JP3918999B2 - Direct methanol fuel cell system and its operation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct methanol fuel cell system capable of generating electricity by directly supplying an aqueous methanol solution as a liquid fuel and, more specifically, to a method for operating or storing the system in a cold region. The present invention relates to a configuration of a suitable direct methanol fuel cell system and an operation method capable of smoothly starting the system.
[0002]
[Prior art]
In recent years, countermeasures to environmental problems and resource problems have been emphasized, and fuel cells have been actively developed as one of the countermeasures. In particular, direct methanol fuel cells that directly use methanol power as a liquid fuel for power generation without reforming or gasification are simple in structure, small in size, and easy to reduce in weight. It is attracting attention as a power source for equipment, a power source for computers, and a portable power source.
[0003]
The direct methanol fuel cell described above has a configuration in which both sides of the electrolyte are sandwiched between a negative electrode and a positive electrode, an aqueous methanol solution as a liquid fuel is supplied to the negative electrode, and air as an oxidant gas is supplied to the positive electrode. It consists of a cell stack in which a plurality of cells having a configuration to be supplied are stacked. In this cell stack, an aqueous methanol solution is supplied to the negative electrode of each cell, air is supplied to the positive electrode, and generated by an electrochemical reaction of each cell. A separator having a channel groove and a manifold for discharging the reaction product is inserted between the cells.
[0004]
That is, the flow channel and manifold of the separator serve to supply an aqueous methanol solution to the negative electrode, supply air to the positive electrode, and discharge generated carbon dioxide from the negative electrode and discharged water from the positive electrode. .
[0005]
In such a direct methanol fuel cell, when an aqueous methanol solution is supplied to the negative electrode and air is supplied to the positive electrode, methanol and water react at the negative electrode to generate carbon dioxide and release hydrogen ions and electrons. Oxygen in the air takes in the hydrogen ions and electrons that have passed through the electrolyte to generate water, and generates electric energy in an external circuit.
[0006]
In the direct methanol fuel cell described above, it is preferable to increase the concentration of the methanol aqueous solution from the viewpoint of its output characteristics. However, when the concentration is increased, the methanol aqueous solution permeates the electrolyte composed of the proton conductive solid polymer membrane ( Therefore, it is necessary to determine the concentration of the methanol aqueous solution in consideration of the decrease in efficiency due to the increase in the permeation amount of the methanol aqueous solution. In other words, the output characteristics and efficiency depend on the operating temperature and the methanol aqueous solution. There is a feature that it greatly depends on operating conditions such as the concentration of air and the amount of air supplied.
[0007]
In addition, such a direct methanol fuel cell is preferably operated at an ambient temperature of 30 to 90 ° C. in order to stably obtain a high output, but the operable temperature range is 0 to 100 ° C. Since such direct methanol fuel cells can be installed or stored indoors or outdoors in cold regions as distributed power sources, even in such cases, startup is smooth. Making it possible is becoming essential. That is, it has been essential to be able to start up smoothly even if installed or stored in an atmosphere at a temperature of -20 ° C.
[0008]
[Problems to be solved by the invention]
However, proton conductive solid polymer membranes such as Nafion (registered trademark) used as an electrolyte for direct methanol fuel cells have water in the membrane, and direct methanol fuel cells are used in the atmosphere described above. When installed, it not only freezes and does not start smoothly, but once it has been operated and stored in the atmosphere described above, water remaining in the positive electrode, the separator on the positive electrode side or the piping system is frozen. As a result, there was a problem that the restart could not be performed smoothly.
[0009]
[Means for Solving the Problems]
The present invention has been made to solve the above-described problems. The invention according to claim 1 is configured such that a negative electrode and a positive electrode are opposed to each other through an electrolyte composed of a proton conductive solid polymer film. An aqueous methanol solution having a cell provided with a structure for supplying an oxidant gas to the positive electrode or a cell stack in which a plurality of these cells are stacked, and a methanol concentration of 1 to 8% supplied to the cell or the cell stack And a temperature raising means for raising a temperature of the liquid fuel by supplying a part of the liquid fuel from the fuel storage unit between the fuel storage unit and the cell or the cell stack. It is characterized by that. According to the first aspect of the present invention, even when starting up in an atmosphere such as −20 ° C. or when restarting after storing in the above-mentioned atmosphere after operating once, Since the temperature of the liquid fuel can be increased up to about 30 ° C., which is a temperature at which stable operation is possible, the start-up and restart under the atmosphere described above can be performed smoothly and more than necessary by the temperature raising means. It is possible to prevent the aqueous methanol solution from being consumed .
[0010]
In the direct methanol fuel cell system of the present invention , it is preferable to inject and hold at least a part of the liquid fuel from the fuel storage unit into the cell or the cell stack during standby of the system operation. According to this, it is possible to prevent the freezing of moisture in the proton conductive solid polymer membrane by the injected liquid fuel, and further, when a part of the liquid fuel is also injected into the piping system connected to the cell or the cell stack. The problem of water remaining in the piping system and hindering restarting can also be solved.
[0011]
The invention described in claim 2 is characterized in that, in the direct methanol fuel cell system described in claim 1 , the temperature raising means has a bypass flow path for bypassing it. According to the second aspect of the present invention, after starting or restarting, the liquid fuel can be supplied to the cell or the cell stack via the bypass flow path. Can be prevented.
[0013]
In the direct methanol fuel cell system of the present invention , the fuel storage unit includes a fuel tank that stores a liquid fuel mainly composed of an aqueous methanol solution whose concentration is maintained at 1 to 8%, and a concentration of 8 to 60%. consists of a high-concentration methanol tank composed mainly of the aqueous methanol solution is maintained, it is preferred that a heating device is provided between the high-concentration methanol tank and a cell or cell stack. According to this , at the time of start-up and restart, a part of the methanol aqueous solution maintained at a relatively high concentration of 8 to 60% can be supplied to the temperature raising means and the temperature can be quickly raised. At the same time, the temperature of the system can be increased by the crossover of the aqueous methanol solution, so that the startup and restart described above can be performed more smoothly.
[0014]
In the direct methanol fuel cell system of the present invention , it is preferable to inject and hold a part of the high-concentration methanol aqueous solution from the high-concentration methanol tank into at least a cell or a cell stack during standby of the system operation. According to this , water freezing in the proton conductive solid polymer membrane can be prevented by the high concentration methanol aqueous solution injected, and a part of the high concentration methanol aqueous solution is also injected into the piping system connected to the cell or cell stack. By doing so, the problem that water remains in the piping system and the restarting is hindered can be solved.
[0015]
A cell having a configuration in which a negative electrode and a positive electrode are opposed to each other through an electrolyte composed of a proton conductive solid polymer membrane, a liquid fuel is supplied to the negative electrode, and an oxidant gas is supplied to the positive electrode, or a plurality of such cells are stacked. In the operation method of the direct methanol fuel cell system according to the present invention, the direct methanol fuel cell system of the present invention is operated, wherein the direct methanol fuel cell system provided with a fuel storage section for storing the cell or the liquid fuel supplied to the cell stack is provided. A temperature raising means is provided between the fuel storage unit and the cell or cell stack to supply a part of the liquid fuel from the fuel storage unit to increase the temperature of the liquid fuel. It is preferable to increase the temperature of the liquid fuel by supplying to the temperature means. According to this , even in the case of startup or restart in an atmosphere of −20 ° C., it can be performed smoothly.
[0016]
In the operation method of the direct methanol fuel cell system of the present invention , the temperature raising means has a bypass flow path that bypasses the temperature raising means, and after starting, bypasses between the fuel storage unit and the cell or the cell stack. It is preferable to communicate with each other through a flow path. According to this , after starting or restarting, the liquid fuel can be flowed to the bypass flow path, so that it is possible to prevent the liquid fuel from being consumed more than necessary by the temperature raising means.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on the embodiments.
[0018]
FIG. 1 is a block diagram of a direct methanol fuel cell system according to an embodiment of the present invention. The feature of the direct methanol fuel cell system is that a cell stack 10 in which a plurality of cells are stacked has an aqueous methanol solution as a liquid fuel at the negative electrode. Configuration 1 for supplying, Configuration 2 for supplying air as an oxidant gas to the positive electrode, Configuration 3 for discharging a carbon dioxide produced at the negative electrode and a methanol aqueous solution that did not contribute to the reaction, Water produced at the positive electrode, The structure 4 for discharging the air that has not contributed to the reaction is provided. The structure 1 has a temperature raising means 6 for raising the temperature of the aqueous methanol solution at the time of start-up on the path leading to the fuel storage unit 5 for storing the liquid fuel, and this A bypass flow path 7 for bypassing the temperature raising means 6 and supplying the activated liquid fuel to the cell stack 10 is provided.
[0019]
The temperature raising means 6 preferably has the structure shown in FIG. That is, as shown in FIG. 2, a part of the pipe leading to the fuel storage unit 5 for storing the methanol aqueous solution is a porous pipe 61, and a glass fiber 62 coated with a platinum catalyst is an outer periphery of the porous pipe 61. Further, a synthetic resin-made outer tube 63 that also serves as a heat insulating layer, in which a large number of air introduction ports 630 are opened on the outer periphery of the glass fiber 62, is provided. When the aqueous methanol solution passes through the temperature raising means 6 having such a structure, it oozes into the glass fiber 62 from the porous pipe 61 and is oxidized by contacting air and the platinum catalyst to generate reaction heat and is porous. The aqueous methanol solution in the pipe 61 is heated, which can contribute to smooth start-up and restart of the direct methanol fuel cell system.
[0020]
In order to investigate the amount of heat generated by the temperature raising means 6, a porous pipe 61 having a length of 40 cm is prepared, and a glass fiber 62 coated with a platinum catalyst is wound around the porous pipe 61. A synthetic resin sheathing tube 63 that also serves as a heat insulating layer with an air inlet 630 is provided between the cell stack 10 and the fuel storage unit 5. When a methanol aqueous solution having a temperature of 0 ° C. and a concentration of 3% was flowed from the storage section 5 into the porous pipe 61 at 300 ml / min, the temperature of the methanol aqueous solution flowing out in about 20 minutes became 30 ° C. Thus, it was found that the air can be started by supplying air to the cell stack 10. On the other hand, when the same investigation was conducted without providing such a temperature raising means 6, the temperature of the methanol aqueous solution did not change even after 20 minutes, and it started even when air was supplied to the cell stack 10. I couldn't. The calorific value in this case is determined by the speed at which the methanol aqueous solution oozes from the porous pipe 61 (speed at which the methanol aqueous solution flows), the amount of platinum catalyst applied to the glass fiber 62, and the shape of the air inlet 630. It is preferable to determine appropriately according to the temperature at which the aqueous solution is heated.
[0021]
【Example】
Next, the above-described embodiment will be described based on specific examples.
[0022]
Example 1
FIG. 3 is a diagram showing the configuration of the direct methanol fuel cell system according to the first embodiment, in which the fuel storage unit 5 is a fuel tank 51 for storing a methanol aqueous solution having a concentration of 1 to 8% as a main component. is there. In this case, when the system is started or restarted in an atmosphere of −20 ° C., the aqueous methanol solution is supplied to the temperature raising means 6 through the pump 16 and the valve 15 to oxidize it. Since the temperature of methanol aqueous solution can be raised, the starting and restarting can be performed smoothly. Further, in FIG. 3, a bypass flow path 7 that bypasses the temperature raising means 6 is provided, and after the system is started or restarted, the aqueous methanol solution passes through the bypass flow path 7 and the cell stack via the pump 11 and the valve 12. 10 can be supplied. Thereby, it can prevent that methanol aqueous solution is oxidized more than necessary. In FIG. 3, reference numeral 23 denotes a valve for injecting an aqueous methanol solution into the configuration 2 when it is installed or stored in a cold region, which will be described later, and is closed during normal operation.
[0023]
(Example 2)
FIG. 4 is a diagram showing a configuration of a direct methanol fuel cell system according to the second embodiment. The fuel storage unit 5 includes a fuel tank 51 for storing a methanol aqueous solution having a concentration of 1 to 8% as a main component, and a main component. Is a high-concentration methanol tank 52 for storing a methanol aqueous solution having a concentration of 8 to 60%, and the methanol aqueous solution can be supplied from the fuel tank 51 to the cell stack 10 via the pump 11 and the valve 12, and the high-concentration methanol tank The high-concentration aqueous methanol solution can be supplied from 52 to the cell stack 10 via the pump 13, the valve 14, and the temperature raising means 6. In this case, when the system is started or restarted in an atmosphere of −20 ° C., the high-concentration methanol aqueous solution is heated from the high-concentration methanol tank 52 via the pump 13, the valve 18 and the valve 14. When this is supplied and oxidized, the temperature of the aqueous methanol solution can be quickly raised, and the temperature rise of the system can be promoted by crossover with a relatively high concentration of aqueous methanol solution. Furthermore, it can be performed smoothly. After startup, the pump 13 is stopped, the valves 18 and 14 are closed, and an aqueous methanol solution is supplied from the fuel tank 51 to the cell stack 10 via the pump 11 and the valve 12. Also in FIG. 4, a bypass channel 7 that bypasses the temperature raising means 6 is provided so that various configurations are possible. For example, by providing the bypass flow path 7, the valve 17 and the pump 19 as shown in FIG. 4, after the system is started or restarted, the valve 14 is closed and the valve 17 is opened as necessary. If a high concentration aqueous methanol solution can be supplied to the fuel tank 51, the concentration of the aqueous methanol solution in the fuel tank 51 can be controlled to be 1 to 8%. In addition, a function of supplying an aqueous methanol solution from the fuel tank 51 to the temperature raising means 6 via the pump 19, the valve 17, and the valve 14 can be provided. Further, when starting the cell stack 10 under a normal atmosphere, the high concentration methanol is transferred from the high concentration methanol tank 52 to the cell stack 10 via the pump 13, the valve 18, the valve 17, the pump 19, the pump 11 and the valve 12. Although a function of supplying an aqueous solution can be provided, the pump 19 may be omitted if only this function is provided.
[0024]
The cell has a negative electrode separator for supplying a liquid fuel such as a methanol aqueous solution to the negative electrode through an electrolyte composed of a proton conductive solid polymer membrane such as Nafion (registered trademark). The positive electrode side separator for supplying oxidizing gas, such as air, to the said positive electrode is provided. The negative electrode is a mixture of Nafion (registered trademark) and PTFE (polytetrafluoroethylene) in a conductive catalyst such as C (carbon) -Pt-Ru, and the positive electrode is, for example, C ( This is a mixture of Nafion (registered trademark) and PTFE (polytetrafluoroethylene) in a conductive catalyst such as (carbon) -Pt.
[0025]
Next, when operating such a direct methanol fuel cell system under normal conditions, the valve 21 shown in FIGS. 3 and 4 is opened and air is sent from the air blower 22 to the positive electrode of the cell stack 10. At the same time, the valve 12 is opened and a methanol aqueous solution is supplied from the fuel storage 5 to the negative electrode of the cell stack 10 by the pump 11. When transporting to a cold area of 5 ° C. or lower, or when installing or storing in preparation for operation in a cold area where the ambient temperature is −5 ° C. or lower, the valves 17 and 12 are opened as shown in FIG. Then, a high-concentration methanol aqueous solution is injected from the high-concentration methanol tank 52 to the cell stack 10 through the pump 11 and held therein. At this time, the high-concentration methanol aqueous solution is supplied not only to the cell stack 10 but also from the valve 12 to the configuration 1 for supplying liquid fuel to the negative electrode of the cell (pipe system), from the configuration 1 to the positive electrode of the cell via the valve 23. It is also preferable to inject into the path (pipe system) leading to the configuration 2 for supplying the oxidant gas, the configuration 3 for discharging carbon dioxide generated at the negative electrode, and the configuration 4 for discharging water generated at the positive electrode. It should be noted that such implantation can be similarly performed in the first embodiment shown in FIG. As a result, even in the cold district described above, the positive electrode, the separator on the positive electrode side, or the path (pipe system) can be filled with the high-concentration methanol aqueous solution, so that freezing of water remaining on the positive electrode and the positive electrode can be prevented. Moreover, at the time of starting, the high concentration methanol aqueous solution mentioned above can be removed by sending air from the air blower 22 to the positive electrode of the cell stack 10.
[0026]
In the above-described liquid fuel direct supply type fuel cell system, the cell stack 10 is formed by stacking a plurality of cells. However, the cell stack 10 may be replaced with a single cell.
[0027]
The concentration of the aqueous methanol solution stored in the high-concentration methanol tank 52 is about 8% or more when the ambient temperature is about −5 ° C., and about 25% or more when the ambient temperature is about −20 ° C. If the temperature is about −40 ° C., it is preferably about 40% or more. However, if the concentration is 60% or more, the possibility of ignition increases. Therefore, the upper limit of the concentration is preferably 60%.
[0028]
Further, the concentration of the aqueous methanol solution stored in the fuel tank 51 is maintained at 1 to 8%, which is a range in which good output characteristics can be obtained in consideration of a decrease in efficiency due to an increase in the permeation amount of methanol. It is good to do.
[0029]
【The invention's effect】
As described above, the present invention is useful for providing a configuration of a liquid fuel direct supply type fuel cell suitable for being installed in a cold region and an operation method capable of smoothly starting the fuel cell. It can contribute to the expansion of applications.
[Brief description of the drawings]
FIG. 1 is a block diagram of a direct methanol fuel cell system according to an embodiment of the present invention.
FIG. 2 is a diagram showing a structure of a temperature raising unit.
FIG. 3 is a diagram showing an example of a direct methanol fuel cell system according to an embodiment of the present invention.
FIG. 4 is a diagram showing another example of the direct methanol fuel cell system according to the embodiment of the present invention.
[Explanation of symbols]
5 Fuel Storage Unit 6 Temperature Raising Means 7 Bypass Channel 10 Cell Stack 51 Fuel Tank 52 High Concentration Methanol Tank

Claims (2)

A cell having a configuration in which a negative electrode and a positive electrode are opposed to each other through an electrolyte composed of a proton conductive solid polymer membrane, a liquid fuel is supplied to the negative electrode, and an oxidant gas is supplied to the positive electrode, or a plurality of such cells are stacked. A fuel storage part for storing a methanol aqueous solution having a methanol concentration of 1 to 8% to be supplied to the cell or the cell stack, and the fuel is provided between the fuel storage part and the cell or the cell stack. A direct methanol fuel cell system comprising a temperature raising means for raising a temperature of a liquid fuel by supplying a part of the liquid fuel from a storage unit. 2. The direct methanol fuel cell system according to claim 1, wherein the temperature raising means has a bypass passage for bypassing the temperature raising means.

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