JP6702170B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  For example, a redox flow type fuel cell system as disclosed in Patent Documents 1 and 2 is known. Redox (RedOx: Reduction / Oxidation) is reduction and oxidation.

  This fuel cell system realizes an oxidation-reduction reaction at the cathode by circulating a cathode solution containing a mediator (oxidation-reduction substance) such as polyoxometalate (POM) between the cathode and the regenerator. .. After being reduced at the cathode, the mediator is regenerated by being oxidized by a regenerator and is supplied again to the cathode.

Special table 2012-526344 gazette Special table 2011-510465 gazette

  Since the oxidation reaction of the mediator in the regenerator is a gas-liquid reaction, its reaction rate is slower than that of a gas reaction. For this reason, for example, when the fuel cell has a high output, the regeneration capacity of the mediator becomes insufficient with respect to the required output, and there is a possibility that sufficient power cannot be obtained from the fuel cell. On the other hand, if the size of the regenerator is increased, more time can be spent for the oxidation reaction, so sufficient power can be obtained from the fuel cell even at high output, but the fuel cell system becomes larger and energy efficiency is improved. However, there is a problem in that

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel cell system in which the regeneration performance of the mediator is improved without increasing the size.

Fuel The fuel cell system described herein, in which the cathode, the anode, having said cathode and a proton conductive membrane between the anode, the mediator supplied to the cathode, which is supplied to the anode A fuel cell that generates electricity by reducing with protons generated from a gas, and a regenerator that oxidizes the mediator reduced with the fuel gas with an oxidant gas introduced from an introduction port and sends it to the cathode from a delivery port. , the mediator from the vicinity of the outlet, and a circulating device for circulating in the vicinity of the reproducing apparatus of an external pump and the inlet via the path.

  According to the present invention, the reproduction performance of the mediator can be improved without increasing the size.

It is a block diagram which shows the fuel cell system of 1st Example. It is a block diagram which shows the fuel cell system of 2nd Example. It is a block diagram which shows the fuel cell system of 3rd Example. It is a flow chart which shows an example of operation of a control device.

(First embodiment)
FIG. 1 is a configuration diagram showing the fuel cell system of the first embodiment. The fuel cell system is of a redox flow type, is mounted on a vehicle such as an automobile, and supplies electric power PW to a motor that drives the vehicle.

  The fuel cell system includes a hydrogen tank 11, a fuel gas pressure regulating valve 12, a fuel cell 13, a purge valve 14, a hydrogen circulation pump Ph, a regenerator 21, a redox potential monitor 22, and a solution circulation pump Po. It has a return circulation pump Pc and an air compressor C.

  The fuel cell 13 is connected to a fuel gas supply path R10 for supplying hydrogen gas, which is an example of fuel gas, and a fuel gas discharge path R11 for discharging hydrogen gas used for power generation. A hydrogen tank 11 and a fuel gas pressure regulating valve 12 are connected in this order to the fuel gas supply path R10.

The hydrogen tank 11 is a hydrogen gas (H ₂ ) supply device, and stores hydrogen gas in a high pressure state inside. Hydrogen gas is introduced from the hydrogen tank 11 to the anode of the fuel cell 13 via the fuel gas pressure regulating valve 12. The pressure of hydrogen gas is adjusted by passing through the fuel gas pressure regulating valve 12.

  The hydrogen gas (that is, off gas) discharged from the fuel cell 13 is guided to the fuel gas discharge path R11. A purge valve 14 is provided in the middle of the fuel gas discharge path R11. The purge valve 14 is normally closed, but is opened when purging hydrogen gas from the fuel gas discharge passage R11.

  A recirculation route R12 branches off from the fuel gas discharge route R11. The branched recirculation path R12 is connected to the fuel gas supply path R10. A hydrogen circulation pump Ph is provided in the recirculation route R12, and the hydrogen circulation pump Ph guides the hydrogen gas discharged to the fuel gas discharge route R11 to the fuel gas supply route R10 via the recirculation route R12. . The hydrogen gas introduced from the recirculation route R12 to the fuel gas supply route R10 is resupplied to the fuel cell 13.

  Hydrogen gas is supplied to the anode of the fuel cell 13, and a cathode solution containing POM (polyoxometallate) that is a mediator is supplied to the cathode of the fuel cell 13. The fuel cell 13 is configured as a laminated body (stack) of a plurality of fuel cells, and each fuel cell has an electrolyte membrane 13b sandwiched between an anode electrode 13a and a cathode electrode 13c, and an anode electrode 13a and a cathode electrode 13c. Equipped with.

  The electrolyte membrane 13b is, for example, a polymer electrolyte membrane formed of a fluorine-based sulfonic acid polymer as a solid polymer material, and has good proton conductivity in a wet state. It is desirable that the anode electrode 13a and the cathode electrode 13c have, for example, a porous structure, in which pressure loss is suppressed and the reaction area is large. The anode electrode 13a is provided with a platinum catalyst, and the hydrogen gas supplied to the anode electrode 13a is changed into protons (hydrogen ions) by the platinum catalyst.

On the other hand, a cathode solution containing POM circulates between the cathode electrode 13c and the regenerator 21. POM is a compound containing vanadium, molybdenum, tungsten, and the like. The chemical formula of POM is represented by, for example, XM ¹ _12-m M ² _m O ₄₀ ^n- . Here, X is, for example, P, Si, S, Ge, M ¹ is, for example, Mo, W, and M ² is, for example, V. Moreover, m is 1-12.

At the cathode electrode 13c, the POM in the cathode solution is reduced by being combined with the protons that have moved from the anode electrode 13a, and changed to POM-H (reduced body). That is, at the cathode electrode 13c, a reaction of POM+e ⁻ +H ⁺ →POM-H occurs. In addition, e ⁻ represents an electron.

  In this way, the fuel cell 13 generates power by reducing the POM in the cathode solution supplied to the cathode with the fuel gas supplied to the anode. The electric power PW obtained by the power generation is supplied to, for example, a motor that drives a vehicle.

  A solution supply path R20 for supplying a cathode solution and a solution discharge path R21 for discharging the cathode solution used for power generation are connected between the fuel cell 13 and the regenerator 21. A solution circulation pump Po for circulating a cathode solution between the fuel cell 13 and the regenerator 21 is connected to the solution discharge path R21, and a redox potential (redox) of POM in the cathode solution is connected to the solution supply path R20. A redox potential monitor 22 for measuring (potential) is connected.

  The solution circulation pump Po re-supplies the cathode solution to the cathode of the fuel cell 13. More specifically, the solution circulation pump Po generates a circulating flow of the cathode solution between the fuel cell 13 and the regenerator 21, thereby pumping the catholyte solution discharged from the fuel cell 13 to the regenerator 21. The cathode solution discharged from the regenerator 21 is pressure-fed to the fuel cell 13.

  Further, the POM regeneration state in the regeneration device 21 is detected by measuring the redox potential with the redox potential monitor 22. It is determined that the higher the redox potential (for example, 0.8 to 1.2 (V)), the better the POM oxidation in the regenerator 21 is.

The air compressor C supplies air to the regenerator 21 via the oxidant gas supply passage R30. The air compressor C takes in air containing oxygen (O ₂ ) from the outside of the vehicle and sends it to the regeneration device 21 under pressure. In the present embodiment, given air as an example of the oxidant gas, it can also be used oxygen or ozone as an oxidant gas.

The regeneration device 21 regenerates POM (oxidant) by oxidizing POM-H in the cathode solution discharged from the cathode of the fuel cell 13 with oxygen contained in air. The oxidation reaction performed in the regenerator 21 is represented by O ₂ +4POM-H→2H ₂ O+4POM.

  The regenerator 21 is connected to a solution supply path R20 for re-supplying the regenerated POM to the fuel cell 13 and an oxidant gas exhaust path R31 for exhausting the air not used for the oxidation reaction. ing. The regeneration device 21 discharges the remaining air from the oxidant gas discharge passage R31.

  The reduction reaction of POM is performed in, for example, a cylindrical reaction chamber provided in the regenerator 21. Air is introduced into the reaction chamber of the regenerator 21 from the air compressor C, and a cathode solution is introduced from the cathode of the fuel cell 13.

  The regenerator 21 is connected to the solution discharge passage R21 at the solution introduction port 21a on the bottom surface L of the reaction chamber, and is connected to the oxidant gas supply passage R30 at the air supply port 21c on the bottom surface L of the reaction chamber. The regenerator 21 is connected to the solution supply passage R20 at the solution outlet 21b on the upper surface U of the reaction chamber and is connected to the oxidant gas exhaust passage R31 at the air outlet 21d on the upper surface U of the reaction chamber. The solution delivery port 21b is an example of the delivery port.

  The regenerator 21 introduces the cathode solution from the solution introduction port 21a of the bottom surface L of the reaction chamber, and the introduced cathode solution flows from the bottom surface L to the top surface U in the reaction chamber as shown by the dotted line. The regenerator 21 delivers the cathode solution to the fuel cell 13 from the solution delivery port 21b on the upper surface U of the reaction chamber. The solution introduction port 21a is an example of the introduction port.

  Further, the regenerator 21 introduces air from the air supply port 21c on the bottom surface L of the reaction chamber. A filter 21g made of, for example, a fine porous body is provided on the bottom surface L of the reaction chamber, and air is introduced into the reaction chamber of the regenerator 21 as fine bubbles B in order to promote the oxidation reaction. As shown by the dotted line, the air rises from the bottom surface L to the top surface U in the reaction chamber and is discharged from the air discharge port 21d of the top surface U.

  Since the oxidation reaction of POM in the regenerator 21 is a gas-liquid reaction, its reaction rate is slower than that of a gas reaction or the like. For this reason, for example, when the fuel cell 13 has a high output, the regeneration capacity of the POM becomes insufficient with respect to the required output, and there is a possibility that sufficient power cannot be obtained from the fuel cell 13. On the other hand, if the size of the regenerator 21 is increased, the time for the oxidation reaction can be increased, and thus sufficient power can be obtained from the fuel cell even at high output, but the fuel cell system becomes large and energy consumption is reduced. There is a problem of reduced efficiency.

  Therefore, the fuel cell system is provided with a return circulation pump Pc and a return circulation path R32 that circulate the POM from the solution outlet 21b side of the regenerator 21 to the air supply port 21c side. The recursive circulation path R32 connects the recursive circulation pump Pc and the regeneration device 21. The return circulation pump Pc and the return circulation path R32 are examples of a circulation device.

  More specifically, the recursive circulation path R32 is connected to the recursive outlet 21e on the upper surface U of the reaction chamber and the recursive inlet 21f on the side surface near the bottom surface L of the reaction chamber. Therefore, the cathode solution near the upper surface U of the reaction chamber is returned to the vicinity of the bottom surface L of the reaction chamber via the recursive circulation path R32. That is, the cathode solution on the solution delivery port 21b side circulates on the air supply port 21c side.

  In the vicinity of the air supply port 21c on the bottom surface L of the reaction chamber, the oxygen concentration in the air becomes higher than in the vicinity of the solution delivery port 21b on the upper surface U of the reaction chamber. This is because the closer to the upper surface U of the reaction chamber of the regenerator 21, the amount of oxygen consumed in the oxidation reaction increases.

  Therefore, by circulating a part of the cathode solution discharged from the regenerator 21 from the solution outlet 21b side of the regenerator 21 to the air supply port 21c side, the non-oxidized POM-H in the cathode solution is changed to oxygen. It becomes possible to oxidize near the high-concentration air supply port 21c. As a result, the regeneration device 21 can exhibit a sufficient regeneration ability for the required output even when the fuel cell 13 has a high output. Regarding the air supply amount, for example, by maintaining the stoichiometric ratio of air at 2 or more, it is possible to avoid the lack of oxygen in the regeneration device 21.

  Further, in the present embodiment, the recurrence circulation pump Pc and the recurrence circulation path R32 are connected to the regeneration device 21, but it is not necessary to increase the size of the regeneration device 21 itself. Therefore, the increase in the size of the entire fuel cell system is suppressed, so that the fuel cell system according to the present embodiment can be installed even in a small installation space such as an automobile.

  Therefore, according to the fuel cell system of the present embodiment, the regeneration performance of the mediator is improved without increasing the size.

(Second embodiment)
FIG. 2 is a configuration diagram showing the fuel cell system of the second embodiment. 2, the same components as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

  In the first embodiment, the cathode solution and the air in the regenerator 21 flow from the bottom surface L of the reaction chamber toward the upper surface U, but the present invention is not limited to this. The air flow directions may be opposite to each other.

  In the regeneration device 21 of this example, the solution inlet 21a is provided on the upper surface U of the reaction chamber, and the solution outlet 21b is provided on the bottom surface L of the reaction chamber. Therefore, the cathode solution flows from the upper surface U to the bottom surface L in the reaction chamber of the regenerator 21.

  The recursive outlet 21e and the recursive inlet 21f are provided near the bottom surface L of the reaction chamber. More specifically, the recursive outlet 21e is provided on the side surface near the solution outlet 21b, and the recursive inlet 21f is provided on the side surface near the air supply port 21c. The recursive discharge port 21e and the recursive introduction port 21f are present, for example, at symmetrical positions with the center of the bottom surface L in between when the regeneration chamber is viewed from above.

  Therefore, the return circulation pump Pc and the return circulation path R32 can circulate a part of the cathode solution discharged from the regenerator 21 from the solution outlet 21b side of the regenerator 21 to the air supply port 21c side. .. Therefore, as in the first embodiment, it is possible to oxidize unoxidized POM-H in the cathode solution near the air supply port 21c where the oxygen concentration is high.

(Third embodiment)
FIG. 3 is a configuration diagram showing the fuel cell system of the third embodiment. 3, the same components as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

  In the first and second embodiments, the return circulation pump Pc and the return circulation path R32 always circulate the cathode solution. However, when it is necessary according to the state of the fuel cell 13 as in this example. The cathode solution may be circulated only in the above.

  The fuel cell system includes a control device 3, a hydrogen tank 11, a fuel gas pressure regulating valve 12, a fuel cell 13, a purge valve 14, a hydrogen circulation pump Ph, a regeneration device 21, a redox potential monitor 22, and a three-way valve. It has a valve 23, a solution circulation pump Po, and an air compressor C.

  The three-way valve 23 is provided on the solution supply path R20 on the downstream side of the redox potential monitor 22, and is connected to the solution discharge path R21 via the return circulation path R23. The three-way valve 23 opens and closes the valve in accordance with a control signal from the control device 3 to switch the flow direction of the cathode solution between the direction Da toward the cathode of the fuel cell 13 and the direction Db toward the solution discharge passage R21.

  When the three-way valve 23 sets the flow direction of the cathode solution to the direction Da, the cathode solution circulates between the fuel cell 13 and the regenerator 21. Further, when the three-way valve 23 sets the flowing direction of the catholyte solution as the direction Db, the catholyte solution circulates from the solution delivery port 21b side of the regenerator 21 to the air supply port 21c side. The solution supply passage R20, the solution discharge passage R21, the return circulation passage R23, the three-way valve 23, and the solution circulation pump Po are examples of the circulation device.

  The control device 3 includes, for example, a CPU (Central Processing Unit) circuit, acquires the redox potential from the redox potential monitor 22, and controls the three-way valve 23 by a control signal based on the redox potential. Examples of the control device 3 include an electronic control unit (ECU).

  Examples of the case where the reproducing apparatus 21 is required to have a high reproducing ability include a case where a high load continues, a case where a low load changes to a high load, and a case where the idling state occurs after the high load. As an example, the control device 3 switches the flowing direction of the cathode solution of the three-way valve 23 from the direction Da to the direction Db according to the idling state after the high load.

  Therefore, in the idling state after the high load, the cathode solution is not delivered from the regenerator 21 to the fuel cell 13, and the solution of the regenerator 21 is delivered via the recursive circulation path R23 so as to bypass the fuel cell 13. It circulates from the outlet 21b side to the air supply port 21c side. As a result, the regeneration device 21 promotes the oxidation of the POM, and thus, even if a high load state occurs after idling, the cathode solution containing the sufficiently oxidized POM can be supplied to the fuel cell 13.

  FIG. 4 is a flowchart showing an operation example of the control device 3. At the start of this operation, the flow direction of the cathode solution of the three-way valve 23 is set to the direction Da.

  The control device 3 acquires the redox potential from the redox potential monitor 22 (step St1). Next, the control device 3 compares the redox potential with the threshold value THa (step St2).

  When the oxidation-reduction potential is equal to or higher than the threshold value THa (No in step St2), the control device 3 executes the process of step St1 again. In this case, the control device 3 does not switch the direction of the three-way valve 23 because the oxidation of POM is good.

  When the oxidation-reduction potential is less than the threshold value THa (Yes in step St2), the control device 3 switches the flowing direction of the cathode solution of the three-way valve 23 from the direction Da to the direction Db (step St3). In this case, since the POM is not sufficiently oxidized, the control device 3 controls the three-way valve 23 to circulate the cathode solution sent from the regenerator 21 to the regenerator 21 to ensure sufficient POM. Oxidize.

  Next, the control device 3 acquires the redox potential from the redox potential monitor 22 (step St4). Next, the control device 3 compares the redox potential with the threshold value THb (step St5).

  When the oxidation-reduction potential is less than the threshold value THb (No in step St5), the control device 3 executes the process of step St4 again. In this case, the control device 3 maintains the switching direction of the three-way valve 23 because the oxidation of POM has not reached a sufficient level.

  Further, when the oxidation-reduction potential is equal to or higher than the threshold value THb (Yes in step St5), the control device 3 switches the flow direction of the cathode solution of the three-way valve 23 from the direction Db to the direction Da (step St6). In this case, since the POM has reached a sufficient degree of oxidation, the control device 3 returns the direction of the three-way valve 23 to the original direction to circulate the cathode solution again between the regenerator 21 and the cathode of the fuel cell 13.

  Here, the threshold THb may be the same as the threshold THa, or may be larger than the threshold THa. In this case, the control device 3 does not repeat switching and switching back of the three-way valve 23 even when the oxidation-reduction potential fluctuates in the vicinity of the threshold value THa, so the control of the three-way valve 23 is stabilized. The thresholds THa and THb may be 0.8 to 0.85 (V), for example.

  As described above, in the fuel cell system of this example, since the three-way valve 23 is controlled based on the oxidation-reduction potential of POM, the cathode solution sent from the regenerator 21 is circulated to the regenerator 21 in a timely manner to ensure sufficient POM. Can be oxidized to

  Although the control device 3 of the present example controls the three-way valve 23 according to the redox potential, the present invention is not limited to this. For example, as indicated by the dotted line in FIG. 3, the voltmeter E measures the OCV (Open Circuit Voltage) of the fuel cell 13, and the control device 3 replaces the redox potential with the OCV. The three-way valve 23 may be controlled based on In this case, in steps St1 and St4 of the flowchart of FIG. 4, OCV is acquired instead of the redox potential, and in steps St2 and St5, OCV is compared with the thresholds THa and THb instead of the redox potential. Also in this case, the above-described effects can be obtained.

  The embodiment described above is an example of the preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

13 Fuel Cell 21 Regeneration Device 21a Solution Inlet 21b Solution Outlet 21c Air Supply 21d Air Outlet 22 Redox Potential Monitor Pc Recursive Circulation Pump R32 Recursive Circulation

Claims (1)

A cathode, an anode, having said cathode and a proton conductive membrane between the anode, the mediator supplied to the cathode, generates electricity by reduction with protons resulting from the supplied fuel gas to the anode A fuel cell,
A regenerator that oxidizes the mediator reduced by the fuel gas with an oxidant gas introduced from an inlet and delivers it to the cathode from an outlet.
Fuel cell system comprising a circulation device for circulating the mediator from the vicinity of the outlet, in the vicinity of the inlet port via an external pump and route of the reproducing apparatus.

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