sufficiently maintained by the internal ion-exchange groups.

Next, a third specific example will be described. The third specific example of the water-repellent layer 42 is composed of a deposition layer obtained by depositing a water-repellent material having a reactive gas permeability on the gas-phase side surface of the electrolyte 40 in the catalyst layer via the gas phase.
As the water-repellent material used for the deposition layer, specifically,
Suitable examples include CF ₄ , polytetrafluoroethylene (hereinafter, referred to as “PTFE”), and fluorinated pitch.

Various vapor deposition methods can be used depending on the type of water repellent material used. For example, when CF ₄ is used as the water repellent material,
A plasma processing method is preferred. When the plasma treatment using CF ₄ is performed on the surface of the electrolyte 40 in the catalyst layer, the mono- to multi-molecular carbon fluoride film is coated on the gas-phase side of the electrolyte 40 in the catalyst layer according to the treatment conditions. Can be formed.

Further, for example, PTFE is used as a water-repellent material.
When using, a sputtering method is suitable. When the PTFE sputtering process is performed on the surface of the electrolyte 40 in the catalyst layer, the PTFE having an arbitrary thickness can be formed according to the processing conditions.
The E film can be formed on the gas phase side surface of the electrolyte 40 in the catalyst layer.

For example, when pitch fluoride is used as the water-repellent material, the vapor contact method is preferred. When the pitch fluoride is brought into vapor contact with the electrolyte 40 in the catalyst layer, a pitch fluoride film having an arbitrary thickness can be formed on the gas-phase side surface of the electrolyte 40 in the catalyst layer according to the processing conditions.

Since a fluorine-based water-repellent material is generally hardly soluble in a solvent, a uniform coating made of the water-repellent material is formed on the gas-phase side surface of the electrolyte 40 in the catalyst layer by applying a solution. It is difficult to do. On the other hand, according to the method of depositing through the gas phase, the electrolyte 40 in the catalyst layer is used.
A uniform coating can be formed along the microscopic irregularities on the surface. Moreover, since the deposited layer obtained by such a method has a reaction gas permeability, the catalyst layer 34
There is no hindrance to the diffusion of the reaction gas into the reactor.

Next, a fourth specific example will be described. In a fourth specific example of the water-repellent layer 42, a solid polymer electrolyte having a hydrophobic segment at an end of a main chain or a side chain (hereinafter, referred to as a “hydrophobic electrolyte”) is used as the electrolyte 40 in the catalyst layer.
And the uneven distribution layer obtained by uneven distribution of the hydrophobic segment on the gas phase side surface of the electrolyte 40 in the catalyst layer.

Here, the hydrophobic segment is represented by the general formula: C
It refers to an atomic group represented by F ₃ — (CF ₂ ) _n —. The hydrophobic segment may be linear or may be in the middle of the branch. In general, as n increases, the water repellency of the hydrophobic segment tends to increase. On the other hand, the value of n hardly affects the reaction gas permeability. Therefore, the value of n is the required water repellency,
It can be arbitrarily selected in consideration of, for example, ease of production of the hydrophobic electrolyte. In order to impart high water repellency to the unevenly distributed layer, n is preferably 2 or more, and more preferably 10 or more. However, if n exceeds 200, the solubility decreases and it becomes difficult to form a catalyst layer. Therefore, n is preferably 200 or less.

The portion of the hydrophobic electrolyte other than the hydrophobic segment is not particularly limited. That is, the hydrophobic electrolyte may be one in which a hydrophobic segment is bonded to the terminal or side chain of the main chain of the solid polymer electrolyte in which all or a part of the polymer skeleton is fluorinated, or contains fluorine. The hydrocarbon-based solid polymer electrolyte may be one in which a hydrophobic segment is bonded to the terminal or side chain of the main chain.

As a specific example of such a hydrophobic electrolyte, one in which a hydrophobic segment is bonded to the terminal or side chain of the main chain of a perfluorocarbon sulfonic acid polymer is mentioned as a preferred example. As the electrolyte 40 in the catalyst layer, a hydrophobic electrolyte may be used alone, or a mixture of a hydrophobic electrolyte and an electrolyte having no hydrophobic segment may be used.

The electrolyte 40 in the catalyst layer containing a hydrophobic electrolyte
Then, a mixed solution of the catalyst and the catalyst supported on the carrier is applied to the surface of the solid polymer electrolyte membrane 20, and the solvent is removed, whereby the catalyst layer 34 is formed. At this time, as the solvent is removed, the hydrophobic segments are arranged on the gas-phase side surface of the electrolyte 40 in the catalyst layer, and an uneven distribution layer is formed on the gas-phase side surface of the electrolyte 40 in the catalyst layer. Since the unevenly distributed layer thus obtained has water repellency and has a reaction gas permeability, the diffusion layer 32 does not impede the diffusion of the reaction gas to the catalyst layer 34, and does not impede the diffusion layer 32. Water discharge can be suppressed.

Next, a method for manufacturing the polymer electrolyte fuel cell according to the present invention will be described. The polymer electrolyte fuel cell according to the present invention can be manufactured by various methods. In the first manufacturing method, first, the solid polymer electrolyte membrane 20
After the catalyst layer 34 is formed on both surfaces of the catalyst layer 34, the water-repellent layer 42 is uniformly formed on the surface of the electrolyte 40 in the catalyst layer using the above-described various methods, and then the diffusion layer 32 is formed on the surface of the catalyst layer 34. How to In this case, the diffusion layer 32 is
4 or may be simply brought into contact by fastening when assembling the cells.

The carrier 36 or the catalyst 38 in the catalyst layer 34
Is completely covered with the electrolyte 40 in the catalyst layer, after the water-repellent layer 42 is uniformly formed on the gas-phase side surface of the electrolyte 40 in the catalyst layer, the bonding or fastening of the diffusion layer 32 is performed. ,
The protruding part of the surface of the diffusion layer 32 is the water repellent layer 42.
Then, the catalyst layer 34 and the diffusion layer 32 are electrically connected to each other. By sandwiching both sides of such a membrane electrode assembly 10 with a separator having a reaction gas flow path, a polymer electrolyte fuel cell that operates stably even under non-humidified conditions can be obtained.

In the second manufacturing method, first, a sheet-like catalyst layer 34 is formed, and then a water-repellent layer 42 is uniformly formed on the surface of the electrolyte 40 in the catalyst layer by using the above-described various methods. In this method, the catalyst layer 34 on which the water-repellent layer 42 is formed is joined to the solid polymer electrolyte membrane 20, and the diffusion layer 32 is formed on the surface of the catalyst layer 34. Also in this case, the diffusion layer 3
2 may be joined or just contacted by fastening

In the third manufacturing method, first, the catalyst layer 34 is formed on the surface of the solid polymer electrolyte membrane 20, then the diffusion layer 32 is formed on the surface of the catalyst layer 34, and then the hydrophobic layer is formed from the diffusion layer 32 side. This is a method of forming a water-repellent layer 42 on the gas-phase side surface of the electrolyte 40 in the catalyst layer by performing impregnation / polycondensation of a reactive metalloxane precursor, treatment with a base, vapor-phase deposition of a water-repellent material, and the like. Even with such a method, a polymer electrolyte fuel cell that can operate stably under non-humidified conditions can be obtained.

In the fourth manufacturing method, first, a catalyst layer 34 is formed on the diffusion layer 32, and then a water-repellent layer 42 is formed on the surface of the electrolyte 40 in the catalyst layer from the diffusion layer 32 side.
This is a method of joining with 0.

In the above-described manufacturing method, each of the electrodes has a two-layer structure of the catalyst layer 34 and the diffusion layer 32. However, when the catalyst layer 34 covered with the water-repellent layer 42 is used as an electrode as it is. Can be manufactured by the same method as described above, except that the step of forming the diffusion layer 32 on the surface of the catalyst layer 34 is omitted and the step of forming an electron conduction path is added.

[0068]

EXAMPLES (Example 1) A polymer electrolyte fuel cell was manufactured by the following procedure. That is, using a Nafion membrane (N112, manufactured by DuPont) as a solid polymer electrolyte membrane,
In order to remove organic substances and the like contained in the membrane and obtain a complete proton type, a 10% H ₂ O ₂ aqueous solution, 0.5 MH ₂ SO
It boiled in order of ₄ aqueous solution and pure water, and was dried.

Next, a catalyst layer (13 cm ² ) was formed on a tetrafluoroethylene sheet, and this was hot-pressed (140 ° C., 4.9 MPa) on both surfaces of the solid polymer electrolyte membrane.
Was transferred. Next, a diffusion layer (made by E-TEK) was further hot-pressed (14
Bonding was performed at 0 ° C. and 7.35 MPa).

Next, over the entire surface of the catalyst layer on the cathode side,
A solution (fluorine solvent) of 300 μl of (3,3,3-trifluoropropyl) trimethoxysilane (manufactured by Chisso Corporation) was uniformly dropped. Next, a diffusion layer was stacked on the surface of the catalyst layer on the cathode side, and hot pressed (140 ° C., 7.3).
5MPa) and simultaneously with the bonding of the diffusion layer,
The condensation of (3-trifluoropropyl) trimethoxysilane was performed. Both sides of the obtained membrane / electrode assembly were sandwiched by separators having a reaction gas flow path to obtain a polymer electrolyte fuel cell.

(Comparative Example 1) On the surface of the catalyst layer on the cathode side,
A polymer electrolyte fuel cell was manufactured according to the same procedure as in Example 1 except that (3,3,3-trifluoropropyl) trimethoxysilane was not dropped.

Using the polymer electrolyte fuel cells obtained in Example 1 and Comparative Example 1, a trap experiment for measuring the amount of water discharged from the cathode and the anode was performed. The conditions of the trap experiment were as follows: hydrogen and air were used as the fuel gas and the oxidizing gas, respectively.
° C, current density 0.5 A / cm ² , excess fuel ratio 2, excess air ratio 1.77. Under these conditions, continuous operation was performed for 3 hours, during which time the amount of water discharged from the cathode side and the anode side was measured. Table 1 shows the results. Further, during the trap experiment, the voltage and resistance of the cell were sequentially measured, and the average value was obtained. Table 2 shows the results.

[0073]

[Table 1]

[0074]

[Table 2]

Table 1 shows that in Example 1 in which the water-repellent layer was formed on the surface of the catalyst layer on the cathode side, the ratio of the amount of water discharged from the cathode side to the total amount of water discharged was smaller.
This is because, by forming a water-repellent layer on the surface of the electrolyte in the catalyst layer on the cathode side, the discharge of generated water from the cathode side to the gas phase side is suppressed, and the generated water not discharged from the cathode side is reduced to the anode side. Because it spread more.

Table 2 shows that Example 1 has a higher voltage and a lower resistance. This is because the diffusion of oxygen is not hindered by the water-repellent layer on the cathode side, and a part of the generated water not discharged from the cathode side is reused for humidification of the solid polymer electrolyte membrane. Was maintained in an appropriate water-containing state.

Next, using the fuel cells obtained in Example 1 and Comparative Example 1, non-humidifying rolling was performed under different cell temperatures, and changes in voltage and resistance were examined. The operating conditions are
Hydrogen and air were used as the fuel gas and the oxidizing gas, respectively, and were humidified at both electrodes, the current density was 0.5 A / cm ² , the excess fuel ratio was 1.2, and the excess air ratio was 1.77. The cell temperature was increased by 2.5 ° C. every 30 minutes. FIG.
Shows the relationship between cell temperature and voltage. FIG. 3 shows the relationship between cell temperature and resistance.

In the case of Comparative Example 1, when the cell temperature was set at 80 ° C., power could be stably generated even under the condition that the electrodes were not humidified. However, when the cell temperature was increased to 82.5 ° C., the resistance increased rapidly, and an output voltage could not be obtained. On the other hand, in the case of Example 1, the resistance increased and the voltage decreased as the cell temperature increased, but the voltage of about 0.4 V was stable even when the cell temperature was increased to 87.5 ° C. Was obtained.

From the above results, when the water-repellent layer is formed on the gas-phase side surface of the electrolyte in the catalyst layer on the cathode side, the solid polymer electrolyte membrane can be properly hydrated by the generated water even under non-humidifying conditions without external humidification. It was found that the battery was maintained in a state and stable and high battery performance was obtained. In addition, it was found that the water content of the solid polymer electrolyte membrane could be maintained at an appropriate level even under high cell temperature conditions.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. is there.

For example, in the above embodiment, an example in which a cation exchange type electrolyte is used as the solid polymer electrolyte membrane has been described, but an anion exchange type electrolyte may be used as the solid polymer electrolyte membrane. In addition, the method of dehumidifying an electrolyte according to the present invention is particularly suitable for a polymer electrolyte fuel cell, but the method of the present invention is applicable to other types of fuel cells in which water management of the electrolyte is essential. (For example, a phosphoric acid fuel cell, an alkaline fuel cell, and the like) can be similarly applied.

[0082]

According to the present invention, there is provided a polymer electrolyte fuel cell having a membrane / electrode assembly in which electrodes are joined to both surfaces of a polymer electrolyte membrane. At least one of the electrodes is supported on a catalyst or a carrier. A catalyst layer containing a catalyst and an electrolyte in the catalyst layer, and the gas-phase surface of the electrolyte in the catalyst layer is covered with a water-repellent layer having a reaction gas permeability, so that there is no humidification without humidification by auxiliary equipment. Under such conditions, the solid polymer electrolyte membrane is maintained in an appropriate water-containing state, and there is an effect that a high output can be stably obtained.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view on the air electrode side of a polymer electrolyte fuel cell according to the present invention.

FIG. 2 is a diagram showing the relationship between cell temperature and voltage under non-humidified conditions.

FIG. 3 is a diagram showing the relationship between cell temperature and resistance under non-humidified conditions.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Membrane electrode assembly 20 Solid polymer electrolyte membrane 30 Cathode 32 Diffusion layer 34 Catalyst layer 36 Carrier 38 Catalyst 40 Electrolyte in catalyst layer 42 Water repellent layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tomo Morimoto 41-cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture F-term in Toyota Central R & D Laboratories Co., Ltd. 5H018 AA06 AS03 BB08 BB16 5H026 AA06 BB04 BB10 CX04 CX05

Claims (5)

[Claims] 1. A solid polymer electrolyte fuel cell comprising a membrane / electrode assembly having electrodes joined to both sides of a solid polymer electrolyte membrane, wherein at least one of the electrodes comprises a catalyst or a catalyst supported on a carrier and a catalyst. A polymer electrolyte fuel cell, comprising: a catalyst layer containing an inner layer electrolyte; and a gas-phase surface of the inner catalyst layer covered with a water-repellent layer having a reactive gas permeability. 2. The water-repellent layer is a polycondensate layer obtained by applying a solution containing a hydrophobic metalloxane precursor to the gas-phase side surface of the electrolyte in the catalyst layer and subjecting the solution to polycondensation. 9. The polymer electrolyte fuel cell according to item 1. 3. The solid layer according to claim 1, wherein the water-repellent layer is a base layer obtained by performing an acid-base reaction between a base and an ion exchange group on a gas phase side surface of the electrolyte in the catalyst layer. Molecular fuel cell. 4. The water-repellent layer is a deposited layer obtained by depositing a water-repellent material having a reactive gas permeability on a gas-phase side surface of the electrolyte in the catalyst layer via a gas phase. 2. The polymer electrolyte fuel cell according to 1. 5. The water-repellent layer uses an electrolyte in which a hydrophobic segment is bonded to a terminal or a side chain of a main chain as an electrolyte in the catalyst layer, and the hydrophobic segment is unevenly distributed on a gas phase side surface of the catalyst layer. 2. An unevenly distributed layer obtained by causing
9. The polymer electrolyte fuel cell according to item 1.