JP2000058093A - Fuel cell layered body and method for detecting electrolyte supplying time - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery at low cost, while detecting a shortage of the electrolyte with a simple structure and while facilitating the assembling of a fuel cell by providing a temperature sensor in the only unit cell positioned at a central part of at least any one of the cell blocks. SOLUTION: A temperature sensor 15a is provided in two block central unit cells 1A. Since these unit cells are laminated at a central part of a cell block 13, the distance from each cooling plate 12 is the longest, and the operation temperature becomes higher than that of other unit cell. Scattered quantity of the electrolyte from a unit cell becomes larger, higher the temperature becomes, and the change of the cell temperature of the block central unit cell 1A having the highest cell temperature with the lapse of time can be monitored. The shortage of the electrolyte can be surely, comprehended at an early time without providing a temperature sensor in all unit cells, and the electrolyte supplying time can be detected. The temperature detecting unit of the temperature sensor 15A to be provided is provided at a position, at which the electrolyte is scattered at the highest speed within the block central unit cell 1A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell having a matrix impregnated with an electrolyte between an anode and a cathode. In particular, the present invention focuses on the cell temperature dependence of the amount of electrolyte scattered from the matrix, and adjusts the timing of electrolyte replenishment. The present invention relates to a fuel cell stack and an electrolyte replenishment timing detecting method which grasps and prevents electrolyte shortage in all unit cells of the fuel cell stack, and improves the power generation characteristics and life thereof.

[0002]

2. Description of the Related Art FIG. 4 is an exploded perspective view of a main part showing a basic structure of a fuel cell. As shown in the figure, an anode 3 is provided on one main surface of a flat matrix 2 holding an electrolyte.
A unit cell 1 is formed by closely disposing an oxidant electrode 4 on the other main surface, and a gas-permeable porous member having a fuel gas flow path 7 is formed on the outer surface of the fuel electrode 3. A base material 5 and a gas-permeable porous base material 6 having an oxidant gas flow path 8 are arranged on the outer surface of the oxidant electrode 4. In this configuration, the fuel gas containing high-concentration hydrogen gas flows through the fuel gas flow path 7 and is supplied to the fuel electrode 3, and the oxidant gas containing oxygen flows through the oxidizing gas flow path 8 and the oxidant electrode If you supply to 4,
Electric energy is obtained by the electrochemical reaction. However, since the generated voltage obtained by one unit cell 1 is a low voltage of less than 1 V, a plurality of unit cells 1 are stacked with a separator 9 interposed therebetween so as to be electrically connected in series to increase the generated voltage. The method has been adopted.

FIG. 5 shows a conventional fuel cell stack. A stack of a plurality of unit cells 1 is called a cell block 13, and a fuel cell stack 10 is formed by stacking a plurality of cell blocks 13 via a cooling plate 12 that removes reaction heat accompanying power generation. The temperature of the unit cell 1 is usually
2 or is estimated from the measured value of the temperature sensor 15 provided in the cooling pipe.

In the fuel cell stack having the above-described structure, the electrolyte in each unit cell 1 gradually scatters with the flow of the fuel gas and the oxidizing gas, and the amount of the electrolyte present in the unit cell 1 decreases. To go. The decrease in the electrolyte in the matrix 2 lowers the gas sealing property between the fuel gas and the oxidizing gas, causing damage to the cell due to a direct reaction,
In the worst case, it could cause an explosion.

FIG. 6 shows the correlation between the amount of electrolyte scattered from the unit cell 1 and the cell temperature. As shown in FIG. 6, the amount of scattered electrolyte increases as the cell temperature increases. When the load of the fuel cell is constant, it is possible to predict the amount of scattered electrolyte to some extent from the cell temperature and the operation time.However, the operation of the fuel cell usually involves various load fluctuations, and the temperature of each unit cell accordingly increases. Therefore, it was difficult to reliably detect the electrolyte supply time. Further, since the cell temperature of each unit cell varies depending on the distance from the cooling plate, the amount of scattered electrolyte differs for each unit cell as shown in FIG. 7, and therefore, the power generation voltage of the cell block or the entire battery stack decreases. In the conventional method of replenishing the electrolyte at the time of the replenishment, when the replenishment is performed by detecting the voltage drop, the unrecoverable electrode due to the direct reaction between the fuel gas and the oxidizing gas is applied to the unit cell already having the largest scattering amount. Damage was often in progress.

Further, if electrolyte is replenished at an early stage in order to prevent such damage to the electrodes, the electrolyte in the unit cell will be excessive in some unit cells, and consequently the fuel gas or oxidizing gas electrode In some cases, the diffusivity in the inside is reduced, and the cell characteristics may be reduced. As described above, for normal power generation of the fuel cell over a long period of time, it is indispensable to know the appropriate electrolyte supply time.

Japanese Patent Application Laid-Open No. Hei 5-251103 discloses a method for monitoring the electrolyte supply timing of a fuel cell, in which a temperature measuring terminal, for example, a thermocouple terminal is provided in a groove serving as a gas flow path provided in an electrode substrate of each unit cell. And a method of indirectly estimating the electrolytic mass in the matrix by monitoring the temperature of each unit cell is disclosed. That is,
When the electrolyte decreases below a certain amount, the fuel gas or the oxidizing gas leaks to the opposite electrode through the electrolyte layer, and the cell temperature starts to increase due to the direct reaction between the fuel gas and the oxidizing gas. It is possible to estimate the electrolytic mass.

[0008] In such a method, unlike the above-described method of measuring the voltage drop of the cell block or the entire battery stack, even if the remaining amount of the electrolyte in each unit cell varies, all of the unit cells are not changed. Since the remaining amount of the electrolyte can be grasped, the timing of replenishing the electrolyte can be detected before the unit cell having the largest amount of the scattered electrolyte is damaged by the direct reaction between the fuel gas and the oxidizing gas.

[0009]

However, in such a method of monitoring the temperatures of all the unit cells, temperature measuring terminals must be provided in all of the tens to hundreds of unit cells constituting the fuel cell stack. This leads to an increase in the number of assembly steps and an increase in cost. Further, by detecting the electrolyte replenishment time by measuring only a part of the unit cell temperature, the temperature is not monitored before the electrolyte replenishment time is detected due to the difference in the remaining amount of the electrolyte in each unit cell. Any other unit cell may be damaged by electrolyte shortage.

Therefore, in the present invention, all the unit cells have a simple structure without providing a temperature measuring terminal, and in any of the unit cells, the fuel gas and the oxidizing gas are not directly exchanged due to lack of electrolyte in the matrix layer. An object of the present invention is to provide a method for detecting the timing of electrolyte replenishment before the reaction causes electrode damage or the like.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a fuel cell stack in which a plurality of unit cells are stacked and a cell block is stacked with a cooling plate interposed therebetween. , A temperature sensor is provided in a unit cell located substantially at the center of at least one of the cell blocks. With this, among the plurality of unit cells constituting the cell block, only the central unit cell having the highest cell temperature and the fastest electrolyte scattering speed will be monitored, so that it is not necessary to provide a temperature sensor for all unit cells. In addition, it is possible to detect the shortage of the electrolyte, and to provide a fuel cell stack that is easy to assemble and that is low in cost.

Further, the amount of electrolyte impregnated in the matrix of the unit cell in which the temperature sensor is arranged is made smaller than the amount of electrolyte impregnated in the matrix of another unit cell, so that the electrolyte scattering speed of each unit cell varies. Even when the temperature sensor is installed, the unit cell in which the temperature sensor is installed becomes insufficient in electrolyte earlier than other cells, so that early and reliable detection of electrolyte supply timing is possible, and a more reliable fuel cell stack Can be provided.

Further, by locating the temperature detecting portion of the temperature sensor at the portion where the electrolyte scatter speed is fastest in the unit cell plane in which the temperature sensor is disposed, it is possible to detect the electrolyte supply time earlier. .

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

[0015]

Embodiment 1 An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram of a fuel cell stack to which the present invention is applied. A temperature sensor 15A is installed in each of the two block central unit cells 1A. These unit cells are
Since the stacking position in the cell block 13 is at the center, the distance from each cooling plate 12 is the longest, and the operating temperature is higher than other unit cells. As described above, the amount of electrolyte scattered from the unit cell increases as the temperature increases, and therefore, by monitoring the time-dependent change in the cell temperature of the block central unit cell 1A having the highest cell temperature, the unit cell in which the electrolyte shortage occurs first Therefore, it is possible to monitor only the temperature, and to reliably detect the shortage of the electrolyte at an early stage without providing the temperature sensors in all the unit cells, and to detect the supply time of the electrolyte.

In this embodiment, the fuel cell stack 10
Among the plurality of cell blocks 13 constituting the above, two block central unit cells 1A belonging to a cell block near the center of the fuel cell stack 10 are selected and the temperature sensors 15A are provided, respectively. It is also possible to provide each in the central unit cell 1A. Further, it is desirable to install the temperature detecting portion of the installed temperature sensor 15A at a position where the electrolyte scattering speed is the fastest in the plane of the block central unit cell 1A.

For example, in a fuel cell in which the fuel gas and the oxidant gas flow in the directions as shown in FIG. It is known that the electrolyte scattering speed is the highest in the vicinity C between the region B and the region B where the temperature is high, and it is preferable to install the temperature sensor 15B at this position from the viewpoint of early detection of the electrolyte supply time.

[0018]

Embodiment 2 Next, a configuration according to a second embodiment of the present invention will be described. In this configuration, in addition to the configuration of the first embodiment,
The amount of the electrolyte impregnated in the matrix of at least one of the unit cells in the block central unit cell 1A into which the temperature sensor is inserted is made smaller than the amount of the electrolyte impregnated in the matrix of the other unit cells.

Although the temperature of the block central unit cell 1A in each cell block 13 is almost the same, there is a possibility that a slight variation occurs when the electrolyte in the unit cell runs short. Therefore, at least one unit cell of the central block unit cell 1A in which the temperature sensor 15A is installed is provided with the matrix 2 when the fuel cell stack 10 is manufactured.
If the amount of electrolyte impregnated into (see FIG. 4) is smaller than that of the other unit cells, there is a variation in the timing of electrolyte shortage among the other block central unit cells 1A without the temperature sensor 15A. However, as shown in FIG. 3, since the block central unit cell 1A monitored by the temperature sensor 15A is in the shortage state of the electrolyte earlier than the other block central unit cells 1A, any one of the unit cells 1 In this case, it is possible to reliably detect the time of electrolyte supply before the electrolyte shortage occurs.

Each unit cell 1 in the cell block 13
The temperature distribution in the stacking direction can be predicted from the design conditions and operating conditions of the fuel cell stack 10, and therefore, when replenishing the electrolyte, the unit located at the stacking position where the cell temperature is high according to the temperature distribution in the cell block 13 It is advisable to replenish the cell with a relatively large amount of electrolyte and the unit cell in the stacking position with a low cell temperature with a small amount of electrolyte.

In replenishing the electrolyte of the fuel cell stacks of Examples 1 and 2, the cell temperature starts increasing as shown in FIG. 3 under a certain operating condition, and a predetermined allowable value is set. It was judged that it was time to replenish the electrolyte when it exceeded, and the replenishment of the electrolyte was performed. Specifically, the detection signal of the temperature sensor is sent to the control unit of the fuel cell power generation device, and when the detection value exceeds a preset upper limit, an alarm is output to the control screen of the fuel cell power generation device, and the alarm is output. The output time was determined as the electrolyte replenishment time, and the electrolyte was replenished.

Further, when the cell temperature further rises and exceeds a second upper limit set in advance to a temperature higher than the upper limit, power generation is stopped in order to prevent damage to the battery.

[0023]

As described above, the present invention relates to a fuel cell stack formed by stacking a plurality of unit blocks formed by stacking a plurality of unit cells with a cooling plate interposed therebetween. By providing a temperature sensor in a unit cell located substantially at the center of one of the cell blocks, it is possible to detect electrolyte shortage with a simple configuration without providing a temperature sensor in all unit cells, and assemble a fuel cell. , And a low-cost fuel cell stack could be provided.

Further, by making the amount of electrolyte impregnated in the matrix of the unit cell in which the temperature sensor is arranged smaller than the amount of electrolyte impregnated in the matrix of the other unit cells, early and reliable detection of the electrolyte supply time can be achieved. This has made it possible to provide a more reliable fuel cell stack. Further, by locating the temperature detecting section of the temperature sensor at the portion where the electrolyte scatter speed is fastest in the unit cell plane where the temperature sensor is disposed, it is possible to detect the electrolyte supply time earlier.

[Brief description of the drawings]

FIG. 1 is a schematic view of a fuel cell stack according to an embodiment of the present invention.

FIG. 2 is a diagram showing a position of a temperature sensor inserted into a unit cell of the fuel cell stack according to the embodiment of the present invention.

FIG. 3 is a diagram showing a time-dependent change in temperature of a unit cell of a fuel cell stack according to an embodiment of the present invention.

FIG. 4 is an exploded perspective view of a main part showing a basic configuration of the fuel cell.

FIG. 5 is a schematic view of a conventional fuel cell stack.

FIG. 6 is a graph showing a change over time in temperature of a unit cell of a conventional fuel cell stack.

FIG. 7 is a diagram showing a relationship between a power generation time of a fuel cell and a unit cell temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Unit cell 2 Matrix 3 Fuel electrode 4 Oxidant electrode 5 Fuel electrode side porous base material 6 Oxidant electrode side porous base material 7 Fuel gas flow path 8 Oxidant gas flow path 9 Separator 10 Fuel cell stack 12 Cooling plate 13 Cell block 14 Clamping plate 15, 15A Temperature sensor 8

Claims (4)

[Claims] 1. A fuel cell stack formed by stacking a plurality of cell blocks formed by stacking a plurality of unit cells with a cooling plate interposed therebetween, at least substantially at the center of at least one of the cell blocks. A fuel cell stack comprising a temperature sensor provided in a unit cell located in the fuel cell stack. 2. The fuel cell stack according to claim 1, wherein the amount of electrolyte impregnated in the matrix of the unit cell in which the temperature sensor is disposed is smaller than the amount of electrolyte impregnated in the matrix of another unit cell. body. 3. The fuel cell stack according to claim 1, wherein the temperature detecting section of the temperature sensor is located at a portion of the unit cell where the temperature sensor is disposed, where the electrolyte scatters at the highest speed. body. 4. The fuel cell stack according to claim 1, wherein a time when any one of the cell temperatures detected by the temperature sensor rises above a predetermined value under a certain operating condition. A method for detecting an electrolyte replenishment time of a fuel cell stack, characterized by judging an electrolyte replenishment time.