JP4561158B2 - Fuel cell - Google Patents

Description

  The present invention relates to a relatively small fuel cell suitable as a power source for portable electronic devices and the like.

  A fuel cell basically consists of a fuel electrode and an air electrode arranged with an electrolyte layer in between. Hydrogen is supplied to the fuel electrode and oxygen is supplied to the air electrode to generate a direct current by an electrochemical reaction. Let Since the electromotive force of the cell, which is the smallest unit for generating electricity, is small, it is necessary to connect a plurality of cells in series in order to obtain a voltage required by a device that uses a fuel cell as a power source. Configured in the form of a stack.

  As a system for supplying fuel to each cell constituting the stack, conventionally, a fuel circulation system for supplying fuel in series to a plurality of cells constituting the stack and supplying fuel discharged from the stack again, and a plurality of There is a fuel non-circulation system in which fuel is supplied in parallel to the cells and the fuel discharged from the stack is not circulated. In the fuel circulation system, the fuel concentration decreases toward the downstream side in the supply direction, and the concentration of the re-supplied fuel also decreases. Therefore, an auxiliary device such as a fuel concentration adjuster must be provided. In a fuel cell to which this fuel circulation system is applied, in order to prevent the fuel concentration from decreasing on the downstream side, the cross-sectional area of the downstream fuel flow path is increased to increase the fuel flow rate, and the current density distribution for each cell Is known (see Patent Document 1).

On the other hand, the fuel non-circulation method is a method that accurately supplies only the amount of fuel that contributes to power generation to each cell, and there is a merit that auxiliary equipment such as a fuel concentration regulator that is indispensable in the fuel circulation method is unnecessary. This is an effective method for battery miniaturization.
JP 2002-260710 A (pages 4-7, FIG. 1)

  In a fuel cell that uses liquid as fuel, such as a direct methanol fuel cell (DMFC), a membrane electrode assembly (hereinafter referred to as MEA) sandwiched between separators is a fuel. It must be wet enough. While fuel is supplied during power generation, it is maintained in a wet state, but when power generation is stopped and left unattended, the fuel supplied to the fuel flow path is discharged to the outside through the fuel discharge line, When the MEA is dried, there is a problem that it takes time until the MEA gets wet with fuel when power generation is started next, and the startup time becomes long. Further, when the drying of the MEA has further progressed, there is a possibility that power generation becomes impossible.

  An object of the present invention is to provide a fuel cell that makes it possible to maintain the MEA wet with fuel even when power generation is stopped when fuel is not supplied.

  In order to achieve the above object, a first invention of the present application is a fuel cell in which a stack is constituted by a plurality of cells, and used fuel is supplied to each cell and used for power generation, and used fuel is discharged from a fuel discharge port to the outside. When the stack is in a power generation posture, at least one portion of the fuel discharge pipe connected to the fuel discharge port is at a position higher than the fuel flow path formed inside the stack. Is formed.

  According to the above configuration, even if the power generation is stopped and the fuel is not supplied, the fuel is left in the fuel flow path because the fuel discharge passage is formed in the fuel discharge pipe. Thus, the MEA constituting the cell is prevented from being dried, and it is prevented that the start-up delay occurs when the power generation is started next due to the drying, and the generation of power cannot be prevented due to excessive drying progress.

  The second invention of the present application is a fuel cell in which a stack is constituted by a plurality of cells, and spent fuel after being supplied to each cell and used for power generation is discharged from a fuel outlet to the outside. The fuel discharge pipe connected to the fuel discharge port is formed with a fuel outflow prevention pipe portion at a position higher than the fuel flow path formed in the stack regardless of the stack posture. Features.

  According to the above configuration, even when the power generation is stopped and the fuel is not supplied, the fuel discharge channel is formed in the fuel discharge channel, so that the fuel remains in the fuel channel. Thus, drying of the MEA constituting the cell can be prevented. In fuel cells applied to portable electronic devices, it is not known what the orientation of the stack will be when power generation is stopped, but the fuel outflow will be higher than the fuel flow path regardless of the orientation of the stack in the fuel discharge pipe. The above object is achieved by forming the prevention pipe portion.

  In each of the above configurations, a fuel purifier that burns and purifies spent fuel is connected immediately after the fuel outflow prevention pipe portion, and a straight pipe portion that is directly connected to the discharge port is formed without bending the piping from the fuel purifier. By doing so, it is possible to prevent deterioration of the catalyst of the fuel purifier without leaving the liquid after combustion in the fuel purifier.

  According to the present invention, the fuel remains in the fuel flow path even when the fuel cell is stopped and the fuel is not supplied, so that the MEA does not dry in the state of being left. It is possible to prevent the start-up delay at the start and the generation of power generation impossible due to excessive drying. Further, even if a fuel purifier is provided in the fuel discharge pipe provided with the fuel outflow prevention pipe portion, it is possible to prevent the life of the pipe from being reduced.

  The fuel cell according to the present embodiment is configured as a direct methanol fuel cell, and methanol is directly supplied to the cell as fuel. In the cell, as shown in FIG. 2, an MEA 6 having a fuel electrode on one surface of an electrolyte polymer membrane and an air electrode on the other surface is attached to a seal rubber 10 as shown in FIG. The electrode is opposed and the fuel electrode is opposed to the surface of the separator 4b where the fuel flow path 8 is formed, and is sandwiched between the separators 4a and 4b. In FIG. 2, the separators 4a and 4b show the surfaces on which the air flow paths 9 are formed, but the fuel flow paths 8 are formed on the other surface as shown in FIG.

  Here, eight cells 3a to 3h are stacked, and in appearance, the cell stack 2 is configured such that separators 4a to 4i are stacked as shown in FIG. 3, and the cells 3a to 3h are connected in series. Thus, the required output voltage can be taken out.

  FIG. 1 shows a fuel flow path 8 formed in nine separators 4a to 4i forming eight cells 3a to 3h and forming a partition between the cells 3a to 3h, and a supply path for supplying fuel thereto. And a discharge path for discharging spent fuel after flowing through the fuel flow path 8 and being used for power generation.

  Although not shown in FIG. 1, the separators 4b to 4i are stacked on the separator 4a at the lower end of the stack. The separators 4b to 4i are stacked on the separator 4a. As shown in FIG. 1, a fuel flow path 8 that is folded back in the longitudinal direction of the lower surface is formed, and an air flow path 9 is formed in a row in the short direction of the upper surface. In the stacked separator 4i at the upper end, a fuel channel 8 is formed by folding back in the longitudinal direction of the lower surface, and no air channel 9 is formed on the opposite surface.

  The cell laminate 2 is provided with end plates 5a and 5b on both sides thereof, and is bound between the two, whereby the seal rubber 10 is sandwiched between the separators 4a to 4i and the MEA 6 is sealed. Since fuel is supplied from the fuel flow path 8 to the fuel electrode of the MEA 6 and air is supplied from the air flow path 9 to the air electrode, the reaction between hydrogen in the fuel and oxygen in the air is caused by a reaction. An electromotive force is generated between the fuel electrode and the air electrode.

  FIG. 4 shows an example of a fuel supply path to the fuel flow path 8 of the separator 4b corresponding to the cell 3a and a fuel supply path to the fuel flow path 8 of the separator 4f corresponding to the cell 3e. As shown in this example, for each of the cells 3a to 3h, the separator 4e disposed above the predetermined separator 4b to 4e from the individual fuel introduction passages 13a to 13e bored in the separator 4a to 4e disposed below. The fuel is supplied to the predetermined separators 4e to 4i from the individual fuel introduction paths 13e to 13i bored in .about.4i. The individual fuel introduction paths 13a to 13h pass through predetermined separators 4a to 4i that supply fuel to the cells 3a to 3h as supply destinations, and are outside the fuel flow path by O-rings 18 fitted into the recesses 21 in the supply holes. Is prevented from leaking out.

  The fuel flow will be described for the fuel supply paths for the cells 3a and 3e shown in FIG. In the case of the cell 3a, the fuel fed to the individual fuel supply port 11a passes from the individual fuel supply path 12a to the fuel introduction port 14b formed in the separator 4b through the individual fuel introduction hole 13a penetrating the separator 4a. Then, the fuel is guided from the fuel individual guide channel 15b formed in the separator 4b to the power generation start end 16 which is the entrance of the fuel channel 8. The fuel flowing from the power generation start end 16 to the fuel flow path 8 is supplied to the fuel electrode of the MEA 6 of the cell 3a and contributes to power generation, reaches the power generation end 17 which is the outlet of the fuel flow path 8 and flows to the fuel discharge hole 19 to end plate. It is discharged to the outside from a fuel discharge port 20 provided in 5a.

  In the case of the cell 3e, the fuel supplied to the individual fuel supply port 11e is formed in the separator 4f through the individual fuel introduction hole 13e penetrating the separators 4i, 4h, 4g, and 4f from the individual fuel supply path 12e. Then, the fuel enters the individual fuel introduction port 14f and is guided from the individual fuel guide channel 15f formed in the separator 4f to the power generation start end 16 which is the inlet of the fuel channel 8. The fuel that flows from the power generation start end 16 to the fuel flow path 8 is supplied to the fuel electrode of the MEA 6 of the cell 3e and contributes to power generation, reaches the power generation end 17 that is the outlet of the fuel flow path 8 and flows to the fuel discharge hole 19 to end plate. It is discharged to the outside from a fuel discharge port 20 provided in 5a.

  The same fuel is supplied to the cells 3a to 3h, but the flow path lengths from the individual fuel supply ports 11a to 11h to the power generation start ends 16 of the cells 3a to 3h are formed to be equidistant. That is, the sum of the lengths of the individual fuel introduction holes 13a to 13h and the lengths of the individual fuel guide channels 15b to 15i formed in the separators 4b to 4i from the individual fuel introduction ports 14b to 14h shown in FIG. The distance is formed to be equal for each of the cells 3a to 3h. Accordingly, the fuel supplied to the individual fuel supply ports 11a to 11h is supplied almost simultaneously to the power generation start ends 16 of the cells 3a to 3h, and the cells 3a to 3h generate power at the same time, and the eight cells 3a to 3h The power generation performance of the stacks 1 connected in series is stabilized.

  As shown in FIG. 5, the fuel that has flowed through the fuel flow path 8 of each separator 4b-4i and supplied hydrogen to the fuel electrode penetrates from the power generation terminal 17 of the fuel flow path 8 in the stacking direction of the separators 4a-4i. The fuel flows down the fuel discharge hole 19 and is discharged to the outside through a fuel discharge port 20 formed in the end plate 5a. The fuel discharge hole 19 prevents fuel leakage by an O-ring 23 fitted in a discharge hole recess 22 formed around the fuel discharge hole 19 formed in the separators 4a to 4h.

  The spent fuel discharged from the fuel discharge port 20 is discharged to the outside from a fuel discharge pipe 25 connected to the fuel discharge port 20 by piping. As shown in FIG. 6, the fuel discharge pipe 25 is drawn out from the lower part of the stack 2 and then changed upward so that at least one of the pipes is located at the top, That is, after forming the fuel outflow prevention pipe portion 25a bent so as to be positioned above the fuel flow path 8 formed in the separator 4i, the pipe end is opened to a predetermined discharge location. With the configuration of the fuel discharge pipe 25, even if the power generation is stopped and the fuel supply is stopped, the fuel in the fuel flow path 8 formed in the separators 3b to 3i has the fuel outflow prevention pipe portion 25a. Even if it is not discharged because it is formed, and it is left for a long time with power generation stopped, the MEA 6 is maintained in the upper body wet with the fuel, and the start-up delay or the power generation cannot be made when it is started next time. Can be prevented.

  The small fuel cell as shown in the present embodiment is intended to be applied as a power source for portable electronic devices such as a notebook computer, in which case the fuel cell is not necessarily in a horizontal state, and is particularly stacked when not in use. 1 cannot predict which surface of upper, lower, left and right is located below. Therefore, in the configuration of the fuel discharge pipe 25 shown in FIG. 6, the fuel flows out from the fuel flow path 8. Therefore, as shown in FIG. 7, when the fuel discharge pipe 25 is routed and piped, when the normal position with the end plate 5a down, that is, when the surface (A) shown in the figure is up, the fuel outflow prevention pipe section 25a is located. Is present above the fuel flow path 8, the fuel does not flow out of the fuel flow path 8. Further, in the state where the (B) surface is down, the fuel outflow prevention pipe portion 25c, which is the terminal portion of the fuel discharge pipe 25, is present above the fuel flow path 8. There is no fuel spill. Further, in the state where the (C) plane is down, the fuel outflow prevention pipe portion 25b of the fuel discharge pipe 25 is present above the fuel flow path 8, so that the fuel flows out from the fuel flow path 8. There is no end. Further, in the state where the (A) surface is down, the fuel outflow prevention pipe portion 25b of the fuel discharge pipe 25 exists above the fuel flow path 8, so that the fuel flows out of the fuel flow path 8. There is no end.

  Further, since unburned fuel components remain in the spent fuel, it is desirable to discharge through the fuel purifier 26. As shown in FIG. 8, the fuel purifier 26 is disposed immediately after the outflow prevention pipe portion 25a, and is not bent from the fuel purifier 26 so that the liquid that has passed through the fuel purifier 26 is quickly discharged. A straight pipe portion 28 directly connected to the discharge port is provided. With this configuration, the liquid is not left in the fuel purifier 26, and the life of the catalyst used in the fuel purifier 26 can be extended and the life of the fuel purifier 26 can be extended. .

  As described above, according to the present invention, even when the power generation of the fuel cell is stopped and left unattended, the MEA can be prevented from being dried, and when the power generation is restarted, the start-up is performed promptly and the life is extended. A fuel cell that achieves the above can be provided.

The perspective view which shows the structure of the fuel supply flow path of the fuel cell which concerns on embodiment. The perspective view which shows the structure of a cell. The perspective view which shows the structure of a stack. Sectional drawing which shows the fuel supply flow path formed in the separator. Sectional drawing which shows the fuel discharge flow path formed in the separator. The schematic diagram which shows the 1st structural example of a fuel discharge pipeline. The schematic diagram which shows the 2nd structural example of a fuel discharge pipeline. The schematic diagram which shows the structure which provided the fuel purifier in the fuel discharge pipeline.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stack 3a-3h Cell 4a-4i Separator 5a, 5b End plate 8 Fuel flow path 9 Air flow path 11a-11h Fuel individual supply port 19 Fuel discharge hole 20 Fuel discharge port 25 Fuel discharge line 25a, 25b Outflow prevention pipe part 25c Terminal section 26 Fuel purifier 28 Straight pipe section

Claims (3)

A fuel cell comprising a stack comprising a plurality of cells , using a liquid as a fuel, supplying fuel to each cell and discharging spent fuel to the outside from a fuel outlet after being supplied for power generation. When the fuel is in a power generation posture, at least one portion of the fuel discharge pipe connected to the fuel discharge port is formed with a fuel outflow prevention pipe portion that is positioned higher than the fuel flow path formed inside the stack. A fuel cell. A fuel cell comprising a stack comprising a plurality of cells , using a liquid as fuel, supplying fuel to each cell, and discharging spent fuel to the outside from a fuel outlet after being supplied for power generation. The fuel discharge pipe connected to the discharge port is formed with a fuel outflow prevention pipe portion at a position higher than the fuel flow path formed inside the stack regardless of the stack posture. A fuel cell. A fuel purifier for combusting and purifying spent fuel is connected immediately after the fuel outflow prevention pipe section, and a pipe extending from the fuel purifier is formed in a straight pipe section directly connected to the discharge port without being bent. 3. The fuel cell according to 1 or 2.

Images