fuel cell unit

Abstract

To provide a fuel cell unit that can suppress a decrease in performance even when stored for a long period of time.SOLUTION: While a stack is not supplying power to an external load, a fuel cell unit uses an air supply valve to block an air supply passage (S17), uses an air exhaust valve to block an air exhaust passage (S19), and shuts off the supply of air to a cathode electrode. The fuel cell unit uses a hydrogen exhaust valve to block a hydrogen exhaust passage (S21), uses a hydrogen supply valve to open a hydrogen supply passage (S23), and supplies hydrogen to an anode electrode. The fuel cell unit uses the hydrogen supply valve to block the hydrogen supply passage (S25), and shuts off the supply of hydrogen to the anode electrode. After shutting off the supply of hydrogen to the anode electrode, the fuel cell unit waits on standby until the stack voltage measured by a voltage measurement part becomes less than a prescribed voltage threshold value (S27).SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a fuel cell unit. [Background technology]

[0002] When an oxide film forms on the catalyst of the cathode electrode of a fuel cell, the performance of the fuel cell decreases. For this reason, a technology has been proposed to remove the oxide film from the catalyst and activate it. Patent Document 1 discloses a catalyst activation method for a fuel cell. In this catalyst activation method, the catalyst of the cathode electrode is activated by the following procedure. First, hydrogen is sealed in the anode, the air supply line side of the cathode electrode is sealed, and the air exhaust line side of the cathode electrode is opened to the atmosphere. Next, the air exhaust line side of the cathode electrode is sealed and maintained in this state. This reduces the cell voltage to below the reduction potential of the oxide film formed on the catalyst of the cathode electrode, activating the catalyst of the cathode electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6614120 Summary of the Invention [Problem to be solved by the invention]

[0004] In the catalyst activation method described in Patent Document 1, hydrogen is sealed in the anode while the air exhaust line side of the cathode is open to the atmosphere. This can cause hydrogen that has permeated the cathode side to be discharged through the exhaust line, or air to enter the fuel cell through the exhaust line. For example, if the fuel cell is stored in this state for a long period of time without generating electricity, the catalyst may be re-oxidized by air, which can cause a decrease in the performance of the fuel cell.

[0005] An object of the present invention is to provide a fuel cell unit that can suppress performance degradation even when stored for a long period of time. [Means for solving the problem]

[0006] A fuel cell unit according to the present invention comprises a stack having at least one cell having an anode, a cathode, and a catalyst; a plurality of flow paths including a hydrogen supply path for supplying hydrogen to the anode, a hydrogen discharge path for discharging hydrogen from the anode, an air supply path for supplying air to the cathode, and an air discharge path for discharging air from the cathode; a plurality of valves including a hydrogen supply valve capable of opening and closing the hydrogen supply path, a hydrogen discharge valve capable of opening and closing the hydrogen discharge path, an air supply valve capable of opening and closing the air supply path, and an air discharge valve capable of opening and closing the air discharge path; a voltage measurement unit that measures a stack voltage, which is a voltage between the anode and the cathode of the stack; and a control unit that controls the plurality of valves to open and close the plurality of flow paths, wherein the control unit is configured to measure the stack voltage when the stack is not supplying power to an external load. a hydrogen supply process in which, after the air supply to the cathode is blocked by the air blocking process, the hydrogen discharge channel is blocked by the hydrogen discharge valve and the hydrogen supply channel is opened by the hydrogen supply valve to supply hydrogen to the anode; a hydrogen blocking process in which, after hydrogen has been supplied to the anode by the hydrogen supply process, the hydrogen supply channel is blocked by the hydrogen supply valve to block the hydrogen supply channel to block the supply of hydrogen to the anode; and a first waiting process in which, after the supply of hydrogen to the anode is blocked by the hydrogen blocking process, the stack voltage measured by the voltage measurement unit is waited until the stack voltage measured by the voltage measurement unit becomes less than a predetermined voltage threshold.

[0007] With hydrogen and air filled in the stack, the fuel cell unit waits until the stack voltage falls below the voltage threshold. At this time, the oxidized portion of the catalyst is reduced and activated by the hydrogen. During the process of filling the stack with hydrogen, the air supply path and air discharge path are blocked, preventing air from entering the stack through the air supply path and air discharge path. Therefore, even if the fuel cell unit is stored for a long period of time without supplying power to an external load, performance degradation can be suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an outline of a fuel cell unit 1. [Figure 2] 10 is a graph showing the change over time in stack power (maximum) of fuel cell 1A. [Figure 3] 1 is a graph showing the change over time in the reaction overvoltage of fuel cell 1A. [Figure 4] 3 is a block diagram showing the electrical configuration of a control device 6. FIG. [Figure 5] 10 is a flowchart of a main process. [Figure 6] 10 is a graph showing the change over time in stack voltage of fuel cell 1A. [Figure 7] 10 is a graph showing the change over time in stack power of fuel cell 1A. [Figure 8] 10 is a flowchart of a power generation process. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of a fuel cell unit 1 according to the present invention will be described with reference to the drawings. The drawings are used to explain the technical features that can be adopted by the present invention, and the configuration of the device described therein is not intended to be limiting but is merely an illustrative example.

[0010] <Outline of Fuel Cell Unit 1> 1, an overview of the fuel cell unit 1 will be described. The fuel cell unit 1 includes a fuel cell 1A, multiple flow paths 20, multiple valves 20A, pumps 31 and 32, a filter 33, a hydrogen supply source 41, an air supply source 42, a voltage measurement unit 5, and a control device 6.

[0011] The fuel cell 1A has a stack structure in which 16 cells 10 are stacked. Adjacent cells 10 are separated by separators (not shown). Each cell 10 has an anode 11, a cathode 12, and an electrolyte (e.g., a solid polymer electrolyte membrane) 13. The electrolyte 13 is sandwiched between the anode 11 and the cathode 12. The anode 11 includes an anode electrode 11A and an anode catalyst 11B. The cathode 12 includes a cathode electrode 12A and a cathode catalyst 12B. The anode electrode 11A and the cathode electrode 12A are electrodes. The anode catalyst 11B and the cathode catalyst 12B are made of, for example, Pt supported on acetylene black. Note that the materials for the anode catalyst 11B and the cathode catalyst 12B are not limited to the exemplified materials and may be other materials. The separator is in the form of a plate and is placed between each cell 10. One surface of the separator has a hydrogen flow path facing the anode 11A of the cell 10, and the other surface has an oxidant flow path facing the cathode 12A of the cell 10. In this embodiment, air is used as the oxidant.

[0012] The 16 cells 10 are connected in series. The fuel cell 1A outputs a voltage to the output terminal 100. The voltage output to the output terminal 100 is equal to the sum of the voltages between the anode 11A and cathode 12A of each cell 10. Hereinafter, this voltage will be referred to as the "stack voltage." The fuel cell unit 1 can supply power to an external load Ld connected externally to the output terminal 100 by applying the stack voltage to the external load Ld.

[0013] The hydrogen supply source 41 is an intake port for hydrogen and functions as a supply source of hydrogen consumed by the fuel cell 1A. For example, the hydrogen supply source 41 is connected to a hydrogen tank (not shown), and hydrogen stored in the hydrogen tank is taken in. The hydrogen supply source 41 may be connected to a hydrogen tank or a water electrolysis device. The air supply source 42 is an intake port for air and functions as a supply source of air consumed by the fuel cell 1A. For example, air from the atmosphere is taken in by the air supply source 42. The air supply source 42 may be connected to an air tank or a water electrolysis device. The pressure of the hydrogen from the hydrogen supply source 41 is set higher than the pressure of the air from the air supply source 42.

[0014] The multiple flow paths 20 include a hydrogen supply path 21, a hydrogen discharge path 22, an air supply path 23, an air discharge path 24, and a hydrogen circulation path 25. The hydrogen supply path 21, the hydrogen discharge path 22, and the hydrogen circulation path 25 are pipes through which hydrogen flows. The hydrogen supply path 21 supplies hydrogen from a hydrogen supply source 41 to the anode 11A of each cell 10. The hydrogen discharge path 22 discharges hydrogen from the anode 11A of each cell 10. The hydrogen circulation path 25 circulates hydrogen not consumed in the cell 10 to the hydrogen supply path 21 by flowing hydrogen from the hydrogen discharge path 22 toward the hydrogen supply path 21 outside the stack of the fuel cell 1A. The air supply path 23 and the air discharge path 24 are pipes through which air flows. The air supply path 23 supplies air from an air supply source 42 to the cathode 12A of each cell 10. The air exhaust passage 24 exhausts air from the cathode 12A of each cell 10.

[0015] The pump 31 is disposed in the hydrogen circulation path 25. The pump 31 forms a flow of hydrogen in the hydrogen circulation path 25 from the hydrogen discharge path 22 toward the hydrogen supply path 21. The pump 32 is disposed in the air supply path 23. The pump 32 forms a flow of air in the air supply path 23 from the air supply source 42 toward the cathode 12A of each cell 10. The filter 33 is disposed in the air supply path 23 between the air supply source 42 and the pump 32. The filter 33 removes impurities from the air flowing through the air supply path 23.

[0016] The multiple valves 20A include a hydrogen supply valve 21A, a hydrogen discharge valve 22A, an air supply valve 23A, and an air discharge valve 24A. The hydrogen supply valve 21A is provided in the hydrogen supply path 21. The hydrogen supply valve 21A is a solenoid valve that can open and close the hydrogen supply path 21. The hydrogen discharge valve 22A is provided in the hydrogen discharge path 22. The hydrogen discharge valve 22A is a solenoid valve that can open and close the hydrogen discharge path 22. The air supply valve 23A is provided in the air supply path 23. The air supply valve 23A is a solenoid valve that can open and close the air supply path 23. The air discharge valve 24A is provided in the air discharge path 24. The air discharge valve 24A is a solenoid valve that can open and close the air discharge path 24.

[0017] The voltage measurement unit 5 includes a voltage dividing resistor and an AD converter. The voltage dividing resistor is connected to the output terminal 100 and divides the stack voltage. The AD converter is driven by the power generated by the fuel cell 1A. The AD converter can be driven at a voltage of, for example, approximately 2V. The AD converter is connected to the voltage dividing resistor and converts the voltage between both ends of the voltage dividing resistor into digital data and outputs it. The voltage dividing resistor and AD converter correspond to an internal load connected to the fuel cell 1A inside the fuel cell unit 1. The control device 6 is a well-known PC and is responsible for overall control of the fuel cell unit 1.

[0018] <Power generation principle of fuel cell 1A> Hydrogen is supplied from a hydrogen supply source 41 to the anode electrode 11A of the anode 11 via a hydrogen supply path 21. The hydrogen is decomposed into hydrogen ions and electrons by the anode catalyst 11B of the anode 11. The hydrogen ions flow toward the cathode 12 via the electrolyte 13. The electrons flow toward the cathode electrode 12A of the cathode 12 via the output terminal 100 and an external load Ld. As a result, power is supplied to the external load Ld.

[0019] Air is supplied to the cathode electrode 12A of the cathode 12 from the air supply source 42 via the air supply path 23. At the cathode catalyst 12B of the cathode 12, hydrogen ions flowing from the anode 11 via the electrolyte 13, electrons flowing via the output terminal 100, and oxygen molecules of the air combine to generate water.

[0020] <Performance degradation of fuel cell 1A> If the fuel cell 1A is stored without an external load Ld connected to the output terminal 100, the cathode catalyst 12B may be oxidized by air and deteriorated, resulting in a decrease in the performance of the fuel cell 1A.

[0021] Figure 2 shows the change over time in the maximum value of the power output from fuel cell 1A (hereinafter referred to as "stack power"). The horizontal axis of Figure 2 shows the storage period from the first power generation of fuel cell 1A. The maximum value of the stack power of fuel cell 1A when the storage period was set to one month was measured a total of three times.

[0022] As shown in Figure 2, the maximum stack power value when fuel cell 1A is stored for 0, 1, and 2 months is approximately constant at 1600 W. The average value of the maximum stack power value when fuel cell 1A is stored for 0, 1, and 2 months is shown by the dashed dotted line. On the other hand, when fuel cell 1A is stored for 3 months, the maximum stack power value is reduced by approximately 17% from the average value. Furthermore, when fuel cell 1A is stored for 6 months, the maximum stack power value is reduced by approximately 23% from the average value.

[0023] 3 shows the change over time in the reaction overvoltage of the fuel cell 1 A. The reaction overvoltage is an index showing the state of the fuel cell 1 A. The smaller the reaction overvoltage value, the better the performance of the fuel cell 1 A.

[0024] As shown in Figure 3, when the storage period of fuel cell 1A is 0 month and 1 month, the reaction overvoltage is constant at 0.43 V. On the other hand, when the storage period of fuel cell 1A is 2 months, 3 months, and 6 months, the reaction overvoltage is 0.45 V, 0.48 V, and 0.49 V, respectively, which are larger than the values ​​when the storage period is 0 month and 1 month.

[0025] The change in each index (maximum stack power, reaction overvoltage) shown in Figure 2 or Figure 3 is presumed to be due to oxidation of the cathode catalyst 12B. From these results, it can be seen that when the fuel cell 1A is stored for at least three months or more, the deterioration of the cathode catalyst 12B becomes significant. In contrast, in this embodiment, the fuel cell unit 1 executes the main processing (see Figure 5) and power generation processing (see Figure 8) described below to prevent performance degradation when the fuel cell 1A is stored without an external load Ld connected to the output terminal 100.

[0026] <Electrical configuration of control device 6> 4, the electrical configuration of the control device 6 will be described. The control device 6 includes a CPU 61, a storage device 62, an input unit 63, and an output unit 64. The CPU 61 is electrically connected to the storage device 62, the input unit 63, the output unit 64, the plurality of valves 20A, the pumps 31 and 32, and the voltage measurement unit 5.

[0027] The CPU 61 controls the entire fuel cell unit 1, including the control device 6. The storage device 62 stores programs that the CPU 61 uses to execute the main processing (see FIG. 5) and power generation processing (see FIG. 8), which will be described later. The storage device 62 also stores flags used in the main processing and power generation processing. The flags indicate whether the fuel cell 1A is in a state where it can supply power to the external load Ld. Hereinafter, when the flag is set to 1, it is said that the "flag is ON." When the flag is set to 0, it is said that the "flag is OFF." When the flag is ON, it indicates that the fuel cell 1A is in a state where it can supply power to the external load Ld. When the flag is OFF, it indicates that the fuel cell 1A is not in a state where it can supply power to the external load Ld.

[0028] The storage device 62 also stores a predetermined time Td as a predetermined period of time. The value of the predetermined time Td is not particularly limited, but may be, for example, three months, which is the storage period of the fuel cell 1A during which deterioration of the cathode catalyst 12B becomes noticeable.

[0029] The storage device 62 also stores a voltage threshold Vh as a predetermined voltage threshold. The value of the voltage threshold Vh is not particularly limited, but is set to, for example, a value greater than the power generation lower limit of the fuel cell 1A. More specifically, the power generation lower limit of each of the 16 cells 10 included in the fuel cell 1A is 0.1 V, so the power generation lower limit of the entire 16 cells 10 connected in series is 1.6 V (= 0.1 × 16). For this reason, the voltage threshold Vh is set to a value greater than the power generation lower limit of 1.6 V (for example, 2.2 V).

[0030] The input unit 63 is a keyboard and accepts input operations for the fuel cell unit 1. The output unit 64 is a display and outputs the status of the fuel cell unit 1 and the like.

[0031] The CPU 61 controls the pump 31 to allow hydrogen in the hydrogen discharge channel 22 to flow toward the hydrogen supply channel 21 via the hydrogen circulation channel 25. The CPU 61 controls the pump 32 to allow air to flow from the air supply source 42 toward the cathode 12A of each cell 10 via the air supply channel 23. The CPU 61 controls the plurality of valves 20A to open and close the plurality of flow channels 20.

[0032] The CPU 61 acquires the digital data output from the AD converter of the voltage measurement unit 5. Based on the acquired digital data, the CPU 61 can identify the voltage between both ends of the voltage dividing resistor of the voltage measurement unit 5, and can identify the stack voltage of the fuel cell 1A based on the identified voltage.

[0033] <Main processing> The main processing will be described with reference to Figure 5. The main processing is initiated by CPU 61 reading and executing a program stored in storage device 62 when fuel cell 1A is in a storage state after manufacture and has never supplied power to external load Ld, or when fuel cell 1A is in a storage state after power generation has ended and has no external load Ld connected to output terminal 100. At this time, hydrogen supply path 21 is closed by hydrogen supply valve 21A, hydrogen discharge path 22 is closed by hydrogen discharge valve 22A, air supply path 23 is closed by air supply valve 23A, and air discharge path 24 is closed by air discharge valve 24A.

[0034] The CPU 61 turns on a flag stored in the storage device 62 to indicate that the fuel cell 1A is in a state where it can supply power to the external load Ld (S11). The CPU 61 determines whether a predetermined time Td has elapsed since the flag was turned on in the process of S11 (S13). If the CPU 61 determines that the predetermined time Td has not elapsed (S13: NO), the process proceeds to S14. The CPU 61 determines whether power generation has started in the process of S45 of the power generation process (see FIG. 8) described later (S14). If the CPU 61 determines that power generation has started (S14: YES), the main process ends. In this case, the main process starts after power generation has ended in the process of S49 of the power generation process (see FIG. 8) described later, when the fuel cell 1A is in a stored state where the external load Ld is not connected to the output terminal 100. On the other hand, if the CPU 61 determines that power generation has not started (S14: NO), the process returns to S13. The CPU 61 waits while repeating the determination in S14 until a predetermined time Td has elapsed since the flag was set ON, during which time the fuel cell 1A remains in a state where it can supply power to the external load Ld.

[0035] On the other hand, if the predetermined time Td has elapsed since the flag was turned ON, it is possible that the fuel cell 1A has been stored for the predetermined time Td and that the cathode catalyst 12B has been oxidized. Therefore, when the CPU 61 determines that the predetermined time Td has elapsed since the flag was turned ON (S13: YES), it turns the flag OFF (S15) to indicate that the fuel cell 1A is not in a state where it can supply power to the external load Ld.

[0036] The CPU 61 executes the processes of S17 to S27 to reduce and activate the oxidized cathode catalyst 12B. The CPU 61 controls the air supply valve 23A to temporarily open and then close the air supply path 23 (S17). Next, the CPU 61 controls the air exhaust valve 24A to temporarily open and then close the air exhaust path 24 (S19). This causes the CPU 61 to cut off the supply of air to the cathode 12A.

[0037] The CPU 61 controls the hydrogen discharge valve 22A to temporarily open the hydrogen discharge channel 22 and then close it (S21). Next, the CPU 61 controls the hydrogen supply valve 21A to open the hydrogen supply channel 21 (S23). As a result, the CPU 61 supplies hydrogen to the anode 11A while the air supply channel 23 and the air discharge channel 24 are closed. Note that the hydrogen supply source 41 stores hydrogen at a pressure higher than the air pressure at least in the cathode 12A. Therefore, hydrogen at a pressure higher than the air in the cathode 12A is supplied to the anode 11A.

[0038] Thereafter, the CPU 61 controls the hydrogen supply valve 21A to close the hydrogen supply path 21 (S25), thereby cutting off the supply of hydrogen to the anode 11A.

[0039] In fuel cell 1A, if hydrogen is supplied to anode 11A between S23 and S25, a potential difference is formed between anode 11A and cathode catalyst 12B, which has been degraded by oxygen in the air remaining at cathode 12A and oxidation, causing a temporary rise in stack voltage. Subsequently, hydrogen supplied to anode 11A decomposes, generating hydrogen ions, which pass through electrolyte 13 and reach cathode 12A, where the oxidized cathode catalyst 12B reacts with the hydrogen ions. At the same time, some of the supplied hydrogen molecules pass through electrolyte 13 and reach cathode 12A, where they come into contact with and are reduced by cathode catalyst 12B, which has been degraded by oxidation. These phenomena reduce the oxidized cathode catalyst 12B, activating it. Because the pressure of the hydrogen supplied to the anode 11A is higher than the pressure of the air at the cathode 12A, as activation of the cathode catalyst 12B progresses, the cathode 12A becomes filled with not only nitrogen from the air but also hydrogen that has permeated from the anode 11A, maintaining the activity of the cathode catalyst 12B and reducing the stack voltage. When the stack voltage drops below the voltage threshold Vh, the CPU 61 determines that the oxidized cathode catalyst 12B has been sufficiently reduced.

[0040] Fig. 6 shows the relationship between the stack voltage and the time elapsed since hydrogen was supplied to the anode 11A between S23 and S25. Fig. 6 shows the change in stack voltage over time when the pressure of hydrogen supplied to the anode 11A is set to 45 KPaG, 40 KPaG, 30 KPaG, 20 KPaG, and 10 KPaG.

[0041] 6, after hydrogen is supplied to the anode 11A, the stack voltage temporarily rises to approximately 15 V and then drops to below the voltage threshold Vh. When the hydrogen pressure is 10 KPaG, the time required for the stack voltage to start rising and the subsequent time required for the stack voltage to drop below the voltage threshold Vh are longer than when the hydrogen pressure is 45 KPaG, 40 KPaG, 30 KPaG, or 20 KPaG. Therefore, in order to rapidly reduce and stably activate the oxidized cathode catalyst 12B, the pressure of the hydrogen supplied to the anode 11A between steps S23 and S25 is preferably 20 KPaG or higher.

[0042] If hydrogen is supplied to the anode 11A between S23 and S25 and the stack voltage temporarily rises, the AD converter of the voltage measurement unit 5 starts operating with the power of the fuel cell 1A. The CPU 61 acquires digital data output from the AD converter that has started operating. As shown in FIG. 5, the CPU 61 identifies the stack voltage of the fuel cell 1A based on the acquired digital data. The CPU 61 determines whether the identified stack voltage is less than the voltage threshold Vh (S27). If the CPU 61 determines that the identified stack voltage is equal to or greater than the voltage threshold Vh (S27: NO), the process returns to S27. The CPU 61 waits until the stack voltage becomes less than the voltage threshold Vh.

[0043] If the CPU 61 determines that the identified stack voltage is less than the voltage threshold Vh (S27: YES), it determines that the oxidized cathode catalyst 12B has been sufficiently reduced, and in this case, the CPU 61 turns on a flag to indicate that the fuel cell 1A is in a state where it can supply power to the external load Ld (S29).

[0044] The CPU 61 determines whether a predetermined time Td has elapsed since the flag was turned on in the process of S11 (S31). If the CPU 61 determines that the predetermined time Td has not elapsed (S31: NO), the process proceeds to S32. The CPU 61 determines whether power generation has started in the process of S45 of the power generation process (see FIG. 8) described later (S32). If the CPU 61 determines that power generation has started (S32: YES), the main process ends. In this case, after power generation has ended in the process of S49 of the power generation process (see FIG. 8) described later, the main process starts in a storage state in which the external load Ld is not connected to the output terminal 100. On the other hand, if the CPU 61 determines that power generation has not started (S32: NO), the process returns to S31. The CPU 61 waits while repeating the determination in S32 until the predetermined time Td has elapsed since the flag was turned on. During this time, the fuel cell 1A remains in a state in which it can supply power to the external load Ld. Furthermore, the hydrogen supply path 21, the hydrogen discharge path 22, the air supply path 23, and the air discharge path 24 remain closed.

[0045] When the CPU 61 determines that the predetermined time Td has elapsed since the flag was set ON (S31: YES), the process returns to S15. The CPU 61 repeatedly executes the processes of S15 to S29 again. As a result, the process for reducing the oxidized cathode catalyst 12B is repeatedly executed at a cycle of the predetermined time Td.

[0046] If the sealing power of the cathode 12A is insufficient or deteriorates, outside air may enter the cathode 12A, causing oxidation and deterioration of the cathode catalyst 12B. Even in such cases, by repeating the processes of S15 to S29 at a cycle of a predetermined time Td, the cathode catalyst 12B can be reactivated during storage of the fuel cell 1A, and the performance of the fuel cell 1A can be maintained for a long period of time.

[0047] Figure 7 shows the change over time in the stack power of the fuel cell 1A. The horizontal axis of Figure 7 shows the time that has elapsed since the fuel cell 1A started generating power.

[0048] The maximum stack power of the fuel cell 1A that has never supplied power to the external load Ld and has been stored for zero months is approximately 1600 W. On the other hand, for the fuel cell 1A that has been stored for three months without supplying power to the external load Ld, the maximum stack power before the main process is applied is approximately 1250 W, a decrease of approximately 22% compared to the case where the storage period is zero. On the other hand, for the fuel cell 1A that has been stored for three months without supplying power to the external load Ld, the maximum stack voltage after the main process is applied is approximately 1600 W, which is almost the same as the case where the storage period is zero months. From these results, it can be seen that even for the fuel cell 1A that has been stored for three months without supplying power to the external load Ld, the oxidized cathode catalyst 12B is sufficiently reduced and the cathode catalyst 12B is activated by executing the main process.

[0049] <Power generation processing> The power generation process will be described with reference to Fig. 8. The power generation process is started by the CPU 61 reading and executing a program stored in the storage device 62 at the same timing as the start of the main process (see Fig. 5). The power generation process is executed in parallel with the main process.

[0050] The CPU 61 determines whether a start command for starting power supply from the fuel cell 1A to the external load Ld has been received via the input unit 63 (S41). If the CPU 61 determines that a start command has not been received (S41: NO), the CPU 61 returns the process to S41. The CPU 61 waits until a start command is received.

[0051] When the CPU 61 determines that a start command has been received via the input unit 63 (S41: YES), it determines whether the flag is ON (S43). When the CPU 61 determines that the flag is OFF (S43: NO), it means that the fuel cell 1A is not in a state where it can supply power to the external load Ld, and so it returns the process to S41. In this case, the fuel cell 1A does not generate power, and power is not supplied to the external load Ld. On the other hand, when the CPU 61 determines that the flag is ON (S43: YES), it means that the fuel cell 1A is in a state where it can supply power to the external load Ld, and so it advances the process to S45.

[0052] An external load Ld is connected to the output terminal 100. The CPU 61 executes the following process to start power generation (S45).

[0053] The CPU 61 controls the air supply valve 23A to open the air supply path 23 and drive the pump 32. This starts the supply of air to the cathode 12A. The CPU 61 controls the air discharge valve 24A to open the air discharge path 24. This causes the nitrogen and hydrogen remaining in the cathode 12A to be discharged with the supplied air. The CPU 61 also controls the hydrogen supply valve 21A to open the hydrogen supply path 21. This starts the supply of hydrogen to the anode 11A. The CPU 61 controls the hydrogen discharge valve 22A to open the hydrogen discharge path 22. Thereafter, the hydrogen discharge valve 22A is closed and the pump 31 is started to drive, thereby starting the circulation of hydrogen to the anode 11A. This allows unreacted hydrogen from the hydrogen supplied to the anode 11A to be reused without being discharged.

[0054] Hydrogen supplied to the anode 11A is decomposed into hydrogen ions and electrons by the anode catalyst 11B. The electrons flow toward the cathode 12A via the output terminal 100 and the external load Ld, thereby supplying power to the external load Ld. At the cathode catalyst 12B, the hydrogen ions flowing from the anode 11 via the electrolyte 13, the electrons flowing via the output terminal 100, and oxygen molecules from the air at the cathode 12 combine to generate water.

[0055] The CPU 61 determines whether an end command to end power supply to the external load Ld has been received via the input unit 63 (S47). If the CPU 61 determines that an end command has not been received (S47: NO), the process returns to S47. The CPU 61 continues power generation until an end command is received.

[0056] When the CPU 61 determines that it has received an end command via the input unit 63 (S47: YES), it controls the air supply valve 23A to close the air supply path 23. The CPU 61 controls the air discharge valve 24A to close the air discharge path 24. This blocks the supply of air to the cathode 12A. The CPU 61 also controls the hydrogen supply valve 21A to close the hydrogen supply path 21. The CPU 61 controls the hydrogen discharge valve 22A to close the hydrogen discharge path 22. This blocks the supply of hydrogen to the anode 11A. As a result, the CPU 61 ends power generation (S49). The CPU 61 returns the process to S41.

[0057] <Actions and Effects of This Embodiment> With the stack filled with hydrogen and air (S17 to S25), the fuel cell unit 1 waits until the stack voltage becomes less than the voltage threshold Vh (S27). At this time, the oxidized cathode catalyst 12B is reduced and activated by hydrogen ions. Note that, since the air supply path 23 and the air discharge path 24 are blocked during the process of supplying hydrogen to the fuel cell 1A (S17, S19), air does not enter the fuel cell 1A via the air supply path 23 and the air discharge path 24. Therefore, even if the fuel cell unit 1 is stored for a long period of time with the external load Ld not connected to the output terminal 100, performance degradation can be suppressed.

[0058] Through the process of S23, the fuel cell unit 1 supplies hydrogen at a higher pressure than the air at the cathode 12A to the anode 11A. In this case, the fuel cell unit 1 appropriately supplies hydrogen to the anode 11A, preventing backflow of hydrogen. Furthermore, because hydrogen at a higher pressure than the air at the cathode 12A is supplied to the anode 11A, hydrogen molecules can permeate the cathode 12B side and react with the oxidized cathode catalyst 12B.

[0059] When the fuel cell unit 1 determines that the stack voltage is less than the voltage threshold Vh (S27: YES), it turns on a flag (S29) to indicate that the fuel cell 1A is in a state where it can supply power to the external load Ld. The fuel cell unit 1 waits in this state until a predetermined time Td has elapsed (S31). During this time, the hydrogen supply path 21, the hydrogen discharge path 22, the air supply path 23, and the air discharge path 24 remain blocked. In this case, the fuel cell 1A remains filled with hydrogen and air from the time the oxidized cathode catalyst 12B is activated until power supply to the external load Ld begins, and air is prevented from entering the fuel cell 1A. Therefore, the fuel cell unit 1 can prevent the cathode catalyst 12B from being oxidized by air until power supply to the external load Ld begins.

[0060] The fuel cell unit 1 sets the voltage threshold Vh to 2.2V, which is higher than 1.6V, the lower limit of power generation for all 16 cells 10. In this case, the fuel cell unit 1 can prevent the cells 10 from being damaged due to the stack voltage falling below the voltage threshold Vh. Furthermore, the fuel cell unit 1 can maintain a state in which the fuel cell 1A is generating power while the oxidized cathode catalyst 12B is being reduced by hydrogen ions (S27). In this case, both the reduction reaction of the oxidized cathode catalyst 12B and the power generation reaction occur, allowing the oxygen in the air in the fuel cell 1A to be efficiently consumed. In this case, the amount of air remaining in the fuel cell 1A during storage can be reduced, and the fuel cell unit 1 can therefore prevent the cathode catalyst 12B from being oxidized by air during storage.

[0061] Unlike the processes of S17 and S19 of the main process, if the air discharge path 24 is opened or closed before the air supply path 23, impurities in the air may enter the cathode 12A via the air discharge path 24. In contrast, the fuel cell unit 1 opens and closes the air supply path 23 before the air discharge path 24. Note that the air supply path 23 is provided with a filter 33, which removes impurities in the air flowing through the air supply path 23. Therefore, the fuel cell unit 1 can prevent impurities from entering the cathode 12A via the air supply path 23.

[0062] When the stack voltage falls below the voltage threshold Vh (S27: YES) and a predetermined time Td has elapsed since the flag was turned ON (S31: YES), the fuel cell unit 1 executes processing (S15 to S29) to reduce the oxidized cathode catalyst 12B. Therefore, if the fuel cell unit 1 is stored for the predetermined time Td or longer, the cathode catalyst 12B is repeatedly activated at intervals of the predetermined time Td. Therefore, even if the fuel cell unit 1 is stored for a long period of time, degradation of the performance of the fuel cell 1A can be suppressed.

[0063] The fuel cell unit 1 drives the voltage measurement unit 5 with the power generated by the fuel cell 1A while the oxidized cathode catalyst 12B is being reduced by hydrogen ions. In other words, the power consumed during activation of the cathode catalyst 12B is consumed by the voltage measurement unit 5. In this case, both the reduction reaction of the oxidized cathode catalyst 12B and the power generation reaction occur, allowing the oxygen in the air inside the fuel cell 1A to be consumed efficiently. Therefore, the fuel cell unit 1 can prevent the cathode catalyst 12B from being oxidized by oxygen while waiting for the stack voltage to fall below the voltage threshold Vh.

[0064] <Modification> The present invention is not limited to the above-described embodiment, and various modifications are possible. The number of cells 10 of the fuel cell 1A is not limited to the above-described embodiment, and may be 1 to 15, or 17 or more. The multiple valves 20A are not limited to solenoid valves, and may be other mechanisms capable of opening and closing the multiple flow paths 20. The control device 6 of the fuel cell unit 1 is not limited to a PC. For example, the control device 6 may be a control box that controls the entire fuel cell unit 1.

[0065] The CPU 61 may determine the voltage between the anode 11A and the cathode 12A of any one of the 16 cells 10 of the fuel cell 1A based on the digital data output from the voltage measurement unit 5. In the process of S27, the CPU 61 may wait until the determined voltage becomes less than 0.1 V, which is the lower limit voltage of a single cell 10.

[0066] The CPU 61 may simultaneously execute the processes of S17 and S19 of the main processing. That is, the air supply channel 23 and the air discharge channel 24 may be blocked at the same time. The CPU 61 may also interchange the processes of S21 and S23 of the main processing. That is, the hydrogen discharge channel 22 may be blocked after the hydrogen supply channel 21 is opened.

[0067] If, during processing of S27 of the main processing, the stack voltage does not become less than the voltage threshold Vh for a predetermined period of time or longer, the CPU 61 may display a screen on the output unit 64 to notify that an abnormality has occurred in the fuel cell 1A.

[0068] The predetermined time Td is not limited to three months, but may be one, two, four months, etc. The CPU 61 may set a different predetermined time Td depending on the elapsed storage period of the fuel cell 1A. For example, the CPU 61 may set the predetermined time Td so that the longer the storage period from the state after manufacture of the fuel cell 1A when power has never been supplied to the external load Ld, the longer the predetermined time Td becomes. Furthermore, the predetermined time Td used as the criterion in S13 may be set to a period longer than the predetermined time Td used as the criterion in S31. The predetermined time Td used as the criterion in S13 may be set to a period shorter than the predetermined time Td used as the criterion in S31.

[0069] The voltage threshold Vh is not limited to 2.2V. For example, the voltage threshold Vh may be any value greater than 1.6V, which is the lower limit of power generation for the entire cell 10. Alternatively, the voltage threshold Vh may be equal to or less than 1.6V, for example, 0V. The CPU 61 may set a different voltage threshold Vh depending on the storage period of the fuel cell 1A. For example, the CPU 61 may set the voltage threshold Vh so that the longer the storage period from the state after manufacture of the fuel cell 1A in which power has never been supplied to the external load Ld, the smaller the voltage threshold Vh.

[0070] The fuel cell unit 1 may have a pump in the hydrogen supply passage 21. This pump may deliver hydrogen from the hydrogen supply source 41 to the anode electrode 11A so that hydrogen at a higher pressure than the air at the cathode electrode 12A is supplied to the anode electrode 11A.

[0071] The CPU 61 may open the hydrogen discharge path 22 and discharge hydrogen from the fuel cell 1A at any time between when it determines that the stack voltage is less than the voltage threshold Vh (S27: YES) and when a predetermined time Td has elapsed (S31).

[0072] As the filter 33, a filter of a type appropriate for the impurities to be removed, such as a screen filter or a depth filter, may be used.

[0073] The CPU 61 does not necessarily perform the processes of S15 to S29 in the main process at a cycle of a predetermined time Td. For example, after receiving a power generation start command, the CPU 61 may execute the processes of S15 to S29 and activate the cathode catalyst 12B until power supply to the external load Ld is started.

[0074] The AD converter of the voltage measurement unit 5 does not necessarily need to be driven by the power of the fuel cell 1A. For example, the voltage measurement unit 5 may be driven by the power supply of the control device 6.

[0075] When the CPU 61 turns on a flag by the processes of S11 and S29 in the main process, it may start power generation and supply power to the external load Ld regardless of whether a start command is received via the input unit 63.

[0076] <Others> The CPU 61 is an example of the "control unit" of the present invention. The processes of S17 and S19 are an example of the "air cutoff process" of the present invention. The processes of S21 and S23 are an example of the "hydrogen supply process" of the present invention. The process of S25 is an example of the "hydrogen cutoff process" of the present invention. The process of S27 is an example of the "first standby process" of the present invention.

Explanation of Reference Numerals

[0077] 1: Fuel cell unit 1A: Fuel cell 5: Voltage measurement unit 10: Cell 11A: Anode electrode 11B: Anode catalyst 12A: Cathode electrode 12B: Cathode catalyst 21: Hydrogen supply path 21A: Hydrogen supply valve 22: Hydrogen discharge path 22A: Hydrogen discharge valve 23: Air supply path 23A: Air supply valve 24: Air discharge path 24A: Air discharge valve 33: Filter 61 :CPU

Claims

1. a stack having at least one cell having an anode, a cathode, and a catalyst; a plurality of flow paths including a hydrogen supply path for supplying hydrogen to the anode, a hydrogen discharge path for discharging hydrogen from the anode, an air supply path for supplying air to the cathode, and an air discharge path for discharging air from the cathode; a plurality of valves including a hydrogen supply valve capable of opening and closing the hydrogen supply path, a hydrogen discharge valve capable of opening and closing the hydrogen discharge path, an air supply valve capable of opening and closing the air supply path, and an air discharge valve capable of opening and closing the air discharge path; a voltage measuring unit that measures a stack voltage, which is a voltage between the anode and the cathode of the stack; a control unit that controls the plurality of valves to open and close the plurality of flow paths; Equipped with The control unit When the stack is not supplying power to an external load, an air shutoff process of shutting off the supply of air to the cathode by closing the air supply path with the air supply valve and closing the air discharge path with the air discharge valve; a hydrogen supply process in which, after the air supply to the cathode is blocked by the air blocking process, the hydrogen discharge channel is closed by the hydrogen discharge valve, the hydrogen supply channel is opened by the hydrogen supply valve, and hydrogen is supplied to the anode; a hydrogen shutoff process in which, after hydrogen is supplied to the anode electrode by the hydrogen supply process, the hydrogen supply passage is closed by the hydrogen supply valve to shut off the supply of hydrogen to the anode electrode; a first standby process of waiting until the stack voltage measured by the voltage measurement unit becomes less than a predetermined voltage threshold after the supply of hydrogen to the anode electrode is shut off by the hydrogen shutoff process; A fuel cell unit characterized by performing the above.

2. The hydrogen supply process is 2. The fuel cell unit according to claim 1, wherein hydrogen is supplied to the anode at a pressure higher than that of the air supplied to the cathode.

3. The control unit After waiting until the voltage becomes less than the voltage threshold value in the first waiting process, a second waiting process is further executed in which the stack waits in a state in which it can supply power to the external load; The plurality of flow paths are maintained in a closed state during the second standby process.

3. The fuel cell unit according to claim 1 or 2.

4. 4. The fuel cell unit according to claim 1, wherein the voltage threshold is a value greater than a lower limit of power generation of the stack.

5. A filter is provided in the air supply path, The air blocking treatment is 5. The fuel cell unit according to claim 1, wherein the air supply passage is closed by the air supply valve, and then the air discharge passage is closed by the air discharge valve.

6. The control unit After waiting until the voltage becomes less than the voltage threshold value in the first waiting process, a determination process is further performed to determine whether a predetermined time has elapsed; A fuel cell unit as described in any one of claims 1 to 5, characterized in that if the judgment process determines that the predetermined time has elapsed, the air blocking process, the hydrogen supply process, the hydrogen blocking process, and the first standby process are executed again.

7. The first standby process includes:

7. A fuel cell unit as described in any one of claims 1 to 6, characterized in that the stack voltage measured by the voltage measuring unit, which is driven by the power generated by the stack, waits until it becomes less than the voltage threshold.

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