Control method for a fuel cell system

Abstract

The present application relates to a control method for a fuel cell system. The control method for a fuel cell system includes: acquiring a poisoning rate of an electrode catalyst of the fuel cell; when the poisoning rate of the electrode catalyst is greater than a prescribed value α, performing a potential maintenance operation that maintains the potential of the fuel cell in a first potential range; and after the potential maintenance operation has been performed, performing a potential change operation that repeats a cycle in which the potential of the fuel cell is changed between an upper limit potential and a lower limit potential of a second potential range, wherein the second potential range is higher than the first potential range.

Description

Technical Field

[0001] This invention relates to a control method for a fuel cell system. Background Technology

[0002] In fuel cells, during power generation, in addition to the main reaction (2H+), + +2e - In addition to the reaction (+(1 / 2)O2→H2O), a side reaction also occurs (2H + +O2+2e - →H2O2). The hydrogen peroxide (H2O2) produced in the side reaction reacts with Fe, which has already flowed into the membrane electrode assembly (MEA) as an impurity, to generate free radicals. These free radicals attack the electrolyte membrane and thus damage its electrolyte material. As a result, due to the impact of protons (H2O2)... + The reduced conductivity of fuel cells may lead to a decrease in fuel cell performance.

[0003] Excessive damage to the electrolyte material can create pores in the electrolyte membrane, allowing hydrogen to leak from the anode to the cathode, potentially leading to reduced fuel efficiency. In the worst-case scenario, the vehicle may come to a standstill. Various inventions have been proposed to address this problem.

[0004] For example, Japanese Unexamined Patent Application Publication No. 2007-12375 (JP 2007-12375A) discloses a method for replenishing and complexing hydrogen peroxide and removing hydrogen peroxide from a fuel cell by pre-adding Ti(SO4)2 to an electrolyte material. Japanese Unexamined Patent Application Publication No. 2008-218100 (JP 2008-218100 A) discloses a method for coating a portion of the edge of an electrolyte membrane with a sealing member and adding a peroxide decomposition catalyst to at least a portion of the sealing member used for coating the electrolyte membrane, wherein one surface of the electrolyte membrane is not coated with an electrode.

[0005] In methods disclosed in JP 2007-12375A, JP 2008-218100A, etc., hydrogen peroxide detoxification is performed by removing hydrogen peroxide from the fuel cell via replenishment or decomposition after hydrogen peroxide has already been generated in the fuel cell. However, these methods take measures after hydrogen peroxide is generated, rather than before. Because fuel cells require the use of specific additives to perform hydrogen peroxide detoxification, the impact of the conflict between cost and performance due to the addition of additives needs to be fully considered. When more hydrogen peroxide is generated than expected, the amount of hydrogen peroxide generated cannot be determined externally, and therefore it is unclear whether the amount of additive added before fuel cell operation will be the appropriate amount required to satisfactorily perform hydrogen peroxide detoxification.

[0006] On the other hand, Japanese Unexamined Patent Application Publication No. 2020-181665 (JP

[0007] Patent application 2020-181665A discloses a control method for a fuel cell system that prevents hydrogen peroxide generation based on two facts: 1) the generation rate of hydrogen peroxide in the fuel cell is slight when the poisoning rate of the electrode catalyst is less than a threshold γ; and 2) the poisoning rate of the electrode catalyst can be reduced by a potential-changing operation that repeatedly changes the potential of the fuel cell between high and low potentials. In this method, the poisoning rate of the electrode catalyst is predicted from the reduction and oxidation wave curves obtained by cyclic voltammetry, and the estimated hydrogen peroxide generation rate becomes greater than a predetermined value and suddenly increases when the poisoning rate of the electrode catalyst exceeds a threshold. In this case, by performing a potential-changing operation that repeatedly changes the potential of the fuel cell between high and low potentials and reducing the poisoning rate of the electrode catalyst, the generation rate of hydrogen peroxide in the electrode catalyst is reduced. Summary of the Invention

[0008] However, in the control method for a fuel cell system disclosed in JP 2020-181665 A, when the potential of the fuel cell is repeatedly changed between high and low potentials during a potential-changing operation, the extraction and re-aggregation of the catalyst metal (such as platinum) used as a catalyst included in the electrodes may be repeated, and thus the catalyst metal particles may become coarser. Accordingly, the surface area of ​​the catalyst metal particles that contribute to the reaction may decrease, and the catalyst included in the electrodes may deteriorate. As a result, there is concern about a reduction in fuel cell performance.

[0009] This invention provides a control method for fuel cell systems that can suppress catalyst degradation.

[0010] According to one aspect of the present invention, a control method for a fuel cell system is provided, the control method comprising: acquiring a poisoning rate of an electrode catalyst of the fuel cell; when the poisoning rate of the electrode catalyst is greater than a predetermined value α, performing a potential maintenance operation, the potential maintenance operation maintaining the potential of the fuel cell within a first potential range; and after the potential maintenance operation has been performed, performing a potential changing operation, the potential changing operation repeating a cycle in which the potential of the fuel cell changes between an upper limit potential and a lower limit potential of a second potential range, wherein...

[0011] The second potential range is higher than the first potential range.

[0012] The fuel cell system according to the present invention can suppress catalyst degradation.

[0013] The control method for a fuel cell system may further include calculating, based on a predetermined relationship between the number of potential-changing operations and the poisoning rate of the electrode catalyst, the optimal number of cycles required to reduce the poisoning rate of the electrode catalyst to a target value. The potential-changing operation may include repeating the cycle a number of times corresponding to the optimal number of cycles.

[0014] According to the present invention, the degradation of the catalyst can be suppressed. Attached Figure Description

[0015] The features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, wherein similar symbols denote similar elements, and wherein:

[0016] . Figure 1 This is a diagram that schematically illustrates the configuration of a fuel cell system performing a control method for a fuel cell system according to one embodiment;

[0017] . Figure 2 This is a flowchart illustrating a control method for a fuel cell system according to an embodiment;

[0018] . Figure 3 This is a graph illustrating the measurement results of the current density change when the potential of the fuel cell element has been scanned using cyclic voltammetry in the control method for a fuel cell system according to an embodiment.

[0019] . Figure 4 This is a graph illustrating the relationship between the poisoning rate of the electrode catalyst and the hydrogen peroxide production rate under a predetermined current density in a predetermined operating state of the fuel cell element according to an embodiment.

[0020] . Figure 5 This is a graph illustrating a predetermined relationship between the number of cycles of potential-changing operation and the poisoning rate of the electrode catalyst according to an embodiment; and

[0021] . Figure 6 This is a graph illustrating the potential change of a fuel cell element during a potential change operation according to an embodiment. Detailed Implementation

[0022] Hereinafter, a control method for a fuel cell system according to an embodiment of the present invention will be described. The control method for a fuel cell system according to this embodiment is a method comprising: acquiring the poisoning rate of an electrode catalyst of a fuel cell element (poisoning rate acquisition step); when the poisoning rate of the electrode catalyst is greater than a predetermined value α, performing a potential maintenance operation (potential maintenance operation execution step), the potential maintenance operation maintaining the potential of the fuel cell element within a first potential range; and after the potential maintenance operation has been performed, performing a potential change operation (potential change operation execution step), the potential change operation repeating a cycle in which the potential of the fuel cell changes between an upper limit potential and a lower limit potential of a second potential range, wherein the second potential range is higher than the first potential range.

[0023] The following will briefly describe an example of a control method for a fuel cell system according to this embodiment.

[0024] Fuel cell system

[0025] First, before describing the control method for a fuel cell system according to this embodiment, the fuel cell system for performing the control method for the fuel cell system will be described below. Figure 1 This is a diagram that schematically illustrates the configuration of a fuel cell system implementing the control method for a fuel cell system according to this embodiment.

[0026] As in Figure 1 As illustrated, the fuel cell system 1 according to this embodiment includes a fuel cell 100, a fuel cell converter 200, a secondary battery 300, a secondary battery converter 400, a switching circuit 450, a DC / AC inverter 500, a drive motor 600, and a control unit 700.

[0027] The fuel cell system 1 also includes a fuel cell lead wire EW1, a secondary battery lead wire EW2, and a DC lead wire EW3. The fuel cell lead wire EW1 electrically connects the fuel cell 100 and the fuel cell converter 200. The secondary battery lead wire EW2 electrically connects the secondary battery 300 and the secondary battery converter 400. The DC lead wire EW3 is connected in parallel with the DC / AC inverter 500 to the fuel cell converter 200 and the secondary battery converter 400.

[0028] Fuel cell 100 is a solid polymer fuel cell and generates direct current (DC) electricity. Fuel cell 100 generates electricity by allowing hydrogen gas (H2) and oxygen gas (O2) supplied to fuel cell element 110 to react with each other in an electrochemical reaction. The electricity generated by fuel cell 100 is input to fuel cell converter 200, secondary battery converter 400, and DC / AC inverter 500 via fuel cell lead wire EW1.

[0029] The fuel cell 100 has a stacked structure in which multiple fuel cell elements 110, serving as unit modules for power generation, are stacked. Each fuel cell element 110 includes an electrolyte membrane formed of a polymer ion exchange membrane. Each fuel cell element 110 includes, for example, an anode electrode on one side of the electrolyte membrane and a cathode electrode on the other side of the electrolyte membrane. The anode electrode is the reaction site where the electrode reaction on the anode side takes place and includes a catalyst for promoting the electrode reaction near its contact surface with the electrolyte membrane. The cathode electrode is the reaction site where the electrode reaction on the cathode side takes place and, similarly to the anode electrode, includes a catalyst near its contact surface with the electrolyte membrane. Here, "electrode catalyst" refers to the catalyst included in the cathode electrode.

[0030] The fuel cell converter 200 is a boost converter that boosts the output voltage of the fuel cell 100 to a target voltage and outputs the boosted voltage. The fuel cell converter 200 is electrically connected to the DC / AC inverter 500 via the DC wire EW3.

[0031] The secondary battery 300, together with the fuel cell 100, serves as the power source for the fuel cell system 1. The secondary battery 300 is charged using the electricity generated by the fuel cell 100. The charged electricity from the secondary battery 300 is then input to drive the motor 600. The secondary battery 300 is formed from a lithium-ion battery. The secondary battery 300 can also be another type of battery, such as a lead-acid battery, a nickel-cadmium battery, or a nickel-metal hydride battery.

[0032] The secondary battery converter 400 is a boost / buck converter device and has a configuration similar to that of the fuel cell converter 200. The secondary battery converter 400 regulates the voltage of the secondary battery lead EW2 and controls the charging / discharging of the secondary battery 300. When the output power of the fuel cell converter 200 is insufficient for the target, the secondary battery converter 400 causes the secondary battery 300 to discharge electricity. On the other hand, when regenerative power is generated in the drive motor 600, the secondary battery converter 400 causes the secondary battery 300 to charge with regenerative power. The secondary battery converter 400 may have a configuration different from that of the fuel cell converter 200.

[0033] The switching circuit 450 is disposed between the fuel cell 100 and the fuel cell converter 200, and serves as a switching circuit that switches the polarity of the electrodes of the fuel cell 100 connected to the secondary battery 300 during the proton pumping process, which will be described later, when the fuel cell 100 generates electricity.

[0034] The DC / AC inverter 500 converts the power supplied as DC power from the fuel cell 100 and the secondary battery 300 via DC wire EW3 into three-phase alternating current (AC) power. The DC / AC inverter 500 is electrically connected to the drive motor 600 via AC wire and supplies three-phase AC power to the drive motor 600. Under the control of the control unit 700, the DC / AC inverter 500 converts the regenerative power generated by the drive motor 600 into DC power and inputs the DC power into the secondary battery 300 via DC wire EW3.

[0035] The drive motor 600 constitutes the main power source of the fuel cell system 1. The drive motor 600 is an electric motor that converts the three-phase AC power supplied from the DC / AC inverter 500 into rotational power.

[0036] The fuel cell system 1 also includes an anode gas supply unit 22, an anode gas supply channel 28, and an anode gas exhaust channel 38. The fuel cell system 1 also includes an oxygen gas supply unit 42, an oxygen gas supply channel 43, a nitrogen gas supply unit 44, a nitrogen gas supply channel 45, a switching valve 46, a cathode gas supply channel 48, and a cathode gas exhaust channel 58.

[0037] The anode gas supply unit 22 is a unit that supplies hydrogen gas to each fuel cell element 110 of the fuel cell 100. The anode gas supply unit 22 may include, for example, a hydrogen container for storing hydrogen gas under pressure and a regulating valve for adjusting the amount of hydrogen gas supplied. The anode gas supply unit 22 is connected to the end of the hydrogen gas flow channel in the fuel cell 100 via the anode gas supply channel 28. Exhaust gas, which is the anode gas, is discharged to the outside of the fuel cell system 1 via the anode gas exhaust channel 38.

[0038] The oxygen supply unit 42 is a unit that supplies air, including oxygen gas, to each fuel cell element 110 of the fuel cell 100. The oxygen supply unit 42 may include, for example, an air pump capable of adjusting the amount of oxygen gas supplied. The oxygen supply unit 42 is connected to the end of the cathode gas flow channel in the fuel cell 100 via an oxygen supply channel 43 and a cathode gas supply channel 48.

[0039] The nitrogen gas supply unit 44 is a unit that supplies nitrogen gas (N2), a non-oxygen gas excluding oxygen, to each fuel cell element 110 of the fuel cell 100. The nitrogen gas supply unit 44 may include, for example, a nitrogen container and a regulating valve for adjusting the amount of nitrogen gas supplied. The nitrogen gas supply unit 44 is connected to the end of the cathode gas flow channel in the fuel cell 100 via a nitrogen gas supply channel 45 and a cathode gas supply channel 48.

[0040] A switching valve 46 is provided at the connection point of the oxygen gas supply channel 43, the nitrogen gas supply channel 45, and the cathode gas supply channel 48. By switching the switching valve 46, the state in which oxygen gas can be supplied to each fuel cell element 110 via the oxygen gas supply channel 43 and the cathode gas supply channel 48, and the state in which nitrogen gas can be supplied to each fuel cell element 110 via the nitrogen gas supply channel 45 and the cathode gas supply channel 48, can be switched between. Cathode exhaust gas is discharged to the outside of the fuel cell system 1 via the cathode gas exhaust channel 58.

[0041] The fuel cell system 1 also includes a first voltmeter VM1, a galvanometer IM, and a second voltmeter VM2. The first voltmeter VM1 and the galvanometer IM are disposed in the fuel cell lead wire EW1. The second voltmeter VM2 is disposed in the DC lead wire EW3.

[0042] The first voltmeter VM1 measures the output voltage of the fuel cell 100 and inputs the measured output voltage as a signal to the control unit 700. The ammeter IM measures the output current of the fuel cell 100 and inputs the measured output current as a signal to the control unit 700. The second voltmeter VM2 measures the output voltage of the fuel cell converter 200 and inputs the measured output voltage as a signal to the control unit 700.

[0043] The control unit 700 is capable of controlling the constituent units of the fuel cell system 1. The control unit 700 includes a poisoning countermeasure processing unit 710 as a functional unit. The control unit 700 controls the components of the fuel cell system 1 as described above. Figure 1 The dashed arrows in the diagram indicate the transmission and reception of signals (such as drive signals) to and from the constituent units of the fuel cell system 1 to execute the control methods for the fuel cell system, which will be described later.

[0044] Control methods for fuel cell systems

[0045] A control method for a fuel cell system according to an embodiment will be described below. Figure 2 This is a flowchart illustrating a control method for a fuel cell system according to this embodiment.

[0046] In the control method for a fuel cell system according to an embodiment, firstly, as in Figure 2 The poisoning rate of the electrode catalyst for each fuel cell element 110 is calculated schematically (poisoning rate acquisition step S10).

[0047] In step S10, which involves obtaining the poisoning rate, as in... Figure 1Schematic diagram: An external meter 20 is electrically connected to the fuel cell 100, and the current density Pa when the potential of the fuel cell element 110 is 0.9 volts is measured using the external meter 20 via cyclic voltammetry. Then, the current density Pa when the potential of the fuel cell element 110 is 0.9 volts is calculated using expression (1), which will be described later.

[0048] The poisoning rate of the electrode catalyst in fuel cell element 110 is calculated. Details will be described below.

[0049] . Figure 3 This is a graph illustrating the measurement results of the change in current density when the potential of the fuel cell element has been scanned using cyclic voltammetry in the control method for a fuel cell system according to this embodiment. Figure 3 In the diagram, La1 and La2 are curves representing the current density of the electrode catalyst of fuel cell element 110 in a state of poisoning due to poisoning contributors (such as organic materials with polar functional groups). La1 represents the reduction wave generated when the potential of fuel cell element 110 is scanned from high to low potential, and La2 represents the oxidation wave generated when the potential of fuel cell element 110 is scanned from low to high potential. On the other hand, Lb1 and Lb2 are curves representing the current density of the electrode catalyst of fuel cell element 110 in a state of non-poisoning. Lb1 represents the reduction wave generated when the potential of fuel cell element 110 is scanned from high to low potential, and Lb2 represents the oxidation wave generated when the potential of fuel cell element 110 is scanned from low to high potential. Figure 3 Schematic diagram: In curve Lb1, the current density is maximized when the potential of fuel cell element 110 is close to 0.9 volts. The potential at which the current density is maximized is the potential that maximizes the oxygen adsorption rate on the electrode catalyst of fuel cell element 110 required for power generation. In a poisoned state of the electrode catalyst of fuel cell element 110, oxygen adsorption on the electrode catalyst is hindered. Accordingly, in curve La1, as indicated by arrow A, the current density when the potential of fuel cell element 110 is 0.9 volts is lower than the current density in curve Lb1. On the other hand, in curves La1 and Lb1, the oxygen adsorption rate on the electrode catalyst of fuel cell element 110 is minimized when the potential of fuel cell element 110 is close to 0.4 volts. The unpoisoned state of the electrode catalyst of the fuel cell element 110 is the state in which the current density is saturated when the potential of the fuel cell element 110 is reduced to 0.9 volts by repeating a potential change operation 100 times on the fuel cell element 110 in a state where the electrode catalyst is poisoned as will be described later (where the poisoning rate of the electrode catalyst is 70%).

[0050] As described above, the poisoning rate of the electrode catalyst of fuel cell element 110 can be calculated based on the decrease in current density indicated by arrow A. Specifically, when Pa is defined as the current density at a potential of 0.9 volts in curve La1, Pa0 is defined as the current density at a potential of 0.4 volts in curve La1, Pb is defined as the current density at a potential of 0.9 volts in curve Lb1, and Pb0 is defined as the current density at a potential of 0.4 volts in curve Lb1, the poisoning rate of the electrode catalyst of fuel cell element 110 is defined by expression (1).

[0051] The poisoning rate of the electrode catalyst = (1 - (Pa - Pa0) / (Pb - Pb0)) × 100…(1)

[0052] The current density Pb ​​is the current density when the electrode catalyst of the fuel cell element 110 is not poisoned and is therefore constant. As poisoning of the electrode catalyst of the fuel cell element 110 proceeds, the current density Pa decreases relative to Pb. On the other hand, the current densities Pa0 and Pb0 are determined based on the characteristics of the electrode catalyst of the fuel cell element 110 and are the same. Accordingly, the poisoning rate of the electrode catalyst, as defined by expression (1), is 0% because Pa = Pb is satisfied when poisoning of the electrode catalyst of the fuel cell element 110 is not proceeding, and increases as poisoning of the electrode catalyst proceeds. In the poisoning rate acquisition step S10, the current density Pa is measured when the potential of the fuel cell element 110 is 0.9 volts as described above, and the poisoning rate of the electrode catalyst of the fuel cell element 110 is calculated from the current density Pa using expression (1).

[0053] Then, as in Figure 2 In the illustration, it is determined whether the poisoning rate of the electrode catalyst calculated in the poisoning rate acquisition step S10 is equal to or less than a specified value α (determination step S20).

[0054] . Figure 4 This is a graph illustrating the relationship between the poisoning rate of the electrode catalyst and the hydrogen peroxide production rate under a predetermined current density in a predetermined operating state of the fuel cell element according to an embodiment. Figure 4 The diagram illustrates the operation of the fuel cell element 110 at a relative humidity of 165% RH at a speed of 0.2 A / cm². 2 The relationship between the poisoning rate of the electrode catalyst and the hydrogen peroxide production rate at a given current density is described. Here, the "hydrogen peroxide production rate" is calculated by dividing the amount of hydrogen peroxide produced [mol] by the amount of water produced in the electricity generation [mol].

[0055] The value [%] is obtained by multiplying the quotient of the sum of the amount of hydrogen peroxide produced [mol] and the amount of hydrogen peroxide produced by 100.

[0056] As in Figure 4 As illustrated, when the poisoning rate of the electrode catalyst is equal to or less than a predetermined value α, the hydrogen peroxide production rate is slight. However, when the poisoning rate of the electrode catalyst is greater than the predetermined value α, the hydrogen peroxide production rate suddenly increases with the increase of the poisoning rate of the electrode catalyst. In the determination step S20, the poisoning countermeasure processing unit 710 of the control unit 700 determines, based on the pre-stored predetermined value α, whether the poisoning rate of the electrode catalyst calculated in the poisoning rate acquisition step S10 is equal to or greater than the predetermined value α, or any value β greater than the predetermined value α.

[0057] Then, as in Figure 2 As illustrated, when the poisoning rate of the electrode catalyst calculated in the poisoning rate acquisition step S10 is any value β greater than the predetermined value α, a potential maintenance operation is performed (potential maintenance operation execution step S30), which maintains the potential of the fuel cell element 110 within the first potential range.

[0058] When it is determined in determination step S20 that the poisoning rate of the electrode catalyst is any value β greater than the predetermined value α, the poisoning countermeasure processing unit 710 of the control unit 700 performs a potential maintenance operation in the potential maintenance operation execution step S30. On the other hand, when it is determined in determination step S20 that the poisoning rate of the electrode catalyst is equal to or less than the predetermined value α, the poisoning countermeasure processing unit 710 of the control unit 700 terminates this control of the fuel cell system.

[0059] During potential maintenance operation, the poisoning countermeasures unit 710 changes the gas supplied to the fuel cell element 110 via the cathode gas supply channel 48 from oxygen gas supplied by the oxygen gas supply unit 42 to nitrogen gas supplied by the nitrogen gas supply unit 44 by switching valve 46. Accordingly, in this state, hydrogen gas is supplied to the anode electrode of the fuel cell element 110 and nitrogen gas is supplied to the cathode electrode. In this state, the poisoning countermeasures unit 710 connects the positive and negative electrodes of the secondary battery 300 to the negative electrode (negative electrode during power generation) and positive electrode (positive electrode during power generation) of the fuel cell 100 by controlling the switching circuit 450. By further controlling the fuel cell converter 200 and the secondary battery converter 400, the poisoning countermeasure processing unit 710 supplies power from the secondary battery 300 to the fuel cell 100 and performs a proton pumping process that scans the potential of the fuel cell element 110 at a predetermined rate (e.g., 20 mV / s) from the lower limit (e.g., -0.5 V) to the upper limit (e.g., less than 0.1 V) of a first potential range.

[0060] Accordingly, by maintaining the potential of the fuel cell element 110 at a potential lower than that in the potential-changing operation described later and reducing the oxidized catalyst metal surface of the electrode catalyst, the interaction between the electrode catalyst and the poisoned contributors (such as organic materials including polar functional groups) is suppressed, and the adsorption of the poisoned contributors on the electrode catalyst is reduced. This is because the protons (H+) that diffuse from the anode electrode are... + ) and electrons supplied from secondary battery 300 - The two react with each other, thus generating hydrogen gas (H2) in the cathode electrode of the fuel cell element 110. Through the heat of reaction of the poisoned contributor, the poisoned contributor is softened, and the action of pushing the poisoned contributor with hydrogen gas is performed. Accordingly, the minimum number of potential-changing operations required to reduce the poisoning rate of the electrode catalyst of the fuel cell element 110 from an arbitrary value β to a predetermined value α (target value) can be reduced.

[0061] Then, as in Figure 2 As illustrated, based on a predetermined relationship between the number of cycles in the potential-changing operation and the poisoning rate of the electrode catalyst, the minimum number of cycles in the potential-changing operation that can reduce the poisoning rate of the electrode catalyst to a specified value α (target value) is calculated as the optimal number of cycles (optimal number of cycles calculation step S40).

[0062] . Figure 5 This is a graph illustrating the predetermined relationship between the number of cycles of potential-changing operation and the poisoning rate of the electrode catalyst according to an embodiment. Figure 5 The diagram illustrates the relationship between the number of potential-changing cycles and the electrode catalyst poisoning rate when a potential-maintaining operation has already been performed on a fuel cell element 110 where the electrode catalyst poisoning rate is 70%, followed by a potential-changing operation. It also illustrates the relationship between the number of potential-changing cycles and the electrode catalyst poisoning rate when the potential-changing operation is performed on the fuel cell element 110 under the same conditions, without performing a potential-maintaining operation on that fuel cell element. For example, in... Figure 5 The diagram illustrates that, in both cases where the potential maintenance operation is performed and where it is not performed, the poisoning rate of the electrode catalyst decreases inversely proportionally to the number of cycles of the potential changing operation. The curves in these two cases show that poisoning contributors with weak adsorption on the electrode catalyst can be removed regardless of whether the potential maintenance operation is performed, and that these contributors can be easily removed by performing the potential changing operation. When the potential maintenance operation is not performed, the poisoning rate of the electrode catalyst decreases to 0% after 100 cycles of repeating the potential changing operation. When the potential maintenance operation is performed, the poisoning rate of the electrode catalyst decreases to 0% after 60 cycles of repeating the potential changing operation. Figure 5 It can be seen that the minimum number of potential-changing operations required to reduce the poisoning rate of the electrode catalyst from an arbitrary value β to a specified value α is (ε-γ) when the potential maintenance operation is performed, and can be reduced by (Δ-ε) compared to the case where the potential maintenance operation is not performed.

[0063] When a potential change operation is performed after a potential maintenance operation has already been performed on the fuel cell element 110 where the electrode catalyst poisoning rate is 70%, the poisoning countermeasure processing unit 710 of the control unit 700 stores the relationship between the number of cycles of the potential change operation and the electrode catalyst poisoning rate. In the optimal cycle number calculation step S40, when a potential change operation is performed after a potential maintenance operation has already been performed on the fuel cell element 110 where the electrode catalyst poisoning rate is 70%, the poisoning countermeasure processing unit 710 of the control unit 700 calculates the minimum number of cycles (ε-γ) of the potential change operation that can reduce the electrode catalyst poisoning rate from an arbitrary value β to a predetermined value α as the optimal cycle number based on the relationship between the number of cycles of the potential change operation and the electrode catalyst poisoning rate.

[0064] Then, as in Figure 2 The diagram illustrates the execution of a potential change operation (potential change operation execution step S50), which repeats the cycle of changing the potential of the fuel cell element 110 between the upper and lower limits of the second potential range with an optimal number of cycles, wherein the second potential range is higher than the first potential range.

[0065] . Figure 6 This is a graph illustrating the potential change of the fuel cell element during a potential change operation according to an embodiment. In the potential change operation execution step S50, the poisoning countermeasure processing unit 710 of the control unit 700 changes the gas supplied to the fuel cell element 110 via the cathode gas supply channel 48 from nitrogen gas supplied from the nitrogen gas supply unit 44 to oxygen gas supplied from the oxygen gas supply unit 42 by switching the switching valve 46. Accordingly, in this state, hydrogen gas is supplied to the anode electrode of the fuel cell element 110 and oxygen gas is supplied to the cathode electrode. In this state, the poisoning countermeasure processing unit 710 connects the positive and negative electrodes of the secondary battery 300 to the positive and negative electrodes of the fuel cell 100 by controlling the switching circuit 450. Subsequently, by further controlling the fuel cell converter 200 and the secondary battery converter 400, the poisoning countermeasure processing unit 710 performs a potential change operation that changes the output current and output voltage of the fuel cell 100 as measured by the ammeter IM and the first voltmeter VM1, such that the following cycle is repeated as described in... Figure 6The optimal number of cycles is illustrated in the diagram, where the potential of the fuel cell element 110 is changed between an upper limit potential (e.g., 0.9 V) and a lower limit potential (e.g., 0.1 V) in a second potential range higher than the first potential range. Through this potential-changing operation, when the potential of the fuel cell element 110 increases, the poisoned contributors adsorbed on the electrode catalyst are removed by oxidation. On the other hand, when the potential of the fuel cell element 110 decreases, the adsorption force of the poisoned contributors on the electrode catalyst decreases, and the output current of the fuel cell element 110 increases to generate water in the fuel cell element 110, thereby enabling the washing away of the poisoned contributors with the generated water. Accordingly, the poisoned contributors can be removed. As a result, the poisoning rate of the electrode catalyst of the fuel cell element 110 can be reduced from an arbitrary value β to a predetermined value α. After the potential-changing operation execution step S50, the poisoning countermeasure processing unit 710 of the control unit 700 again executes the poisoning rate acquisition step S10.

[0066] By employing the control method for a fuel cell system according to this embodiment, the minimum number of potential-changing cycles required to reduce the poisoning rate of the electrode catalyst in the fuel cell element 110 from an arbitrary value β to a predetermined value α (target value) can be reduced by performing a potential-maintaining operation. By calculating the minimum number of potential-changing cycles as the optimal number of cycles and then repeating the potential-changing operation cycle at the optimal number of cycles, the poisoning rate of the electrode catalyst can be reduced to the predetermined value α. Accordingly, by performing the potential-changing operation, the increase in the hydrogen peroxide production rate in the fuel cell element 110 can be suppressed, and thus the damage to the electrolyte membrane can be suppressed. Furthermore, by reducing the number of potential-changing operation cycles, the coarsening of catalyst metal particles caused by repeated extraction and re-aggregation of the catalyst metal used in the electrode catalyst can be suppressed, and thus the degradation of the electrode catalyst can be suppressed. Noise generated during the potential-changing operation cycle can be reduced, and the decrease in fuel efficiency caused by the potential-changing operation can be suppressed.

[0067] Details of the control method for a fuel cell system according to this embodiment will be described below.

[0068] Steps to obtain poisoning rate

[0069] In the poisoning rate acquisition step, the poisoning rate of the electrode catalyst of the fuel cell element was obtained.

[0070] The method for obtaining the poisoning rate of the electrode catalyst is not particularly limited, and for example, the following method can be used as the control method according to this embodiment: the method is to measure the current density Pa when the potential of the fuel cell element is close to 0.9 volts by using cyclic voltammetry with an external meter and then calculate the poisoning rate of the electrode catalyst of the fuel cell element from the current density Pa using expression (1).

[0071] The current densities Pa and Pb in expression (1) are not particularly limited, as long as they define the poisoning rate of the electrode catalyst, and can be current densities when the potential has a value other than 0.9 V (e.g., 0.85 V), as long as they are current densities when the potential is close to 0.9 V. The current densities Pa0 and Pb0 in expression (1) are not particularly limited, as long as they define the poisoning rate of the electrode catalyst, and can be current densities when the potential has a value other than 0.4 V (e.g., 0.3 V), as long as they are current densities when the potential is close to 0.4 V.

[0072] Potential maintenance operation execution steps

[0073] During the potential maintenance operation, when the poisoning rate of the electrode catalyst exceeds the specified value α,

[0074] A potential maintenance operation is performed to maintain the potential of the fuel cell element within a first potential range. Here, "potential of the fuel cell element" refers to the potential of the cathode electrode of the fuel cell element relative to the anode electrode.

[0075] The specified value α for the poisoning rate of the electrode catalyst is not particularly limited, and is, for example, a value that increases the production rate of hydrogen peroxide when the poisoning rate of the electrode catalyst is greater than the specified value α, thus causing problems with the electrolyte membrane.

[0076] The method for performing the potential maintenance operation is not particularly limited, as long as it can maintain the potential of the fuel cell element within a first potential range below the second potential range. For example, a method for performing a proton pumping process to maintain the potential of the fuel cell element within the first potential range can be used, such as the method for performing the potential maintenance operation according to the embodiment. Here, the "proton pumping process" refers to generating protons H in the anode electrode. + And through the electrolyte membrane, protons H +

[0077] The process involves moving the protons to the cathode electrode, causing a proton reaction that produces H2 at the cathode electrode. An example of a method for performing a proton pumping process to maintain the potential of a fuel cell element within a first potential range is a method of performing a proton pumping process by scanning the potential of the fuel cell element at a predetermined rate (e.g., 20 mV / s) from the lower limit potential (e.g., a potential equal to or greater than -0.5 V) to the upper limit potential (e.g., a potential less than 0.2 V) of the first potential range, while hydrogen gas is supplied to the anode electrode of the fuel cell element and nitrogen gas is supplied to the cathode electrode. An example of a proton pumping process performed by this method could be a process of scanning the potential of the fuel cell element within the first potential range. For example, the method of supplying gas to the cathode electrode during proton pumping could be a method of supplying an inert gas such as nitrogen, helium, neon, or argon to the cathode electrode, or a method of not supplying gas to the cathode electrode.

[0078] A method for performing potential maintenance operation can be to maintain the potential of the fuel cell element within a first potential range when the fuel cell generates electricity by supplying hydrogen gas to the anode electrode and oxygen gas to the cathode electrode. This method allows for the reduction of oxidized catalyst metal surfaces on the electrode catalyst by maintaining the potential of the fuel cell element below a second potential range, and allows for the removal of poisoning contributors by generating water in the cathode electrode. Correspondingly, potential-changing operations can be used to more effectively mitigate poisoning and reduce the optimal number of potential-changing cycles. The method of maintaining the potential of the fuel cell element within the first potential range when the fuel cell generates electricity by supplying hydrogen gas to the anode electrode and oxygen gas to the cathode electrode can be employed, for example, by maintaining the potential of the fuel cell element at a potential equal to or less than 0.2 volts (e.g., 0.2 volts, which may be a potential less than 0.2 volts according to the second potential range) for five minutes or longer (e.g., one hour).

[0079] .Steps for performing a potential change operation

[0080] In the potential change operation execution step, the potential change operation is performed after the potential maintenance operation has been performed. This potential change operation repeats the cycle of changing between the upper limit potential and the lower limit potential of the second potential range of the fuel cell element, wherein the second potential range is higher than the first potential range.

[0081] The upper limit of the second potential range is not particularly limited, as long as it is sufficient to remove the poisoned contributor, and preferably, for example, from 0.8 V to 1.0 V. This is because when the upper limit potential is equal to or greater than the lower limit of the range, the poisoned contributor can be effectively removed by oxidation. This is also because when the upper limit potential is equal to or less than the upper limit of the range, the degradation of the electrode catalyst can be suppressed. The lower limit of the second potential range is not particularly limited, as long as it is higher than the first potential range and is sufficient to remove the poisoned contributor, and preferably, for example, from 0.1 V to 0.2 V. This is because when the lower limit potential is equal to or greater than the lower limit of the range, excessive water production can be prevented. This is also because when the lower limit potential is equal to or less than the upper limit of the range, the effect of washing away the poisoned contributor with the generated water can be effectively enhanced.

[0082] The time period of a single cycle of the potential change operation is not particularly limited, as long as it achieves the effect of removing poisoned contributors, and is preferably in the range of 1 to 3 seconds, for example. This is because the effect of removing poisoned contributors is effective when the time period of a single cycle is within this range.

[0083] Steps for calculating the optimal number of loops

[0084] The control method for a fuel cell system according to this embodiment preferably employs the following method, which further performs a step of calculating an optimal number of cycles for potential-changing operations that can reduce the poisoning rate of the electrode catalyst to a target value based on a predetermined relationship between the number of cycles of potential-changing operations and the poisoning rate of the electrode catalyst (optimal cycle number calculation step), and repeating the cycle at this optimal number of cycles during the potential-changing operations. This is because the cycle of potential-changing operations can be repeated a number of times that the poisoning rate of the electrode catalyst can be reduced to the target value.

[0085] Specifically, an example of the predetermined relationship between the number of cycles of the potential-changing operation and the poisoning rate of the electrode catalyst is the relationship between the number of cycles of the potential-changing operation and the poisoning rate of the electrode catalyst when a potential-maintaining operation has been performed on the fuel cell element and a potential-changing operation is performed on the same fuel cell element.

[0086] The predetermined relationship between the number of cycles of potential-changing operation and the poisoning rate of the electrode catalyst can be determined in advance through experiments or simulations based on the configuration of fuel cell elements and fuel cell system and the conditions of potential-changing operation and potential-maintaining operation.

[0087] The target value for the poisoning rate of the electrode catalyst is not particularly limited, and is preferably equal to or less than the specified value α. The optimal number of cycles is not particularly limited, as long as it is the number of potential-changing operations that can reduce the poisoning rate of the electrode catalyst to the target value, and preferably the minimum number of potential-changing operations that can reduce the poisoning rate of the electrode catalyst to the target value can be used.

[0088] While the control method for a fuel cell system according to embodiments of the present invention has been described in detail above, the present invention is not limited to these embodiments, and various design changes can be made thereto without departing from the spirit of the invention as described in the appended claims.

Claims

1. A control method for a fuel cell system, the control method comprising: To obtain the poisoning rate of the electrode catalyst in a fuel cell; When the poisoning rate of the electrode catalyst is greater than a specified value, a potential maintenance operation is performed. The potential maintenance operation is the operation of maintaining the potential of the fuel cell within a first potential range when the fuel cell generates electricity by supplying hydrogen to the anode electrode and oxygen to the cathode electrode. as well as After the potential maintenance operation has been performed for five minutes or more, a potential change operation is performed, which repeats the following cycle in which the potential of the fuel cell changes between the upper and lower limits of a second potential range, wherein the lower limit of the second potential range is higher than the first potential range. The control method further includes: calculating, based on a predetermined relationship between the number of cycles of the potential-changing operation and the poisoning rate of the electrode catalyst, the minimum number of cycles required to reduce the poisoning rate of the electrode catalyst to a target value. Specifically, the minimum number of loops for the potential change operation when performing the potential maintenance operation is less than the minimum number of loops for the potential change operation when not performing the potential maintenance operation, and the minimum number of loops for the potential change operation when performing the potential maintenance operation is calculated as the optimal number of loops. The potential change operation includes repeating the cycle a number of times corresponding to the optimal number of cycles.

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