JP2019186160A - Fuel cell system - Google Patents

Abstract

To appropriately maintain moisture content of an electrolyte membrane of a fuel cell that generates power using liquid organic hydride and oxidant gas.SOLUTION: A fuel cell system 200 includes: a fuel cell 100 to generate power using liquid organic hydride and oxidant gas; a feeder 11 to feed liquid organic hydride to the fuel cell; an oxidant gas feeder 9 to feed oxidant gas to the fuel cell; a humidifier 10 to humidify oxidant gas fed to the fuel cell; a gas passage 4 through which off-oxidant gas discharged from the fuel cell flows; a valve 8 provided in the gas passage: and a controller 50 to adjust the aperture of the valve according to output current of the fuel cell.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to fuel cell systems.

Since depletion of fossil fuels such as coal and oil and global warming due to CO ₂ are regarded as problems, in recent years, efforts have been actively made toward an energy society that does not depend on fossil fuels. As one of such efforts, development of a fuel cell system is underway.

In the fuel cell system, when hydrogen (H ₂ ) is supplied to the anode of the fuel cell, at the anode, hydrogen liberates electrons on the catalyst layer to become protons (H ⁺ ). At this time, protons pass through the electrolyte membrane and move to the cathode of the fuel cell, while electrons pass through the external load and move to the cathode. At the cathode, an oxidant gas is supplied, and a reaction occurs between protons and electrons and oxygen (O ₂ ) in the oxidant gas to generate water. In this way, power generation is performed in the fuel cell system.

  The above fuel cell system using hydrogen gas as fuel has already been commercialized, but hydrogen gas is a dilute gas at normal temperature and normal pressure, so it is inconvenient to store and transport compared to liquid fuel. It is.

  In view of this, a fuel cell system has been proposed that includes a tank filled with a liquid organic hydride (hereinafter sometimes referred to as an organic hydride liquid) having a higher energy density than gas (see, for example, Non-Patent Document 1).

  Here, in the case of a polymer electrolyte fuel cell (hereinafter referred to as PEFC), if the electrolyte membrane is not sufficiently humidified, the proton conductivity of the electrolyte membrane may be lowered. However, since organic hydrides such as MCH in the tank are non-polar substances, they are difficult to mix with polar substances such as water. Therefore, Non-Patent Document 1 discloses a configuration in which an organic hydride liquid is vaporized by a vaporizer, and a configuration in which a mixed gas is supplied to the anode of the PEFC in a state where the organic hydride gas from the vaporizer and water vapor are mixed. Yes.

Kariya N. et al, Chem. Commun. 2003, 690

  However, in the conventional example, when supplying liquid organic hydride to the fuel cell, it has not been studied to keep the moisture content of the electrolyte membrane of the fuel cell appropriately.

  One aspect of the present disclosure has been made in view of such circumstances, and even when liquid organic hydride is supplied to a fuel cell, a reduction in the moisture content of the electrolyte membrane of the fuel cell is reduced as compared with the prior art. A fuel cell system is provided.

  In order to solve the above problems, a fuel cell system according to an aspect of the present disclosure includes a fuel cell that generates electric power using a liquid organic hydride and an oxidant gas, a feeder that supplies the liquid organic hydride to the fuel cell, An oxidant gas supplier for supplying an oxidant gas to the fuel cell, a humidifier for humidifying the oxidant gas supplied to the fuel cell, and a gas flow path through which off-oxidant gas discharged from the fuel cell flows And a valve provided in the gas flow path, and a controller for adjusting the opening of the valve in accordance with the output current of the fuel cell.

  The fuel cell system according to one embodiment of the present disclosure has an effect that a decrease in the moisture content of the electrolyte membrane of the fuel cell can be reduced as compared with the conventional case even when liquid organic hydride is supplied to the fuel cell.

FIG. 1 is a diagram illustrating an example of a fuel cell system according to an embodiment.

  In the case of supplying liquid organic hydride to the fuel cell, intensive studies have been conducted to appropriately maintain the moisture content of the electrolyte membrane of the fuel cell, and the following knowledge has been obtained.

  In a fuel cell, it is necessary to keep the electrolyte membrane in a wet state so as to obtain high proton conductivity in the electrolyte membrane. Therefore, conventionally, the anode gas and the cathode gas supplied to the fuel cell are often humidified in advance by, for example, a humidifier. For example, the amount of water contained in the anode gas and the cathode gas can be adjusted by controlling the temperature of the humidifier.

  In this way, water management of the electrolyte membrane of the fuel cell has been appropriately performed conventionally.

  However, when the organic hydride liquid is supplied to the anode of the fuel cell, water cannot be supplied from the anode side of the fuel cell, so that the moisture content of the electrolyte membrane tends to decrease on the anode side of the fuel cell.

Further, during power generation of the fuel cell, protons generated at the anode of the fuel cell and, for example, one water molecule present on the anode side of the fuel cell form a hydrogen bond to form H ₃ O ⁺ ions. Then, H ₃ O ⁺ ions move to the cathode side through the electrolyte membrane (electroosmosis). In other words, in the process of electroosmosis, the water present on the anode side of the fuel cell moves along with the protons and moves to the cathode. Therefore, as the output current of the fuel cell increases, the water content of the electrolyte membrane on the anode side of the fuel cell increases. The rate is further reduced.

  When the water content of the electrolyte membrane is reduced on the anode side of the fuel cell, the proton conductivity of the electrolyte membrane may be deteriorated.

  By the way, the flow rate (movement amount) of the water in the electrolyte membrane is formulated by the following formula (1).

In Equation (1), the first term on the right side represents the flow rate (j _EOD ) of electroosmotic water generated along with proton conduction in the electrolyte membrane. The second term on the right side represents the permeate flow rate (j _P ) of water generated by the difference in chemical potential (chemical potential gradient) between the anode and cathode of the fuel cell. That is, the amount of water movement of the electrolyte membrane is determined by the balance between the former electroosmotic water flow rate (j _EOD ) and the latter water permeation flow rate (j _P ). And since the chemical potential is pressure dependent (eg, proportional), the chemical potential gradient governing the latter water permeation flow rate (j _P ) depends on the pressure difference between the anode and cathode of the fuel cell (eg, ,Proportional.

From the above viewpoints, the inventors have found that the permeate flow rate (j _P ) of water moving from the cathode to the anode of the fuel cell can be controlled by changing the pressure difference between the cathode and the anode of the fuel cell. The inventors have arrived at the following aspects of the present disclosure. For example, if the pressure on the anode side of the fuel cell is fixed and the pressure on the cathode side of the fuel cell is increased, the permeate flow rate (j _P ) of water moving from the cathode of the fuel cell to the anode increases. It is possible to reduce the decrease in the moisture content of the electrolyte membrane on the anode side.

  That is, the fuel cell system according to the first aspect of the present disclosure includes a fuel cell that generates power using a liquid organic hydride and an oxidant gas, a feeder that supplies the liquid organic hydride to the fuel cell, and an oxidant for the fuel cell. An oxidant gas supply device that supplies gas, a humidifier that humidifies the oxidant gas supplied to the fuel cell, a gas flow path through which off-oxidant gas discharged from the fuel cell flows, and a gas flow path are provided. And a controller that adjusts the opening of the valve in accordance with the output current of the fuel cell.

According to such a configuration, the fuel cell system of this aspect can reduce the decrease in the moisture content of the fuel cell as compared with the conventional case even when liquid organic hydride is supplied to the fuel cell. That is, the controller adjusts the valve opening according to the output current of the fuel cell, thereby changing the pressure difference between the cathode and anode of the fuel cell, so that the water moving from the cathode of the fuel cell to the anode is changed. The permeation flow rate (j _P ) can be appropriately controlled. Then, the water content of the electrolyte membrane on the anode side of the fuel cell can be appropriately compensated by such movement of the electrolyte membrane.

For example, as the output current of the fuel cell increases or decreases, the pressure on the cathode side of the fuel cell is increased or decreased by adjusting the valve opening while the pressure on the anode side of the fuel cell is fixed. Then, the permeation flow rate (j _P ) of the water moving from the cathode of the fuel cell to the anode increases and decreases, so that it is possible to appropriately reduce the decrease in the moisture content of the electrolyte membrane on the anode side of the fuel cell. As an example, the valve opening is adjusted so that the permeate flow rate (j _P ) of water moving from the cathode to the anode of the fuel cell is larger than the flow rate (j _EOD ) of the electroosmotic water (j _P > j _EOD ). May be.

  Thus, the fuel cell system of this aspect can appropriately suppress the deterioration of the proton conductivity of the electrolyte membrane due to the decrease in the moisture content of the electrolyte membrane on the anode side of the fuel cell.

  Furthermore, the fuel cell system according to the present embodiment can simplify the apparatus configuration as compared with the invention described in Non-Patent Document 1 because a vaporizer or the like is not required when power is generated by the fuel cell using the organic hydride.

  In the fuel cell system according to the second aspect of the present disclosure, in the fuel cell system according to the first aspect, the controller may decrease the opening of the valve when the output current of the fuel cell increases.

As the output current of the fuel cell increases, the flow rate of electroosmotic water (j _EOD ) increases. In this case, the fuel cell system of the present embodiment increases the permeation flow rate (j _P ) of water moving from the cathode of the fuel cell to the anode by increasing the pressure on the cathode side of the fuel cell by controlling the small opening of the valve. Can do. Thereby, it can reduce effectively that the moisture content of an electrolyte membrane falls on the anode side of a fuel cell.

  In the fuel cell system according to the third aspect of the present disclosure, in the fuel cell system according to the first aspect and the second aspect, the controller may increase the opening of the valve when the output current of the fuel cell decreases.

When the output current of the fuel cell decreases, the electroosmotic water flow rate (j _EOD ) decreases. In this case, the fuel cell system of this aspect can reduce the permeate flow rate (j _P ) of water moving from the cathode of the fuel cell to the anode by reducing the pressure on the cathode side of the fuel cell by controlling the large opening of the valve. it can. Thereby, it is possible to perform control so that water does not become excessive on the anode side of the fuel cell.

  The fuel cell system according to the fourth aspect of the present disclosure is the fuel cell system according to any one of the first to third aspects, wherein the dew point of the oxidant gas at the inlet of the fuel cell is higher than the operating temperature of the fuel cell. The oxidant gas may be humidified with a humidifier.

  According to such a configuration, the fuel cell system of this aspect can appropriately humidify the oxidant gas supplied to the fuel cell so that the electrolyte membrane of the fuel cell can be maintained in a sufficiently wet state.

  Hereinafter, embodiments of the present disclosure will be specifically described with reference to the drawings. In addition, all embodiment described below shows a comprehensive or specific example. Therefore, numerical values, shapes, materials, components, arrangement positions and connection forms of components shown in the following embodiments are examples, and are not intended to limit the present disclosure. In addition, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims indicating the highest concept are described as optional constituent elements. In the drawings, the same reference numerals are sometimes omitted. In addition, the drawings schematically show each component for easy understanding, and there are cases where the shape and dimensional ratio are not accurately displayed.

(Embodiment)
FIG. 1 is a diagram illustrating an example of a fuel cell system according to an embodiment.

  In the example shown in FIG. 1, the fuel cell system 200 includes a fuel cell 100, an oxidant gas supply device 9, a humidifier 10, a supply device 11, a gas flow path 4, a valve 8, and a controller 50. . Here, the fuel cell 100 includes an electrolyte membrane 5, an anode AN, and a cathode CA.

  In the fuel cell system 200 of the present embodiment, the fuel cell 100 is disposed so as to partition the inside of the container. The region on the anode AN side of the vessel constitutes the anode chamber 6 through which the organic hydride liquid passes, and the region on the cathode CA side of the vessel constitutes the cathode chamber 7 through which the oxidant gas passes.

  However, this configuration is merely an example, and is not limited to this example.

  The electrolyte membrane 5 may have any configuration as long as the electrolyte membrane has proton conductivity. Examples of the electrolyte membrane 5 include a polymer electrolyte membrane. As a material for the polymer electrolyte membrane, for example, an organic polymer material having a polar group such as a strong acid group such as a sulfone group and a phosphoric acid group and a weak acid group such as a carboxyl group can be used. Specific examples include sulfonated poly (4-phenoxybenzoyl-1,4-phenylene), sulfonate group-containing perfluorocarbons, and the like. The latter is commercialized as Nafion (registered trademark, manufactured by DuPont).

  The anode AN is provided on one main surface of the electrolyte membrane 5. The anode AN is an electrode including a catalyst that oxidizes hydrogen in the organic hydride liquid. The anode AN may have any configuration as long as it is an electrode including such a catalyst. As the catalyst metal of such a catalyst, for example, a catalyst metal such as Pt, Pd, Ru, Rh, Ir, Au, Ag, Ni, Fe, Cu, a combination thereof, or a combination of these oxides, nitrides, etc. Although it can be used, it is not limited to these. Examples of the catalyst carrier include carbon. The anode AN may include a diffusion layer for diffusing the organic hydride liquid. When the anode AN is provided with such a diffusion layer, the diffusion layer is porous and conductive. It should be noted that water repellent treatment may be performed at an appropriate position on the surface of the material constituting the diffusion layer. Thereby, since water can be efficiently drained from the diffusion layer, generation of flooding in the diffusion layer can be suppressed.

  The cathode CA is provided on the other main surface of the electrolyte membrane 5. The cathode CA is an electrode including a catalyst that reduces protons. The cathode CA may have any configuration as long as it is an electrode including such a catalyst. As a catalyst metal of such a catalyst, for example, Pt can be used, but is not limited thereto. Examples of the catalyst carrier include carbon. The cathode CA may include a gas diffusion layer for diffusing the oxidant gas. When the cathode CA includes such a gas diffusion layer, the gas diffusion layer is porous and conductive. It should be noted that water repellent treatment may be performed at an appropriate position on the surface of the material constituting the gas diffusion layer. Thereby, since water can be efficiently drained from the gas diffusion layer, occurrence of flooding in the gas diffusion layer can be suppressed.

  The supply device 11 is a device that supplies an organic hydride liquid to the fuel cell 100. In this example, the organic hydride liquid is supplied from the supply device 11 to the anode chamber 6 in which the anode AN of the fuel cell 100 is provided.

  The supply device 11 may have any configuration as long as the organic hydride liquid can be supplied to the fuel cell 100. For example, a positive displacement pump can be used as the feeder 11, but is not limited thereto.

  An organic hydride (hydrogenated aromatic compound) is a compound in a state where hydrogen is stored by bonding hydrogen to the aromatic compound. “Organic hydride (hydrogenated aromatic compound)” is a compound in which hydrogen is added to all carbon-carbon double bonds of an aromatic compound, and does not contain a carbon-carbon unsaturated bond in the molecule.

  The aromatic compound may be a monocyclic aromatic compound or a polycyclic aromatic compound. Monocyclic aromatic compounds include benzene and phenol with a polar functional group on benzene, benzyl alcohol, O-cresol, m-cresol, p-cresol, cyclohexanecarboxaldehyde, and the like. Polycyclic aromatic compounds include 1-naphthol, 2-naphthol, 2-anthracenol, 9-anthrol and the like.

  Although it does not specifically limit as a hydrogenated aromatic compound, For example, bicyclic hydrogenated aromatics, such as monocyclic hydrogenated aromatics, such as a cyclohexane, a methylcyclohexane, and a dimethylcyclohexane, tetralin, a decalin, a methyl decalin, And tricyclic hydrogenated aromatics such as tetradecahydroanthracene. In particular, methylcyclohexane, tetralin and the like are preferably used.

  The organic hydride liquid may be mixed with a substance that functions as a mediator. Examples of such substances include quinone mediators such as 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), chloranil, and benzoquinone, ferrocene, and tetrathiafulvalene. It is not limited.

  The oxidant gas supplier 9 is a device that supplies oxidant gas to the fuel cell 100. In this example, the oxidizing gas is supplied to the cathode chamber 7 in which the cathode CA of the fuel cell 100 is provided by the oxidizing gas supplier 9.

The oxidant gas supply unit 9 may have any configuration as long as the oxidant gas can be supplied to the fuel cell 100. As the oxidant gas supply device 9, for example, a positive displacement blower, a mass flow controller or the like can be used, but is not limited thereto. Examples of the oxidant gas include, but are not limited to, air, oxygen (O ₂ ), a mixed gas of oxygen and an inert gas (such as nitrogen and argon), and the like.

  The humidifier 10 is a device that humidifies the oxidant gas supplied to the fuel cell 100. The humidifier 10 may have any configuration as long as the oxidant gas supplied to the fuel cell 100 can be humidified. The humidifier 10 may be, for example, a bubbling humidifier or a device that mixes an oxidant gas and water vapor. Although the illustration is omitted in the former case, the humidifier 10 includes a bubbling tank provided in the oxidant gas path, a heater for heating water in the bubbling tank, and a temperature detector for detecting the water temperature in the bubbling tank. Etc.

  Note that the oxidant gas dew point at the inlet of the fuel cell 100 (inlet of the cathode chamber 7) is larger than the operating temperature of the fuel cell 100 so that the electrolyte membrane 5 of the fuel cell 100 can be maintained in a sufficiently wet state. It is desirable to humidify the oxidant gas with the humidifier 10. For example, in the case where the humidifier 10 is a bubbling humidifier, the water temperature in the bubbling tank is made higher than the operating temperature of the fuel cell 100, so that the dew point of the oxidant gas is higher than the operating temperature of the fuel cell 100. Can also be increased.

  The gas passage 4 is a passage through which off-oxidant gas discharged from the fuel cell 100 flows. Specifically, of the oxidant gas supplied to the cathode chamber 7 by the oxidant gas supply device 9, the oxidant gas (off-oxidant gas) that was not used for power generation of the fuel cell 100 is the gas flow path 4. Through the cathode chamber 7 (for example, in the atmosphere).

  The valve 8 is provided in the gas flow path 4. Examples of the valve 8 include, but are not limited to, an electromagnetic valve that can take an arbitrary opening degree.

  The controller 50 adjusts the opening degree of the valve 8 according to the output current of the fuel cell 100. For example, when the output current of the fuel cell 100 is changed by increasing or decreasing the power consumption of the external load, the controller 50 adjusts the opening degree of the valve 8 according to this output current.

  For example, when the output current of the fuel cell 100 increases, the controller 50 decreases the opening degree of the valve 8. Then, the pressure loss in the gas flow path 4 increases, and the pressure on the cathode CA side of the fuel cell 100 (the pressure in the cathode chamber 7) increases.

  For example, when the output current of the fuel cell 100 decreases, the controller 50 increases the opening degree of the valve 8. Then, since the pressure loss of the gas flow path 4 becomes small, the pressure on the cathode CA side of the fuel cell 100 (the pressure in the cathode chamber 7) decreases.

  Although not shown, the fuel cell system 200 may include a pressure gauge that measures the pressure in the cathode chamber 7. Thereby, the controller 50 can perform feedback control based on the measurement data of the pressure gauge so that the pressure in the cathode chamber 7 becomes a desired pressure.

  The controller 50 may have any configuration as long as it has a control function. The controller 50 includes, for example, an arithmetic circuit (not shown) and a storage circuit (not shown) that stores a control program. Examples of the arithmetic circuit include an MPU and a CPU. An example of the memory circuit is a memory. The controller 50 may be configured by a single controller that performs centralized control, or may be configured by a plurality of controllers that perform distributed control in cooperation with each other.

As described above, the fuel cell system 200 of the present embodiment can reduce the decrease in the moisture content of the fuel cell 100 as compared with the conventional case even when supplying liquid organic hydride to the fuel cell 100. That is, the controller 50 adjusts the opening degree of the valve 8 in accordance with the output current of the fuel cell 100, whereby the pressure difference between the cathode CA and the anode AN of the fuel cell 100 is changed. The permeation flow rate (j _P ) of the water moving from the cathode CA to the anode AN can be appropriately controlled. Then, the water content decrease of the electrolyte membrane 5 on the anode AN side of the fuel cell 100 can be appropriately compensated by such movement of the electrolyte membrane 5.

For example, as the output current of the fuel cell 100 increases or decreases, the pressure on the cathode CA side of the fuel cell 100 (in the cathode chamber 7) is adjusted by adjusting the opening of the valve 8 while the pressure on the anode AN side of the fuel cell 100 is fixed. Increase or decrease the pressure. Then, the permeation flow rate (j _P ) of water moving from the cathode CA of the fuel cell to the anode AN increases / decreases, so that the water content of the electrolyte membrane 5 can be appropriately reduced on the anode AN side of the fuel cell 100. As an example, the permeation flow rate (j _P ) of water moving from the cathode CA to the anode AN of the fuel cell 100 is larger than the flow rate (j _EOD ) of the electroosmotic water (j _P > j _EOD ). The opening degree may be adjusted.

  Thus, the fuel cell system 200 of the present embodiment can appropriately suppress the deterioration of the proton conductivity of the electrolyte membrane 5 due to the decrease in the moisture content of the electrolyte membrane 5 on the anode AN side of the fuel cell 100. .

Specifically, when the output current of the fuel cell 100 increases, the flow rate (j _EOD ) of electroosmotic water increases. In this case, the fuel cell system 200 of the present embodiment permeates water moving from the cathode CA of the fuel cell 100 to the anode AN by increasing the pressure on the cathode CA side of the fuel cell 100 by controlling the small opening of the valve 8. The flow rate (j _P ) can be increased. Thereby, it can reduce effectively that the moisture content of the electrolyte membrane 5 falls by the anode AN side of the fuel cell 100. FIG.

Conversely, when the output current of the fuel cell 100 decreases, the electroosmotic water flow rate (j _EOD ) decreases. In this case, the fuel cell system 200 of the present embodiment reduces the pressure on the cathode CA side of the fuel cell 100 by controlling the large opening of the valve 8 so that the permeate flow rate of water moving from the cathode CA of the fuel cell 100 to the anode AN. (j _P ) can be reduced. Thereby, it is possible to perform control so that water does not become excessive on the anode AN side of the fuel cell 100.

  Furthermore, since the fuel cell system 200 of this embodiment does not require a carburetor or the like when generating power with the fuel cell 100 using an organic hydride, the apparatus configuration is simplified compared to the invention described in Non-Patent Document 1. Can be

  From the above description, many modifications and other embodiments of the present disclosure are apparent to persons skilled in the art. Accordingly, the foregoing description is to be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the disclosure. Details of the structure and / or function may be substantially changed without departing from the spirit of the present disclosure.

  One aspect of the present disclosure can be used in a fuel cell system that can reduce a decrease in the moisture content of an electrolyte membrane of a fuel cell as compared with the conventional case even when liquid organic hydride is supplied to the fuel cell.

4: Gas channel 5: Electrolyte membrane 6: Anode chamber 7: Cathode chamber 8: Valve 9: Oxidant gas supply device 10: Humidifier 11: Supply device 50: Controller 100: Fuel cell 200: Fuel cell system AN: Anode CA: Cathode

Claims (4)

A fuel cell that generates electricity using liquid organic hydride and oxidant gas;
A feeder for supplying liquid organic hydride to the fuel cell;
An oxidant gas supplier for supplying an oxidant gas to the fuel cell;
A humidifier for humidifying the oxidant gas supplied to the fuel cell;
A gas flow path through which off-oxidant gas discharged from the fuel cell flows;
A valve provided in the gas flow path;
A controller for adjusting the opening of the valve according to the output current of the fuel cell;
A fuel cell system comprising:   The fuel cell system according to claim 1, wherein the controller decreases the opening of the valve when the output current of the fuel cell increases.   The fuel cell system according to claim 1 or 2, wherein the controller increases the opening of the valve when the output current of the fuel cell decreases.   The fuel cell system according to any one of claims 1 to 3, wherein the humidifier humidifies the oxidant gas so that a dew point of the oxidant gas at the inlet of the fuel cell becomes higher than an operating temperature of the fuel cell. .

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