Fuel cell system

Abstract

In fuel cell systems that perform scavenging, this suppresses the degradation of the electrolyte membrane. [Solution] A fuel cell system comprising a fuel gas system, an oxidizer gas system, and a control device, wherein the control device can perform scavenging control, and in scavenging control, scavenging on the anode side is started first, followed by scavenging on the cathode side.

Description

[[Technical Field]]

[0001] The present disclosure relates to a fuel cell system. [[Background Art]]

[0002] Patent Document 1 discloses that in a fuel cell system, the scavenging time and start timing of anode scavenging are set based on the water content of the cathode, and the anode scavenging time and start timing are determined based on the water content of the cathode. [[Prior Art Literature]] [[Patent Literature]]

[0003] [[Patent Document 1]] Japanese Unexamined Patent Application Publication No. 2024-106454 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0004] When scavenging is performed as in Patent Document 1, the cathode dries first, so liquid water containing impurities on the anode side easily moves to the cathode side, and the electrolyte membrane is prone to degradation.

[0005] An object of the present disclosure is to suppress degradation of an electrolyte membrane in a fuel cell system that performs scavenging. [[Means for Solving the Problem]]

[0006] The present application discloses a fuel cell system including a fuel gas system, an oxidant gas system, and a control device, wherein the control device can perform scavenging control, and in the scavenging control, scavenging on the anode side is started first, and then scavenging on the cathode side is started.

[0007] In the scavenging control, the scavenging on the cathode side may be configured to start after the water content on the anode side becomes equal to or less than a predetermined value.

[0008] In scavenging control, the system may be configured to start scavenging on the cathode side after a certain period of time has elapsed following the start of scavenging on the anode side. [Effects of the Invention]

[0009] According to the fuel cell system of this disclosure, by scavenging the anode first and then starting cathode scavenging, it is possible to make it difficult for the liquid water on the anode side to move, thereby suppressing the deterioration of the electrolyte membrane. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a conceptual diagram showing the configuration of the fuel cell system 10. [Figure 2] Figure 2 illustrates the flow of the scavenging control S10. [Modes for carrying out the invention]

[0011] In fuel cell systems, scavenging is performed when power generation ends. Immediately after power generation ends, the cathode side is wet from upstream to downstream with water generated by power generation, while the anode side becomes wet as water diffuses from the area wet downstream of the cathode towards the anode. Therefore, under all power generation conditions, the amount of liquid water is less on the anode side than on the cathode side. Oxygen that permeates from the cathode to the anode combines with hydrogen to produce hydrogen peroxide, generating radicals that decompose a large amount of the electrolyte membrane components on the anode side. However, these radicals become more concentrated in the small amount of liquid water, making the corrosive environment more severe. As a result, the anode side contains many impurities (e.g., Fe ions originating from the stainless steel separator) in the small amount of liquid water, while the cathode side contains fewer impurities (e.g., the aforementioned Fe ions) in the large amount of liquid water. In this state, the anode and cathode are scavenged. However, if the anode and cathode are scavenged simultaneously, the cathode is scavenged with a large flow rate of dry air, while the anode is scavenged with a low flow rate (for fuel efficiency) of hydrogen moistened by circulation. As a result, the cathode dries out first, and liquid water reverse-diffuses from the anode to the cathode. This reverse diffusion of liquid water incorporates impurities (such as the Fe ions mentioned above) into the electrolyte membrane, accelerating the Fenton reaction that generates radicals from hydrogen peroxide and thus accelerating membrane degradation.

[0012] To address this issue, this disclosure suppresses the deterioration of the electrolyte membrane by drying the anode side first, followed by drying the cathode side with a delay. More specific examples of this approach are described below.

[0013] The gas used for scavenging (drainage) as described below may be an oxidizing gas, fuel gas, nitrogen gas, etc. The gas used for scavenging the cathode may be an oxidizing gas, nitrogen gas, etc. The gas used for scavenging the anode may be a fuel gas, nitrogen gas, etc.

[0014] Furthermore, the fuel cell system of this disclosure may be used mounted on a mobile body such as a vehicle, or it may be used mounted on a generator that supplies power to an external source. The vehicle may be a fuel cell vehicle or the like. Examples of mobile bodies other than vehicles include railways, ships, and aircraft. The fuel cell system of this disclosure may be used mounted on a mobile body such as a vehicle that can also run on the power of a secondary battery. The mobile body may have drive units such as a motor, inverter, and hybrid control system. The hybrid control system may be capable of driving the mobile body by using both the output of the fuel cell and the power of the secondary battery.

[0015] Furthermore, in this specification, the reaction gas supplied to the anode is a fuel gas, and the reaction gas supplied to the cathode is an oxidizing gas. The fuel gas is a gas mainly containing hydrogen, and may be pure hydrogen. The oxidizing gas is a gas containing oxygen, and may be oxygen, air, dry air, etc.

[0016] 1. Example of a fuel cell system configuration Figure 1 is a schematic diagram showing one example of a fuel cell system 10 of the present disclosure. The fuel cell system 10 shown in Figure 1 comprises a fuel cell 11, an oxidizer gas system 20, a fuel gas system 30, an impedance measuring instrument (not shown), and a control device (FC-ECU) 40. For convenience, the cooling system is omitted from Figure 1.

[0017] 1.1.Fuel cell The fuel cell 11 may consist of only one single cell, which is the smallest unit of power generation, or it may be a fuel cell stack (sometimes referred to as an FC stack, stack, etc.) which is a stack of multiple single cells. In this disclosure, both a single cell and a fuel cell stack are referred to as a fuel cell. The number of stacked single cells is not particularly limited and may range from 2 to several hundred, for example.

[0018] A single cell of a fuel cell typically comprises a membrane electrode gas diffusion layer assembly. The membrane electrode gas diffusion layer assembly has, in this order, an anode gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode gas diffusion layer.

[0019] The cathode (oxidizer electrode) includes a cathode catalyst layer and a cathode-side gas diffusion layer. The anode (fuel electrode) includes an anode catalyst layer and an anode-side gas diffusion layer. The cathode catalyst layer and the anode catalyst layer are collectively referred to as the catalyst layer. The catalyst layer may comprise, for example, a catalytic metal that promotes electrochemical reactions, a proton-conducting electrolyte, and an electronically conductive support. Examples of catalytic metals include platinum (Pt) and alloys of Pt with other metals (e.g., a Pt alloy mixed with cobalt and nickel). The electrolyte may be a fluororesin. For example, a Nafion solution may be used as the fluororesin. The catalyst metal is supported on a carrier, and in each catalyst layer, a carrier supporting the catalyst metal (catalyst-supporting carrier) and an electrolyte may coexist. Examples of the carrier for supporting the catalyst metal include generally commercially available carbon materials such as carbon.

[0020] The cathode-side gas diffusion layer and the anode-side gas diffusion layer are collectively referred to as gas diffusion layers. The gas diffusion layer may be a conductive member or the like having gas permeability. Examples of the conductive member include carbon porous bodies such as carbon cloth and carbon paper, and metal porous bodies such as metal mesh and foamed metal.

[0021] The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include fluorine-based electrolyte membranes such as water-containing perfluorosulfonic acid thin films, and hydrocarbon-based electrolyte membranes. As the electrolyte membrane, for example, a Nafion membrane (manufactured by DuPont) may be used.

[0022] The unit cell may optionally include two separators that sandwich both surfaces of the membrane electrode gas diffusion layer assembly. One of the two separators is an anode-side separator, and the other is a cathode-side separator. In the present disclosure, the anode-side separator and the cathode-side separator are collectively referred to as separators. The separator may have holes that constitute manifolds such as supply holes and discharge holes for allowing fluids such as reaction gas and cooling medium to flow in the stacking direction of the unit cells. As the cooling medium, for example, cooling water such as a mixed solution of ethylene glycol and water can be used to prevent freezing at low temperatures. Furthermore, cooling air can be used as the cooling medium. Examples of the supply holes include a fuel gas supply hole, an oxidant gas supply hole, and a cooling medium supply hole. Examples of the discharge holes include a fuel gas discharge hole, an oxidant gas discharge hole, and a cooling medium discharge hole.

[0023] The separator may have a reaction gas channel on the side in contact with the gas diffusion layer. Alternatively, the separator may have a cooling medium channel on the side opposite to the side in contact with the gas diffusion layer to maintain a constant temperature in the fuel cell.

[0024] The separator may be a gas-impermeable conductive material. Examples of conductive materials include dense carbon, which is compressed to be gas-impermeable, and press-formed metal plates (e.g., iron, aluminum, and stainless steel). The separator may also have a current-collecting function. Furthermore, considering the problematic effects of Fe ions as described above, the effectiveness is particularly pronounced when using iron or stainless steel as the separator in this disclosure.

[0025] The fuel cell 11 may have manifolds such as an inlet manifold through which each supply port is connected, and an outlet manifold through which each discharge port is connected. Inlet manifolds include anode inlet manifolds, cathode inlet manifolds, and cooling medium inlet manifolds. Outlet manifolds include anode outlet manifolds, cathode outlet manifolds, and cooling medium outlet manifolds.

[0026] 1.2. Oxidizing gas system The oxidizer gas system 20 supplies oxidizer gas to the fuel cell 11 and discharges off-gas from the fuel cell 11. The oxidizer gas system 20 has an air compressor 22, a pressure sensor P, a temperature sensor T, an inlet sealing valve 23, a pressure regulating valve 24, and a bypass valve 25 in the oxidizer side flow path 21.

[0027] The oxidizer-side flow path 21 includes an oxidizer gas supply flow path 21a, an oxidizer gas off-gas flow path 21b, and a bypass flow path 21c.

[0028] [Oxidizing gas supply channel 21a and equipment provided therein] The oxidant gas supply channel 21a is a channel for supplying oxidant gas to the fuel cell 11, and connects the outside of the fuel cell system 10 to the cathode inlet of the fuel cell 11. The oxidant gas supply channel 21a enables the supply of oxidant gas from the air compressor 22 to the cathode of the fuel cell. The cathode inlet may be an oxidant gas supply port, a cathode inlet manifold, or the like. The oxidizer gas supply channel 21a is equipped with an air compressor 22, a pressure sensor P, a temperature sensor T, and an inlet sealing valve 23.

[0029] The air compressor 22 comprises bearings, a rotor, and a housing. The air compressor 22 is electrically connected to a control device 40, and the rotational speed of its rotor is controlled according to a control signal from the control device 40. The inlet sealing valve 23 is a valve located downstream of the air compressor 22 and is electrically connected to the control device 40. The control device 40 opens the inlet sealing valve 23, supplying oxidant gas to the cathode of the fuel cell 11. The flow rate of oxidant gas supplied to the cathode may also be adjusted by adjusting the opening degree of the inlet sealing valve 23.

[0030] A pressure sensor P, a temperature sensor T, a flow sensor (not shown), and the like may be placed downstream of the air compressor 22 in the oxidizer gas supply channel 21a. The pressure sensor P is a device that measures the pressure value of the cathode and is electrically connected to the control device 40. The control device 40 acquires the cathode pressure value measured by the pressure sensor P. The temperature sensor T is a device that measures the cathode temperature and is electrically connected to the control device 40. The control device 40 acquires the cathode temperature measured by the temperature sensor T. The flow sensor is a device that measures the flow rate of the oxidizer gas and is electrically connected to the control device 40. The control device 40 acquires the flow rate of the oxidizer gas measured by the flow sensor.

[0031] [Oxidizer-off discharge channel 21b and equipment provided therewith] The oxidant off-gas discharge channel 21b connects the cathode outlet of the fuel cell 11 to the outside of the fuel cell system 10. The oxidant off-gas discharge channel 21b allows the oxidant off-gas, which is the oxidant gas discharged from the cathode of the fuel cell 11, to be discharged to the outside of the fuel cell system 10. The cathode outlet may be an oxidant gas discharge port, a cathode outlet manifold, etc. A pressure regulating valve 24 may be placed in the oxidant off-gas discharge channel 21b. The pressure regulating valve 24 is electrically connected to the control device 40. When the control device 40 opens the pressure regulating valve 24, the oxidant off-gas, which is the reacted oxidant gas, is discharged to the outside of the fuel cell system 10 through the oxidant off-gas discharge channel 21b. The oxidant gas pressure supplied to the cathode (cathode pressure) may also be adjusted by adjusting the opening degree of the pressure regulating valve 24. The oxidant off-gas may have the same components as the oxidant gas, or it may be oxygen, air, dry air, etc., or it may contain water vapor, etc.

[0032] [Bypass channel 21c and equipment provided therein] The bypass channel 21c connects the oxidant gas supply channel 21a and the oxidant off-gas discharge channel 21b, and is a channel that bypasses the fuel cell 11. The bypass channel 21c branches off from the oxidant gas supply channel 21a at a branching point downstream of the air compressor 22 of the oxidant gas supply channel 21a, bypasses the fuel cell 11, and merges with the oxidant off-gas discharge channel 21b downstream of the pressure regulating valve 24 of the oxidant off-gas discharge channel 21b.

[0033] A bypass valve 25 may be placed in the bypass passage 21c. The bypass valve 25 may be a valve with an adjustable opening degree, or it may be a three-way valve for the oxidizer gas. In the case of a three-way valve for the oxidizer gas, it may be placed at the branching point which is the uppermost part of the bypass passage, and it also serves as an oxidizer gas inlet sealing valve. The bypass valve 25 is electrically connected to the control device 40, and when the control device 40 opens the bypass valve 25, at least a portion of the oxidizer gas can be supplied to the oxidizer off-gas discharge channel 21b, bypassing the fuel cell 11. If the bypass valve 25 is a three-way valve for oxidizer gas, when it is not necessary to supply oxidizer gas to the fuel cell 11, the control device 40 can close the valve on the downstream side of the oxidizer gas supply channel 21a and open the valve on the bypass channel 21c side of the bypass valve 25, so that the flow of oxidizer gas goes from the oxidizer gas supply channel 21a to the bypass channel 21c, thereby supplying the entire amount of oxidizer gas to the oxidizer off-gas discharge channel 21b.

[0034] [others] The oxidizer gas system 20 may include a cooler (intercooler) downstream of the air compressor 22 in the oxidizer gas supply channel 21a. The cooler may be located downstream of the air compressor 22 in the oxidizer gas supply channel 21a and upstream of the branching point with the bypass channel 21c. A cooler may perform its cooling function by circulating the cooling medium of the cooling system inside and outside the cooler.

[0035] The oxidizer gas system 20 may include a humidifier downstream of the air compressor 22 in the oxidizer gas supply channel 21a. The humidifier may be located downstream of the air compressor 22 in the oxidizer gas supply channel 21a and downstream of the branching point with the bypass channel 21c. The humidifier may be positioned across the oxidizer gas supply channel 21a and the oxidizer off-gas discharge channel 21b.

[0036] 1.3. Fuel Gas System The fuel gas system 30 supplies fuel gas to the fuel cell 11, discharges off-gas from the fuel cell 11, and recirculates a portion of it. The fuel gas system 30 includes a fuel gas agent side passage 31, an ejector 32, an inlet sealing valve (LSV or injector (INJ)) 33, an intermediate pressure sensor (intermediate pressure hydrogen sensor) 34, an anode gas-liquid separator 35, and an exhaust drain valve 36. The fuel gas is supplied, for example, by a fuel tank, specifically a liquid hydrogen tank and a compressed hydrogen tank.

[0037] The fuel gas agent side passage 31 includes a fuel gas supply passage 31a, a fuel off-gas discharge passage 31b, and a circulation passage 31c.

[0038] [Fuel gas supply channel 31a and equipment provided therein] The fuel gas supply channel 31a connects a fuel gas supply unit, such as a fuel tank, to the anode inlet of the fuel cell 11. The fuel gas supply channel 31a enables the supply of hydrogen-containing fuel gas to the anode of the fuel cell 11. The anode inlet may be a fuel gas supply port, an anode inlet manifold, or the like.

[0039] The ejector 32 may be placed at the junction of the fuel gas supply passage 31a and the circulation passage 31c. Furthermore, an inlet sealing valve 33 may be placed upstream of the ejector 32 in the fuel gas supply passage 31a. The inlet sealing valve 33 is electrically connected to the control device 40, and when the control device 40 opens the inlet sealing valve 33, fuel gas is supplied to the anode of the fuel cell 11. The flow rate of fuel gas supplied to the anode may also be adjusted by adjusting the opening degree of the inlet sealing valve 33. The inlet sealing valve 33 may be a linear solenoid valve, an injector, etc.

[0040] The intermediate pressure sensor 34 may be located upstream of the inlet sealing valve 33 of the fuel gas supply passage 31a. The intermediate pressure sensor 34 measures the anode pressure value and is electrically connected to the control device 40. The control device 40 acquires the anode pressure value measured by the intermediate pressure sensor 34.

[0041] [Fuel off-gas discharge passage 31b and equipment provided therein] The fuel off-gas discharge channel 31b connects the anode outlet of the fuel cell 11 to the outside of the fuel cell system 10. The anode outlet may be a fuel gas discharge port, an anode outlet manifold, etc. The fuel off-gas may include fuel gas that has passed through the anode unreacted, and water generated at the cathode that has reached the anode. The fuel off-gas may also include corrosive substances generated in the catalyst layer and electrolyte membrane, and oxidizing gases that may be supplied to the anode during scavenging.

[0042] An anode gas-liquid separator 35 is positioned at the branching point between the fuel off-gas discharge channel 31b and the circulation channel 31c. The gas separated by the gas-liquid separator 35 moves into the circulation channel 31c, while the liquid moves to the downstream side of the fuel off-gas discharge channel 31b. An exhaust drain valve 36 may be located downstream of the anode gas-liquid separator 35 in the fuel off-gas discharge passage 31b. The exhaust drain valve 36 is electrically connected to the control device 40, and its opening and closing are controlled by the control device 40.

[0043] [Circulation channel 31c] The circulation passage 31c branches off from the fuel off-gas discharge passage 31b at the branching point (anode gas-liquid separator 35) with the fuel off-gas discharge passage 31b, and merges with the fuel gas supply passage 31a at the junction (ejector 32) with the fuel gas supply passage 31a, circulating the fuel off-gas as a circulating gas within the fuel gas system.

[0044] 1.4. Impedance measuring instruments The impedance measuring instrument is a device for measuring the impedance of the anode, and any known instrument can be used. The impedance measuring instrument is electrically connected to the control device 40, and is configured so that the control device 40 can acquire the obtained impedance.

[0045] 1.5. Control Device The control device 40 includes, for example, a processing unit such as a CPU (Central Processing Unit), a ROM (Read-Only Memory) for storing control programs and control data processed by the CPU, a storage device such as a RAM (Random Access Memory) mainly used as various work areas for control processing, and an input / output interface. The control unit may also be, for example, a power control unit (PCU) and an electronic control unit (ECU). The control device 40 may be electrically connected to an ignition switch, which may be mounted on the vehicle. The control device 40 may also be able to operate using an external power source even when the ignition switch is turned off.

[0046] One of the functions of the control device is to calculate the water content of the anode based on the anode's impedance obtained from an impedance measuring instrument. This can be done by pre-storing a data set showing the relationship between the anode's impedance and its water content, and then referring to this data set to obtain the water content of the fuel cell's anode.

[0047] 1.5. Others The fuel cell system 10 may include a cooling system (not shown). The cooling system is a system for regulating the temperature of the fuel cell. The cooling system has a cooling medium flow path, which allows the cooling medium to circulate inside and outside the fuel cell. The cooling medium flow path communicates with a cooling medium supply port and a cooling medium discharge port provided in the fuel cell, which allows the cooling medium to circulate inside and outside the fuel cell. A cooling medium supply unit may be provided in the cooling medium flow path. The cooling medium supply unit is electrically connected to the control device 40. The cooling medium supply unit is driven according to a control signal from the control unit. The control unit controls the flow rate of the cooling medium supplied from the cooling medium supply unit to the fuel cell. This controls the temperature of the fuel cell 11. The cooling medium supply unit may be, for example, a cooling water pump. The cooling medium flow path may be equipped with a radiator for dissipating heat from the cooling medium and a reserve tank for storing the cooling medium.

[0048] The fuel cell system 10 may be equipped with a battery. The battery (secondary battery) can be any type that is capable of charging and discharging, and examples of conventionally known secondary batteries include nickel-metal hydride secondary batteries and lithium-ion secondary batteries. The secondary battery may also include an energy storage element such as an electric double-layer capacitor, and may be configured by connecting multiple batteries in series. The secondary battery supplies power to the air compressor, etc. The secondary battery may be rechargeable from an external power source in the vehicle, such as a household power supply, or it may be charged by the output of the fuel cell. The charging and discharging of the secondary battery may be controlled by the control device 40.

[0049] 2. Scavenging control Figure 2 shows the flow of scavenging control S10 in one example configuration. In this configuration, scavenging control S10 is performed by acquiring information by the control device 40 described above and controlling based on the results of calculations performed by the program using the acquired information. The following describes each process of the scavenging control S10.

[0050] 2.1. Start of anode-side scavenging S11 At the start of anode-side scavenging S11, scavenging on the anode side is initiated. In other words, when scavenging control is started, scavenging on the anode side is initiated first.

[0051] 2.2. Impedance Acquisition S12 In impedance acquisition S12, the anode impedance is obtained from the impedance measuring instrument described above.

[0052] 2.3. Anode water content calculation S13 In the anode water content calculation S13, the water content on the anode side is calculated from the impedance on the anode side obtained in impedance acquisition S12.

[0053] 2.4. Determination of water content S14 In the water content determination S14, it is determined whether the water content on the anode side, calculated in the anode water content calculation S13, is below a predetermined value (threshold). If the moisture content does not reach the threshold, the response is "No," and the process returns to impedance acquisition S12. Anode scavenging continues during this time. On the other hand, if the water content falls below the threshold, the response is "Yes," and the process proceeds to S15. Anode scavenging continues during this time.

[0054] 2.5. Start of cathode-side scavenging S15 At the start of cathode-side scavenging S15, scavenging on the cathode side is initiated. After this, the scavenging control ends when scavenging of both the anode and cathode is completed.

[0055] 3. Effects, etc. In this configuration, scavenging is initiated from the anode side first, and scavenging of the cathode is initiated only after the water content falls below a certain value (threshold). This suppresses the movement of liquid water from the anode side to the cathode side, thereby suppressing the deterioration of the electrolyte membrane.

[0056] In the above-described example, we explained a case where the anode's water content is obtained before starting the cathode's scavenging to obtain a more reliable effect. However, the effect is achieved by starting the cathode's scavenging after a certain amount of anode scavenging has progressed, so the example is not limited to the above. For example, it is conceivable to control the system so that the cathode's scavenging is started after a predetermined time has elapsed since the anode's scavenging began, based on a database obtained in advance through tests or other means. [Explanation of symbols]

[0057] 10…Fuel cell system, 11…Fuel cell, 20…Oxidizing gas system, 30…Fuel gas system, 40…Control device, S10…Scavenging control

Claims

1. A fuel cell system comprising a fuel gas system, an oxidizer gas system, and a control device, The control device can perform scavenging control. In the aforementioned scavenging control, scavenging on the anode side is started first, followed by scavenging on the cathode side. Fuel cell system.

2. The fuel cell system according to claim 1, wherein the scavenging control starts scavenging the cathode side after the water content on the anode side falls below a certain value.

3. The fuel cell system according to claim 1, wherein in the scavenging control, scavenging on the cathode side is started after a certain period of time has elapsed since the scavenging on the anode side was started.

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