JP2008186782A - Operation method of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an operation method of a fuel cell in which a temperature difference between electrodes necessary for uniforming water balance is created for sure. <P>SOLUTION: An operation is conducted in a temperature of an anode side separator at 5°C or lower than a temperature of a cathode side separator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell operation method, and more particularly to a fuel cell operation method capable of generating a temperature difference between an anode side and a cathode side with an electrolyte membrane interposed therebetween.

  Electrolyte membranes used in fuel cells require water molecules for the movement of hydrogen ions in the interior thereof, and show high hydrogen ion conductivity only in a state containing moisture. For this reason, if the water in the fuel cell is insufficient and the electrolyte membrane is dried, the power generation performance of the fuel cell is greatly reduced as the conductivity of hydrogen ions is reduced. On the contrary, when surplus moisture exists in the vicinity of the electrolyte membrane, the supply of the reaction gas is hindered by the water, so that the power generation performance of the fuel cell is also lowered. In particular, since water is generated by the reaction between hydrogen and oxygen at the cathode, excess water is likely to be generated near the cathode.

  Therefore, in order to maintain high power generation performance in the fuel cell, it is important to satisfy both the drainage of excess water in the fuel cell and the moisture retention of the electrolyte membrane. As a means for this, water transportation inside the fuel cell, specifically, the transportation of moisture from the cathode side to the anode side in the electrolyte membrane is promoted to correct the water balance between the cathode side and the anode side. It is considered effective.

Conventionally, a technique disclosed in Patent Document 1 is known as a technique for correcting the water balance in the fuel cell. This prior art utilizes the feature of the electrolyte membrane that the electrolyte membrane can contain more water at higher temperatures. Specifically, by making the cathode temperature higher than the anode temperature, a water concentration gradient is generated in the electrolyte membrane, facilitating the diffusion of water from the cathode to the anode, and the water balance in the fuel cell. Is made uniform.
JP 2001-15138 A

  However, in order to improve the power generation performance of the fuel cell, it is not necessary to simply set the cathode temperature higher than the anode temperature, but there is an appropriate temperature difference range to obtain the desired effect. it is conceivable that. On the other hand, it is actually not easy to accurately manage the temperature of each electrode. This is because a separator made of metal or carbon has high thermal conductivity, and the heat of the electrode diffuses through the separator.

  The present invention has been made in order to solve the above-described problems, and provides a fuel cell operating method capable of reliably generating a temperature difference necessary for uniform water balance between electrodes. With the goal.

In order to achieve the above object, a first invention provides a fuel cell including means for generating a temperature difference between an anode side and a cathode side with an electrolyte membrane interposed therebetween.
The operation is performed with the temperature of the separator adjacent to the anode being 5 ° C. or more lower than the temperature of the separator adjacent to the cathode.

According to a second invention, in the first invention,
The means for generating the temperature difference is to provide a difference between the temperature of the anode gas supplied to the anode and the temperature of the cathode gas supplied to the cathode,
By making the temperature of the anode gas lower than the temperature of the cathode gas, the temperature of the separator adjacent to the anode is lowered by 5 ° C. or more than the temperature of the separator adjacent to the cathode.

According to a third invention, in the first invention,
The means for causing the temperature difference includes flowing a refrigerant for cooling the anode and a refrigerant for cooling the cathode through separate flow paths, and the temperature of the refrigerant for cooling the anode and the temperature of the refrigerant for cooling the cathode. Is to make a difference between
By making the temperature of the refrigerant for cooling the anode lower than the temperature of the refrigerant for cooling the cathode, the temperature of the separator adjacent to the anode is lowered by 5 ° C. or more than the temperature of the separator adjacent to the cathode. It is a feature.

According to a fourth aspect of the present invention, a plurality of fuel cells, each having both sides of an electrolyte membrane sandwiched between an anode and a cathode and sandwiched between both sides by a separator, are stacked, and each stacked fuel cell is insulated from adjacent fuel cells. In the fuel cell stack in which the same poles face each other across the body and the refrigerant flow path, and the separator of each fuel cell is connected in series with an external circuit to the separator of another fuel cell,
By making the temperature of the refrigerant flowing between the separators adjacent to the anode lower than the temperature of the refrigerant flowing between the separators adjacent to the cathode, the temperature of the separator adjacent to the anode is made lower than the temperature of the separator adjacent to the cathode. Is characterized by operating at a temperature lower than 5 ° C.

  According to the present invention, by making the temperature of the separator adjacent to the anode 5 ° C. or more lower than the temperature of the separator adjacent to the cathode, the temperature difference necessary for uniform water balance can be reliably generated between the electrodes. The power generation performance of the fuel cell can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Features of this embodiment]
FIG. 1 is a diagram showing a schematic configuration of a fuel cell to which the present invention is applied. The fuel cell 8 is configured by sandwiching the membrane electrode assembly 2 from both sides with conductive separators 4 and 6. Although not shown, the membrane electrode assembly 2 has a structure in which an anode is joined to one surface of a solid polymer electrolyte membrane and a cathode is joined to the other surface. A gas diffusion layer made of a porous material is further laminated on the surface of each electrode. A gas flow path 4a through which hydrogen gas flows is formed between the membrane electrode assembly 2 and the separator 4 adjacent to the anode. A gas flow path 6a through which air flows is formed between the membrane electrode assembly 2 and the separator 6 adjacent to the cathode. In FIG. 1, the separators 4 and 6 are processed to form the gas flow paths 4a and 6a. However, a porous layer is provided between the membrane electrode assembly 2 and the separators 4 and 6. It may be a gas flow path. A refrigerant flow path is provided on the outer surface of each separator 4, 6. The fuel cell 8 is cooled from the outer surface by the refrigerant flowing through the refrigerant flow path.

  The operation method of the fuel cell according to the present embodiment is characterized in that the temperature of the anode side separator 4 is lowered by 5 ° C. or more than the temperature of the cathode side separator 6 when the fuel cell 8 is operated. Since the separators 4 and 6 are made of metal or carbon, they have high thermal conductivity. For this reason, when a plurality of fuel cells 8 are stacked and used as a fuel cell stack, thermal diffusion from the cathode side to the anode side occurs between the adjacent fuel cells 8 via the separators 4 and 6. Therefore, although it is not easy to accurately manage the temperature of each electrode, the temperature management targets are the separators 4 and 6, and the temperature of the anode-side separator 4 is 5 ° C. lower than the temperature of the cathode-side separator 6. In this case, a temperature difference necessary for uniforming the water balance can be reliably generated between the electrodes.

FIG. 2 is a diagram showing the results of an experiment in which the influence of the temperature difference between the electrodes on the power generation performance of the fuel cell 8 is examined. In the experiment, the load of the fuel cell 8, that is, the current density (A / cm ² ) is selected in a plurality of values within the operating range, and the cell voltage (V) and cell resistance are selected at each value of the selected current density (A / cm ² ). (Ohm · cm ² ) is measured.

  In the experiment shown in FIG. 2, the temperature of the cathode-side separator 6 is fixed at 80 ° C., and the temperature of the anode-side separator 4 is 80 ° C. (Comparative Example 1), 75 ° C. (Example 1), 70 ° C. (Example). 2) Different data from 60 ° C. (Example 3) are taken. In the experiment, the temperature difference between the separators 4 and 6 is generated by making the temperature of the refrigerant on the anode side lower than the temperature of the refrigerant on the cathode side. The hydrogen gas supplied to the anode is adjusted so that the relative humidity is 100% at a temperature of 53 ° C. at the inlet of the fuel cell 8. The air supplied to the cathode is also adjusted so that the relative humidity is 100% at a temperature of 53 ° C. at the inlet of the fuel cell 8.

  According to the experimental results shown in FIG. 2, the power generation performance of Examples 1 to 3 is clearly higher than that of Comparative Example 1. In the experiment, an attempt was made to adjust the temperature difference between the separators 4 and 6 within a range of 0 to 5 ° C. However, it is not easy to adjust the temperature of each refrigerant so as to realize such a small temperature difference, and the result is substantially the same as in Comparative Example 1. From these results, it was confirmed that high power generation performance can be obtained by setting the temperature of the anode-side separator 4 to be 5 ° C. or more lower than the temperature of the cathode-side separator 6.

Furthermore, in addition to the experiment at the operating temperature of 80 ° C., the experiment was also performed under the high temperature condition of the operating temperature of 90 ° C. Also in this experiment, the load of the fuel cell 8, that is, the current density (A / cm ² ) is selected in a plurality of values within the operating range, and the cell voltage (V) and the cell are selected at each value of the selected current density (A / cm ² ). Resistance (Ohm · cm ² ) was measured. FIG. 3 is a diagram showing the results of an experiment in which the influence of the temperature difference between the electrodes on the power generation performance of the fuel cell 8 under high temperature conditions is examined.

  In the experiment shown in FIG. 3, the temperature of the cathode-side separator 6 is fixed at 90 ° C., and the temperature of the anode-side separator 4 is 90 ° C. (Comparative Example 2), 80 ° C. (Example 4), 70 ° C. (Example). Each data is taken differently from 5). In the experiment, the temperature difference between the separators 4 and 6 is generated by making the temperature of the refrigerant on the anode side lower than the temperature of the refrigerant on the cathode side. The hydrogen gas supplied to the anode is adjusted so that the relative humidity is 100% at a temperature of 53 ° C. at the inlet of the fuel cell 8. The air supplied to the cathode is also adjusted so that the relative humidity is 100% at a temperature of 53 ° C. at the inlet of the fuel cell 8.

  According to the experimental results shown in FIG. 3, the power generation performance is clearly higher in Examples 4 and 5 than in Comparative Example 2. That is, it was confirmed that high power generation performance can be obtained by providing a clear temperature difference between the separators 4 and 6 even under high temperature conditions. In the experiment, the temperature difference between the separators 4 and 6 is set to 10 ° C. However, as described above, this temperature difference may be 5 ° C. or more. However, if the operating temperature is high, the temperature difference between the separators 4 and 6 is increased accordingly, so that a temperature difference can be clearly generated between the electrodes.

[Specific configuration example of fuel cell stack]
Hereinafter, the configuration of the fuel cell stack for facilitating the temperature of the anode-side separator to be lower by 5 ° C. or more than the temperature of the cathode-side separator will be specifically described. FIG. 4 is an exploded view showing a configuration of a fuel cell stack suitable for applying the present invention. In FIG. 4, each member constituting the fuel cell stack is shown exploded in the stacking direction. However, the configuration of the fuel cell stack shown in FIG. 4 is one configuration example of the fuel cell stack to which the present invention can be applied, and the application of the present invention is not limited to the configuration of such a configuration.

  The fuel cell stack is configured by stacking a plurality of fuel cells (hereinafter referred to as cells) 8. The configuration shown in FIG. 4 has the characteristics of the cells 8. Each cell 8 is arranged so that the same polarity as the adjacent cell 8 faces each other. That is, this fuel cell stack is configured by alternately stacking cells 8A arranged with the anode-side separator 4 facing the stacking direction and cells 8B arranged with the cathode-side separator 6 facing the stacking direction. Yes. Hereinafter, when distinguishing cells having different orientations, they are denoted by reference numerals 8A and 8B, and when not distinguished, they are denoted by reference numeral 8.

  An insulator 10 or 20 is disposed between the adjacent cells 8A and 8B. This is because when the adjacent cells 8A and 8B are directly stacked, the anode electrodes or the cathode electrodes are connected to each other. A refrigerant flow path 12 through which a refrigerant flows is formed inside the insulator 10 disposed between the anode side separators 4 of the cells 8A and 8B. A coolant channel 22 through which a coolant flows is also formed inside the insulator 20 disposed between the cathode side separators 6 of the cells 8A and 8B. By forming the coolant flow paths 12 and 22 in the insulators 10 and 20 in this way, the shape of the separators 4 and 6 can be simplified, and the structure for sealing the coolant can be simplified. Can do.

  Since the insulators 10 and 12 are disposed between the plurality of stacked cells 8, the cells 8 are separated from each other. However, in order for the assembly of these cells 8 to function as a fuel cell stack, each cell 8 needs to be connected in series. Therefore, the fuel cell stack includes an external circuit 30 as means for connecting the cells 8 in series. The external circuit 30 electrically connects the anode side separator 4 of the cell 8B to the cathode side separator 6 of the cell 8A from the outside, and connects the cathode side separator 6 of the cell 8B to the anode side separator 4 of the reverse side cell 8A from the outside. Electrically connected.

  According to the configuration shown in FIG. 4, each cell 8 is stacked so that the same polarity as the adjacent cell 8 faces each other, so that the anode and the cathode are not adjacent to each other with the separators 4 and 6 interposed therebetween. Both electrodes are adjacent to each other with an electrolyte membrane having a remarkably lower thermal conductivity than that of the separators 4 and 6. According to such a configuration, thermal diffusion between the electrodes can be suppressed, and management of the temperature difference between the electrodes becomes easy. Further, by arranging the insulator 10 or 12 between the adjacent cells 8A and 8B, the temperature management can be performed integrally while electrically insulating the same polarity of the adjacent cells 8A and 8B. .

  In the configuration shown in FIG. 4, for example, the following method can be considered as a method of providing a temperature difference of 5 ° C. or more between the anode side separator 4 and the cathode side separator 6. The method is to create a temperature difference between the refrigerant flowing in the anode-side refrigerant flow path 12 and the refrigerant flowing in the cathode-side refrigerant flow path 22. This is because the thermal diffusion between the electrodes can be suppressed according to the configuration shown in FIG. 4, so that the temperature difference between the refrigerants can be made the temperature difference between the separators 4 and 6 as it is.

  If the refrigerant flowing in the anode-side refrigerant flow path 12 and the refrigerant flowing in the cathode-side refrigerant flow path 22 are different systems, the temperature of the refrigerant flowing in each refrigerant flow path 12, 22 can be set individually. it can. In that case, the temperature difference of the refrigerant is controlled according to the operating temperature of the fuel cell stack. For example, when the operating temperature is 80 ° C., the temperature difference of the refrigerant is controlled so that a difference of 5 ° C. or more is generated between the separators 4 and 6, and when the operating temperature is 90 ° C., the temperature difference of 10 ° C. or more is The temperature difference of the refrigerant is controlled so as to occur between the six. According to this, even when the operating temperature of the fuel cell stack changes, it is possible to always maintain the power generation performance of the fuel cell in the highest state.

  Establishing a temperature difference between the hydrogen gas supplied to the anode and the air supplied to the cathode is also effective in providing a temperature difference of 5 ° C. or more between the separators 4 and 6. If hydrogen gas having a temperature lower than that of the air supplied to the cathode is supplied to the air, the temperature of the anode-side separator 4 is advantageously reduced to a lower level than the temperature of the cathode-side separator 6.

  It is also effective to make the cathode-side separator 6 thicker than the anode-side separator 4 to provide a temperature difference of 5 ° C. or more between the separators 4 and 6. According to this, since the heat capacity on the cathode side is larger than the heat capacity on the anode side, the cathode side is less likely to be cooled by the refrigerant than the anode side, resulting in a clear temperature difference between the separators 4 and 6. become. The same effect can be obtained by making a difference between the thickness of the cathode-side insulator 20 and the thickness of the anode-side insulator 10.

  Making the cathode-side separator 6 and the anode-side separator 4 with different materials having different thermal conductivities is also effective in providing a temperature difference of 5 ° C. or more between the separators 4 and 6. If the thermal conductivity of the cathode separator 6 is made smaller than that of the anode separator 4, the cathode side is less likely to be cooled by the refrigerant than the anode side, resulting in a temperature difference between the separators 4 and 6. Can be made. The same effect can be obtained by forming the cathode-side insulator 20 and the anode-side insulator 10 with different materials having different thermal conductivities.

  Making the cathode-side diffusion layer thicker than the anode-side diffusion layer is also effective in providing a temperature difference of 5 ° C. or more between the separators 4 and 6. This is because if the thickness of the diffusion layer is increased, the heat capacity is increased accordingly, so that heat is easily generated inside. Further, as a result of the increase in internal resistance, an increase in heat generated by the resistance is also advantageous in causing a temperature difference between the separators 4 and 6.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

It is a figure which shows schematic structure of the fuel cell to which this invention is applied. It is a figure which shows the result of the experiment which investigated the influence which the temperature difference between electrodes has on the power generation performance of a fuel cell. It is a figure which shows the result of the experiment which investigated the influence which the temperature difference between electrodes has on the power generation performance of a fuel cell in high temperature conditions. FIG. 2 is an exploded view showing a configuration of a fuel cell stack suitable for applying the present invention.

Explanation of symbols

2 Membrane electrode assembly 4 Anode separator 4a Gas flow path 6 Cathode side separator 6a Gas flow path 8, 8A, 8B Fuel cell (cell)
DESCRIPTION OF SYMBOLS 10 Anode side insulator 12 Anode side refrigerant flow path 20 Cathode side insulator 22 Cathode side refrigerant flow path 30 External circuit

Claims (4)

In a fuel cell comprising means for causing a temperature difference between the anode side and the cathode side across the electrolyte membrane,
The fuel cell operating method is characterized in that the operation is performed by lowering the temperature of the separator adjacent to the anode by 5 ° C. or more than the temperature of the separator adjacent to the cathode. The means for generating the temperature difference is to provide a difference between the temperature of the anode gas supplied to the anode and the temperature of the cathode gas supplied to the cathode,
The temperature of the separator adjacent to the anode is lowered by 5 ° C. or more than the temperature of the separator adjacent to the cathode by lowering the temperature of the anode gas than the temperature of the cathode gas. How to operate a fuel cell. The means for causing the temperature difference includes flowing a refrigerant for cooling the anode and a refrigerant for cooling the cathode through separate flow paths, and the temperature of the refrigerant for cooling the anode and the temperature of the refrigerant for cooling the cathode. Is to make a difference between
By making the temperature of the refrigerant for cooling the anode lower than the temperature of the refrigerant for cooling the cathode, the temperature of the separator adjacent to the anode is lowered by 5 ° C. or more than the temperature of the separator adjacent to the cathode. 2. A method of operating a fuel cell according to claim 1, wherein A plurality of fuel cells are formed by sandwiching both sides of an electrolyte membrane between an anode and a cathode and sandwiching both sides with a separator. Each stacked fuel cell sandwiches an adjacent fuel cell, an insulator, and a coolant channel. In the fuel cell stack that is arranged so that the same poles face each other, and the separator of each fuel cell is connected in series with an external circuit to the separator of another fuel cell,
By making the temperature of the refrigerant flowing between the separators adjacent to the anode lower than the temperature of the refrigerant flowing between the separators adjacent to the cathode, the temperature of the separator adjacent to the anode is made lower than the temperature of the separator adjacent to the cathode. And operating at a temperature lower than 5 ° C.

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