JPH07114937A - Fuel cell - Google Patents

Abstract

PURPOSE:To provide a fuel cell of high reliability by preventing corrosion of various kinds of materials. CONSTITUTION:A gas seal member 12 and an O-ring 13 are interposed between a fuel cell lamination 14 and a manifold 11, between which an intermediate electrode 19 is disposed on a side of the O-ring 13 while an insulating film 21 is disposed on a side of the manifold 11 along the O-ring 13. The intermediate electrode 19 is located in approximately the same height as an undermost electrode of the fuel cell lamination 14, where at least one point is introduced out so as to be electrically connected. After passing an ammeter 22, the introducing-out portion of the intermediate electrode 19 is connected at one end thereof to the manifold 11 serving as an earth while at the other end thereof to a current collecting plate 17 via a variable resistor 23 and a DC power source 24.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a fuel cell, and more particularly,
The present invention relates to corrosion prevention of a laminated body in which a large number of unit batteries are laminated.

[0002]

2. Description of the Related Art In a conventional fuel cell, no measures have been taken to prevent corrosion of a laminated body in which a large number of unit cells are laminated, merely by relying on insulation.

[0003]

For example, in a phosphoric acid type fuel cell using phosphoric acid as an electrolyte, a unit composed of an air electrode 3 carrying a catalyst 2, a fuel electrode 4 and a matrix 5 held between both electrodes. In order to supply and discharge air 8 and fuel 9 as shown by arrows to a laminated body in which a large number of batteries 1 are laminated via a gas separator 6 and which are clamped together with a manifold receiving plate 7 by a clamping jig (not shown). In the fuel cell stack 14 shown in FIG. 7 in which the manifold 11 is fixed to the four faces of the stack by using the gas seal member 12 that also serves as an electrical insulator and the gasket such as the O-ring 13, the manifold 11 is generally used. Is used as the ground potential or one of the upper and lower potentials of the laminated battery. FIG. 8 is a plan view showing the main part of the gas seal portion of the fuel cell stack 14, but electrical insulation is provided by the gas seal member 12, the O ring 13, and the fluororesin-based coating layer 15 on the inner surface of the manifold 11. ing. An electrical equivalent circuit of this is shown in FIG. 1-1
1-n are unit batteries, and the insulation resistances 10-1 to 10-1 are provided between the unit cells and the manifold, which is at ground potential.
They are connected by 0- (n + 1).

When the fuel cell generates electricity in this state,
The main load current 16 flows through the load Z as indicated by the arrows, and the currents 20-1 through 20-n as indicated by the arrows respectively flow through the unit batteries 1-1 through 1-n. At this time, insulation resistances 10- and 10- (n + 1) except insulation resistance 10-
The currents flowing through 2 to 10-n are extremely small because the currents due to the batteries above and below the respective resistances cancel each other out, and the insulation resistances 10-1 and 10- (n + 1) are equal to the total voltage of the laminated battery and the insulation resistance. A very large current due to 10-1 and 10- (n + 1) will flow. This current is applied to point P ~
Considering S, points P and R are currents flowing out, and there is no particular problem as long as all the currents are due to electrons, but at point P, the water in phosphoric acid is electrolyzed by the presence of phosphoric acid and hydrogen Ions and active oxygen are generated, and hydrogen ions flow as an ion current at the facing point Q, while one active oxygen is at point P.
There was a problem of corroding carbon and other materials. Considering further over time, insulation resistance 10-1 to 10- (n + 1)
However, there was a problem that the phosphoric acid as the electrolyte gradually penetrated, and the resistance tended to decrease, and the corrosion proceeded further. That is, in the conventional fuel cell, there is a problem that the corrosion of various materials is not a leakage current due to ions and effective measures have not been taken.

An object of the present invention is to prevent corrosion of various materials and provide a highly reliable fuel cell.

[0006]

The above-mentioned object is to electrically cut off a circuit in a portion where a leakage current due to ions flows, and to provide an intermediate electrode and an insulating film in the circuit so that the leakage current due to ions flows into an intermediate portion. This is achieved by constructing an electric circuit including a DC power source, a variable resistance, an ammeter and a controller so as to cancel this current between the electrodes.

[0007]

[Function] When the fuel cell is in a power generation state, a leakage current due to ions tends to flow, but the voltage of the DC power supply
Or adjust the resistance to cancel the ionic current,
Eliminates generation of active oxygen and prevents corrosion of various materials used in fuel cells.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, a fuel cell stack 14 comprises a unit cell 1 composed of an air electrode 3 carrying a catalyst 2, a fuel electrode 4 and a matrix 5 sandwiched between both electrodes, with a gas separator 6 interposed therebetween. A large number of layers are laminated, and these are laminated together with the manifold receiving plate 7, the current collecting plate 17, and the insulating plate 18 by a clamping jig (not shown) to form a laminated body.

A manifold 11 is fixed to the four side surfaces of the fuel cell stack 14 so that air 8 can be supplied as indicated by the arrow and fuel 9 can be supplied and discharged so as to be orthogonal to the air 8.

Further, between the fuel cell stack 14 and the manifold 11, a gas seal member 12 that also serves as an electrical insulator and a gasket such as an O-ring 13 are provided. Further, an intermediate electrode 19 is provided between the O-ring 13 and the manifold 11 on the O-ring 13 side,
An insulating film 21 is provided on the first side substantially along the O-ring. The intermediate electrode 19 is disposed at a position substantially equal to the height of the lowermost electrode 3 of the fuel cell stack 14, and is wider than the width of the O-ring. Further, at least one place is led out so that it can be electrically connected. Since the insulating film 21 insulates the intermediate electrode 19 from the manifold 11, it is made larger than the intermediate electrode. Intermediate electrode 19
The derivation part of (1) is connected to the manifold 11 which is grounded at one end after passing through the ammeter 22 and is connected to the collector plate 17 through the variable resistor 23 and the DC power source 24 at one end. Further, the intermediate electrode 19 and the insulating film 21 are similarly arranged at the lower portion and the target position on the uppermost side of the fuel cell stack 14.
In the controller 25, the variable resistor 23 can be adjusted so that the current instruction value is always zero.

With the above structure, the temperature of the fuel cell is raised to a predetermined temperature and an electromotive force is generated in each unit cell 1 by introducing the reaction gas into each electrode, and the gas seal member 12 and the O ring 13 are formed. An electric circuit that connects the manifold 11 and the manifold 11 is formed, and an electric current that causes corrosion tends to flow in the lowermost and uppermost circuits of the fuel cell stack 14. However, this current is canceled by the variable resistor 23 and the DC power supply 24, and the corrosion of the material is suppressed. This will be explained in more detail by the equivalent circuit shown in FIG.

In FIG. 2, a gas seal member 12 which insulates the unit batteries 1-1 to 1-n and the manifold 11 from each other.
Of the insulation resistances 10-1 to 10- (n + 1), the currents flowing through the insulation resistances 10-2 to 10-n are offset by the currents from the batteries above and below the respective resistances. The currents flowing through are current 20-1 and current 2
0-2 offset each other to almost zero. The current flowing through the lowermost insulation resistance 10-1 can be controlled by the control device 25 and the variable resistance 23 so that the current of the ammeter 22 is always zero, so that the corrosion at the point P hardly occurs.

That is, the current 20-1 is the resistance 21a of the insulating film.
Since -1 is much larger than the resistance of the ammeter 22, it flows to the ammeter side at the point Q. Therefore, this current 20-
The variable resistance 2 is applied to the points P ₀ , Q ₀ , Q, P for canceling the current 1
3. If the control device 25 controls so that the ammeter indication value is always zero, the insulation resistance 1
Since the current flowing through 0-1 can be eliminated, in other words, the current due to the ions flowing out of the point P can be reduced to zero, corrosion of that portion can be eliminated. It should be noted that although the current flows out at the point P ₀ , corrosion does not occur at this portion because it is not due to ions but due to electrons. In addition, the insulation resistance 10-1
Insulation resistance 1 can be suppressed by strengthening the insulation of the electrode and suppressing the ion current 20-1 in this part, although corrosion at the bottom can be suppressed.
Since the current 20-2 flowing through 0-2 cannot be canceled, the members of the unit battery 1-2 are corroded, and the corrosion cannot be suppressed as a whole.

On the other hand, the points R ₀ , R, S,
If a current is caused to flow through S ₀ by the variable resistor 23 and the DC power supply 24 and the controller 25 controls so that the ammeter indicated value is always zero, the occurrence of corrosion can be almost eliminated by the same action as the lowermost part.

According to the present invention, by forming an electric circuit so as to cancel the leakage current due to ions, it is possible to eliminate corrosion of various materials of the fuel cell and provide a highly reliable fuel cell.

Although the intermediate electrode 19 is inserted between the O-ring 13 and the manifold 11 via the insulating film 21 in the present invention, the intermediate electrode 19 is inserted between the gas seal member 12 and the O-ring 13 to form the insulating film. Even if 21 is omitted, almost the same effect can be obtained.

Further, it is preferable to make the ammeter 22, the variable resistor 23, the DC power source 24, and the control device 25 into an integrated electronic load device so that the current is always zero so as to reduce the cost and the size. Especially effective.

The invention of FIGS. 3 and 4 is an example applied to an internal manifold type fuel cell which is often found in molten carbonate type fuel cells.

The characteristic feature of the internal manifold type unit cell is that a gas passage is provided in the separator 6a.
The other members are the same as the type having the manifold. In the intermediate electrode of the present invention, the insulating film 21 is sandwiched between 19a and 19a.
and is provided in the middle of the end seal portion 26 (often the matrix 5 also serves as this) of at least one unit cell 1 of the fuel cell stack 14 and does not contact the separator 6a. It is arranged as follows. An ammeter 22 is connected to the intermediate electrodes 19a and 19b. Also, the bottom separator and the top separator 6
A variable resistor 23 and a DC power supply 24 are connected between a and. Reference numeral 25 is a control device, which is configured to take in the signal from the ammeter 22 and control the variable resistor 23 as in the case of the invention of FIG. 27 is a gas header for supplying and discharging gas to the fuel cell main body.

With this structure, the fuel cell is heated to a predetermined temperature, and an electromotive force is generated in each unit cell 1 by introducing a reaction gas into each electrode. Leakage current due to ions flows in the end seal portion 26 that is a short-circuit portion, and corrosion occurs in the separator 6a in contact with the end seal portion and especially on the side surface where current flows. According to the present invention, this current is generated. Is a variable resistor 23,
The DC power supply 24 cancels each other out, and corrosion of the material is suppressed. This operation will be described in more detail with reference to the equivalent circuit shown in FIG.

The currents that short-circuit the respective unit batteries 1-1 to 1-n due to the resistance of the end seal portion which is the liquid short-circuit portion are canceled by the adjacent batteries, and P and Q are indicated by broken line arrows. , R, S, which is a current flowing through the DC power supply 24, the variable resistor 23, and the controller 25, and this current is canceled by the current flowing through P ₀ , R ₀ , S, and Q, and finally P _0. , R ₀ , S, R, P, Q, and the ionic current flowing from S to Q and flowing out, that is, the current causing corrosion becomes zero. Therefore, the separator 6a is not corroded. Also, Q
The current from P to P ₀ is due to electrons, which does not cause corrosion.

According to the present embodiment, even in the internal manifold type fuel cell, the electric circuit is configured so as to cancel the leakage current due to the ions, so that the fuel cell in which corrosion of various materials of the fuel cell is eliminated can be provided. it can.

The invention of FIGS. 5 and 6 is an example applied to a cooling device for a fuel cell. Since a fuel cell generates heat almost as much as an electric output in a cell reaction, it is necessary to insert a cooler for cooling the plurality of unit cells.

In FIG. 5, reference numeral 34 denotes a battery group in which a plurality of unit batteries are stacked, which are stacked alternately with a cooler 28 having a cooling pipe 29 therein and which are not shown together with the manifold receiving plate 7 and the like. Tightened by the device,
The fuel cell stack 14 is formed.

The cooling water 31 is supplied all at once by the cooling mother pipe 30, and is branched by the branch pipe 32 as shown by the arrows.
Sent to. The cooling pipe 29 is generally grounded to the cooling mother pipe 30 and is insulated by the insulating tube 33 because the cooling medium is water. The lowermost branch pipe 32 is divided into a tubular intermediate electrode 19 and an insulating tube 33a.
An ammeter 22, a variable resistance 23, and a DC power supply 24 are connected between the intermediate electrode 19 and the cooling pipe 29, and a control device 25 for controlling these is provided. The uppermost cooler is also equipped with the same device as the lower part. In general, the cooling pipe 29 is provided in order to prevent the cooling pipe 29 from having a float potential.
And have the same potential. Further, the drain side of the cooler 28 is omitted because the drawing becomes complicated, but like the supply side, it is collectively drained by a cooling mother pipe and is insulated.

With the above structure, the electromotive force is generated by raising the temperature of the fuel cell to a predetermined temperature and introducing the reaction gas into each electrode, and the electric output can be obtained, but it is almost the same as the electric output. Cooling water is supplied to cool the heat generation of the battery and to control the battery group 27 to reach a predetermined temperature. Although this cooling water is sufficiently cleaned by ion exchange resin or the like to increase its resistance, the cooling mother pipe 30 is grounded, while the cooling pipe 29 has a high voltage, so it is insulated by the insulating tube 33a. However, an ionic current that causes corrosion is about to flow.
However, similar to FIG. 1 and FIG. 3, this current is canceled by the DC power supply 24, the variable resistor 23, and the control device 25, and the corrosion of the cooling pipe 29 and the like is prevented.

The equivalent circuit shown in FIG. 6 will be described in more detail. 27-1 to 27-3 are output voltages of the battery group between the coolers, and are connected to the cooling mother pipe having the ground potential by the liquid resistances 33-1 to 33-4 of the insulating pipe 33. Also, 33a
-1, 33a-2 are liquid resistances of the insulating tube 33a. When the cell group has an electromotive force during the operation of the fuel cell, currents 20-1 to 20-3 tend to flow in the respective circuits.
In the liquid resistances 33-2 and 33-3, the currents due to the adjacent battery groups cancel each other out and no current flows, so that the cooling pipes in this portion do not corrode. This is the same as in the conventional fuel cell, but there is no current that cancels the current 20-1 at the point P, which is the contact portion with the liquid in the cooling pipe 29 of the cooler 28 at the bottom, so there is a current flowing out. Corrosion occurred (the same is true at point S). However, in the present invention, the variable resistor 23, the DC power source 24, and the controller 25 cause the point P,
This can be canceled by passing a current through P ₀ , Q ₀ , and Q,
Corrosion can be prevented. That is, since the liquid resistance 33-1 of the current 20-1 is much larger than the internal resistance of the ammeter 22 at the point Q, the current 20-1 flows to the ammeter side. Therefore, if the current of the ammeter 22 is controlled so that it is always zero, the point P
Can prevent corrosion. Also in the uppermost cooling pipe, corrosion at the point S can be prevented by passing a current that cancels out at the points S, S ₀ , R ₀ , and R.

According to this embodiment, a fuel cell is provided in which the corrosion of each material of the cooling system such as the cooling pipe of the fuel cell is eliminated by constructing the electric circuit so as to cancel the leakage current due to the ions flowing through the cooling water. can do.

[0030]

According to the present invention, the intermediate electrode and the insulating film are provided in the portion where the leakage current due to the ions flows, and the current is canceled between the portion where the leakage current flows due to the ions and the intermediate electrode. By constructing an electric circuit consisting of a DC power supply, a variable resistance, an ammeter, and a control device, it is possible to control so that the ionic current, which is the main cause of corrosion, will always be zero. Can be provided.

In the present invention, the current is controlled by changing the resistance, but it is also possible to fix the resistance and control the voltage. It is also possible to use, for example, an electronic load device in which a DC power supply, a variable resistance, an ammeter and a control device are integrated.

Further, in the present invention, the manifold, the end seal portion and the cooler portion have been described, but they are all effective for the portion where ionic leakage current flows.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a fuel cell of the present invention.

FIG. 2 is an equivalent electric circuit diagram of a fuel cell.

FIG. 3 is a partial cross-sectional view of an internal manifold type fuel cell.

FIG. 4 is an equivalent electric circuit diagram of an internal manifold type fuel cell.

FIG. 5 is an explanatory diagram of a cooling configuration of a fuel cell.

FIG. 6 is an equivalent electric circuit diagram of a cooling component of the fuel cell.

FIG. 7 is a partial cross-sectional view of a conventional fuel cell.

FIG. 8 is a plan view showing a main part of a manifold seal portion of a conventional fuel cell.

FIG. 9 is an equivalent electric circuit diagram of a conventional fuel cell.

[Explanation of symbols]

3 ... Air electrode, 4 ... Fuel electrode, 5 ... Matrix, 11 ... Manifold, 14 ... Fuel cell stack, 19 ... Intermediate electrode,
21 ... Insulating film, 22 ... Ammeter, 23 ... Variable resistance, 24 ...
DC power supply, 25 ... control device, 26 ... end seal portion, 2
8 ... Cooler, 29 ... Cooling pipe, 32 ... Branch pipe, 33a ... Insulating tube.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiichiro Ono 1-1-1 Kokubun-cho, Hitachi-shi, Ibaraki Hitachi Kokubun factory (72) Inventor Masamitsu Nakazawa 1-1-1 Kokubun-cho, Hitachi-shi, Ibaraki No. 1 Stock company Hitachi Kokubu factory

Claims (6)

[Claims] 1. A fuel cell in which a matrix containing an electrolyte is sandwiched between an air electrode and a fuel electrode, an intermediate electrode is inserted in a part of a circuit where an ionic leakage current flows, and an ionic leakage current is introduced. A fuel cell, wherein an electric circuit is configured to cancel the leakage current between a portion where the leakage current flows out and the intermediate electrode. 2. The fuel cell according to claim 1, wherein the electric circuit provided to cancel the leakage current is composed of a DC power source, a resistor, an ammeter and a controller. 3. The DC power supply, resistor,
A fuel cell that is an electronic load device in which an ammeter and a control device are integrated. 4. The fuel cell stack according to claim 1, wherein the portion where the ionic leakage current flows is between the fuel cell stack and the manifold for supplying and discharging the reaction gas, and the fuel cell stack and the manifold. A fuel cell in which an intermediate electrode is provided between the fuel cell stack and the intermediate electrode, and a DC power supply, a resistance, an ammeter, and a control device are provided between the fuel cell stack and the intermediate electrode. 5. The fuel cell according to claim 1, wherein the fuel cell is an internal manifold type, and the portion through which the ionic leakage current flows is an end seal portion. A fuel cell provided with an intermediate electrode, and a DC power supply, a resistance, an ammeter and a control device provided between the intermediate electrodes. 6. The cooling pipe of a cooler for cooling the fuel cell stack, and a branch pipe for supplying and discharging cooling water to and from the cooling pipe, wherein a portion where the ionic leakage current flows is provided in the cooling pipe. And a part of the branch pipe is divided, a tubular intermediate electrode is connected, the branch pipe is connected by an insulating tube, and the cooling pipe and the tubular intermediate electrode are connected. Fuel cell with DC power supply, resistance, ammeter, and controller installed in