Fuel cell system

Abstract

To provide a fuel cell system that can suppress electrode deterioration and irreversible damage to a fuel cell at the time of refreshment operation and increase recovery amount with respect to output reduction by the refreshment operation.SOLUTION: A fuel cell system 1 includes a controller for controlling an action state of a fuel cell so as to repeat a normal operation for outputting power to an external load C and a refreshment operation for recovering output reduction of a fuel cell 10 as one cycle. In the refreshment operation, a discharging action for discharging the fuel cell in a state in which supply of liquid fuel is stopped and output to the external load C is stopped, and an entire supply stopping action for stopping the output to the external load C and discharging of the fuel cell 10 by stopping supply of an oxidant and liquid fuel to the fuel cell 10 after termination of the discharging action are enabled.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] In a solid polymer electrolyte fuel cell using liquid fuel, an anode catalyst layer and an anode-side diffusion layer are generally laminated on one side of an electrolyte membrane, and a cathode catalyst layer and a cathode-side diffusion layer are laminated on the other side. Liquid fuel is directly supplied to the anode catalyst layer through the anode-side diffusion layer, and an oxidant is supplied from the outside to the cathode catalyst layer through the cathode-side diffusion layer, causing an electrode reaction to generate electricity. In such a solid polymer electrolyte fuel cell, the output gradually decreases during continuous operation due to the electrode reaction generating gas on the anode side, which inhibits the fuel supply, and deterioration due to use. Patent Document 1 discloses a configuration in which the output of the fuel cell and the supply of fuel to the anode side are stopped during operation, and a short circuit is formed between the anode and cathode to forcibly discharge the fuel, thereby recovering from the decrease in output by performing refresh operation control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-146209 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the configuration disclosed in Patent Document 1, during discharge under refresh operation control, the anode side diffusion layer becomes gaseous due to carbon dioxide generated by the decomposition reaction of the liquid fuel remaining in the anode side diffusion layer, and the cathode side diffusion layer is also gaseous due to the air supplied during normal operation, so if the short circuit lasts for a long time, the electrolyte membrane dries out and is irreversibly damaged.In addition, since the fuel supply is stopped during refresh operation, if discharge under refresh operation control continues even after the fuel remaining in the anode side diffusion layer is consumed, the anode side electrode corrodes and irreversibly deteriorates.

[0005] In addition, in the configuration disclosed in Patent Document 1, when normal operation and refresh operation are continuously performed, poisoning substances accumulate in the anode-side electrode catalyst, and the amount of recovery from the output drop caused by the refresh operation decreases. As a result, even if the refresh operation is performed, a sufficient amount of recovery cannot be obtained. As a result, the refresh operation can only be expected to have an effect of suppressing the output drop, so there is room for improvement.

[0006] The present invention aims to provide a fuel cell system that can suppress irreversible damage and electrode deterioration to a fuel cell during refresh operation, and can increase the amount of recovery of output reduction caused by refresh operation. [Means for solving the problem]

[0007] One aspect of the present invention is a fuel cell configured to be capable of outputting electric power through an electrode reaction by reacting a liquid fuel with an oxidant; a control device that cycles between a normal operation in which power is output from the fuel cell to an external load and a refresh operation in which a drop in the output of the fuel cell is restored; A fuel cell system comprising: In the refresh operation, a discharge operation in which the supply of liquid fuel to the fuel cell is stopped and an oxidant is supplied to the fuel cell, thereby discharging the fuel cell while the output to the external load is stopped; The fuel cell system is configured so that, after the discharge operation is completed, a total supply stop operation can be performed to stop output to the external load and discharge of the fuel cell by continuing to stop the supply of liquid fuel to the fuel cell and stopping the supply of oxidant to the fuel cell. Effect of the Invention

[0008] According to the fuel cell system of the above aspect, the removal of poisoning substances from the electrode catalyst can be promoted by performing a total supply stop operation during the refresh operation. This can increase the amount of recovery from the output drop caused by the refresh operation. In addition, since the total supply stop operation is performed after the discharge operation in the refresh operation is completed, irreversible damage to the fuel cell and electrode deterioration caused by the discharge operation can be suppressed.

[0009] As described above, according to the above aspect, it is possible to provide a fuel cell system that can suppress irreversible damage and electrode deterioration to the fuel cell during refresh operation, and can increase the amount of recovery of output reduction due to refresh operation. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a conceptual diagram showing the configuration of a fuel cell system in a first embodiment. [Diagram 2] FIG. 1 is a conceptual cross-sectional view showing the configuration of a fuel cell in a first embodiment. [Diagram 3] FIG. 2 is a block diagram showing the configuration of a control device in the first embodiment. [Figure 4] FIG. 1A is a conceptual diagram illustrating a cycle between a normal operation and a refresh operation including a discharge operation and a total supply halt operation in the first embodiment; FIG. 1B is a conceptual diagram illustrating a cycle between a normal operation and a refresh operation including a discharge operation. [Diagram 5]FIG. 4 is a conceptual diagram showing a change in output voltage for each cycle during normal operation immediately before a refresh operation in the first embodiment. [Figure 6] 4A is a conceptual diagram showing the change over time of a parameter based on impedance in a fuel cell when the fuel cell is discharged in embodiment 1, and FIG. 4B is a conceptual diagram showing the change over time of the absolute value of the rate of change of the same parameter. [Figure 7] FIG. 4 is a graph showing the change over time in internal resistance of a fuel cell after the start of a total supply stop operation in the first embodiment. [Figure 8] FIG. 2 is a flow diagram illustrating the operation control of the fuel cell system 1 in the first embodiment. [Figure 9] FIG. 11 is a flow diagram illustrating operation control of the fuel cell system 1 in a modified embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (Embodiment 1) 1. Configuration of fuel cell system 1 In the first embodiment, as shown in FIG. 1, the fuel cell system 1 includes a fuel cell 10 and a control device 50. The fuel cells 10 are stacked as single cells U to form a fuel cell stack 100. The stacked single cells U in the fuel cell stack 100 are held by a holder H and a bolt B. A first pump 102 that pressurizes and supplies formic acid, which is a liquid fuel stored in a fuel tank 101, is connected to a connection part K1 via a pipe in the fuel cell stack 100. A second pump 104 that pressurizes and supplies oxygen gas as an oxidant (oxidant gas) stored in a gas tank 103 is connected to a connection part K2 via a pipe in the fuel cell stack 100. The operations of the first pump 102 and the second pump 104 are controlled by the control device 50.

[0012] 2. Configuration of fuel cell 10 As shown in Fig. 2, the fuel cell 10 includes an electrolyte membrane 11, an anode catalyst layer 12, and a cathode catalyst layer 13. The anode catalyst layer 12 is laminated on one side of the electrolyte membrane 11, and the cathode catalyst layer 13 is laminated on the other side to form an MEA (Membrane-Electrode-Assembly) which is an electrode structure. The anode catalyst layer 12 and the cathode catalyst layer 13 are formed, for example, by coating each side of the electrolyte membrane 11 with a metal catalyst such as platinum (Pt) or palladium (Pd), carbon to which the metal catalyst has been added, and an electrolyte. The fuel cell 10 is arranged so that the surface direction of the electrolyte membrane 11 is parallel to the vertical direction Y.

[0013] An anode side diffusion layer 21 is laminated on the anode catalyst layer 12, and a cathode side diffusion layer 22 is laminated on the cathode catalyst layer 13. The anode side diffusion layer 21 and the cathode side diffusion layer 22 are each made of a porous material and each have a large number of pores.

[0014] An anode-side separator 31 is laminated on the anode-side diffusion layer 21 on the side opposite to the anode catalyst layer 12. The anode-side separator 31 can be made of, for example, a resin material. A plurality of ribs (not shown) extending in the vertical direction Y are provided on the surface of the anode-side separator 31 facing the anode catalyst layer 12, and a flow path 33 for liquid fuel is formed by grooves formed between the plurality of ribs. The flow path 33 is configured so that pressurized liquid fuel is supplied via a first pump 102. The liquid fuel supplied to the flow path 33 permeates from the flow path 33 into the pores of the anode-side diffusion layer 21. A cathode-side separator 32 is laminated on the cathode-side diffusion layer 22 on the side opposite to the cathode catalyst layer 13. The cathode-side separator 32 can be configured similarly to the anode-side separator 31. The cathode-side diffusion layer 22 is supplied with pressurized oxidant via a second pump 104 through the flow path 34.

[0015] Examples of the fuel supplied to the anode-side diffusion layer 21 and the anode catalyst layer 12 of the fuel cell 10 include liquid fuels such as formic acid (HCOOH), methanol (CHOH), and ethanol (CHOH), and in this embodiment 1, the fuel cell 10 is a direct formic acid fuel cell (DFAFC) that directly uses formic acid as the liquid fuel. Examples of the oxidant (oxidant gas) supplied to the cathode-side diffusion layer 22 and the cathode catalyst layer 13 of the fuel cell 10 include oxygen (O) gas and air, and in this embodiment 1, the case where oxygen gas is used is illustrated.

[0016] 3. Configuration of the control device 50 The control device 50 is composed of an arithmetic processing device and a memory device, and is configured to repeat, as shown in FIG. 4, a normal operation in which power is output from the fuel cell 10 to an external load C, and a refresh operation in which the output of the fuel cell 10 is stopped and the fuel cell 10 is discharged to recover from a decrease in output, as one cycle.

[0017] 3, the control device 50 includes an impedance acquisition unit 51, a decrease degree acquisition unit 52, an increase degree acquisition unit 53, a comparison unit 54, a cycle adjustment unit 55, a duration adjustment unit 56, and a switching unit 57. The operating state and each component will be described in detail below.

[0018] 3-1. Normal operation In normal operation, both liquid fuel and oxidant are supplied to the fuel cell 10, thereby outputting power to an external load C. In Figures 4(a) and 4(b), the duration of normal operation is indicated by an arrow TA. The duration TA of normal operation can be set according to the power required by the external load C. Furthermore, the duration TA of normal operation can be set to a fixed value for control purposes.

[0019] 3-2. Refreshing operation In the refresh operation, at least a discharge operation is performed. In the discharge operation, the supply of liquid fuel to the fuel cell 10 is stopped, an oxidant is supplied to the fuel cell 10, and a switching unit 57 (described later) disconnects the fuel cell 10 from an external load C and connects the fuel cell 10 to a discharge circuit D. This causes the fuel cell 10 to discharge. In Figures 4(a) and 4(b), the duration of the discharge operation is indicated as TB. Furthermore, the duration of the discharge operation TB can be a fixed value for control purposes.

[0020] In the discharge operation, when the supply of liquid fuel to the fuel cell 10 is stopped, the liquid fuel remaining in the fuel cell 10 is consumed by discharging. As a result, the concentration of the reaction solution in the fuel cell 10 decreases, causing the poisoning substances attached to the anode catalyst layer 12 to separate from the anode catalyst layer 12, and the active area of ​​the anode catalyst layer 12 that was reduced by the poisoning substances is restored. If discharging is continued even after the liquid fuel has been consumed, the anode electrode will corrode and irreversible deterioration will occur in the anode electrode.

[0021] In the refresh operation, a total supply stop operation can be performed after the discharge operation is completed. The total supply stop operation continues to stop the supply of liquid fuel to the fuel cell 10, stops the supply of oxidant to the fuel cell 10, and disconnects the fuel cell 10 from the discharge circuit D, thereby stopping the output to the external load C and the discharge of the fuel cell 10. In FIG. 4(a), the duration of the total supply stop operation is indicated as TC. As shown in FIG. 4(a) and FIG. 4(b), the refresh operation always performs a discharge operation in each cycle, but the total supply stop operation may be performed only in specific cycles, and there may be cycles in which the total supply stop operation is not performed. Furthermore, the duration TC of the total supply stop operation can be a variable value in terms of control.

[0022] During the above-mentioned discharge operation, the total supply stop operation is performed before the liquid fuel remaining in the fuel cell 10 is completely consumed, thereby preventing corrosion of the anode catalyst layer 12. In addition, since the reaction solution concentration in the fuel cell 10 remains low even during the total supply stop operation, the poisoning substances attached to the anode catalyst layer 12 are separated from the anode catalyst layer 12, and the active area of ​​the anode catalyst layer 12 can be restored.

[0023] 3-3. Impedance acquisition unit 51 The impedance acquisition unit 51 acquires the impedance in the fuel cell 10. The configuration of the impedance acquisition unit 51 is not limited, but can be configured by connecting a low resistance measuring device (not shown) to the output terminal T, for example.

[0024] 3-4. Decrease degree acquisition part 52 The decrease degree acquisition unit 52 acquires the decrease degree of the amount of recovery of the decreased output due to the discharge operation in the refresh operation. The decrease degree can be calculated based on the impedance of the fuel cell 10 acquired by the impedance acquisition unit 51. For example, the decrease degree can be expressed as the difference between the initial impedance of the fuel cell 10 and the impedance at the end of the discharge operation in the refresh operation.

[0025] 3-5. Increase degree acquisition unit 53 The increase degree acquisition unit 53 acquires the increase degree of the output due to the total supply stop operation in the refresh operation. The increase degree can be calculated based on the impedance of the fuel cell 10 acquired by the impedance acquisition unit 51. For example, it can be expressed as the difference between the impedance at the start of the total supply stop operation in the fuel cell 10 and the impedance at the end of the total supply stop operation. The increase degree can also be a preset value.

[0026] 3-6. Comparison section 54 The comparison unit 54 compares the degree of decrease acquired by the decrease degree acquisition unit 52 with the degree of increase acquired by the increase degree acquisition unit 53 .

[0027] 3-7. Cycle Adjustment Unit 55 The cycle adjustment unit 55 specifies a cycle in which the total supply stop operation is performed in the refresh operation. The cycle adjustment unit 55 can specify the cycle based on the comparison result of the comparison unit 54. For example, the cycle in which the total supply stop operation is performed can be specified so that the comparison result of the comparison unit 54 specifies the cycle in which the total supply stop operation is performed at a timing when the degree of decrease is equal to the degree of increase. In the example shown in FIG. 5, when a cycle in which normal operation and a refresh operation only including a discharge operation are performed is repeated 35 times, the degree of decrease becomes equal to the degree of increase, so that the next cycle is specified as a cycle in which a refresh operation including a normal operation, a discharge operation, and a total supply stop operation is performed. Then, 35 cycles in which a refresh operation only including a normal operation and a discharge operation is performed and one cycle in which a refresh operation including a total supply stop operation is performed are set as one set, and the set is repeatedly executed. This makes it possible to maintain the amount of recovery of the reduced output for each set.

[0028] 3-8. Duration adjustment unit 56 3 adjusts at least one of the duration TA of normal operation, the duration TB of the discharging operation, and the duration TC of the total supply stop operation in the fuel cell 10. For example, the duration TB of the discharging operation can be set to a preset fixed value, and the duration TC of the total supply stop operation can be adjusted. Also, the duration TA of normal operation and the duration TB of the discharging operation can be set to fixed values, and the duration TC of the total supply stop operation can be adjusted.

[0029] The duration TB of the discharge operation can be adjusted to a time when the absolute value of the rate of change of the parameter based on the impedance of the fuel cell 10 acquired by the impedance acquisition unit 51 becomes equal to or less than a predetermined reference value P after the absolute value of the rate of change of the parameter based on the impedance of the fuel cell 10 becomes a maximum value, as shown in FIG. 6(a), at the beginning of the discharge, the parameter based on the impedance of the fuel cell 10 is substantially constant, and as shown in FIG. 6(b), the absolute value of the rate of change of the parameter is also extremely low. As shown in FIG. 6(a), when time T1 has elapsed from the start of the discharge, the parameter begins to change significantly, and as shown in FIG. 6(b), the absolute value of the rate of change of the parameter also increases, and at time Tm, the absolute value of the rate of change of the parameter becomes a maximum value Pmax. If the discharge is continued thereafter, the absolute value of the rate of change of the parameter decreases, as shown in FIG. 6(b), and at time T2, the absolute value of the rate of change of the parameter becomes a minimum value Pmin, and the parameter also becomes an extreme value, as shown in FIG. 6(a). If the discharge is continued thereafter, the absolute value of the rate of change of the parameter increases again, as shown in FIG. 6(b), and the parameter also changes rapidly, as shown in FIG. 6(a).

[0030] Here, the reference value P can be the time when the absolute value of the rate of change of the parameter falls within the range between the maximum value Pmax and the minimum value Pmin. Note that the minimum value Pmin has a value of 0, and the maximum value Pmax can vary depending on the configuration of the fuel cell 10 and the fuel cell system 1.

[0031] The duration adjustment unit 56 can adjust the durations TA, TB, and TC based on the power requirement from the external load C and the system output Wt, which is the output of the fuel cell system 1. Here, the system output Ws can be expressed by the formula Wt=TA / (TA+TB+TC)×Wc, using the cell output Wc, which is the output of the cell constituting the fuel cell 10. The duration adjustment unit 56 can change TC while keeping TA and TB fixed, so that the system output Wt satisfies the power requirement while keeping the cell output Wc at a predetermined value. This eliminates the need for a configuration to adjust the cell output Wc, simplifying the configuration of the fuel cell system 1.

[0032] The duration adjustment unit 56 adjusts the durations TA, TB, and TC as follows: For example, if the cell output Wc is M, TA=300 seconds, TB=60 seconds, and TC=0 seconds, the system output Wt can be expressed as 0.83M based on the formula TA / (TA+TB+TC)×Wc, and 83% of the cell output Wc is the system output Wt. If TA=300 seconds, TB=60 seconds, and TC=240 seconds, the system output Wt can be expressed as 0.50M based on the formula TA / (TA+TB+TC)×Wc, and 50% of the cell output Wc is the system output Wt. In this way, by simply changing TC, the system output Wt can be changed while the cell output Wc remains constant, and the required power can be satisfied.

[0033] The value of the cell output Wc is not limited as long as it is within the operating range of the cells constituting the fuel cell 10, but it is preferable to set it to a relatively high value. In the configuration in which the system output Wt is changed by adjusting the duration TC of the total supply stop operation described above, the system output Wt cannot be made larger than the value of the cell output Wc, so by increasing the value of the cell output Wc in advance, a wide setting range for the system output Wt can be ensured.

[0034] The duration TC of the total supply stop operation is preferably set to a predetermined reference value or more. The reference value can be set based on the impedance (internal resistance) of the fuel cell 10. In the example shown in Fig. 7, during the total supply stop operation, the internal resistance of the fuel cell 10 decreases from the start of the total supply stop operation until a predetermined time TC1 is reached, but becomes almost constant after the predetermined time TC1. By setting the reference value TC1 based on this and adjusting the duration TC of the total supply stop operation to the reference value TC1 or more, it is possible to reliably reduce the internal resistance of the fuel cell 10, i.e., to increase the reduced output.

[0035] 3-9. Switching unit 57 3 switches the operation cycle in the fuel cell system 1 between normal operation and refresh operation based on the adjustment results of the cycle adjustment unit 55 and the duration adjustment unit 56. Furthermore, as described above, the refresh operation is either a cycle in which only a discharge operation is performed, or a cycle in which a full supply stop operation is performed after the discharge operation.

[0036] The operating cycle can be switched by a combination of supplying and stopping the supply of liquid fuel to the fuel cell 10, supplying and stopping the supply of oxidant to the fuel cell 10, connecting and disconnecting the fuel cell system 1 to an external load C, and connecting and disconnecting the fuel cell system 1 to a discharge circuit D.

[0037] That is, in normal operation, liquid fuel is supplied to the fuel cell 10, an oxidant is supplied to the fuel cell 10, the fuel cell system 1 and the external load C are connected, and the fuel cell system 1 and the discharge circuit D are disconnected.

[0038] In addition, during the discharge operation in the refresh operation, the supply of liquid fuel to the fuel cell 10 is stopped, the supply of oxidant to the fuel cell 10 is maintained, the fuel cell system 1 is disconnected from the external load C, and the fuel cell system 1 is connected to the discharge circuit D.

[0039] In addition, during the full supply stop operation in the refresh operation, the supply of liquid fuel to the fuel cell 10 is kept stopped, the supply of oxidant to the fuel cell 10 is stopped, the connection between the fuel cell system 1 and the external load C is kept disconnected, and the connection between the fuel cell system 1 and the discharge circuit D is disconnected.

[0040] 4. Operation control of fuel cell system 1 The operation control of the fuel cell system 1 of this embodiment will be described with reference to the flow diagram of Fig. 8. First, in step S1 of Fig. 8, the switching unit 57 supplies liquid fuel to the fuel cell 10, supplies an oxidant to the fuel cell 10, connects the fuel cell system 1 to the external load C, and disconnects the fuel cell system 1 from the discharge circuit D, thereby starting normal operation.

[0041] In step S2, after the normal operation duration TA, which is a fixed value for control, has elapsed, in step S3, the switching unit 57 stops the supply of liquid fuel to the fuel cell 10, maintains the supply of oxidant to the fuel cell 10, disconnects the fuel cell system 1 from the external load C, connects the fuel cell system 1 to the discharge circuit D, and starts the discharge operation of the refresh operation.

[0042] In step S4, after the duration TB of the discharging operation, which is a fixed value for control, has elapsed, in step S5, the cycle adjustment unit 55 determines whether or not it is a specific cycle in which a total supply stop operation is performed. As described above, the determination of whether or not it is a specific cycle is made based on whether or not the comparison result of the comparison unit 54 indicates that the degree of decrease acquired by the decrease degree acquisition unit 52 is equivalent to the degree of increase acquired by the increase degree acquisition unit.

[0043] If it is determined in step S5 that the cycle is not a specific cycle, the process proceeds to No in step S5, and the refresh operation is stopped in step S6. Then, in step S7, it is determined whether or not an output stop signal for the fuel cell system 1 has been received. If an output stop signal has been received, the process proceeds to Yes in step S7, and the flow ends. On the other hand, if an output stop signal has not been received, the process proceeds to No in step S7, and steps S1 and onward are carried out again.

[0044] On the other hand, if it is determined in step S5 that it is a specific cycle, the process proceeds to Yes in step S5, and in step S8, the duration TC of the total supply stop operation is adjusted by the duration adjustment unit 56. Then, in step S9, the total supply stop operation of the refresh operation is started. After that, in step S10, after the duration TC of the total supply stop operation has elapsed, the process proceeds to the above-mentioned step S6 to stop the refresh operation, and step S7 and subsequent steps are carried out as described above.

[0045] In this flow, the total supply stop operation is performed only when it is determined in step S5 that it is a specific cycle. Alternatively, however, the total supply stop operation may be performed in all cycles of refresh operation based on the modified flow shown in FIG. 9.

[0046] In this modified embodiment, steps equivalent to those in the flow shown in Fig. 7 of the first embodiment are given the same reference numerals and their description is omitted. In this modified embodiment, steps S1 to S4 shown in Fig. 9 are performed, and after step S4, steps S8 to S10 are performed, and then steps S6 and S7 are performed. This allows a full supply stop operation to be performed in all cycles of refresh operation.

[0047] 5. Effects According to the fuel cell system 1 of the first embodiment, the removal of poisoning substances from the electrode catalyst can be promoted by performing a total supply stop operation during the refresh operation. This can increase the amount of recovery from the output drop caused by the refresh operation. In addition, since the total supply stop operation is performed after the discharge operation in the refresh operation is completed, irreversible damage to the fuel cell and electrode deterioration caused by the discharge operation can be suppressed.

[0048] In the first embodiment, the control device 50 performs a discharge operation and a total supply stop operation in a refresh operation in a specific cycle, and performs only a discharge operation in a refresh operation in other cycles. This allows the total supply stop operation to be performed at the timing when the recovery amount from the output drop starts to decrease, so that the recovery amount from the output drop can be maintained while maintaining a high output.

[0049] In the first embodiment, the timing of performing the specific cycle in which the total supply stop operation is performed is determined based on the degree of decrease in the output reduction recovery amount due to the discharge operation and the degree of increase in the output reduction recovery amount due to the total supply stop operation. This allows the total supply stop operation to be performed at a timing when the output reduction recovery amount has decreased with high accuracy, so that the output reduction recovery amount can be further maintained while maintaining a high output.

[0050] In the above modified embodiment, the control device 50 performs a discharge operation and a total supply stop operation in the refresh operation in all cycles, which eliminates the need to determine whether or not to perform a total supply stop operation, thereby reducing the calculation load.

[0051] Furthermore, in the first embodiment, the duration TB of the discharging operation is determined based on the impedance of the fuel cell 10. This makes it possible to suppress deterioration of the fuel cell 10 due to the discharging operation.

[0052] Furthermore, in the first embodiment, the control device 50 adjusts the duration TC of the total supply stop operation or the timing of performing the total supply stop operation (the execution timing of a specific cycle) to satisfy the power requirement from the external load C. This makes it possible to maintain the cell output of the fuel cell 10 constant and satisfy the power requirement while stabilizing the fuel cell 10.

[0053] In the first embodiment, the duration TB of the discharge operation in the refresh operation is fixed to a predetermined time, and the duration TC of the total supply stop operation is variable. This makes it possible to maintain the cell output of the fuel cell 10 constant with simple control, and to satisfy the required power while stabilizing the fuel cell 10.

[0054] Furthermore, in the present embodiment 1, the duration TA of normal operation is fixed to a predetermined time. This makes it possible to maintain the cell output of the fuel cell 10 constant with even simpler control, thereby stabilizing the fuel cell 10 and satisfying the required power.

[0055] In the first embodiment, the duration TC of the total supply stop operation is set within a preset range, which ensures that the total supply stop operation can reliably increase the amount of recovery from the output drop.

[0056] As described above, according to this embodiment 1 and its modified forms, it is possible to provide a fuel cell system 1 that can suppress irreversible damage and electrode deterioration to the fuel cell 10 during refresh operation, and can increase the amount of recovery of output reduction due to refresh operation.

[0057] The present invention is not limited to the above-mentioned first embodiment and the modified embodiments, and can be applied to various embodiments without departing from the gist of the present invention. [Explanation of symbols]

[0058] 1: fuel cell system, 10: fuel cell, 11: electrolyte membrane, 12: anode catalyst layer, 13: cathode catalyst layer, 21: anode side diffusion layer, 22: cathode side diffusion layer, 31: anode side separator, 32: cathode side separator, 33: flow path, 50: control device, 51: impedance acquisition unit, 52: decrease degree acquisition unit, 53: increase degree acquisition unit, 54: comparison unit, 55: cycle adjustment unit, 56: duration adjustment unit, 57: switching unit 57

Claims

1. a fuel cell configured to be capable of outputting electric power through an electrode reaction by reacting a liquid fuel with an oxidant; a control device that controls the operating state of the fuel cell so that a normal operation in which power is output from the fuel cell to an external load and a refresh operation in which a drop in the output of the fuel cell is restored are repeated as one cycle; A fuel cell system comprising: In the refresh operation, a discharge operation in which the supply of liquid fuel to the fuel cell is stopped and an oxidant is supplied to the fuel cell, thereby discharging the fuel cell while the output to the external load is stopped; The fuel cell system is configured to be able to perform a total supply stop operation to stop output to the external load and discharge of the fuel cell by continuing to stop the supply of liquid fuel to the fuel cell and stopping the supply of oxidant to the fuel cell after the discharge operation is completed.

2. 2. The fuel cell system according to claim 1, wherein the control device performs the discharging operation and the total supply stop operation during refresh operation in a specific cycle, and performs only the discharging operation during refresh operation in other cycles.

3. 3. The fuel cell system according to claim 2, wherein the timing for performing the specific cycle is determined based on a degree of decrease in an amount of recovery from a decrease in output due to the discharge operation and a degree of increase in an amount of recovery from a decrease in output due to the total supply halt operation.

4. 2. The fuel cell system according to claim 1, wherein the control device performs the discharge operation and the total supply stop operation in a refresh operation in a full cycle.

5. 5. The fuel cell system according to claim 1, wherein the duration of the discharge operation is determined based on the impedance of the fuel cell.

6. The fuel cell system according to any one of claims 1 to 4, wherein the control device controls the total supply stop operation to satisfy the required power from the external load by adjusting the duration of the total supply stop operation or the timing of performing the total supply stop operation.

7. 7. The fuel cell system according to claim 6, wherein in the refresh operation, the duration of said discharge operation is fixed to a predetermined time, and the duration of said total supply stop operation is variable.

8. 8. The fuel cell system according to claim 7, wherein the duration of the normal operation is fixed to a predetermined time.

9. 8. The fuel cell system according to claim 7, wherein the duration of the total supply cutoff operation is set within a preset range.

10. 5. The fuel cell system according to claim 1, wherein the liquid fuel is formic acid.

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