Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-01-12
2002-05-28
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000
Reexamination Certificate
active
06395416
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a separator for various kinds of fuel batteries.
2. Description of the Related Art
An apparatus which uses hydrogen, fossil fuel, or the like, as fuel for directly converting chemical reaction energy generated in an oxidation reaction of the fuel into electric energy is known. This apparatus is generally called a fuel battery.
There are several kinds of fuel batteries. A fuel battery called a solid polymer type is known as one of these kinds of fuel batteries. As shown in
FIG. 5
, the solid polymer type fuel battery
100
has a structure in which a large number of cells are connected in series or in parallel. Each of the cells has a structure fin which a positive electrode
10
, an electrolyte
11
of a sold polymer, a negative electrode
12
and a separator
101
are laminated successively. Further, generally, supporting power collectors
13
are interposed between the electrodes
10
and the separators
101
and between the electrodes
12
and the separators
101
.
Each of the separators
101
has channels (grooves)
104
formed in both surfaces. Fuel gas or oxidizer gas is supplied to the respective channels
104
through fuel gas introduction holes
101
a
and oxidizer gas introduction holes
101
b
. Further, the separator
101
has cooling water introduction holes
101
c
to form a structure in which cooling water is made to flow through the holes
101
c.
The operation of a basic fuel battery
100
is as follows. Incidentally, description will be made with attention paid to one cell in order to simplify the description.
In the operation, fuel gas to be oxidized, such as hydrogen, or the like, is supplied to the negative electrode
12
whereas oxidizer gas, such as oxygen, air, or the like, is supplied to the positive electrode
10
. The fuel gas and the oxidizer gas are introduced respectively through the fuel gas introduction holes
101
a
and the oxidizer gas introduction holes
101
b
of the separator
101
and flow through the channels
104
formed in the opposite surfaces of the separator
101
.
In the negative electrode
12
, the fuel gas is decomposed into electrons and cations (protons in the case where hydrogen is used as fuel) by the action of a catalytic material.
The cations generated in the negative electrode
12
move to the positive electrode
10
while passing through the electrolyte
11
, so that the cations come into contact with the oxidizer gas such as oxygen, or the like, flowing in the positive electrode
10
.
The positive electrode
10
is connected to the negative electrode
12
through a load (not shown). The electrons generated in the negative electrode
12
move to the positive electrode
10
through the load.
In the positive electrode
10
, the cations of the fuel which have passed through the electrode
11
are oxidized by an oxidizer. When, for example, hydrogen and oxygen are used as fuel gas and oxidizer gas respectively, an oxidation reaction of oxygen and hydrogen occurs in the positive electrode
10
.
On this occasion, electrons separated from the fuel in the negative electrode
12
move from the negative electrode
12
to the positive electrode
10
through the load to thereby contribute to the oxidation reaction in the positive electrode
10
. Electromotive force is generated by the movement of the electrons.
The fuel battery
100
generally has a structure in which a large number of cells are laminated to be connected in series so that a predetermined voltage is obtained. The number of cells to be laminated is generally from the order of tens to the order of hundreds or more.
Further, in the structure in which such a large number of cells are laminated, adjacent cells are separated from each other by the separator
101
.
Except for the edge portion of the laminated structure, the fuel gas such as hydrogen, or the like, flows through one surface of the separator
101
and the oxidizer gas such as oxygen, or the like, flows through the other surface of the separator
101
.
Because the fuel gas and the oxidizer gas must not be mixed with each other, it is a matter of course that the separator
101
requires a function of separating the two gases from each other. That is, the separator
101
requires gas-tightness so that no gas permeates through the separator
101
per se.
Further, because the separator
101
serves also as a member for electrically connecting the laminated cells to each other directly, the separator
101
requires a high electrically conductive property (low resistance) as the quality of the material thereof.
Further, the separator
101
requires resistance to water generated as a result of oxidation (water resistance), corrosion resistance to electrolyte contained in the electrolyte
11
and corrosion resistance to the oxidizer.
Further, because a strong compressing force is applied to the separator
101
in a condition that cells are laminated one another, the separator
101
requires great strength to withstand the compressing force.
As configuration for satisfying the aforementioned requirements, there are the following techniques.
One of the techniques is a technique of obtaining the separator
101
by cutting a block which is obtained by baking a vitreous carbon material also called glassy carbon (baked carbon).
Channels
104
are formed in the separator
101
so that the fuel gas and the oxidizer gas are made to flow through the channels
104
. Because glassy carbon is deformed greatly when baked, such a method that the separator
101
is produced by baking glassy carbon after molding the glassy carbon in a non-baked state cannot be applied. It is, therefore, necessary to obtain a required shape by cutting a glassy carbon block after the block is obtained by baking.
The baked glassy carbon is, however, so hard that high cost is required for cutting such baked glassy carbon. Furthermore, cutting loss occurs, so that the material is wasted. In view of this point, high cost is also required.
As another technique for obtaining the separator
101
, there is a method of obtaining the separator
101
from a mixed or kneaded matter. The mixed or kneaded matter is prepared by mixing or kneading a resin with a carbon type electrically conductive filler such as graphite powder or expansive graphite powder.
In this method, a predetermined shape can be obtained at a low cost by molding or hot-pressing. That is, a predetermined channel structure (a gas path structure which makes gas flow evenly) can be obtained relatively easily.
Although it is preferable, from the standpoint of electric power generating efficiency, that the electrically conductive property of the separator
101
is high, the amount of the electrically conductive filler to be mixed must be increased for obtaining the high electrically conductive property. As a result, there arises a problem that both strength and movability are lowered. Further, because the starting material is powder, there is another problem that dimensional stability in molding is bad.
Further, the separator
101
requires a function of enclosing the fuel gas and the oxidizer gas in predetermined channels
104
to prevent the gases from leaking out of the cell (sealing function). The sealing function is, however, spoiled when dimensional stability is lowered.
Further, because a large compressing force is applied to the cells in a state in which the cells are laminated, the separator
101
requires strength to withstand the compressing force. If the separator
101
is deformed, cracked or partially broken by the compressing force, the aforementioned gas-tightness or sealing property is spoiled undesirably. It is apparent also from this standpoint that increase in amount of the carbon type electrically conductive filler to be mixed is disadvantageous. That is, it is apparent that the strength of the separator
101
is lowered if the amount of the carbon type electrically conductive filler to be mixed is increased.
Furthermore, increase in amount of the electrically conductive filler to be mixed brings ab
Shiraishi Mitsuoki
Suzuki Shinzaburo
Tanemoto Masahito
Ueda Katsunori
Alejandro R
Kalafut Stephen
Nichias Corporation
Nixon & Vanderhye P.C.
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