JPS59119679A - Electrode for fuel cell - Google Patents

Abstract

PURPOSE:To improve the property of a carbon carrier and increase the activity and performance of a catalyst of an electrode for a fuel cell by using graphite powder prepared by heating with a specified metal oxide as graphite carrying a noble metal catalyst. CONSTITUTION:At least one kind of metal oxide selected from K2O, Na2O, or Al2O3 is uniformly mixed with graphite powder, and they are heated in an atmosphere of argon. New pores are formed in graphite powder by this treatment. A noble metal catalyst prepared by carrying a noble metal of platinum group on the graphite is spreaded in a porous substrate with a binder to form an electrode for a fuel cell. Carrying ability of noble metal powder and conductivity in horizontal and vertical directions of carbon powder are increased by this process. Therefore, a fuel cell using this electrode provides high cativity and long life.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a novel fuel cell electrode, and particularly to a novel fuel cell electrode that improves the performance of the fuel cell by improving the properties of the carbon support. .

[Technical background of the invention]

An electrolyte retainer between a pair of spaced apart fuel electrodes and oxidizer electrodes)
In an acid electrolyte fuel cell in which an IJ gas is arranged, both of the above electrodes are usually made by kneading a noble metal catalyst consisting of noble metal particles supported on a carbon powder carrier with a binder and applying it onto a porous substrate. Manufactured by. As is well known, in an electrode formed by coating a catalyst on a substrate, which is made by supporting noble metal particles such as platinum on a carrier, the activity of the catalyst largely depends on the properties of the carrier. Furthermore, when the battery is operated, catalyst particles on the carrier tend to agglomerate, reducing its surface area and resulting in performance deterioration, a phenomenon called sintering. The phenomenon of electrolyte corrosion and dissolution resulting in performance deterioration also largely depends on the properties of the carrier. Thus, there has been a demand for the development of an electrode having a catalyst carrier that is effective in meeting the demands of engineering universities for higher performance and longer life when commercializing fuel cells.

[Problems with conventional technology]

The general properties of carbon powder used as an electrode catalyst carrier are that it has good conductivity, is chemically stable at high temperatures and pressures, and has a large specific surface area so that noble metal fine particles can be thinly dispersed. Carbon powders include activated carbon, carbon black, and graphite. Activated carbon has a specific surface area of 1000
m”/y and has a highly porous structure. Carbon black is also produced by combustion of organic materials with high carbon content, and can be porous or non-porous. Graphite There are natural and man-made carbons.In addition, there are also non-crystalline glassy carbons, cellulose carbons, etc.

In order to investigate the effects of these carbon powder carriers, a cathode electrode was made with the same amount of platinum supported and its performance was tested. As a result, the carbon powder carriers showed better performance in the order of graphite, carbon black, and activated carbon. known C
IJatiOnal Fuel CellElemin
ar, July / DetO, P3ri,
It has been reported that when P, 5tonehart6 thl) a, that is, carbon black is heat-treated, graphitization progresses, and the activity for oxygen reduction reaction increases accordingly. Therefore, graphite powder is expected to be necessary in the construction of high-performance electrodes. Graphite powder that has been heat-treated has high performance.

However, this graphite powder has a layered structure, and its electrical conductivity differs greatly between the horizontal and vertical directions, and the drawback is that the electrical conductivity in the vertical direction is quite low. Another drawback is that graphite powder generally has a low ability to support fine noble metal particles.

[Purpose of the invention]

Therefore, an object of the present invention is to provide a fuel cell electrode with improved catalyst activity and performance by improving the properties of graphite powder used as carbon powder supporting a catalyst.

[Summary of the invention]

Therefore, the present invention provides a fuel cell electrode in which a noble metal catalyst in which noble metal particles are supported on carbon powder is coated on a porous substrate together with a binder.
The present invention provides an electrode for a fuel cell characterized by using graphite powder heat-treated with at least seven metal oxides selected from the group consisting of Na2O, Al, and O.

[Detailed description of the invention]

To explain the present invention in more detail, the present invention uses graphite powder that has been heat-treated by adding a metal oxide.
, sodium oxide, NaYO1, aluminum oxide, Al,
20. is used. These metal oxides are at least ls
i is used. That is, seven types are usually used, but several types can be used in combination. This graphite powder has an average particle size of 0J-jμ
The metal oxide is preferably used as a powder of a similar size. The amount to be added is preferably in the range of 0.0/-0.0, Oj of graphite powder/metal oxide. There is no effect below this range, and the effect will not change even if added beyond this range.

After adding the above-mentioned metal oxide to the graphite powder and mixing it uniformly, it is heated at a temperature of 300 to 3JO''C for 73 to 3 minutes in an atmosphere of an inert gas such as nitrogen or argon. Add graphite powder to the graphite powder.
When heated with any of the metal oxides in the graphite powder, new pores are formed in the graphite powder, and by introducing alkali metal or aluminum metal between the layers, the conductivity is as high in the vertical direction as in the horizontal direction. can be given.

The graphite powder obtained in this way is then used to prepare a fuel cell electrode in the same manner as in the conventional method. That is, graphite powder obtained by adding at least seven of the above metal oxides and heat-treating in an inert gas atmosphere is slowly cooled and then dispersed in water.
A solution of a noble metal compound consisting of a platinum group metal such as platinum that acts as a catalyst, such as a chloroplatinic acid solution, is added and stirred.

An excess amount of sodium formate is further added to the mixture, and the mixture is stirred with ultrasonic waves for 3 to 1 hours. After passing through suction f and thoroughly washing with water until chlorine ions are no longer observed in the r liquid, it is dried to obtain noble metal catalyst powder in which fine particles of platinum, for example, are supported on carbon powder.

The precious metal catalyst powder thus obtained is then thoroughly kneaded with an appropriate amount of a water-repellent binder, such as a dispersion of polytetrafluoroethylene (trade name: Teflon Dispersion 1), to form a binder with the catalyst powder. A mixture of the agents is applied to a porous substrate, such as carbon paper, by appropriate means such as spraying, coating, or dipping, and is then applied to a porous substrate, such as carbon paper, under an inert gas atmosphere as described above. O'C
A fuel cell electrode is produced by heating and firing to a temperature of .

In order to completely coat the substrate, the coating may be carried out by suctioning from the back surface of the porous substrate using a vacuum pump and then by spraying or spraying. The electrode thus obtained has an increased capacity to support noble metal particles and has increased conductivity, allowing for the construction of higher performance fuel cells.

Similarly, when using such an electrode as a fuel cell electrode, the following conditions must be met: ■ Mechanical strength when stacking unit cells, ■ High electrical conductivity, ■ Gas permeability, and ■ High temperature and high pressure resistance. Examples include physical and chemical stability. In order to produce an electrode that satisfies these conditions, it is necessary to select carbon paper as a porous substrate, carbon powder as a carrier for a noble metal catalyst, and the method of mixing the noble metal catalyst and binder or its application. It is necessary to consider the law.

When coating a supported catalyst on a porous substrate selected as described above, some graphite powders (or carbon black) have small particle diameters, so they do not have pores when sprayed or sprayed. There is a problem in that most of the noble metal particles pass through the back surface of the transparent substrate. In addition, in a unit cell using such an electrode, for example, if phosphoric acid-containing SiO powder is used as a matrix, reaction gas is blocked by seeping of SiC fine particles to the back surface of the electrode, which inhibits the electrode reaction. there were. Attempts have been made to reduce the permeation rate by selecting a starting binder or increasing its amount, but no effective results have been obtained.

However, according to the present inventors, when coating a supported catalyst on a substrate such as the one described above, a mixture of graphite powder serving as a carrier and a binder is preliminarily mixed with at least two
It has been found that by applying and pressing the catalyst more than once, it is possible to prevent the catalyst particles from permeating to the back surface of the carrier during spraying.

Now, graphite powder gy is dispersed in water xtomt and stirred with a mixer. Add 6 d of 30% Teflon Dayne Purge to this, stir gently, and then spray to reduce the nozzle pressure.
Spray onto the porous substrate at 4 y.

At this time, when measuring the suction pressure on the back surface of this substrate, 'I: 1c
It was mAq. Next, in the same manner, when a dispersion of only graphite powder was further layered and spray-coated on the substrate, the suction pressure from the back surface increased to qOtYnAq. Finally, flake graphite powder 25F with an average particle size of 5 microns supporting precious metal fine particles was dispersed in 200 ml of water, and 30 titeflon difluoride/gml was added and stirred gently. As shown in Figure 3 of the drawings, when the coating was further applied by spray coating, the suction pressure from the back side increased to /Ocmk. In this figure, the black circle indicates the suction pressure when activated carbon is sprayed once.

This suction pressure from the back side of the substrate is the adhesion rate of the touch on the substrate,
In other words, it is a measure of the transmittance of catalyst particles to the back surface of the substrate. For example, when carbon powder with a large particle size, such as when fine metal particles are supported on activated carbon, is suctioned by the same vacuum pump, the suction pressure reaches 00 tnA. This is thought to be because activated carbon particles completely cover the surface of the porous substrate by spraying, which improves suction efficiency from the back surface of the substrate and increases the degree of vacuum.In this case, the catalyst permeates to the back surface of the substrate. It is thought that there are almost no.

Similarly, even if the number of spray coatings is increased, the permeation of the reactive gas will not be suppressed and therefore the performance of the battery will not be impaired.

Thus, in the present invention, when a noble metal catalyst made by supporting noble metal fine particles on heat-treated graphite powder to which a metal oxide has been added is well kneaded with a binder, it is applied onto a porous substrate by spraying or spraying. Prior to application, a mixture of graphite powder and a binder or a dispersion of graphite powder is sprayed onto at least a solid porous substrate, and then a catalyst is supported. It is preferable to apply graphite powder by spraying.

[Embodiments of the invention]

Example 1: Graphite powder 309, potassium oxide, 20! After adding f and mixing uniformly, in argon gas -! At 00″C/
Heat treat for j minutes. The mixture is dispersed in slowly cooled and drained water O0d, and a chloroplatinic acid solution of 73-10 is added thereto and stirred.

An excess amount of sodium formate is added to the mixture, and the mixture is ultrasonically stirred for 3 to 5 hours. The solution is filtered by suction and washed with water until no chlorine ions are observed in the solution, and then dried to obtain a platinum catalyst powder. The catalyst particles obtained in this manner were dispersed in water 3θd, stirred, and 30% Teflon disbarge solution was added and stirred.The resulting mixture was sprayed onto a porous substrate made of carbon paper, and after being crimped with a roller. 33o” in nitrogen gas
An electrode was obtained by heating and firing at SO for a minute at c.

When a unit cell is assembled using the electrodes obtained in this way, it is possible to assemble a higher performance battery that exhibits a higher battery voltage than a battery using conventional electrodes, as seen in the curve in Figure 7. did it. In addition, this electrode exhibits strong resistance to dissolution corrosion and can form a long-life electrode, as shown in Figure 1. The first figure is here OmA /6n:
This figure shows the change in terminal voltage over time during polarization at a rated current of 1. The fuel used here was 10% hydrogen and 2 carbon dioxide gas.
0%, the oxidizing agent was air, the temperature was 190°C, and the pressure was normal pressure. Curve 1 in FIG. 1.2 is for a battery using an electrode made by the conventional method as in Example 1, except that no metal oxide was added.

Example.

1 p of scaly graphite powder with an average particle size of jμ is dispersed in -〇〇 m/ of water and stirred with a mixer. After adding 6d of 30% Teflon dispersion and stirring, the surface area was 00i, the thickness was 0.41 ms, the porosity was 70%, the area resistance was 4t (
While suctioning the back surface of a porous substrate made of carbon paper (Ωi), spray coating is applied onto the porous substrate at a nozzle pressure of 3-4. After pressing lightly with a roller, etc., apply the same mixture again.

Finally, after dispersing and stirring separately prepared fine graphite powder my supporting platinum particles in water θO-, 30% Teflon disbarge/gd was added and stirred, and the mixture was applied to Mr. A as described above. Further spray coating on the porous substrate
After being pressed with a roller, the electrode was baked at 330'C in nitrogen gas for 9 minutes.

When a unit cell was assembled using the electrode thus obtained, it exhibited high activity characteristics as seen in the curve of FIG. 4. On the other hand, in the case of a battery using an electrode according to the conventional method in which no single coating was applied in advance, the same curve (■) appeared. The fuel, oxidizer, and other components used at this time were the same as in Example 1.

〔Effect of the invention〕

As described above, according to the present invention, as carbon powder, O, N
By using graphite powder obtained by adding at least one type of metal oxide of group a, Ol, AI, and 03 and subjecting it to heat treatment, the ability to support noble metal particles in the graphite powder can be improved, and the ability to support noble metal particles in the horizontal direction can be improved. At the same time, efforts were made to improve conductivity in the vertical direction, and the properties of the carbon powder carrier were improved, making it extremely effective in achieving high activation and long life of fuel cells using this material. It is.

[Brief explanation of drawings]

Figure 1 is a graph showing a comparison of the polarization performance of batteries using electrodes found in Example/ and electrodes created by the conventional method. Figure 2 is a graph showing batteries using electrodes in Example/ and electrodes created by the conventional method. Figure 3 is a graph showing the increase in suction pressure from the back surface of a porous substrate depending on the number of times graphite powder particles are sprayed onto the porous substrate, and Figure 4 is a graph showing the increase in suction pressure from the back surface of the substrate as seen in Example λ. 2 is a graph showing a comparison of the polarization performance of a battery using an electrode obtained by a conventional method and an electrode obtained by a conventional method.

Claims (1)

[Claims] In a fuel cell electrode in which a noble metal catalyst in which noble metal particles are supported on carbon powder is coated on a porous substrate together with a binder, the carbon powder is selected from the group consisting of K, 01NaYO, and A1YO5. An electrode for a fuel cell characterized by using graphite powder that has been heat-treated together with at least seven selected metal oxides.