JP2000243404A - Electrode for fuel cell and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid polymer fuel cell capable of increasing a reaction area inside an electrode and ensuring high performance by contacting a solid polymer electrolyte with a catalyst fully and uniformly in a fuel cell using a hydrogen ion conductive solid polymer electrolyte film. SOLUTION: This fuel cell comprises an electrode electrolyte joined body having a lamination of a hydrogen ion conductive solid polymer electrolyte film, a pair of electrodes having a catalytic reaction layer with the hydrogen ion conductive solid polymer electrolyte film sandwiched therebetween, and a pair of diffusion layers with the electrodes sandwiched therebetween. In this case, the electrode comprises at least a catalyst body with catalyst particles supported on a hydrophilic carbonaceous material, a hydrogen ion conductive polymer electrolyte, and a repellent carbonaceous material.

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 an electrode which is a component of the fuel cell.

[0002]

2. Description of the Related Art In recent years, polymer electrolyte fuel cells have attracted attention as power supplies for electric vehicles and distributed power supplies. At present, the required ionic conductivity of a polymer electrolyte used in a polymer electrolyte fuel cell is maintained when the polymer electrolyte is sufficiently wetted with water. On the other hand, the electrode reaction as a battery is a reaction for generating water generated at a three-phase interface of a catalyst, a polymer electrolyte, and a reaction gas. If the gas stays in the electrode or the diffusion layer, gas diffusion becomes worse, and the battery characteristics are deteriorated.

[0003] From such a viewpoint, for the electrodes used in the polymer electrolyte fuel cell, measures are taken to promote moisturization of the polymer electrolyte and discharge of water. As a general electrode, an electrode obtained by forming a carbon powder supporting a noble metal serving as a catalyst layer on a porous conductive electrode substrate serving as a gas diffusion layer is used. As the porous conductive substrate, carbon paper or carbon cloth made of carbon fiber is used. These porous conductive substrates are subjected to a water-repellent treatment using a dispersion liquid of a polytetrafluoroethylene-based material in advance, so that the water generated by the electrode reaction is quickly discharged, and Generally, the electrolyte membrane and the polymer electrolyte in the electrode are brought into a moderately wet state. Also,
As another method, a countermeasure for mixing water-repellent carbon particles into the electrode catalyst layer and discharging excess water from the electrode catalyst layer has been taken.

[0004]

As described above, the electrodes used in the conventional polymer electrolyte fuel cell are those obtained by subjecting a porous conductive substrate serving as a gas diffusion layer to a water-repellent treatment. For this reason, although the water discharge property is improved in the gas diffusion layer, the water discharge property in the catalyst layer and the gas diffusion property to the catalyst layer are deteriorated. There was a problem that the battery characteristics deteriorated.

[0005] Further, when carbon which has been subjected to a water-repellent treatment using sub-micron-order polytetrafluoroethylene-dispersed particles is introduced into the electrode catalyst layer, the polymer electrolyte in the catalyst layer is subjected to the water-repellent carbon. If a large amount of particles are adsorbed and the degree of contact between the polymer electrolyte and the catalyst fine particles is insufficient and uneven, or if the catalyst fine particles are covered with PTFE, a sufficient three-phase interface cannot be secured. There was a problem to say. Furthermore, if the carbon particles carrying the catalyst fine particles serving as a catalyst exhibit water repellency, the wet state of the polymer electrolyte in the polymer electrolyte membrane or the electrode catalyst layer shifts to the drying direction, and the battery characteristics deteriorate. There was a problem to do.

Thus, there is a need for a high-performance electrode designed so that water does not stay in the electrode catalyst and the polymer electrolyte is kept in an appropriate wet state.

[0007]

In order to solve the above problems, an electrode for a fuel cell according to the present invention comprises a hydrogen ion conductive solid polymer electrolyte membrane and a catalyst sandwiching the hydrogen ion conductive solid polymer electrolyte membrane. In a fuel cell including a pair of electrodes having a reaction layer and an electrode-electrolyte assembly in which a pair of diffusion layers sandwiching the electrode are stacked, the electrode includes a catalyst in which catalyst particles are supported on a hydrophilic carbon material. , A hydrogen ion conductive polymer electrolyte and a water-repellent carbon material.

At this time, it is effective that a hydrophilic layer is chemically bonded to a part or the entire surface of the catalyst particles.

Further, the catalyst body in which the catalyst particles are supported on the hydrophilic carbon material is selectively disposed on the hydrogen ion conductive polymer electrolyte membrane side, and the water-repellent carbon material is selectively disposed on the diffusion layer side. desirable.

At this time, it is effective that the water-repellent carbon material has a monomolecular layer in which a part or the whole surface of the carbon material is chemically bonded to a silane coupling agent having a hydrophobic part.

It is effective that the hydrophilic carbon material has a monomolecular layer in which a part or the entire surface of the carbon material is chemically bonded to a silane coupling agent having a hydrophilic site.

In the above, the carbon material and the silane coupling agent are chemically bonded via at least one functional group selected from a phenolic hydroxyl group, a carboxyl group, a lactone group, a carbonyl group, a quinone group and a carboxylic anhydride. Is valid.

[0013] In addition, the method for producing a silane coupling agent includes immersing at least one of the catalyst particles or the carbon material in a solvent containing a silane coupling agent, so that at least a part of the surface of the catalyst particles or the carbon material has After chemically adsorbing the ring agent, the surface of the catalyst particles or the surface of the carbon material is chemically bonded to silicon atoms in the molecules of the silane coupling agent to form a layer having hydrophilicity or water repellency. It is characterized by doing.

[0014]

As described above, in the fuel cell electrode according to the present invention, since the catalyst layer is composed of the polymer electrolyte, the hydrophilic carbon material, and the water-repellent carbon material, the electrode reaction does not occur. In the vicinity of the generated three-phase interface, moisture is appropriately held by the hydrophilic carbon material, and excess water is quickly discharged by the adjacent water-repellent carbon material.

As a result, even when the fuel cell is operated at a relatively low current density, high characteristics can be expected while maintaining a constant water retention capacity of the electrode by the hydrophilic carbon material. In addition, when operated at a relatively high current density, excess water is quickly discharged by the water-repellent carbon material located very close to the hydrophilic carbon material, and the flooding phenomenon is less likely to occur, thereby improving battery performance. I do.

When the hydrophilic carbon material is disposed on the polymer electrolyte membrane side and the water-repellent carbon material is disposed on the gas diffusion layer side,
The polymer electrolyte membrane side becomes more highly humidified atmosphere, the ionic conductivity of the polymer electrolyte membrane is improved, and the battery characteristics are improved.

Further, in the fuel cell electrode of the present invention, on the surface of the carbon particles, the hydrolyzable group of the silane coupling agent having a hydrophobic part is formed by the water in the solution or the air, and the water adsorbed on the carbon surface. It is hydrolyzed to change into an active silanol group (≡SiOH) and reacts with a functional group on the carbon surface to form a strong bond. As a result, a very microscopic monomolecular water-repellent layer having a thickness of several nm to several tens nm is formed on the surface of the carbon particles. By using the water-repellent carbon particles, even if the electrode is formed by mixing with the hydrophilic catalyst-supporting carbon particles, the catalyst particles in the electrode are coated as in the case of using the submicron-order PTFE dispersion particles. And does not hinder the supply of the reaction gas.

Furthermore, in the fuel cell of the present invention, the hydrolyzable group of the silane coupling agent is formed on the surface of the catalyst particles or on the surface of the carbon particles carrying the catalyst, as described above, in the same manner as described above. Is hydrolyzed by water adsorbed on the carbon surface to form active silanol groups (≡SiOH)
And reacts with functional groups on the carbon surface to form strong bonds. By providing the silane coupling agent with a hydrophilic group such as a sulfone group or a carboxyl group, the catalyst surface becomes hydrophilic, and a wet state near the three-phase interface is maintained.

As described above, when the electrode of the present invention is used, in the vicinity of the three-phase interface where an electrode reaction occurs, the wet state is appropriately maintained by the hydrophilic catalyst-carrying carbon particles, and excess water generated is adjacent. Since water is rapidly discharged by the water-repellent carbon, a polymer electrolyte fuel cell having higher performance than before can be constructed.

Hereinafter, the fuel cell of the present invention will be described with reference to the drawings.

[0021]

EXAMPLES (Example 1) First, a method for producing a water-repellent carbon material will be described. The entire surface of the carbon powder was directly adsorbed with a silane coupling agent by a chemical adsorption method in a nitrogen gas atmosphere to form a monomolecular film composed of the silane coupling agent. The silane coupling agent, CH ₃ having a linear hydrocarbon chain - (CH ₂₎ n-SiC
Using l ₃ (n is an integer of 10 or more and 25 or less), a hexane solution dissolved at a concentration of 1% by weight was prepared, and the carbon particles were immersed. The carbon particles used at this time were made of graphitizable carbon having a phenolic hydroxyl group and a carboxyl group remaining on the surface, and a dehydrochlorination reaction of this functional group with the above-mentioned silane coupling agent -SiCl ₃ was carried out. A monomolecular water-repellent film was formed using a ring agent. This is shown in FIG.

In FIG. 1, 1 is a carbon particle, and 2 is a monomolecular water-repellent film. The thickness of the monomolecular water-repellent film 2 was about 2 to 10 nm. Here, by changing the molecular weight of the single molecule, this film thickness could be made 1 to 100 nm. The material for chemical adsorption is not limited to the silane-based surfactant used in this embodiment, as long as it contains a group having a binding property to an —OH group, for example, a ≡SiCl group.

Next, a hydrophilic carbon powder carrying 25% by weight of platinum as an electrode catalyst and the water-repellent carbon material were mixed, and a polyfluorocarbon polymer electrolyte pendant to -SO ₃ H group was added thereto. Dispersed solution (FSS-1,
(Made by Asahi Glass) and butanol.
This ink was applied on carbon paper (TGP-H-120, manufactured by Toray, thickness: 360 μm) serving as a gas diffusion layer by a screen printing method, and then butanol was removed by heating and drying. A.

In the above process, a platinum powder-supporting carbon powder having a large number of functional groups on the surface and having a hydrophilic property (Vulcan XC72R, manufactured by Cabot Corporation) was used. The amount of platinum per unit area is 0.5 mg / cm
^{And 2} . Furthermore, the mixed weight ratio of the platinum-supported hydrophilic carbon powder, the water-repellent carbon material, and the polyfluorocarbon-based polymer electrolyte was 100: 20: 3 after finishing.

Next, a comparative electrode B was prepared. The comparative electrode B has a conventionally proposed configuration in which a carbon powder supporting a noble metal serving as a catalyst and a water repellent are formed on a porous conductive electrode base material serving as a gas diffusion layer. Was. The porous conductive base material is the same carbon paper (TGP-H-120, Toray Co., Ltd.
60 μm) and subjected to a water-repellent treatment using a solution (FSS-1, manufactured by Asahi Glass) in which a polyfluorocarbon-based polymer electrolyte preliminarily pendant to an —SO ₃ H group was dispersed. In the above configuration, a carbon powder having a small surface functional group and exhibiting water repellency (Tenka Perak, manufactured by Denki Kagaku Kogyo) was used. Further, the water-repellent agent was used a solution prepared by dispersing the -SO ₃ H groups pendent polyfluorocarbon polymer electrolyte (FSS-1, manufactured by Asahi Glass). The other configuration was the same as the electrode A described above.

The electrode A of the present embodiment thus manufactured
And the electrode B of the comparative example were connected to a polymer electrolyte membrane (Dupon).
And Nafion 112) and hot pressed to produce an electrode-electrolyte assembly. This was set in the unit for cell measurement shown in FIG. 2 to form a unit cell. In FIG. 2, reference numerals 3, 4, and 5 indicate the electrode-electrolyte junctions.

In these cells, hydrogen gas is supplied to the fuel electrode, air is supplied to the air electrode, the cell temperature is 75 ° C., and the fuel utilization is 8%.
0%, air utilization rate 30%, gas humidification 75% hydrogen gas
° C and air were adjusted to a dew point of 65 ° C. FIG. 3 shows the current-voltage characteristics of the battery at this time.

In FIG. 3, it was confirmed that the electrode using the electrode A of the present example exhibited superior characteristics as compared with the electrode B having a conventionally proposed configuration. This is because
When a water-repellent carbon powder treated with a silane coupling agent is used, as in the case of a PTFE-supported carbon powder using PTFE dispersion particles on the order of submicrons, the catalyst fine particles in the electrode are coated and reacted gas. It is thought that it is because it does not hinder the supply of

Example 2 In this example, an electrode was prepared in which the electrode catalyst layer was disposed on the polymer electrolyte membrane side and the water-repellent carbon particles were disposed on the diffusion layer side, and the characteristics were evaluated. First, the catalyst-supporting carbon powder shown in Example 1 and the water-repellent carbon powder treated with the silane coupling agent were applied as separate inks to form electrodes. This is shown in FIG. First,
Water-repellent carbon powder (Tenka Purac, manufactured by Denki Kagaku Kogyo) is made into ink using butanol, and carbon paper (manufactured by Toray,
(TGP-H-120, film thickness: 360 μm). After drying, the catalyst-carrying carbon powder 6, the solution containing dispersed -SO ₃ H groups pendent polyfluorocarbon polymer electrolyte of the polymer electrolyte solution (FSS-1, manufactured by Asahi Glass)
Then, the ink was formed using butanol, and then applied on the carbon paper 8 coated with the water-repellent carbon powder 7 by a screen printing method to produce an electrode.

Using the electrode thus fabricated, an electrode
An electrolyte joined body was prepared, and the unit cell shown in FIG. 700 mA / cm ²
Table 1 shows the battery voltage when a current of? Table 1
In Table 2, the characteristics of the battery using the electrodes A and B prepared in Example 1 are also shown. In Table 1, by using an electrode in which the electrode catalyst layer employed in Example 2 was provided on the polymer electrolyte membrane side and water-repellent carbon particles were provided on the diffusion layer side,
It was found that the same performance as that obtained by mixing and using the carbon powder treated with the silane coupling agent of Example 1 was exhibited. From this, it has been found that a battery having more excellent characteristics can be constituted by using an electrode in which the electrode catalyst layer is disposed on the polymer electrolyte membrane side and the water-repellent carbon particles are disposed on the diffusion layer side.

[0031]

[Table 1]

(Example 3) Next, the catalyst-carrying carbon powder was
FIG. 5 shows a case where treatment is performed using a silane coupling agent. Using the platinum-supported carbon powder used in Example 1, instead of the silane coupling agent used in Example 1, ClSO ₂ − having a hydrocarbon chain and a fluorocarbon chain in the main chain and having a sulfone group at the terminal. (C
_{H 2) n- (CF 2)} m-SiCl 3 (n, m are used 25 an integer) in 10 above, by reaction with water vapor,
A monomolecular film 10 having a sulfone group was formed on the surface of the platinum particles 9 and the surface of the carbon particles 1. This monomolecular film exhibits hydrophilicity due to the presence of a sulfone group at the terminal. Further, the silane coupling agent is not limited to the silane-based surfactant shown in the examples as long as it contains a site exhibiting hydrophilicity.

The platinum-supported carbon powder subjected to the hydrophilic treatment and the water-repellent carbon powder treated with the silane coupling agent used in Example 1 were mixed, and an electrode was prepared in the same manner as in Example 1 and used. The unit cell shown in FIG. 2 was prepared.

When the characteristics of this battery were evaluated under the same conditions as in Example 1, the voltage at a current density of 700 mA / cm ² was 720 mV. This is a characteristic higher than that of the battery prepared in Example 1. This is because the wettability near the three-phase interface is improved by performing hydrophilic treatment on the carbon powder supporting the catalyst fine particles using a silane coupling agent. I think it is due to the improvement.

In the present invention, a chlorosilane-based surfactant having a sulfone group is used as the silane coupling agent. However, as long as the silane coupling agent has a hydrophilic site, for example, it has a site such as a carboxyl group. Anything is fine. In this case, both the catalyst fine particles and the carbon particles are treated, but if the present invention can be applied, only one of them can be treated. In addition, the carbon powder used,
The present invention is not limited to this embodiment as long as the present invention can be applied to the catalyst-supporting carbon powder.

[0036]

As is apparent from the above description of the embodiments, in the fuel cell according to the present invention, the catalyst layer is composed of the polymer electrolyte, the hydrophilic catalyst-carrying carbon particles, and the water-repellent carbon particles. Therefore, in the vicinity of the three-phase interface where an electrode reaction occurs, the wet state is appropriately maintained by the hydrophilic catalyst-carrying carbon particles, and excess water is quickly discharged by the adjacent water-repellent carbon.

When the hydrophilic catalyst-carrying carbon particles are arranged on the polymer electrolyte membrane side and the water-repellent carbon particles are arranged on the gas diffusion layer side, the polymer electrolyte membrane side becomes a highly humidified atmosphere and the polymer electrolyte membrane becomes more humidified. The ionic conductivity of the membrane is improved, and the battery characteristics are improved.

Further, in the fuel cell of the present invention, on the surface of the carbon particles, the hydrolyzable group of the silane coupling agent having a hydrophobic site is hydrolyzed by water in solution or air, and water adsorbed on the carbon surface. Then, it is converted into an active silanol group (≡SiOH) and reacts with a functional group on the carbon surface to form a strong bond. As a result, a very microscopic monomolecular water-repellent layer having a thickness of several nm to several tens nm is formed on the surface of the carbon particles. By using the water-repellent carbon particles, even if the electrode is formed by mixing with the hydrophilic catalyst-carrying carbon particles, the catalyst fine particles in the electrode are coated as in the case of using PTFE dispersion particles of submicron order. And does not hinder the supply of the reaction gas.

Further, in the fuel cell of the present invention, the hydrolyzable group of the silane coupling agent is formed on the surface of the catalyst particles or on the surface of the carbon particles carrying the catalyst in the same manner as described above. Is hydrolyzed by water adsorbed on the carbon surface to form active silanol groups (≡SiOH)
And reacts with functional groups on the carbon surface to form strong bonds. By providing the silane coupling agent with a hydrophilic group such as a sulfone group or a carboxyl group, the catalyst surface becomes hydrophilic, and a wet state near the three-phase interface is maintained.

As described above, when the electrode of the present invention is used, in the vicinity of the three-phase interface where the electrode reaction occurs, the wet state is appropriately maintained by the hydrophilic catalyst-carrying carbon particles, and excess water generated is adjacent. Since water is rapidly discharged by the water-repellent carbon, a polymer electrolyte fuel cell having higher performance than before can be constructed.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a configuration of a carbon particle surface used in a first embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between current and voltage of a single fuel cell according to the first embodiment of the present invention;

FIG. 3 is a conceptual diagram showing the configuration of a catalyst-carrying carbon particle according to a second embodiment of the present invention.

FIG. 4 is a conceptual diagram showing a configuration of an electrode according to a second embodiment of the present invention.

FIG. 5 is a conceptual diagram showing the configuration of a catalyst-carrying carbon particle according to a third embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 carbon particles 2 monomolecular water-repellent film 3 solid polymer electrolyte membrane 4 negative electrode 5 positive electrode 6 catalyst-supporting carbon powder 7 water-repellent carbon powder 8 carbon paper

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasushi Sugawara 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. 72) Inventor Hisao Gyoten 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Male 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Hideo Ohara 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 1006 Matsushita Electric Industrial Co., Ltd. (72) Kazufumi Nishida, Inventor Kazuma Kadoma, Osaka Prefecture 1006 Matsushita Electric (72) Inventor Osamu Sakai 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Teruhito Kanbara 1006 Odama Kadoma, Kadoma City, Osaka Matsushita Electric Industrial F Reference) 5H018 AA06 AS01 BB05 BB16 CC06 DD08 EE03 EE05 EE19 5H026 AA06 BB03 BB10 CX04 EE02 EE05 EE19 5H027 AA06

Claims (7)

[Claims] 1. An electrode electrolyte junction comprising a hydrogen ion conductive solid polymer electrolyte membrane, a pair of electrodes sandwiching the hydrogen ion conductive solid polymer electrolyte membrane, and a pair of diffusion layers sandwiching the electrode. A fuel cell, comprising: a catalyst body having catalyst particles supported on a hydrophilic carbon material; a hydrogen ion conductive polymer electrolyte; and a water-repellent carbon material. Electrodes. 2. The fuel cell electrode according to claim 1, wherein a hydrophilic layer is chemically bonded to at least a part of the surface of the catalyst particles. 3. A catalyst body in which catalyst particles are supported on a hydrophilic carbon material is selectively disposed on a hydrogen ion conductive polymer electrolyte membrane side, and a water-repellent carbon material is selectively disposed on a diffusion layer side. 3. The electrode for a fuel cell according to claim 1, wherein: 4. The water-repellent carbon material has a monomolecular layer in which a part or the entire surface of the carbon material is chemically bonded to a silane coupling agent having a hydrophobic part. Or the electrode for a fuel cell according to 3. 5. The hydrophilic carbon material has a layer in which a part or the whole surface of the carbon material is chemically bonded to a silane coupling agent having a hydrophilic part.
5. The electrode for a fuel cell according to 2, 3 or 4. 6. A phenolic hydroxyl group, a carboxyl group,
The fuel cell according to claim 4, wherein the carbon material and the silane coupling agent are chemically bonded via at least one functional group selected from a lactone group, a carbonyl group, a quinone group, and a carboxylic anhydride. Electrodes. 7. At least one of catalyst particles or carbon material
By immersing the seed in a solvent containing a silane coupling agent, the silane coupling agent is chemically adsorbed on at least a part of the catalyst particle surface or the carbon material surface, and then the catalyst particle surface or the carbon material surface And forming a layer having hydrophilicity or water repellency by forming a chemical bond with silicon atoms in the molecules of the silane coupling agent.
7. A method for producing a fuel cell electrode according to item 6.