JP4506193B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell.

  A fuel cell is a system that converts chemical energy into electrical energy by supplying fuel and an oxidant to an electrode. The fuel cell has features such as the product is water and does not pollute the environment, and the theoretical power generation efficiency is high. Therefore, in recent years, the fuel cell has been put into practical use as a power source for automobiles, household cogeneration systems, etc. Development is underway. Therefore, a technique for increasing the power generation efficiency is regarded as extremely important for the practical application of fuel cells.

One technique for increasing the power generation efficiency is the reuse of used gas. In Patent Document 1, a gas supply passage, a gas discharge passage, a gas supply passage, and a gas discharge passage are branched outside a portion corresponding to an MEA (Membrane Electrode Assembly) of the separator. There is disclosed a structure including an ejector provided with a connecting passage and having a suction passage for sucking used gas into the gas supply passage on the gas supply passage side of the communication passage. Patent Document 2 discloses a related technique in a similar technical field.
JP 2002-280028 A JP 2003-77506 A

  However, in the structure disclosed in Patent Document 1, the flow velocity is increased by the ejector at the most downstream portion of the flow path, but the ejector portion is disposed outside the reaction region outside the MEA. There was a problem that gas with a high flow rate was not used effectively.

  Accordingly, an object of the present invention is to provide a fuel cell in which the gas is effectively used to the maximum extent in the reaction region to improve the power generation efficiency.

In order to solve the above problems, the present invention takes the following means. That is,
The invention according to claim 1 is a fuel cell comprising electrodes disposed on both sides of an electrolyte, and a separator disposed on the outside of each of the electrodes and having a gas flow path. Utilizing the flow rate of the gas supplied to the upstream part, the gas in the downstream part of the gas flow path is sucked into the upstream part, and the gas flow direction is determined in cooperation with the MEA provided on the surface facing the MEA of the separator. An ejector having a peak portion that is regulated and has a venturi shape and a nozzle overlaps the electrode in the stacking direction in which the MEA and the separator are stacked , and is sandwiched between the separator and the electrode. Provided is a fuel cell that is disposed.

The invention of claim 2 is the fuel cell according to claim 1, the gas supply port to the gas flow path, characterized in that provided above the gravity direction center in the plane.

According to a third aspect of the present invention, in the fuel cell according to the first or second aspect, the connecting passage that connects the gas flow path to the manifold that supplies gas to the gas flow path is directed from the upstream side to the downstream side of the gas flow. Thus, the cross-sectional area of the passage is reduced .

According to a fourth aspect of the present invention, in the fuel cell according to any one of the first to third aspects, the gas discharge port in the gas flow path, the opening / closing means at the discharge port , and the operation of the opening / closing means are controlled. wherein the Ru comprising control means for.
The invention according to claim 5 includes a closed operation step in which a gas discharge port is provided in the gas flow path, and an opening / closing means is provided at the discharge port, and the opening / closing means is closed for operation. 4. A method for using the fuel cell according to any one of 3 above.

  According to the first aspect of the present invention, the gas at the most downstream portion is sucked into the most upstream portion by the ejector so as to increase the gas flow velocity in the reaction region plane. Since gas always flows and stirs over the entire surface of the MEA, which is the reaction region, stagnation is less likely to occur and the power generation efficiency of the fuel cell can be increased. In general, when the gas flow rate is high, a high output can be obtained. Therefore, the reaction efficiency can be improved by disposing an ejector portion in which the gas flow rate is high in the reaction region plane.

  According to the invention of claim 2, the gas that participated in the reaction contains moisture, and this moisture gradually gathers under the reaction region by gravity, whereas the gas supply port to the gas flow path Since the ejector is provided above the center in the vertical direction, the hydrogen that is effectively used for the reaction can be sucked into the upper part without sucking moisture, and can be used for the reaction again.

  According to the invention of claim 3, since the connecting passage is formed so that the cross-sectional area gradually becomes smaller in the gas flow direction, the gas flow velocity can be increased and the suction effect by the ejector can be enhanced.

  According to the invention of claim 4, when the gas discharge port opening / closing means is set to “closed” and the closed mode operation is performed, the gas is circulated in the reaction region plane, and the gas flow in the reaction region plane is The reaction can be further promoted because the gas can be stirred by adding a flow to the gas with an ejector.

  FIG. 1 shows a part of a fuel cell system applied to a fuel cell vehicle. The fuel cell system includes a fuel cell 10 according to the present invention, a high-pressure hydrogen tank 1 for supplying fuel hydrogen gas to the fuel cell 10, a controller 14 for controlling the discharge system of the fuel cell 10, and the like. . The fuel cell 10 is a battery cell in which electrodes having a structure such as a porous layer capable of diffusing a gas are formed on both surfaces of an electrolyte and laminated with a conductive separator interposed between the layers. The output voltage can be taken out. In the drawing, only the structure of the battery cell 10a in which the electrodes 12 and 13 are formed on both surfaces of the electrolyte membrane 11 is shown for convenience of explanation. One electrode is the fuel electrode 12 and the other electrode is the air electrode 13. The fuel cell 10 is a power supply for a motor for driving the vehicle, and generates a DC high voltage of about 300V. The voltage generated by the fuel cell 10 is always detected by a voltage sensor 23 provided in the output circuit. The power generation voltage of the fuel cell 10 is output to an inverter 15 that supplies a current corresponding to a command torque or the like to the motor. Further, the power generation voltage of the fuel cell 10 is stepped down to about 12 V by a DC-DC converter (not shown), and is output to various auxiliary devices mounted on the vehicle and a battery as a secondary battery for supplying power to them. Is done.

  A hydrogen gas passage 17 is led from the high-pressure hydrogen tank 1 to the fuel inlet port 16 of the fuel cell 10, and fuel hydrogen gas adjusted to a predetermined pressure by a regulator 18 provided in the hydrogen gas passage 17 is supplied to the fuel inlet port 16. Supplied. The fuel hydrogen gas diffuses into the fuel electrode 12 through a flow path formed between the fuel electrode 12 of the fuel cell 10 and the separator. When a predetermined timing or condition is satisfied, the gas in the cell is discharged from the gas outlet port 19 at the most downstream end of the flow path. The gas outlet port 19 is connected to a discharge path 20 described later. In addition, air is supplied to the air electrode 13 of the fuel cell 10 from the air inlet port 21, and the air diffuses into the air electrode 13 through a flow path formed between the air electrode 13 and the separator of the battery cell. I will do it.

  In the fuel cell 10, as described above, the fuel hydrogen gas supplied to the fuel electrode 12 and the oxidizing gas such as air supplied to the air electrode 13 perform a cell reaction to generate electric power. As the air travels, nitrogen in the oxidizing gas and moisture for humidification ooze out from the air electrode 13 to the fuel electrode 12 side through the electrolyte membrane 11. As a result, the partial pressure of nitrogen or water vapor increases, the concentration of unused fuel hydrogen gas present in the gas in the cell gradually decreases, and the power generation capacity decreases. In order to cope with this, a discharge path 20 is provided to discharge gas with increased nitrogen or water vapor concentration from the fuel electrode 12. A discharge valve 22, which is an electromagnetic two-way valve, is provided in the middle of the discharge path 20. In this fuel cell system, when a predetermined condition is reached, the discharge valve 22 is opened, nitrogen and moisture in the fuel electrode 12 are discharged, and a sufficient amount of fuel hydrogen gas is newly introduced from the high-pressure hydrogen tank 1. Yes. For this purpose, the fuel cell system is provided with a controller 14 that uses the discharge valve 22 as one of the objects to be controlled.

  The controller 14, which is also a control means for controlling the entire fuel cell system, is mainly composed of a microprocessor, and includes a ROM and / or a RAM as required. A detection signal of the voltage sensor 23 that detects the output voltage of the fuel cell 10 is input to the input port 14 a of the controller 14. An opening / closing operation command signal for the discharge valve 22 is output from the output port 14b of the controller.

  FIG. 2 shows a flowchart of the opening / closing control of the discharge valve 22 executed by the microprocessor of the controller 14. First, when the process is started, the discharge valve 22 is closed (step S1). In the subsequent step S2, it is determined whether or not the voltage of the fuel cell 10 has dropped below a predetermined threshold value. This determination is made based on the detection signal of the voltage sensor 23. If an affirmative determination is made in step S2, an “open” operation command for the discharge valve 22 is issued, and the discharge valve 22 enters the “open” state (step S3). If a negative determination is made in step S2, the process returns to step S1, and the processes of steps S1 and S2 are repeated. When the discharge valve 22 is opened, nitrogen and moisture in the cell are discharged, so that the effective fuel hydrogen gas concentration in the cell is increased and the power generation capacity of the fuel cell gradually recovers. Therefore, in step S4, it is determined whether or not the voltage of the fuel cell 10 has recovered to a predetermined threshold value. If an affirmative determination is made in step S4, the process returns to step S1, the discharge valve 22 is closed again, and the processes in and after step S2 are repeated. If a negative determination is made in step S4, the process returns to step S3, and the subsequent processes are repeated.

  The fuel cell 10 constituting such a fuel cell system has a great feature in the following points.

  FIG. 3 is a front view schematically showing the fuel electrode (anode) 12 of the fuel cell 10. A large rectangle is shown in the center of the drawing as the separator 30, and the MEA 40 is disposed inside thereof. The separator 30 is provided with a fuel inlet port 16 and a gas outlet port 19. As described above, the hydrogen gas passage 17 is led from the high-pressure hydrogen tank 1 to the fuel inlet port 16, and the fuel hydrogen gas adjusted to a predetermined pressure by the regulator 18 provided in the hydrogen gas passage 17 is supplied to the fuel inlet port 16. Have been supplied. Further, as described above, the discharge path 20 is led to the gas outlet port 19, and the discharge path 20 is provided with a discharge valve 22. When the concentration of nitrogen and moisture in the cell increases and the power generation capacity of the fuel cell decreases, and the generated voltage falls below a predetermined value, the discharge valve 22 is opened and the gas in the fuel cell is discharged from the discharge path 20.

  A nozzle 31 is attached to the reaction region surface side of the fuel inlet port 16. In the drawing, the separator 30, the MEA 40, and the nozzle 31 are shown on the same plane, but actually, the separator 30, the nozzle 31, and the MEA 40 are arranged in this order from the front side to the back side of the drawing. The nozzle 31 has a substantially conical shape, and portions corresponding to the bottom and top of the cone are opened. A portion corresponding to the bottom of the cone opens toward the fuel inlet port 16 (hereinafter referred to as “opening 32”). The portion corresponding to the top of the cone, that is, the injection hole of the nozzle 31 is open in the reaction region plane (hereinafter referred to as “injection hole 33”). The opening 32 and the injection hole 33 are communicated with each other by a substantially conical gas passage (connection passage) 34.

  On the surface of the separator 30 that faces the MEA 40, there is formed a peak 35 that regulates the flow direction of the fuel gas in cooperation with the MEA 40 in the reaction region plane. The crest 35 has a horizontal portion 35a that divides the reaction region surface up and down, an inclined portion 35b that extends from one end of the horizontal portion 35a toward the nozzle 31, and one end at the end of the inclined portion 35b. And a bending portion 35 c that bends along the outer periphery of 31. The inclined portion 35b and the curved portion 35c form a venturi shape.

The fuel hydrogen gas injected into the reaction region surface of the fuel electrode 12 from the nozzle 31 is decomposed into hydrogen ions and electrons by the force of the catalyst.
A fuel electrode (anode) ^{_{side: H 2 → 2H + + 2e}} - ( Equation 1)
Since the electrolyte membrane 11 has a property of allowing only ions to pass therethrough, the generated electrons cannot pass through the electrolyte membrane 11 and move to the air electrode 13 through an external circuit. In the fuel cell 10, electricity is generated by the movement of the electrons. The generated hydrogen ions pass through the electrolyte membrane 11 which is an ionic conductor and move to the air electrode 13. On the other hand, the oxygen supplied to the air electrode 13 reacts with hydrogen ions and electrons that have moved to the air electrode 13 to generate water.
Air electrode (cathode) side: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O

  It is preferable from the viewpoint of power generation efficiency that the reaction of Formula 1 above in the fuel electrode 12 occurs uniformly over the entire reaction region of the fuel electrode 12. For this reason, in the fuel cell 10 of the present invention, the injection hole 33 of the nozzle 31 is disposed rightward in the upstream portion (upper left of the drawing) of the gas flow path. With this configuration, the new fuel hydrogen gas injected into the reaction region from the injection hole 33 of the nozzle 31 is stirred and mixed with the gas in the cell in the upper portion of the reaction region (the portion indicated by symbol A in FIG. 3). Is done. Furthermore, since the crest 35 having the horizontal portion 35a, the inclined portion 35b, and the curved portion 35c is formed in the separator 30, the flow of the gas in the cell is regulated by these, and the fuel hydrogen gas is watched in the reaction region plane. It is circulated around. On the other hand, as described above, as the reaction proceeds, nitrogen in the oxidizing gas and moisture for humidification ooze out from the air electrode 13 to the fuel electrode 12 side through the electrolyte membrane 11. Since these have a higher density than hydrogen, they tend to stay exclusively in the lower part of the reaction region plane (region represented by B in the figure).

  In the fuel cell 10 of the present invention, the venturi shape is formed at the peak portion 35. Therefore, when new hydrogen gas is injected from the nozzle 31, the ejector effect causes water vapor and nitrogen remaining in the lower portion of the reaction region to be retained. It is sucked up together with unreacted hydrogen gas to the upstream side of the gas flow path, mixed with new hydrogen gas in the region indicated by A in the drawing, and circulated again in the reaction region. As a result, nitrogen and moisture are prevented from staying in the downstream portion of the gas flow path at the lower part of the reaction region, and the reaction of the formula 1 in the fuel electrode 12 can be promoted over the entire surface of the reaction region. In addition, since these gas flow paths are all contained in the reaction region plane, the reaction in the fuel electrode is sufficiently performed. Therefore, the power generation efficiency of the fuel cell 10 can be increased. Further, since the reaction gas containing moisture is recirculated, it is not necessary to humidify the fuel hydrogen. Therefore, a humidifier can be omitted. Such an effect of the present invention is particularly effective in a state in which the exhaust valve 22 is closed and the fuel gas is repeatedly circulated in the reaction region surface, that is, “closed mode operation”.

  FIG. 4 is a view for explaining the structure of the nozzle 31. (A) is a side view of the fuel cell 10, and (b) is a front view showing the fuel cell 10 from the fuel electrode 12 side. In FIG. 4, when there is the same member as that shown in FIG. 3, the same reference numerals as those shown in FIG. 4A, the fuel cell 10 includes an MEA 40 in which an electrolyte membrane and a diffusion layer are disposed on both sides thereof at the center, and separators 30a and 30 are disposed on both sides thereof. The separator 30a is disposed on the air electrode 13 side, and the separator 30 is disposed on the fuel electrode 12 side. As shown in the figure, in the present embodiment, the nozzle 31 is manufactured separately from the fuel electrode-side separator 30 and has a structure in which the nozzle 31 is fixed so as to be sandwiched between the walls of the separator 30.

  In the present invention, the position where the injection hole 33 of the nozzle 31 is disposed is not particularly limited. From the viewpoint of not sucking moisture (excluding water vapor) staying in the lower part of the reaction region, any position other than the lowermost part of the reaction region may be used. However, in order to circulate the fuel hydrogen gas in the reaction region, the injection hole 33 needs to be above the horizontal portion 35a of the peak portion 35, and in order to circulate the fuel hydrogen gas uniformly in the reaction region. For this, it is preferable to arrange the horizontal portion 35a in the vicinity of the central portion in the vertical direction of the reaction region. In order to cope with such an arrangement, the nozzle 31 is preferably arranged above the center in the vertical direction of the reaction region surface.

  The nozzle 31 preferably has a gas passage 34 formed so that its cross-sectional area decreases from the fuel inlet port 16 side toward the injection hole 33. With this configuration, the flow rate of the fuel hydrogen gas can be increased, and a sufficient amount of suction due to the ejector effect can be ensured.

  In the fuel cell 10 of the present invention, the nozzle 31 may be formed directly on the separator 30, but from the viewpoint of forming the injection hole 33 small, a metal nozzle or injection molding separate from the separator 30. It is preferable to use a plastic nozzle according to In the case of a metal nozzle, a non-conductive film coated on the surface is preferable from the viewpoint of suppressing a short circuit in the fuel cell.

  The material of the separator 30 that constitutes the fuel cell 10 of the present invention and the material such as the electrolyte, electrode, and catalyst that constitute the MEA 40 are not particularly limited, and those normally used for fuel cells are utilized. can do. For example, the separator 30 was supported on a carbonaceous material as a catalyst, a dense carbon or stainless steel or other corrosion-resistant metal material compressed with carbon, and an electrolyte, a fluororesin such as a perfluorosulfonic acid polymer, or a catalyst. As the anode and the cathode, such as platinum or an alloy made of platinum and another metal, a carbon cloth woven with carbon fibers can be used.

  In addition, although the example which applied this invention to the fuel electrode 12 was demonstrated above, this invention is not limited to this, It can apply also to the air electrode 13. FIG. In this case, there is an advantage that it is not necessary to humidify the air.

It is a figure which shows a part of fuel cell system applied to the fuel cell vehicle. It is a figure which shows the flowchart of the opening / closing control of a discharge valve which the microprocessor of a controller performs. It is a front view which shows the fuel electrode of a fuel cell roughly. It is a figure explaining the structure of a nozzle.

Explanation of symbols

1 High-pressure hydrogen tank 10 Fuel cell 11 Electrolyte membrane (electrolyte)
DESCRIPTION OF SYMBOLS 12 Fuel electrode 13 Air electrode 14 Controller 15 Inverter 16 Fuel inlet port 17 Hydrogen gas 18 Regulator 19 Gas outlet port 20 Exhaust path 21 Air inlet port 22 Exhaust valve 23 Voltage sensor 30, 30a Separator 31 Nozzle 32 Opening 33 Injection hole 34 Gas Aisle (connection aisle)
35 Yamabe 40 MEA

Claims (5)

Electrodes disposed on both sides of the electrolyte;
A fuel cell comprising a separator disposed on the outside of each electrode and having a gas flow path,
Using the flow velocity of the gas supplied to the upstream part of the gas flow path, the gas in the downstream part of the gas flow path is sucked into the upstream part, and provided on the surface facing the MEA of the separator, An ejector having a crest that cooperates to regulate the flow direction of the gas and has a venturi shape, and a nozzle overlaps the electrode in a stacking direction in which the MEA and the separator are stacked , and A fuel cell, wherein the fuel cell is disposed in a plane sandwiched between the separator and the electrode. 2. The fuel cell according to claim 1, wherein the gas supply port to the gas flow path is provided above the center in the gravitational direction in the plane. 3. The cross-sectional area of a connecting passage that connects a manifold that supplies gas to the gas flow path and the gas flow path decreases from the upstream side to the downstream side of the gas flow. A fuel cell according to claim 1. 4. The gas discharge port according to claim 1, further comprising: a gas discharge port in the gas flow path; an opening / closing unit at the discharge port; and a control unit that controls the operation of the opening / closing unit. Fuel cell. 4. The gas discharge port according to claim 1, further comprising: a closed operation step in which the gas discharge port is provided with an opening / closing unit at the discharge port, and the opening / closing unit is closed to operate. 4. A method for using the fuel cell according to 1.

Images