JP2003068330A - Solid polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell of high efficiency in generation of electrical power by removing surplus water which exists in a electrode and a solid polymer electrolyte layer and promoting diffusion of gas into the electrode. SOLUTION: The solid polymer fuel cell in which a fuel electrode and an oxidant electrode are disposed respectively on both sides of the solid polymer electrolyte layer, a fuel passage is provided on the side which faces the fuel electrode and an oxidant passage is provided on the side which faces the oxidant electrode, and a water retention layer which is formed from a conductive material and a water retention resin and has plural through holes, is provided on the fuel electrode and/or the oxidant electrode, solves the problem.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid polymer type fuel cell having good power generation efficiency, and more specifically, to removing excess water existing in the electrode and the solid polymer electrolyte layer to the electrode of the fuel cell. The present invention relates to a polymer electrolyte fuel cell in which fuel and an oxidant are efficiently supplied.

[0002]

2. Description of the Related Art A cross-sectional view of a unit cell of a conventional polymer electrolyte fuel cell is shown in FIG. The solid polymer electrolyte membrane 101 is sandwiched by two electrodes of a fuel electrode 102 and an oxidant electrode 103 from both sides, and a catalyst is supported on both electrodes. The fuel electrode 10
Fuel gas (hydrogen) is supplied to 2 and the oxidizer electrode 10
Oxidizer gas (oxygen) is supplied to 3. Further, a pair of current collectors 104 are arranged so as to sandwich the fuel electrode 102 and the oxidizer electrode 103 from both sides, and the current collector 104 and the fuel electrode 10 are arranged.
2. The space between the current collector 104 and the oxidant electrode 103 serves as the fuel channel 105 and the oxidant channel 106, respectively. Since the output voltage of the unit cell thus configured is as low as 1 V or less, a plurality of unit cells are stacked to form a polymer electrolyte fuel cell stack having a desired output voltage.

Each of the fuel electrode 102 and the oxidant electrode 103 has a structure in which a catalyst layer containing a catalytically active substance is supported by a porous electrode base material having conductivity, and a fuel flow path composed of a plurality of parallel grooves. Fuel electrode 102 through the electrode base material 105
Hydrogen as a fuel supplied to the oxidant and oxygen as an oxidant supplied from the oxidant channel 106 to the oxidant electrode 103,
A solid polymer electrolyte / catalyst / reaction gas three-phase interface is formed on each catalyst layer, and the reaction shown by the following reaction formula proceeds.

Fuel electrode: H ₂ → 2H ⁺ + 2e ⁻ (Equation 1) Oxidizer electrode: 2H ⁺ + 2e ⁻ + 1 / 2O ₂ → H ₂ O (Equation 2) That is, as shown in Equation 1 on the fuel electrode 102 side. In addition, an electrochemical reaction that decomposes hydrogen molecules into hydrogen ions and electrons
On the side of the oxidant electrode 103, an electrochemical reaction for producing water from hydrogen ions, electrons, and oxygen is performed as shown in Formula 2. Hydrogen ions generated by the reaction of the formula 1 on the fuel electrode 102 side permeate the solid polymer electrolyte membrane 101 in a hydrated state with water molecules, and are provided for the reaction of the formula 2 on the oxidant electrode 103 side.

In order to carry out these reactions efficiently and continuously, it is necessary to continuously supply the fuel and the oxidant to the fuel electrode 102 and the oxidant electrode 103, and to quickly remove the produced substances from the vicinity of the electrodes. . Specifically, at the oxidizer electrode 103, it is necessary to continuously supply oxygen as an oxidizer and remove water as a product. Unless water is removed promptly, the water film formed near the electrodes makes it difficult to supply oxygen to the oxidizer electrode 103, and the electrode reaction is stopped.

On the other hand, it is hydrated hydrogen ions that serve as charge carriers inside the solid polymer electrolyte membrane 101 held between the fuel electrode 102 and the oxidant electrode 103. The reason why hydrogen ions move from the fuel electrode to the oxidizer electrode in the solid polymer electrolyte membrane is that the solid polymer electrolyte membrane has a property of selectively diffusing hydrated hydrogen ions. Therefore,
In order to smoothly progress the entire battery reaction and improve the power generation efficiency, it is necessary to always keep the solid polymer electrolyte in a wet state so that it is saturated with water.

That is, there are conflicting requirements that the solid polymer electrolyte membrane 101 be kept in an appropriate wet state, and that the fuel electrode 102 and the oxidant electrode 103 suppress the formation of a water film that prevents gas permeation of the fuel and the oxidant. Satisfaction is required for high efficiency of the fuel cell.

In order to solve the above problems, Japanese Patent Laid-Open No. 7-3
Japanese Patent No. 26361 discloses a fuel cell in which fine particles of a water-absorbing material are dispersed in an electrode having a press-formed body of short carbon fibers as a base material. In the fuel cell having this structure, the water-absorbing material in the oxidant electrode positively absorbs the water generated in the oxidant electrode by the reaction of the above-described equation 2, and the excess water in the electrode is removed. Therefore, it has been found that the formation of a water film at the oxidizer electrode is suppressed and the efficiency of the fuel cell is improved.

However, since the crosslinked polyacrylic acid salt or the like used as the water absorbing material in the publication does not have conductivity, increasing the blending ratio of the water absorbing material in the electrode in order to improve the water absorbing ability of the electrode. However, the conductivity of the electrode is lowered, which leads to an increase in energy loss due to an increase in internal resistance. That is, in order to suppress the energy loss to a small level, the content ratio of the water-absorbing material that can be mixed has an upper limit (in the publication, the water-absorbing material is contained in the electrode in an amount of about 10% by volume). The limit can be kept low. Therefore, even if the amount of generated water increases due to a sudden increase in load, excess water exceeding the water absorption capacity of the electrode is not absorbed by the electrode, and a water film is formed on the electrode surface to supply gas to the electrode. Hinder.

On the other hand, Japanese Patent No. 3022528 discloses that
By providing a plate with ribs (grooves) that sandwich the fuel cell from both sides to form a gas flow path, and by providing the rib on the fuel electrode side of the plate with a porous water retention layer composed of a water retention resin and carbon , A method of maintaining the entire solid polymer layer in a wet state has been proposed. In the fuel cell with this configuration, since the water retention layer is provided in the gas flow path for fuel supply,
The humidity in the gas flow channel rises, and as a result, the solid polymer layer is wet. However, since the ribbed plate provided with the water retaining layer in the publication is mainly intended to humidify the solid polymer electrolyte layer from the fuel electrode side, removal of excess water generated on the oxidizer side has not been achieved. .

As described above, none of the above-mentioned prior arts has sufficient ability to remove excess water generated in the electrode during high load operation. Therefore, the problem to be solved by the present invention is to remove excess water existing in the electrode and the solid polymer electrolyte layer to promote the diffusion of gas into the electrode and to supply a fuel cell with high power generation efficiency. Is.

[0012]

According to the present invention, a fuel electrode and an oxidant electrode are provided on opposite sides of a solid polymer electrolyte layer, and a fuel channel and an oxidant electrode are exposed on the side facing the fuel electrode. A fuel cell having an oxidant flow path on its side, wherein a water retention layer formed of a conductive material and a water retention resin and having a plurality of through holes is formed on the fuel electrode and / or the oxidant electrode, A polymer electrolyte fuel cell provided on the road side and / or the oxygen flow path side is provided to solve the above problems.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, an electrode means a fuel electrode or an oxidant electrode, a gas means a fuel gas or an oxidant gas, and a gas passage means a fuel passage or an oxidant passage. Means water, and means a liquid and / or atomized body mainly composed of water. The fuel cell of the present invention is characterized in that it is mainly composed of a solid polymer electrolyte layer, an electrode, a gas channel and a water retention layer.

As the solid polymer electrolyte layer, a cation exchange membrane having a sulfone group as an ion exchange group for hydrogen ions can be used. Specifically, perfluorocarbon sulfonic acid resin, PSSA-PVA (polystyrene sulfonate polyvinyl alcohol copolymer)
And PSSA-EVOH (polyethylene sulfonic acid ethylene vinyl alcohol copolymer) and the like. Of these, those made of perfluorocarbon sulfonic acid resin are preferable, and specifically, Nafion membrane manufactured by DuPont, USA, Flemion membrane manufactured by Asahi Glass Co., Ltd., and Aciplex membrane manufactured by Asahi Kasei Corporation are used.

Since the electrochemical reaction in the fuel cell occurs at the interface between the electrode and the electrolyte, the electrochemical characteristics of the electrolyte membrane greatly affect the current-voltage characteristics of the fuel cell. In particular, since the series resistance is reduced by thinning the film, the current-voltage characteristic is improved. In the case of the resin, the film thickness is 20 to 200.
It is preferable to manufacture it to have a thickness of about μm. The ionic conductivity is 5 × 10 ^-2 to 1 × 10 ^-1 (Ωcm) ^-1 at 25 ° C.
Therefore, the resistance per unit area is about 0.05 to 0.4Ω in the case of the above film thickness.

The solid polymer electrolyte membrane is obtained by forming a resin precursor into a membrane by a known method such as hot press molding, roll molding, extrusion molding, and subjecting it to hydrolysis and acidification treatment. It can also be obtained by a solvent casting method from a solution in which a fluorine-based cation exchange resin is dissolved in a solvent such as alcohol.

For the electrode used in the present invention, a porous substrate such as carbon, carbon paper, carbon molded body, carbon sintered body, sintered metal, foamed metal or metal fiber aggregate, which is subjected to water repellent treatment, is used. be able to. An electrode of a fuel cell that uses a gaseous fuel has a known porous structure (specific surface area: 50 to 100 m ² /) for both the fuel electrode and the oxidizer electrode so that the electrode does not rate the diffusion of gas.
Preference is given to using graphite with g) as electrode material.

As the electrode of a fuel cell using a liquid fuel, it is preferable to use a graphite electrode in which liquid easily permeates and the pressure loss of fuel supply is small. In particular, in order to effectively utilize the diffusion of the liquid fuel into the electrode due to the capillary phenomenon, it is preferable that the fuel electrode has a porous pore diameter of 300 μm or less.
If the pore size is larger than 300 μm, the effect of diffusion due to the capillary force cannot be obtained.

A catalyst layer may be further applied to these electrodes for use. For the catalyst layer, a carbon material containing an alloy of a transition metal such as platinum, iron, nickel, cobalt, ruthenium and platinum or fine particles of an oxide thereof as a catalyst can be used. Platinum is preferable when the fuel is pure hydrogen, and platinum-ruthenium alloy is preferable when the fuel contains hydrocarbons. The amount of catalyst is about 5 to about 50% by weight, preferably about 10 to about 30% by weight, based on the electrode.

The catalyst layer can be attached to the electrode by the following method. For example, a mixture of platinum and ruthenium fine metal powder as it is, or supported on carbon having a large surface area, mixed with an alcohol solution containing polytetrafluoroethylene or a solid polymer electrolyte acting as a binder and a water repellent, A method of spraying onto a porous electrode such as carbon paper and joining with a solid polymer electrolyte by hot pressing or the like (US Pat. No. 5,599,638)
Alternatively, a mixture of platinum and fine powder of ruthenium or its oxide is mixed with an alcohol solution containing a solid polymer electrolyte, the catalyst mixed solution is applied on a polytetrafluoroethylene plate, and after drying, a polytetrafluoroethylene plate is obtained. Peeled off, transferred onto a porous electrode such as carbon paper, and joined with a solid polymer electrolyte by hot pressing or the like (X. Ren et al., J. Electroch.
em. Soc. , 143, L12 (1996)) and the like.

Since it is necessary to sufficiently secure the three-phase interface of electrolyte / catalyst / reaction gas, the electrode is preferably formed integrally with the solid polymer electrolyte membrane in close contact with it. In order to make them integral, hot press at 100 to 200 ° C. under pressure to join the solid polymer electrolyte membrane with the electrodes of the fuel electrode and the oxidizer electrode,
It can be integrated and laminated.

Gas passages are provided on the side facing the respective electrodes. For example, the gas flow path can be provided by stacking a current collector or a separator having a flow path, which will be described later, on the side facing the electrode.

The water retention layer can be formed on the oxygen flow channel side and / or the fuel flow channel using a conductive material and a water retention resin as raw materials. When formed on the oxygen channel side, the water retention layer removes excess water generated at the oxidizer electrode, and when formed on the fuel channel side, in order to keep the solid polymer electrolyte membrane wet, Water is supplied to the solid polymer electrolyte membrane.

The water-retaining effect of the water-retaining resin is as follows: physical adsorption utilizing the capillary force increased by making the resin porous;
There is chemical adsorption due to the suction force that acts between hydrophilic groups and water molecules, but in the case of physical adsorption, the volume expansion occurs due to the porous water content, and the adhesion between the electrode and the water retention layer becomes weak due to long-term use. May be. In this case, the original function of the water retention layer to remove excess water from the electrode surface cannot be achieved. Further, when the through hole formed in the water retention layer is pressed by the volume expansion and the hole is sealed, gas supply through the through hole can hardly be performed. Considering these factors, it is desirable to use water retention mainly based on chemical adsorption rather than water retention based on physical adsorption due to the porosity of the resin.

The water-retaining resin is preferably a resin having one or more groups selected from the group consisting of a hydrophilic group such as a carboxyl group, a hydroxy group, a quaternary amino group and a sulfonic acid group, and an acid or a base. A resin having a hydroxy group that is less affected by the above is particularly preferable.

When the degree of hydroxylation of the water-retaining resin is less than 2, sufficient water retention cannot be obtained. On the contrary, when it exceeds 50, the swelling of the entire water-retaining layer cannot be ignored and the through holes may be pressed. Therefore, the water retention resin component has a degree of hydroxylation of 2 to 5
A range of 0 is preferred.

Specifically, the water-retaining resin is preferably one or more resins selected from the group consisting of cellulose resins, phenol resins and hydroxystyrene resins.

As the cellulose resin, cellulose 3
Alkyl cellulose (methyl cellulose, ethyl cellulose, propyl cellulose, as a product obtained by etherifying a part or all of individual hydroxy groups with alkyl halide, aryl halide, benzyl halide, propylene oxide, halogenated alcohol, etc.
Benzyl cellulose, etc.), hydroxyethyl cellulose, alkyl hydroxyalkyl cellulose (ethyl hydroxyethyl cellulose, ethyl hydroxypropyl cellulose, etc.) and the like.

Similarly, as a product obtained by etherifying hydroxyl groups of cellulose with monochloroacetic acid or its alkali salt, carboxymethyl cellulose (C
MC), cellulose acetate (cellulose acetate), cellulose propionate, cellulose butyrate, cellulose acetate butyrate, and mixtures of these cellulose derivatives, and copolymers obtained by esterifying the hydroxy group of cellulose with an acid such as acetic acid or an acid anhydride. Examples include coalescence.

In particular, alkyl cellulose which is etherified (alkoxylated and aralkoxylated) with a lower alkyl group (eg, methyl, ethyl, propyl group, etc.) and a lower alkyl group substituted with an aromatic ring (eg, benzyl group) is It is preferable because it is less affected by light and moisture, has excellent thermal characteristics (softening point of 120 ° C. or higher), and is conversely flexible even at low temperatures and has mechanical toughness. However, when the degree of etherification of the alkyl cellulose resin is 95% or more, the water retaining property is remarkably deteriorated, and when it is 40% or less, the flexibility of the resin is too high to form a paste and it becomes difficult to maintain the shape itself. A degree of etherification of 95% is preferred. It is also possible to produce a resin such as an alkyl hydroxyalkyl cellulose by etherifying a cellulose with a halogenated alkyl alcohol and an alkyl halide while adjusting the degree of hydroxylation of the cellulose. In this case, the hydroxy groups are the sum of the hydroxy groups from the halogenated alkyl alcohol and the hydroxy groups of the cellulose body.

There are no special starting materials for the phenol resin, and generally widely used materials such as phenol and lower alkyl and alkoxy substitution products of phenol may be used. In addition, the phenol resin is manufactured by
Depending on the difference in the ratio of formalin and the type of catalyst), it is roughly classified into two types: novolac resin and resol resin. In particular,
The former repeats addition reaction-condensation reaction alternately and undergoes a dehydration reaction of the following formula, resulting in a structure with a stable composition as shown in the structural formula on the right side of the formula below. Novolac resins have very high thermal stability (dimensional stability) and mechanical strength. Therefore, the novolac resin is preferable as the phenol resin.

Further, when about 1 to 20% of hexamethylenetetramine or the like is added as a curing agent and polymerized, a cured resin is formed by crosslinking and the dimensional stability is further improved.

[0033]

[Chemical 1]

Recently, as a hydroxystyrene resin, L
It is possible to use a photoresist that is widely used as a photoresist for SI. Among them, the hydroxystyrene resin is preferably a copolymer of hydroxystyrene and butadiene. The hydroxystyrene resin can further increase the film strength by copolymerizing hydroxystyrene with butadiene, acrylonitrile, butyl methacrylate or the like. Among them, a copolymer of hydroxystyrene, butadiene and acrylonitrile is particularly preferable. The ratio of the copolymer to the hydroxystyrene resin is preferably 50% mol or less in consideration of the water retention rate.

Cellulose resin, phenol resin and hydroxystyrene resin have the property that they are difficult to hydrolyze even in the environment of the cell operating temperature of the polymer electrolyte fuel cell of about 60 to 90 ° C. Furthermore, in order to prevent the water retention structure of the resin from deteriorating due to external factors such as heat and moisture, and at the same time, to stabilize the shape, the water retention resin is crosslinked and the water retention resin is a three-dimensional crosslinked resin. Is preferred.

The three-dimensional cross-linking resin may be either a thermosetting resin or a thermoplastic resin, but in view of maintaining the water retention of the film after long-term use and stability against repeated temperature changes, the thermosetting resin Resins are preferred.

As a cross-linking method, for example, when synthesizing an alkyl cellulose, a part of the alkyl halide compound is replaced with a divalent alkyl halide compound (for example, dichloroethane) and the reaction is carried out in an autoclave. There is also a method of adding a diisocyanate compound to the above-mentioned alkyl cellulose resin and a method of adding an organo compound. The organo compound is preferable as a cross-linking agent because it has a high reactivity with a hydroxy group and a decrease in water retention due to cross-linking is small. As the cross-linking agent, hexamethylene diisocyanate, p-phenylene diisocyanate, hexamethylene tetramine and the like can be used. In the crosslinking reaction, it is preferable that 5 to 50% of the total number of hydroxy groups in the water retentive resin is crosslinked. Therefore, it is preferable to add the crosslinking agent to the resin in such an amount that the above-mentioned crosslinking ratio is obtained.

The water retaining layer is in direct contact with the electrode, and when the fuel cell of the present invention has a current collector, the water retaining layer is preferably in contact with the current collector. At this time, an electric current can be taken out to an external circuit by moving the electric charge from the electrode to the current collector through the water retention layer. Therefore, since it is necessary to reduce the internal resistance in the water retention layer, it is possible to improve the conductivity by blending the conductive material as the main component. This minimizes the drop in fuel cell output voltage,
The power generation efficiency of the fuel cell can be improved.

As the conductive material, conductive carbon black, graphite, activated carbon, various metals and the like can be used. Of these, conductive carbon black is preferably used. As the conductive carbon black, acetylene black and the like can be used, and carbon black that is usually commercially available can be used, but soft carbon carbon black having particularly good conductivity is particularly preferable. The iodine adsorption amount of carbon black can be used as a criterion for determining the conductivity of carbon black. This iodine adsorption amount is JIS: K-1469-84.
Conductive carbon black is 100
It is preferable to have the above iodine adsorption amount. Among graphite, porous graphite and colloidal graphite (particle size: about 0.8 μm) recently developed for bearing alloys and the like are particularly preferable because they have high conductivity.

The conductive material is about 50 for the entire water retention layer.
It is preferably contained in a proportion of ˜95% by weight. When the conductive material is contained in this proportion, it is morphologically stable,
It is possible to produce a water retaining layer having high conductivity without impairing water retaining ability. When the weight ratio of the conductive material is 50% or less, the specific resistance of the water retaining layer rapidly increases, and the internal resistance loss between the electrode and the current collector increases, so that the output voltage decreases. On the other hand, if the weight ratio exceeds 95%, chips or cavities occur during the formation of the water retention layer, making it difficult to maintain and process the film form. Therefore, by containing the conductive material in this weight ratio, the fuel cell having a small internal voltage drop can be configured without the water retaining layer hindering the current flow from the electrode to the current collector.

When a thermoplastic resin such as a cellulose resin and a hydroxystyrene resin is used, the water-retaining layer contains about 5 to 50% by weight of the water-retaining resin and optionally a cross-linking agent, and a suitable organic solvent (for example, methanol or Alcohol such as ethanol, ethyl acetate, N-methylpyrrolidone, tetrahydrofuran, etc.) and dissolved in the solution to about 95-
A conductive material such as 50% by weight of carbon black is dispersed, and the dispersion is uniformly applied onto the electrode on the side where the water retaining layer is formed by an applicator method or a spray method,
It is prepared by heating and drying at a temperature of about 100 to 200 ° C. for about 10 minutes to 2 hours.

Also in the case of a thermosetting resin such as a phenol resin, a resin paste obtained by the same method as described above is applied and dried on the electrode. The created water retention layer is about 5
A thin film having a thickness of ˜500 μm, preferably about 100-300 μm.

Since the water retention layer can be produced on the electrode by a relatively simple and low-cost process such as coating and drying (crosslinking), the production cost of the fuel battery cell can be reduced by adding the water retention layer to the electrode. The increase can be minimized. The bonding between the electrode surface and the water retention layer is the chemical property of the water retention resin contained in the water retention layer (retention of adsorption groups).
It is also possible to use either or both of the joining by the method and the mechanical joining depending on the surface condition of the electrode.

The water-retaining layer has through-holes through which gas can be conducted from the oxidant channel to the oxidant electrode and / or from the fuel channel to the fuel electrode. For example, when a through-hole is formed from the oxidant channel to the oxidant electrode, the through-hole allows the gas supplied from the oxidant channel to pass through the water retention layer to smoothly cause the solid electrolyte in the fuel cell reaction. It has the function of sending it to the membrane side.

The smaller the diameter of the through holes, the more difficult it is for moisture to enter the through holes that have been subjected to the water repellent treatment, and the gas permeability is improved. However, the fluorine ablation method used for producing the through holes is improved. Argon Excimer Laser and Krypton Fluoride Excimer Laser can be used with the smallest aperture (range up to 1 / e ² of peak intensity)
Is 0.01 mm, the laser aperture used when forming the through hole must be larger than 0.01 mm.
Therefore, the hole diameter of the through hole is preferably larger than about 0.01 mm.

On the other hand, the output current of the fuel cell is large,
A large amount of water is generated at the oxidizer electrode, and water may stay inside the through holes. It is known that the maximum diameter of a water drop is 1.8 to 2.2 mm on a super water-repellent surface having a receding contact angle close to 180 °, which indicates the degree of water repellency of the surface in contact with the water drop. Therefore, when a through hole having a hole diameter of 2 mm or more is formed, all water droplets can enter the through hole, so that the water droplet stays in the through hole, and it becomes difficult for gas to pass through the through hole. Therefore, the diameter of the through hole is preferably smaller than about 2 mm. The diameter of the through-holes is therefore greater than about 0.01 mm, less than about 2 mm, more preferably about 0.1-1 mm, even more preferably about 0.4 mm.
~ 0.6 mm.

A laser ablation method can be used to form the through holes. According to the laser ablation method, by utilizing the difference in the absorption coefficient of the laser beam between the material of the water retention layer and the material of the underlying oxidant electrode, the water retention layer is etched by the laser beam, and Even when the water retaining layer is laminated, the holes can be selectively formed only in the water retaining layer. Therefore, the underlying oxidant electrode is not damaged, and the holes that penetrate only the water retention layer can be formed in a short time by laser irradiation.

In the laser ablation method, an argon fluoride excimer laser (wavelength 193 nm) or a krypton fluoride excimer laser (wavelength 248 nm) is used as a laser light source. The laser beam is applied to the water retaining layer with a focal aperture of about 0.01 to 2 mm using a spherical (spherical) lens or a cylindrical (cylindrical) lens. The water retention layer (which is integrated with the electrolyte membrane and the electrode) is fixed to the stage,
The stage side is moved in a predetermined step within the range of 0.6 to 3 mm and laser irradiation is performed to form a large number of through holes in the water retention layer. If a spherical lens is used, a hole having a shape close to a circle is formed, but if a cylindrical lens is used, it is possible to make a slit-shaped or arbitrary rectangular hole.

Since water is produced at the oxidizer electrode during operation of the fuel cell, if the water content becomes excessive, the through holes of the water retaining layer may be clogged with water and the gas passage may be blocked. In order to prevent this, the inner surface of the through hole of the water retention layer
It is preferably water repellent. Examples of the water repellent treatment include applying a coating of a water repellent resin. When the coating of the water-repellent resin is applied to the inside of the through hole, the inner surface of the through hole becomes difficult to wet. Therefore, on the water-repellent surface, the water in the through holes forms water droplets and is easily discharged to the gas flow path according to gravity, so that the gas can smoothly pass through the through holes.

As a typical water-repellent resin, there may be mentioned polyethylene composed of a monomer (fluoroethylene) in which at least one hydrogen of ethylene is replaced by fluorine. Specific examples thereof include homopolymers such as vinylidene fluoride and vinylene fluoride, and copolymers thereof with ethylene, propylene, vinylidene chloride and the like. Of these, a copolymer of vinylidene fluoride and hexafluoropropylene is preferable. The water-repellent resin used may be a mixture of one or more copolymers.

In order to form the coating film of the water-repellent resin, a method of applying a solution of the water-repellent resin and then stabilizing the resin can be used. For this method, it is preferable to use a copolymer as the water-repellent resin, which is easily dissolved in an organic solvent such as dimethylformamide (DMF), dimethylacetamide, or diethylene glycol and whose solution is easily prepared.

As a method of applying the water-repellent resin to the inside of the through-hole, a method of directly injecting the solution of the water-repellent resin into the through-hole using a special syringe having a urethane foam at the tip of an injection needle. Can be used. Specifically, by this method, a urethane solution is impregnated with the solution by injecting a resin solution from an injection needle inserted into the through hole, and the resin solution is applied to the inner wall surface of the through hole through the urethane foam. To do. According to this method, since the water-repellent resin film is not formed on the portions other than the through holes, there is no possibility that the water-repellent resin film is formed on the entire water-retaining layer and water is not transmitted at all.

In order to stabilize the water-repellent resin applied inside the through-hole, a method of crosslinking the resin with ultraviolet rays or heat can be used. The coating film of the water-repellent resin has a solution concentration of 5 to 20 in the organic solvent such as DMF.
What was melt | dissolved by weight% is apply | coated to the inside of a through-hole as mentioned above, and it heat-drys at about 50-200 degreeC for about 1-5 hours, and is produced.

The form of the water-repellent resin film formed in the through holes of the water retaining layer after the above steps is shown in FIG. 5 (a). A water-repellent resin film 11 is formed in the through hole 8 of the water retention layer 7,
The diameter of the through hole 8 is narrowed or the hole is blocked.
Therefore, the inside of the through hole is again etched with laser light to remove a part of the water-repellent resin coating film, thereby obtaining the through-hole covered with the water repellent resin coating film as shown in FIG. 5B.

The reason why the inside of the through hole is etched again with laser light is to widen the narrowed or blocked through hole and secure a constant diameter of the through hole. In order to increase the hole diameter of the through hole while leaving the produced water-repellent resin coating on the inner wall surface of the through hole by etching again, the laser diameter of the laser beam used during etching is set to the value when the through hole is first formed. It should be smaller than the one used.

The pore diameter of the water retaining layer obtained after etching the inside of the through hole again is preferably about 0.01 to 2 mm,
It is more preferably about 0.1 to 1 mm, and even more preferably about 0.4 to 0.6 mm.

In terms of gas permeability, it is desirable that the volume ratio of the through holes to the entire water retention layer is larger, but if the volume ratio exceeds 50%, the adhesion between the electrode and the water retention layer is reduced, and It becomes difficult to maintain the shape of the water retention layer itself. Further, when the volume ratio is less than 10%, the apparent gas-permeable blockage area facing the electrode side from the gas flow channel is reduced, which contributes to the reduction in gas permeability, which contributes to the reduction in gas permeability of the electrode. This offsets the contribution of improving the gas permeability by removing water from the surface. Therefore, when the ratio is less than 10%, the gas permeability is lower than that in the case where the water retention layer is not provided on the electrode. Therefore, the ratio is preferably 10% or more and 50% or less.

The through-holes of the water retention layer may be mortar-shaped with the hole diameter on the fuel flow path side larger than the hole diameter on the fuel electrode side and / or the hole diameter on the oxidant flow path side larger than the hole diameter on the oxidant electrode side. preferable. This is because if the hole diameter on the fuel channel side and the hole diameter on the fuel electrode side are the same, and / or the hole diameter on the oxidant channel side and the hole diameter on the oxidant electrode side are the same, that is, if the through holes are cylindrical, This is because water is likely to stay in the through holes due to the surface tension of.

The details will be described with reference to FIG. Figure 4
Inside, 1 is a solid polymer electrolyte membrane, 3 is an oxidizer electrode, 7 is a water retention layer, 8 is a through hole, and 10 is water. Capillary force F is
It is inversely proportional to the pore diameter r of the capillary. Therefore, FIG.
In the case of the cylindrical through hole as shown in (a), since the hole diameter r is constant, the capillary force F in the through hole is uniform. On the other hand, FIG.
In the case of the mortar-shaped through hole as shown in (b), since the hole diameter r increases toward the oxidant flow path side, the capillary force F
Is reduced, and moisture adhesion to the inner wall of the through hole is reduced. Therefore, by forming the through hole into a mortar shape, the capillary force F of the hole is increased.
And the retention of water in the pores can be reduced. Further, when the water does not stay in the through hole, the hole diameter on the oxidant channel side is made large, so that the oxidant gas does not easily stay in the through hole 8 and the fresh oxidant gas smoothly flows. Since it penetrates into the through holes 8 and is supplied to the oxidizer electrode 3, there is also an effect that the gas supply state to the electrodes is further improved.

Further, in order for the water retaining layer to remove excess water efficiently, the adhesion to the electrode is important, but since the mortar-shaped through hole has a small electrode side hole diameter, The contact area can be increased. Therefore, the ability to remove excess water is improved, and the water retention layer is less likely to be peeled off from the electrode, improving long-term durability.

As another method of forming the through-holes in the water-retaining layer, a water-retaining layer having the through-holes is separately prepared, and then the inner surface of the through-hole is optionally subjected to the water repellent treatment as described above to form the water-retaining layer. A fuel cell having the same structure as the above can also be manufactured by placing it on the electrode. In this method, in order to effectively remove the water on the electrode surface by the water absorption effect of the water retaining layer, it is necessary to bring the electrode and the water retaining layer into close contact with each other. In order to bring the electrode and the water retaining layer into close contact with each other, a method of placing a water retaining layer on the electrode, stacking a nonwoven fabric on the water retaining layer, and sandwiching the water retaining layer and the electrode with the nonwoven fabric can be used.

A fuel cell in which a fuel electrode, an electrolyte layer, an oxidizer electrode and a water retaining layer are laminated may be held by a current collector from both the upper surface and the lower surface of the lamination. The current collector is made of a porous material having gas permeability, such as porous carbon. A fuel flow path is formed in the current collector on the fuel side, and an oxidizer that is a flow path for collecting water generated at the oxidizer electrode is formed in the current collector on the oxidizer electrode side. When the flow channel is formed, it is not necessary to separately form the fuel flow channel and the oxidant flow channel, and therefore the fuel cell can be thinned, which is preferable.

The fuel cell of the present invention further comprises a separator. The separator is a metal plate or graphite,
It is sufficient if the fuel and the oxidant gas do not pass through.
A separator made of a metal such as stainless steel is preferable because it is easy to process. On the other hand, when the fuel is a gas that easily weakens the metal, it is preferable to use a separator made of glassy carbon or the like, which can be grooved relatively easily and is not easily embrittled.

The fuel supplied to the fuel electrode is classified into gaseous fuel and liquid fuel depending on the type of fuel cell. Generally, hydrogen gas is used as the gaseous fuel and methanol is used as the liquid fuel.

The present invention will be described in detail below. The following examples are general ones, and the present invention is not limited to these. Example 1 Two graphite electrode sheets (film thickness 400 μm)
Solid polymer electrolyte membrane (DuPont, USA, Nafion 117, film thickness 170 μm) 1 sandwiched between 2
Hot pressing was performed at 150 ° C. for 60 seconds under a pressure of about 00 kg / cm ² to join and integrate the fuel electrode 2 and the oxidizer electrode 3 with the solid polymer electrolyte membrane 1 to obtain a laminated membrane. As a water retention layer material, 45% by weight of benzyl cellulose, 55% by weight of acetylene black, and an extremely small amount of hexamethylene diisocyanate were dissolved in n-methylpyrrolidone (solid content 10% by weight remained), and the laminated film obtained by the above process Of the oxidizer on the electrode surface side and then dried (drying temperature: 150 ° C., 30 minutes) to obtain a film thickness of 100 μm.
m water retaining layer 7 was prepared.

Then, through holes 8 were formed on the surface of the water retaining layer by irradiating an argon fluoride excimer laser at intervals of 1.5 mm. The laser beam is emitted as a circular focus with a diameter of 0.5 mm by using a spherical lens, and the inner diameter is set to 0.
A hole having a size of about 4 to 0.6 mm was formed in the water retention layer 7. Here, the fuel cell unit including the water retention layer was fixed on the stage, and the plurality of through holes were formed by moving the stage at regular intervals using a micrometer.

Examples 2 to 7 A water retention layer was prepared in the same manner as in Example 1 except that the water retention resin, the conductive material and its ratio shown in Table 1 and the crosslinking agent were used.

[Table 1] Note: 1) Iodine adsorption amount of the above carbon black (mg /
All of g) exceeded 100. 2) Oil absorption (cm ³ / 100g) is JIS K6221
-82 Oil absorption amount Measured using the B method.

The graphite electrode thus obtained and the water-retaining layer 7 are joined to each other by the chemical properties of the water-retaining resin (holding of the adsorbing group) and the mechanical properties depending on the surface condition of the oxidizer electrode. It showed a composite type adhesiveness with dynamic bonding. Room temperature (20 ° C,
Humidity 40% and high temperature and humidity (80 ° C, humidity 90)
%), The permeability of the oxidant gas (O ₂ ) was measured, and the result was compared with that of Example 1 in which the water retention layer was not formed and the integrated laminated membrane of the electrolyte membrane (Comparative Example). . The results of these measurements are shown in Table 2 together with the porosity and the film thickness.
However, the gas permeability is 0.5 atm for oxygen on the surface of the water retention layer.
The flow rate of the gas that was introduced and passed through was measured with a soap film flow meter. The porosity was measured using a mercury porosimeter, and the film thickness was measured using a step thickness meter. The receding contact angle measured by a contact angle meter with water drops placed on the water retention layer of each example is
All of Examples 1 to 7 were within the range of 20 to 40 °.

[0068]

[Table 2]

From the results shown in Table 2, comparing the gas permeability of the electrode- and electrolyte-integrated water retention layer with that of the comparative example having no water-retention layer, the electrode and electrolyte-integrated water retention layers of Examples 1 to 7 were Since it is covered with the water retention layer, the gas permeability at 20 ° C. is lower than that of the comparative example, but at 80 ° C., the gas permeability is higher than that of the comparative example. That is, even if the temperature condition changes, the gas permeability of the electrode and electrolyte-integrated laminate provided with the water retention layer does not decrease so much. This indicates that the water absorption effect of the water retention layer reduced the retention of water droplets at the electrode underlying the water retention layer, thus improving the gas permeability.

When the water retention layer film thickness is thinner than 100 μm (Example 5), the transmittance at 80 ° C. is 5 which is the value at 20 ° C.
6%, but when thicker than 100 μm (other than Example 5), the transmittance at 80 ° C. is 70% of the value at 20 ° C.
It corresponds to the above. Therefore, if the water retention layer has a film thickness of 100 μm or more, it is possible to suppress a decrease in gas permeability of the water retention layer in a high temperature and high humidity state.

Further, when comparing the gas permeability and the porosity of the electrode and the electrolyte-integrated water retaining layer in Examples 1 to 7, the decrease rate of the gas permeability due to the temperature change from 20 ° C. to 80 ° C. It is almost the same as the reduction rate of porosity, and it is considered that the reduction of gas permeability is mainly due to the reduction of porosity. Therefore, in order to further improve the gas permeability, it is important to improve the porosity of the through holes and reduce the retention of water droplets in the through holes. This is detailed in Examples 9 and 10.

A fuel cell (see FIG. 1) in which the electrode and electrolyte-integrated water retention layer of Example 2 was sandwiched by a current collector having a gas flow path, and an electrode and electrolyte-integrated electrolyte without water retention layer A 0.5 M aqueous methanol solution was supplied as a fuel to a fuel cell (see FIG. 2) in which the laminated film was sandwiched by a current collector having a gas flow path, and the cell characteristics were changed under the operating temperature of 70 ° C. It was measured. Fuel cell without water retention layer has a limiting current density of 1
While it was 00 mA / cm ² , the fuel cell provided with the water retention layer obtained 110 mA / cm ² . Therefore, it was confirmed that the formation of the water retention layer reduces the concentration polarization due to the insufficient gas supply to the electrodes, and the output current density can be improved.

Example 8 The water retention layer was formed by changing the weight ratio (B / (A + B)) of the graphite (porous type) of the conductive material (B) used in Example 2 to 40 to 100%. It was produced and the relationship between the ratio and the specific resistance was measured. The result is shown in FIG.
However, graphite (porous type) having an iodine adsorption amount of 125 was used. The specific resistance of the film is measured by the 4-probe method, and the obtained resistance value (Ω) is calculated as the volume average specific resistance (Ω ·
It was converted to cm and displayed (SRIS-2301). The measurement was performed under the conditions of a temperature of 20 ° C. and a humidity of 40%.

FIG. 3 shows that the resistance of the water retaining layer increases as the weight ratio B / (A + B) decreases. In addition, a drastic increase in resistivity is observed especially in the region where the weight ratio is 50% or less.
It is necessary to add 0% or more of a conductive material. Further, in the actual production of the water retention layer, if the weight ratio of the conductive material exceeds 95%, the layer formation itself is difficult. Therefore, the range of the weight ratio is preferably 50% to 95%.

Example 9 Inside the pores of the electrode and electrolyte-integrated water retaining layer of Example 1,
Using a syringe in which the tip of the needle is covered with polyurethane foam, inject a solution of a copolymer of vinylidene fluoride and hexafluoropropylene dissolved in an organic solvent (DMF) in an amount of 10% by weight, and at 120 ° C for about 5 hours. It was dried by heating.
The through-hole 8 is again irradiated with an argon fluoride excimer laser beam adjusted so that the focal diameter is 0.2 to 0.3 mm, and a hole having an inner diameter of 0.3 to 0.4 mm is formed in the water retention layer 7. It was made. At this time, the focus position of the laser beam needs to be aligned with the through hole 8, so that
In the same manner as when the through hole 8 was formed in No. 7, the fuel battery cell including the water retention layer 7 was fixed at the same position on the sledge, and the micrometer attached to the stage was used for alignment.

The gas permeability and the porosity of the obtained water retaining layer were measured in the same manner as in Examples 1-7. However, the atmosphere was measured under three conditions: condition 1 (temperature 20 ° C, humidity 40%), condition 2 (temperature 40 ° C, humidity 85%) and condition 3 (temperature 80 ° C, humidity 95%). The results are shown in Table 3. The receding contact angle of the water-repellent coating made of a copolymer of vinylidene fluoride and hexafluoropropylene was 135 °.

Example 10 A film of a water-repellent resin was prepared in the same manner as in Example 9 except that the electrode and electrolyte-integrated water retention layer of Example 2 were used instead of the electrode and electrolyte-integrated water retention layer of Example 1. . With respect to the obtained electrode and electrolyte-integrated water retention layer, the gas permeability and the porosity were measured in the same manner as in Example 9, and the results are shown in Table 3. The receding contact angle of the water-repellent resin coating is
As in Example 9, it was 135 °.

[0078]

[Table 3]

By covering the inside of the through hole 8 with the coating 11 of the water-repellent resin, the hole diameter was narrowed.
Comparing these results with those of Examples 1 and 2 before the water repellent treatment, under the condition 1, the porosity decreased by slightly less than 60%. Accordingly, the gas permeability is slightly lower,
Since the water repellency inside the through hole 8 is improved (the receding contact angle was about 30 ° before the water repellency treatment, but 135 after the treatment).
It is understood that the porosity does not decrease so much even under the high temperature and high humidity conditions such as the conditions 2 and 3. That is, although the through-hole diameter was narrowed by forming the water-repellent resin film 11, the water repellency was improved and the retention of water droplets in the through-hole was reduced. Therefore, the gas permeability under high temperature and high humidity conditions is substantially higher than that before the water-repellent treatment. To do. In addition, the actual amount of water produced in the oxidizer electrode 3 and the atmospheric conditions change depending on the operating state of the fuel cell, but in particular, the temperature inside the fuel cell rises and is appropriate even during high-load operation with a large amount of water produced. Since a sufficient gas permeability can be ensured, the gas supply to the electrode is stable and the concentration polarization due to the gas shortage can be reduced. Therefore, a stable gas permeability can be obtained regardless of the atmosphere, and the power generation efficiency during high load operation is improved.

A 0.5 M aqueous solution of methanol was used as a fuel in a fuel cell in which the electrode having the water-repellent resin coating of Example 10 and the electrolyte-integrated water retaining layer were sandwiched by a current collector having a gas flow path. As a result, the cell characteristics were measured under the condition of an operating temperature of 70 ° C., and the electrode not having the water-repellent resin coating of Example 2 and the electrolyte-integrated water retention layer were held by a current collector having a gas flow path. It was compared with the fuel cell prepared. The limiting current density was 115 mA / cm ² for the fuel cell including the electrode and the electrolyte-integrated water retaining layer of Example 10, and the output was higher than that of the fuel cell including the electrode and the electrolyte-integrated water retaining layer of Example 2. The current density improved by about 5%. That is, it was possible to improve the limiting current density by reducing the gas concentration polarization and improve the power generation efficiency.

[0081]

As described above, according to the present invention, the water generated in the electrode of the fuel cell can be absorbed by the water retaining layer and the gas can be supplied to the electrode through the through hole of the water retaining layer. It is possible to reduce the occurrence of the gas concentration polarization and improve the power generation efficiency. Further, since the water retention layer can be easily formed by a process of dissolving the water retention resin in a solvent and then applying it, heating and drying, an increase in manufacturing cost can be suppressed.

Further, by subjecting the inside of the through-hole to the water-repellent treatment, the gas permeability through the water retention layer at high temperature and high humidity is improved, so that a stable gas is formed on the electrode surface irrespective of the operating state of the fuel cell. Since it can be supplied, the operation efficiency can be further improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a cell structure of a polymer electrolyte fuel cell according to one embodiment of the present invention.

FIG. 2 is a schematic diagram of a cell structure of a conventional polymer electrolyte fuel cell.

FIG. 3 is a graph showing the relationship between the weight ratio of the conductive material contained in the water retention layer and the specific resistance in the polymer electrolyte fuel cell of the present invention.

FIG. 4 is a schematic view showing the shape of a through hole formed in the water retention layer of the present invention.

FIG. 5 is a schematic view showing a step of forming a water-repellent resin film on the through hole of the present invention.

[Explanation of symbols]

1 Solid polymer electrolyte membrane 2 fuel pole 3 oxidizer pole 4 Current collector 5 Fuel flow path 6 Oxidant channel 7 water retention layer 8 through holes 9 Fuel cells 10 moisture 11 Water-repellent resin coating 101 solid polymer electrolyte membrane 102 fuel pole 103 Oxidizer pole 104 Current collector 105 Fuel flow path 106 Oxidant channel

Claims (16)

[Claims] 1. A fuel electrode and an oxidant electrode are provided opposite to each other on both sides of the solid polymer electrolyte layer, and a fuel channel is provided on the side facing the fuel electrode.
A fuel cell having an oxidant flow path on the side facing the oxidant electrode, wherein the fuel electrode and / or the oxidant electrode is formed of a conductive material and a water retentive resin, and has a plurality of through holes. A polymer electrolyte fuel cell provided with a layer. 2. The conductive material is 50 for the entire water retention layer.
The polymer electrolyte fuel cell according to claim 1, wherein the solid polymer fuel cell is contained in a proportion of ˜95 wt%. 3. The polymer electrolyte fuel cell according to claim 1, wherein the conductive material is conductive carbon black. 4. The water-retaining resin is a resin having one or more groups selected from the group consisting of a carboxyl group, a hydroxy group, a quaternary amino group and a sulfonic acid group. The polymer electrolyte fuel cell according to any one of 1 to 3. 5. The polymer electrolyte fuel cell according to claim 4, wherein the water-retaining resin is a resin having a hydroxy group, and the degree of hydroxylation thereof is in the range of 2 to 50. 6. The polymer electrolyte fuel cell according to claim 1, wherein the water retention resin is a cellulose resin, a phenol resin or a hydroxystyrene resin. 7. The polymer electrolyte fuel cell according to claim 6, wherein the cellulose resin is an alkyl cellulose resin. 8. The polymer electrolyte fuel cell according to claim 6, wherein the phenol resin is a novolac resin. 9. The solid polymer fuel according to claim 6, wherein the hydroxystyrene resin is a copolymer of hydroxystyrene and butadiene or a copolymer of hydroxystyrene and butadiene and acrylonitrile. battery. 10. The polymer electrolyte fuel cell according to claim 1, wherein the water retention resin is a three-dimensional crosslinked resin. 11. The polymer electrolyte fuel cell according to claim 10, wherein the three-dimensional crosslinked resin is obtained by using an organo compound as a crosslinker. 12. The polymer electrolyte fuel cell according to claim 1, wherein the water retention layer has a thickness of about 5 to 500 μm. 13. The polymer electrolyte fuel cell according to claim 1, wherein the inner surface of the through hole of the water retaining layer is treated to be water repellent. 14. The diameter of the through holes of the water retention layer is about 0.01.
The polymer electrolyte fuel cell according to any one of claims 1 to 13, wherein the polymer electrolyte fuel cell is larger than mm and less than about 2 mm. 15. The water-retaining layer has one through-hole for the water-retaining layer.
It is provided by 0 to 50% by volume.
15. The polymer electrolyte fuel cell according to any one of 14 to 14. 16. The through hole of the water retaining layer, when the water retaining layer is provided on the fuel electrode, the hole diameter of the through hole of the water retaining layer on the fuel flow path side is larger than the hole diameter of the through hole on the fuel electrode side, and / or
Alternatively, when the water retention layer is provided on the oxidant electrode, the hole diameter of the through hole of the water retention layer on the oxidant channel side is a mortar shape larger than the hole diameter of the through hole on the oxidant electrode side. 15. The polymer electrolyte fuel cell according to any one of 15.