JP2002298890A - Defective cell detection method for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely detect a unit cell causing a cross leak from a generation part, without damaging the unit cell. SOLUTION: Helium gas (He) is added to a fuel gas to be supplied to a fuel electrode 6, the respective voltages of unit cells 2, before and after the addition of helium gas are measured; and the unit cell 2 causing the cross leak from the generation part is detected from the reduction degree of voltage. The concentration of helium gas in air exhaust gas is measured, to measure the concentration of helium gas leaked to an air electrode 7. When the reduction degree of voltage is large, and the leaked helium gas concentration is high, this cell is determined as being the unit cell 2 causing the cross leak from the generation part, and when the leaked helium gas concentration is low even with a high reduction degree of voltage, it is determined that the deterioration of gas diffusibility of the fuel electrode 6 has occurred.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphoric acid type in which a unit cell is formed by pressing a fuel electrode on one side of an electrolyte and an air electrode on the other side, and a plurality of the unit cells are laminated. The present invention relates to a method for detecting a defective cell of a fuel cell such as a fuel cell or a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art The cause of performance deterioration of a fuel cell is as follows.
Some are caused by a decrease in gas diffusivity of the electrode, some are caused by gas leakage (cross leak) from the power generation part (electrolyte), some are caused by catalyst deterioration, and some are caused by increase in electrolyte resistance. It is roughly divided. Conventionally, methods for determining these deterioration factors include a method of measuring an open circuit voltage, an oxygen utilization test, a hydrogen utilization test, and a load fluctuation test.

However, in the case of unit cell deterioration, the above-mentioned causes of deterioration are often compounded, and it is difficult to determine what the main deterioration is. In particular, when a cross leak occurs in the power generation part of the unit cell,
If the operation is continued as it is, the cross leak is further deteriorated due to the reaction heat at the air electrode, etc., and often causes serious troubles such as spreading to the deterioration of the catalyst. It is very important to determine the presence or absence of a substack that includes it.

As a method of determining such a cross leak, a method of measuring an open circuit voltage among the above-mentioned methods is relatively effective. Conventionally, a method of measuring the open circuit voltage is employed. .

[0005]

However, the method of measuring the open circuit voltage has a drawback that the unit cell is deteriorated particularly in a high temperature state since the unit cell is exposed to a high voltage. Further, the method of measuring the open circuit voltage has a drawback that a leak from the peripheral portion of the unit cell or a portion that does not significantly affect the reaction is determined as causing cross leak.

The present invention has been made in view of such circumstances, and the invention according to claims 1 and 3 causes a cross leak from a power generation portion without damaging a unit cell. It is an object of the present invention to enable a unit cell or a sub-stack to be accurately detected, and an object of the invention according to claim 2 to be able to detect a decrease in gas diffusivity of an anode.

[0007]

The invention according to claim 1 is
In order to achieve the above object, a fuel cell is formed by pressing a fuel electrode on one surface of an electrolyte and an air electrode on the other surface to form a unit cell, and a plurality of the unit cells are stacked. A defective cell detection method, wherein helium gas is added to the fuel gas supplied to the fuel electrode, and the unit cells before and after the addition of the helium gas,
Alternatively, a voltage of each of the sub-stacks including a plurality of the unit cells is measured, and a unit cell or a sub-stack which causes a cross leak from the power generation part is detected from a degree of the voltage drop.

According to a second aspect of the present invention, there is provided a method of detecting a defective cell of a fuel cell according to the first aspect, wherein the concentration of helium gas leaking into the air electrode is attained. Is measured, and the degree of cross leak is detected from the measured density and the degree of voltage decrease.

According to a third aspect of the present invention, in order to achieve the above object, a unit cell is formed by pressing a fuel electrode on one surface of an electrolyte and an air electrode on the other surface. A method for detecting a defective cell of a fuel cell in which a plurality of the unit cells are stacked, wherein helium gas is added to air supplied to the air electrode, and before and after the helium gas is added, respectively. The unit cell, or, while measuring the voltage of each of the sub-stack composed of a plurality of unit cells, measure the concentration of helium gas that has leaked into the fuel electrode, from the measured concentration and the degree of decrease in voltage, It is characterized by detecting a unit cell or a substack causing a cross leak from a power generation part.

[0010]

According to the configuration of the method for detecting a defective cell of a fuel cell according to the first aspect of the present invention, helium gas, which is inert and has good diffusibility, is added to the fuel gas supplied to the fuel electrode to reduce cross leak. In the causing unit cell or sub-stack, it is estimated that helium gas with good diffusibility diffuses to the air electrode side, impeding the electrode reaction at the air electrode, and the degree of voltage drop is larger than that of a normal cell. Focusing on this fact, it is possible to detect a unit cell or a sub-stack causing a cross leak from the power generation part based on the degree of voltage drop.

Further, according to the configuration of the method for detecting a defective cell of a fuel cell according to the second aspect of the present invention, the unit cell or the sub-stack in which the gas diffusion property of the fuel electrode is reduced is not caused by the cross leak. Focusing on the fact that the voltage drop before and after the addition of helium gas increases despite the fact that the leak is unlikely to occur, measure the concentration of helium gas that has leaked into the air electrode. Thus, it can be determined whether the cause is a cross leak or a decrease in gas diffusivity at the fuel electrode. More specifically, if the degree of voltage drop is large and the concentration of leaked helium gas is high, it is determined that the unit cell or substack is causing a cross leak from the power generation part, while the voltage drop is low. Even if the degree is large,
If the concentration of the leaked helium gas is low, it can be determined that the unit cell or the sub-stack has a low gas diffusion property of the fuel electrode.

Further, according to the configuration of the method for detecting defective cells of a fuel cell according to the third aspect of the present invention, helium gas which is inert and has good diffusibility is added to the air supplied to the air electrode, so that the power generation portion In a unit cell or sub-stack that causes cross-leak from, helium gas with good diffusibility leaks from the air electrode side to the fuel electrode side, impeding the electrode reaction at the fuel electrode, and comparing with a normal cell. Focusing on the fact that the degree of voltage drop is estimated to be large,
A unit that causes cross-leak from the power generation part when the degree of voltage drop is large and the concentration of leaked helium gas is high, in addition to measuring the concentration of helium gas leaked into the fuel electrode It is possible to determine that the cell or the substack is a cell or a substack, and to detect a unit cell or a substack causing a cross leak from the power generation portion.

[0013]

Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a fuel cell to which a method for detecting a defective cell of a fuel cell according to the present invention is applied. The fuel cell 1 is configured by stacking a large number of unit cells 2.

Each unit cell 2 contains a reformer 3 as a fuel gas.
The reformed gas (hydrogen-rich gas) produced in the above is supplied. A raw fuel supply pipe 4 is connected to the reformer 3 to reform a raw fuel such as natural gas or methanol to produce a reformed gas.

The unit cell 2 has a fuel electrode 6 crimped on one surface of an electrolyte 5 and an air electrode 7 crimped on the other surface, as shown in a schematic configuration diagram of a main part of FIG. Pole 6
A separator 8 is provided on the surface of the air electrode 7 opposite to the electrolyte 5.

To explain the first embodiment of the method of the present invention, helium gas (He) is added to the fuel cell 1 as described above, and helium gas is added to the fuel gas supplied to the anode 6. Before and after the addition, the voltage of each unit cell 2... Is measured, and the unit cell 2 causing the cross leak from the power generation part is detected from the degree of the voltage drop. The concentration of helium gas leaked into the air electrode 7 is measured by measuring the concentration of helium gas in the air exhaust gas. The measurement of the helium gas concentration is performed by sampling air exhaust gas discharged from the fuel electrode 6 and performing gas chromatography analysis or the like.

With the above configuration, the degree of cross leak is detected from the degree of voltage drop and the measured concentration of helium gas. If the degree of voltage drop is large and the concentration of leaked helium gas is high, It can be determined that the unit cell 2 causes a cross leak from the power generation part.

On the other hand, even if the degree of the voltage drop is large, when the concentration of the leaked helium gas is low, it can be determined that the gas diffusivity of the fuel electrode 6 is lowered. In this case, by adjusting the temperature of a humidifier (not shown) for supplying humidified steam to the fuel cell 1, the degree of drying of the electrolyte membrane at the boundary with the electrolyte 5 is adjusted, and the gas diffusivity of the fuel electrode 6 is adjusted. Can be improved.

Next, a second embodiment of the method of the present invention will be described. The helium gas is added to the air supplied to the air electrode 7, the voltage of each unit cell 2 is measured before and after the helium gas is added, and the concentration of the helium gas in the fuel exhaust gas is measured. Thus, the concentration of the helium gas leaked into the fuel electrode 6 is measured, and the first concentration is determined based on the measured concentration and the degree of voltage decrease.
As in the embodiment, a unit cell causing a cross leak is detected from the power generation part.

In the case of the second embodiment, the degree of voltage drop in the case of cross leakage or a decrease in gas diffusivity of the fuel electrode 6 is smaller than in the case of the first embodiment. Is effective in determining that there is a cross leak at the air electrode 7.

Next, a specific experimental example according to the first embodiment will be described. In a phosphoric acid fuel cell using 320 unit cells 2, about 5% of helium gas (He) is added to the fuel gas supplied to the anode 6, before and after the helium gas is added. When the voltage of each sub-stack (voltage of eight unit cells) was measured, the results shown in the graph of the voltage of each sub-stack and the voltage change before and after the addition of helium gas in FIG. 3 were obtained.

From the above results, in the No. 36 sub-stack,
It is clear that the voltage drop is greater than the other sub-stacks. At this time, when the concentration of helium gas in the air exhaust gas discharged from the air electrode 7 was measured, the concentration of the helium gas in the air exhaust gas was 5,000 ppm. The leak was detected. This No.3
When the sub-stack of Fig. 6 was disassembled, it was confirmed that a cross leak had occurred, and it was confirmed that the method of the present invention was extremely effective in detecting a defective cell causing a cross leak from the power generation part. Was.

The method of the present invention is not limited to the case where the voltage is measured for each unit cell 2 and the performance degradation of the unit cell 2 is evaluated.
For example, a configuration may be adopted in which a voltage is measured for each sub-stack in which 5 to 8 unit cells 2 are defined as one unit, and performance degradation is evaluated in the sub-stack.

The method of the present invention usually monitors a change in the cell voltage of the fuel cell 1, and may be performed when the voltage drops. Further, for example, it may be performed simultaneously with the replacement time of the filter or the ion exchange resin membrane.

[0025]

As is apparent from the above description, according to the method for detecting a defective cell of a fuel cell according to the first aspect of the present invention,
Helium gas that is inert and has good diffusibility is added to the fuel gas supplied to the fuel electrode, and based on the degree of voltage drop before and after the addition of the helium gas, a unit cell or a unit cell that causes cross leak from the power generation part Since the sub-stack is detected, the unit cell or sub-stack that causes a cross leak from the power generation part can be removed without damaging the unit cell such as deterioration due to high voltage as in the conventional method of measuring the open circuit voltage. It can be detected with high accuracy. Moreover, this detection method can be performed during normal operation because the inert helium gas is added, and for a fuel cell that takes a long time to start and stop, a defective cell can be detected while the operation is continued, Extremely effective.

According to the method for detecting defective cells of a fuel cell according to the second aspect of the present invention, in addition to measuring the voltage before and after the addition of helium gas, the concentration of helium gas leaking into the air electrode is measured. However, since the presence or absence of cross leak is directly checked, not only the unit cell or sub-stack causing cross leak from the power generation part, but also the unit where not the cross leak but the gas diffusion property of the fuel electrode is reduced Cells or substacks can also be detected, which is extremely useful. In the case of a unit cell or sub-stack in which the gas diffusion property of the anode is reduced, for example, in a polymer electrolyte fuel cell, the temperature of the humidifier is adjusted with respect to the humidifier that supplies humidified steam to the anode. By doing so, the degree of drying of the electrolyte membrane can be adjusted to reduce the voltage drop of the unit cell or sub-stack, and it can be avoided that the cell is erroneously determined to be a defective cell and replaced, thereby improving economical efficiency.

According to the method for detecting a defective cell of a fuel cell according to the third aspect of the present invention, helium gas which is inert and has good diffusibility is added to the air supplied to the air electrode, and before and after the addition of the helium gas. Unit cells or sub-stacks that cause cross-leak from the power generation part based on the degree of voltage drop in the unit cell, so that unit cells such as deterioration due to high voltage as in the conventional method of measuring open circuit voltage Alternatively, it is possible to accurately detect a unit cell or a sub stack causing a cross leak from a power generation portion without damaging the sub stack. Moreover, this detection method can be performed during normal operation because the inert helium gas is added, and for a fuel cell that takes a long time to start and stop, a defective cell can be detected while the operation is continued, Extremely effective.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a fuel cell to which a method for detecting a defective cell of a fuel cell according to the present invention is applied.

FIG. 2 is a schematic configuration diagram of a main part of a fuel cell.

FIG. 3 is a graph showing a voltage of each unit cell (sub-stack) and a voltage change before and after helium gas addition.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fuel cell power generation system 2 ... Unit cell 5 ... Electrolyte 6 ... Fuel electrode 7 ... Air electrode

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Osamu Yamazaki 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi F-term in Osaka Gas Co., Ltd. (reference) 5H027 AA04 AA06 KK31 KK54 MM04 MM09

Claims (3)

[Claims] 1. A method for detecting a defective cell of a fuel cell, comprising forming a unit cell by pressing a fuel electrode on one surface of an electrolyte and an air electrode on the other surface thereof, and laminating a plurality of the unit cells. A helium gas is added to the fuel gas supplied to the fuel electrode, and the unit cells before and after the helium gas is added, or each of the sub-stacks each including a plurality of the unit cells. A method for detecting a defective cell of a fuel cell, comprising measuring a voltage and detecting a unit cell or a sub-stack causing a cross leak from a power generation part based on a degree of decrease in the voltage. 2. The method for detecting a defective cell of a fuel cell according to claim 1, wherein the concentration of helium gas leaking into the air electrode is measured, and the degree of cross leak is determined from the measured concentration and the degree of decrease in voltage. A method for detecting a defective cell of a fuel cell to be detected. 3. A method for detecting a defective cell in a fuel cell, comprising forming a unit cell by pressing a fuel electrode on one surface of an electrolyte and an air electrode on the other surface thereof, and laminating a plurality of the unit cells. Helium gas is added to the air supplied to the air electrode,
The voltage of the unit cell before and after the addition of the helium gas, or the voltage of each of the sub-stacks composed of a plurality of the unit cells, and the concentration of the helium gas leaked into the fuel electrode A method for detecting a defective cell of a fuel cell, comprising: detecting a unit cell or a sub-stack causing a cross leak from a power generation portion from a measured concentration and a degree of voltage decrease.