JP3430166B2 - Porous conductive plate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous conductive plate used as a power supply in a solid polymer water electrolyzer or as a current collector in a solid polymer fuel cell, and more particularly, it is composed of a titanium sintered body. The present invention relates to a porous conductive plate.

[0002]

2. Description of the Related Art A water electrolysis cell for producing hydrogen and oxygen using a polymer electrolyte membrane is of a so-called filter press type. Specifically, a unit is formed by disposing a power supply member on both sides of a membrane electrode assembly formed by joining catalyst layers on both sides of a polymer electrolyte membrane, and laminating a large number of these units. A configuration in which electrodes are provided on both end sides is generally adopted.

The power feeder here is made of a porous conductive plate and is arranged in close contact with an adjacent membrane electrode assembly. The use of a porous conductive plate as a power supply means that it is necessary to pass an electric current, it is necessary to supply water for the water electrolysis reaction, and it is necessary to quickly discharge the gas generated by the water electrolysis reaction. It depends on

The structure of the fuel cell using the polymer electrolyte membrane is exactly the same as that of the water electrolysis cell, and porous conductive plates are arranged on both sides of the membrane electrode assembly. In the case of a fuel cell, since hydrogen is used as fuel to obtain electric power, this porous conductive plate is called a current collector plate.

As for the porous conductive plate used as a power supply in such a solid polymer type water electrolyzer or as a current collector in a solid polymer type fuel cell, it is necessary to have a characteristic that it can be used in an oxidizing atmosphere. Titanium materials have been studied together with carbon.Among the titanium materials, especially the sintered body has a smooth surface, and it attracts attention because it is difficult to damage the adjacent membrane electrode assembly and it is easy to obtain an appropriate porosity. ing.

As the porous conductive plate made of a titanium sintered body, a crushed powder of titanium sponge or a titanium powder sintered plate obtained by sintering powder produced by pulverizing sponge titanium by hydrodehydrogenation, Japanese Patent Laid-Open No. 11-302891 discloses a titanium fiber sintered plate obtained by compression-molding and sintering titanium fibers, and a titanium fiber sintered plate on which a plasma sprayed layer of titanium metal is further formed. ing.

[0007]

However, the conventional porous conductive plates made of these titanium sintered bodies have the following problems.

Although the titanium powder sintered body has the advantage that the surface is smooth and does not damage the adjacent membrane electrode assembly, it has poor press formability and is easily cracked, so that it is fatal that a thin product having a large area cannot be manufactured. There are some restrictions. On the other hand, the titanium fiber sintered plate has good formability and can be manufactured thin and having a large area, but has a sharp undulation on the surface and a large fiber interval. Therefore, there is a high risk of damaging the membrane electrode assembly when it is pressed against the adjacent membrane electrode assembly. In addition, there is a problem that the contact resistance with the membrane electrode assembly increases.

In contrast to these, Japanese Patent Laid-Open No. 11-302891
The titanium fiber sintered plate disclosed in Japanese Patent Laid-Open Publication No. 2003-242242 has a plasma sprayed layer of titanium metal formed on the surface of the titanium fiber sintered plate. Since the gap is eliminated, it can be said that the moldability and the contact with the membrane electrode assembly are both excellent.

However, in addition to the extra cost of plasma spraying, the titanium fiber sintered plate and the plasma sprayed layer on the surface thereof have different porosities and shapes of the titanium material, so that the electrical resistance is increased at the joint interface between them. As a result, the electric resistance of the porous conductive plate becomes higher than the apparent porosity. As a result, a large loss voltage is generated in a water electrolysis cell used at a high current density of, for example, 1 to 3 A / cm ² . Further, it goes without saying that such a loss voltage cannot be easily allowed even in a fuel cell.

Further, it is feared that a large change in the porosity at the bonding interface may adversely affect the liquid permeability and the air permeability.

The object of the present invention is not only excellent in moldability, but also excellent in surface smoothness without coating such as plasma spraying, and moreover, it is easy to manufacture and is excellent in economical efficiency. To provide a conductive plate.

[0013]

In order to achieve the above object, the present inventors have paid attention to spherical gas atomized titanium powder. Spherical gas atomized titanium powder is a powder of titanium or titanium alloy produced by the gas atomization method, the individual particles, since the molten droplets of titanium or titanium alloy is solidified during scattering, the surface is It has a smooth spherical shape. The particle size is, for example, 10 on average.
It can be made extremely fine with 0 μm or less.

By the way, the particle shape of titanium powder produced by crushing titanium sponge or hydrodehydrogenation is irregular. Spherical titanium powder can also be produced by the rotating electrode method, but the average particle size obtained is generally 400 μm.
It is m or more.

The present inventors have made use of the spherical gas atomized titanium powder having the above-mentioned characteristics to assume a sintered plate for a power supply in a solid polymer type water electrolyzer and a current collector in a solid polymer type fuel cell. Was experimentally manufactured, and its characteristics and the like were evaluated. As a result, the following was revealed.

The spherical gas atomized titanium powder has excellent fluidity, and when it is placed in a sintering container, it is filled to a sufficient density without applying pressure. Then, when this is sintered, sufficient mechanical strength is secured even in the case of a thin and large area. The porosity preferable as the power supply and the current collector can be easily obtained without any special operation. The surface has high smoothness, and even if it is not coated by plasma spraying or the like, there is no possibility of adhering to an adjacent membrane electrode assembly and damaging the membrane electrode assembly. Therefore, the loss voltage due to the increased resistance at the junction interface is also
Also, adverse effects on liquid permeability and air permeability are avoided.

That is, the sintered body using the spherical gas atomized titanium powder does not even have to be pressurized in the manufacturing process and is not surface-coated after the manufacturing process. As a current collector in a molecular fuel cell, it exhibits extremely excellent suitability in terms of both performance and economy.

The porous conductive plate of the present invention was developed on the basis of such findings, and is a porous material used as a power supply in a solid polymer type water electrolyzer or a current collector in a solid polymer type fuel cell. The conductive plate is composed of a sintered body of spherical gas atomized titanium powder.

As the spherical gas atomized titanium powder,
For example, the following three types classified according to the particle size range are commercially available. That is, fine particles of 45 μm or less, 45 to 150 μm
There are three types of coarse particles of m and 150 μm or more, which are coarser.

The particle size of the spherical gas atomized titanium powder used in the porous conductive plate of the present invention is not particularly limited, and there is no problem at the level of the above-mentioned commercial products, but even in the gas atomization method, extremely fine particles can be obtained. It is difficult to industrially produce with high yield. Further, in the case of coarse particles, when a thin porous body is manufactured, the number of contact points between titanium powders with respect to the thickness of the porous body is reduced, so that there is a fear of insufficient strength.
Therefore, the average particle size is preferably 10 to 150 μm.

Regarding the porosity of the porous conductive plate, a commercially available spherical gas atomized titanium powder is used, and a porosity of 35 to 55% can be obtained without applying pressure during filling or sintering. According to the investigation by the present inventors, this porosity is preferable in terms of electrical / mechanical characteristics in the porous conductive plate made of a titanium powder sintered body. It should be noted that it is also possible to apply pressure during filling or sintering, or adjust the porosity to 35% or less depending on the selection of sintering conditions.

The porosity can be controlled by adjusting the sintering temperature, selecting the particle size, pressurizing, and the like. As a general tendency, as the sintering temperature increases, the contact area increases, and the porosity decreases. Similarly, when the particle size is small, the contact area increases, and the porosity tends to decrease. If pressure is applied during filling or sintering, the porosity will decrease. Further, when the particle diameter becomes large relative to the plate thickness of the porous conductive plate, the porosity tends to increase. With these combinations, the porosity is arbitrarily controlled within a relatively wide range. It should be noted that the extreme reduction or increase in the porosity causes deterioration in the efficiency of receiving water or gas in the reaction and insufficient strength of the porous conductive plate.

The size of the porous conductive plate is appropriately selected according to the sizes of the power supply body and the current collector to be manufactured.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 are cross-sectional views showing a filling form of spherical gas atomized powder.

First, as shown in FIG. 1, a spherical gas atomized titanium powder 1 having a predetermined particle size is filled in a sintering container 2 made of high density alumina without pressure. The inner shape of the sintering container 2 is a thin plate shape corresponding to the shape of the porous conductive plate to be manufactured.
Next, the spherical gas atomized titanium powder 1 filled in the sintering container 2 is vacuum-sintered without pressure.

The sintering temperature is preferably 850 to 1200 ° C., which is much lower than the melting point of titanium. Sintering temperature is 850 ℃
If it is less than, sufficient sintering is not performed. If the temperature exceeds 1200 ° C., even if no pressure is applied, the sintered portion is not limited to the contact portion between the individual particles and the particles are fused to each other, so that it may not be possible to ensure an appropriate porosity.

With such a method, 50 mm square × 1 mm thick,
Three types of porous conductive plates having dimensions of 0.5 mm thickness and 0.2 mm thickness were manufactured as examples of the present invention.

The spherical gas atomized titanium powder is the above-mentioned commercial product, and coarse particles (45 to 150 μm) are used for 1 mm thickness and 0.5 mm thickness, and fine particles (45 μm or less) for 0.2 mm thickness. used. The degree of vacuum in vacuum sintering is 7 × 10 −3 Pa, and the sintering temperature is about 10 for coarse particles.
The temperature was set to 00 ° C and to 900 ° C for fine particles. The temperature holding time was about 15 minutes for both coarse particles and fine particles. The porosity of each manufactured porous conductive plate was about 45%.

The electric resistance of the produced porous conductive plate was measured by the four-terminal method, and it was 10 mΩ with a thickness of 1 mm.
The thickness of 0.5 mm was 15 mΩ, and the thickness of 0.2 mm was 12 mΩ by using fine particles. Regarding the properties, the spherical gas atomized titanium powder was aligned along the upper surface of the bottom portion of the sintering container, whereby the surface was flattened.
Further, due to the good fluidity of the spherical gas atomized titanium powder, a relatively uniform porosity was obtained over the entire porous conductive plate.

For comparison, a commercial product of hydrodehydrogenated titanium powder (particle size range 50 to 150 μm, average particle size 100 μ)
m) was sintered to produce a porous conductive plate having a size of 50 mm square × 1 mm thickness, 0.5 mm thickness and a porosity of 45%. Press molding was required to obtain a porosity of 45%. The electric resistance was equivalent to that of the example, but the strength was insufficient. It is presumed that this is because the titanium powder particles are not bonded uniformly because the irregularly shaped particles are used. This appears in the variation in the porosity of the entire porous conductive plate.

On the other hand, the commercially available titanium fiber sintered plate (thickness 0.8 mm) had a large porosity of 60% and a high electric resistance of 30 mΩ. Although the strength was sufficient, the surface had minute sharpness to the extent that it could not be pressed into contact with the membrane electrode assembly. On one surface of this titanium fiber sintered body, the commercially available spherical gas atomized titanium powder was plasma-sprayed in argon gas to a thickness of 0.2 mm to make the total thickness 1 mm. The overall porosity is 45%,
Although the surface was flattened, the electric resistance was still as high as 20 mΩ, which was twice that of the example.

In the above-mentioned embodiment, the sintering temperature for coarse particles was set to about 1000 ° C., but if this sintering temperature was set to 1100 ° C., the porosity decreased to about 40%. Also, the sintering temperature is 9
The porosity increased to about 50% at a temperature of 00 ° C. All porous conductive plates had high strength, excellent surface smoothness, and low resistance.

As a method for further improving the smoothness of the surface,
For example, there is a method in which spherical gas atomized titanium powder is filled into a sintering container having a required size while applying vibration. According to this vibration filling, as shown in FIG. 2, not only the surface in contact with the upper surface of the bottom of the sintering container 2 but also the surface on the opening side is improved in smoothness, and the porosity is further homogenized. Also,
As shown in FIG. 3, it is also effective to configure the sintering container 2 so that the inner plate-shaped space is oriented vertically. When the inner plate-shaped space is oriented vertically, the filled spherical gas atomized titanium powder 1 receives a load in the plate thickness direction due to its own weight from both side surfaces, and the smoothness of both surfaces is improved. In either method, the porosity is reduced by increasing the filling rate,
Both can be used together.

As a molding method, in addition to natural filling and vacuum sintering, a spherical gas atomized titanium powder kneaded with a binder is molded into a green body by a doctor blade method, an injection molding method, an extrusion method or the like, and then the binder is formed. May be removed and sintered. It is also possible to roll the porous conductive plate after sintering or roll the green body to further smooth the surface and adjust the porosity. Further, reducing the particle size distribution of the spherical gas atomized titanium powder is also effective for smoothing the surface.

[0035]

As described above, since the porous conductive plate of the present invention is made of a sintered body of spherical gas atomized titanium powder and has excellent formability, a thin and large area product can be easily manufactured. it can. Even if the coating such as plasma spraying is not performed, the surface is excellent in smoothness, so that the protection property and contact property with respect to the membrane electrode assembly can be improved without increasing the electric resistance, and the economy is also excellent.
With these, a high-performance power supply and current collector can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a filling form of spherical gas atomized powder.

FIG. 2 is a cross-sectional view showing another example of a filling form of spherical gas atomized powder.

FIG. 3 is a cross-sectional view showing still another example of a filling form of spherical gas atomized powder.

[Explanation of symbols]

1 Spherical gas atomized titanium powder 2 Sintering container

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI H01M 8/10 H01M 8/10 (72) Inventor Masamichi Kato 1 Higashihama-cho, Amagasaki-shi, Hyogo Sumitomo Sitix Amagasaki (56 ) Reference JP 2000-328279 (JP, A) JP 8-333605 (JP, A) JP 8-269761 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) ) C25B 11/10 B22F 1/00 B22F 5/00 C25B 1/00-15/08 H01M 8/02 H01M 8/10

Claims (3)

(57) [Claims] 1. A porous conductive material which is used as a power supply in a solid polymer type water electrolyzer or as a current collector in a solid polymer type fuel cell, and is composed of a sintered body of spherical gas atomized titanium powder. Board. 2. The porous conductive plate according to claim 1, which has a porosity of 35 to 55%. 3. The porous conductive plate according to claim 1, wherein the spherical gas atomized titanium powder has an average particle size of 10 to 150 μm.