JPH0878033A - Solid polymer fuel cell and its operation method - Google Patents

Abstract

PURPOSE: To adequately hold the state of an electrolyte film to stabilize operation by controlling the flow of a heating medium to a solid polymer fuel cell to control cell surface inside temperature distribution so that reaction gas outlet side temperature is always higher than others. CONSTITUTION: An electrolyte layer made of a solid polymer film is interposed between a fuel electrode and an oxidizing agent electrode to constitute a cell. A plurality of cells are stacked through a separator, and a heating medium flow path is arranged to form a stack 11. A fuel gas and an oxidizing gas are supplied to the cell to generate d.c. power. In the solid polymer fuel cell, valves 3 to 6 are installed in heating medium flow paths 13 to 17 for circulating a heating medium to the stack 11. In the start of operation of the cell or during low load operation, the heating medium is passed from the lower part of the cell surface to the upper part. During normal operation, a cooling medium is passed from the upper part to the lower part. Cell surface inside temperature is adequately controlled to prevent drying and produced water condensation on the surface of a solid electrolyte film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention appropriately controls the in-plane temperature distribution of a solid polymer electrolyte fuel cell at any time of startup, low load operation and steady operation to provide a solid polymer electrolyte. The present invention relates to a method and a device for preventing the membrane from drying and excessively wetting, and performing a stable operation of a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art Fuel cells are classified into solid polymer fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid electrolyte fuel cells, etc., depending on the type of electrolyte used and the operating temperature. Be separated. Compared to other fuel cell systems, the polymer electrolyte fuel cell has a higher tolerance for the differential pressure between both electrodes, and because it is easier to pressurize the cell, a high output density can be obtained. It has the feature that a carbon dioxide-containing gas can be used. Furthermore, because it is a low temperature operation type,
There are few restrictions in terms of battery constituent materials, and it can be started at room temperature in a short time.

FIG. 5 shows the basic structure of a polymer electrolyte fuel cell. The unit cell 8 has an anode 74a and a cathode 74b on both surfaces of the solid polymer electrolyte membrane 7, and further has current collectors 75a and 75b on both outer surfaces thereof. The current collector 75a is a fuel gas passage. 29a and the current collector 75b have an oxidant gas passage 29b. Further, the outside thereof is sandwiched by the gas impermeable separators 76a and 76b.

To maintain high power generation efficiency of a fuel cell,
Since it is necessary to keep the solid polymer electrolyte membrane in a wet state, the reaction gas is humidified in advance and then supplied to the cell. The fuel gas and the oxidant gas supplied to the cell are consumed by the following electrochemical reaction at the three-phase interface formed by the catalyst in each catalyst layer and the solid polymer electrolyte.

[0005]

[Chemical formula 1] H ₂ → 2H ⁺ + 2e ^- anode

[0006]

Embedded image (1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O cathode As described above, water is produced at the cathode as a whole reaction, and the protons moving from the anode to the cathode are in the solid polymer film. To move in the hydrated state, that is, water is generated on the cathode side. Since the polymer electrolyte fuel cell is a low-temperature operation type, the produced water is liquid, and one that passes through the polymer electrolyte membrane from the cathode to the anode due to its concentration gradient, or one that remains as water droplets in the cathode There is. In any case, it is necessary to remove the generated water to the outside of the system because the cell characteristics deteriorate due to the reduction of reaction sites due to the generated water near the electrode catalyst layer, the inhibition of the reaction gas diffusion, the local swelling of the solid polymer electrolyte membrane, etc. There is.

Regarding a cooling method of a polymer electrolyte fuel cell that has been conventionally adopted, as shown in, for example, Japanese Patent Application Laid-Open No. 5-144451 and Japanese Patent Application No. 5-269344, a cooling unit is provided inside. There is a cooling unit in which a cooling medium is circulated to form an in-plane temperature distribution of the fuel cell.
FIG. 6 shows a cell cross-sectional view of a polymer electrolyte fuel cell which represents a conventional means for forming a temperature distribution in a cell surface.

A plurality of cooling medium flow paths 65 are provided in the separators 76a and 76b in parallel with the reaction gas flow paths 29a and 29b.
Is provided, and the cooling medium and the reaction gas are made to flow in the same direction, the cooling medium flowing in from one end of the separators 76a and 76b absorbs heat generated by power generation of the cells and rises in temperature. Low on the reaction gas inlet side,
It becomes higher on the reaction gas outlet side. Since the reaction product water is released as water vapor into the reaction gas flowing through the reaction gas passage, the water vapor concentration in the reaction gas gradually increases in the flowing process, that is, the water vapor pressure gradually increases. By forming the reaction gas outlet side temperature to be high, the water vapor absorption capacity at the reaction gas outlet side is maintained. That is, by controlling the reaction gas so that it flows into the reaction gas passage from the side where the in-cell temperature is low and is discharged from the side where the in-cell temperature is high, the water vapor pressure of the reaction gas and the catalyst layer reaction The saturated water vapor pressure in each part is low in the in-plane temperature of the cell, low in the high temperature side, and high in the high temperature side. Therefore, in any part of the cell surface, the generation and the discharge of water are balanced, so that the solid polymer electrolyte membrane is prevented from being dried and the catalyst layer is prevented from being excessively wetted due to the condensation of the generated water. In addition, it is possible to prevent deterioration of battery characteristics.

FIG. 7 schematically shows a heating medium piping system of a conventional polymer electrolyte fuel cell. The temperature of the heat medium in the heat medium tank 1 is controlled, and this heat medium pump 2 is circulated as a cooling medium by the heat medium pump 2, and the cooling medium is transferred from the heat medium upper port 12 to the heat medium lower port 10 inside the stack 11. Flow through. Here, the heat medium is
Since the reaction heat is absorbed when flowing through the heat medium flow path, a temperature distribution in the cell plane that gradually increases in the reaction gas flowing direction is formed.

By the way, the heat balance of the fuel cell is constituted by internal heat generation by power generation, heat radiation to the outside of the cell, and exhaust heat by cooling water. Therefore, when the power generation is low, that is, in the low load operation, the heat radiation to the outside of the system becomes larger than the heat generation inside the fuel cell, and the temperature of the cell may decrease.
This state is called low load operation. Since the temperature of the fuel cell is low during such low load operation and startup, a heating medium is supplied as a heat medium to raise the operating temperature of the fuel cell.

[0011]

In the conventional method for operating a fuel cell as described above, the heating medium at the time of start-up and at the time of low-load operation flows while flowing from the upper part inside the cell surface to the lower part inside the cell surface. The fuel cell in the low temperature state takes heat to lower the temperature, and the temperature distribution in the lower part is lower in the cell plane than in the upper part. For this reason, there is a drawback that the generated water is not smoothly discharged at the time of starting the fuel cell and at the time of low load operation.

In view of the above-mentioned problems of the prior art, the present invention prevents drying and condensation of generated water on the surface of the solid polymer electrolyte membrane in any state of starting the fuel cell, low load operation and steady operation. It is an object of the present invention to provide an appropriate polymer electrolyte fuel cell and its operating method.

[0013]

To achieve the above object, first of all, a single cell integrated body (stack) in which a plurality of cells, which receive a supply of a fuel gas and an oxidant gas and generate a direct current power, are stacked through a separator, A heat medium flow path for allowing a heat medium that is a cooling medium or a heating medium to flow therethrough in each of the cells or in each of a plurality of cells in the stack, and the cells include an electrolyte layer formed of a solid polymer membrane; In a method of operating a polymer electrolyte fuel cell having a fuel electrode (anode) and an oxidant electrode (cathode), which are respectively disposed with the electrolyte layer sandwiched between them, during start-up, low-load operation and steady-state operation In any state, the heat medium is passed through so that the temperature inside the cell surface is higher than the reaction gas inlet side temperature (cell surface upper temperature) than the reaction gas outlet side temperature (cell surface lower temperature). Letting it flow More is achieved.

In the method for operating a polymer electrolyte fuel cell described above, the heating medium is caused to flow from the lower part inside the cell surface to the upper part inside the cell surface at the time of start-up or low load operation, and within the cell surface during steady operation. This is achieved by flowing the cooling medium from the upper part to the lower part in the cell plane. In the method for operating the polymer electrolyte fuel cell, it is achieved by reversing the heat medium flow direction at the time of startup or low load operation and the heat medium flow direction at the time of steady operation. .

Further, a unit cell stack (stack) in which a plurality of cells, which receive the supply of the fuel gas and the oxidant gas and generate DC power, are stacked via a separator, and each cell in the stack or Each of a plurality of cells is provided with a heat medium passage for allowing a heat medium that is a cooling medium or a heating medium to flow therethrough, the heat medium tank and a heat medium circulation pump, and the cell is an electrolyte composed of a solid polymer membrane. In a polymer electrolyte fuel cell having a layer, and a fuel electrode (anode) and an oxidant electrode (cathode), which are arranged with the electrolyte layer sandwiched therebetween, a heat transfer medium at start-up or during predetermined low load operation is used. This is achieved by providing a heat medium flow direction switching valve device that reverses the flow direction and the heat medium flow direction during steady operation.

Further, in the above solid polymer fuel cell, the heat medium flow direction switching valve device is achieved by having four on / off valves. Further, in the polymer electrolyte fuel cell, the heat medium flow direction switching valve device is achieved by including two three-way valves.
In the polymer electrolyte fuel cell described above, the heat medium flow direction switching valve device is achieved by including a 5-way valve.

In the polymer electrolyte fuel cell, a temperature sensor for measuring the inlet / outlet temperature of the heat carrier of the polymer electrolyte fuel cell, and the output of the temperature sensor are used to determine the temperature of the heat medium above and below the heat medium below the heat medium. When the inlet / outlet temperature is higher, the heat medium is made to flow from the upper part to the lower part in the cell surface, and when the inlet / outlet temperature of the heat medium upper part is higher than the inlet / outlet temperature of the lower part of the heat medium, And a control device for controlling the current to flow from the upper part to the upper part.

[0018]

[Operation] When the fuel cell is started or when a predetermined low load operation is performed, the heating medium is caused to flow from the lower part inside the cell surface to the upper part inside the cell surface, and at the time of steady operation, it is cooled from the upper part inside the cell surface to the lower part inside the cell surface. By controlling using the heat medium flow direction switching valve device so that the medium flows, the temperature inside the cell surface is always higher than the reaction gas inlet side temperature (upper cell surface inside temperature) than the reaction gas outlet side temperature (cell It can be operated by maintaining the lower temperature in the plane). This ensures that at startup,
In all cases of low load operation and steady operation,
The saturated steam pressure in the reaction part of the catalyst layer is always higher in the lower part than in the upper part in the cell surface, and this tendency balances with the increasing tendency of the reaction gas steam pressure from the upper part in the cell surface to the lower part due to water generation. Can be realized. That is, since the generation and discharge of water are balanced, it is possible to prevent deterioration of cell characteristics due to condensation of generated water and drying of the solid polymer electrolyte membrane.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1; FIG. 1 is one of the embodiments of the present invention according to claim 5, and schematically shows a piping system of a heating medium of a polymer electrolyte fuel cell. At the time of starting the fuel cell or at the time of low load operation, the heat medium in the heat medium tank 1 is heated to raise the temperature of the fuel cell and sent to the system by the heat medium pump 2. By opening the valve 4 and the valve 5 and closing the valve 3 and the valve 6, the heating medium is supplied to the valve 4, the heat medium passage 16 and the heat medium passage 17
It flows through, enters the stack 11 from the lower heat medium inlet / outlet 10 in the cell plane, heats the stack, and is discharged from the upper heat medium inlet / outlet 12 in the cell plane. Then, it returns to the inside of the heat medium tank 1 via the heat medium path 13, the valve 5, and the heat medium path 15. When the temperature of the heat medium reaches a predetermined value, heating of the heat medium tank 1 becomes unnecessary and the circulation is continued as it is, but when the temperature of the heat medium further rises to the predetermined temperature, the valves 4 and 5 are closed and the valves 3 and 3 are closed. 6 is opened to let the heat medium flow as a cooling medium, and the mode is switched to the cooling mode of the fuel cell, and the steady operation is performed. The cooling medium is pressure-fed by the heat medium pump from the heat medium tank 1, and the valve 3,
It flows through the heat medium passage 13, and the upper heat medium inlet / outlet port 1 in the cell plane
2 enters the stack 11, cools the stack, and is discharged from the lower heat medium inlet / outlet 10 in the cell plane. Then, it returns to the inside of the heat medium tank 1 via the heat medium path 17, the heat medium path 14, the valve 6, and the heat medium path 15. What is called a valve here is of any type such as a manual valve, a solenoid valve, a pneumatic valve, a type that can be used for power saving, such as a magnetlatch valve, a mechanical latch valve, etc. Anything can be adopted.

Embodiment 2; FIG. 2 is one of different embodiments of the present invention according to claim 6 and schematically shows a piping system of a heat medium of a polymer electrolyte fuel cell. The same parts as those in the schematic diagram shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. The present embodiment differs from the first embodiment in that the piping system is simplified by using a three-way solenoid valve, and can be operated with low power consumption.

Similar to the path shown in FIG. 1, at the time of starting the fuel cell or operating at low load, the heat medium tank 1, the heat medium pump 2, the heat medium path 16, the valve 20, the heat medium path 1
7, the heating medium flows through the cell surface lower heat medium inlet / outlet 10, the cell surface upper heat medium inlet / outlet 12, the valve 19, and the heat medium passage 15. On the contrary, during steady operation, the heat medium tank 1, the heat medium pump 2, the valve 19, the heat medium path 13, the upper heat medium inlet / outlet 12 in the cell plane, and the lower heat medium inlet / outlet 1 in the cell plane
The cooling medium flows in the order of 0, the heat medium passage 17, the valve 20, the heat medium passage 14, and the heat medium passage 15.

Embodiment 3; FIG. 3 is one of different embodiments of the present invention according to claim 7, and schematically shows a piping system of a heat medium of a polymer electrolyte fuel cell. The same parts as those in the schematic diagram shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. The present embodiment differs from the first and second embodiments in that the piping system is further simplified by using a 5-way solenoid valve, and can be operated with further power saving.

At the time of starting the fuel cell or operating at low load, the connection port 21 and the connection port 24 of the five-way solenoid valve 26,
The connection port 22 and the connection port 25 are connected, and the connection port 23
Is closed. Therefore, the heating medium is supplied into the stack 11 from the lower heat medium inlet / outlet 10 in the cell plane, and discharged toward the upper heat medium inlet / outlet 12 in the cell plane, and the heat medium tank 1
Return to On the contrary, during steady operation, the five-way solenoid valve 26
The connection port 21 and the connection port 23, the connection port 22 and the connection port 24 are connected, and the connection port 25 is closed. Therefore,
The cooling medium is supplied into the stack 11 from the upper heat medium inlet / outlet port 12 in the cell plane, discharged toward the lower heat medium inlet / outlet port 10 in the cell plane, and returned to the heat medium tank 1.

In any of the first, second, and third embodiments described above, a state in which the heat medium upper inlet / outlet 12 is at a higher temperature than the heat medium lower inlet / outlet 10 is set to a predetermined low load state or no load state ( At the time of startup), the means for detecting the temperature of the upper and lower inlet / outlet ports of the heat medium is, for example, a temperature sensor. In addition, in the first to third embodiments, other than the above-described method of determining the start-up time or the predetermined low load state and the steady state based on the output of the temperature sensor, for example, the fluctuation of the load current of the fuel cell is detected. It can also be done by doing. However, in that case, the reversal of the in-cell temperature distribution has a certain delay in the timing of reaching a predetermined low load state, and this needs to be taken into consideration. Further, in any of Examples 1, 2 and 3, the operating methods of Claims 1, 2 and 3 can be carried out in the polymer electrolyte fuel cell.

Embodiment 4; FIG. 4 is one of the different embodiments of the present invention according to claim 8 and schematically shows a piping system of a heat medium of a polymer electrolyte fuel cell. The same parts as those in the schematic diagrams shown in FIGS. 1 and 3 are designated by the same reference numerals, and the description thereof will be omitted. FIG. 4 shows the heat medium upper port 1
2 and a temperature sensor 40 near the lower entrance 10 of the heat medium,
The third embodiment is different from the third embodiment in that each unit is provided with a control device 18, and the control device 18 is arranged in the control device 41, and a method of comparatively measuring each temperature is adopted.

The inlet / outlet temperature of the polymer electrolyte fuel cell of the heat medium is detected by the temperature sensors 40 and 41, and the output signals of the temperature sensors 40 and 41 are input to the control device 18. The control device 18 determines the flow direction of the heat medium to flow into the fuel cell based on the output signals of the temperature sensors 40 and 41, and further determines the flow direction of the five-way valve 2.
Switching control is performed by the connection ports 21 to 25 of 6. When the heat medium outlet temperature is higher than the heat medium inlet temperature in the stack 11, that is, when the temperature detected by the temperature sensor 41 is higher than the temperature detected by the temperature sensor 40, the cooling medium is moved from the upper part to the lower part in the cell plane. When the heat medium inlet temperature is higher than the heat medium outlet temperature, conversely, the heating medium is controlled so as to flow from the lower part in the cell plane to the upper part. The control device 18 also includes temperature sensors 40 and 41.
It is determined whether the heat medium of the fuel cell should be used as the heating medium or the cooling medium based on the output of 1. and the heat medium in the heat medium tank 1 is heated or cooled by the temperature control device (not shown) based on this determination. The heating medium and the cooling medium are obtained, for example, by controlling the temperature of the heating medium by a temperature control device (not shown) provided with a heating heater and a cooling device provided in the heating medium tank 1.

[0027]

According to the present invention, by adopting the above-described structure and operating method, the reaction gas is always supplied at any time of starting, low load operation and steady operation of the polymer electrolyte fuel cell. It can be operated by controlling so that the reaction gas outlet side temperature (cell surface lower temperature) is higher than the inlet side temperature (cell surface upper temperature), and prevents the solid polymer electrolyte membrane from drying and excessive wetting. As a result, stable cell output characteristics can always be obtained.

Further, since the solenoid valve is used in the heat medium pipe passage, the pipe can be simplified and the work can be simplified. Furthermore, by using the temperature sensor control device in the heat medium piping path, it becomes possible to automatically control the in-plane temperature distribution of the fuel cell unit.

[Brief description of drawings]

FIG. 1 is a heat medium piping system diagram of a polymer electrolyte fuel cell according to an embodiment of the present invention.

FIG. 2 is a heat medium piping system diagram of a polymer electrolyte fuel cell according to another embodiment of the present invention.

FIG. 3 is a heat medium piping system diagram of a polymer electrolyte fuel cell according to still another embodiment of the present invention.

FIG. 4 is a heat medium piping control system diagram equipped with a temperature sensor for a polymer electrolyte fuel cell according to still another embodiment of the present invention.

FIG. 5: Basic configuration diagram of polymer electrolyte fuel cell

FIG. 6 is a cell cross-sectional view of a conventional polymer electrolyte fuel cell in a cooling configuration that forms a temperature distribution in a cell plane.

FIG. 7: Heat medium piping control system diagram of a conventional polymer electrolyte fuel cell

[Explanation of symbols]

 1 Heat medium tank 2 Heat medium pump 3, 4, 5, 6 Valve 19, 20 3 Directional valve 26 5 Directional valve 21 to 25 5 Directional valve connection port 13 to 17 Heat medium path 18 Controller 8 Single cell 7 Solid polymer Electrolyte membrane 11 Stack 74 a Anode 74 b Cathode 75 a, 75 b Current collector 65 Coolant channel 12 Heat medium upper inlet / outer 10 Heat medium lower inlet / outer 40 Temperature sensor 41 Temperature sensor 29 a Fuel gas passage 29 b Oxidant gas Flow path 76 a, 76 b Separator

Claims (8)

[Claims] 1. A unit cell integrated body (stack) in which a plurality of cells, which receive a supply of a fuel gas and an oxidant gas and generate direct current power, are stacked via a separator, and each of the cells in the stack, or For multiple cells,
A heating medium flow path for passing a heating medium that is a cooling medium or a heating medium is provided, and the cell includes an electrolyte layer made of a solid polymer membrane, and fuel electrodes (anodes) respectively arranged with the electrolyte layer sandwiched therebetween. )
In a method of operating a polymer electrolyte fuel cell having an oxidizer electrode (cathode) and an oxidizer electrode (cathode), the cell surface temperature is the temperature at the inlet side of the reaction gas at any of startup, low load operation and steady operation. A method for operating a polymer electrolyte fuel cell, characterized in that the heat medium is caused to flow so that the reaction gas outlet side temperature (cell surface lower temperature) is higher than the (cell surface upper temperature). 2. The method for operating a polymer electrolyte fuel cell according to claim 1, wherein the heating medium is made to flow from the lower part inside the cell surface to the upper part inside the cell surface at the time of start-up or low load operation, and at the time of steady operation. A method for operating a polymer electrolyte fuel cell, characterized in that a cooling medium is caused to flow from an upper portion in the cell plane to a lower portion in the cell plane. 3. The operating method of the polymer electrolyte fuel cell according to claim 1, wherein the heat medium flowing direction at the time of start-up or low load operation is opposite to the heat medium flowing direction at the time of steady operation. A method for operating a polymer electrolyte fuel cell, comprising: 4. A unit cell integrated body (stack) in which a plurality of cells, which receive a supply of a fuel gas and an oxidant gas and generate a direct current power, are stacked with a separator interposed therebetween, and in the stack, each cell or each cell. For multiple cells,
A heat medium passage for allowing a heat medium that is a cooling medium or a heating medium to flow therethrough; and a heat medium tank and a heat medium circulation pump, wherein the cell is an electrolyte layer made of a solid polymer membrane, and the electrolyte layer. Fuel electrodes (anode) that are respectively placed across the
In a polymer electrolyte fuel cell having a cathode and an oxidizer electrode (cathode), a heat medium in which the heat medium flowing direction at the time of start-up or a predetermined low load operation is opposite to the heat medium flowing direction at the time of steady operation A polymer electrolyte fuel cell comprising a flow direction switching valve device. 5. The polymer electrolyte fuel cell according to claim 4, wherein the heat medium flow direction switching valve device has four on / off valves. 6. A polymer electrolyte fuel cell according to claim 4, wherein the heat medium flow direction switching valve device comprises two three-way valves. 7. The polymer electrolyte fuel cell according to claim 4, wherein the heat medium flow direction switching valve device has a five-way valve. 8. The solid polymer fuel cell according to claim 4, wherein a temperature sensor for measuring the inlet / outlet temperature of the heat medium in the polymer electrolyte fuel cell, and the output of the temperature sensor are used to determine the inlet / outlet temperature of the upper portion of the heat medium. If the lower heating medium inlet / outlet temperature is higher, the heating medium is made to flow from the upper part to the lower portion in the cell plane, and if the heating medium upper / lower inlet temperature is higher than the lower heating medium inlet / outlet temperature, the heating medium is A polymer electrolyte fuel cell, which is provided with a control device for controlling the flow from the lower part to the upper part in the cell plane.